V. Michael Whitehead

Acquired and inherited disorders of cobalamin and folate in children

Cobalamin deficiency in the newborn usually results from cobalamin deficiency in the mother. Megaloblastic anaemia, pancytopenia and failure to thrive can be present, accompanied by neurological deficits if the diagnosis is delayed. Most cases of spina bifida and other neural tube defects result from maternal folate and/or cobalamin insufficiency in the periconceptual period. Polymorphisms in a number of genes involved in folate and cobalamin metabolism exacerbate the risk. Inborn errors of cobalamin metabolism affect its absorption, (intrinsic factor deficiency, Imerslund‐Gräsbeck syndrome) and transport (transcobalamin deficiency) as well as its intracellular metabolism affecting adenosylcobalamin synthesis (cblA and cblB), methionine synthase function (cblE and cblG) or both (cblC, cblD and cblF). Inborn errors of folate metabolism include congenital folate malabsorption, severe methylenetetrahydrofolate reductase deficiency and formiminotransferase deficiency. The identification of disease‐causing mutations in specific genes has improved our ability to diagnose many of these conditions, both before and after birth.

Intestinal Conversion of Folinic Acid to 5‐Methyltetrahydrofolate in Man

Summary. In three adult subjects undergoing diagnostic umbilical vein catheteriza‐tion, the active stereoisomer of folinic acid (dl,‐5‐formyltetrahydrofolate) was metabolized during absorption and appeared in hepatic portal venous plasma as 5‐methyltetrahydrofolate. A small amount of 5‐formyltetrahydrofolate and probably of 10‐formylfolate was detected in hepatic portal venous plasma early during absorption as well.

Red blood cell methotrexate and folate levels in children with acute lymphoblastic leukemia undergoing therapy: a Pediatric Oncology Group pilot study.

SummaryWe enrolled children with acute lymphoblastic leukemia (ALL) in a Pediatric Oncology Group (POG) pilot study to monitor erythrocyte (RBC) methotrexate (MTX) and folate (F) levels before and during treatment. The mean value for RBCF at diagnosis was 0.86±0.46 nmol/ml RBC in the 214 patients who achieved remission and 1.21±0.74 nmol/ml RBC in the 10 patients who did not (P=0.020). Folate levels tended to increase during remission induction, but they dropped following an intensive consolidation with methotrexate to levels that were sustained throughout chemotherapy treatment. Methotrexate levels reached mean values of approximately 0.15 nmol/ml RBC at the end of an intensive methotrexate consolidation, then fell to levels that were sustained throughout maintenance therapy. There was a weak correlation between improved event-free survival and higher RBCMTX levels after consolidation, but no correlation was found between improved survival and the level of RBCMTX or RBCF during maintenance therapy. A larger study with more complete data is needed to determine whether RBCMTX or RBCF might be useful in predicting event-free survival in patients with ALL.

Hepatic failure secondary to indicine n‐oxide toxicity. A pediatric oncology group study

Indicine N‐oxide, a pyrrolizidine alkaloid, was given to a five‐year‐old boy with refractory acute myelocytic leukemia. Three days after receiving the drug the patient developed signs and symptoms of acute hepatic failure. The patient died nine days after receiving the drug and an autopsy showed massive hepatic necrosis. The acute hepatic failure observed in this patient may have been secondary to indicine N‐oxide toxicity. Cancer 52:61‐63, 1983.

Phase I trial of indicine-N-oxide in children with leukemia and solid tumors: a Pediatric Oncology Group study

SummaryA phase I trial of indicine-N-oxide was carried out in 12 children with solid tumors and in 16 with leukemia. Doses of 5, 6, and 7.5 g/m2 were given parenterally as a 15-min infusion every 3 weeks. The maximum tolerated dose in patients with solid tumors was 7.5 g/m2 and the dose-limiting toxicity was myelosuppression. In leukemia, the maximum tolerated dose was 6.0 g/m2 and hepatotoxicity was dose-limiting. Half of the children with leukemia showed elevations in transaminase levels and one child died of massive hepatic necrosis. This hepatotoxicity limits the use of indicine-N-oxide in children with leukemia. Antineoplastic activity was limited to a transient reduction in the numbers of circulating leukemic cells.

