R-253 disrupts microtubule networks in multiple tumor cell lines

pH-sensitive nanomedicine of novel tubulin polymerization inhibitor for lung metastatic melanoma

Microtubule binding agents such as paclitaxel and vincristine have activity in metastatic melanoma. However, even responsive tumors develop resistance, highlighting the need to investigate new drug molecules. Here, we showed that a new compound, CH-2-102, developed by our group, has high anti-tumor efficacy in human and murine melanoma cells. We confirmed that CH-2-102 robustly suppresses the microtubule polymerization process by directly interacting with the colchicine binding site. Our results unveil that CH-2-102 suppresses microtubule polymerization and subsequently induces G2 phase cell arrest as one of the possible mechanisms. Notably, CH-2-102 maintains its efficacy even in the paclitaxel resistance melanoma cells due to different binding sites and a non-Pgp substrate. We developed a pH-responsive drug-polymer Schiff bases linker for high drug loading into nanoparticles (NPs). Our CH-2-102 conjugated NPs induced tumor regression more effectively than Abraxane® (Nab-paclitaxel, N-PTX), free drug, and non-sensitive NPs in B16-F10 cell-derived lung metastasis mouse model. Furthermore, our results suggest that the formulation has a high impact on the in vivo efficacy of the drug and warrants further investigation in other cancers, particularly taxane resistant. In conclusion, the microtubule polymerization inhibitor CH-2-102 conjugated pH-responsive NPs induce tumor regression in lung metastasis melanoma mice, suggesting it may be an effective strategy for treating metastatic melanoma.

New 3-Aryl-2-(2-thienyl)acrylonitriles with High Activity Against Hepatoma Cells

New 2-(thien-2-yl)-acrylonitriles with putative kinase inhibitory activity were prepared and tested for their antineoplastic efficacy in hepatoma models. Four out of the 14 derivatives were shown to inhibit hepatoma cell proliferation at (sub-)micromolar concentrations with IC50 values below that of the clinically relevant multikinase inhibitor sorafenib, which served as a reference. Colony formation assays as well as primary in vivo examinations of hepatoma tumors grown on the chorioallantoic membrane of fertilized chicken eggs (CAM assay) confirmed the excellent antineoplastic efficacy of the new derivatives. Their mode of action included an induction of apoptotic capsase-3 activity, while no contribution of unspecific cytotoxic effects was observed in LDH-release measurements. Kinase profiling of cancer relevant protein kinases identified the two 3-aryl-2-(thien-2-yl)acrylonitrile derivatives 1b and 1c as (multi-)kinase inhibitors with a preferential activity against the VEGFR-2 tyrosine kinase. Additional bioinformatic analysis of the VEGFR-2 binding modes by docking and molecular dynamics calculations supported the experimental findings and indicated that the hydroxy group of 1c might be crucial for its distinct inhibitory potency against VEGFR-2. Forthcoming studies will further unveil the underlying mode of action of the promising new derivatives as well as their suitability as an urgently needed novel approach in HCC treatment.

Efficacy of the novel tubulin polymerization inhibitor PTC-028 for myelodysplastic syndrome

Monomer tubulin polymerize into microtubules, which are highly dynamic and play a critical role in mitosis. Therefore, microtubule dynamics are an important target for anticancer drugs. The inhibition of tubulin polymerization or depolymerization was previously targeted and exhibited efficacy against solid tumors. The novel small molecule PTC596 directly binds tubulin, inhibits microtubule polymerization, downregulates MCL‐1, and induces p53‐independent apoptosis in acute myeloid leukemia cells. We herein investigated the efficacy of PTC‐028, a structural analog of PTC596, for myelodysplastic syndrome (MDS). PTC‐028 suppressed growth and induced apoptosis in MDS cell lines. The efficacy of PTC028 in primary MDS samples was confirmed using cell proliferation assays. PTC‐028 synergized with hypomethylating agents, such as decitabine and azacitidine, to inhibit growth and induce apoptosis in MDS cells. Mechanistically, a treatment with PTC‐028 induced G2/M arrest followed by apoptotic cell death. We also assessed the efficacy of PTC‐028 in a xenograft mouse model of MDS using the MDS cell line, MDS‐L, and the AkaBLI bioluminescence imaging system, which is composed of AkaLumine‐HCl and Akaluc. PTC‐028 prolonged the survival of mice in xenograft models. The present results suggest a chemotherapeutic strategy for MDS through the disruption of microtubule dynamics in combination with DNA hypomethylating agents.

