A Novel Target for Enhancing Sensitivity to Platinum-Based Chemotherapy in MIBC - Expert Commentary
Five human bladder cancer lines were used. From each of these parental lines, cisplatin, gemcitabine, or gemcitabine plus cisplatin (GemCis)-resistant sublines were developed. A genome-wide CRISPR screen in the GemCis-resistant derivative lines treated with GemCis uncovered 46 genes that were synthetic lethal. The majority of these genes were involved in DNA damage and repair pathways. Similarly, transcriptomic analysis showed that the most significantly and consistently upregulated genes were involved in DNA damage response and repair. One specific gene, NPEPPS, that encodes an aminopeptidase was found to be consistently upregulated in the resistant derivatives. This was validated at the protein level. Furthermore, NPEPPS was one of the top synthetic lethal hits in the CRISPR screen.
The investigators subsequently focused on NPEPPS and generated knockdowns in GemCis-resistant lines, which resulted in enhanced cisplatin but not gemcitabine sensitivity. Knockdown of NPEPPS also resulted in increased intracellular levels of cisplatin. Next, the researchers established xenograft models in mice using GemCis-resistant cells with or without NPEPPS knockdown. Mice were then treated with GemCis or PBS. NPEPPS knockdown alone and Gem treatment alone significantly reduced tumor growth compared to controls. GemCis treatment in mice with NPEPPS knockdown exhibited the strongest reduction in tumor growth. These findings were captured in a linear mixed-effects model comparing tumor volume change at baseline and after treatment, revealing tumor growth inhibition by NPEPPS knockdown (p = 0.00178), GemCis treatment (p < 0.0001), or the combination of NPEPPS knockdown and GemCis treatment (p < 0.0001). Mice treated with GemCis and mice with NPEPPS knockdown had a 14-day survival advantage, while mice with NPEPPS knockdown treated with GemCis had a 25-day survival advantage (p < 0.0001). Finally, these findings were validated in patient-derived organoids (PDOs) that were generated from MIBC patients undergoing transurethral resection of bladder tumor (n = 5) or radical cystectomy (n = 2). Five PDOs were generated prior to chemotherapy, one was generated after chemotherapy, and one was generated from a patient who did not receive chemotherapy. NPEPPS was found to be highly expressed in the organoids. Similarly, cisplatin treatment along with pharmacological inhibition of NPEPPS with tosedostat led to a significant reduction in cell viability. Cisplatin plus tosedostat also eliminated PDO regrowth.
The findings presented in this study have important translational implications. Clinical trials on tosedostat for leukemias, myelomas, and solid tumors have shown that it is well-tolerated but exhibits modest effects as a single-agent treatment. Tosedostat could potentially be tested in combination with cisplatin-containing regimens to reduce the dose of cisplatin and associated toxicity, in addition to enhancing overall response.
Written by: Bishoy M. Faltas, MD, Director of Bladder Cancer Research, Englander Institute for Precision Medicine, Weill Cornell Medicine
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