Abstract 1583: Bcl-6 as a potential therapeutic target for bladder cancer

Abstract Introduction and Objectives: B-cell lymphoma 6 (Bcl-6) is known to be a nuclear protein and a master transcription factor for regulation of T follicular helper cells (TFH cells) proliferation. Previously, we reported on the increased angiogenic potential of human prostate cancer cells that overexpressed the Bcl-2. Comparative genomic profiling of the endothelial cells treated with/without conditioned media from Bcl-2-overexpressing human prostate cancer cells revealed approximately 250 differentially expressed genes. Interestingly, bioinformatics analysis identified Bcl-6 as one of several secreted proteins on the list. In this study, we first confirmed that Bcl-6 exists in liquid biopsy, and secondly evaluate the effect of Bcl-6 neutralization on angiogenesis and tumor growth in in vitro and in vivo models. Methods: We first analyzed Bcl-6 levels in serum and urine by ELISA. Then we tested the effect of Bcl-6 antibody for the following: ability to inhibit in vitro and in vivo angiogenesis, ability to inhibit cellular proliferation, and tumor growth in cell line-derived xenograft model. Results: First, we found that Bcl-6 exists in urine and serum. Interestingly, Bcl-6 level was significantly higher in cancer patients than healthy subjects. Next, we identified the effective clone tube formation assay. Then we further tested the effect of the antibody and exogenous Bcl-6 on cell proliferation, tube formation, and tube disruption in HUVEC. The exogenous Bcl-6 did not enhance cell proliferation of HUVEC. On the other hand, the Bcl-6 antibody significantly inhibited tube formation in HUVEC, but not tube disruption. Subsequently, we performed Matrigel plug assay to evaluate the effect on angiogenesis in vivo. The CD31 positive cells in Matrigel plug were significantly reduced by the Bcl-6 antibody treatment. To evaluate the effect on tumor growth, we first performed the cell proliferation assay to evaluate the effect on tumor growth in vitro. The Bcl-6 antibody significantly inhibited the cell proliferation of T24 and UM-UC-3 cell lines highly expressing Bcl-6. Finally, we tested the effect of the Bcl-6 antibody on tumor growth in an animal model. Intratumoral injection of Bcl-6 antibody (15 μg/tumor, twice weekly) significantly inhibited the tumor growth. Conclusions: This is the first time to identify that Bcl-6 may be a secreted protein and found that neutralization of Bcl-6 by antibody inhibits angiogenesis and tumor growth in both in vitro and in vivo. The results suggest that neutralizing Bcl-6 by antibody could be a promising therapeutic agent in bladder cancer. Citation Format: Hideki Furuya, Kaoru Murakami, Nari Kim, Charles J. Rosser. Bcl-6 as a potential therapeutic target for bladder 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 1583.