Development of Indoleamine 2,3-Dioxygenase 1 Inhibitors for Cancer Therapy and Beyond: A Recent Perspective.

Ortiz‐Meoz R.F., Wang L., Matico R., Rutkowska‐Klute A., De la Rosa M., Bedard S., Midgett R., Strohmer K., Thomson D., Zhang C., Mebrahtu M., Guss J., Totoritis R., Consler T., Campobasso N., et. al.

Indoleamine-2,3-dioxygenase 1 (IDO1) is a heme-containing enzyme that catalyzes the rate-limiting step in the kynurenine pathway of tryptophan (TRP) metabolism. As it is an inflammation-induced immunoregulatory enzyme, pharmacological inhibition of IDO1 activity is currently being pursued as a potential therapeutic tool for the treatment of cancer and other disease states. As such, a detailed understanding of the mechanism of action of IDO1 inhibitors with various mechanisms of inhibition is of great interest. Comparison of an apo-form-binding IDO1 inhibitor (GSK5628) to the heme-coordinating compound, epacadostat (Incyte), allows us to explore the details of the apo-binding inhibition of IDO1. Herein, we demonstrate that GSK5628 inhibits IDO1 by competing with heme for binding to a heme-free conformation of the enzyme (apo-IDO1), whereas epacadostat coordinates its binding with the iron atom of the IDO1 heme cofactor. Comparison of these two compounds in cellular systems reveals a long-lasting inhibitory effect of GSK5628, previously undescribed for other known IDO1 inhibitors. Detailed characterization of this apo-binding mechanism for IDO1 inhibition might help design superior inhibitors or could confer a unique competitive advantage over other IDO1 inhibitors vis-a-vis specificity and pharmacokinetic parameters.

Hu M., Zhou W., Wang Y., Yao D., Ye T., Yao Y., Chen B., Liu G., Yang X., Wang W., Xie Y.

Cancer immunotherapy is revolutionizing oncology and has emerged as a promising strategy for the treatment of multiple cancers. Indoleamine 2,3-dioxygenase 1 (IDO1), an immune checkpoint, plays an important role in tumor immune escape through the regulation of multiple immune cells and has been regarded as an attractive target for cancer immunotherapy. Proteolysis Targeting Chimeras (PROTAC) technology has emerged as a new model for drug research and development for its advantageous mechanism. Herein, we reported the application of PROTAC technology in targeted degradation of IDO1, leading to the discovery of the first IDO1 PROTAC degrader 2c, which induced significant and persistent degradation of IDO1 with maximum degradation (dmax) of 93% in HeLa cells. Western-blot based mechanistic studies indicated that IDO1 was degraded by 2c through the ubiquitin proteasome system (UPS). Label-free real-time cell analysis (RTCA) indicated that 2c moderately improved tumor-killing activity of chimeric antigen receptor-modified T (CAR-T) cells. Collectively, these data provide a new insight for the application of PROTAC technology in tumor immune-related proteins and a promising tool to study the function of IDO1.

Pu Q., Zhang H., Guo L., Cheng M., Doty A.C., Ferguson H., Fradera X., Lesburg C.A., McGowan M.A., Miller J.R., Geda P., Song X., Otte K., Sciammetta N., Solban N., et. al.

Indoleamine-2,3-dioxygenase 1 (IDO1) inhibition and its combination with immune checkpoint inhibitors like pembrolizumab have drawn considerable attention from both academia and the pharmaceutical industry. Here, we describe the discovery of a novel class of highly potent IDO1 heme-displacing inhibitors featuring a unique bicyclo[1.1.1]pentane motif. Compound 1, evolving from an ALIS (automated ligand identification system) hit, exhibited excellent potency but lacked the desired pharmacokinetic profile due to extensive amide hydrolysis of the benzamide moiety. Replacing the central phenyl ring in 1 with a bicyclo[1.1.1]pentane bioisostere effectively circumvented the amide hydrolysis issue, resulting in the discovery of compound 2 with a favorable overall profile such as excellent potency, selectivity, pharmacokinetics, and a low predicted human dose.

