Indole Compounds in Oncology: Therapeutic Potential and Mechanistic Insights.

Cancer remains a formidable global health challenge, with current treatment modalities such as chemotherapy, radiotherapy, surgery, and targeted therapy often hindered by low efficacy and adverse side effects. The indole scaffold, a prominent heterocyclic structure, has emerged as a promising candidate in the fight against cancer. This review consolidates recent advancements in developing natural and synthetic indolyl analogs, highlighting their antiproliferative activities against various cancer types over the past five years. These analogs are categorized based on their efficacy against common cancer types, supported by biochemical assays demonstrating their antiproliferative properties. In this review, emphasis is placed on elucidating the mechanisms of action of these compounds. Given the limitations of conventional cancer therapies, developing targeted therapeutics with enhanced selectivity and reduced side effects remains a critical focus in oncological research.

Iridium-catalyzed diacylmethylation of tyrosine and its peptides with sulfoxonium ylides.

Pyridyloxy-directed Ir(III)-catalyzed diacylmethylation of protected tyrosines was achieved with alkyl and (hetero)aryl sulfoxonium ylides, furnishing tyrosine-based unnatural amino acids in good yields. Furthermore, the late stage exemplification of the strategy was successfully accomplished in tyrosine-containing dipeptides, tripeptides and tetrapeptides in moderate yields. This methodology is distinguished by its site-selectivity, tolerance of sensitive functional groups, scalability, and retention of the chiral configuration for tyrosine motifs.

Ursolic Acid Conjugates: A New Frontier in Anticancer Drug Development.

New Ursolic Acid (UA) conjugates were synthesized using optimized synthetic protocols through the molecular hybridization approach at C-3 and C-28. This resulted in the targeted molecules being produced in good yields. Some of the synthesized conjugates showed significantly relevant bioactivity against mammalian cells and in animal models of cancers. Selected UA conjugates were tested against bladder and breast cancer cell lines. The conjugates showed moderate to significantly enhanced antiproliferative activities against Triple Negative Breast Cancer (TNBC; MDA-MB 231), which is an aggressive tumor making up about 10-15% of all breast cancers and bladder (T24 and 5637) cancer cell lines. These properties were superior to the parent UA. Among all the synthesized compounds, 18c and 18d have exhibited promising antiproliferative and cytotoxic properties against all tested cancer cell lines. However, 18d has proved to be exceptionally selective for cancer cell lines, showing more cytotoxicity towards them than normal epithelial cells (MCF-12A). Compound 18d has demonstrated cytotoxicity against tumor cells, including those intrinsically resistant to chemotherapy drugs such as 2-difluoro-deoxy cytidine (Gemcitabine). The activity of the UA conjugates on tumor cells was mediated by multiple cytotoxic mechanisms, including drug-induced cytotoxic autophagy and programmed cell death, indicating a novel possibility of combination therapy.

Targeting Chemoresistance in Advanced Bladder Cancers with a Novel Adjuvant Strategy.

Advanced urinary bladder cancer is characterized by rapid progression and development of therapy resistance. About 30% of the patients are diagnosed with high-grade tumors (grade > T2a). A typical nonsurgical treatment is systemic chemotherapy using cisplatin (C) and gemcitabine (G). However, treatment failure and subsequent disease progression are common in treated patients, and adjuvant therapies are not significantly effective. The therapeutic potential of a molecular hybrid of ursolic acid (UA), a pentacyclic-triterpene conjugated to N-methyl piperazine (UA4), was tested on both naïve (WT) and gemcitabine-resistant (GemR) variants of two human invasive bladder cancer cell lines, 5637 and T24. UA4 killed 5637 (4 µmol/L), T24 (4 µmol/L) WT, and GemR cells in vitro at equal potency. Pretreatment with UA4 followed by G synergistically killed WT and GemR cells by >50% compared with G followed by UA4. Oral gavage of UA4 (100 mg/kg) inhibited WT and GemR tumor growth in athymic mice. UA4 + G was more effective against GemR tumors than either drug alone. Studies revealed cytotoxic autophagy as a mechanism of UA4 cytotoxicity. UA4 induced moderate apoptosis in T24 but not in 5637 cells. Mitochondrial integrity and function were most affected by UA4 because of high levels of reactive oxygen species, disruption of mitochondrial membrane, and cell cycle arrest. These effects were enhanced in the UA4 + G combination. UA4 was well-tolerated in mice, and oral gavage led to a serum level >1 µmol/L with no systemic toxicity. These results show the potential of UA4 as a nontoxic alternative treatment for high-grade bladder cancer.

