Betulinyl Sulfamates as Anticancer Agents and Radiosensitizers in Human Breast Cancer Cells

A comparative study of diaryl urea molecules with and without sulfonamide group on Carbonic anhydrase IX and XII inhibition and its consequence on breast cancer cells

To investigate the intrinsic relation between carbonic anhydrase inhibition and anticancer activity, we have prepared four sets of diaryl urea molecules and tested for the inhibition of hCA-IX and XII on two breast cancer cell lines. Among 21 compounds, compound J2 (with -SO2NH2 group) and J16 (without -SO2NH2 group) showed the best activity under normoxic and hypoxic conditions. The IC50 values of J16 for MDA-MB-231 and MCF-7 cells, under normoxic condition were 6.3 and 3.7 µM respectively, which are 1.9/3.3 and 15.8 times better than U-4-Nitro and SLC-0111 respectively. Whereas, under the hypoxic condition the corresponding values were 12.4 and 1.1 µM (MDA-MB-231 and MCF-7 cells respectively), which are equal/8 times better than U-4-Nitro. Whereas, J2 showed better IC50 value than U-4-Nitro (6.3 µM) under normoxic condition for both MDA-MB-231 and MCF-7 cells (1.9/2.7 times). Compound J2 inhibits the activity of hCA-IX and XII in nanomolar concentration [Ki values 4.09 and 9.10 nM respectively with selectivity ratio of 1.8 and 0.8 with hCA-II]. The crystal structure and modelling studies demonstrates that the inhibition of CAs arises due to the blocking of the CO2 coordination site of zinc in its catalytic domain. However, J16 was found to be unable to inhibit the activity of hCAs (Ki > 89000 nM). qPCR and western blot analysis showed a significant reduction (1.5 to 20 fold) of the transcription and expression of HIF1A, CA9 and CA12 genes in presence of J2 and J16. Both J2 and J16 found to reduce accumulation of HIF-1α protein by inhibiting the chaperone activity of hHSP70 with IC50 values of 19.4 and 15.3 µM respectively. Perturbation of the hCA-IX and XII activity by binding at active site or by reduced expression or by both leads to the decrease of intracellular pH, which resulted in concomitant increase of reactive oxygen species by 2.6/2.0 (MCF-7) and 2.9/1.8 (MDA-MB-231) fold for J2/J16. Increased cyclin D1 expression in presence of J2 and J16 was presumed to be indirectly responsible for the apoptosis of the cancer cells. Expression of the other apoptosis markers Bcl-2, Bim, caspase 9 and caspase 3 substantiated the apoptosis mechanism. However, decreased transcription/expression of HIF1A/HIF-1α and hCA-IX/XII also implies the inhibition of the extracellular signal-regulated kinase pathway by J2 and J16.

pH regulators and their inhibitors in tumor microenvironment

As an important characteristic of tumor, acidic tumor microenvironment (TME) is closely related to immune escape, invasion, migration and drug resistance of tumor. The acidity of the TME mainly comes from the acidic products produced by the high level of tumor metabolism, such as lactic acid and carbon dioxide. pH regulators such as monocarboxylate transporters (MCTs), carbonic anhydrase IX (CA IX), and Na+/H+ exchange 1 (NHE1) expel protons directly or indirectly from the tumor to maintain the pH balance of tumor cells and create an acidic TME. We review the functions of several pH regulators involved in the construction of acidic TME, the structure and structure-activity relationship of pH regulator inhibitors, and provide strategies for the development of small-molecule antitumor inhibitors based on these targets.

Betulinic acid in the treatment of breast cancer: Application and mechanism progress

Betulinic acid (BA) is a pentacyclic triterpene compound, which can be obtained by separation, chemical synthesis and biotransformation. BA has excellent biological activities, especially its role in the treatment of breast cancer deserves attention. Its mechanisms mainly include inducing mitochondrial oxidative stress, regulating specific protein (Sp) transcription factors, inhibiting breast cancer metastasis, inhibiting glucose metabolism and NF-κB pathway. In addition, BA can also increase the sensitivity of breast cancer cells to other chemotherapy drugs such as paclitaxel and reduce its toxic side effects. This article reviews the application and possible mechanism of BA in the treatment of breast cancer.

