Alpha-tocopherol protects against cisplatin-induced toxicity without interfering with antitumor efficacy

Oxidative Damage as a Fundament of Systemic Toxicities Induced by Cisplatin-The Crucial Limitation or Potential Therapeutic Target?

Cisplatin, an inorganic complex of platinum, is a chemotherapeutic drug that has been used for 45 years. Despite the progress of pharmaceutical sciences and medicine and the successful application of other platinum complexes for the same purpose, cisplatin is still the therapy of choice in many cancers. Treatment for testicular, ovarian, head and neck, urothelial, cervical, esophageal, breast, and pulmonary malignancies is still unthinkable without the use of this drug. However, cisplatin is also known for many side effects, of which the most pronounced are nephrotoxicity leading to acute renal failure, neurotoxicity, and ototoxicity. Mechanistic studies have proven that one of the conditions that plays a major role in the development of cisplatin-induced toxicities is oxidative stress. Knowing the fact that numerous antioxidants can be used to reduce oxidative stress, thereby reducing tissue lesions, organ failure, and apoptosis at the cellular level, many studies have defined antioxidants as a priority for investigation as a cotreatment. To investigate the mechanism of antioxidant action in vivo, many animal models have been employed. In the last few years, studies have mostly used rodents and zebrafish models. In this article, some of the most recent investigations that used animal models are listed, and the advantages and disadvantages of such experimental studies are pointed out.

Effects of natural products on cisplatin ototoxicity and chemotherapeutic efficacy

INTRODUCTION

Cisplatin is a very effective chemotherapeutic agent against a variety of solid tumors. Unfortunately, cisplatin causes permanent sensorineural hearing loss in at least two-thirds of patients treated. There are no FDA approved drugs to prevent this serious side effect.

AREAS COVERED

This paper reviews various natural products that ameliorate cisplatin ototoxicity. These compounds are strong antioxidants and anti-inflammatory agents. This review includes mostly preclinical studies but also discusses a few small clinical trials with natural products to minimize hearing loss from cisplatin chemotherapy in patients. The interactions of natural products with cisplatin in tumor-bearing animal models are highlighted. A number of natural products did not interfere with cisplatin anti-tumor efficacy and some agents actually potentiated cisplatin anti-tumor activity.

EXPERT OPINION

There are a number of natural products or their derivatives that show excellent protection against cisplatin ototoxicity in preclinical studies. There is a need to insure uniform standards for purity of drugs derived from natural sources and to ensure adequate pharmacokinetics and safety of these products. Natural products that protect against cisplatin ototoxicity and augment cisplatin's anti-tumor effects in multiple studies of tumor-bearing animals are most promising for advancement to clinical trials. The most promising natural products include honokiol, sulforaphane, and thymoquinone.

Gallic acid and/or cerium oxide nanoparticles synthesized by gamma-irradiation protect cisplatin-induced nephrotoxicity via modulating oxidative stress, inflammation and apoptosis

Cisplatin is one of the most significant anticancer. However, its use is associated with numerous toxicities especially nephrotoxicity. The main aim of this work was to examine the protective effect of Gallic acid (GA) and/or cerium oxide nanoparticles (CONPs) synthesized by gamma-irradiation on cisplatin-induced nephrotoxicity in rats. To do that, 48 adult male albino rats were separated into eight groups and received GA (100 mg/kg orally) and/or CONPs (15 mg/kg i. p.) for 10 days before injection with a single dose of cisplatin (7.5 mg/kg i. p.). The findings showed that cisplatin treatment impaired kidney functioning as shown by elevated serum levels of urea and creatinine. Additionally, the oxidative stress indicators (MDA and NO), levels of NF-kB, pro-inflammatory cytokines (IL1-and TNF-) and pro-apoptotic proteins (BAX and caspase-3) were raised after cisplatin injection, while levels of intrinsic anti-oxidants (CAT, SOD, and GSH) and anti-apoptotic protein (Bcl-2) were reduced. Moreover, renal toxicity was confirmed by alteration in normal histological architecture of the kidneys. On the other hand, pretreatment with CONPs and/or GA ameliorated cisplatin-induced nephrotoxicity as evidenced by improvement of renal function parameters and levels of oxidative stress, inflammatory and apoptotic markers in renal tissue along with the renal histopathological changes. This study clarifies how GA and CONPs protect against cisplatin-induced nephrotoxicity and demonstrates any potential synergism between them. Therefore, they can be considered as promising nephroprotective agents during chemotherapy.

Cisplatin Neurotoxicity Targets Specific Subpopulations and K+ Channels in Tyrosine-Hydroxylase Positive Dorsal Root Ganglia Neurons

Among the features of cisplatin chemotherapy-induced peripheral neuropathy are chronic pain and innocuous mechanical hypersensitivity. The complete etiology of the latter remains unknown. Here, we show that cisplatin targets a heterogeneous population of tyrosine hydroxylase-positive (TH+) primary afferent dorsal root ganglion neurons (DRGNs) in mice, determined using single-cell transcriptome and electrophysiological analyses. TH+ DRGNs regulate innocuous mechanical sensation through C-low threshold mechanoreceptors. A differential assessment of wild-type and vitamin E deficient TH+ DRGNs revealed heterogeneity and specific functional phenotypes. The TH+ DRGNs comprise; fast-adapting eliciting one action potential (AP; 1-AP), moderately-adapting (≥2-APs), in responses to square-pulse current injection, and spontaneously active (SA). Cisplatin increased the input resistance and AP frequency but reduced the temporal coding feature of 1-AP and ≥2-APs neurons. By contrast, cisplatin has no measurable effect on the SA neurons. Vitamin E reduced the cisplatin-mediated increased excitability but did not improve the TH+ neuron temporal coding properties. Cisplatin mediates its effect by targeting outward K+ current, likely carried through K2P18.1 (Kcnk18), discovered through the differential transcriptome studies and heterologous expression. Studies show a potential new cellular target for chemotherapy-induced peripheral neuropathy and implicate the possible neuroprotective effects of vitamin E in cisplatin chemotherapy.

