Abstract 5188: Immunostaining of MRP-1 protein in circulating tumor cells predicts shorter progression free survival in metastatic colorectal cancer patients

Abstract

Abstract Background: colorectal cancer (CRC) is the third leading cause of cancer death in both men and women in the United States (Siegel et al., 2014). So, it is important to look for novel biomarkers to identify and define the best treatment for patients with this disease. Circulating Tumor Cells (CTCs) have been appointed for many researchers as a manner to follow up patients at current status. MRP-1 protein acts as an ATP-dependent efflux pump, naturally protecting cells from both toxic and therapeutic compounds. It works as a drug resistant protein, generally with irinotecan-based chemotherapy (Cole, 2014; Gazzaniga et al., 2010). Objective: to study the presence of MRP-1 protein in CTCs and its predictable value in treatment resistance, evaluating the time of progression free survival (PFS). Methods: This present cohort (n = 18) belongs to a larger cohort of patients (n = 54) treated with many chemotherapeutic agents combined with 5-FU. The results of 5-FU resistance were presented previously in AACR annual meeting 2014. The blood was collected prospectively from patients with metastatic CRC. Blood was collected before the beginning of chemotherapy. The sample was filtered on ISET (Isolation by Size of Epithelial Tumor Cells, Rarecells, France) according to manufacture procedure. CTCs fixed on spots from ISET membranes were stained by immunocytochemistry with anti- MRP-1 antibody (1/100) and counterstained with hematoxylin-eosyn. Leucocytes were identified by anti-CD45 antibody. CTCs were analyzed by light microscope and quantified by 1 mL of blood. Results: here we analyzed blood samples of 18 mCRC patients who underwent irinotecan-based chemotherapy, with or without 5-FU. The median age was 54 years-old (32 - 80) and 77.7% were male. All the patients included were clinical stage IV with tumors classified as adenocarcinoma. The median CTC number detected was 1.5 CTC/ml (0 - 13.75) at baseline. Immunostaining of MRP-1 in CTCs was performed in all samples and 4 (21%) were found positive. By Kaplan-Meier test we observed that patients with CTC MRP-1 positive had shorter PFS than patients CTC MRP-1 negative (2.1 vs. 9.8 months respectively; P = 0.003). Interestingly, patients irinotecan resistant do not belong to the same group of patients 5-FU resistant (CTC TYMS positive, link: http://www.abstractsonline.com/Plan/ViewAbstract.aspx?mID = 3404&sKey = f39b6e91-7d91-4e03-a37e-3bc3724bade3&cKey = 1fa1e08e-af70-461a-9275-d8cdc2dd7b14&mKey = 6ffe1446-a164-476a-92e7-c26446874d93). Conclusion: the necessity of novel tools to follow up and to predict treatment response has been increasing. Here, we proposed a potential protein found in CTCs, MRP-1, which might represent a powerful tool to manage and triage patients candidate to receive treatment with irinotecan. Furthermore, we are the first group to demonstrate the role of MRP-1 in CTCs as a predictive factor for patients with metastatic CRC. Citation Format: Emne A. Abdallah, Ludmilla T. D. Chinen, Virgílio S. Silva, Natalia B. Mingues, Marcelo C. Machado Netto, José Luiz Gasparini Júnior, Bruna M. M. Rocha, Juliana V. Romero, Marcilei E. C. Buim, Mitzi Brentani, Marcello F. Fanelli. Immunostaining of MRP-1 protein in circulating tumor cells predicts shorter progression free survival in metastatic colorectal cancer patients. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5188. doi:10.1158/1538-7445.AM2015-5188