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Biomedical subjects

B A Kamen

Publications and source records attributed to B A Kamen.

At least 19 recordsLinked to original sources
PubMed2001

Effects of overexpression of gamma-Glutamyl hydrolase on methotrexate metabolism and resistance.

Intracellular metabolism of methotrexate (MTX) to MTX-polyglutamates (MTXPG) is one determinant of cytotoxicity. Steady-state accumulation of MTXPG seems to depend on the activity of two enzymes: folylpolyglutamate synthetase (FPGS), which adds glutamate residues, and gamma-glutamyl hydrolase (GGH), which removes them. Overexpression of GGH would be expected to decrease intracellular MTXPG, thereby increasing efflux of MTX and decreasing cytotoxicity. Increased expression of GGH has been shown to be associated with resistance to MTX in human sarcoma cell lines and a rat hepatoma cell line. To clarify the specific role of GGH in determining MTX sensitivity, we investigated the phenotype produced by forced GGH overexpression in two cell types. Furthermore, because MTX and folic acid share metabolic pathways, we measured the effects of GGH overexpression on folic acid metabolism. The full-length cDNA for GGH, subcloned into a constitutive expression vector, was transfected into a human fibrosarcoma (HT-1080) and a human breast carcinoma (MCF-7) cell line. Compared with the clones containing an empty vector, the GGH-overexpressing cells express 15- to 30-fold more GGH mRNA, more GGH protein, and 15- to 90-fold more GGH enzyme activity. GGH overexpression altered MTX accumulation and metabolism to long-chain polyglutamates. In contrast to expectations, however, GGH overexpression did not confer resistance to short MTX exposures in either cell line. Changes in MTX metabolism were found to be balanced by alterations in accumulation and metabolism of folic acid. The ratio of MTX:folate accumulation may be a better predictor of MTX cytotoxicity than the accumulation of either alone. We conclude that, at least for these two cell lines, GGH overexpression alone is insufficient to produce clinical resistance to MTX.

Antimetabolites, Antineoplastic↗
PubMed2000

Glutathione S-transferase genotypes in children who develop treatment-related acute myeloid malignancies.

Epipodophyllotoxin-associated secondary myeloid leukemia is a devastating complication of acute lymphoblastic leukemia (ALL) therapy. The risk factors for treatment-related myeloid leukemia remain incompletely defined. Genetic deficiencies in glutathione S-transferase (GST) activities have been linked to higher frequencies of a number of human malignancies. Our objective was to determine whether the null genotype for GSTM1, GSTT1, or both, was more frequent in children with ALL who developed treatment-related myeloid malignancies as compared to those who did not. A PCR technique was used to assay for the null genotype for GSTM1 and GSTT1 in 302 children with ALL, 57 of whom also subsequently developed treatment-related acute myeloid leukemia or myelodysplastic syndrome. Among children with ALL who did not develop treatment-related myeloid malignancies, the frequencies of GSTM1 and GSTT1 wild-type, GSTM1 null-GSTT1 wild-type, GSTM1 wild-type-GSTT1 null, and GSTM1 and GSTT1 null genotypes were 40%, 42%, 9% and 9%, respectively. The corresponding frequencies for patients who developed acute myeloid malignancies were 42%, 32%, 11% and 16%, respectively (P = 0.26). A statistically significant increase in the frequency of the GST null genotype was observed in male patients who developed myeloid malignancies as compared to male ALL control patients (P = 0.036), but was not observed in female patients (P = 0.51). Moreover, a logistic regression analysis of possible predictors for myeloid malignancies, controlling for gender and race, did not reveal an association of GSTM1 or GSTT1 null genotypes (P = 0.62 and 0.11, respectively) with treatment-related malignancies. Our data suggest that GSTM1 and GSTT1 null genotypes may not predispose to epipodophyllotoxin-associated myeloid malignancies.

Antineoplastic Agents, Phytogenic↗
PubMed2000

Fractionated cyclophosphamide and etoposide for children with advanced or refractory solid tumors: a phase II window study.

