N-acetylcysteine modifies cis-dichlorodiammineplatinum-induced effects in bladder cancer cells

Oxidative stress in cancer therapy: Friend or enemy?

Excessive cellular oxidative stress is widely perceived as a key factor in pathophysiological conditions and cancer development. Healthy cells use several mechanisms to maintain intracellular levels of reactive oxygen species (ROS) and overall redox homeostasis to avoid damage to DNA, proteins, and lipids. Cancer cells, in contrast, exhibit elevated ROS levels and upregulated protective antioxidant pathways. Counterintuitively, such elevated oxidative stress and enhanced antioxidant defence mechanisms in cancer cells provide a therapeutic opportunity for the development of drugs with different anticancer mechanisms of action (MoA). In this review, oxidative stress and the role of ROS in cells are described. The tumour-suppressive and tumour-promotive functions of ROS are discussed to compare these two different therapeutic strategies (increasing or decreasing ROS to fight cancer). Clinically approved drugs with demonstrated oxidative stress anticancer MoAs are highlighted before describing examples of metal-based anticancer drug candidates causing oxidative stress in cancer cells via novel MoAs.

Self-assembled ruthenium and osmium nanosystems display a potent anticancer profile by interfering with metabolic activity

Amphiphilic ruthenium and osmium complexes auto-assemble to nanosystems that poison mitochondria and show highly promising in vitro and in vivo anticancer activity.

Natural products as a means of overcoming cisplatin chemoresistance in bladder cancer

Cisplatin remains an integral part of the treatment for muscle invasive bladder cancer. A large number of patients do not respond to cisplatin-based chemotherapy and efficacious salvage regimens are limited. Immunotherapy has offered a second line of treatment; however, only approximately 20% of patients respond, and molecular subtyping of tumors indicates there may be significant overlap in those patients that respond to cisplatin and those patients that respond to immunotherapy. As such, restoring sensitivity to cisplatin remains a major hurdle to improving patient care. One potential source of compounds for enhancing cisplatin is naturally derived bioactive products such as phytochemicals, flavonoids and others. These compounds can activate a diverse array of different pathways, many of which can directly promote or inhibit cisplatin sensitivity. The purpose of this review is to understand current drug development in the area of natural products and to assess how these compounds may enhance cisplatin treatment in bladder cancer patients.

Compensatory combination of romidepsin with gemcitabine and cisplatin to effectively and safely control urothelial carcinoma

BACKGROUND

Human urothelial carcinoma (UC) has a high tendency to recur and progress to life-threatening advanced diseases. Advanced therapeutic regimens are needed to control UC development and recurrence.

METHODS

We pursued in vitro and in vivo studies to understand the ability of a triple combination of gemcitabine, romidepsin, and cisplatin (Gem+Rom+Cis) to modulate signalling pathways, cell death, drug resistance, and tumour development.

RESULTS

Our studies verified the ability of Gem+Rom+Cis to synergistically induce apoptotic cell death and reduce drug resistance in various UC cells. The ERK pathway and reactive oxygen species (ROS) played essential roles in mediating Gem+Rom+Cis-induced caspase activation, DNA oxidation and damage, glutathione reduction, and unfolded protein response. Gem+Rom+Cis preferentially induced death and reduced drug resistance in oncogenic H-Ras-expressing UC vs. counterpart cells that was associated with transcriptomic profiles related to ROS, cell death, and drug resistance. Our studies also verified the efficacy and safety of the Gem plus Rom+Cis regimen in controlling UC cell-derived xenograft tumour development and resistance.

CONCLUSIONS

More than 80% of UCs are associated with aberrant Ras-ERK pathway. Thus the compensatory combination of Rom with Gem and Cis should be seriously considered as an advanced regimen for treating advanced UCs, especially Ras-ERK-activated UCs.

