Concentrations of insulin glargine and its metabolites during long-term insulin therapy in type 2 diabetic patients and comparison of effects of insulin glargine, its metabolites, IGF-I, and human insulin on insulin and igf-I receptor signaling

ADO09, a co-formulation of pramlintide and insulin A21G, lowers body weight versus insulin lispro in type 1 diabetes

AIM

To study safety, efficacy and weight loss with ADO09, a co-formulation of insulin A21G and pramlintide, in type 1 diabetes.

MATERIALS AND METHODS

A randomized, two-arm ambulatory 16-week study compared ADO09 with insulin lispro in 80 participants with type 1 diabetes. We compared changes of weight, glycated haemoglobin, glycaemic patterns during continuous glucose monitoring, and insulin doses at baseline and at the end of treatment.

RESULTS

A significant and continuing weight loss, the primary endpoint, was observed with ADO09 compared with lispro as prandial insulin. In the whole group, the weight loss with ADO09 relative to lispro was 2.1 kg. Glycaemic control was relatively good (7.7% mean glycated haemoglobin) in both groups and did not change during treatment. Prandial insulin doses were reduced by 21% in the ADO09 group, whereas basal insulin dosage was not modified. Gastrointestinal symptoms were more frequent with ADO09, but no clear difference in hypoglycaemia was observed.

CONCLUSIONS

These results extend previous observations on the efficacy and safety of this insulin/pramlintide co-formulation. They show a beneficial effect on weight, using less mealtime insulin and without increased hypoglycaemia.

(Ultra-)long-acting insulin analogues versus NPH insulin (human isophane insulin) for adults with type 2 diabetes mellitus

BACKGROUND

Evidence that antihyperglycaemic therapy is beneficial for people with type 2 diabetes mellitus is conflicting. While the United Kingdom Prospective Diabetes Study (UKPDS) found tighter glycaemic control to be positive, other studies, such as the Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial, found the effects of an intensive therapy to lower blood glucose to near normal levels to be more harmful than beneficial. Study results also showed different effects for different antihyperglycaemic drugs, regardless of the achieved blood glucose levels. In consequence, firm conclusions on the effect of interventions on patient-relevant outcomes cannot be drawn from the effect of these interventions on blood glucose concentration alone. In theory, the use of newer insulin analogues may result in fewer macrovascular and microvascular events.

OBJECTIVES

To compare the effects of long-term treatment with (ultra-)long-acting insulin analogues (insulin glargine U100 and U300, insulin detemir and insulin degludec) with NPH (neutral protamine Hagedorn) insulin (human isophane insulin) in adults with type 2 diabetes mellitus.

SEARCH METHODS

For this Cochrane Review update, we searched CENTRAL, MEDLINE, Embase, ICTRP Search Portal and ClinicalTrials.gov. The date of the last search was 5 November 2019, except Embase which was last searched 26 January 2017. We applied no language restrictions.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) comparing the effects of treatment with (ultra-)long-acting insulin analogues to NPH in adults with type 2 diabetes mellitus.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials, assessed risk of bias, extracted data and evaluated the overall certainty of the evidence using GRADE. Trials were pooled using random-effects meta-analyses.

