Phase I and pharmacokinetic study of the novel anthracycline derivative 5-imino-13-deoxydoxorubicin (GPX-150) in patients with advanced solid tumors.

PURPOSE: 5-imino-13-deoxydoxorubicin (DIDOX; GPX-150) is a doxorubicin analog modified in two locations to prevent formation of cardiotoxic metabolites and reactive oxygen species. Preclinical studies have demonstrated anti-cancer activity without cardiotoxicity. A phase I study was performed in order to determine the maximum-tolerated dose (MTD) of GPX-150 in patients with metastatic solid tumors. METHODS: GPX-150 was administered as an intravenous infusion every 21 days for up to 8 cycles. An accelerated dose escalation was used for the first three treatment groups. The dosing groups were (A) 14 mg/m(2), (B) 28 mg/m(2), (C), 56 mg/m(2), (D) 84 mg/m(2), (E) 112 mg/m(2), (F) 150 mg/m(2), (G) 200 mg/m(2), and (H) 265 mg/m(2). Pharmacokinetic samples were drawn during the first 72 h of cycle 1. RESULTS: The MTD was considered to be reached at the highest dosing level of 265 mg/m(2) since dose reduction was required in 5 of 6 patients for neutropenia. The most frequent adverse events were neutropenia, anemia, fatigue, and nausea. No patients experienced cardiotoxicity while on the study. The best overall response was stable disease in four (20 %) patients. Pharmacokinetic analysis revealed an AUC of 8.0 (±2.6) µg · h/mL, a clearance of 607 (±210) mL/min/m(2) and a t1/2ß of 13.8 (±4.6) hours. CONCLUSIONS: GPX-150 administered every 21 days has an acceptable side effect profile and no cardiotoxicity was observed. Further investigation is needed to determine the efficacy of GPX-150 in anthracycline-sensitive malignancies.

Doxorubicin cardiac dysfunction: effects on calcium regulatory proteins, sarcoplasmic reticulum, and triiodothyronine.

Utilizing a model of chronic doxorubicin cardiomyopathy, this study examines the relationship between changes in expression and function of calcium handling proteins and contractile dysfunction. A possible mechanism to account for this relationship is suggested. New Zealand white rabbits were injected with either doxorubicin (1 mg/kg, twice weekly for 8 wk) or 0.9% NaCl. Gene transcript, protein levels, and the function of several proteins from the left ventricle were assessed. Protein levels of sarcoplasmic reticulum (SR) Ca2+ transporting ATPase (SERCA2a and b), Ca2+ release channel (RYR2), calsequestrin, Na/Ca exchanger, mRNA levels of RYR2, and [3H]-ryanodine binding (B(max)) to RYR2 were significantly decreased in doxorubicin-treated rabbits; protein levels of phospholamban, dihydropyridine receptor alpha2 subunit, and SR Ca2+ loading rates were not decreased. However, only protein levels of SERCA2 and RYR2, mRNA levels of RYR2, and Bmax of RYR2 significantly regressed with left-ventricular fractional shortening. Analysis of contractile function of atrial preparations isolated from doxorubicin-treated rabbits revealed that doxorubicin diminished contractility (dF/dt) of rest-potentiated contractions consistent with SR dysfunction. Serum concentrations of free triiodothyronine (T3) decreased in doxorubicin-treated rabbits. Our results suggest that chronic doxorubicin administration in the rabbit causes a SR-dependent contractile dysfunction that may result, in part, from decreased T3.

Species comparison of adenosine A1 receptors in isolated mammalian atrial and ventricular myocardium.

Various species have been used as models to study the effects of adenosine (ADO) on atrial and ventricular myocardium, but few direct tissue comparisons between species have been made. This study further characterizes adenosine A(1) receptor binding, adenylate cyclase activity and direct and indirect A(1) receptor-mediated functional activity in atrial and ventricular tissue from Sprague-Dawley rats and Hartley guinea pigs. Rat right atria (RA) were found to be significantly more sensitive to cyclopentyladenosine (CPA), while guinea pig left atria (LA) were more sensitive to CPA. After the addition of isoproterenol (ISO), the reduction of CPA response in rat RA was significantly greater than in guinea pig; however, after ISO treatment, the guinea pig LA was more sensitive to CPA than the rat. Adenylate cyclase inhibition by CPA was significantly greater in atria and ventricles obtained from guinea pig than rat. In competition binding experiments, guinea pig RA had significantly more high affinity sites than rat, but the K(i)s were not significantly different. There were no significant differences between guinea pig LA and rat LA. Guinea pig ventricular tissue had fewer high affinity sites than rat without any differences in their K(i) values. In antagonist saturation experiments, the density and affinity of A(1) receptors in guinea pig cardiac membranes were significantly greater than in rat. Our results indicate definite species differences as well as tissue differences between rat and guinea pig. These differences must be considered when interpreting studies using rat and guinea pig tissue as models for cardiac function.

Arginine to lysine 108 substitution in recombinant CYP1A2 abolishes methoxyresorufin metabolism in lymphoblastoid cells.

1. Cytochrome P4501A2 (CYP1A2) activates a large number of procarcinogens to carcinogens. Phytochemicals such as flavones can inhibit CYP1A2 activity competitively, and hydroxylated derivatives of flavone (galangin) may be potent, selective inhibitors of CYP1A2 activity relative to CYP1A1 activity. Molecular modelling of the CYP1A2 interaction with hydroxylated derivatives of flavone suggests that a number of hydrophobic residues of the substrate-binding domain engage in hydrogen bonding with such inhibitors. 2. We have tested this model using site-directed mutagenesis of these residues in expression plasmids transfected into the human B-lymphoblastoid cell line, AHH-1 TK+/-. 3. Consistent with the molecular model's predicted placement in the active site, amino acid substitutions at the predicted residues abolished CYP1A2 enzymatic activity. 4. Transfected cell lines contained equal amounts of immunoreactive CYP1A2. 5. Our results support the molecular model's prediction of the critical amino acid residues present in the hydrophobic active site, residues that can hydrogen bond with CYP1A2 inhibitors and modify substrate binding and/or turnover.