Antioxidants as precision weapons in war against cancer chemotherapy induced toxicity - Exploring the armoury of obscurity

Cancer is the leading cause of mortality worldwide, accounting for almost 13% of deaths in the world. Among the conventional cancer treatments, chemotherapy is most frequently carried out to treat malignant cancer rather than localised lesions which is amenable to surgery and radiotherapy. However, anticancer drugs are associated with a plethora of side effects. Each drug, within every class, has its own set of adverse reactions which may cause patient incompliance and deterioration of the quality of life. One of the major causes of adverse reactions, especially for drugs targeting DNA, is the excessive production of reactive oxygen species (ROS) and subsequent build up of oxidative stress. To curb these undesired side effects, several dietary supplements have been tested, amongst which antioxidants have gained increasing popularity as adjuvant in chemotherapy. However, many oncologists discourage the use of antioxidant rich food supplements because these may interfere with the modalities which kill cancer by generating free radicals. In the present review, all studies reporting concomitant use of several antioxidants with chemotherapy are indiscriminately included and discussed impartially.

The effect of supplementation of thirteen different antioxidants and their analogues as a single agent or in combination with chemotherapy has been compiled in this article. The present review encompasses a total of 174 peer-reviewed original articles from 1967 till date comprising 93 clinical trials with a cumulative number of 18,208 patients, 56 animal studies and 35 in vitro studies. Our comprehensive data suggests that antioxidant has superior potential of ameliorating chemotherapeutic induced toxicity. Antioxidant supplementation during chemotherapy also promises higher therapeutic efficiency and increased survival times in patients.

Should Patients Undergoing Chemotherapy and Radiotherapy Be Prescribed Antioxidants?

In September 2005, CA: A Cancer Journal for Clinicians published a warning by Gabriella D’Andrea, MD, against the concurrent use of antioxidants with radiotherapy and chemotherapy. However, several deficiencies of the CA article soon became apparent, not least the selective omission of prominent studies that contradicted the author’s conclusions. While acknowledging that only large-scale, randomized trials could provide a valid basis for therapeutic recommendations, the author sometimes relied on laboratory rather than clinical data to support her claim that harm resulted from the concurrent use of antioxidants and chemotherapy. She also sometimes extrapolated from chemoprevention studies rather than those on the concurrent use of antioxidants per se. The article overstated the degree to which the laboratory data diverged in regard to the safety and efficacy of antioxidant therapy: in fact, the preponderance of data suggests a synergistic or at least harmless effect with most high-dose dietary antioxidants and chemotherapy. The practical recommendations made in the article to avoid the general class of antioxidants during chemotherapy are inconsistent, in that if antioxidants were truly a threat to the efficacy of standard therapy, antioxidant-rich foods, especially fruits and vegetables, ought also be proscribed during treatment. Yet no such recommendation is made. Furthermore, the wide-scale use by both medical and radiation oncologists of synthetic antioxidants (eg, amifostine) to control the adverse effects of cytotoxic treatments is similarly overlooked. In sum, this CA article is incomplete: there is far more information available regarding antioxidant supplements as an appropriate adjunctive cancer therapy than is acknowledged. Patients would be well advised to seek the opinion of physicians who are adequately trained and experienced in the intersection of 2 complex fields, that is, chemotherapeutics and nutritional oncology. Physicians whose goal is comprehensive cancer therapy should refer their patients to qualified integrative practitioners who have such training and expertise to guide patients. A blanket rejection of the concurrent use of antioxidants with chemotherapy is not justified by the preponderance of evidence at this time and serves neither the scientific community nor cancer patients.

P2X7 receptor blockade protects against cisplatin-induced nephrotoxicity in mice by decreasing the activities of inflammasome components, oxidative stress and caspase-3

Nephrotoxicity is a common complication of cisplatin chemotherapy and thus limits the use of cisplatin in clinic. The purinergic 2X7 receptor (P2X7R) plays important roles in inflammation and apoptosis in some inflammatory diseases; however, its roles in cisplatin-induced nephrotoxicity remain unclear. In this study, we first assessed the expression of P2X7R in cisplatin-induced nephrotoxicity in C57BL/6 mice, and then we investigated the changes of renal function, histological injury, inflammatory response, and apoptosis in renal tissues after P2X7R blockade in vivo using an antagonist A-438079. Moreover, we measured the changes of nod-like receptor family, pyrin domain containing proteins (NLRP3) inflammasome components, oxidative stress, and proapoptotic genes in renal tissues in cisplatin-induced nephrotoxicity after treatment with A-438079. We found that the expression of P2X7R was significantly upregulated in the renal tubular epithelial cells in cisplatin-induced nephrotoxicity compared with that of the normal control group. Furthermore, pretreatment with A-438079 markedly attenuated the cisplatin-induced renal injury while lightening the histological damage, inflammatory response and apoptosis in renal tissue, and improved the renal function. These effects were associated with the significantly reduced levels of NLRP3 inflammasome components, oxidative stress, p53 and caspase-3 in renal tissues in cisplatin-induced nephrotoxicity. In conclusions, our studies suggest that the upregulated activity of P2X7R might play important roles in the development of cisplatin-induced nephrotoxicity, and P2X7R blockade might become an effective therapeutic strategy for this disease.

