Cytochromes P450 1A2 and 3A4 Catalyze the Metabolic Activation of Sunitinib.

Sunitinib is a multitargeted tyrosine kinase inhibitor associated with idiosyncratic hepatotoxicity. The mechanisms of this toxicity are unknown. We hypothesized that sunitinib undergoes metabolic activation to form chemically reactive, potentially toxic metabolites which may contribute to development of sunitinib-induced hepatotoxicity. The purpose of this study was to define the role of cytochrome P450 (P450) enzymes in sunitinib bioactivation. Metabolic incubations were performed using individual recombinant P450s, human liver microsomal fractions, and P450-selective chemical inhibitors. Glutathione (GSH) and dansylated GSH were used as trapping agents to detect reactive metabolite formation. Sunitinib metabolites were analyzed by liquid chromatography-tandem mass spectrometry. A putative quinoneimine-GSH conjugate (M5) of sunitinib was detected from trapping studies with GSH and dansyl-GSH in human liver microsomal incubations, and M5 was formed in an NADPH-dependent manner. Recombinant P450 1A2 generated the highest levels of defluorinated sunitinib (M3) and M5, with less formation by P450 3A4 and 2D6. P450 3A4 was the major enzyme forming the primary active metabolite N-desethylsunitinib (M1). In human liver microsomal incubations, P450 3A inhibitor ketoconazole reduced formation of M1 by 88%, while P450 1A2 inhibitor furafylline decreased generation of M5 by 62% compared to control levels. P450 2D6 and P450 3A inhibition also decreased M5 by 54 and 52%, respectively, compared to control. In kinetic assays, recombinant P450 1A2 showed greater efficiency for generation of M3 and M5 compared to that of P450 3A4 and 2D6. Moreover, M5 formation was 2.7-fold more efficient in human liver microsomal preparations from an individual donor with high P450 1A2 activity compared to a donor with low P450 1A2 activity. Collectively, these data suggest that P450 1A2 and 3A4 contribute to oxidative defluorination of sunitinib to generate a reactive, potentially toxic quinoneimine. Factors that alter P450 1A2 and 3A activity may affect patient risk for sunitinib toxicity.

Approach for targeting Ras with small molecules that activate SOS-mediated nucleotide exchange.

Aberrant activation of the small GTPase Ras by oncogenic mutation or constitutively active upstream receptor tyrosine kinases results in the deregulation of cellular signals governing growth and survival in ∼30% of all human cancers. However, the discovery of potent inhibitors of Ras has been difficult to achieve. Here, we report the identification of small molecules that bind to a unique pocket on the Ras:Son of Sevenless (SOS):Ras complex, increase the rate of SOS-catalyzed nucleotide exchange in vitro, and modulate Ras signaling pathways in cells. X-ray crystallography of Ras:SOS:Ras in complex with these molecules reveals that the compounds bind in a hydrophobic pocket in the CDC25 domain of SOS adjacent to the Switch II region of Ras. The structure-activity relationships exhibited by these compounds can be rationalized on the basis of multiple X-ray cocrystal structures. Mutational analyses confirmed the functional relevance of this binding site and showed it to be essential for compound activity. These molecules increase Ras-GTP levels and disrupt MAPK and PI3K signaling in cells at low micromolar concentrations. These small molecules represent tools to study the acute activation of Ras and highlight a pocket on SOS that may be exploited to modulate Ras signaling.

Novel GlyT1 inhibitor chemotypes by scaffold hopping. Part 2: development of a [3.3.0]-based series and other piperidine bioisosteres.

This Letter describes the development and SAR of a novel series of GlyT1 inhibitors derived from a scaffold hopping approach, in lieu of an HTS campaign, which provided intellectual property position. Members within this new [3.3.0]-based series displayed excellent GlyT1 potency, selectivity, free fraction, and modest CNS penetration. Moreover, enantioselective GlyT1 inhibition was observed, within this novel series and a number of other piperidine bioisosteric cores.

Classics in Chemical Neuroscience: Dextromethorphan (DXM).

Dextromethorphan (DXM) was introduced in 1958 as the first non-opioid cough suppressant and is indicated for multiple psychiatric disorders. It has been the most used over-the-counter cough suppressant since its emergence. However, individuals quickly noticed an intoxicating and psychedelic effect if they ingested large doses. DXM's antagonism at N-methyl-d-aspartate receptors (NMDAr) is thought to underly its efficacy in treating acute cough, but supratherapeutic doses mimic the activity of dissociative hallucinogens, such as phencyclidine and ketamine. In this Review we will discuss DXM's synthesis, manufacturing information, drug metabolism, pharmacology, adverse effects, recreational use, abuse potential, and its history and importance in therapy to present DXM as a true classic in chemical neuroscience.

Classics in Chemical Neuroscience: Amitriptyline.