PURPOSE: Cyclophosphamide (CPA) has a broad spectrum of activity against solid tumors. Hepatic self-induction of the active metabolite 4-hydroxycyclophosphamide occurs after repeated administration. We evaluated the clinical efficacy of a window regimen that administers fractionated CPA in conjunction with etoposide (VP16) in children with advanced or refractory solid tumors. PATIENTS AND METHODS: Seventeen children with advanced (n = 12) or refractory (n = 5) solid tumors were entered onto this phase II window study. The treatment regimen consisted of intravenous (IV) CPA 500 mg/m(2)/d and IV VP16 100 mg/m(2)/d. Both drugs were administered daily by short infusions for 5 consecutive days. RESULTS: A total of 34 courses were administered, with a median of two courses per patient. The median interval between chemotherapy courses was 21 days (range, 17 to 35 days). Thirty-three courses were assessable for toxicity, and all patients were assessable for response. No life-threatening toxicities were observed. The incidence of grade 3 or 4 neutropenia was 94% and of fever and neutropenia 38%. Fever and neutropenia occurred after 12 of 26 courses without recombinant human granulocyte colony-stimulating factor (rhG-CSF) and after one of eight courses with rhG-CSF (P =. 09). Grade 3 or 4 thrombocytopenia occurred after 10 courses (29%). There were no positive blood cultures. One heavily pretreated patient developed a localized perirectal abscess that required drainage. There were 10 patients (59%) with partial responses, four (23.5%) with stable disease, and three with progressive disease. CONCLUSION: Fractionated IV CPA and VP16 over 5 days can be safely administered in children with advanced or refractory solid tumors and has notable antineoplastic activity.

Adolescent↗
PubMed1999

Carboplatin for the treatment of children with newly diagnosed optic chiasm gliomas: a phase II study.

Management of low grade optic glioma in children and adolescents remains controversial. Treatment with chemotherapy may delay or eliminate the need for radiation therapy. Children with newly diagnosed optic chiasm glioma were eligible for enrollment in this phase II trial and received intravenous carboplatin (CBDCA) (560 mg/m2) every four weeks. Patients were monitored closely for toxicity and tumor status. Twelve children were enrolled. Six patients had stable disease, four a partial response and two progressed on therapy. Overall progression free survival was 83 +/- 11%. The median duration of follow-up was 38.6 months (range 18-63 months). No deaths were noted in our series. Thrombocytopenia was the major toxicity, and two patients required platelet transfusions. One child developed an urticarial reaction requiring discontinuation of therapy. Another child developed unilateral high frequency hearing loss. No renal toxicity was encountered. We have demonstrated that carboplatin can eliminate or delay radiation therapy in children and adolescents with low grade optic glioma. CBDCA deserves further investigation in larger clinical trials as a treatment for children with optic chiasm glioma.

Adolescent↗
PubMed1999

Mice lacking the folic acid-binding protein Folbp1 are defective in early embryonic development.

Periconceptional folic acid supplementation reduces the occurrence of several human congenital malformations, including craniofacial, heart and neural tube defects. Although the underlying mechanism is unknown, there may be a maternal-to-fetal folate-transport defect or an inherent fetal biochemical disorder that is neutralized by supplementation. Previous experiments have identified a folate-binding protein (Folbp1) that functions as a membrane receptor to mediate the high-affinity internalization and delivery of folate to the cytoplasm of the cell. In vitro, this receptor facilitates the accumulation of cellular folate a thousand-fold relative to the media, suggesting that it may be essential in cytoplasmic folate delivery in vivo. The importance of an adequate intracellular folate pool for normal embryogenesis has long been recognized in humans and experimental animals. To determine whether Folbp1 is involved in maternal-to-fetal folate transport, we inactivated Folbp1 in mice. We also produced mice lacking Folbp2, another member of the folate receptor family that is GPI anchored but binds folate poorly. Folbp2-/- embryos developed normally, but Folbp1-/- embryos had severe morphogenetic abnormalities and died in utero by embryonic day (E) 10. Supplementing pregnant Folbp1+/- dams with folinic acid reversed this phenotype in nullizygous pups. Our results suggest that Folbp1 has a critical role in folate homeostasis during development, and that functional defects in the human homologue (FOLR1) of Folbp1 may contribute to similar defects in humans.

Animals↗
PubMed1998

Receptor-mediated folate uptake is positively regulated by disruption of the actin cytoskeleton.

