Abstract
Insulin analogue X10 has a higher mitogenic potency than native human insulin in vitro and supra-pharmacological doses of insulin X10 increased the incidence of mammary tumours in rats. Compared to native human insulin, insulin X10 has increased binding affinity to the insulin receptor and the IGF-1 receptor, but it is not known whether either or both characteristics are important for stimulation of cell proliferation in vivo. The aim of this study was to explore how increased binding affinity to the insulin receptor or the IGF-1 receptor contributes to stimulation of cell proliferation in vivo. A mouse xenograft model was established with rat L6 myoblast cells transfected with the human insulin receptor (L6hIR cells) and effects of supra-pharmacological doses of native human insulin, insulin X10 or novel insulin analogues with increased binding affinity to either the insulin receptor or the IGF-1 receptor were examined. Treatment with insulin X10 and insulin analogues with increased binding affinity to either the insulin receptor or the IGF-1 receptor increased growth of L6hIR cell xenografts significantly compared to native human insulin. Thus, increased binding affinity to the insulin receptor and the IGF-1 receptor are each independently linked to increased growth of L6hIR cell xenografts in vivo.
Highlights
Insulin analogue X10 has a higher mitogenic potency than native human insulin in vitro and suprapharmacological doses of insulin X10 increased the incidence of mammary tumours in rats
In previous studies it has been reported that human insulin (HI) and certain insulin analogues stimulated growth of tumour cells in vivo only via binding to the IR6–9, but more recently it was demonstrated that HI and insulin analogue X10 (IX10) are able to activate the IGF-1 receptor (IGF-1R) on cancer cells in vivo[10]
This correlated with increased mitogenic potency in H4IIE cells (Table 1), where the mitogenic response is mediated via the insulin receptor (IR) (Supplementary Table S1)
Summary
Insulin analogue X10 has a higher mitogenic potency than native human insulin in vitro and suprapharmacological doses of insulin X10 increased the incidence of mammary tumours in rats. A mouse xenograft model was established with rat L6 myoblast cells transfected with the human insulin receptor (L6hIR cells) and effects of supra-pharmacological doses of native human insulin, insulin X10 or novel insulin analogues with increased binding affinity to either the insulin receptor or the IGF-1 receptor were examined. Compared to human insulin (HI), IX10 binds with increased affinity to the insulin receptor (IR) and the IGF-1 receptor (IGF-1R) and has delayed dissociation rate upon binding to the IR3–5 It is not known if each of these characteristics independently are involved in enhanced stimulation of growth in vivo, even though these characteristics in the case with IX10 all appear linked with an increased tumour incidence in rats. With two novel insulin analogues, designed to have increased binding affinity to either the IR or the IGF-1R, was examined, to establish how these characteristics influence cellular growth in vivo
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