The promise of precision medicine is to improve patient outcomes by making better therapeutic choices based on cancer causing somatic mutations. This strategy has shown limited success in colorectal cancer, in part because the genetic rules governing resistance and sensitivity are not fully elucidated. Direct drug sensitivity testing of individual patient-derived organoids is an attractive addition to this decision process because it does not require understanding of all drug-somatic mutation interactions. Individual patients avatars can be challenged with a variety of drugs and response used to inform patient care. We have developed a panel of colon cancer organoid avatars and uniquely tagged each one with a lentiviral vector possessing identifying DNA sequence bar codes flanked by common PCR primers. Each bar-code is uniquely identifiable and quantifiable from a mixture of organoids by nanopore sequencing of a common PCR product. Treatment of the mixture of organoid avatars over time under multiple drug conditions and sampling at different time points allowed the real-time monitoring of relative Darwinian fitness of each organoid in the mixture. We demonstrated the utility of this approach at identifying both expected and novel drug responses for individual organoids. Resistance to both nutlin and irinotecan were correctly predicted by TP53 somatic mutations while sensitivity to both lapatinib and ibrutinib were best predicted by mutations in EGFR signaling pathway. Patterns of drug response revealed unexpected common mechanisms. Future work will focus on informing patient care decisions with these results and determining if improvements in patient outcomes are realized. Citation Format: Shrey Patel, Sana Khalili, Victoria Moy, Emma Gray, Sawyer Lyons, Riley Brents, Carolyn Banister, Phillip J. Buckhaults. A multiplex organoid avatar drug testing platform for precision medicine [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB162.
TP53 mutations are present in all molecular subtypes of breast cancer and often correlate with de-creased survival; however, few therapeutic options exist for patients with TP53-mutant breast can-cers. To discover therapeutic strategies for these patients, we investigated the sensitivity of 129 FDA-approved chemotherapies to TP53-KO and TP53-WT MCF7 breast adenocarcinoma cells and found p53 loss to confer sensitivity to 5-fluorouracil (5-FU). We then treated the p53-null cells and isogenic controls with F10, a second-generation polymeric fluoropyrimidine, and found this preferential cytotoxicity of TP53-KO cells to be significantly magnified. F10 killing could only minimally be rescued by addition of exogenous uridine, whereas it was completely abrogated by addition of exogenous thymidine, suggesting DNA incorporation to be central to the cytotoxic mechanism of action. Furthermore, F10 killing of p53-null cells was persistent even in heterogeneous cellular mixtures more reflective of natural tumor evolution. Together, our results suggest F10 may widen the therapeutic window for TP53-mutant breast cancer by enhancing genotoxicity in cells resistant to apoptosis.
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