Receptor-mediated folate uptake is initiated by binding of ligand to a glycosyl phosphatidylinositol-anchored protein, folate receptor alpha (FR alpha). This receptor is expressed in a limited number of normal tissues but is overexpressed in a large number of epithelial malignancies. FR alpha synthesis, at least in part, is regulated by endogenous folate and by hormones in some cells, but much less is known about the control of function. Recently, we showed that phorbol 12-myristate 13-acetate increases the rate of receptor cycling, increases the rate of folate delivery, and causes the majority of the receptor to reside on the cell surface in nonmalignant cells in vitro (C. M. Lewis et al., Biochim. Biophys. Acta, 1401: 157-169, 1998). However, based upon effects (or lack of effects) of specific inhibitors of protein kinase C, the mechanism of action of phorbol 12-myristate 13-acetate is not likely via protein kinase C. Because exo- and endocytosis are controlled by the actin cytoskeleton, we tested cytochalasin D and latrunculin B, actin-disrupting agents, on FR alpha-mediated folate uptake. Disruption of the actin cytoskeleton reversibly increases the proportion of receptors on the cell surface and increases the rate of 5-methyltetrahydrofolate delivery. Disrupting microtubules with nocodazole had no effect. The increased rate of folate delivery caused by cytochalasin D is not observed in FR-negative cell lines. Although we have not yet identified the upstream effectors, likely candidates include small G-proteins such as rho, which are known to cause actin polymerization. In addition to identifying the machinery for receptor-mediated folate uptake, it may be important to integrate this new data into studies of FR alpha as a tumor antigen for imaging or delivering molecules via anti-FR antibodies or compounds coupled to folic acid.

Actins↗
PubMed1998

PMA alters folate receptor distribution in the plasma membrane and increases the rate of 5-methyltetrahydrofolate delivery in mature MA104 cells.

MA104 cells (a monkey kidney cell line) can internalize 5-methyltetrahydrofolate via a receptor mediated process termed potocytosis. Uptake is initiated by binding to an external folate receptor which cycles to an internal, but membrane bound compartment. These two pools can be measured by determining the amount of [3H]ligand removed by an acid-saline wash, i.e. acid labile and acid resistant pools. When assayed in confluent nonmitotic cells, 2/3 of the folate receptor pool is located in an internal (acid resistant) compartment, but phorbol 12-myristate 13-acetate (PMA) causes a shift such that 65-75% of the receptor pool resides on the surface of the plasma membrane. This new steady state is likely the result of an increased rate of receptor movement. In addition, PMA increases the rate of 5-methyl[3H]tetrahydrofolate delivery to the cytoplasm 1.8 fold. Using known inhibitors of potocytosis, we were able to show that the increased rate of delivery is receptor mediated. Comparison of the time courses of the PMA effects on folate receptor redistribution assessed by membrane binding of [3H]folic acid and 5-methyl[3H]tetrahydrofolate delivery to the cytoplasm suggests that PMA may be activating more than one protein kinase C independent signal transduction pathway. PMA is the first reported positive modulator of receptor mediated folate uptake.

Animals↗
PubMed1998

Toxicity, pharmacokinetics, and in vitro hemodialysis clearance of ifosfamide and metabolites in an anephric pediatric patient with Wilms' tumor.

PURPOSE: We evaluated the in vitro hemodialysis ratio and subsequent toxicity and pharmacokinetics of ifosfamide in an anephric patient with Wilms' tumor. METHODS: An in vitro model was used to determine the extraction ratio of ifosfamide by dialysis. The toxicity and plasma concentrations of ifosfamide, chloroacetaldehyde, and 4-hydroxyifosfamide were then determined over 24 h after a single 1.6 g/m2 dose of ifosfamide. Plasma concentrations were also measured before and after ten dialysis sessions during four courses of ifosfamide therapy. RESULTS: The in vitro hemodialysis model showed that ifosfamide was cleared with an extraction ratio of 86.7+/-0.5% and remained constant even at low concentrations of drug. The mean decrease in vivo following hemodialysis for ifosfamide, chloroacetaldehyde, and 4-hydroxyifosfamide were 86.9%, 77.2%, and 36.2%, respectively. The pharmacokinetic parameters for ifosfamide using model-independent methods were calculated: Vd = 0.23 l/kg, t1/2 = 4.8 h, and ClT = 3.30 l/h per m2. Ifosfamide-associated neurotoxicity was noted within hours of drug administration and improved rapidly following hemodialysis. CONCLUSIONS: The results of our study suggest that the pharmacokinetics of parent ifosfamide may not be substantially altered in patients with renal failure. Hemodialysis was shown to remove ifosfamide, chloroacetaldehyde, and 4-hydroxyifosfamide from the blood stream. Hemodialysis was also shown to reverse ifosfamide-related neurotoxicity.