Comparative analysis of the seasonal influence on polyphenolic content, antioxidant capacity, identification of bioactive constituents and hepatoprotective biomarkers by in silico docking analysis in Premna integrifolia L

The present study reports the effect of different seasons on polyphenol content and antioxidant potential of ethanolic, methanolic, ethyl acetate, and aqueous extracts of leaves, stems, and roots of Premna integrifolia. Ethyl acetate extract of leaves (EAEPI) collected in the rainy season showed potent antioxidant activity with highest total phenol (74.33 ± 2.26 µg/mg, gallic acid equivalent), and flavonoid (98.83 ± 0.26 µg/mg, rutin equivalent) content. Therefore, EAEPI extract was subjected to characterization by UHPLC-Q-TOF-MS/MS and GC-MS analysis for the identification of active constituents. UHPLC-Q-TOF-MS/MS analysis in + ve ion mode revealed the presence of eight polyphenolic compounds namely quercetin-3-D-xyloside, kaempferol-3,7-O-bis-alpha-L-rhamnoside, isorhamnetin-3-Oglucoside, luteolin-3',7-di-O-glucoside, eriodictyol-7-O-glucoside, syringetin-3-O-galactoside, petunidin-3-O-beta-glucopyranoside and vitexin-2″-O-rhamnoside. GC-MS analysis confirmed the presence of 26 compounds with six major compounds viz; citronellol, phytol acetate, campesterol, squalene, stigmasterol, and hexadecanoic acid. These compounds are reported for the first time from P. integrifolia except phytol and stigmasterol. Our previous study validates the hepatoprotective potential of P. integrifolia but there was no idea about the bioactive compound responsible for the activity. So, in present work, the major compounds identified in spectrometry analysis were subjected to in silico docking against an important liver enzyme alanine amino transaminase to confirm its hepatoprotective properties. Docking analysis validates the presence of two hepatoprotective lead compounds stigmasterol, and campesterol, which satisfy the drug-likeness criteria with good absorption, distribution, metabolism, and toxicity properties. Thus, present work gives a clear insight about the influence of season on the total polyphenolic constituent in different plant parts of P. integrifolia, their antioxidant potential and preclinical evaluation of hepatoprotective lead compounds.

Protective Effects of Vitamin E on Chemotherapy-Induced Peripheral Neuropathy: A Meta-Analysis of Randomized Controlled Trials

INTRODUCTION

Chemotherapy-induced peripheral neuropathy (CIPN) is a common symptom, but prophylactic measures cannot still be carried out effectively. In addition, the efficacy of vitamin E in preventing peripheral neurotoxicity caused by chemotherapy is inconclusive. Therefore, we collected the relevant randomized controlled trials (RCTs) and performed a meta-analysis to examine whether the vitamin E has a positive effect in CIPN.

METHODS

We searched PubMed, EMBASE, Cochrane, and other databases in December 2019 for eligible trials. Two reviewers conducted the analysis independently when studies were homogeneous enough.

RESULTS

Eight RCTs, involving 488 patients, were identified. Upon pooling these RCTs, patients who received vitamin E supplementation of 600 mg/day had a lower incidence of CIPN (risk ratio [RR] 0.31; 95% confidence interval [CI] 0.14-0.65; p = 0.002) than the placebo group. Vitamin E played a key role in decreasing the incidence of peripheral neuropathy in the cisplatin chemotherapy group (RR 0.28; 95% CI 0.14-0.54; p = 0.0001). Moreover, vitamin E supplementation significantly decreased patients' sural amplitude after 3 rounds of chemotherapy (RR -2.66; 95% CI -5.09 to -0.24; p = 0.03) in contrast with that of placebo supplementation, while no significant difference was observed when patients were treated with vitamin E after 6 rounds of chemotherapy. In addition, the vitamin E-supplemented group had better improvement in the neurotoxicity score and lower incidence of reflexes and distal paraesthesias than the control group.

CONCLUSION

Available data in this meta-analysis showed that vitamin E supplementation can confer modest improvement in the prevention of CIPN.

Antioxidant Supplementation in the Treatment of Neurotoxicity Induced by Platinum-Based Chemotherapeutics-A Review

Cancer represents one of the most pernicious public health problems with a high mortality rate among patients worldwide. Chemotherapy is one of the major therapeutic approaches for the treatment of various malignancies. Platinum-based drugs (cisplatin, oxaliplatin, carboplatin, etc.) are highly effective chemotherapeutic drugs used for the treatment of several types of malignancies, but their application and dosage are limited by their toxic effects on various systems, including neurotoxicity. Simultaneously, researchers have tried to improve the survival rate and quality of life of cancer patients and decrease the toxicity of platinum-containing drugs by combining them with non-chemotherapy-based drugs, dietary supplements and/or antioxidants. Additionally, recent studies have shown that the root cause for the many side effects of platinum chemotherapeutics involves the production of reactive oxygen species (ROS) in naive cells. Therefore, suppression of ROS generation and their inactivation with antioxidants represents an appropriate approach for platinum drug-induced toxicities. The aim of this paper is to present an updated review of the protective effects of different antioxidant agents (vitamins, dietary antioxidants and supplements, medicaments, medicinal plants and their bioactive compounds) against the neurotoxicity induced by platinum-based chemotherapeutics. This review highlights the high potential of plant antioxidants as adjuvant strategies in chemotherapy with platinum drugs.

Neurotoxicity of antineoplastic drugs: Mechanisms, susceptibility, and neuroprotective strategies

This review summarizes the adverse effects on the central and/or peripheral nervous systems that may occur in response to antineoplastic drugs. In particular, we describe the neurotoxic side effects of the most commonly used drugs, such as platinum compounds, doxorubicin, ifosfamide, 5-fluorouracil, vinca alkaloids, taxanes, methotrexate, bortezomib and thalidomide. Neurotoxicity may result from direct action of compounds on the nervous system or from metabolic alterations produced indirectly by these drugs, and either the central nervous system or the peripheral nervous system, or both, may be affected. The incidence and severity of neurotoxicity are principally related to the dose, to the duration of treatment, and to the dose intensity, though other factors, such as age, concurrent pathologies, and genetic predisposition may enhance the occurrence of side effects. To avoid or reduce the onset and severity of these neurotoxic effects, the use of neuroprotective compounds and/or strategies may be helpful, thereby enhancing the therapeutic effectiveness of antineoplastic drug.