Amitriptyline was the second tricyclic antidepressant to appear on the market for major depressive disorder under the brand name Elavil in 1961. Since its emergence, amitriptyline has been an effective therapeutic in various disease states and disorders but has also been a concerning source of cardiotoxicity. Amitriptyline inhibits serotonin and norepinephrine reuptake as well as produces off-target activity at histaminergic, muscarinic, and various other receptors. Its role as a modulator of monoamines helped further establish the monoamine theory to understand various mood disorders, paving the way for the now more common selective serotonin/norepinephrine reuptake inhibitors. In this review, we will discuss amitriptyline's synthesis, manufacturing information, drug metabolism, pharmacology, adverse effects, and its history and importance in therapy to present amitriptyline as a true classic in chemical neuroscience.

Synthesis and SAR of N-(4-(4-alklylpiperazin-1-yl)phenyl)benzamides as muscarinic acetylcholine receptor subtype 1 (M1) anatgonists.

This Letter describes the synthesis and SAR, developed through an iterative analog library approach, of a novel series of selective M(1) mAChR antagonists, based on an N-(4-(4-alkylpiperazin-1-yl)phenyl)benzamide scaffold for the potential treatment of Parkinson's disease, dystonia and other movement disorders. Compounds in this series possess M(1) antagonist IC(50)s in the 350 nM to >10 microM range with varying degrees of functional selectivity versus M(2)-M(5).

Classics in Chemical Neuroscience: Pramipexole.

Pramipexole was first manufactured by Pharmacia and Upjohn in July 1997 under the United States brand names of Mirapex and Mirapex ER. Pramipexole is classified as a nonergoline aminobenzothiazole compound that selectively agonizes the dopamine D2-like receptor subfamily, which includes the D2, D3, and D4 receptor subtypes. Pramipexole is a unique compound in its therapeutic potential because it has D3-preferring properties. The D3 receptor target has implications in both motor and psychiatric symptoms of Parkinson's disease, restless leg syndrome, and bipolar and unipolar depression. Currently, pramipexole is approved to treat signs and symptoms of idiopathic Parkinson's disease and moderate to severe symptoms of primary restless leg syndrome. Parkinson's disease is characterized by tremor, bradykinesia, rigidity, gait disorders, and a disturbance of posture due to a decrease in dopamine stores in the substantia nigra with the consequent presence of Lewy bodies. Restless leg syndrome is a neurologic sensorimotor disorder characterized by a compelling urge to move the body/limb to relieve this uncomfortable sensation. In this Review, we will discuss the synthesis, drug metabolism, pharmacology, adverse effects, history, and the importance of pramipexole to neuroscience and describe its role in therapy.

Progress toward the total synthesis of lucentamycin A: total synthesis and biological evaluation of 8-epi-lucentamycin A.

Synthetic efforts toward the cytotoxic peptides lucentamycins A-D are described that resulted in the total synthesis and biological evaluation of 8-epi-lucentamycin A in 15 steps with 2.2% overall yield. The key epi-nonproteogenic 3-methyl-4-ethylideneproline was synthesized via a titanium-mediated cycloisomerization reaction.

Synthesis and SAR of analogs of the M1 allosteric agonist TBPB. Part II: Amides, sulfonamides and ureas--the effect of capping the distal basic piperidine nitrogen.

This letter describes the further synthesis and SAR, developed through an iterative analog library approach, of analogs of the highly selective M1 allosteric agonist TBPB by deletion of the distal basic piperidine nitrogen by the formation of amides, sulfonamides and ureas. Despite the large change in basicity and topology, M1 selectivity was maintained.

Synthesis and SAR of analogues of the M1 allosteric agonist TBPB. Part I: Exploration of alternative benzyl and privileged structure moieties.

This Letter describes the first account of the synthesis and SAR, developed through an iterative analogue library approach, of analogues of the highly selective M1 allosteric agonist TBPB. With slight structural changes, mAChR selectivity was maintained, but the degree of partial M1 agonism varied considerably.

DARK Classics in Chemical Neuroscience: Psilocybin.

Psilocybin is found in a family of mushrooms commonly known as "magic mushrooms" that have been used throughout history to induce hallucinations. In the late 1950s Albert Hofmann, of Sandoz Laboratories, identified and synthesized the psychoactive compounds psilocybin and psilocin which are found in psilocybe mushrooms. Psilocybin was marketed by Sandoz as Indocybin for basic psychopharmacological and therapeutic clinical research. Psilocybin saw a rapid rise in popularity during the 1960s and was classed as a Schedule I drug in 1970. This led to a significant decrease in psilocybin research. Recently, however, preliminary studies with psilocybin have shown promise as potential for the treatment of obsessive compulsive disorder, alcohol addiction, tobacco addiction, and major depressive disorder, and the treatment of depression in terminally ill cancer patients. This review describes in detail the synthesis, metabolism, pharmacology, adverse drug reactions, and importance of psilocybin to neuroscience in the past and present.

Discovery of Aminopiperidine Indoles That Activate the Guanine Nucleotide Exchange Factor SOS1 and Modulate RAS Signaling.