Effects of N-acetyl-L-cysteine on bleomycin induced oxidative stress in malignant testicular germ cell tumors

Testicular cancer is a very common cancer in males aged 15-44 years. Bleomycin is used in chemotherapy regimens in the treatment of patients having testicular germ-cell tumor. Bleomycin generates oxygen radicals, induces oxidative cleavage of DNA strand and induces apoptosis in cancer cells. There is no study in the literature investigating effects of N-Acetyl-L-Cysteine (NAC) on bleomycin-induced oxidative stress in testicular germ cell tumors. For this reason, we studied effects of NAC on oxidative stress produced in wild-type NTera-2 and p53-mutant NCCIT testis cancer cells incubated with bleomycin and compared the results with H(2)O(2) which directly produces oxidative stress. We determined protein carbonyl content, thiobarbituric acid reactive substances (TBARS), glutathione (GSH), 8-isoprostane, lipid hydroperoxide levels and total antioxidant capacity in both testicular cancer cells. Bleomycin and H(2)O(2) significantly increased 8-isoprostane, TBARS, protein carbonyl and lipid hydroperoxide levels in NTera-2 and NCCIT cells. Bleomycin and H(2)O(2) significantly decreased antioxidant capacity and GSH levels in both cell lines. Co-incubation with NAC significantly decreased lipid hydroperoxide, 8-isoprostane, protein carbonyl content and TBARS levels increased by bleomycin and H(2)O(2). NAC enhanced GSH levels and antioxidant capacity in the NTera-2 and NCCIT cells. It can be concluded that NAC diminishes oxidative stress in human testicular cancer cells induced by bleomycin and H(2)O(2).

Silymarin selectively protects human renal cells from cisplatin-induced cell death

CONTEXT

Cisplatin-induced nephrotoxicity has been accepted as an important obstacle for efficient cisplatin-based chemotherapy. Silymarin from seeds of milk thistle [Silybum marianum L. (Asteraceae)] has been shown to possess various potential pharmacological properties; however, whether or not this agent selectively protects renal cells from cisplatin-induced cell death with no interfering effect on cancer cells is not clear.

OBJECTIVE

Potential of silymarin in protection of cisplatin-induced renal cell death without compromising effect on anticancer activity of cisplatin was demonstrated in this study.

MATERIALS AND METHODS

Cisplatin-induced cell death was evaluated in human proximal tubular HK-2, lung carcinoma H460, and melanoma G361 cells using MTT, Hoechst 33342, and propidium iodide assays.

RESULTS

Cisplatin induced both apoptosis and necrosis in HK-2 cells and caused a decrease in cell viability by ~40% and 60% at the doses of 25 and 100 µM, respectively. Pretreatment with 25-200 µM of silymarin significantly protected against cisplatin-induced cell death in a dose-dependent manner. In contrast, pretreatment of silymarin (25-100 µM) caused no significant change on cisplatin-induced cell death in H460 cells but significantly potentiated cisplatin-induced apoptosis in G361 cells.

DISCUSSION AND CONCLUSION

These findings reveal the selectivity of silymarin in protection of renal cells from cisplatin-induced cell death and could be beneficial for the development of this considerately safe compound as a renoprotective agent.