Kumar S., Jaipuri F.A., Waldo J.P., Potturi H., Marcinowicz A., Adams J., Van Allen C., Zhuang H., Vahanian N., Link C., Brincks E.L., Mautino M.R.

A series of different prodrugs of indoximod, including estesrs and peptide amides were synthesized with the aim of improving its oral bioavailability in humans. The pharmacokinetics of prodrugs that were stable in buffers, plasma and simulated gastric and intestinal fluids was first assessed in rats after oral dosing in solution or in capsule formulation. Two prodrugs that produced the highest exposure to indoximod in rats were further tested in Cynomolgus monkeys, a species in which indoximod has oral bioavailability of 6–10% and an equivalent dose-dependent exposure profile as humans. NLG802 was selected as the clinical development candidate after increasing oral bioavailability (>5-fold), C max (6.1–3.6 fold) and AUC (2.9–5.2 fold) in monkeys, compared to equivalent molar oral doses of indoximod. NLG802 is extensively absorbed and rapidly metabolized to indoximod in all species tested and shows a safe toxicological profile at the anticipated therapeutic doses. NLG802 markedly enhanced the anti-tumor responses of tumor-specific pmel-1 T cells in a melanoma tumor model. In conclusion, NLG802 is a prodrug of indoximod expected to increase clinical drug exposure to indoximod above the current achievable levels, thus increasing the possibility of therapeutic effects in a larger fraction of the target patient population. • Prodrugs of indoximod were investigated to increase oral bioavailability and maximum exposure. • NLG802 (Leu-1-methyl(D)Trp-COOEt) was selected as the clinical development candidate. • NLG802 produced >5-fold increase in bioavailability for indoximod in monkeys, increasing exposure above expected therapeutic level in humans.

Li Y., Zhang S., Wang R., Cui M., Liu W., Yang Q., Kuang C.

Indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase (TDO) are promising drug development targets due to their implications in pathologies such as cancer and neurodegenerative diseases. The search for IDO1 inhibitor has been intensely pursued but there is a paucity of potent TDO and IDO1/TDO dual inhibitors. Natural product tryptanthrin has been confirmed to bear IDO1 and/or TDO inhibitory activities. Herein, twelve novel tryptanthrin derivatives were synthesized and evaluated for the IDO1 and TDO inhibitory potency. All of the compounds were found to be IDO1/TDO dual inhibitors, in particular, compound 9a and 9b bore IDO1 inhibitory activity similar to that of INCB024360, and compound 5a and 9b had remarkable TDO inhibitory activity superior to that of the well-known TDO inhibitor LM10. This work enriches the collection of IDO1/TDO dual inhibitors and provides chemical molecules for potential development into drugs.

Mammoli A., Coletti A., Ballarotto M., Riccio A., Carotti A., Grohmann U., Camaioni E., Macchiarulo A.

A large number of crystallographic structures of IDO1 in different ligand-bound and -unbound states have been disclosed over the last decade. Yet, only a few of them have been exploited for structure-based drug design (SBDD) campaigns. In this study, we analyzed the structural motifs and molecular-recognition properties of three groups of IDO1 structures: 1) structures containing the heme group and inhibitors in the catalytic site; 2) heme-free structures of IDO1; 3) substrate-bound structures of IDO1. The results suggest that unrelated conformations of the enzyme have been solved with different ligand-induced changes of secondary motifs that localize even in regions remote from the catalytic site. Moreover, the study identified an uncharted region of molecular-recognition space covered by IDO1 binding sites that could guide the selection of diverse structures for additional SBDD studies aimed at the identification of novel lead compounds with differentiated chemical scaffolds.

Liu C., Nan Y., Xia Z., Gu K., Chen C., Dong X., Ju D., Zhao W.

