DISCUSSION PAPER: L-ASPARAGINASE INDUCED ALTERATION OF AMETHOPTERIN (METHOTREXATE) ACTIVITY IN MOUSE LEUKEMIA L5178Y

The effect of asparaginase therapy on methotrexate toxicity and efficacy in children with acute lymphoblastic leukemia

Asparaginase and methotrexate (MTX), both essential for pediatric acute lymphoblastic leukemia therapy, are often used concomitantly. Depending on the sequence, in vitro, asparaginase inhibits MTX-polyglutamate (MTXPG) formation, and side effects overlap. MTX toxicity and efficacy, reflected by intracellular erythrocyte MTXPG's, were compared between children treated with and without asparaginase during high dose MTX (HD-MTX) courses of the DCOG ALL-11 protocol (NL50250.078.14). Seventy-three patients, of whom 23 received asparaginase during the HD-MTX courses, were included. Grade 3-4 leukopenia and neutropenia occurred more often (59% and 86% vs. 30% and 62%). The number of infections, grade 3-4 hepatotoxicity, nephrotoxicity, and neurotoxicity did not differ. Patients with asparaginase had lower MTXPG levels, although to a lesser extent than in vitro studies. Although patients with asparaginase during HD-MTX courses showed more myelosuppression, this had no (serious) clinical consequences. Regarding the MTX efficacy, the schedule-related antagonism seen in in vitro seems less important in vivo.

High-Dose Methotrexate-Leucovorin Rescue Therapy: Selected Application in Non-Hodgkin's Lymphoma

Methotrexate with leucovorin rescue (HDMTX-LV rescue), has been used to treat solid tumors and non-Hodgkin's lymphomas (NHL). We studied the use of HDMTX-LV rescue in patients with widespread NHL with histologic diagnosis of diffuse poorly differentiated lymphocytic and diffuse histiocytic including involvement of the central nervous system (CNS) and/or bone marrow. The prognosis with conventional chemotherapy is extremely poor. Three patients have bone marrow involvement, 2 patients CNS, and 2 both. These patients were unresponsive to conventional chemotherapy and had a rapid progression of their disease. Therapy with HDMTX-LV rescue induced responses in 5 patients: 2 patients achieved a complete remission and three a partial remission. Regression of CNS involvement was observed in 3 patients; bone marrow toxicity was not observed. Only 1 patient failed to respond. These data suggest that HDMTX-LV rescue may be useful as primary therapy in lymphoma patients with CNS and/or bone marrow involvement.

Sequential administration of methotrexate and asparaginase in relapsed or refractory pediatric acute myeloid leukemia

BACKGROUND

The efficacy of combination chemotherapy with methotrexate (MTX) and asparaginase is not well known in relapsed and refractory acute leukemia after contemporary therapy.

PROCEDURE

A retrospective study of pediatric patients with relapsed or refractory acute myeloid leukemia (AML) who received MTX and asparaginase as a salvage therapy at St. Jude Children Research Hospital was performed. MTX was given intravenously followed by a dose of asparaginase intramuscularly or intravenously 24 hours later. The chemotherapy cycle was repeated every 7-10 days. Response, survival, and toxicities were evaluated.

RESULTS

Fifteen patients, median age 10.5 years (range, 1.1-18.5 years), were treated. Median number of previous therapeutic regimens was three (range, 1-4). Six patients responded to treatment (three had morphologic complete remission with incomplete blood count recovery, two had partial remission, and one had stable disease for 16 months), and four are still alive. Three of six responders had monoblastic leukemia, and also developed tumor lysis syndrome. The 1- and 2-year overall survival rates are 35.6% and 17.8%, respectively. The most common adverse event was transient elevation of transaminases (nine patients). Two patients developed pancreatitis. Episodes of febrile neutropenia were rare (two patients), and most courses (75 out of 93 total courses) were given in an outpatient setting.

CONCLUSIONS

Combination chemotherapy with MTX and asparaginase appears to be an effective salvage therapy and well tolerated in patients with relapsed or refractory childhood AML, even in those heavily pretreated with contemporary frontline or salvage therapy.

Challenges and opportunities in childhood cancer drug development

Advances made in the treatment of childhood malignancies over the past four decades have resulted in overall 5-year survival rates of approximately 80%. However, despite these advances, several childhood cancers still have unacceptably low cure rates, and, even when treatment is successful, the acute and long-term morbidity of current therapy can be substantial. The development of molecularly targeted anticancer drugs offers the prospect of more effective therapy with fewer side effects, but will require increasing partnership between governments, and the academic and private sectors.

A Genome-Wide View of the In vitro Response to l-Asparaginase in Acute Lymphoblastic Leukemia

To investigate the effect of l-asparaginase on acute lymphoblastic leukemia (ALL), we used cDNA microarrays to obtain a genome-wide view of gene expression both at baseline and after in vitro exposure to l-asparaginase in cell lines and pediatric ALL samples. In 16 cell lines, a baseline gene expression pattern distinguished l-asparaginase sensitivity from resistance. However, for 28 pediatric ALL samples, no consistent baseline expression pattern was associated with sensitivity to l-asparaginase. In particular, baseline expression of asparagine synthetase (ASNS) was not predictive of response to l-asparaginase. After exposure to l-asparaginase, 5 cell lines and 10 clinical samples exhibited very similar changes in the expression of a large number of genes. However, the gene expression changes occurred more slowly in the clinical samples. These changes included a consistent increase in expression of tRNA synthetases and solute transporters and activating transcription factor and CCAAT/enhancer binding protein family members, a response similar to that observed with amino acid starvation. There was also a consistent decrease in many genes associated with proliferation. Taken together, the changes seem to reflect a consistent coordinated response to asparagine starvation in both cell lines and clinical samples. Importantly, in the clinical samples, increased expression of ASNS after l-asparaginase exposure was not associated with in vitro resistance to l-asparaginase, indicating that ASNS-independent mechanisms of in vitro l-asparaginase resistance are common in ALL. These results suggest that targeting particular genes involved in the response to amino acid starvation in ALL cells may provide a novel way to overcome l-asparaginase resistance.

Enhancement of anticancer agent activity by selective inhibition of rapidly proliferating tissues of the host

Most cytotoxic drugs used in cancer therapy do not discriminate between neoplastic and normal proliferating cells. To avoid irreversible damage to vital host tissues, such as bone marrow and intestine, drugs must be administered at dosages which usually prove insufficient to eradicate all of the neoplastic cells present. This review focuses on an approach to improve cancer chemotherapy by selectively protecting normal, proliferating cells during treatment, thereby permitting the administration of otherwise lethal doses of drug. Preclinical in vivo studies of cytokinetic modulation with interferon, or L-histidinol, as well as recent clinical studies of interferon modulation of the activity of 5-fluorouracil are reviewed.