Biodistribution of Self-Assembling Polymer-Gemcitabine Conjugate after Systemic Administration into Orthotopic Pancreatic Tumor Bearing Mice

Abstract

Therapeutic efficacy of gemcitabine (GEM) is severely limited due to its rapid metabolism by enzymatic deamination in vivo. We recently determined its therapeutic efficacy before (F-GEM) and after conjugation to poly(ethylene glycol)-block-poly(2-methyl-2-carboxyl-propylene carbonate) (mPEG-b-PCC-g-GEM-g-DC, abbreviated as P-GEM) in subcutaneous and orthotopic pancreatic tumor bearing mice. In this study, pharmacokinetic (PK) parameters and biodistribution profiles of F-GEM and P-GEM were determined after intravenous injection into orthotopic pancreatic tumor bearing NSG mice. To assess the short-term toxicity, the levels of hematological, hepatic, and renal injury markers were measured after 24 h postadministration into these mice. P-GEM was distributed to all the major organs, with higher accumulation in the liver, spleen, and tumor compared to F-GEM. Area under the curve (AUC), elimination half-life (t_1/2), and mean residence time (MRT) of P-GEM treated group were significantly higher compared to those of F-GEM treated group: 246,425 ± 1605 vs 83,591 ± 1844 ng/mL × h as AUC, 5.77 ± 2.02 vs 1.99 ± 0.09 h as t_1/2, and 4.45 ± 0.15 vs 1.12 ± 0.13 h as MRT. Further, P-GEM exhibited negligible systemic toxicity as evidenced by almost similar alanine aminotransferase (ALT) and aspartate aminotransferase (AST) values for both P-GEM and F-GEM. These results suggest that P-GEM protects GEM from degradation and provides sustained drug release, resulting in enhanced GEM delivery to the tumor by more than 2.5-fold compared to F-GEM. Hence, P-GEM is a promising gemcitabine conjugated polymeric micelle for treating pancreatic cancer.

Keywords: biodistribution; gemcitabine; pancreatic cancer; pharmacokinetics; polymeric micelles.

Figure 1

(a) Luciferase expression from orthotopic pancreatic tumors after imaging of pancreas in NSG mice. Each mouse received ∼2 million MIA PaCa-2 cells. (b) Tumor morphology.

Figure 2

Plasma concentration/of gemcitabine after single injection of free and polymer conjugated gemcitabine (F-GEM and P-GEM) in the tail vein of NSG mice at GEM equivalent dose of 40 mg/kg. Results are represented as the mean ± SD of four mice.

Figure 3

Plasma dFdU concentration after single injection of free and polymer conjugated gemcitabine (F-GEM and P-GEM) in the tail vein of NSG mice at GEM equivalent dose of 40 mg/kg. The values are the mean ± SD of four mice.

Figure 4

Ratio of the plasma concentration of dFdU to gemcitabine (GEM) in mice after single injection of free and polymer conjugated gemcitabine (F-GEM and P-GEM) in the tail vein of NSG mice at GEM equivalent dose of 40 mg/kg.

Figure 5

Tissue accumulation of free and polymer conjugated gemcitabine (F-GEM and P-GEM) after injection into the tail vein of NSG mice at a dose of 40 mg/kg GEM equivalent dose. Results are presented as the mean ± SD of four mice.

Figure 6

Gemcitabine concentration in major organs after single injection of free and polymer conjugated gemcitabine (F-GEM and P-GEM) at GEM equivalent dose of 40 mg/kg. Results are represented as the mean ± SD of four mice.