MAIN RESULTS

We identified 24 RCTs. Of these, 16 trials compared insulin glargine to NPH insulin and eight trials compared insulin detemir to NPH insulin. In these trials, 3419 people with type 2 diabetes mellitus were randomised to insulin glargine and 1321 people to insulin detemir. The duration of the included trials ranged from 24 weeks to five years. For studies, comparing insulin glargine to NPH insulin, target values ranged from 4.0 mmol/L to 7.8 mmol/L (72 mg/dL to 140 mg/dL) for fasting blood glucose (FBG), from 4.4 mmol/L to 6.6 mmol/L (80 mg/dL to 120 mg/dL) for nocturnal blood glucose and less than 10 mmol/L (180 mg/dL) for postprandial blood glucose, when applicable. Blood glucose and glycosylated haemoglobin A1c (HbA1c) target values for studies comparing insulin detemir to NPH insulin ranged from 4.0 mmol/L to 7.0 mmol/L (72 mg/dL to 126 mg/dL) for FBG, less than 6.7 mmol/L (120 mg/dL) to less than 10 mmol/L (180 mg/dL) for postprandial blood glucose, 4.0 mmol/L to 7.0 mmol/L (72 mg/dL to 126 mg/dL) for nocturnal blood glucose and 5.8% to less than 6.4% HbA1c, when applicable. All trials had an unclear or high risk of bias for several risk of bias domains. Overall, insulin glargine and insulin detemir resulted in fewer participants experiencing hypoglycaemia when compared with NPH insulin. Changes in HbA1c were comparable for long-acting insulin analogues and NPH insulin. Insulin glargine compared to NPH insulin had a risk ratio (RR) for severe hypoglycaemia of 0.68 (95% confidence interval (CI) 0.46 to 1.01; P = 0.06; absolute risk reduction (ARR) -1.2%, 95% CI -2.0 to 0; 14 trials, 6164 participants; very low-certainty evidence). The RR for serious hypoglycaemia was 0.75 (95% CI 0.52 to 1.09; P = 0.13; ARR -0.7%, 95% CI -1.3 to 0.2; 10 trials, 4685 participants; low-certainty evidence). Treatment with insulin glargine reduced the incidence of confirmed hypoglycaemia and confirmed nocturnal hypoglycaemia. Treatment with insulin detemir compared to NPH insulin found an RR for severe hypoglycaemia of 0.45 (95% CI 0.17 to 1.20; P = 0.11; ARR -0.9%, 95% CI -1.4 to 0.4; 5 trials, 1804 participants; very low-certainty evidence). The Peto odds ratio for serious hypoglycaemia was 0.16, 95% CI 0.04 to 0.61; P = 0.007; ARR -0.9%, 95% CI -1.1 to -0.4; 5 trials, 1777 participants; low-certainty evidence). Treatment with detemir also reduced the incidence of confirmed hypoglycaemia and confirmed nocturnal hypoglycaemia. Information on patient-relevant outcomes such as death from any cause, diabetes-related complications, health-related quality of life and socioeconomic effects was insufficient or lacking in almost all included trials. For those outcomes for which some data were available, there were no meaningful differences between treatment with glargine or detemir and treatment with NPH. There was no clear difference between insulin-analogues and NPH insulin in terms of weight gain. The incidence of adverse events was comparable for people treated with glargine or detemir, and people treated with NPH. We found no trials comparing ultra-long-acting insulin glargine U300 or insulin degludec with NPH insulin.

AUTHORS' CONCLUSIONS

While the effects on HbA1c were comparable, treatment with insulin glargine and insulin detemir resulted in fewer participants experiencing hypoglycaemia when compared with NPH insulin. Treatment with insulin detemir also reduced the incidence of serious hypoglycaemia. However, serious hypoglycaemic events were rare and the absolute risk reducing effect was low. Approximately one in 100 people treated with insulin detemir instead of NPH insulin benefited. In the studies, low blood glucose and HbA1c targets, corresponding to near normal or even non-diabetic blood glucose levels, were set. Therefore, results from the studies are only applicable to people in whom such low blood glucose concentrations are targeted. However, current guidelines recommend less-intensive blood glucose lowering for most people with type 2 diabetes in daily practice (e.g. people with cardiovascular diseases, a long history of type 2 diabetes, who are susceptible to hypoglycaemia or older people). Additionally, low-certainty evidence and trial designs that did not conform with current clinical practice meant it remains unclear if the same effects will be observed in daily clinical practice. Most trials did not report patient-relevant outcomes.

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.

Serum Insulin Bioassay Reflects Insulin Sensitivity and Requirements in Type 1 Diabetes

CONTEXT

Insulin resistance could increase insulin requirements in type 1 diabetes (T1D). Current insulin immunoassays do not detect insulin analogs. Kinase insulin receptor (IR) activation (KIRA) bioassays specific for human IR isoforms A (IR-A) and B (IR-B) permit assessment of all circulating insulin bioactivity. We studied whether IR-A and IR-B KIRA assays are related to direct measures of insulin sensitivity or insulin doses in T1D.

