Design, Synthesis, and Structure-Activity Relationship of Tetrahydropyrido[4,3-d]pyrimidine Derivatives as Potent Smoothened Antagonists with in Vivo Activity

Design, synthesis and evaluation of novel UDCA-aminopyrimidine hybrids as ATX inhibitors for the treatment of hepatic and pulmonary fibrosis

To discover novel anti-fibrotic agents, a series of UDCA-aminopyrimidine hybrids were designed and synthesized as potent ATX inhibitors by molecular hybridization strategy. The ATX inhibitory activities of all synthesized compounds were evaluated using the LPC choline release assay. The preliminary structure-activity relationship was concluded. Among them, 12a and 12h exhibited the strongest ATX inhibitory activities with IC50 values of 7.62 ± 0.62 and 7.51 ± 0.72 nM respectively, which were 9-fold more effective than the positive control drug GLPG-1690. Molecular docking studies revealed that 12a and 12h occupied the hydrophobic pocket and tunnel of the ATX binding site. The cytotoxicity assay of 12a and 12h revealed that they had no obvious toxicity at concentrations up to 80 μM, therefore their anti-hepatic fibrosis and anti-pulmonary fibrosis activities were further investigated. The results suggested that 12a and 12h significantly decreased the gene and protein expression of α-SMA, COL1A1 and FN in both TGF-β1-induced HSC-LX2 and CCC-HPF-1 cells. In addition, 12a and 12h significantly inhibited cells migration in both TGF-β1-induced HSC-LX2 and CCC-HPF-1 cells. Preliminary mechanistic studies indicated that 12a and 12h exerted anti-hepatic fibrosis and anti-pulmonary fibrosis effects by inhibiting the TGF-β/Smad signaling pathway. Overall, our findings suggested that 12a and 12h might be two promising anti-fibrotic agents, or might serve as two new lead compounds for the further development of anti-fibrotic agents.

Identification of solamargine as a cisplatin sensitizer through phenotypical screening in cisplatin-resistant NSCLC organoids

Although Cisplatin (DDP) is a widely used first-line chemotherapy medication, DDP resistance is one of the main causes of treatment failure in advanced lung cancer. Therefore, it is urgent to identify DDP sensitizers and investigate the underlying molecular mechanisms. Here we utilized DDP-resistant organoids established from tumor biopsies of patients with relapsed lung cancers. In this study, we identified Solamargine as a potential DDP sensitizer through screening a natural product library. Mechanically, Solamargine induced G0/G1-phase arrest and apoptosis in DDP-resistant lung cancer cell lines. Gene expression analysis and KEGG pathway analysis indicated that the hedgehog pathway was suppressed by Solamargine. Moreover, Gli responsive element (GRE) reporter gene assay and BODIPY-cyclopamine binding assay showed that Solamargine inhibited the hedgehog pathway via direct binding to SMO protein. Interestingly, Solamargine and DDP showed a synergetic effect in inhibiting DDP-resistant lung cancer cell lines. Taken together, our work herein revealed Solamargine as a hedgehog pathway inhibitor and DDP-sensitizer, which might provide a new direction for further treatment of advanced DDP-resistant lung cancer patients.

Design, synthesis, and evaluation of potent RIPK1 inhibitors with in vivo anti-inflammatory activity

RIPK1 plays a key role in the necroptosis pathway that regulates inflammatory signaling and cell death in various diseases, including inflammatory and neurodegenerative diseases. Herein, we report a series of potent RIPK1 inhibitors, represented by compound 70. Compound 70 efficiently blocks necroptosis induced by TNFα in both human and mouse cells (EC₅₀ = 17-30 nM). Biophysical assay demonstrates that compound 70 potently binds to RIPK1 (K_d = 9.2 nM), but not RIPK3 (K_d > 10,000 nM). Importantly, compound 70 exhibits greatly improved metabolic stability in human and rat liver microsomes compared to compound 6 (PK68), a RIPK1 inhibitor reported in our previous work. In addition, compound 70 displays high permeability in Caco-2 cells and excellent in vitro safety profiles in hERG and CYP assays. Moreover, pre-treatment of 70 significantly ameliorates hypothermia and lethal shock in SIRS mice model. Lastly, compound 70 possesses favorable pharmacokinetic parameters with moderate clearance and good oral bioavailability in SD rat. Taken together, our work supports 70 as a potent RIPK1 inhibitor and highlights its potential as a prototypical lead for further development in necroptosis-associated inflammatory disorders.

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.

