Solution-phase synthesis and biological evaluation of triostin A and its analogues

Marine-Derived Leads as Anticancer Candidates by Disrupting Hypoxic Signaling through Hypoxia-Inducible Factors Inhibition

The inadequate vascularization seen in fast-growing solid tumors gives rise to hypoxic areas, fostering specific changes in gene expression that bolster tumor cell survival and metastasis, ultimately leading to unfavorable clinical prognoses across different cancer types. Hypoxia-inducible factors (HIF-1 and HIF-2) emerge as druggable pivotal players orchestrating tumor metastasis and angiogenesis, thus positioning them as prime targets for cancer treatment. A range of HIF inhibitors, notably natural compounds originating from marine organisms, exhibit encouraging anticancer properties, underscoring their significance as promising therapeutic options. Bioprospection of the marine environment is now a well-settled approach to the discovery and development of anticancer agents that might have their medicinal chemistry developed into clinical candidates. However, despite the massive increase in the number of marine natural products classified as 'anticancer leads,' most of which correspond to general cytotoxic agents, and only a few have been characterized regarding their molecular targets and mechanisms of action. The current review presents a critical analysis of inhibitors of HIF-1 and HIF-2 and hypoxia-selective compounds that have been sourced from marine organisms and that might act as new chemotherapeutic candidates or serve as templates for the development of structurally similar derivatives with improved anticancer efficacy.

Design, Synthesis, and Conformation-Activity Study of Unnatural Bridged Bicyclic Depsipeptides as Highly Potent Hypoxia Inducible Factor-1 Inhibitors and Antitumor Agents

By carrying out structural modifications based on the bicyclic peptide structure of echinomycin, we successfully synthesized various powerful antitumor derivatives. The ring conformation in the obtained compounds was restricted by cross-linking with an unnatural bond. The prepared derivatives were demonstrated to strongly suppress the hypoxia inducible factor (HIF)-1 transcriptional activation and hypoxia induction of HIF-1 protein expression. Particularly, alkene-bridged derivative 12 exhibited remarkably potent cytotoxicity (IC₅₀ = 0.22 nM on the MCF-7 cell line) and HIF-1 inhibition (IC₅₀ = 0.09 nM), which considerably exceeded those of echinomycin. Conformational analyses and molecular modeling studies revealed that the biological activities were enhanced following restriction of the conformation by cross-linking through a metabolically stable and rigid bridge bond. In addition, we proposed a new globular conformation stabilized by intramolecular π stacking that can contribute to the biological effects of bicyclic depsipeptides. The developments presented in the current study serve as a useful guide to expand the chemical space of peptides in drug discovery.

Natural Product Bis-Intercalator Depsipeptides as a New Class of Payloads for Antibody-Drug Conjugates

A potent class of DNA-damaging agents, natural product bis-intercalator depsipeptides (NPBIDs), was evaluated as ultrapotent payloads for use in antibody-drug conjugates (ADCs). Detailed investigation of potency (both in cells and via biophysical characterization of DNA binding), chemical tractability, and in vitro and in vivo stability of the compounds in this class eliminated a number of potential candidates, greatly reducing the complexity and resources required for conjugate preparation and evaluation. This effort yielded a potent, stable, and efficacious ADC, PF-06888667, consisting of the bis-intercalator, SW-163D, conjugated via an N-acetyl-lysine-valine-citrulline- p-aminobenzyl alcohol- N, N-dimethylethylenediamine (AcLysValCit-PABC-DMAE) linker to an engineered variant of the anti-Her2 mAb, trastuzumab, catalyzed by transglutaminase.

Targeting Transcription Factors for Cancer Treatment

Transcription factors are involved in a large number of human diseases such as cancers for which they account for about 20% of all oncogenes identified so far. For long time, with the exception of ligand-inducible nuclear receptors, transcription factors were considered as “undruggable” targets. Advances knowledge of these transcription factors, in terms of structure, function (expression, degradation, interaction with co-factors and other proteins) and the dynamics of their mode of binding to DNA has changed this postulate and paved the way for new therapies targeted against transcription factors. Here, we discuss various ways to target transcription factors in cancer models: by modulating their expression or degradation, by blocking protein/protein interactions, by targeting the transcription factor itself to prevent its DNA binding either through a binding pocket or at the DNA-interacting site, some of these inhibitors being currently used or evaluated for cancer treatment. Such different targeting of transcription factors by small molecules is facilitated by modern chemistry developing a wide variety of original molecules designed to specifically abort transcription factor and by an increased knowledge of their pathological implication through the use of new technologies in order to make it possible to improve therapeutic control of transcription factor oncogenic functions.

