Bioactive Bismuth Compounds: Is Their Toxicity a Barrier to Therapeutic Use?

Bismuth compounds are considered relatively non-toxic, with their low solubility in aqueous solutions (e.g., biological fluids) being the major contributing factor to this property. Bismuth derivatives are widely used for the treatment of peptic ulcers, functional dyspepsia, and chronic gastritis. Moreover, the properties of bismuth compounds have also been extensively explored in two main fields of action: antimicrobial and anticancer. Despite the clinical interest of bismuth-based drugs, several side effects have also been reported. In fact, excessive acute ingestion of bismuth, or abuse for an extended period of time, can lead to toxicity. However, evidence has demonstrated that the discontinuation of these compounds usually reverses their toxic effects. Notwithstanding, the continuously growing use of bismuth products suggests that it is indeed part of our environment and our daily lives, which urges a more in-depth review and investigation into its possible undesired activities. Therefore, this review aims to update the pharmaco-toxicological properties of bismuth compounds. A special focus will be given to in vitro, in vivo, and clinical studies exploring their toxicity.

Decoding the secrets: how conformational and structural regulators inhibit the human 20S proteasome

Acquired resistance to drugs that modulate specific protein functions, such as the human proteasome, presents a significant challenge in targeted therapies. This underscores the importance of devising new methodologies to predict drug binding and potential resistance due to specific protein mutations. In this work, we conducted an extensive computational analysis to ascertain the effects of selected mutations (Ala49Thr, Ala50Val, and Cys52Phe) within the active site of the human proteasome. Specifically, we sought to understand how these mutations might disrupt protein function either by altering protein stability or by impeding interactions with a clinical administered drug. Leveraging molecular dynamics simulations and molecular docking calculations, we assessed the effect of these mutations on protein stability and ligand affinity. Notably, our results indicate that the Cys52Phe mutation critically impacts protein-ligand binding, providing valuable insights into potential proteasome inhibitor resistance.

Artificial intelligence for prediction of biological activities and generation of molecular hits using stereochemical information

In this work, we develop a method for generating targeted hit compounds by applying deep reinforcement learning and attention mechanisms to predict binding affinity against a biological target while considering stereochemical information. The novelty of this work is a deep model Predictor that can establish the relationship between chemical structures and their corresponding [Formula: see text] values. We thoroughly study the effect of different molecular descriptors such as ECFP4, ECFP6, SMILES and RDKFingerprint. Also, we demonstrated the importance of attention mechanisms to capture long-range dependencies in molecular sequences. Due to the importance of stereochemical information for the binding mechanism, this information was employed both in the prediction and generation processes. To identify the most promising hits, we apply the self-adaptive multi-objective optimization strategy. Moreover, to ensure the existence of stereochemical information, we consider all the possible enumerated stereoisomers to provide the most appropriate 3D structures. We evaluated this approach against the Ubiquitin-Specific Protease 7 (USP7) by generating putative inhibitors for this target. The predictor with SMILES notations as descriptor plus bidirectional recurrent neural network using attention mechanism has the best performance. Additionally, our methodology identify the regions of the generated molecules that are important for the interaction with the receptor's active site. Also, the obtained results demonstrate that it is possible to discover synthesizable molecules with high biological affinity for the target, containing the indication of their optimal stereochemical conformation.

Therapeutic potential of glutaminyl cyclases: Current status and emerging trends

Glutaminyl cyclase (QC) activity has been identified as a key effector in distinct biological processes. Human glutaminyl-peptide cyclotransferase (QPCT) and glutaminyl-peptide cyclotransferase-like (QPCTL) are considered attractive therapeutic targets in many human disorders, such as neurodegenerative diseases, and a range of inflammatory conditions, as well as for cancer immunotherapy, because of their capacity to modulate cancer immune checkpoint proteins. In this review, we explore the biological functions and structures of QPCT/L enzymes and highlight their therapeutic relevance. We also summarize recent developments in the discovery of small-molecule inhibitors targeting these enzymes, including an overview of preclinical and clinical studies.

New Scaffolds of Proteasome Inhibitors: Boosting Anticancer Potential by Exploiting the Synergy of In Silico and In Vitro Methodologies

Cancer is a complex multifactorial disease whose pathophysiology involves multiple metabolic pathways, including the ubiquitin-proteasome system, for which several proteasome inhibitors have already been approved for clinical use. However, the resistance to existing therapies and the occurrence of severe adverse effects is still a concern. The purpose of this study was the discovery of novel scaffolds of proteasome inhibitors with anticancer activity, aiming to overcome the limitations of the existing proteasome inhibitors. Thus, a structure-based virtual screening protocol was developed using the structure of the human 20S proteasome, and 246 compounds from virtual databases were selected for in vitro evaluation, namely proteasome inhibition assays and cell viability assays. Compound 4 (JHG58) was shortlisted as the best hit compound based on its potential in terms of proteasome inhibitory activity and its ability to induce cell death (both with IC50 values in the low micromolar range). Molecular docking studies revealed that compound 4 interacts with key residues, namely with the catalytic Thr1, Ala20, Thr21, Lys33, and Asp125 at the chymotrypsin-like catalytic active site. The hit compound is a good candidate for additional optimization through a hit-to-lead campaign.

