Copy number alterations of the tumor-suppressor gene PTEN occur frequently in primary prostate cancer and are prognostic for relapse post-radiotherapy (RT). Preclinical modelling supports elevated CXC-chemokine signaling as a critical mediator of PTEN-depleted disease progression, and therapeutic resistance. Our objective was to establish the correlation of PTEN-deficiency with CXC-chemokine signaling and its association with clinical outcome following RT. Techniques employed included gene cluster and survival analysis of prostate cancer datasets; in vitro biologic assays extending to RT-PCR, immunoblotting, clonogenic survival assays and flow cytometry; and the use of two in vivo PTEN-deficient xenograft models. Analysis of gene expression data from the MSKCC cohort characterized a PTENLOW/CXCR1HIGH/CXCR2HIGH cluster of tumors that associates with earlier time to biochemical recurrence (HR 5.87, p<0.001). Further analysis was conducted on a gene expression profile derived from the FASTMAN retrospective radiotherapy patient sample cohort (248 diagnostic biopsy samples with median follow-up data >90 months). Kaplan-Meier analysis confirmed that PTENLOW/CXCR1HIGH/CXCR2HIGH tumors were associated with a significantly reduced time to biochemical recurrence (HR 2.65, p<0.001) and the development of metastasis (HR: 3.51, p<0.001) following RT treatment. In vitro, CXCL-signaling was further amplified following exposure of PTEN-deficient CaP cell lines to ionizing radiation (IR; 2-3 Gy). Inhibition of CXCR1/2-signaling in all PTEN-depleted cell-based models increased IR sensitivity (dose enhancement range 1.13 to 1.39), mediated by apoptosis induction in DU145 cells (p53-mutant) or senescence in 22RV1 cells (p53-WT). Reconstitution of PTEN in PTEN-null PC3 cells abrogated the radiosensitivity afforded by a CXCR1/2-signaling blockade. In vivo, administration of a CXCR1/2-targeted pepducin (x1/2pal-i3) in combination with IR to PTEN-null PC3 and PTEN-depleted DU145 xenografts attenuated tumor growth and progression compared to control or radiation alone (p<0.001). Post-mortem analysis confirmed that x1/2pal-i3 administration attenuated IR-induced CXCL-signaling and antiapoptotic protein expression (Bcl-2, c-FLIP). Our data confirm the clinical association of PTEN-deficiency with elevated CXC-chemokine signaling in human prostate cancer, the association of this cluster with adverse clinical outcomes, and demonstrates that IR exposure selectively potentiates this signaling pathway in PTEN-deficient tumor cells. Interventions targeting CXC-chemokine signaling may provide an effective strategy to combine with radiotherapy, especially in locally advanced prostate cancers with known presence of PTEN-deficient foci.

Citation Format: Chris W.D. Armstrong, Jonathan A. Coulter, Chee Wee Ong, Pamela J. Maxwell, Karl T. Butterworth, Oksana Lyubomska, Melissa J. LaBonte, Silvia Berlingeri, Rebecca Gallagher, Steven M. Walker, Joe M. O’Sullivan, Suneil Jain, Ian G. Mills, Manuel Salto-Tellez, Timothy Illidge, Richard D. Kennedy, Kevin M. Prise, David J.J. Waugh. Radio-resistance of PTEN-deficient prostate tumors is enhanced by treatment-induced chemokine signaling and is associated with biochemical recurrence and development of metastasis [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr B035.