Synthesis and Evaluation of Anticancer Activities of Novel C-28 Guanidine-Functionalized Triterpene Acid Derivatives

G-quadruplex-mediated specific recognition, stabilization and transcriptional repression of bcl-2 by small molecule

The presence of the G-quadruplex (G4) structure in the promoter region of the human bcl-2 oncogenes makes it a promising target for developing anti-cancer therapeutics. Bcl-2 inhibits apoptosis, and its frequent overexpression in cancer cells contributes to tumor initiation, progression, and resistance to therapy. Small molecules that can specifically bind to bcl-2 G4 with high affinity and selectivity are remaining elusive. Here, we report that small molecule 1,3-bis-) furane-2yl-methylidene-amino) guanidine (BiGh) binds to bcl-2 G4 DNA structure with very high affinity and selectivity over other genomic G4 DNA structures and duplex DNA. BiGh stabilizes folded parallel conformation of bcl-2 G4 via non-covalent and electrostatic interactions and increases the thermal stabilization up to 15 °C. The ligand significantly suppresses the bcl-2 transcription in HeLa cells by a G4-dependent mechanism and induces cell cycle arrest which promotes apoptosis. The in silico ADME profiling confirms the potential 'drug-likeness' of BiGh. Our results showed that BiGh stabilizes the bcl-2 G-quadruplex motif, downregulates the bcl-2 gene transcription as well as translation process in cervical cancer cells, and exhibits potential anti-cancer activity. This work provides a potential platform for the development of lead compound(s) as G4 stabilizers with drug-like properties of BiGh for cancer therapeutics.

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.

Discovery of potent Guanidine derivative that selectively binds and stabilizes the human BCL-2 G-quadruplex DNA and downregulates the transcription

Small molecules that interact with quadruplexes offer a wide range of potential applications, including not just as medications but also as sensors for quadruplexes structures. The BCL-2 is a proto-oncogene that often gets mutated in lethal cancer and could be an interesting target for developing an anti-cancer drug. In the present study, we have employed various biophysical techniques such as fluorescence, CD, Isothermal calorimeter, gel retardation, and PCR stop assay, indicating that Guanidine derivatives GD-1 and GD-2 selectively interact with high affinity with BCL-2 G-quadruplex over other G-quadruplex DNA and duplex DNA. The most promising small molecule GD-1 increases the thermostability of the BCL-2 GQ structure by 12°C. Our biological experiments such as ROS generation, qRT-PCR, western blot, TFP based Reporter assay, show that the GD-1 ligand causes a synthetic lethal interaction by suppressing the expression BCL-2 genes via interaction and stabilization of its the promoter G-quadruplexes in HeLa cells and act as a potential anti-cancer agent.

The impact of counterions in biological activity: case study of antibacterial alkylguanidino ureas

Abstract

Trifluoroacetic acid (TFA), due to its strong acidity and low boiling point, is extensively used in protecting groups-based synthetic strategies. Indeed, synthetic compounds bearing basic functions, such as amines or guanidines (commonly found in peptido or peptidomimetic derivatives), developed in the frame of drug discovery programmes, are often isolated as trifluoroacetate (TF-Acetate) salts and their biological activity is assessed as such in in vitro, ex vivo, or in vivo experiments. However, the presence of residual amounts of TFA was reported to potentially affect the accuracy and reproducibility of a broad range of cellular assays (e. g. antimicrobial susceptibility testing, and cytotoxicity assays) limiting the further development of these derivatives. Furthermore, the impact of the counterion on biological activity, including TF-Acetate, is still controversial. Herein, we present a focused case study aiming to evaluate the activity of an antibacterial AlkylGuanidino Urea (AGU) compound obtained as TF-Acetate (1a) and hydrochloride (1b) salt forms to highlight the role of counterions in affecting the biological activity. We also prepared and tested the corresponding free base (1c). The exchange of the counterions applied to polyguanidino compounds represents an unexplored and challenging field, which required significant efforts for the successful optimization of reliable methods of preparation, also reported in this work. In the end, the biological evaluation revealed a quite similar biological profile for the salt derivatives 1a and 1b and a lower potency was found for the free base 1c.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s11030-022-10505-6.

From Marine Metabolites to the Drugs of the Future: Squalamine, Trodusquemine, Their Steroid and Triterpene Analogues

This review comprehensively describes the recent advances in the synthesis and pharmacological evaluation of steroid polyamines squalamine, trodusquemine, ceragenins, claramine, and their diverse analogs and derivatives, with a special focus on their complete synthesis from cholic acids, as well as an antibacterial and antiviral, neuroprotective, antiangiogenic, antitumor, antiobesity and weight-loss activity, antiatherogenic, regenerative, and anxiolytic properties. Trodusquemine is the most-studied small-molecule allosteric PTP1B inhibitor. The discovery of squalamine as the first representative of a previously unknown class of natural antibiotics of animal origin stimulated extensive research of terpenoids (especially triterpenoids) comprising polyamine fragments. During the last decade, this new class of biologically active semisynthetic natural product derivatives demonstrated the possibility to form supramolecular networks, which opens up many possibilities for the use of such structures for drug delivery systems in serum or other body fluids.

