Carbon Chain Length in a Novel Anticancer Aryl-Urea Fatty Acid Modulates Mitochondrial Targeting, Reactive Oxygen Species Production and Cell Killing.

The cancer cell mitochondrion could be a promising target for the development of new anticancer agents. 16-([3-chloro-5-(trifluoromethyl)-phenyl]carbamoylamino)hexadecanoic acid (2) is a novel aryl-urea fatty acid that targets the mitochondrion in MDA-MB-231 breast cancer cells and activates cell death. In the present study, the relationships between alkyl chain length in 2 analogues, mitochondrial disruption and cell killing were evaluated. The chain-contracted C13-analogue 7 c optimally disrupted the mitochondrial membrane potential (IC50 4.8±0.8 µM). In addition, annexin V-FITC/7-AAD assays demonstrated that 7 c was the most effective cell killing analogue and C11 BODIPY (581/591) assays demonstrated that 7 c was also most effective in generating reactive oxygen species in MDA-MB-231 cells. Together, carbon chain length is a key factor that determines the capacity of 2 analogues to disrupt the mitochondrial membrane, induce the production of reactive oxygen species and kill breast cancer cells. As an aryl-urea with enhanced activity and improved drug-like properties, 7 c may be a suitable lead molecule for entry into a program of development of these molecules as anticancer agents.

Protonophoric and mitochondrial uncoupling activity of aryl-carbamate substituted fatty acids.

Aryl-urea substituted fatty acids are protonophores and mitochondrial uncouplers that utilise a urea-based synthetic anion transport moiety to carry out the protonophoric cycle. Herein we show that replacement of the urea group with carbamate, a functional group not previously reported to possess anion transport activity, produces analogues that retain the activity of their urea counterparts. Thus, the aryl-carbamate substituted fatty acids uncouple oxidative phosphorylation and inhibit ATP production by collapsing the mitochondrial proton gradient. Proton transport proceeds via self-assembly of the deprotonated aryl-carbamates into membrane permeable dimeric species, formed by intermolecular binding of the carboxylate group to the carbamate moiety. These results highlight the anion transport capacity of the carbamate functional group.

Structure-Activity Relationship and Mechanistic Studies of Bisaryl Urea Anticancer Agents Indicate Mitochondrial Uncoupling by a Fatty Acid-Activated Mechanism.

Targeting the cancer cell mitochondrion is a promising approach for developing novel anticancer agents. The experimental anticancer agent N,N'-bis(3,5-dichlorophenyl)urea (SR4) induces apoptotic cell death in several cancer cell lines by uncoupling mitochondrial oxidative phosphorylation (OxPhos) using a protein-free mechanism. However, the precise mechanism by which SR4 depolarizes mitochondria is unclear because SR4 lacks an acidic functional group typically found in protein-independent uncouplers. Recently, it was shown that structurally related thioureas can facilitate proton transport across lipid bilayers by a fatty acid-activated mechanism, in which the fatty acid acts as the site of protonation/deprotonation and the thiourea acts as an anion transporter that shuttles deprotonated fatty acids across the phospholipid bilayer to enable proton leak. In this paper, we show that SR4-mediated proton transport is enhanced by the presence of free fatty acids in the lipid bilayer, indicating that SR4 uncouples mitochondria through the fatty acid-activated mechanism. This mechanistic insight was used to develop a library of substituted bisaryl ureas for structure-activity relationship studies and subsequent cell testing. It was found that lipophilic electron-withdrawing groups on bisaryl ureas enhanced electrogenic proton transport via the fatty acid-activated mechanism and had the capacity to depolarize mitochondria and reduce the viability of MDA-MB-231 breast cancer cells. The most active compound in the series reduced cell viability with greater potency than SR4 and was more effective at inhibiting adenosine triphosphate production.

Mitochondrial uncoupler SHC517 reverses obesity in mice without affecting food intake.

