A phase I and pharmacologic study of the MDR converter GF120918 in combination with doxorubicin in patients with advanced solid tumors.

BACKGROUND: Resistance to chemotherapy can partly be explained by the activity of membrane bound P-glycoprotein. Competitive inhibition of P-glycoprotein, by multidrug resistance (MDR) converters, may overcome this MDR. Previously studied MDR converters either have serious intrinsic side effects or considerably influence the pharmacokinetics of cytotoxic agents at concentrations theoretically required to convert MDR. GF120918 is a third-generation MDR converter with high affinity for P-glycoprotein and can be given orally. We performed a phase 1 study with escalating doses of GF120918 in combination with doxorubicin. PATIENTS AND METHODS: The study group comprised 46 patients with advanced solid tumors. Doxorubicin was administered on day 1 (cycle 1), GF120918 on days 22-24 (cycle 2), and on days 29-33 with doxorubicin administered on day 31 (cycle 3). Pharmacokinetics of both GF120918 and doxorubicin were studied. The starting daily dose of GF120918 was 50 mg and was to be increased in subsequent cohorts until a steady state plasma level of 100 ng/ml was reached. The starting dose of doxorubicin was 50 mg/m2 and was to be increased after reaching the target dose level of GF120918. RESULTS: In 37 of the 46 patients, full pharmacokinetic data from the three scheduled cycles were obtained. Pharmacokinetics of GF120918 showed a less than linear increase in Cmax with increasing doses, with considerable interpatient variation. The target steady-state plasma level for GF120918 was exceeded in 12 out of 19 patients who received 400 mg GF120918 alone twice daily and in 12 of 17 patients who received 400 mg GF120918 twice daily in combination with doxorubicin. GF120918 pharmacokinetics were not influenced by coadministration of doxorubicin. The doxorubicin AUC was only marginally influenced by GF120918 and only at the highest dose levels. In these patients there was a significant increase in the AUC of doxorubicinol in cycle 3 as compared to cycle 1. Hematologic toxicity mainly consisted of neutropenia and was more severe in cycle 3 than in cycle 1 (13 vs 5 patients with grade 4 neutropenia, P=0.003). Neutropenic fever was the dose-limiting toxicity at a doxorubicin dose of 75 mg/m2 with 400 mg GF120918 twice daily. The toxicity of GF120918 was limited to somnolence in eight patients and occasional gastrointestinal complaints. CONCLUSION: GF120918 is an MDR converter with only minimal side effects at a dose level yielding concentrations able to convert the action of P-glycoprotein in vitro. A doxorubicin dose of 60 mg/m2 on day 3 in combination with 400 mg GF120918 twice daily on days 1-5 is an acceptable regimen for further clinical trials.

Population pharmacokinetic and dynamic analysis of the topoisomerase I inhibitor lurtotecan in phase II studies.

Population pharmacokinetic-dynamic analysis was prospectively integrated in a broad phase II program of lurtotecan (GI147211), a novel camptothecin derived topoisomerase I inhibitor, to determine the population pharmacokinetic profile in a larger population, to estimate individual pharmacokinetic parameters and to investigate relationships with clinical outcome. A sparse sampling method was applied during course one, which involved two sampling time-points. A Bayesian algorithm was used to estimate individual pharmacokinetic parameters, in particular total plasma clearance (CL) and volume of distribution. In total, samples were collected of 109 (63%) of 173 patients. Pharmacokinetic-dynamic evaluation could be carried out successfully in 85 (78%) of the sampled patients. CL of lurtotecan showed substantial variability (mean 87 +/- 28 L/h) and was of the same magnitude as in the phase I studies where full pharmacokinetic curves were used. Residual variability in the population estimate of CL was 9.9%. No significant relationships were observed between exposure parameters and toxicity nor likelihood of tumor response, however the latter relationship may well have been obscured by the heterogeneity of the studied population. Prospective implementation of large scale population pharmacokinetic-dynamic analysis is feasible and important to establish whether interpatient variability in drug exposure is a major determinant of toxicity or activity.

Androgen antagonists: Potential role in prostate cancer prevention.

