In vitro Antitumor Activity and Electrochemical Studies of Bio-Electroactive Anthraquinone Derivatives in Glioblastoma

Abstract

This study investigated the antiglioblastoma potential of nine synthetic anthraquinone derivatives (SAQDs). SAQDs were tested for their in vitro cytotoxicity against PBMCs and GBM02 cells. For PBMC, SAQDs showed no cytotoxic effects up to 100 µM. Four most promising SAQDs (1, 4, 5, and 9) demonstrated significant activity against GBM02, with selectivity index >4.54 for 1, >1.30 for 4 and 5, and >1.19 for 9. These compounds induced morphological changes, incluing cell rounding, cytoplasmic vacuolation, and membrane rupture, and inhibited cell migration. Due to the pharmacological role of oxidative stress, electrochemical methods were used to compare the reductive and oxidative capacities of the SAQD with their antitumor activity. Considering the reported findings, it is feasible to confirm that some SAQDs have antitumor effects, supporting additional studies of AQ for developing novel anticancer medications. Due to the small number of compounds investigated, it was not possible to observe a relationship between electrochemical and biological data. However, the electrochemical data are new and could be used to prepare other compounds on this line. CV data revealed that the sulfone’s electron-withdrawing effect facilitated the reduction. At the same time, the sulfides had shown less positive potential for oxidation waves due to the presence of electron-donating groups.

Key words
anthraquinones; cells; glioblastoma; electroactivity

INTRODUCTION

Glioblastoma (GBM) is the most prevalent and malignant primary tumor of the central nervous system, accounting for 47.7% of all malignant neoplasms. With significant frequency and a greater incidence rate among older people, the incidence rate rises. The aggressiveness of the condition leads to a low patient survival rate and a median overall survival of a few months despite the increased interest in research on new treatments due to the poor prognosis in recent years (Kleckner et al. 2019).

In addition to complex issues to solve, GBM offers several therapeutic failures. These include the disease’s high complexity, location in hard-to-reach areas, high rate of treatment resistance, immunosuppressive environment, and presence of the blood-brain barrier. Furthermore, therapies are expensive and painful, and the side effects are often severe (Delello Di Filippo et al. 2021).

Since reactive oxygen species (ROS) have been demonstrated to have both tumor-promoting and tumor-inhibiting qualities, their involvement in carcinogenesis is debatable. Because they can cause rapid rises in ROS levels, several common chemotherapies are lethal to cancer cells. The field of cancer treatment may benefit greatly from the development of new oriented treatments that target antioxidant pathways (Gorrini et al. 2013)

ROS are essential in regulating normal cellular processes, but when unregulated, they contribute to the developing and worsening of several human diseases (Sies et al. 2017, Valko et al. 2007). Different types of cancer are associated with disturbed intracellular redox balance and oxidative stress (OS) (Pelicano et al. 2004). Several of them have increased ROS levels compared to normal cells, their accelerated metabolism and/or alterations in several signaling pathways (Xiaoqin et al. 2024), leading to high ROS levels considerably closer to the critical redox threshold at which cell death is not induced (Glorieux et al. 2024).

On the other hand, hypoxia in the tumor microenvironment (TME) and antioxidant defense significantly limit the therapeutic efficacy of reactive oxygen species (ROS), which show promise in cancer therapy by speeding up tumor cell death. Although oxidative stress amplification has been effectively used for tumor therapy, interactions between cancer cells and other TME variables typically result in ineffective tumor treatments (Zou et al. 2025).

One of the primary qualities anticipated in new drug candidates is selectivity, which leads to the idea that the more contemporary prototypes suggest exploring novel and distinct avenues for potential action, the more likely it is that an anticancer effect will be developed (Pelicano et al. 2004, Perillo et al. 2020).

Anticancer agents are often associated with substances that somehow modulate redox species through bioreduction or bio-oxidation. As such, quinones are compounds well suited to these effects, as they can use the preexisting redox states of diseased cells, organelles, parasites, and microbes for therapeutic benefit. Their ability to function as multitargeted compounds represents a viable framework for developing new drug prototypes. Redox modulation and choice of conditions can promote selectivity. This is a key parameter observed in several cases: cancer cells become more sensitive and brittle than healthy cells or tissues (Hillard et al. 2008, Paiva et al. 2015, Silva et al. 2020), with a relevant bridge with immune cells (Dash et al. 2025).

The literature reports the relevance of biomimetic benzo- and naphthoquinones (ubiquinones and vitamin K), which participate in the mitochondrial electron chain pathways. Despite essential contributions (Malik et al. 2021), Anthraquinones have been less studied in this regard. They exhibit several biological activities that demonstrate their significance in traditional medicine (Sieveking et al. 2014, Sirazhetdinova et al. 2020). As representatives, daunorubicin, doxorubicin, emodin and analogues are included in the WHO Essential Medicines and Drug Bank (WHO 2023).

The present study investigated the antitumor activity of nine synthetic anthraquinone derivatives (SAQDs), which structures are illustrated in Figure 1. They have been synthesized according to literature procedures (Almeida et al. 2019, Arcella & Sanchez 2021).

Figure 1
Structures of TMZ and the Synthetic Anthraquinones Derivatives (SAQDs).

Their antitumor activity was evaluated through cell viability assays on glioblastomas of the GBM02 lineage using the MTT method, and their cytotoxic effect was assessed on peripheral blood mononuclear cells (Malik et al. 2021). The most promising derivatives were submitted to morphological analysis and cell migration (Gao & Teng 2015).

As redox cyclers, these compounds were also studied by electrochemical methods, which include as advantages, the fast response time and the possibility of mimicking and clarifying the mechanism of biological action, providing a rapid, oxidative/reductive metabolic fingerprint of molecules/drugs, offering advantages over conventional methods (Hillard et al. 2008, Paiva et al. 2015, Perillo et al. 2020). They are powerful and valuable in the characterization and design of redox-modulating agents (Hillard et al. 2008). They are informative for drug metabolism and function before in vitro and in vivo trials. Most of the compounds were analyzed using cyclic voltammetry to assess their electroactivity.

The compounds under our investigation are bifunctional: the electrophilic quinone and the aromatic sulfides or sulfone groups. The last two decades have grown interest in chalcogen-containing agents with potential redox-modulating properties. Specific redox catalysts containing quinone- and chalcogen-bearing building blocks have shown considerable promise when assayed toward cancer cells and other biological targets (Doering et al. 2010). Certain compounds were deemed intelligent redox agents because they exhibited significant selectivity in responding to distinct redox signatures and quirks within cells (Doering et al. 2010). Quinones utilize several mechanisms to exert a cytotoxic effect (Silva 2020). Of particular interest is their ability to redox cycle with triplet oxygen, forming superoxide and peroxide capable of inflicting damage (ROS generators) (Viswanathan et al. 2013). In contrast, organosulfur compounds (so-called ROS-users) can use ROS and speed up reactions with redox-sensitive proteins and enzymes, ultimately causing malfunction and cell death (Jabbarzadeh Kaboli et al. 2020). They can also behave as antioxidants, depending on concentration and contact time (Ferreira et al. 2009).

