A double-masked placebo-controlled trial assessing effects of various doses of BTS 67,582, a novel insulinotropic agent, on fasting hyperglycemia in NIDDM patients

Novel strategies for the pharmacological management of type 2 diabetes

Type 2 diabetes is characterized by high concentrations of glucose in the blood, which is caused by decreased secretion of insulin from the pancreas and decreased insulin action. This condition is prevalent worldwide and is associated with morbidity and mortality secondary to complications such as myocardial infarction, stroke and end-stage renal disease. The importance of tight control of blood glucose in either preventing or delaying the progression of complications is recognized. Currently, there are many therapeutic options to treat hyperglycemia in type 2 diabetes. However, tight control is difficult to achieve and is often associated with side-effects. Recent advances in understanding insulin secretion, action and signaling have led to the development of new pharmacological agents. In this article, we review new molecules that are promising candidates for the future management of diabetes, focusing on their mechanism of action, efficacy, safety profile and potential benefits compared with pharmacological agents that are available currently.

Insulinotropic meglitinide analogues

The loss of early-phase insulin secretion is an important and early event in the natural history of type 2 diabetes. Because a normal pattern of insulin secretion is essential for the effective control of postprandial metabolism, a rational basis for the development of agents that target early-phase insulin release exists. Conventional oral hypoglycaemic agents do not target, or adequately control, postprandial glycaemia. The emergence of new classes of oral agent with a more specific mode of action provides, for the first time, an opportunity to restore early-phase insulin release. One such drug class is the meglitinide analogues (repaglinide, nateglinide, and mitiglinide). These drugs are ideally suited for combination use with metformin. They could also prove effective in combination with a thiazolidinedione, a drug class that targets insulin resistance. Exogenous insulin is frequently required in the late management of type 2 diabetes. However, one hope for newer combinations of diabetic drugs is that the functional life of the beta cell can be extended, thereby delaying the need for insulin injections.

Pathophysiology and pharmacological treatment of insulin resistance

Diabetes mellitus type 2 is a world-wide growing health problem affecting more than 150 million people at the beginning of the new millennium. It is believed that this number will double in the next 25 yr. The pathophysiological hallmarks of type 2 diabetes mellitus consist of insulin resistance, pancreatic beta-cell dysfunction, and increased endogenous glucose production. To reduce the marked increase of cardiovascular mortality of type 2 diabetic subjects, optimal treatment aims at normalization of body weight, glycemia, blood pressure, and lipidemia. This review focuses on the pathophysiology and molecular pathogenesis of insulin resistance and on the capability of antihyperglycemic pharmacological agents to treat insulin resistance, i.e., a-glucosidase inhibitors, biguanides, thiazolidinediones, sulfonylureas, and insulin. Finally, a rational treatment approach is proposed based on the dynamic pathophysiological abnormalities of this highly heterogeneous and progressive disease.

Novel sulfonylurea and non-sulfonylurea drugs to promote the secretion of insulin

The onset of type 2 diabetes is characterized by two determining factors: the insufficient ability to secrete insulin and/or the resistance to its biological action. Although in a very small proportion of individuals, one of those two metabolic abnormalities is the leading cause of diabetes, in most subjects, the coexistence of both appears to be necessary for the clinical manifestation of diabetes. Current biomedical research continues to clarify the relative contributions of these defects to the pathogenesis of type 2 diabetes, and novel pharmacological agents are specifically designed to correct either the impaired insulin secretory activity or the resistance to the action of insulin. The aim of this article is to provide a critical review of new sulfonylurea and non-sulfonylurea drugs that have been recently introduced for the treatment of diabetes, as well as drugs that are still under investigation and are likely to be made available in the near future.

Induced desensitization of the insulinotropic effects of antidiabetic drugs, BTS 67 582 and tolbutamide

Acute and chronic mechanisms of action of novel insulinotropic antidiabetic drug, BTS 67 582 (1, 1-dimethyl-2-(2-morpholinophenyl)guanidine fumarate), were examined in the stable cultured BRIN-BD11 cell line. BTS 67 582 (100 - 400 microM) stimulated a concentration-dependent increase (P<0.01) in insulin release at both non-stimulatory (1.1 mM) and stimulatory (8. 4 mM) glucose. Long-term exposure (3 - 18 h) to 100 microM BTS 67 582 in culture time-dependently decreased subsequent responsiveness to acute challenge with 200 microM BTS 67 582 or 200 microM tolbutamide at 12 - 18 h (P<0.001). Similarly 3 - 18 h culture with the sulphonylurea, tolbutamide (100 microM), also effectively suppressed subsequent insulinotropic responses to both BTS 67 582 and tolbutamide. Culture with 100 microM BTS 67 582 or 100 microM tolbutamide did not affect basal insulin secretion, cellular insulin content, or cell viability and exerted no influence on the secretory responsiveness to 200 microM of the imidazoline, efaroxan. While 18 h BTS 67 582 culture did not affect the insulin-releasing actions (P<0.001) of 16.7 mM glucose, 10 mM arginine, 30 mM KCl, 25 microM forskolin or 10 nM phorbol-12-myristate 13-acetate (PMA), significant inhibition (P<0.001) of the insulinotropic effects of 10 mM 2-ketoisocaproic acid (KIC) and 10 mM alanine were observed. These data suggest that BTS 67 582 shares a common signalling pathway to sulphonylurea but not imidazoline drugs. Desensitization of drug action may provide an important approach to dissect sites of action of novel and established insulinotropic antidiabetic agents.