Hypoxia-inducible factor-1 (HIF-1) inhibitors from the last decade (2007 to 2016): A "structure-activity relationship" perspective

Tumor hypoxia is a common feature in most solid tumors and is associated with overexpression of the hypoxia response pathway. Overexpression of the hypoxia-inducible factor (HIF-1) protein leads to angiogenesis, metastasis, apoptosis resistance, and many other pro-tumorigenic responses in cancer development. HIF-1 is a promising target in cancer drug development to increase the patient's response to chemotherapy and radiotherapy as well as the survival rate of cancer patients. Since up to 1% of genes are hypoxia-sensitive, a target-specific HIF-1 inhibitor may be a better clinical candidate in cancer drug discovery. Though no HIF-1 inhibitor is clinically available to date, a lot of effort has been applied during the last decade in search of potent HIF-1 inhibitors. In this review, we will summarize the structure-activity relationship of ten different chemotypes reported to be HIF-1 inhibitors in the last decade (2007-2016), their mechanisms of action for HIF-1 inhibition, progress in the way of target-specific inhibitors, and problems associated with current inhibitors. It is anticipated that the results of these research on the medicinal chemistry of HIF-1 inhibitors will provide decent information in the design and development of future inhibitors.

Design, synthesis, molecular docking of new lipophilic acetamide derivatives affording potential anticancer and antimicrobial agents

Fifteen new substituted N-2-(2-oxo-3-phenylquinoxalin-1(2H)-yl) acetamides 5a-f, 6a-f, and 8a-c were synthesized by reacting ethyl 2-(2-oxo-3-phenylquinoxalin-1(2H)-yl)acetate with various primary amines including benzylamines, sulfonamides, and amino acids. The in vitro antimicrobial screening of the target compounds was screened to assess their antibacterial and antifungal activity. As a result, seven compounds namely; 5a, 5c, 5d, 6a, 6c, 8b and 8c showed a promising broad spectrum antibacterial activity against both Gram-positive and Gram-negative strains. Among these, the analogs 5c and 6d were nearly as equiactive as ciprofloxacin drug. Meanwhile, four compounds namely; 5c, 6a, 6f and 8c exhibited appreciable antifungal activity with MIC values range 33-40 mg/mL comparable with clotrimazole (MIC 25 mg/mL). In addition, the anticancer effects of the synthesized compounds were evaluated against three cancer lines. The data obtained revealed the benzylamines and sulpha derivatives were the most active compounds especially 5f and 6f ones. Further EGFR enzymatic investigation was carried out for these most active compounds 5f and 6f resulting in inhibitory activity by 1.89 and 2.05 µM respectively. Docking simulation was performed as a trial to study the mechanisms and binding modes of these compounds toward the enzyme target, EGFR protein kinase enzyme. The results revealed good compounds placement in the active sites and stable interactions similar to the co-crystallized reference ligand. Collectively, the analogs 5f and 6f could be further utilized and optimized as good cytotoxic agents.

Echinomycin inhibits adipogenesis in 3T3-L1 cells in a HIF-independent manner

Obesity is a risk factor for many diseases including diabetes, cancer, cardiovascular disease, and chronic kidney disease. Obesity is characterized by the expansion of white adipose tissue (WAT). Hypertrophy and hyperplasia of adipocytes cause tissue hypoxia followed by inflammation and fibrosis. Its trigger, preadipocyte differentiation into mature adipocytes, is finely regulated by transcription factors, signal molecules, and cofactors. We found that echinomycin, a potent HIF-1 inhibitor, completely inhibited adipogenesis in 3T3-L1 WAT preadipocytes by affecting the early phase of mitotic clonal expansion. The dose required to exert the effect was surprisingly low and the time was short. Interestingly, its inhibitory effect was independent of HIF-1 pathways. Time-course DNA microarray analysis of drug-treated and untreated preadipocytes extracted a major transcription factor, CCAAT/enhancer-protein β, as a key target of echinomycin. Echinomycin also inhibited adipogenesis and body weight gain in high fat diet mice. These findings highlight a novel role of echinomycin in suppressing adipocyte differentiation and offer a new therapeutic strategy against obesity and diabetes.

Hypoxia inducible factor down-regulation, cancer and cancer stem cells (CSCs): ongoing success stories

In cancers, hypoxia inducible factor 1 (HIF-1) is an over-expressed transcription factor, which regulates a large set of genes involved in tumour vascularization, metastases, and cancer stem cells (CSCs) formation and self-renewal. This protein has been identified as a relevant target in oncology and several HIF-1 modulators are now marketed or in advanced clinical trials. The purpose of this review is to summarize the advances in the understanding of its regulation and its inhibition, from the medicinal chemist point of view. To this end, we selected in the recent literature relevant examples of "hit" compounds, including small-sized organic molecules, pseudopeptides and nano-drugs, exhibiting in vitro and/or in vivo both anti-HIF-1 and anti-tumour activities. Whenever possible, a particular emphasis has been dedicated to compounds that selectively target CSCs.