Design, synthesis and activity of novel 2,6-disubstituted purine derivatives, potential small molecule inhibitors of signal transducer and activator of transcription 3

Journey of PROTAC: From Bench to Clinical Trial and Beyond

Proteolysis-targeting chimeras (PROTACs) represent a transformative advancement in drug discovery, offering a method to degrade specific intracellular proteins. Unlike traditional inhibitors, PROTACs are bifunctional molecules that target proteins for elimination, enabling the potential treatment of previously "undruggable" proteins. This concept, pioneered by Crews and his team, introduced the use of small molecules to link a target protein to an E3 ubiquitin ligase, inducing ubiquitination and subsequent degradation of the target protein. By promoting protein degradation rather than merely inhibiting function, PROTACs present a novel therapeutic strategy with enhanced specificity and effectiveness, especially in areas such as cancer and neurodegenerative diseases. Since their initial discovery, the field of PROTAC research has rapidly expanded with numerous PROTACs now designed to target a wide range of disease-relevant proteins. The substantial research, investment, and collaboration across academia and the pharmaceutical industry reflect the growing interest in PROTACs. This Review discusses the journey of PROTACs from initial discovery to clinical trials, highlighting advancements and challenges. Additionally, recent developments in fluorescent and photogenic PROTACs, used for real-time tracking of protein degradation, are presented, showcasing the evolving potential of PROTACs in targeted therapy.

Anticancer potential and structure activity studies of purine and pyrimidine derivatives: an updated review

Cancer is the world's leading cause of death impacting millions of lives globally. The increasing research over the past several decades has focused on the development of new anticancer drugs, but still cancer continues to be a global health challenge. Thus, several new alternative therapeutic strategies have been tried for the drug design and discovery. Purine and pyrimidine heterocyclic compounds have received attention recently due to their potential in targeting various cancers. It is evident from the recently published data over the last decade that incorporation of the purine and pyrimidine rings in the synthesized derivatives resulted in the development of potent anticancer molecules. This review presents synthetic strategies encompassing several examples of recently developed purine and pyrimidine-containing compounds as anticancer agents. In addition, their structure-activity relationships are represented in the schemes indicating the fragment or groups that are essential for the enhanced anticancer activities. Purine and pyrimidines combined with other heterocyclic compounds have resulted in many novel anticancer molecules that address the challenges of drug resistance. The purine and pyrimidine derivatives showed significantly enhanced anticancer activities against targeted receptor proteins with numerous compounds with an IC50 value in the nanomolar range. The review will support medicinal chemists and contribute in progression and development of synthesis of more potent chemotherapeutic drug candidates to mitigate the burden of this dreadful disease.

Discovery of benzochalcone derivative as a potential antigastric cancer agent targeting signal transducer and activator of transcription 3 (STAT3)

Gastric cancer remains a significant health burden worldwide. In continuation of our previous study and development of effective small molecules against gastric cancer, a series of benzochalcone analogues involving heterocyclic molecules were synthesised and biologically evaluated in vitro and in vivo. Among them, the quinolin-6-yl substituted derivative KL-6 inhibited the growth of gastric cancer cells (HGC27, MKN28, AZ521, AGS, and MKN1) with a submicromolar to micromolar range of IC₅₀, being the most potent one in this series. Additionally, KL-6 significantly inhibited the colony formation, migration and invasion, and effectively induced apoptosis of MKN1 cells in a concentration-dependent manner. The mechanistic study revealed that KL-6 could concentration-dependently suppress STAT3 phosphorylation, which may partly contribute to its anticancer activity. Furthermore, in vivo antitumour study on the MKN1 orthotopic tumour model showed that KL-6 effectively inhibited tumour growth (TGI of 78%) and metastasis without obvious toxicity. Collectively, compound KL-6 may support the further development of candidates for gastric cancer treatment.

TNP Analogues Inhibit the Virulence Promoting IP3-4 Kinase Arg1 in the Fungal Pathogen Cryptococcus neoformans

New antifungals with unique modes of action are urgently needed to treat the increasing global burden of invasive fungal infections. The fungal inositol polyphosphate kinase (IPK) pathway, comprised of IPKs that convert IP₃ to IP₈, provides a promising new target due to its impact on multiple, critical cellular functions and, unlike in mammalian cells, its lack of redundancy. Nearly all IPKs in the fungal pathway are essential for virulence, with IP_3-4 kinase (IP_3-4K) the most critical. The dibenzylaminopurine compound, N2-(m-trifluorobenzylamino)-N6-(p-nitrobenzylamino)purine (TNP), is a commercially available inhibitor of mammalian IPKs. The ability of TNP to be adapted as an inhibitor of fungal IP_3-4K has not been investigated. We purified IP_3-4K from the human pathogens, Cryptococcus neoformans and Candida albicans, and optimised enzyme and surface plasmon resonance (SPR) assays to determine the half inhibitory concentration (IC₅₀) and binding affinity (K_D), respectively, of TNP and 38 analogues. A novel chemical route was developed to efficiently prepare TNP analogues. TNP and its analogues demonstrated inhibition of recombinant IP_3-4K from C. neoformans (CnArg1) at low µM IC₅₀s, but not IP_3-4K from C. albicans (CaIpk2) and many analogues exhibited selectivity for CnArg1 over the human equivalent, HsIPMK. Our results provide a foundation for improving potency and selectivity of the TNP series for fungal IP_3-4K.

