Abstract
Gemcitabine has limited clinical benefits in pancreatic ductal adenocarcinoma. The solvent-based traditional taxanes docetaxel and paclitaxel have not shown clinical results superior to gemcitabine. Nab-paclitaxel, a water-soluble albumin-bound paclitaxel, may carry superior distribution properties into the tumor microenvironment and has shown efficacy in multiple tumor types. We evaluated nab-paclitaxel effects compared with gemcitabine or docetaxel. For pancreatic ductal adenocarcinoma cells AsPC-1, BxPC-3, MIA PaCa-2 and Panc-1, gemcitabine IC50 ranged from 494nM to 23.9 μM; docetaxel IC50 range was from 5 to 34nM; nab-paclitaxel IC50 range was from 243nM to 4.9 μM. Addition of IC25 dose of docetaxel or nab-paclitaxel decreased gemcitabine IC50. Net tumor growth inhibition after gemcitabine, docetaxel or nab-paclitaxel was 67, 31 and 72%, which corresponded with intratumoral proliferative and apoptotic indices. Tumor stromal density was decreased by nab-paclitaxel and to a lesser extent by docetaxel as measured through reduction in α-smooth muscle actin, S100A4 and collagen 1 expression. Animal survival was prolonged after nab-paclitaxel treatment (41 days, P < 0.002) compared with gemcitabine (32 days, P = 0.005), docetaxel (32 days, P = 0.005) and controls (20 days). Survival in nab-paclitaxel/gemcitabine and docetaxel/gemcitabine sequential treatment groups was not superior to nab-paclitaxel alone. Low-dose combination of gemcitabine with nab-paclitaxel or docetaxel was more effective compared with controls or gemcitabine alone but not superior to regular dose nab-paclitaxel alone. Combination treatment of gemcitabine+nab-paclitaxel or gemcitabine+docetaxel increased gemcitabine concentration in plasma and tumor. The superior antitumor activity of nab-paclitaxel provides a strong rationale for considering nab-paclitaxel as first-line monotherapy in pancreatic ductal adenocarcinoma.