pI-shifted insulin analogs with extended in vivo time action and favorable receptor selectivity

Sensitive and label-free SPR biosensing platforms for high-throughput screening of plasma membrane receptors interactions with insulin-like targets of hypoglycaemic activity

Progress in medical sciences aims for tailored therapy of civilization diseases like diabetes. Preclinical screening of new medicines superior to insulin should include the verification of their affinity to the membrane receptors naturally stimulated by this hormone: insulin receptor isoforms A and B and insulin-like growth factor receptor. Considering that the affinity constants obtained using different experimental conditions are incomparable, it is essential to develop a robust and reliable method to analyze these interactions. The versatile SPR platform developed in this study enables the evaluation of the bioactivity of hypoglycaemic molecules. Thanks to the comprehensive characterization of miscellaneous aspects of the analytical platform, including the design of the SPR biosensor receptor layer, ensuring interaction specificity, as well as the quality control of the standards used (human insulin, HI; long-acting insulin analog: glargine, Gla), the feasibility of the method of equilibrium and kinetic constants determination for insulin-like targets was confirmed. SPR assays constructed in the direct format using IR-A, IR-B, and IGF1-R receptor proteins show high sensitivities and low detection limits towards insulin and glargine detection in the range of 18.3-53.3 nM with no signs of mass transport limitations. The improved analytical performance and stability of SPR biosensors favor the acquisition of good-quality kinetic data, while preservation of receptors activity after binding to long-chain carboxymethyldextran, combined with spontaneous regeneration, results in stability and long shelf life of the biosensor, which makes it useful for label-free insulin analogs biosensing and thus extensive screening in diabetic drugs discovery.

A dose titration protocol for once-daily insulin glargine 300 U/mL for the treatment of diabetes mellitus in dogs

BACKGROUND

In purpose-bred dogs, insulin glargine 300 U/mL (IGla300) has long duration of action, peakless time-action profile, and low potency, making it suitable for use as a basal insulin.

HYPOTHESIS

To evaluate IGla300 in client-owned diabetic dogs monitored using a flash glucose monitoring system (FGMS).

ANIMALS

Ninety-five client-owned diabetic dogs, newly diagnosed or previously treated with other insulin formulations, with or without concurrent diseases.

METHODS

Prospective multi-institutional study. Clinical signs and standardized assessment of FGMS data, using treatment and monitoring guidelines established a priori, guided dose adjustments and categorization into levels of glycemic control.

RESULTS

The initial IGla300 dose was 0.5 U/Kg q24h for newly diagnosed dogs and (median dose [range]) 0.8 U/Kg (0.2-2.5) q24h for all dogs. Glycemic control was classified as good or excellent in 87/95 (92%) dogs. The IGla300 was administered q24h (1.9 U/kg [0.2-5.2]) and q12h (1.9 U/kg/day [0.6-5.0]) in 56/95 (59%) and 39/95 (41%) dogs, respectively. Meal-time bolus injections were added in 5 dogs (0.5 U/kg/injection [0.3-1.0]). Clinical hypoglycemia occurred in 6/95 (6%) dogs. Dogs without concurrent diseases were more likely to receive IGla300 q24h than dogs with concurrent diseases (72% vs 50%, respectively; P = .04).

CONCLUSIONS AND CLINICAL IMPORTANCE

Insulin glargine 300 U/mL can be considered a suitable therapeutic option for once-daily administration in diabetic dogs. Clinicians should be aware of the low potency and wide dose range of IGla300. In some dogs, twice-daily administration with or without meal-time bolus injections may be necessary to achieve glycemic control. Monitoring with FGMS is essential for dose titration of IGla300.

Insulin Therapy in Small Animals, Part 1: General Principles

Understanding the pharmacology of insulin and how it relates to the pathophysiology of diabetes can lead to better clinical outcomes. No insulin formulation should be considered "best" by default. Insulin suspensions (NPH, NPH/regular mixes, lente, and PZI) as well as insulin glargine U100 and detemir are intermediate-acting formulations that are administered twice daily. For a formulation to be an effective and safe basal insulin, its action should be roughly the same every hour of the day. Currently, only insulin glargine U300 and insulin degludec meet this standard in dogs, whereas in cats, insulin glargine U300 is the closest option.