Indoleamine 2,3-dioxygenase 1 (IDO1) is closely associated with immune escape in many tumor tissues, and is considered to be a valuable therapeutic target in cancer immunotherapy. In this study, the modification of amino sidechain was performed with the hydroxyamidine core kept intact to optimize lead compound Epacadostat. 19 new compounds with hydrazide, thietane or sulfonamide moiety as polar capping group in sidechain were prepared and their IDO1 inhibitory activities were evaluated. Sulfonamide 3a showed potent IDO1 inhibition in both enzymatic and cellular assays with the IC50 value of 71 nM and EC50 value of 11 nM, respectively. Furthermore, in vivo Lewis lung cancer (LLC) allograft studies of 3a indicated that it handicapped the tumor growth with similar efficacy to Epacadostat. Molecular docking demonstrated that the change of polar capping group affords influence on the orientation of amino ethylene side chain and forms new hydrogen bonding.

White C., McGowan M.A., Zhou H., Sciammetta N., Fradera X., Lim J., Joshi E.M., Andrews C., Nickbarg E.B., Cowley P., Trewick S., Augustin M., von Köenig K., Lesburg C.A., Otte K., et. al.

Indoleamine-2,3-dioxygenase-1 (IDO1) has emerged as a target of significant interest to the field of cancer immunotherapy, as the upregulation of IDO1 in certain cancers has been linked to host immune evasion and poor prognosis for patients. In particular, IDO1 inhibition is of interest as a combination therapy with immune checkpoint inhibition. Through an Automated Ligand Identification System (ALIS) screen, a diamide class of compounds was identified as a promising lead for the inhibition of IDO1. While hit 1 possessed attractive cell-based potency, it suffered from a significant right-shift in a whole blood assay, poor solubility, and poor pharmacokinetic properties. Through a physicochemical property-based approach, including a focus on lowering AlogP98 via the strategic introduction of polar substitution, compound 13 was identified bearing a pyridyl oxetane core. Compound 13 demonstrated improved whole blood potency and solubility, and an improved pharmacokinetic profile resulting in a low predicted human dose.

Van den Eynde B.J., van Baren N., Baurain J.

Indoleamine-2,3 dioxygenase 1 (IDO1) contributes to tumor immunosuppression by enzymatically degrading tryptophan, which is required for T cell activity, and producing kynurenine. Small-molecule inhibitors, such as epacadostat, have been developed to block IDO1 activity. In preclinical models, they can restore antitumoral T cell immunity and synergize with immune checkpoint inhibitors or cancer vaccines. Based on encouraging clinical results in early phase trials, a randomized phase III study (ECHO-301/KN-252) was launched in metastatic melanoma to test the benefit of adding epacadostat to the reference pembrolizumab therapy. The result was negative. We briefly review the clinical trials that investigated epacadostat in cancer patients and discuss possible explanations for this negative result. We end by suggesting paths to resume clinical development of compounds targeting the IDO1 pathway, which in our view remains an attractive target for cancer immunotherapy.

Serafini M., Torre E., Aprile S., Grosso E.D., Gesù A., Griglio A., Colombo G., Travelli C., Paiella S., Adamo A., Orecchini E., Coletti A., Pallotta M.T., Ugel S., Massarotti A., et. al.

In this study, a successful medicinal chemistry campaign that exploited virtual, biophysical, and biological investigations led to the identification of a novel class of IDO1 inhibitors based on a benzimidazole substructure. This family of compounds is endowed with an extensive bonding network in the protein active site, including the interaction with pocket C, a region not commonly exploited by previously reported IDO1 inhibitors. The tight packing of selected compounds within the enzyme contributes to the strong binding interaction with IDO1, to the inhibitory potency at the low nanomolar level in several tumoral settings, and to the selectivity toward IDO1 over TDO and CYPs. Notably, a significant reduction of L-Kyn levels in plasma, together with a potent effect on abrogating immunosuppressive properties of MDSC-like cells isolated from patients affected by pancreatic ductal adenocarcinoma, was observed, pointing to this class of molecules as a valuable template for boosting the antitumor immune system.

Huang Y., Ogbechi J., Clanchy F.I., Williams R.O., Stone T.W.

