Correlation of F0F1-ATPase inhibition and antiproliferative activity of apoptolidin analogues

Antimetastatic Activity of Apoptolidin A by Upregulation of N-Myc Downstream-Regulated Gene 1 Expression in Human Colorectal Cancer Cells

Colorectal cancer (CRC) is one of the most prevalent tumors with high metastatic potential; consequently, finding new drug candidates that suppress tumor metastasis is essential. Apoptolidin A is a macrocyclic lactone produced by Amycolatopsis sp. DW02G. It exhibits significant cytotoxicity against several cancer cell lines, but its effects on CRC cells remain unknown. Therefore, the present study investigated the antiproliferative and antimetastatic activities of apoptolidin A and its underlying molecular mechanisms in CRC cells. Apoptolidin A effectively inhibited CRC cell growth and colony formation. The induction of G0/G1 phase cell cycle arrest was associated with the downregulation of cyclin D1 and CDK4/6 expression. Long-term exposure to apoptolidin A also induced apoptosis as confirmed by the downregulation and upregulation of Bcl-2 and Bax expression, respectively. Moreover, apoptolidin A effectively upregulated the suppressed expression of N-Myc downstream-regulated gene 1 (NDRG1), a tumor suppressor gene, in a concentration-dependent manner in CRC cells. The antimetastatic potential of apoptolidin A was also correlated with the expression of epithelial–mesenchymal transition (EMT) biomarkers, including the upregulation of E-cadherin and downregulation of N-cadherin, vimentin, snail, and MMP9 in CRC cells. These findings suggest that apoptolidin A exerts antiproliferative and antimetastatic activities by regulating the NDRG1-activated EMT pathway in CRC cells.

F1Fo adenosine triphosphate (ATP) synthase is a potential drug target in non-communicable diseases

F₁F_o adenosine triphosphate (ATP) synthase, also known as the complex V, is the central ATP-producing unit in the cells arranged in the mitochondrial and plasma membranes. F₁F_o ATP synthase also regulates the central metabolic processes in the human body driven by proton motive force (Δp). Numerous studies have immensely contributed toward highlighting its regulation in improving energy homeostasis and maintaining mitochondrial integrity, which otherwise gets compromised in illnesses. Yet, its role in the implication of non-communicable diseases remains unknown. F₁F_o ATP synthase dysregulation at gene level leads to reduced activity and delocalization in the cristae and plasma membranes, which is directly associated with non-communicable diseases: cardiovascular diseases, diabetes, neurodegenerative disorders, cancer, and renal diseases. Individual subunits of the F₁F_o ATP synthase target ligand-based competitive or non-competitive inhibition. After performing a systematic literature review to understand its specific functions and its novel drug targets, the present article focuses on the central role of F₁F_o ATP synthase in primary non-communicable diseases. Next, it discusses its involvement through various pathways and the effects of multiple inhibitors, activators, and modulators specific to non-communicable diseases with a futuristic outlook.

Mitochondrial Side Effects of Surgical Prophylactic Antibiotics Ceftriaxone and Rifaximin Lead to Bowel Mucosal Damage

Despite their clinical effectiveness, a growing body of evidence has shown that many classes of antibiotics lead to mitochondrial dysfunction. Ceftriaxone and Rifaximin are first choice perioperative antibiotics in gastrointestinal surgery targeting fundamental processes of intestinal bacteria; however, may also have negative consequences for the host cells. In this study, we investigated their direct effect on mitochondrial functions in vitro, together with their impact on ileum, colon and liver tissue. Additionally, their impact on the gastrointestinal microbiome was studied in vivo, in a rat model. Rifaximin significantly impaired the oxidative phosphorylation capacity (OxPhos) and leak respiration in the ileal mucosa, in line with increased oxidative tissue damage and histological changes following treatment. Ceftriaxone prophylaxis led to similar changes in the colon mucosa. The composition and diversity of bacterial communities differed extensively in response to antibiotic pre-treatment. However, the relative abundances of the toxin producing species were not increased. We have confirmed the harmful effects of prophylactic doses of Rifaximin and Ceftriaxone on the intestinal mucosa and that these effects were related to the mitochondrial dysfunction. These experiments raise awareness of mitochondrial side effects of these antibiotics that may be of clinical importance when evaluating their adverse effects on bowel mucosa.

