UCLA research could enhance treatments for drug-resistant melanoma

Melanoma is the deadliest form of skin cancer, killing more than 8,000 in the U.S. each year. Approximately 40 percent of advanced melanoma tumors are driven to grow by the presence of mutations in a gene known as the BRAF gene. And although new drugs called BRAF inhibitors have shown an ability to rapidly shrink melanoma tumors, BRAF-mutated tumors often resist early treatment and only partially respond to BRAF inhibitors, which leaves behind cancer cells that can eventually grow into new tumors.

Today, two studies by researchers from UCLA's Jonsson Comprehensive Cancer Center were published online in the journal Cancer Discovery that provide critical insights into two important ways that tumors resist BRAF inhibitors. The researchers found the key cell-signaling pathways used by BRAF-mutant melanoma to learn how to become resistant to inhibitor drugs, and how the limited focus of BRAF inhibitors allows melanoma cells to evolve and become drug-resistant. The studies will appear later in the journal's print edition.

Led by Dr. Roger Lo, a member of the Jonsson Cancer Center and associate professor and director of the melanoma clinic in dermatology, the studies utilized patients' biopsy samples to give researchers powerful information that can be translated directly into the clinic. Specifically, the findings should help oncologists make better use of BRAF inhibitor drugs in combination with other drugs for melanoma patients.

In the first study, Lo and colleagues discovered how tumor cells escaped the effects of BRAF inhibitors by tracking the outgrowth of melanoma cells that had learned from different cell-signaling pathways how to become BRAF inhibitor–resistant. This work, based on an analysis of 100 biopsies from patients who had been treated with BRAF inhibitors, revealed that BRAF inhibitor–resistant tumors use a variety of different signaling routes to learn resistance and that people can have more than one resistance route. Clinical trials have rarely studied these phenomena at the molecular level, which Lo said provides a much more robust view of the scale and scope of the problem.

Understanding the mechanisms of tumor resistance could help doctors identify the optimal combination of inhibitor drugs to block multiple resistance routes, which eventually could shrink tumors for a much longer period, or eradicate them completely.

"By helping us understand the core resistance pathways and tumor heterogeneity, fitness and mutational patterns that emerge under drug selection, this study lays a foundation for clinical trials to investigate the mechanisms of tumor progression in BRAF-mutant melanoma patients," Lo said.

Melanoma is the most aggressive form of skin cancer. Patients with advanced disease, such as lymph node involvement and distant metastases, have 5-year survival rates of 50% and 10-20%, respectively. This poor prognosis largely results from resistance to conventional chemotherapy, namely cytotoxic drugs. The basis for drug resistance in melanoma is most likely dysregulation of apoptosis, although other mechanisms including drug transport, detoxification, and enhanced DNA repair may also play a role. Defects at multiple levels and in both major apoptotic pathways have been described in melanoma. Our laboratory has identified an inhibitor of apoptosis, termed survivin, that is expressed in melanoma and required for maintenance of melanoma cell viability. Targeting of survivin and other apoptotic regulators increases the sensitivity of melanoma cells to cytotoxic drugs, and may provide a promising new therapeutic approach to cancer.