The ameliorative effects of ceftriaxone and vitamin E against cisplatin-induced nephrotoxicity

Nephrotoxicity is a common adverse effect of treatment with cisplatin (CDDP). This study was performed to evaluate the antioxidant and nephroprotective efficacy of ceftriaxone (CTX) and vitamin E (Vit.E), alone and in combination against CDDP-induced acute renal injury. Fifty-six male albino rats were equally divided into seven groups, receiving (I) normal saline, (II) CTX (100 mg/kg, intraperitoneal [i.p] injection), (III) Vit.E (100 mg/kg orally), (IV) CDDP (5 mg/kg i.p injection), (V) CDDP plus CTX, (VI) CDDP plus Vit.E, and (VII) CDDP plus CTX in combination with Vit.E. All treatments were administered daily for 10 days except CDDP, which was given as a single dose at the sixth day of the study. Compared to normal control rats, CDDP-injected rats showed significantly (p < 0.05) higher serum levels of renal injury biomarkers (uric acid, urea, and creatinine) and tumor necrosis factor-α (TNF-α), as well as increased renal tissue concentrations of malondialdehyde, nitric oxide, and TNF-α. Moreover, CDDP administration was associated with significantly lower (p < 0.05) renal tissue levels of reduced glutathione and activities of endogenous antioxidant enzymes (glutathione peroxidase, superoxide dismutase, and catalase) and total antioxidant capacity. All these alterations were significantly ameliorated in CDDP-injected rats, receiving CTX and/or Vit.E, compared to rats receiving CDDP alone. Interestingly, the antioxidant and anti-inflammatory effects were more marked in the CTX-Vit.E combination group, compared to groups receiving either drug alone. In conclusion, CTX and Vit.E (especially in combination) could counteract the nephrotoxic effect of CDDP, probably through their antioxidant activities.

Comparison of the Effects of Omega 3 and Vitamin E on Palcitaxel-Induced Peripheral Neuropathy

BACKGROUND

Paclitaxel-induced peripheral neuropathy is the most important side effect limiting the use of this medication.

AIM

This study aimed to compare the effects of omega-3 and vitamin E on the incidence of peripheral neuropathy in patients receiving Taxol.

METHODS

In this clinical trial, 63 patients who were a candidate for receiving taxol, were enrolled based on inclusion and exclusion criteria. In group O, patients received 640 mg omega-3 three times a day, and group E, received 300 mg vitamin E two times a day. Patients took the supplements up to three months after the onset of Taxol. Group P received placebo for a similar period. All patients referred to a neurologist for electrophysiological evaluation before the onset of chemotherapy and at months 1 and 3. The presence of neuropathy and its progression was recorded by the neurologist.

RESULTS

Neurological examination in this study indicated that 6 patients (28.6%) in Group O, 7 patients (33.3%) in group E, and 15 patients (71.4%) in placebo group started peripheral neuropathy. There was a significant difference between intervention groups and the placebo group (p = 0.0001) and no significant difference between intervention groups (p = 0.751).

CONCLUSION

Our data suggested that vitamin E and omega-3 may significantly reduce the incidence of Paclitaxel-induced peripheral neuropathy. Routine administration of such supplements that have no special side effect for patients under chemotherapy may greatly enhance their quality of life.

The Protective Effect of Naringenin-Oxime on Cisplatin-Induced Toxicity in Rats

The aim of this study is to examine the protective effect of naringenin-oxime (NOX) on cisplatin-induced major organ toxicity and DNA damage in rats. Thirty-five male Wistar albino rats were equally split into five groups as follows: control (i.p., 0.1 ml of saline), Cis administration (i.p., 7 mg/kg b.w.), NOX treatment (i.p., 20 mg/kg b.w., daily for ten days), Cis + NOX20, and Cis + NOX40 combination (i.p., 20 and 40 mg/kg b.w., daily for ten days). Serum and peripheral blood mononuclear leukocytes (PBMC) were obtained from blood. Malondialdehyde, glutathione, total antioxidant and oxidant status, and catalase were measured in serum, liver, and kidney, and oxidative stress index was calculated. In parallel, paraoxonase and arylesterase activities were tested in liver and serum. We used 8-OHdOG as a marker for DNA damage in serum via ELISA and in PMBC via comet assay. Treatment with Cis elevated the levels of serum biochemical parameters, oxidative stress, and DNA damage. Pretreatments of NOX restored biochemical and oxidative stress parameters in serum, renal, and liver tissues (p < 0.01) and reduced 8-OHdG level, a finding further supported by comet assay in PBMC. Observations of the present study support the fact that treatment with NOX prevents Cis-induced hepatotoxicity, nephrotoxicity, and genotoxicity by restoring antioxidant system.

The effects of the antioxidant α-tocopherol succinate on cisplatin-induced ototoxicity in HEI-OC1 auditory cells

CONCLUSION

D-α-tocopherol succinate significantly reduced a cisplatin-induced hair cell loss in HEI-OC1 cell lines. These effects were mediated by its scavenging activity against reactive oxygen species (ROS) and inhibition of apoptosis.

OBJECTIVES

Alpha-tocopherol is a class of methylated phenols, known as fat-soluble antioxidants, and is a different form of vitamin E, which reduces free radicals and acts as an antioxidant. We hypothesized that the antioxidative effect of α-tocopherol could protect against cisplastin-induced cytotoxicity, and thus evaluated its effects on cisplatin-induced ototoxicity in HEI-OC1 auditory cells.

METHODS

HEI-OC1 cells were pretreated with D-α-tocopherol succinate at a concentration of 10 µM for 24 h, and then exposed to 15 µM cisplatin for 48 h. The cellular viability was measured by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. The intracellular ROS level was measured by using a fluorescent dye, 2',7'-dichlorofluorescein diacetate (DCFH-DA). Both Annexin V-FITC and propidium iodide (PI) staining were performed to analyze the pattern of apoptosis. The enzymatic activity of caspase-3 was assayed with caspase3/CPP32 fluorometric assay kit. Also, it was assessed by immunoblotting technique of poly-ADP-ribose polymerase (PARP).

RESULTS

Pretreatment with 10 µM D-α-tocopherol succinate protected HEI-OC1 auditory cells against cisplatin-induced cytotoxicity. D-α-tocopherol succinate significantly reduced the cisplatin-induced increase in ROS. D-α-tocopherol succinate treatment induced a 15% reduction of ROS and 50% decrease in necrosis and late apoptosis as compared to cisplatin treatment. D-α-tocopherol succinate also decreased the activation of caspase-3 and reduced levels of cleaved poly-ADP-ribose polymerase (PARP).

Effect of Vitamin E on Oxaliplatin-induced Peripheral Neuropathy Prevention: A Randomized Controlled Trial

BACKGROUND

Peripheral neuropathy is one of the most important limitations of oxaliplatin base regimen, which is the standard for the treatment of colorectal cancer. Evidence has shown that Vitamin E may be protective in chemotherapy-induced peripheral neuropathy. The aim of this study is to evaluate the effect of Vitamin E administration on prevention of oxaliplatin-induced peripheral neuropathy in patients with colorectal cancer.

METHODS

This was a prospective randomized, controlled clinical trial. Patients with colorectal cancer and scheduled to receive oxaliplatin-based regimens were enrolled in this study. Enrolled patients were randomized into two groups. The first group received Vitamin E at a dose of 400 mg daily and the second group observed, until after the sixth course of the oxaliplatin regimen. For oxaliplatin-induced peripheral neuropathy assessment, we used the symptom experience diary questionnaire that completed at baseline and after the sixth course of chemotherapy. Only patients with a score of zero at baseline were eligible for this study.

