Melanoma is the deadliest form of skin cancer and represents a paradigm for chemo-resistance.
We aim to understand resistance mechanisms in melanoma in order to provide the basis for improved targeted therapeutic strategies. The serine/threonine kinase, B-RAF, is somatically mutated in 40-60% of melanomas. Mutant B- RAF hyper-activates MEK-ERK1/2 signaling and is required for melanoma growth and invasion. A phase I clinical trial with the RAF inhibitor, PLX4032 (RG7204/Vemurafenib) yielded promising results in mutant B-RAF melanoma patients. However, 19% of patients were intrinsically resistant to B-RAF inhibitors and most initial responders are now relapsing from acquired drug resistance. An inability to eradicate tumors is also evident using in vivo models in which RAF/MEK inhibitors potently inhibit mutant B-RAF-driven melanoma growth but treatment cessation results in rapid tumor re-growth. The mechanisms underlying resistance to B-RAF inhibitors are unknown and must be elucidated to optimize future clinical trials. Our studies will focus on the stemness factor, FOXD3, which is up-regulated following B-RAF inhibition in mutant B-RAF melanoma cells.
In Aim 1 of this application, we will determine the role of FOXD3 in melanoma growth and resistance to B-RAF inhibitors in vivo.
In Aim 2, we will identify mechanisms regulating FOXD3 in mutant B-RAF melanomas.
In Aim 3, we will determine the role of ERBB3, a direct target of FOXD3, in eliciting the effects of RAF inhibitors. Our experimental approaches are innovative in that we modulate B-RAF activity using clinical grade inhibitors and molecular biology approaches in physiologically relevant in vitro and in vivo models. At the completion of our experiments, we expect to have identified a novel resistance-promoting mechanism and provided evidence for utilizing FOXD3 and/or ERBB3 as a biomarker for B-RAF inhibitor resistant melanoma cells.

Public Health Relevance

Melanoma is the deadliest form of skin cancer and current treatment options are poor. Our application focuses on recent advances in therapeutics designed to target a signaling protein, B-RAF that is expressed in a mutant form in approximately 40-60% of melanomas. An inhibitor of RAF elicits short term clinical benefit in the majority of melanoma patients;however, mechanisms of intrinsic (primary) resistance and acquired (secondary) resistance are apparent. We expect that our results will lead to an understanding of resistance mechanisms in this highly aggressive cancer.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
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Tumor Cell Biology Study Section (TCB)
Program Officer
Lin, Alison J
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Thomas Jefferson University
Schools of Medicine
United States
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Sanchez, Ileine M; Aplin, Andrew E (2014) Hippo: hungry, hungry for melanoma invasion. J Invest Dermatol 134:14-6
Basile, Kevin J; Le, Kaitlyn; Hartsough, Edward J et al. (2014) Inhibition of mutant BRAF splice variant signaling by next-generation, selective RAF inhibitors. Pigment Cell Melanoma Res 27:479-84
Kugel 3rd, Curtis H; Aplin, Andrew E (2014) Adaptive resistance to RAF inhibitors in melanoma. Pigment Cell Melanoma Res 27:1032-8
Kugel 3rd, Curtis H; Hartsough, Edward J; Davies, Michael A et al. (2014) Function-blocking ERBB3 antibody inhibits the adaptive response to RAF inhibitor. Cancer Res 74:4122-32
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