LAUSR

Colorectal Cancer (CRC) and Pancreatic Ductal Adenocarcinoma (PDAC) are the most lethal cancers worldwide. Despite initial response to standard-of-care therapy, a significant proportion of CRC/PDAC cancers relapse and progress to metastatic disease with poor overall survival (OS). Thus, better treatment options are urgently needed. Genetic alterations in the tumor suppressor p53 gene (TP53) are found in most CRC and PDAC cases and contribute to cancer relapse, progression, and metastasis. Even though the functional consequences of p53 mutations have been extensively studied, there are no FDA approved drug or their combination targeting p53 mutant (p53mut) cancers. Here we present a novel inducer-amplifier strategy for selective targeting p53-deficient CRC and PDAC. The Cancer Genome Atlas (TCGA) data showed elevated tumor mutational burden (TMB) and high expression levels of Base-Excision Repair (BER) in p53mut CRC and PADC. Assessment of the BER activity in CRC and PADC cells by a new methodology with deoxyuridine analogues ethynyl-deoxyuridine (EdU) and trifluorothymidine (TFT) revealed a significant delay in removal of genomic EdU and TFT in p53-deficient cells compared to isogenic p53 wildtype (p53wt) cells. Notably, p53-deficient cells accumulated in late S/G2 phase. Further, deoxyuridine analogues such as TFT-containing TAS102 induced buildup of DNA damage in p53-deficient cancer cells. Mechanistically, TAS102 did not block DNA replication but rather provoked activation of DNA Damage Response (DDR) resulting in DNA breaks in p53-deficient cells, while p53wt repaired the DNA lesion. This response was further enhanced by poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) leading to elevated cell death selectively in p53-deficient cancer cells, along with accumulation of cells in G2 phase. PARPi alone did not induce DNA damage in cancer cells. In preclinical in vivo models, the TAS102-PARPi combination was far more effective than either drug alone in the p53mut Cell-Derived Xenograft (CDX) and Patient-Derived xenograft (PDX) models. Immunohistochemistry data showed that the two-drug combination increased DNA damage and cell death while decreasing cell proliferation in p53-mutant models. In comparison, the two-drug combination and TAS102 exhibited comparable effectiveness in p53wt PDX model. Notably, the two-drug therapy did not exhibit significant toxicity in mouse models. In summary, this work demonstrates that our novel inducer-amplifier strategy provides effective treatment option for aggressive p53-deficient CRC and PDAC cancers while limiting adverse toxic events and improving the quality of life for cancer patients. Citation Format: Mohammed M. Alruwaili, Justin Zonneville, Mohammed A. Alqarni, Priyanka Rajan, Hannah Serio, Robert Straubinger, Christos Fountzilas, Andrei Bakin. Evaluation of a novel two-drug combination strategy for p53-deficient colorectal and pancreatic cancers [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 3397.