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 detemir is a fully efficacious, low affinity agonist at the insulin receptor.

AIM: To compare the properties of insulin detemir with human insulin or insulin aspart in various in vitro and in vivo experiments, thereby highlighting the importance of performing dose-response studies when investigating insulin analogues, in this study specifically insulin detemir. METHODS: Displacement of membrane-associated insulin receptors from human and rat hepatocytes, and from Chinese Hamster Ovary cells over-expressing human insulin receptor (CHO-hIR) at varying albumin concentrations is measured. Lipogenesis in primary rat adipocytes over time and the effects in the simultaneous presence of insulin detemir and human insulin or insulin aspart are assessed. The hyperinsulinaemic euglycaemic clamp technique in rats is used to establish dose-response curves for multiple metabolic endpoints and to investigate the effects of the simultaneous presence of insulin detemir and human insulin. RESULTS: Both in vitro and in vivo, insulin detemir shows full efficacy and right-shifted parallel dose-response curves compared with human insulin. The potency estimates are different between the in vivo and in vitro conditions and among different in vitro conditions, that is the potency decreases in vitro with increasing albumin concentration. The effects of insulin detemir and human insulin are additive both in vitro and in vivo. CONCLUSIONS: Insulin detemir is fully efficacious compared with human insulin on all metabolic endpoints measured in vitro and in vivo. The fact that the potency estimates are method-dependent emphasizes the importance of establishing full dose-response relationships when characterizing insulin detemir.

Action profile of cobalt(III)-insulin. A novel principle of protraction of potential use for basal insulin delivery.

The Co(3+)-insulin hexamer is an extraordinary stable insulin hexamer that has no affinity for the insulin receptor per se but is converted into active insulin in vivo. In the present study, we evaluated the action profile of Co(3+)-insulin after subcutaneous injection into nondiabetic pigs and showed that the Co(3+)-hexamer does not dissociate before absorption. After absorption, Co(3+)-insulin is accumulated in the bloodstream because the complex is distributed and eliminated more slowly than human insulin. The degree of protraction of Co(3+)-insulin is similar to that of NPH insulin when evaluated in an euglycemic glucose clamp. We suggest that the long plasma half-life and a gradual in vivo activation contribute to prolong the effect of Co(3+)-insulin. The Co(3+)-insulin hexamer provides a novel principle of protraction of potential use for basal insulin delivery to the diabetic patient.

Correlations of receptor binding and metabolic and mitogenic potencies of insulin analogs designed for clinical use.

In recent years, analogs of human insulin have been engineered with the aim of improving therapy for people with diabetes. To ensure that the safety profile of the human hormone is not compromised by the molecular modifications, the toxico-pharmacological properties of insulin analogs should be carefully monitored. In this study, we compared the insulin and IGF-I receptor binding properties and metabolic and mitogenic potencies of insulin aspart (B28Asp human insulin), insulin lispro (B28Lys,B29Pro human insulin), insulin glargine (A21Gly,B31Arg,B32Arg human insulin), insulin detemir (NN304) [B29Lys(epsilon-tetradecanoyl), desB30 human insulin], and reference insulin analogs. Receptor affinities were measured using purified human receptors, insulin receptor dissociation rates were determined using Chinese hamster ovary cells overexpressing the human insulin receptor, metabolic potencies were evaluated using primary mouse adipocytes, and mitogenic potencies were determined in human osteosarcoma cells. Metabolic potencies correlated well with insulin receptor affinities. Mitogenic potencies in general correlated better with IGF-I receptor affinities than with insulin receptor off-rates. The 2 rapid-acting insulin analogs aspart and lispro resembled human insulin on all parameters, except for a slightly elevated IGF-I receptor affinity of lispro. In contrast, the 2 long-acting insulin analogs, glargine and detemir, differed significantly from human insulin. The combination of the B31B32diArg and A21Gly substitutions provided insulin glargine with a 6- to 8-fold increased IGF-I receptor affinity and mitogenic potency compared with human insulin. The attachment of a fatty acid chain to LysB29 provided insulin detemir with reduced receptor affinities and metabolic and mitogenic potencies but did not change the balance between mitogenic and metabolic potencies. The safety implications of the increased growth-stimulating potential of insulin glargine are unclear. The reduced in vitro potency of insulin detemir might explain why this analog is not as effective on a molar basis as human insulin in humans.