AIMS: Mitochondrial uncouplers decrease caloric efficiency and have potential therapeutic benefits for the treatment of obesity and related metabolic disorders. Herein we investigate the metabolic and physiologic effects of a recently identified small molecule mitochondrial uncoupler named SHC517 in a mouse model of diet-induced obesity. METHODS: SHC517 was administered as an admixture in food. The effect of SHC517 on in vivo energy expenditure and respiratory quotient was determined by indirect calorimetry. A dose-finding obesity prevention study was performed by starting SHC517 treatment concomitant with high fat diet for a period of 12 days. An obesity reversal study was performed by feeding mice western diet for 4 weeks prior to SHC517 treatment for 7 weeks. Biochemical assays were used to determine changes in glucose, insulin, triglycerides, and cholesterol. SHC517 concentrations were determined by mass spectrometry. RESULTS: SHC517 increased lipid oxidation without affecting body temperature. SHC517 prevented diet-induced obesity when administered at 0.05% and 0.1% w/w in high fat diet and reversed established obesity when tested at the 0.05% dose. In the obesity reversal model, SHC517 restored adiposity to levels similar to chow-fed control mice without affecting food intake or lean body mass. SHC517 improved glucose tolerance and fasting glucose levels when administered in both the obesity prevention and obesity reversal modes. CONCLUSIONS: SHC517 is a mitochondrial uncoupler with potent anti-obesity and insulin sensitizing effects in mice. SHC517 reversed obesity without altering food intake or compromising lean mass, effects that are highly sought-after in anti-obesity therapeutics.

Expansion of the structure-activity relationship of branched chain fatty acids: Effect of unsaturation and branching group size on anticancer activity.

Branched chain fatty acids (BCFAs) are a class of fatty acid with promising anticancer activity. The BCFA 13-methyltetradecanoic acid (13-MTD) inhibits tumour growth in vivo without toxicity but efficacy is limited by moderate potency, a property shared by all known BCFAs. The mechanism of action of BCFAs has not been fully elucidated, and in the absence of a clearly defined target optimisation of BCFA potency must rely on structure-activity relationships. Our current understanding of the structural features that promote BCFA anticancer activity is limited by the low structural diversity of reported BCFAs.The aim of this study was to examine the effects of two new structural modifications- unsaturation and branching group size- on BCFA activity. Thus, homologous series of saturated and cis-Δ11 unsaturated BCFAs were synthesised bearing methyl, ethyl, propyl and butyl branching groups, and were screened in vitro for activity against three human cancer cell lines. Potencies of the new BCFAs were compared to 13-MTD and an unbranched monounstaurated fatty acid (MUFA) bearing a cis-Δ11 double bond. The principal findings to emerge were that the anticancer activity of BCFAs was adversly affected by larger branching groups but significantly improved by incorporation of a cis-Δ11 double bond into the BCFA alkyl chain. This study provides new structure-activity relationship insights that may be used to develop BCFAs with improved potency and therapeutic potential.

Carbon Chain Length Modulates MDA-MB-231 Breast Cancer Cell Killing Mechanisms by Mitochondrially Targeted Aryl-Urea Fatty Acids.

Targeting the tumor cell mitochondrion could produce novel anticancer agents. We designed an aryl-urea fatty acid (1 g; 16({[4-chloro-3-(trifluoromethyl)phenyl]carbamoyl}amino)hexadecanoic acid) that disrupted the mitochondrion and decreased MDA-MB-231 breast cancer cell viability. To optimize the aryl-ureas the present study evaluated mitochondrial targeting by 1 g analogues containing alkyl chains between 10-17 carbons. Using the dye JC-1, the C12-C17 analogues efficiently disrupted the mitochondrial membrane potential (IC50 s 3.5±1.2 to 7.6±1.1 µM) and impaired ATP production; shorter analogues were less active. 7-Aminoactinomycin D/annexin V staining and flow cytometry showed that these agents activated the killing mechanisms of necrosis and apoptosis to varying extents (7-aminoactinomycin D/annexin V staining ratios 4.3-6.0). Indeed, 1 g and its C17 analogue preferentially activated necrosis and apoptosis, respectively (ratios 2.1 and 16). Taken together, alkyl chain length is a determinant of mitochondrial targeting by aryl-ureas and can be varied to develop analogues that activate apoptosis or necrosis in a regulated fashion.

Antiproliferative activities of tricyclic amides derived from ß-caryophyllene via the Ritter reaction against MDA-MB-231 breast cancer cells.

A library of novel tricyclic amides has been synthesised via the Ritter reaction from ß-caryophyllene 1 and its monoepoxy derivative 4. The compounds were assessed for antiproliferative activities against the aggressive MDA-MB-231 breast cancer cell line. Of the synthesised compounds, eight were active. 3c and 6b were the most potent and inhibited proliferation with IC50 of 9.7 and 8.2 µM, respectively. Mechanistic studies revealed differences in their antiproliferative actions. 6b inhibited cell cycle progression and induced predominantly apoptotic cell death. In contrast, 3c did not affect cell cycle kinetics and favoured necrotic over apoptotic pathways. Screening against mammalian cells (VERO cells) indicates that 3c and 6b were more active towards MDA-MB-231 cells than noncancerous cells. Facile synthesis and biological results suggest that these caryophyllene derived amides are viable lead compounds for further development.

