Let-7f microRNA expression within established bladder cancer subtypes and upregulation with recombinant interferon-alpha.

Abstract

462 Background: Let7f is a microRNA (miR) that may act as a tumor suppressor in multiple human malignancies. In patients with BCG-refractory non-muscle invasive bladder cancer, detectable let7f levels in the urine of patients undergoing treatment with adenoviral vector-mediated IFNα gene therapy (clinical trial setting) were found to be prognostic of treatment response at 12 months. Here we sought to define the association of let7f with clinical bladder cancer phenotypes within The Cancer Genome Atlas (TCGA) cohort and characterize the role of let7f in preclinical models. Methods: Using miRNA sequencing data from the published TCGA 2018 bladder cohort (n = 412), let7f miR expression was characterized and stratified by molecular subtype (basal-squamous, luminal, luminal-infiltrated, luminal-papillary, and neuronal). Kaplan-Meier analyses were performed to compare survival (upper vs lower median, by let7f expression level). The murine urothelial carcinoma cell line MB49 was cultured in colonies of 105 and in vitro administrations of 100U/mL of recombinant mu-IFNα were performed with cells harvested at 0, 2, 8, 12, and 24 hours. Let7f miR expression levels were then determined by qRT-PCR. Results: Within the TCGA cohort, let7f expression levels were found to be lower in the more aggressive basal-squamous (median = 12.8), luminal-infiltrated (median = 12.9), and neuronal (median = 12.4) subtypes relative to the luminal (median = 13.2) and luminal-papillary (median = 13.3) subtypes (p < 0.001). Survival analysis demonstrated a trend towards improved survival in the high let7f expressers, but this did not reach statistical significance. In MB49 cells treated with mu-IFNα, there was a time-dependent increase in let7f miR expression suggesting that IFNα may play a role in upregulation of this potential tumor suppressor. Conclusions: Let7f miR is downregulated in more aggressive subtypes of MIBC. IFNα upregulates let7f expression in MB49 cells, and the inability to do so may comprise an escape mechanism for IFNα-treated tumors. Let7f miR may serve as a novel biomarker to identify aggressive phenotypes and treatment failures for bladder tumors treated with IFNα-based gene therapy.