Targeting Chemoresistance in Advanced Bladder Cancers with a Novel Adjuvant Strategy.

Advanced urinary bladder cancer (BC) is characterized by rapid progression and development of therapy resistance. About 30% of the patients are diagnosed with high-grade tumors (Grade >T2a). A typical non-surgical treatment is systemic chemotherapy using Cisplatin (C) and Gemcitabine (G). However, treatment failure and subsequent disease progression are common in treated patients, and adjuvant therapies are not significantly effective. The therapeutic potential of a molecular hybrid of Ursolic Acid (UA), a pentacyclic-triterpene conjugated to N-methyl piperazine (UA4), was tested on both naïve (WT) and Gemcitabine-resistant (GemR) variants of two human invasive BC cell lines, 5637 and T24. UA4 killed 5637 (4µM), T24 (4µM) WT, and GemR cells invitro at equal potency. Pretreatment with UA4 followed by G synergistically killed WT and GemR cells by >50% compared to G followed by UA4. Oral gavage of UA4 (100 mg/kg) inhibited WT and GemR tumor growth in athymic mice. UA4 + G was more effective against GemR tumors than either drug alone. Studies revealed cytotoxic autophagy as a mechanism of UA4 cytotoxicity. UA4 induced moderate apoptosis in T24 but not in 5637 cells. Mitochondrial integrity and function were most affected by UA4 due to high levels of reactive oxygen species (ROS), disruption of mitochondrial membrane, and cell cycle arrest. These effects were enhanced in the UA4+G combination. UA4 was well-tolerated in mice, and oral gavage led to a serum level >1µM with no systemic toxicity. These results show the potential of UA4 as a non-toxic alternative treatment for high-grade BC.

Molecular Hybridization of Alkaloids Using 1,2,3-Triazole-Based Click Chemistry.

Alkaloids found in multiple species, known as 'driver species', are more likely to be included in early-stage drug development due to their high biodiversity compared to rare alkaloids. Many synthetic approaches have been employed to hybridize the natural alkaloids in drug development. Click chemistry is a highly efficient and versatile reaction targeting specific areas, making it a valuable tool for creating complex natural products and diverse molecular structures. It has been used to create hybrid alkaloids that address their limitations and serve as potential drugs that mimic natural products. In this review, we highlight the recent advancements made in modifying alkaloids using click chemistry and their potential medicinal applications. We discuss the significance, current trends, and prospects of click chemistry in natural product-based medicine. Furthermore, we have employed computational methods to evaluate the ADMET properties and drug-like qualities of hybrid molecules.

Rhodium-Catalyzed Regioselective C3Ar Functionalization of Tyrosines with Maleimides and Its Late-Stage Peptide Exemplification.

Pyridyloxy-directed Rh(III)-catalyzed regioselective C3Ar-H alkenylation of protected tyrosines was achieved with N-aryl and N-alkyl maleimides, furnishing a series of maleimide-appended tyrosine-based unnatural amino acids in good yields. Further, the late-stage exemplification of the strategy was successfully accomplished on tyrosine-containing dipeptides, tripeptides, and tetrapeptides in moderate reactivity. Also, the chemical applications of the strategy were successfully executed toward nailing tyrosine with other amino acids via a maleimide linker and intramolecular hydroarylation to produce tyrosine-centered stapled products and succinimide-glued macrocyclized products, respectively.

Indole-Based Compounds as Potential Drug Candidates for SARS-CoV-2.

The COVID-19 pandemic has posed a significant threat to society in recent times, endangering human health, life, and economic well-being. The disease quickly spreads due to the highly infectious SARS-CoV-2 virus, which has undergone numerous mutations. Despite intense research efforts by the scientific community since its emergence in 2019, no effective therapeutics have been discovered yet. While some repurposed drugs have been used to control the global outbreak and save lives, none have proven universally effective, particularly for severely infected patients. Although the spread of the disease is generally under control, anti-SARS-CoV-2 agents are still needed to combat current and future infections. This study reviews some of the most promising repurposed drugs containing indolyl heterocycle, which is an essential scaffold of many alkaloids with diverse bio-properties in various biological fields. The study also discusses natural and synthetic indole-containing compounds with anti-SARS-CoV-2 properties and computer-aided drug design (in silico studies) for optimizing anti-SARS-CoV-2 hits/leads.

Spiroindole-containing compounds bearing phosphonate group of potential Mpro-SARS-CoV-2 inhibitory properties.

