In vitro model for resistance in oncogene-dependent tumors at the limit of radiological detectability

In solid tumors, the response to targeted therapy is typically short-lived, as therapy-resistant mutants can quickly expand during therapy. Here we analyze the spectrum of such resistance mutations coexisting in a large population of cancer cells. We use an iterative scheme of artificial evolution to amplify and isolate different resistance mechanisms. As a proof of concept, we apply our scheme to PC-9 cells, a human non-small cell lung cancer cell line with an activating EGFR mutation. The mechanisms we find comprise the well-known gatekeeper-mutation T790M in EGFR, a mutation in NRAS, the amplification of MET-ligand HGF, as well as induction of AKT-mTOR signaling. In this model, a combination of four drugs targeting these mechanisms prevents not only the expansion of resistant cells, but also inhibits the growth of drug-tolerant cells, which can otherwise act as a reservoir for further resistance mutations. These data suggest that a finite number of drugs specifically acting on individual resistant clones may be able to control resistance in oncogenically driven lung cancer.