MATERIALS AND METHODS

General procedure for the synthesis of aromatic sulfides

Sulfur-containing anthraquinones with different substitution patterns were obtained with reasonable to good yields, following the methodology described in the literature (Almeida et al. 2019).

Cell line

The GBM02 human tumor line was established in the laboratory of Professor Vivaldo Moura Neto, Department of Anatomy of the Biomedical Sciences Institute of the Federal University of Rio de Janeiro. It was obtained from surgical procedures, with the approval of the Research Ethics Committee of the University Hospital Clementino Fraga Filho (protocol number: CEPHUCFF n. 002/01).

Cell viability assay

The assay followed Clementino-Neto et al., 2022. GBM02 cells were plated in 96-well plates at a concentration of 6x103 cells per 100 µL of DMEM/F12 medium; then, they were submitted to a 37 ºC with a 5% CO₂ atmosphere overnight to achieve a better adherence before treatment. Cells were treated with the anthraquinone derivatives (100, 30, 10, 3, 1, and 0.3 μM) to obtain their IC₅₀. The standard drug temozolamide (TMZ) (900, 600, 300, 100, 30, 10, 1, 0.1, 0.01 μM) was used as the positive control. Cells were also treated with controls: DMEM/F12 (only medium), DMF 0.1% (solvent), DMSO 0.1% (solvent), and Triton™ X-100 (lysis control). After treatment, the cells were maintained under the conditions described above for 48 and 72 hours. At the end of the incubation period, the supernatant was discarded; 50 μL of MTT solution (0.5 mg/mL) was added to each well, and cells were incubated for two more hours to the MTT reduction reaction to formazan. In addition, in the lysis control wells, Triton™ X-100 was added before the addition of MTT. Then, the supernatant was discarded, and the cells were lysed with 50 µL of DMSO. Finally, for quantitative determination, the wells were analyzed in a microplate reader at a wavelength of 530 nm ThermoPlate® (Mosmann 1983).

Evaluation of viability on peripheral blood mononuclear cells (PBMC)

Peripheral blood samples were collected from a blood bag of volunteer donors at the Hospital Universitario Professor Alberto Antunes (HUPAA/UFAL), approved by the Ethics Committee for Research with Human Beings, by Plataforma Brasil, under protocol number 6.094.651/2023. Then, they were diluted in PBS (0.1 M) in equal volumes. The formed solution was added to a falcon tube containing histopaque® (2:1). Following that; samples were centrifuged (2,837 rpm, at 26 °C, 30 minutes), which, due to the density of the histopaque®, the divided visible layers were: lower layer containing red blood cells; intermediate layer containing blood mononuclear cells and histopaque®; and upper layer containing serum. The intermediate layer was collected and submitted to two additional centrifugations of 10 minutes each (2,136 rpm and 1,638 rpm, subsequently, at 26 °C) so that the histopaque® was eliminated and only blood cells, such as monocytes and lymphocytes, remained (Ulmer et al. 1984). The solution with isolated monocytes and lymphocytes was cultivated in 96-well plates with RPMI medium (4x105 cells per 50 µL). Then, cells were treated with the anthraquinone derivatives (100, 30, 10, 3, 1, and 0.3 μM) and the standard drug TMZ (900, 600, 300, 100, 30, 10, 1, 0.1, 0.01 μM). Cells were also treated with controls: DMEM/F12 (only medium), DMF 0.1% (solvent), DMSO 0.1% (solvent), and Triton™ X-100 (lysis control). After treatment, the cells were maintained under 37 °C and 5% CO₂ atmosphere for 72 hours. At the end of the incubation period, 20 µL of MTT (5 mg/mL) was added to each well, and the cells were incubated for 4 more hours under the abovementioned conditions. Then, the supernatant was discarded, and the cells were lysed with 200 µL of DMSO. After 20 minutes, for quantitative evaluation, the wells were analyzed in a microplate reader at a wavelength of 550 nm ThermoPlate® (Mosmann 1983).

Evaluation of the selectivity of the anthraquinone derivatives on GBM02

The selectivity index (SI) of anthraquinone derivatives was calculated to assess each derivative’s ability to kill GBM02 cell lines selectively. The SI was calculated by dividing the 50% cytotoxic concentration (CC₅₀) for peripheral blood mononuclear cells (PBMC) by the 50% inhibitory concentration (IC₅₀) of GBM02 cell growth. Thus, the higher the value of SI, the more selective the SAQD will be for glioblastoma.

Evaluation of the effect of the anthraquinone derivatives on the morphology of GBM02

GBM02 cells were plated in 24-well plates (6x103 cells per well) containing 500 µL of DMEM/F12 and 13 mm coverslips attached. Treatments were performed after incubation of the cells in a 37 °C and 5% CO₂ atmosphere for 24 hours to achieve better adherence. After treatments, cells were incubated in the same conditions described for 72 hours. Then, the supernatant was removed, and the cells were washed three times with PBS and fixed with methanol for 2 minutes. Subsequently, the fixed cells were stained with rapid panoptic®. The coverslips were washed with distilled water, dried for 24 hours, and glued to slides with Canada balsam®. The microphotographs displaying the morphology of GBM02 cells after the treatments were obtained through an optical microscope (10x and 40x objectives).

Evaluation of the anti-migratory effect of the anthraquinone derivatives on GBM02 - “Scratch assay.”

GBM02 cells were plated in 24-well plates (1x105 cells per well) with 400 µL of DMEM/F12 and incubated overnight in a 37 °C and 5% CO₂ atmosphere to achieve better adherence. When cells reached a confluency of 90-95%, the assay was performed. First, with a 200 µL tip, a vertical line was made in the center of each well to form a region without cells. Then, the supernatant was discarded to remove suspended cells, and 400 µL of DMEM/F12 medium was added. This moment was set as T0, in which microphotographs of each well were taken with an inverted optical microscope (4x objective), and the photographed locations were marked. Anthraquinone derivatives 1, 4, 5, and 9 were used at concentrations based on their IC₅₀ and ½ IC₅₀: 20 and 10 µM; 70 and 30 µM; 70 and 30 µM; and 80 and 40 µM, respectively. In addition, TMZ was used at 300 µM. Cells were also treated with only TMZ (100 µM), DMF (0.1%), and DMEM/F12 medium. The medium was not supplemented with fetal bovine serum to avoid or minimize cell proliferation, which could induce a bias toward investigating the anti-migratory effect. After treatment, cells were incubated for 24 hours in the abovementioned conditions. The following day, defined as T24, a second microphotograph was captured for each compound in the previously marked area. Thus, the treatments were evaluated qualitatively on migrating the GBM02 cells to the region without cells (Liang et al. 2007). The quantitative analysis was performed in Fiji ImageJ®, which calculates the empty area of the wells at T0 and T24, along with the percentage of inhibition of cell migration in the different treatment groups. The following equation was used for this: % of GBM02 cell migration = 100 – (Empty area at T24 × 100) / (Empty area at T0).

