Therapeutic Liposomes for Prostate Cancer Targeted by Phage Fusion Coat Proteins

Abstract

Cancer diagnosis and treatment is complicated by the molecular similarity of the malignant cells to normal cells. This creates a constant need for the development of probes accurately distinguishing between diseased and healthy cells. I describe here the selection of phage probes for prostate carcinoma cells and further demonstrate the potential of these probes as navigating ligands for therapeutic liposomes. Landscape libraries, our primary tools in the identification of ligands for a variety of targets are defined by their diversity and repertoire. We used two landscape libraries to identify phage probes for PC3 cells. The specificity and selectivity of these probes was demonstrated with cell association assays, fluorescence microscopy and flow cytometry. Landscape phage particles are composed of 4000 units of the major coat protein pVIII with unique membranophilic properties. We hypothesized that once extracted from the phage particle these entities could serve as targeting ligands for liposomes. In a streptavidin based model we were able to demonstrate that streptavidin-specific pVIII units insert into liposomes and invest the same with affinity towards streptavidin. We adopted the same technique to derive PC3-specific phage coat protein units from the previously identified phage probes to be used as targeting ligands for fluorescently-labeled and drug-loaded liposomes. Targeting has been shown to improve the therapeutic efficiency of liposomal drugs. We hypothesized that liposomal therapeutics targeted to PC3 cells via PC3 specific phage coat protein would achieve improved cytotoxic effects as against non-targeted formulations. In fluorescence microscopy and flow cytometry studies we demonstrated that targeted labeled liposomes associated with the target PC3 cells better than the control cells. Further, we demonstrated that grafting of the PC3-specific phage fusion protein units onto DOXIL improves the cytotoxic performance of the liposome encapsulated doxorubicin using in vitro cytotoxicity studies. The identification of landscape phage probes for different carcinomas from landscape phage libraries may provide an impetus for harnessing the same in various diagnostic and therapeutic applications. Further, the simplicity of our approach for the construction of targeted liposomal formulations allows for the creation of a combinatorial system of production of therapeutic liposomes for different types of cancer.