Fibrillation of human insulin B-chain by pulsed hydrogen-deuterium exchange mass spectrometry

Insulin forms amyloid fibrils under slightly destabilizing conditions, and B-chain residues are thought to play an important role in insulin fibrillation. Here, pulsed hydrogen-deuterium exchange mass spectrometry (HDX-MS), far-UV circular dichroism spectroscopy, thioflavin T (ThioT) fluorescence, turbidity, and soluble fraction measurements were used to monitor the kinetics and mechanisms of fibrillation of human insulin B-chain (INSB) in acidic solution (1 mg/mL, pH 4.5) under stressed conditions (40°C, continuous shaking). Initially, INSB rapidly formed β-sheet-rich oligomers that were protected from HD exchange and showed weak ThioT binding. Subsequent fibril growth and maturation was accompanied by even greater protection from HD exchange and stronger ThioT binding. With peptic digestion of deuterated INSB, HDX-MS suggested early involvement of the N-terminal (1-11, 1-15) and central (12-15, 16-25) fragments in fibril-forming interactions, whereas the C-terminal fragment (25-30) showed limited involvement. The results provide mechanistic understanding of the intermolecular interactions and structural changes during INSB fibrillation under stressed conditions and demonstrate the application of pulsed HDX-MS to probe peptide fibrillation.

Translational aspect in peptide drug discovery and development: An emerging therapeutic candidate

In the last two decades, protein-protein interactions (PPIs) have been used as the main target for drug development. However, with larger or superficial binding sites, it has been extremely difficult to disrupt PPIs with small molecules. On the other hand, intracellular PPIs cannot be targeted by antibodies that cannot penetrate the cell membrane. Peptides that have a combination of conformational rigidity and flexibility can be used to target difficult binding interfaces with appropriate binding affinity and specificity. Since the introduction of insulin nearly a century ago, more than 80 peptide drugs have been approved to treat a variety of diseases. These include deadly diseases such as cancer and human immunodeficiency virus infection. It is also useful against diabetes, chronic pain, and osteoporosis. Today, more research is being done on these drugs as lessons learned from earlier approaches, which are still valid today, complement newer approaches such as peptide display libraries. At the same time, integrated genomics and peptide display libraries are new strategies that open new avenues for peptide drug discovery. The purpose of this review is to examine the problems in elucidating the peptide-protein recognition mechanism. This is important to develop peptide-based interventions that interfere with endogenous protein interactions. New approaches are being developed to improve the binding affinity and specificity of existing approaches and to develop peptide agents as potentially useful drugs. We also highlight the key challenges that must be overcome in peptide drug development to realize their potential and provide an overview of recent trends in peptide drug development. In addition, we take an in-depth look at early efforts in human hormone discovery, smart medicinal chemistry and design, natural peptide drugs, and breakthrough advances in molecular biology and peptide chemistry.

Characterization and impact of peptide physicochemical properties on oral and subcutaneous delivery

Peptides, an emerging modality within the biopharmaceutical industry, are often delivered subcutaneously with evolving prospects on oral delivery. Barrier biology within the subcutis or gastrointestinal tract is a significant challenge in limiting absorption or otherwise disrupting peptide disposition. Aspects of peptide pharmacokinetic performance and ADME can be mitigated with careful molecular design that tailors for properties such as effective size, hydrophobicity, net charge, proteolytic stability, and albumin binding. In this review, we endeavor to highlight effective techniques in qualifying physicochemical properties of peptides and discuss advancements of in vitro models of subcutaneous and oral delivery. Additionally, we will delineate empirical findings around the relationship of these physicochemical properties and in vivo (animal or human) impact. We conclude that robust peptide characterization methods and in vitro techniques with demonstrated correlations to in vivo data are key routines to incorporate in the drug discovery and development to improve the probability of technical and commercial success of peptide therapeutics.

One hundred years of insulin: Is it time for smart?

Smarter understanding of diabetes pathophysiology and pharmacology of insulin therapy can lead to better clinical outcomes. Rather than looking for an insulin formulation that is considered "best" for a general population, it could be appropriate to seek the "smart" insulin choice, tailored to the specific clinical situation. Different treatment goals should be considered, with pros and cons to each. Ideally, insulin therapy in most diabetic dogs should mimic a "basal-bolus" pattern. The "intermediate"-acting insulin formulations might provide better "bolus" treatment in dogs than the rapid-acting formulations used in people. In patients with some residual beta cell function such as many diabetic cats, administering only a "basal" insulin might lead to complete normalisation of blood glucose concentrations. Insulin suspensions (neutral protamine Hagedorn, neutral protamine Hagedorn/regular mixes, lente and protamine zinc insulin) as well as insulin glargine U100 and detemir are "intermediate"-acting formulations that are administered twice daily. For a formulation to be an effective and safe "basal" insulin, its action should be roughly the same every hour of the day. Currently, only insulin glargine U300 and insulin degludec meet this standard in dogs, whereas in cats, insulin glargine U300 is the closest option.

