Amanda K. Pearce

Development of a polymer theranostic for prostate cancer

Theranostics offers an improved treatment strategy for prostate cancer by facilitating simultaneous targeting of tumour cells with subsequent drug delivery and imaging. In this report we describe the synthesis of hyperbranched polymers that are biocompatible, can specifically target and be internalised by prostate cancer cells (through targeting of prostate-specific membrane antigen – PSMA) and ultimately facilitate controlled delivery of a model drug. The theranostic also incorporates a far-red fluorescent dye that allows tracking of the polymer via optical imaging. Controlled synthesis of the polymer is achieved via reversible addition fragmentation chain transfer polymerisation of polyethylene glycol monomethyl methacrylate, with ethylene glycol dimethacrylate as the branching agent. Incorporation of 20 mol% of an hydrazide-methacrylate monomer allows post-ligation of a model drug, fluorene-2-carboxaldehyde, through a hydrolytically-degradable hydrazone linkage. The rate of degradation of this particular linker was enhanced at endosomal pH (pH = 5.5) where [similar]95% of the model drug was released in 4 hours compared to less than 5% released over the same period at physiological pH. The theranostic showed high uptake into prostate cancer cells expressing prostate-specific membrane antigen, while minimal uptake was observed in PC3 cells negative for PSMA, highlighting the enhanced efficacy of the targeting ligand.

Evaluation of Polymeric Nanomedicines Targeted to PSMA: Effect of Ligand on Targeting Efficiency

Targeted nanomedicines offer a strategy for greatly enhancing accumulation of a therapeutic within a specific tissue in animals. In this study, we report on the comparative targeting efficiency toward prostate-specific membrane antigen (PSMA) of a number of different ligands that are covalently attached by the same chemistry to a polymeric nanocarrier. The targeting ligands included a small molecule (glutamate urea), a peptide ligand, and a monoclonal antibody (J591). A hyperbranched polymer (HBP) was utilized as the nanocarrier and contained a fluorophore for tracking/analysis, whereas the pendant functional chain-ends provided a handle for ligand conjugation. Targeting efficiency of each ligand was assessed in vitro using flow cytometry and confocal microscopy to compare degree of binding and internalization of the HBPs by human prostate cancer (PCa) cell lines with different PSMA expression status (PC3-PIP (PSMA+) and PC3-FLU (PSMA-). The peptide ligand was further investigated in vivo, in which BALB/c nude mice bearing subcutaneous PC3-PIP and PC3-FLU PCa tumors were injected intravenously with the HBP-peptide conjugate and assessed by fluorescence imaging. Enhanced accumulation in the tumor tissue of PC3-PIP compared to PC3-FLU highlighted the applicability of this system as a future imaging and therapeutic delivery vehicle.

Targeting Nanomedicines to Prostate Cancer: Evaluation of Specificity of Ligands to Two Different Receptors In Vivo

PurposeThis manuscript utilised in vivo multispectral imaging to demonstrate the efficacy of two different nanomedicine formulations for targeting prostate cancer.MethodsPegylated hyperbranched polymers were labelled with fluorescent markers and targeting ligands against two different prostate cancer markers; prostate specific membrane antigen (PSMA) and the protein kinase, EphrinA2 receptor (EphA2). The PSMA targeted nanomedicine utilised a small molecule glutamate urea inhibitor of the protein, while the EphA2 targeted nanomedicine was conjugated to a single-chain variable fragment based on the antibody 4B3 that has shown high affinity to the receptor.ResultsHyperbranched polymers were synthesised bearing the different targeting ligands. In the case of the EphA2-targeting nanomedicine, significant in vitro uptake was observed in PC3 prostate cancer cells that overexpress the receptor, while low uptake was observed in LNCaP cells (that have minimal expression of this receptor). Conversely, the PSMA-targeted nanomedicine showed high uptake in LNCaP cells, with only minor uptake in the PC3 cells. In a dual-tumour xenograft mouse model, the nanomedicines showed high uptake in tumours in which the receptor was overexpressed, with only minimal non-specific accumulation in the low-expression tumours.ConclusionsThis work highlighted the importance of clearly defining the target of interest in next-generation nanomedicines, and suggests that dual-targeting in such nanomedicines may be a means to achieve greater efficacy.