This article summarizes discussions of the importance of androgens and androgen antagonists in the genesis of prostate cancer. These discussions occurred at a recent symposium on prostate cancer chemoprevention sponsored by the National Cancer Institute. Considerable information exists indicating the importance of androgens in the development of prostate cancer. Trials in breast cancer indicate that estrogen antagonists prevent breast cancer-suggesting, by analogy, that the blockade of androgen action might prevent the emergence of prostate cancer. The 5alpha-reductase inhibitors block the intracellular metabolism of testosterone and inhibit the growth of the prostate. Limited data suggest that 5alpha-reductase inhibitors reduces prostate-specific antigen in men with localized and advanced, primary or recurrent prostate cancer. An ongoing national trial of 18,000 men over 50 years of age has completed accrual and will evaluate whether a standard dose of finasteride will prevent the development of prostate cancer. The toxicity profile of finasteride (Proscar, Merck & Co., West Point, PA), the only approved 5alpha-reductase inhibitor, is favorable leading to its evaluation as a potential chemopreventive agent for prostate cancer. Anti-androgens such as bicalutamide (Casodex, AstraZeneca, Wilmington, DE) are active in the treatment of prostate cancer and comparable, in some trials, to testicular androgen suppression. These data suggest that antiandrogens may be active in the prevention of prostate cancer; however, the toxicity of antiandrogens (gynecomastia, gastrointestinal toxicity) poses concerns for application in prevention studies. Opportunities for study of factors predictive or associated with the development of prostate cancer and new agents that may interrupt this process offer numerous leads that may reduce the incidence of prostate cancer.

Clinical pharmacokinetics of doxorubicin in combination with GF120918, a potent inhibitor of MDR1 P-glycoprotein.

Previous clinical investigations with doxorubicin indicated that modulators of P-glycoprotein dramatically decrease the systemic clearance of the drug, which complicates the interpretation of toxicity and response data. In the present study, we examined the pharmacokinetics of doxorubicin and GF120918, a novel potent P-glycoprotein inhibitor, in cancer patients in a search for more selective modulation of multidrug resistance (MDR). Seven cohorts (46 patients) received sequential treatments with doxorubicin alone by a 5 min i.v. bolus (50-75 mg/m2), oral GF120918 alone (50 mg q.d.-400 mg b.i.d.), and the combination of doxorubicin and GF120918. Serial blood and urine samples were taken during both treatment courses and analyzed for doxorubicin and its metabolite doxorubicinol by a liquid chromatographic assay. The pharmacokinetic characteristics of doxorubicin in the presence or absence of GF120918 indicate a very minor overall effect of the modulator, except at the highest combined dose level (i.e. 75 mg/m2 plus 400 mg b.i.d.). A limited number of patients experienced significantly increased exposure to doxorubicinol upon combined treatment, which was associated with concomitantly higher plasma levels of GF120918. Sigmoidal maximum-effect models revealed significant correlations (p<0.02) between the area under the curve of doxorubicinol and the percent decrease in neutrophils and platelets. Sigmoidicity factors in the fitted Hill equation were similar between both treatment courses, suggesting no pharmacodynamic potentiation of doxorubicinol myelotoxicity by GF120918. Our data indicate that GF120918 at the tested doses of combination treatment achieves plasma concentrations that reverse MDR in experimental models and it lacks the significant kinetic interaction with doxorubicin observed previously with other modulators. Hence, it may be possible in future trials to assess the contribution of a potent inhibitor of P-glycoprotein activity to the toxicity and activity of doxorubicin with the knowledge that profound plasma pharmacokinetic interactions are unlikely.

Flow cytometric assay of modulation of P-glycoprotein function in whole blood by the multidrug resistance inhibitor GG918.