DESIGN

We evaluated 31 adult patients with T1D (age 45.7 ± 1.6 years, body mass index 28.8 ± 0.7 kg/m2). Serum IR-A and IR-B bioactivities were measured by KIRA bioassays. Insulin sensitivity of glucose production (Ra) was measured by the euglycemic hyperinsulinemic clamp technique in which a low insulin dose (0.4 mU/kg/min for 240 minutes) was combined with D-[3-3H] glucose infusion to measure rates of Ra and utilization and insulin action on antilipolysis from suppression of serum free fatty acids.

RESULTS

Baseline circulating IR-A bioactivity was 53 ± 7 pmol/L, and IR-B bioactivity was 81 ± 11 pmol/L. Compared with baseline, insulin infusion significantly increased IR-A (P < 0.001) and IR-B (P < 0.001) bioactivities. Fasting IR-A and IR-B bioactivities were positively related to endogenous Ra (r = 0.44, P = 0.01 and r = 0.38, P < 0.05). Fasting IR-A (r = 0.43, P = 0.02) and IR-B (r = 0.47, P = 0.01) bioactivities were significantly correlated with insulin requirements and glycosylated hemoglobin (IR-A: r = 0.52, P = 0.002; IR-B: r = 0.48, P = 0.006).

CONCLUSIONS

Circulating IR-A and IR-B bioactivities are associated with insulin resistance, high insulin requirements, and poor glycemic control in T1D. Measurement of IR bioactivity by KIRA assays provides a tool to assess the amount of biologically active insulin in groups of T1D patients treated with insulin analogs.

Development and validation of a cell based assay for the detection of neutralizing antibodies against recombinant insulins

Recombinant biopharmaceuticals can induce generation of anti-drug antibodies, which could potentially neutralize therapeutic drug activity. In this report, we describe development and validation of a cell-based assay for detection of neutralizing antibodies (Nab) against insulin and insulin analogues. In order to achieve clinically meaningful sensitivity the method used an early signalling event, insulin induced insulin receptor phosphorylation as the endpoint. Percentage insulin receptor phosphorylation in cell lysates was measured using ECL based ELISA. Presence of neutralizing antibodies (Nab) in samples will inhibit insulin induced receptor phosphorylation and consequently lead to a reduction in the percentage of phosphorylated insulin receptor. Additionally, usage of human insulin receptor overexpressing recombinant CHO cell line further improved the assay sensitivity by reducing the fixed drug (EC50) concentration used for induction of receptor phosphorylation. To ensure adequate free drug tolerance a pre-treatment step was introduced, where serum samples underwent acid dissociation and charcoal extraction before drug incubation. In order to distinguish ADA positive samples containing true Nab from samples containing non-antibody phosphorylation inhibitory serum factors, a confirmatory tier was integrated based on immunodepletion using protein AGL mix. Assay parameters including determination of screening and confirmatory cut-points, intra and inter assay precision, selectivity, specificity and stability were assessed during validation in accordance with recent regulatory guidelines and white papers. The advantage of selecting insulin receptor phosphorylation as assay endpoint made the assay capable of detecting Nab against insulin and insulin analogues.

Treatment with insulin analogs, especially Glargine and Lispro, associates with better renal function and higher hemoglobin levels in Type 1 diabetic patients with impaired kidney function

OBJECTIVES

The influence of type of insulin treatment - insulin analogs versus human insulin - on the development of diabetes related vascular complications has been sparsely investigated. We examine here possible differences regarding kidney function and hemoglobin levels.

METHODS

Multiple linear regression was used to investigate the relationship between the following characteristics measured in 509 type 1 diabetic patients who were recruited in an outpatient practice: current clinical status and treatment modalities, type of injected insulin and the routine laboratory parameters hemoglobin, HbA1c, serum creatinine, eGFR, hs CRP and urinary albumin/creatinine ratio.

RESULTS

Compared with human insulin, multiple regression analysis taking into account possible confounders revealed that treatment with insulin analogs was associated with increased eGFR (+7.1 ml/min; P=0.0002), lower urinary albumin/creatinine ratio (ratio logarithm -0.4; P=0.003) and higher hemoglobin concentration (+0.31 g/dl; P=0.04). Stratification by type of insulin showed the best renal status for treatment with insulins Glargine and Lispro. Differences were consistent both for patients with normal (eGFR → 90 ml/min) and with an impaired (eGFR ← 90 ml/min) kidney function.

