Chemotherapeutic agent permeability to normal brain and delivery to avian sarcoma virus-induced brain tumors in the rodent: Observations on problems of drug delivery

Four chemotherapeutic agents (cyclophosphamide, 5-fluorouracil (5-FU), methotrexate (MTX), and bleomycin) were given intravenously to rats harboring the avian sarcoma virus-induced glioma. Drug content in brain, tumor, and systemic tissue was measured. The uptake of drug and the consistency of drug levels in normal brain and tumor varied widely among these agents. [¹⁴C]Cyclophosphamide and its metabolites penetrated normal brain and, to a greater extent, brain tumor. [¹⁴C]5-FU and its metabolites also entered normal brain and brain tumor, but to a lesser extrent than [¹⁴C]cyclophosphamide and its metabolites. Immunoreactive MTX entry into tumor was variable, ranging from 30 to 1080 ng/g of tissue, with only minimal concentrations in normal brain. After conventional doses, immunoreactive bleomycin levels in tumor were also variable, ranging from 24 to 164 μunits/g of tissue, and little if any drug entered surrounding brain. In addition, the cerebrovascular permeability of 5-FU and MTX in normal rats was measured. Utilizing the method of Rapoport, the PA (product of permeability and capillary surface area) of 5-FU was found to be 6- to 12-fold greater than that of MTX. The PA of both drugs was increased 4- to 7-fold after osmotic blood-brain barrier opening. The variable 'leakiness' of glial tumors, both experimentally and clinically, as well as the varied permeabilities of different water-soluble chemotherapeutic agents, makes the drug delivery problem in brain tumors a very complex issue.