Microwave-assisted reaction of 3,5-bis((E)-ylidene)-1-phosphonate-4-piperidones 3a‒g with azomethine ylide (produced through interaction of isatins 4 and sarcosine 5) cycloaddition afforded the corresponding (dispiro[indoline-3,2'-pyrrolidine-3',3″-piperidin]-1″-yl)phosphonates 6a‒l in excellent yields (80-95%). Structure of the synthesized agents was evidenced by single crystal X-ray studies of 6d, 6i and 6l. Some of the synthesized agents revealed promising anti-SARS-CoV-2 properties in the viral infected Vero-E6 cell technique with noticeable selectivity indices. Compounds 6g and 6b are the most promising agents synthesized (R = 4-BrC6H4, Ph; R' = H, Cl, respectively) with considerable selectivity index values. Mpro-SARS-CoV-2 inhibitory properties supported the anti-SARS-CoV-2 observations of the potent analogs synthesized. Molecular docking studies (PDB ID: 7C8U) are consistent with the Mpro inhibitory properties. The presumed mode of action was supported by both experimentally investigated Mpro-SARS-CoV-2 inhibitory properties and explained by docking observations.

Potential RNA-dependent RNA polymerase (RdRp) inhibitors as prospective drug candidates for SARS-CoV-2.

The SARS-CoV-2 pandemic is considered as one of the most disastrous pandemics for human health and the world economy. RNA-dependent RNA polymerase (RdRp) is one of the key enzymes that control viral replication. RdRp is an attractive and promising therapeutic target for the treatment of SARS-CoV-2 disease. It has attracted much interest of medicinal chemists, especially after the approval of Remdesivir. This study highlights the most promising SARS-CoV-2 RdRp repurposed drugs in addition to natural and synthetic agents. Although many in silico predicted agents have been developed, the lack of in vitro and in vivo experimental data has hindered their application in drug discovery programs.

New NSAID Conjugates as Potent and Selective COX-2 Inhibitors: Synthesis, Molecular Modeling and Biological Investigation.

New sets of ibuprofen and indomethacin conjugates comprising triazolyl heterocycle were synthesized via click chemistry, adopting an optimized protocol through the molecular hybridization approach affording the targeted agents in good yields. The new non-steroidal anti-inflammatory drug (NSAID) conjugates were designed and synthesized and could be considered as potential drug candidates for the treatment of pain and inflammation. The anti-inflammatory properties were investigated for all the synthesized conjugates. Among 14 synthesized conjugates, four (5a, 5b, 5d, and 5e) were found to have significant anti-inflammatory properties potency 117.6%, 116.5%, 93.8%, and 109.1% in comparison to reference drugs ibuprofen (97.2%) and indomethacin (100%) in the rat paw edema carrageenan test without any ulcerogenic liability. The suppression effect of cytokines IL-6, TNF-α, and iNOS in addition to NO in the LPS-induced RAW264.7 cells supports the promising anti-inflammatory properties observed in the ibuprofen conjugates. In addition, several conjugates showed promising peripheral and central analgesic activity. The selectivity index (SI) of compound 5a (23.096) indicates the significant efficacy and selectivity for COX-2 over COX-1. Molecular modeling (docking and QSAR) studies described the observed biological properties.

DNA Gyrase as a Target for Quinolones.

Bacterial DNA gyrase is a type II topoisomerase that can introduce negative supercoils to DNA substrates and is a clinically-relevant target for the development of new antibacterials. DNA gyrase is one of the primary targets of quinolones, broad-spectrum antibacterial agents and are used as a first-line drug for various types of infections. However, currently used quinolones are becoming less effective due to drug resistance. Common resistance comes in the form of mutation in enzyme targets, with this type being the most clinically relevant. Additional mechanisms, conducive to quinolone resistance, are arbitrated by chromosomal mutations and/or plasmid-gene uptake that can alter quinolone cellular concentration and interaction with the target, or affect drug metabolism. Significant synthetic strategies have been employed to modify the quinolone scaffold and/or develop novel quinolones to overcome the resistance problem. This review discusses the development of quinolone antibiotics targeting DNA gyrase to overcome bacterial resistance and reduce toxicity. Moreover, structural activity relationship (SAR) data included in this review could be useful for the development of future generations of quinolone antibiotics.

Spirooxindole: A Versatile Biologically Active Heterocyclic Scaffold.

Spirooxindoles occupy an important place in heterocyclic chemistry. Many natural spirooxindole-containing compounds have been identified as bio-promising agents. Synthetic analogs have also been synthesized utilizing different pathways. The present article summarizes the recent development of both natural and synthetic spirooxindole-containing compounds prepared from isatin or its derivatives reported in the last five years. The spirooxindoles are categorized based on their mentioned biological properties.

Azomethine Ylides-Versatile Synthons for Pyrrolidinyl-Heterocyclic Compounds.