Mitochondria-Targeting 1,5-Diazacyclooctane-Spacered Triterpene Rhodamine Conjugates Exhibit Cytotoxicity at Sub-Nanomolar Concentration against Breast Cancer Cells

1,5-Diazacyclooctane was prepared by a simple synthetic sequence and coupled to pentacyclic triterpenoic acids oleanolic acid, ursolic acid, betulinic acid, platanic acid, and asiatic acid; these amides were activated with oxalyl chloride and reacted with rhodamine B or rhodamine 101 to yield conjugates. The conjugates were screened in SRB assays with various human breast cancer cell lines (MDA-MB-231, HS578T, MCF-7, and T47D) and found to exert cytotoxic activity even at a low concentration. Therefore, for an asiatic acid rhodamine 101 conjugate (28), an IC₅₀ = 0.60 nM was determined and found to induce apoptosis in MDA-MB-231 and HS578T cells. Extra experiments showed the compound to act as a mitocan and to induce inhibition of proliferation or growth arrest in MDA-MB-231 cells at lower doses followed by an induction of apoptosis at higher doses. Furthermore, differential responses to proliferation inhibition and apoptosis induction may explain differential sensitivity of mammary cell lines to compound 28.

Anticancer Effects of Propolis Extracts Obtained Using the Cold Separation Method on Breast Cancer Cell Lines

Propolis and its extracts show a wide spectrum of biological activity. Due to the necessity to use high temperatures and high polarity in the eluent, the obtained extracts are depleted of active compounds. The new, cold separation method allows obtaining a qualitatively better product containing a number of chemical compounds absent in extracts obtained using high-temperature methods. The purpose of our study was to evaluate the biological activity of propolis extracts produced with the cold separation method in four female breast cancer cell lines: MDA-MB-231, MDA-MB-468, MCF-7, and T-47D. The results of the breast cancer cell viability were obtained using the MTT test. Propolis extracts at 75 and 80% showed similar cytotoxicity against cancer cells, with the polyphenol fraction 75% being slightly more negative for cells. Propolis extracts at concentrations of 50, 75, and 100 µg/mL significantly reduced cell viability. With the exception of the MDA-MB-231 line, cell viability was also decreased after incubation with a concentration of 25 µg/mL. Our results suggest that propolis extracts obtained with the cold separation method may be considered as promising compounds for the production of health-promoting supplements.

Design and synthesis of new adamantyl derivatives as promising antiproliferative agents

A series of adamantyl carboxamide derivatives containing sulfonate or sulfonamide moiety were designed as multitargeted inhibitors of ectonucleotide pyrophosphatases/phosphodiesterases (NPPs) and carbonic anhydrases (CAs). The target compounds were investigated for their antiproliferative activity against NCI-60 cancer cell lines panel. Three main series composed of 3- and 4-aminophenol, 4-aminoaniline, and 5-hydroxyindole scaffolds were designed based on a lead compound (A). Compounds 1e (benzenesulfonyl) and 1i (4-fluorobenzenesulfonyl) of 4-aminophenol backbone exhibited the most promising antiproliferative activity. Both compounds exhibited a broad-spectrum and potent inhibition against all the nine tested cancer subtypes. Both compounds showed nanomolar IC50 values over several cancer cell lines that belong to leukemia and colon cancer such as K-562, RPMI-8226, SR, COLO 205, HCT-116, HCT-15, HT29, KM12, and SW-620 cell lines. Compounds 1e and 1i induced apoptosis in K-562 leukemia cells in a dose-dependent manner. Compound 1i showed the highest cytotoxic activity with IC50 value of 200 nM against HT29 cell line. In addition, compounds 1e and 1i were tested against normal breast cells (HME1) and normal skin fibroblast cells (F180) and the results revealed that the compounds are safe toward normal cells compared to cancers cells. Enzymatic assays against NPP1-3 and carbonic anhydrases II, IX, and XII were performed to investigate the possible molecular target(s) of compounds 1e and 1i. Furthermore, a molecular docking study was performed to predict the binding modes of compounds 1e and 1i in the active site of the most sensitive enzymes subtypes.