Synthesis and Characterization of Phenylboronic Acid-Modified Insulin With Glucose-Dependent Solubility

Glucose-responsive insulin represents a promising approach to regulate blood glucose levels. We previously showed that attaching two fluorophenylboronic acid (FPBA) residues to the C-terminal B chain of insulin glargine led to glucose-dependent solubility. Herein, we demonstrated that relocating FPBA from B chain to A chain increased the baseline solubility without affecting its potency. Furthermore, increasing the number of FPBA groups led to increased glucose-dependent solubility.

Purification of Modified Therapeutic Proteins Available on the Market: An Analysis of Chromatography-Based Strategies

Proteins, which have inherent biorecognition properties, have long been used as therapeutic agents for the treatment of a wide variety of clinical indications. Protein modification through covalent attachment to different moieties improves the therapeutic's pharmacokinetic properties, affinity, stability, confers protection against proteolytic degradation, and increases circulation half-life. Nowadays, several modified therapeutic proteins, including PEGylated, Fc-fused, lipidated, albumin-fused, and glycosylated proteins have obtained regulatory approval for commercialization. During its manufacturing, the purification steps of the therapeutic agent are decisive to ensure the quality, effectiveness, potency, and safety of the final product. Due to the robustness, selectivity, and high resolution of chromatographic methods, these are recognized as the gold standard in the downstream processing of therapeutic proteins. Moreover, depending on the modification strategy, the protein will suffer different physicochemical changes, which must be considered to define a purification approach. This review aims to deeply analyze the purification methods employed for modified therapeutic proteins that are currently available on the market, to understand why the selected strategies were successful. Emphasis is placed on chromatographic methods since they govern the purification processes within the pharmaceutical industry. Furthermore, to discuss how the modification type strongly influences the purification strategy, the purification processes of three different modified versions of coagulation factor IX are contrasted.

Review: Glucose-sensitive insulin

BACKGROUND

Hypoglycemia, the condition of low blood sugar, is a common occurance in people with diabetes using insulin therapy. Protecting against hypoglycaemia by engineering an insulin preparation that can auto-adjust its biological activity to fluctuating blood glucose levels has been pursued since the 1970s, but despite numerous publications, no system that works well enough for practical use has reached clinical practise.

SCOPE OF REVIEW

This review will summarise and scrutinise known approaches for producing glucose-sensitive insulin therapies. Notably, systems described in patent applications will be extensively covered, which has not been the case for earlier reviews of this area.

MAJOR CONCLUSIONS

The vast majority of published systems are not suitable for product development, but a few glucose-sensitive insulin concepts have recently reached clinical trials, and there is hope that glucose-sensitive insulin will become available to people with diabetes in the near future.

Insulin exits skeletal muscle capillaries by fluid-phase transport

Before insulin can stimulate myocytes to take up glucose, it must first move from the circulation to the interstitial space. The continuous endothelium of skeletal muscle (SkM) capillaries restricts insulin's access to myocytes. The mechanism by which insulin crosses this continuous endothelium is critical to understand insulin action and insulin resistance; however, methodological obstacles have limited understanding of endothelial insulin transport in vivo. Here, we present an intravital microscopy technique to measure the rate of insulin efflux across the endothelium of SkM capillaries. This method involves development of a fully bioactive, fluorescent insulin probe, a gastrocnemius preparation for intravital microscopy, an automated vascular segmentation algorithm, and the use of mathematical models to estimate endothelial transport parameters. We combined direct visualization of insulin efflux from SkM capillaries with modeling of insulin efflux kinetics to identify fluid-phase transport as the major mode of transendothelial insulin efflux in mice. Model-independent experiments demonstrating that insulin movement is neither saturable nor affected by insulin receptor antagonism supported this result. Our finding that insulin enters the SkM interstitium by fluid-phase transport may have implications in the pathophysiology of SkM insulin resistance as well as in the treatment of diabetes with various insulin analogs.

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.