Ubiquitin-specific protease 7 (USP7): an emerging drug target for cancer treatment

INTRODUCTION

Ubiquitin-specific protease 7 (USP7) also known as herpesvirus-associated ubiquitin-specific protease (HAUSP) is a well-characterized cysteine protease that belongs to the largest subfamily of deubiquitinating enzymes (DUBs). It is involved in multiple signaling pathways, some of them dysregulated in malignant tumors. USP7 inhibition can lead to cell growth arrest and apoptosis through inhibition of tumor promoters and stabilization of tumor suppressors, making it a promising druggable target for cancer therapy.

AREAS COVERED

This review covers the structure of USP7, its function in multiple signaling pathways and relevance in cancer, as well as recent advances and future perspectives in the development of USP7 inhibitors for cancer therapy.

EXPERT OPINION

Literature reports display the multiple antitumor activities of USP7 inhibitors, both in vitro and in vivo. Nonetheless, none have entered clinical trials so far, highlighting the need to delve into a deeper understanding of USP7 binding sites and the development of more accurate compound screening methods. Despite these challenges, further development of USP7 inhibitors is promising as a valuable new approach for cancer treatment, including the ability to address chemoresistance.

Design, synthesis, and biological evaluation of new arjunolic acid derivatives as anticancer agents

Arjunolic acid (AA) is a pentacyclic triterpenoid with promising anticancer properties. A series of novel AA derivatives containing a pentameric A-ring with an enal moiety, combined with additional modifications at C-28, were designed and prepared. The biological activity on the viability of human cancer and non-tumor cell lines was evaluated in order to identify the most promising derivatives. Additionally, a preliminary study of the structure-activity relationship was carried out. The most active derivative, derivative 26, also showed the best selectivity between malignant cells and non-malignant fibroblasts. For compound 26, the anticancer molecular mechanism of action in PANC-1 cells was further studied and the results showed that this derivative induced a cell-cycle arrest at G0/G1 phase and significantly inhibited the wound closure rate of PANC-1 cancer cells in a concentration-dependent manner. Additionally, compound 26 synergistically increased the cytotoxicity of Gemcitabine, especially at a concentration of 0.24 μM. Moreover, a preliminary pharmacological study indicated that at lower doses this compound did not demonstrate toxicity in vivo. Taken together, these findings suggest that compound 26 may be a valuable compound for the development of new pancreatic anticancer treatment, and further studies are needed to explore its full potential.

Recent advances in oridonin derivatives with anticancer activity

Cancer is a leading cause of mortality responsible for an estimated 10 million deaths worldwide in 2020, and its incidence has been rapidly growing over the last decades. Population growth and aging, as well as high systemic toxicity and chemoresistance associated with conventional anticancer therapies reflect these high levels of incidence and mortality. Thus, efforts have been made to search for novel anticancer drugs with fewer side effects and greater therapeutic effectiveness. Nature continues to be the main source of biologically active lead compounds, and diterpenoids are considered one of the most important families since many have been reported to possess anticancer properties. Oridonin is an ent-kaurane tetracyclic diterpenoid isolated from Rabdosia rubescens and has been a target of extensive research over the last few years. It displays a broad range of biological effects including neuroprotective, anti-inflammatory, and anticancer activity against a variety of tumor cells. Several structural modifications on the oridonin and biological evaluation of its derivatives have been performed, creating a library of compounds with improved pharmacological activities. This mini-review aims to highlight the recent advances in oridonin derivatives as potential anticancer drugs, while succinctly exploring their proposed mechanisms of action. To wind up, future research perspectives in this field are also disclosed.

Proteolysis-Targeting Chimeras (PROTACs) targeting the BCR-ABL for the treatment of chronic myeloid leukemia - a patent review

INTRODUCTION

PROteolysis-TArgeting Chimeras (PROTACs) allow the selective degradation of a protein of interest (POI) by the ubiquitin-proteasome system (UPS). With this unique mechanism of action, the research and development of PROTACs that target the Breakpoint Cluster Region Abelson (BCR-ABL) tyrosine kinase (TK) has been increasing dramatically, as they are promising molecules in the treatment of Chronic Myeloid Leukemia (CML), one of the main hematological malignancies, which results from an uncontrolled myeloproliferation due to the constitutive activation of BCR-ABL.

AREAS COVERED

This review summarizes the patents/applications published in the online databases like Espacenet or World Intellectual Property Organization regarding PROTACs that promote BCR-ABL degradation. Patents will be described mostly in terms of chemical structure, biochemical/pharmacological activities, and potential clinical applications.

EXPERT OPINION

The recent discovery of the enormous potential of PROTACs led to the creation of new compounds capable of degrading BCR-ABL for the treatment of CML. Although still in reduced numbers, and in the pre-clinical phase of development, some compounds have already been shown to overcome some of the difficulties presented by conventional BCR-ABL inhibitors, such as the well-known imatinib. Therefore, it is very likely that some of the present PROTACs will enter future CML therapy in the coming years.

