A phase II study of weekly edatrexate (10-EDAM) in metastatic melanoma. A National Cancer Institute of Canada Clinical Trials Group study

Differential chemosensitivity to antifolate drugs between RAS and BRAF melanoma cells

BACKGROUND

The importance of the genetic background of cancer cells for the individual susceptibility to cancer treatments is increasingly apparent. In melanoma, the existence of a BRAF mutation is a main predictor for successful BRAF-targeted therapy. However, despite initial successes with these therapies, patients relapse within a year and have to move on to other therapies. Moreover, patients harbouring a wild type BRAF gene (including 25% with NRAS mutations) still require alternative treatment such as chemotherapy. Multiple genetic parameters have been associated with response to chemotherapy, but despite their high frequency in melanoma nothing is known about the impact of BRAF or NRAS mutations on the response to chemotherapeutic agents.

METHODS

Using cell proliferation and DNA methylation assays, FACS analysis and quantitative-RT-PCR we have characterised the response of a panel of NRAS and BRAF mutant melanoma cell lines to various chemotherapy drugs, amongst them dacarbazine (DTIC) and temozolomide (TMZ) and DNA synthesis inhibitors.

RESULTS

Although both, DTIC and TMZ act as alkylating agents through the same intermediate, NRAS and BRAF mutant cells responded differentially only to DTIC. Further analysis revealed that the growth-inhibitory effects mediated by DTIC were rather due to interference with nucleotide salvaging, and that NRAS mutant melanoma cells exhibit higher activity of the nucleotide synthesis enzymes IMPDH and TK1. Importantly, the enhanced ability of RAS mutant cells to use nucleotide salvaging resulted in resistance to DHFR inhibitors.

CONCLUSION

In summary, our data suggest that the genetic background in melanoma cells influences the response to inhibitors blocking de novo DNA synthesis, and that defining the RAS mutation status could be used to stratify patients for the use of antifolate drugs.

A phase II study of Irofulven (MGI 114) in patients with stage IV melanoma

Sixteen patients with stage IV melanoma, who were heavily pretreated, received 11 mg/m2/day of intravenous Irofulven for five consecutive days every 28 days. There were no objective tumor responses, although one patient exhibited stable disease after 4 cycles. The most common toxicities were grade 1/2 nausea, vomiting, fatigue, anemia, and thrombocytopenia. One patient required a dose reduction for an elevated creatinine while another patient required cessation of treatment because of acute ataxia that may have been related to Irofulven. Based upon these data, Irofulven does not demonstrate significant antitumor activity to warrant further investigation in advanced melanoma.

Phase II trial of edatrexate in relapsed or refractory germ cell tumors: a Southwest Oncology Group study (SWOG 9124)

Up to 30% of patients with advanced germ cell tumors will fail induction chemotherapy or will relapse. New agents with activity in this still potentially curable subgroup of patients are needed. Edatrexate (10-ethyl, 10-deaza-aminopterin) is a methotrexate analogue that has preclinical and clinical activity in breast, lung, and head and neck cancers, as well as in non-Hodgkin's lymphomas. A phase II trial of edatrexate in relapsed or refractory malignant germ cell tumors was conducted by the Southwest Oncology Group (SWOG). Twenty-five patients were enrolled in the trial. Edatrexate was administered intravenously at a dose of 80 mg/m2 weekly for four weeks followed by a one-week rest period. The treatment course was repeated every five weeks. Among the 23 patients evaluable for response, there were no objective responses with all patients developing progressive disease. Thirteen patients (56%) developed Grade 3-4 toxicities, predominantly stomatitis and malaise/fatigue/lethargy. One patient developed Grade 4 anemia while another developed grade 4 anemia and thrombocytopenia. No patients discontinued treatment due to toxicity nor were there any toxic deaths. Edatrexate administered in this dose and schedule has no antitumor activity and has substantial toxicity in patients with relapsed or refractory germ cell tumors.