New benzoxanthone derivatives as topoisomerase inhibitors and DNA cross-linkers

Synthesis and evaluation of 7-(3-aminopropyloxy)-substituted flavone analogue as a topoisomerase IIα catalytic inhibitor and its sensitizing effect to enzalutamide in castration-resistant prostate cancer cells

Prostate cancer patients primarily receive androgen receptor (AR)-targeted drugs as a primary treatment option because prostate cancer is associated with highly activated AR signaling. AR amplification made prostate cancer cells viable under treatment of AR-targeted therapy, leading to castration resistance. AR amplification was more common in enzalutamide-resistant patients. As a strategy to overcome castration resistance and to improve the efficacy of enzalutamide, second-generation nonsteroidal antiandrogen drugs for castration-resistant prostate cancer (CRPC) including topoisomerase II (topo II) poisons such as etoposide and mitoxantrone, have been administered in combination with enzalutamide. In the present study, it was confirmed that amplification of topo IIα, but not I and IIβ, was directly and proportionally associated with poor clinical outcome of Prostate cancer. Among a novel series of newly designed and synthesized 7-(3-aminopropyloxy)-substituted flavone analogues, compound 6, the most potent derivative, was further characterized and identified as a topo IIα catalytic inhibitor that intercalates into DNA and binds to the DNA minor groove with better efficacy and less genotoxicity than etoposide, a topo II poison. Compound 6 showed remarkable efficacy in inhibiting AR-negative CRPC cell growth and sensitizing activity to enzalutamide in AR-positive CRPC cells, thus confirming the potential of topo IIα catalytic inhibitor to overcome resistance to androgen deprivation therapy.

Rh(III)-Catalyzed Oxidative C-H Activation/Annulation of Salicylaldehydes with Masked Enynes for the Synthesis of Chromones

A rhodium(III)-catalyzed oxidative C-H activation/annulation of salicylaldehydes with propargylic acetates has been developed for the regioselective synthesis of 3-vinyl chromones in good yields with broad functional group tolerance. 3-Vinyl chromones were converted into biologically active benzo[c]xanthone by I₂-mediated oxidative electrocyclization.

Synthesis, Characterization and Anticancer Efficacy Evaluation of Benzoxanthone Compounds toward Gastric Cancer SGC-7901

Three benzoxanthone derivatives were synthesized through a new photochemical strategy. The in vitro cytotoxic activity of these compounds was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and their partition coefficients (logP) were measured by shake flask method. The pK_a values of the compounds were detected by potentionmetric titration. The interaction of the compounds with calf thymus DNA (CT-DNA) was investigated by electronic absorption, luminescence spectra and viscosity. A molecular docking analysis was performed. The antitumor efficacy of the compounds was evaluated by cell apoptosis, cell cycle arrest, intracellular Ca²⁺ concentrations and reactive oxygen species (ROS) levels. The mitochondrial membrane potential was assayed using JC-1 (5,5′,6,6′-tetrachloro-1,1,3′,3′-tetraethyl-imidacarbocyanine iodide) as the fluorescence probe. The expression of Bcl-2 family protein, caspase 3 and poly ADP-ribose polymerase (PARP) was explored by western blot. The results showed that the compounds induced apoptosis through a ROS-mediated mitochondrial dysfunction pathway. This work provides an efficient approach to synthesize benzoxanthone derivatives, and is helpful for understanding the apoptotic mechanism.

Aspergillus derived mycotoxins in food and the environment: Prevalence, detection, and toxicity