Highlights in USP7 inhibitors for cancer treatment

Ubiquitin-specific protease 7 (USP7) is a member of one of the most largely studied families of deubiquitylating enzymes. It plays a key role modulating the levels of multiple proteins, including tumor suppressors, transcription factors, epigenetic modulators, DNA repair proteins, and regulators of the immune response. The abnormal expression of USP7 is found in various malignant tumors and a high expression signature generally indicates poor tumor prognosis. This suggests USP7 as a promising prognostic and druggable target for cancer therapy. Nonetheless, no approved drugs targeting USP7 have already entered clinical trials. Therefore, the development of potent and selective USP7 inhibitors still requires intensive research and development efforts before the pre-clinical benefits translate into the clinic. This mini review systematically summarizes the role of USP7 as a drug target for cancer therapeutics, as well as the scaffolds, activities, and binding modes of some of the most representative small molecule USP7 inhibitors reported in the scientific literature. To wind up, development challenges and potential combination therapies using USP7 inhibitors for less tractable tumors are also disclosed.

Deep generative model for therapeutic targets using transcriptomic disease-associated data-USP7 case study

The generation of candidate hit molecules with the potential to be used in cancer treatment is a challenging task. In this context, computational methods based on deep learning have been employed to improve in silico drug design methodologies. Nonetheless, the applied strategies have focused solely on the chemical aspect of the generation of compounds, disregarding the likely biological consequences for the organism's dynamics. Herein, we propose a method to implement targeted molecular generation that employs biological information, namely, disease-associated gene expression data, to conduct the process of identifying interesting hits. When applied to the generation of USP7 putative inhibitors, the framework managed to generate promising compounds, with more than 90% of them containing drug-like properties and essential active groups for the interaction with the target. Hence, this work provides a novel and reliable method for generating new promising compounds focused on the biological context of the disease.

Therapeutic targeting of PD-1/PD-L1 blockade by novel small-molecule inhibitors recruits cytotoxic T cells into solid tumor microenvironment

Background

Inhibiting programmed cell death protein 1 (PD-1) or PD-ligand 1 (PD-L1) has shown exciting clinical outcomes in diverse human cancers. So far, only monoclonal antibodies are approved as PD-1/PD-L1 inhibitors. While significant clinical outcomes are observed on patients who respond to these therapeutics, a large proportion of the patients do not benefit from the currently available immune checkpoint inhibitors, which strongly emphasize the importance of developing new immunotherapeutic agents.

Methods

In this study, we followed a transdisciplinary approach to discover novel small molecules that can modulate PD-1/PD-L1 interaction. To that end, we employed in silico analyses combined with in vitro, ex vivo, and in vivo experimental studies to assess the ability of novel compounds to modulate PD-1/PD-L1 interaction and enhance T-cell function.

Results

Accordingly, in this study we report the identification of novel small molecules, which like anti-PD-L1/PD-1 antibodies, can stimulate human adaptive immune responses. Unlike these biological compounds, our newly-identified small molecules enabled an extensive infiltration of T lymphocytes into three-dimensional solid tumor models, and the recruitment of cytotoxic T lymphocytes to the tumor microenvironment in vivo, unveiling a unique potential to transform cancer immunotherapy.

Conclusions

We identified a new promising family of small-molecule candidates that regulate the PD-L1/PD-1 signaling pathway, promoting an extensive infiltration of effector CD8 T cells to the tumor microenvironment.

A patent review of glutaminyl cyclase inhibitors (2004-present)

Introduction: Glutaminyl cyclase (QC) enzymes catalyze the post-translational processing of several substrates with N-terminal glutamine or glutamate to form pyroglutamate (pE) residue. In addition to physiological functions, emerging evidence demonstrates that human QCs play a part in pathological processes in diverse diseases such as Alzheimer's disease (AD), inflammatory and cancer diseases.Areas covered: In recent years, efforts to effectively develop QC small-molecule inhibitors have been made and different chemical classes have been disclosed. This review summarizes the patents/applications regarding QC inhibitors released from 2004 (first patent) to now. The patents are mostly described in terms of chemical structures, biochemical/pharmacological activities, and potential clinical applications.Expert opinion: For more than 15 years of research, the knowledge on the QC activity domain has considerably increased and therapeutic potential of QC inhibitors has been explored. An important number of studies and patents have been published to expand the use of QC inhibitors. QC enzymes are pharmacologically interesting targets to be used as an AD-modifying therapy, or for other QC-associated disorder. Distinct classes of chemical scaffolds and potential clinical uses have been claimed by various organizations. For the coming years, there is much to experience in the QC field.

New BACE1 Chimeric Peptide Inhibitors Selectively Prevent AβPP-β Cleavage Decreasing Amyloid-β Production and Accumulation in Alzheimer's Disease Models

BACKGROUND

A disease-modifying therapy for Alzheimer's disease (AD) is still an unmet clinical need. The formation of amyloid-β (Aβ) requires the initial cleavage of the amyloid-β protein precursor (AβPP) by BACE1 (beta-site AβPP cleaving enzyme 1), which is a prime therapeutic target for AD.

OBJECTIVE

We aimed to design and develop a selective BACE1 inhibitor suitable to AD treatment.

METHODS

The new BACE1 inhibitors consist on a chimeric peptide including a sequence related to the human Swedish mutant form of AβPP (AβPPswe) conjugated with the TAT carrier that facilitates cell membrane permeation and the crossing of the blood-brain barrier. Additionally to the chimeric peptide in the L-form, we developed a D-retroinverso chimeric peptide. The latter strategy, never used with BACE1 inhibitors, is considered to favor a significantly higher half-life and lower immunogenicity.