How to achieve a predictable basal insulin?

The development of insulin analogues over the last two decades have aimed at optimising the pharmacokinetic profile of subcutaneously injected insulin for therapeutic use in diabetes mellitus. Rapid acting analogues were successfully engineered and marketed in the late 1990's. In engineering long-acting analogues it has been a particular challenge to obtain action profiles that would be predictable from day to day in the same person. The most recent approach has been to acylate the insulin molecule with a fatty acid which provides the insulin molecule with a specific affinity for albumin. The first clinically available agent of this type is insulin detemir. Pharmacological studies have shown that reversible albumin binding will protract absorption following subcutaneous injection but still allow the insulin molecule to be recognised by the insulin receptor following dissociation from the carrier protein. Moreover, the molecular features of insulin detemir are attractive in that the molecule can be formulated as a neutral aqueous solution and does not precipitate after injection. Together with an important buffering mechanism effected by plasma albumin binding, this explains a highly significant reduction of within-subject variability of pharmacodynamic response observed in repeat isoglycaemic clamp studies where insulin detemir was compared to other basal insulin products. No safety considerations have been identified in using albumin as an insulin carrier to protract and buffer insulin action. In assessing the clinical attractiveness of insulin analogues, it is furthermore critically important to consider how the molecular modifications impact efficacy and safety. A number of pharmacological studies have shown that insulin detemir overall retains the molecular pharmacological properties of native human insulin, including a physiological balance between metabolic and mitogenic potencies. Taken together, insulin detemir provides an attractive novel approach for predictive basal insulin delivery to people with diabetes.

The cobalt(III)-insulin hexamer is a prolonged-acting insulin prodrug.

The insulin hexamer has two high-affinity metal ion binding sites, each involving three HisB10 residues, one from each dimer. Insulin hexamers containing Co2+ at both these sites were oxidized to form a stable Co(3+)-insulin complex. It is shown that the Co(3+)-coordinated insulin monomers are released extremely slowly in aqueous solution at pH 8.0, and that the hexamer does not spontaneously dissociate into subunits at nanomolar concentrations of insulin. The Co(3+)-insulin hexamer is not recognized by the insulin receptor in vitro but the complex shows a protracted action profile following subcutaneous (s.c.) injection into rabbits. The Co(3+)-insulin hexamer provides a novel prodrug approach to a soluble, prolonged-acting insulin preparation of potential use for basal insulin delivery in the treatment of diabetes.

Effect of fatty acids and selected drugs on the albumin binding of a long-acting, acylated insulin analogue.

NN304 (LysB29-tetradecanoyl, des(B30)-insulin) is a new soluble, long-acting insulin analogue that is tightly bound to human serum albumin differentiating it from human insulin. In the present study, we investigate the effect of fatty acids and selected drugs on the binding of NN304 to human serum albumin in vitro. Binding of the first fatty acid equivalent to albumin does not affect the binding of NN304. None of the tested drugs compete with the binding of NN304 at drug-to-albumin concentration ratios of < 1. The binding of NN304 is shown to be independent of binding of drugs in the two major binding pockets that are located in domains IIA and IIIA of the albumin molecule. Tolbutamide and glibenclamide do not compete with NN304 for binding to albumin at therapeutic drug-to-albumin concentration ratios. High concentrations of acetylsalicylic acid and ibuprofen decrease the affinity of NN304 for albumin, but these interactions occur at drug-to-albumin concentration ratios that are higher than clinically relevant. In conclusion, NN304 is unlikely to be involved in clinically significant drug interactions at the albumin binding level. The unique ligand binding properties of serum albumin and its abundance in the extracellular fluids makes fatty acid acylation and albumin binding an attractive protraction principle for insulin and potentially also for other peptide drugs.

Albumin binding and time action of acylated insulins in various species.

