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A number of carborane-containing porphyrins were administered to mice bearing subcutaneously transplanted mammary carcinomas. Administration was via serial intraperitoneal (i.p.) injections to assess their relative toxicities and tumour affinities. Three analogues of the natural porphyrin heme and four tetraphenylporphyrins (TPPs) were given at total doses of 78-245 micrograms g-1 body weight. The water-insoluble TPPs were less toxic to mice, and delivered greater amounts of boron to tumour than did the water-soluble TPPS and the heme analogues. One such compound, NiTCP-H, delivered more than 100 micrograms B g-1 to tumour tissue with a tumour:blood boron concentration ratio greater than 500:1 and a tumour: brain boron concentration ratio greater than 50:1, 4 days after the last of six i.p. injections given over 2 days. Another TPP analogue, NiTCP, delivered approximately 50 micrograms B g-1 to tumour with similar boron concentrations in normal tissues. Neither compound was toxic to mice at total doses of approximately 200 micrograms g-1 body weight. In contrast, the heme analogues were toxic and, with the exception of VCDP, delivered less boron to tumour than NiTCP and NiTCP-H. The two porphyrins with the greatest potential for application to boron neutron capture therapy (BNCT), NiTCP and NiTCP-H, yielded higher tumour:blood and tumour:brain boron concentration ratios in mice than could be achieved with p-boronophenylalanine (BPA) and sodium mercaptoundecahydrododecaborate (BSH), the compounds which are currently being used in clinical trials of BNCT in the treatment of glioblastoma. The boron delivered by each of the porphyrins tested remained in tumour tissue longer than did boron delivered by either BPA or BSH. The copper and nickel chelates of these porphyrins behave identically in vivo. The former offer the potential for imaging by 67Cu-mediated single photon emission computed tomography (SPECT) to aid BNCT treatment planning.

Purpose: Intraperitoneal (IP) injection of the solubilized fructose complex of L-p-boronophenylalanine (BPA-F) produced higher boron concentrations in a rat brain tumor model than was possible using intragastric (IG) administration of L-p-boronophenylalanine (BPA). The effectiveness of IP BPA-F was compared to IG BPA in boron neutron capture therapy irradiations of the 9L rat brain tumor model., Methods and Materials: The time course of boron accumulation in tumor and normal tissues was determined in male F344 rats bearing either SC or intracerebral 9L gliosarcomas following a single IP injection of BPA-F. On day 14 after inoculation of intracranial tumors, rats were irradiated with single doses of either: 250 kVp X rays; the thermal neutron beam of the Brookhaven Medical Research Reactor following IG administration of BPA; or thermal neutrons following IP injection of BPA-F. Magnetic resonance imaging was used to visualize the tumor scars and to assess damage to the normal brain in long-term survivors., Results: 4 h after IP injection of 1200 mg/kg of BPA-F the boron concentrations in tumor, blood, and normal brain were 89.6 +/- 7.6, 27.7 +/- 2.8 and 17.5 +/- 1.5 micrograms 10B/g, respectively. Two IG doses of BPA (750 mg/kg each, 3 h apart) produced 39 +/- 5, 12 +/- 1 and 10 +/- 1 micrograms 10B/g in tumor, blood and brain, respectively at 5 h after the second dose. Three groups of rats were treated with thermal neutrons: one following IG BPA and two groups following IP BPA-F. The total physical absorbed doses to the tumor in the three BNCT groups were 15.5 Gy (IG BPA, n = 12), 17.0 Gy (IP BPA-F, n = 8), and 31.5 Gy (IP BPA-F, n = 8), respectively. The median survival of the untreated controls was 22 days. The median survival of the rats treated with 22.5 Gy of 250 kVp X rays (n = 23) was 35 days with 20% long-term survivors. Fifty percent of the rats in the IG BPA + thermal neutrons group survived over 1 year. All rats in both groups that received IP BPA-F + thermal neutrons have survived over 8 months. Magnetic resonance imaging of the brains of the long-term boron neutron capture therapy survivors showed a scar at the site of tumor implantation in all animals. In the IP BPA-F high-dose group one rat showed evidence of edema and one rat showed a fluid-filled cyst replacing the tumor., Conclusion: The use of IP BPA-F has significantly improved long-term survival compared to IG BPA. The high percentage of long-term tumor control (100%, n = 16) in the intracerebral rat 9L gliosarcoma brain tumor model, together with little or no damage to the surrounding normal brain in the majority of surviving animals, demonstrate the substantial therapeutic gain produced by boron neutron capture therapy.