Statistical analysis

Results were expressed as mean ± standard error of the mean (s.e.m.). The statistical differences between the groups were analyzed using Analysis of Variance (ANOVA) followed by Dunnett’s post-hoc test. Values were considered significant when *p < 0.05, **p < 0.01, and ***p < 0.001. The analysis was performed in GraphPad Prism® 7.0. The optical microscopy images from the morphology and scratch assay were analyzed using the Fiji ImageJ® version 2.0.0/2015.

Electrochemical investigation

The electrochemical investigation of the chosen compounds (1-9) was performed to evaluate their electrochemical behaviors in aprotic medium, aiming to identify trend’s structure x cytotoxic activities. Cyclic voltammetry (CV) experiments were performed with a conventional undivided three-electrode cell, using an µAutolabIII (FRA2) potentiostat (Echo Chemie, Utrecht, the Netherlands), coupled to a microcomputer, interfaced by a NOVA® software. The working electrode was a glass carbon electrode (GCE) (d = 3 mm), the counter electrode, a Pt wire, and the reference electrode Ag|AgCl|Cl− (3.0 mol L-1 KCl). GCE was cleaned by mechanical polishing with alumina on a polishing felt (BAS polishing kit). Electrochemical reductions and oxidations were performed in aprotic media (MeCN + n-Bu₄NPF₆ solution 0.1 mol L-1). Each compound (1.0 x 10-3 mol L-1) was added to the supporting electrolyte, and the solution was deoxygenated with argon, before the CV measurements. The scan rate varied from 20.0 to 500.0 mV s-1. The cell was covered with aluminum paper during the experiments to minimize photoreactions. All experiments were performed at room temperature (25 + 1 oC). At the end of each quinone analysis, ferrocene was added as an internal redox probe.

RESULTS

Induction of GBM02 cell death by anthraquinone derivatives

The anti-tumor activity on GBM was performed after 48 hours and 72 hours of treatment (Table I). After 48 hours, TMZ, the standard drug used, showed no activity. Thus, it was not feasible to calculate its IC₅₀ and the percentage of maximum cytotoxicity at the highest concentration used (900 µM). The IC₅₀ could not be calculated for the anthraquinone derivatives because their maximum cytotoxicity did not reach 50%. After 72 hours, TMZ displayed the same behavior as observed before. However, considering the SAQDs, four of them showed antitumor effects, presenting, respectively, IC₅₀ and maximum cytotoxicity of 1 (22.00 ± 2.83 µM; 56.71 ± 2.55 %), 4 (75.00 ± 4.24 µM; 54.93 ± 3.39%), 5 (76.50 ± 9.19 µM; 55.90 ± 5.67 %), and 9 (84.00 ± 4.24 µM; 56.14 ± 3.74%).

Table I
Effect of SAQDs and TMZ on the viability of GBM02 glioblastomas in the MTT assay (after 48 and 72 hours). Results refer to: a50% Inhibitory Concentrati_on (IC50) calculated from toxic concentration-response curves. bMedia ± standard error of the average of the maximum effect (Emax) in triplicates of a representative experiment. Analyzed by ANOVA One-way followed by Dunnett post-test. ***p < 0.001 relative to the DMF group (0.1%). NC: Not determined Maximum cytotoxicity for cells up to 100 µM concentration compared to the DMF group.

Treatments	48 h		72 h
	IC50 a (µM ± s.e.m.)	Emaxb (%± s.e.m.)	IC50a (µM ± s.e.m.)	Emaxb (% ± s.e.m.)
TMZ	>900	NC	>900	NC
1	>100	42.31 ± 2.09***	22.00 ± 2.83	56.71 ± 2.55***
2	>100	22.91 ± 2.27***	>100	29.80 ± 5.58***
3	>100	28.52 ± 4.14***	>100	31.44 ± 4.26***
4	>100	28.36 ± 6.98***	75.00 ± 4.24	54.93 ± 3.39***
5	>100	35.90 ± 3.13***	76.50 ± 9.19	55.90 ± 5.67***
6	>100	43.11 ± 4.72***	>100	33.01 ± 6.94***
7	>100	44.23 ± 1.44***	>100	29.04 ± 1.19***
8	>100	23.24 ± 10.38***	>100	31.08 ± 3.64***
9	>100	47.11 ± 1.36***	84.00 ± 4.24	56.14 ± 3.74***

• Results refer to: a50% Inhibitory Concentration (IC₅₀) calculated from toxic concentration-response curves. bMedia ± standard error of the average of the maximum effect (Emax) in triplicates of a representative experiment. Analyzed by ANOVA One-way followed by Dunnett post-test. ***p < 0.001 relative to the DMF group (0.1%). NC: Not determined Maximum cytotoxicity for cells up to 100 µM concentration compared to the DMF group.

Evaluation of the cytotoxicity of anthraquinone derivatives on PBMC (monocytes and lymphocytes)

Table II shows the cell viability of PBMC (monocytes and lymphocytes) after treatment with the SAQDs and the standard drug TMZ. TMZ and most of the SAQDs did not demonstrate statistically significant cytotoxicity in the test, presenting values of maximum cytotoxicity lower than 19% and CC₅₀ higher than the maximum concentration used (100 µM). However, compounds 5, 8, and 9 significantly reduced the cell viability.

Table II
Inhibition of peripheral blood mononuclear cells (PBMC) proliferation by anthraquinone derivatives and TMZ after 72 h at 100 µM and selectivity of the substances against GBM02. The results refer to: an a50% inhibitory concentrati_on (IC50) calculated by concentration-response curves. bMedia ± standard error of the average of the maximum effect (Emax) in triplicates of a representative experiment. Analyzed by ANOVA One-way followed by Dunnett post-test. *p<0.05, **p<0.01 relative to the DMF group (0.1%). SI: selectivity index. NC: Not determined maximum cytotoxicity for cells up to 100 µM concentration compared to the DMF group.

Treatment (µM)	CC50 (µM ± s.e.m.)a	Cmax (% ± s.e.m.)b	SIc against GBM02
TMZ	>900	NC	-
1	>100	NC	>4.54
2	>100	NC	-
3	>100	NC	-
4	>100	NC	>1.33
5	>100	14.48 ± 6.20*	>1.31
6	>100	NC	-
7	>100	NC	-
8	>100	18.72 ± 7.24**	-
9	>100	16.37 ± 3.00*	>1.19

• The results refer to: an a50% inhibitory concentration (IC₅₀) calculated by concentration-response curves. bMedia ± standard error of the average of the maximum effect (Emax) in triplicates of a representative experiment. Analyzed by ANOVA One-way followed by Dunnett post-test. *p<0.05, **p<0.01 relative to the DMF group (0.1%). SI: selectivity index. NC: Not determined maximum cytotoxicity for cells up to 100 µM concentration compared to the DMF group.