Synthesis, cloning and expression of a novel pre-miniproinsulin analogue gene in Escherichia coli

In the present study, a novel pre-miniproinsulin analogue was designed to have a short 9 residue sequence replacing the 35 residue C-chain, one lysine and one arginine added to the C-terminus of the B-chain in combination with glycine and arginine substitution at A21 and B29, respectively, and a 16-residue fusion partner comprising the pentapeptide sequence (PSDKP) of the N-terminus of human tumor necrosis factor-α (TNF-α), 6 histidine residues for Ni²⁺ chelated affinity purification and a pentapeptide ending with methionine for ease of chemical cleavage fused at the N-terminus. Homology modeling of the designed protein against miniproinsulin (protein databank file 1 efeA) as a template showed that the distance between the α-carbons of the C-terminus of the B-chain and the N-terminus of the A-chain did not change; the root-mean-square deviation of the backbone atoms between the structures of modeled miniproinsulin and miniproinsulin template was 0.000 Å. DNA sequencing of the synthesized gene showed 100% identity with theoretical sequence. The gene was constructed taking into account the codon preference of Escherichia coli (CAI value 0.99) in order to increase the expression rate of the DNA in the host strain. The designed gene was synthesized using DNA synthesis technology and then cloned into the expression plasmid pET-24a(+) and propagated in E. coli strain JM109. Gene expression was successful in two E. coli strains: namely JM109(DE3) and BL21(DE3)pLysS. SDS–PAGE analysis was carried out to check protein size and to check and optimize expression. Rapid screening and purification of the resulting protein was carried out by Ni–NTA technology. The identity of the expressed protein was verified by immunological detection method of western blot using polyclonal rabbit antibody against insulin.

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.

Discovery of high potency, single-chain insulin analogs with a shortened B-chain and nonpeptide linker

A series of novel, single chain insulin analogs containing polyethylene glycol based connecting segments were synthesized by native chemical ligation and tested for biological activity. While the full length single chain insulin analogs exhibited low potency, deletion of amino acids B26-B30 unexpectedly generated markedly higher activity. This observation is unprecedented in all previous studies of single chain insulin analogs and is consistent with the presumption that in the native hormone this sequence must translocate to achieve high potency insulin receptor interaction. Optimization of the sequence yielded an insulin analog with potency and selectivity comparable to that of native insulin. These results establish a basis for discovery of novel higher potency, single chain insulin analogs of shortened length.

Design of non-standard insulin analogs for the treatment of diabetes mellitus

Structure-based protein design has enabled the engineering of insulin analogs with improved pharmacokinetic and pharmacodynamic properties. Exploiting classical structures of zinc insulin hexamers, the first insulin analog products focused on destabilization of subunit interfaces to obtain rapid-acting (prandial) formulations. Complementary efforts sought to stabilize the insulin hexamer or promote higher-order self-assembly within the subcutaneous depot toward the goal of enhanced basal glycemic control with reduced risk of hypoglycemia. Current products either operate through isoelectric precipitation (insulin glargine, the active component of Lantus; Sanofi-Aventis, Paris, France) or employ an albumin-binding acyl tether (insulin detemir, the active component of Levemir; Novo-Nordisk, Basværd, Denmark). In the past year second-generation basal insulin analogs have entered clinical trials in an effort to obtain ideal flat 24-hour pharmacodynamic profiles. The strategies employ non-standard protein modifications. One candidate (insulin degludec; Novo-Nordisk a/s) undergoes extensive subcutaneous supramolecular assembly coupled to a large-scale allosteric reorganization of the insulin hexamer (the TR transition). Another candidate (LY2605541; Eli Lilly and Co., Indianapolis, IN, USA) utilizes coupling to polyethylene glycol to delay absorption and clearance. On the other end of the spectrum, advances in delivery technologies (such as microneedles and micropatches) and excipients (such as the citrate/zinc-ion chelator combination employed by Biodel, Inc., Danbury, CT, USA) suggest strategies to accelerate PK/PD toward ultra-rapid-acting insulin formulations. Next-generation insulin analogs may also address the feasibility of hepatoselective signaling. Although not in clinical trials, early-stage technologies provide a long-range vision of "smart insulins" and glucose-responsive polymers for regulated hormone release.

Plasma exposure to insulin glargine and its metabolites M1 and M2 after subcutaneous injection of therapeutic and supratherapeutic doses of glargine in subjects with type 1 diabetes

OBJECTIVE

In vivo, after subcutaneous injection, insulin glargine (21(A)-Gly-31(B)-Arg-32(B)-Arg-human insulin) is enzymatically processed into 21(A)-Gly-human insulin (metabolite 1 [M1]). 21(A)-Gly-des-30(B)-Thr-human insulin (metabolite 2 [M2]) is also found. In vitro, glargine exhibits slightly higher affinity, whereas M1 and M2 exhibit lower affinity for IGF-1 receptor, as well as mitogenic properties, versus human insulin. The aim of the study was to quantitate plasma concentrations of glargine, M1, and M2 after subcutaneous injection of glargine in male type 1 diabetic subjects.

