Targeted brain tumor treatment-current perspectives.

Brain tumor is associated with poor prognosis. The treatment option is severely limited for a patient with brain tumor, despite great advances in understanding the etiology and molecular biology of brain tumors that have lead to breakthroughs in developing pharmaceutical strategies, and ongoing NCI/Pharma-sponsored clinical trials. We reviewed the literature on molecular targeted agents in preclinical and clinical studies in brain tumor for the past decade, and observed that the molecular targeting in brain tumors is complex. This is because no single gene or protein can be affected by single molecular agent, requiring the use of combination molecular therapy with cytotoxic agents. In this review, we briefly discuss the potential molecular targets, and the challenges of targeted brain tumor treatment. For example, glial tumors are associated with over-expression of calcium-dependent potassium (K(Ca)) channels, and high grade glioma express specific K(Ca) channel gene (gBK) splice variants, and mutant epidermal growth factor receptors (EGFRvIII). These specific genes are promising targets for molecular targeted treatment in brain tumors. In addition, drugs like Avastin and Gleevec target the molecular targets such as vascular endothelial cell growth factor receptor, platelet-derived growth factor receptors, and BRC-ABL/Akt. Recent discovery of non-coding RNA, specifically microRNAs could be used as potential targeted drugs. Finally, we discuss the role of anti-cancer drug delivery to brain tumors by breaching the blood-brain tumor barrier. This non-invasive strategy is particularly useful as novel molecules and humanized monoclonal antibodies that target receptor tyrosine kinase receptors are rapidly being developed.

Neurotoxic effect of acamprosate, n-acetyl-homotaurine, in cultured neurons.

Acamprosate (AC), N-acetyl-homotaurine, has recently been introduced for treating alcohol craving and reducing relapses in weaned alcoholics. AC may exert its action through the taurine system rather than the glutamatergic or GABAergic system. This conclusion is based on the observations that AC strongly inhibits the binding of taurine to taurine receptors while it has little effect on the binding of glutamate to glutamate receptors or muscimol to GABA(A) receptors. In addition, AC was found to be neurotoxic, at least in neuronal cultures, triggering neuronal damage at 1 mM. The underlying mechanism of AC-induced neuronal injury appears to be due to its action in increasing the intracellular calcium level, [Ca2+](i). Both AC-induced neurotoxicity and elevation of [Ca2+](i) can be prevented by taurine suggesting that AC may exert its effect through its antagonistic interaction with taurine receptors.

S-methyl-N,N-diethylthiocarbamate sulfoxide elicits neuroprotective effect against N-methyl-D-aspartate receptor-mediated neurotoxicity.

Glutamatergic neurotransmission, particularly of the NMDA receptor type, has been implicated in the excitotoxic response to several external and internal stimuli. In the present investigation, we report that S-methyl-N,N-diethylthiocarbamate sulfoxide (DETC-MeSO) selectively and specifically blocks the NMDA receptor subtype of the glutamate receptors, and attenuates glutamate-induced neurotoxicity in rat-cultured primary neurons. Other major ionotropic glutamate receptor subtypes, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and kainate, were insensitive to DETC-MeSO both in vitro and in vivo. Disulfiram, the parent compound of DETC-MeSO, also inhibits glutamate receptors partially in vivo; however, it fails to inhibit glutamate receptors in mice pretreated with N-butyl imidazole, a cytochrome P450 enzyme inhibitor, implicating the need for bioactivation of disulfiram to be an effective antagonist. We showed that glutamate-induced increase in (45)Ca2+ was attenuated in rat-cultured primary neurons following pretreatment with DETC-MeSO. The Ca2+ influx into primary neurons, studied by confocal microscopy of the fluorescent Ca2+ dye fura-2, demonstrated a complete attenuation of NMDA-induced Ca2+ influx. Similarly, DETC-MeSO attenuated NMDA-induced (45)Ca2+ uptake. Glutamate-induced (45)Ca2+ uptake and Ca2+ influx, however, were partially blocked by DETC-MeSO, and this is consistent with both in vitro and in vivo studies in which DETC-MeSO partially blocked mouse brain glutamate receptors. In addition, DETC-MeSO pretreatment effectively prevented seizures in mice induced either by NMDA, ammonium acetate, or ethanol-induced kindling seizures, all of which are believed to be mediated by NMDA receptors. These data demonstrate that DETC-MeSO produces the neuroprotective effect through antagonism of NMDA receptors in vivo.

