Non-metabolisable insulin glargine does not promote breast cancer growth in a mouse model of type 2 diabetes

Increased insulin receptor binding and increased IGF-1 receptor binding are linked with increased growth of L6hIR cell xenografts in vivo

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.

SGLT2 inhibition slows tumor growth in mice by reversing hyperinsulinemia

Background

Obesity confers an increased risk and accelerates the progression of multiple tumor types in rodents and humans, including both breast and colon cancer. Because sustained weight loss is rarely achieved, therapeutic approaches to slow or prevent obesity-associated cancer development have been limited, and mechanistic insights as to the obesity-cancer connection have been lacking.

Methods

E0771 breast tumors and MC38 colon tumors were treated in vivo in mice and in vitro with two mechanistically different insulin-lowering agents, a controlled-release mitochondrial protonophore (CRMP) and sodium-glucose cotransporter-2 (SGLT2) inhibitors, and tumor growth and glucose metabolism were assessed. Groups were compared by ANOVA with Bonferroni’s multiple comparisons test.

Results

Dapagliflozin slows tumor growth in two mouse models (E0771 breast cancer and MC38 colon adenocarcinoma) of obesity-associated cancers in vivo, and a mechanistically different insulin-lowering agent, CRMP, also slowed breast tumor growth through its effect to reverse hyperinsulinemia. In both models and with both agents, tumor glucose uptake and oxidation were not constitutively high, but were hormone-responsive. Restoration of hyperinsulinemia by subcutaneous insulin infusion abrogated the effects of both dapagliflozin and CRMP to slow tumor growth.

Conclusions

Taken together, these data demonstrate that hyperinsulinemia per se promotes both breast and colon cancer progression in obese mice, and highlight SGLT2 inhibitors as a clinically available means of slowing obesity-associated tumor growth due to their glucose- and insulin-lowering effects.

Activation of insulin receptors and IGF-1 receptors in COLO-205 colon cancer xenografts by insulin and insulin analogue X10 does not enhance growth under normo- or hypoglycaemic conditions

AIMS/HYPOTHESIS

Recent studies with normal rats and mouse allograft models have reported that insulin and insulin analogues do not activate the IGF-1 receptor in vivo, and that this characteristic therefore cannot be responsible for the increased incidence of mammary tumours observed for the insulin analogue X10 in chronic toxicity studies with Sprague Dawley rats. This is in clear contrast to reports of insulin and insulin analogues in vitro. Clarification of this is important for understanding the mechanisms behind possible growth-promoting effects of insulin analogues, and will have implications for the development of novel insulin analogues.

METHODS

We established a xenograft model in BALB/c nude mice with the human colon cancer cell line COLO-205, which expresses human insulin and IGF-1 receptors, and explored the acute and chronic effects of treatment with supra-pharmacological doses of human insulin, insulin analogue X10 and human IGF-1. With a novel antibody, acute IGF-1 receptor activation was also examined in various tissues from normal rats treated with human insulin, insulin analogue X10 or human IGF-1. Finally, the effects of pharmacologically relevant doses of human insulin and insulin analogue X10 on receptor activation and growth of COLO-205 xenograft were explored in BALB/c nude mice with alloxan-induced hyperglycaemia.

RESULTS

In normal rats and in BALB/c nude mice bearing a COLO-205 cell xenograft, treatment with supra-pharmacological doses of human insulin, insulin analogue X10 or human IGF-1 resulted in activation of insulin receptors as well as IGF-1 receptors. Treatment of diabetic nude mice with pharmacologically relevant doses of human insulin or insulin analogue X10, which decreased blood glucose from hyperglycaemic levels to the normoglycaemic range, did not increase IGF-1 receptor activation. Furthermore, repeated treatment with supra-pharmacological as well as pharmacological doses of human insulin or insulin analogue X10 did not influence the growth of COLO-205 xenografts.

CONCLUSIONS/INTERPRETATION

This study demonstrates that activation of IGF-1 receptors in cancer cells by insulin and insulin analogues cannot be considered as a purely in vitro phenomenon. It does occur in vivo in animal models, although only after treatment with supra-pharmacological doses. Furthermore, treatment with insulin or insulin analogue X10 did not influence the growth of COLO-205 xenografts under normo- or hypoglycaemic conditions. Further studies are needed before a conclusion can be reached on whether IGF-1 receptor activation by insulin analogues correlates with increased growth in vivo.