RESEARCH DESIGN AND METHODS

Glargine, M1, and M2 were determined in blood samples obtained from 12, 11, and 11 type 1 diabetic subjects who received single subcutaneous doses of 0.3, 0.6, or 1.2 units · kg(-1) glargine in a euglycemic clamp study. Glargine, M1, and M2 were extracted using immunoaffinity columns and quantified by a specific liquid chromatography-tandem mass spectrometry assay. Lower limit of quantification was 0.2 ng · mL(-1) (33 pmol · L(-1)) per analyte.

RESULTS

Plasma M1 concentration increased with increasing dose; geometric mean (percent coefficient of variation) M1-area under the curve between time of dosing and 30 h after dosing (AUC(0-30h)) was 1,261 (66), 2,867 (35), and 4,693 (22) pmol · h · L(-1) at doses of 0.3, 0.6, and 1.2 units · kg(-1), respectively, and correlated with metabolic effect assessed as pharmacodynamics-AUC(0-30h) of the glucose infusion rate following glargine administration (r = 0.74; P < 0.01). Glargine and M2 were detectable in only one-third of subjects and at a few time points.

CONCLUSIONS

After subcutaneous injection of glargine in male subjects with type 1 diabetes, exposure to glargine is marginal, if any, even at supratherapeutic doses. Glargine is rapidly and nearly completely processed to M1 (21(A)-Gly-human insulin), which mediates the metabolic effect of injected glargine.

Insulin analogs for the treatment of diabetes mellitus: therapeutic applications of protein engineering

The engineering of insulin analogs represents a triumph of structure-based protein design. A framework has been provided by structures of insulin hexamers. Containing a zinc-coordinated trimer of dimers, such structures represent a storage form of the active insulin monomer. Initial studies focused on destabilization of subunit interfaces. Because disassembly facilitates capillary absorption, such targeted destabilization enabled development of rapid-acting insulin analogs. Converse efforts were undertaken to stabilize the insulin hexamer and promote higher-order self-assembly within the subcutaneous depot toward the goal of enhanced basal glycemic control with reduced risk of hypoglycemia. Current products either operate through isoelectric precipitation (insulin glargine, the active component of Lantus(®); Sanofi-Aventis) or employ an albumin-binding acyl tether (insulin detemir, the active component of Levemir(®); Novo-Nordisk). To further improve pharmacokinetic properties, modified approaches are presently under investigation. Novel strategies have recently been proposed based on subcutaneous supramolecular assembly coupled to (a) large-scale allosteric reorganization of the insulin hexamer (the TR transition), (b) pH-dependent binding of zinc ions to engineered His-X(3)-His sites at hexamer surfaces, or (c) the long-range vision of glucose-responsive polymers for regulated hormone release. Such designs share with wild-type insulin and current insulin products a susceptibility to degradation above room temperature, and so their delivery, storage, and use require the infrastructure of an affluent society. Given the global dimensions of the therapeutic supply chain, we envisage that concurrent engineering of ultra-stable protein analog formulations would benefit underprivileged patients in the developing world.

Insulin X10 revisited: a super-mitogenic insulin analogue

The molecular safety of insulin analogues has received a great deal of attention over the last year. In particular, attention has been directed to the mitogenic properties of insulin analogues as compared with human insulin. Understanding the mechanisms implicated in mediating mitogenic effects of insulin is therefore of particular interest. In this review we detail the story of the rapid-acting insulin analogue known as X10, which was the first insulin analogue in clinical development, but ended up being discontinued at an early clinical development stage following findings of mammary tumours in female Sprague-Dawley rats. The molecular characteristics of insulin X10, along with its interaction at both the IGF-1 receptor and the insulin receptor, have provided us with important insights into mechanisms implicated in metabolic and mitogenic signalling of insulin analogues.

Insulin therapy in diabetes and cancer risk: current understanding and implications for future study: proceedings from a meeting of a European Insulin Safety Consensus Panel, convened and sponsored by Novo Nordisk, held Tuesday October 5, 2010 at The Radisson Edwardian Heathrow Hotel, Hayes, Middlesex, UK

INTRODUCTION

Interest in the possibility of certain insulin treatments having the potential to modify cancer development and prognosis was reawakened in 2009, following publication of several epidemiological studies addressing this issue. This interest extends to how diabetes itself and cancer might be linked, and makes desirable an exchange of expert views and knowledge to enhance understanding in this subject among those treating diabetes and cancer, or those developing diabetes therapies.

METHODS

A European meeting was convened with participants invited based on known relevant interests in endocrinology, oncology, epidemiology, and insulin analog design and investigation. Experts in these fields were invited to present on relevant topics, with open discussions held after each presentation.

