Strategy and planning for chemopreventive drug development: clinical development plans II.

This is the second publication of Clinical Development Plans from the National Cancer Institute, Division of Cancer Prevention and Control, Chemoprevention Branch and Agent Development Committee. The Clinical Development Plans summarize the status of promising chemopreventive agents regarding evidence for safety and chemopreventive efficacy in preclinical and clinical studies. They also contain the strategy for further development of these drugs, addressing pharmacodynamics, drug effect measurements, intermediate biomarkers for monitoring efficacy, toxicity, supply and formulation, regulatory approval, and proposed clinical trials. Sixteen new Clinical Development Plans are presented here: curcumin, dehydroepiandrosterone, folic acid, genistein, indole-3-carbinol, perillyl alcohol, phenethyl isothiocyanate, 9-cis-retinoic acid, 13-cis-retinoic acid, l-selenomethionine and 1, 4-phenylenebis(methylene)selenocyanate, sulindac sulfone, tea, ursodiol, vitamin A, and (+)-vorozole. The objective of publishing these plans is to stimulate interest and thinking among the scientific community on the prospects for developing these and future generations of chemopreventive drugs.

Effects of simulated increased gravity on the rate of aging of rats: implications for the rate of living theory of aging.

Ever since Pearl proposed the rate of living theory of aging numerous studies have demonstrated its validity in poikilotherms. In mammals, however, satisfactory experimental demonstration is still lacking because an externally imposed increase of basal metabolic rate of these animals (e.g. by placement in the cold) is usually accompanied by general homeostatic disturbance and stress. The present study was based on the finding that rats exposed to slightly increased gravity are able to adapt with little chronic stress but at a higher level of basal metabolic expenditure (increased 'rate of living'). The rate of aging of 17-mth-old rats that had been exposed to 3.14 times normal gravity in an animal centrifuge for 8 mth was larger than of controls as shown by apparently elevated lipofuscin content in heart and kidney, reduced numbers and increased size of mitochondria of heart tissue, and inferior liver mitochondria respiration (reduced 'efficiency': 20% larger ADP: 0 ratio, P less than 0.01; reduced 'speed': 8% lower respiratory control ratio, P less than 0.05). On the other hand, steady-state food intake per day per kg body weight, which is presumably proportional to 'rate of living' or specific basal metabolic expenditure, was about 18% higher than in controls (P less than 0.01) after an initial 2-mth adaptation period. Finally, though half of the centrifuged animals lived only a little shorter than controls (average about 343 vs. 364 days on the centrifuge, difference statistically nonsignificant), the remaining half (longest survivors) lived on the centrifuge an average of 520 days (range 483-572) compared to an average of 574 days (range 502-615) for controls, computed from onset of centrifugation, or 11% shorter (P less than 0.01). Therefore, these results show that a moderate increase of the level of basal metabolism of young adult rats adapted to hypergravity compared to controls in normal gravity is accompanied by a roughly similar increase in the rate of organ aging and reduction of survival, in agreement with Pearl's rate of living theory of aging, previously experimentally demonstrated only in poikilotherms.

The effect of pregnancy on the biliary excretion of [14C]phenytoin in the rat.

The biliary excretion of [14C]phenytoin (DPH) was examined in pregnant and nonpregnant female control rats. After administration of [14C]DPH (1 mg/kg i.v.), the bile concentration (nanomoles per milliliter) and biliary excretion (nanomoles per minute per kilogram) of the glucuronide conjugate of the major primary metabolite of DPH, 5-phenyl-5-p-hydroxyphenyl[4-14C] hydantoin ([14C)]HPPH), was significantly decreased at 15 and 30 min in pregnant rats relative to controls. Bile flow averaged 50 and 70 microliter/min/kg in control and pregnant rats, respectively. The concentration in blood of [14C]HPPH-glucuronide was increased 2 to 6-fold in pregnant rats relative to controls. After administration of [14C]HPPH (10 mg/kg i.v.), the disappearance of [14C]HPPH from the blood, biliary excretion and bile concentration of [14C]HPPH-glucuronide were very similar in control and pregnant rats. The blood concentration of [14C]HPPH-glucuronide was elevated 2 to 6-fold in pregnant rats and the half-life was increased from 43 min in controls to 70 min in pregnant rats. Maximal bile/blood concentration ratios of [14C]HPPH-glucuronide were 630 and 300 in control and pregnant rats, respectively, indicating a decreased ability of the liver to concentrate the glucuronide in the bile in pregnancy.