CONCLUSIONS

Present results suggest that treatment of type 1 diabetic patients with normal and impaired renal function with insulin analogs, especially Glargine and Lispro, is associated with better kidney function, lower urinary albumin/creatinine ratio and lower hemoglobin concentration compared to therapy with human insulin. If confirmed by other studies, treatment with insulin analogs may be a further possibility in delaying progression of nephropathy and in preventing early hemoglobin decline.

Insulin receptor isoforms: an integrated view focused on gestational diabetes mellitus

The human insulin receptor (IR) exists in two isoforms that differ by the absence (IR-A) or the presence (IR-B) of a 12-amino acid segment encoded by exon 11. Both isoforms are functionally distinct regarding their binding affinities and intracellular signalling. However, the underlying mechanisms related to their cellular functions in several tissues are only partially understood. In this review, we summarize the current knowledge in this field regarding the alternative splicing of IR isoform, tissue-specific distribution and signalling both in physiology and disease, with an emphasis on the human placenta in gestational diabetes mellitus (GDM). Furthermore, we discuss the clinical relevance of IR isoforms highlighted by findings that show altered insulin signalling due to differential IR-A and IR-B expression in human placental endothelium in GDM pregnancies. Future research and clinical studies focused on the role of IR isoform signalling might provide novel therapeutic targets for treating GDM to improve the adverse maternal and neonatal outcomes.

Potency of Full-Length MGF to Induce Maximal Activation of the IGF-I R Is Similar to Recombinant Human IGF-I at High Equimolar Concentrations

AIMS

To compare full-length mechano growth factor (full-length MGF) with human recombinant insulin-like growth factor-I (IGF-I) and human recombinant insulin (HI) in their ability to activate the human IGF-I receptor (IGF-IR), the human insulin receptor (IR-A) and the human insulin receptor-B (IR-B), respectively. In addition, we tested the stimulatory activity of human MGF and its stabilized analog Goldspink-MGF on the IGF-IR.

METHODS

The effects of full-length MGF, IGF-I, human mechano growth factor (MGF), Goldspink-MGF and HI were compared using kinase specific receptor activation (KIRA) bioassays specific for IGF-I, IR-A or IR-B, respectively. These assays quantify activity by measuring auto-phosphorylation of the receptor upon ligand binding.

RESULTS

IGF-IR: At high equimolar concentrations maximal IGF-IR stimulating effects generated by full-length MGF were similar to that of IGF-I (89-fold vs. 77-fold, respectively). However, EC50 values of IGF-I and full-length MGF for the IGF-I receptor were 0.86 nmol/L (95% CI 0.69-1.07) and 7.83 nmol/L (95% CI: 4.87-12.58), respectively. No IGF-IR activation was observed by human MGF and Goldspink-MGF, respectively. IR-A/IR-B: At high equimolar concentrations similar maximal IR-A stimulating effects were observed for full -length MGF and HI, but maximal IR-B stimulation achieved by full -length MGF was stronger than that by HI (292-fold vs. 98-fold). EC50 values of HI and full-length MGF for the IR-A were 1.13 nmol/L (95% CI 0.69-1.84) and 73.11 nmol/L (42.87-124.69), respectively; for IR-B these values were 1.28 nmol/L (95% CI 0.64-2.57) and 35.10 nmol/L (95% 17.52-70.33), respectively.

CONCLUSIONS

Full-length MGF directly stimulates the IGF-IR. Despite a higher EC50 concentration, at high equimolar concentrations full-length MGF showed a similar maximal potency to activate the IGF-IR as compared to IGF-I. Further research is needed to understand the actions of full-length MGF in vivo and to define the physiological relevance of our in vitro findings.

