Haplotype variations in glutathione transferase zeta 1 influence the kinetics and dynamics of chronic dichloroacetate in children.

Dichloroacetate (DCA) is biotransformed by glutathione transferase zeta 1 (GSTZ1), a bifunctional enzyme that, as maleylacetoacetate isomerase (MAAI), catalyzes the penultimate step in tyrosine catabolism. DCA inhibits GSTZ1/MAAI, leading to delayed plasma drug clearance and to accumulation of potentially toxic tyrosine intermediates. Haplotype variability in GSTZ1 influences short-term DCA kinetics in healthy adults, but the impact of genotype in children treated chronically with DCA is unknown. Drug kinetics was studied in 17 children and adolescents with congenital mitochondrial diseases administered 1,2-(13) C-DCA. Plasma drug half-life and trough levels varied 3-6-fold, depending on GSTZ1/MAAI haplotype and correlated directly with urinary maleylacetone, a substrate for MAAI. However, chronic DCA exposure did not lead to progressive accumulation of plasma drug concentration; instead, kinetics parameters plateaued, consistent with the hypothesis that equipoise is established between the inhibitory effect of DCA on GSTZ1/MAAI and new enzyme synthesis. GSTZ1/MAAI haplotype variability affects DCA kinetics and biotransformation. However, these differences appear to be stable in most individuals and are not associated with DCA plasma accumulation or drug-associated toxicity in young children.

Phase 1 trial of dichloroacetate (DCA) in adults with recurrent malignant brain tumors.

BACKGROUND: Recurrent malignant brain tumors (RMBTs) carry a poor prognosis. Dichloroacetate (DCA) activates mitochondrial oxidative metabolism and has shown activity against several human cancers. DESIGN: We conducted an open-label study of oral DCA in 15 adults with recurrent WHO grade III - IV gliomas or metastases from a primary cancer outside the central nervous system. The primary objective was detection of a dose limiting toxicity for RMBTs at 4 weeks of treatment, defined as any grade 4 or 5 toxicity, or grade 3 toxicity directly attributable to DCA, based on the National Cancer Institute's Common Toxicity Criteria for Adverse Events, version 4.0. Secondary objectives involved safety, tolerability and hypothesis-generating data on disease status. Dosing was based on haplotype variation in glutathione transferase zeta 1/maleylacetoacetate isomerase (GSTZ1/MAAI), which participates in DCA and tyrosine catabolism. RESULTS: Eight patients completed at least 1 four week cycle. During this time, no dose-limiting toxicities occurred. No patient withdrew because of lack of tolerance to DCA, although 2 subjects experienced grade 0-1 distal parasthesias that led to elective withdrawal and/or dose-adjustment. All subjects completing at least 1 four week cycle remained clinically stable during this time and remained on DCA for an average of 75.5 days (range 26-312). CONCLUSIONS: Chronic, oral DCA is feasible and well-tolerated in patients with recurrent malignant gliomas and other tumors metastatic to the brain using the dose range established for metabolic diseases. The importance of genetic-based dosing is confirmed and should be incorporated into future trials of chronic DCA administration.

Population pharmacokinetics of intramuscular quinine in children with severe malaria.

We present the first population pharmacokinetic analysis of quinine in patients with Plasmodium falciparum malaria. Ghanaian children (n = 120; aged 12 months to 10 years) with severe malaria received an intramuscular loading dose of quinine dihydrochloride (20 mg/kg of body weight). A two-compartment model with first-order absorption and elimination gave post hoc estimates for pharmacokinetic parameters that were consistent with those derived from non-population pharmacokinetic studies (clearance [CL] = 0.05 liter/h/kg of body weight; volume of distribution in the central compartment [V(1)] = 0.65 liter/kg; volume of distribution at steady state = 1.41 liter/kg; half-life at beta phase = 19.9 h). There were no covariates (including age, gender, acidemia, anemia, coma, parasitemia, or anticonvulsant use) that explained interpatient variability in weight-normalized CL and V(1). Intramuscular quinine was associated with minor, local toxicity in some patients (13 of 108; 12%), and 11 patients (10%) experienced one or more episodes of postadmission hypoglycemia. A loading dose of intramuscular quinine results in predictable population pharmacokinetic profiles in children with severe malaria and may be preferred to the intravenous route of administration in some circumstances.

Inhibition of glutathione S-transferase zeta and tyrosine metabolism by dichloroacetate: a potential unifying mechanism for its altered biotransformation and toxicity.

Dichloroacetate (DCA) inhibits its own metabolism and is converted to glyoxylate by glutathione S-transferase zeta (GSTz). GSTz is identical to maleylacetoacetate isomerase, an enzyme of tyrosine catabolism that converts maleylacetoacetate (MAA) to fumarylacetoacetate and maleylacetone (MA) to fumarylacetone. MAA and MA are alkylating agents. Rats treated with DCA for up to five days had markedly decreased hepatic GSTz activity and increased urinary excretion of MA. When dialyzed cytosol obtained from human liver was incubated with DCA, GSTz activity was unaffected. In contrast, DCA incubation inhibited enzyme activity in dialyzed hepatic cytosol from rats. Incubation of either rat or human hepatic cytosol with MA led to a dose dependent inhibition of GSTz. These data indicate that humans or rodents exposed to DCA may accumulate MA and/or MAA which inhibit(s) GSTz and, consequently, DCA biotransformation. Moreover, DCA-induced inhibition of tyrosine catabolism may account for the toxicity of this xenobiotic in humans and other species.