Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.5.1.3 (dihydrofolate reductase)
 5,819 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In studies on (antitumor antibody)-drug conjugates as potential antitumor agents, the amide derivatives of methotrexate (MTX) with cysteine and with 2-mercaptoethylamine (cysteamine) (MTX-Cys and MTX-MEA, respectively) were linked via a disulfide bond with a monoclonal antibody (alpha MM46) to a mouse mammary tumor MM46 with attached 3-(2-pyridyldithio) propionyl groups to give conjugates of MTX with alpha MM46 (MTX-Cys-SS-alpha MM46 and MTX-MEA-SS-alpha MM46, respectively). These two conjugates are both linked by a disulfide bond and are very similar in structure, but MTX-MEA-SS-alpha MM46 showed only weak in vitro cytotoxicity against MM46 cells, whereas MTX-Cys-SS-alpha MM46 had strong cytotoxicity. The cytotoxicity of the latter was comparable to that of the conventional direct MTX-alpha MM46 conjugate prepared with an MTX-active ester. However, this conjugate had a greater selectivity than that of the direct conjugate, calculated as the IC50 (concentration of a conjugate by MTX equivalence required for suppression of the number of viable MM46 cells to 50% of that of the untreated control) for the corresponding nonspecific conjugate divided by the IC50 for the alpha MM46 conjugate. The inhibitory activities of MTX-Cys and MTX-MEA on dihydrofolate reductase were similar. The cytotoxicity of MTX-Cys-SS-alpha MM46 was not affected by thiamine pyrophosphate, an inhibitor of the active transport of MTX across the cell membrane, but was decreased significantly by ammonium chloride, a lysosomotropic amine. However, the cytotoxicity was decreased only to a small extent by leupeptin, an inhibitor of lysosomal cysteine proteases cathepsins B, H, and L. These results suggest that the cytotoxicity is mediated by lysosomes, and may involve lysosomal enzymes other than cathepsins B, H, and L.
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PMID:Cytotoxicities of two disulfide-bond-linked conjugates of methotrexate with monoclonal anti-MM46 antibody. 278 2

The binding of methotrexate (MTX) to IgG in conjugates was examined by studies on a direct MTX conjugate with a monoclonal antibody (aMM46) to mouse mammary tumor MM46 cells and corresponding irrelevant antibody and normal gamma-globulin conjugates, all prepared by the active ester method with MTX N-succinimidyl ester (MTX-OSu). The binding was examined in terms of effects on the potency and selectivity of the cytotoxic activity of the aMM46 conjugate. The results obtained supported the following conclusions: (a) MTX-OSu reacts not only with the amino group of IgG to give an amide bond, but also with another group(s) to give a less stable bond(s) such as an ester bond; (b) in contrast to the amide bond-linked MTX, which is taken up by the cells by endocytic internalization, a substantial portion of the MTX linked by an ester or other less stable bond(s) is released from the conjugates extracellularly and enters the cells by the MTX active transport system, as revealed by the inhibitory effect of thiamine pyrophosphate on the cytotoxicity; (c) this MTX linked by a less stable bond(s) that causes nonspecific cytotoxicity can be removed by treatment with hydroxylamine; (d) the overall cytotoxicity of aMM46-MTX decreased on removal of this less stably linked MTX, suggesting that the lysosomal degradation of the conjugate carrying amide bond-linked MTX to liberate MTX derivatives of low molecular weight is insufficient; (e) the liberation of low-molecular-weight substances in the lysosomes is probably more important for efficient entry of active substances into the cytosol, than for inhibition of the activity of dihydrofolate reductase, because after hydroxylamine treatment, the amide bond-linked MTX showed greater decrease in drug cytotoxicity than in inhibitory activity against dihydrofolate reductase; (f) in combination with hydroxylamine treatment, insertion between MTX and IgG of a linkage capable of ready cleavage in lysosomes deserves exploitation as a method for making potent conjugates with less nonspecific activity.
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PMID:Nature of linkage and mode of action of methotrexate conjugated with antitumor antibodies: implications for future preparation of conjugates. 325 66