RESULTS

Concern over the potential mitogenic properties of certain insulin analogs has arisen from some (but not all) epidemiological studies, although confounding factors render interpretation controversial. Future epidemiological studies are likely to strengthen confidence in drawing conclusions. Meanwhile, pharmacological studies, and a consideration of cancer pathophysiology, implicate increased insulin-like growth factor-1 receptor affinity, and/or deranged insulin receptor interaction/signaling properties as possible a priori causes for concern with some insulin analogs. Again, interpretation of the body of pharmacological evidence is confounded by the array of test systems and methodologies used, and by studies frequently succumbing to methodological pitfalls. Reassuringly, most available insulin analogs do not differ in their receptor interaction response profile to human insulin, and for those that do there are reasons to question any potential clinical relevance. Nevertheless, it is desirable that new experimental models are devised that can better determine the likely clinical consequences of any variance in receptor response profile versus human insulin.

CONCLUSION

More data are required to increase our understanding of this issue. To facilitate and disseminate such understanding, close cooperation and communication between diabetologists, epidemiologists, oncologists, and insulin engineers will be essential.

Self-association of long-acting insulin analogues studied by size exclusion chromatography coupled to multi-angle light scattering

Two structurally very different insulin analogues analysed here, belong to a class of analogues of which two have been reported to have a protracted action through self-assembly to high molar mass in subcutis. The process of self-association of insulin analogues Lys(B29) (N(ε)ω-carboxyheptadecanoyl) des(B30) human insulin and Lys(B29) (N(ε)-lithocholyl) des(B30) human insulin was investigated using size exclusion chromatography (SEC) in connection with multi-angle light-scattering. Self-assembly to high molar mass was obtained by exchanging the formulation containing phenolic preservatives with an isotonic eluent during SEC. It was shown that increasing amounts of zinc in the formulations of the two analogues increased the size of the self assemblies formed during gel filtration. The addition of 0.2 mM phenol to the elution buffer slowed down the self-association process of zinc containing formulations and shed light on the initial association process. The results indicated that a dihexamer is a possible building block during self-association of Lys(B29) (N(ε)ω-carboxyheptadecanoyl) des(B30) human insulin. Surprisingly, in the absence of zinc the two analogues behaved very differently. Lys(B29) (N(ε)ω-carboxyheptadecanoyl) des(B30) human insulin was in equilibrium between oligomers smaller than a hexamer, whereas Lys(B29) (N(ε)-lithocholyl) des(B30) human insulin self-associated and formed even larger complexes than in the presence of zinc.

Differences in bioactivity between human insulin and insulin analogues approved for therapeutic use- compilation of reports from the past 20 years

In order to provide comprehensive information on the differences in bioactivity between human insulin and insulin analogues, published in vitro comparisons of human insulin and the rapid acting analogues insulin lispro (Humalog®), insulin aspart ( NovoRapid®), insulin glulisine (Apidra®), and the slow acting analogues insulin glargine (Lantus®), and insulin detemir (Levemir®) were gathered from the past 20 years (except for receptor binding studies). A total of 50 reports were retrieved, with great heterogeneity among study methodology. However, various differences in bioactivity compared to human insulin were obvious (e.g. differences in effects on metabolism, mitogenesis, apoptosis, intracellular signalling, thrombocyte function, protein degradation). Whether or not these differences have clinical bearings (and among which patient populations) remains to be determined.

[Safety of insulin analogues: what to evaluate, how to do it, and how to interpret the results]

The widespread use of insulin analogues is based not only on the pharmacokinetics of these preparations, which is much closer to the physiology of insulin secretion under normal conditions, but also on their safety and effectiveness. The publication of a possible association between the use of a long-acting insulin analogue (glargine) and breast cancer has caused uneasiness among the medical community regarding the safety of these analogues. The mechanism of increased tumor activity of insulin analogues is explained by the fact that they act through insulin receptors (IR) and insulin-like growth factor-1 (IGF-1R), stimulating cell growth and inhibiting apoptosis. There are two major mechanisms: an increase in the binding time of insulin to IR and increased activation of IGF-1R. Therefore, to evaluate the safety of an analogue, the slower dissociation rate from its insulin receptor must be excluded, as well as the increased affinity for the IGF-1 receptor. This is equivalent to an index of mitogenic/metabolic activity of less than 1. These aspects can only be evaluated through study of cell lines and animal testing, which are reductionist models that cannot always be extrapolated to humans. To date, there are no data to question the safety of insulin analogues in general. However, the results of observational studies and some in vitro studies, suggesting a potential risk of mitogenicity with the administration of glargine, have caused some alarm among the medical community. Until now, there are no data to refute or confirm this risk and, therefore, evaluation of the existing data is crucial to obtain objective information.

