A strategy for selective anti-cancer drug concentration increase in rat glioma tissue with Ca²⁺-channel blocker co-administration: calcium kinetics in intra-glioma arteriolar smooth muscle cells

Summary

A rat glioma model was employed to estimate the Ca²⁺ kinetics in the tumor arteriolar smooth muscle cells. Electron microcytochemistry revealed that the density of intracellular Ca²⁺ deposits in the intra-tumor arteriolar smooth muscle cells was significantly greater, with slightly higher membrane Ca²⁺-adenosine triphosphatase (ATPase) activity, compared to the contralateral cerebral arterioles. Furthermore, the administration of tyrphostin, a tyrosine kinase inhibitor, specifically increased only the intra-tumor blood flow. These findings suggest that the condition of the intra-tumor arteriole alters the susceptibility to contraction by the accelerated Ca²⁺ influx into the cytoplasm mediated through the tyrosine kinase pathway. After the administration of diltiazem, which also has a blocking effect on the Ca²⁺-channel mediated through this pathway, the local intra-tumor blood flow showed an increase of 39% with a marked decrease of intracellular Ca²⁺ concentration of the arteriolar smooth muscle cells in the tumor, while the blood flow in the basal ganglia increased by only 8%. The intra-tumor concentration of Nimustine-HCI (ACNU) with co-administration of diltiazem was significantly increased compared to that without the co-administration. Co-administration of diltiazem may be a valuable strategy in chemotherapy for glioma in affording the selective increase of intra-tumor concentration of the anti-cancer drug.