Insulin analogs: Assessment of insulin mitogenicity and IGF-I activity.

The metabolic activity of insulin has been studied extensively in vitro and in vivo, based on the initial assessment of insulin receptor affinity, followed by methods to estimate the metabolic activity in vitro. These estimates provide some guidance about the biological activity which will be found in vivo; they need to be confirmed and supplemented by testing the glucose-lowering activity in animals (mice, rats, dogs, pigs). The biological effects (hypoglycemic activity) are related to the direct activation of the insulin receptor and subsequent signaling through intracellular mechanisms. The second group of biological effects is related to cell proliferation (mitogenic activity), which may be mediated by the insulin receptor, by the IGF-I receptor, and by hybrids of the two receptors. The evaluation of the relevance of mitogenicity estimates may be performed in in vitro and in vivo. One approach is cell proliferation in benign and malignant cell lines, for example, on mammary epithelial cell lines MCF-10 and MCF-7 (Milazzo et al. 1997)