RESULTS

Thirty-two patients were randomized to the Vitamin E group and 33 to the control group. There was no difference in the mean peripheral neuropathy score changes (after - before) between two groups, after sixth course of the oxaliplatin base regimen (mean difference [after - before] of Vitamin E group = 6.37 ± 2.85, control group = 6.57 ± 2.94; P = 0.78). Peripheral neuropathy scores were significantly increased after intervention compared with a base line in each group (P < 0.001).

CONCLUSIONS

The results from this current trial demonstrate a lack of benefit for Vitamin E in preventing oxaliplatin-induced peripheral neuropathy.

Curcumin Ameliorates Functional and Structural Abnormalities in Cisplatin-induced Neuropathy

Peripheral neuropathy is one of the major side effects of cisplatin; however, effective treatments are lacking. Curcumin is a polyphenol found in the root of Curcuma longa and has been shown neuroprotective against several neurological diseases. Nevertheless, its effects on cisplatin neuropathy remain unclear. This study aimed to clarify this issue by inducing neuropathy in the rats with intraperitoneal injection of cisplatin 2 mg/kg twice a week for 5 consecutive weeks. Curcumin 200 mg/kg/day was given by gavage to a group of cisplatin-treated rats during these five weeks. The results showed that cisplatin induced thermal hypoalgesia in the 5^th week which could be prevented by curcumin. In the 5^th and 8^th weeks, sciatic motor nerve conduction velocity was reduced in the cisplatin compared with the control groups. Curcumin significantly attenuated this deficit. Morphometric analysis of L4 dorsal root ganglia from the cisplatin group revealed nuclear and nucleolar atrophy including loss of neurons in the 8^th week. These alterations were significantly blocked by curcumin. Moreover, curcumin also ameliorated the reduced myelin thickness in the sciatic nerve of cisplatin-treated rats. Taken together, our findings suggest the favorable effects of curcumin on both functional and structural abnormalities in cisplatin neuropathy. Future studies are needed to clarify the exact underlying mechanisms.

Nephroprotective activities of rosmarinic acid against cisplatin-induced kidney injury in mice

Rosmarinic acid (RA) is a natural phenolic compound with a broad range of applications, from food preservatives to cosmetics. Increasing amounts of evidence suggests its beneficial effects against various pathological conditions. The aim of this study was to investigate the therapeutic activity of rosmarinic acid (RA) against cisplatin (CP)-induced nephrotoxicity. RA was administered by oral gavage at doses of 1, 2 and 5mg/kg for two successive days, 48 h after intraperitoneal CP injection (13 mg/kg). Twenty four hours later, mice were sacrificed. Treatment with RA significantly ameliorated histopathological changes and the increase in serum creatinine and blood urea nitrogen (BUN) induced by CP. Oxidative stress induced by CP, evidenced by increased renal 4-hydroxynonenal (4-HNE), cytochrome P450 2E1 (CYP2E1) and heme oxygenase (HO-1) expression, was significantly reduced by RA administration. Moreover, RA inhibited the expression of nuclear factor-kappaB (NF-κB) and tumor necrosis factor-α (TNF-α), indicating the inhibition of inflammation. Additionally, RA exhibited antiapoptotic activity through the reduction of p53, phosphorylated p53 and active caspase-3 expression in the kidneys. These findings show that RA ameliorates CP-induced oxidative stress, inflammation and apoptosis in the kidneys. The nephroprotective activity of RA could be, at least in part, attributed to reduced CYP2E1 expression.

Protective effects of vitamins E, B and C and l-carnitine in the prevention of cisplatin-induced ototoxicity in rats

Objective:

This experimental study aimed to investigate the effects of vitamins E, B and C and l-carnitine in preventing cisplatin-induced ototoxicity.

Methods:

Twenty-five adult, male, Wistar albino rats were randomly allocated to receive intraperitoneal cisplatin either alone or preceded by vitamins B, E or C or l-carnitine. Auditory brainstem response (i.e. hearing thresholds and wave I–IV intervals) and distortion product otoacoustic emissions (i.e. signal-to-noise ratios) were recorded before and 72 hours after cisplatin administration.

Results:

The following statistically significant differences were seen: control group pre- vs post-treatment wave I–IV interval values (p < 0.05); control vs vitamin E and B groups' I–IV interval values (p < 0.05); control vs other groups' hearing thresholds; vitamin E vs vitamin B and C and l-carnitine groups' hearing thresholds (p < 0.05); and vitamin B vs vitamin C and l-carnitine groups' hearing thresholds (p < 0.05). Statistically significant decreases were seen when comparing the initial and final signal-to-noise ratios in the control, vitamin B and l-carnitine groups (2000 and 3000 Hz; p < 0.01), and the initial and final signal-to-noise ratios in the control group (at 4000 Hz; p < 0.01).

Conclusion:

Vitamins B, E and C and l-carnitine appear to reduce cisplatin-induced ototoxicity in rats. The use of such additional treatments to decrease cisplatin-induced ototoxicity in humans is still under discussion.

The contribution of oxidative stress to drug-induced organ toxicity and its detection in vitro and in vivo

INTRODUCTION

Nowadays the 'redox hypothesis' is based on the fact that thiol/disulfide couples such as glutathione (GSH/GSSG), cysteine (Cys/CySS) and thioredoxin ((Trx-(SH)2/Trx-SS)) are functionally organized in redox circuits controlled by glutathione pools, thioredoxins and other control nodes, and they are not in equilibrium relative to each other. Although ROS can be important intermediates of cellular signaling pathways, disturbances in the normal cellular redox can result in widespread damage to several cell components. Moreover, oxidative stress has been linked to a variety of age-related diseases. In recent years, oxidative stress has also been identified to contribute to drug-induced liver, heart, renal and brain toxicity.

AREAS COVERED

This review provides an overview of current in vitro and in vivo methods that can be deployed throughout the drug discovery process. In addition, animal models and noninvasive biomarkers are described.

EXPERT OPINION

Reducing post-market drug withdrawals is essential for all pharmaceutical companies in a time of increased patient welfare and tight budgets. Predictive screens positioned early in the drug discovery process will help to reduce such liabilities. Although new and more efficient assays and models are being developed, the hunt for biomarkers and noninvasive techniques is still in progress.