The importance of the kynurenine pathway in normal immune system function has led to an appreciation of its possible contribution to autoimmune disorders such as rheumatoid arthritis. Indoleamine-2,3-dioxygenase (IDO) activity exerts a protective function, limiting the severity of experimental arthritis, whereas deletion or inhibition exacerbates the symptoms. Other chronic disorder with an inflammatory component, such as atherosclerosis, are also suppressed by IDO activity. It is suggested that this overall anti-inflammatory activity is mediated by a change in the relative production or activity of Th17 and regulatory T cell populations. Kynurenines may play an anti-inflammatory role also in CNS disorders such as Huntington’s disease, Alzheimer's disease and multiple sclerosis, in which signs of inflammation and neurodegeneration are involved. The possibility is discussed that in Huntington’s disease kynurenines interact with other anti-inflammatory molecules such as Human Lymphocyte Antigen-G which may be relevant in other disorders. Kynurenine involvement may account for the protection afforded to animals with cerebral malaria and trypanosomiasis when they are treated with an inhibitor of kynurenine-3-monoxygenase (KMO). There is some evidence that changes in IL-10 may contribute to this protection and the relationship between kynurenines and IL-10 in arthritis and other inflammatory conditions should be explored. In addition, metabolites of kynurenine downstream of KMO, such as anthranilic acid and 3-hydroxy-anthranilic acid can influence inflammation, and the ratio of these compounds is a valuable biomarker of inflammatory status although the underlying molecular mechanisms of the changes require clarification. Hence it is essential that more effort be expended to identify their sites of action as potential targets for drug development. Finally, we discuss increasing awareness of the epigenetic regulation of IDO, for example by DNA methylation, a phenomenon which may explain differences between individuals in their susceptibility to arthritis and other inflammatory disorders.

Song X., Sun P., Wang J., Guo W., Wang Y., Meng L., Liu H.

Indoleamine 2,3-dioxygenase 1 (IDO1) is the enzyme catalyzing the oxidative metabolism of tryptophan, which accounts for cancer immunosuppression in tumor microenvironment. Several compounds targeting IDO1 have been reported and epacadostat shows strong inhibitory activity against IDO1, which is further studied in clinic trails. However, its pharmacokinetic profiles are not satisfactory. The half-life of epacadostat is 2.4 h in human and dosage is 50 mg BID in the phase III clinic trial. To overcome the shortcomings of epacadostat, structure-based drug design was performed to improve the pharmacokinetic profiles via changing the metabolic pathway of epacadostat and to enhance anti-tumor potency. A novel series of 1,2,5-oxadiazole-3-carboximidamide derivatives bearing cycle in the side chain were designed, synthesized, and biologically evaluated for their anti-tumor activity. Most of them exhibited potent activity against hIDO1 in enzymatic assays and in HEK293T cells over-expressing hIDO1. Among them, compound 23, 25 and 26 showed significant inhibitory activity against hIDO1 (IC50 = 108.7, 178.1 and 139.1 nM respectively) and in HEK293T cells expressing hIDO1 (cellular IC50 = 19.88, 68.59 and 57.76 nM respectively). Moreover, compound 25 displayed improved PK property with longer half-life (t1/2 = 3.81 h in CD-1 mice) and better oral bioavailability (F = 33.6%) compared with epacadostat. In addition, compound 25 showed similar potency to inhibit the growth of CT-26 syngeneic xenograft compared to epacadostat, making it justifiable for further investigation.

Hua S., Chen F., Wang X., Gou S.

A series of novel conjugates comprising tublin and IDO inhibitors were designed, synthesized and evaluated for their antiproliferative activity. Among them, HI5, composed of combretastatin A-4 (CA-4) and (D)-1-methyltryptophan (D-MT) by a linker, exhibited the most potent antitumor activity, in particular with higher IC50 value (0.07 μM) than CA-4 (0.21 μM) against HeLa cancer cell line. Mechanism studies indicated that HI5 can inhibit tubulin polymerization and cell migration, cause G2/M phase arrest, concurrent induce apoptosis via the mitochondrial dependent apoptosis pathway and cause reactive oxidative stress generation in HeLa cells. Furthermore, HI5 can inhibit IDO expression and decrease kynurenine production, leading to stimulating T cells activation and proliferation to enhance antitumor immunity in vitro. Interestingly, HI5 can effectively limit the tumor growth in the HeLa xenograft mice models without causing significant loss of body weight. Consequently, such a conjugation can be a potent and safe immunochemotherapeutic method for improving cancer therapy.