The effect of an insulin releasing agent, BTS 67582, on advanced glycation end product formation in vitro

BTS 67582 (1,1-dimethyl-2-(2-morpholinophenyl) guanidine fumarate) is an insulin-releasing agent currently in phase II clinical trials. Its effect on advanced glycation end product (AGE) formation was measured in the BSA/D-glucose and L-lysine/glucose-6-phosphate assay systems and Amadori product formation was measured in the BSA/D-glucose assay system, following a 3 week incubation period. In the BSA/D-glucose assay system, 200 mM BTS 67582 caused an approximate 70% inhibition in AGE formation (p<0.001), whilst at 20 mM and 2 mM it caused a marginal inhibition (21%, (p<0.001) and 8% respectively). 200 mM and 20 mM aminoguanidine-HCl inhibited AGE formation by 95% and 69% (p<0.001), respectively, whereas 2 mM aminoguanidine-HCl had no significant effect. Tolbutamide (200 microM) and glibenclamide (100 microM) had significant, but only marginal, effects on AGE formation (16% and 17%, respectively, p<0.01). In the BSA/D-glucose assay system 200 mM BTS 67582 and 200 mM aminoguanidine-HCl retarded Amadori product formation by 88% (p<0.001) and 60% (p<0.01), respectively. BTS 67582 at 20 mM and 2 mM was shown to inhibit Amadori product formation by 67% and 57%, respectively, (p<0.01). In the lysine and glucose-6-phosphate assay system 200 mM BTS 67582 and 200 mM aminoguanidine-HCl were shown to inhibit AGE formation by about 70% and 96% (p<0.001), respectively. Tolbutamide (200 microM) and glibenclamide (100 microM) had no significant effect on AGE formation.

Effect of 1,1-dimethyl-2-[2-morpholinophenyl]guanidine fumarate on pancreatic islet function

The modality of the insulinotropic action of 1,1-dimethyl-2-[2-morpholinophenyl]guanidine fumarate (BTS 67 582), a new antidiabetic agent, was investigated in rat pancreatic islets. At a 0.1 mM concentration, which was sufficient to cause a close-to-maximal secretory response, BTS 67 582 failed to affect the utilization and oxidation of exogenous D-glucose, but slightly augmented 14CO2 production from islets prelabelled with either L-[U-14C]glutamine or [U-14C]palmitate. BTS 67 582 (0.1 mM) also failed to affect biosynthetic activity in islets incubated with L-[4-3H]phenylalanine. It augmented insulin release from islets incubated for 90 min in the absence or presence of D-glucose (2.8 to 16.7 mM), this coinciding with stimulation of 45Ca net uptake. In perifused islets deprived of extracellular D-glucose for 45 min, BTS 67 582 (0.1 mM) decreased 86Rb outflow from prelabelled islets, but failed to increase 45Ca efflux and insulin release. In the presence of D-glucose (7.0 mM), BTS 67 582, whilst failing to decrease 86Rb+ outflow, provoked rapid, sustained and rapidly reversible increases of both 45Ca2+ efflux and insulin output. The latter increases were attenuated, but not totally suppressed, in the absence of extracellular Ca2+. BTS 67 582 (0.1 mM) suppressed the inhibitory action of diazoxide (0.25 mM) upon glucose-stimulated insulin release, but nevertheless augmented insulin output from islets incubated in the presence of 90 mM K+. These findings support the view that the insulinotropic action of BTS 67 582 is mainly attributable to the inactivation of ATP-sensitive K+ channels. An intracellular redistribution of Ca2+ ions may also participate, however, to the islet functional response to BTS 67 582.

Treatment of type 2 diabetes mellitus

Although most patients with type 2 diabetes mellitus can be initially managed with diet and exercise alone, most eventually require at least oral agents if not insulin to maintain glycemic control. Appropriate therapeutic regimens may be difficult to design, given the diversity of drugs available for clinical use. Physicians must consider not only glycemic control, but also patient preference, concomitant medical conditions, and cost when designing therapeutic regimens.

