Design and synthesis of luotonin A-derived topoisomerase targeting scaffold with potent antitumor effect and low genotoxicity.

Conventional topoisomerase (Topo) inhibitors typically usually exert their cytotoxicity by damaging the DNAs, which exhibit high toxicity and tend to result in secondary carcinogenesis risk. Molecules that have potent topoisomerase inhibitory activity but involve less DNA damage provide more desirable scaffolds for developing novel chemotherapeutic agents. In this work, we broke the rigid pentacyclic system of luotonin A and synthesized thirty-three compounds as potential Topo inhibitors based on the devised molecular motif. Further investigation disclose that two compounds with the highest antiproliferation activity against cancer cells, 5aA and 5dD, had a distinct Topo I inhibitory mechanism different from those of the classic Topo I inhibitors CPT or luteolin, and were able to obviate the obvious cellular DNA damage typically associated with clinically available Topo inhibitors. The animal model experiments demonstrated that even in mice treated with a high dosage of 50 mg/kg 5aA, there were no obvious signs of toxicity or loss of body weight. The tumor growth inhibition (TGI) rate was 54.3 % when 20 mg/kg 5aA was given to the T24 xenograft mouse model, and 5aA targeted the cancer tissue precisely without causing damage to the liver and other major organs.

Design, Synthesis, and Antifungal Evaluation of Luotonin A Derivatives against Phytopathogenic Fungi.

Crop diseases caused by fungi threaten food security and exacerbate the food crisis. Inspired by the application of fungicide candidates from natural products in agrochemical discovery, a series of luotonin A derivatives were designed, synthesized, and evaluated for their antifungal activities against five plant fungi. Most of these compounds exhibited significant fungicidal activity against Botrytis cinerea in vitro with EC50 values less than 1 µg/mL. Among them, compounds w7, w8, w12, and w15 showed superior antifungal activity against B. cinerea with EC50 values of 0.036, 0.050, 0.042, and 0.048 µg/mL, respectively, which were more potent than boscalid (EC50 = 1.790 µg/mL). Preliminary mechanism studies revealed that compound w7 might pursue its antifungal activity by disrupting the fungal cell membrane and cell wall. Moreover, in vivo bioassay also indicated that compound w7 could be effective for the control of B. cinerea. The above results evidenced the potential of luotonin A derivatives as novel and promising candidate fungicides.

Luotonin A and Its Derivatives as Novel Antiviral and Antiphytopathogenic Fungus Agents.

Plant diseases caused by viruses and fungi have posed a serious threat to global agricultural production. The discovery of new leads based on natural products is an important way to innovate pesticides. In this work, natural product luotonin A was found to have good antiviral activity against tobacco mosaic virus (TMV) for the first time. A series of luotonin A derivatives were designed, synthesized, and evaluated for their antiviral activities and fungicidal activities systematically. Most compounds displayed better antiviral activities against TMV than commercial ribavirin. Compounds 9k, 12b, and 12d displayed about similar inhibitory effects as ningnanmycin (inhibitory rates of 55, 57, and 59% at 500 µg/mL for inactivation, curative, and protection activities in vivo, respectively), the best antiviral agent at present, and emerged as novel antiviral leads for further research. We selected 9k for further antiviral mechanism research via transmission electron microscopy and molecular docking, which revealed that compound 9k can interact with TMV coat protein through the hydrogen bond, leading to its polymerization, thus preventing virus assembly. Further fungicidal activity tests showed that these compounds also showed broad-spectrum fungicidal activities against 14 kinds of phytopathogenic fungi. Especially, compound 14 with a 100% antifungal effect against Botrytis cinereal emerged as a lead for further research. This work provides a reference for the development of agricultural active ingredients based on Chinese medicine plants.

A-ring and E-ring modifications of the cytotoxic alkaloid Luotonin A: Synthesis, computational and biological studies.

