MP84-15 PREVENT METASTASIS BY DOUBLE CHIMERIC ANTIGEN RECEPTOR T CELLS TARGETING CIRCULATING CANCER CELLS FOR PROSTATE CANCER TREATMENT

Abstract

INTRODUCTION AND OBJECTIVES: We and others have demonstrated that the androgen receptor (AR) is essential for the development and progression of prostate cancer. Although androgendeprivation therapy (ADT) is effective initially, unfortunately, metastatic prostate cancer often recurs as so-called castration resistant prostate cancer (CRPC). Overexpression of AR, AR hypersensitivity, c-terminal truncated AR variants, as well as altered steroid metabolism are considered the main mechanisms for CRPC. Current anti-AR treatments (Abiraterone and Enzalutamide) for CRPC only extend patient survival for approximately 5 months, indicating novel therapeutic agents are urgently needed. It has been shown that AR variants possess an intact and functional N-terminal domain that contains several key motifs and tyrosine residues involved in AR transactivation. METHODS: We recently designed a 14-amino acid peptide spanning the 355-368 residues (ARi14 peptide) on AR N-terminal, consisting of the partial transactivation activation unit-1 and three key tyrosine residues involved in CRPC progression. Multiple prostate cancer cell lines were used in the experiments. Trypan blue and Alamar Blue assays were used to assess cell proliferation. Western blot and anti-AR immunoprecipitation were conducted to assess AR protein levels and tyrosine phosphorylation. Quantitative RT-PCR was performed to assess PSA mRNA expression. RESULTS: Treatment of multiple AR-positive prostate cancer cells with this short peptide induced a significant reduction of AR protein, as well as AR transactivation in a luciferase reporter assay in a time-dependent manner. However, AR gene expression at the mRNA level was not altered. Further analysis revealed that ARi14 peptide abolished androgen-stimulated AR tyrosine phosphorylation in LNCaP cells, indicating a disruption of AR with its tyrosine kinase. In 22RV1 cells that harbor AR variants the ARi14 peptide dramatically reduced the protein levels of full length AR and AR variants, abolished AR-target PSA gene expression and also suppressed 22RV1 cell proliferation that Enzalutamide failed to do so. Sequence mutation analysis demonstrated that the C-terminal 8 residue portion (361-368aa) of the ARi14 is the key element for its anti-AR activities. CONCLUSIONS: Our data demonstrated that the novel short peptide ARi14 exerts a potent anti-AR activity by inducing AR protein degradation possibly through reduced tyrosine phosphorylation in Enzalutamide-resistant prostate cancer cells.