We sought to develop an assay for measuring the inhibition of P-glycoprotein (Pgp) function in whole blood as an indicator of in vivo drug activity. Since the CD56(+) subset of peripheral blood lymphocytes (PBLs) has been shown to express functional Pgp, the changes in rhodamine 123 (R123) uptake by CD56(+) PBLs from GG918-treated and untreated whole blood were used as the basis for these studies. In an ex vivo study, heparin-treated whole blood was obtained from normal volunteers, and GG918 and R123 were added at various concentrations for time course analyses of dye loading. GG918 concentrations from 2.5 to 800 nm were tested in incubations ranging from 15 min to 3 h prior to R123 addition. R123 loading times ranged from 0 to 80 min. Flow cytometric analyses of the CD56(+) PBLs indicated that the resolution of Pgp inhibition was dependent on inhibitor concentration and time of R123 loading and independent of the R123 concentrations tested. In this ex vivo assay model, a dose-dependent response was seen for GG918 with a 2-fold increase in cellular R123 intensity being produced at a drug concentration of 80 nm. When this assay method was applied to blood samples from volunteers dosed p.o. with GG918, similar shifts in R123 fluorescence of the CD56(+) PBLs were observed with significant increases in R123 intensity occurring at serum concentrations as low as 40 nm. In contrast to assays in which target cell populations are enriched prior to testing, the addition of the substrate (R123) directly to the blood sample combined with the segregation of the target cells by specific immunofluorescence provides the investigator an indication of in situ activity of circulating drug. Thus, CD56(+) PBLs may prove useful as a surrogate target for monitoring multidrug resistance inhibitor activity in situ.

Protective effect of Sn-protoporphyrin against doxorubicin-induced perturbations of heme metabolism.

The administration of doxorubicin, an anti-tumor antibiotic, to rodents resulted in an increase in heme oxygenase activity and a decrease in delta-aminolevulinate (ALA) synthase activity and in cellular heme and cytochrome P450 content in liver. Sn-protoporphyrin, a potent inhibitor of heme degradation both in vitro and in vivo, when administered to rodents prior to doxorubicin, mitigates the drug-induced toxic actions which are reflected by the drug-induced decreases of both cellular heme and cytochrome P450 content. Sn-protoporphyrin thus provides a pharmacological means of protecting against the toxic effects of doxorubicin and other drugs which enhance heme oxygenase activity and thus decrease cellular heme and cytochrome P450 content in vivo.

The influence of antineoplastic chemotherapy on antipyrine metabolism in man.

When either Doxorubicin or Mitomycin-C was administered to patients, antipyrine clearance was respectively unaltered or increased. Antipyrine was administered to patients two days prior to and one day after their first course of the chemotherapeutic drug. Antipyrine clearance increased an average of 11.2% in the 5 patients that received Doxorubicin (not significant) and 15.2% in the six patients that received Mitomycin-C (P = 0.033, students t-test). The altered clearance is likely due to a rapid induction of the mixed function oxidase system by the chemotherapy as other parameters that could influence clearance were stable throughout the study (volume of distribution, weight, creatinine clearance and liver function tests). It is unlikely that the prechemotherapy antipyrine dose accounted for this change. The administration of these two antitumor antibiotics in humans may modestly increase the mixed function oxidase activity that is responsible for the metabolism of antipyrine. These findings are in direct contrast to markedly decreased mixed-function oxidase activity observed in the rodent pretreated with the same chemotherapy.

Red blood cell aggregation versus blood clot formation in ionic and nonionic contrast media.

The effects of ionic and nonionic radiographic contrast media on human blood in plastic syringes were investigated in an in vitro double-blind study. Venous blood, which was drawn into plastic syringes containing one of four (iohexol, iopamidol, diatrizoate sodium meglumine, and ioxaglate sodium meglumine) contrast media, was visually inspected at predetermined time intervals before and after mixing. Aliquots of the mixtures of blood and contrast media also were evaluated microscopically. Irregular red blood cell (RBC) aggregates were observed with the nonionic contrast media. Pronounced RBC morphologic alterations occurred with diatrizoate (ionic), and marked crenation was observed with ioxaglate (ionic). Observed aggregates were freely disaggregated in isotonic saline. Recovered supernatant blood from centrifuged aliquots of the mixtures was evaluated for clot formation. There was no evidence of blood clot formation within 1 hour after blood was introduced into syringes containing either ionic or nonionic contrast media. This time period exceeded the normal clotting time, since blood in syringes without contrast media formed clots within 30 to 45 minutes. Both the nonionic and ionic contrast media prolonged coagulation.

