Abstract 251: Aptamer conjugated prostate specific membrane antigen (PSMA) targeting EGCG nanobioconjugate for prostate cancer prevention and treatment

Earlier 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 green tea polyphenol, (-)-epigallocatechin-3-gallate (EGCG) for prostate cancer (PCa) therapy. Here we employed the idea of targeted uptake of therapeutic nanoparticles, a potentially powerful technology. Using PCa as a model, we report the efficacy of EGCG encapsulated in chitosan nanoparticles surface functionalized with the A10 2′-fluoropyrimidine RNA aptamers that recognize the extracellular domain of the prostate-specific membrane antigen (PSMA), henceforth called chit-EGCG-Apt. Prepared bioconjugates were spherical in shape with a unimodal size distribution, with diameter around 200 nm and a zeta potential of -30 mV. Cellular binding and uptake of the fluorescent nanosystem was detected suggesting PSMA specific internalization and accumulation. Next, we determined the EGCG release kinetics and observed a sustained and constant release of EGCG from the nanobioconjugates. To test the biological efficacy, we first determined the efficacy of chit-EGCG-Apt for its cytotoxic response in several human prostate carcinoma cells. We observed that chit-EGCG-Apt lead to an increased anti-proliferative activity in PCa cells, with a better efficacy in PSMA positive cells (LNCaP and C4-2) than in PSMA negative PC3 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. Our next goal was to ascertain if EGCG in chit-EGCG-Apt retains its mechanistic identity. Chit-EGCG-Apt treatment (10 and 20 μM) to LNCaP cells 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 DR4, DR5, TNFR1, FADD, TRADD death receptor pathway proteins, (v) increase in the levels of annexin V positive cells, (vi) increase in TdT positive cells (additional information to suggest induction of apoptosis), and (vii) modulation of p21, p27, CDK 4 and 6 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 40 μM of the native EGCG. The nanobioconjugate also demonstrated a significant inhibition of invasive potential of several PCa cells in scratch wound assay and 3-dimensional spheroid BME cell invasion assay. 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, Minakshi Nihal, Vaqar M. Adhami, Rahime Jashari, Shaker A. Mousa, Hasan Mukhtar. Aptamer conjugated prostate specific membrane antigen (PSMA) targeting EGCG nanobioconjugate for prostate cancer prevention and treatment. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 251. doi:10.1158/1538-7445.AM2014-251