Discovery of a Potent RIPK3 Inhibitor for the Amelioration of Necroptosis-Associated Inflammatory Injury

Necroptosis is a form of regulated necrosis that requires the activation of receptor-interacting kinase 3 (RIPK3 or RIP3) and its phosphorylation of the substrate MLKL (mixed lineage kinase domain-like protein). Necroptosis has emerged as important cell death involved in the pathogenesis of various diseases including inflammatory diseases, degenerative diseases, and cancer. Here, we discovered a small molecule Zharp-99 as a potent inhibitor of necroptosis through blocking the kinase activity of RIPK3. Zharp-99 efficiently blocks necroptosis induced by ligands of the death receptor and Toll-like receptor as well as viral infection in human, rat and mouse cells. Zharp-99 strongly inhibits cellular activation of RIPK3, and MLKL upon necroptosis stimuli. Zharp-99 directly blocks the kinase activity of RIPK3 without affecting RIPK1 kinase activity at the tested concentration. Importantly, Zharp-99 exerts effective protection against TNF-α induced systemic inflammatory response syndrome in the mouse model. Zharp-99 displays favorable in vitro safety profiles and in vivo pharmacokinetic parameters. Thus, our study demonstrates Zharp-99 as a potent inhibitor of RIPK3 kinase and also highlights its potential for further development of new approaches for treating necroptosis-associated inflammatory disorders.

New 2-aminopyrimidine derivatives and their antitrypanosomal and antiplasmodial activities

Abstract

Novel 2-aminopyrimidine derivatives were prepared from acyclic starting materials, benzylidene acetones and ammonium thiocyanates, via 5 steps, including ring closure, aromatization, S-methylation, oxidation to methylsulfonyl compounds, and formation of guanidines with suitable amines. The prepared compounds differ from each other by the substitutions of their amino group and of their phenyl ring. The 2-aminopyrimidines were tested by use of microplate assays for their in vitro activities against a causative organism of sleeping sickness, Trypanosoma brucei rhodesiense, as well as against a causative organism of malaria, Plasmodium falciparum NF54. Their cytotoxic properties were determined with L-6 cells (rat skeletal myoblasts). Some of the compounds exhibited quite good antitrypanosomal activity, and others showed excellent antiplasmodial activity. The influence of the structural modifications on these activities is discussed.

Graphic abstract

Design, synthesis, and evaluation of pyrrolidine based CXCR4 antagonists with in vivo anti-tumor metastatic activity

The chemokine receptor CXCR4 has been proposed as a drug target based on its important functions in HIV infection, inflammation/autoimmune diseases and cancer metastasis. Herein we report the design, synthesis and evaluation of novel CXCR4 antagonists based on a pyrrolidine scaffold. The structural exploration/optimization identified numerous potent CXCR4 antagonists, represented by compound 46, which displayed potent binding affinity to CXCR4 receptor (IC₅₀ = 79 nM competitively displacing fluorescent 12G5 antibody) and inhibited CXCL12 induced cytosolic calcium flux (IC₅₀ = 0.25 nM). Moreover, in a transwell invasion assay, compound 46 significantly mitigated CXCL12/CXCR4 mediated cell migration. Compound 46 exhibited good physicochemical properties (MW 367, logD_7.4 1.12, pKa 8.2) and excellent in vitro safety profiles (e.g., hERG patch clamp IC₅₀ > 30 μM and minimal CYP isozyme inhibition). Importantly, 46 displayed much improved metabolic stability in human and rat liver microsomes. Lastly, 46 demonstrated marked efficacy in a cancer metastasis model in mice. These results strongly support 46 as a prototypical lead for the development of promising CXCR4 antagonists as clinical candidates.

Design, synthesis, and evaluation of novel CXCR4 antagonists based on an aminoquinoline template

The chemokine receptor CXCR4 has been explored as a drug target due to its involvement in pathological conditions such as HIV infection and cancer metastasis. Here we report the structure-activity relationship study of novel CXCR4 antagonists based on an aminoquinoline template. This template is devoid of the chiral center in the classical tetrahydroquinoline (THQ) ring moiety and therefore can be easily synthesized. A number of potent CXCR4 antagonists were identified, exemplified by compound 3, which demonstrated excellent binding affinity with CXCR4 receptor (IC₅₀ = 57 nM) and inhibited CXCL12 induced cytosolic calcium increase (IC₅₀ = 0.24 nM). Furthermore, compound 3 potently inhibited CXLC12/CXCR4 mediated cell migration in a transwell invasion assay. The simplified synthetic approach combined with good physicochemical properties (e.g. MW 362, clogP 2.1, PSA 48, pKa 7.0 for compound 3) demonstrate the potential of this aminoquinoline template as a novel scaffold to develop CXCR4 antagonists.

