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

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 concise review on hPXR ligand-recognizing residues and structure-based strategies to alleviate hPXR transactivation risk

The human pregnane X receptor (hPXR) regulates the expression of major drug metabolizing enzymes. A wide range of drug candidates bind and activate hPXR, and hence are at risk of increasing drug-drug interactions and reducing clinical efficacy. hPXR structural features that function as hot spots for ligand binding are identified and highlighted in this concise review. Based on literature structure-activity relationship data as case studies, structure-based strategies to mitigate hPXR transactivation are summarized for medicinal chemists.

Designing Out PXR Activity on Drug Discovery Projects: A Review of Structure-Based Methods, Empirical and Computational Approaches

This perspective discusses the role of pregnane xenobiotic receptor (PXR) in drug discovery and the impact of its activation on CYP3A4 induction. The use of structural biology to reduce PXR activity on drug discovery projects has become more common in recent years. Analysis of this work highlights several important molecular interactions, and the resultant structural modifications to reduce PXR activity are summarized. The computational approaches undertaken to support the design of new drugs devoid of PXR activation potential are also discussed. Finally, the SAR of empirical design strategies to reduce PXR activity is reviewed, and the key SAR transformations are discussed and summarized. In conclusion, this perspective demonstrates that PXR activity can be greatly diminished or negated on active drug discovery projects with the knowledge now available. This perspective should be useful to anyone who seeks to reduce PXR activity on a drug discovery project.

Medulloblastoma drugs in development: Current leads, trials and drawbacks

Medulloblastoma (MB) is the most common malignant brain tumor in children. Current treatment for MB includes surgical resection, radiotherapy and chemotherapy. Despite significant progress in its management, a portion of children relapse and tumor recurrence carries a poor prognosis. Based on their molecular and clinical characteristics, MB patients are clinically classified into four groups: Wnt, Hh, Group 3, and Group 4. With our increased understanding of relevant molecular pathways disrupted in MB, the development of targeted therapies for MB has also increased. Targeted drugs have shown unique privileges over traditional cytotoxic therapies in balancing efficacy and toxicity, with many of them approved and widely used clinically. The aim of this review is to present the recent progress on targeted chemotherapies for the treatment of all classes of MB.

State of the art of Smo antagonists for cancer therapy: advances in the target receptor and new ligand structures

Since the Hedgehog signaling pathway has been associated with cancer, it has emerged as a therapeutic target for cancer therapy. The main target among the key Hedgehog proteins is the GPCR-like Smo receptor. Therefore, some Smo antagonists that have entered clinical trials, including the US FDA-approved drugs vismodegib and sonidegib, to treat basal cell carcinoma and medulloblastoma. However, early resistance of these drugs has spawned the need to understand the molecular bases of this phenomena. We therefore reviewed details about Smo receptor structures and the best Smo antagonist chemical structures. In addition, we discussed strategies that should be considered to develop new, safer generations of Smo antagonists that avoid current clinical limitations.

Strategies to target the Hedgehog signaling pathway for cancer therapy

Hedgehog (Hh) signaling is an essential pathway in the human body, and plays a major role in embryo development and tissue patterning. Constitutive activation of the Hh signaling pathway through sporadic mutations or other mechanisms is explicitly associated with cancer development and progression in various solid malignancies. Therefore, targeted inhibition of the Hh signaling pathway has emerged as an attractive and validated therapeutic strategy for the treatment of a wide range of cancers. Vismodegib, a first-in-class Hh signaling pathway inhibitor was approved by the US Food and Drug Administration in 2012, and sonidegib, another potent Hh pathway inhibitor, received FDA's approval in 2015 as a new treatment of locally advanced or metastatic basal cell carcinoma. The clinical success of vismodegib and sonidegib provided strong support for the development of Hh signaling pathway inhibitors via targeting the smoothened (Smo) receptor. Moreover, Hh signaling pathway inhibitors aimed to target proteins, which are downstream or upstream of Smo, have also been pursued based on the identification of additional therapeutic benefits. Recently, much progress has been made in Hh singling and inhibitors of this pathway. Herein, medicinal chemistry strategies, especially the structural optimization process of different classes of Hh inhibitors, are comprehensively summarized. Further therapeutic potentials and challenges are also discussed.

