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Biomedical subjects

B Chabner

Publications and source records attributed to B Chabner.

At least 19 recordsLinked to original sources
PubMed1996

Clinical reversal of multidrug resistance.

Reversal of drug resistance offers the hope of increasing the efficacy of conventional chemotherapy. We tested dexverapamil as a P-glycoprotein antagonist in combination with EPOCH chemotherapy in refractory non-Hodgkin's lymphoma. In a cross-over design, dexverapamil was added to EPOCH after disease stabilization or progression occurred. Objective responses were observed in 10 of 41 assessable patients. Biopsies for mdr-1 were obtained before EPOCH treatment and at the time of cross-over to dexverapamil. Levels of mdr-1 were low before EPOCH, but increased four-fold or more in 42% of patients in whom serial samples were obtained. Pharmacokinetic analysis revealed median peak concentrations of dexverapamil and its metabolite, nor-dexverapamil, of 1.66 mumol/l and 1.58 mumol/l, respectively. Since both are comparable antagonists, a median peak total reversing concentration of 3.24 mumol/l was achieved. Pharmacokinetic analysis of doxorubicin and etoposide levels confirmed a delay in the clearance of doxorubicin ranging from 5% to 24%; no change in the pharmacokinetics of etoposide was observed. This study provides sufficient rationale for testing dexverapamil in a randomized clinical trial.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Clinical Reversal of Multidrug Resistance.

Reversal of drug resistance offers the hope of increasing the efficacy of conventional chemotherapy. We tested dexverapamil as a P-glycoprotein antagonist in combination with EPOCH chemotherapy in refractory non-Hodgkin's lymphoma. In a cross-over design, dexverapamil was added to EPOCH after disease stabilization or progression occurred. Objective responses were observed in 10 of 41 assessable patients. Biopsies for mdr-1 were obtained before EPOCH treatment and at the time of cross-over to dexverapamil. Levels of mdr-1 were low before EPOCH, but increased fourfold or more in 42% of patients in whom serial samples were obtained. Pharmacokinetic analysis revealed median peak concentrations of dexverapamil and its metabolite, nor-dexverapamil, of 1.66 µmol/l and 1.58 µmol/l, respectively. Since both are comparable antagonists, a median peak total reversing concentration of 3.24 µmol/l was achieved. Pharmacokinetic analysis of doxorubicin and etoposide levels confirmed a delay in the clearance of doxorubicin ranging from 5% to 24%; no change in the pharmacokinetics of etoposide was observed. This study provides sufficient rationale for testing dexverapamil in a randomized clinical trial.

Journal Article↗
PubMed1989

Characterization of de novo folate synthesis in Pneumocystis carinii and Toxoplasma gondii: potential for screening therapeutic agents.

Drug therapy studies imply that Pneumocystis carinii and Toxoplasma gondii possess the enzymes necessary for de novo folate synthesis. To verify this, incorporation of [3H]paraaminobenzoic acid [( 3H]PABA) into reduced folates by P. carinii and T. gondii was investigated. Both organisms synthesized tritiated reduced folates. In P. carinii, 10-formyltetrahydrofolate and tetrahydrofolate, and in T. gondii, 5-formyltetrahydrofolate were the major synthesized folates. P. carinii remained metabolically active in vitro for only a few days. Because current systems for screening antipneumocystis agents are cumbersome, the utility of this assay system for screening therapeutic agents was investigated. Sulfonamides and pentamidine efficiently inhibited de novo folate synthesis in P. carinii. Inhibitors of dihydrofolate reductase such as trimethoprim and trimetrexate were poor inhibitors for P. carinii but efficient inhibitors for T. gondii. This study demonstrates the first unambiguous evidence of metabolic activity in P. carinii, and provides a potential assay for efficiently screening antipneumocystis drugs in vitro.

4-Aminobenzoic Acid↗
PubMed1988

Efficacy of trimetrexate, a potent lipid-soluble antifolate, in the treatment of rodent Pneumocystis carinii pneumonia.