Protective effect of bixin on cisplatin-induced genotoxicity in PC12 cells

Bixin is the main carotenoid found in annatto seeds (Bixa orellana L.) and is responsible for their reddish-orange color. The antioxidant properties of this compound are associated with its ability to scavenge free radicals, which may reduce damage and protect tissues against toxicity caused by anticancer drugs such as cisplatin. In this study, the genotoxicity and antigenotoxicity of bixin on cisplatin-induced toxicity in PC12 cells was assessed. Cytotoxicity was evaluated using the MTT assay, mutagenicity, genotoxicity, and protective effect of bixin were evaluated using the micronucleus test and comet assay. PC12 cells were treated with bixin (0.05, 0.08, and 0.10μg/mL), cisplatin (0.1μg/mL) or a combination of both bixin and cisplatin. Bixin was neither cytotoxic nor genotoxic compared to the controls. In the combined treatment bixin significantly reduced the percentage of DNA in tail and the frequency of micronuclei induced by cisplatin. This result suggests that bixin can function as a protective agent, reducing cisplatin-induced DNA damage in PC12 cells, and it is possible that this protection could also extend to neuronal cells. Further studies are being conducted to better understand the mechanisms involved in the activity of this protective agent prior to using it therapeutically.

Vitamin E prevents buthionine sulfoximine-induced biochemical disorders in the rat

Antioxidant therapy can improve the protection and metabolic activity of cells and tissues. In this study, the effect of vitamin E administration on buthionine sulfoximine (BSO)-induced glutathione (GSH) depletion in the rat lung and liver was investigated. Hepatic GSH was depleted by intraperitoneal administration of BSO (4 mmol kg−1), twice a day, for 30 days to rats. We also investigated whether the lung and liver mitochondrial GSH contents were influenced by BSO administration and whether an extracellular supply of vitamin E could prevent the changes caused by BSO-mediated GSH depletion. Glutathione levels in lung and liver tissues were depleted by 47% and 60%, respectively. Depletion of hepatic and pulmonary GSH in turn causes decline in the levels of mitochondrial GSH, leading to impaired antioxidant defence function of mitochondria. Both the cytosolic and mitochondrial glutathione disulfides (GSSG) were altered during BSO treatment, and led to drastic increase in GSSG/GSH redox status. One of the experimental groups was given vitamin E (65 mg (kg diet)−1) mixed with rat feed. The rats fed with vitamin E were found to have partially restored GSH levels in liver and lung, diminished levels of TBARS and minimized tissue damage. The current findings suggest that the impaired glutathione and glutathione-dependent enzyme status may be correlated with the elevated lipid peroxidation and mitochondrial membrane damage and that vitamin E therapy to the BSO-administered rats prevents the above changes. However, vitamin E did not have any effect on the activity of γ-glutamyl cysteine synthetase (γ-GCS).

Central and peripheral nervous system toxicity of common chemotherapeutic agents

Central and peripheral nervous system toxicity are frequent complications of most chemotherapy regimens, often leading to reduction of dosages or cessation of the responsible drugs. However, sometimes the afflicted toxicity may not be reversible, especially if it is not recognized early, further compromising the quality of life of the cancer patients. The most common chemotherapeutic agents that might cause CNS toxicity manifested as encephalopathy of various severities include methotrexate, vincristine, ifosfamide, cyclosporine, fludarabine, cytarabine, 5-fluorouracil, cisplatin and the interferons (alpha > beta). Involvement of the peripheral nervous system manifested as distal peripheral neuropathy results after therapy with cisplatin, vincristine, taxanes, suramin and thalidomide. Although several compounds have been proposed as neuroprotective agents, few have been shown to be active against the chemotherapy induced neurotoxicity.

Metabolomics: a tool for personalizing medicine?

The concept of personalized medicine is based upon using personal genetic information to predict individual responses to drug therapy. However, environmental factors such as diet, energy status, gut microbiota, health status and age will influence the expression of one’s genetic potential. Metabolomics data from biofluid and tissue sample analysis hold information regarding a patient’s genotype and phenotype. Metabolomics data can be rapidly collected from biofluid samples over time, providing temporal metabolic analyses of patient samples. In addition to metabolic markers of a patient’s phenotype, metabolomics can provide markers of drug efficacy, toxicity and clearance.

Chemotherapy-induced peripheral neuropathy: prevention and treatment strategies

Chemotherapy-induced peripheral neuropathy (CIPN) is a major dose limiting side effect of many commonly used chemotherapeutic agents, including platinum drugs, taxanes, epothilones and vinca alkaloids, and also newer agents such as bortezomib and lenolidamide. Symptom control studies have been conducted looking at ways to prevent or alleviate established CIPN. This manuscript provides a review of studies directed at both of these areas. New evidence strongly suggests that intravenous calcium and magnesium therapy can attenuate the development of oxaliplatin-induced CIPN, without reducing treatment response. Accumulating data suggest that vitamin E may also attenuate the development of CIPN, but more data regarding its efficacy and safety should be obtained prior to its general use in patients. Other agents that look promising in preliminary studies, but need substantiation, include glutamine, glutathione, N-acetylcysteine, oxcarbazepine, and xaliproden. Effective treatment of established CIPN, however, has yet to be found. Lastly, paclitaxel causes a unique acute pain syndrome which has been hypothesised to be caused by neurologic injury. No drugs, to date, have been proven to prevent this toxicity.

Zingiber officinale Roscoe alone and in combination with alpha-tocopherol protect the kidney against cisplatin-induced acute renal failure

Oxidative stress due to abnormal production of reactive oxygen molecules (ROM) is believed to be involved in the etiology of toxicities of many xenobiotics. Evidences suggested that ROM is involved in the nephrotoxicity of a widely used synthetic anticancer drug cisplatin. The nephroprotective effects of ethanol extract of Zingiber officinale alone and in combination with vitamin E (alpha-tocopherol) were evaluated using cisplatin (single dose of 10 mg/kg body wt, i.p) induced acute renal damage in mice. The results of the study indicated that Z. officinale significantly and dose dependently protected the nephrotoxicity induced by cisplatin. The serum urea and creatinine levels in the cisplatin alone treated group were significantly elevated (P<0.01) with respect to normal group of animals. The levels were reduced in the Z. officinale (250 and 500 mg/kg, p.o) plus cisplatin, vitamin E (250 mg/kg) plus cisplatin, and Z. officinale (250 mg/kg) with vitamin E plus vitamin E treated groups. The renal antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) activities and level of reduced glutathione (GSH) were declined; level of malondialdehyde (MDA) was elevated in the cisplatin alone treated group. The activities of SOD, CAT GPx and level of GSH were elevated and level of MDA declined significantly (P<0.05) in the Z. officinale (250 and 500 mg/kg) plus cisplatin and Z. officinale (250 mg/kg) with vitamin E plus cisplatin treated groups. The protective effect of Z. officinale (250 mg/kg body wt) was found to be better than that of vitamin E (250 mg/kg body wt). The results also demonstrated that combination of Z. officinale (250 mg/kg) with vitamin E (250 mg/kg) showed a better protection compared to their 250 mg/kg alone treated groups. This study concluded that ethanol extract of Z. officinale alone and in combination with vitamin E partially ameliorated cisplatin-induced nephrotoxicity. This protection is mediated either by preventing the cisplatin-induced decline of renal antioxidant defense system or by their direct free radical scavenging activity.

