Conditional generation of free radicals by selective activation of alkoxyamines: towards more effective and less toxic targeting of brain tumors.

Brain tumors are an important cause of suffering and death. Glioblastoma are the most frequent primary tumors of the central nervous system in adults. They are associated with a very poor prognosis, since only 10% of GBM patients survive 5 years after diagnosis. Medulloblastoma are the most frequent brain malignancies in childhood; they affect the cerebellum in children under 10 years of age in 75% of cases. The current multimodal treatment comes at the expense of serious and often long-lasting side effects. Herein, we propose the synthesis of a library of novel alkoxyamines as anticancer drug candidates. The most efficient molecule, ALK4, was selected based on its ability to inhibit both survival and migration of GBM and MB cells in 2D cultures and in 3D tumor spheroids. A fluorescent derivative was used to show the early cytosolic accumulation of ALK4 in tumor cells. Spontaneous homolysis of ALK4 led to the release of alkyl radicals, which triggered the generation of reactive oxygen species, fragmentation of the mitochondrial network and ultimately apoptosis. To control its homolytic process, the selected alkoxyamine was bioconjugated to a peptide selectively recognized by matrix metalloproteases. This bioconjugate, named ALK4-MMPp, successfully inhibited survival, proliferation, and invasion of GBM and MB tumor micromasses. We further developed innovative brain and cerebellum organotypic models to monitor treatment response over time. It confirmed that ALK4-MMPp significantly impaired tumor progression, while no significant damage was observed on normal brain tissue. Lastly, we showed that ALK4-MMPp was well-tolerated in vivo by zebrafish embryos. This study provides a new strategy to control the activation of alkoxyamines, and revealed the bioconjugate ALK4-MMPp bioconjugate as a good anticancer drug candidate.

A clickable melphalan for monitoring DNA interstrand crosslink accumulation and detecting ICL repair defects in Fanconi anemia patient cells.

Fanconi anemia (FA) is a genetic disorder associated with developmental defects, bone marrow failure and cancer. The FA pathway is crucial for the repair of DNA interstrand crosslinks (ICLs). In this study, we have developed and characterized a new tool to investigate ICL repair: a clickable version of the crosslinking agent melphalan which we name click-melphalan. Our results demonstrate that click-melphalan is as effective as its unmodified counterpart in generating ICLs and associated toxicity. The lesions induced by click-melphalan can be detected in cells by post-labelling with a fluorescent reporter and quantified using flow cytometry. Since click-melphalan induces both ICLs and monoadducts, we generated click-mono-melphalan, which only induces monoadducts, in order to distinguish between the two types of DNA repair. By using both molecules, we show that FANCD2 knock-out cells are deficient in removing click-melphalan-induced lesions. We also found that these cells display a delay in repairing click-mono-melphalan-induced monoadducts. Our data further revealed that the presence of unrepaired ICLs inhibits monoadduct repair. Finally, our study demonstrates that these clickable molecules can differentiate intrinsic DNA repair deficiencies in primary FA patient cells from those in primary xeroderma pigmentosum patient cells. As such, these molecules may have potential for developing diagnostic tests.

From a drug repositioning to a structure-based drug design approach to tackle acute lymphoblastic leukemia.

Cancer cells utilize the main de novo pathway and the alternative salvage pathway for deoxyribonucleotide biosynthesis to achieve adequate nucleotide pools. Deoxycytidine kinase is the rate-limiting enzyme of the salvage pathway and it has recently emerged as a target for anti-proliferative therapies for cancers where it is essential. Here, we present the development of a potent inhibitor applying an iterative multidisciplinary approach, which relies on computational design coupled with experimental evaluations. This strategy allows an acceleration of the hit-to-lead process by gradually implementing key chemical modifications to increase affinity and activity. Our lead compound, OR0642, is more than 1000 times more potent than its initial parent compound, masitinib, previously identified from a drug repositioning approach. OR0642 in combination with a physiological inhibitor of the de novo pathway doubled the survival rate in a human T-cell acute lymphoblastic leukemia patient-derived xenograft mouse model, demonstrating the proof-of-concept of this drug design strategy.