Cis-dichlorodiammineplatinum upregulates angiotensin II type 1 receptors through reactive oxygen species generation and enhances VEGF production in bladder cancer

We previously reported that angiotensin II type 1 receptor (AT1R) antagonists enhanced the cytotoxity of cis-dichlorodiammineplatinum (CDDP) in a bladder cancer xenograft model. To elucidate the synergistic mechanism, we investigated whether reactive oxygen species (ROS) generation induced by CDDP may affect the regulation of AT1R expression. Five invasive human bladder cancer cell lines, T24, UMUC-3, 5637, KU-1, and KU-19-19, were used in the in vitro study. For the in vivo study, T24 cells were used. We also examined AT1R and vascular endothelial growth factor (VEGF) expression in human bladder cancer specimens that had been treated with CDDP-based chemotherapy. The in vitro study showed that AT1R expression was significantly upregulated by CDDP in T24, KU-1, and KU-19-19 cells. On the other hand, AT1R expression was not changed in UMUC-3 and 5637 cells. ROS generation was also significantly upregulated by CDDP in T24, KU-1, and KU-19-19 cells. The upregulation of AT1R expression induced by CDDP was significantly suppressed by scavenging free radicals. Angiotensin II induced VEGF production in CDDP-treated cells; however, the AT1R antagonist significantly inhibited the increase in VEGF. The in vivo study results also showed that CDDP treatment upregulated AT1R expression, resulting in increased VEGF. Clinical specimens from patients who underwent cystectomy after neoadjuvant CDDP-based chemotherapy showed significantly higher AT1R and VEGF expression than corresponding transurethral resection specimens. Our findings indicate that CDDP upregulates AT1R expression though ROS generation and enhances VEGF production. Therefore, AT1R blockade may be an effective strategy for bladder cancer in combination with CDDP-based chemotherapy.

Valproic acid resensitizes cisplatin-resistant ovarian cancer cells

Although certain inhibitors of histone deacetylases have been shown to induce cytotoxicity alone or in combination with chemotherapeutic agents in cancer cells, the molecular mechanism is not clear. The goal of the present study was to determine whether the antiseizure drug valproic acid (2-propylpentanoic acid; VPA), which is also able to inhibit histone deacetylase, exhibits synergistic cytotoxicity with cisplatin, and the possible pathways for this. Our results clearly show that VPA not only exhibits synergistic cytotoxicity with cisplatin in all of the ovarian carcinoma cells tested, but also can resensitize the cells that have acquired resistance to cisplatin. Consistent with the increased cytotoxicity, cotreatment with VPA was shown to upregulate the cisplatin-mediated DNA damage revealed by phosphorylation of ataxia telangiectasia mutation and histone H2AX. Reactive oxygen species accumulation and tumor suppressor phosphatase and tensin homolog (PTEN) overexpression, which could contribute to the enhanced cytotoxicity, were also observed to be upregulated by VPA. Because PTEN knockdown by small interference RNA or antioxidant treatment can reduce cisplatin-mediated cytotoxicity, it is suggested that upregulation of PTEN and reactive oxygen species by VPA contributes to the enhancement of cisplatin-mediated cytotoxicity. These results with resensitization of cisplatin-resistant cells particularly may provide benefits in the treatment of ovarian cancer patients.

Chronic low vitamin intake potentiates cisplatin-induced intestinal epithelial cell apoptosis in WNIN rats

AIM: To investigate if cisplatin alters vitamin status and if VR modulates cisplatin induced intestinal apoptosis and oxidative stress in Wistar/NIN (WNIN) male rats.

METHODS: Weanling, WNIN male rats (n = 12 per group) received adlibitum for 17 wk: control diet (20% protein) or the same with 50% vitamin restriction. They were then sub-divided into two groups of six rats each and administered cisplatin (2.61 mg/kg bodyweight) once a week for three wk or PBS (vehicle control). Intestinal epithelial cell (IEC) apoptosis was monitored by morphometry, Annexin-V binding, M30 cytodeath assay and DNA fragmentation. Structural and functional integrity of the villus were assessed by villus height / crypt depth ratio and activities of alkaline phosphatase, lys, ala-dipeptidyl amino-peptidase, respectively. To assess the probable mechanism(s) of altered apoptosis, oxidative stress parameters, caspase-3 activity, and expression of Bcl-2 and Bax were determined.

