Regulation of Androgen Receptor by NXTAR Long non-coding RNA in Prostate Cancer and its Therapeutic Implications

Abstract Androgen receptor (AR) signaling continues to play a dominant role in all stages of prostate cancer (PC), including castration-resistant prostate cancers (CRPCs) that have developed resistance to second generation of AR-antagonists e.g. enzalutamide. We identified a long non-coding RNA (lncRNA), NXTAR (LOC105373241), located convergently to the AR gene that is repressed in human prostate tumors and cell lines, and discovered that its reinstatement promotes binding upstream of the AR promoter, causing significant loss of expression of AR and its splice variant AR-V7. Paradoxically, AR binds to NXTAR promoter, and inhibition of AR by ACK1/TNK2 small molecule inhibitor, (R)-9b, excluded AR from binding to NXTAR promoter. Consequently, histone acetyltransferase GCN5 bound and deposited H3K14 acetylation marks enhancing NXTAR expression. Translational relevance of the negative regulation of AR became apparent when an oligonucleotide derived from NXTAR exon 5 (NXTAR-N5) suppressed AR/AR-V7 expression and prostate cancer cells proliferation. In addition, pharmacological restoration of NXTAR using (R)-9b abrogated enzalutamide-resistant prostate xenograft tumor growth. Overall, our study uncovers a negative feed forward loop, wherein NXTAR acts as a novel prostate tumor-suppressing lncRNA by inhibiting AR/AR-V7 expression, which in turn upregulates NXTAR levels, compromising enzalutamide-resistant prostate cancer. The restoration of NXTAR could be a new therapeutic modality for patients who have acquired resistance to second-generation AR-antagonists. Based on these data we hypothesize that (i) the therapeutic oligonucleotide NXTAR-N5, or (ii) its combination with the ACK1 inhibitor (R)-9b, or (iii) WEE1 inhibitor, AZD-1775 that restores NXTAR levels could be new therapeutic modalities for patients who have acquired resistance to second- generation AR-antagonists. To address this hypothesis, we will pursue the following aims: Aim 1. Determine the mechanism of NXTAR suppression in CRPCs. Aim 2. Synthesis of PSMA targeted `Bivalent and Trivalent’ nanoparticles with NXTAR-N5 oligo, (R)- 9b or/and AZD-1775 inhibitor payloads. Aim 3. In vivo characterization of Bi/Trivalent nanoparticles to overcome Enz-resistance in prostate cancer models, and patient derived xenografts (PDXs).