RESULTS

We found that both chimeric peptides inhibit recombinant BACE1 activity and decrease Aβ40/42 production in Neuro-2a (N2A) cells expressing AβPPswe without inducing cytotoxicity. The intraperitoneal administration of these peptides to 3xTg-AD mice decreased plasma and brain Aβ40/42 levels, as well as brain soluble AβPPβ production. Also, a reduction of insoluble Aβ was observed in the brain after chronic treatment. Noteworthy, the chimeric peptides selectively inhibited the AβPP-β cleavage relatively to the proteolysis of other BACE1 substrates such as close homologue of L1 (CHL1) and seizure-related gene 6 (SEZ6).

CONCLUSIONS

Overall these new BACE1 chimeric peptideshold promising potential as a selective disease-modifying therapy for AD.

Breakthroughs in Medicinal Chemistry: New Targets and Mechanisms, New Drugs, New Hopes-7

Breakthroughs in Medicinal Chemistry [...].

Combining Virtual Screening Protocol and In Vitro Evaluation towards the Discovery of BACE1 Inhibitors

The treatment options for a patient diagnosed with Alzheimer’s disease (AD) are currently limited. The cerebral accumulation of amyloid-β (Aβ) is a critical molecular event in the pathogenesis of AD. When the amyloidogenic β-secretase (BACE1) is inhibited, the production of Aβ peptide is reduced. Henceforth, the main goal of this study is the discovery of new small bioactive molecules that potentially reach the brain and inhibit BACE1. The work was conducted by a customized molecular modelling protocol, including pharmacophore-based and molecular docking-based virtual screening (VS). Structure-based (SB) and ligand-based (LB) pharmacophore models were designed to accurately screen several drug-like compound databases. The retrieved hits were subjected to molecular docking and in silico filtered to predict their ability to cross the blood–brain barrier (BBB). Additionally, 34 high-scoring compounds structurally distinct from known BACE1 inhibitors were selected for in vitro screening assay, which resulted in 13 novel hit-compounds for this relevant therapeutic target. This study disclosed new BACE1 inhibitors, proving the utility of combining computational and in vitro approaches for effectively predicting anti-BACE1 agents in the early drug discovery process.

Chalcone derivatives targeting mitosis: synthesis, evaluation of antitumor activity and lipophilicity

This study describes the synthesis of a series of chalcones, including pyrazole and α,β-epoxide derivatives, and evaluation of their cell growth inhibitory activity in three human tumor cell lines, as well as their lipophilicity using liposomes as a biomimetic membrane model. Structure-activity and structure-lipophilicity relationships were established for the synthetized chalcones. From this work, nine chalcones (3, 5, 9, 11, 15-19) showing suitable drug-like lipophilicity with potent growth inhibitory activity were identified, being the growth inhibitory effect of compounds 15-17 associated with a pronounced antimitotic effect. Compounds 15-17 affected spindle assembly and, as a consequence, arrested cells at metaphase in NCI-H460 cells, culminating in cell death. Amongst the compounds tested, compound 15 exhibited the highest antimitotic activity as revealed by mitotic index calculation. Moreover, 15 was able to enhance chemosensitivity of tumor cells to low doses of paclitaxel in NCI-H460 cells. The results indicate that 15 exerts its antiproliferative activity by affecting microtubules and causing cell death subsequently to a mitotic arrest, and thus has the potential for antitumor activity.

Madecassic Acid Derivatives as Potential Anticancer Agents: Synthesis and Cytotoxic Evaluation

A series of novel madecassic acid (1) derivatives was synthesized, and their cytotoxicity was evaluated against the NCI-60 panel of cancer cell lines. Several analogues exhibited broad-spectrum cytotoxic activities over all nine tumor types represented in the panel, with more potent antiproliferative activities observed against selected cancer cell lines, including multidrug-resistant phenotypes. Among them, compound 29 showed GI₅₀ (50% growth inhibition) values ranging from 0.3 to 0.9 μM against 26 different tumor cell lines and selectivity for one colon (COLO 205) and two melanoma (SK-MEL-5 and UACC-257) cell lines at the TGI (total growth inhibition) level. The mode of action of 29 was predicted by CellMiner bioinformatic analysis and confirmed by biochemical and cell-based experiments to involve inhibition of the DNA replication process, particularly the initiation of replication, and disruption of mitochondrial membrane potential. The present findings suggest this novel madecassic acid derivative may have potential as an anticancer therapeutic lead for both solid and hematological tumors.

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 Biological Evaluation of New Madecassic Acid Derivatives Targeting ERK Cascade Signaling

In the present study, a series of novel madecassic acid derivatives was synthesized and screened against the National Cancer Institute's 60 human cancer cell line panel. Among them, compounds 5, 12, and 17 displayed potent and highly differential antiproliferative activity against 80% of the tumor cells harboring the B-Raf^V600E mutation within the nanomolar range. Structure-activity analysis revealed that a 5-membered A ring containing an α,β-unsaturated aldehyde substituted at C-23 with a 2-furoyl group seems to be crucial to produce this particular growth inhibition signature. In silico analysis of the cytotoxicity pattern of these compounds identified two highly correlated clinically approved drugs with known B-Raf^V600E inhibitory activity. Follow-up analysis revealed inhibition of the ERK signaling pathway through the reduction of cellular Raf protein levels is a key mechanism of action of these compounds. In particular, 17 was the most potent compound in suppressing tumor growth of B-Raf^V600E-mutant cell lines and displayed the highest reduction of Raf protein levels among the tested compounds. Taken together, this study revealed that modifications of madecassic acid structure can provide molecules with potent anticancer activity against cell lines harboring the clinically relevant B-Raf^V600E mutation, with compound 17 identified as a promising lead for the development of new anticancer drugs.

