Therapeutic Resistance to BRAF/MEK inhibitors in BRAF-mutant Melanoma

Melanoma is the most serious type of skin cancer. It is estimated that approximately 7,650 people in the United States will die from melanoma in 2022. BRAF mutations induce abnormal cell proliferation and cause over 50% of metastatic melanoma cases. Since cancer cells exhibit dependency on mutations in cancer-causing genes, targeting BRAF mutations is an ideal therapeutic strategy to effectively suppress cancer cell proliferation. Indeed, targeting BRAF and MEK, a downstream effector of BRAF, has shown promising clinical outcomes, becoming the standard treatment for patients with metastatic BRAF-mutant melanoma. However, about half of patients develop resistance to BRAF/MEK inhibitors after 11 months of treatment. This has increased the urgency for developing more effective therapeutic strategies to overcome resistance to these drugs. Elucidating the molecular mechanisms behind drug resistance is critical to rationally design therapeutic strategies to overcome resistance. While secondary genetic mutations causing drug resistance have been well documented, emerging evidence suggests that small subsets of melanoma cells rapidly adapt to drugs without acquiring any new mutations. This results in the growth of residual cancer cells that eventually drive the emergence of resistance mutations responsible for disease recurrence in the patient. Thus, the suppression of rapid drug adaptation is crucial for inhibiting the eventual acquisition of resistance mutations. However, the mechanism driving rapid adaptation to BRAF/MEK inhibitors and the growth of residual cancer cells remains unclear. Using bulk analysis of tumor tissue, it is challenging to study the mechanisms underlying drug resistance during the early stage of drug treatment given the heterogeneity of the tumors, the rarity of residual cancer cells, and the plasticity of individual cancer cells. Therefore, novel approaches that allow the tracking of single cells and monitoring of cellular events are needed. We recently developed a multiplexed-sensor system that enables the systematic assessment of the BRAF/MEK pathway and cell proliferation in individual melanoma cells. By combining live-cell fluorescent biosensor imaging, synthetic tools to manipulate protein activity, and systematic single-cell quantitative analyses, we propose to study the molecular mechanism underlying resistance to BRAF and MEK inhibitors. Furthermore, our interdisciplinary team of basic and translational investigators will evaluate our therapeutic strategy in melanoma models. Results from this proposal will not only provide new insights into drug resistance but also new therapeutic opportunities to overcome drug resistance.