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On account of their significance as apoptosis inducing agents, merging indole and 3-hydrazinoindolin-2-one scaffolds is a logic tactic for designing pro-apoptotic agents. Consequently, 27 hybrids (6a–r, 9a–f and 11a–c) were synthesised and evaluated for their cytotoxicity against MCF-7, HepG-2 and HCT-116 cancer cell lines. SAR studies unravelled that N-propylindole derivatives were the most active compounds such as 6n (MCF-7; IC50=1.04 µM), which displayed a significant decrease of cell population in the G2/M phase and significant increase in the early and late apoptosis by 19-folds in Annexin-V-FTIC assay. Also, 6n increased the expression of caspase-3, caspase-9, cytochrome C and Bax and decreased the expression of Bcl-2. Moreover, compounds 6i, 6j, 6n and 6q generated ROS by significant increase in the level of SOD and depletion of the levels of CAT and GSH-Px in MCF-7.

As a continuation for our previous work, a novel set of N -alkylindole-isatin conjugates ( 7 , 8a–c , 9 and 10a–e ) is here designed and synthesised with the prime aim to develop more efficient isatin-based antitumor candidates. Utilising the SAR outputs from the previous study, our design here is based on appending four alkyl groups with different length (ethyl and n-propyl), bulkiness (iso-propyl) and unsaturation (allyl) on N -1 of indole motif, with subsequent conjugation with different N -unsubstituted isatin moieties to furnish the target conjugates. As planned, the adopted strategy achieved a substantial improvement in the growth inhibitory profile for the target conjugates in comparison to the reported lead VI . The best results were obtained with N -propylindole –5-methylisatin hybrid 8a which displayed broad spectrum anti-proliferative action with efficient sub-panel GI 50 (MG-MID) range from 1.33 to 4.23 µM, and promising full-panel GI 50 (MG-MID) equals 3.10 µM, at the NCI five-dose assay. Also, hybrid 8a was able to provoke cell cycle disturbance and apoptosis in breast T-47D cells as evidenced by the DNA flow cytometry and Annexin V-FITC/PI assays. Furthermore, hybrid 8a exhibited good inhibitory action against cell cycle regulator CDK2 protein kinase and the anti-apoptotic Bcl-2 protein (IC 50 = 0.85 ± 0.03 and 0.46 ± 0.02 µM, respectively). Interestingly, molecular docking for hybrid 8a in CDK2 and Bcl-2 active sites unveiled that N -propyl group is involved in significant hydrophobic interactions. Taken together, the results suggested conjugate 8a as a promising lead for further development and optimisation as an efficient antitumor drug.

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The rapid progress in understanding the molecular biology of cancer has made a large impact on the design and development of novel therapeutic strategies prompted by the multi-factorial limitations of the current chemotherapeutic modalities. Given that the development of newer antineoplastic drugs continues to rely heavily on isolation from natural sources rather than applications based on rational drug design and combinatorial chemistry, fungal secondary metabolites rank high on the list of potential targets for the discovery of novel chemotherapeutic agents. They represent a diverse group of bioactive compounds characterized by their origin and biosynthetic pathways. Also, they serve as regulators, chemical messengers in developmental processes, or as antibiotics. A broad variety of fungal secondary metabolites possess potent antitumor activity. Alpha sarcin, gliotoxins, trichodimerol, L-lysine alpha-oxidase, fumagillin, declauxin, chrysanthones, fungal-derived low molecular weight inhibitors of angiogenesis e.g. TNP-470, retamycin, daunorubicin, and doxorubicin all have been shown to exert potent antitumor activity. Inhibition of protein synthesis, induction of DNA breakage and apoptosis, as well as blockade of angiogenesis are examples of the multiple antitumor mechanisms of fungal secondary metabolites. The current review explores the potential use of fungal secondary metabolites as antineoplastic drugs with special reference to the novel hepatoma growth-inhibition factor that we recently characterized from Trichoderma viride.