Singe-cell approaches for a priori identification of drug-resistant cancer cells
Spontaneous genetic mutations allow an initially drug-sensitive population of cancer cells to acquire a drug-resistant phenotype. However, little is known about how drug-sensitive cells first evade drug action and survive in the presence of drug, a phenomenon referred to as “drug tolerance” that represents a crucial step on the road to resistance. Here we use single-cell time-lapse microscopy to study the early signaling response of BRAFV600E melanoma cells to clinical BRAF inhibitors. By multiplexing live-cell sensors for MAPK signaling, PI3K/AKT signaling, and cell-cycle progression, we show that there is a small population of melanoma cells that are initially drug-sensitive and enter quiescence in response to drug, but then acquire drug tolerance and resume proliferation within a few days of drug treatment. ERK activity is immediately reduced after BRAF inhibitor treatment in all cells, but re-activates in the sub-population of drug-tolerant cells prior to cell-cycle re-entry. We also find that while AKT signaling is moderately active in untreated BRAFV600E melanoma cells, AKT activity increases gradually in all cells upon treatment with BRAF inhibitors. Combination therapy, using a BRAF inhibitor and an ERK or AKT pathway inhibitor, results in fewer drug-tolerant cells and more cell killing. Our results suggest that acquisition of drug tolerance can occur within 2-3 days, long before the genetic mutations that cause bona fide drug resistance arise. Knowledge of how cells quickly rewire signaling networks in response to targeted therapies may lead to the development of combination of cancer therapies that can reduce the emergence of drug resistance in cancer.
Arnold O. Beckman exemplifies the meaning of the word humanitarian. Combined with his unwavering enthusiasm for life, his keen sense of humor and his strong moral and ethical principles, he is a national icon.