Niemann–Pick type C disease (NPCD) was first described in 1914 and affects approximately 1 in 150 000 live births. It is characterized clinically by diverse symptoms affecting liver, spleen, motor control, and brain; premature death invariably results. Its molecular origins were traced, as late as 1997, to a protein of late endosomes and lysosomes which was named NPC1. Mutation or absence of this protein leads to accumulation of cholesterol in these organelles. In this review, we focus on the intracellular events that drive the pathology of this disease. We first introduce endocytosis, a much‐studied area of dysfunction in NPCD cells, and survey the various ways in which this process malfunctions. We briefly consider autophagy before attempting to map the more complex pathways by which lysosomal cholesterol storage leads to protein misregulation, mitochondrial dysfunction, and cell death. We then briefly introduce the metabolic pathways of sphingolipids (as these emerge as key species for treatment) and critically examine the various treatment approaches that have been attempted to date.

Niemann-Pick type C disease (NPCD) is a neurodegenerative disease associated with increases in cellular cholesterol and glycolipids and most commonly caused by defective NPC1, a late endosomal protein. Using ratiometric probes we find that NPCD cells show increased endolysosomal pH. In addition U18666A, an inhibitor of NPC1, was found to increase endolysosomal pH, and the number, size and heterogeneity of endolysosomal vesicles. NPCD fibroblasts and cells treated with U18666A also show disrupted targeting of fluorescent lipid BODIPY-LacCer to high pH vesicles. Inhibiting non-lysosomal glucocerebrosidase (GBA2) reversed increases in endolysosomal pH and restored disrupted BODIPY-LacCer trafficking in NPCD fibroblasts. GBA2 KO cells also show decreased endolysosomal pH. NPCD fibroblasts also show increased expression of a key subunit of the lysosomal proton pump vATPase on GBA2 inhibition. The results are consistent with a model where both endolysosomal pH and Golgi targeting of BODIPY-LacCer are dependent on adequate levels of cytosolic-facing GlcCer, which are reduced in NPC disease. Niemann-Pick type C disease (NPCD) is a devastating neurodegenerative condition most commonly due to mutations in NPC1 [1,2] a protein of late endosomes and lysosomes [3]. (Due to difficulties in precisely distinguishing these two sets of organelles the term endolysosome will be used here to include both.) Mutations in NPC1 are associated with impaired endocytic transport via decreased endolysosomal calcium release [4,5]. In turn, endocytosis and luminal calcium are dependent on correct endolysosomal acidification [4] and have been found to be controlled by glycolipids in neurons [6], melanocytes [7], plant vacuoles [8] and C. elegans [9]. It is increasingly apparent that aberrant lysosomal GlcCer in Gaucher disease is associated with elevated endolysosomal pH [10-13]. Glycolipids, vital for mammals [14], are also implicated in membrane trafficking [10,15]. Similarly in yeast the NPC1 homologue ncr1 regulates both vacuolar pH [16] and glycolipid transport [17]. An overview of sphingolipid metabolism highlighting the connection with endocytosis is offered in Fig. S1. Does NPC1 affect endolysosomal pH? Conflicting evidence has been found both in disease fibroblasts [5,16,18-20] and in cells treated with U18666A, a putative inhibitor of NPC1 [5,21-23]. If endocytic traffic is delayed then probes which permeate all acidic organelles will show increased pH values even though fully mature lysosomes still acidify correctly. We used such a general probe to

A series of 4-substituted pyrimido[4,5-d]azepines that are potent, selective 5-HT2C receptor partial agonists is described. A rational medicinal chemistry design strategy to deliver CNS penetration coupled with SAR-based optimization of selectivity and agonist potency provided compounds with the desired balance of preclinical properties. Lead compounds 17 (PF-4479745) and 18 (PF-4522654) displayed robust pharmacology in a preclinical canine model of stress urinary incontinence (SUI) and no measurable functional agonism at the key selectivity targets 5-HT2A and 5-HT2B in relevant tissue-based assay systems. Utilizing recent advances in the structural biology of GPCRs, homology modeling has been carried out to rationalize binding and agonist efficacy of these compounds.