The host defense derived
peptide was assessed in different model systems with increasing complexity employing the highly aggressive NRAS mutated
melanoma metastases cell line MUG-Mel2. Amongst others, fluorescence microscopy and spectroscopy, as well as cell death studies were applied for liposomal, 2D and 3D in vitro models including
tumor spheroids without or within skin models and in vivo mouse xenografts. Summarized, MUG-Mel2 cells were shown to significantly expose the negatively charged
lipid phosphatidylserine on their plasma membranes, showing they are successfully targeted by RDP22. The
peptide was able to induce cell death in MUG-Mel2 2D and 3D cultures, where it was able to kill
tumor cells even inside the core of
tumor spheroids or inside a
melanoma organotypic model. In vitro studies indicated cell death by apoptosis upon
peptide treatment with an LC50 of 8.5 µM and seven-fold specificity for the
melanoma cell line MUG-Mel2 over normal dermal fibroblasts. In vivo studies in mice xenografts revealed effective
tumor regression upon intratumoral
peptide injection, indicated by the strong clearance of pigmented
tumor cells and tremendous reduction in
tumor size and proliferation, which was determined histologically. The
peptide RDP22 has clearly shown high potential against the
melanoma cell line MUG-Mel2 in vitro and in vivo.