SESN2 Knockdown Increases Betulinic Acid-Induced Radiosensitivity of Hypoxic Breast Cancer Cells

Betulinic acid (BA) is a natural compound well known for its anti-inflammatory, anti-viral, anti-bacterial, anti-malarial effects and anti-tumor properties. Its enhanced cytotoxicity in tumor cells and induction of cell death in various cancer entities qualifies BA as an interesting candidate for novel treatment concepts. Our analyses showed enhanced cytotoxicity and radiosensitization under hypoxic conditions in human breast cancer cells. So far, the underlying mechanisms are unknown. Therefore, we investigated the BA-treated human breast cancer cell lines MDA-MB-231 and MCF-7 under normoxic and hypoxic conditions based on microarray technology. Hypoxia and BA regulated a variety of genes in both breast cancer cell lines. KEGG pathway analysis identified an enrichment of the p53 pathway in MCF-7 cells (wtp53) under hypoxia. In MDA-MB-231 cells (mtp53) an additional BA incubation was required to activate the p53 signaling pathway. Fourteen down-regulated and up-regulated genes of the p53 pathway were selected for further validation via qRT-PCR in a panel of five breast cancer cell lines. The stress-induced gene Sestrin-2 (SESN2) was identified as one of the most strongly up-regulated genes after BA treatment. Knockdown of SESN2 enhanced BA-induced ROS production, DNA damage, radiosensitivity and reduced autophagy in breast cancer cells. Our results identified SESN2 as an important target to enhance the radiobiological and anti-tumor effects of BA on breast cancer cells.

Betulin Sulfonamides as Carbonic Anhydrase Inhibitors and Anticancer Agents in Breast Cancer Cells

Hypoxia-regulated protein carbonic anhydrase IX (CA IX) is up-regulated in different tumor entities and correlated with poor prognosis in breast cancer patients. Due to the radio- and chemotherapy resistance of solid hypoxic tumors, derivatives of betulinic acid (BA), a natural compound with anticancer properties, seem to be promising to benefit these cancer patients. We synthesized new betulin sulfonamides and determined their cytotoxicity in different breast cancer cell lines. Additionally, we investigated their effects on clonogenic survival, cell death, extracellular pH, HIF-1α, CA IX and CA XII protein levels and radiosensitivity. Our study revealed that cytotoxicity increased after treatment with the betulin sulfonamides compared to BA or their precursors, especially in triple-negative breast cancer (TNBC) cells. CA IX activity as well as CA IX and CA XII protein levels were reduced by the betulin sulfonamides. We observed elevated inhibitory efficiency against protumorigenic processes such as proliferation and clonogenic survival and the promotion of cell death and radiosensitivity compared to the precursor derivatives. In particular, TNBC cells showed benefit from the addition of sulfonamides onto BA and revealed that betulin sulfonamides are promising compounds to treat more aggressive breast cancers, or are at the same level against less aggressive breast cancer cells.

MSBA-S - A pentacyclic sulfamate as a new option for radiotherapy of human breast cancer cells

Many pentacyclic triterpenoids show anti-cancer and anti-inflammatory properties. Recently, we detected a pronounced cytotoxicity and radiosensitivity of two betulinyl sulfamates in human breast cancer cells. Besides betulinic acid scaffold (BSBA-S), we synthesized several new sulfamate-coupled scaffolds from oleanolic acid (OSBA-S), ursolic acid (USBA-S), platanic acid (PSBA-S) and maslinic acid (MSBA-S). Highest cytotoxicity was monitored in breast cancer cell lines after MSBA-S treatment showing in SRB assays IC₅₀ values between 3.7 μM and 5.8 μM. Other sulfamate/triterpene conjugates, however, were less cytotoxic holding IC₅₀ values between 6.6 μM and >50 µM, respectively. MSBA-S-treated breast cancer cells displayed significantly reduced clonogenic survival and an increased rate of apoptosis as compared to the other conjugates. In addition, MSBA-S in combination with irradiation resulted in effects on radiosensitivity in MDA-MB-231 cells (DMF₁₀ = 1.14). In particular, ROS formation was strongly assessed in MSBA-S-treated breast cancer cells. Our findings suggest that the sulfamate derivative of maslinic acid MSBA-S might be a new option for the radiation therapy in breast cancer cells.

Combined 3-O-acetylbetulin treatment and carbonic anhydrase IX inhibition results in additive effects on human breast cancer cells