Trimetrexate is a lipid-soluble antifolate that has been shown in vitro to be a much more potent inhibitor of Pneumocystis carinii dihydrofolate reductase than the conventionally used inhibitor trimethoprim. To evaluate the in vivo efficacy of trimetrexate, steroid-treated rats which spontaneously develop P. carinii pneumonia were used. Rats treated with trimetrexate (25 mg/kg/d) plus sulfamethoxazole (250 mg/kg/d) orally responded at least as well as rats treated with trimethoprim (50 mg/kg/d) plus sulfamethoxazole. Trimetrexate alone administered orally was ineffective in treating P. carinii infection, but subcutaneous (sc) trimetrexate (7 mg/kg/d) significantly decreased the intensity of infection compared to controls. Trimetrexate is a potent antifolate that may provide an effective alternative to pentamidine and trimethoprim-sulfamethoxazole for treatment of P. carinii pneumonia in humans.

Administration, Oral↗
PubMed1988

High dose intravenous methotrexate with leucovorin rescue in rheumatoid arthritis.

Five patients with severe, treatment refractory rheumatoid arthritis were treated with high dose intravenous methotrexate (500 mg/m2) followed by leucovorin (50 mg/m2). Four courses of chemotherapy were given over a 2-month interval. At the end of the final course, there was a 50% or greater improvement in joint swelling and pain indices and morning stiffness in all patients. Clinical responses persisted for 6-14 weeks posttherapy. High dose methotrexate-leucovorin was associated with a significant reduction in DR antigen expression on peripheral Leu 2, Leu 3 and Leu 4 lymphocytes.

Arthritis, Rheumatoid↗
PubMed1982

Decreased nocturnal plasma melatonin peak in patients with estrogen receptor positive breast cancer.

Plasma melatonin concentrations were determined over a period of 24 hours in 20 women with clinical stage I or II breast cancer. In ten of the patients, whose tumors were estrogen receptor positive, the nocturnal increase in plasma melatonin was much lower than that observed in eight control subjects. Women with the lowest peak concentration of melatonin had tumors with the highest concentrations of estrogen receptors. A significant correlation was found between the peak plasma melatonin concentration and the tumor estrogen receptor concentration in 19 of the patients. These data suggest that low nocturnal melatonin concentrations may indicate the presence of estrogen receptor positive breast cancer and could conceivably have etiologic significance.

Adult↗
PubMed1982

Influence of tetrahydrouridine on the pharmacokinetics of intrathecally administered 1-beta-D-arabinofuranosylcytosine.

Tetrahydrouridine (THU), a potent inhibitor of cytidine deaminase, has been shown to increase the antitumor activity of 1-beta-D-arabinofuranosylcytosine (ara-C) both in vitro and in vivo. In initial studies, which examined the cerebrospinal fluid (CSF) pharmacokinetics of intrathecally (i.t.) administered THU, the drug was found to be slowly cleared from the CSF with alpha and beta half-lives of 1 and 8 hr, respectively. In subsequent experiments, both i.v. pretreatment with THU and concomitant i.t. injection of THU were found to retard the disappearance of i.t. ara-C from the CSF, although the effect of i.t. THU was more profound. ara-C given alone was cleared from CSF with alpha and beta half-lives of 27.5 +/- 6.7 and 115.6 +/- 0.4 (S.D.) min, respectively. Pretreatment with i.v. THU resulted in alpha and beta half-lives of 10.4 +/- 1.5 and 85.7 +/- 11.1, respectively, whereas concomitant administration of i.t. THU resulted in a single half-life of 96 +/- 0.7. The mean calculated clearance rates for ara-C alone, ara-C plus i.v. THU, and ara-C plus i.t. THU were 7.5, 6.2, and 4.2 ml/hr, respectively. This effect appeared to be primarily due to THU inhibition of ara-C deamination, since a decrease in formation of 1-beta-D-arabinofuranosyluracil in the CSF was observed when ara-C was given in the presence of THU (either i.t. or i.v.). No acute neurotoxicity was noted after administration of either i.t. THU alone or i.t. THU with ara-C. The ability of THU to alter CSF ara-C pharmacokinetics may have potential therapeutic value.

Animals↗
PubMed1981

Melatonin inhibition and pinealectomy enhancement of 7,12-dimethylbenz(a)anthracene-induced mammary tumors in the rat.

