Discovery of a novel DNA binding agent via design and synthesis of new thiazole hybrids and fused 1,2,4-triazines as potential antitumor agents: Computational,spectrometric and in silico studies

New series of furan–thiazole hybrids (3a-f), thiazolo[2,3-c]-1,2,4-triazines (4a-f), their bioisosteres 1,3,4-thiadiazolo[2,3-c]-1,2,4-triazines (8a-d) and 1,2,4-triazino[4,3-b]-1,2,4-triazines (13a-e) were designed, synthesized and evaluated for their in vitro antitumor activities at the National Cancer Institute (NCI, USA). Among the synthesized compounds, 3d was found to exhibit promising broad spectrum antitumor activity (GI₅₀ MG-MID = 14.22 µM) in a five-dose assay against the full panel NCI-cancer cell lines. 3d displayed higher antitumor activity against most tested cancer cell lines than 5-FU as reference. COMPARE analysis and molecular electrostatic potential computational study revealed that 3d probably exerts its antitumor properties through DNA binding similar to Clomesone. Further DNA binding studies using fluorescent terbium (Tb⁺³) probe revealed increased fluroresence of DNA-3d-Tb⁺³ mixture due to damage of the double-stranded DNA. Also, UV–vis absorption study was conducted which showed hyperchromic shift in DNA absorption confirming 3d-induced DNA damage. The assessed potency of 3d-induced DNA damage of calf thymus DNA showed a concentration as low as 2.04 ng/mL for a detectable DNA damage. Moreover, in silico calculation of physicochemical properties and druglikeness were in compliance to Lipinski’s rule.     

Mitomycin C linked to DNA minor groove binding agents: synthesis, reductive activation, DNA binding and cross-linking properties and in vitro antitumor activity

Mitomycin C (MC) is a natural cytotoxic agent used in clinical anticancer chemotherapy. Its antitumor target appears to be DNA. Upon bioreductive activation MC alkylates and cross-links DNA. MC derivatives were synthesized in which MC was linked to DNA minor groove binding agents, analogous to netropsin and distamycin. One, two and three N-methylpyrrole carboxamide units were conjugated with MC by a (CH2)5-tether to the 7-amino group of MC (11, 12 and 13, respectively). In contrast to MC 11, 12 and 13 displayed non-covalent affinity to DNA. Their bioreductive activation by NADPH-cytochrome c reductase proceeded as fast as that of MC. Metabolites arising from reductive and low-pH activation were characterized and found to be analogous to those of MC. DNA cross-linking activities were weak and decreased with an increasing number of N-methylpyrrole carboxamide units linked with the mitomycin molecule. No adducts were formed with calf thymus DNA in detectable amounts. In vitro antitumor activities of 11-13 were determined using the NCI in vitro antitumor screen. The conjugates 11-13 are growth inhibitory; however, their activities are 1.5-2 orders of magnitude lower than that of MC. COMPARE analysis indicates that the mechanism of the action of 11 and 12 correlates moderately with MC but negatively with distamycin. Conjugate 13 correlates neither with MC nor with distamycin. The results suggest that the basic cause of the observed low activity of the MC-minor groove binder conjugates is the fast irreversible decay of the activated MC, competing effectively with the slow drug delivery to CpG sites, required for the alkylation.     

Structure-based design,synthesis and biological testing of etoposide analog epipodophyllotoxin–N-mustard hybrid compounds designed to covalently bind to topoisomerase II and DNA

Drugs that target DNA topoisomerase II isoforms and alkylate DNA represent two mechanistically distinct and clinically important classes of anticancer drugs. Guided by molecular modeling and docking a series of etoposide analog epipodophyllotoxin–N-mustard hybrid compounds were designed, synthesized and biologically characterized. These hybrids were designed to alkylate nucleophilic protein residues on topoisomerase II and thus produce inactive covalent adducts and to also alkylate DNA. The most potent hybrid had a mean GI₅₀ in the NCI-60 cell screen 17-fold lower than etoposide. Using a variety of in vitro and cell-based assays all of the hybrids tested were shown to target topoisomerase II. A COMPARE analysis indicated that the hybrids had NCI 60-cell growth inhibition profiles matching both etoposide and the N-mustard compounds from which they were derived. These results supported the conclusion that the hybrids displayed characteristics that were consistent with having targeted both topoisomerase II and DNA.     

Erythrofordins D and E,two new cassaine-type diterpenes from Erythrophleum suaveolens

Two new cassaine-type diterpenoids, namely erythrofordins D (1) and E (2), sourced from a Cameroon collection of Erythrophleum suaveolens were isolated and assessed for anti-tumor activity. In the NCI-60 cancer cell assay, erythrofordins D (1) and E (2) were found to be cytotoxic in the low micro molar ranges with a mean GI₅₀ value of 2.45 and 0.71?µM, mean TGI value of 9.77 and 2.29?µM, and a mean LC₅₀ of 26.92 and 11.48?µM for 1 and 2 respectively. Using the COMPARE algorithm, the new compounds were found to have similar NCI-60 response profiles to the known cardiac glycosides hyrcanoside and strophanthin. In addition, in an assay examining the viability and contractile function in human cardiomyocytes derived from induced pluripotent stem-cells, erythrofordins showed cardiotoxicity effects at concentrations as low as 0.03?µg/mL.     

Synthesis and in vitro characterization of platinum(II) anticancer coordinates using FTIR spectroscopy and NCI COMPARE: A fast method for new compound discovery

Platinum-based drugs have been used for several decades to treat various cancers successfully. Cisplatin is the original compound in this class; it cross-links DNA, resulting in cell cycle arrest and cell death via apoptosis. Cisplatin is effective against several tumor types but exhibits toxic side effects; in addition, tumors often develop resistance. An original in vitro approach is proposed to determine whether platinum-based research compounds are good candidates for further study by comparing them to marketed drugs using FTIR spectroscopy and the COMPARE analysis from the NCI. Both methods can produce fingerprints and highlight differences between the compounds, classifying the candidates and revealing promising derivatives.     

Discovery of anti-cancer activity for benzo[1,2,4]triazin-7-ones: Very strong correlation to pleurotin and thioredoxin reductase inhibition

The thioredoxin (Trx)–thioredoxin reductase (TrxR) system plays a key role in maintaining the cellular redox balance with Trx being over-expressed in a number of cancers. Inhibition of TrxR is an important strategy for anti-cancer drug discovery. The natural product pleurotin is a well-known irreversible inhibitor of TrxR. The cytotoxicity data for benzo[1,2,4]triazin-7-ones showed very strong correlation (Pearson correlation coefficients ∼0.8) to pleurotin using National Cancer Institute COMPARE analysis. A new 3-CF₃ substituted benzo[1,2,4]triazin-7-one gave submicromolar inhibition of TrxR, although the parent compound 1,3-diphenylbenzo[1,2,4]triazin-7-one was more cytotoxic against cancer cell lines. Benzo[1,2,4]triazin-7-ones exhibited different types of reversible inhibition of TrxR, and cyclic voltammetry showed characteristic quasi-reversible redox processes. Cell viability studies indicated strong dependence of cytotoxicity on substitution at the 6-position of the 1,3-diphenylbenzo[1,2,4]triazin-7-one ring.