Abstract 5263: Prostate-specific membrane antigen (PSMA)-targeting nanobioconjugate-encapsulated green tea polyphenol EGCG for prostate cancer prevention and therapy

Initially we introduced the idea of employing nanotechnology to improve the outcome of natural agents in chemoprevention and coined the term ‘Nanochemoprevention’. Recently we reported the efficacy of chitosan nanoparticles encapsulating (-)-epigallocatechin-3-gallate (EGCG) for prostate cancer (PCa) prevention and therapy. Here we employed the concept of targeted uptake of therapeutic nanoparticles, a potentially powerful technology to enhance the efficacy of EGCG for PCa management. We developed chitosan nanobioconjugates encapsulating EGCG and surface functionalized with the A10 2′-fluoropyrimidine RNA aptamers that recognize the extracellular domain of the PSMA, henceforth called chit-EGCG-Apt. Cellular binding and uptake of the fluorescent nanosystem was detected suggesting PSMA specific internalization and accumulation. Further, we observed that chit-EGCG-Apt lead to a PSMA specific increase of anti-proliferative activity in PCa cells, with a better efficacy in PSMA positive cells (LNCaP and C4-2) than in PSMA negative (PC3 and DU145) cells and a decrease in IC50 by at least half the dose of the native agent. Further, we also observed a significant inhibition in the colony formation potency of PCa cells when treated with chit-EGCG-Apt as compared to the native EGCG with the effects more distinct in PSMA positive cells. Next, we established that EGCG in chit-EGCG-Apt retains its mechanistic identity and observed that the treatment resulted in significant (i) shift in Bax/Bcl-2 ratio in favor of apoptosis, (ii) increase in PARP cleavage, (iii) inhibition in caspase 3, 7, 8 and 9, and other key regulators of apoptosis, (iv) modulation of death receptor pathway proteins, and (v) cyclin dependent kinase inhibitors in addition to arrest of the cells in S phase of the cell cycle. Importantly, these effects were only visible at higher doses of the native EGCG. The nanobioconjugate also demonstrated a significant inhibition of invasive potential of several PCa cells and 3-dimensional spheroid BME cell invasion assay. Further, chit-EGCG-Apt treated mice implanted with androgen sensitive CWR22R(nu)1 cells showed significant inhibition in tumor growth and decreased serum PSA levels reciprocating our in vitro findings. In tumor tissues of mice treated with Chit-EGCG-Apt there was significant (i) induction of poly (ADP-ribose) polymerases cleavage, (ii) increase in the protein expression of Bax with concomitant decrease in Bcl-2, (iii) activation of caspases, and (iv) reduction in Ki-67 and proliferating cell nuclear antigen, as compared to native EGCG. We further observed inhibition of angiogenesis, invasion and metastasis markers in these tissues. Translation of these data to appropriate animal model systems could pave way for prostate cancer therapy in humans. Citation Format: Imtiaz A. Siddiqui, Dhruba J. Bharali, Rahime Jashari, Vaqar M. Adhami, Shaker A. Mousa, Hasan Mukhtar. Prostate-specific membrane antigen (PSMA)-targeting nanobioconjugate-encapsulated green tea polyphenol EGCG for prostate cancer prevention and therapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5263.