Highlights in BACE1 Inhibitors for Alzheimer's Disease Treatment

Alzheimer's disease (AD) is a severe neurodegenerative disorder and the most common type of dementia in the elderly. The clinical symptoms of AD include a progressive loss of memory and impairment of cognitive functions interfering with daily life activities. The main neuropathological features consist in extracellular amyloid-β (Aβ) plaque deposition and intracellular Neurofibrillary tangles (NFTs) of hyperphosphorylated Tau. Understanding the pathophysiological mechanisms that underlie neurodegeneration in AD is essential for rational design of neuroprotective agents able to prevent disease progression. According to the "Amyloid Cascade Hypothesis" the critical molecular event in the pathogenesis of AD is the accumulation of Aβ neurotoxic oligomers. Since the proteolytic processing of Amyloid Precursor Protein (APP) by β-secretase (beta-site APP cleaving enzyme 1, BACE1) is the rate-limiting step in the production of Aβ, this enzyme is considered a major therapeutic target and BACE1 inhibitors have the potential to be disease-modifying drugs for AD treatment. Therefore, intensive efforts to discover and develop inhibitors that can reach the brain and effectively inhibit BACE1 have been pursued by several groups worldwide. The aim of this review is to highlight the progress in the discovery of potent and selective small molecule BACE1 inhibitors over the past decade.

Novel PARP-1 Inhibitor Scaffolds Disclosed by a Dynamic Structure-Based Pharmacophore Approach

PARP-1 inhibition has been studied over the last decades for the treatment of various diseases. Despite the fact that several molecules act as PARP-1 inhibitors, a reduced number of compounds are used in clinical practice. To identify new compounds with a discriminatory PARP-1 inhibitory function, explicit-solvent molecular dynamics simulations using different inhibitors bound to the PARP-1 catalytic domain were performed. The representative structures obtained were used to generate structure-based pharmacophores, taking into account the dynamic features of receptor-ligand interactions. Thereafter, a virtual screening of compound databases using the pharmacophore models obtained was performed and the hits retrieved were subjected to molecular docking-based scoring. The drug-like molecules featuring the best ranking were evaluated for their PARP-1 inhibitory activity and IC₅₀ values were calculated for the top scoring docked compounds. Altogether, three new PARP-1 inhibitor chemotypes were identified.

Synthesis and cytotoxic activity of novel A-ring cleaved ursolic acid derivatives in human non-small cell lung cancer cells

Ursolic acid (UA) is a pentacyclic triterpenoid with recognized anticancer properties. We prepared a series of new A-ring cleaved UA derivatives and evaluated their antiproliferative activity in non-small cell lung cancer (NSCLC) cell lines using 2D and 3D culture models. Compound 17, bearing a cleaved A-ring with a secondary amide at C3, was found to be the most active compound, with potency in 2D systems. Importantly, even in 3D systems, the effect was maintained albeit a slight increase in the IC50. The molecular mechanism underlying the anticancer activity was further investigated. Compound 17 induced apoptosis via activation of caspase-8 and caspase-7 and via decrease of Bcl-2. Moreover, induction of autophagy was also detected with increased levels of Beclin-1 and LC3A/B-II and decreased levels of mTOR and p62. DNA synthetic capacity and cell cycle profiles were not affected by the drug, but total RNA synthesis was modestly but significantly decreased. Given its activity and mechanism of action, compound 17 might represent a potential candidate for further cancer research.

Synthesis and anticancer activity of novel fluorinated asiatic acid derivatives

A series of novel fluorinated Asiatic Acid (AA) derivatives were successfully synthesized, tested for their antiproliferative activity against HeLa and HT-29 cell lines, and their structure activity relationships were evaluated. The great majority of fluorinated derivatives showed stronger antiproliferative activity than AA in a concentration dependent manner. The most active compounds have a pentameric A-ring containing an α,β-unsaturated carbonyl group. The compounds with better cytotoxic activity were then evaluated against MCF-7, Jurkat, PC-3, A375, MIA PaCa-2 and BJ cell lines. Derivative 14 proved to be the most active compound among all tested derivatives and its mechanism of action was further investigated in HeLa cell line. The results showed that compound 14 induced cell cycle arrest in G0/G1 stage as a consequence of up-regulation of p21(cip1/waf1) and p27(kip1) and down-regulation of cyclin D3 and Cyclin E. Furthermore, compound 14 was found to induce caspase driven-apoptosis with activation of caspases-8 and caspase-3 and the cleavage of PARP. The cleavage of Bid into t-Bid, the up-regulation of Bax and the down-regulation of Bcl-2 were also observed after treatment of HeLa cells with compound 14. Taken together, these mechanistic studies revealed the involvement of extrinsic and intrinsic pathways in the apoptotic process induced by compound 14. Importantly, the antiproliferative activity of this compound on the non-tumor BJ human fibroblast cell line is weaker than in the tested cancer cell lines. The enhanced potency (between 45 and 90-fold more active than AA in a panel of cancer cell lines) and selectivity of this new AA derivative warrant further preclinical evaluation.

