Hydroxamic acid - A novel molecule for anticancer therapy

A comparative study on the metal complexes of an anticancer estradiol-hydroxamate conjugate and salicylhydroxamic acid

Hydroxamic acids bearing an (O,O) donor set are well-known metal-chelating compounds with diverse biological activities including anticancer activity. Since steroid conjugation with a pharmacophoric moiety may have the potential to improve this effect, a salicylhydroxamic acid-estradiol hybrid molecule (E2HA) was synthesized. Only minimal effect of the conjugation on the proton dissociation constants was observed in comparison to salicylhydroxamic acid (SHA). The complexation with essential metal ions (iron, copper) was characterized, since E2HA may exert its cytotoxicity through the binding of these ions in cells. UV-visible spectrophotometric and pH-potentiometric titrations revealed the formation of high-stability complexes, while the Fe(III) preference over Fe(II) was proved by cyclic voltammetry and spectroelectrochemical measurements. Complex formation with half-sandwich Rh(III)(η⁵-Cp*) and Ru(II)(η⁶-p-cymene) organometallic cations was also studied as it may improve the anticancer effect and the pharmacokinetic profile of the ligand. At equimolar concentration the speciation is complicated because of the presence of mononuclear and binuclear complexes. The complexes readily react with small molecules e.g. glutathione, 1-methylimidazole and nucleosides, having major effect on solution speciation, namely mixed-ligand complex formation and ligand displacement occur. These processes serve as models for the interactions with biomolecules in the body. E2HA exerted moderate anticancer activity (IC₅₀ = 25-59 μM) in the tested three human cancer cell lines (Colo205, Colo320 and MCF-7), while being non-toxic on non-cancerous MRC-5 cells. Meanwhile, SHA was inactive in the same cells. Complexation with half-sandwich Rh(III) and Ru(II) cations had only a minor improvement on the cytotoxic effect of E2HA.

Cancer Metabolism: Fasting Reset, the Keto-Paradox and Drugs for Undoing

In tumor cells, ketolysis "via" succinyl-CoA: 3-oxoacid-CoAtransferase (SCOT) and acetyl-CoA acetyltransferase 1 (ACAT1) is a major source of mitochondrial acetyl-CoA. Active ACAT1 tetramers stabilize by tyrosine phosphorylation, which facilitates the SCOT reaction and ketolysis. Tyrosine phosphorylation of pyruvate kinase PK M2 has the opposite effect, stabilizing inactive dimers, while pyruvate dehydrogenase (PDH), which is already inhibited by phosphorylation, is acetylated by ACAT1 and is doubly locked. This closes the glycolytic supply of acetyl-CoA. In addition, since tumor cells must synthesize fatty acids to create new membranes, they automatically turn off the degradation of fatty acids into acetyl-CoA ("via" the malonyl-CoA brake for the fatty acid carnityl transporter). Thus, inhibiting SCOT the specific ketolytic enzyme and ACAT1 should hold back tumor progression. However, tumor cells are still able to take up external acetate and convert it into acetyl-CoA in their cytosol "via" an acetyl-CoA synthetase, which feeds the lipogenic pathway; additionally, inhibiting this enzyme would make it difficult for tumor cells to form new lipid membrane and survive.

β-Carotene-production methods, biosynthesis from Phaffia rhodozyma, factors affecting its production during fermentation, pharmacological properties: A review

β-Carotene is the most treasured provitamin A carotenoid molecule exhibiting antioxidant and coloring properties and significant applications in the food, pharmaceutical, and nutraceutical industries. β-Carotene has many biological functions within the human body; however, it is not synthesized within the human body, so its requirements are fulfilled through food and pharmaceuticals. Its manufacturing via chemical synthesis or extraction from plants offers low yields with excessive manufacturing expenses, which attracted the researchers toward microbial production of β-carotene. This alternative provides higher yield and low expenses and thus is more economical. Phaffia rhodozyma is a basidiomycetous yeast that is utilized to prevent cardiovascular diseases and cancer and to enhance immunity and antiaging in people. This paper reviews the methods of production of β-carotene, biosynthesis of β-carotene fromP. rhodozyma, factors affecting β-carotene production during fermentation, and pharmacological properties of β-carotene.