Azomethine ylides are nitrogen-based three-atom components commonly used in [3+2]-cycloaddition reactions with various unsaturated 2π-electron components. These reactions are highly regio- and stereoselective and have attracted the attention of organic chemists with respect to the construction of diverse heterocycles potentially bearing four new contiguous stereogenic centers. This review article complies the most important [3+2]-cycloaddition reactions of azomethine ylides with various olefinic, unsaturated 2π-electron components (acyclic, alicyclic, heterocyclic, and exocyclic ones) reported over the past two decades.

Modified Curcumins as Potential Drug Candidates for Breast Cancer: An Overview.

Breast cancer (BC), the most common malignancy in women, results from significant alterations in genetic and epigenetic mechanisms that alter multiple signaling pathways in growth and malignant progression, leading to limited long-term survival. Current studies with numerous drug therapies have shown that BC is a complex disease with tumor heterogeneity, rapidity, and dynamics of the tumor microenvironment that result in resistance to existing therapy. Targeting a single cell-signaling pathway is unlikely to treat or prevent BC. Curcumin (a natural yellow pigment), the principal ingredient in the spice turmeric, is well-documented for its diverse pharmacological properties including anti-cancer activity. However, its clinical application has been limited because of its low solubility, stability, and bioavailability. To overcome the limitation of curcumin, several modified curcumin conjugates and curcumin mimics were developed and studied for their anti-cancer properties. In this review, we have focused on the application of curcumin mimics and their conjugates for breast cancer.

Ursolic Acid Analogs as Potential Therapeutics for Cancer.

Ursolic acid (UA) is a pentacyclic triterpene isolated from a large variety of vegetables, fruits and many traditional medicinal plants. It is a structural isomer of Oleanolic Acid. The medicinal application of UA has been explored extensively over the last two decades. The diverse pharmacological properties of UA include anti-inflammatory, antimicrobial, antiviral, antioxidant, anti-proliferative, etc. Especially, UA holds a promising position, potentially, as a cancer preventive and therapeutic agent due to its relatively non-toxic properties against normal cells but its antioxidant and antiproliferative activities against cancer cells. Cell culture studies have shown interference of UA with multiple pharmacological and molecular targets that play a critical role in many cells signaling pathways. Although UA is considered a privileged natural product, its clinical applications are limited due to its low absorption through the gastro-intestinal track and rapid elimination. The low bioavailability of UA limits its use as a therapeutic drug. To overcome these drawbacks and utilize the importance of the scaffold, many researchers have been engaged in designing and developing synthetic analogs of UA via structural modifications. This present review summarizes the synthetic UA analogs and their cytotoxic antiproliferative properties reported in the last two decades.

Synthesis of Potential Antiviral Agents for SARS-CoV-2 Using Molecular Hybridization Approach.

We synthesized a set of small molecules using a molecular hybridization approach with good yields. The antiviral properties of the synthesized conjugates against the SAR-CoV-2 virus were investigated and their cytotoxicity was also determined. Among all the synthesized conjugates, compound 9f showed potential against SARS-CoV-2 and low cytotoxicity. The conjugates' selectivity indexes (SIs) were determined to correlate the antiviral properties and cytotoxicity. The observed biological data were further validated using computational studies.

Development of spiro-3-indolin-2-one containing compounds of antiproliferative and anti-SARS-CoV-2 properties.

A series of 1″-(alkylsulfonyl)-dispiro[indoline-3,2'-pyrrolidine-3',3″-piperidine]-2,4″-diones 6a‒o has been synthesized through regioselective multi-component azomethine dipolar cycloaddition reaction of 1-(alkylsulfonyl)-3,5-bis(ylidene)-piperidin-4-ones 3a‒h. X-ray diffraction studies (6b‒d,h) confirmed the structures. The majority of the synthesized analogs reveal promising antiproliferation properties against a variety of human cancer cell lines (MCF7, HCT116, A431 and PaCa2) with good selectivity index towards normal cell (RPE1). Some of the synthesized agents exhibit potent inhibitory properties against the tested cell lines with higher efficacies than the standard references (sunitinib and 5-fluorouracil). Compound 6m is the most potent. Multi-targeted inhibitory properties against EGFR and VEGFR-2 have been observed for the synthesized agents. Flow cytometry supports the antiproliferation properties and shows the tested agents as apoptosis and necrosis forming. Vero cell viral infection model demonstrates the anti-SARS-CoV-2 properties of the synthesized agents. Compound 6f is the most promising (about 3.3 and 4.8 times the potency of the standard references, chloroquine and hydroxychloroquine). QSAR models explain and support the observed biological properties.