Plasma Stability and Plasma Metabolite Concentration-Time Profiles of Oligo(Lactic Acid)8-Paclitaxel Prodrug Loaded Polymeric Micelles

Abstract

Paclitaxel (PTX) is a frequently prescribed chemotherapy drug used to treat a wide variety of solid tumors. Oligo(lactic acid)₈-PTX prodrug (o(LA)₈-PTX) loaded poly(ethylene glycol)-b-poly(lactic acid) (PEG-b-PLA) micelles have higher loading, slower release and higher antitumor efficacy in murine tumor models over PTX-loaded PEG-b-PLA micelles. The goal of this work is to study plasma stability of o(LA)₈-PTX-loaded PEG-b-PLA micelles and its pharmacokinetics after IV injection in rats. In rat plasma, o(LA)₈-PTX prodrug is metabolized into o(LA)₁-PTX and PTX. In human plasma, o(LA)₈-PTX is metabolized more slowly into o(LA)₂-PTX, o(LA)₁-PTX, and PTX. After IV injection of 10 mg/kg PTX-equiv of o(LA)₈-PTX prodrug loaded PEG-b-PLA micelles in Sprague-Dawley rats, metabolite abundance in plasma follows the order: o(LA)₁-PTX > o(LA)₂-PTX > o(LA)₄-PTX > o(LA)₆-PTX. Bile metabolite profiles of the o(LA)₈-PTX prodrug is similar to plasma metabolite profiles. In comparison to equivalent doses of Abraxane®, plasma PTX exposure is two orders of magnitude higher for Abraxane® than PTX from o(LA)₈-PTX prodrug loaded PEG-b-PLA micelles, and plasma o(LA)₁-PTX exposure is fivefold higher than PTX from Abraxane®, demonstrating heightened plasma metabolite exposure for enhanced antitumor efficacy.

Keywords: metabolite; paclitaxel; polymeric micelle; prodrug.

Figure 1.

Intensity-averaged (A) and volume-averaged (B) size distributions of o(LA)₈-PTX micelle as measured by DLS. Freeze-dried samples were reconstituted in 1 mL water, then further diluted in water, PBS or NaCl and measured at 25 °C. Traces represent the average of twelve measurements.

Figure 2.

LC chromatogram of o(LA)₈-PTX micelle following incubation in ACN/PBS after 8 hours (A), 24 hours (B) and 96 hours (C). Samples were prepared at 50 μg/mL o(LA)₈-PTX concentration and incubated at 37 °C with gentle agitation. Following injection onto the LC-Orbitrap, metabolites were identified based on m/z values in a positive ESI full scan, then further subjected to MS/MS fragmentation to determine ideal PRM transitions.

Figure 3.

LCMS chromatograms of o(LA)₈-PTX micelle following incubation in human (A) or Sprague Dawley rat (B) plasma after 24 hours. Samples were prepared in the plasma matrices at an o(LA)₈-PTX concentration of 50 μg/mL and analyzed by LC-Orbitrap.

Figure 4.

Average peak area-time profiles in plasma using PRM detection. Sprague Dawley rats were administered a single IV dose of o(LA)₈-PTX micelle at 10 mg PTX-equivalent/kg, and plasma samples were analyzed by LC-Orbitrap using peak area to estimate relative abundance (n = 5; mean ± SD).

Figure 5.

Plasma concentration-time profiles of individual (A) and summed (B) bioactive metabolites of o(LA)₈-PTX micelle versus Abraxane^® (n = 3–5 per group, mean ± SD). Sprague Dawley rats were administered a single 10 mg PTX-equivalent/kg dose of Abraxane^® or o(LA)₈-PTX micelle, and plasma was collected and analyzed by LCMS using electrospray ionization and an Orbitrap analyzer. PTX_d5 was used as an internal standard, and m/z ions were monitored by the PRM transitions determined during the in vitro study.

Figure 6.

Bile concentration-time profiles of the major metabolites in Sprague Dawley rats administered a single IV dose of o(LA)₈-PTX micelle or Abraxane^® (n = 3–5 per group; mean ± SD).

Figure 7.

Average peak area-time profiles of (LA)₈-PTX micelle metabolites in bile of Sprague Dawley rats. Bile samples were analyzed by LC-Orbitrap using peak area to estimate relative abundance (n = 5; mean ± SD).