Target Design of Novel Histone Deacetylase 6 Selective Inhibitors with 2-Mercaptoquinazolinone as the Cap Moiety

Epigenetic alterations found in all human cancers are promising targets for anticancer therapy. In this sense, histone deacetylase inhibitors (HDACIs) are interesting anticancer agents that play an important role in the epigenetic regulation of cancer cells. Here, we report 15 novel hydroxamic acid-based histone deacetylase inhibitors with quinazolinone core structures. Five compounds exhibited antiproliferative activity with IC50 values of 3.4-37.8 µM. Compound 8 with a 2-mercaptoquinazolinone cap moiety displayed the highest antiproliferative efficacy against MCF-7 cells. For the HDAC6 target selectivity study, compound 8 displayed an IC50 value of 2.3 µM, which is 29.3 times higher than those of HDAC3, HDAC4, HDAC8, and HDAC11. Western blot assay proved that compound 8 strongly inhibited tubulin acetylation, a substrate of HDAC6. Compound 8 also displayed stronger inhibition activity against HDAC11 than the control drug Belinostat. The inhibitory mechanism of action of compound 8 on HDAC enzymes was then explored using molecular docking study. The data revealed a high binding affinity (-7.92 kcal/mol) of compound 8 toward HDAC6. In addition, dock pose analysis also proved that compound 8 might serve as a potent inhibitor of HDAC11.

Molecular photoswitches in aqueous environments

Molecular photoswitches enable dynamic control of processes with high spatiotemporal precision, using light as external stimulus, and hence are ideal tools for different research areas spanning from chemical biology to smart materials. Photoswitches are typically organic molecules that feature extended aromatic systems to make them responsive to (visible) light. However, this renders them inherently lipophilic, while water-solubility is of crucial importance to apply photoswitchable organic molecules in biological systems, like in the rapidly emerging field of photopharmacology. Several strategies for solubilizing organic molecules in water are known, but there are not yet clear rules for applying them to photoswitchable molecules. Importantly, rendering photoswitches water-soluble has a serious impact on both their photophysical and biological properties, which must be taken into consideration when designing new systems. Altogether, these aspects pose considerable challenges for successfully applying molecular photoswitches in aqueous systems, and in particular in biologically relevant media. In this review, we focus on fully water-soluble photoswitches, such as those used in biological environments, in both in vitro and in vivo studies. We discuss the design principles and prospects for water-soluble photoswitches to inspire and enable their future applications.

Cracking a cancer code histone deacetylation in epigenetic: the implication from molecular dynamics simulations on efficacy assessment of histone deacetylase inhibitors

Epigenetic changes, histone acetylation and deacetylation in chromatin have been intensively studied due to their significance in regulating the gene expression. According to the type of tumor, the levels of histone deacetylases (HDAC) are varied. HDAC inhibitors are a new promising class of compounds that inhibit the proliferation of tumor cells. In this study, the inhibitory efficacy of some HDAC inhibitors such as vorinostat, panobinostat, abexinostat, belinostat, resminostat, dacinostat and pracinostat was studied using molecular dynamics simulation. The inhibitory efficacy was estimated by computing the enzyme's stability, positional stability of the individual amino acids and interaction energies of HDLP-inhibitor complexes. It is hoped that this investigation may improve our understanding of the atomic-level description of the inhibitor binding site and how the HDAC inhibitors change the environment of the enzyme's active site. The results obtained from the root-mean-square deviation, the radius of gyration, solvent-accessible surface area, root-mean-square fluctuation, stride server and Ramachandran plot have revealed that the stability of HDLP enzyme with vorinostat, panobinostat and abexinostat is higher than the other studied complexes. According to the calculated values for MM-PBSA, LIE, semi-LIE binding free energies and interaction energies, the stability of the HDLP enzyme varies as panobinostat > abexinostat > vorinostat where resminostat complex showed relatively low stability. The ligandability and drugability values also give the same trend as above. The findings revealed that the panobinostat and abexinostat are potential lead compounds as reference inhibitor vorinostat. Therefore, it is possible to use these drugs as HDAC inhibitors in clinical practices. Also, the outcomes of this study could be utilized to identify new inhibitors for clinical research.Communicated by Ramaswamy H. Sarma.

Enzymatic Synthesis of Ricinoleyl Hydroxamic Acid Based on Commercial Castor Oil, Cytotoxicity Properties and Application as a New Anticancer Agent

BACKGROUND

New anticancer agents that rely on natural/healthy, not synthetic/toxic, components are very much needed.