Nanoparticulate delivery of potent microtubule inhibitor for metastatic melanoma treatment

Melanoma is the most aggressive type of skin cancer, which readily metastasizes through lymph nodes to the lungs, liver, and brain. Since the repeated administration of most chemotherapeutic drugs develops chemoresistance and severe systemic toxicities, herein we synthesized 2-(4-hydroxy-1H-indol-3-yl)-1H-imidazol-4-yl)(3,4,5-trimethoxyphenyl) methanone (abbreviated as QW-296), a novel tubulin destabilizing agent with little susceptible to transporter-mediated drug resistance. QW-296 disturbed the microtubule dynamics at the nanomolar concentration in A375 and B16F10 melanoma cells. QW-296 binding to colchicine-binding site on tubulin protein was confirmed by molecular modeling and tubulin polymerization assay. QW-296 significantly inhibited A375 and B16F10 cell proliferation, induced G2/M cell cycle arrest and led to apoptosis and cell death. To improve its aqueous solubility, QW-296 was encapsulated into methoxy poly(ethyleneglycol)-b-poly(carbonate-co-lactide) [mPEG-b-P(CB-co-LA)] polymeric nanoparticles by solvent evaporation, with the mean particle size of 122.0 ± 2.28 nm and drug loading of 3.70% (w/w). Systemic administration of QW-296 loaded nanoparticles into C57/BL6 albino mice bearing lung metastatic melanoma at the dose of 20 mg/kg 4 times a week for 1.5 weeks resulted in significant tumor regression and prolonged mouse median survival without significant change in mouse body weight. In conclusion, QW-296 loaded nanoparticles have the potential to treat metastatic melanoma.

Development of an image-based screening system for inhibitors of the plastidial MEP pathway and of protein geranylgeranylation

In a preceding study we have recently established an in vivo visualization system for the geranylgeranylation of proteins in a stably transformed tobacco BY-2 cell line, which involves expressing a dexamethasone-inducible GFP fused to the prenylable, carboxy-terminal basic domain of the rice calmodulin CaM61, which naturally bears a CaaL geranylgeranylation motif (GFP-BD-CVIL). By using pathway-specific inhibitors it was there demonstrated that inhibition of the methylerythritol phosphate (MEP) pathway with oxoclomazone and fosmidomycin, as well as inhibition of protein geranylgeranyl transferase type 1 (PGGT-1), shifted the localization of the GFP-BD-CVIL protein from the membrane to the nucleus. In contrast, the inhibition of the mevalonate (MVA) pathway with mevinolin did not affect this localization. Furthermore, in this initial study complementation assays with pathway-specific intermediates confirmed that the precursors for the cytosolic isoprenylation of this fusion protein are predominantly provided by the MEP pathway. In order to optimize this visualization system from a more qualitative assay to a statistically trustable medium or a high-throughput screening system, we established now new conditions that permit culture and analysis in 96-well microtiter plates, followed by fluorescence microscopy. For further refinement, the existing GFP-BD-CVIL cell line was transformed with an estradiol-inducible vector driving the expression of a RFP protein, C-terminally fused to a nuclear localization signal (NLS-RFP). We are thus able to quantify the total number of viable cells versus the number of inhibited cells after various treatments. This approach also includes a semi-automatic counting system, based on the freely available image processing software. As a result, the time of image analysis as well as the risk of user-generated bias is reduced to a minimum. Moreover, there is no cross-induction of gene expression by dexamethasone and estradiol, which is an important prerequisite for this test system.

Development of an image-based screening system for inhibitors of the plastidial MEP pathway and of protein geranylgeranylation

We have recently established an in vivo visualization system for the geranylgeranylation of proteins in a stably transformed tobacco BY-2 cell line, which involves expressing a dexamethasone-inducible GFP fused to the prenylable, carboxy-terminal basic domain of the rice calmodulin CaM61, which naturally bears a CaaL geranylgeranylation motif (GFP-BD-CVIL). By using pathway-specific inhibitors it was demonstrated that inhibition of the methylerythritol phosphate (MEP) pathway with oxoclomazone and fosmidomycin, as well as inhibition of protein geranylgeranyl transferase type 1 (PGGT-1), shifted the localization of the GFP-BD-CVIL protein from the membrane to the nucleus. In contrast, the inhibition of the mevalonate (MVA) pathway with mevinolin did not affect this localization. Furthermore, complementation assays with pathway-specific intermediates confirmed that the precursors for the cytosolic isoprenylation of this fusion protein are predominantly provided by the MEP pathway. In order to optimize this visualization system from a more qualitative assay to a statistically trustable medium or a high-throughput screening system, we established new conditions that permit culture and analysis in 96-well microtiter plates, followed by fluorescence microscopy. For further refinement, the existing GFP-BD-CVIL cell line was transformed with an estradiol-inducible vector driving the expression of a RFP protein, C-terminally fused to a nuclear localization signal (NLS-RFP). We are thus able to quantify the total number of viable cells versus the number of inhibited cells after various treatments. This approach also includes a semi-automatic counting system, based on the freely available image processing software. As a result, the time of image analysis as well as the risk of user-generated bias is reduced to a minimum. Moreover, there is no cross-induction of gene expression by dexamethasone and estradiol, which is an important prerequisite for this test system.

