Tumor vascular targeting with tumor necrosis factor alpha and chemotherapeutic drugs.

The poor selectivity of chemotherapeutic drugs for neoplastic cells may lead to dose-limiting side effects that compromise clinical outcomes. Moreover, heterogeneous tumor perfusion and vascular permeability, and increased interstitial pressure, could represent critical barriers that limit the penetration of drugs into neoplastic cells distant from tumor vessels and, consequently, the effectiveness of chemotherapy. We have recently developed two strategies for increasing the local concentration of chemotherapeutic drugs in tumors and their therapeutic index, based on tumor vascular targeting. First, we have found that vascular targeting with minute amounts of tumor necrosis factor alpha (TNF-alpha), an inflammatory cytokine able to increase vascular permeability, alters tumor barriers and increases the penetration of chemotherapeutic drugs in subcutaneous tumors in mouse models. Targeted delivery of TNF-alpha to tumor vessels was achieved by coupling this cytokine with cyclic CNGRC peptide, an aminopeptidase N (CD13) ligand that targets the tumor neovasculature. Second, we have observed that encapsulation of doxorubicin into liposomes able to home to tumor vessels markedly improves drug uptake by neuroblastoma tumors, in an orthotopic xenograft model, and its therapeutic index. Targeted delivery of liposomes was achieved by coupling linear GNGRG peptide to the surface of liposomal doxorubicin. Vascular targeting, either indirectly with NGR-TNF-alpha or directly with NGR-targeted liposomes, could be a novel strategy for increasing the therapeutic index of chemotherapeutic drugs.