Apoptolidin family glycomacrolides target leukemia through inhibition of ATP synthase

Cancer cells have long been recognized to exhibit unique bioenergetic requirements. The apoptolidin family of glycomacrolides are distinguished by their selective cytotoxicity towards oncogene-transformed cells, yet their molecular mechanism remains uncertain. We used photoaffinity analogs of the apoptolidins to identify the F₁ subcomplex of mitochondrial ATP synthase as the target of apoptolidin A. Cryogenic electron microscopy (cryo-EM) of apoptolidin and ammocidin-ATP synthase complexes revealed a novel shared mode of inhibition that was confirmed by deep mutational scanning of the binding interface to reveal resistance mutations which were confirmed using CRISPR-Cas9. Ammocidin A was found to suppress leukemia progression in vivo at doses that were tolerated with minimal toxicity. The combination of cellular, structural, mutagenesis, and in vivo evidence defines the mechanism of action of apoptolidin family glycomacrolides and establishes a path to address oxidative phosphorylation-dependent cancers.

Defueling the cancer: ATP synthase as an emerging target in cancer therapy

Reprogramming of cellular metabolism is a hallmark of cancer. Mitochondrial ATP synthase (MAS) produces most of the ATP that drives the cell. High expression of the MAS-composing proteins is found during cancer and is linked to a poor prognosis in glioblastoma, ovarian cancer, prostate cancer, breast cancer, and clear cell renal cell carcinoma. Cell surface-expressed ATP synthase, translocated from mitochondrion to cell membrane, involves the angiogenesis, tumorigenesis, and metastasis of cancer. ATP synthase has therefore been considered a therapeutic target. We review recent various ATP synthase inhibitors that suppress tumor growth and are being tested for the clinic.

Stereochemistries and Biological Properties of Oligomycin A Diels-Alder Adducts

Oligomycin A is a potent antibiotic and antitumor agent. However, its applications are restricted by its high toxicity and low bioavailability. In this study, we obtained Oligomycin A Diels-Alder adducts with benzoquinone and N-benzylmaleimide and determined their absolute configurations by combining ¹H and ROESY NMR data with molecular mechanics conformational analysis and quantum chemical reaction modeling. The latter showed that adduct stereochemistry is controlled by hydrogen bonding of the Oligomycin A side-chain isopropanol moiety with the carbonyl group of the dienophile. Biological studies showed that the Diels-Alder modification of the Oligomycin A diene system resulted in a complex antiproliferative potential pattern. The synthesized adducts were determined to be more active against the triple-negative (ERα, PR, and HER2 negative) breast cancer cell line MDA-MB-231 and lung carcinoma cell line A-549 compared to Oligomycin A. Meanwhile, Oligomycin A was more potent against myeloid leukemia cell line K-562 and breast carcinoma cell line MCF-7 than its derivatives. Thus, modification of the diene moiety of Oligomycin A is a promising strategy for developing novel antitumor agents based on its scaffold.

Inhibitors of F1F0-ATP synthase enzymes for the treatment of tuberculosis and cancer

The spectacular success of the mycobacterial F₁F₀-ATP synthase inhibitor bedaquiline for the treatment of drug-resistant tuberculosis has generated wide interest in the development of other inhibitors of this enzyme. Work in this realm has included close analogues of bedaquiline with better safety profiles and 'bedaquiline-like' compounds, some of which show potent antibacterial activity in vitro although none have yet progressed to clinical trials. The search has lately extended to a range of new scaffolds as potential inhibitors, including squaramides, diaminoquinazolines, chloroquinolines, dihydropyrazolo[1,5-a]pyrazin-4-ones, thiazolidinediones, diaminopyrimidines and tetrahydroquinolines. Because of the ubiquitous expression of ATP synthase enzymes, there has also been interest in inhibitors of other bacterial ATP synthases, as well as inhibitors of human mitochondrial ATP synthase for cancer therapy. The latter encompass both complex natural products and simpler small molecules. The review seeks to demonstrate the breadth of the structural types of molecules able to effectively inhibit the function of variants of this intriguing enzyme.