Table II also displays the selectivity index (SI) of SAQDs against GBM02. Compounds 1, 4, 5, and 9 were more toxic to GBM02 cells than to PBMCs, with SI values exceeding 4.55, 1.33, 1.31, and 1.19, respectively. As TMZ had an IC₅₀ > 900 µM and other anthraquinone derivatives had an IC₅₀ > 100 µM, their SI could not be determined.

Effect of anthraquinone derivatives on the morphology of GBM02

The SAQDs that showed higher antitumor activity in GBM02 and lower cytotoxicity in PBMC were selected for evaluation on the morphology of GBM02 cells. Thus, tumor cells were treated with 1, 4, 5, and 9, and after 72 hours, cell morphology was evaluated. Figure 2 shows that cells treated with DMSO (0.1%) and DMF (0.1%) showed protoplasmic morphology with elongated extensions, which is typical for GBM02 cells. The same was observed in cells treated with TMZ (no effect on the morphology). The chosen anthraquinone derivatives were used at concentrations equal to IC₅₀ and ½IC₅₀, as respectively described next: 1 (20 and 10 uM); 4 and 5 (70 and 30 µM); 9 (80 and 40 µM). Results showed that treatment with these compounds induced a reduction in the number of cells, as well as atypical morphology with rounded cell cytoplasm (circles) and the presence of debris (squares) (Figure 2). Treatment with the derivatives also caused the loss of cytoplasmic content through the rupture of the nuclear membrane, with the leakage of its contents (squares) and the formation of cytoplasmic vacuoles (circles) (Figure 3).

Figure 2
Representative microphotographs of the effect of SAQDs and TMZ on the GBM02 morphology. Results refer to the morphological analysis of the GBM02 cells obtained from optical microscopy (10x). a: DMSO 0.1%; b: TMZ 300 µM; c: DMF 0.1%; d: 1 10 µM; e: 1 20 µM; f: 4 70 µM; g: 4 30 µM; h: 5 70 µM; i: 5 30 µM; j: 9 90 µM; k: 9 40 µM; circles: cells with rounded or amorphous cytoplasm; squares: cell debris.

Figure 3
Representative microphotographs of the effect of SAQDs and TMZ on the GBM02 detailed morphology. Results refer to the morphological analysis of the GBM02 cells obtained from optical microscopy (40x). a: DMSO 0.1%; b: TMZ 300 µM; c: DMF 0.1%; d: 1 10 µM; e: 1 20 µM; f: 4 70 µM; g: 4 30 µM; h: 5 70 µM; i: 5 30 µM; j: 9 90 µM; k: 9 40 µM; circles: cytoplasmatic vacuoles and contente leakage; squares: cellular membrane rupture and contente leakage.

Anti-migratory effect of anthraquinone derivatives on GBM02 – “ Scratch assay ”

Anthraquinones 1, 4, 5, and 9 were also used in the scratch assay (Figure 4), being tested at their respective IC₅₀ and ½ IC₅₀ concentrations: 20 and 10 µM; 70 and 30 µM; 70 and 30 µM; and 80 and 40 µM, respectively. Additionally, TMZ was evaluated at a concentration of 300 µM.

Figure 4
Representative microphotographs of the effect of SAQDs and TMZ on the GBM02 cell migration. Results refer to the qualitative analysis of the GBM02 cell migration obtained from inverted optical microscopy (4x). T₀ - a1: DMF 0.1%; a2: TMZ 300 µM; a3: 1 10 µM; a4: 4 30 µM; a5: 5 30 µM; a6: 9 40 µM; T₂₄ - b1: DMF 0.1%; b2: TMZ 300 µM; b3: 1 10 µM; b4: 4 30 µM; b5: 5 30 µM; b6: 9 40 µM; a: percentage of GBM migration in medium, DMF (0.1%), TMZ (100 µM), or 1 (10 µM); b: percentage of GBM migration in medium, DMF (0.1%), TMZ (100 µM), 4 (30 µM) or 5 (30 µM); c: percentage of GBM migration in medium, DMF (0.1%), TMZ (100 µM), or 9 (40 µM).

After 24 hours of treatment (using only concentrations equal to ½IC50), they presented a trend of decreased cell migration, especially sulp1 and 4, when compared to the control group treated with DMF (0.1%). This can be visually confirmed by comparing the microphotographs of T₀ and T₂₄, shown in Figure 4. Also, it is possible to observe that TMZ did not inhibit cell migration. Figure 4 also presents the migratory activity (%) of tumor cells after treatment with the tested compounds, allowing for the calculation of the migration percentage. It was observed that the migratory capacity of GBM02 cells was only 16% when treated with compound 1, 29.38% with compound 4, 51.14% with compound 5, and 51.85% with compound 9. TMZ did not exhibit an antimigratory effect.

Electrochemistry

As shown in earlier sections, some sulfide- and sulfone-derived anthraquinones may be considered potential leads.

Through cyclic voltammetry (CV) studies, valuable information about the oxidation and reduction processes may be compared to their biological behavior in vitro and in vivo.

In the present case, CV was used to investigate the electrochemical behavior of nine SAQDs (1, 2, 3, 4, 5, 6, 7, 8 and 9). The obtained profiles confirmed the presence of the two individuals’ redox centers.

In typical measurements, CV was recorded in an aprotic medium (MeCN+ TBAPF₆, 0.1 mol L-1), which resembles the membrane environment, at a scan rate of 100 mV s-1. This enabled the determination of each compound’s electrochemical reduction (from 0.5 up to -3.0 V) and oxidation (from -0.5 V up to 2.0 V) behaviors, with the cathodic and anodic peak potential listed in Table III.

Table III
Electrochemical parameters.