A novel hedgehog inhibitor for the treatment of hematological malignancies

The hedgehog-smoothened (HH/SMO) pathway has been proposed as a potential therapeutic target for hematological malignancies. Our previous studies designed a series of HH inhibitors with novel scaffolds distinctive from vismodegib, the first Food and Drug Administration-approved HH inhibitor for the treatment of basal-cell carcinoma and medulloblastoma. In the present study, we evaluated these HH inhibitors against blood cancers and found that HH78 displayed potent activity in suppressing the HH signaling pathway. HH78 competitively bound to SMO and suppressed the transcriptional activity of GLI by the luciferase reporter gene assay and the measurement of HH/SMO-downregulated genes, including cyclin D2, cyclin E, PTCH1, PTCH2, and GLI. HH78 at low micromolar concentrations induced significant cancer cell apoptosis showed by increased caspase-3 activation, annexin V-staining and downregulated prosurvival proteins, including c-Myc, Bcl-2, Mcl-1, and Bcl-xL. In contrast, vismodegib did not show any effects on these apoptotic events. HH78 also suppressed the activation of the AKT/mTOR pathway, which cross-talks with the HH/SMO pathway. Finally, HH78 inhibited the growth of human leukemia K562 in nude mice xenografts with no overt toxicity. Collectively, the present study identified a novel HH inhibitor with great potential for the treatment of hematological malignancies.

Structural optimization on a virtual screening hit of smoothened receptor

The Hedgehog (Hh) pathway plays a critical role during embryonic development by controlling cell patterning, growth and migration. In adults, the function of Hh pathway is curtailed to tissue repair and maintenance. Aberrant reactivation of Hh signaling has been linked to tumorigenesis in various cancers, such as basal cell carcinoma (BCC) and medulloblastoma. The Smoothened (Smo) receptor, a key component of the Hh pathway which is central to the signaling transduction, has emerged as an attractive therapeutic target for the treatment of human cancers. Taking advantage of the availability of several crystal structures of Smo in complex with different antagonists, we have previously conducted a molecular docking-based virtual screening to identify several compounds which exhibited significant inhibitory activity against the Hh pathway activation (IC₅₀ < 10 μM) in a Gli-responsive element (GRE) reporter gene assay. The most potent compound (ChemDiv ID C794-1677: 47 nM) showed comparable Hh signaling inhibition to the marketed drug vismodegib (46 nM). Herein, we report our structural optimization based on the virtual screening hit C794-1677. Our efforts are aimed to improve potency, decrease cLogP, and remove potentially metabolic labile/toxic pyrrole and aniline functionalities presented in C794-1677. The optimization led to the identification of numerous potent compounds exemplified by 25 (7.1 nM), which was 7 folds more potent compared with vismodegib. In addition, 25 was much less lipophilic compared with C794-1677 and devoid of the potentially metabolic labile/toxic pyrrole and aniline functional groups. Furthermore, 25 exhibited promising efficacy in inhibiting Gli1 mRNA expression in NIH3T3 cells with either wildtype Smo or D473H Smo mutant. These results represented significant improvement over the virtual screening hit C794-1677 and suggested that compound 25 can be used as a good starting point to support lead optimization.

Targeting the Oncoprotein Smoothened by Small Molecules: Focus on Novel Acylguanidine Derivatives as Potent Smoothened Inhibitors

Hedgehog-GLI (HH) signaling was originally identified as a critical morphogenetic pathway in embryonic development. Since its discovery, a multitude of studies have reported that HH signaling also plays key roles in a variety of cancer types and in maintaining tumor-initiating cells. Smoothened (SMO) is the main transducer of HH signaling, and in the last few years, it has emerged as a promising therapeutic target for anticancer therapy. Although vismodegib and sonidegib have demonstrated effectiveness for the treatment of basal cell carcinoma (BCC), their clinical use has been hampered by severe side effects, low selectivity against cancer stem cells, and the onset of mutation-driven drug resistance. Moreover, SMO antagonists are not effective in cancers where HH activation is due to mutations of pathway components downstream of SMO, or in the case of noncanonical, SMO-independent activation of the GLI transcription factors, the final mediators of HH signaling. Here, we review the current and rapidly expanding field of SMO small-molecule inhibitors in experimental and clinical settings, focusing on a class of acylguanidine derivatives. We also discuss various aspects of SMO, including mechanisms of resistance to SMO antagonists.

Overcoming the emerging drug resistance of smoothened: an overview of small-molecule SMO antagonists with antiresistance activity

Hedgehog (HH) signaling pathway plays vital roles in controlling embryonic cell fate and homeostatic, and becomes dormant in mature individuals, aberrant activation of HH signaling pathway is involved in a number of human cancers. Smoothened (SMO), a vital transducer of HH signaling pathway, attracts significant attentions in HH signaling pathway-related cancer therapy. The approval of SMO antagonists vismodegib proves that SMO is a promising therapeutic target, and a number of SMO antagonists are reported since then. However, high incidence of tumor recurrence with the clinical application of vismodegib urges exploring of novel drugs with antiresistance profiles. This review provides an overview of SMO mutations reported in the literature, crystal structures of SMO, as well as reported antagonists with antiresistance profiles.