A series of new Luotonin A derivatives with substituents at rings A and E was synthesized, together with some E-ring-unsubstituted derivatives. Subsequently, the compound library was examined in silico for their binding into a previously proposed site in the DNA/topoisomerase I binary complex. Whereas no convincing correlation between docking scores and biological data from in vitro assays could be found, one novel 4,9-diamino Luotonin A derivative had strong antiproliferative activity based on massive G2/M phase arrest. As this biological activity clearly differs from the reference compound Camptothecin, this strongly indicates that at least some Luotonin A derivatives may be potent antiproliferative agents, however with a different mode of action.

Discovery of luotonin A analogues as potent fungicides and insecticides: Design, synthesis and biological evaluation inspired by natural alkaloid.

The prevention and control of plant diseases and insect pests is the most crucial issue facing crop protection. To discover novel pesticide candidates with diverse chemical structures from natural products, a series of luotonin A analogues were designed, synthesized and evaluated for their antifungal and insecticidal activities. Most of these compounds exhibited potent activity against Botrytis cinerea, Magnaporthe oryzae and Aphis craccivora. Among them, the antifungal activity of compound 10s against B. cinerea was comparable to azoxystrobin (EC50 = 0.09 mM) and against M. oryzae (EC50 = 0.19 mM) was slightly weaker than that of azoxystrobin (EC50 = 0.17 mM). Compounds 10k and 10o are the most active compounds against A. craccivora having identical mortality value of 42.05% at 50 µg/mL, respectively, which were slightly lower than pymetrozine (51.14%) at the same concentration. Revealed morphological changes of the fungal cell surface by scanning electron microscopy indicated that luotonin A analogues might exert their antifungal activity by destroying fungal cell membrane and cell wall. Furthermore, the results of the in vivo protective and curative activities of the compound 10s against S. sclerotiorum and B. cinerea showed that the curative effect was stronger than its protective effect and the curative effects reached 67.17% and 73.82% at 80 µg/mL respectively. The above results further demonstrated the potential of luotonin A analogues as novel fungicides and insecticides.

Position-Selective Synthesis and Biological Evaluation of Four Isomeric A-Ring Amino Derivatives of the Alkaloid Luotonin A.

Following two orthogonal synthetic routes, a series of all four possible A-ring amino derivatives of the natural product Luotonin A (a known Topoisomerase I inhibitor) was synthesized. In both strategies, intramolecular cycloaddition reactions are the key step. The target compounds were obtained in good yields by mild catalytic transfer hydrogenation of the corresponding nitro precursors. In-vitro evaluation of the antiproliferative activity towards human tumor cell lines revealed the 4-amino compound (5b) to be the most effective agent, showing an interesting profile of cytotoxic activity. Among other effects, a significant G2/M cell cycle arrest was observed for this compound, suggesting that either Topoisomerase I is not the only biological target, or that some atypical mechanism is responsible for inhibition of this enzyme.

A theranostic nanocomposite system based on iron oxide-drug nanocages for targeted magnetic field responsive chemotherapy.

In this work, a theranostic nanocage system was developed for the targeted delivery of the anti-cancer agents camptothecin (CPT) and luotonin A (LuA). The core of the nanocage system (Fe3O4@OA-AD-SP NCs) was formed by biogenically synthesized Fe3O4 nanoparticles (NPs) decorated with a model anti-cancer drug (AD) and biosurfactant saponin (SP). The Fe3O4@OA-AD-SP NCs showed a high lipophilic AD loading efficiency (>80%) and a controlled pH-responsive drug release in stimulated cancerous cells in pH 6.4 media buffer. In addition, Fe3O4@OA-AD-SP NCs exhibited better serum protein binding efficacy at physiological pH values (7.4), furthering the important role of SP surface decoration. Particularly, these NCs showed better chemotherapeutic efficacy when examined in MCF-7 and HeLa cancer cell lines with a specific targeting capacity. Therefore, this study provides a new nano platform based on magnetic targeting and pH responsive lipophilic anticancer drug delivery to the cancer site.

One pot synthesis of new poly(vinyl alcohol) blended natural polymer based magnetic hydrogel beads: Controlled natural anticancer alkaloid delivery system.

