Abstract 4345: PSMA-targeted theranostic nanoplex combining TRAIL gene cDNA and prodrug enzyme delivery for prostate cancer treatment.
Authors: Chen Zhihang , Penet Marie-France Penet , Krishnamachary Balaji , Li Cong , Winnard Paul T. , Pomper Martin G. , Bhujwalla Zaver M. 
Published: August 2014

Abstract
Prostate cancer (PCa) is the second leading cause of death from cancer in men in the U.S, and there is a compelling need for the development of effective treatments for metastatic PCa. Theranostic approaches that combine detection with treatment hold significant promise for cancer-cell-specific treatments especially with molecular reagents such as cDNA or siRNA that can increase or decrease the expression of genes of interest. We have reported on a prostrate specific membrane antigen (PSMA)-based platform to deliver a prodrug enzyme and small interfering RNA (siRNA) to downregulate gene expression for theranostic imaging of metastatic PCa[1]. Here we expanded this platform for gene delivery and expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) cDNA. PSMA, which is highly expressed by castration-resistant PCa, was used for PCa-specific delivery and localization of the nanoplex that delivered TRAIL cDNA and a prodrug enzyme, bacterial cytosine deaminase (bCD). TRAIL has been reported to specifically kill malignant cells but to be relatively nontoxic to normal cells. The GFP-TRAIL cDNA used expresses a GFP-TRAIL fusion protein that can be detected with optical imaging to evaluate cDNA expression. The prodrug enzyme bCD converts the non-toxic prodrug 5-fluorocytosine (5-FC) to the active cytotoxic drug 5-fluorouracil (5-FU) that can be monitored by 19F MRS. Our prototype nanoplex was synthesized by conjugating: (i) a low molecular weight urea-based PSMA targeting moiety (2-(3-[1-carboxy-5-[7-(2,5-dioxo-pyrrolidin-1-yloxycarbonyl)-heptanoylamino]-pentyl]-ureido)-pentanedioic acid, (ii) the prodrug-activating enzyme bCD that converts nontoxic 5-FC to cytotoxic 5-FU, (iii) the near-infrared fluorescent probe Cy5.5 labeled linker poly-L-lysine (PLL), and (iv) the GFP-TRAIL pDNA delivery vector: PEI (polyethyleneimine)-PEG (polythethyeneglycol) co-grafted-polymer. Imaging studies with PSMA targeted nanoplexes were performed with PC-3 human prostate cancer cells genetically engineered to overexpress PSMA (PC3-PIP); non-PSMA expressing PC-3 cells (PC3-Flu) were used as controls. Cell imaging studies indicated higher expression of GFP-TRAIL fusion protein in PC3-PIP cells. In vivo images obtained from PIP and Flu tumors demonstrated increased accumulation of the nanoplex in PIP tumors. In ex vivo imaging studies, increased uptake of the nanoplex as detected by Cy5.5 fluorescence, and higher expression of GFP in PIP compared to Flu tumors was observed. 19F MRS indicated the prodrug enzyme bCD efficiently converted the prodrug 5-FC to 5-FU at 24 h. Tumor growth studies showed increased inhibition of PIP tumor growth. Collectively, these data demonstrate the ability to express a gene of interest using a theranostic nanoplex specifically targeting cancer cells.
Citation Format: Zhihang Chen, Marie-France Penet Penet, Balaji Krishnamachary, Cong Li, Paul T. Winnard, Martin G. Pomper, Zaver M. Bhujwalla. PSMA-targeted theranostic nanoplex combining TRAIL gene cDNA and prodrug enzyme delivery for prostate cancer treatment. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4345. doi:10.1158/1538-7445.AM2013-4345