Insulins acylated with fatty acids at the epsilon-amino group of LysB29 constitute a new class of insulin analogs, which are prolonged-acting due to albumin binding. In the present study it is shown that the affinity of fatty acid acylated insulins for albumin varies considerably (> 50-fold) among species. The relative affinities of acylated insulin for albumin in human, pig, and rabbit serum are about 1:1:5:35. The several fold higher binding affinity in rabbit serum than in pig serum is reflected in a relatively more protracted effect after sc injection in rabbits than in pigs. Due to the similar binding affinities in pig serum and human serum, the pig model should provide a useful estimate of the degree of protraction of acylated insulin in humans. The results emphasize that species differences in ligand binding can be of major importance in the preclinical evaluation of highly albumin bound drugs.

Engineering predictability and protraction in a basal insulin analogue: the pharmacology of insulin detemir.

The suboptimal nature of the absorption profiles of human insulin formulations following subcutaneous administration has prompted the development of insulin analogues better suited for therapeutic use in diabetes mellitus. A particular challenge has been to engineer long-acting agents that do not produce unduly variable responses from one injection to another. One recent approach that has met with success has been to acylate, the insulin molecule with a fatty acid, thereby enabling reversible albumin binding. The first clinically available agent of this type is insulin detemir. Pharmacological studies have established that this principle is effective in prolonging action, primarily by retarding absorption. The solubility of insulin detemir in the vial and after injection and an important buffering mechanism effected by plasma albumin binding explain a significant decrease in within-subject variability of pharmacodynamic response observed in repeat isoglycaemic clamp studies where insulin detemir was compared to other basal insulin products. Owing to the extremely high ratio of albumin-binding sites to insulin detemir molecules at therapeutic concentrations, no safety considerations have been identified pertaining to albumin binding. The insulin detemir molecule retains the molecular pharmacological properties of native human insulin, including a physiological balance between metabolic and mitogenic potencies. Thus, insulin detemir offers the promise of an improved tolerability:efficacy ratio in the clinical setting.

Preliminary studies on the in vivo fate of FITC-dextrans and naproxen-dextran ester prodrugs administered i.v. to rabbits.

The plasma half life and the urinary recovery after i.v. administration to rabbits (35 mg/kg) of FITC-dextrans and naproxen-dextran ester prodrugs of molecular weights 40,000 and 70,000 were determined by employing a HP(SEC) procedure with fluorescence detection. The conjugates disappeared from the blood stream roughly according to first-order kinetics at a rate only slightly influenced by the molecular weight and faster than the parent carrier dextrans. 15-30% of the dose of the derivatives was eliminated through the kidneys as compared to 44% (T-40) and 17% (T-70) of the parent dextrans. Liver uptake of the compounds was assumed to be the main additional elimination pathway as 46% of an i.v. dose of FITC dextran T-70 was found in the liver four hours after the injection, whereas only minor amounts were detected in the spleen, lungs and the kidneys. The molecular weight distribution of the conjugates in the circulation shifted continuously in the high molecular weight direction. The role of the liver in plasma clearance of the conjugates and the influence of the molecular weight and electric charge on the in vivo fate of the dextran derivatives are discussed.

High-performance size-exclusion chromatographic procedure for the determination of fluoresceinyl isothiocyanate dextrans of various molecular masses in biological media.

A high-performance size-exclusion chromatographic procedure, using Nucleosil Diol, for the quantitative analysis of fluoresceinyl isothiocyanate dextrans of various molecular masses (10,000-150,000) in biological media was developed. The influence of the molecular mass and the degree of substitution of the conjugates on the chromatographic behaviour are discussed. In addition to quantitation, the molecular mass of the conjugates with degree of substitution below 1.6 could be estimated from the chromatograms. Linear standard calibration curves were obtained at concentrations down to 0.050 micrograms ml-1 in rabbit plasma and urine and homogenates of rabbit liver, lymph node and muscle when the derivative (degree of substitution 0.85) was monitored by fluorescence detection (lambda ex = 493 nm, lambda em = 520 mm). The fluoresceinyl isothiocyanate dextrans were found to be stable for more than three days at 37 degrees in all biological media under investigation. A pH-rate profile for the alkaline hydrolysis of fluoresceinyl isothiocyanate dextrans was constructed. The applicability of the method to pharmacokinetic studies was demonstrated by recording the plasma concentration-time profile of a fluoresceinyl isothiocyanate dextran T-70 conjugate following intravenous injection to a rabbit. In relation to future pharmacokinetic investigations on dextran conjugates, the results reported indicate that labelling of the parent dextran with fluoresceinyl isothiocyanate and monitoring of the fluoresceinyl isothiocyanate dextran conjugate throughout the organism using the described method is a promising development.

