The role of phosphatidylinositol 4-phosphate 5-kinase type І alpha (PIP5K1α) and utility of its inhibitor for targeting metastatic cancer

Prostate cancer (PCa) is the most common cause of cancer-related death in men after lung cancer. Annually, more than 9000 new cases are diagnosed in Sweden and 2500 of them die each year. Metastatic prostate cancer can be treated with castration. However, the disease eventually recurs within 2 years in more aggressive form and becomes insensitive to castration which is termed as castration resistant prostate cancer (CRPC). Currently, effective treatment for CRPC is lacking. Numerous studies have shown that even under castrated level of androgen, the androgen receptor (AR) signaling pathway is constitutively active, which promotes the growth of CRPC cells.
Alterations such as AR gene amplification, AR mutation and expression of truncated variants of AR (ARVs) is commonly observed in CRPC patients and through these alterations, CRPC cells become hypersensitive to extremely low level of androgen or become independent of androgens. Furthermore, hyperactivation of the phosphoinositide 3-kinase (PI3K)/AKT pathway is frequently observed in metastatic CRPC patients. The PI3K/Akt pathway can enable the cells to survive in the absence of androgen. In the studies presented in my thesis, I have revealed the importance of a kinase called the phosphatidylinositol 4-phosphate 5-kinase type І alpha (PIP5K1α) in
cancer progression and therapeutic resistance. The PIP5K1α kinase acts as the upstream activator of the PI3K/AKT pathway by producing the substrate phosphatidylinositol-4,5-bisphosphate (PIP2) necessary for the activation of the
PI3K/AKT signaling pathway. We, for the first time have shown that high level of PIP5K1α and its product PIP2 is a common event in cancer patients and is negatively associated with survival of prostate cancer and breast cancer patients. Furthermore, higher expression of PIP5K1α is associated with the expression of AR variant-7 (AR-V7) which is responsible for enzalutamide resistance in CRPC. We have discovered an inhibitor of PIP5K1α, ISA-2011B through high-throughput kinase screening method. By performing the in-vitro and in-vivo experiments we have shown that AKT activation can be inhibited by ISA-2011B treatment and by siRNA-mediated knockdown of PIP5K1α. ISA-2011B was effective in reducing tumor size in xenograft mouse models and it has reduced the AR-V7 expression thereby circumventing enzalutamide resistance. Moreover, ISA-2011B inhibited proliferation and induced apoptosis
in both luminal A and triple negative (TNBC) breast cancer cell lines. In addition, ISA-2011B showed no cytotoxic effect in normal like MCF-10A breast cancer cell line. Our xenograft study further showed the anticancer effect of ISA-2011B on MDA-MB-231 TNBC tumor. Standard chemotherapeutic agent docetaxel showed almost identical
result compared to ISA-2011B in supressing tumor growth. Moreover, we also studied the interconnection between PIP5K1α and immunomodulatory proteins in prostate cancer cells which may play an important role in controlling inflammatory processes.

Our data strongly suggests that PIP5K1α can be developed as a novel drug target in metastatic cancer and ISA-2011B is an important drug candidate for blocking the PI3K / AKT signaling in a subset of patients.