PROTACs as Therapeutic Modalities for Drug Discovery in Castration-Resistant Prostate Cancer.

Castration-resistant prostate cancer (CRPC) presents significant challenges in clinical management due to its resistance to conventional androgen receptor (AR)-targeting therapies. The advent of proteolysis targeting chimeras (PROTACs) has revolutionized cancer therapy by enabling the targeted degradation of key molecular players implicated in CRPC progression. In this review we discuss the developments of PROTACs for CRPC treatment, focusing on AR and other CRPC-associated regulators. We provide an overview of the strategic trends in AR PROTAC development from the aspect of targeting site selection and preclinical antitumor evaluation, as well as updates on AR degraders in clinical applications. Additionally, we briefly address the current status of selective AR degrader development. Furthermore, we review new developments in PROTACs as potential CRPC treatment paradigms, highlighting those targeting chromatin modulators BRD4, EZH2, and SWI/SNF; transcription regulator SMAD3; and kinases CDK9 and PIM1. Given the molecular targets shared between CRPC and neuroendocrine prostate cancer (NEPC), we also discuss the potential of PROTACs in addressing NEPC.

L1CAM mediates neuroendocrine phenotype acquisition in prostate cancer cells.

BACKGROUND: A specific type of prostate cancer (PC) that exhibits neuroendocrine (NE) differentiation is known as NEPC. NEPC has little to no response to androgen deprivation therapy and is associated with the development of metastatic castration-resistant PC (CRPC), which has an extremely poor prognosis. Our understanding of genetic drivers and activated pathways in NEPC is limited, which hinders precision medicine approaches. L1 cell adhesion molecule (L1CAM) is known to play an oncogenic role in metastatic cancers, including CRPC. However, the impact of L1CAM on NEPC progression remains elusive. METHODS: L1CAM expression level was investigated using public gene expression databases of PC cohorts and patient-derived xenograft models. L1CAM knockdown was performed in different PC cells to study in vitro cell functions. A subline of CRPC cell line CWR22Rv1 was established after long-term exposure to abiraterone to induce NE differentiation. The androgen receptor-negative cell line PC3 was cultured under the tumor sphere-forming condition to enrich cancer stemness features. Several oxidative stress inducers were tested on PC cells to observe L1CAM-mediated gene expression and cell death. RESULTS: L1CAM expression was remarkably high in NEPC compared to CRPC or adenocarcinoma tumors. L1CAM was also correlated with NE marker expressions and associated with the adenocarcinoma-to-NEPC progression in gene expression databases and CRPC cells with NE differentiation. L1CAM also promoted cancer stemness and NE phenotypes in PC3 cells under cancer stemness enrichment. L1CAM was also identified as a reactive oxygen species-induced gene, by which L1CAM counteracted CRPC cell death triggered by ionizing radiation. CONCLUSIONS: Our results unveiled a new role of L1CAM in the acquisition of the NE phenotype in PC, contributing to the NE differentiation-related therapeutic resistance of CRPC.

Hypoxia-induced long non-coding RNA HIF1A­AS2 regulates stability of MHC class I protein in head and neck cancer.

Intratumoral hypoxia not only promotes angiogenesis and invasiveness of cancer cells, but also creates an immunosuppressive microenvironment that facilitates tumor progression. However, the mechanisms by which hypoxic tumor cells disseminate immunosuppressive signals remain unclear. In this study, we demonstrate that a hypoxia-induced long non-coding RNA (lncRNA) HIF1A Antisense RNA 2 (HIF1A-AS2) is upregulated in both hypoxic tumor cells and hypoxic tumor-derived exosomes (TEXs) in head and neck squamous cell carcinoma (HNSCC). Hypoxia-inducible factor 1 alpha 1 (HIF-1α) was found to directly bind to the regulatory region of HIF1A-AS2 to enhance its expression. HIF1A-AS2 reduced the protein stability of major histocompatibility complex class I (MHC-I) by promoting the interaction between the autophagy cargo receptor Neighbor of BRCA1 gene 1 protein (NBR1) and MHC-I, thereby increasing the autophagic degradation of MHC-I. In HNSCC samples, the expression of HIF1A-AS2 was found to correlate with hypoxic signatures and advanced clinical stages. Patients with high HIF-1α and low HLA-ABC expression showed reduced infiltration of CD8+ T cells. These findings define a mechanism of hypoxia-mediated immune evasion in HNSCC through downregulation of antigen-presenting machinery via intracellular or externalized hypoxia-induced lncRNA.

The miRNAs 203a/210-3p/5001-5p regulate the androgen/androgen receptor/YAP-induced migration in prostate cancer cells.

BACKGROUND: Prostate cancer (PCa) patients with elevated level of androgen receptor (AR) correlate with higher metastatic incidence. Protein expression of AR and its target gene prostate-specific antigen (PSA) are elevated in metastatic prostate tumors as compared to organ-confined tumors. Androgen treatment or elevation of AR promotes metastasis of PCa in cell culture and murine model. However, under androgen depleted condition, AR suppressed cell mobility and invasiveness of PCa cells. Androgen deprivation therapy in PCa patients is associated with higher risk of cancer metastasis. We therefore investigated the dual roles of AR and miRNAs on PCa metastasis. METHODS: The PC-3AR (PC-3 cells re-expressing AR) and LNCaP cells were used as PCa cell model. Transwell migration and invasion assay, wound-healing assay, zebrafish xenotransplantation assay, and zebrafish vascular exit assay were used to investigate the role of AR and androgen on PCa metastasis. Micro-Western Array, co-immunoprecipitation and Immunofluorescence were applied to dissect the molecular mechanism lying underneath. The miRNA array, miRNA inhibitors or plasmid, and chromatin immunoprecipitation assay were used to study the role of miRNAs on PCa metastasis. RESULTS: In the absence of androgen, AR repressed the migration and invasion of PCa cells. When androgen was present, AR stimulated the migration and invasion of PCa cells both in vitro and in zebrafish xenotransplantation model. Androgen increased phospho-AR Ser81 and yes-associated protein 1 (YAP), decreased phospho-YAP Ser217, and altered epithelial-mesenchymal transition (EMT) proteins in PCa cells. Co-IP assay demonstrated that androgen augmented the interaction between YAP and AR in nucleus. Knockdown of YAP or treatment with YAP inhibitor abolished the androgen-induced migration and invasion of PCa cells, while overexpression of YAP showed opposite effects. The miRNA array revealed that androgen decreased hsa-miR-5001-5p but increased hsa-miR-203a and hsa-miR-210-3p in PC-3AR cells but not PC-3 cells. Treatment with inhibitors targeting hsa-miR-203a/hsa-miR-210-3p, or overexpression of hsa-miR-5001-5p decreased YAP expression as well as suppressed the androgen-induced migration and invasion of PCa cells. Chromatin immunoprecipitation (ChIP) assay demonstrated that AR binds with promoter region of has-miR-210-3p in the presence of androgen. CONCLUSIONS: Our observations indicated that miRNAs 203a/210-3p/5001-5p regulate the androgen/AR/YAP-induced PCa metastasis.