VPAC receptor mediated tumor cell targeting by protamine based nanoparticles.

The receptors for vasoactive intestinal peptide (VIP), VPAC1-, VPAC2-, and PAC1-receptor are overexpressed by various tumor cells. VIP can target these receptors and transport conjugates into the cell. However, the use of VIP for tumor cell targeting is hampered by the peptides short half-lives due to enzymatic degradation. Because protamine-based nanoparticles (proticles) protect the peptide and serve as peptide depot, we explored the potential of proticles as carrier for VIP-conjugated molecules. The VIP-loaded proticles were stable as shown by Fluorescence Correlation Spectroscopy. With Confocal Laser Scanning Microscopy, we observed VIP-loaded proticles to specifically target the tumor cells. The cell binding triggered the substance release and conjugate internalization of VIP-Cy3 in vitro and ex vivo by human tumors. We observed VIP releasing proticle depots distributed in rat tissue and human tumors. Our findings warrant further studies to explore the proticles potential to enable peptide-mediated targeting for in vivo and clinical applications.

Depot formulation of vasoactive intestinal peptide by protamine-based biodegradable nanoparticles.

Drug delivery of protein and peptide-based drugs, which represent a growing and important therapeutic class, is hampered by these drugs' very short half-lives. High susceptibility towards enzymatic degradation necessitates frequent drug administration followed by poor adherence to therapy. Among these drugs is vasoactive intestinal peptide (VIP), a potent systemic and pulmonary vasodilator, which is a promising drug for the treatment of idiopathic pulmonary arterial hypertension (IPAH). Encapsulation of VIP into the nanoparticle matrix of biodegradable protamine-oligonucleotide nanoparticles (proticles) protects the peptide against rapid enzymatic degradation. Additionally, the nanoparticle matrix will be able to sustain drug release. Proticles consist of 18mer non-sense oligonucleotides and protamine, a polycationic arginine-rich peptide. VIP encapsulation occurs during self-assembly of the components. Within the present study, we evaluate nanoparticle size (hydrodynamic diameter) and zeta potential of VIP-loaded proticles as well as encapsulation efficiency and VIP release. Further, the pharmacological VIP response of "encapsulated VIP" is investigated using an ex vivo lung arterial model system. We found satisfying encapsulation efficiency (up to 80%), VIP release (77-87%), and an appropriate nanoparticle size (177-251 nm). Investigations on rat pulmonary arteries showed a modified VIP response of proticle-associated VIP. We noted differences in the profile of artery relaxation where VIP proticles lead to a 20-30% lower relaxation maximum than aqueous VIP solutions followed by prolonged vasodilatation. Our data indicate that proticles could be a feasible drug delivery system for a pulmonary VIP depot formulation.

Inhalable liposomal formulation for vasoactive intestinal peptide.

Inhalation of vasoactive intestinal peptide (VIP) was suggested as promising treatment option of various lung diseases like asthma and pulmonary hypertension. However, the medical use of peptides is limited by their short half-life due to rapid enzymatic degradation in the airways. For that reason, we recently developed unilamellar nano-sized VIP-loaded liposomes (VLL). Now we investigated their applicability for inhalation purposes. After nebulisation by a mouthpiece ventilation inhaler we found the particle size almost unaffected, being in a size range appropriate for bronchiolar deposition; we observed no peptide release due to nebulisation. The VIP release kinetics from VLL were tested by an ex vivo vasorelaxation model. Exposure to target organs revealed an immediate response, which was significantly retarded for VLL as compared to free VIP (p=0.001). Using vasorelaxation as endpoint, we observed a sustained release and an extended pharmacological effect compared to equimolar free VIP. The liposomes have the potential to improve VIP inhalation therapy by providing a "dispersible peptide depot" in the bronchi. Thereby, the release of VIP from liposomes may be triggered by exposure to cells, i.e. directly by ligand-receptor interactions.