	E pcI (V)	E paI (V)	E1/2 1/2(E pcI + E paI)	E pcII (V)	E paII (V)	E1/2 1/2(EpcII+ EpaII)	ΔE 1( E pcI- E paI) (mV)	ΔE 2 E pcII- E paII) (mV)	ΔE 3( E pcI- E pcII) (mV)
1	-0.75	-0.70	-0.72	-1.32	-1.25	-1.29	44	73	59
2	-0.85	-0.78	-0.82	-1.34	-1.27	-1.31	73	73	49
3	-0.88	-0.80	-0.84	-1.44	-1.35	-1.39	78	83	56
4	-0.86	-0.82	-0.84	-1.38	-1.32	-1.35	44	58	52
5	-0.72	-0.64	-0.68	-1.27	-1.19	-1.23	73	83	55
6	-0.72	-0.64	-0.68	-1.32	-1.24	-1.28	78	83	60
7	-0.73	-0.65	-0.69	-1.30	-1.21	-1.26	73	93	58
9	-0,73	-0, 66	-0.69	-1.31	-1.20	-1.25	73	112	58
10	-0.88	-0.82	-0.85	-1.32	-1.24	-1.28	68	78	43
11	-0.87	-0.80	-0.84	-1.38	-1.30	-1.34	78	83	51

The choice of the aprotic media is well established in the literature (Prince et al. 2022). In the present case, to allow a better understanding concerning structural aspects and electrochemical parameters, two additional substances were analysed: 10 and 11, for which no biological data was obtained. The amounts were very low, just enough to do CVs.

As expected for SAQDs, all the sulfides (1-4) had shown electrochemical activity in the cathodic and anodic arms of the CV, represented herein by the profiles of compound 3 (Figure 5a). Conversely, the sulfones (5-9), were electroactive only in the cathodic section of the CV, herein represented by compound 7 (Figure 5b).

Figure 5
Cyclic voltammetry (CV) of the compounds 3 and 7 (1 mM) in MeCN + TBAPF₆ (0.1 M), glassy carbon electrode (GCE), the counter electrode was a Pt wire, and the reference electrode was Ag|AgCl|Cl− (3.0 mol L-1 KCl), cathodic direction from 0 V, ν = 0.1 V s–1, potential range: -2.8 V - +2.0 V. (1) From 0.0 V up to -2.8 V and back to +2.0 V, returning to 0 V; (2) Several potential’s invertions; (3) graph of the analysis of the current vs. ν½.

The CV profiles of the sulfides are represented by three reduction waves (Ic, IIc, IIIc), the first two monoelectronic, diffusion-controlled, with a quasi-reversible one-electron uptake, associated with the oxidation peaks (Ia, IIa), with a ΔEpc of 78.1 mV, and 83.1 mV. The third one (IIIc) is close to the electrolyte discharge, with an irreversible nature. The other compounds have a similar profile, except for the halogenated ones. For them, represented by compound 2, the second wave IIc is broader and representative of associated electron transfer processes (Figure 6).

Figure 6
Cyclic voltammetry (CV) of compound 2 (1 mM) in MeCN + TBAPF₆ (0.1 M), glassy carbon electrode (GCE), the counter electrode was a Pt wire, and the reference electrode was Ag|AgCl|Cl− (3.0 mol L-1 KCl), cathodic direction from 0 V, ν = 0.1 V s–1, potential range: -2.8 V - +2.0 V.

The cathodic and anodic potentials of each anthraquinone studied are listed in Table III. As expected for anthraquinones, all voltammograms presented two pairs of waves (Ic/Ia, IIc/IIa) in the cathodic region, which are related to the reduction in two successive steps of the quinone moiety. The first reduction forms the AQ• −, followed by an extra electron uptake to give the dianion (AQ2-).

We observed that the first and second cathodic waves (Ic, IIc) presented quasi-reversible characteristics (Table III, ΔE ₁ varied from 43.94 to 78.13 mV, ΔE₂ varied from 58.6 to 92.77 mV), accompanied by their corresponding oxidation waves (Ia, IIa).

Considering the data presented in Table III, we can classify the compounds studied in order of the ease of reduction, using the EpcI values ​​(cathodic peak potential of the first reduction process). The less negative the potential, the greater its electrophilicity and the easier the reduction process.

$$5\sim 6>7>9>1>2>4>11>3>10$$

The CV profiles of the analyzed compounds allow us to determine the effects of the S-substituent and their oxidation number on reduction and oxidation. The reduction is favored by the sulfone (greater electron-withdrawing effects), as observed in the values of peaks Ic and IIc, which are the more electrophilic SAQDs (compounds 5, 6, 7).

Concerning the sulfides, trifluoromethyl, as a strong electronegative group through inductive effect, decreases the electron density locally and, by extension, in the anthraquinone function, which results in an anodic shift in the cathodic peak.

DISCUSSION

Finding novel GBM treatments remains challenging due to ineffectiveness and safety concerns. New medications or chemical leads, including synthetic and natural quinone derivatives, are being investigated as potential treatments for this disease (Lim et al. 2020).

In this context, GBM02 cells were subjected to in vitro biological tests to examine the anticancer activity of the SAQDs. First, the MTT colorimetric method was used to assess the viability of GBM02 cells. In this method, cells were treated with the compounds, and their responses were measured after 48 and 72 hours (Table I). At the maximum tested dose of 100 µM, after 48 hours, the SAQDs substantially reduced (***p < 0.001) the viability of tumor cells. However, calculating the IC₅₀ was not possible, since the compound treatment was unable to inhibit 50% of the viability.

At the highest tested dose of 100 µM, after 48 hours, SAQDs significantly reduced (***p < 0.001) tumor cell viability. However, it was not possible to calculate the IC₅₀, as treatment with anthraquinones did not inhibit 50% of viability. Notably, SAQDs exhibited a more pronounced maximal cytotoxic effect compared to TMZ, the standard first-line chemotherapy drug for glioblastoma. TMZ was observed to be inactive even at a concentration of 900 µM after 48 hours of treatment, which is nine times higher than the maximum concentration at which SAQDs were tested.

Upon close examination of the data, 1, 6, 7, and 9 showed a tendency toward the development of anticancer activity at 48 hours. Considering this, a 72 hours treatment was performed. After prolonged exposure, a statistically significant antitumor effect (***p < 0.001) of SAQDs was observed, highlighting derivatives 1 (sulfur CF₃-substituted-anthraquinone), 4 (m-Cl-aryl-substituted-anthraquinone), 5 (sulfone p-Me-phenyl-substituted-anthraquinone), and 9 (sulfone m-OMe-aryl-substituted-anthraquinone), with IC₅₀ values of 22.00, 75.00, 76.50, and 84.00 µM, respectively. Again, TMZ was inactive at a concentration of 900 µM after 72 hours of treatment, demonstrating the promising nature of the active derivatives tested.

In line with our findings, Sirazhetdinova et al. (2020) tested a variety of hydroxyanthraquinones against the SNB-19 GBM cell. Using the MTT assay, they found IC₅₀ values ranging from 5.77 ± 0.23 to 41.8 ± 5.27 µM after 72 hours of treatment, confirming the anticancer potential of this chemical class. Similarly, other anthraquinones have been reported to exhibit high in vitro anti-glioblastoma activity, including danthron (Lu et al. 2010), mitoxantrone (Senbabaoglua et al. 2016), naphtho[2,3-f]quinoxaline-7,12-dione (Huang et al. 2023), and aloe-emodin (Arcella et al. 2018).