RESULTS: Cisplatin per se decreased plasma vitamin levels and they were the lowest in VR animals treated with cisplatin. As expected VR increased only villus apoptosis, whereas cisplatin increased stem cell apoptosis in the crypt. However, cisplatin treatment of VR rats increased apoptosis both in villus and crypt regions and was associated with higher levels of TBARS, protein carbonyls and caspase-3 activity, but lower GSH concentrations. VR induced decrease in Bcl-2 expression was further lowered by cisplatin. Bax expression, unaffected by VR was increased on cisplatin treatment. Mucosal functional integrity was severely compromised in cisplatin treated VR-rats.

CONCLUSION: Low intake of vitamins increases the sensitivity of rats to cisplatin and promotes intestinal epithelial cell apoptosis.

Chemical blockage of the proteasome inhibitory function of bortezomib: impact on tumor cell death

The proteasome inhibitor bortezomib is emerging as a potent anti-cancer agent. Still, recent clinical trials have revealed a significant secondary toxicity of bortezomib. Consequently, there is much interest in dissecting the mechanism of action of this compound to rationally improve its therapeutic index. The cytotoxic effect of bortezomib is frequently characterized by interfering with downstream events derived from the accumulation of proteasomal targets. Here we identify the first chemical agent able to act upstream of the proteasome to prevent cell killing by bortezomib. Specifically, we show that the polyhydroxyl compound Tiron can function as a competitive inhibitor of bortezomib. This effect of Tiron was surprising, since it is a classical radical spin trap and was expected to scavenge reactive oxygen species produced as a consequence of bortezomib action. The inhibitory effect of Tiron against bortezomib was selective, since it was not shared by other antioxidants, such as vitamin E, MnTBAP, L-N-acetyl-cysteine, and FK-506. Comparative analyses with nonboronated proteasome inhibitors (i.e. MG132) revealed a specificity of Tiron for bortezomib. We exploited this novel feature of Tiron to define the "point of no return" of proteasome inhibition in melanoma cells and to block cell death in a three-dimensional model of human skin. Cells from T-cell lymphoma, breast carcinoma, and non-small cell lung cancer were also responsive to Tiron, suggesting a broad impact of this agent as a bortezomib blocker. These results may have important implications for the analysis of bortezomib in vivo and for the design of drug mixtures containing proteasome inhibitors.

Inhibition of tumor angiogenesis during cisplatin chemotherapy for bladder cancer improves treatment outcome

OBJECTIVES

To investigate the effect of inhibiting tumor angiogenesis during cisplatinum-(II)-diamine dichloride (cisplatin) chemotherapy of bladder cancer (BC) in a rat model.

METHODS

Bladder cancer was induced in 64 male rats using 0.05% N-butyl-N-(4-hydroxybutyl)-nitrosamine in their water supply for 20 weeks. The animals were then divided randomly into four groups of 16 rats each: a control BC group (group 1); a BC group treated with cisplatin (0.25 mg/kg body weight) by intraperitoneal injection twice every week (group 2); a BC group treated with the antiangiogenic factor TNP-470 (30 mg/kg body weight) by intraperitoneal injection twice every week (group 3); and a BC group treated with cisplatin plus TNP-470 (group 4, treatment regimens as described). Per group, 4 rats were killed weekly after the start of treatment, for 4 weeks. BC was confirmed using histologic characteristics, and the treatment outcomes were determined by measuring tumor microvascular density and cell proliferation and apoptosis indexes (PI and AI, respectively).

RESULTS

All animals had confirmed BC. Both group 3 (TNP-470) and group 4 (cisplatin plus TNP-470) had significantly decreased microvascular density compared with group 1 (P <0.05). Although both the PI and AI were significantly different between group 4 (cisplatin plus TNP-470) and group 1 (control BC; P <0.05), neither the PI nor AI was significantly different between group 2 (cisplatin) and group 4 (cisplatin plus TNP-470; P >0.05).

CONCLUSIONS

TNP-470 in conjunction with cisplatin chemotherapy resulted in a decrease in the microvascular density of BC in a rat model. However, TNP-470 did not appear to have a significant impact on the cisplatin effect against BC as measured by apoptosis and cell proliferation.