Aryl urea substituted fatty acids: a new class of protonophoric mitochondrial uncoupler that utilises a synthetic anion transporter.

Respiring mitochondria establish a proton gradient across the mitochondrial inner membrane (MIM) that is used to generate ATP. Protein-independent mitochondrial uncouplers collapse the proton gradient and disrupt ATP production by shuttling protons back across the MIM in a protonophoric cycle. Continued cycling relies on the formation of MIM-permeable anionic species that can return to the intermembrane space after deprotonation in the mitochondrial matrix. Previously described protonophores contain acidic groups that are part of delocalised π-systems that provide large surfaces for charge delocalisation and facilitate anion permeation across the MIM. Here we present a new class of protonophoric uncoupler based on aryl-urea substituted fatty acids in which an acidic group and a π-system are separated by a long alkyl chain. The aryl-urea group in these molecules acts as a synthetic anion receptor that forms intermolecular hydrogen bonds with the fatty acid carboxylate after deprotonation. Dispersal of the negative charge across the aryl-urea system produces lipophilic dimeric complexes that can permeate the MIM and facilitate repeated cycling. Substitution of the aryl-urea group with lipophilic electron withdrawing groups is critical to complex lipophilicity and uncoupling activity. The aryl-urea substituted fatty acids represent the first biological example of mitochondrial uncoupling mediated by the interaction of a fatty acid and an anion receptor moiety, via self-assembly.

Nanoparticles in Cancer Treatment: Opportunities and Obstacles.

In the United States, the estimated number of new cancer cases in 2018 will be approx. 1.7 million. Historically, combination chemotherapy has been the primary choice of treatment. However, chemotherapeutics have pharmaceutical limitations, among which include problems with stability and aqueous solubility. Likewise, dose limiting toxicity is significant with nonspecific toxicity to healthy cells, hair loss, loss of appetite, peripheral neuropathy and diarrhea being typical side effects. The emergence of Multidrug resistance (MDR) also presents s a significant challenge for the successful treatment of cancer whereby cancer cells become cross resistant to many of the chemotherapeutic agents used. Nanotechnology presents a new frontier for cancer treatment. It holds potential in minimizing systemic toxicity through the development of functionalized particles for targeted treatment. They also provide an alternative strategy to circumvent multidrug resistance as they have a capacity to by-pass the drug efflux mechanism associated with this phenotype. Aside from the advantages they offer in treatment, nanoparticles are also emerging to be valuable diagnostic entities. This article highlights the various ways nanotechnology is being used to improve the treatment and management of cancer. We also discuss the opportunities and obstacles in this area and provide an up to date review of progress in the treatment of cancer.

Proteins regulating the intercellular transfer and function of P-glycoprotein in multidrug-resistant cancer.

Chemotherapy is an essential part of anticancer treatment. However, the overexpression of P-glycoprotein (P-gp) and the subsequent emergence of multidrug resistance (MDR) hampers successful treatment clinically. P-gp is a multidrug efflux transporter that functions to protect cells from xenobiotics by exporting them out from the plasma membrane to the extracellular space. P-gp inhibitors have been developed in an attempt to overcome P-gp-mediated MDR; however, lack of specificity and dose limiting toxicity have limited their effectiveness clinically. Recent studies report on accessory proteins that either directly or indirectly regulate P-gp expression and function and which are necessary for the establishment of the functional phenotype in cancer cells. This review discusses the role of these proteins, some of which have been recently proposed to comprise an interactive complex, and discusses their contribution towards MDR. We also discuss the role of other pathways and proteins in regulating P-gp expression in cells. The potential for these proteins as novel therapeutic targets provides new opportunities to circumvent MDR clinically.

Synthesis and in vitro biological evaluation of thiosulfinate derivatives for the treatment of human multidrug-resistant breast cancer.