Facile one-pot synthesis has been demonstrated for new biocompatible and dual responsive magnetic iron oxide nanoparticles cross-linked poly(vinyl alcohol) (PVA) blended natural polymer chitosan (CS) based hydrogel beads (mCS-PVA) as a controlled natural anticancer alkaloid Luotonin A (LuA) delivery system. The prepared magnetic hydrogel beads were characterized using powder X-ray diffraction measurement, Fourier transform-infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and vibrating sample magnetometer. The magnetic hydrogel beads are exhibited significant water retention and follow the second order kinetic model in swelling study. The swelling ratio of the magnetic gel beads increased by the addition of PVA and showed a maximum swelling ratio of 40.83 ± 1.01 g/g and follows non-Fickian water transport mechanism. Stimuli responsive mCS and mCS-PVA hydrogel beads functionalized with LuA is demonstrated for controlled release at physiological pH and under magnetic field. The magnetic hydrogel beads show highest LuA releasing efficacy at acidic medium (pH = 5.0) with maximum efficiency of 73.33 ± 1.44%. This efficacy may also be tuned by altering the external magnetic field as well as the weight percentage (wt %) of polyethylene glycol. It is clearly that the newly produced magnetic hydrogel beads can be served as an effective intestinal LuA delivery system. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 543-551, 2018.

A Facile Oxidative Opening of the C-Ring in Luotonin A and Derivatives.

An oxidative ring opening reaction of the central ring C in the alkaloid Luotonin A and two of its derivatives was found to occur upon heating with an excess amine and potassium carbonate in dimethylsulfoxide (DMSO) solution in the presence of air oxygen. The structure of the novel amide-type products was elucidated and a possible mechanism for this reaction is proposed. Four of the new compounds show moderate in vitro anticancer activity towards human colon adenocarcinoma cells.

DNA interaction, antimicrobial, antioxidant and anticancer studies on Cu(II) complexes of Luotonin A.

Luotonin A (L), a novel natural cytotoxic and anti-inflammatory alkaloid, chelated with copper(II) to improve its cytotoxic effect against the cancer cells. The complexes [Cu(L)H2OCl]Cl (1) and [Cu(L)2]Cl2 (2) are prepared by using copper(II) chloride and L with ligand/metal molar ratio of 1:1 and 2:1 respectively. A solution of complexes 1 &2 are characterized by physical spectroscopic methods using Ultraviolet-visible (UV-Vis) spectrophotometer, Fourier Transform-Infra red (FT-IR) spectroscopy, Electron Para magnetic Resonance Spectroscopy (EPR) and by electrochemical methods. The interaction of these complexes 1 &2 with calf thymus (CT-DNA) have been investigated by physical methods to propose the modes of DNA binding with the complexes 1 &2. Absorption spectral titration studies of complex 1 with CT-DNA shows a red-shift of 5nm with the DNA binding affinity of Kb, 8.65×103M-1, but complex 2does not show any red-shift with binding constant Kb, 7.32×103M-1 reveals that the complex 1 binding with DNA strongly than complex 2 and the binding occurs in between the base pairs of DNA as intercalation. Strong interactions of the two complexes 1 & 2 with CT-DNA have also been confirmed by fluorescence spectral titration studies. The evaluated values of KSV and Kass shows that, the complexes 1 &2 interact with DNA through the intercalation, coincide with other partial intercalators strongly than the free ligand L. Complex 1 exhibits potent antioxidant activity with SC50 value of 23.9±0.69µM is evaluated by DPPH radical scavenging assay and which has potent antimicrobial activity against pathogens than 2 and L. The anticancer activity of L, complexes 1 &2 against human breast cancer cell line (MCF-7) and cervical cancer cell line (HeLa) has also been studied by using fluorescence staining method. The IC50 values of L, complexes 1&2 against MCF-7 and HeLa cell lines with the incubation time intervals of 24hrs are 1 (5.0±0.25, 12.0±0.30µM)<2 (6.5±0.27, 15.0±0.30µM)