RESUMO
A series of O-alkylated tropolones and related alpha-ketohydroxy compounds were evaluated for their biological activities and were shown to present an expected ribonucleotide reductase inhibition and cytotoxicity against some cancer cell lines but no antitubulin activity. Pharmacomodulation studies were realised to understand and enhance the observed activities. These original benzylic, heterocyclic and allylic compounds have been synthesised by a phase-transfer catalysed O-alkylation developed in our laboratories.
Assuntos
Inibidores Enzimáticos/síntese química , Inibidores Enzimáticos/farmacologia , Ribonucleotídeo Redutases/antagonistas & inibidores , Tropolona/análogos & derivados , Tropolona/farmacologia , Animais , Biopolímeros , Encéfalo , Divisão Celular/efeitos dos fármacos , DNA/biossíntese , Desenho de Fármacos , Avaliação Pré-Clínica de Medicamentos , Inibidores Enzimáticos/química , Espectroscopia de Ressonância Magnética , Microtúbulos/química , Microtúbulos/metabolismo , Ribonucleotídeo Redutases/metabolismo , Relação Estrutura-Atividade , Suínos , Tropolona/síntese química , Tropolona/química , Tubulina (Proteína)/metabolismo , Células Tumorais CultivadasRESUMO
A screening program aimed at the discovery of new antimicrotubule agents yielded RPR112378 and RPR115781, two natural compounds extracted from the Indian plant Ottelia alismoides. We report their isolation, structural determination, and mechanisms of action. RPR112378 is an efficient inhibitor of tubulin polymerization (IC(50) = 1.2 microM) and is able to disassemble preformed microtubules. Regarding tubulin activity, RPR115781 is 5-fold less active than RPR112378. Tubulin-RPR112378 complexes, when isolated by gel filtration, were able to block further tubulin addition to growing microtubules, a mechanism that accounts for the substoichiometric effect of the drug. RPR112378 was found to prevent colchicine binding but not vinblastine binding to tubulin. Although colchicine binding is known to induce an increase of tubulin GTPase activity, no such increase was observed with RPR112378. We show that RPR112378 is a highly cytotoxic compound and that RPR115781 is 10, 000-fold less active as an inhibitor of KB cell growth. Part of the cytotoxicity of RPR112378 is probably caused by a reaction of addition with sulfhydryl groups, an observation that has not been made with RPR115781. In conclusion, these molecules represent a new class of inhibitors of microtubule assembly with potential therapeutic value.
Assuntos
Indanos/farmacologia , Magnoliopsida/química , Microtúbulos/efeitos dos fármacos , Moduladores de Tubulina , Antineoplásicos Fitogênicos/farmacologia , Sítios de Ligação , Sobrevivência Celular/efeitos dos fármacos , Colchicina/farmacologia , Células HeLa , Humanos , Células KB , Extratos Vegetais/química , Reagentes de Sulfidrila/química , Tubulina (Proteína)/metabolismo , Vimblastina/farmacologiaRESUMO
The systematic variation of the potent antitumor agent mitozolomide (1) is extended to cover alteration of substituents at positions 6 and 8 and to change the imidazo[5,1-d]-1,2,3,5-tetrazinone (1) skeleton to the isomeric pyrazolo-[5,1-d]-1,2,3,5-tetrazinone (17) skeleton. The series of eight 6-alkyl and 6-aralkyl derivatives of 1 showed optimal antitumor activity when the group was small or linear, but activity diminished as size and branching of this substituent increased. This may reflect altered transport characteristics, or failure of the enlarged derivatives to fit a binding site, or possibly a reduced tendency for the derivatives having bulky groups at position 6 to hydrolytically generate the putatively active triazenes (21). Testing of 14 derivatives of 1 differently substituted at position 8 revealed a complex structure-activity relationship, with good antitumor activity obtained for carbamoyl and sulfamoyl groups bearing small substituents. The 8-methylsulfonyl compound had noteworthy activity, but the 8-cyano, 8-nitro, and 8-phenyl derivatives were devoid of useful antitumor activity in these tests. From the limited number of pyrazolotetrazinones (17) reported here, it is suggested that the same conclusions as regards activity also hold true for this ring system.