Prodrug development and the role of reactive oxygen species in beta-lapachone-mediated cell death.

摘要

beta-Lapachone, an o-naphthoquinone, is a novel chemotherapeutic and radiosensitizing agent that targets cancer versus normal cells due to endogenous overexpression (5- to 20-fold) of NAD(P)H:quinone oxidoreductase 1 (NQO1). A deficiency, or inhibition, of NQO1 renders cells resistant to beta-lapachone. Since NQO1 is inducible in mammalian cells after ionizing or UV radiation, or after tamoxifen treatment, beta-lapachone has great potential for treating specific cancers with elevated/inducible NQO1 levels (e.g. breast, non-small cell lung, pancreas, colon and prostate cancers). Many normal tissues express low levels of NQO1 that may "bioactivate" beta-lapachone and cause unwanted side effects. Also, beta-lapachone is a hydrophobic molecule that may not circulate well when administered systemically. A prodrug form of beta-lapachone that becomes active in a tumor specific manner, and is also more soluble in aqueous solutions may circumvent these problems. We hypothesize that beta-lapachone, or a prodrug form of beta-lapachone, will be efficacious against cancers that overexpress NQO1. Furthermore, we propose that reactive oxygen species (ROS) production due to beta-lapachone bioactivation by NQO1 is necessary, but not sufficient, for cancer cell death.; We report the development of mono(arylimino) derivatives of beta-lapachone as potential prodrugs. These derivatives undergo hydrolytic conversion to beta-lapachone at rates dependent on the electron-withdrawing strength of their substituent groups and pH of the diluent. Once converted, beta-lapachone derivatives caused NQO1-dependent, micro-calpain-mediated cell death in cancer cells identical to that caused by beta-lapachone. Interestingly, co-administration of N-acetyl-L-cysteine (NAC), an efficient reactive oxygen scavenger, prevented derivative-induced cytotoxicity by direct modification, preventing their conversion to beta-lapachone. NAC did not affect beta-lapachone lethality.; The use of beta-lapachone mono(arylimino) prodrug derivatives, or more specifically a derivative converted in a tumor-specific manner (i.e., in the acidic local environment of the tumor tissue), should reduce normal tissue toxicity while eliciting tumor-selective cell killing by NQO1 bioactivation.; We demonstrated that NQO1 reduced beta-lapachone to an unstable hydroquinone that rapidly underwent a two-step oxidation back to beta-lapachone. Here, we show that the resultant futile cycling consumes oxygen (O2) and generates ROS. One mole of beta-lapachone induced the consumption of ∼2 moles of O2 within 30 minutes. Inhibition of this robust redox cycling required high NAC concentrations or overexpression of manganese superoxide dismutase with NQO1 modulation by dicoumarol. This ROS formation led to DNA damage, poly(ADP-ribose) polymerase-1 hyperactivation, NAD+/ATP depletion and cell death. ROS generation was upstream of subsequent cytosolic calcium increases. Since BAPTA-AM spared survival, but not redox cycling, beta-lapachone-mediated ROS formation appears necessary, but not sufficient to induce cell death. Knowledge of NQO1-dependent ROS formation by beta-lapachone will be used to improve therapy with this compound.