The effects of the pineal hormone, melatonin, and of pinealectomy on the incidence of mammary adenocarcinoma in Sprague-Dawley rats treated with 7,12-dimethylbenz(alpha)-anthracene (DMBA) were investigated. Melatonin (2.5 mg/kg), begun on the same day as DMBA (5 mg) treatment and given daily in the afternoon for 90 days, significantly reduced the incidence of mammary tumors from 79% (control) to 20% (treated) (p less than 0.002). Rats pinealectomized at 20 days of age and treated with 7 mg of DMBA at 50 days of age had a higher incidence of tumors (88%) compared to control animals (22%). Fifteen mg of DMBA, which resulted in a higher incidence of tumors, reduced the difference between pinealectomized and control animals. Melatonin only partially reversed the effects of pinealectomy, reducing the incidence from 87% (pinealectomy alone) to 63% (pinealectomy plus melatonin); however, the tumor incidence was still lower (27%) in nonpinealectomized, melatonin-treated animals. Assessment of plasma prolactin, luteinizing hormone, follicle-stimulating hormone, estradiol, and cortisol in DMBA-treated tumor-free and tumor-bearing animals revealed a significantly lower plasma prolactin concentration [27 +/- 5 (S.E.) ng/ml] in melatonin-treated animals as compared to vehicle-treated animals [65 +/- 8 ng/ml]. The concentration of plasma prolactin was less in melatonin-treated, pinealectomized rats (55 +/- 10 ng/ml) as compared to vehicle-treated, pinealectomized animals (101 +/- 13 ng/ml). Other hormones were not affected by melatonin treatment. These data support the hypothesis that melatonin inhibits the development of DMBA-induced mammary tumors in the rat while removal of the pineal gland stimulates development of such tumors. Additionally, these experiments provide evidence that these effects may be mediated by a suppression of plasma prolactin levels.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1978

Role of pineal gland in aetiology and treatment of breast cancer.

The hypothesis that diminished function of the pineal gland may promote the development of breast cancer in human beings is suggested by the relation between breast cancer and prolonged oestrogen excess, and by the observation that the pineal secretion, melatonin, inhibits ovarian oestrogen production, pituitary gonadotrophin production, and sexual development and maturation. The hypothesis is supported by the following points. (1) Pineal calcification is commonest in countries with high rates of breast cancer and lowest in areas with a low incidence; the incidences of pineal calcification and of breast cancer are moderate among the black population in the United States. (2) Chlorpromazine raises serum-melatonin; there are reports that psychiatric patients taking chlorpromazine have a lower incidence of breast cancer. (3) Although information is lacking on breast cancer, the pineal and melatonin may influence tumour induction and growth in experimental animals. (4) The demonstration of a melatonin receptor in human ovary suggests a direct influence of this hormone on the ovarian function, and possibly oestrogen production. (5) Impaired pineal secretion is believed to be an important factor triggering puberty (early menarche is a risk factor for breast cancer).

Breast Neoplasms↗
PubMed1978

Allopurinol kinetics.

A spectrophotometric assay for measuring allopurinol and oxipurinol has been developed which can detect as little as 5 X 10(-8) M of each in serum and urine. With this assay, serum disappearance characteristics of intravenous and orally administered allopurinol have been investigated in man. Serum concentrations of both allopurinol and oxipurinol reach levels above 1 X 10(-5) M within minutes of intravenous administration and within 1 or 2 hr of oral administration of 300 mg allopurinol. Patients receiving 300 mg allopurinol daily show a mean serum concentration of 3 X 10(-5) M oxipurinol (range, 0.9 to 9 X 10(-5) M). Serum half-lives of allopurinol and oxipurinol were 39 +/- 11 min and 13.6 +/- 2.8 hr, respectively. Estimates of renal clearance were 13.6 and 18.9 ml/min for allopurinol and 23.2 and 30.6 ml/min for oxipurinol in 2 patients studied. The metabolic conversion of allopurinol to oxipurinol in man does not appear to be altered by long-term therapy with allopurinol, which suggests that this conversion takes place by way of an enzymatic reaction not strongly inhibited by either substrate or product. These results suggest the possibility of a nonxanthine oxidase enzymatic pathway for this conversion.

Administration, Oral↗
PubMed1978

Disseminated cryptococcosis presenting as palpable purpura.

Disseminated cryptococcosis with palpable purpura as the initial clinical manifestation developed in a patient with diffuse histiocytic lymphoma. Cryptococcal vascular injury in a thrombocytopenic cancer patient best explains this previously unreported presentation of cryptococcosis. Purpuric presentations of disseminated fungal infection are likely to increase in frequency as cancer therapy becomes more aggressive.

Biopsy↗