Induction of human cytochrome P450 3A4 by the irreversible myeloperoxidase inactivator PF-06282999 is mediated by the pregnane X receptor

1. 2-(6-(5-Chloro-2-methoxyphenyl)-4-oxo-2-thioxo-3,4-dihydropyrimidin-1(2H)-yl) acetamide (PF-06282999) is a member of the thiouracil class of irreversible inactivators of human myeloperoxidase enzyme and a candidate for the treatment of cardiovascular disease. PF-06282999 is an inducer of CYP3A4 mRNA and midazolam-1'-hydroxylase activity in human hepatocytes, which is consistent with PF-06282999-dose dependent decreases in mean maximal plasma concentrations (C_max) and area under the plasma concentration time curve (AUC) of midazolam in humans following 14-day treatment with PF-06282999. 2. In the present study, the biochemical mechanism(s) of CYP3A4 induction by PF-06282999 was studied. Incubations in reporter cells indicated that PF-06282999 selectively activated human pregnane X receptor (PXR). Treatment of human HepaRG cells with PF-06282999 led to ∼14-fold induction in CYP3A4 mRNA and 5-fold increase in midazolam-1'-hydroxylase activity, which was nullified in PXR-knock out HepaRG cells. TaqMan® gene expression analysis of human hepatocytes treated with PF-06282999 and the prototypical PXR agonist rifampin demonstrated increases in mRNA for CYP3A4 and related CYPs that are regulated by PXR. 3. Docking studies using a published human PXR crystal structure provided insights into the molecular basis for PXR activation by PF-06282999. Implementation of PXR transactivation assays in a follow-on discovery campaign should aid in the identification of back-up compounds devoid of PXR activation and CYP3A4 induction liability.

2-D lanthanide–organic complexes constructed from 6,7-dihydropyrido(2,3-d)pyridazine-5,8-dione: synthesis, characterization and photoluminescence for sensing small molecules

The 2-D lanthanide–organic complex [(EuHPDH)(ox)(H₂O)]_n, synthesized under hydrothermal conditions, shows high potential for sensing small molecules by its luminescence properties in different emulsions.

Hedgehog pathway inhibitors: a patent review (2009--present)

INTRODUCTION

The hedgehog (Hh) pathway is a developmental signaling pathway that plays a key role in directing cellular growth and tissue patterning during embryonic development. Dysregulation of Hh signaling has been linked to the development of a variety of human tumors, and numerous drug development programs in both academia and industry are actively exploring inhibitors of the pathway as anti-cancer agents.

AREAS COVERED

This review surveys the recent patent literature (2009 - 2012) for Hh pathway inhibitors as treatments for a variety of human malignancies.

EXPERT OPINION

To date, all of the pathway inhibitors that have entered clinical trials and the majority of compounds identified via high-throughput screens target smoothened (Smo), a transmembrane protein that is essential for pathway signaling. While these compounds have shown initial promise in preclinical and clinical trials, several mechanisms of resistance to Smo inhibitors have been identified. Even with this knowledge, the majority of small-molecule pathway inhibitors disclosed in the recent patent literature directly target Smo. The continued identification of Hh pathway inhibitors that function either upstream or downstream is warranted not only to combat these emerging resistance mechanisms, but also to help elucidate the various cellular mechanisms that control both normal and oncogenic pathway signaling.

Synthesis and cytotoxic evaluation of some new phthalazinylpiperazine derivatives

A new series of 1,4-disubstituted phthalazinylpiperazine derivatives 7a-f, 12a-f and 20a-f were designed and synthesized in order to develop potent and selective antitumor agents. The target compounds were screened for their cytotoxic activities against A549, HT-29 and MDA-MB-231 cancer cell lines in vitro. Among them, compounds 7a-f exhibited excellent selectivity for MDA-MB-231 with IC(50) values ranging from 0.013 µM to 0.079 µM. The most promising compound, 7e (IC(50) = 2.19 µM, 2.19 µM, 0.013 µM), was 9.3, 10, and 4.9 × 10(3) times more active than vatalanib (IC(50) = 20.27 µM, 21.96 µM, 63.90 µM), respectively.