Abstract 2622: Paclitaxel directed screening to identify novel anti-cancer drugs
Authors: Wingate Joseph , Garcia Diana Gonzalez , Parra Karla , Batson Serina , Martinez Joel , Ontiveros Ivan Sosa , Aguilera Renato , Varela Armando , Valenzuela Paloma , Armendariz Marcos , Clifton Chloe , Levario Arlene , Chacon Angelica , Villagrana Andres , Sanchez Emmanuel , Bocci Guido , Francia Giulio 
Published: September 2020

Among the main challenges for the treatment of breast cancers is disease spread which is often coupled with resistance to chemotherapy. Furthermore, patients with late stage breast cancer go through first- and second-line therapies before they are candidates for new and/or experimental therapies. At such late stages, tumors that might have responded to new therapies have evolved to express multi-drug resistance - conceivably as a consequence of exposure to the initial therapies. Many mechanisms have been proposed to contribute to drug resistance, ranging from (but not limited to) reduced drug penetration and the activity of drug efflux pumps through to cell-adhesion mediated resistance to cell death. To address these challenges we sought to determine whether; a) tumor metastasis to different secondary sites generates location-specific tumor phenotypes that alter sensitivity to chemotherapy and, b) whether pre-treatment of tumors to conventional paclitaxel (PTX) chemotherapy alters their sensitivity to new drugs. First, we implanted 2x10(5) human luciferase-positive LM2-4 human breast cancer cells intracardiacally into SCID mice (n=15), which resulted 2 weeks later in the development of widespread metastases to the lungs, liver, spleen, and bone. For some of the mice bearing such metastases, PTX therapy (20mg/kg, i.p.) was administered 24 hours before the mice were euthanized. Next, we used RNA sequencing of isolated LM2-4 metastatic nodules to determine the impact of the location of metastases on transcriptome profiles (assessed by 40 million reads per each total RNA sample, followed by Principal Component Analysis). This study revealed that lung metastases have similar signatures to metastases to spleen and ovary, and to metastases in those organs following PTX therapy, while such transcriptome profiles are all quite distinct from those of metastases of the same tumor to the liver. These changes presumably are due to different cell-cell interactions of tumor cells in the different organs, as well as a consequence of the different microenvironments. Second, we set up a drug screen of LM2-4 breast cancer cells recovering from 1nM paclitaxel 24hr exposure in vitro to test for drugs that are toxic to the tumor cells following PTX pre-exposure. A screen of 30,000 small molecule drugs thus far identified 7 hit compounds. Our results serve a proof of concept that the location of metastases can alter the tumor cell phenotype, as can pre-treatment with PTX, and suggest that in some cases therapy ought to be tailored to the location of metastasis. Based on those results we identified drugs that may be useful in hampering the tumor cell recovery from PTX chemotherapy. Our work serves as a test ground for stratifying tumors based on their tissue of tumor spread, and provide a rationale for identifying drugs that hamper recovery of tumor cells to chemotherapy agents often incorporated into first and second line therapies, such as paclitaxel.

Citation Format: Joseph Wingate, Diana Gonzalez Garcia, Karla Parra, Serina Batson, Joel Martinez, Ivan Sosa Ontiveros, Renato Aguilera, Armando Varela, Paloma Valenzuela, Marcos Armendariz, Chloe Clifton, Arlene Levario, Angelica Chacon, Andres Villagrana, Emmanuel Sanchez, Guido Bocci, Giulio Francia. Paclitaxel directed screening to identify novel anti-cancer drugs [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2622.