Antitumor activity is directly related to the decrease in the viability of tumor cells, thus making it the starting point in the discovery of new anticancer drugs. Still, these new drug prototypes must not affect healthy human cells. Therefore, evaluating the cytotoxic effects of the anthraquinone derivatives on PBMC is essential.

After treating the PBMCs with SAQDs and TMZ for 72 hours, the viability of the cells was assessed. Except for the sulfones 5, 8, and 9, which were able to statistically reduce (*p < 0.05) the PBMC viability at the maximum concentration (100 µM), most derivatives and TMZ did not show any signs of cytotoxicity at the tested concentrations against PBMC. Nevertheless, this result was not seen in more than 50% of the cell population, indicating that the chemicals in question had an IC₅₀ greater than 100 µM against PBMC.

Interestingly, when anthraquinone emodin and thymoquinone (a benzoquinone) were evaluated regarding the deleterious effect they could cause on PBMC, it was observed that emodin presented lower cytotoxicity than thymoquinone. Specifically, concentrations of 20 and 7 μg/mL of emodin and thymoquinone resulted in over 40% cell death (Bhattacharjee et al. 2020). On the other hand, a study by Castro et al. (2023), showed that 2’-OH-Torosaol, another anthraquinone, did not affect PBMC viability.

The quinones tested in this study can be well tolerated by healthy human cells, as shown by treating peripheral blood monolayer cells (PBMC) with the compounds in the study.

Considering the effect of the anthraquinone derivatives on GMB02 and PBMC, the selectivity index (SI) calculation provided data showing that compounds 1, 4, 5, and 9 were more selective against tumor cells (Table II). Compared to compound 1, with an SI > 4.55, compounds 4, 5, and 9 likely exhibit lower cytotoxic selectivity for tumor cells, with an SI < 2. Due to the higher TMZ concentration used for IC₅₀ calculation (900 µM), results were not expressed for this compound.

The SI is crucial for identifying new anticancer drugs. Higher SI values indicate greater safety, reducing the likelihood of side effects and enhancing selectivity for cancer cells over normal cells. This guides the selection of molecules for drug development (Kumar et al. 2020). While the SI values in this study are not exceptionally high (>4.54 for 1, >1.30 for 4 and 5, and >1.19 for 9), we must weigh the risks against the benefits, as the FDA does when approving new drugs. For conditions with a poor prognosis, such as AIDS or glioblastoma, the standards may be more lenient, given the potential benefits outweighing the risks. With that, the 1, 4, 5, and 9 derivatives were selected to proceed with other tests due to the possible antitumor activity presented the assumption of not presenting deleterious action in monocytes and lymphocytes.

It is known that to ensure the success of tumor elimination, a novel therapeutic approach is required to prevent tumor cell resistance and give new medicines the ability to cause apoptosis (Ghaemi et al. 2020). The GBM02 morphology evaluation test following SAQD treatment aimed to determine whether these derivatives can induce apoptosis at the cellular level by looking for indications of this induction in tumor cells.

Following 72 hours of exposure of GBM02 cells to 1, 4, 5, and 9, results showed that they were able to induce cell death. The cytoplasm of the cells was amorphous and spherical, and there was cellular debris, cytoplasmic vacuoles with leaking content, and membrane rupture-related loss of cellular content. In GBM02, TMZ did not affect the shape. These structural alterations are hypothesized to be related to promoting cell death induced by anthraquinone derivatives.

The morphological characteristics observed in tumor cells are highly suggestive of cell death: the amorphization and sphericity of the cytoplasm indicate a loss of structural integrity of the cell; the presence of cellular debris, which are dispersed cell fragments, indicate the rupture of the plasma membrane and the release of cellular content into the extracellular medium; cytoplasmic vacuoles with extravasated content suggest rupture of organelles and loss of cellular compartmentalization; the rupture of the plasma membrane leads to the loss of cellular content (D’Arcy 2019).

It is known that excessive ROS production can induce both apoptosis and necrosis (Hancock et al. 2001). We hypothesize that the anthraquinones tested here induce necrosis in GBM02 cells by increasing ROS levels. Supporting our hypothesis, Lin et al. (2021) reported that the anthraquinone 1-[(E)-4-(1-hydroxy-9,10-anthraquinone-3-yloxy)but-2-enyl]-1H-1,2,3-triazole-4,5-dicarboxylic dimethyl ester-induced necrosis and ROS production in PC3 prostate cancer cells.

Moreover, DNA alkylating agents are known to induce necrosis in tumor cells (Proskuryakov & Gabai 2010). The most potent anthraquinone in our study, derivative 1, contains a trifluoromethyl radical. The high electronegativity of fluorine atoms gives this radical a strong electrophilic character, making it highly reactive towards DNA. Its small size and lipophilicity likely facilitate its interaction with specific DNA sites and its entry into cells, respectively.

Yu et al. (2020) showed results for the induction of apoptosis in the U251 cell lineage of GBM while treated with 2-methoxy-6-acetyl-7-methyljuglone, a quinone derivative. They found that this compound directly activated quinone oxidoreductase 1, which is related to programmed cell death, along with the induction of rapid generation of ions and cytosolic accumulation of protons.

Nevertheless, given that morphological analyses alone are inadequate to determine the specific type of cell death being elicited, in order to validate our hypothesis, further assays employing flow cytometry techniques are required and will be carried out in the future.

In addition, the limited survival and poor prognosis for patients with GBM are often characterized by the fact that the current therapy is not able to reach many tumor cells. The non-affected cells usually infiltrate the tissue around the tumor. Generally, these cells are not removed by surgical resection or reached by radiotherapy, as they are located outside the tumor area.

Through processes in the tissue from which the tumor started, GBM cells exhibit an infiltrative migration in which they utilize the perivascular space of preexisting blood arteries. This makes chemotherapy more challenging to administer and raises the possibility that tumor cells will spread to other organs and tissues, which might result in the formation of metastases (Ghaemi et al. 2020).

The anti-migratory effect of the chosen compounds on GBM cells (scratch assay) was evaluated to determine whether they could inhibit this feature. The derivatives 1, 4, 5, and 9 showed a statistically anti-migratory effect (***p<0.001). As such, the chemical approaches for synthesizing these compounds provided a structure capable of inhibiting this critical feature of GBM cells.

Hernández-Rodríguez et al. (2020) studied the anti-migratory effect of pure zone, a sesquiterpene benzoquinone. They found that this substance decreased cell migration, reinforcing the results obtained from the tested anthraquinone derivatives.

Regarding the electrochemical part, Table III shows that the reduction potentials undergo anodic shifts due to the presence of electron-withdrawing groups. The difference between sulfides and sulfoxides’ effects was between 0.130 and 0.150 V, while the -CF₃ substituent enhances the reduction facility around 0.130 mV. Regarding biological cytotoxicity against glioblastoma cells, except for compound 4, the more electrophilic compounds demonstrate better performance.