Modulation of response to cancer chemotherapeutic agents by diet constituents – Is the available evidence sufficiently robust for rational advice for patients?

BACKGROUND

Patients who are diagnosed with cancer want advice on how they may alter their diet or which diet supplements they should take to augment chemotherapy.

METHODS

We conducted a review of the literature mostly from the last 15 years on the interaction between dietary constituents and antineoplastic therapy in preclinical rodent models and in clinical trials.

RESULTS

Studies have explored the effect of predominantly antioxidant vitamins and folate on efficacy or toxicity mediated by cisplatin and anthracyclins. Cisplatin toxicity in rodents was ameliorated by vitamin E. The design of clinical studies of dietary agents in combination with cytotoxic agents has been very heterogeneous and results have been inconclusive.

CONCLUSIONS

Whilst preclinical experiments hint at a potential benefit of certain dietary agents, the evidence emanating from clinical studies does not allow firm conclusions to be made. Future studies should explore physiological doses of dietary agent and include pharmacokinetic and pharmacodynamic measurements.

Dietary supplements in patients with cancer: risks and key concepts, part 1

PURPOSE

The risks and key concepts regarding the use of dietary supplements in patients with cancer are described.

SUMMARY

There are six common characteristics of dietary supplements that must be addressed when used by patients with cancer. Clinicians must establish if the supplement is an antioxidant, is an anticoagulant or procoagulant, has immunosuppressive or immunomodulating properties, has hormonal properties, has known safety issues, and has known or theoretical drug interactions. These six characteristics of the dietary supplements commonly used by patients with cancer are reviewed to aid in the analysis of the scientific data and communication of the results with the patient or family members. A framework upon which clinicians can adequately help patients make informed decisions regarding the use of complimentary and alternative medicine and dietary supplements is also described. When evaluating the appropriateness of a supplement for use by a patient with cancer, clinicians must conduct a safety review (evaluate the six characteristics). If the supplement is considered safe, an efficacy review must be conducted, after which the clinicians can recommend the supplement's use, accept the patient's decision to use the supplement if no or inconclusive evidence exists, or discourage use if there is conclusive evidence supporting inefficacy. Available resources for locating information regarding dietary supplements are also discussed.

CONCLUSION

Counseling patients with cancer about dietary supplements requires a systematic thought process that considers the available theories and data, as well as the patients' views about the agents.

Novel antioxidant technology for prostate cancer chemoprevention and treatment

The mechanisms underlying prostate carcinogenesis are not firmly elucidated. An exciting area of research in this regard asks whether prostate cancer results from the consequences of lifelong exposure of prostate tissue to oxidative stress. This article reviews the laboratory-based literature on oxidative stress and its possible role in prostate carcinogenesis. The progression of clinical studies focusing on the relationship between antioxidant supplementation and risk of developing prostate cancer are discussed, along with the patent literature since 2003 involving novel antioxidant technology applicable to prostate cancer prevention and treatment. In particular, recently published in vitro experiments with a novel alpha-tocopherol analogue, 2,2,5,7,8-pentamethyl-6-chromonal, which characterised its unique spectrum of antioxidant and antiandrogen properties in prostate cancer cell lines, is discussed. In addition, recent patent applications and supporting findings from the literature surrounding: i) cisplatin tocopherol compounds; ii) coix seed soft capsules with vitamin E; iii) vitamin E succinate (alpha-tocopheryl succinate); iv) lycopene preparations with other carotenoids; v) compounds of the ginger family; vi) novel aryl-carbaldehyde oxime derivatives; vii) novel phenyl quinoline derivatives; and viii) resveratrol, its derivatives and preparations thereof are discussed as they relate to prostate cancer chemoprevention and treatment.

Preventing paclitaxel-induced peripheral neuropathy: a phase II trial of vitamin E supplementation

A randomized, controlled trial was performed to assess the efficacy and safety of vitamin E supplementation for prophylaxis against paclitaxel-induced peripheral neuropathy (PIPN). Thirty-two patients undergoing six courses of paclitaxel-based chemotherapy were randomly assigned to receive either chemotherapy with vitamin E (300 mg twice a day, Group I) or chemotherapy without vitamin E supplementation (Group II). A detailed neurological examination and electrophysiological study was performed during and 3 months after chemotherapy. The severity of PIPN was summarized by means of a modified Peripheral Neuropathy (PNP) score. The incidence of neurotoxicity differed significantly between groups, occurring in 3/16 (18.7%) patients assigned to the vitamin E supplementation group and in 10/16 (62.5%) controls (P=0.03). The relative risk (RR) of developing PIPN was significantly higher in controls than in vitamin E group patients (RR=0.3, 95% confidence interval (CI)=0.1-0.9). Mean PNP scores were 2.25+/-5.1 (range 0-15) for patients in Group I and 11+/-11.63 (range 0-32) for those in Group II (P=0.01). Vitamin E supplementation was well tolerated and showed an excellent safety profile. This study shows that vitamin E effectively and safely protects patients with cancer from the occurrence of paclitaxel-induced peripheral nerve damage. A double-blind, placebo-controlled trial is needed to confirm these results.

Possible protective effects of alpha-tocopherol on enhanced induction of reactive oxygen species by 2-methoxyestradiol in tumors

Several non-surgical tumor treatment modalities produce their cytotoxic activity by generating reactive oxygen species (ROS). Anti-oxidative enzymes such as superoxide dismutase (SOD) or exogenously supplied antioxidants may therefore reduce the efficacy of these treatments. The aim of the present study was to analyze the impact of (i) inhibiting SOD using 2-methoxyestradiol (2-ME), or (ii) application of alpha-tocopherol, on the cellular damage induced by hyperthermia (HT) in experimental tumors. DS-sarcoma cells grew either in culture or as solid tumors subcutaneously implanted in rats. In vitro, DS-cells were incubated with 2-ME, and cell proliferation, ROS formation, lipid peroxidation and apoptosis were measured. In vivo, DS-sarcomas were treated with a ROS-generating hyperthermia combined with 2-ME or alpha-tocopherol application. Inhibition of SOD by 2-ME in vitro induced pronounced oxidative injury resulting in reduced proliferation. In vivo, ROS-generating hyperthermia led to local tumor control in 23% of the animals. The additional inhibition of SOD by 2-ME increased the control rate by approximately 50%. Application of alpha-tocopherol was found to have no effect on local tumor control, either in combination with ROS-generating hyperthermia or when 2-ME was additionally applied. Inhibition of SOD during ROS-generating hyperthermia results in pronounced cell injury and an improved local tumor control whereas exogenously applied vitamin E seems not to have an impact on oxidative stress.

