[Experiences with modified BFM protocols in the treatment of children with acute lymphoblastic leukemia (ALL) in East Germany 1981-1991]

Prevention of high-dose-methotrexate neurotoxicity by adequate folinic acid rescue is possible even after central nervous system irradiation

Neurotoxicity, especially associated with therapy for acute lymphatic leukemia, has been attributed by many to the use of methotrexate (MTX). After radiotherapy this has been reported even more frequently but no explanation has been suggested apart from "a complex interaction". The hypothesis presented here is as follows: (1) Inadequate folinic acid rescue alone accounts for MTX-induced neurotoxicity. (2) Adequate folinic acid after MTX can prevent neurotoxicity. (3) Higher doses of MTX require a disproportionately higher dose of folinic acid than MTX to prevent toxicity. Doubling the dose of MTX has required tripling and quadrupling the folinic acid dose to prevent neurotoxicity. Assuming that central nervous system radiotherapy increases the cerebrospinal fluid levels of MTX and folinic acid proportionally, the folinic acid level may now not be enough to prevent neurotoxicity. This neurotoxicity occurs when MTX is given after (but not before) radiotherapy, and can be prevented by appropriate doses of folinic acid. (4) There is no evidence that within the dose range currently being used, the administration of larger quantities of folinic acid to prevent neurotoxicity compromises prognosis. This hypothesis is supported by a large amount of published data. Critical reanalysis of studies that ostensibly contradict parts of the hypothesis showed that they, in fact, support it.

Defining the appropriate dosage of folinic acid after high-dose methotrexate for childhood acute lymphatic leukemia that will prevent neurotoxicity without rescuing malignant cells in the central nervous system

Neurotoxicity after the administration of methotrexate continues to worry physicians. However, inadequate folinic acid rescue is often not considered as a cause of this complication. To clarify whether adequate folinic acid rescue prevents methotrexate-induced neurotoxicity without reducing the cure rate in childhood ALL, published evidence that supported or refuted this claim was investigated. A literature search was conducted and the authors of the relevant studies were contacted. The published data supported the contention that neurotoxicity can be prevented by adequate folinic acid rescue even after very high doses of methotrexate. The safe minimum dose of folinic acid can be defined in terms of the dose of methotrexate given; the time to start of rescue is probably less important. There was no evidence that higher doses of folinic acid, such as those used after methotrexate in the treatment of osteosarcoma, rescue leukemia cells. No change in cure rate was found in relation to changes in scheduling or clinically relevant doses of folinic acid rescue. The accumulation of folinic acid in the cerebrospinal fluid did not seem to be of clinical relevance. No studies indicate that doses of folinic acid after high-dose methotrexate administration interfere with the killing of leukemia cells, nor that delaying the start of rescue beyond a certain point increases the antileukemic effect; neurotoxicity will, however, be increased. Review of current protocols that use low-dose folinic acid rescue and are associated with neurotoxicity is highly recommended.

The multidrug resistance-associated protein 3 (MRP3) is associated with a poor outcome in childhood ALL and may account for the worse prognosis in male patients and T-cell immunophenotype

The family of multidrug resistance-associated proteins (MRPs) belongs to the superfamily of adenosine triphosphate-binding-cassette (ABC) transporters, which have the ability to function as outward pumps for chemotherapeutic drugs and therefore might be involved in drug resistance. In this study the expression of the MRP2, MRP3, MRP4, MRP5, and SMRP genes was measured using TaqMan real-time polymerase chain reaction (PCR) in 103 children with previously untreated acute lymphoblastic leukemia (ALL) (precursor B-cell ALL [B-ALL], n = 71; T-cell ALL [T-ALL], n = 32). All 5 genes were expressed with a great variability. Only MRP3 expression was associated with a significantly worse prognosis (P =.008). The median expression of MRP3 was 10-fold higher in T-ALL than in precursor B-ALL (P <.001) and 4-fold higher in male patients than in female patients (P <.001). The prognostic impact of MRP3 was independent of immunophenotype or sex. Higher levels of MRP3 were found in patients with a poor in vivo response to prednisone, but this could not be confirmed in an independent case-control study (40 patients) for prednisone response. In healthy donors, the median expression of MRP4 was 4-fold higher in bone marrow and 8-fold higher in CD34+ stem cells compared with peripheral blood (P =.002). Our results suggest that MRP3 is involved in drug resistance in childhood ALL. It therefore represents an interesting target to overcome multidrug resistance. High levels of MRP3 could possibly be the reason for the poorer prognosis of male patients or patients who have T-ALL. Similar to other members of the family of ABC transporters, MRP4 seems to be a marker for immature stem cells.