Tumor priming by Apo2L/TRAIL reduces interstitial fluid pressure and enhances efficacy of liposomal gemcitabine in a patient derived xenograft tumor model

Interstitial fluid pressure (IFP) is elevated in tumors and high IFP, a negative cancer prognosticator, is known to limit the uptake and efficacy of anti-tumor therapeutics. Approaches that alter the tumor microenvironment and enhance uptake of therapeutics are collectively referred to as tumor "priming". Here we show that the cytotoxic biological therapy Apo2L/TRAIL can prime the tumor microenvironment and significantly lower IFP in three different human tumor xenograft models (Colo205, MiaPaca-2 and a patient gastrointestinal adenocarcinoma tumor xenograft). We found that a single dose of Apo2L/TRAIL resulted in a wave of apoptosis which reached a maximum at 8 h post-treatment. Apoptotic debris subsequently disappeared concurrent with an increase in macrophage infiltration. By 24 h post-treatment, treated tumors appeared less condensed with widening of the stromal areas which increased at 48 and 72 h. Analysis of tumor vasculature demonstrated a significant increase in overall vessel size at 48 and 72 h although the number of vessels did not change. Notably, IFP was significantly reduced in these tumors by 48 h after Apo2L/TRAIL treatment. Administration of gemcitabine at this time resulted in increased tumor uptake of both gemcitabine and liposomal gemcitabine and significantly improved anti-tumor efficacy of liposomal gemcitabine. These results suggest that Apo2L/TRAIL has a potential as a tumor priming agent and provides a rationale for developing a sequencing schema for combination therapy such that an initial dose of Apo2L/TRAIL would precede administration of gemcitabine or other therapies.