Glucocorticoids are stress hormones with regulatory effects on carbohydrate, protein and lipid metabolism. Cortisol (or hydrocortisone in rodent) is the most important human glucocorticoid. 11-beta hydroxyl steroid dehydrogenase or 11 beta-HSD1 (11β-HSD-1) is a member of the short chain dehydrogenase super-family of enzymes which converts functionally inert cortisone to active cortisol locally, in a pre-receptor manner. Given that the enzyme is abundantly expressed in metabolically important tissues, such as adipose, muscle, and liver, that become resistant to insulin action in Type 2 Diabetes, inhibition of 11β-HSD-1 offers the potential to restore the glucose lowering action of insulin in these tissues without impacting the central HPA. Another important 11-beta hydroxyl steroid dehydrogenase, namely Type 2 11-beta-HSD (11β-HSD-2), which converts cortisol into cortisone, is a unidirectional dehydrogenase mainly located in kidney and protects minerallocorticoid receptors from illicit activation by glucocorticoids.
Multiple lines of evidence indicate that 11β-HSD-1-mediated intracellular cortisol production may have a pathogenic role in Obesity, Type 2 Diabetes and its co-morbidities.
In humans, treatment with non-specific inhibitor carbenoxolone improves insulin sensitivity in lean healthy volunteers and people with type2 diabetes (Walker B R et al (1995)). Likewise, 11β-HSD-1 activity was decreased in liver and increased in the adipose tissue of obese individuate. Similarly 11β-HSD-1 mRNA was found to be increased in both visceral and subcutaneous adipose tissue of obese patients (Desbriere R et al (2006)) and was positively related to BMI and central obesity in Pima Indians, Caucasians and Chinese youth (Lindsay R S et al (2003), Lee Z S et al (1999)). Adipose tissue 11β-HSD-1 and Hexose-6-Phosphate Dehydrogenase gene expressions have also been shown to increase in patients with type 2 diabetes mellitus (Uçkaya G et al (2008)). In human skeletal muscle 11β-HSD-1 expression was found to be positively associated with insulin resistance (Whorwood C B et al (2002)). Increased 11β-HSD-1 expression was also seen in diabetic myotubes (Abdallah B M et al (2005)).
Various studies have been conducted in rodent models to substantiate the role of 11β-HSD-1 in diabetes and obesity. For example, over-expression of 11β-HSD-1 specifically in adipose tissue causes development of metabolic syndrome (glucose intolerance, obesity, dyslipidemia and hypertension) in mice (Masuzaki H et al (2001)). Conversely, when 11β-HSD-1 gene was knocked out, the resulting mice showed resistance to diet induced obesity and improvement of the accompanying dysregulation of glucose and lipid metabolism (Kotelevtsev Y et al (1997), Morton N M et al (2001), Morton N M et al (2004)). In addition, treatment of diabetic mouse models with specific inhibitors of 11β-HSD-1 caused a decrease in glucose output from the liver and overall increase in insulin sensitivity (Alberts P et al (2003)).
The results of the preclinical and early clinical studies suggest that the treatment with a selective and potent inhibitor of 11β-HSD-1 will be an efficacious therapy for type 2 diabetes, obesity and metabolic syndrome.
The role of 11β-HSD-1 as an important regulator of liver glucocorticoid level and thus of hepatic glucose production is well substantiated. Hepatic insulin sensitivity was improved in healthy human volunteers treated with the non-specific 11β-HSD-1 inhibitor carbenoxolone (Walker B R (1995)). Many in vitro and in vivo (animal model) studies showed that the mRNA levels and activities of two key enzymes (PEPCK and G6PC) in gluconeogenesis and glycogenolysis were reduced by reducing 11β-HSD-1 activity. Data from these models also confirm that inhibition of 11β-HSD-1 will not cause hypoglycemia, as predicted since the basal levels of PEPCK and G6Pase are regulated independently of glucocorticoids (Kotelevtsev Y (1997)).
In the pancreas cortisol is shown to inhibit glucose induced insulin secretion as well as increase stress induced beta cell apoptosis. Inhibition of 11β-HSD-1 by carbenoxolone in isolated murine pancreatic beta-cells improves glucose-stimulated insulin secretion (Davani B et al (2000)). Recently, it was shown that 11β-HSD-1 within alpha cells regulates glucagon secretion and in addition may act in a paracrine manner to limit insulin secretion from beta cells (Swali A et al (2008)). Levels of 11β-HSD-1 in islets from ob/ob mice were shown to be positively regulated by glucocorticoids and were lowered by a selective 11β-HSD-1 inhibitor and a glucocorticoid receptor antagonist. Increased levels of 11β-HSD-1 were associated with impaired GSIS (Ortsater H et al (2005)). In Zuker diabetic rats, troglitazone treatment improved metabolic abnormalities with a 40% decline in expression of 11β-HSD-1 in the islets (Duplomb L et al (2004)). Cortisol inhibition may lead to an increase in the insulin gene transcription and a normalization of first phase insulin secretion (Shinozuka Y et al (2001)).