Antineoplastic Agents, Alkylating↗
PubMed1998

Phase I and pharmacokinetic trial of aminopterin in patients with refractory malignancies.

PURPOSE: Aminopterin (AMT) is a potent folate analog that is no longer in routine clinical use. Because of laboratory data that suggests improved metabolism of AMT versus methotrexate (MTX) in lymphoblasts, we developed a phase I trial to determine the maximum-tolerated dose (MTD), dose-limiting toxicity (DLT), and pharmacokinetic profile of AMT. PATIENTS AND METHODS: Twenty patients with refractory malignancies were treated. The starting dose of AMT was 2.5 mg/m2 every 12 hours for two doses weekly: the dose of AMT was decreased and leucovorin (LV) rescue was added after the DLT was observed. Pharmacokinetics were performed after both intravenous (i.v.) and oral AMT administration. RESULTS: Mucosal toxicity was dose-limiting and resulted in the need for a dose reduction (dose level 2: AMT 2 mg/m2 every 12 hours for two doses weekly) and, subsequently, the addition of scheduled LV rescue (dose level 3: AMT 2 mg/m2 every 12 hours for two doses followed by LV 5 mg/m2 orally every 12 hours for two doses, starting 24 hours after the second dose of AMT). The mean areas under the curve (AUC) for the i.v. (n = 14) and oral (n = 13) doses were 1.20 +/- 0.09 (SE) and 1.05 +/- 0.14 micromol x h/L respectively. The half-life was 3.64 +/- 0.28 hours and the oral bioavailability in 12 matched subjects was 83.5% +/- 8.3%. One patient with endometrial adenocarcinoma achieved a complete response (CR) and remains on therapy at 11+ months. Seven patients had stable disease (SD) for 8 weeks or greater, which included one patient with a metastatic nerve sheath tumor who was stable for 9 months. CONCLUSION: We conclude that AMT has good oral bioavailability and that, when given on a q12 hour x two weekly schedule, the MTD is 2 mg/m2 with delayed LV rescue.

Administration, Oral↗
PubMed1998

Accumulation of methotrexate polyglutamates, ploidy and trisomies of both chromosomes 4 and 10 in lymphoblasts from children with B-progenitor cell acute lymphoblastic leukemia: a Pediatric Oncology Group Study.

Levels of accumulation of methotrexate polyglutamates were measured in vitro in lymphoblasts obtained at diagnosis from children with B-progenitor cell acute lymphoblastic leukemia (pro-B ALL). They were compared to numerical and structural chromosomal abnormalities present in these leukemic cells. In a series of 95 patients, the percent with high lymphoblast methotrexate polyglutamate levels increased with the increase in modal number of total chromosomes (p<0.001). Thus, lymphoblast methotrexate polyglutamate accumulation appeared to be closely linked to the extent of hyperdiploidy in childhood pro-B ALL. Lymphoblasts from 35 (88%) of the 40 children with hyperdiploid (>50 chromosomes) and 23 (88%) of 26 with hyperdiploid (DNA Index >1.16) pro-B ALL accumulated high levels of methotrexate polyglutamate, suggesting that they were more sensitive to methotrexate cytotoxicity. While children with hyperdiploid (DNA Index >1.16) pro-B ALL have a good prognosis, those with trisomies of both chromosomes 4 and 10, almost all of whom are hyperdiploid, have an even better outcome. There was no significant difference in methotrexate polyglutamate levels in lymphoblasts from 19 children with and 21 without trisomies of both chromosomes 4 and 10 (p = 0.25). The improved response to multi-agent chemotherapy conferred by the presence of trisomies of both chromosomes 4 and 10 in such patients may be due to increased sensitivity of their lymphoblasts to one or more anti-leukemic agents in addition to methotrexate.

Adolescent↗
PubMed1998

Translocations involving chromosome 12p11-13, methotrexate metabolism, and outcome in childhood B-progenitor cell acute lymphoblastic leukemia: a Pediatric Oncology Group study.

