Receptor binding characteristics and cytotoxicity of insulin-methotrexate.

Aim: To characterize the receptor binding affinity and cytotoxicity of insulin-methotrexate (MTX) for the potential utilization of insulin as carriers for carcinoma target drugs.

Methods: MTX was covalently linked to insulin. Insulin-MTX conjugate was purified by Sephadex G-25 column and analyzed by high performance liquid chromatography. Hepatocellular carcinoma cell membrane fractions were isolated by sucrose density gradient centrifugation. Competitive displacement of (125)I-insulin with insulin and insulin-MTX binding to insulin receptors were carried out. Cytoreductive effect of insulin-MTX on human hepatoma BEL7402 cells and human hepatocyte cell line HL7702 was evaluated using the MTT assay.

Results: Insulin-MTX competed as effectively as insulin with (125)I-insulin for insulin receptors. The values of Kd for insulin-MTX and insulin were 93.82+/-19.32 nmol/L and 5.01+/-1.24 nmol/L, respectively. The value of Kd for insulin-MTX was significantly increased in comparison with insulin (t=7.2532, n=4, P<0.005). Insulin-MTX inhibited the growth of human hepatoma cells (BEL7402) almost as potently as MTX. The inhibitory effect reached a peak on the 5 th day when the growth of cells was inhibited by 79% at a concentration of 5.0 microg/mL insulin-MTX. Treatment with 5.0 microg/mL of MTX and 5.0 microg/mL of insulin-MTX merely resulted in inhibition of HL7702 cells by 31.5% and 7.8% on the 5 th day.

Conclusion: Insulin-MTX specifically recognizes insulin receptors and inhibits the growth of BEL7402 cells. These results suggest that insulin can be used as a carrier in receptor mediated carcinoma-targeting therapy.