Pregnane X Receptor: Prediction and Attenuation of Human CYP3A4 Enzyme Induction and Drug–Drug Interactions

Ensemble Docking Approach to Mitigate Pregnane X Receptor-Mediated CYP3A4 Induction Risk

Three structurally closely related dopamine D1 receptor positive allosteric modulators (D1 PAMs) based on a tetrahydroisoquinoline (THIQ) scaffold were profiled for their CYP3A4 induction potentials. It was found that the length of the linker at the C5 position greatly affected the potentials of these D1 PAMs as CYP3A4 inducers, and the level of induction correlated well with the activation of the pregnane X receptor (PXR). Based on the published PXR X-ray crystal structures, we built a binding model specifically for these THIQ-scaffold-based D1 PAMs in the PXR ligand-binding pocket via an ensemble docking approach and found the model could explain the observed CYP induction disparity. Combined with our previously reported D1 receptor homology model, which identified the C5 position as pointing toward the solvent-exposed space, our PXR-binding model coincidentally suggested that structural modifications at the C5 position could productively modulate the CYP induction potential while maintaining the D1 PAM potency of these THIQ-based PAMs.

A randomized controlled trial of ganaxolone in posttraumatic stress disorder

Preclinical and clinical research supports a role for neuroactive steroids in the pathophysiology of posttraumatic stress disorder (PTSD). We investigated ganaxolone (a synthetic 3β-methylated derivative of allopregnanolone, a GABAergic neuroactive steroid) for treatment of PTSD in a proof-of-concept, multisite, double-blind, placebo-controlled trial. Veteran and non-veteran participants (n = 112) were randomized to ganaxolone or placebo at biweekly escalating doses of 200, 400, and 600 mg twice daily for 6 weeks. During an open-label 6-week extension phase, the initial ganaxolone group continued ganaxolone, while the placebo group crossed over to ganaxolone. Eighty-six and 59 participants, respectively, completed the placebo-controlled and open-label phases. A modified intent-to-treat mixed model repeated measures analysis revealed no significant differences between the effects of ganaxolone and placebo on Clinician Administered PTSD Symptom (CAPS) scores, global well-being, negative mood, or sleep. Dropout rates did not differ between groups, and ganaxolone was generally well tolerated. Trough blood levels of ganaxolone at the end of the double-blind phase were, however, lower than the anticipated therapeutic level of ganaxolone in >35% of participants on active drug. Pharmacokinetic profiling of the ganaxolone dose regimen used in the trial and adverse event sensitivity analyses suggest that under-dosing may have contributed to the failure of ganaxolone to out-perform placebo. Future investigations of ganaxolone may benefit from higher dosing, rigorous monitoring of dosing adherence, a longer length of placebo-controlled testing, and targeting of treatment to PTSD subpopulations with demonstrably dysregulated pre-treatment neuroactive steroid levels. Clinicaltrials.gov identifier: NCT01339689.

2015 Philip S. Portoghese Medicinal Chemistry Lectureship. Curing Hepatitis C Virus Infection with Direct-Acting Antiviral Agents: The Arc of a Medicinal Chemistry Triumph

The development of direct-acting antiviral agents that can cure a chronic hepatitis C virus (HCV) infection after 8-12 weeks of daily, well-tolerated therapy has revolutionized the treatment of this insidious disease. In this article, three of Bristol-Myers Squibb's HCV programs are summarized, each of which produced a clinical candidate: the NS3 protease inhibitor asunaprevir (64), marketed as Sunvepra, the NS5A replication complex inhibitor daclatasvir (117), marketed as Daklinza, and the allosteric NS5B polymerase inhibitor beclabuvir (142), which is in late stage clinical studies. A clinical study with 64 and 117 established for the first time that a chronic HCV infection could be cured by treatment with direct-acting antiviral agents alone in the absence of interferon. The development of small molecule HCV therapeutics, designed by medicinal chemists, has been hailed as "the arc of a medical triumph" but may equally well be described as "the arc of a medicinal chemistry triumph".

Identification and Preclinical Pharmacology of the γ-Secretase Modulator BMS-869780

Alzheimer's disease is the most prevalent cause of dementia and is associated with accumulation of amyloid-β peptide (Aβ), particularly the 42-amino acid Aβ1-42, in the brain. Aβ1-42 levels can be decreased by γ-secretase modulators (GSM), which are small molecules that modulate γ-secretase, an enzyme essential for Aβ production. BMS-869780 is a potent GSM that decreased Aβ1-42 and Aβ1-40 and increased Aβ1-37 and Aβ1-38, without inhibiting overall levels of Aβ peptides or other APP processing intermediates. BMS-869780 also did not inhibit Notch processing by γ-secretase and lowered brain Aβ1-42 without evidence of Notch-related side effects in rats. Human pharmacokinetic (PK) parameters were predicted through allometric scaling of PK in rat, dog, and monkey and were combined with the rat pharmacodynamic (PD) parameters to predict the relationship between BMS-869780 dose, exposure and Aβ1-42 levels in human. Off-target and safety margins were then based on comparisons to the predicted exposure required for robust Aβ1-42 lowering. Because of insufficient safety predictions and the relatively high predicted human daily dose of 700 mg, further evaluation of BMS-869780 as a potential clinical candidate was discontinued. Nevertheless, BMS-869780 demonstrates the potential of the GSM approach for robust lowering of brain Aβ1-42 without Notch-related side effects.

Glossary of terms used in medicinal chemistry. Part II (IUPAC Recommendations 2013)

The evolution that has taken place in medicinal chemistry practice as a result of major advances in genomics and molecular biology arising from the Human Genome Project has carried with it an extensive additional working vocabulary that has become both integrated and essential terminology for the medicinal chemist. Some of this augmented terminology has been adopted from the many related and interlocked scientific disciplines with which the modern medicinal chemist must be conversant, but many other terms have been introduced to define new concepts and ideas as they have arisen. In this supplementary Glossary, we have attempted to collate and define many of the additional terms that are now considered to be essential components of the medicinal chemist’s expanded repertoire.

Structure-based design of novel benzoxazinorifamycins with potent binding affinity to wild-type and rifampin-resistant mutant Mycobacterium tuberculosis RNA polymerases

By utilization of three-dimensional structure information of rifamycins bound to RNA polymerase (RNAP) and the human pregnane X receptor (hPXR), representative examples (2b-d) of a novel subclass of benzoxazinorifamycins have been synthesized. Relative to rifalazil (2a), these analogues generally display superior affinity toward wild-type and Rif-resistant mutants of the Mycobacterium tuberculosis RNAP but lowered antitubercular activity in cell culture under both aerobic and anaerobic conditions. Lowered affinity toward hPXR for some of the analogues is also observed, suggesting a potential for reduced Cyp450 induction activity. Mouse and human microsomal studies of analogue 2b show it to have excellent metabolic stability. Mouse pharmacokinetics in plasma and lung show accumulation of 2b but with a half-life suggesting nonoptimal pharmacokinetics. These studies demonstrate proof of principle for this subclass of rifamycins and support further expansion of structure-activity relationships (SARs) toward uncovering analogues with development potential.

Addressing PXR liabilities of phthalazine-based hedgehog/smoothened antagonists using novel pyridopyridazines

Pyridopyridazine antagonists of the hedgehog signaling pathway are described. Designed to optimize our previously described phthalazine smoothened antagonists, a representative compound eliminates a PXR liability while retaining potency and in vitro metabolic stability. Moreover, the compound has improved efficacy in a hedgehog/smoothened signaling mouse pharmacodynamic model.