Children with B-progenitor cell acute lymphoblastic leukemia whose lymphoblasts at diagnosis accumulate high levels of methotrexate (MTX) and MTX polyglutamates (MTXPGs) appear to have a good prognosis. This has been attributed to increased sensitivity of their blast cells to MTX. However, the proportion of children who are cured of B-progenitor cell acute lymphoblastic leukemia exceeds the number whose lymphoblasts accumulate high MTXPG levels. We report that lymphoblasts from patients with < 50 chromosomes who have translocations that involve the short arm of chromosome 12 accumulate low levels of MTXPGs. These patients appear to have an excellent survival because none of 14 patients with translocations affecting 12p has relapsed, 26-79 months following diagnosis.

Antimetabolites, Antineoplastic↗
PubMed1998

High-dose trimetrexate and minimal-dose leucovorin: a case for selective protection?

Our objective was to find the minimum dose of leucovorin (LV; 5-formyltetrahydrofolate) needed to potentially provide selective protection of normal tissue in patients with tumors resistant to methotrexate (MTX) by virtue of transport during prolonged therapy with high-dose trimetrexate (TMTX). Based upon the known daily requirement for folate, that tumors are often resistant to methotrexate via a transport-based mechanism, and that large doses of trimetrexate can be given with large doses of leucovorin for the treatment of patients with Pneumocystis carinii, a protocol was designed to find the minimum LV dose required to allow the administration of large doses of TMTX. Patients were treated in 28-day cycles consisting of 14 consecutive days of oral TMTX (45 mg/m2 every 12 h), followed by 14 days of rest. The dose of concurrent LV was started at 5 mg/m2 twice daily. Cohorts of patients received successive half doses of LV so long as three consecutive patients had less than or equal to grade 3 toxicity. Ten patients received 29 courses of therapy. The most common toxicities encountered were thrombocytopenia (38%), mucositis (14%), and neutropenia (10%). At a LV dose of 2.5 mg/m2, toxicities were consistently limited to less than or equal to grade 3 and only one episode of grade 4 hematological toxicity. Although there was marked interpatient variability, the minimally effective LV dose for selective protection seems to be 2.5 mg/m2. If tumors are resistant to methotrexate because of decreased transport of drug (and also folate), then the same pharmacological principle used to develop TMTX/LV for the treatment of P. carinii may be applied to treatment of some patients with cancer.

Adolescent↗
PubMed1997

Elevation of homocysteine and excitatory amino acid neurotransmitters in the CSF of children who receive methotrexate for the treatment of cancer.

PURPOSE: Folate deficiency, either by diet or drug, increases plasma homocysteine (Hcy). Hcy damages cerebrovascular endothelium, and hyperhomocysteinemia is a risk factor for stroke. Hcy is metabolized to excitatory amino acid (EAA) neurotransmitters, such as homocysteic acid (HCA) and cysteine sulfinic acid (CSA), which may cause seizures and excitotoxic neuronal death. We postulated that excess Hcy and EAA neurotransmitters may partly mediate methotrexate (MTX)-associated neurotoxicity. PATIENTS AND METHODS: In this retrospective analysis, we used high-performance liquid chromatography (HPLC) to measure Hcy, HCA, and CSA in CSF from two groups of children: (1) a control group of patients with no MTX exposure, and (2) a treatment group of patients who had received MTX no more than 7 days before a scheduled lumbar puncture. RESULTS: The treatment group had a significantly (P = .0255) greater concentration of Hcy in CSF (0.814 micromol/L +/- 0.215 [mean +/- SEM], n = 23) than the control group (0.210 micromol/L +/- 0.028, n = 34). HCA and CSA were not detected in CSF from control patients (n = 29); however, MTX caused marked accumulation of CSF HCA (119.1 micromol/L +/- 32.0, n = 16) and CSA (28.4 micromol/L +/- 7.7, n = 16) in the treatment group. Patients with neurologic toxicity at the time of lumbar puncture had many of the highest concentrations of Hcy, HCA, and CSA. CONCLUSION: These data support our hypothesis that MTX-associated neurotoxicity may be mediated by Hcy and excitotoxic neurotransmitters.

Antimetabolites, Antineoplastic↗