The following description of the background of the invention is provided simply as an aid in understanding the invention and is not admitted to describe or constitute prior art to the invention.
ATP-sensitive potassium (KATP) channels play important roles in a variety of tissues by coupling cellular metabolism to electrical activity. The KATP channel has been identified as an octameric complex of two unrelated proteins, which assemble in a 4:4 stoichiometry. The first is a pore forming subunit, Kir6.x, which forms an inwardly rectifying K+ channel; the second is an ABC (ATP binding cassette) transporter, also known as the sulfonylurea receptor (SURx) (Babenko, et al., Annu. Rev. Physiol., 60:667-687 (1998)). The Kir6.x pore forming subunit is common for many types of KATP channels, and has two putative transmembrane domains (identified as TM1 and TM2), which are linked by a pore loop (H5). The subunit that comprises the SUR receptor includes multiple membrane-spanning domains and two nucleotide-binding folds.
According to their tissue localization, KATP channels exist in different isoforms or subspecies resulting from the assembly of the SUR and Kir subunits in multiple combinations. The combination of the SUR1 with the Kir6.2 subunits (SUR1/Kir6.2) typically forms the adipocyte and pancreatic B-cell type KATP channels, whereas the SUR2A/Kir6.2 and the SUR2B/Kir6.2 or Kir6.1 combinations typically form the cardiac type and the smooth muscle type KATP channels, respectively (Babenko, et al., Annu. Rev. Physiol., 60:667-687 (1998)). There is also evidence that the channel may include Kir2.x subunits. This class of potassium channels are inhibited by intracellular ATP and activated by intracellular nucleoside diphosphates. Such KATP channels link the metabolic status of the cells to the plasma membrane potential and in this way play a key role in regulating cellular activity. In most excitatory cells, KATP channels are closed under normal physiological conditions and open when the tissue is metabolically compromised (e.g. when the (ATP:ADP) ratio falls). This promotes K+ efflux and cell hyperpolarization, thereby preventing voltage-operated Ca2+ channels (VOCs) from opening. (Prog Res Research, (2001) 31:77-80).
Potassium channel openers (PCOs or KCOs) (also referred to as channel activators or channel agonists), are a structurally diverse group of compounds with no apparent common pharmacophore linking their ability to antagonize the inhibition of KATP channels by intracellular nucleotides. Diazoxide is a PCO that stimulates KATP channels in pancreatic β-cells (see Trube, et al., Pfluegers Arch kEur J Physiol, 407, 493-99 (1986)). Pinacidil and chromakalim are PCOs that activate sarcolemmal potassium channels (see Escande, et al., Biochem Biophys Res Commun, 154, 620-625 (1988); Babenko, et al., J Biol Chem, 275(2), 717-720 (2000)). Responsiveness to diazoxide has been shown to reside in the 6th through 11th predicted transmembrane domains (TMD6-11) and the first nucleotide-binding fold (NBF1) of the SUR1 subunit.
Diazoxide, which is a nondiuretic benzothiadiazine derivative having the formula 7-chloro-3-methyl-2H-1,2,4-benzothiadiazine 1,1-dioxide (empirical formula C8H7ClN2O2S), is commercialized in three distinct formulations to treat two different disease indications; 1) hypertensive emergencies and 2) hyperinsulinemic hypoglycemic conditions. Hypertensive emergencies are treated with Hyperstat IV, an aqueous formulation of diazoxide for intravenous use, adjusted to pH 11.6 with sodium hydroxide. Hyperstat IV is administered as a bolus dose into a peripheral vein to treat malignant hypertension or sulfonylurea overdose. In this use, diazoxide acts to open potassium channels in vascular smooth muscle, stabilizing the membrane potential at the resting level, and preventing vascular smooth muscle contraction.
Hyperinsulinemic hypoglycemic conditions are treated with Proglycem, an oral pharmaceutical version of diazoxide useful for administration to infants, children and adults. It is available as a chocolate mint flavored oral suspension, which includes 7.25% alcohol, sorbitol, chocolate cream flavor, propylene glycol, magnesium aluminum silicate, carboxymethylcellulose sodium, mint flavor, sodium benzoate, methylparaben, hydrochloric acid to adjust the pH, poloxamer 188, propylparaben and water. Diazoxide is also available as a capsule with 50 or 100 mg of diazoxide including lactose and magnesium stearate.
Several experimental formulations of diazoxide have been tested in humans and animals. These include an oral solution tested in pharmacodynamic and pharmacokinetic studies and a tablet formulation under development as an anti-hypertensive, but never commercialized (see Calesnick, et al., J. Pharm. Sci. 54:1277-1280 (1965); Reddy, et al., AAPS Pharm Sci Tech 4(4):1-98, 9 (2003); U.S. Pat. No. 6,361,795).