Tin-protoporphyrin inhibits heme oxygenase and prevents the decline in hepatic heme and cytochrome P-450 contents produced in nude mice by tumor transplantation.

Heme and hemeprotein perturbations are present in nude mice bearing transplanted tumors. Hepatic microsomal heme oxygenase activity is increased 50-100% in tumor bearing nu/nu mice when compared with normal controls. This elevation in activity of the rate-limiting enzyme of heme degradation is associated with a 50% depletion of microsomal heme and cytochrome P-45 concentrations in liver. The synthetic heme analogue, Sn-protoporphyrin, a potent inhibitor of heme oxygenase, lowers the activity of heme oxygenase in tumor bearing animals to below control levels. This effect is associated with a normalization of hepatic heme and cytochrome P-450 contents. These findings might have implications for protecting normal cells during tumor growth and chemotherapy.

Dose dependent suppression of hepatic cytochrome P-450 content by doxorubicin and Mitomycin-C: correlation with antipyrine biotransformation.

Doxorubicin (DOX) and Mitomycin-C (MMC) are two anthraquinones which, when administered to rats, result in a decrease in the content of hepatic cytochrome P-450 and mixed function oxidase activities. DOX administration produced a dose-dependent immediate decrease in cytochrome P-450 content at all doses but a parallel dose-dependent decrease in the rate of antipyrine metabolite formation of the two higher doses. The lower dose of DOX produced an increase in metabolite formation and produced a less than 20% reduction in cytochrome P-450 content. MMC administration produced an immediate, modest (less than 10% of control levels) suppression of hepatic cytochrome P-450 content, and had no effect on antipyrine metabolite formation. These findings demonstrates that two drugs of the same class can produce similar suppressions of cytochrome P-450 content and that a threshold suppression of cytochrome P-450 content is needed to produce alterations in in vivo drug biotransformations.

Porphyria cutanea tarda associated with the acquired immune deficiency syndrome.

Three male subjects with cutaneous symptoms and biochemical signs typical of porphyria cutanea tarda (PCT) developed acquired immune deficiency syndrome (AIDS). All three were in a classic high risk group for the latter disease and developed a typical progressive illness. Two patients succumbed to opportunistic infections; the third is alive but critically ill. The symptomatic prodrome of AIDS developed concurrently with or followed the onset of symptoms of PCT in all three individuals. PCT and AIDS are both uncommon disorders; their association in three patients is thus of inherent clinical interest. If this association is not coincidental, it raises the possibility that the occurrence of photosensitivity, skin lesions, and evidence of biochemical changes characteristic of PCT may, in certain patients at risk for AIDS, presage the subsequent full clinical expression of the latter disease.

Diet-hormone interactions: protein/carbohydrate ratio alters reciprocally the plasma levels of testosterone and cortisol and their respective binding globulins in man.

The aim of this study was to determine if a change in protein/carbohydrate ratio influences plasma steroid hormone concentrations. There is little information about the effects of specific dietary components on steroid hormone metabolism in humans. Testosterone concentrations in seven normal men were consistently higher after ten days on a high carbohydrate diet (468 +/- 34 ng/dl, mean +/- S.E.) than during a high protein diet (371 +/- 23 ng/dl, p less than 0.05) and were accompanied by parallel changes in sex hormone binding globulin (32.5 +/- 2.8 nmol/l vs. 23.4 +/- 1.6 nmol/l respectively, p less than 0.01). By contrast, cortisol concentrations were consistently lower during the high carbohydrate diet than during the high protein diet (7.74 +/- 0.71 micrograms/dl vs. 10.6 +/- 0.4 micrograms/dl respectively, p less than 0.05), and there were parallel changes in corticosteroid binding globulin concentrations (635 +/- 60 nmol/l vs. 754 +/- 31 nmol/l respectively, p less than 0.05). The diets were equal in total calories and fat. These consistent and reciprocal changes suggest that the ratio of protein to carbohydrate in the human diet is an important regulatory factor for steroid hormone plasma levels and for liver-derived hormone binding proteins.

