Abstract 1756: Targeting LIFR/c-Myc Axis to Overcome Docetaxel Resistance in Prostate Cancer
Authors: Halder Sushanta , Muniyan Sakthivel , Chirravuri-Venkata Ramakanth , Nimmakayala Rama Krishna , Nallasamy Palanisamy , Nair Hareesh B. , Ponnusamy Moorthy P , Batra Surinder K. , Seshacharyulu Parthasarathy 
Published: April 2023

Abstract
Background: Docetaxel has been the most effective chemotherapeutic option after the emergence of Castration-resistant prostate cancer (CRPC). However, more than 50% of patients develop Docetaxel Resistance (DoceR) within three years of treatment. It also shows severe adverse effects that lead to dose reduction and treatment failure. Thus, targeting the underlying mechanism of DoceR could improve survival benefits for CRPC patients. In this study, we identified leukemia inhibitory factor receptor (LIFR) as a candidate for DoceR. We targeted it with EC914, a first-in-class oral small molecule, to overcome DoceR in CRPC.
Methods: We developed three DoceR (PC3-R60, 22Rv1-R110, and LNCaP(C-83)-R50) isogeneic sub-lines by chronic Docetaxel treatment for six months. We analyzed those cell lines for drug resistance markers using RT-PCR and western blot. We evaluated the effect of EC914 in overcoming DoceR using cytotoxicity assay in Incucyte® live imaging system, colony survival assay, apoptosis induction, and cell cycle arrest using FACS analysis. RNA-seq analysis revealed molecular pathways related to EC914-mediated Docetaxel- sensitivity. In addition, we utilized RT-PCR and western blot analysis to examine EC914-responsive cancer stem cell (CSC) and LIFR/STAT pathway-related genes and proteins. Finally, we adopted human and mouse syngeneic PCa cells and patient-derived xenograft models to test the in vivo efficacy of EC914 in combination with Docetaxel.
Results: LIFR showed significantly high mRNA and protein expression in Docetaxel resistant PCa cell model. EC914 combined with Docetaxel reduced considerably in vitro tumorigenicity (proliferation (p&lt;0 01), colony growth (p&lt;0 01)), induced apoptosis (p&lt;0 01), and arrested cells in the G2/M and S phase (p&lt;0 01) of the cell cycle. The combination also affected the CSC population and markers expression in DoceR PCa cells. Expression of cleaved caspase 3, caspase 9, and PARP-1 further validated apoptosis induction. Global transcriptome analysis identified EC914 treatment targets c-Myc pathway enrichment. Specifically, we found sixteen c-Myc pathway-related genes downregulated significantly (p&lt;0 05) in transcriptomic and qRT-PCR validation. Knockdown of LIFR reduces phospho-STAT3 and phospho c-Myc without altering total STAT and c-Myc proteins. Mice subcutaneous implantation of human (p&lt;0 05) and mouse (p&lt;0 05) syngeneic PCa cells and patient-derived tissue (p=0 003) reduced xenograft tumor growth upon treatment with EC914 combined with Docetaxel.
Conclusion: For the first time, we identified c-Myc pathway genes as potential LIFR signaling targets to overcome docetaxel resistance. Our findings support a new role and mechanism(s) of LIFR in CRPC and could inhibit MYC-addicted tumors.
Citation Format: Sushanta Halder, Sakthivel Muniyan, Ramakanth Chirravuri-Venkata, Rama Krishna Nimmakayala, Palanisamy Nallasamy, Hareesh B. Nair, Moorthy P Ponnusamy, Surinder K. Batra, Parthasarathy Seshacharyulu. Targeting LIFR/c-Myc Axis to Overcome Docetaxel Resistance in Prostate Cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1756.