Abstract B32: GRP55 antagonists alter tumor microenvironment and inhibit tumor growth in a pancreatic tumor xenograft model

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Abstract (R,R’)-4’-Methoxy-1-naphthylfenoterol ((R,R’)-MNF) and (R,S’)-MNF are GPR55 inhibitors that reduce proliferation in pancreatic cancer cell lines. The IC50 values for [3H]-thymidine incorporation in PANC-1 cells were 0.11 ± 0.08 µM {(R,S’)-MNF} and 0.65 ± 0.25 µM {(R,R’)-MNF}. (R,R’)-MNF and (R,S’)-MNF attenuate the activities of the β producing decreased expression and nuclear translocation of pyruvate kinase M2, β-catenin and HIF-1α, thereby reducing cyclin D1 expression with concomitant G1/S cell cycle arrest. MNF reduces the expression and function of multidrug exporters in PANC-1 cells and tumor tissues, thereby increasing the sensitivity to other chemotherapeutic agents. The compounds also attenuate expression and function of enzymes and transporters associated with glycolysis including the MCT4 lactate exporter, thereby reducing L-lactate concentration in the tumor microenvironment. We now report the effect of (R,S’)-MNF on the growth of a PANC-1 tumor maintained as a xenograft in mice. Protocol: PANC-1 cells maintained in vitro as monolayer culture were harvested at an exponential growth phase, counted and each mouse inoculated subcutaneously at the right flank region with 5x106 cells in 0.1ml of PBS. On Day 8, mice were weighed and tumor volumes measured (mean tumor size 142mm3), and assigned to groups (n = 10) using randomized block design based on their tumor volumes. The mice received an ip injection (10mL/g) five times per week for 3 weeks of vehicle, 20% hydroxypropyl-beta-cyclodextrin (Control), 20mg/kg (R,S’)-MNF or 40mg/kg (R,S’)-MNF. The animals were checked daily for morbidity and mortality and weight and tumor volume measured twice weekly. On Day 33, the mice were euthanized by cervical extension, body weight, tumor weights and volumes were obtained and the tumors snap frozen. Results: (R,S’)-MNF produced significant dose-dependent inhibition of tumor growth. determined as % change in tumor volume relative to control. In animals treated with 20mg/kg (R,S’)-MNF there was 51.1±5.2% (** p < 0.01) inhibition and a 74.1±2.8% (*** p < 0.005) inhibition in animals receiving 40mg/kg (R,S’)-MNF. No mice were lost to treatment limiting toxicities. There was no significant change in weight between pre-dose and Day 33 for the animals in the control and 20mg/kg (R,S’)-MNF groups while on Day 33 the average weight of the animals receiving 40mg/kg (R,S’)-MNF was significantly lower 9.9±3.7% (*p < 0.05) than their pre-dose weights. The (R,S’)-MNF associated reduction of protein expression in tumor tissues, including pyruvate kinase M2, β-catenin, HIF-1α and MCT4 will be presented as will the changes in tumor/plasma concentrations of L-lactate. Citation Format: Nagendra S. Singh, Irving W. Wainer.{Authors}. GRP55 antagonists alter tumor microenvironment and inhibit tumor growth in a pancreatic tumor xenograft model. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr B32.