Activation of cyclic AMP/PKA pathway inhibits bladder cancer cell invasion by targeting MAP4-dependent microtubule dynamics

OBJECTIVE

With the notorious reputation of the vicious invasion, the bladder cancer is the most common malignant tumor of the urinary system. Inhibiting invasion through microtubule dynamics interruption has emerged as an important treatment of bladder cancer. Here we investigated the role of the cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) pathway in human bladder cancer cells invasion.

MATERIALS AND METHODS

With or without the treatment of various cAMP elevators, we assessed invasive and migrated capabilities of T24 and UM-UC-3, two high-grade invasive bladder cancer cell lines, using matrigel transwell inserts assay and scratch wound healing assay. The microtubule (MT) dynamics were examined by immunofluorescence and immunoblotting. Microtubule-Associated Protein 4 (MAP4) was silenced to investigate its role in tumor invasion. We also analyzed gene expression of MAP4 in 34 patients with bladder cancer using immunohistochemical staining assay. The interaction between PKA and MAP4 was examined by co-immunoprecipitation.

RESULTS

We used cAMP elevators and small interfering RNA of MAP4 here, found that both of them can potently inhibit the invasion and the migration of bladder cancer cells by disrupting microtubule (MT) cytoskeleton. Consistently, the bladder cancer grade is positively correlated with the protein level of MAP4. Furthermore, we found that cAMP/PKA signaling can disrupt MT cytoskeleton by the phosphorylation of MAP4.

CONCLUSION

Our results indicated that the cAMP/PKA signaling pathway might inhibit bladder cancer cell invasion by targeting MAP4-dependent microtubule dynamics, which could be exploited for the therapy of invasive bladder cancer.

Triptolide inhibits proliferation and invasion of malignant glioma cells

Malignant glioma is the most devastating and aggressive tumor in brain, characterized by rapid proliferation and diffuse invasion. Chemotherapy and radiotherapy are the pivotal strategies after surgery; however, high drug resistance of malignant glioma and the blood-brain barrier usually render chemotherapy drugs ineffective. Here, we find that triptolide, a small molecule with high lipid solubility, is capable of inhibiting proliferation and invasion of malignant glioma cells effectively. In both investigated malignant glioma cell lines, triptolide repressed cell proliferation via inducing cell cycle arrest in G0/G1 phase, associated with downregulation of G0/G1 cell cycle regulators cyclin D1, CDK4, and CDK6 followed by reduced phosphorylation of retinoblastoma protein (Rb). In addition, triptolide induced morphological change of C6 cells through downregulation of protein expression of MAP-2 and inhibition of activities of GTPases Cdc42 and Rac1/2/3, thus significantly suppressing migratory and invasive capacity. Moreover, in an in vivo tumor model, triptolide delayed growth of malignant glioma xenografts. These findings suggest an important inhibitory action of triptolide on proliferation and invasion of malignant glioma, and encourage triptolide as a candidate for glioma therapy.

Open innovation for phenotypic drug discovery: The PD2 assay panel

Phenotypic lead generation strategies seek to identify compounds that modulate complex, physiologically relevant systems, an approach that is complementary to traditional, target-directed strategies. Unlike gene-specific assays, phenotypic assays interrogate multiple molecular targets and signaling pathways in a target "agnostic" fashion, which may reveal novel functions for well-studied proteins and discover new pathways of therapeutic value. Significantly, existing compound libraries may not have sufficient chemical diversity to fully leverage a phenotypic strategy. To address this issue, Eli Lilly and Company launched the Phenotypic Drug Discovery Initiative (PD(2)), a model of open innovation whereby external research groups can submit compounds for testing in a panel of Lilly phenotypic assays. This communication describes the statistical validation, operations, and initial screening results from the first PD(2) assay panel. Analysis of PD(2) submissions indicates that chemical diversity from open source collaborations complements internal sources. Screening results for the first 4691 compounds submitted to PD(2) have confirmed hit rates from 1.6% to 10%, with the majority of active compounds exhibiting acceptable potency and selectivity. Phenotypic lead generation strategies, in conjunction with novel chemical diversity obtained via open-source initiatives such as PD(2), may provide a means to identify compounds that modulate biology by novel mechanisms and expand the innovation potential of drug discovery.