In human skeletal muscle 11β-HSD-1 expression is positively associated insulin resistance and increased expression of 11β-HSD-1 was also reported in type 2 diabetic myotubes (Abdallah B M et al (2005)). Recently the contribution of cortisol in muscle pathology is being considered for modulating its action. Very recently it has been demonstrated that targeted reduction or pharmacological inhibition of 11β-HSD-1 in primary human skeletal muscle prevents the effect of cortisone on glucose metabolism and palmitate oxidation (Salehzadeh F et al (2009)). Over activity of cortisol in muscle leads to muscle atrophy, fibre type switch and poor utilization of glucose due to insulin resistance. Cortisol might have a direct role in reducing muscle glucose uptake.
Obesity is an important factor in Metabolic syndrome as well as in the majority (>80%) of type 2 diabetics, and omental (visceral) fat appears to be of central importance. 11β-HSD-1 activity is increased in the both visceral and subcutaneous adipose tissue of obese individual (Lindsay R S et al (2003)). Cortisol activity in adipose is known to increase the adipogenic program. Inhibition of 11β-HSD-1 activity in pre-adipocytes has been shown to decrease the rate of differentiation into adipocytes (Bader T et al (2002)). This is predicted to result in diminished expansion (possibly reduction) of the omental fat depot, i.e., reduced central obesity (Bujalska I J et al (1997) and (2006)). Intra-adipose cortisol levels have been associated with adipose hypertrophy, independent of obesity (Michailidou Z et al (2006)).
Cortisol in coordination with adrenergic signalling is also known to increase lipolysis which leads to increase in plasma free fatty acid concentrations which, in turn, is the primary cause of many deleterious effects of obesity (TomLinson J W et al (2007)).
Adrenalectomy attenuates the effect of fasting to increase both food intake and hypothalamic neuropeptide Y expression. This supports the role of glucocorticoids in promoting food intake and suggests that inhibition of 11β-HSD-1 in the brain might increase satiety and therefore reduce food intake (Woods S C (1998)). Inhibition of 11β-HSD-1 by a small molecule inhibitor also decreased food intake and weight gain in diet induced obese mice (Wang S J Y et al (2006)).
The effects discussed above therefore suggest that an effective 11β-HSD-1 inhibitor would have activity as an anti-obesity agent.
Cortisol in excess can also trigger triglyceride formation and VLDL secretion in liver, which can contribute to hyperlipidemia and associated dyslipidemia. It has been shown that 11β-HSD-1−/− transgenic mice have markedly lower plasma triglyceride levels and increased HDL cholesterol levels indicating a potential atheroprotective phenotype (Morton N M et al (2001)). In a diet-induced obese mouse model, a non-selective inhibitor of 11β-HSD-1 reduced plasma free fatty acid as well as triacylglycerol (Wang S J et al (2006)). Over-expression of 11β-HSD-1 in liver increased liver triglyceride and serum free fatty acids with the up regulation of hepatic lipogenic genes (Paterson J M et al (2004). It has been illustrated that inhibition of 11β-HSD-1 improves triglyceridemia by reducing hepatic VLDL-TG secretion, with a shift in the pattern of TG-derived fatty acid uptake toward oxidative tissues, in which lipid accumulation is prevented by increased lipid oxidation (Berthiaume M et al (2007)).
Atherosclerotic mouse model (APOE −/−) which are susceptible to atheroma when fed high fat diet, are protected against development of atherosclerosis when treated with 11β-HSD-1 inhibitors (Hermanowski-Vostaka A et al, (2005)).
Inhibition of 11β-HSD-1 in mature adipocytes is expected to attenuate secretion of the plasminogen activator inhibitor 1 (PAI-1)—an independent cardiovascular risk factor (Halleux C M et al (1999)). Furthermore, there is a clear correlation between glucocorticoid activity and cardiovascular risk factor suggesting that a reduction of the glucocorticoid effects would be beneficial (Walker B R et al (1998), Fraser R et al (1999)).
The association between hypertension and insulin resistance might be explained by increased activity of cortisol. Recent data show that the intensity of dermal vasoconstriction after topical application of glucocorticoids is increased in patients with essential hypertension (Walker B R et al (1998)). Glucocorticoid was shown to increase the expression of angiotensin receptor in vascular cell and thus potentiating the renin-angiotensin pathway (Ullian M E et al (1996)), (Sato A et al (1994)). Role of cortisol in NO signalling and hence vasoconstriction has been proved recently (Liu Y et al (2009)). These findings render 11β-HSD-1 a potential target for controlling hypertension and improving blood-flow in target tissues.
