Improved Drug Delivery to Brain Metastases by Peptide-Mediated Permeabilization of the Blood-Brain Barrier.

Patients with melanoma have a high risk of developing brain metastasis, which is associated with a dismal prognosis. During early stages of metastasis development, the blood-brain barrier (BBB) is likely intact, which inhibits sufficient drug delivery into the metastatic lesions. We investigated the ability of the peptide, K16ApoE, to permeabilize the BBB for improved treatment with targeted therapies preclinically. Dynamic contrast enhanced MRI (DCE-MRI) was carried out on NOD/SCID mice to study the therapeutic window of peptide-mediated BBB permeabilization. Further, both in vivo and in vitro assays were used to determine K16ApoE toxicity and to obtain mechanistic insight into its action on the BBB. The therapeutic impact of K16ApoE on metastases was evaluated combined with the mitogen-activated protein kinase pathway inhibitor dabrafenib, targeting BRAF mutated melanoma cells, which is otherwise known not to cross the intact BBB. Our results from the DCE-MRI experiments showed effective K16ApoE-mediated BBB permeabilization lasting for up to 1 hour. Mechanistic studies showed a dose-dependent effect of K16ApoE caused by induction of endocytosis. At concentrations above IC50, the peptide additionally showed nonspecific disturbances on plasma membranes. Combined treatment with K16ApoE and dabrafenib reduced the brain metastatic burden in mice and increased animal survival, and PET/CT showed that the peptide also facilitated the delivery of compounds with molecular weights as large as 150 kDa into the brain. To conclude, we demonstrate a transient permeabilization of the BBB, caused by K16ApoE, that facilitates enhanced drug delivery into the brain. This improves the efficacy of drugs that otherwise do not cross the intact BBB.

Integrin αV ß3 can substitute for collagen-binding ß1 -integrins in vivo to maintain a homeostatic interstitial fluid pressure.

NEW FINDINGS: What is the central question of this study? Collagen-binding ß1 -integrins function physiologically in cellular control of dermal interstitial fluid pressure (PIF ) in vivo and thereby participate in control of extravascular fluid volume. During anaphylaxis, simulated by injection of compound 48/80, integrin αV ß3 takes over this physiological function. Here we addressed the question whether integrin αV ß3 can replace collagen-binding ß1 -integrin to maintain a long-term homeostatic PIF . What is the main finding and its importance? Mice lacking the collagen-binding integrin α11 ß1 show a complex dermal phenotype with regard to the interstitial physiology apparent in the control of PIF . Notably dermal PIF is not lowered with compound 48/80 in these animals. Our present data imply that integrin αV ß3 is the likely candidate that has taken over the role of collagen-binding ß1 -integrins for maintaining a steady-state homeostatic PIF . A better understanding of molecular processes involved in control of PIF is instrumental for establishing novel treatment regimens for control of oedema formation in anaphylaxis and septic shock. ABSTRACT: Accumulated data indicate that cell-mediated contraction of reconstituted collagenous gels in vitro can serve as a model for cell-mediated control of interstitial fluid pressure (PIF ) in vivo. A central role for collagen-binding ß1 -integrins in both processes has been established. Furthermore, integrin αV ß3 takes over the role of collagen-binding ß1 -integrins in mediating contraction after perturbations of collagen-binding ß1 -integrins in vitro. Integrin αV ß3 is also instrumental for normalization of dermal PIF that has been lowered due to mast cell degranulation with compound 48/80 (C48/80) in vivo. Here we demonstrate a role of integrin αV ß3 in maintaining a long term homeostatic dermal PIF in mice lacking the collagen-binding integrin  α11 ß1 (α11-/- mice). Measurements of PIF were performed after circulatory arrest. Furthermore, cell-mediated integrin αV ß3 -directed contraction of collagenous gels in vitro depends on free access to a collagen site known to bind several extracellular matrix (ECM) proteins that form substrates for αV ß3 -directed cell attachment, such as fibronectin and fibrin. A streptococcal collagen-binding protein, CNE, specifically binds to and blocks this site on the collagen triple helix. Here we show that whereas CNE perturbed αV ß3 -directed and platelet-derived growth factor BB-induced normalization of dermal PIF after C48/80, it did not affect αV ß3 -dependent maintenance of a homeostatic dermal PIF . These data imply that dynamic modification of the ECM structure is needed during acute patho-physiological modulations of PIF but not for long-term maintenance of a homeostatic PIF . Our data thus show that collagen-binding ß1 -integrins, integrin αV ß3 and ECM structure are potential targets for novel therapy aimed at modulating oedema formation and hypovolemic shock during anaphylaxis.