Current oral formulations of diazoxide are labeled for dosing two or three times per day at 8 or 12 hour intervals. Most patients receiving diazoxide are dosed three times per day. Commercial and experimental formulations of diazoxide are characterized by rapid drug release following ingestion with completion of release in approximately 2 hours.
Current oral formulations of diazoxide in therapeutic use result in a range of adverse side effects including dyspepsia, nausea, diarrhea, fluid retention, edema, reduced rates of excretion of sodium, chloride, and uric acid, hyperglycemia, vomiting, abdominal pain, ileus, tachycardia, palpitations, and headache (see current packaging insert for the Proglycem). Oral treatment with diazoxide is used in individuals experiencing serious disease where failing to treat results in significant morbidity and mortality. The adverse side effects from oral administration are tolerated because the benefits of treatment are substantial. The adverse side effects profile of oral diazoxide limit the utility of the drug in treating obese patients at doses within the labeled range of 3 to 8 mg/kg per day.
The effect of diazoxide in animal models of diabetes and obesity (e.g. obese and lean Zucker rats) has been reported. See e.g. Alemzadeh et al. (Endocrinology 133:705-712 (1993), Alemzadeh et al. (Metabolism 45:334-341 (1996)), Alemzadeh et al. (Endocrinology 140:3197-3202 (1999)), Stanridge et al. (FASEB J 14:455-460 (2000)), Alemzadeh et al. (Med Sci Monit 10(3): BR53-60 (2004)), Alemzadeh and Tushaus (Endocrinology 145(12):3476-3484 (2004)), Aizawa et al. (J of Pharma Exp Ther 275(1): 194-199 (1995)), and Surwit et al. (Endocrinology 141:3630-3637 (2000)).
The effect of diazoxide in humans with obesity or diabetes has been reported. See e.g., Wigand and Blackard (Diabetes 28(4):287-291 (1979); evaluation of diazoxide on insulin receptors), Ratzmann et al. (Int J Obesity 7(5):453-458 (1983); glucose tolerance and insulin sensitivity in moderately obese patients), Marugo et al. (Boll Spec It Biol Sper 53:1860-1866 (1977); moderate dose diazoxide treatment on weight loss in obese patients), Alemzadeh et al. (J Clin Endocr Metab 83:1911-1915 (1998); low dose diazoxide treatment on weight loss in obese hyperinsulinemic patients), Guldstrand et al. (Diabetes and Metabolism 28:448-456 (2002); diazoxide in obese type II diabetic patients), Ortqvist et al. (Diabetes Care 27(9):2191-2197 (2004); beta-cell function measured by circulating C-peptide in children at clinical onset of type 1 diabetes), Bjork et al. (Diabetes Care 21(3):427-430 (1998); effect of diazoxide on residual insulin secretion in adult type I diabetes patients), and Qvigstad et al., (Diabetic Medicine 21:73-76 (2004)).
U.S. Pat. No. 5,284,845 describes a method for normalizing blood glucose and insulin levels in an individual exhibiting normal fasting blood glucose and insulin levels and exhibiting in an oral glucose tolerance test, elevated glucose levels and at least one insulin level abnormality selected from the group consisting of a delayed insulin peak, an exaggerated insulin peak and a secondary elevated insulin peak. According to this reference, the method includes administering diazoxide in an amount from about 0.4 to about 0.8 mg/kg body weight before each meal in an amount effective to normalize the blood glucose and insulin levels.
U.S. Pat. No. 6,197,765 describes administration of diazoxide for treatment for syndrome-X, and resulting complications, that include hyperlipidemia, hypertension, central obesity, hyperinsulinemia and impaired glucose intolerance. According to this reference, diazoxide interferes with pancreatic islet function by ablating endogenous insulin secretion resulting in a state of insulin deficiency and high blood glucose levels equivalent to that of diabetic patients that depend on exogenous insulin administration for normalization of their blood glucose levels.
U.S. Pat. No. 2,986,573 describes diazoxide and alkali metal salts for the treatment of hypertension.
U.S. Pat. No. 5,629,045 describes diazoxide for topical ophthalmic administration.
WO 98/10786 describes use of diazoxide in the treatment of X-syndrome including obesity associated therewith.
U.S. Patent publication no. 2003/0035106 describes diazoxide containing compounds for reducing the consumption of fat-containing foods.
U.S. Patent publication no. 2004/0204472 describes the use of a Cox-2 inhibitor plus diazoxide in the treatment of obesity.
U.S. Patent publication no. 2002/0035106 describes use of KATP channel openers including diazoxide and metal salts for reducing the consumption of fat containing food.