[Experimental study in a rat brain tumor by combined treatment with cis-DDP and irradiation]

Convection enhanced delivery of carboplatin in combination with radiotherapy for the treatment of brain tumors

The purpose of this study was to further evaluate the therapeutic efficacy of convection enhanced delivery (CED) of carboplatin in combination with radiotherapy for treatment of the F98 rat glioma. Tumor cells were implanted stereotactically into the brains of syngeneic Fischer rats, and 13 or 17 d. later carboplatin (20 μg/10 μl) was administered by either CED over 30 min or by Alzet osmotic pumps (0.5 μg/μl/h for 168 h.) beginning at 7 d after tumor implantation. Rats were irradiated with a 15 Gy fractionated dose (5 Gy × 3) of 6 MV photons to the whole brain beginning on the day after drug administration. Other groups of rats received either carboplatin or X-irradiation alone. The tumor carboplatin concentration following CED of 20 μg in 10 μl was 10.4 μg/g, which was equal to that observed following i.v. administration of 100 mg/kg b.w. Rats bearing small tumors, treated with carboplatin and X-irradiation, had a mean survival time (MST) of 83.4 d following CED and 111.8 d following pump delivery with 40% of the latter surviving >180 d (i.e. cured) compared to 55.2 d for CED and 77.2 d. for pump delivery of carboplatin alone and 31.8 d and 24.2 d, respectively, for X-irradiated and untreated controls. There was no microscopic evidence of residual tumor in the brains of all long-term survivors. Not surprisingly, rats with large tumors had much shorter MSTs. Only modest increases in MSTs were observed in animals that received either oral administration or CED of temozolomide plus X-irradiation (23.2 d and 29.3 d) compared to X-irradiation alone. The present survival data, and those previously reported by us, are among the best ever obtained with the F98 glioma model. Initially, they could provide a platform for a Phase I clinical trial to evaluate the safety and potential therapeutic efficacy of CED of carboplatin in patients with recurrent glioblastomas, and ultimately a Phase II trial of carboplatin in combination with radiation therapy.

Cure of Fisher Rats Bearing Radioresistant F98 Glioma Treated with cis-Platinum and Irradiated with Monochromatic Synchrotron X-Rays

High-grade gliomas are usually of poor prognosis, and conventional radiotherapy, even combined with chemotherapy, still fails to improve the survival of patients. Here, we propose an innovative therapeutic approach combining synchrotron radiation with cis-diamminedichloroplatinum (II) (CDDP). As suggested previously, monochromatic synchrotron irradiation of CDDP at 78.8 keV, just above the 78.4 keV platinum absorption K-edge, leads to an enhanced photoelectric effect and an increased local toxicity. To select a particular radiation energy that could provide supra-additive effect, we used pulsed-field gel electrophoresis to assess yields of DNA double-strand breaks induced in rat F98 glioma cells after CDDP treatment combined with synchrotron X-rays. Thereafter, intracerebral CDDP injection combined with synchrotron X-rays was applied to Fisher rats bearing F98 glioma. CDDP concentrations were mapped by synchrotron X-ray microfluorescence. An extra number of more slowly repaired double strand breaks were observed when irradiating CDDP-treated F98 cells at 78.8 keV. In vivo treatments were then performed with different radiation doses and CDDP concentrations. All cell inoculations in rat brain resulted in tumor development, and tumor presence was controlled by computed tomography. Among all of the conditions tested, the combination of 3 micro g of CDDP with 15 Gy resulted in the largest median survival time (206 days). After 1 year, about 34% of treated rats were still alive. This preclinical finding, validated by molecular analysis, represents the most protracted survival reported with this radioresistant glioma model and demonstrates the interest in powerful monochromatic X-ray sources as new tools for cancer treatments.

Enhanced survival of glioma bearing rats following boron neutron capture therapy with blood-brain barrier disruption and intracarotid injection of boronophenylalanine

Boronophenylalanine (BPA) has been used for boron neutron capture therapy (BNCT) of brain tumors in both experimental animals and humans. The purpose of the present study was to determine if the efficacy of BNCT could be enhanced by means of intracarotid (i.c.) injection of BPA with or without blood-brain barrier disruption (BBB-D) and neutron irradiation using a rat brain tumor model. For biodistribution studies, F98 glioma cells were implanted stereotactically into the brains of Fischer rats, and 12 days later BBB-D was carried out by i.c. infusion of 25% mannitol (1.373 mOsmol/ml), followed immediately by i.c. administration of 300, 500 or 800 mg of BPA/kg body weight (b.w.). At the 500 mg dose a fourfold increase in tumor boron concentration (94.5 micrograms/g) was seen at 2.5 hours after BBB-D. compared to 20.8 micrograms/g in i.v. injected animals. The best composite tumor to normal tissue ratios were observed at 2.5 hours after BBB-D, at which time the tumor: blood (T: Bl) ratio was 10.9, and the tumor: brain (T:Br) ratio was 7.5, compared to 3.2 and 5.0 respectively for i.v. injected rats. In contrast, animals that had received i.c. BPA without BBB-D had T : Bl and T:Br ratios of 8.5 and 5.9, respectively, and the tumor boron concentration was 42.7 micrograms/g. For therapy experiments, initiated 14 days after intracerebral implantation of F98 glioma cells, 500 mg/kg b.w. of BPA were administered i.v. or i.c. with or without BBB-D, and the animals were irradiated 2.5 hours later at the Brook-haven Medical Research Reactor with a collimated beam of thermal neutrons delivered to the head. The mean survival time for untreated control rats was 24 +/- 3 days, 30 +/- 2 days for irradiate controls, 37 +/- 3 days for those receiving i.v. BPA, 52 +/- 15 days for rats receiving i.c. BPA without BBB-D, and 95 +/- 95 days for BBB-D followed by i.c. BPA and BNCT. The latter group had a 246% increase in life span (ILS) compared to untreated controls and a 124% ILS compared to that of i.v. injected animals. These survival data are the best ever obtained with the F98 glioma model and suggest that i.c. administration of BPA with or without BBB-D may be useful as a means to increase the efficacy of BNCT.

Effects of cisplatin and amphotericin B on DNA adduct formation and toxicity in malignant glioma and normal tissues in rat

In an attempt to modify the cytotoxicity of cisplatin, amphotericin B (AmB) was given as pretreatment to BDIX rats with intracerebral BT4C glioma implants. Ten animals given AmB 5 mg/kg i.p. followed by cisplatin 5 mg/kg i.p. displayed massive haematuria within 24 h after treatment and died a few days later. The antitumoral effect could not, therefore, be evaluated. Histopathological examination of the kidneys showed extensive tubular necrosis. No signs of apoptotic cell death were found using in situ end labelling with biotin-labelled nucleotides or with DNA integrity analysis in agarose gel electrophoresis. An immunohistochemical method for analysis of cisplatin-DNA adducts was used to elucidate the distribution of cisplatin in brain tumour, normal brain and kidney. Addition of AmB to cisplatin caused increased adduct formation in kidneys, particularly in tubular cells. It seems plausible that the nephrotoxicity, at least in part, was mediated by increased levels of cisplatin-DNA adducts. Pretreatment with AmB did not have any obvious effect on the formation of adducts in the cerebral cortex. The adduct levels in the tumours from animals pretreated with AmB were not significantly increased compared with those treated with cisplatin only. Thus, addition of AmB to cisplatin caused excessive nephrotoxicity suggesting a decrease in the therapeutic ratio of cisplatin.