Design of Hedgehog pathway inhibitors for cancer treatment

Hedgehog (Hh) signaling is involved in the initiation and progression of various cancers and is essential for embryonic and postnatal development. This pathway remains in the quiescent state in adult tissues but gets activated upon inflammation and injuries. Inhibition of Hh signaling pathway using natural and synthetic compounds has provided an attractive approach for treating cancer and inflammatory diseases. While the majority of Hh pathway inhibitors target the transmembrane protein Smoothened (SMO), some small molecules that target the signaling cascade downstream of SMO are of particular interest. Substantial efforts are being made to develop new molecules targeting various components of the Hh signaling pathway. Here, we have discussed the discovery of small molecules as Hh inhibitors from the diverse chemical background. Also, some of the recently identified natural products have been included as a separate section. Extensive structure-activity relationship (SAR) of each chemical class is the focus of this review. Also, clinically advanced molecules are discussed from the last 5 to 7 years. Nanomedicine-based delivery approaches for Hh pathway inhibitors are also discussed concisely.

Potential use of CXCL12/CXCR4 and sonic hedgehog pathways as therapeutic targets in medulloblastoma

Medulloblastoma (MB) is the most common malignant brain tumor occurring in children, and although high long-term survival rates have been reached with current therapeutic protocols, several neurological injuries are still observed among survivors. It has been shown that the development of MB is highly dependent on the microenvironment surrounding it and that the CXCL12 chemokine and its receptor, CXCR4 and the Sonic Hedgehog (SHH) pathway are crucial for cerebellar development, coordinating proliferation and migration of embryonic cells and malfunctions in these axes can lead to MB development. Indeed, the concomitant overactivation of these axes was suggested to define a new MB molecular subgroup. New molecules are being studied, aiming to inhibit either CXCR4 or the SHH pathways and have been tested in preclinical settings for the treatment of cancers. The use of these molecules could improve MB treatment and save patients from aggressive surgery, chemotherapy and radiotherapy regimens, which are responsible for severe neurological consequences. This review aims to summarize current data about the experimental inhibition of CXCR4 and SHH pathways in MB and its potential implications in treatment of this cancer.

Discovery of a potent hedgehog pathway inhibitor capable of activating caspase8-dependent apoptosis

Aberrant activation of Hedgehog (Hh) signaling is associated with the development of numerous human cancers. Vismodegib is the first Hh inhibitor approved for anti-cancer therapy by targeting Smoothened (SMO), a critical regulator of the Hh pathway. However, acquisition of drug resistance to vismodegib occurs overtime. Apoptosis is a prevalent form of programmed cell death that is executed by caspases. Induction of tumor cell apoptosis represents an attractive therapeutic strategy to eliminate tumor cells. To explore new Hh antagonists with apoptosis-inducing activity, we screened a set of ∼300 potential SMO antagonists with novel scaffold structures. Hh003 was found to induce caspase-dependent apoptosis while vismodegib did not activate apoptotic response in human colon and pancreatic cancer cells. Compared to vismodegib, Hh003 exerted similar inhibitory effects on the Hh pathway. Hh003 could induce caspase8 activation and the silence of caspase8 significantly inhibited Hh003-induced apoptosis. Remarkably, Hh003 showed stronger inhibitory effects on the formation of tumor colonies in vitro and colorectal tumor growth in vivo than vismodegib. These findings suggest that Hh003 exerts enhanced anti-tumor effects by activating caspase8-dependent apoptosis compared to vismodegib. The combined property of Hh inhibition and apoptosis induction of Hh003 presents great potential for the development of novel anti-cancer therapy.

Design, synthesis, and structure-activity-relationship of a novel series of CXCR4 antagonists

The important roles of the CXCL12/CXCR4 axis in numerous pathogenic pathways involving HIV infection and cancer metastasis make the CXCR4 receptor an attractive target for the development of therapeutic agents. Through scaffold hybridization of a few known CXCR4 antagonists, a series of novel aminopyrimidine derivatives was developed. Compound 3 from this new scaffold demonstrates excellent binding affinity with CXCR4 receptor (IC₅₀ = 54 nM) and inhibits CXCL12 induced cytosolic calcium increase (IC₅₀ = 2.3 nM). Furthermore, compound 3 possesses good physicochemical properties (MW 353, clogP 2.0, PSA 48, pKa 6.7) and exhibits minimal hERG and CYP isozyme (e.g. 3A4, 2D6) inhibition. Collectively, these results strongly support further optimization of this novel scaffold to develop better CXCR4 antagonists.