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A gene transfer strategy for making bone marrow cells resistant to trimetrexate
H T Spencer1, S E Sleep, J E Rehg
1Department of Biochemistry, St Jude Children's Research Hospital, Memphis, TN 38101 USA.
Blood
|March 15, 1996
Summary
This study developed a gene therapy using a mutant dihydrofolate reductase (DHFR) enzyme to protect bone marrow from the anticancer drug trimetrexate (TMTX). The L22Y variant effectively shielded hematopoiesis from TMTX toxicity in mice.
Area of Science:
- Oncology
- Gene Therapy
- Hematopoiesis
Background:
- Trimetrexate (TMTX) is an antifolate anticancer drug with potential benefits but is limited by severe myelosuppression.
- Previous studies used mutant dihydrofolate reductase (DHFR) genes to confer methotrexate (MTX) resistance, suggesting a similar strategy for TMTX.
Purpose of the Study:
- To identify a DHFR variant conferring maximal TMTX resistance.
- To evaluate the efficacy of a retroviral vector expressing the optimal DHFR variant for protecting hematopoietic cells from TMTX toxicity in vivo.
Main Methods:
- Screened six human DHFR variants for TMTX resistance in fibroblasts.
- Transduced murine hematopoietic progenitor cells with a retroviral vector encoding the L22Y DHFR variant.
- Assessed protection from TMTX-induced neutropenia and reticulocytopenia in mice reconstituted with transduced bone marrow cells.
Main Results:
- A DHFR variant with a Leu-to-Tyr mutation at codon 22 (L22Y) conferred a 100-fold increase in TMTX resistance.
- L22Y-transduced hematopoietic progenitor cells exhibited high-level TMTX resistance in vitro.
- In vivo studies demonstrated that the L22Y vector protected hematopoiesis from TMTX toxicity, with protection levels correlating to proviral copy number.
Conclusions:
- The L22Y retroviral vector is highly effective in protecting hematopoiesis from trimetrexate toxicity.
- This gene therapy approach holds promise for enhancing the therapeutic application of TMTX in cancer treatment.