Development of effective immunotherapy for triple negative breast cancer by WEE1 kinase inhibition

Abstract Treatment options for triple negative breast cancer (TNBC) are limited because they are usually insensitive to most available hormonal or targeted therapeutic agents owing to their triple negative nature. Exciting clinical results using immune checkpoint inhibitors (ICI) directed against PD-1/PD-L1 have been reported. However, only a subset of patients (~20%) respond to ICI. Therefore, identifying rational combinations is needed to enhance the efficacy of immunotherapy in TNBC. We demonstrated there that inhibition of WEE1, a G2/M cell cycle checkpoint regulator induced by DNA damage, increased expression levels of MHC-I, and pro-inflammatory chemokines (CXCL9 and CXCL10) together with PD-L1 in human and mouse TNBC cells. Consequently, WEE1 inhibition enhanced cytotoxic T-lymphocyte (CTL)-mediated killing of tumor cells, and CTL infiltration into the tumor, making tumors susceptible to anti-PD-1 mAb immune checkpoint blockade in mouse TNBC models in a CD8+ T cell–dependent manner. Mechanistically, WEE1 inhibition triggered the cellular damage stress and interferon response through the double-stranded DNA/RNA (dsDNA/RNA) by activating the TLR9/IRF7 pathway. Furthermore, combining WEE1 inhibition and TLR9 agonist CpG DNA resulted in tumor regression, facilitating an effective antitumor T cell response. Our findings have rapid translational implications for the exploration of WEE1 inhibitors alongside agents that stimulate CD8+ T cell activity, including ICI and TLR9 agonists, which are both clinically available to treat TNBC patients. We acknowledge the funding support from NCI R01CA222963 and DoD W81XWH-19-1-0106.