CDC7 inhibition impairs neuroendocrine transformation in lung and prostate tumors through MYC degradation

Neuroendocrine (NE) transformation is a mechanism of resistance to targeted therapy in lung and prostate adenocarcinomas leading to poor prognosis. Upregulation of the cell cycle kinase CDC7 occurred in tumors undergoing NE transformation, after TP53/RB1 co-inactivation, leading to induced sensitivity to the CDC7 inhibitor simurosertib. CDC7 inhibition suppressed NE transdifferentiation and extended response to targeted therapy in in vivo models of NE transformation by inducing the proteasome-mediated degradation of MYC, implicated in stemness and histological transformation. Ectopic overexpression of a degradation-resistant MYC isoform reestablished the NE transformation phenotype observed on targeted therapy, even in the presence of simurosertib. CDC7 inhibition also markedly extended response to standard cytotoxics in lung and prostate small cell carcinoma models. These results nominate CDC7 inhibition as a strategy to constrain lineage plasticity and to effectively treat NE tumors. As simurosertib clinical efficacy trials are ongoing, this concept could be readily translated for patients at risk. Overall design: 4-10 male 6-week-old NOD.Cg-Prkdc Il2rg/SzJ (NSG) mice were subcutaneously engrafted per treatment arm and until tumors reached 100-150 mm3. At that point, mice were randomized into groups and treated with either vehicle, simurosertib (40 mg/kg p.o. QDx3), enzalutamide (10 mg/kg p.o. QDx5), osimertinib (25 mg/kg p.o. QDx5) or their combination. Mice weights and tumor volumes were measured twice a week and mice were sacrificed when tumors reached humane endpoint (volume = 1000 mm3). The number of mice per treatment arm were selected according to previous experience with the models and response to treatments. Blinding was not performed. All animal experiments were approved by the Memorial Sloan Kettering Cancer Center (MSKCC) Animal Care and Use Committee (#13-07-007).