Bendamustine–PAMAM Conjugates for Improved Apoptosis, Efficacy, and in Vivo Pharmacokinetics: A Sustainable Delivery Tactic

Abstract

Successful delivery of a chemotherapeutic agent like bendamustine still remains a challenge in clinical conditions like chronic lymphatic leukemia (CLL), non-Hodgkin lymphoma (NHL), and multiple myeloma. We have conjugated bendamustine to polyamidoamine (PAMAM) dendrimers after conjugating with N-(hydroxyethyl)maleimide (spacer) via an ester bond. The particle size of PAMAM-bendamustine conjugate was 49.8 ± 2.5 nm. In vitro drug release resulted in sustained release with improved solution stability of drug up to 72 h. In a 24 h cytotoxicity study by MTT assay against human monoblastic leukemia cells (THP-1), the IC50 value for PAMAM-bendamustine was 32.1 ± 4.8 μM compared to 50.42 ± 3.4 μM and 2303 ± 106.5 μM for bendamustine and PAMAM dendrimer, respectively. Significantly higher cell uptake and apoptosis were observed in THP-1 cells by PAMAM-bendamustine conjugate which was confirmed by flow cytometry and confocal laser scanning microscopy. Preliminary in vivo studies undertaken included pharmacokinetics studies, organ distribution studies, and tumor inhibition studies. In healthy Wistar rat model (1CBM IV push model), the pharmacokinetic studies revealed that bioavailability and t1/2 increased significantly, i.e., almost 8.5-fold (193.8 ± 1.116 vs 22.8 ± 0.158 μg mL-1/h) and 5.1-fold (0.75 ± 0.005 vs 3.85 ± 0.015 h), respectively, for PAMAM-bendamustine conjugate compared to pure bendamustine ( p < 0.05), however, clearance and volume of distribution were found to be decreased compared to those of free drug. The study suggests that PAMAM-bendamustine conjugate was not only stable for the longer period but also least toxic and highly taken up by THP-1 cells to exert an anticancer effect at the reduced dose. Tumor inhibition and biodistribution studies in tumor-bearing BALB/c mice revealed that PAMAM-bendamustine conjugate was more effective than the pure drug and showed higher accumulation in the tumor.