(M1130-03-15) Synergistic Chemotherapy for Prostate Cancer Mediated by Brusatol and Docetaxel-Loaded Nanoparticles: Cell Cycle Arrest and Apoptosis Mechanisms

Purpose: The use of docetaxel in prostate cancer is limited by different resistance mechanisms and toxicity. The combination of docetaxel with brusatol, a multitarget inhibitor known for its potent anticancer activity, in a nanoparticle platform is expected to improve efficacy by targeting diverse tumor subpopulations and producing synergistic antitumor effects. To this end, this study evaluated the co-encapsulation of brusatol and docetaxel in a stealth nanoparticle platform for its cytotoxic potential in cellular models of human prostate cancer.

Methods: The particle size and size distribution of the blank and drug-loaded nanoparticles were determined by dynamic light scattering while the structural morphology of the nanoparticles was analyzed using transmission electron microscopy (TEM). The drug loading and drug release profile of brusatol and docetaxel from the nanoparticles were evaluated by analytical high-performance chromatography. Biological assays carried out include in vitro cytotoxicity assays, cell cycle assays using flow cytometry, evaluation of caspase 3/7 activity, and immunoblotting using LNCaP and PC-3 as cellular models of prostate cancer.

Results: The particle size of the nanoparticles ranges from 182.57 ± 1.90 nm to 201.87 ± 1.40 nm. TEM confirms a core-corona structure consistent with the presence of polyethylene glycol corona on the hydrophobic polylactide-co-glycolide (PLGA) core. Data from drug loading studies reveal that as the feed amount of docetaxel relative to brusatol increased, the percent loading of docetaxel increased. The drug release isotherm show that encapsulated drugs were released over 24 hours. The nanoparticle formulations exhibited concentration and time-dependent toxicity against LNCaP and PC-3 cell lines, and the cytotoxic effects of brusatol and docetaxel were synergistic (combination index < 1). Flow cytometry evaluations show that the mechanisms involved in cancer cell growth inhibition were biphasic cell cycle arrest in the G1 and G2/M phase corresponding to the reported effects of brusatol and docetaxel, respectively, with progression to cell death. In addition, PC-3 cells exhibited increased caspase 3/7 activity compared to LNCaP cells following treatment with the nanoparticle formulation. Lastly, immunoblots reveal that downregulation of survivin protein expression is one of the mechanisms by which brusatol- and docetaxel-loaded nanoparticles sensitize prostate cancer cells to chemotherapy-induced death.

Conclusion: The site-specific delivery of brusatol and docetaxel using a stealth PLGA nanoparticle platform inhibits the progression of prostate cancer cells through cell cycle arrest, caspase activation mechanisms, and other cellular apoptosis mechanisms showing potential to improve the chemo-adjuvant response in the treatment of prostate cancer. The developed nanoparticle platform is suitable for prostate cancer treatment and may be used in cases of docetaxel resistance.

Acknowledgements: We acknowledge financial support 5 SC1 GM131982-03 from the NIGMS, National Institutes of Health to Simeon K. Adesina (Grant #12630547).