In vitro metabolic and mitogenic signaling of insulin glargine and its metabolites

Background

Insulin glargine (Lantus®) is a long-acting basal insulin analog that demonstrates effective day-long glycemic control and a lower incidence of hypoglycemia than NPH insulin. After subcutaneous injection insulin glargine is partly converted into the two main metabolites M1 ([Gly^A21]insulin) and M2 ([Gly^A21,des-Thr^B30]insulin). The aim of this study was to characterize the glargine metabolites in vitro with regard to their insulin receptor (IR) and IGF-1 receptor (IGF1R) binding and signaling properties as well as their metabolic and mitogenic activities.

Methods

The affinity of human insulin, insulin glargine and its metabolites to the IR isoforms A and B or IGF1R was analyzed in a competitive binding assay using SPA technology. Receptor autophosphorylation activities were studied via In-Cell Western in CHO and MEF cells overexpressing human IR-A and IR-B or IGF1R, respectively. The metabolic response of the insulins was studied as stimulation of lipid synthesis using primary rat adipocytes. Thymidine incorporation in Saos-2 cells was used to characterize the mitogenic activity.

Conclusions

The binding of insulin glargine and its metabolites M1 and M2 to the IR were similar and correlated well with their corresponding autophosphorylation and metabolic activities in vitro. No differences were found towards the two IR isoforms A or B. Insulin glargine showed a higher affinity for IGF1R than insulin, resulting in a lower EC₅₀ value for autophosphorylation of the receptor and a more potent stimulation of thymidine incorporation in Saos-2 cells. In contrast, the metabolites M1 and M2 were significantly less active in binding to and activation of the IGF1R and their mitogenicity in Saos-2 cells was equal to human insulin. These findings strongly support the idea that insulin glargine metabolites contribute with the same potency as insulin glargine to blood glucose control but lead to significantly reduced growth-promoting activity.

Insulin analogues and cancer risk: cause for concern or cause célèbre?

People with diabetes, particularly those with type 2 diabetes, may be at an increased risk of cancer. Furthermore, their cancer risk may be modified by treatment choices. In this respect, metformin may be protective, whereas insulin and insulin analogues can function as growth factors and therefore have theoretical potential to promote tumour proliferation. Analogues causing inappropriate prolonged stimulation of the insulin receptor, or excess stimulation of the IGF-1 receptor, are the most likely to show mitogenic properties in laboratory studies. Some recent epidemiological studies appear to be consistent with these experimental findings, suggesting that there could be different relative risks for cancer associated with different insulins, although these studies have attracted some methodological criticism. However, it is biologically plausible that hormonal factors that influence neoplasia could begin to manifest their effects in surprisingly short timescales (within 2 years) and hence these epidemiological studies justify further research. Even if future research were to document an increase in cancer risk among insulin users, this would be unlikely to significantly diminish the favourable benefit-risk ratio for patients requiring insulin therapy. There is a need for further population studies and for the development of new laboratory models that are more sophisticated than previous experimental methods employed to assess potential tumour growth-promoting properties of insulins.

Supramolecular protein engineering: design of zinc-stapled insulin hexamers as a long acting depot

Bottom-up control of supramolecular protein assembly can provide a therapeutic nanobiotechnology. We demonstrate that the pharmacological properties of insulin can be enhanced by design of "zinc staples" between hexamers. Paired (i, i+4) His substitutions were introduced at an alpha-helical surface. The crystal structure contains both classical axial zinc ions and novel zinc ions at hexamer-hexamer interfaces. Although soluble at pH 4, the combined electrostatic effects of the substitutions and bridging zinc ions cause isoelectric precipitation at neutral pH. Following subcutaneous injection in a diabetic rat, the analog effected glycemic control with a time course similar to that of long acting formulation Lantus. Relative to Lantus, however, the analog discriminates at least 30-fold more stringently between the insulin receptor and mitogenic insulin-like growth factor receptor. Because aberrant mitogenic signaling may be associated with elevated cancer risk, such enhanced specificity may improve safety. Zinc stapling provides a general strategy to modify the pharmacokinetic and biological properties of a subcutaneous protein depot.