METHODS

Ricinoleyl hydroxamic acid (RHA) was synthesized from castor oil and hydroxylamine using Lipozyme TL IM as a catalyst. To optimize the conversion, the effects of the following parameters were investigated: type of organic solvent, period of reaction, amount of enzyme, the molar ratio of reactants and temperature. The highest conversion was obtained when the reaction was carried out under the following conditions: hexane as a solvent; reaction period of 48 hours; 120 mg of Lipozyme TL IM/3 mmol oil; HA-oil ratio of 19 mmol HA/3 mmol oil; and temperature of 40°C. The cytotoxicity of the synthesized RHA was assessed using human dermal fibroblasts (HDF), and its application towards fighting cancer was assessed using melanoma and glioblastoma cancer cells over a duration of 24 and 48 hours.

RESULTS

RHA was successfully synthesized  and it demonstrated strong anticancer activity against glioblastoma and melanoma cells at as low as a 1 µg/mL concentration while it did not demonstrate any toxicity against HDF cells.

CONCLUSION

This is the first report on the synthesis of RHA with great potential to be used as a new anticancer agent.

Design, in silico studies, and synthesis of new 1,8-naphthyridine-3-carboxylic acid analogues and evaluation of their H1R antagonism effects

New 1,8-naphthyridine-3-carboxylic acid derivatives were designed, synthesized and evaluated for their in vivo antihistaminic activity on guinea pig trachea by using chlorpheniramine as the standard drug. It was found that compound 5a1 displayed a promising bronchorelaxant effect in conscious guinea pigs using the in vivo model. A molecular docking study was performed to understand the molecular interaction and binding mode of the compounds in the active site of the H1 receptor. Furthermore, in silico computational studies were also performed to predict the binding modes and pharmacokinetic parameters of these derivatives. Prior to the start of experimental lab work, PASS software was used to predict the biological activities of these compounds. An in silico PASS, Swiss ADME assisted docking approach was found to be suitable to derive and synthesize effective antihistaminic agents for the present study.

New 1,8-naphthyridine-3-carboxylic acid derivatives were designed, synthesized and evaluated for their in vivo antihistaminic activity on guinea pig trachea by using chlorpheniramine maleate as the standard drug.

An unexpected new pathway for nitroxide radical production via more reactve nitrogen-centered amidyl radical intermediate during detoxification of the carcinogenic halogenated quinones by N-alkyl hydroxamic acids

We found previously that nitroxide radical of desferrioxamine (DFO^•) could be produced from the interaction between the classic iron chelating agent desferrioxamine (DFO, an N-alkyl trihydroxamic acid) and tetrachlorohydroquinone (TCHQ), one of the carconogenic quinoind metabolites of the widely used wood preservative pentachlorophenol. However, the underlying molecular mechanism remains unclear. Here N-methylacetohydroxamic acid (N-MeAHA) was synthesized and used as a simple model compound of DFO for further mechanistic study. As expected, direct ESR studies showed that nitroxide radical of N-MeAHA (Ac-(CH₃)NO^•) can be produced from N-MeAHA/TCHQ. Interestingly and unexpectedly, when TCHQ was substituted by its oxidation product tetrachloro-1,4-benzoquinone (TCBQ), although Ac-(CH₃)NO^• could also be produced, no concurrent formation of tetrachlorosemiquinone radical (TCSQ^•) and TCHQ was detected, suggesting that Ac-(CH₃)NO^• did not result from direct oxidation of N-MeAHA by TCSQ^• or TCBQ as proposed previously. To our surprise, a new nitrogen-centered amidyl radical was found to be generated from N-MeAHA/TCBQ, which was observed by ESR with the spin-trapping agents and further unequivacally identified as Ac-(CH₃)N^• by HPLC-MS. The final product of amidyl radical was isolated and identified as its corresponding amine. Analogous radical homolysis mechanism was observed with other halogenated quinoid compounds and N-alkyl hydroxamic acids including DFO. Interestingly, amidyl radicals were found to induce both DNA strand breaks and DNA adduct formation, suggesting that N-alkyl hydroxamic acids may exert their potential side-toxic effects via forming the reactive amidyl radical species. This study represents the first report of an unexpected new pathway for nitroxide radical production via hydrogen abstration reaction of a more reactive amidyl radical intermediate during the detoxification of the carcinogenic polyhalogenated quinones by N-alkyl hydroxamic acids, which provides more direct experimental evidence to better explain not only our previous finding that excess DFO can provide effective but only partial protection against TCHQ (or TCBQ)-induced biological damage, and also the potential side-toxic effects induced by DFO and other N-alkyl hydroxamic acid drugs.