Looking at the carcinogenicity of human insulin analogues via the intrinsic disorder prism

Therapeutic insulin, in its native and biosynthetic forms as well as several currently available insulin analogues, continues to be the protein of most interest to researchers. From the time of its discovery to the development of modern insulin analogues, this important therapeutic protein has passed through several stages and product generations. Beside the well-known link between diabetes and cancer risk, the currently used therapeutic insulin analogues raised serious concerns due to their potential roles in cancer initiation and/or progression. It is possible that structural variations in some of the insulin analogues are responsible for the appearance of new oncogenic species with high binding affinity to the insulin-like growth factor 1 (IGF1) receptor. The question we are trying to answer in this work is: are there any specific features of the distribution of intrinsic disorder propensity within the amino acid sequences of insulin analogues that may provide an explanation for the carcinogenicity of the altered insulin protein?

Glargine metabolism over 24 h following its subcutaneous injection in patients with type 2 diabetes mellitus: a dose-response study

BACKGROUND AND AIMS

After subcutaneous injection insulin glargine is rapidly metabolized to M1 and M2. In vitro, both M1 and M2 have metabolic effects and bind to IGF-1R similarly to human insulin, whereas glargine exhibits a higher affinity for the IGF-1R and greater mitogenetic effects. The present study was specifically designed to establish the dose-response metabolism of glargine over 24 h following s.c. injection in T2DM subjects on long-term use of glargine.

METHODS AND RESULTS

Ten subjects with T2DM were studied during 24 h after s.c. injection of 0.4 (therapeutic) and 0.8 (high dose) U/kg of glargine on two separate occasions during euglycaemic clamps (cross-over design). Glargine, M1 and M2 over 24 h period were determined in appropriately processed plasma samples by a specific liquid chromatography-tandem mass spectrometry assay. Plasma M1 concentration (AUC0-24 h) was detected in all subjects and increased by increasing the glargine dose from therapeutic to high dose (p = 0.008). Glargine was detectable in 6 (therapeutic dose) and 9 (high dose) out of the 10 subjects and also increased by increasing the dose (p = 0.031). However, glargine concentration (AUC0-24 h--high dose) represented at most only 9.7% (4.6-15%) of the total amount of insulin measured in the blood. M2 was not detected at all.

CONCLUSION

In T2DM people on long-term use of insulin glargine, even with higher doses (0.8 U/kg), glargine is nearly totally metabolized to the active metabolite M1. Glargine is often detectable in plasma, but its concentration remains well below that needed in vitro to potentiate IGF-1R binding and mitogenesis.

Pathophysiology and treatment of type 2 diabetes: perspectives on the past, present, and future

Glucose metabolism is normally regulated by a feedback loop including islet β cells and insulin-sensitive tissues, in which tissue sensitivity to insulin affects magnitude of β-cell response. If insulin resistance is present, β cells maintain normal glucose tolerance by increasing insulin output. Only when β cells cannot release sufficient insulin in the presence of insulin resistance do glucose concentrations rise. Although β-cell dysfunction has a clear genetic component, environmental changes play an essential part. Modern research approaches have helped to establish the important role that hexoses, aminoacids, and fatty acids have in insulin resistance and β-cell dysfunction, and the potential role of changes in the microbiome. Several new approaches for treatment have been developed, but more effective therapies to slow progressive loss of β-cell function are needed. Recent findings from clinical trials provide important information about methods to prevent and treat type 2 diabetes and some of the adverse effects of these interventions. However, additional long-term studies of drugs and bariatric surgery are needed to identify new ways to prevent and treat type 2 diabetes and thereby reduce the harmful effects of this disease.

Classifying the adverse mitogenic mode of action of insulin analogues using a novel mechanism-based genetically engineered human breast cancer cell panel

