Sea Urchin Embryo Model As a Reliable in Vivo Phenotypic Screen to Characterize Selective Antimitotic Molecules. Comparative evaluation of Combretapyrazoles, -isoxazoles, -1,2,3-triazoles, and -pyrroles as Tubulin-Binding Agents.

A series of both novel and reported combretastatin analogues, including diarylpyrazoles, -isoxazoles, -1,2,3-triazoles, and -pyrroles, were synthesized via improved protocols to evaluate their antimitotic antitubulin activity using in vivo sea urchin embryo assay and a panel of human cancer cells. A systematic comparative structure-activity relationship studies of these compounds were conducted. Pyrazoles 1i and 1p, isoxazole 3a, and triazole 7b were found to be the most potent antimitotics across all tested compounds causing cleavage alteration of the sea urchin embryo at 1, 0.25, 1, and 0.5 nM, respectively. These agents exhibited comparable cytotoxicity against human cancer cells. Structure-activity relationship studies revealed that compounds substituted with 3,4,5-trimethoxyphenyl ring A and 4-methoxyphenyl ring B displayed the highest activity. 3-Hydroxy group in the ring B was essential for the antiproliferative activity in the diarylisoxazole series, whereas it was not required for potency of diarylpyrazoles. Isoxazoles 3 with 3,4,5-trimethoxy-substituted ring A and 3-hydroxy-4-methoxy-substituted ring B were more active than the respective pyrazoles 1. Of the azoles substituted with the same set of other aryl pharmacophores, diarylpyrazoles 1, 4,5-diarylisoxazoles 3, and 4,5-diaryl-1,2,3-triazoles 7 displayed similar strongest antimitotic antitubulin effect followed by 3,4-diarylisoxazoles 5, 1,5-diaryl-1,2,3-triazoles 8, and pyrroles 10 that showed the lowest activity. Introduction of the amino group into the heterocyclic core decreased the antimitotic antitubulin effect of pyrazoles, triazoles, and to a lesser degree of 4,5-diarylisoxazoles, whereas potency of the respective 3,4-diarylisoxazoles was increased.

Efficient Synthesis of Glaziovianin A Isoflavone Series from Dill and Parsley Extracts and Their in Vitro/in Vivo Antimitotic Activity.

A concise six-step protocol for the synthesis of isoflavone glaziovianin A (GVA) and its alkoxyphenyl derivatives 9 starting with readily available plant metabolites from dill and parsley seeds was developed. The reaction sequence involved an efficient conversion of the key intermediate epoxides 7 into the respective ß-ketoaldehydes 8 followed by their Cu(I)-mediated cyclization into the target series 9. The biological activity of GVA and its derivatives was evaluated using a panel of seven human cancer cell lines and an in vivo sea urchin embryo assay. Both screening platforms confirmed the antimitotic effect of the parent GVA (9cg) and its alkoxy derivatives. Structure-activity relationship studies suggested that compounds 9cd and 9cf substituted with trimethoxy- and dillapiol-derived B-rings, respectively, were less active than the parent 9cg. Of the evaluated human cancer cell lines, the A375 melanoma cell line was the most sensitive to the tested molecules. Notably, the target compounds were not cytotoxic against human peripheral blood mononuclear cells up to 10 µM concentration. Phenotypic readouts from the sea urchin assay unequivocally suggest a direct microtubule-destabilizing effect of isoflavones 9cg, 9cd, and 9cf.

3-(5-)-Amino-o-diarylisoxazoles: regioselective synthesis and antitubulin activity.

A regioselective synthesis of both 5-amino- and 3-aminodiarylisoxazoles substituted with polyalkoxyaryl pharmacophores has been validated. Starting materials for the synthetic scheme were easily available from plant extracts. The targeted molecules were further tested in the phenotypic sea urchin embryo assay to identify compounds with antimitotic microtubule destabilizing activity. Structure-activity relationship studies suggested that the structural features essential for potent antiproliferative activity include: 1) 5-aminoisoxazole bridge linking biaryl substituents (rings A and B); 2) unsubstituted 5-amino group; 3) 3,4,5-methoxy substituted benzene and 4-methoxy benzene pharmacophores as rings A and B, respectively. The most potent compounds also showed strong in vitro cytotoxicity in NCI60 anticancer drug screen against a panel of 60 human cancer cell lines, including multi-drug resistant cells.

