Design, synthesis, and evaluation of potent Wnt signaling inhibitors featuring a fused 3-ring system

Modulators for palmitoylation of proteins and small molecules

As an essential form of lipid modification for maintaining vital cellular functions, palmitoylation plays an important role in in the regulation of various physiological processes, serving as a promising therapeutic target for diseases like cancer and neurological disorders. Ongoing research has revealed that palmitoylation can be categorized into three distinct types: N-palmitoylation, O-palmitoylation and S-palmitoylation. Herein this paper provides an overview of the regulatory enzymes involved in palmitoylation, including palmitoyltransferases and depalmitoylases, and discusses the currently available broad-spectrum and selective inhibitors for these enzymes.

Current status of carbazole hybrids as anticancer agents

The drug resistance and low specificity of current available chemotherapeutics to cancer cells are the main reasons responsible for the failure of cancer chemotherapy and remain dramatic challenges for cancer therapy, creating an urgent need to develop novel anticancer agents. Carbazole nucleus, widely distributed in nature, is a predominant feature of a vast array of biologically active compounds. Carbazole derivatives exhibited potential antiproliferative activity against different cancer cell lines by diverse mechanisms, inclusive of arrest cell cycle and induce apoptosis, and several anticancer agents are carbazole-based compounds. Thus, carbazole derivatives represent a fertile source for discovery of novel anticancer therapeutic agents. Over the past several years, a variety of carbazole hybrids have been developed as potential anticancer agents. The present review focuses on the recent progress, from 2016 until now, in knowledge on anticancer properties, structure-activity relationships and mechanisms of action of carbazole hybrids to provide a basis for development of relevant therapeutic agents.

Small-Molecule Inhibitors Targeting the Canonical WNT Signaling Pathway for the Treatment of Cancer

Canonical WNT signaling is an important developmental pathway that has attracted increased attention for anticancer drug discovery. From the production and secretion of WNT ligands, their binding to membrane receptors, and the β-catenin destruction complex to the expansive β-catenin transcriptional complex, multiple components have been investigated as drug targets to modulate WNT signaling. Significant progress in developing WNT inhibitors such as porcupine inhibitors, tankyrase inhibitors, β-catenin/coactivators, protein-protein interaction inhibitors, casein kinase modulators, DVL inhibitors, and dCTPP1 inhibitors has been made, with several candidates (e.g., LGK-974, PRI-724, and ETC-159) in human clinical trials. Herein we summarize recent progress in the drug discovery and development of small-molecule inhibitors targeting the canonical WNT pathway, focusing on their specific target proteins, in vitro and in vivo activities, physicochemical properties, and therapeutic potential. The relevant opportunities and challenges toward maintaining the balance between efficacy and toxicity in effectively targeting this pathway are also highlighted.

Insights of tankyrases: A novel target for drug discovery

Tankyrases are the group of enzymes belonging to a class of Poly (ADP-ribose) polymerase (PARP) recently named ADP-ribosyltransferase (ARTD). The two isoforms of tankyrase i.e. tankyrase1 (TNKS1) and tankyrase2 (TNKS2) were abundantly expressed in various biological functions in telomere regulation, Wnt/β-catenin signaling pathway, viral replication, endogenous hormone regulation, glucose transport, cherubism disease, erectile dysfunction, and apoptosis. The structural analysis, mechanistic information, in vitro and in vivo studies led identification and development of several classes of tankyrase inhibitors under clinical phases. In the nutshell, this review will drive future research on tankyrase as it enlighten the structural and functional features of TNKS 1 and TNKS 2, different classes of inhibitors with their structure-activity relationship studies, molecular modeling studies, as well as past, current and future perspective of the different class of tankyrase inhibitors.

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.

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

Medulloblastoma is one of the most prevalent brain tumors in children. Aberrant hedgehog (Hh) pathway signaling is thought to be involved in the initiation and development of medulloblastoma. Vismodegib, the first FDA-approved cancer therapy based on inhibition of aberrant hedgehog signaling, targets smoothened (Smo), a G-protein coupled receptor (GPCR) central to the Hh pathway. Although vismodegib exhibits promising therapeutic efficacy in tumor treatment, concerns have been raised from its nonlinear pharmacokinetic (PK) profiles at high doses partly due to low aqueous solubility. Many patients experience adverse events such as muscle spasms and weight loss. In addition, drug resistance often arises among tumor cells during treatment with vismodegib. There is clearly an urgent need to explore novel Smo antagonists with improved potency and efficacy. Through a scaffold hopping strategy, we have identified a series of novel tetrahydropyrido[4,3-d]pyrimidine derivatives, which exhibited effective inhibition of Hh signaling. Among them, compound 24 is three times more potent than vismodegib in the NIH3T3-GRE-Luc reporter gene assay. Compound 24 has a lower melting point and much greater solubility compared with vismodegib, resulting in linear PK profiles when dosed orally at 10, 30, and 100 mg/kg in rats. Furthermore, compound 24 showed excellent PK profiles with a 72% oral bioavailability in beagle dogs. Compound 24 demonstrated overall favorable in vitro safety profiles with respect to CYP isoform and hERG inhibition. Finally, compound 24 led to significant regression of subcutaneous tumor generated by primary Ptch1-deficient medulloblastoma cells in SCID mouse. In conclusion, tetrahydropyrido[4,3-d]pyrimidine derivatives represent a novel set of Smo inhibitors that could potentially be utilized to treat medulloblastoma and other Hh pathway related malignancies.