Concentration-dependent collateral sensitivity of cisplatin-resistant gastric cancer cell sublines

The cisplatin-resistant gastric cancer cell sublines, SNU-601/Cis2 and /Cis10, were 49 and >530 times more resistant to cisplatin, respectively, compared with the drug-sensitive cells, SNU-601/WT. The SNU-601/Cis2 showed cross-resistance to carboplatin, heptaplatin, doxorubicin, mitomycin C, and 5-fluorouracil compared with the SNU-601/WT whereas the SNU-601/Cis10 displayed collateral sensitivity to these drugs with the exception of cisplatin compared with the SNU-601/Cis2, suggesting that the cross-resistance and collateral sensitivity of cisplatin-resistant gastric cancer cells are dependent upon cisplatin concentrations. Altered expression of the antioxidant and transporter genes (metallothionein, catalase, superoxide dismutases, P-glycoprotein, and the breast cancer resistance protein) was involved in these phenotypes of the cisplatin-resistant gastric cancer cell lines.

Cisplatin induces endoplasmic reticulum stress and nucleus-independent apoptotic signaling

DNA damage is believed to be the main cause of the antiproliferative effect of cisplatin, a cornerstone agent in anticancer therapy. However, cisplatin can be expected to react also with nucleophiles other than DNA. Using enucleated cells (cytoplasts) we demonstrate here that cisplatin-induced apoptotic signaling may occur independently of DNA damage. Cisplatin-induced caspase-3 activation in cytoplasts required calcium and the activity of the calcium-dependent protease calpain. It is known that calpain activation may be associated with endoplasmic reticulum (ER) stress, suggesting that the ER is a cytosolic target of cisplatin. Consistent with this hypothesis, cisplatin induced calpain-dependent activation of the ER-specific caspase-12 in cytoplasts as well as in intact cells. Cisplatin also induced increased expression of Grp78/BiP, another marker of ER stress. By contrast, the DNA-damaging topoisomerase II inhibitor etoposide did not induce apoptotic signaling in cytoplasts nor ER stress in intact cells. We have thus identified a novel mechanism of action of cisplatin. The results have implications for the understanding of resistance mechanisms as well as the unique efficiency of this drug.

Bcl-2 has differing effects on the sensitivity of breast cancer cells depending on the antineoplastic drug used

The aim of this paper was to evaluate the role of bcl-2 in the susceptibility of the MCF7 ADR human breast carcinoma line overexpressing the P-170 glycoprotein (P-170) to various drugs. The sensitivity to four multidrug resistance (MDR)-related drugs (doxorubicin (ADR), vincristine (VCR), vinblastine (VBL), actinomycin D (ACTD)) and three MDR-non-related drugs (cisplatin (DDP), bischloroethylnitrosourea (BCNU), 5-fluorouracil (5-FU)) was evaluated by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay in three bcl-2-overexpressing clones obtained from the MCF7 ADR line. We found that the bcl-2-overexpressing clones show increased resistance to DDP and BCNU, while no difference to 5-FU were observed between the control cells and bcl-2 transfectants. Surprisingly, bcl-2-overexpressing clones displayed an increased sensitivity compared with the control cells to the MDR-related drugs ADR, VCR, VBL and ACTD. Focusing on DDP and ADR, we found that the increased resistance of the bcl-2 transfectants to DDP was correlated to their ability to prevent apoptosis, while the enhanced sensitivity to ADR was associated with an increased ADR accumulation and a decreased ADR efflux. Moreover, while bcl-2 overexpression does not induce changes in P-170 glycoprotein expression, it did induce a reduction of the adenosine triphosphate (ATP) levels and basal protein kinase C (PKC) activity, both of which have a crucial role in the regulation of the MDR phenotype. In conclusion, the effect of bcl-2 on antineoplastic sensitivity observed in this study underscores the idea that bcl-2 may have distinct biological effects depending on the anticancer drug used.

Induction of apoptosis in malignant pleural mesothelioma cells by activation of the Fas (Apo-1/CD95) death-signal pathway

OBJECTIVE

Although well characterized in several solid tumors, the effects of Fas/Fas ligand interactions in malignant pleural mesothelioma cells have not been defined. The present study was undertaken to examine the functional status of the Fas/Fas ligand pathway in malignant pleural mesothelioma cells and to determine the feasibility of targeting this death-signal pathway for molecular intervention in patients with mesotheliomas.