Kazmierski W.M., Xia B., Miller J., De la Rosa M., Favre D., Dunham R.M., Washio Y., Zhu Z., Wang F., Mebrahtu M., Deng H., Basilla J., Wang L., Evindar G., Fan L., et. al.

We report the discovery of a novel indoleamine 2,3-dioxygenase-1 (IDO1) inhibitor class through the affinity selection of a previously unreported indole-based DNA-encoded library (DEL). The DEL exemplar, spiro-chromane 1, had moderate IDO1 potency but high in vivo clearance. Series optimization quickly afforded a potent, low in vivo clearance lead 11. Although amorphous 11 was highly bio-available, crystalline 11 was poorly soluble and suffered disappointingly low bio-availability because of solubility-limited absorption. A prodrug approach was deployed and proved effective in discovering the highly bio-available phosphonooxymethyl 31, which rapidly converted to 11 in vivo. Obtaining crystalline 31 proved problematic, however; thus salt screening was performed in an attempt to circumvent this obstacle and successfully delivered greatly soluble and bio-available crystalline tris-salt 32. IDO1 inhibitor 32 is characterized by a low calculated human dose, best-in-class potential, and an unusual inhibition mode by binding the IDO1 heme-free (apo) form.

Mondanelli G., Coletti A., Greco F.A., Pallotta M.T., Orabona C., Iacono A., Belladonna M.L., Albini E., Panfili E., Fallarino F., Gargaro M., Manni G., Matino D., Carvalho A., Cunha C., et. al.

Significance Indoleamine 2,3-dioxygenase 1 (IDO1) is an immunoregulatory enzyme that transforms tryptophan into kynurenine, an endogenous agonist of the aryl hydrocarbon receptor (AhR) whose activation sustains IDO1 expression and activity over the long term in dendritic cells (DCs). Here we found that N -acetylserotonin (NAS), a tryptophan metabolite produced along the serotonin pathway, acts as a positive allosteric modulator (PAM) of IDO1 and thus increases kynurenine-mediated AhR activation in DCs. NAS effects on IDO1 translated into protection of mice from neuroinflammation and reinstallment of physiologic IDO1 activity in peripheral blood mononuclear cells from patients with relapsing-remitting multiple sclerosis.

Paranthaman P., Veerappapillai S.

Zhang A., Fan T., Liu Y., Yu G., Li C., Jiang Z.

Regulatory T cells (Tregs), an essential component of the human immune system, are a heterogeneous group of T lymphocytes with the ability to suppress immune responses and maintain immune homeostasis. Recent evidence indicates that Tregs may impair antitumor immunity and facilitate cancer progression by weakening functions of effector T cells (Teffs). Consequently, targeting Tregs to eliminate them from tumor microenvironments to improve Teffs’ activity could emerge as an effective strategy for cancer immunotherapy. This review outlines the biology of Tregs, detailing their origins, classification, and crucial markers. Our focus lies on the complex role of Tregs in cancer’s development, progression and treatment, particularly on their suppressive role upon antitumor responses via multiple mechanisms. We delve into Tregs’ involvement in immune checkpoint blockade (ICB) therapy, their dual effect on cancer immunotherapy and their potential biomarkers for ICB therapy effectiveness. We also summarize advances in the therapies that adjust Tregs to optimize ICB therapy, which may be crucial for devising innovative cancer treatment strategies.

Meenakshy C. ., Sruthi S., Jayasree E. ., Sandhya K., Deepthi A.