CRCM5484: A BET-BDII Selective Compound with Differential Anti-leukemic Drug Modulation.

Differentially screening the Fr-PPIChem chemical library on the bromodomain and extra-terminal (BET) BRD4-BDII versus -BDI bromodomains led to the discovery of a BDII-selective tetrahydropyridothienopyrimidinone (THPTP)-based compound. Structure-activity relationship (SAR) and hit-to-lead approaches allowed us to develop CRCM5484, a potent inhibitor of BET proteins with a preferential and 475-fold selectivity for the second bromodomain of the BRD3 protein (BRD3-BDII) over its first bromodomain (BRD3-BDI). Its very low activity was demonstrated in various cell-based assays, corresponding with recent data describing other selective BDII compounds. However, screening on a drug sensitivity and resistance-profiling platform revealed its ability to modulate the anti-leukemic activity in combination with various FDA-approved and/or in-development drugs in a cell- and context-dependent differential manner. Altogether, the results confirm the originality of the THPTP molecular mode of action in the bromodomain (BD) cavity and its potential as a starting scaffold for the development of potent and selective bromodomain inhibitors.

Discovery of dihydrofuranoallocolchicinoids - Highly potent antimitotic agents with low acute toxicity.

Two series of heterocyclic colchicinoids bearing ß-methylenedihydrofuran or 2H-pyran-2-one fragments were synthesized by the intramolecular Heck reaction. Methylenedihydrofuran compounds 9a and 9h were found to be the most cytotoxic among currently known colchicinoids, exhibiting outstanding antiproliferative activity on tumor cell lines in picomolar (0.01-2.1 nM) range of concentrations. Compound 9a potently and substoichiometrically inhibits microtubule formation in vitro, being an order of magnitude more active in this assay than colchicine. Derivatives 9a and 9h revealed relatively low acute toxicity in mice (LD50 ≥ 10 mg/kg i.v.). The X-Ray structure of colchicinoid 9a bound to tubulin confirmed interaction of this compound with the colchicine binding site of tubulin.

Allocolchicinoids bearing a Michael acceptor fragment for possible irreversible binding of tubulin.

We describe an attempt to apply the concept of covalent binding towards the highly active allocolchicinoids selected on the basis of SAR analysis of previously synthesized molecules. To achieve the irreversible binding of the agent to the cysteine residues of the colchicine site of tubulin protein, we synthesized a number of new allocolchicinoids bearing the acceptor moiety. Some of the new derivatives possess cytotoxic activity against COLO-357, BxPC-3, HaCaT, and HEK293 cell lines in a low nanomolar range of concentrations. A substoichiometric mode of microtubule assembly inhibition was demonstrated. The most active compounds possess close to colchicine general toxicity on mice.

Triangular Regulation of Cucurbit[8]uril 1:1 Complexes.

Triangular shapes have inspired scientists over time and are common in nature, such as the flower petals of oxalis triangularis, the triangular faces of tetrahedrite crystals, and the icosahedron faces of virus capsids. Supramolecular chemistry has enabled the construction of triangular assemblies, many of which possess functional features. Among these structures, cucurbiturils have been used to build supramolecular triangles, and we recently reported paramagnetic cucurbit[8]uril (CB[8]) triangles, but the reasons for their formation remain unclear. Several parameters have now been identified to explain their formation. At first sight, the radical nature of the guest was of prime importance in obtaining the triangles, and we focused on extending this concept to biradicals to get supramolecular hexaradicals. Two sodium ions were systematically observed by ESI-MS in trimer structures, and the presence of Na+ triggered or strengthened the triangulation of CB[8]/guest 1:1 complexes in solution. X-ray crystallography and molecular modeling have allowed the proposal of two plausible sites of residence for the two sodium cations. We then found that a diamagnetic guest with an H-bond acceptor function is equally good at forming CB[8] triangles. Hence, a guest molecule containing a ketone function has been precisely triangulated thanks to CB[8] and sodium cations as determined by DOSY-NMR and DLS. A binding constant for the triangulation of 1:1 to 3:3 complexes is proposed. This concept has finally been extended to the triangulation of ditopic guests toward network formation by the reticulation of CB[8] triangles using dinitroxide biradicals.