Disulfiram augments oxidative stress in rat brain following bilateral carotid artery occlusion.

We examined the brain oxidative stress which accompanies 30 min of bilateral carotid artery ligation (BCAL) in terms of changes in brain levels of glutathione; reduced (GSH) and oxidized (GSSG) forms and the exacerbation of oxidative stress by disulfiram (DSF). These results indicate that BCAL alone decreases GSH content and limits glutathione reductase (GR) activity, and these changes were enhanced by DSF pretreatment. Similar observations were recorded with DSF alone. GR activity (74.3 +/- 4.0 micromol min(-1) mg(-1) tissue; p < 0.001) and GSH content (1.23 +/- 0.06 micromol min(-1) g(-1) tissue; p < 0.001) was attenuated in rats subjected to synergistic effect of BCAL and DSF with a concomitant increase of GSSG (0.006 +/- 0.006 micromol min(-1) g(-1) tissue; p < 0.001). Recovery of GSH/GSSG level and GR activity during reperfusion following 30 min BCAL was considerably delayed (96 h) in the BCAL and DSF group as compared to the recovery time of 24 h in the group subjected to BCAL-reperfusion alone. Perturbation of GSH/GSSG homeostasis as a result of BCAL was augmented by DSF. These findings clearly demonstrate central nervous system oxidative stress due to a BCAL-DSF synergistic effect. Based on the results obtained with this model, we conclude that DSF increases brain oxidative stress and this may be detrimental to alcoholics who might drink and develop an acetaldehyde-induced hypotension while taking DSF.

Glutathione carbamoylation with S-methyl N,N-diethylthiolcarbamate sulfoxide and sulfone. Mitochondrial low Km aldehyde dehydrogenase inhibition and implications for its alcohol-deterrent action.

S-Methyl N,N-diethylthiolcarbamate sulfoxide (DETC-MeSO) and sulfone (DETC-MeSO2) both inhibit rat liver low Km aldehyde dehydrogenase (ALDH2) in vitro and in vivo (Nagendra et al., Biochem Pharmacol 47: 1465-1467, 1994). DETC-MeSO has been shown to be a metabolite of disulfiram, but DETC-MeSO2 has not. Studies were carried out to further investigate the inhibition of ALDH2 by DETC-MeSO and DETC-MeSO2. In an in vitro system containing hydrogen peroxide and horseradish peroxidase, the rate of DETC-MeSO oxidation corresponded to the rate of DETC-MeSO2 formation. Carbamoylation of GSH by both DETC-MeSO and DETC-MeSO2 was observed in a rat liver S9 fraction. Carbamoylation of GSH was not observed in the presence of N-methylmaleimide. In in vitro studies, DETC-MeSO and DETC-MeSO2 were equipotent ALDH2 inhibitors when solubilized mitochondria were used, but DETC-MeSO was approximately four times more potent than DETC-MeSO2 in intact mitochondria. In studies with rats, the dose (i.p. or oral) required to inhibit 50% ALDH2 (ED50) was 3.5 mg/kg for DETC-MeSO and approximately 35 mg/kg for DETC-MeSO2, approximately a 10-fold difference. Furthermore, maximum ALDH2 inhibition occurred 1 hr after DET(-MeSO administration, whereas maximal ALDH2 inhibition occurred 8 hr after DETC-MeSO2 dosing. DETC-MeSO is, therefore, not only a more potent ALDH2 inhibitor than DETC-MeSO2 in vivo, but also in vitro when intact mitochondria are utilized. The in vitro results thus support the in vivo findings. Since oxidation of DETC-MeSO can occur both enzymatically and non-enzymatically, it is possible that DETC-MeSO2 is formed in vivo. DETC-MeSO2, however, is not as effective as DETC-MeSO in inhibiting ALDH2, probably because it has difficulty penetrating the mitochondrial membrane. Thus, even if DETC-MeSO2 is formed in vivo from DETC-MeSO, it is the metabolite DETC-MeSO that is most likely responsible for the inhibition of ALDH2 after disulfiram administration.