Synergistic antitumor activity of histamine plus melphalan in isolated limb perfusion: Preclinical studies

Background: We have previously shown how tumor response of isolated limb perfusion (ILP) with melphalan was improved when tumor necrosis factor alpha (TNF-α) was added. Taking into account that other vasoactive drugs could also improve tumor response to ILP, we evaluated histamine (Hi) as an alternative to TNF-α. Methods: We used a rat ILP model to assess the combined effects of Hi and melphalan (n = 6) on tumor regression, melphalan uptake (n = 6), and tissue histology (n = 2) compared with Hi or melphalan alone. We also evaluated the growth of BN-175 tumor cells as well as apoptosis, necrosis, cell morphology, and paracellular permeability of human umbilical vein endothelial cells (HUVECs) after Hi treatment alone and in combination with melphalan. Results: The antitumor effect of the combination of Hi and melphalan in vivo was synergistic, and Hi-dependent reduction in tumor volume was blocked by H₁ and H₂ receptor inhibitors. Tumor regression was observed in 66% of the animals treated with Hi and melphalan, compared with 17% after treatment with Hi or melphalan alone. Tumor melphalan uptake increased and vascular integrity in the surrounding tissue was reduced after ILP treatment with Hi and melphalan compared with melphalan alone. In vitro results paralleled in vivo results. BN-175 tumor cells were more sensitive to the cytotoxicity of combined treatment than HUVECs, and Hi treatment increased the permeability of HUVECs. Conclusions: Hi in combination with melphalan in ILP improved response to that of melphalan alone through direct and indirect mechanisms. These results warrant further evaluation in the clinical ILP setting and, importantly, in organ perfusion.