Targeting FZD6 creates therapeutically actionable vulnerabilities for advanced prostate cancer

Wnt signaling is a complex pathway consisting of numerous ligands and frizzled (FZD) receptors. These signaling components are widely expressed in human prostate tissues and often undergo upregulation or mutation in advanced prostate cancers. Enhanced Wnt signaling promotes prostate cancer cell proliferation, metastasis, and resistance to therapy. However, targeting pan-Wnt signaling poses challenges due to tissue toxicity. We show that FZD6 is the most highly expressed and frequently amplified Wnt receptor in advanced human prostate cancers. Knockdown of FZD6 suppresses both in vitro and in vivo growth of various prostate cancer cell lines and patient-derived xenograft models. FZD6 knockdown impairs DNA double-strand break (DSB) repair, as determined by both resolution of γH2AX foci and DNA DSB repair reporter assays. Mechanistically, FZD6 knockdown-induced growth suppression is linked to reduced activities of SRC kinase and STAT3, while DNA damage repair deficiency is mediated through WEE1 downregulation via PLK1. Knockdown of FZD6 enhances the therapeutic efficacy of genotoxic agents for prostate cancer cells. A kinome-wide CRISPR-Cas9 knockout screen reveals that FZD6 inhibition sensitizes prostate cancer cells to the inhibition of PKMYT1, a WEE kinase family member. Collectively, we demonstrate that targeting a single FZD receptor highly expressed in prostate cancers can yield significant therapeutic efficacy, and uncover therapeutic vulnerabilities associated with FZD6 inhibition.