PI3Kδ as a Novel Therapeutic Target for Aggressive Prostate Cancer

Abstract

Phosphoinositide 3-kinases (PI3Ks) signaling represents an important pathway regulating cell proliferation, survival, invasion, migration, and metabolism. Notably, PI3K/AKT/mTOR signaling is frequently dysregulated in the majority of malignancies. Among the class IA PI3Ks (PI3Kα/β/δ), emerging evidence has implicated that PI3Kδ is not only overexpressed in leukocytes but also in solid tumors, including prostate cancer. The critical role of PI3Kδ in tumorigenesis and in the creation of a suppressive tumor microenvironment, along with the recent finding of PI3Kδ splice isoforms in promoting tumor aggressiveness and resistance, further demonstrates the potential of developing novel PI3Kδ-targeted cancer therapies. In this review, we comprehensively describe the functional mechanisms underlying the PI3Kδ-driven tumor progression and immune regulation in prostate cancer diseases. Furthermore, the recent preclinical and clinical studies on the development of PI3Kδ-/PI3K-targeted inhibitors as single agents and in combination therapies (with chemotherapy, radiation, hormone therapy, or immunotherapy) are summarized. Finally, we discuss the potential novel therapies for improving the treatment efficacies, as well as the current limitations and challenges of PI3Kδ-based therapies for prostate cancer.

Keywords: PI3K/AKT/mTOR signaling; PI3Kδ and pan-PI3K inhibitors; androgen receptor inhibitors; combination therapies; immune checkpoint blockers; phosphoinositide 3-kinases delta (PI3Kδ); splice isoforms; tumor immune microenvironment.

Figure 1

PI3Kδ-mediated signaling cascade in prostate cancer. Overexpression of PI3Kδ stimulates the hyperactivation of AKT/mTOR signaling, cross-interacts with AR signaling, enhances PD-L1 expression, and increases and activates Tregs and MDSCs. Consequently, the PI3Kδ overexpression leads to promotion of cell proliferation, growth, survival, metastasis, angiogenesis, anti-apoptosis, and drug resistance and further creates a suppressive immune microenvironment in prostate cancer. RTK: receptor tyrosine kinase; AR: androgen receptor; P: phosphorylated; Treg: regulatory T cell; MDSC: myeloid-derived suppressor cell; CD8+ T: CD8-positive T lymphocyte.