Histone deacetylases (HDACs) are an attractive drug target for the treatment of human breast cancer (BC), and therefore, HDAC inhibitors (HDACis) are being used in preclinical and clinical studies. The need to understand the scope of the mode of action of HDACis, as well as the report of the co-crystal structure of HDAC6/SS-208 at the catalytic site, provoked us to develop an isoxazole-based lead structure called 4-(2-(((1-(3,4-dichlorophenyl)-1H-1,2,3-triazol-4-yl)methyl)thio) pyrimidin-4-yl) morpholine (5h) and 1-(2-(((3-(p-tolyl) isoxazol-5-yl)methyl)thio) pyrimidin-4-yl) piperidin-4-one (6l) that targets HDACs in human BC cells. We found that the compound 5h or 6l could inhibit the proliferation of BC cells with an IC₅₀ value of 8.754 and 11.71 µM, respectively. Our detailed in silico analysis showed that 5h or 6l compounds could target HDAC in MCF-7 cells. In conclusion, we identified a new structure bearing triazole, isoxazole, and thiouracil moiety, which could target HDAC in MCF-7 cells and serve as a base to make new drugs against cancer.

Nuclear factor kappa beta (NF-κB) is a transcriptional factor that plays a crucial role in regulating cancer cell proliferation. Therefore, the inhibition of NF-κB activity by small molecules may be beneficial in cancer therapy. In this report, methyl-thiol-bridged oxadiazole and triazole heterocycles were synthesized via click chemistry and it was observed that the lead structure, 2-(((1-(3,4-dichlorophenyl)-1H-1,2,3-triazol-4-yl)methyl)thio)-5-(4-methoxybenzyl)-1,3,4-oxadiazole (4c), reduced the viability of MCF-7 cells with an IC₅₀ value of 7.4 µM. Compound 4c also caused concentration-dependent loss of cell viability in chronic myelogenous leukemia (CML) cells. Furthermore, compound 4c inhibited the activation of NF-κB in human CML cells as observed by nuclear translocation and DNA binding assays. Functionally, compound 4c produced PARP cleavage and also suppressed expression of Bcl-2/xl, MMP-9, COX-2, survivin, as well as VEGF, resulting in apoptosis of CML cells. Moreover, ChIP assay showed that compound 4c decreased the binding of COX-2 to the p65 gene promoter. Detailed in silico analysis also indicated that compound 4c targeted NF-κB in CML cells. In conclusion, a novel structure bearing both triazole and oxadiazole moieties has been identified that can target NF-κB in CML cells and may constitute a potential novel drug candidate.

In breast cancer (BC), STAT3 is hyperactivated. This study explored the design of imidazopyridine-tethered pyrazolines as a de novo drug strategy for inhibiting STAT3 phosphorylation in human BC cells. This involved the synthesis and characterization of two series of compounds namely, 1-(3-(2,6-dimethylimidazo [1,2-a]pyridin-3-yl)-5-(3-nitrophenyl)-4,5-dihydro-1H-pyrazol-1-yl)-2-(4-(substituted)piperazin-1-yl)ethanone and N-substituted-3-(2,6-dimethylimidazo[1,2-a]pyridin-3-yl)-5-(3-nitrophenyl)-4,5-dihydro-1H-pyrazoline-1-carbothioamides. Compound 3f with 2,3-dichlorophenyl substitution was recognized among the tested series as a lead structure that inhibited the viability of MCF-7 cells with an IC₅₀ value of 9.2 μM. A dose- and time-dependent inhibition of STAT3 phosphorylation at Tyr705 and Ser727 was observed in MCF-7 and T47D cells when compound 3f was added in vitro. Calculations using density functional theory showed that the title compounds HOMOs and LUMOs are situated on imidazopyridine-pyrazoline and nitrophenyl rings, respectively. Hence, compound 3f effectively inhibited STAT3 phosphorylation in MCF-7 and T47D cells, indicating that these structures may be an alternative synthon to target STAT3 signaling in BC.

Nuclear factor kappa B (NF–κB) is a potential therapeutic target in breast cancer. In the current study, a new class of oxazine– and piperazine–linked pyrimidines was developed as inhibitors of NF–κB, overcoming the complexity of the oxazine structure found in nature and enabling synthesis under laboratory conditions. Among the series of synthesized and tested oxazine–pyrimidine and piperazine–pyrimidine derivatives, compounds 3a and 5b inhibited breast cancer cell (MCF–7) viability with an IC₅₀ value of 9.17 and 6.29 µM, respectively. In silico docking studies showed that the pyrimidine ring of 3a and the 4–methoxybenzyl thiol group of 5b could strongly bind the p65 subunit of NF–κB, with the binding energies −9.32 and −7.32 kcal mol⁻¹. Furthermore, compounds 3a and 5b inhibited NF–κB in MCF–7 breast cancer cells. In conclusion, we herein report newer structures that target NF–κB in BC cells.

The development of environment-friendly new Poly-adenosine diphosphate (ADP)-ribose Polymerase (PARP) inhibitors are highly essential because of their involvement in the survival of cancer cells. Therefore, a library of indazolyl-substituted-1,3,4-oxadiazoles known to inhibit PARP in cancer cells was synthesized by a green protocol. Furthermore, the cytotoxic effects of these compounds were evaluated in human MCF-7 breast cancer (BC) cells, which revealed that the compound 2-(3-bromo-4-nitrophenyl)-5-(1-methyl-1H-indazol-3-yl)-1,3,4-oxadiazole (8) inhibited viability with an IC₅₀ value of 1.57 µM. Since the oxadiazole structure was extensively used in medicinal chemistry applications, the reported environment-friendly protocol was superior to the conventional method. Further, computational mechanistic studies revealed that the oxadiazole ring formation occurred spontaneously when compared to the conventional method. Additionally, the in silico bioinformatic studies of oxadiazole binding towards PARP1 showed that compound 8 could bind to PARP1 with higher binding energy (BE) of −7.29 kcal/mol when compound to compound 5s (BE = −7.17 kcal/mol), a known PARP cleavage oxadiazole structure (2-(3,4-Dimethoxybenzyl)-5-(3-(2-fluoro-3-methylpyridin-4-yl)phenyl)-1,3,4-oxadiazole) indicative of the improvement in the optimization process. In conclusion, a newer indazolyl-oxadiazole compound is reported, which could serve as a lead in developing PARP inhibitors in BC cells.

Metastasis, the dissemination of tumor cells, stands as the second most prominent contributor to mortality arising from breast cancer. To counteract this phenomenon, the molecular markers associated with angiogenesis, particularly vascular endothelial growth factor (VEGF) and its receptor (VEGFR), have emerged as promising strategies for impeding the progression of tumor cells. Compounds like pyrimidines, coumarins, oxadiazoles, and triazoles have undergone comprehensive investigations due to their notable anticancer potential, highlighting their encouraging capacities in inhibiting VEGFR-2, an essential mediator of angiogenesis signaling. Herein, we have synthesized pyrimidine–triazoles and oxadiazole–triazoles using electrochemical and conventional methods. The newly synthesized compounds were evaluated for anticancer activity against MCF-7 breast cancer cells, and it was found that the compounds 8a and 8b showed IC₅₀ values of 5.29 and 15.54 μM, respectively. Our in silico mode of action revealed that these compounds could target VEGFR-2, which was further evidenced by our in silico structure-based bioinformatic analysis. In conclusion, we reported an electrochemical method to prepare novel drug-like compounds, based on triazole and other heterocyclic hybrids, that could be used to design VGFR-targeting drugs.