Aspergillus species are the paramount ubiquitous fungi that contaminate various food substrates and produce biochemicals known as mycotoxins. Aflatoxins (AFTs), ochratoxin A (OTA), patulin (PAT), citrinin (CIT), aflatrem (AT), secalonic acids (SA), cyclopiazonic acid (CPA), terrein (TR), sterigmatocystin (ST) and gliotoxin (GT), and other toxins produced by species of Aspergillus plays a major role in food and human health. Mycotoxins exhibited wide range of toxicity to the humans and animal models even at nanomolar (nM) concentration. Consumption of detrimental mycotoxins adulterated foodstuffs affects human and animal health even trace amounts. Bioaerosols consisting of spores and hyphal fragments are active elicitors of bronchial irritation and allergy, and challenging to the public health. Aspergillus is the furthermost predominant environmental contaminant unswervingly defile lives with a 40-90 % mortality risk in patients with conceded immunity. Genomics, proteomics, transcriptomics, and metabolomics approaches useful for mycotoxins' detection which are expensive. Antibody based detection of toxins chemotypes may result in cross-reactivity and uncertainty. Aptamers (APT) are single stranded DNA (ssDNA/RNA), are specifically binds to the target molecules can be generated by systematic evolution of ligands through exponential enrichment (SELEX). APT are fast, sensitive, simple, in-expensive, and field-deployable rapid point of care (POC) detection of toxins, and a better alternative to antibodies.

The synthesis and anticancer activities of chiral epoxy-substituted chromone analogs

Human DNA topoisomerases (topos) have been recognized as a good target molecule for the development of anticancer drugs because they play an important role in solving DNA topological problems caused by DNA strand separation during replication and transcription. In this study, we designed and synthesized 11 novel chromone backbone compounds possessing epoxy and halohydrin substituents with chirality. In the topos inhibition test, compounds 2, 9, 10, and 11 showed comparable topo I inhibitory activity at concentration of 100 μM compared to camptothecin, and all of the synthesized compounds showed moderate topo IIα inhibitory activity. Among them, compounds 9, 10 and 11 were more potent than the others in both topo I and IIα inhibitory activity. Compound 11 showed the most potent cell antiproliferative activity against all tested cancer cell lines with particularly strong inhibition (an IC₅₀ of 0.04 µM) of K562 myelogenous leukemia cancer cell proliferation. In the brief structure-activity relationship analysis, there was no clear correlation between stereochemistry and topos inhibitory and cytotoxic activity. 5(R),7(S)-bisepoxy-substituted compound 11 was the most potent DNA cross-linker and induced G2/M arrest in a cell cycle assay in a dose- and time-dependent manner. After the treatment time period induced apoptosis in K562 cells without increasing G2/M-phase cells. Overall, compound 11 showed good consistent inhibitory biological activity related to cancer cell proliferation.

Intestinal P-glycoprotein inhibitors, benzoxanthone analogues

OBJECTIVES

The inhibitors of P-glycoprotein (P-gp) which limits an access of exogenous compounds in the luminal membrane of the intestine have been studied to enhance the intestinal P-gp-mediated absorption of anticancer drugs.

METHODS

Inhibition of the efflux pump by synthesized benzoxanthone derivatives was investigated in vitro and in vivo. MCF-7/ADR cell line was used for cytotoxicity assay and [³ H]-daunomycin (DNM) accumulation/efflux study. Eight benzoxanthone analogues were tested for their effects on DNM cytotoxicity. Among them, three analogues were selected for the accumulation/efflux and P-gp ATPase studies. Paclitaxel (PTX), a P-gp substrate anticancer drug, was orally administered to rats with/without compound 1 (8,10-bis(thiiran-2-ylmethoxy)-7H-benzo[c]xanthen-7-one). The pharmacokinetic parameters of PTX in the presence/absence of compound 1 were evaluated from the plasma concentration-time profiles.

KEY-FINDINGS

Compound 1 increased the DNA accumulation to 6.5-fold and decreased the DNM efflux to approximately 1/2 in the overexpressing P-gp cell line. Relative bioavailability (RB) of PTX in rats was significantly increased up to 3.2-fold by compound 1 (0.5 or 2 mg/kg).

CONCLUSIONS

Benzoxanthone analogue, compound 1 is strongly suggested to be a promising inhibitor of P-gp to improve an oral absorption of compounds for cancer therapy.

Arylxanthones and arylacridones: a synthetic overview

Arylxanthones and arylacridones although not yet found in nature are becoming an important group of heterocyclic compounds due to their promising biological activities. Their central cores, xanthone and acridone, are recognized as interesting motifs for drug development mainly to be used in antitumour chemotherapy. The synthesis of this type of compounds is still scarce but several successful examples were recently published and a large variety of arylated xanthone and acridone derivatives were prepared. A systematic survey of the literature dedicated to their synthesis will be presented and discussed in this review.