Design of an insulin analog with enhanced receptor binding selectivity: rationale, structure, and therapeutic implications

Insulin binds with high affinity to the insulin receptor (IR) and with low affinity to the type 1 insulin-like growth factor (IGF) receptor (IGFR). Such cross-binding, which reflects homologies within the insulin-IGF signaling system, is of clinical interest in relation to the association between hyperinsulinemia and colorectal cancer. Here, we employ nonstandard mutagenesis to design an insulin analog with enhanced affinity for the IR but reduced affinity for the IGFR. Unnatural amino acids were introduced by chemical synthesis at the N- and C-capping positions of a recognition alpha-helix (residues A1 and A8). These sites adjoin the hormone-receptor interface as indicated by photocross-linking studies. Specificity is enhanced more than 3-fold on the following: (i) substitution of Gly(A1) by D-Ala or D-Leu, and (ii) substitution of Thr(A8) by diaminobutyric acid (Dab). The crystal structure of [D-Ala(A1),Dab(A8)]insulin, as determined within a T(6) zinc hexamer to a resolution of 1.35 A, is essentially identical to that of human insulin. The nonstandard side chains project into solvent at the edge of a conserved receptor-binding surface shared by insulin and IGF-I. Our results demonstrate that modifications at this edge discriminate between IR and IGFR. Because hyperinsulinemia is typically characterized by a 3-fold increase in integrated postprandial insulin concentrations, we envisage that such insulin analogs may facilitate studies of the initiation and progression of cancer in animal models. Future development of clinical analogs lacking significant IGFR cross-binding may enhance the safety of insulin replacement therapy in patients with type 2 diabetes mellitus at increased risk of colorectal cancer.

Prediction of protein solubility from calculation of transfer free energy

Solubility plays a major role in protein purification, and has serious implications in many diseases. We studied the effects of pH and mutations on protein solubility by calculating the transfer free energy from the condensed phase to the solution phase. The condensed phase was modeled as an implicit solvent, with a dielectric constant lower than that of water. To account for the effects of pH, the protonation states of titratable side chains were sampled by running constant-pH molecular dynamics simulations. Conformations were then selected for calculations of the electrostatic solvation energy: once for the condensed phase, and once for the solution phase. The average transfer free energy from the condensed phase to the solution phase was found to predict reasonably well the variations in solubility of ribonuclease Sa and insulin with pH. This treatment of electrostatic contributions combined with a similar approach for nonelectrostatic contributions led to a quantitative rationalization of the effects of point mutations on the solubility of ribonuclease Sa. This study provides valuable insights into the physical basis of protein solubility.

Design of an active ultrastable single-chain insulin analog: synthesis, structure, and therapeutic implications

Single-chain insulin (SCI) analogs provide insight into the inter-relation of hormone structure, function, and dynamics. Although compatible with wild-type structure, short connecting segments (<3 residues) prevent induced fit upon receptor binding and so are essentially without biological activity. Substantial but incomplete activity can be regained with increasing linker length. Here, we describe the design, structure, and function of a single-chain insulin analog (SCI-57) containing a 6-residue linker (GGGPRR). Native receptor-binding affinity (130 +/- 8% relative to the wild type) is achieved as hindrance by the linker is offset by favorable substitutions in the insulin moiety. The thermodynamic stability of SCI-57 is markedly increased (DeltaDeltaG(u) = 0.7 +/- 0.1 kcal/mol relative to the corresponding two-chain analog and 1.9 +/- 0.1 kcal/mol relative to wild-type insulin). Analysis of inter-residue nuclear Overhauser effects demonstrates that a native-like fold is maintained in solution. Surprisingly, the glycine-rich connecting segment folds against the insulin moiety: its central Pro contacts Val(A3) at the edge of the hydrophobic core, whereas the final Arg extends the A1-A8 alpha-helix. Comparison between SCI-57 and its parent two-chain analog reveals striking enhancement of multiple native-like nuclear Overhauser effects within the tethered protein. These contacts are consistent with wild-type crystal structures but are ordinarily attenuated in NMR spectra of two-chain analogs, presumably due to conformational fluctuations. Linker-specific damping of fluctuations provides evidence for the intrinsic flexibility of an insulin monomer. In addition to their biophysical interest, ultrastable SCIs may enhance the safety and efficacy of insulin replacement therapy in the developing world.

Mass spectrometric determination of insulins and their degradation products in sports drug testing

Insulins' anabolic and anti-catabolic properties have supposedly led to its misuse in sport. Hence, doping control assays were developed to allow the unequivocal identification of synthetic insulin analogs and metabolic products derived from human insulin and its artificial counterparts in urine and plasma specimens. Analyses were based on immunoaffinity purification and subsequent characterization of target analytes by top-down sequencing-based approaches, which were conducted with hybrid tandem mass spectrometers that consisted of either quadrupole-linear ion trap or linear ion trap-orbitrap analyzers. Diagnostic product ions and analytical strategies are presented and discussed in light of the need to unambiguously identify misused drugs in urine and plasma specimens for doping control.