Design, Synthesis And Antitumor Activities Study Of 1,2,4-Benzotriazine-1,4-dioxide And Analogues

The hypoxic cells in solid tumor lead to their resistance to radiotherapy and chemotherapy,as well as increasing the probability of tumor metastases.However,tumor hypoxia also provides a target for the therapeutic strategies.One such strategy is to use bioreductive prodrugs.There are four main classes of bioreductive prodrugs: nitroaromatics/heterocyclics,quinones,N-oxides and metal complexes.Among the N-oxides,tirapazamine(3-amine-1,2,4-benzotriazine-1,4-dioxide,TPZ)as one of the most promising prodrugs is in phaseâ…¡andâ…¢clinical trials.Some studies indicate the diffusion ability of tirapazamine derivatives can affect their efficiency of therapy.And one of the most reliable methods for improving their diffusion ability is to increase its lipophilicity by incorporating with a properly lipophilic group.In order to find some compounds with higher activity against tumor in hypoxia,tirapazamine was chosen as the lead structure,while some small lipophilic groups were introduced into the C-3 amino group and electron-adopting substituents or electron-donating substituents were introduced into the benzene ring of tirapazamine.Thirty-four tirapazamine derivatives have been synthesized and evaluated for their cytotoxic activities against several human cancer lines in hypoxia and in normoxia.The result showed that most tested compounds had higher cytotoxic activities and hypoxic selectivity than tirapazamine,and their cytotoxic potency was highly dependent on structures of the substituents in the benzene ring and at the 3-position.The side chains at the 3-position of TPZ could intensively influence the cytotoxic activity.When the side chain was alkyl group or aromatic group,the compouds showed lower IC₅₀values than TPZ for most of the tested cancer cell lines.When the group was electron-adopting substituents such as chlorine or nitro group in the benzene ring,they showed lower IC₅₀values than those with electron-donating substituents such as methyl or methyloxy group.Further mechanism study revealed that cytotoxic activity of these compounds might be mediated by modulation of p53 protein expression and mitochondrial membrane potential (△Ψm).Cytotoxicity of tirapazamine derivatives was positive correlated with their lipophilicity shown as retention index(RI).On the basis of previous study,we choose quinoxaline-1,4-dioxide,another one of the most promising prodrugs among the N-oxides,as the lead structure.In order to find some compounds with higher antitumor activity in hypoxia,while substituted phenyl group were introduced into the C-2 position and 3-ethylthio/ethylsulfinyl/ ethylsulfonyl/phenylthio/phenylsulfonyl/alkylamino groups were introduced into the C-3 position of the ring of quinoxaline,fourty-one 2-substituted-phenyl-3-ethylthio/ ethylsulfinyl/ethylsulfonyl/phenylthio/phenylsulfonyl-7-substituted-quinoxaline-1,4-dioxid e and thirty-two 2-substituted-phenyl-3-alkylamino-7-substituted-quinoxaline 1,4-dioxide were synthesized and screened for their cytotoxic activity in vitro against human cancer cell lines in hypoxia and in normoxia.The result showed that 2-substituted-phenyl-3-ethylsulfinyl/ethylsulfonyl/phenylsulfonyl-7-substituted-quinoxaline-1,4-dioxides showed higher activity both in hypoxia and in normoxia,thus 2-substituted-phenyl-alkylamino-7-substituted-quinoxaline-1,4-dioxides showed lower activity.The study of antitumor mechanism of one potent compound 161 in hypoxia showed that mitochondria loss and protein regulation pathway be involved in the cytotoxicity of the class of compounds.