ABSTRACTSynthesis of 18 tryptanthrin‐triazole hybrid molecules by employing Cu(I)‐catalyzed azide‐alkyne [3 + 2] cycloaddition (CuAAC) between tryptanthrin oxime O‐propargyl ether and aromatic azides is described here. The exclusive formation of E‐triazoles was confirmed by theoretical studies using the M06‐2x/6–311++G(d,p) level. From the synthesized triazoles, four of them have been selected and were subjected to in vitro anticancer activity studies against selected cell lines. Furthermore, in silico studies have been conducted for the most active compound, 5h, and it suggested that various noncovalent interactions and one conventional hydrogen bond enhance the stability of the complex (binding affinity = −11.29 kcal/mol). ADMET (Absorption, Distribution, Metabolism, Excretion and Toxicity) studies also prove the increased biological potency of 5h.

Jiang K., Wang Q., Chen X., Wang X., Gu X., Feng S., Wu J., Shang H., Ba X., Zhang Y., Tang K.

Ozgencil F., Beyza Gunindi H., Eren G.

In mammals, nicotinamide phosphoribosyltransferase (NAMPT) is a crucial enzyme in the nicotinamide adenine dinucleotide (NAD+) synthesis pathway catalyzing the condensation of nicotinamide (NAM) with 5-phosphoribosyl-1-pyrophosphate (PRPP) to produce nicotinamide mononucleotide (NMN). Given the pivotal role of NAD+ in a range of cellular functions, including DNA synthesis, redox reactions, cytokine generation, metabolism, and aging, NAMPT has become a promising target for many diseases, notably cancer. Therefore, various NAMPT inhibitors have been reported and classified as first and second-generation based on their chemical structures and design strategies, dual-targeted being one. However, most NAMPT inhibitors suffer from several limitations, such as dose-dependent toxicity and poor pharmacokinetic properties. Consequently, there is no clinically approved NAMPT inhibitor. Hence, research on discovering more effective and less toxic dual-targeted NAMPT inhibitors with desirable pharmacokinetic properties has drawn attention recently. This review summarizes the previously reported dual-targeted NAMPT inhibitors, focusing on their design strategies and advantages over the single-targeted therapies.

Devadoss T., Rajendra Y.K., Rajesh R.B., Sambhaji B.C.

Indoleamine-2,3-dioxygenase (IDO) is an enzyme that catalyzes the conversion of tryptophan to N-formylkynurenine, and it is the rate-limiting step in the kynurenine pathway. The increased IDO activity is well correlated with many diseases and disorders. Hence, inhibition of IDO will suppress the proliferation of cancer cells and exhibit beneficial effects on cancer patients. This book chapter focuses on the structure of IDO’s active site, the pharmacophore of IDO inhibitors, the most widely studied IDO inhibitors, and the discovery of new IDO inhibitors for treating lung cancer. The second part of this chapter discusses the inhibitors of transforming growth factor-β (TGF-β) receptor I. TGF-β is a group of polypeptide molecules acting like hormones or like local mediators. They are present in both vertebrates and invertebrates. Dysregulation of the TGF-β pathway leads to the development of several diseases and disorders. It includes immune dysfunction, fibrosis, cerebrovascular diseases, and cancer. Inhibiting the TGF-β signaling pathway leads to beneficial effects in cancer. This section focuses on different targets of TGF-β signaling pathways, the most widely studied TGF-β receptor I inhibitors from the synthetic and natural origin, the structure of TGF-β receptor I and pharmacophoric elements of TGF-β receptor I inhibitors, and the discovery of new TGF-β receptor I inhibitors for the treatment of lung cancer.

de Sena Murteira Pinheiro P., Franco L.S., Montagnoli T.L., Fraga C.A.

Chen Y., Lu Z., He W., Zhu H., Lu W., Shi J., Sheng J., Xie W.

The step-economical synthesis of C2, C3-unsubstituted 1-aminoindole derivatives through rhodium-catalyzed annulation of hydrazines with vinylene carbonate.

Zhang J., Liu J., Kong K., Li X., Zhang Q.