Why All the Fuss about Oxidative Phosphorylation (OXPHOS)?

Certain subtypes of cancer cells require oxidative phosphorylation (OXPHOS) to survive. Increased OXPHOS dependency is frequently a hallmark of cancer stem cells and cells resistant to chemotherapy and targeted therapies. Suppressing the OXPHOS function might also influence the tumor microenvironment by alleviating hypoxia and improving the antitumor immune response. Thus, targeting OXPHOS is a promising strategy to treat various cancers. A growing arsenal of therapeutic agents is under development to inhibit this biological process. This Perspective provides an overview of the structure and function of OXPHOS complexes, their biological functions in cancer, relevant research tools and models, as well as the limitations of OXPHOS as drug targets. We also focus on the current development status of OXPHOS inhibitors and potential therapeutic strategies to strengthen their clinical applications.

Natural products and other inhibitors of F1FO ATP synthase

F₁F_O ATP synthase is responsible for the production of >95% of all ATP synthesis within the cell. Dysregulation of its expression, activity or localization is linked to various human diseases including cancer, diabetes, and Alzheimer's and Parkinson's disease. In addition, ATP synthase is a novel and viable drug target for the development of antimicrobials as evidenced by bedaquiline, which was approved in 2012 for the treatment of tuberculosis. Historically, natural products have been a rich source of ATP synthase inhibitors that help unravel the role of F₁F_O ATP synthase in cellular bioenergetics. During the last decade, new modulators of ATP synthase have been discovered through the isolation of novel natural products as well as through a ligand-based drug design process. In addition, new data has been obtained with regards to the structure and function of ATP synthase under physiological and pathological conditions. Crystal structure studies have provided a significant insight into the rotary function of the enzyme and may provide additional opportunities to design a new generation of inhibitors. This review provides an update on recently discovered ATP synthase modulators as well as an update on existing scaffolds.

A Therapeutic Role for the F1FO-ATP Synthase

Recently, the F₁F_O-ATP synthase, due to its dual role of life enzyme as main adenosine triphosphate (ATP) maker and of death enzyme, as ATP dissipator and putative structural component of the mitochondrial permeability transition pore (mPTP), which triggers cell death, has been increasingly considered as a drug target. Accordingly, the enzyme offers new strategies to counteract the increased antibiotic resistance. The challenge is to find or synthesize compounds able to discriminate between prokaryotic and mitochondrial F₁F_O-ATP synthase, exploiting subtle structural differences to kill pathogens without affecting the host. From this perspective, the eukaryotic enzyme could also be made refractory to macrolide antibiotics by chemically produced posttranslational modifications. Moreover, because the mitochondrial F₁F_O-ATPase activity stimulated by Ca²⁺ instead of by the natural modulator Mg²⁺ is most likely involved in mPTP formation, effectors preferentially targeting the Ca²⁺-activated enzyme may modulate the mPTP. If the enzyme involvement in the mPTP is confirmed, Ca²⁺-ATPase inhibitors may counteract conditions featured by an increased mPTP activity, such as neurodegenerative and cardiovascular diseases and physiological aging. Conversely, mPTP opening could be pharmacologically stimulated to selectively kill unwanted cells. On the basis of recent literature and promising lab findings, the action mechanism of F₁ and F_O inhibitors is considered. These molecules may act as enzyme modifiers and constitute new drugs to kill pathogens, improve compromised enzyme functions, and limit the deathly enzyme role in pathologies. The enzyme offers a wide spectrum of therapeutic strategies to fight at the molecular level diseases whose treatment is still insufficient or merely symptomatic.

