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Development of methotrexate alpha-peptides as prodrugs for activation by enzyme-monoclonal antibody conjugates
1Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, CA 92037, USA.
Abstract:
Selective delivery of lethal concentrations of drugs to tumors, allowing the latter to be eradicated without damage to other tissues, continues to be a major goal in cancer chemotherapy. Prodrugs (i.e. drugs that have been derivatized to prevent uptake into cells or interaction with targets), activated by enzyme-monoclonal antibody conjugates positioned at tumor sites, offer promise for achieving this objective. Methotrexate alpha-peptides (derivatives in which an amino acid is linked to the alpha-carboxyl group of the glutamate moiety) are ideal prodrugs, since they are not transported into cells and can be converted to the parent drug by carboxypeptidases. The L,L-diastereomer of MTX-alpha-Phe, synthesized in good yield by treatment of the p-nitrophenyl ester of 4-amino-4-deoxy-10-methylpteroic acid with Glu-alpha-Phe, was hydrolyzed readily by carboxypeptidase A (CP-A). Conjugate was prepared by derivatizing the enzyme and monoclonal antibody KS1/4 with linkers containing maleimide and sulfhydryl groups, respectively; interaction of these groups to form a stable thioether bond joined the proteins. When administered in vitro to UCLA-P3 human lung adenocarcinoma cells (ca. 5 x 10(4) antibody binding sites/cell) that had been pre-treated with the conjugate (whose antibody KS1/4 is targeted to these cells), and excess conjugate removed by extensive washing, MTX-Phe (ID50 = 6.3 x 10(-8) M) approached the toxicity of MTX (ID50 = 4.5 x 10(-8) M). In the absence of conjugate, MTX-Phe was much less toxic (ID50 = 2.2 x 10(-6) M).
Insights
Targeted cancer therapy uses enzyme-monoclonal antibody conjugates to activate methotrexate alpha-peptides (MTX-Phe) prodrugs at tumor sites. This approach selectively delivers lethal drug concentrations, minimizing damage to healthy tissues.
Area of Science:
- Oncology
- Biochemistry
- Drug Delivery
Background:
- Selective drug delivery to tumors is crucial for effective cancer chemotherapy with minimal side effects.
- Prodrugs activated by enzyme-monoclonal antibody conjugates offer a promising strategy for targeted cancer treatment.
- Methotrexate alpha-peptides are ideal prodrugs due to their inability to enter cells and their activation by carboxypeptidases.
Purpose of the Study:
- To evaluate the efficacy of a novel enzyme-monoclonal antibody conjugate system for targeted activation of a methotrexate prodrug.
- To assess the selective toxicity of the activated prodrug against cancer cells in vitro.
Main Methods:
- Synthesis of the L,L-diastereomer of methotrexate alpha-phenylalanine (MTX-Phe) prodrug.
- Preparation of an enzyme-monoclonal antibody conjugate using maleimide and sulfhydryl linkers.
- In vitro testing of MTX-Phe toxicity on UCLA-P3 human lung adenocarcinoma cells in the presence and absence of the conjugate.
Main Results:
- The MTX-Phe prodrug was effectively synthesized and hydrolyzed by carboxypeptidase A.
- The enzyme-monoclonal antibody conjugate specifically targeted cancer cells.
- In vitro, MTX-Phe activated by the conjugate demonstrated toxicity comparable to the parent drug, methotrexate (MTX).
Conclusions:
- Enzyme-monoclonal antibody conjugates can selectively activate prodrugs at tumor sites.
- This targeted approach significantly enhances the therapeutic potential of methotrexate prodrugs.
- The study demonstrates a viable strategy for improving the efficacy and safety of cancer chemotherapy.
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