Abstract B86: Immunomodulatory effects of LL-37/CRAMP in prostate cancer progression.

Prostate cancer (PCa) is the most common type of cancer among males in the United States. However, even with advanced diagnostic capacity and conventional therapies such as surgery and chemotherapy, the 5-year survival rate for disseminated disease is approximately 36 months suggesting the need for finding alterate targets and therapies to increase patient survival. We have recently demonstrated that LL-37, an antimicrobial peptide that plays an important role in innate immune response against microbial pathogens, and its mouse orthologue CRAMP (Cathelicidin-related antimicrobial peptide) plays an important role in the progression of PCa both in humans and in a spontaneously developing mouse PCa model, respectively. Over-expression of CRAMP has also been recently reported in a few human epithelial cancers including carcinomas of the breast and lung. Results of our recent studies also demonstrated that targeted knock-down of CRAMP expression in a mouse PCa cell line, derived from the transgenic adenocarcinoma mouse prostate (TRAMP) model, TRAMP C1, resulted in decreased level of myeloid-derived suppressor cells (MDSC) in the spleen upon syngeneic transplantation. Based on these findings, the present study determined the role of LL-37/CRAMP in immune modulation during PCa progression. C57BL/6 mice were subcutaneously implanted with 3 different PCa cell lines; TRAMP C1 (CRAMPhigh), TRAMP C1scrambled (CRAMPhigh) and TRAMP C1CRAMPshRNA (CRAMPlow). Mice in TRAMP C1 and TRAMP C1scrambled groups developed measurable tumors starting from 45 days post-implantation, whereas mice implanted with TRAMP C1CRAMPshRNA showed measurable tumors from 120 days post-implantation suggesting that high levels of CRAMP expression in TRAMP C1 and TRAMP C1scrambled groups promote prostate tumor growth in vivo. Immune cell phenotyping was performed on cells collected from spleen and tumor at day 50 and 55 post-implantation to identify modulation in infiltrating immune cells as a surrogate for decrease in tumor growth due to abrogation of CRAMP expression. The result indicated a higher number of neutrophils infiltrating to the tumor site from the spleen during the initial stages of tumor growth in TRAMP C1 and TRAMP C1scrambled groups, while high numbers of neutrophils remained in the spleen of TRAMP C1CRAMPshRNA group during that time point. Elevated numbers of MDSC were observed both in spleen and in tumor microenvironment in TRAMP C1 and TRAMP C1scrambled groups suggesting that MDSC may further promote PCa growth whereas mice in the TRAMP C1CRAMPshRNA group showed significantly low level of MDSC in spleen, even when compared to control mice, at earlier time point. The number of plasmacytoid dendritic cells (pDC) both in spleen and tumor in TRAMP C1 and TRAMP C1scrambled groups was low while significantly high numbers of pDC were observed in spleen in TRAMP C1CRAMPshRNA group suggesting that high numbers of pDC may suppress the tumor growth by exerting pro-inflammatory response through cytokines such as IL-12. Altogether, the data suggest that CRAMP promotes PCa growth and plays an important role in immunomodulation during PCa progression. The CRAMP induces infiltration of neutrophils to tumor site and increased number of MDSC in both spleen and tumor, which may induce immunosuppression. Since CRAMP triggers protumorigenic stimuli including angiogenesis, invasion and key immune modulation to promote the tumor growth, LL-37/CRAMP may be used as a possible therapeutic target for PCa treatment. Ongoing tumor challenge studies in CRAMP knockout mouse model will shed more light to confirm these observations and to possibly extend the findings in human patients as a potential therapeutic target. Citation Format: Ha-Ram Cha, Anandi Sawant, Carnella Lee, Jonathan Hensel, George Tsuladze, Selvarangan Ponnazhagan. Immunomodulatory effects of LL-37/CRAMP in prostate cancer progression. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology: Multidisciplinary Science Driving Basic and Clinical Advances; Dec 2-5, 2012; Miami, FL. Philadelphia (PA): AACR; Cancer Res 2013;73(1 Suppl):Abstract nr B86.