Human heart failure is associated with a diminished contractile response to 0-adrenergic agonists. We hypothesized that alterations in the activity of a guanine nucleotide-binding regulatory protein (G protein) might be partially responsible for this abnormality. We therefore measured the activity of G proteins in failing human myocardium utilizing bacterial toxin-catalyzed ADP ribosylation. The activity of a 40,000-mol wt pertussis toxin substrate (aG40) was increased by 36% in failing human hearts when compared with nonfailing controls. In contrast, there was no change in the level of the stimulatory regulatory subunit (G.). The increased activity in aG40 was associated with a 30% decrease in basal as well as 5'-guanylyl imidodiphosphate-stimulated adenylate cyclase activity. These data suggest that increased aG40 activity is a new marker for failing myocardium and may account at least in part for the diminished responsiveness to 01-adrenergic agonists in the failing human heart.
Hexamethylene bisacetamide (HMBA, NSC 95580) has been demonstrated to be the most effective of the known and studied polar-planar compounds at inducing differentiation in a wide variety of leukemic and nonleukemic cell lines. Although HMBA demonstrated no antineoplastic activity in preclinical testing, it was selected for clinical development on the basis of its potent differentiating capabilities in vitro. In this phase I study, HMBA was administered as a continuous five-day infusion every 3 weeks to patients with advanced cancer. Twenty-three patients received 35 evaluable courses at doses that ranged from 4.8 to 33.6 g/m2/d. Dose-limiting toxicities included renal insufficiency, a hyperchloremic metabolic acidemia/acidosis, and CNS toxicities manifested by agitation and delirium, which progressed to coma in one patient who developed concomitant renal insufficiency. Moderate myelosuppression, mucositis, nausea, and vomiting were also observed. The pharmacokinetics of HMBA best fit a single compartmental model and disposition is primarily by renal elimination. Renal excretion of HMBA and of the primary metabolite, 6-acetoamidohexanoic acid, together account for the disposition of 66% to 93% (mean, 74%) of the infused drug. Based on this trial, the maximum tolerated and recommended phase II doses for HMBA administered on this schedule are 33.6 and 24 g/m2/d, respectively. However, since steady-state HMBA levels at these doses were in the range of 1 to 2 mmol/L, only approaching the lower limit demonstrated for in vitro differentiating effectiveness, and because of evidence suggesting that the exposure period is an important variable in the induction of differentiation, additional studies examining longer periods of infusion are warranted.
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