Adding targeted inhibition of PI3K and MAPK signaling pathways to standard chemotherapy in experimental pancreatic cancer.

Abstract

278 Background: Treatment of pancreatic ductal adenocarcinoma (PDAC) remains a formidable challenge as gemcitabine (Gem) plus nab-paclitaxel (NPT) represent the current standard for systemic therapy of advanced PDAC. More than 90% of PDAC tumors harbor an activating mutation in the KRAS oncogene. Currently no therapeutics exist that can effectively target this oncogene product, but alternative strategies focus on inhibition of downstream effectors of KRAS signaling pathways. The RAF-MEK-ERK (MAPK) and the AKT-PI3K signaling pathways are well-described mediators of KRAS induced transformation and tumorigenesis and can be explored as targets for combination therapy. Methods: We evaluated combination treatment benefits of NPT+Gem with the MEK inhibitor trametinib (Tra) and the AKT inhibitor MK-2206 (MK) in experimental xenografts to test their therapeutic potential against PDAC. Results: Median animal survival in human intraperitoneal PDAC xenografts in mice revealed that the median survival was 21 days in controls; this was significantly improved by the NPT+Gem combination (35 days, a 67% increase over controls, p = 0.0007). Median survival was further increased by addition of MK-2206 or trametinib to NPT+Gem chemotherapy group: NPT+Gem+MK (39 days, a 86% increase over controls, p = 0.0003), NPT+Gem+Tra (43 days, a 105% increase over controls, p = 0.0003) and NPT+Gem+MK+Tra (48 days, a 129% increase over controls, p = 0.002). In human subcutaneous PDAC xenografts, MK-2206 or trametinib were able to enhance NPT+Gem effects. Compared to controls (100±34.8), the percent net local tumor growth in different therapy groups was: NPT+Gem 21.8±5.9 (p = 0.003), NPT+Gem+MK 17.2±4.8 (p = 0.002), NPT+Gem+Tra 7.1±11.2 (p = 0.002) and NPT+Gem+MK+Tra 5.7±9.1 (p = 0.001). In vivo effects of Tra and MK correlated with reduced expression of phospho-ERK and phospho-AKT in Western blots of tumor samples. Conclusions: These findings suggest that the effects of NPT+Gem can be enhanced through combined inhibition of MAPK and PI3K signaling pathways, which clinically could yield in improved antitumor results.