January 8, 2015

Study tracks combination therapy to treat melanoma

Melanoma is the most lethal form of skin cancer, with high mortality rates. While new drugs have been approved to treat the disease, patients nearly always develop resistance to the therapies and the cancer advances.

Ann Richmond, Ph.D., left, Anna Vilgelm, M.D., Ph.D., and colleagues are studying combined therapies to treat many different sub-types of melanoma. (photo by John Russell)

Melanoma is the most lethal form of skin cancer, with high mortality rates. While new drugs have been approved to treat the disease, patients nearly always develop resistance to the therapies and the cancer advances.

This is especially relevant for patients with a mutation in the BRAF gene who generally have a robust, but temporary, response to BRAF inhibitor therapies. Researchers have been trying to identify therapies that can be combined to improve patient response.

A new study, led by first author Anna Vilgelm, M.D., Ph.D., a Vanderbilt postdoctoral fellow, and corresponding author Ann Richmond, Ph.D., Ingram Professor of Cancer Research, and Senior Research Career Scientist, Tennessee Valley Healthcare System Department of Veterans Affairs, indicates that two therapies already in clinical development as single agents may work in combination to treat many subtypes of melanoma. The study was published online recently in Cancer Research.

The investigators’ ultimate target was to block cell proliferation and induce cell death by targeting two proteins — MDM2, a protein which facilitates degradation of the tumor suppressor p53, and Aurora kinase A (AURKA), a protein that regulates cell division and growth. TP53, the gene that encodes p53, is seldom mutated in melanoma, which makes the activation of the p53 cellular pathway through MDM2 targeting feasible. AURKA is often highly expressed in melanoma tumor cells.

Early tests of an AURKA inhibitor found that the drug was stopping tumor cells from multiplying, making them big and sluggish (senescent), but the cells still weren’t dying. So Vilgelm decided to combine this therapy with a second drug (MDM2 antagonist) which kills tumor cells by restoring p53 function.

“The tumor cells made senescent by treatment with the AURKA inhibitor were not dying and might later start growing again, so we wanted to treat them with this agent that induces p53 and death of the senescent cells.

“The senescent cells also release cytokines that bring in immune cells to help remove and kill the senescent tumor cells,” said Vilgelm.

The investigators tested the combination therapy in several melanoma mouse models, including one that grafts human melanoma tumor samples directly into the mouse.

Richmond said combining the MDM2 antagonist drug with the AURKA inhibitor worked as a form of indirect immunotherapy and blocked the growth of the tumors.

“The combined effect of inducing senescence and then blocking MDM2 led to massive production of chemokines that recruited immune cells that helped participate in the inhibition of tumor growth,” Richmond said.

“The majority of the tumors that we tested were able to respond to the therapy, regardless of BRAF gene mutation, suggesting that a large cohort of patients could be treated with these drugs, including patients whose tumors had developed resistance to BRAF inhibitor therapy,” said Vilgelm.

The authors say the results provide a sound rationale for further studies of the combination therapy.

Other investigators involved in the study include Jeff Pawlikowski, Ph.D., Yan Liu, Ph.D., OrianaHawkins, Ph.D., Tyler Davis, Ph.D., Kevin Weller M.S., Linda Horton, M.S., Colt McClain, M.D., Gregory Ayers, M.S., Jeffrey Sosman, M.D., Mark Kelley, M.D., and Jeffrey Johnston, Ph.D., Vanderbilt; Jessica Smith, B.S., Meharry Medical College; David Turner, Ph.D., David Essaka, Ph.D., and Clinton Stewart, Ph.D., St. Jude Children’s Research Hospital, Memphis, Tennessee; and Jeffrey Ecsedy, Ph.D., Takeda Pharmaceuticals, Osaka, Japan. The Tennessee Valley Healthcare System, Department of Veterans Affairs, also participated in the study.

The study was supported by funding from the Department of Veterans Affairs (5101BX000196-04), the National Institutes of Health (CA116021, CA116021-S1, CA90625, 5T32CA119925-03, 1F32CA171895-01, GM084333 and CA68485), and a Senior Research Career Scientist Award to Richmond.