Hypoxia plays a key role in tumor progression and resistance to radiotherapy. Expression of the transmembrane-tethered enzyme carbonic anhydrase IX (CA IX) is strongly induced by hypoxia. High CA IX expression levels correlate with poor prognosis in cancer patients. Previously, we showed that the downregulation of CA IX expression by siRNA interference and the inhibition of CA IX activity results in increased cytotoxicity, inhibition of migration and radiosensitization of hypoxic cancer cells. Betulinic acid (BA) is a natural compound derived from birch bark. It has shown promising anti-tumor effects due to its cancer cell specific cytotoxic properties. We have shown that BA inhibits the HIF-1α pathway, resulting in apoptosis, inhibition of migration and enhanced cytotoxicity of breast cancer cells. In this study, we investigate the effects of the novel betulin derivative 3-O-acetylbetulin (3-AC) and carbonic anhydrase inhibitors (CAI) octyl disulfamate (OCT) or 4-(3-[4-fluorophenyl]ureido)benzenesulfonamide (SLC-0111), on cellular and radiobiological parameters in MDA-MB-231 and MCF-7 cells. Treatment with 3-AC or OCT alone only caused moderate cytotoxicity, reduction in cell migration, ROS production and DNA damage. However, the combined treatment with 3-AC and CAI strongly enhanced radiosensitivity, increased cytotoxicity, inhibited cell motility and enhanced DNA damage. Our findings suggest that the combination of two bioactive drugs 3-AC and a CAI, such as OCT or SLC-0111, could be a promising therapeutic approach for targeting hypoxic tumor cells.

Hypoxia increases the apoptotic response to betulinic acid and betulin in human non-small cell lung cancer cells

Betulinic acid and betulin show promising activity against cancers cells, but the mechanism of their action is still unclear. In this study, non-small cell lung cancer (NSCLC) cell lines: A549, H358 and NCI-H1703 were treated with betulinic acid and betulin under normoxic and hypoxic conditions as hypoxia is critically involved in the response of solid tumors to chemotherapy. The treatment inhibits viability and proliferation of NSCLC cells. The anti-proliferative effect was induced by G1 cell cycle arrest with increased p21 expression and decreased cyclin D1 and cyclin B1 expression. Additionally, downregulation of p-GSK3β activity and the Wnt/β-catenin pathway were also observed under hypoxia. We found that hypoxia increased apoptosis in NSCLC cells. Cell death was associated with changes in the expression of proteins involved in the mitochondrial apoptosis pathway and induction of apoptotic death by caspase activation. Additionally, hypoxia exposure deregulated HIF-1α and p53 expression levels. Importantly, treatment with betulinic acid and betulin reduced colony-forming ability under normoxia, however, only betulinic acid reduced clonogenic activity under hypoxia. Our findings that betulinic acid increases apoptotic cell death and clonogenic activity under hypoxic conditions reveal new attractive strategies for treating hypoxic cancer tumors, such as NSCLC.

Evaluation of sulfonate and sulfamate derivatives possessing benzofuran or benzothiophene nucleus as inhibitors of nucleotide pyrophosphatases/phosphodiesterases and anticancer agents

Ectonucleotidases are a broad family of ectoenzymes that play a crucial role in purinergic cell signaling. Ecto-nucleotide pyrophosphatases/phosphodiesterases (NPPs) belong to this group and are important drug targets. In particular, NPP1 and NPP3 are known to be druggable targets for treatment of impaired calcification disorders (including pathological aortic calcification) and cancer, respectively. In this study, we investigated a series of sulfonate and sulfamate derivatives of benzofuran and benzothiophene as potent and selective inhibitors of NPP1 and NPP3. Compounds 1c, 1g, 1n, and 1s are the most active NPP1 inhibitors (IC₅₀ values in the range 0.12-0.95 µM). Moreover, compounds 1e, 1f, 1j, and 1l are the most potent inhibitors of NPP3 (IC₅₀ ranges from 0.12 to 0.95 µM). Compound 1d, 1f and 1t are highly selective inhibitors of NPP1 over NPP3, whereas compounds 1m and 1s are found to be highly selective towards NPP3 over NPP1. Structure-activity relationship (SAR) study has been discussed in detailed. With the aid of molecular docking studies, a common binding mode of these compounds and suramin (the standard inhibitor) was revealed, where the sulfonate group acts as a cation-binding moiety that comes in close contact with the zinc ion of the active site. Moreover, cytotoxic evaluation against MCF-7 and HT-29 cancer cell lines revealed that compound 1r is the most cytotoxic towards MCF-7 cell line with IC₅₀ value of 0.19 µM. Compound 1r is more potent and selective against cancer cells than normal cells (WI-38) as compared to doxorubicin.

Antiproliferative activity of cycloalkanecarboxamide derivatives possessing sulfonate or sulfamate moiety

A series of cycloalkanecarboxamide-containing sulfonate and sulfamate derivatives were prepared, and their antiproliferative activity was tested against NCI-60 cancer cell lines panel. Compound 1f possessing cyclohexyl and p-(tert-butyl)benzenesulfonate moieties was the most active among all the target compounds. It exerted broad-spectrum anticancer activity against all the nine cancer types involved in the NCI-60 panel. Additionally, compound 1g containing cyclohexyl and p-fluorobenzenesulfonate moieties was the most potent against HT29 colon cancer cell line (IC₅₀ = 4.73 µM) with selectivity index more than 4.23 towards HT29 than normal fibroblasts. It exerts its antiproliferative activity against HT29 through the induction of apoptosis (increasing caspase 3/7 activity) but not necrosis. Structure-activity relationship studies are presented in detail.