Synthesis and biological evaluation of novel asiatic acid derivatives with anticancer activity

Structural modification of asiatic acid afforded derivatives with improved anticancer activity.

Synthesis of chiral hexacyclic steroids via [8π + 2π] cycloaddition of diazafulvenium methides

16-Dehydropregnenolone acetate reacted with diazafulvenium methides to afford novel chiral 4,5,6,7-tetrahydropyrazolo[1,5-a]pyridine-fused steroids.

Antileishmanial activity of semisynthetic lupane triterpenoids betulin and betulinic acid derivatives: synergistic effects with miltefosine

Leishmaniasis is a neglected tropical disease (NTDs), endemic in 88 countries, affecting more than 12 million people. The treatment consists in pentavalent antimony compounds, amphotericin B, pentamidine and miltefosine, among others. However, these current drugs are limited due to their toxicity, development of biological resistance, length of treatment and high cost. Thus, it is important to continue the search for new effective and less toxic treatments.

The anti-Leishmania activity of sixteen semisynthetic lupane triterpenoids derivatives of betulin (BT01 to BT09) and betulinic acid (AB10 to AB16) were evaluated. Drug interactions between the active compounds and one current antileishmanial drug, miltefosine, were assessed using the fixed ratio isobologram method. In addition, effects on the cell cycle, apoptosis/necrosis events, morphology and DNA integrity were studied. The derivatives BT06 (3β-Hydroxy-(20R)-lupan-29-oxo-28-yl-1H-imidazole-1-carboxylate) and AB13 (28-(1H-imidazole-1-yl)-3,28-dioxo-lup-1,20(29)-dien-2-yl-1H-imidazole-1-carboxylate) were found to be the most active, with IC₅₀ values of 50.8 µM and 25.8 µM, respectively. Interactions between these two compounds and miltefosine were classified as synergistic, with the most effective association being between AB13 and miltefosine, where decreases of IC₅₀ values to 6 µM were observed, similar to the miltefosine activity alone. AB13 induced significant morphological changes, while both derivatives produced anti-proliferative activity through cell cycle arrest at the G0/G1 phase. Neither of these derivatives induced significant apoptosis/necrosis, as indicated by phosphatidylserine externalization and DNA fragmentation assays. In addition, neither of the derivatives induced death in macrophage cell lines. Thus, they do not present any potential risk of toxicity for the host cells.

This study has identified the betulin derivative BT06 and the betulinic acid derivative AB13 as promising molecules in the development of new alternative therapies for leishmaniasis, including those involving combined-therapy with miltefosine.

Steroidal 5α-reductase and 17α-hydroxylase/17,20-lyase (CYP17) inhibitors useful in the treatment of prostatic diseases

The role of steroidal inhibitors of androgen biosynthesis as potential weapons in the treatment of prostatic diseases, such as benign prostatic hyperplasia and prostatic cancer will be reviewed. Two enzymes have been targeted in the development of inhibitors that potentially could be useful in the management of such conditions. 5α-Reductase is primarily of interest in benign prostatic disease, though some role in the chemoprevention of prostatic carcinoma have been considered, whereas the 17α-hydroxylase/17,20-lyase (CYP17) enzyme is of interest in the treatment of malignant disease. An overview of the main achievements obtained during the past years will be presented, however special focus will be made on steroidal molecules that reached clinical trials or have been commercially launched. Relevant examples of such drugs are finasteride, dutasteride, abiraterone acetate and galeterone (TOK-001, formerly known as VN/124-1). This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

Anticancer steroids: linking natural and semi-synthetic compounds

Steroids, a widespread class of natural organic compounds occurring in animals, plants and fungi, have shown great therapeutic value for a broad array of pathologies. The present overview is focused on the anticancer activity of steroids, which is very representative of a rich structural molecular diversity and ability to interact with various biological targets and pathways. This review encompasses the most relevant discoveries on steroid anticancer drugs and leads through the last decade and comprises 668 references.

Ursane-type pentacyclic triterpenoids as useful platforms to discover anticancer drugs

This review highlights the potential of natural and semisynthetic ursane-type triterpenoids as candidates for the design of multi-target bioactive compounds, with focus on their anticancer effects. A brief illustration of the biosynthesis, sources, and general biological effects of the main classes of naturally occurring pentacyclic triterpenoids (PTs) are provided.

Synthesis of novel ursolic acid heterocyclic derivatives with improved abilities of antiproliferation and induction of p53, p21waf1 and NOXA in pancreatic cancer cells

A series of new heterocyclic derivatives of ursolic acid 1 were synthesized and evaluated for their antiproliferative activity against AsPC-1 pancreatic cancer cells. Compounds 24-32, with an α,β unsaturated ketone in conjugation with an heterocyclic ring in ring A have improved antiproliferative activities. Compound 32 is the most active compound with an IC(50) of 1.9 μM which is sevenfold more active than ursolic acid 1. Compound 32 arrests cell cycle in G1 phase and induces apoptosis in AsPC-1 cells with upregulation of p53, p21(waf1) and NOXA protein levels.

