Molecular mechanism of action of new 1,4-naphthoquinones tethered to 1,2,3-1H-triazoles with cytotoxic and selective effect against oral squamous cell carcinoma.

The oral squamous cell carcinoma (OSCC) stands out as a public health problem due to its high incidence and low survival rate, despite advances in diagnosis and treatment. Moreover, the most commonly chemotherapeutic agents for OSCC, such as carboplatin and cisplatin, generate important side effects, evidencing the urgency in developing new drugs. Naphthoquinones are an important class of natural products or synthetic compounds with cytotoxic effect demonstrated on different cancer types. In the present study, thirty-five 1,4-naphthoquinones tethered to 1,2,3-1H-triazoles were synthesized and the antitumor activity and molecular mechanisms were evaluated in several assays including in vitro and in vivo models of OSCC and normal oral human cells. Compounds 16a, 16b and 16 g were able to induce cytotoxicity in three different tumor cell lines of human OSCC (SCC4, SCC9 and SCC25) and were more toxic and selective to tumor cells (Selective Index, SI > 2) than classical and chemically similar controls (Carboplatin and Lapachol). Compound 16 g showed the higher SI value. Besides, compounds 16a, 16b and 16 g significantly reduced colony formation of SCC9 cells in the tested concentrations. Hemolytic assay using compounds 16a, 16b and 16 g at high concentrations showed no compound exhibited hemolysis higher than 5%, similar to controls. In vivo acute toxicity study showed that 16 g was the only one, among the three compounds, with no apparent limiting toxic effects on mice in the tested concentrations. Thus, the investigation of cell death mechanisms was conducted with this compound. 16 g does not trigger ROS production nor binds to DNA. On the other hand, compound 16 g induced microtubule disorganization, and molecular modeling studies suggests a potential mechanism of action related to inhibition of topoisomerases and/or hPKM2 activities. Cell morphology, pyknotic nuclei presence, cleaved caspase-3 staining and viability assays using caspase-3 inhibitors demonstrate compound 16 g induced cell death through apoptosis. Among the 35 synthesized triazole naphthoquinones, compound 16 g was the most effective compound against OSCC cells, presenting high cytotoxicity (~35 µM), selectivity (SI ~ 6) and low acute toxicity on animals, and therefore might be considered for future cancer therapy.

Natural products from Brazilian biodiversity identified as potential inhibitors of PknA and PknB of M. tuberculosis using molecular modeling tools.

Mycobacterium tuberculosis was discovered in 1882 by Robert Koch but, since its discovery, the tuberculosis (TB) epidemic has endured, being one of the top 10 causes of death worldwide. Drug-resistant TB continues to be a public health threat and bioactive compounds with a new mode of action (MoA) are needed to overcome this. Since natural products are described as important sources for the development of new drugs, the objective of this work was to identify potential ligands from Brazilian natural products (NPs) for M. tuberculosis targets using molecular modeling tools. Using chemogenomics we identified the Serine/Threonine Protein Kinase PknB as a putative target for 13 NPs from a database from Brazilian biodiversity (NuBBE). Literature data supported further investigation of NuBBE105, NuBBE598, NuBBE936, NuBBE964, NuBBE1045, and NuBBE1180 by molecular docking and dynamics. Key interactions were observed with PknB and simulations confirmed stability and favorable binding energies. Considering structural similarity with PknB, we further explored binding of the NPs to PknA, critical for M. tuberculosis survival, and all of them resembled important interactions with the enzyme, showing stable and favorable binding energies, whilst van der Waals interactions seem to play a key role for binding to PknA and PknB. NuBBE936 and NuBBE1180 have already had their antimycobacterial activity reported and our results can provide a basis for their MoA. Finally, the other NPs which have not been tested against M. tuberculosis deserve further investigation, aiming at the discovery of antimycobacterial drug candidates with innovative MoA.