A randomized controlled trial evaluating the efficacy and safety of vitamin E supplementation for protection against cisplatin-induced peripheral neuropathy: final results

AIM

A randomized, open label with blind assessment, controlled trial was performed to assess efficacy and adverse-event profile of vitamin E, given as supplementation for prophylaxis against cisplatin-induced peripheral neuropathy (CIPN).

PATIENTS AND METHODS

A total of 30 patients scheduled to receive six courses of cumulative cisplatin-based regimens were randomly allocated to treatment and control groups and were then studied by means of neurological examination and electrophysiological study. Patients assigned to group I (n=14) orally received vitamin E at a daily dose of 600 mg/day during chemotherapy and 3 months after its cessation were compared to patients of group II (n=16), who received no vitamin E supplementation and served as controls. The severity of neurotoxicity was summarized by means of a modified Peripheral Neuropathy (PNP) score.

RESULTS

The incidence of neurotoxicity differed significantly between groups, occurring in 3/14 (21.4%) of patients assigned to the vitamin E supplementation group and in 11/16 (68.5%) of controls (p=0.026). The relative risk (RR) of developing neurotoxicity was significantly higher in case of controls, RR=2.51, 95% C.I.=1.16-5.47. Mean PNP scores were 4.99+/-1.33 for patients of group I and 10.47+/-10.62 for controls, (p=0.023). None of the adverse events or deaths occurred, were judged as likely to be related to the vitamin E supplementation.

CONCLUSION

Vitamin E effectively and safely protects patients with cancer from occurrence of cisplatin neurotoxicity.

Assessment of a dietary questionnaire in cancer patients receiving cytotoxic chemotherapy

PURPOSE

Few studies have examined the influence of diet on survival and chemotherapy-associated toxicities in patients with cancer. Although several comprehensive dietary questionnaires have been validated and calibrated in healthy populations, similar studies have not been performed among cancer patients.

METHODS

Two hundred patients with colorectal, breast, or neuroendocrine cancer undergoing treatment with cytotoxic chemotherapy completed a self-administered, 131-item, semiquantitative food frequency questionnaire. Using the questionnaire, we calculated dietary intakes of carotenoids, tocopherols, and fatty acids, and correlated these values with relevant biomarkers measured in simultaneously collected plasma specimens.

RESULTS

The Pearson correlation coefficients for various carotenoids as measured by the questionnaire, with the corresponding measurements in plasma specimens, ranged from 0.33 to 0.44 (all P < .001), adjusted for total energy intake, body mass index, age, sex, smoking status, and total plasma cholesterol. Similarly, the adjusted correlation between self-reported total vitamin E intake and plasma alpha-tocopherol was 0.34 (P < .001). Correlations between questionnaire and plasma measurements of trans-fat, eicosapentaenoic acid, and docosahexaenoic acid were 0.55, 0.29, and 0.42 (all P < .001), respectively. These levels of correlation are consistent with those reported in similar studies of self-reported diet in otherwise healthy populations.

CONCLUSION

Among patients with cancer receiving cytotoxic chemotherapy, questionnaire-based measurements of various micronutrients and dietary factors appeared to predict meaningful differences in the corresponding measurements in plasma specimens. This dietary questionnaire could offer an informative and practical means for assessing the influence of diet in cancer patients receiving chemotherapy.

Multiple dietary antioxidants enhance the efficacy of standard and experimental cancer therapies and decrease their toxicity

Cancer patients can be divided into 3 groups: those receiving standard or experimental therapy, those who have become unresponsive to these therapies, and those in remission at risk for recurrence or a second new cancer. While impressive progress in standard cancer therapy has been made, the value of this therapy in the management of solid tumors may have reached a plateau. At present, there is no strategy to reduce the risk of recurrence of the primary tumors or of a second cancer among survivors. Patients unresponsive to standard or experimental therapies have little option except for poor quality of life for the remainder of life. Therefore, additional approaches should be developed to improve the efficacy of current management of cancer. In this review, the author proposes that an active nutritional protocol that includes high doses of multiple dietary antioxidants and their derivatives (vitamin C, alpha-tocopheryl succinate, and natural beta-carotene), but not endogenously made antioxidants (glutathione- and antioxidant enzyme-elevating agents), when administered as an adjunct to radiation therapy, chemotherapy, or experimental therapy, may improve its efficacy by increasing tumor response and decreasing toxicity. This nutritional protocol can also be used when patients become unresponsive to standard therapy or experimental therapy to improve quality of life and possibly increase the survival time. The authors also propose that after completion of standard therapy and/or experimental therapy, a maintenance nutritional protocol that contains lower doses of antioxidants and their derivatives, together with modification in diet and lifestyle, may reduce the risk of recurrence of the original tumor and development of a second cancer among survivors. Experimental data and limited human studies suggest that use of these nutritional approaches may improve oncologic outcomes and decrease toxicity. This review also discusses the reasons for the current debates regarding the use of antioxidants during radiation or chemotherapy.

Cysteine peptidase and its inhibitor activity levels and vitamin E concentration in normal human serum and colorectal carcinomas

AIM: Cysteine peptidase (CP) and its inhibitor (CPI) are a matrix protease that may be associated with colorectal carcinoma invasion and progression, and vitamin E is also a stimulator of the immunological system. Our purpose was to determine the correlation between the expression of cysteine peptidases and their endogenous inhibitors, and the level of vitamin E in sera of patients with colorectal cancer in comparison with healthy individuals.

METHODS: The levels of cysteine peptidases and their inhibitors were determined in the sera of patients with primary and metastatic colorectal carcinoma and healthy individuals using fluorogenic substrate, and the level of vitamin E was determined by HPLC.

RESULTS: The levels of cysteine peptidases and their inhibitors were significantly higher in the metastatic colorectal cancer patients than that in the healthy controls (P<0.05). The activity of CP increased 2.2-fold, CPI 2.8-fold and vitamin E decreased 3.4-fold in sera of patients with metastasis in comparison with controls. The level of vitamin E in healthy individuals was higher, whereas the activity of cysteine peptidases and their inhibitors associated with complexes was lower than that in patients with cancer of the digestive tract.