Organosulfur compounds derived from Allium vegetables have long been recognized for various therapeutic effects, including anticancer activity. Allicin, one of the main biologically active components of garlic, shows promise as an anticancer agent; however, instability makes it unsuitable for clinical application. The aim of this study was to investigate the effect of stabilized allicin derivatives on human breast cancer cells in vitro. In this study, a total of 22 stabilized thiosulfinate derivatives were synthesized and screened for their in vitro antiproliferative activities against drug-sensitive (MCF-7) and multidrug-resistant (MCF-7/Dx) human adenocarcinoma breast cancer cells. Assays for cell death, apoptosis, cell cycle progression and mitochondrial bioenergetic function were performed. Seven compounds (4b, 7b, 8b, 13b, 14b, 15b and 18b) showed greater antiproliferative activity against MCF-7/Dx cells than allicin. These compounds were also selective towards multidrug-resistant (MDR) cells, a consequence attributed to collateral sensitivity. Among them, 13b exhibited the greatest anticancer activity in both MCF-7/Dx and MCF-7 cells, with IC50 values of 18.54±0.24 and 46.50±1.98 µmol/L, respectively. 13b altered cellular morphology and arrested the cell cycle at the G2/M phase. Additionally, 13b dose-dependently induced apoptosis, and inhibited cellular mitochondrial respiration in cells at rest and under stress. MDR presents a significant obstacle to the successful treatment of cancer clinically. These results demonstrate that thiosulfinate derivatives have potential as novel anticancer agents and may offer new therapeutic strategies for the treatment of chemoresistant cancers.

Antiproliferative activities of alkaloid-like compounds.

Tricyclic alkaloid-like compounds were synthesised in a few steps, via the bridging Ritter reaction. The compounds were evaluated for their antiproliferative activity against the MCF-7 and the aggressive MDA-MB-231 breast cancer cells. The anti-cancer activities of 2c were found to be selective towards the aggressive and more challenging to treat triple negative (MDA-MB-231) cell line while exhibiting no antiproliferative activities towards the MCF-7 cells at the highest concentration tested (50 µM). The IC50 of compound 2c was determined to be 7.9 µM for the MDA-MB-231 cell line. Furthermore, 2c arrested cell cycle at the G2/M phase and induced apoptosis in a dose-dependent manner. Besides in-house anti-cancer screening, compound 3 was selected for anti-cancer screening by the National Cancer Institute and was found to have broad anti-cancer activity with selectivity against particular leukaemia, colon, melanoma, and breast cancer cell lines. Cytotoxicities of compounds 2c and 3 were also tested against noncancerous mammalian cells (VERO cell line), and found to be selective towards cancerous cells. The facile synthetic route, unique chemical structures and the biological data make these alkaloid-like compounds worthwhile lead compounds for further anti-cancer drug development.

Targeting microparticle biogenesis: a novel approach to the circumvention of cancer multidrug resistance.

Microparticles (MPs) are released from most eukaryotic cells after the vesiculation of the plasma membrane and serve as vectors of long and short-range signaling. MPs derived from multidrug resistant (MDR) cancer cells carry molecular components of the donor cell such as nucleic acids and proteins, and can alter the activity of drug-sensitive recipient cells through the transfer of their cargo. Given the substantial role of MPs in the acquisition and dissemination of MDR, we propose that the inhibition of MP release provides a novel therapeutic approach. This study characterises the effect of a panel of molecules known to act on MP-biosynthetic pathways. We demonstrate a differential effect by these molecules on MP inhibition that appear dependent on the release of intracellular calcium stores following activation with the calcium ionophore A23187. Calpain inhibitor, PD-150606; a selective inhibitor of Rho-associated, coiled-coil containing protein kinase (ROCK), Y-27632; and the vitamin B5 derivative pantethine, inhibited MP release only upon prior activation with A23187. Calpain inhibitor II showed significant inhibition in the absence of cell activation, whereas the vitamin B5 derivatives cystamine dihydrochloride and cysteamine hydrochloride showed no effect on MP inhibition under either condition. In contrast the classical pharmacological inhibitor of MDR, the calcium channel blocker Verapamil, showed an increase in MP formation on resting cells. These results suggest a potential role for calcium in the mechanism of action for PD-150606, Y-27632 and pantethine. These molecules, together with calpain inhibitor II have shown promise as modulators of MP release and warrant consideration as potential candidates for the development of an alternative therapeutic strategy for the prevention of MP-mediated MDR in cancer.

Cell-derived microparticles: new targets in the therapeutic management of disease.

Intercellular communication is essential to maintain vital physiological activities and to regulate the organism's phenotype. There are a number of ways in which cells communicate with one another. This can occur via autocrine signaling, endocrine signaling or by the transfer of molecular mediators across gap junctions. More recently communication via microvesicular shedding has gained important recognition as a significant pathway by which cells can coordinate the spread and dominance of selective traits within a population. Through this communication apparatus, cells can now acquire and secure a survival advantage, particularly in the context of malignant disease. This review aims to highlight some of the functions and implications of microparticles in physiology of various disease states, and present a novel therapeutic strategy through the regulation of microparticle production.