Unexpected activation of N-alkyl hydroxamic acids to produce reactive N-centered free radicals and DNA damage by carcinogenic chlorinated quinones under normal physiological conditions

We found recently that benzohydroxamic acid (BHA) could detoxify the chlorinated quinoid carcinogens via an unusual Lossen rearrangement reaction. However, it is not clear what would happen when the nitrogen hydrogen of BHA was substituted with methyl and other alkyl groups. Here we show that N-methyl benzohydroxamic acid (N-MeBHA, a simple model compound for the classic iron-chelator deferoxamine, which is a typical N-alkyl trihydroxamic acid) could react with 2,5-dichloro-1,4-benzoquinone (DCBQ) to form a relatively stable initial carbon-oxygen bonding conjugation intermediate CBQ-O-N-MeBHA. However, the major final product was identified, unexpectedly, as a carbon-nitrogen bonding conjugate CBQ(OH)-N(CH₃)-COAr, which is the rearranged isomer of CBQ-O-N-MeBHA. Interestingly, a new 18-line nitrogen-centered radical and a carbon-centered quinone ketoxy radical were observed by the ESR spin-trapping method, which was further confirmed by HPLC-MS and ¹⁵N-isotope labeling methods. We further found that both new DNA adducts and DNA strand breaks could be produced by the reactive nitrogen-centered radical. Taken together, we propose that the reaction between DCBQ and N-MeBHA was not via the Lossen rearrangement, but rather through a novel radical homolysis and recoupling pathway. Analogous results were observed for other chlorinated quinones and N-alkyl hydroxamic acids including the widely-used trihydroxamate iron-chelating drug deferoxamine. This represents the first report of unexpected radical pathway for the reaction between chlorinated quinones and N-alkyl hydroxamic acids under normal physiological conditions, which may have broad biological and environmental significance for future study of carcinogenic chloroquinones and hydroxamic acid drugs.

Geranium thunbergii extract-induced G1 phase cell cycle arrest and apoptosis in gastric cancer cells

Geranium thunbergii is a traditional East Asian medicine for stomach diseases including dysentery and stomach ulcers in East Asia and has been reported to possess biological activity. The benefits of G. thunbergii in gastric cancer are unknown. In this study, we demonstrate that G. thunbergii extract suppresses proliferation and induces death and G1/S cell cycle arrest of gastric cancer cells. Proliferation was significantly inhibited in a time- and dose-dependent manner. Cell cycle arrest was associated with significant decreases in CDK4/cyclinD1 complex and CDK2/cyclinE complex genes expression. In addition, the protein expression of caspase-3 was decreased and that of activated poly (ADP-ribose) polymerase (PARP) was increased, which indicated apoptosis. The expressions of the Bax and Bcl-2, which are apoptosis related proteins, were upregulated and down-regulated, respectively. The results indicate that G. thunbergii extract can inhibit proliferation and induce both G/S cell cycle arrest and apoptosis of gastric cancer cells. Also, the induction of apoptosis involved the intrinsic pathways of the cells. Take the results, we suggest that G. thunbergii extract has anti-gastric cancer activity and may be a potential therapeutic candidate for gastric cancer.

Structures of rhenium(I) complexes with 3-hydroxyflavone and benzhydroxamic acid as O,O'-bidentate ligands and confirmation of π-stacking by solid-state NMR spectroscopy

