Potentiation of BCNU antitumor efficacy by 9-substituted O 6-benzylguanines. Effect of metabolism

Autor: S. C. Schold, Anthony E. Pegg, Moschel Rc, Demetrius M. Kokkinakis
Rok vydání: 2000
Předmět:
Zdroj: Cancer Chemotherapy and Pharmacology. 45:69-77
ISSN: 0344-5704
Popis: Purpose: O6-Benzylguanine (BG), an O6-methylguanine-DNA methyltransferase (MGMT) inactivator, potentiates the efficacy of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and of other DNA chloroethylating and methylating anticancer drugs and is currently undergoing clinical trials. O6-Benzyl-2′-deoxyguanosine (dBG), a less effective MGMT inactivator than BG in vitro, is at least as effective as BG in combination with BCNU against tumor xenografts in athymic mice. In order to identify the mechanism of dBG activation in in vivo systems we tested the metabolism, ability to inactivate MGMT, and efficacy to potentiate BCNU in vivo of two additional 9-substituted derivatives of BG, namely O6-benzyl-9-cyanomethylguanine (CMBG) and O6-benzylguanosine (BGS). Methods: Metabolism and disposition of these drugs was examined in athymic mice and Sprague-Dawley rats. MGMT suppression was determined in human medulloblastoma (Daoy) tumor xenografts in athymic mice following treatment with BGS, dBG, and CMBG and was compared with the loss of resistance to BCNU as determined by tumor growth delays. Results: Growth delays at 25 mg/m2 BCNU and 133 mg/m2 BG or equimolar doses of CMBG, BGS or dBG were 23.0, 2.5, 21.3 days, and 30.4 days, respectively. The above differences did not correlate with the ED50s of 0.2, 13, 11 μM, and 2 μM determined for the above compounds, respectively, in cell free extracts. Differences in the efficacies of the 9-substituted compounds did correlate, however, with the extent of their metabolic conversion to BG. The maximum concentrations of BG in blood achieved after the administration of equimolar (250 μmol/kg) doses of CMBG, BGS and dBG were 10, 30 μM, and 55 μM, respectively. Although such levels were lower than those achieved in circulation by administration of an equimolar amount of BG, BG levels persisted longer following treatments with BGS or dBG than after treatment with BG itself. Formation of BG was required for continuous and prolonged (>16 h) suppression of MGMT activity to non-detectable levels (
Databáze: OpenAIRE
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