Abstract B003: Evolutionary games in radiotherapy resistance: Exploiting an immunologic double bind in advanced prostate cancer
Authors: Luddy Kimberly A. , West Jeffery , Robertson-Tessi Mark , Anderson Alexander R.A. , Bursell Taylor M. , Marignol Laure , O'Farrelly Cliona , Gatenby Robert 
Published: May 2022

Abstract
Evolution-informed therapy exploits the ecological and evolutionary consequences of drug resistance to inhibit the expansion of treatment resistant populations prolonging time to progression. One strategy, termed an evolutionary double bind, uses an initial therapy to elicit a specific adaptive mechanism that is then selectively targeted by a follow-on therapy. Typically, the second therapy is most effective in the recurrent setting and less effective when given upfront. Here we examine combining radiation therapy followed by immunotherapy as a double bind strategy. Radiotherapy (RT) can induce lethal double-strand DNA breaks in tumor cells and radiosensitivity is governed by the cells’ DNA repair capabilities. Radioresistant cancer cells upregulate DNA damage response pathways, which are mediated by ataxia telangiectasia mutated (ATM) and ataxia telangiectasia and Rad3-related (ATR) proteins. However, successful adaptations to RT and other DNA damaging agents can increase natural killer (NK) cell ligand expression on tumor cells increasing their vulnerability to the immune system. We evolved two cell lines, derived from a single population (22Rv1), with differing RT sensitivities (RT-sensitive and RT-resistant). We demonstrate RT-resistant cells upregulate NK cell ligands, including major histocompatibility complex class I chain-related protein A/B (MICA/B), poliovirus receptor (PVR), and PVRL2, resulting in a 2-fold increase in sensitivity to NK cell mediated killing. We conducted a multidisciplinary investigation of this potential evolutionary double bind through in vitro studies of radiation-sensitive and radiation-resistant cells treated with RT, NK cell therapy alone, or in combinations to parameterize evolution-based mathematical models. Mathematical modeling quantified three potential aspects of a double-bind: cost of resistance, inter-specific competition between RT-sensitive and RT-resistant lines, and preferential targeting of RT-resistant lines by NK cells. Despite a slower intrinsic growth rate, the RT-resistant population out competed the RT-sensitive cells in co-cultures at all seeding frequencies in the absence of treatment. Radiotherapy slowed overall growth but strongly selected for RT-resistant cells. NK cell therapy alone suppressed the RT-resistant population but maintained a residual population of radiation-sensitive cells. RT followed by NK cells was the most effective at reducing overall tumor burden, even in cases with an initially large RT-resistant fraction. We conclude RT followed by immunotherapy produces an evolutionary double bind that can be exploited in heterogenous tumors to limit RT resistance. Furthermore, model simulations predict extinction of both populations by sequential RT and NK cell therapy is achievable.
Citation Format: Kimberly A. Luddy, Jeffery West, Mark Robertson-Tessi, Alexander R.A. Anderson, Taylor M. Bursell, Laure Marignol, Cliona O'Farrelly, Robert Gatenby. Evolutionary games in radiotherapy resistance: Exploiting an immunologic double bind in advanced prostate cancer [abstract]. In: Proceedings of the AACR Special Conference on the Evolutionary Dynamics in Carcinogenesis and Response to Therapy; 2022 Mar 14-17. Philadelphia (PA): AACR; Cancer Res 2022;82(10 Suppl):Abstract nr B003.