On the design of urokinase-labile prodrugs II. Structure-activity relationships in the urokinase catalyzed hydrolysis of H-GluGlyArg-anilides and -benzylamide.

Six H-GluGlyArg-anilides with different ortho or para substituents in the aniline group, and H-GluGlyArg-benzylamide were synthesized. KM and kcat for the urokinase-catalyzed hydrolysis of the compounds were determined at 37 degrees C and pH 7.40. In the initial rate measurements, HPLC was used for product quantitation. KM varied between 0.20 mM and 8.9 mM, whereas kcat varied between 0.8s-1 and 16.5s-1 for the investigated substrates. A Hammett plot and a "Charton plot" of the rate data are presented. kcat were, to a minor extent, dependent on the pKa of the leaving group, whereas steric effects had a more marked influence on the overall rate constant. A o-benzyl substituent in the aniline-leaving group exerts less sterical hindrance to the enzymatic hydrolysis than expected from the Charton plot. The significance of the results in relation to the development of urokinase labile dextran prodrugs in discussed.

Albumin binding of insulins acylated with fatty acids: characterization of the ligand-protein interaction and correlation between binding affinity and timing of the insulin effect in vivo.

Albumin is a multifunctional transport protein that binds a wide variety of endogenous substances and drugs. Insulins with affinity for albumin were engineered by acylation of the epsilon-amino group of LysB29 with saturated fatty acids containing 10-16 carbon atoms. The association constants for binding of the fatty acid acylated insulins to human albumin are in the order of 10(4)-10(5) M-1. The binding apparently involves both non-polar and ionic interactions with the protein. The acylated insulins bind at the long-chain fatty acid binding sites, but the binding affinity is lower than that of the free fatty acids and depends to a relatively small degree on the number of carbon atoms in the fatty acid chain. Differences in affinity of the acylated insulins for albumin are reflected in the relative timing of the blood-glucose-lowering effect after subcutaneous injection into rabbits. The acylated insulins provide a breakthrough in the search for soluble, prolonged-action insulin preparations for basal delivery of the hormone to the diabetic patient. We conclude that the biochemical concept of albumin binding can be applied to protract the effect of insulin, and suggest that derivatization with albumin-binding ligands could be generally applicable to prolong the action profile of peptide drugs.

Meconium drug screening of stillborn infants: a feasibility study.

OBJECTIVE: Meconium drug testing of liveborn infants is highly sensitive (87%) and specific (100%). Accurate knowledge of drug use in mothers of stillborns would be beneficial. We determined the feasibility of noninvasive meconium drug screening for opiates and cocaine in stillborns. METHODS: Stillborn infants delivered at our hospital had meconium collected using a 4-mm spatula inserted into the anus. Specimens were analyzed using gas chromatography. Charts were reviewed. RESULTS: Of the 30 specimens obtained, 26 were below the optimal amount needed (0.5 g). Regardless, all samples were analyzed and three were positive for cocaine (10%), none for opiates. Two of the 3 positive samples were of 'insufficient quantity'. In one, the presumptive cause of fetal demise was diabetes, with no additional factors suggesting substance abuse. The other fetal loss was due to idiopathic preterm labor at 21.5 weeks, with a positive UDS. CONCLUSION: In this pilot study, inability to obtain an optimal volume of meconium occurred frequently. However, important and unexpected laboratory data were generated even with 'insufficient quantity'. This highlights the need to develop more refined methodologies for this screening tool in stillborn fetuses.

Secretory expression of human albumin domains in Saccharomyces cerevisiae and their binding of myristic acid and an acylated insulin analogue.