Integrated Strategy for Lead Optimization Based on Fragment Growing: The Diversity-Oriented-Target-Focused-Synthesis Approach.

Over the past few decades, hit identification has been greatly facilitated by advances in high-throughput and fragment-based screenings. One major hurdle remaining in drug discovery is process automation of hit-to-lead (H2L) optimization. Here, we report a time- and cost-efficient integrated strategy for H2L optimization as well as a partially automated design of potent chemical probes consisting of a focused-chemical-library design and virtual screening coupled with robotic diversity-oriented de novo synthesis and automated in vitro evaluation. The virtual library is generated by combining an activated fragment, corresponding to the substructure binding to the target, with a collection of functionalized building blocks using in silico encoded chemical reactions carefully chosen from a list of one-step organic transformations relevant in medicinal chemistry. The proof of concept was demonstrated using the optimization of bromodomain inhibitors as a test case, leading to the validation of several compounds with improved affinity by several orders of magnitude.

Dual protein kinase and nucleoside kinase modulators for rationally designed polypharmacology.

Masitinib, a highly selective protein kinase inhibitor, can sensitise gemcitabine-refractory cancer cell lines when used in combination with gemcitabine. Here we report a reverse proteomic approach that identifies the target responsible for this sensitisation: the deoxycytidine kinase (dCK). Masitinib, as well as other protein kinase inhibitors, such as imatinib, interact with dCK and provoke an unforeseen conformational-dependent activation of this nucleoside kinase, modulating phosphorylation of nucleoside analogue drugs. This phenomenon leads to an increase of prodrug phosphorylation of most of the chemotherapeutic drugs activated by this nucleoside kinase. The unforeseen dual activity of protein kinase inhibition/nucleoside kinase activation could be of great therapeutic benefit, through either reducing toxicity of therapeutic agents by maintaining effectiveness at lower doses or by counteracting drug resistance initiated via down modulation of dCK target.

Protein-Protein Interaction Inhibition (2P2I)-Oriented Chemical Library Accelerates Hit Discovery.

Protein-protein interactions (PPIs) represent an enormous source of opportunity for therapeutic intervention. We and others have recently pinpointed key rules that will help in identifying the next generation of innovative drugs to tackle this challenging class of targets within the next decade. We used these rules to design an oriented chemical library corresponding to a set of diverse "PPI-like" modulators with cores identified as privileged structures in therapeutics. In this work, we purchased the resulting 1664 structurally diverse compounds and evaluated them on a series of representative protein-protein interfaces with distinct "druggability" potential using homogeneous time-resolved fluorescence (HTRF) technology. For certain PPI classes, analysis of the hit rates revealed up to 100 enrichment factors compared with nonoriented chemical libraries. This observation correlates with the predicted "druggability" of the targets. A specific focus on selectivity profiles, the three-dimensional (3D) molecular modes of action resolved by X-ray crystallography, and the biological activities of identified hits targeting the well-defined "druggable" bromodomains of the bromo and extraterminal (BET) family are presented as a proof-of-concept. Overall, our present study illustrates the potency of machine learning-based oriented chemical libraries to accelerate the identification of hits targeting PPIs. A generalization of this method to a larger set of compounds will accelerate the discovery of original and potent probes for this challenging class of targets.

Exploring Selective Inhibition of the First Bromodomain of the Human Bromodomain and Extra-terminal Domain (BET) Proteins.

A midthroughput screening follow-up program targeting the first bromodomain of the human BRD4 protein, BRD4(BD1), identified an acetylated-mimic xanthine derivative inhibitor. This compound binds with an affinity in the low micromolar range yet exerts suitable unexpected selectivity in vitro against the other members of the bromodomain and extra-terminal domain (BET) family. A structure-based program pinpointed a role of the ZA loop, paving the way for the development of potent and selective BET-BRDi probes.

Synthesis and biological evaluation of furanoallocolchicinoids.

