Abstract PL04-03: Heterogeneity, drug resistance, and clonal evolution in colorectal cancers

Abstract

Abstract When metastatic cancers are challenged with targeted agents almost invariably a subset of cells insensitive to the drug emerges. As a result, in most instances, targeted therapies are only transiently effective in patients. Strategies to prevent or overcome resistance are therefore essential to design the next generation of clinical trials. How can we overcome the near-certainty of disease recurrence following treatment with targeted agents? To address this question a deeper understanding of the evolutive nature of cancer cells is necessary. We used colorectal cancer (CRC) as a model system to test the hypothesis that by understanding tumor's evolution the emergence of drug resistance can be controlled. We find that clonal dynamics can be monitored in real time in the blood of patients, and liquid biopsies can be used to intercept the emergence of resistant clones before relapses are clinically manifest. We discovered that a multistep clonal evolution process driven by progressive increases in drug fitness underlies the development of resistance in cells and patient avatars. To have long-term efficacy, the use of targeted therapies must take into account the continuous evolution of cancer cells, that is to say, therapies must adapt to tumor evolution. One possibility is to anticipate the changes the tumors will make. For example, by knowing in advance how CRC cells overcome resistance to EGFR blockade, we devised further rounds of therapy. Another approach is to unleash the ability of the immune system to recognize drug resistant cells. We tested this possibility in syngeneic mouse models of CRC sensitive to targeted therapies. Our findings indicate that manipulation of the mutational loads can trigger prolonged therapeutic responses that are not observed when cancer cells are challenged with targeted drugs alone. We postulate that rationally combined targeted and immuno-therapies can restrain tumor evolution, and can limit the emergence of drug resistance thus leading to long-term responses. Citation Format: Alberto Bardelli. Heterogeneity, drug resistance, and clonal evolution in colorectal cancers. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr PL04-03.