Abstract 1880: Validation of protein arginine methyltransferase 5 (PRMT5) as a candidate therapeutic target in the canine model of non-Hodgkin lymphoma

Abstract

Abstract Introduction: Lymphoma is a common, aggressive malignancy in dogs. While generally responsive to upfront combination chemotherapy with traditional cytotoxic drugs, remission times are short and cures rare. New treatment strategies are therefore needed. Protein arginine methyltransferase 5 (PRMT5) is a type II protein arginine methyltransferase (PRMT) enzyme whose relevance to cancer biology has become increasingly evident as more studies have shown this enzyme to be involved in the regulation of multiple major signaling pathways affecting cell death, proliferation, and malignant transformation. While the mechanism behind many of these cell-transforming capabilities of PRMT5 remains unknown, knockdown of PRMT5 expression by genetic or pharmacologic means has been shown to modulate the methylation status of target proteins and exert antitumor effects in vitro and in vivo. Consequently, PRMT5 small-molecule inhibitors are in early preclinical development. Methods: In this study, we characterized patterns of PRMT5 expression and correlated these with histologic subtype using canine lymphoma tissue microarrays (TMAs). We characterized expression of PRMT5 in canine lymphoma tissues and methylation targets in canine B-cell lymphoma cell lines and treated them with different PRMT5 inhibitors to determine effects on PRMT5, target proteins and antitumor activity. We also assessed PRMT5 inhibition ex vivo in patient B-cell lymphomas via flow cytometry and assessment of apoptosis with annexin V/PI staining. Results: Canine diffuse large B-cell lymphoma showed cytoplasmic staining for PRMT5 (48.8% strong, 50.0% weak, n = 165) compared to negative or weak staining in normal and hyperplastic lymph nodes (n = 40). Lymphoblastic T-cell lymphoma samples showed strong nuclear staining (40%, n= 10). No nuclear staining was appreciated in normal or hyperplastic lymph nodes. Similarly, canine B-cell lines showed high expression of PRMT5. PRMT5 small-molecule inhibitors inhibited growth of CLBL-1 and 17-71 canine lymphoma cell lines. Histone (H3R8 and H4R3) methylation status was suppressed at their respective IC50s. Ex vivo treatment of canine patient tumor cells showed suppression of growth at 24 hours. Conclusion: We have demonstrated that PRMT5 is expressed in canine lymphomas and that PRMT5 inhibition can suppress the growth of canine lymphoma cells, supporting the continued use of the spontaneous canine lymphoma model for the preclinical development of PRMT5 inhibitors. Citation Format: Kyle A. Renaldo, Lindsay E. Courtney, Konstantin Shilo, Robert A. Baiocchi, William C. Kisseberth. Validation of protein arginine methyltransferase 5 (PRMT5) as a candidate therapeutic target in the canine model of non-Hodgkin lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1880.