BTS 67 582 stimulates insulin secretion from perifused rat pancreatic islets

The novel antidiabetic agent BTS 67 582 (1,1-dimethyl-2-[2-(4-morpholinophenyl)]guanidine monofumarate) demonstrated a concentration-dependent stimulation of insulin release in perifused rat pancreatic islets. EC50 values of 7.7 microM and 6.3 microM were obtained for BTS 67 582 in the presence of 8 mM glucose, after islets were pre-equilibrated with 4 and 8 mM glucose respectively. In contrast, there was little or no stimulation of insulin release at substimulatory (4 mM) or maximal stimulatory (15 mM) glucose concentrations. The plasma EC50 value for the glucose lowering effect of BTS 67 582 in fasted normal rats was 3.9 microM indicating a similar potency in vivo. In islets, BTS 67 582 completely antagonised (EC50 value of 13.2 microM) the actions of the selective ATP-dependent K+ channel opener diazoxide indicating K+ channel blocking activity. BTS 67 582 only weakly reversed the alpha2-adrenoceptor mediated inhibition of insulin release in islets (EC50 of 83 microM). BTS 67 582, like other imidazoline/guanidine insulin releasing agents, appears to promote insulin release via an effect on the islet ATP-dependent K+ channel which is not mediated by binding to the sulphonylurea receptor.

Drug treatment of non-insulin-dependent diabetes mellitus in the 1990s. Achievements and future developments

Non-insulin-dependent diabetes mellitus (NIDDM, type 2 diabetes) is a heterogeneous disease resulting from a dynamic interaction between defects in insulin secretion and insulin action. There are various pharmacological approaches to improving glucose homeostasis, but those currently used in clinical practice either do not succeed in restoring normoglycaemia in most patients or fail after a variable period of time. For glycaemic regulation, 4 classes of drugs are currently available: sulphonylureas, biguanides (metformin), alpha-glucosidase inhibitors (acarbose) and insulin, each of which has a different mode and site of action. These standard pharmacological treatments may be used individually for certain types of patients, or may be combined in a stepwise fashion to provide more ideal glycaemic control for most patients. Adjunct treatments comprise a few pharmacological approaches which may help to improve glycaemic control by correcting some abnormalities frequently associated with NIDDM, such as obesity (serotoninergic anorectic agents) and hyperlipidaemia (benfluorex). There is intensive pharmaceutical research to find new drugs able to stimulate insulin secretion (new sulphonylurea or nonsulphonylurea derivatives, glucagon-like peptide-1), improve insulin action (thiazolidinediones, lipid interfering agents, glucagon antagonists, vanadium compounds) or reduce carbohydrate absorption (miglitol, amylin analogues, glucagon-like peptide-1). Further studies should demonstrate the superiority of these new compounds over the standard antidiabetic agents as well as their optimal mode of administration, alone or in combination with currently available drugs.

New non-sulfonylurea insulin secretagogues

Current treatments for non-insulin dependent diabetes mellitus (NIDDM) remain far from ideal. The universal finding of islet dysfunction characterised by the absence of first phase insulin secretion, even prior to the level of hyperglycaemia diagnostic of NIDDM, challenges the rationale for treatments that only enhance insulin action. To date, however, the sulfonylureas are the only insulin secretagogues available and even the most rapid acting of these fail to restore early insulin release in response to meals. Four novel non-sulfonylurea insulin secretagogues are in advanced clinical development: A-4166, KAD-1229, BTS 67 582 and repaglinide. These promising new agents control prandial hyperglycaemia by augmenting the early insulin response to meals. Preclinical and early clinical data suggest that their potencies vary considerably, as do their pharmacokinetics and, importantly, their pharmacodynamics. The two shortest-acting compounds, A-4166 and KAD-1229, will be developed to be taken prior to each main meal, while the slower, longer duration agents, repaglinide and BTS 67 582, may be developed to be taken twice daily. With a sufficiently rapid onset and short duration of action, the new non-sulfonylurea insulin secretagogues may improve or even restore the impairment of early insulin secretion without inducing the prolonged hyperinsulinaemia characteristic of sulfonylureas. Treatment with these new agents will immediately improve prandial glucose control and with continued treatment these agents are expected to improve the overall metabolic state. Furthermore, a short-acting secretagogue will have minimal propensity to elicit prolonged or delayed hypoglycaemia and it is expected that by minimising chronic hyperinsulinaemia the weight gain that accompanies sulfonylurea treatment will be avoided. In summary, the new non-sulfonylurea insulin secretagogues will make an important contribution to the limited and inadequate armamentarium currently available for the treatment of NIDDM, and their use in combination with insulin sensitising agents may provide, for the first time, an approximation to ideal metabolic control in NIDDM.