The synthesis and crystal structures of two new rhenium(I) complexes obtained utilizing benzhydroxamic acid (BHAH) and 3-hydroxyflavone (2-phenylchromen-4-one, FlavH) as bidentate ligands, namely tetraethylammonium fac-(benzhydroxamato-κ²O,O')bromidotricarbonylrhenate(I), (C₈H₂₀N)[ReBr(C₇H₆NO₂)(CO)₃], 1, and fac-aquatricarbonyl(4-oxo-2-phenylchromen-3-olato-κ²O,O')rhenium(I)-3-hydroxyflavone (1/1), [Re(C₁₅H₉O₃)(CO)₃(H₂O)]·C₁₅H₁₀O₃, 3, are reported. Furthermore, the crystal structure of free 3-hydroxyflavone, C₁₅H₁₀O₃, 4, was redetermined at 100 K in order to compare the packing trends and solid-state NMR spectroscopy with that of the solvate flavone molecule in 3. The compounds were characterized in solution by ¹H and ¹³C NMR spectroscopy, and in the solid state by ¹³C NMR spectroscopy using the cross-polarization magic angle spinning (CP/MAS) technique. Compounds 1 and 3 both crystallize in the triclinic space group P-1 with one molecule in the asymmetric unit, while 4 crystallizes in the orthorhombic space group P2₁2₁2₁. Molecules of 1 and 3 generate one-dimensional chains formed through intermolecular interactions. A comparison of the coordinated 3-hydroxyflavone ligand with the uncoordinated solvate molecule and free molecule 4 shows that the last two are virtually completely planar due to hydrogen-bonding interactions, as opposed to the former, which is able to rotate more freely. The differences between the solid- and solution-state ¹³C NMR spectra of 3 and 4 are ascribed to inter- and intramolecular interactions. The study also investigated the potential labelling of both bidentate ligands with the corresponding fac-^99mTc-tricarbonyl synthon. All attempts were unsuccessful and reasons for this are provided.

Epigenetics in Metastatic Breast Cancer: Its Regulation and Implications in Diagnosis, Prognosis and Therapeutics

Despite advances in the treatment regimen, the high incidence rate of breast cancer (BC) deaths is mostly caused by metastasis. Recently, the aberrant epigenetic modifications, which involve DNA methylation, histone modifications and microRNA (miRNA) regulations become attractive targets to treat metastatic breast cancer (MBC). In this review, the epigenetic alterations of DNA methylation, histone modifications and miRNA regulations in regulating MBC are discussed. The preclinical and clinical trials of epigenetic drugs such as the inhibitor of DNA methyltransferase (DNMTi) and the inhibitor of histone deacetylase (HDACi), as a single or combined regimen with other epigenetic drug or standard chemotherapy drug to treat MBCs are discussed. The combined regimen of epigenetic drugs or with standard chemotherapy drugs enhance the therapeutic effect against MBC. Evidences that epigenetic changes could have implications in diagnosis, prognosis and therapeutics for MBC are also presented. Several genes have been identified as potential epigenetic biomarkers for diagnosis and prognosis, as well as therapeutic targets for MBC. Endeavors in clinical trials of epigenetic drugs against MBC should be continued although limited success has been achieved. Future discovery of epigenetic drugs from natural resources would be an attractive natural treatment regimen for MBC. Further research is warranted in translating research into clinical practice with the ultimate goal of treating MBC by epigenetic therapy in the near future.

Novel therapeutic features of disulfiram against hepatocellular carcinoma cells with inhibitory effects on a disintegrin and metalloproteinase 10

Our previous genome-wide association study identified the anti-tumor ligand MHC class I polypeptide-related sequence A (MICA) as a susceptibility gene for hepatitis C virus-induced hepatocellular carcinoma (HCC). We subsequently proved that pharmacological restoration of membrane-bound MICA in HCC cells boosted natural killer cell-mediated anti-cancer effects, confirming that a MICA sheddase, a disintegrin and metalloproteinase 10 (ADAM10), is a therapeutic target. We here searched for approved drugs with inhibitory effects on ADAM10 in vitro, and the anti-alcoholism agent, disulfiram, was identified. Disulfiram elevated membrane-bound MICA levels and reduced production of soluble MICA, an immunological decoy, while simultaneously not having unfavorable off-target effects on natural killer cells and normal human hepatocytes. Functional analyses indicated a mode of non-zinc-binding inhibition of ADAM10 by disulfiram, which also suppressed HCC cell migration. These effects of disulfiram against HCC are expected to further the development of novel therapeutic regimens.

Photochemistry of Acetohydroxamic Acid in Solid Argon. FTIR and Theoretical Studies

The products formed during exposure of the CH₃CONHOH/Ar (AHA/Ar) matrices to the full output of the Xe lamp and to 225 nm OPO radiation are studied. The irradiation promotes the isomerization, 1Z → 1E, and AHA photodissociation reactions. Four pairs of coproducts are experimentally found to appear in the photolysis, they form the complexes: CH₃OH···HNCO (1), H₂O···CH₃NCO (2), H₂O···CH₃CNO (3) and CO···CH₃NHOH (4). The structures of the complexes were optimized at the MP2 computational level with the 6-311++G(2d,2p) and aug-cc-pVTZ basis sets. Three local minima were predicted for the complex (1), two for the complexes (2) and (3) and four local minima were found for the complex (4). The comparison of the theoretical spectra with the experimental ones allowed us to determine the structures of the complexes formed in the matrix. The mechanisms of the reaction channels leading to formation of the four coproducts are proposed. It is concluded that the first step in formation of the (1), (2) and (3) complexes is the scission of the N-O bond whereas the creation of the complex (4) is due to the cleavage of the C-N bond.