CONCLUSION: These results suggest that the serum levels of CP and their inhibitors could be an indicator of the prognosis for patients with metastatic colorectal cancer. Vitamin E can be administered prophylactically to prevent digestive tract neoplasmas.

Genome-Wide Identification of Genes Conferring Resistance to the Anticancer Agents Cisplatin, Oxaliplatin, and Mitomycin C

Cisplatin is a crucial agent in the treatment of many solid tumors, yet many tumors have either acquired or intrinsic resistance to the drug. We have used the homozygous diploid deletion pool of Saccharomyces cerevisiae, containing 4728 strains with individual deletion of all nonessential genes, to systematically identify genes that when deleted confer sensitivity to the anticancer agents cisplatin, oxaliplatin, and mitomycin C. We found that deletions of genes involved in nucleotide excision repair, recombinational repair, postreplication repair including translesional synthesis, and DNA interstrand cross-link repair resulted in sensitivity to all three of the agents, although with some differences between the platinum drugs and mitomycin C in the spectrum of required translesional polymerases. Putative defective repair of oxidative damage (imp2'Delta strain) also resulted in sensitivity to platinum and oxaliplatin, but not to mitomycin C. Surprisingly in light of their different profiles of clinical activity, cisplatin and oxaliplatin have very similar sensitivity profiles. Finally, we identified three novel genes (PSY1-3, "platinum sensitivity") that, when deleted, demonstrate sensitivity to cisplatin and oxaliplatin, but not to mitomycin C. Our results emphasize the importance of multiple DNA repair pathways responsible for normal cellular resistance to all three of the agents. Also, the similarity of the sensitivity profiles of the platinum agents with that of the known DNA interstrand cross-linking agent mitomycin C, and the importance of the gene PSO2 known to be involved in DNA interstrand cross-link repair strongly suggests that interstrand cross-links are important toxic lesions for cisplatin and oxaliplatin, at least in yeast.

Vitamin E reduces cisplatin ototoxicity

OBJECTIVES/HYPOTHESIS

Cisplatin ototoxicity is a major dose-limiting factor in the treatment of several neoplasms. Vitamin E, a slow-acting free radical scavenger, has been shown to ameliorate nephrotoxicity and endothelial cell damage in animals receiving cisplatin. The purpose of the study was to determine the effectiveness of vitamin E as an otoprotectant.

STUDY DESIGN

Prospective, randomized controlled trial in the rat model.

METHODS

Wistar rats (weight, 261-386 g) were sedated using 172.4 mg/kg intramuscular ketamine and 3.4 mg/kg xylazine. Baseline auditory brainstem response (ABR) testing was performed in response to clicks and 8-, 16-, and 32-kHz tone bursts. After auditory thresholds were determined, the animals received intraperitoneal drug administration according to one of three group classifications. Group 1 received 4 g/kg vitamin E followed after 30 minutes by 16 mg/kg cisplatin. Group 2 received 6 mL/kg soybean oil followed after 30 minutes by cisplatin. Group 3 received soybean oil followed after 30 minutes by 16 mL/kg saline. After 3 days' follow-up, ABR testing was performed and threshold changes were recorded. Cochleae were removed and processed for scanning electron microscopy after follow-up auditory testing was carried out.

RESULTS

Group 2 animals showed marked hearing loss with average threshold shifts of 28.75 +/- 2.3 dB for clicks, 30.0 +/- 1.9 dB at 8 kHz, 21.25 +/- 4.0 dB at 16 kHz, and 45.0 +/- 4.2 dB at 32 kHz. No significant loss was observed in group 3 with shifts of 2 +/- 1.3 dB, 3 +/-3.0 dB, -2.2 +/- 3.1 dB, and -1.1 +/- 4.0 dB for clicks and tone bursts at 8, 16, and 32 kHz, respectively. Significant protection was seen in group 1 animals compared with group 2 animals. In the former group, threshold shifts of 12.5 +/- 3.1 dB for clicks, 7.5 +/- 2.5 dB at 8 kHz, 5.0 +/- 3.3 dB at 16 kHz, and 24.4 +/- 5.6 dB at 32 kHz were observed. These findings were supported by the scanning electron microscope observations that severe outer hair cell destruction occurred in group 2 rats, whereas outer hair cells were preserved to a much greater extent in the cochleae of rats in group 1 that were pretreated with vitamin E.

CONCLUSION

Vitamin E appears to have a protective effect against cisplatin ototoxicity.

Cisplatin-evoked DNA fragmentation in normal and cancer cells and its modulation by free radical scavengers and the tyrosine kinase inhibitor STI571

Cis-diamminedichloroplatinum(II) (cisplatin, cis-DDP) is well studied anticancer drug, whose activity can be attributed to its ability to form adducts with DNA, but this drug can also form DNA-damaging free radicals, however this mechanism of cisplatin action is far less explored. Using the comet assay we studied cisplatin-induced DNA damage in the presence of spin traps: DMPO and PBN, Vitamins A, C and E as well as the tyrosine kinases inhibitor STI571 in normal human lymphocytes and leukemic K562 cells. The latter cells express the BCR/ABL fusion protein, which can be a target of the tyrosine kinase inhibitor STI571. A 20 h incubation with cisplatin at 1-10 microM induced DNA cross-links and DNA fragmentation in normal and cancer cells. Cisplatin could induce intra- and interstrand DNA-DNA cross-links as well as DNA-protein cross-links. DNA damage in K562 cells was more pronounced than in normal lymphocytes. In the presence of spin traps and vitamins we noticed a decrease in the DNA fragmentation in both cell types. Co-treatment of the lymphocytes with cisplatin at 10 microM and STI571 at 0.25 microg/ml caused an increase of DNA fragmentation in comparison with DNA fragmentation induced by cisplatin alone. In the case of K562 cells, an increase of DNA fragmentation was observed after treatment with cisplatin at 1 microM. Our results indicate that the free radicals scavengers could decrease DNA fragmentation induced by cisplatin in the normal and cancer cells, but probably they have no effect on DNA cross-linking induced by the drug. The results obtained with the BCR/ABL inhibitor suggest that K562 cells could be more sensitive towards co-treatment of cisplatin and STI571. Our results suggest also that aside from the BCR/ABL other factors such as p53 level, signal transduction pathways and DNA repair processes can be responsible for the increased sensitivity of K562 cells to cisplatin compared with normal lymphocytes.