Oncogenic KIT Induces Replication Stress and Confers Cell Cycle Checkpoint Vulnerability in Melanoma.

Acral and mucosal melanomas arise from sun-protected sites, disproportionately impact darker-skinned individuals, and exact higher mortality than common types of cutaneous melanoma. Genetically, acral and mucosal melanomas harbor more alterations of KIT than typical cutaneous melanomas. Because KIT-mutated melanomas remain largely treatment resistant, we set out to create a faithful murine KIT-driven allograft model to define newer therapeutic strategies. Using the prevalent human KITK642E activating mutation, the murine mKITK641E cellular avatars show features of transformation in vitro and tumorigenicity in immunocompetent C57BL/6J mice. mKITK641E cells proliferate more rapidly, exhibit greater chromosomal aberrations, and sustain three-dimensional spheroid expansion and aggressive tumor growth in C57BL/6J mice compared with their vector-controlled cells. We further verified the functional dependence of these cells on KITK641E with both genetic and pharmacologic suppression. Using these cells, we performed a screen of 199 kinase inhibitors and identified a selective vulnerability to Chk1/ATR inhibition in the KITK641E-activated cells. Mechanistically, we subsequently showed that KITK641E induces a significantly increased level of replication stress compared with murine vector‒controlled cells. These results showcase an allograft model of human KIT-driven melanomas, which uncovered an unappreciated role for replication stress in KIT melanomagenesis and implicated a possible therapeutic strategy with Chk1/ATR inhibitors.