4-1BB Aptamer-Based Immunomodulation Enhances the Efficacy of Ionizing Radiation in a Preclinical Murine Tumor Model

Abstract

Purpose/Objective(s): In head and neck, pancreatic, and breast cancers, tumor engraftment into immune-deficient mice is mediated by tumorinitiating cells (TICs) and has been associated with a poor prognosis. Volkmer et al proposed three distinct bladder TIC populations: CD90 + CD44 + CD49f+ (basal), CD90-CD44 + CD49f+ (intermediate) and CD90-CD44-CD49f+ (differentiated) TICs. However, the prognostic significance and the relationship between tumor engraftment and urothelial TICs has yet to be established. TICs have also been implicated in radiation resistance but this has not been investigated in bladder cancer. We investigated the distribution of TIC populations in patient-derived xenografts from bladder cancer patients as well as the effect of radiation on TIC populations. Materials/Methods: We injected fragments of 40 primary bladder tumors intradermally in NOD-SCID mice. After intradermal injection, 23 of the 40 primary human bladder tumors engrafted to produce patient-derived xenografts. Using flow cytometry, we have analyzed the proportion of TIC populations. We irradiated these patient-derived xenografts with 20 Gy and analyzed the surviving TIC cell populations. Results: Total TIC content per tumor ranged from 0.03% to 67%. The average TIC content per tumor of basal, intermediate and differentiated TICs was 2.42% (range, 0-17%), 5.68% (range, 0-67%), and 16.1% (range, 0-61%), respectively. Tumors that regrew following 20 Gy were enriched 2 to 3 fold for basal TICs. Conclusions: All bladder tumors contain TICs; however, heterogeneity exists with regard to the distribution of the TIC populations. We continue to accrue human bladder cancer derived xenografts and to analyze their TIC content with the goal of defining the relationship between growth in NOD-SCID mice and clinical outcome. Our preliminary results identify radioresistant TICs and molecular analysis of these cells is underway. We hypothesize that patient-derived xenografts may identify patients with radioresistant TIC populations and that patients that do not have significant numbers of these radioresistant TICs may be suitable for bladder-sparing therapy. Author Disclosure: O.D. Offor: A. Employee; University of Chicago Medicine. J. Namm: A. Employee; University of Chicago Medicine. M. Beckett: A. Employee; University of Chicago Medicine. G. Steinberg: K. Advisory Board; Bladder Cancer Advocacy Network. R.R. Weichselbaum: A. Employee; University of Chicago Medicine.