Insulin analogues are widely used in clinical practice. Modifications on the insulin molecular structure can affect the affinity and activation towards two closely related receptor tyrosine kinases: the insulin receptor (INSR) and the insulin-like growth factor 1 receptor (IGF1R). A switch towards higher IGF1R affinity is likely to emphasize mitogenesis rather than glucose metabolism. Relevant well-validated experimental tools to address the insulin analogue activation of either INSR or IGF1R are missing. We have established a panel of human MCF-7 breast cancer cell lines either ectopically expressing the INSR (A or B isoform) in conjunction with a stable knockdown of the IGF1R or ectopically expressing the IGF1R in conjunction with a stable knockdown of the INSR. In these cell lines, we systematically evaluated the INSR and IGF1R receptor activation and downstream mitogenic signalling of all major clinical relevant insulin analogues in comparison with insulin and IGF1R. While most insulin analogues primarily activated the INSR, the mitogenic activation pattern of glargine was highly similar to IGF1 and insulin AspB10, known to bind IGF1R and induce carcinogenesis. Yet, in a long-term proliferation assay, the proliferative effect of glargine was not much different from regular insulin or other insulin analogues. This was caused by the rapid enzymatic conversion into its two metabolic active metabolites M1 and M2, with reduced mitogenic signalling through the IGF1R. In summary, based on our new cell models, we identified a similar mitogenic potency of insulin glargine and AspB10. However, rapid enzymatic conversion of glargine precludes a sustained activation of the IGF1R signalling pathway.

Insulin analogs and cancer: a note of caution

In view of the lifelong exposure and large patient populations involved, insulin analogs with an increased mitogenic effect in comparison to human insulin may potentially constitute a major health problem, since these analogs may possibly induce the growth of pre-existing neoplasms. At present, the available data suggest that insulin analogs are safe. In line with these findings, we observed that serum of diabetic patients treated with insulin analogs, compared to that of diabetic patients treated with human insulin, did not induce an increased phosphorylation of tyrosine residues of the insulin-like growth factor-I receptor (IGF-IR). However, the classical model of the IGF-IR signaling may be insufficient to explain (all) mitogenic effects of insulin analogs since also non-canonical signaling pathways of the IGF-IR may play a major role in this respect. Although phosphorylation of tyrosine residues of the IGF-IR is generally considered to be the initial activation step within the intracellular IGF-IR signaling pathway, it has been found that cells undergo a signaling switch under hyperglycemic conditions. After this switch, a completely different mechanism is utilized to activate the mitogenic (mitogen-activated protein kinase) pathways of the IGF-IR that is independent from tyrosine phosphorylation of the IGF-IR. At present it is unknown whether activation of this alternative intracellular pathway of the IGF-IR occurs during hyperglycemia in vivo and whether it is stronger in patients treated with (some) insulin analogs than in patients treated with human insulin. In addition, it is unknown whether the insulin receptors (IRs) also undergo a signaling switch during hyperglycemia. This should be investigated in future studies. Finally, relative overexpression of IR isoform A (IR-A) in (pre) cancer tissues may play a key role in the development and progression of human cancers during treatment with insulin (analogs). Further studies are required to unravel whether the IR-A is involved in the development of cancers and whether, in this respect (some) insulin analogs differ from human insulin.

Liver kinase B1 expression promotes phosphatase activity and abrogation of receptor tyrosine kinase phosphorylation in human cancer cells

Aberrant receptor tyrosine kinase phosphorylation (pRTK) has been associated with diverse pathological conditions, including human neoplasms. In lung cancer, frequent liver kinase B1 (LKB1) mutations correlate with tumor progression, but potential links with pRTK remain unknown. Heightened and sustained receptor activation was demonstrated by LKB1-deficient A549 (lung) and HeLaS3 (cervical) cancer cell lines. Depletion (siRNA) of endogenous LKB1 expression in H1792 lung cancer cells also correlated with increased pRTK. However, ectopic LKB1 expression in A549 and HeLaS3 cell lines, as well as H1975 activating-EGF receptor mutant lung cancer cell resulted in dephosphorylation of several tumor-enhancing RTKs, including EGF receptor, ErbB2, hepatocyte growth factor receptor (c-Met), EphA2, rearranged during transfection (RET), and insulin-like growth factor I receptor. Receptor abrogation correlated with attenuation of phospho-Akt and increased apoptosis. Global phosphatase inhibition by orthovanadate or depletion of protein tyrosine phosphatases (PTPs) resulted in the recovery of receptor phosphorylation. Specifically, the activity of SHP-2, PTP-1β, and PTP-PEST was enhanced by LKB1-expressing cells. Our findings provide novel insight on how LKB1 loss of expression or function promotes aberrant RTK signaling and rapid growth of cancer cells.