Mechanisms of rapid cancer cell reprogramming initiated by targeted receptor tyrosine kinase inhibitors and inherent therapeutic vulnerabilities

Emily K. Kleczko, Lynn E. Heasley

Receptor tyrosine kinase (RTK) pathways serve as frequent oncogene drivers in solid cancers and small molecule and antibody-based inhibitors have been developed as targeted therapeutics for many of these oncogenic RTKs. In general, these drugs, when delivered as single agents in a manner consistent with the principles of precision medicine, induce tumor shrinkage but rarely complete tumor elimination. Moreover, acquired resistance of treated tumors is nearly invariant such that monotherapy strategies with targeted RTK drugs fail to provide long-term control or cures. The mechanisms mediating acquired resistance in tumors at progression treated with RTK inhibitors are relatively well defined compared to the molecular and cellular understanding of the cancer cells that persist early on therapy. We and others propose that these persisting cancer cells, termed "residual disease", provide the reservoir from which acquired resistance eventually emerges. Herein, we will review the literature that describes rapid reprogramming induced upon inhibition of oncogenic RTKs in cancer cells as a mechanism by which cancer cells persist to yield residual disease and consider strategies for disrupting these intrinsic responses for future therapeutic gain.