Search

The mitotic regulator Wee1 is a critical regulator of G2/M cell cycle checkpoint and DNA damage response pathways. Wee1-targeted agents are under active clinical investigation in multiple cancer types. However, Wee1 and its inhibitors have not been well studied in prostate cancer, particularly neuroendocrine prostate cancer (NEPC). In this study, we investigated the therapeutic potential of Wee1 inhibitor AZD1775 and its synthetic lethal combination with Chk1 inhibitor in the context of NEPC. Our data demonstrated increased Wee1 expression in NEPC cells and tumors. Treatment of NEPC cells with AZD1775 inhibited NEPC tumor cell survival with greater potency as compared to other prostate cancer cells, demonstrating increased vulnerability of NEPC cells to Wee1 inhibition. We further identified synthetic lethality between the inhibition of Wee1 and several protein kinases, particularly Chk1, another key G2/M checkpoint kinase. Using an autochthonous adenocarcinoma mouse prostate (TRAMP) model that gives rise to NEPC tumors, we assessed the efficacy of AZD1775 and a highly selective Chk1 inhibitor SRA737 as single agents and in combination on the progression, survival, and metastatic spread of NEPC tumors in vivo. AZD1775 and SRA737 when used as single agents significantly suppressed tumor growth, improved overall survival, and incidence of distant metastases of mice with NEPC tumors. The combination of AZD1775 and SRA737 on a sequential 2-wk treatment schedule was more efficacious in suppressing tumor growth and metastasis than each drug alone in castrated TRAMP NEPC tumors. Mechanistically, the combination of Chk1 and Wee1 inhibitors synergized to reduce the inhibitory phosphorylation of CDK1 at Y15 and Cdc25c at S216, resulting in enhanced activation of CDK1/cyclin B complex, abrogation of G2/M checkpoint, and consequent premature mitotic entry, which ultimately led to mitotic catastrophe and apoptosis. Our findings provide promising preclinical evidence supporting the therapeutic values of Wee1 and Chk1 inhibitors as single agents and in combination for the treatment of NEPC. Citation Format: Yapeng Chao, Yuzhou Chen, Yu Liu, Jaclyn A. Connelly, Hong Wang, Qiming Jane Wang. Wee1 inhibition and its synthetic lethal combination with Chk1 inhibition in mouse model of neuroendocrine prostate cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5015.

The catalytic domain of overexpressed protein kinase C (PKC)-δ mediates phorbol 12-myristate 13-acetate (PMA)-induced differentiation or apoptosis in appropriate model cell lines. To define the portions of the catalytic domain that are critical for these isozyme-specific functions, we constructed reciprocal chimeras, PKC-δ/εV5 and -ε/δV5, by swapping the V5 domains of PKC-δ and -ε. PKC-δ/εV5 failed to mediate PMA-induced differentiation of 32D cells, showing the essential nature of the V5 domain for PKC-δ's functionality. The other chimera, PKC-ε/δV5, endowed inactive PKC-ε with nearly all PKC-δ's apoptotic ability, confirming the importance of PKC-δ in this function. Green fluorescent protein (GFP)-tagged PKC-δV5 and -ε/δV5 in A7r5 cells showed substantial basal nuclear localization, while GFP-tagged PKC-ε and -δ/εV5 showed significantly less, indicating that the V5 region of PKC-δ contains determinants critical to its nuclear distribution. PKC-ε/δV5-GFP showed much slower kinetics of translocation to membranes in response to PMA than parental PKC-ε, implicating the PKC-εV5 domain in membrane targeting. Thus, the V5 domain is critical in several of the isozyme-specific functions of PKC-δ and -ε.

Phorbol esters, analogs of diacylglycerol, induce apoptosis in androgen-sensitive LNCaP prostate cancer cells. Although the apoptotic pathways induced by PMA are well characterized, little is known of PMA-regulated pro-survival pathways such as ERK1/2 and Akt. We now provide experimental evidence to indicate that PKD1 promotes survival signals in LNCaP cells in response to PMA treatment. In turn, PMA induces dose- and time-dependent downregulation of PKD1 to facilitate apoptosis. This effect can be blocked by PKC inhibitor Ro 31-8220, indicating that PKC activation is required for PKD1 downregulation. Depletion of endogenous PKCδ and PKCε reveals that PKD1 activation and subsequent downregulation are mainly controlled by PKCδ. Knockdown of endogenous PKD1 and PKD2 decreases ERK1/2 and Akt activities and potentiates PMA-induced apoptosis as measured by cleaved PARP and sub-G0/G1 population, whereas overexpression of wild-type and constitutive-active PKD1 enhances ERK1/2 and Akt activities and suppresses PMA-induced apoptosis. Further analysis shows that the downregulation of PKD1 is mediated by ubiquitin/proteasome degradation pathway. In summary, our data indicate that PKD1 plays a pro-survival role in PMA-induced apoptosis by modulating downstream ERK1/2 and Akt activities. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3127.