Abstract P3-06-14: Inhibition of PRKCQ enhances chemosensitivity of triple negative breast cancer by regulating EMT and Bim

Background/Rationale: While some patients with triple negative breast cancer (TNBC) achieve long-term remission with standard-of-care chemotherapy, many have cancers that are chemotherapy resistant, putting them at risk for metastatic recurrence. There is also a lack of targeted therapies for TNBC, highlighting the need for novel therapeutic strategies for this subtype. PRKCQ, a member of the novel protein kinase C family, is preferentially expressed in TNBC compared to other breast cancer subtypes and we previously reported that PRKCQ expression is sufficient to promote oncogenic activities (growth-factor independent growth, anoikis resistance and migration). In addition, PRKCQ suppression inhibits growth of TNBC tumor xenografts. We sought to determine if PRKCQ expression modulation impacts sensitivity of triple negative breast cancer cells to standard of care chemotherapy and whether PRKCQ inhibition could be a strategy to enhance chemosensitivity of drug-resistant TNBC. Methods: We determined the effects of modulating PRKCQ expression, using PRKCQ cDNA or shRNA vectors, on sensitivity of TNBC cells to the apoptotic effects of standard-of-care chemotherapy, including those cancers that are relatively chemotherapy resistant at baseline. We also determined the mechanisms by which PRKCQ regulates sensitivity to chemotherapy. Results: Increased PRKCQ expression in non-transformed MCF-10A breast epithelial cells promotes resistance to the apoptosis-inducing effects of Doxorubicin or Paclitaxel treatment. These effects are dependent on PRKCQ kinase activity as a catalytically inactive PRKCQ failed to promote resistance. Downregulation of PRKCQ or inhibition of its kinase activity enhanced sensitivity of TNBC cells to chemotherapy. PRKCQ impacts chemotherapy sensitivity of TNBC by regulating epithelial-mesenchymal transition (EMT) and expression of Bim, a pro-apoptotic Bcl2 family protein. Conclusions. PRKCQ promotes resistance of TNBC to standard of care chemotherapies by promoting EMT and suppressing pro-apoptotic Bim. Inhibiting PRKCQ expression or activity sensitizes TNBC cells to chemotherapy and could be an effective strategy to overcome chemotherapy resistance of a subset of triple negative breast cancers, thereby improving patient outcomes. Citation Format: Hanna Yoko Irie, Jessica H. Byerly, Elisa R. Port. Inhibition of PRKCQ enhances chemosensitivity of triple negative breast cancer by regulating EMT and Bim [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-06-14.