Deregulated RAS activity, often the result of mutation, is implicated in approximately 30% of all human cancers. Despite this statistic, no clinically successful treatment for RAS-driven tumors has yet been developed. One approach for modulating RAS activity is to target and affect the activity of proteins that interact with RAS, such as the guanine nucleotide exchange factor (GEF) son of sevenless homologue 1 (SOS1). Here, we report on structure-activity relationships (SAR) in an indole series of compounds. Using structure-based design, we systematically explored substitution patterns on the indole nucleus, the pendant amino acid moiety, and the linker unit that connects these two fragments. Best-in-class compounds activate the nucleotide exchange process at submicromolar concentrations in vitro, increase levels of active RAS-GTP in HeLa cells, and elicit signaling changes in the mitogen-activated protein kinase-extracellular regulated kinase (MAPK-ERK) pathway, resulting in a decrease in pERK1/2T202/Y204 protein levels at higher compound concentrations.

Classics in chemical neuroscience: levodopa.

Levodopa was the first and most successful breakthrough in the treatment of Parkinson's disease (PD). It is estimated that PD affects approximately 1 million people in the United States alone. Although PD was discovered in 1817, prior to levodopa's discovery there was not an effective treatment for managing its symptoms. In 1961, Hornykiewicz pioneered the use of levodopa to enhance dopamine levels in the striatum, significantly improving symptoms in many patients. With the addition of carbidopa in 1974, the frequency of gastrointestinal adverse drug reactions (ADRs) was significantly reduced, leading to the modern treatment of PD. Although levodopa treatment is more than 50 years old, it remains the "gold standard" for PD treatment. This Review describes in detail the synthesis, metabolism, pharmacology, ADRs, and importance of levodopa therapy to neuroscience in the past and present.

Discovery of potent myeloid cell leukemia 1 (Mcl-1) inhibitors using fragment-based methods and structure-based design.

Myeloid cell leukemia 1 (Mcl-1), a member of the Bcl-2 family of proteins, is overexpressed and amplified in various cancers and promotes the aberrant survival of tumor cells that otherwise would undergo apoptosis. Here we describe the discovery of potent and selective Mcl-1 inhibitors using fragment-based methods and structure-based design. NMR-based screening of a large fragment library identified two chemically distinct hit series that bind to different sites on Mcl-1. Members of the two fragment classes were merged together to produce lead compounds that bind to Mcl-1 with a dissociation constant of <100 nM with selectivity for Mcl-1 over Bcl-xL and Bcl-2. Structures of merged compounds when complexed to Mcl-1 were obtained by X-ray crystallography and provide detailed information about the molecular recognition of small-molecule ligands binding Mcl-1. The compounds represent starting points for the discovery of clinically useful Mcl-1 inhibitors for the treatment of a wide variety of cancers.

In vivo structure-activity relationship study of dorsomorphin analogues identifies selective VEGF and BMP inhibitors.

The therapeutic potential of small molecule signaling inhibitors is often limited by off-target effects. Recently, in a screen for compounds that perturb the zebrafish embryonic dorsoventral axis, we identified dorsomorphin, the first selective inhibitor of bone morphogenetic protein (BMP) signaling. Here we show that dorsomorphin has significant "off-target" effects against the VEGF (vascular endothelial growth factor) type-2 receptor (Flk1/KDR) and disrupts zebrafish angiogenesis. Since both BMP and VEGF signals are known to be involved in vascular development, we sought to determine whether dorsomorphin's antiangiogenic effects are due to its impact on the BMP or VEGF signals through the development of analogues that target BMP but not VEGF signaling and vice versa. In a structure-activity relationship (SAR) study of dorsomorphin analogues based primarily on their effects on live zebrafish embryos, we identified highly selective and potent BMP inhibitors as well as selective VEGF inhibitors. One of the BMP inhibitors, DMH1, which exclusively targets the BMP but not the VEGF pathway, dorsalized the embryonic axis without disrupting the angiogenic process, demonstrating that BMP signaling was not involved in the angiogenic process. This is one of the first full-scale SAR studies performed in vertebrates and demonstrates the potential of zebrafish as an attractive complementary platform for drug development that incorporates an assessment of in vivo bioactivity and selectivity in the context of a living organism.

Total synthesis of Ciliatamides A-C: stereochemical revision and the natural product-guided synthesis of unnatural analogs.

The first total synthesis of Ciliatamides A-C was completed, leading to a revision of the reported stereochemistry from (S,S) to the (R,R) enantiomers. Due to the expedited route, a library of over 50 unnatural ciliatamide analogs was also prepared.

A new catalytic Cu(II)/sparteine oxidant system for beta,beta-phenolic couplings of styrenyl phenols: synthesis of carpanone and unnatural analogs.

A new catalytic Cu(II)/sparteine system has been developed to promote beta,beta-phenolic couplings of styrenyl phenols en route to carpanone and related unnatural congeners in yields exceeding 85%.