Abstract 3456: Synergistic drug combinations promote the development of resistance in acute myeloid leukemia
Authors: Mason-Osann Emily , Pomeroy Amy E. , Palmer Adam C. , Mettetal Jerome T. 
Published: April 2023

Abstract
Background: Combination therapies are frequently employed as part of cancer treatment, often with the goal of preventing or slowing the development of drug resistance. Empirically developed combination therapies have had remarkable impact on cancer survival, yet the task of using preclinical data to predict combinations that will yield clinical benefits remains a challenge. Current combination strategies often prioritize drug synergy, where short-term effect of a drug combination is more than additive. However, prior studies of antibiotic resistance have shown that synergistic combinations can accelerate the emergence of resistance in bacteria. This occurs because synergistic drugs rely on one another for activity, resistance to one drug in the combination thereby depletes the efficacy of both. Consistent with experimental data on antibiotics, computational models of tumor evolution have predicted that when comparing equally active synergistic and non-synergistic combinations, synergy will accelerate the development of resistance in cancer cells.
Methods: In this study we aim to experimentally determine if synergistic drug combinations promote the development of resistance in acute myeloid leukemia cell lines, MOLM-13 and OCI-AML2. Using live-cell imaging we measured changes in growth rate over 21 days to observe the development of resistance to combination therapies ranging from additive to synergistic (Bliss score range - 1.6 to 19). We tested combinations of Venetoclax, Cytarabine, AZD5991, and AZD1775. We also measured the fitness benefit conferred from acquired resistance by comparing the difference between cellular growth rate during the first 72 hours of treatment and the maximum growth rate achieved by emerging resistant populations over the 21 day treatment.
Results: When controlling for both activity and drug synergy using logistic regression, increased drug synergy is consistently predictive of increased likelihood of resistance development within 21 days (MOLM-13 p=0.001, OCI-AML2 p=0.007, n=150 per cell line). As previously predicted, there is also significant correlation between drug synergy and the fitness benefit of resistance (MOLM-13 R=0.71, p=1.6e-6). Furthermore, using a model of competing drug-sensitive and resistant subpopulations treated with combination therapy, we demonstrate that these observations are a mechanistic consequence of synergistic combination, whereby the fitness benefit acquired by gaining resistance to either drug in a synergistic combination is greater than the fitness benefit in a non-synergistic combination.
Conclusion: Together these data have important implications for preclinical prioritization of combination therapies, and demonstrate that both short-term and long-term measures of drug efficacy can inform preclinical strategies aiming to develop novel combinations of cancer therapies with robust and durable efficacy.
Citation Format: Emily Mason-Osann, Amy E. Pomeroy, Adam C. Palmer, Jerome T. Mettetal. Synergistic drug combinations promote the development of resistance in acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3456.