Semisynthetic ursolic acid fluorolactone derivatives inhibit growth with induction of p21(waf1) and induce apoptosis with upregulation of NOXA and downregulation of c-FLIP in cancer cells

A series of ursolic acid ((1S,2R,4aS,6aR,6aS,6bR,8aR,10S,12aR,14bS)-10-hydroxy-1,2,6a,6b,9,9,12a-heptamethyl-2,3,4,5,6,6a,7,8,8a,10,11,12,13,14b-tetradecahydro-1H-picene-4a-carboxylic acid) derivatives with a 12-fluoro-13,28β-lactone moiety were synthesized using the electrophilic fluorination reagent Selectfluor. The antiproliferative effects of these novel compounds were evaluated in AsPC-1 pancreatic cancer cells, and the structure-activity relationships (SARs) were evaluated. Of the compounds synthesized, ursolic acid derivatives carrying a heterocyclic ring, such as imidazole or methylimidazole, and cyanoenones were among the more potent inhibitors of AsPC-1 pancreatic cancer cell growth. 2-Cyano-3-oxo-12α-fluoro-urs-1-en-13,28β-olide, compound 20, was the most effective inhibitor with IC(50) values of 0.7, 0.9 and 1.8 μM in pancreatic cancer cell lines AsPC-1, MIA PaCa-2 and PANC-1, respectively. This compound also exhibited better antiproliferative activities against breast (MCF7), prostate (PC-3), hepatocellular (Hep G2) and lung (A549) cancer cell lines, with IC(50) values lower than 1 μM. The mechanism of action by which these compounds exert their biological effect was evaluated in AsPC-1 cells using the most potent inhibitor synthesized, compound 20. At 1 μM, the cell cycle arrested at the G1 phase with upregulation of p21(waf1). Apoptosis was induced at an inhibitor concentration of 8 μM with upregulation of NOXA and downregulation of c-FLIP. These data indicate that fluorolactone derivatives of ursolic acid have improved antiproliferative activity, acting through arrest of the cell cycle and induction of apoptosis.

Efficient oxidation of oleanolic acid derivatives using magnesium bis(monoperoxyphthalate) hexahydrate (MMPP): A convenient 2-step procedure towards 12-oxo-28-carboxylic acid derivatives

A new, straightforward and high yielding procedure to convert oleanolic acid derivatives into the corresponding δ-hydroxy-γ-lactones, by using the convenient oxidizing agent magnesium bis(monoperoxyphthalate) hexahydrate (MMPP) in refluxing acetonitrile, is reported. In addition, a two-step procedure for the preparation of oleanolic 12-oxo-28-carboxylic acid derivatives directly from Δ(12)-oleananes, without the need for an intermediary work-up, and keeping the same reaction solvent in both steps, is described as applied to the synthesis of 3,12-dioxoolean-28-oic acid.

New applications for bismuth(III) salts in organic synthesis: from bulk chemicals to steroid and terpene chemistry

Bismuth(III) salts are currently considered efficient and "ecofriendly" reagents and catalysts for the development of new applications in organic synthesis. The preparation of bismuth(III) triflate and its analogues is reviewed as well as some of their applications to the synthesis of bulk chemicals via electrophilic addition and cyclization reactions. The use of bismuth(III) salts in the development of new chemical processes involving steroids and terpenes as substrates is also discussed.

The reaction of azoles with 17-chloro-16-formylandrosta-5,16-dien-3β-yl-acetate: synthesis and structural elucidation of novel 16-azolylmethylene-17-oxoandrostanes

The synthesis and structural elucidation, by 1D and 2D NMR and X-ray diffraction techniques, of novel E/Z 16-azolylmethylene-17-oxoandrostanes 2-9 prepared from the Vilsmeier-Hack reaction product 17-chloro-16-formylandrosta-5,16-dien-3β-yl acetate 1 is reported. The reaction proceeds with pyrrole and pyrrole-alike nitrogen heterocycles such as 7-azaindole, indole, and 3-methylindole, in DMF, at 80°C, in the presence of K(2)CO(3), and allowed the attachment of privileged heterocyclic moieties, through the nitrogen atom to the steroid core at C16 via a methine carbon bridge, which is unprecedented in the literature and of potential synthetic and biological interest. Considerations on the possible reaction mechanism are included. All the synthesized compounds are new and are currently being tested for biological activities.

Bismuth(III) reagents in steroid and terpene chemistry

Steroid and terpene chemistry still have a great impact on medicinal chemistry. Therefore, the development of new reactions or “greener” processes in this field is a contemporaneous issue. In this review, the use of bismuth(III) salts, as “ecofriendly” reagents/catalysts, on new chemical processes involving steroids and terpenes as substrates will be focused. Special attention will be given to some mechanistic considerations concerning selected reactions.

3-Oxo-18α-olean-28,13β-olide

The title terpene, C₃₀H₄₆O₃, is a 28,13β-lactone of oleanolic acid prepared with bis­muth trifluoro­methane­sulfonate (OTf), Bi(OTf)₃·xH₂O. All rings are trans-fused. The X-ray study shows the inversion of the orientation of 18-H in the lactonization reaction. A quantum chemical ab-initio Roothaan Hartree–Fock calculation of the equilibrium geometry of the isolated mol­ecule gives values for bond lengths and valency angles in close agreement with experimental values. The calculation also reproduces the observed mol­ecular conformation, with puckering parameters that agree well with those determined from the crystallographic study.