Recent progress on betulinic acid and its derivatives as antitumor agents: a mini review

Natural products are one of the important sources for the discovery of new drugs. Betulinic acid (BA), a pentacyclic triterpenoid widely distributed in the plant kingdom, exhibits powerful biological effects, including antitumor activity against various types of cancer cells. A considerable number of BA derivatives have been designed and prepared to remove their disadvantages, such as poor water solubility and low bioavailability. This review summarizes the current studies of the structural diversity of antitumor BA derivatives within the last five years, which provides prospects for further research on the structural modification of betulinic acid.

A Review on Recent Developments in the Anticancer Potential of Oleanolic acid and its analogs (2017-2020)

Oleanolic acid (OA) is a pentacyclic triterpenoid class of natural product known to possess a broad range of biological activities, specifically, anticancer. Considering the anticancer potential of OA, a large number of analogs have been prepared by several researchers through modifications at C-3, C-12 and C-28 -COOH to develop the potent anticancer agents with improved cytotoxicity and pharmaceutical properties. Some of the synthesized derivatives have been assessed in clinical trials also. This review summarizes the most recent synthetic and biological efforts in the development of oleanolic acid and its analogs during the period 2017-2020. Reports published during this period revealed that both OA and its analogs possess a remarkable potential for the development of effective anticancer agents along with several others such as anti-inflammatory, anti-viral, anti-microbial and anti-diabetic agents.

Synthesis of the Guanidine Derivative: N-{[(7-(4,5-Dihydro-1H-imidazol-2-yl)-2-(p-tolyl)-6,7-dihydro-2H-imidazo[2,1-c][1,2,4]triazol-3(5H)-ylidene)amino](phenylamino)methylene}benzamide

The guanidine derivative N-{[(7-(4,5-dihydro-1H-imidazol-2-yl)-2-(p-tolyl)-6,7-dihydro-2H-imidazo[2,1-c][1,2,4]triazol-3(5H)-ylidene)amino](phenylamino)methylene}benzamide (3) has been obtained by the reaction of one measure of N-{[7-(4,5-dihydro-1H-imidazol-2-yl)-2-(p-tolyl)-6,7-dihydro-2H-imidazo[2,1-c][1,2,4]triazol-3(5H)-ylidene]carbamothioyl}benzamide (2) with one measure of aniline in the presence of mercury(II) chloride and triethylamine in anhydrous dimethylformamide. The structure of product 3 was confirmed by 1H and 13C-NMR, infrared spectroscopy, and elemental analysis.

Novel bioactive properties of low-polarity fractions from sea-buckthorn extracts (Elaeagnus rhamnoides (L.) A. Nelson) - (in vitro)

Due to the richness of bioactive substances and easy accessibility, sea-buckthorn can be an ingredient of currently popular functional food supporting anti-cancer therapy. Low-polarity fractions from fruit (OL), twigs (GL) and leaves (LL) were investigated. Compared to the previous scientific reports a more detailed analysis of the chemical composition of individual fractions was performed. Cytotoxicity of low-polarity fractions has been investigated and activity compared in human tumor and normal cells cultured in vitro. The genotoxicity and pro-apoptotic properties of low-polarity fractions were also followed on selected cell lines that had proved to be the most sensitive. In the proposed research model being tested, low-polarity fractions act cytotoxically, even 3 times more strongly in cancer cells than normal ones. Measurement of caspase 3/7 activity indicated that cell death occurs through apoptosis. Furthermore, high concentrations of low-polarity fractions have moderate genotoxic properties. Data obtained on the biological properties of low-polarity fractions from sea-buckthorn show that these fractions can potentially support cancer cells elimination. Phytotochemical analysis indicates the key role of the triterpenoids in this process.

Development and Evaluation of Oleanolic Acid Dosage Forms and Its Derivatives

Oleanolic acid is a pentacyclic triterpenoid compound that exists widely in medicinal herbs and other plants. Because of the extensive pharmacological activity, oleanolic acid has attracted more and more attention. However, the structural characteristics of oleanolic acid prevent it from being directly made into new drugs, which limits the application of oleanolic acid. Through the application of modern preparation techniques and methods, different oleanolic acid dosage forms and derivatives have been designed and synthesized. These techniques can improve the water solubility and bioavailability of oleanolic acid and lay a foundation for the new drug development. In this review, the recent progress in understanding the oleanolic acid dosage forms and its derivatives are discussed. Furthermore, these products were evaluated comprehensively from the perspective of characterization and pharmacokinetics, and this work may provide ideas and references for the development of oleanolic acid preparations.