Five Unprecedented Secondary Metabolites from the Spider Parasitic Fungus Akanthomyces novoguineensis

Five new compounds including the glycosylated β-naphthol (1, akanthol), a glycosylated pyrazine (2, akanthozine), and three amide derivatives including a hydroxamic acid derivative (3–5) were isolated from the spider-associated fungus Akanthomyces novoguineensis (Cordycipitaceae, Ascomycota). Their structures were elucidated by using high resolution mass spectrometry (HRMS) and NMR spectroscopy. In this study, the antimicrobial, cytotoxic, anti-biofilm, and nematicidal activities of the new compounds were evaluated. The distribution pattern of secondary metabolites in the species was also revealed in which more isolates of A. novoguineensis were encountered and their secondary metabolite profiles were examined using analytical HPLC with diode array and mass spectrometric detection (HPLC-DAD/MS). Remarkably, all isolated compounds are specifically produced by A. novoguineensis.

Polysaccharides from Korean Citrus hallabong peels inhibit angiogenesis and breast cancer cell migration

Although the peel of the hallabong (Citrus sphaerocarpa) fruit is rich in polysaccharides, which are valuable dietary ingredients for human health, it is normally wasted. The present study aimed to utilize the peel waste and identify properties it may have against breast cancer metastasis. Hallabong peel extract containing crude polysaccharides was fractionated by gel permeation chromatography to produce four different polysaccharide fractions (HBE-I, -II, -III, and -IV). The HBE polysaccharides significantly blocked tube formation of human umbilical vein vascular endothelial cells (HUVECs), at a concentration of 12.5 or 25 μg/mL. Tube formation appeared to be more sensitive to HBE-II than to other HBE polysaccharides. HBE-II also inhibited breast cancer cell migration, through downregulation of matrix metalloproteinase-9 (MMP-9) in MDA-MB-231 triple-negative breast cancer cells. Therefore, inhibition of tube formation and MMP-9-mediated migration observed in HUVEC and MDA-MB-231 cells, respectively, are likely to be important therapeutic targets in triple-negative breast cancer metastasis.

From α-nucleophiles to functionalized aggregates: exploring the reactivity of hydroxamate ion towards esterolytic reactions in micelles

Hydroxamate ions as α-nucleophiles for esterolytic reactions in water and micelles.

Free radicals, natural antioxidants, and their reaction mechanisms

The normal biochemical reactions in our body, increased exposure to the environment, and higher levels of dietary xenobiotic's result in the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS).

Inorganic Phosphate as a Novel Signaling Molecule with Antiproliferative Action in MDA-MB-231 Breast Cancer Cells

Inorganic phosphate (P_i) is an essential nutrient for living organisms. It plays a key role in diverse physiological functions, including osteoblast differentiation and skeletal mineralization. Relevantly, P_i is emerging as an important signaling molecule capable of modulating multiple cellular functions by altering signal transduction pathways, gene expression, and protein abundance in many cell types. To our knowledge, the consequences of elevated P_i on behavior of breast cancer cells have been poorly addressed. In this study we investigate the effects of P_i on proliferation of MDA-MB-231 breast cancer cells. We report that P_i inhibits proliferation of MDA-MB-231 cells by slowing cell cycle progression, without apoptosis occurrence. We found that P_i causes cells to accumulate in G1 phase in a time-dependent manner. Accordingly, G1 accumulation was associated with a decrease of cyclin A and cyclin E and an increase of cell cycle inhibitors p21 and p27 protein levels, respectively. Moreover, the P_i-induced antiproliferative effect was dynamically accompanied by profound changes in ERK1/2 and STAT3 protein and phosphorylation levels in response to P_i. Altogether, our data represent the first evidence of P_i acting as a novel signaling molecule in MDA-MB-231 breast cancer cells, capable of eliciting a strong antiproliferative action and suggest that targeting P_i levels at local sites might represent the rationale for developing novel strategies for therapeutic intervention in triple-negative breast cancer.