In the past decade, concern on glucocorticoid-induced osteoporosis has increased with the widespread use of exogenous glucocorticoids (GC). GC-induced osteoporosis is the most common and serious side-effect for patients receiving GC. Loss of bone mineral density (BMD) is greatest in the first few months of GC use. Mature bone-forming cells (osteoblasts) are considered to be the principal site of action of GC in the skeleton. The whole differentiation of mesenchymal stem cell toward the osteoblast lineage has been proven to be sensitive to GC as well as collagen synthesis (Kim C H et al (1999)). The effects of GC on this process are different according to the stage of differentiation of bone cell precursors. The presence of intact GC signalling is crucial for normal bone development and physiology, as opposed to the detrimental effect of high dose exposure (Pierotti S et al (2008), Cooper M S et al (2000)). Other data suggest a role of 11β-HSD-1 in providing sufficiently high levels of active glucocorticoid in osteoclasts, and thus in augmenting bone resorption (Cooper M S et al (2000)). The negative effect on bone nodule formation could be blocked by the non-specific inhibitor carbenoxolone suggesting an important role of 11β-HSD-1 in the glucocorticoid effect (Bellows C G et al (1998)).
Stress and glucocorticoids influence cognitive function (de Quervain D J et al (1998)). The enzyme 11β-HSD-1 controls the level of glucocorticoid action in the brain also known to contributes to neurotoxicity (Rajan V et al (1996)). It has been also suggested that inhibiting 11β-HSD-1 in the brain may result in reduced anxiety (Tronche F et al (1999)). Thus, taken together, the hypothesis is that inhibition of 11β-HSD-1 in the human brain would prevent reactivation of cortisone into cortisol and protect against deleterious glucocorticoid-mediated effects on neuronal survival and other aspects of neuronal function, including cognitive impairment, depression, and increased appetite.
Recent data suggest that the levels of the glucocorticoid target receptors and the 11β-HSD-1 enzymes determine the susceptibility to glaucoma (Stokes, J. et al. (2000)). Ingestion of carbenoxolone, a non-specific inhibitor of 11β-HSD-1, was shown to reduce the intraocular pressure by 20% in normal subjects. There are evidences that 11β-HSD-1 isozyme may modulate steroid-regulated sodium transport across the NPE, thereby influencing intra ocular pressure (IOP). 11β-HSD-1 is suggested to have a role in aqueous production, rather than drainage, but it is presently unknown if this is by interfering with activation of the glucocorticoid or the mineralocorticoid receptor, or both (Rauz S et al (2001; 2003)).
The multitude of glucocorticoid action is exemplified in patients with prolonged increase in plasma glucocorticoids, so called “Cushing's syndrome”. These patients have prolonged increase in plasma glucocorticoids and exhibit impaired glucose tolerance, type 2 diabetes, central obesity, and osteoporosis. These patients also have impaired wound healing and brittle skin. Administration of glucocorticoid receptor agonist (RU38486) in Cushing's syndrome patients reverses the features of metabolic syndrome (Neiman L K et al (1985)).
Glucocorticoids have been shown to increase risk of infection and delay healing of open wounds. Patients treated with glucocorticoids have 2-5-fold increased risk of complications when undergoing surgery. Glucocorticoids influence wound healing by interfering with production or action of cytokines and growth factors like IGF, TGF-beta, EGF, KGF and PDGF (Beer H D et al (2000)). TGF-beta reverses the glucocorticoid-induced wound-healing deficit in rats by PDGF regulation in macrophages (Pierce G F et al (1989)). It has also been shown that glucocorticoids decrease collagen synthesis in rat and mouse skin in vivo and in rat and human fibroblasts (Oishi Y et al, 2002).
Glucocorticoids have also been implicated in conditions as diverse aspolycystic Ovaries Syndrome, infertility, memory dydsfunction, sleep disorders, myopathy (Endocrinology. 2011 January; 152(1):93-102. Epub 2010 Nov. 24. PMID: 21106871) and muscular dystrophy. As such the ability to target enzymes that have an impact on glucocorticoid levels is expected to provide promise for the treatment of these conditions.
Based on patent literature and company press releases, there are many compound tested for 11β-HSD-1 inhibition in the different stages of drug discovery pipeline.
Incyte Corporation's INCB13739 has proceeded furthest to phase IIb stage of clinical trial. The results of phase IIa trial for type 2 diabetes (28-days, placebo-controlled, two-step hyperinsulinemic clamp studies) showed that it was safe and well tolerated without any serious side effects and hypoglycemia.
Though this molecule significantly improved hepatic insulin sensitivity there was no appreciable improvement in plasma glucose levels. The molecule appeared to be having positive effects on risk factors for cardiovascular disease including reduction of LDL, total cholesterol and triglycerides as well as more modest increases in HDL. INCB13739 is currently being studied in a dose ranging phase IIb trials in T2D patients whose glucose levels are not controlled by metformin monotherapy.
In the pre-clinical stage, Incyte's lead inhibitor INCB13739 was tested in rhesus monkey and was shown to inhibit adipose 11β-HSD-1 (INCB013739, a selective inhibitor of 11β-Hydroxysteroid Dehydrogenase Type 1 (11βHSD1) improves insulin sensitivity and lowers plasma cholesterol over 28 days in patients with type 2 diabetes mellitus.
The evidence therefore strongly suggests that compounds that are inhibitors of 11β-Hydroxysteroid Dehydrogenase would be useful in the treatment of a number of clinical conditions associated with the expression of this enzyme. In addition it would be desirable if the inhibitors were selective inhibitors so as not to interfere with the functioning of closely related enzymes such as 11β-HSD-2 which is known to provide a protective effect in the body.