Synthetic genetic array (SGA) analysis in Saccharomyces cerevisiae and Schizosaccharomyces pombe

A genetic interaction occurs when the combination of two mutations leads to an unexpected phenotype. Screens for synthetic genetic interactions have been used extensively to identify genes whose products are functionally related. In particular, synthetic lethal genetic interactions often identify genes that buffer one another or impinge on the same essential pathway. For the yeast Saccharomyces cerevisiae, we developed a method termed synthetic genetic array (SGA) analysis, which offers an efficient approach for the systematic construction of double mutants and enables a global analysis of synthetic genetic interactions. In a typical SGA screen, a query mutation is crossed to an ordered array of ~5000 viable gene deletion mutants (representing ~80% of all yeast genes) such that meiotic progeny harboring both mutations can be scored for fitness defects. This approach can be extended to all ~6000 genes through the use of yeast arrays containing mutants carrying conditional or hypomorphic alleles of essential genes. Estimating the fitness for the two single mutants and their corresponding double mutant enables a quantitative measurement of genetic interactions, distinguishing negative (synthetic lethal) and positive (within pathway and suppression) interactions. The profile of genetic interactions represents a rich phenotypic signature for each gene and clustering genetic interaction profiles group genes into functionally relevant pathways and complexes. This array-based approach automates yeast genetic analysis in general and can be easily adapted for a number of different genetic screens or combined with high-content screening systems to quantify the activity of specific reporters in genome-wide sets of single or more complex multiple mutant backgrounds. Comparison of genetic and chemical-genetic interaction profiles offers the potential to link bioactive compounds to their targets. Finally, we also developed an SGA system for the fission yeast Schizosaccharomyces pombe, providing another model system for comparative analysis of genetic networks and testing the conservation of genetic networks over millions of years of evolution.

N-(2,6-dimethoxypyridine-3-yl)-9-methylcarbazole-3-sulfonamide as a novel tubulin ligand against human cancer

PURPOSE

We have synthesized a new tubulin ligand N-(2,6-dimethoxypyridine-3-yl)-9-methylcarbazole-3-sulfonamide (IG-105). This work investigates its anticancer effect and mechanism.

EXPERIMENTAL DESIGN

Anticancer efficacy was evaluated at the molecular target, cancer cells and nude mice. The mechanism was explored at submolecular, molecular, and cellular levels.

RESULTS

IG-105 showed a potent activity against human leukemia and solid tumors in breast, liver, prostate, lung, skin, colon, and pancreas with IC(50) values between 0.012 and 0.298 mumol/L. It was also active in drug-resistant tumor cells and not a P-glycoprotein substrate. It inhibited microtubule assembly followed by M-phase arrest, Bcl-2 inactivation, and then apoptosis through caspase pathways. The colchicine pocket on tubulin is the binding site of IG-105. Nude mice experiments showed that IG-105 monotherapy at 100 mg/kg i.p. (q2d) yielded 81% inhibition of Bel-7402 hepatoma growth and at 275 mg/kg i.p. (q2d) completely inhibited the tumor growth. MCF-7 breast cancer in nude mice showed a similar therapeutic response to IG-105. Acute toxicity of IG-105 was not found even at 1,000 mg/kg i.p. In combination with oxaliplatin or doxorubicin, IG-105 converted each of these subcurative compounds into a curative treatment with complete inhibition for tumor growth in the hepatoma-bearing nude mice. The combination was more active than either drug. In no experiment was toxicity increased by combination chemotherapy.

CONCLUSIONS

IG-105 inhibits microtubule assembly by binding at colchicine pocket. It shows a potent anticancer activity in vitro and in vivo and has good safety in mice. We consider IG-105 merits further investigation.

Image-based chemical screening

Technological advances have made it feasible to conduct high-throughput small-molecule screens based on visual phenotypes of individual cells, using automated imaging and analysis. These screens are rapidly moving from being small, proof-of-principle tests to robust and widespread screens of hundreds of thousands of compounds. Automated imaging screens maximize the information obtained in an initial screen and improve the ability to select high-quality leads. In this Perspective, I highlight the key steps necessary for conducting a high-throughput image-based chemical compound screen.