Synthesis and antiproliferative activity of conformationally restricted 1,2,3-triazole analogues of combretastatins in the sea urchin embryo model and against human cancer cell lines.

A series of 1,5-diaryl- and 4,5-diaryl-1,2,3-triazole derivatives of combretastatin A4 were synthesized and evaluated as antimitotic microtubule destabilizing agents using the sea urchin embryo model. Structure-activity relationship studies identified compounds substituted with 3,4,5-trimethoxyphenyl and 3,4-methylenedioxy-5-methoxyphenyl ring A and 4-methoxyphenyl ring B as potent antiproliferative agents with high cytotoxicity against a panel of human cancer cell lines including multi-drug resistant cells. 4,5-Diaryl-1,2,3-triazoles (C-C geometry) were found to be considerably more active than the respective 1,5-diaryl-1,2,3-triazoles (N-C geometry). Compound 10ad' induced G2/M cell cycle arrest and apoptosis in human T-leukemia Jurkat cells via caspase 2/3/9 activation and downregulation of the antiapoptotic protein XIAP. A mitotic catastrophe has been evaluated as another possible cell death mode.

Polyalkoxybenzenes from plants. 5. Parsley seed extract in synthesis of azapodophyllotoxins featuring strong tubulin destabilizing activity in the sea urchin embryo and cell culture assays.

A series of 4-azapodophyllotoxin derivatives with modified rings B and E have been synthesized using allylpolyalkoxybenzenes from parsley seed oil. The targeted molecules were evaluated in vivo in a phenotypic sea urchin embryo assay for antimitotic and tubulin destabilizing activity. The most active compounds identified by the in vivo sea urchin embryo assay featured myristicin-derived ring E. These molecules were determined to be more potent than podophyllotoxin. Cytotoxic effects of selected molecules were further confirmed and evaluated by conventional assays with A549 and Jurkat human leukemic T-cell lines including cell growth inhibition, cell cycle arrest, cellular microtubule disruption, and induction of apoptosis. The ring B modification yielded 6-OMe substituted molecule as the most active compound. Finally, in Jurkat cells, compound induced caspase-dependent apoptosis mediated by the apical caspases-2 and -9 and not caspase-8, implying the involvement of the intrinsic caspase-9-dependent apoptotic pathway.

Novel derivatives of 1,3,4-oxadiazoles are potent mitostatic agents featuring strong microtubule depolymerizing activity in the sea urchin embryo and cell culture assays.

A series of novel 1,3,4-oxadiazole derivatives based on structural and electronic overlap with combretastatins have been designed and synthesized. Initially, we tested all new compounds in vivo using the phenotypic sea urchin embryo assay to yield a number of agents with anti-proliferative, anti-mitotic, and microtubule destabilizing activities. The experimental data led to identification of 1,3,4-oxadiazole derivatives with isothiazole (5-8) and phenyl (9-12) pharmacophores featuring activity profiles comparable to that of combretastatins, podophyllotoxin and nocodazole. Cytotoxic effects of the two lead molecules, namely 6 and 12, were further confirmed and evaluated by conventional assays with the A549 human cancer cell line including cell proliferation, cell cycle arrest at the G2/M phase, cellular microtubule distribution, and finally in vitro microtubule assembly with purified tubulin. The modeling results using 3D similarity (ROCS) and docking (FRED) correlated well with the observed activity of the molecules. Docking data suggested that the most potent molecules are likely to target the colchicine binding site.

In vivo evaluation of indolyl glyoxamides in the phenotypic sea urchin embryo assay.

We have devised a 'one-pot' phenotypic in vivo assay for the rapid evaluation of potential tubulin inhibitors using the sea urchin embryo model. An effect of a small molecule on two specific developmental stages of sea urchin embryo, namely: (i) fertilized egg test for antimitotic activity and (ii) behavioral monitoring of a free-swimming blastulae for changes in the embryo swimming pattern could be quantified by a threshold concentration resulting in respective abnormalities. Derivatives of the clinical candidate D-24851 featured good correlation between activity in tubulin polymerization assay and our in vivo data. Importantly, we demonstrated that in these series, the N-substitution of indole is non-essential to attain profound in vitro and cellular effects.