3β-Hy-droxy-lup-20(29)-en-28-yl 1H-imidazole-1-carboxyl-ate

The title triterpene, C(34)H(52)N(2)O(3), is a C-28 carbamate derivative of betulin prepared in a one-step reaction from the commercially available 1,1'-carbonyl-diimidazole (CDI). All rings are fused trans. The X-ray study shows the retention of the configuration of C-28 with respect to the known chiral centres of the molecule. In the crystal, the mol-ecules are O-H⋯O hydrogen bonded via the hy-droxy group and the carbonyl group of the carbamate function into chains running along the c axis. A quantum-mechanical ab initio Roothaan Hartree-Fock calculation of the equilibrium geometry of the isolated mol-ecule gives values for bond-lengths and valency angles close to the experimental values. The calculations also reproduce the mol-ecular conformation well, with calculated puckering parameters that agree well with the observed values.

Synthesis and structure-activity relationship study of novel cytotoxic carbamate and N-acylheterocyclic bearing derivatives of betulin and betulinic acid

Chemical transformation studies were conducted on betulin and betulinic acid, common plant-derived lupane-type triterpenes. The concise synthesis, via a stepwise approach, of betulin and betulinic acid carbamate and N-acylheterocyclic containing derivatives is described. All new compounds, as well as betulinic acid were tested in vitro for their cytotoxic activity. Most of the compounds have shown a better cytotoxic profile than betulinic acid, including the synthesized betulin derivatives. Compounds 25 and 32 were the most promising derivatives, being up to 12-fold more potent than betulinic acid against human PC-3 cell lines (IC(50) values of 1.1 and 1.8 microM, respectively).

19β,28-Ep-oxy-18α-olean-3β-ol

The title triterpene, C₃₀H₅₀O₂, is an 18α-oleanane derivative prepared by the Wagner–Meerwein rearrangement of betulin with Bi(OTf)₃.xH₂O (OTF is trifluoromethanesulfonate). There are two symmetry-independent mol­ecules in the asymmetric unit that show no significant differences concerning bond lengths and angles. The conformation of the six-membered rings is close to a chair form, while the five-membered epoxide rings adopt envelope conformations. All rings are trans-fused. In the crystal, mol­ecules are held together by O—H⋯O hydrogen bonds. A quantum-mechanical ab initio Roothan Hartree–Fock calculation on the isolated mol­ecule gives values for bond lengths and valency angles close to the experimental values. The calculations also reproduce well the mol­ecular conformation with calculated puckering parameters that match well the observed values.

16α,17α-Ep-oxy-5α-hydr-oxy-6β-nitrooxy-20-oxopregnan-3β-yl acetate

The title steroid, C(23)H(33)NO(8), is a pregnane derivative obtained regio-, stereo- and chemoselectively from the ring opening of the corresponding 5α,6α;16α,17α-diepoxide with bis-muth(III) nitrate. There are two symmetry-independent mol-ecules in the asymmetric unit that show no significant differences concerning bond lengths and angles. All rings are trans-fused. The conformations of the six-membered rings are close to chair forms, while the five-membered ring adopts an envelope conformation. The mol-ecules are held together by an extensive O-H⋯O hydrogen-bonding network of chains runnning along the a axis.

6beta-Hydroxy-5beta-methyl-20-oxo-19-norpregn-9(10)-en-3beta-yl acetate

In the title compound, C(23)H(34)O(4), which is an intermediate in the synthesis of pregnane derivatives with a modified skeleton that show potent abortion-inducing activity, the conformation of ring B is close to half-chair due to the presence of both the C=C double bond and the axial 5beta-methyl group. Rings A and C have conformations close to chair, while ring D has a twisted conformation around the bridgehead C-C bond. Molecules are hydrogen bonded via the hydroxyl and acetoxy groups into infinite chains. Quantum-mechanical ab initio Roothan Hartree-Fock calculations show that crystal packing might be responsible for the low values of the angles between rings A and B, and between ring A and rings C and D, as well as for a different steric position of the methyl ketone side chain compared to the geometry of the free molecule.

3-Oxoandrosta-4,6-dien-17beta-yl 2-methyl-1H-imidazole-1-carboxylate and 3-oxo-5alpha-androst-17beta-yl 2-methyl-1H-imidazole-1-carboxylate: C-H...pi and pi-pi intermolecular interactions

The title compounds, C(24)H(30)N(2)O(3), (I), and C(24)H(34)N(2)O(3), (II), both contain an androstane backbone and a 2-methylimidazole-1-carboxylate moiety at the 17-position. Compound (I) contains two symmetry-independent molecules (denoted 1 and 2), while compound (II) contains just one molecule in the asymmetric unit. The C-C-O-C torsion angle that reflects the twisting of the 2-methylimidazole-1-carboxylate moiety from the mean steroid plane is 143.1 (2) degrees for molecule 1 of (I), 73.1 (3) degrees for molecule 2 of (I) and 86.63 (17) degrees for (II). The significance of this study lies in its observation of significant differences in both molecular conformation and supramolecular aggregation between the molecules of the title compounds. The solid-state conformations compared with those obtained theoretically from ab initio methods for the isolated molecules show large differences, especially in the orientation of the methylimidazole substituent.