METHODS

Fas expression in primary normal human bronchial epithelial cells and 6 malignant pleural mesothelioma cell lines was quantified by means of flow cytometry. The caspase components of the Fas-mediated apoptotic pathway were evaluated by means of Western blot techniques. Soluble Fas ligand-mediated cytotoxicity and apoptosis were evaluated by means of MTS and TUNEL assays, respectively. Cisplatin (3 microg/mL) and lymphokine-activated killer cells were used to enhance mesothelioma sensitivity to soluble Fas ligand. An H2373 nude mouse xenograft model of malignant pleural mesothelioma was established to assess the in vivo effects of soluble Fas ligand.

RESULTS

Four of 6 malignant pleural mesothelioma lines exhibited high levels of Fas expression, and 2 of 4 were inherently susceptible to soluble Fas ligand-mediated cytotoxicity (soluble Fas ligand 50% inhibitory concentration, < 15 ng/mL). Two soluble Fas ligand refractory cell lines (H2052 and H513) exhibited high levels of Fas receptor. Pretreatment with cisplatin resulted in a reduction of 50% inhibitory concentration from infinity to 4.17 +/- 0.14 ng/mL and 10.23 +/- 1.58 ng/mL, respectively. Two additional soluble Fas ligand refractory cell lines (H2595 and REN) expressed low levels of Fas. Exposure of these cells to lymphokine-activated killer cells or lymphokine-activated killer cell-conditioned medium followed by a 24-hour treatment with cisplatin resulted in a significant reduction in 50% inhibitory concentration of soluble Fas ligand and pronounced induction of apoptosis. Intraperitoneally administered soluble Fas ligand mediated regression of H2373 xenografts.

CONCLUSION

The Fas/Fas ligand pathway in mesothelioma cells is either intrinsically intact or can be rendered functional with chemotherapeutic agents or immune effector cells. These preclinical data support further evaluation of strategies to enhance Fas-mediated apoptosis in mesotheliomas.

Methylglyoxal enhances cisplatin-induced cytotoxicity by activating protein kinase Cdelta

The cytotoxic side effects of anti-neoplastic drugs are increased in patients with either type 1 or type 2 diabetes mellitus by a mechanism that is not clearly defined. We report that the circulating glucose metabolite, methylglyoxal (MGO), enhances cisplatin-induced apoptosis by activating protein kinase Cdelta (PKCdelta). We found that treatment of myeloma cells with the antioxidant N-acetylcysteine completely blocked cisplatin-dependent intracellular GSH oxidation, reactive oxygen species (ROS) generation, poly(ADP-ribose) polymerase cleavage, and apoptosis. Importantly, co-treatment of cells with the reactive carbonyl MGO and cisplatin increased apoptosis by 90% over the expected additive effect of combined MGO and cisplatin treatment. This same synergism was also observed when ROS generation was examined. MGO and cisplatin increased PKCdelta activity by 4-fold, and this effect was blocked by the PKCdelta inhibitor rottlerin but not by NAC. Furthermore, rottlerin blocked combined MGO and cisplatin-induced ROS generation and apoptosis. Finally, MGO and cisplatin induced c-Abl activation and c-Abl:PKCdelta association. Rottlerin blocked c-Abl activation, but the c-Abl inhibitor STI-571 increased MGO and cisplatin-induced apoptosis by 50%. Taken together these data indicate that MGO synergistically enhances cisplatin-induced apoptosis through activation of PKCdelta and that PKCdelta is critical to both cell death and cell survival pathways. These findings suggest that in the patient with diabetes mellitus heightened oxidative stress can enhance the cytotoxicity of agents that induce DNA damage.

