Measuring melanoma’s adaptation rate in various drug environments to delay resistance
BRAF and MEK inhibitors have increased survival rates for melanoma patients carrying the BRAFV600E mutation, yet resistance to these inhibitors represents a current challenge to genomics-guided drug treatments. Studies show that acquired mutations can drive resistance to these targeted agents, however little is known about the rate at which resistance to these targeted therapies develop. A need remains for modeling the impact of targeted therapies, drug combinations, and dosing strategies on the rate of tumor adaptation in order to guide development of new treatments that can circumvent resistance. The goal of this project is to test how different treatments affect the fitness of a tumor population over time and promote or delay the emergence of resistance. We developed a novel assay that quantifies the in vitro rate of adaptation by analyzing the progressive changes in sensitivity of the melanoma cell line A375 under constant treatment with two MEK inhibitors, E6201 and trametinib. Cells derived from a shared parental population are split into subpopulations that are treated continuously with drug or vehicle, and divergence from the parental drug sensitivity is analyzed through serial drug-dose-response analyses. Two hypotheses were tested in this experiment: 1) Drug concentration and adaptation rate are positively correlated; and 2) A resistant population will emerge faster in cells treated with cytotoxic E6201 than in cells treated with cytostatic trametinib. Cells were grown for nine days in the presence of vehicle, trametinib IC10, IC30, and IC50, and E6201 IC30. Serial passaging and growth rate analysis continues until growth rates plateau. Current data shows divergence from parental sensitivity after only 27 days of treatment. We were able to successfully quantify this rate of divergence. We now anticipate that with future developments, our assay will contribute to identifying treatment options that delay resistance.