Redox modulation of oxidatively-induced DNA damage by ascorbate enhances both in vitro and ex-vivo DNA damage formation and cell death in melanoma cells

Elevated genomic instability in cancer cells suggests a possible model-scenario for their selective killing via the therapeutic delivery of well-defined levels of further DNA damage. To examine this scenario, this study investigated the potential for redox modulation of oxidatively-induced DNA damage by ascorbate in malignant melanoma (MM) cancer cells, to selectively enhance both DNA damage and MM cell killing. DNA damage was assessed by Comet and ɣH2AX assays, intracellular oxidising species by dichlorofluorescein fluorescence, a key antioxidant enzymatic defence by assessment of catalase activity and cell survival was determined by clonogenic assay. Comet revealed that MM cells had higher endogenous DNA damage levels than normal keratinocytes (HaCaT cells); this correlated MM cells having higher intracellular oxidising species and lower catalase activity, and ranked with MM cell melanin pigmentation. Comet also showed MM cells more sensitive towards the DNA damaging effects of exogenous H2O2, and that ascorbate further enhanced this H2O2-induced damage in MM cells; again, with MM cell sensitivity to induced damage ranking with degree of cell pigmentation. Furthermore, cell survival data indicated that ascorbate enhanced H2O2-induced clonogenic cell death selectively in MM cells whilst protecting HaCaT cells. Finally, we show that ascorbate serves to enhance the oxidising effects of the MM therapeutic drug Elesclomol in both established MM cells in vitro and primary cell cultures ex vivo. Together, these results suggest that ascorbate selectively enhances DNA damage and cell-killing in MM cells. This raises the option of incorporating ascorbate into clinical oxidative therapies to treat MM.

Phase II, randomized, controlled, double-blinded trial of weekly elesclomol plus paclitaxel versus paclitaxel alone for stage IV metastatic melanoma

PURPOSE

Elesclomol is a novel, small-molecule, oxidative stress inducer believed to exert selective cytotoxicity by increasing intracellular concentrations of reactive oxygen species, which results in cell death via mitochondrial apoptosis. We evaluated whether the addition of elesclomol to weekly paclitaxel could improve efficacy in patients with stage IV metastatic melanoma.

PATIENTS AND METHODS

We randomly assigned patients with metastatic melanoma, measurable disease, and one or fewer prior chemotherapy regimens to elesclomol 213 mg/m(2) plus paclitaxel 80 mg/m(2) (E + P) or to paclitaxel 80 mg/m(2) alone at a 2:1 ratio; regimens were given as a 1-hour intravenous infusion weekly, during 3 of every 4 weeks until disease progression per Response Evaluation Criteria in Solid Tumors or death occurred. Patients who experienced progression were unblended, and patients on paclitaxel alone were permitted to cross over to E + P. The primary efficacy end point was progression-free survival (PFS); secondary end points were response rate (RR), toxicity, and overall survival (OS; analyzed post hoc).

RESULTS

At 21 US sites, 53 patients were randomly assigned to E + P, and 28 patients were randomly assigned to paclitaxel. The addition of elesclomol to paclitaxel yielded a doubling of median PFS (112 v 56 days) and a 41.7% risk reduction for disease progression/death (hazard ratio, 0.583; P = .035). Respective RRs for the E + P and paclitaxel groups were 15% and 3%; median OS was 11.9 v 7.8 months. Of patients on paclitaxel alone, 19 (68%) of 28 crossed over to E + P after they experienced progression. Weekly E + P was well tolerated.

CONCLUSION

E + P resulted in a statistically significant doubling of median PFS, with an acceptable toxicity profile and encouraging OS. A multinational, phase III trial (SYMMETRY) of E + P compared with paclitaxel alone in metastatic melanoma has closed.

Management of Metastatic Melanoma 2005

The management of metastatic melanoma in 2005 remains a major clinical challenge. Multidisciplinary treatment planning and careful attention to sites of metastases, tumor biology, and comorbid conditions are critical to making the best clinical decisions for individual patients. No standard of care exists because no systemic therapies have yet shown efficacy in phase III trials. Single-agent or combination chemotherapy has not impacted over-all survival, and response rates are of short duration. High-dose IL-2 produces durable responses in a small subset (7%) of highly selected patients and has considerable toxicity and quality-of-life trade-offs. Biochemotherapy results in overall higher responses, but its impact on overall survival has been disappointing and its toxicity and expense are considerable. Re-searchers are further investigating biochemotherapy modifications with maintenance biotherapy and CNS consolidation in effort to increase durability of responses and prevent or delay the devastating sequela of CNS metastases. Despite a disappointing past, the advancement of science and a better understanding of critical cellular targets and pathways make the future of melanoma research encouraging. Clinical trials are actively studying novel immune potentiators, cytotoxics, and targeted therapies. Combinations of these new agents will likely be necessary to advance the treatment of the dis-ease. All patients should be encouraged to participate in clinical trials.