Applications of Nonenzymatic Catalysts to the Alteration of Natural Products

The application of small molecules as catalysts for the diversification of natural product scaffolds is reviewed. Specifically, principles that relate to the selectivity challenges intrinsic to complex molecular scaffolds are summarized. The synthesis of analogues of natural products by this approach is then described as a quintessential "late-stage functionalization" exercise wherein natural products serve as the lead scaffolds. Given the historical application of enzymatic catalysts to the site-selective alteration of complex molecules, the focus of this Review is on the recent studies of nonenzymatic catalysts. Reactions involving hydroxyl group derivatization with a variety of electrophilic reagents are discussed. C-H bond functionalizations that lead to oxidations, aminations, and halogenations are also presented. Several examples of site-selective olefin functionalizations and C-C bond formations are also included. Numerous classes of natural products have been subjected to these studies of site-selective alteration including polyketides, glycopeptides, terpenoids, macrolides, alkaloids, carbohydrates, and others. What emerges is a platform for chemical remodeling of naturally occurring scaffolds that targets virtually all known chemical functionalities and microenvironments. However, challenges for the design of very broad classes of catalysts, with even broader selectivity demands (e.g., stereoselectivity, functional group selectivity, and site-selectivity) persist. Yet, a significant spectrum of powerful, catalytic alterations of complex natural products now exists such that expansion of scope seems inevitable. Several instances of biological activity assays of remodeled natural product derivatives are also presented. These reports may foreshadow further interdisciplinary impacts for catalytic remodeling of natural products, including contributions to SAR development, mode of action studies, and eventually medicinal chemistry.

Succinylated Apoptolidins from Amycolatopsis sp. ICBB 8242

Two new apoptolidins, 2'-O-succinyl-apoptolidin A (11) and 3'-O-succinyl-apoptolidin A (12), were isolated from the culture broth of an Indonesian Amycolatopsis sp. ICBB 8242. These compounds inhibit the proliferation and viability of human H292 and HeLa cells. However, in contrast to apoptolidin A (1), they do not inhibit cellular respiration in H292 cells. It is proposed that apoptolidins are produced and secreted in their succinylated forms and 1 is the hydrolysis product of 11 and 12.

A novel acyclic oligomycin A derivative formed via retro-aldol rearrangement of oligomycin A

The antibiotic oligomycin A in the presence of K(2)CO(3) and n-Bu(4)NHSO(4) in chloroform in phase-transfer conditions afforded a novel derivative through the initial retro-aldol fragmentation of the 8,9 bond, followed by further transformation of the intermediate aldehyde. NMR, MS and quantum chemical calculations showed that the novel compound is the acyclic oligomycin A derivative, in which the 8,9 carbon bond is disrupted and two polyfunctional branches are connected with spiroketal moiety in positions C-23 and C-25. The tri-O-acetyl derivative of the novel derivative was prepared. The acyclic oligomycin A derivative retained the ability to induce apoptosis in tumor cells at low micromolar concentrations, whereas its antimicrobial potencies decreased substantially. The derivative virtually lost the inhibitory activity against F(0)F(1) ATP synthase-containing proteoliposomes, strongly suggesting the existence of the target(s) beyond F(0)F(1) ATP synthase that is important for the antitumor potency of oligomycin A.

Biosynthesis of the Apoptolidins in Nocardiopsis sp. FU 40

The apoptolidins are 20/21-membered macrolides produced by Nocardiopsis sp. FU40. Several members of this family are potent and remarkably selective inducers of apoptosis in cancer cell lines, likely via a distinct mitochondria associated target. To investigate the biosynthesis of this natural product, the complete genome of the apoptolidin producer Nocardiopsis sp. FU40 was sequenced and a 116 Kb region was identified containing a putative apoptolidin biosynthetic gene cluster. The apoptolidin gene cluster comprises a type I polyketide synthase, with 13 homologating modules, apparently initiated in an unprecedented fashion via transfer from a methoxymalonyl-acyl carrier protein loading module. Spanning approximately 39 open reading frames, the gene cluster was cloned into a series of overlapping cosmids and functionally validated by targeted gene disruption experiments in the producing organism. Disruption of putative PKS and P(450) genes delineated the roles of these genes in apoptolidin biosynthesis and chemical complementation studies demonstrated intact biosynthesis peripheral to the disrupted genes. This work provides insight into details of the biosynthesis of this biologically significant natural product and provides a basis for future mutasynthetic methods for the generation of non-natural apopotolidins.

Light-induced isomerization of apoptolidin a leads to inversion of C2-C3 double bond geometry

The isolation, characterization, and cytotoxicity against H292 cells of apoptolidin G are reported. Apoptolidin G is shown to be derived by a light-induced isomerization of the C2-C3 carbon-carbon double bond of apoptolidin A.

