A novel therapeutic to enhance the immunogenicity of breast cancer cells.

119 Background: Breast cancer is a challenge for immunotherapy because of its inherent genetic heterogeneity and decreased immunogenicity. A possible solution is to generate dying breast cancer cells that operate like a vaccine to stimulate tumor-specific immunity. This is termed immunogenic cell death (ICD) and is characterized by a unique molecular signature, involving the release of molecules that attract and stimulate phagocytes and sensitize tumor cells to killing by natural killer (NK) cells. However, the current doses of drugs used to induce ICD may be too high to translate into clinically relevant regimens. Methods: Our group discovered a novel peptide, CT20p, that is effective at nanomolar concentrations and can be delivered to breast tumors using targeted nanoparticles. CT20p works by inhibiting a unique protein folding complex, called chaperonin-containing TCP-1 (CCT), which is highly expressed in cancer cells but not normal cells. Using triple negative breast cancer (TNBC) and normal cell lines as well as patient-derived tumor cells, we examined the biological consequences of CCT inhibition by CT20p in terms of the induction of endoplasmic reticulum (ER) stress, through the accumulation of unfolded proteins, and the release of the danger signals associate with ICD that could stimulate innate immunity. Results: Dying TNBC cells treated with CT20p displayed alterations in PERK, a mediator of the unfolded protein response (UPR), which resulted in the membrane translocation of calreticulin (Crt), an “eat me”’ signal and a key marker of ICD. CT20p-killed TNBC cells were more readily phagocytosed, and NK cells more effectively killed remaining cancer cells. In our experiments normal breast epithelial cells, macrophages or NK cells were unaffected by CT20p. Conclusions: Our study suggests that inhibition of CCT by CT20p generates dying cancer cells that stimulate innate immune responses, through the release of signals like Crt, to attract phagocytes and promote NK cell cytotoxicity. By enhancing the immunogenicity of breast cancer cells, CT20p could increase responsiveness to to checkpoint inhibitors or cellular immunotherapy, hence providing more complete protection from breast cancer recurrence and metastasis.