Indoleamine 2,3-dioxygenase 1 (IDO1) is the key enzyme that catalyzes the conversion of l-tryptophan (Trp) to N-formyl-kynurenine in the tryptophan-kynurenine (Trp-Kyn) pathway. Overexpression of IDO1 contributes to the depletion of Trp and the accumulation of Kyn, which can result in tumor immune escape. Inhibition of IDO1 can restore the host immune response to eradicate cancer cells. 5-(Pyridin-3-yl)-1H-indole-4,7-dione was developed as the scaffold for a type of IDO1 inhibitors from simplification of the structure of exiguamine A in our previous work. In the present study, we designed and synthesized a series of compounds with different side-chain substituents, and linkers of varying lengths, at the 3-position, to design compounds with an aryl motif that can occupy pocket B of the IDO1 protein. Most compounds exhibited potent IDO1 inhibitory activity with IC50 values at the micromolar level, and 3-(2-((4-fluorobenzyl)amino)ethyl)-5-(3-pyridyl)-1H-indole-4,7-dione (1d) displayed the most potent inhibition with a half-maximal inhibitory concentration (IC50) value of 0.125 μM in an enzymatic assay and a half-maximal effective concentration (EC50) value of 0.821 μM in a cellular assay. Compound 1d showed higher selectivity for IDO1 over indoleamine 2,3-dioxygenase 2 and tryptophan 2,3-dioxygenase at the effective concentration. Molecular docking studies and molecular dynamic simulations suggested that the phenyl ring of these inhibitors can enter into pocket B of IDO1 and interact with the residue Phe 226 through hydrophobic interactions.

Cherney E.C., Williams D.K., Zhang L., Nara S.J.

Huang G., Wang N., Zhang L., Yu J., Chang K., Fan M., Liu Z., Ma L., Cao J.

AbstractAlepterolic acid is a diterpene occurring in the fern Aleuritopteris argentea with potential biological activity that warrants further structural modification. In the present work, sixteen alepterolic acid derivatives were synthesized and evaluated for their anticancer activities. Among them, N‐[m‐(trifluoromethoxy)phenyl] alepterolamide displayed comparable activity (IC50=4.20±0.21 μM) in MCF‐7 cells. Moreover, mechanistic investigations indicated this compound was significantly capable of diminishing cell proliferation and viability of MCF‐7 cells. After treatment with N‐[m‐(trifluoromethoxy)phenyl] alepterolamide, a significant increase in cleaved caspase‐9, cleaved caspase‐3, cleaved poly (ADP‐ribose) polymerase (PARP) and Bax/Bcl2 ratio were observed in MCF‐7 cells, leading to caspase‐dependent apoptotic pathways. Further studies showed this compound promoted cellular apoptosis and inhibited migration in MCF‐7 cells via modulation of the Akt/p70S6K signaling pathway. All these results revealed the potential of N‐[m‐(trifluoromethoxy)phenyl] alepterolamide as an appealing therapeutic drug candidate for breast cancer.

Huang R., Liang Q., Jing X., Wang K., Zhang H., Wang H., Ma X., Wei J., Zhang Y.

Indoleamine-2,3-dioxygenase 1 (IDO1) and signal transducer and activator of transcription 3 (STAT3) have emerged as significant targets in the tumor microenvironment for cancer therapy. In this study, we synthesized three novel 2-amino-1,4-naphthoquinone amide-oxime derivatives and identified them as dual inhibitors of IDO1 and STAT3. The representative compound NK3 demonstrated effective binding to IDO1 and exhibited good inhibitory activity (hIDO1 IC50 = 0.06 μM), leading to its selection for further investigation. The direct interactions between compound NK3 and IDO1 and STAT3 proteins were confirmed through surface plasmon resonance analysis. A molecular docking study of compound NK3 revealed key interactions between NK3 and IDO1, with the naphthoquinone-oxime moiety coordinating with the heme iron. In the in vitro anticancer assay, compound NK3 displayed potent antitumor activity against selected cancer cell lines and effectively suppressed nuclear translocation of STAT3. Moreover, in vivo assays conducted on CT26 tumor-bearing Balb/c mice and an athymic HepG2 xenograft model revealed that compound NK3 exhibited potent antitumor activity with low toxicity relative to 1-methyl-L-tryptophan (1-MT) and doxorubicin (DOX). Overall, these findings provided evidence that the dual inhibitors of IDO1 and STAT3 may offer a promising avenue for the development of highly effective drug candidates for cancer therapy.

