Abstract 2495: SPARC: a bladder cancer tumor-suppressor via targeting metabolic programming
Authors: Almousa Sameh Waleed , Ghoneum Alia , Afify Hesham , Said Neveen 
Published: July 2021

Bladder cancer (BC) is the sixth most common cancer in the United States. Approximately, 75% of BC patients present with non-muscle invasive bladder cancer (NMIBC), which is responsive to local treatment and surveillance. However, recurrence is common with progression to muscle-invasive bladder cancer (MIBC). Forty percent of MIBC patients develop distant metastases, with few treatment options and poor survival. Limited advances have been made in BC therapy with only a few FDA-approved new treatments for advanced disease since 2016 with response rates hovering around 15%. Thus, there is an unmet need for better understanding of the pathobiology of the disease to develop more effective therapeutics. Metabolic re-programming of cancer is increasingly recognized as a hallmark of cancer as cancer cells take advantage of metabolic products to meet the increasing demands of proliferating cells. Our lab has identified the Secreted Protein Acidic Rich in Cysteine (SPARC) as a multi-faceted tumor suppressor within the BC tumor microenvironment. Herein, we sought to elucidate the role of SPARC in regulating metabolic programming in BC and identify pathways that may serve as diagnostic and therapeutic targets. We used three BC cell lines UMUC3, T24 (SPARChigh) and its isogenic SPARClow T24T. We treated BC cells with recombinant SPARC protein and genetically manipulated SPARC expression in these cells. We performed real-time monitoring of the effect of SPARC on bioenergetics using Seahorse assays. In tandem, we profiled transcriptomes of T24, T24T, and T24shSP-cell lines to identify aggressive phenotype signatures using GSEA. We then compared signatures with survival data from BC cohorts from the GEO and TCGA. We found that SPARC inhibited ATP production, basal and maximal respiration, and spare respiratory capacity in BC cell lines. This effect is more pronounced in more aggressive SPARClow T24T cells compared to its isogenic SPARChigh T24 cells. Knockdown of SPARC in BC cell lines not only induced an aggressive phenotype, but also increased ATP production and mitochondrial respiration. Integrated transcriptomic profiling indicated that SPARC-loss is associated with enriched glycolytic, lipidomic, and mitochondrial metabolic pathways. Importantly, in patient samples, SPARC expression negatively correlated with rate limiting enzymes in metabolic pathways associated with lower survival. SPARC loss also associated with oncogenic signatures of EMT, PI3K-AKT-mTOR signaling, and G1/S cell cycle arrest. Our data reveals a novel function of SPARC inhibiting mitochondrial bioenergetics and ATP production that fuel growth and invasion in BC cells. The SPARC-regulated metabolic profile highlights potential vulnerabilities that can be exploited as therapeutic targets.

Citation Format: Sameh Waleed Almousa, Alia Ghoneum, Hesham Afify, Neveen Said. SPARC: a bladder cancer tumor-suppressor via targeting metabolic programming [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2495.