Dietary antioxidants during cancer chemotherapy: impact on chemotherapeutic effectiveness and development of side effects

Several studies suggest that dietary supplementation with antioxidants can influence the response to chemotherapy as well as the development of adverse side effects that results from treatment with antineoplastic agents. Administration of antineoplastic agents results in oxidative stress, i.e., the production of free radicals and other reactive oxygen species (ROS). Oxidative stress reduces the rate of cell proliferation, and that occurring during chemotherapy may interfere with the cytotoxic effects of antineoplastic drugs, which depend on rapid proliferation of cancer cells for optimal activity. Antioxidants detoxify ROS and may enhance the anticancer effects of chemotherapy. For some supplements, activities beyond their antioxidant properties, such as inhibition of topoisomerase II or protein tyrosine kinases, may also contribute. ROS cause or contribute to certain side effects that are common to many anticancer drugs, such as gastrointestinal toxicity and mutagenesis. ROS also contribute to side effects that occur only with individual agents, such as doxorubicin-induced cardiotoxicity, cisplatin-induced nephrotoxicity, and bleomycin-induced pulmonary fibrosis. Antioxidants can reduce or prevent many of these side effects, and for some supplements the protective effect results from activities other than their antioxidant properties. Certain side effects, however, such as alopecia and myelosuppression, are not prevented by antioxidants, and agents that interfere with these side effects may also interfere with the anticancer effects of chemotherapy.

Cell death by reactive oxygen species generated from water-soluble cationic metalloporphyrins as superoxide dismutase mimics

We investigated the effect on cell death of reactive oxygen species induced by water-soluble cationic metalloporphyrins with superoxide dismutase (SOD) activity. The SOD activity of 5,10,15,20-tetrakis(4-N-methylpyridyl)]porphine (MPy(4)P) containing Fe, Mn or Cu was measured using a cytochrome c assay by the xanthine/xanthine oxidase system and stopped-flow kinetic analysis. Cell viability of four cell lines treated with metalloporphyrins, mitomycin c (MMC), or cisplatin was estimated by a trypan blue exclusion assay. FeMPy(4)P with a high SOD activity showed a significant cytotoxicity compared with MMC and cisplatin, while CuMPy(4)P without SOD activity exhibited no cytotoxicity. However, MnMPy(4)P showing an SOD activity as high as that of FeMPy(4)P did not indicate cytotoxicity. These findings suggest that FeMPy(4)P as SOD mimic converts intracellular O2(*-) to H(2)O(2) and that it rapidly reacts with H(2)O(2) to form *OH, causing DNA damage and inducing cell death. On the other hand, MnMPy(4)P did not participate in the Fenton reaction, so that DNA damage in the cells treated with MnMPy(4)P was not observed. In addition, the cytotoxicity by the metalloporphyrin was inversely correlated with the SOD activity of the cells and the selective damage at cellular and DNA levels was confirmed. We believe that for an anticancer drug with antioxidant ability O(2)(*-) is useful as a target molecule to induce selective cell death between cancer and normal cells and that metalloporphyrins showing SOD activity and Fenton-like reaction are a new class of anticancer agents.

Utility of acetylcysteine in treating poisonings and adverse drug reactions

As recognition of the role of free radicals and reactive toxins in the pathogenesis of disease, poisoning, and adverse drug reactions has evolved, interest in the use of acetylcysteine as a modulator of these effects has steadily increased in recent years. Acetylcysteine is commonly thought to serve as a glutathione precursor and consequently can increase or sustain intracellular glutathione which scavenges reactive oxygen species caused by toxins or subsequent tissue injury. At least 10 additional mechanisms of action for acetylcysteine have been demonstrated in various laboratory models, but a unifying framework of its actions is still to be proposed. This paper reviews the current experimental and therapeutic status of acetylcysteine for the treatment of poisonings and adverse drug reactions. Of the 45 potential uses of acetylcysteine that were identified for the treatment of poisonings or adverse drug reactions, 14 of the toxic effects have little support for its use while promising results have been demonstrated for 27 toxicities. Currently, treatment of acute paracetamol (acetaminophen) poisoning is the only widely accepted clinical indication for acetylcysteine as a treatment for poisoning or adverse drug reactions. In many clinical situations acetylcysteine is used empirically utilising modifications of dosage regimens employed for paracetamol poisoning. Often it is difficult to determine the benefit of therapy with acetylcysteine owing to the nature of the toxicity being treated, the use of other therapies, the presence of comorbid conditions, and the small number of patients studied. The diverse and positive nature of the investigations suggest that there is considerable promise in acetylcysteine as a research tool and pharmacological agent.