CONCLUSIONS

The biological tests point to the antitumor potential of the synthetic anthraquinone derivatives, especially 1, 4, 5, and 9. Different studies corroborate the results, suggesting that these anthraquinones are promising chemical structures in discovering and developing new antitumor drugs. As prodrugs, the electrochemistry of SAQD revealed predictable substituent effects in the anodic and cathodic arms of the voltammograms. Despite the small number of compounds, a trend toward a more straightforward reduction (more positive potentials) can be suggested, as evidenced before.

There is an urgent need for new medications because the drawbacks of existing treatments force patients to stop their therapy, which worsens the disease’s progression.

Acknowledgements

The authors thank the State Institute of the Brain Paulo Niemeyer. All the authors are also grateful to Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). R. G. Almeida, G. A. M. Jardim, and E. N. da Silva Júnior are also grateful to CNPq (309774/2020-9, 405052/2021-9, 421655/2023-2, 441404/2023-5, 151734/2024-0), CAPES, and FAPEMIG (APQ-00724-23, APQ-01538-24, APQ-04401-23, APQ-02496-24 and TEC-RED-00081-23) for support. M. S. Alexandre-Moreira and A. C. Queiroz would like to express their gratitude to the funding agencies, as this work was supported by the Instituto Nacional de Ciência e Tecnologia de Fármacos e Medicamentos (573.564/2008-6), FAPEAL (Pro-equipamento 60030.0000001213/2024; Pró-equipamento 60030.0000001205/2024), and British Council (DESIRE project).

