Intravesical instillation of c-MYC inhibitor KSI-3716 suppresses orthotopic bladder tumor growth

Abstract

Purpose: c-MYC is a promising target for cancer therapy but its use is restricted by unwanted, devastating side effects. We explored whether intravesical instillation of the c-MYC inhibitor KSI-3716 could suppress tumor growth in murine orthotopic bladder xenografts.

Materials and methods: The small molecule KSI-3716, which blocks c-MYC/MAX binding to target gene promoters, was used as an intravesical chemotherapy agent. KSI-3716 action was assessed by electrophoretic mobility shift assay, chromatin immunoprecipitation, transcription reporter assay and quantitative reverse transcriptase-polymerase chain reaction. Inhibition of cell proliferation and its mechanism was monitored by cell cytotoxicity assay, EdU incorporation assay and flow cytometry. The in vivo efficacy of KSI-3716 was examined by noninvasive luminescence imaging and histological analysis after intravesical instillation of KSI-3716 in murine orthotopic bladder xenografts.

Results: KSI-3716 blocked c-MYC/MAX from forming a complex with target gene promoters. c-MYC mediated transcriptional activity was inhibited by KSI-3716 at concentrations as low as 1 μM. The expression of c-MYC target genes, such as cyclin D2, CDK4 and hTERT, was markedly decreased. KSI-3716 exerted cytotoxic effects on bladder cancer cells by inducing cell cycle arrest and apoptosis. Intravesical instillation of KSI-3716 at a dose of 5 mg/kg significantly suppressed tumor growth with minimal systemic toxicity.

Conclusions: The c-MYC inhibitor KSI-3716 could be developed as an effective intravesical chemotherapy agent for bladder cancer.

Keywords: 5-ethynyl-2′-deoxyuridine; CDK4; CRE; ChIP; DMSO; EdU; IC(50); PARP; PBS; PCR; PEG; RT-PCR; administration; chromatin immunoprecipitation; consensus response element; cyclin-dependent kinase 4; dimethyl sulfoxide; drug therapy; gene expression; hTERT; half inhibitory concentration; heterografts; human telomerase reverse transcriptase; intravesical; phosphate buffered saline; poly adenosine diphosphate ribose polymerase; polyethylene glycol; polymerase chain reaction; qRT-PCR; quantitative RT-PCR; reverse transcriptase-PCR; urinary bladder neoplasms.