Albumin is organized in three homologous domains formed by double loops stabilized by disulfide bonds. Utilizing a secretory expression system based on a synthetic secretory prepro-leader, the three human serum albumin domains were expressed in the yeast Saccharomyces cerevisiae. Human serum albumin domains I and III were efficiently expressed and secreted, indicating that these domains can form independent structural units capable of folding into stable tertiary structures. In contrast, albumin domain II was not secreted and disappeared early in the secretory pathway. Human serum albumin has the ability to bind a large number of small molecule ligands, including fatty acids, presumably due to its structure and structural flexibility. Purified albumin domain III bound myristic acid, whereas purified albumin domain I did not bind myristic acid. A new soluble long-acting insulin an alogue acylated with myristic acid (Markussen J., et al., Diabetologia 39, 281-288, 1996) bound to domain III and bound markedly more weakly to domain I.

Insulin aspart: a novel rapid-acting human insulin analogue.

In order to improve therapy and increase the quality of life for diabetic patients, it has been of significant interest to develop rapid-acting insulin preparations that mimic the physiological meal-time profile of insulin more closely than soluble human insulin. Insulin aspart (B28Asp human insulin) is a novel rapid-acting insulin analogue that fulfils this criterion. The B28Asp modification weakens the self-association of the insulin molecule and provides a more rapid absorption from the sc. injection site. The preclinical evaluation in vitro and in vivo demonstrates that apart from the more rapid absorption, insulin aspart is equivalent to human insulin. Thus, insulin aspart is equivalent to human insulin on key in vitro parameters such as insulin receptor affinity, insulin receptor dissociation rate, insulin receptor tyrosine kinase activation, IGF-I receptor binding affinity, metabolic and mitogenic potency. In accordance with the equivalent in vitro profiles, the toxico-pharmacological properties of insulin aspart and human insulin are also identical. The available data for insulin aspart and other rapid-acting insulin analogues supports that in vitro assays are sensitive and valuable in the preclinical evaluation of insulin analogues. Clinical studies demonstrate that insulin aspart has a pharmacokinetic and pharmacodynamic profile superior to that of soluble human insulin. In Type 1 diabetic patients on a basal-bolus injection regimen, insulin aspart given immediately before the meals provides an improved postprandial glycaemic control and an improved long-term metabolic control, as compared to soluble human insulin given 30 min before the meals, without increasing the risk of hypoglycaemia. Taken together, the data support the hope that insulin aspart will allow the diabetic patient to combine a more flexible lifestyle with better glycaemic control, without any increased safety risk.

Soluble, fatty acid acylated insulins bind to albumin and show protracted action in pigs.

We have synthesized insulins acylated by fatty acids in the epsilon-amino group of LysB29. Soluble preparations can be made in the usual concentration of 600 nmol/ml (100 IU/ml) at neutral pH. The time for 50% disappearance after subcutaneous injection of the corresponding TyrA14(125I)-labelled insulins in pigs correlated with the affinity for binding to albumin (r = 0.97), suggesting that the mechanism of prolonged disappearance is binding to albumin in subcutis. Most protracted was LysB29-tetradecanoyl des-(B30) insulin. The time for 50% disappearance was 14.3 +/- 2.2 h, significantly longer than that of Neutral Protamine Hagedorn (NPH) insulin, 10.5 +/- 4.3 h (p < 0.001), and with less inter-pig variation (p < 0.001). Intravenous bolus injections of LysB29-tetradecanoyl des-(B30) human insulin showed a protracted blood glucose lowering effect compared to that of human insulin. The relative affinity of LysB29-tetradecanoyl des-(B30) insulin to the insulin receptor is 46%. In a 24-h glucose clamp study in pigs the total glucose consumptions for LysB29-tetradecanoyl des-(B30) insulin and NPH were not significantly different (p = 0.88), whereas the times when 50% of the total glucose had been infused were significantly different, 7.9 +/- 1.0 h and 6.2 +/- 1.3 h, respectively (p < 0.04). The glucose disposal curve caused by LysB29-tetradecanoyl des-(B30) insulin was more steady than that caused by NPH, without the pronounced peak at 3 h. Unlike the crystalline insulins, the soluble LysB29-tetradecanoyl des-(B30) insulin does not elicit invasion of macrophages at the site of injection. Thus, LysB29-tetradecanoyl des-(B30) insulin might be suitable for providing basal insulin in the treatment of diabetes mellitus.