Inhibition of gamma-glutamyl hydrolases in human cells by 2-mercaptomethylglutaric acid

Cultured human lymphocytes and fibroblasts accumulate methotrexate during 24 hours and synthesize methotrexate polyglutamates up to the hexaglutamate, with the triglutamate predominating. In the interval after incubation with methotrexate, drug is lost, metabolites are converted to longer chain-lengths, and methotrexate pentaglutamate predominates. 2-Mercaptomethylglutaric acid, an inhibitor of neutral pH gamma-glutamyl hydrolases in vitro, had little effect on polyglutamate synthesis during incubation of the cells with methotrexate, but maintained for 48 hours almost all the methotrexate as the pentaglutamate when added after the removal of the drug. These findings demonstrate that inhibition of gamma-glutamyl hydrolases is an effective approach to alter the distribution of polyglutamate forms of methotrexate in vivo and indicate that enzymatic hydrolysis may contribute to regulation of polyglutamate chain lengths in human cells.

A Phase I study of acivicin in refractory pediatric solid tumors : A Pediatric Oncology Group Study

Forty-two patients with progressive solid tumors and brain tumors were entered in this Phase I study of the glutamine antagonist acivicin given intravenously over thirty minutes daily for five days. The major toxicities encountered were myelosuppression and central nervous system toxicity (nightmares and somnolence). The maximum tolerated dosage on this schedule was 26 mg/M2 daily for five days. Six patients including three patients with brain tumor had stable disease.

A phase I trial of fazarabine in refractory pediatric solid tumors. A Pediatric Oncology Group study.

SummaryFazarabine is a synthetic analog of cytosine arabinoside and 5-azacytidine that incorporates structural features of both compounds. Xenograft studies showed good activity against a variety of transplanted tumors. Initial studies in adults employed both a continuous infusion schedule and a daily bolus x 5 schedule. Myelotoxicity, especially neutropenia, was dose-limiting, with excessive myelotoxicity seen on the daily bolus x 5 at 72 mg/M2/day. Since short infusions may be administered in Ringers lactate rather than either dimethylsulfoxide or dimethylacetamide required for continuous infusion, this study examined a daily x 5 schedule in children with refractory solid tumors. The initial dosage was 30 mg/M2/day, 80% of the maximum tolerated dosage in adults, with subsequent 30% dosage escalations. A total of 18 patients were enrolled, with a wide spectrum of pediatric solid tumors. Myelosuppression was the only significant toxicity, and was excessive at 78 mg/M2/day. Therefore, on this bolus regimen, 65 mg/M2/day for 5 days was the maximum tolerated dosage. One patient with medulloblastoma had stable disease for 65 days. No other responses were seen.

Ifosfamide with mesna uroprotection and etoposide in recurrent, refractory acute leukemia in childhood: A pediatric oncology group study

Background. Ifosfamide has previously been shown to be active as a single agent and in combination with doxorubicin, etoposide, and teniposide in pediatric solid tumors and adult acute leukemia. The authors performed a dose‐escalation trial of ifosfamide with a fixed dosage of etoposide, with mesna uroprotection, in children with multiply recurrent acute leukemia.

Methotrexate Metabolism by Bone Marrow Cells from Patients with Leukemia

Bone marrow cells from children with leukemia in remission and lymphoblasts and myeloblasts from children with early and late-stage leukemia all accumulated methotrexate during short-term culture and converted it to poly-gamma-glutamyl derivatives. This metabolism was time and dose-dependent. Leukemia cells from two patients with chronic myelocytic leukemia also synthesized methotrexate polyglutamates. Patients varied one from another in the quantity of total non-exchangeable methotrexate and methotrexate polyglutamates present in cells, but highest levels of each of these were seen in late acute lymphoblastic leukemia and in acute myeloblastic leukemia. Co-incubation of leukemic cells with both methotrexate and a ten-fold excess of folinic acid decreased accumulation and polyglutamylation of methotrexate to the same extent as achieved by reducing methotrexate concentration ten-fold. Co-incubation with methotrexate and a ten-fold excess of vincristine did not increase total cell methotrexate and methotrexate polyglutamates in leukemic cells in culture. Such an increase had been anticipated from earlier studies with other cells. Indeed, levels of methotrexate and its derivatives were modestly reduced.