The absence of significant biliary excretion of antipyrine or its metabolites in humans.

Three patients with complete bile duct obstructions requiring a percutaneous biliary fistuala were given an oral dose of antipyrine. Drug elimination was assessed through plasma t1/2 studies and urine and bile excretion of both antipyrine and its metabolites. Urine metabolite patterns were in agreement with reference standards, but analysis of bile revealed no antipyrine metabolites and minimal parent compound (mean of total administered dose excreted from the bile fistulas was 4%). This finding was not predicted from previous experiments in the bile-cannulated rat and suggests caution regarding interspecies extrapolation of data concerning the hepatic disposition of certain commonly used test drugs in clinical pharmacologic studies.

Dietary influences on ethanol metabolism.

Ethanol was orally administered to seven normal volunteers after three dietary control periods. Diet cycle I was high in protein and calories, cycle II was high in protein but hypocaloric, and cycle III was a combined low-protein, hypocaloric diet. Ethanol elimination was significantly altered by the changes in macronutrients. All volunteers demonstrated diminished ethanol clearance while consuming the hypocaloric diets, and further reduction was seen with an inadequate protein intake. A marked dietary influence on ethanol clearance has been demonstrated in normal male volunteers who have not been exposed to previous ethanol consumption.

A comparison of the effects of a macrobiotic diet and a Western diet on drug metabolism and plasma lipids in man.

We have compared the effects of two dietary regimens with different macronutrient compositions--a macrobiotic diet and a Western diet--on drug metabolism and plasma lipids in seven healthy volunteers. The macrobiotic diet, high in carbohydrate, low in protein and fat, and devoid of animal food sources, was eaten for a ten day control period, as was the Western diet, high in calories, fat, and protein, as well as animal food sources. We determined the influences of these diets on the clearance of orally administered antipyrine, oxazepam, and methadone, as well as on plasma lipids. There was a statistically significant change in antipyrine clearance as well as in plasma LDL-cholesterol and HDL-cholesterol after the dietary periods. This suggests that the influence of dietary changes may have some effect on the clearance of therapeutic drugs. However, this is not universal and is probably important when the drug is highly dependent on the mixed-function oxidase system.

The development and application of a radioimmunoassay for dihydrodigoxin, a digoxin metabolite.

The cardioinactive digoxin metabolite, dihydrodigoxin, has been conjugated to bovine serum albumin and to bovine pancreatic ribonuclease by the periodate oxidation method. Rabbits immunized with the dihydrodigoxin-bovine serum albumin conjugate formed antibodies which bound a radioiodinated dihydrodigoxin-ribonuclease conjugate. This binding was inhibited by dihydrodigoxin. After affinity chromatography on a digoxin-ribonuclease-Sephacryl immunoadsorbent to remove antibodies which cross-reacted with digoxin, dihydrodigoxin was 300 times more effective than digoxin in inhibiting the binding of tracer by antibody. Digoxin-absorbed antidihydrodigoxin antibodies were coupled to Sephacryl and were used to develop a solid-phase radioimmunoassay capable of detecting 250 to 500 pg of dihydrodigoxin in 1 ml of human serum or urine. This radioimmunoassay has been used to define the pharmacokinetics of the metabolite in four normal human volunteers who ingested 125 to 500 micrograms of dihydrodigoxin by mouth. Dihydrodigoxin was quickly absorbed, with maximal serum concentrations achieved within 45 to 105 min, followed by a rapid fall in serum immunoreactivity over 2 to 4 hr and then by a slower, more gradual decline. The terminal half-life (beta) in serum varied from 4.24 to 11.9 hr (mean +/- S.E. = 8.1 +/- 1.3 hr). Most of the administered dose was excreted in the urine, with cumulative urinary recovery varying inversely with the dose. Urinary half-lives averaged 13.8 +/- 2.1 hr, and renal clearance rates were similar to those of creatinine. Dihydrodigoxin is rapidly absorbed and excreted in man and appears to be eliminated from the body at a faster rate than digoxin.