Abstract 2331: Loss of LRRC15 in osteosarcoma cells disrupts extracellular matrix integration, intercellular communication, and differentiation

Abstract Background: Leucine rich repeat containing 15 (LRRC15) is a 581 amino acid type 1 transmembrane protein that contains 15 leucine rich repeats. Cysteine clusters flank the LRR domain that functions as the collagen binding domain. LRRC15 has been found to be upregulated during osteogenic differentiation of mesenchymal stem cells, induced by TGFβ, and highly expressed in multiple solid tumors, notably in osteosarcoma (1). Antibody drug conjugates targeting LRRC15 have shown promising activity in pre-clinical studies (2). Results: To investigate the function of LRRC15 in the osteosarcoma microenvironment, we generated inducible shRNA knockdown (KD) derivatives targeting 3’UTR and ORF regions of LRRC15 of four osteosarcoma cell lines. Using these models, we characterized the biological properties of LRRC15 knockdown under 2-D and 3-D growth conditions. We found that LRRC15 KD in 2-D culture resulted in reduced adhesion to extracellular matrix (ECM) components and impaired cell migration. In 3-D spheroid culture, LRRC15 KD severely impacted scaffold-free spheroid compaction and invasion of spheroids embedded in Matrigel. Dysregulation of multiple ECM, cell adhesion and communication pathways were revealed by transcriptomic analysis from samples collected at time points during the LRRC15 KD. Of interest, several key transcription factors including RUNX2, CTNNB1, and SP7 were downregulated in LRRC15 deficient cells. Conclusion: Our comprehensive results establish the importance of LRRC15 as a critical cell-adhesion molecule essential for the maintenance of the osteogenic intercellular communication, invasion and differentiation revealing novel aspects of osteosarcoma cell-biology. Reference:1.Purcell JW, Tanlimco SG, Hickson J, Fox M, Sho M, Durkin L, et al. LRRC15 Is a Novel Mesenchymal Protein and Stromal Target for Antibody-Drug Conjugates. Cancer Res 2018;78:4059-4072.2.Slemmons KK, Mukherjee S, Meltzer P, Purcell JW, Helman LJ. LRRC15 antibody-drug conjugates show promise as osteosarcoma therapeutics in preclinical studies. Pediatr Blood Cancer 2020:e28771. Citation Format: Sanjit Mukherjee, Ankit Jajoo, Jack Zhu, Marbin Pineda, Robert Walker, James Purcell, Lee J Helman, Paul S. Meltzer. Loss of LRRC15 in osteosarcoma cells disrupts extracellular matrix integration, intercellular communication, and differentiation [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 2331.