Evaluation of the Betulinic Acid-Cisplatin conjugate APC and its precursor DE9B for the treatment of human malignant glioma

Despite the existence of multimodal therapy concepts, glioblastoma remains a tumor type with one of the worst prognoses. In particular, the poor prognosis is due to the lack of therapeutic efficacy of chemical agents and irradiation in hypoxic tumor areas. New therapeutic strategies could improve the treatment of glioblastoma. In this study, we investigated the therapeutic efficacy of a conjugate of cisplatin (DDP), a widely used chemotherapeutic agent, and betulinic acid (BA), a natural product from plane tree bark, in glioblastoma cells under different oxygen conditions. We investigated the effects of the BA-DDP conjugate κN',N''-{3-acetyloxy-BA-28-[2-(2-aminoethyl)aminoethyl]amide} dichlorido platinum(II) (APC) and its precursor 3-acetyloxy-BA-28-[2-(2-aminoethyl)aminoethyl]amide (DE9B) on cytotoxicity, cell growth, apoptosis, migration and radiosensitivity compared to BA or DDP alone under different oxygen conditions. Based on the EC₅₀ values, the precursor DE9B exhibited the strongest cytotoxic effects of the analyzed chemotherapeutic agents. The BA-DDP conjugate APC achieved a moderate cytotoxic effect in glioma cells. Both of the newly developed agents induced cell growth delay, apoptosis and inhibition of migration. Furthermore, additive effects could be achieved in combination with irradiation. In contrast to those of BA and DDP, the cell biological effects of APC and DE9B were not influenced by the oxygen concentration. In this study, the linking of BA and DDP did not produce a compound with additive therapeutic effects on glioblastoma cell lines in vitro. Nevertheless, the results of this study suggest that the precursor DE9B is an effective BA derivative for the treatment of glioblastoma in vitro.

Sulfamates in drug design and discovery: Pre-clinical and clinical investigations

In the present article, we reviewed the sulfamate-containing compounds reported as bioactive molecules. The possible molecular targets of sulfamate derivatives include steroid sulfatase enzyme, carbonic anhydrases, acyl transferase, and others. Sulfamate derivatives can help treat hormone-dependent tumors including breast, prostate, and endometrial cancers, Binge eating disorder, migraine, glaucoma, weight loss, and epilepsy. Sulfamate derivatives can act also as calcium sensing receptor agonists and can aid in osteoporosis. Furthermore, acyl sulfamate derivatives can act as antibacterial agents against Gram-positive bacteria. A recent study revealed a new side effect of topiramate, a sulfamate-containing compound, which is sialolithiasis. The structural and biological characteristics of the reviewed compounds are presented in detail.

RNAi-mediated knockdown of CAIX enhances the radiosensitivity of nasopharyngeal carcinoma cell line, CNE-2

Although radiotherapy remains the most powerful as well as the primary treatment modality for nasopharyngeal carcinoma (NPC), approximately 20% of NPC patients still have local recurrence. Carbonic anhydrase IX (CAIX)-related signaling pathways that mediate radioresistance have been found in various kinds of cancer. However, the role of CAIX in NPC radioresistance is still unknown. In this study, we investigated the effect of CAIX silencing on sensitization to ionizing radiation in NPC by using Lipofectamine 2000, which delivers small interfering ribonucleic acid (siRNA) that targets CAIX. Results showed that Lipofectamine 2000 effectively delivered siRNA into the CNE-2 cells, which resulted in the decrease of CAIX expression and cell viability, decrease in cell proliferation and colony formation, and increase in the number of CNE-2 cells stuck in the G₂/M phase of the cell cycle upon induction of ionizing radiation. Increased sensitivity of radiotherapy in CNE-2 cells under hypoxic conditions was correlated with the suppression of CAIX. Cells treated with irradiation in addition to CAIX-siRNA1 demonstrated reduced radiobiological parameters (survival fraction at 2 Gy [SF2]) compared with those treated with irradiation only, with a sensitization-enhancing ratio of 1.47. These findings suggest that CAIX can be a promising therapeutic target for the treatment of radioresistant human NPC.