Influence of radiation on the blood-brain barrier and optimum time of chemotherapy

A pilot study of the destructive effects of radiation on the blood-brain barrier (BBB) was made on 14 patients with localized and limited brain tumors by 99MTc-GH imaging from August 1988 to November 1989. Count/pixel data were obtained from the unirradiated, irradiated, and tumor areas before and after radiotherapy of 30-40 Gy. It was observed that, a) the BBB in the unirradiated area outside the radiation portal was not changed, b) the degree of destructive effect on the BBB in the irradiated normal area was directly proportional to the radiation dose. For 30-40 Gy, the count/pixel change enhances to average 24.7% [(147.6-118.4)/118.4], and c) the BBB in the tumor area is partially destroyed on an average of 22.1% [(206.8-169.4)/169.4] by the tumor. The radiotherapy further enhances this effect to an average of 74.7% [(206.8-118.4)/118.4]. Case 3 showed that before radiation, the degree of destructive effect on the BBB in the tumor area was 22% [(167-137)/137] higher than normal brain tissue. After a dose of 30 Gy of irradiation, it increased to 76.7% [(242-137)/137]; 8 months later it decreased to 17% [(160.3-137)/137]. It has been proven that the BBB can recover at least partially. Based on these observations, the authors believe that in the combined treatment of operated brain tumors, radiotherapy should precede chemotherapy so as to enhance the destruction of the BBB, facilitating the incorporation of drugs into the tumor. The dose at which to start chemotherapy is 20-30 Gy.

Somatic mutation, DNA damage and cytotoxicity induced by benzo[a]pyrenedione/benzo[a]pyrenediol redox couples in cultured mammalian cells

BP-3,6-dione was found to be mutagenic, cytotoxic and to induce DNA damage in a transformed line of Syrian hamster fibroblasts at low concentrations, 2 micrograms/ml and less. Inhibition of sulfate and glucuronic acid conjugating enzymes with salicylamide potentiated the above effects of BP-3,6-dione. Diminishing cellular capacity to scavenge superoxide anion radicals also potentiated the mutagenic and cytotoxic action of the dione. The presence of dicumarol, a specific inhibitor of the two-electron reduction of quinones by DT-diaphorase, afforded some protection against cytotoxicity. The results indicate that BP-3,6-dione undergoes two-electron reduction to an unstable hydroquinone, BP-3,6-diol, or one-electron reduction to a semiquinone radical intermediate and that both of these reduced forms undergo rapid univalent oxidation to generate active reduced oxygen species. The data are consistent with the hypothesis that active oxygen species generated by BP-dione/BP-diol redox cycling are responsible, at least in part, for the mutagenic and cytotoxic effects observed with BP-3,6-dione.