Modulators of the Cystic Fibrosis Transmembrane Conductance Regulator Protein.

Abstract

Cystic fibrosis (CF) is a genetic disorder caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein, which lead to abnormality in water and ion transport across epithelial cells. In particular, the deletion of phenylalanine 508 (F508del) in the cystic fibrosis CFTR anion channel causes misfolding and premature degradation of the protein. The activity of CFTR is essential for the maintenance of electrolyte transport throughout the body, including digestive and respiratory tissues. The main symptom of CF is the fluid imbalance in the lungs, which leads to the accumulation of a highly viscous mucopurulent sputum. Majority of patients affected by CF die from pulmonary disease, even though CF affects other areas including the liver, kidneys, pancreas, and intestine. CF is the most common fatal genetic disease in humans, and up to 10 million people in the United States carry a single copy of the defective gene without ill effects. In contrast, an individual with two copies of the CF associated gene suffers from the debilitating fatal effects of CF. In CF patients, endogenous respiratory epithelial CFTR does not enhance chloride and bicarbonate permeability to the epithelial cells in the lung and other tissues; this lead to disruption in the ion and fluid transport. Consequently, mucus and pathogenic agents accumulate in the lung and cause microbial infections that may turn deadly in CF patients. Furthermore, CF patients may also suffer from gastrointestinal and pancreatic problems. Female subjects may suffer from decreased fertility, while most males with cystic fibrosis are infertile. CFTR has been shown to function as a cAMP-activated chloride channel with a small single channel conductance and a nonrectifying connection. The cAMP/ATP-mediated anion channel is commonly associated with disease processes, which express absorptive and secretory epithelia cell types. There are many reported ATP releases associated with CFTR expression in the cardiac myocytes, human airway epithelial cells, C127 cells, retinal pigment epithelium cells, and red blood cells from normal and CF patients with mechanical stress. CFTR is a member of the ATP-binding cassette (ABC) transporter subfamily, which serves as a cAMP-dependent chloride channel with a unique cytoplasmic regulator. These are guarded by two large transmembrane domains (TMD1 and TMD2) and two intracellular nucleotide binding domains (NBD1 and NBD2). The mutation in the gene causes two distinct defects: a processing defect and a gating defect. The F508del mutation reduces stability of the NBD1 and destabilizes the interactions between the NBD1 and the nucleotide-binding domains, leading to F508del-CFTR retaining in the endoplasmic reticulum (ER). The ABC transporters regulate the transport of a wide variety of pharmacological agents such as anions, xenobiotics, drugs, and so forth. In addition, these transporters also regulate defensive mechanisms like the resistance of malignant cancer cells against chemotherapeutic agents and provide protection against harmful environmental vectors. Consequently, therapeutic agents that modulate ABC transporters may be beneficial in treating diseases and conditions that are mediated and modulated by CFTR protein. Pharmacological therapeutics act directly on mutant CFTR to improve interactions at the interfaces between NBD1 and membrane-spanning domains (MSD1 or MSD2) or stabilize the NBD1 or NBD2 domain. In addition, CFTR modulators may be beneficial for the treatment of secretory diarrheas, which is found in patients with chronic inflammatory bowel disease and acquired immunodeficiency syndrome, where diarrhea could be a dangerous condition. CFTR modulation may be beneficial for other disease areas not directly linked to mutations in CFTR, including chronic obstructive pulmonary disease (COPD), characterized by a progressive and nonreversible airflow blockage, and Sjogren’s syndrome, an autoimmune disease that affects moisture-producing glands throughout the body (eye, mouth, skin, vagina, gut, and so forth). The pyrrolidine substituted compounds in the invention are modulators of the CFRT protein and are useful therapeutics in treating conditions and diseases such as CF.