A series of conformationally flexible furan-derived allocolchicinoids was prepared from commercially available colchicine in good to excellent yields using a three-step reaction sequence. Cytotoxicity studies indicated the potent activity of two compounds against human epithelial and lymphoid cell lines (AsPC-1, HEK293, and Jurkat) as well as against Wnt-1 related murine epithelial cell line W1308. The results of in vitro experiments demonstrated that the major effect of these compounds was the induction of cell cycle arrest in the G2/M phase as a direct consequence of effective tubulin binding. In vivo testing of the most potent furanoallocolchicinoid 10c using C57BL/6 mice inoculated with Wnt-1 tumor cells indicated significant inhibition of the tumor growth.

New Ianthelliformisamine derivatives as antibiotic enhancers against resistant Gram-negative bacteria.

A series consisting of ianthelliformisamimes A, B, and C as well as its synthetic analogues was prepared in high chemical yield, from 27 to 91%, using peptide coupling as the key step, and the compounds were evaluated for their in vitro antibiotic enhancer properties against resistant Gram-negative bacteria and clinical isolates. The mechanism of action of one of these derivatives against Pseudomonas aeruginosa when combined with doxycycline was precisely evaluated utilizing bioluminescence to measure ATP efflux and fluorescence to evaluate membrane depolarization.

The indolylcoumarin COUFIN exhibits potent activity against renal carcinoma cells without affecting hematopoietic system.

The present work describes the anticancer activity of a new indolylcoumarin named COUFIN and more specifically, its efficiency against clear cell renal carcinoma (CCRC). COUFIN inhibited microtubule formation and bound on tubulin to or near the colchicine site. In vitro, COUFIN showed potent anticancer activity on renal carcinoma cells (RCC) both in monolayer (2D culture) (IC50 of 88 ± 8 nM) and multicellular tumor spheroid (3D culture) (IC50 of 180 ± 20 nM). The compound blocked cell cycle transition at G2/M phase, induced a subsequent apoptotic process but did not modulate clonal growth of CFU-GM. On the other hand, the coumarin derivative decreased the activity of P-gp and BCRP but was not substrate for these ABC pumps. In vivo, the indolylcoumarin increased the survival rate after 3 weeks of treatment. Based on the present study, COUFIN was identified as a bifunctional molecule able to inhibit renal carcinoma cells proliferation without being effluxed by ABC proteins. Thus COUFIN could be a promising chemotherapeutic agent for treating tumor cells over-expressing efflux pumps and tumor cells irrigated by vessels lined with endothelial cells responsible of poor distribution of conventional anticancer agents.

2P2I HUNTER: a tool for filtering orthosteric protein-protein interaction modulators via a dedicated support vector machine.

Over the last 10 years, protein-protein interactions (PPIs) have shown increasing potential as new therapeutic targets. As a consequence, PPIs are today the most screened target class in high-throughput screening (HTS). The development of broad chemical libraries dedicated to these particular targets is essential; however, the chemical space associated with this 'high-hanging fruit' is still under debate. Here, we analyse the properties of 40 non-redundant small molecules present in the 2P2I database (http://2p2idb.cnrs-mrs.fr/) to define a general profile of orthosteric inhibitors and propose an original protocol to filter general screening libraries using a support vector machine (SVM) with 11 standard Dragon molecular descriptors. The filtering protocol has been validated using external datasets from PubChem BioAssay and results from in-house screening campaigns. This external blind validation demonstrated the ability of the SVM model to reduce the size of the filtered chemical library by eliminating up to 96% of the compounds as well as enhancing the proportion of active compounds by up to a factor of 8. We believe that the resulting chemical space identified in this paper will provide the scientific community with a concrete support to search for PPI inhibitors during HTS campaigns.

Tumor selective cytotoxic action of a thiomorpholin hydroxamate inhibitor (TMI-1) in breast cancer.

