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Monoclonal antibody targeting of methotrexate (MTX) against MTX-resistant tumour cell lines
1Cancer Research Campaign Laboratories, University of Nottingham, UK.
Abstract:
Several Methotrexate (MTX)-resistant sublines of the osteogenic sarcoma cell line 791T were derived by continuous selection in the presence of MTX and 12-O-tetradecanoylphorbol-13-acetate (TPA). Studies including assays of the uptake and binding of [3H]MTX and fluoresceinated-MTX, determined that these sublines showed diminished MTX transport, and that none of them appeared to overproduce the MTX-target enzyme dihydrofolate reductase. Conjugates of the anti-791T monoclonal antibody 791T/36 linked to MTX via human serum albumin (HSA) were prepared by Dr M.C. Garnett. These were cytotoxic selectively for cells bearing the 791T/36-defined antigen (gp72), and were found to be as cytotoxic to most of the MTX-resistant 791T sublines as they were to parental 791T cells. Furthermore, an anti-MTX/anti-gp72 bispecific antibody 516 augmented the cytotoxicity of HSA-MTX conjugate to the MTX-resistant 791T variant R120 apparently as efficiently as for parental 791T cells. It is suggested that acquired drug resistance caused by deficient transport mechanisms may be partially or wholly overcome by targeting the drug to a readily-internalised cell surface antigen.
Insights
Targeting Methotrexate (MTX) to cell surface antigens overcomes drug resistance in osteosarcoma. This strategy bypasses deficient MTX transport, offering a new approach for resistant cancer cells.
Area of Science:
- Oncology
- Pharmacology
- Biotechnology
Background:
- Methotrexate (MTX) resistance is a significant challenge in osteosarcoma treatment.
- Acquired MTX resistance often results from diminished drug transport rather than enzyme overproduction.
Purpose of the Study:
- To investigate strategies for overcoming MTX resistance in 791T osteosarcoma cells.
- To evaluate the efficacy of antibody-drug conjugates targeting cell surface antigens in resistant cell lines.
Main Methods:
- Derived MTX-resistant 791T osteosarcoma sublines.
- Assessed MTX uptake, binding, and dihydrofolate reductase activity.
- Prepared and tested anti-791T monoclonal antibody (791T/36) conjugates linked to MTX via human serum albumin (HSA).
- Evaluated a bispecific antibody (516) to enhance conjugate efficacy.
Main Results:
- Resistant sublines exhibited reduced MTX transport but not dihydrofolate reductase overproduction.
- HSA-MTX conjugates showed selective cytotoxicity for cells expressing the gp72 antigen.
- Conjugates were equally effective against MTX-resistant and parental 791T cells.
- Bispecific antibody 516 enhanced conjugate efficacy in resistant cells.
Conclusions:
- Targeting cell surface antigens can overcome acquired MTX resistance due to transport defects.
- Antibody-drug conjugates offer a promising approach to treat MTX-resistant osteosarcoma.