Apoptolidins E and F, new glycosylated macrolactones isolated from Nocardiopsis sp

Two new glycosylated macrolactones, apoptolidins E (5) and F (6), were isolated from fermentation of the actinomycete Nocardiopsis sp. and their structures assigned. Lacking the C16 and C20 oxygens of apoptolidin A (1), these macrolides are also the first members of this family to display a 4-O-methyl-l-rhamnose at C9 rather than a 6-deoxy-4-O-methyl-l-glucose.

An approach to the site-selective diversification of apoptolidin A with peptide-based catalysts

We report the application of peptide-based catalysts to the site-selective modification of apoptolidin A (1), an agent that displays remarkable selectivity for inducing apoptosis in E1A-transformed cell lines. Key to the approach was the development of an assay suitable for the screening of dozens of catalysts in parallel reactions that could be conducted using only microgram quantities of the starting material. Employing this assay, catalysts (e.g., 11 and ent-11) were identified that afforded unique product distributions, distinct from the product mixtures produced when a simple catalyst (N,N-dimethyl-4-aminopyridine (10)) was employed. Preparative reactions were then carried out with the preferred catalysts so that unique, homogeneous apoptolidin analogues could be isolated and characterized. From these studies, three new apoptolidin analogues were obtained (12-14), each differing from the other in either the location of acyl group substituents or the number of acetate groups appended to the natural product scaffold. Biological evaluation of the new apoptolidin analogues was then conducted using growth inhibition assays based on the H292 human lung carcinoma cell line. The new analogues exhibited activities comparable to apoptolidin A.

Combined chemical and biosynthetic route to access a new apoptolidin congener

Glycosylation of a synthetic aglycone using precursor-directed biosynthesis is facilitated by a chemical ketosynthase "knockdown" of the apoptolidin producer Nocardiopsis sp. This synthetic approach facilitated the preparation of an unnatural disaccharide derivative of apoptolidin D that substantially restores cytotoxicity against H292 cells and deconvolutes the role of the decorating sugars in apoptolidin bioactivity.

Synthesis and evaluation of the cytotoxicity of apoptolidinones A and D

Apoptolidins A-D are microbial secondary metabolites shown to be selectively cytotoxic against several cancer cell lines and noncytotoxic against normal cells. Total syntheses of apoptolidinones A and D are reported. The efficient synthetic strategy leading to the apoptolidinones features construction of the common 20-membered macrolactone by an intramolecular Suzuki reaction and stereocontrolled aldol reactions establishing the C19/C20 and C22/C23 stereocenters. In contrast to apoptolidin A, the aglycones apoptolidinone A and D were shown to be noncytotoxic when evaluated against human lung cancer cells (H292).

Mitochondrial drugs

Mitochondria are cellular organelles that perform pivotal functions essential for ATP production, homeostasis, and metabolism. Moreover, mitochondria are integral to a variety of cell death and survival pathways. These roles identify mitochondria as a potential target for drugs to treat metabolic and hyperproliferative diseases. Differences in the redox state of pathogenic versus non-pathogenic cells may be exploited to achieve selective anti-proliferative and cytotoxic activity against target cell populations. Pro-oxidant drugs, such as Trisenox and Elesclomol, are demonstrating clinical utility in the treatment of cancer. Results obtained with Bz-423 in mice demonstrate the potential for mitochondria-targeted drugs to control disorders of immune function. Research associating an elevated oxidant state with mitochondrial damage, degenerative disease, and aging dictates the need for a better understanding of when and how pharmacological manipulation of mitochondrial function provides most therapeutic benefit.

Recent advances in the synthesis of carbohydrate analogs

With 3,3,4,4-tetraethoxy-1-butyne as starting material, we are investigating the preparation of a range of alkylated, partially deoxygenated carbohydrate derivatives. In the lecture, an overview of recent results was given, with particular emphasis on progress in the synthesis of perfluoroalkyl-substituted deoxygenated analogs. Since many of the results discussed in the lecture have recently been or are in the process of being published, this paper focuses on our recent advances in preparing fluorinated analogs.