Recent development of imidazole derivatives as potential anticancer agents

Cancer, one of the key health problems globally, is a group of related diseases that share a number of characteristics primarily the uncontrolled growth and invasive to surrounding tissues. Chemotherapy is one of the ways for the treatment of cancer which uses one or more anticancer agents as per chemotherapy regimen. Limitations of most anticancer drugs due to a variety of reasons such as serious side effects, drug resistance, lack of sensitivity and efficacy etc. generate the necessity towards the designing of novel anticancer lead molecules. In this regard, the synthesis of biologically active heterocyclic molecules is an appealing research area. Among heterocyclic compounds, nitrogen containing heterocyclic molecules has fascinated tremendous consideration due to broad range of pharmaceutical activity. Imidazoles, extensively present in natural products as well as synthetic molecules, have two nitrogen atoms, and are five membered heterocyclic rings. Because of their countless physiological and pharmacological characteristics, medicinal chemists are enthused to design and synthesize new imidazole derivatives with improved pharmacodynamic and pharmacokinetic properties. The aim of this present chapter is to discuss the synthesis, chemistry, pharmacological activity, and scope of imidazole-based molecules in anticancer drug development. Finally, we have discussed the current challenges and future perspectives of imidazole-based derivatives in anticancer drug development.

Design and synthesis of epigallocatechin (EGC) analogs selective to inhibit α-amylase over α-glucosidases via the incorporation of caffeine acid and its derivatives

Natural products are a promising and underappreciated reservoir for the preferred chemical scaffolds in the search of antidiabetic drugs. In this study twenty-one EGC-based derivatives selective to inhibit human pancreatic α-amylase (HPA), the enzyme at the top of the starch digestion pyramid, have been designed and synthesized in terms of the lead myricetin-caffeic acid conjugate 1 reported ever. We focus on methylation of caffeic acid, length of a liker, a double bond contained in the linker on the inhibition activity and selectivity of EGC-based conjugates. As a result, methylation of caffeic acid and the length of a linker affect significantly the activity and selectivity of EGC-based conjugates, but the effect of a double in caffeic acid is limited. Conjugate 2a-1 having a six-carbon-atom linker fused to EGC and caffeic acid demonstrates the most ponent inhibitory activity to HPA and its selectivity towards HPA over α-glucosidase by far superior to that construct 1. Molecular docking studies reveal that conjugate 2a-1 accommodates well to the active site of HPA with four hydrogen bonds in the form of the preorganization of two moieties EGC and caffeic acid via π-stacking interaction. Collectively, conjugating caffeic acid and EGC with an appropriate linker possibly provides a new strategy for finding the specific HPA inhibitors in the discovery of anti-diabetes mellitus drugs.

Novel 1,3,4-thiadiazole/oxadiazole-linked honokiol derivatives suppress cancer via inducing PI3K/Akt/mTOR-dependent autophagy

Honokiol is a bioactive biphenolic component derived from Magnoliae officinalis Cortex (known as "Hou Po" in Chinese), a traditional Chinese herbal medicine. A series of novel 1,3,4-thiadiazole/oxadiazole-linked honokiol derivatives were synthesized and tested for anticancer activity against seven human cancer cell lines in this study. Among all derivatives, 8a had the most potent cytotoxic effect on all tested cancer cells, with IC₅₀ values ranging from 1.62 ± 0.19 to 4.61 ± 0.51 µM, which were 10.38-34.36 folds more potent than the parental honokiol (IC₅₀ values of 30.96 ± 1.81-55.67 ± 0.31 µM). On A549, HCT116, and MDA-MB-231 cell lines, 8a demonstrated 5.69-fold, 5.65-fold, and 4.83-fold greater cytotoxicity than cisplatin, respectively. Compound 8a also had higher selectivity (SI values of 8.41-49.38) towards seven cancer cell lines over the normal cell lines than cisplatin (SI values of 1.24-2.52). The analysis of structure-activity relationships (SARs) revealed that honokiol derivatives bearing 1,3,4-thiadiazoles (8a-j) possessed stronger anticancer activity than those containing 1,3,4-oxadiazoles. Further mechanistic investigation indicated that 8a induced cytotoxic autophagy in cancer cells in a time- and dose-independent manner via suppressing the PI3K/Akt/mTOR pathway. Molecular docking suggested that 8a could bind to the PI3Kα active sites. Additionally, 8a inhibited the migration and invasion of A549 and MDA-MB-231 cancer cells.