Insulin glargine affects the expression of Igf-1r, Insr, and Igf-1 genes in colon and liver of diabetic rats

Objective(s):

The mitogenic effect of the analogous insulin glargine is currently under debate since several clinical studies have raised the possibility that insulin glargine treatment has a carcinogenic potential in different tissues. This study aimed to evaluate the Igf-1r, Insr, and Igf-1 gene expression in colon and liver of streptozotocin-induced diabetic rats in response to insulin glargine, neutral protamine Hagedorn (NPH) insulin, and metformin treatments.

Materials and Methods:

Male Wistar rats were induced during one week with streptozotocin to develop Type 2 Diabetes (T2D) and then randomly distributed into four groups. T2D rats included in the first group received insulin glargine, the second group received NPH insulin, the third group received metformin; finally, untreated T2D rats were included as the control group. All groups were treated for seven days; after the treatment, tissue samples of liver and colon were obtained. Quantitative PCR (qPCR) was performed to analyze the Igf-1r, Insr and Igf-1 gene expression in each tissue sample.

Results:

The liver tissue showed overexpression of the Insr and Igf-1r genes (P>0.001) in rats treated with insulin glargine in comparison with the control group. Similar results were observed for the Insr gene (P>0.011) in colonic tissue of rats treated with insulin glargine.

Conclusion:

These observations demonstrate that insulin glargine promote an excess of insulin and IGF-1 receptors in STZ-induced diabetic rats, which could overstimulate the mitogenic signaling pathways.

Long-acting insulin analogs and cancer

AIMS

Hyperinsulinemia is a recognized risk factor for cancer and plays a major role for the increased cancer incidence in diabetic patients. Whether insulin analogs, and particularly long-acting analogs, worsen the pro-cancer effect of excess insulin is still controversial.

DATA SYNTHESIS

In this paper we summarize the biological bases for the potential detrimental effect of long-acting analogs on cancer cells and review the in vitro and in vivo evidence on this issue. Because of their different molecular structure relative to native insulin, insulin analogs may activate the insulin receptor (IR) and the post receptor pathways differently. Most, but not all, in vitro evidence indicate that long-acting analogs may have a stronger mitogenic potency than insulin on cancer cells. Notably insulin glargine, the most studied long-acting analog, also has a higher affinity for the insulin-like growth factor (IGF)-1 receptor, a potent growth mediator. In vitro observations, however, may not reflect what occurs in vivo when analogs are metabolized to derivatives with a different mitogenic activity. Clinical studies, mostly retrospective and predominantly concerning glargine, provide contrasting results. The only perspective trial found no cancer increase in patients treated with glargine. All these studies, however, have severe weaknesses because of the insufficient evaluation of important factors such as dose administered, length of exposure, patient follow-up duration and site-specific cancer investigation. Moreover, whether cancer promotion is a long-acting analog class characteristic or a specific effect of a single agent is not clear.

CONCLUSIONS

In conclusion the carcinogenic risk of long-acting analogs, and specifically glargine, can be neither confirmed nor excluded. A personalized and shared decision, considering all the individual risk factors (metabolic and non-metabolic), is the suggestion for the clinician.

Effects of insulin and analogues on carcinogen-induced mammary tumours in high-fat-fed rats

It is not fully clarified whether insulin glargine, an analogue with a high affinity for insulin-like growth factor-1 receptor (IGF-1R), increases the risk for cancers that abundantly express IGF-1R such as breast cancer or some types of breast cancer. To gain insight into this issue, female Sprague-Dawley rats fed a high-fat diet were given the carcinogen N-methyl-N-nitrosourea and randomly assigned to vehicle (control), NPH (unmodified human insulin), glargine or detemir (n = 30 per treatment). Insulins were given subcutaneously (15 U/kg/day) 5 days a week. Mammary tumours were counted twice weekly, and after 6 weeks of treatment, extracted for analysis. None of the insulin-treated groups had increased mammary tumour incidence at any time compared with control. At 6 weeks, tumour multiplicity was increased with NPH or glargine (P < 0.05) and tended to be increased with detemir (P = 0.2); however, there was no difference among insulins (number of tumours per rat: control = 0.8 ± 0.1, NPH = 1.8 ± 0.3, glargine = 1.5 ± 0.4, detemir = 1.4 ± 0.4; number of tumours per tumour-bearing rat: control = 1.3 ± 0.1, NPH = 2.2 ± 0.4, glargine = 2.7 ± 0.5, detemir = 2.3 ± 0.5). IGF-1R expression in tumours was lower than that in Michigan Cancer Foundation-7 (MCF-7) cells, a cell line that shows greater proliferation with glargine than unmodified insulin. In rats, glargine was rapidly metabolised to M1 that does not have greater affinity for IGF-1R. In conclusion, in this model of oestrogen-dependent breast cancer in insulin-resistant rats, insulin and insulin analogues increased tumour multiplicity with no difference between insulin types.