Summary Pancreatic ductal adenocarcinoma (PDAC) is associated with marked fibrosis and stromal myofibroblasts but their functional contribution remains unknown. Transgenic mice with ability to delete αSMA+ myofibroblasts in pancreatic cancer were generated. Depletion starting at either non-invasive precursor (PanIN) or the PDAC stage led to invasive, undifferentiated tumors with enhanced hypoxia, epithelial-to-mesenchymal transition and cancer stem cells, with diminished animal survival. In PDAC patients, lower myofibroblasts in their tumors also correlated with reduced survival. Suppressed immune surveillance with increased CD4+Foxp3+ Tregs was observed in myofibroblasts depleted mouse tumors. While myofibroblasts depleted tumors did not respond to Gemcitabine, anti-CTLA4 immunotherapy reversed disease acceleration and prolonged animal survival. This study underscores the need for caution in targeting carcinoma-associated fibroblasts in PDAC.

We have developed a method to image tumor-associated lysosomal protease activity in a xenograft mouse model in vivo using autoquenched near-infrared fluorescence (NIRF) probes. NIRF probes were bound to a long circulating graft copolymer consisting of poly-L-lysine and methoxypolyethylene glycol succinate. Following intravenous injection, the NIRF probe carrier accumulated in solid tumors due to its long circulation time and leakage through tumor neovasculature. Intratumoral NIRF signal was generated by lysosomal proteases in tumor cells that cleave the macromolecule, thereby releasing previously quenched fluorochrome. In vivo imaging showed a 12-fold increase in NIRF signal, allowing the detection of tumors with submillimeter-sized diameters. This strategy can be used to detect such early stage tumors in vivo and to probe for specific enzyme activity.

Somatic mutations that activate phosphoinositide 3-kinase (PI3K) have been identified in the p110-α catalytic subunit (PIK3CA) 1. They are most frequently observed in two hotspots: the helical domain (E545K and E542K) and the kinase domain (H1047R). Although the PIK3CA mutants are transforming in vitro, their oncogenic potential has not been assessed in genetically engineered mouse models. Furthermore, clinical trials with PI3K inhibitors have recently been initiated, and it is unknown if their efficacy will be restricted to specific, genetically defined malignancies. In this study, we engineered an inducible bitransgenic mouse model that develops lung adenocarcinomas initiated and maintained by expression of p110-α H1047R. Treatment of these tumors with NVP-BEZ235, a dual pan PI3K/mTOR inhibitor in clinical development, led to marked tumor regression as shown by PET-CT, MRI and microscopic examination. In contrast, mouse lung cancers driven by mutant K-Ras did not substantially respond to single-agent NVP-BEZ235. However, when NVP-BEZ235 was combined with a MEK inhibitor, ARRY-142886, there was dramatic synergy in shrinking these K-Ras mutant cancers. These in vivo studies suggest that inhibitors of the PI3K/mTOR pathway may be active in cancers with PIK3CA mutations, and, when combined with MEK inhibitors, may effectively treat K-RAS mutated lung cancers.