Natural STAT3 inhibitors: A mini perspective

Signal transducer and activator of transcription 3 (STAT3) plays pivotal role in several cellular processes such as cell proliferation and survival and has been found to be aberrantly activated in many cancers. STAT3 is largely believed to be one of the key oncogenes and crucial therapeutic targets. Much research has suggested the leading mechanisms for regulating the STAT3 pathway and its role in promoting tumorigenesis. Therefore, intensive efforts have been devoted to develop potent STAT3 inhibitors and several of them are currently undergoing clinical trials. Nevertheless, many natural products were identified as STAT3 inhibitors but attract less attention compared to the small molecule counterpart. In this review, the development of natural STAT3 inhibitors with an emphasis on their biological profile and chemical synthesis are detailed. The current state of STAT3 inhibitors and the future directions and opportunities for STAT3 inhibitor are discussed.

Imidazoles as Potential Anticancer Agents: An Update on Recent Studies

Nitrogen-containing heterocyclic rings are common structural components of marketed drugs. Among these heterocycles, imidazole/fused imidazole rings are present in a wide range of bioactive compounds. The unique properties of such structures, including high polarity and the ability to participate in hydrogen bonding and coordination chemistry, allow them to interact with a wide range of biomolecules, and imidazole-/fused imidazole-containing compounds are reported to have a broad spectrum of biological activities. This review summarizes recent reports of imidazole/fused imidazole derivatives as anticancer agents appearing in the peer-reviewed literature from 2018 through 2020. Such molecules have been shown to modulate various targets, including microtubules, tyrosine and serine-threonine kinases, histone deacetylases, p53-Murine Double Minute 2 (MDM2) protein, poly (ADP-ribose) polymerase (PARP), G-quadraplexes, and other targets. Imidazole-containing compounds that display anticancer activity by unknown/undefined mechanisms are also described, as well as key features of structure-activity relationships. This review is intended to provide an overview of recent advances in imidazole-based anticancer drug discovery and development, as well as inspire the design and synthesis of new anticancer molecules.

Recent Update on Development of Small-Molecule STAT3 Inhibitors for Cancer Therapy: From Phosphorylation Inhibition to Protein Degradation

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that regulates various biological processes, including proliferation, metastasis, angiogenesis, immune response, and chemoresistance. In normal cells, STAT3 is tightly regulated to maintain a transiently active state, while persistent STAT3 activation occurs frequently in cancers, associating with a poor prognosis and tumor progression. Targeting the STAT3 protein is a potentially promising therapeutic strategy for tumors. Although none of the STAT3 inhibitors has been marketed yet, a few of them have succeeded in entering clinical trials. This Review aims to systematically summarize the progress of the last 5 years in the discovery of directive STAT3 small-molecule inhibitors and degraders, focusing primarily on their structural features, design strategies, and bioactivities. We hope this Review will shed light on future drug design and inhibitor optimization to accelerate the discovery process of STAT3 inhibitors or degraders.

PROTAC: An Effective Targeted Protein Degradation Strategy for Cancer Therapy

Proteolysis targeting chimeric (PROTAC) technology is an effective endogenous protein degradation tool developed in recent years that can ubiquitinate the target proteins through the ubiquitin-proteasome system (UPS) to achieve an effect on tumor growth. A number of literature studies on PROTAC technology have proved an insight into the feasibility of PROTAC technology to degrade target proteins. Additionally, the first oral PROTACs (ARV-110 and ARV-471) have shown encouraging results in clinical trials for prostate and breast cancer treatment, which inspires a greater enthusiasm for PROTAC research. Here we focus on the structures and mechanisms of PROTACs and describe several classes of effective PROTAC degraders based on E3 ligases.

Adenine-based small molecule fluorescent probe for imaging mitochondrial nucleic acid

A small molecule fluorescent probe (probe 1) based on adenine-coumarin derivative was designed and synthesized in this paper. Probe 1 exhibited a significant fluorescence-enhancing response to nucleic acids at 495 nm (for DNA) and 487 nm (for RNA). The fluorescence enhancement of probe 1 for DNA and RNA was 5.68 and 9.73 times respectively, the fluorescence quantum yield was changed from 2.5% to 11.7% and 22.5% accordingly. Meanwhile, an excellent linear relationship of fluorescence intensity at 495 nm or 487 nm versus the nucleic acid concentration (1 μM for probe 1, 0-350 μg/mL for DNA and 0-300 μg/mL for RNA) was obtained. Co-staining and nucleic acid digestion experiments showed that probe 1 could selectively image nucleic acids in mitochondria and nucleoli in HeLa cells.

Triazolopyrimidinium salts: discovery of a new class of agents for cancer therapy

Aim: The [1,2,4]triazolo[1,5-a]pyrimidine core is highly privileged in medicinal chemistry due to its versatile pharmacological activity profile. Recently, the search for novel anticancer agents has focused on [1,2,4]triazolo[1,5-a]pyrimidine derivatives. Results: Our hit functionalization has led to the discovery of new [1,2,4]triazolo[1,5-a]pyrimidinium salts with potential anticancer activity. Among a small library of molecules, compound 9 significantly inhibits cancer cell growth in a panel of in vitro models. Molecular docking studies and preliminary binding assay have displayed that 9 could directly bind the Src homology 2 (SH2) domain of STAT3 protein. Conclusion: Compound 9 is a novel promising lead compound that motivates additional evaluation of [1,2,4]triazolo[1,5-a]pyrimidinium salts as novel potential chemotherapeutics.