QSAR and docking studies on xanthone derivatives for anticancer activity targeting DNA topoisomerase IIα

Due to the high mortality rate in India, the identification of novel molecules is important in the development of novel and potent anticancer drugs. Xanthones are natural constituents of plants in the families Bonnetiaceae and Clusiaceae, and comprise oxygenated heterocycles with a variety of biological activities along with an anticancer effect. To explore the anticancer compounds from xanthone derivatives, a quantitative structure activity relationship (QSAR) model was developed by the multiple linear regression method. The structure-activity relationship represented by the QSAR model yielded a high activity-descriptors relationship accuracy (84%) referred by regression coefficient (r(2)=0.84) and a high activity prediction accuracy (82%). Five molecular descriptors - dielectric energy, group count (hydroxyl), LogP (the logarithm of the partition coefficient between n-octanol and water), shape index basic (order 3), and the solvent-accessible surface area - were significantly correlated with anticancer activity. Using this QSAR model, a set of virtually designed xanthone derivatives was screened out. A molecular docking study was also carried out to predict the molecular interaction between proposed compounds and deoxyribonucleic acid (DNA) topoisomerase IIα. The pharmacokinetics parameters, such as absorption, distribution, metabolism, excretion, and toxicity, were also calculated, and later an appraisal of synthetic accessibility of organic compounds was carried out. The strategy used in this study may provide understanding in designing novel DNA topoisomerase IIα inhibitors, as well as for other cancer targets.

Dithiiranylmethyloxy azaxanthone shows potent anti-tumor activity via suppression of HER2 expression and HER2-mediated signals in HER2-overexpressing breast cancer cells

Dithiiranylmethyloxy azaxanthone (CHO10), which was discovered by screening compounds in a reporter gene assay, inhibited the ESX-Sur2 interaction in a dose-dependent manner with potency similar to canertinib. The intervention of CHO10 during the ESX-Sur2 interaction caused down-regulation of both HER2 gene amplification and HER2 protein expression, which led to the attenuation of HER2-mediated downstream signal cascades and autocrine cell growth in SK-BR-3 cells, which are HER2 overexpressing breast cancer cells. The cell growth inhibitory activity of CHO10 was more potent in HER2-overexpressing breast cancer cells (AU-565, BT474 and SK-BR-3) than in HER2-negative cells (HEK293) and breast cancer cells (MCF-7) that express a basal level of HER2. Treatment with CHO10 in combination with tamoxifen sensitized BT474 cells, tamoxifen-resistant ER-positive breast cancer cell line, toward chemotherapeutic. The anti-tumor activity of CHO10 was validated by the significant reduction in tumor size of NCI-H460 or DLD-1 subcutaneously implanted xenograft tumors through treatment with 1mg/kg five times every other 2days.

Secalonic acid D as a novel DNA topoisomerase I inhibitor from marine lichen-derived fungus Gliocladium sp. T31

CONTEXT

DNA topoisomerase I (topo I) is an essential enzyme which regulates the conformational changes in DNA topology by cleaving and rejoining DNA strands during normal cell growth. The inhibitors of topo I represent a major class of anticancer drugs. In our projects to isolate new anticancer agents from marine-derived fungi, secalonic acid D (SAD) with inhibitory activity on topo I was isolated from the fermentation broth of marine lichen-derived fungus Gliocladium sp. T31, which was collected from marine sediments in South Pole.

OBJECTIVE

The inhibitory activity of SAD on topo I was investigated for the first time.

MATERIALS AND METHODS

The inhibitory effect of SAD on topo I was determined via in vitro supercoil relaxation assays and electrophoretic mobility shift assay (EMSA) using plasmid substrate, pBR322.

RESULTS

SAD displays a considerable inhibition on topo I in a dose-dependent manner with the minimum inhibitory concentration (MIC) of 0.4 µM. Unlike the prototypic DNA topo I poison camptothecin (CPT), SAD inhibits the binding of topo I to DNA but does not induce the formation of topo I-DNA covalent complexes.

DISCUSSION AND CONCLUSION

SAD is an excellent topo I inhibitor and thus a significantly potential anticancer candidate.