Huang J., Chen J.

Imidazoles and (benz)imidazoles are molecular scaffolds frequently found in a variety of pharmaceutical and therapeutic agents. They exhibit distinctive features and can be identified as bioisosteres of amide bonds and indoles with additional sites for receptor interaction. This work provides an overview of advances in (benz)imidazole-based compounds in medicinal chemistry as anticancer, antibacterial, antitubercular, antifungal, antiparasitic, antiviral, antiinflammatory, anti-Alzheimer, antihypertensive, and other medicinal agents. The structure–activity relationships of (benz)imidazole-based compounds and their optimization processes are summarized.

Yang X., Xu L., Yang L., Xu S.

Signal transducer and activator of transcription 3 (STAT3), a transcription factor, regulates gene levels that are associated with cell survival, cell cycle, and immune reaction. It is correlated with the grade of malignancy and the development of various cancers and targeting STAT3 protein is a potentially promising therapeutic strategy for tumors. Over the past 20 years, various compounds have been found to directly inhibit STAT3 activity via different strategies. However, numerous difficulties exist in the development of STAT3 inhibitors, such as serious toxic effects, poor therapeutic effects, and intrinsic and acquired drug resistance. STAT3 inhibitors synergistically suppress cancer development with additional anti-tumor drugs, such as indoleamine 2,3-dioxygenase 1 inhibitors (IDO1i), histone deacetylase inhibitors (HDACi), DNA inhibitors, pro-tumorigenic cytokine inhibitors (PTCi), NF-κB inhibitors, and tubulin inhibitors. Therefore, individual molecule- based dual-target inhibitors can be the candidate alternative or complementary treatment to overcome the disadvantages of just STAT3 or other targets as a monotherapy. In this review, we discuss the theoretical basis for formulating STAT3-based dual-target inhibitors and also summarize their structure–activity relationships (SARs).

Haji N., Faizi M., Koutentis P.A., Carty M.P., Aldabbagh F.

This review uses the National Cancer Institute (NCI) COMPARE program to establish an extensive list of heterocyclic iminoquinones and quinones with similarities in differential growth inhibition patterns across the 60-cell line panel of the NCI Developmental Therapeutics Program (DTP). Many natural products and synthetic analogues are revealed as potential NAD(P)H:quinone oxidoreductase 1 (NQO1) substrates, through correlations to dipyridoimidazo[5,4-f]benzimidazoleiminoquinone (DPIQ), and as potential thioredoxin reductase (TrxR) inhibitors, through correlations to benzo[1,2,4]triazin-7-ones and pleurotin. The strong correlation to NQO1 infers the enzyme has a major influence on the amount of the active compound with benzo[e]perimidines, phenoxazinones, benz[f]pyrido[1,2-a]indole-6,11-quinones, seriniquinones, kalasinamide, indolequinones, and furano[2,3-b]naphthoquinones, hypothesised as prodrugs. Compounds with very strong correlations to known TrxR inhibitors had inverse correlations to the expression of both reductase enzymes, NQO1 and TrxR, including naphtho[2,3-b][1,4]oxazepane-6,11-diones, benzo[a]carbazole-1,4-diones, pyranonaphthoquinones (including kalafungin, nanaomycin A, and analogues of griseusin A), and discorhabdin C. Quinoline-5,8-dione scaffolds based on streptonigrin and lavendamycin can correlate to either reductase. Inhibitors of TrxR are not necessarily (imino)quinones, e.g., parthenolides, while oxidising moieties are essential for correlations to NQO1, as with the mitosenes. Herein, an overview of synthetic methods and biological activity of each family of heterocyclic imino(quinone) is provided.