An in vivo screening platform using PDX models reveals KEAP1, USP22 and other drivers of chemoresistance in small cell lung cancer

Small cell lung cancer (SCLC) is characterized by exquisite chemosensitivity followed by rapid emergence of chemoresistance. To identify genetic events that drive resistance to cisplatin-etoposide chemotherapy, we conducted cDNA overexpression and CRISPR knockout screens in an in vivo platform centered on chemosensitive patient derived xenograft (PDX) models of SCLC. cDNA overexpression screens revealed MYC, MYCN and MYCL as drivers of tumor cell growth through chemotherapy. CRISPR knockout screens identified the KEAP1/NRF2 pathway and members of the SAGA (Spt-Ada-Gcn5 acetyltransferase) complex, including the deubiquitylase USP22. We demonstrated that knockout of either KEAP1 or USP22 switches chemosensitive PDX models to become chemoresistant, with our data supporting distinct molecular consequences of each, including suppression of DNA damage signaling upon USP22 deletion. Data from the IMpower133 clinical trial revealed that a substantial proportion of SCLC patients exhibit KEAP1/NFE2L2 genetic alterations, with activation of an NRF2 transcriptional signature associated with reduced SCLC patient survival with chemotherapy.