TVT-Dox: In vivo efficacy and in vitro molecular mechanism of action Free

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Among the various new targeting ligands identified in cancer therapy, peptides containing the NGR (asparagine-glycine-arginine) motif have been shown to home inside tumors via binding to aminopeptidase N (CD13). Tumor vasculature is shown to specifically express an isoform of CD13 and therefore offers an opportunity to target NGR-peptide linked therapeutic reagents. In the present study, we investigated the anti-tumor activity of NGR targeted liposomal doxorubicin (TVT-Dox) in a human PC-3 prostate cancer xenograft mouse model and in syngeneic B16F1 murine melanoma model. To understand the molecular mechanism of this promising drug candidate, we investigated cell binding, kinetics of drug internalization as well as cytotoxicity of TVT-Dox in vitro.

For in vivo studies, human PC-3 and murine B16F1 melanoma cells were inoculated via S.C route into CD1 nu/nu and C57BL6 mice respectively. TVT-Dox (1, 3 and 6 mg/kg) was administered via i.v route once a week and tumor volumes were measured at timed intervals. We observed a significant dose dependent tumor growth inhibition in both models following treatment with TVT-Dox.

For in vitro studies, various cell lines (HUVEC, SLK, HT-1080 and HT-29) were screened for their expression of CD13 by immunohistochemistry. We observed that TVT-Dox specifically bound to CD13 expressing cells whereas non-targeted liposomal Doxorubicin did not. TVT-Dox was then internalized through the endosomal pathway which eventually led to Doxorubicin localization in the cell nuclei. An in vitro cytotoxicity assay with CD13 positive HUVECs and CD13 negative HT-29 was carried out to evaluate the advantages of the NGR targeting versus the non-targeted liposomal formulation of Doxorubicin. Our results indicated that NGR targeting increased drug cytotoxicity in CD13 positive cells, but not in CD13 negative cells.Results from these studies suggest that targeted delivery of Doxorubicin via NGR-liposomes may substantially improve the therapeutic index due to increased drug accumulation in the tumor and minimize side effects associated with this chemotherapeutic agent.