References

• ALMEIDA RG, CARVALHO RL, NUNES MP, GOMES RS, PEDROSA LF, DE SIMONE CA, GOPI E, GEERTSEN V, GRAVEL E, DORIS E & DA SILVA-JÚNIOR EN. 2019. Carbon nanotube-ruthenium hybrid towards mild oxidation of sulfides to sulfones: Efficient synthesis of diverse sulfonyl compounds. Catal Sci Technol 9: 2742-2748.
• ARCELLA A, OLIVA MA, STAFFIERI S, SANCHEZ M, MADONNA M, RIOZZI B, ESPOSITO V, GIANGASPERO F & FRATI L. 2018. Effects of aloe emodin on U87MG glioblastoma cell growth: In vitro and in vivo study. Environ Toxicol 33: 1160-1167.
• ARCELLA A & SANCHEZ M. 2021. Natural substances to potentiate canonical glioblastoma chemotherapy. J Cancer Ther 33: 276-287.
• BHATTACHARJEE M, UPADHYAY P, SARKER S, BASU A, DAS S, GHOSH A, GHOSH S & ADHIKARY A. 2020. Combinatorial therapy of Thymoquinone and Emodin synergistically enhances apoptosis, attenuates cell migration and reduces stemness efficiently in breast cancer. Biochim Biophys Acta Gen Subj 1864: 129695.
• CASTRO DTH, LEITE DF, DA SILVA BALDIVIA D, DOS SANTOS HF, BALOGUN SO, DA SILVA DB, CAROLLO CA, DE PICOLI SOUZA K & DOS SANTOS EL. 2023. Structural Characterization and Anticancer Activity of a New Anthraquinone from Senna velutina (Fabaceae). Pharmaceuticals 16: 951.
• CLEMENTINO-NETO J ET AL. 2022. In vitro antitumor activity of dialkylamine-1,4-naphthoquinones toward human glioblastoma multiforme cells. N J Chem 46: 4587-4602.
• D’ARCY MS. 2019. Cell death: a review of the major forms of apoptosis, necrosis and autophagy. Cell Biol Int 43: 582-592.
• DASH UC ET AL. 2025. Understanding the molecular bridges between the drugs and immune cell. Pharmacol Therapeutics 267: 108805.
• DELELLO DI FILIPPO L, HOFSTÄTTER AZAMBUJA J, PAES DUTRA JA, TAVARES LUIZ M, LOBATO DUARTE J, NICOLETI LR, OLALLA SAAD ST & CHORILLI M. 2021. Improving temozolomide biopharmaceutical properties in glioblastoma multiforme (GBM) treatment using GBM-targeting nanocarriers. Eur J Pharm Biopharm 168: 76-89.
• DOERING M ET AL. 2010. Synthesis and Selective Anticancer Activity of Organochalcogen Based Redox Catalysts. J Med Chem 53: 6954-6963.
• FERREIRA DCM, TAPSOBA I, ARBAULT S, BOURET Y, MOREIRA MSA, PINTO AV, GOULART MOF & AMATORE C. 2009. Ex vivo Activities of b-Lapachone and a-Lapachone on Macrophages: A Quantitative Pharmacological Analysis Based on Amperometric Monitoring of Oxidative Bursts by Single Cells. ChemBioChem 10: 528-538.
• GAO L & TENG Y. 2015. Exploiting Plug-And-Play Electrochemistry for Drug Discovery. Future Med Chem 8: 567-577.
• GHAEMI S, AREFIAN E, REZAZADEH VALOJERDI R, SOLEIMANI M, MORADIMOTLAGH A & JAMSHIDI ADEGANI F. 2020. Inhibiting the expression of anti-apoptotic genes BCL2L1 and MCL1, and apoptosis induction in glioblastoma cells by microRNA-342. Biomed Pharmacother 121: 109641.
• GLORIEUX C, LIU S, TRACHOOTHAM D & HUANG P. 2024. Targeting ROS in cancer: rationale and strategies. Nat Rev Drug Discov 23: 583-606.
• GORRINI C, HARRIS I & MAK T. 2013. Modulation of oxidative stress as an anticancer strategy. Nat Rev Drug Discov 12: 931-947.
• HANCOCK JT, DESIKAN R & NEILL SJ. 2001. Role of reactive oxygen species in cell signaling pathway. Biochem Soc Trans 29: 345-350.
• HERNÁNDEZ-RODRÍGUEZ M, MENDOZA SÁNCHEZ PI, MARTÍNEZ J, MACÍAS PÉREZ ME, CRUZ ER, ŻOŁEK T, MACIEJEWSKA D, RUVALCABA RM, JIMÉNEZ EM & NICOLÁS-VÁZQUEZ MI. 2020. In Vitro and computational studies of Perezone and Perezone Angelate as potential anti-glioblastoma multiforme agents. Biochimie 171-172: 158-169.
• HILLARD EA, DE ABREU FC, FERREIRA DCM, JAOUEN G, GOULART MOF & AMATORE C. 2008. Electrochemical parameters and techniques in drug development, with an emphasis on quinones and related compounds. Chem Commun 23: 2612-2628.
• HUANG H-S, CHIANG I-T, LAWAL B, WENG Y-S, JENG L-B, KUO Y-C, LIU Y-C & HSU F-T. 2023. A Novel Isotope-labeled Small Molecule Probe CC12 for Anti-glioma via Suppressing LYN-mediated Progression and Activating Apoptosis Pathways. Int J Biol Sci 19: 3209-3225.
• JABBARZADEH KABOLI P ET AL. 2020. Targets and mechanisms of sulforaphane derivatives obtained from cruciferous plants with special focus on breast cancer - contradictory effects and future perspectives. Biomed Pharmacother 121: 109635.
• KLECKNER AS, KLECKNER IR, KAMEN CS, TEJANI MA, JANELSINS MC, MORROW GR & PEPPONE LJ. 2019. Opportunities for cannabis in supportive care in cancer. Ther Adv Med Oncol 11: 1758835919866362.
• KUMAR P, MONDAL I, KULSHRESHTHA R & PATRA AK. 2020. Development of novel ruthenium (ii)–arene complexes displaying potent anticancer effects in glioblastoma cells. Dalton Transactions 49: 13294-13310.
• LIANG CC, PARK AY & GUAN JL. 2007. In vitro scratch assay: A convenient and inexpensive method for analysis of cell migration in vitro. Nat Protoc 2: 329-333.
• LIM EJ ET AL. 2020. Crosstalk between GBM cells and mesenchymal stemlike cells promotes the invasiveness of GBM through the C5a/p38/ZEB1 axis. Neuro Oncol 22: 1452-1462.
• LIN K-W, LIN W-H, SU C-L, HSU H-Y & LIN C-N. 2021. Design, synthesis and antitumour evaluation of novel anthraquinone derivatives. Bioorg Chem 107: 104395.
• LU H-F ET AL. 2010. Danthron Induced Apoptosis Through Mitochondriaand Caspase-3-Dependent Pathways in Human Brain Glioblastoma Multiforms GBM 8401 Cells. Neurochem Res 35: 390-398.
• MALIK MS, ALSANTALI RI, JASSAS RS, ALSIMAREE AA, SYED R, ALSHARIF MA, KALPANA K, MORAD M, ALTHAGAFI II & AHMED SA. 2021. Journey of anthraquinones as anticancer agents – a systematic review of recent literature. RSC Adv 11: 35806-35827.
• MOSMANN T. 1983. Rapid colorimetric assay for cellular growth and survival: Application to proliferation and cytotoxicity assays. J Immunol Methods. 65: 55-63.
• PAIVA YG, FERREIRA FR, SILVA TL, LABBÉ E, BURIEZ O, AMATORE C & GOULART MOF. 2015. Electrochemically Driven Supramolecular Interaction of Quinones and Ferrocifens: An Example of Redox Activation of Bioactive Compounds. Curr Top Med Chem 2: 36-162.
• PELICANO H, CARNEY D & HUANG P. 2004. ROS stress in cancer cells and therapeutic implications. Drug Resist Updates 7: 97-110.
• PERILLO B, DI DONATO M, PEZONE A, DI ZAZZO E, GIOVANNELLI P, GALASSO G, CASTORIA G & MIGLIACCIO A. 2020. ROS in cancer therapy: the bright side of the moon. Exp Mol Med 52: 192-203.
• PRINCE RC, DUTTON PL, GUNNER MR. 2022. The aprotic electrochemistry of quinones. BBA - Bioenergetics 1863: 148558.
• PROSKURYAKOV SY & GABAI VL. 2010. Mechanisms of Tumor Cell Necrosis. Curr Pharm Des 16: 56-68.
• SENBABAOGLUA F, CINGOZA A, KAYAA E, KAZANCIOGLUA S, LACKA NA, ACILANB C & BAGCI-ONDERA T. 2016. Identification of Mitoxantrone as a TRAIL-sensitizing agent for Glioblastoma Multiforme. Cancer Biol Ther 17: 546-557.
• SIES H, BERNDT C & JONES DP. 2017. Oxidative Stress. Annu Rev Biochem 86: 715-748.
• SIEVEKING I ET AL. 2014. 2-Phenylaminonaphthoquinones and related compounds: Synthesis, trypanocidal and cytotoxic activities. Bioorganic Med Chem 22: 4609-4620.
• SILVA TL, AZEVEDO MLSG, FERREIRA FR, SANTOS DC, AMATORE C & GOULART MOF. 2020. Quinone-based molecular electrochemistry and their contributions to medicinal chemistry: A look at the present and future. Curr Opin Electrochem 24: 79-87.
• SIRAZHETDINOVA NS, SAVELYEV VA, FROLOVA TS, BAEV DS, KLIMENKO LS, CHERNIKOV IV, OLESHKO OS, SAROJAN TA, POKROVSKII AG & SHULTS EE. 2020. 1-Hydroxyanthraquinones containing aryl substituents as potent and selective anticancer agents. Molecules 25: 2547.
• ULMER AJ, SCHOLZ W, ERNST M, BRANDT E & FLAD HD. 1984. Isolation and subfractionation of human peripheral blood mononuclear cells (PBMC) by density gradient centrifugation on Percoll. Immunobiology 166: 238-250.
• VALKO M, LEIBFRITZ D, MONCOL J, CRONIN MTD, MAZURA M & TELSER J. 2007. Free radicals and antioxidants in normal physiological functions and human disease. The Internat J Biochem Cell Biol 39: 44-84.
• VISWANATHAN UM, BURKHOLZ T & JACOB C. 2013. Electrochemistry at the Edge of Reason: Chalcogen-Based Redox Systems in Biochemistry and Drug Design. Z Phys Chem 227: 691.
• WHO - WORLD HEALTH ORGANIZATION. 2023. Ginebra. https://www.who.int/publications/i/item/WHO-MHP-HPS-EML-2023.02, accessed on 22_07_2024.
  » https://www.who.int/publications/i/item/WHO-MHP-HPS-EML-2023.02
• XIAOQIN A, WENFENG Y, JINBAO L, DAOLIN T, LI Y & XIN C. 2024. Oxidative cell death in cancer: mechanisms and therapeutic opportunities. Cell Death Disease 15: 556.
• YU J, ZHONG B, JIN L, HOU Y, AI N, GE W, LI L, LIU S, LU JJ & CHEN X. 2020. 2-Methoxy-6-acetyl-7-methyljuglone (MAM) induced programmed necrosis in glioblastoma by targeting NAD(P)H: Quinone oxidoreductase 1 (NQO1). Free Radic Biol Med 152: 336-347.
• ZOU J ET AL. 2025. Tumor microenvironment-responsive engineered hybrid nanomedicine for photodynamic-immunotherapy via multi-pronged amplification of reactive oxygen species. Nat Commun 16: 424.

Publication Dates

• Publication in this collection
  16 June 2025
• Date of issue
  2025

History

• Received
  13 Dec 2024
• Accepted
  13 Mar 2025