Design and Synthesis of Organic Molecules as Antineoplastic Agents

The fight against cancer is one of the most challenging tasks currently for lots of researchers in many fields, such as pharmaceuticals, medicine, and chemicals [...].

Antimicrobial properties of amine- and guanidine-functionalized derivatives of betulinic, ursolic and oleanolic acids: Synthesis and structure/activity evaluation

A series of 34 new amine- and guanidine-functionalized derivatives of betulinic, ursolic, and oleanolic acids were synthesized and tested for their antimicrobial activity against the growth of four bacterial strains (Escherichia coli, Acinetobacter baumannii, Pseudomonas aeruginosa, and Staphylococcus aureus (MRSA)) and two fungal strains (Candida albicans and Cryptococcus neoformans). The obtained compounds were also tested for the cytotoxic effect against HEK293 human embryonic kidney cell line and hemolytic activity against human red blood cells. Most of the prepared amino and guanidinium derivatives of betulinic, ursolic, and oleanolic acids showed a considerably higher bacteriostatic activity against methicillin-resistant S. aureus than the parent compounds. The most active compounds (MICs ≤ 0.25 μg/ml or 0.4-0.5 μM) were superior over the clinically used antibiotic vancomycin in the antibacterial effect (MIC of 1 μg/ml or 0.7 μM). Apart from antibacterial activity, new triterpene acid derivatives exhibited excellent antifungal activity against Cryptococcus neoformans, with MICs values being as low as 0.25 μg/ml (0.4 μM), and were approximately 65 times as active as fluconazole, a known antifungal agent. Four most promising compounds we identified (7, 13, 24, and 33) showed not only high bacteriostatic effect, but also low cytotoxicity against mammalian HEK293 cells and high hemolytic selectivity.

Ursolic and Oleanolic Acids Induce Mitophagy in A549 Human Lung Cancer Cells

Ursolic and oleanolic acids are natural isomeric triterpenes known for their anticancer activity. Here, we investigated the effect of triterpenes on the viability of A549 human lung cancer cells and the role of autophagy in their activity. The induction of autophagy, the mitochondrial changes and signaling pathway stimulated by triterpenes were systematically explored by confocal microscopy and western blotting. Ursolic and oleanolic acids induce autophagy in A549 cells. Ursolic acid activates AKT/mTOR pathways and oleanolic acid triggers a pathway independent on AKT. Both acids promote many mitochondrial changes, suggesting that mitochondria are targets of autophagy in a process known as mitophagy. The PINK1/Parkin axis is a pathway usually associated with mitophagy, however, the mitophagy induced by ursolic or oleanolic acid is just dependent on PINK1. Moreover, both acids induce an ROS production. The blockage of autophagy with wortmannin is responsible for a decrease of mitochondrial membrane potential (Δψ) and cell death. The wortmannin treatment causes an over-increase of p62 and Nrf2 proteins promote a detoxifying effect to rescue cells from the death conducted by ROS. In conclusion, the mitophagy and p62 protein play an important function as a survival mechanism in A549 cells and could be target to therapeutic control.

Synthesis and Antiproliferative Activity of Novel A-Ring Cleaved Glycyrrhetinic Acid Derivatives

A series of new glycyrrhetinic acid derivatives was synthesized via the opening of its ring A along with the coupling of an amino acid. The antiproliferative activity of the derivatives was evaluated against a panel of nine human cancer cell lines. Compound 17 was the most active compound, with an IC50 of 6.1 µM on Jurkat cells, which is 17-fold more potent than that of glycyrrhetinic acid, and was up to 10 times more selective toward that cancer cell line. Further biological investigation in Jurkat cells showed that the antiproliferative activity of compound 17 was due to cell cycle arrest at the S phase and induction of apoptosis.

Synthesis and Antiproliferative Activity of Novel Heterocyclic Glycyrrhetinic Acid Derivatives

A new series of glycyrrhetinic acid derivatives has been synthesized via the introduction of different heterocyclic rings conjugated with an α,β-unsaturated ketone in its ring A. These new compounds were screened for their antiproliferative activity in a panel of nine human cancer cell lines. Compound 10 was the most active derivative, with an IC₅₀ of 1.1 µM on Jurkat cells, which is 96-fold more potent than that of glycyrrhetinic acid, and was 4-fold more selective toward that cancer cell line. Further biological studies performed in Jurkat cells showed that compound 10 is a potent inducer of apoptosis that activates both the intrinsic and extrinsic pathways.