BACKGROUND: Targeted therapies, associated with standard chemotherapies, have improved breast cancer care. However, primary and acquired resistances are frequently observed and the development of new concepts is needed. High-throughput approaches to identify new active and safe molecules with or without an "a priori" are currently developed. Also, repositioning already-approved drugs in cancer therapy is of growing interest. The thiomorpholine hydroxamate compound TMI-1 has been previously designed to inhibit metalloproteinase activity for the treatment of rheumatoid arthritis. We present here the repositioning of TMI-1 drug in breast cancer. METHODOLOGY/PRINCIPAL FINDINGS: We tested the effect of TMI-1 on luminal, basal and ERBB2-overexpressing breast tumor cell lines and on MMTV-ERBB2/neu tumor evolution. We measured the effects on i) cell survival, ii) cell cycle, iii) extrinsic and intrinsic apoptotic pathways, iv) association with doxorubicin, docetaxel and lapatinib, v) cancer stem cells compartment. In contrast with conventional cytotoxic drugs, TMI-1 was highly selective for tumor cells and cancer stem cells at submicromolar range. All non-malignant cells tested were resistant even at high concentration. TMI-1 was active on triple negative (TN) and ERBB2-overexpressing breast tumor cell lines, and was also highly efficient on human and murine "primary" ERBB2-overexpressing cells. Treatment of transgenic MMTV-ERBB2/neu mice with 100 mg/kg/day TMI-1 alone induced tumor apoptosis, inhibiting mammary gland tumor occurrence and development. No adverse effects were noticed during the treatment. This compound had a strong synergistic effect in association with docetaxel, doxorubicin and lapatinib. We showed that TMI-1 mediates its selective effects by caspase-dependent apoptosis. TMI-1 was efficient in 34/40 tumor cell lines of various origins (ED50: 0.6 µM to 12.5 µM). CONCLUSIONS/SIGNIFICANCE: This is the first demonstration of the tumor selective cytotoxic action of a thiomorpholin hydroxamate compound. TMI-1 is a novel repositionable drug not only for the treatment of adverse prognosis breast cancers but also for other neoplasms.

Synthesis and biological evaluation of novel anticancer bivalent colchicine-tubulizine hybrids.

A series of novel antimitotic hybrids were synthesized in good yields by linking of azide-containing colchicine congeners with acetylene-substituted tubulizine-type derivatives using copper-mediated 1,3-dipolar cycloaddition. Obtained compounds exhibit good cytotoxicity against HBL100 epithelial cell lines (IC(50)=0.599-2.93 µÐœ). Several newly synthesized compounds are the substoichiometric inhibitors of microtubule assembly (R=0.41-0.78). The results highlight the importance of the length of spacer linking the tubulin binding ligands in heterodimeric molecules.

Synthesis and biological evaluation of 4-arylcoumarin analogues of combretastatins. Part 2.

A series of A-ring variously methoxylated 4-(3-hydroxy-4-methoxyphenyl)coumarins related to combretastatin A-4 was prepared by cross-coupling reactions. Cytotoxicity studies indicated a potent activity against HBL100 cell line. Substitution patterns on A-ring had only a slight effect on antiproliferative activity. For most cytotoxic compounds, the activity as potential modulators of P-gp and BCRP efflux pumps was evaluated. The results show that compounds 2 and 7 were able to restore mitoxantrone accumulation (BCRP) at concentrations similar to that of cyclosporine A. Compound 7 was the most efficient to reverse P-gp activity. All compounds were found to potently inhibit in vitro microtubule formation via a substoichiometric mode of action for the most part. Compounds 1 and 2 were found to have an apparent affinity binding constant similar to that of combretastatin A-4, i.e., 1 × 10 (6) M(-1). The molecular modeling of coumarin derivatives was performed on the basis of the molecular structure of 7, as determined by single-crystal X-ray crystallography. The calculations suggested that the presence of a methoxy group out of the plane of the chromenone moiety is an important steric hindrance factor embedding the accessibility of those molecules inside the binding pocket on tubulin.

Synthesis and antiprotozoal activity of 4-arylcoumarins.

A large series of 4-arylcoumarins was synthesized by Suzuki-Miyaura cross-coupling reaction and evaluated for antiprotozoal activity against Plasmodium falciparum and Leishmania donovani. Several compounds were found to strongly inhibit the proliferation of human cell line and/or parasites. The 4-(3,4-dimethoxyphenyl)-6,7-dimethoxycoumarin exhibit a potent activity on L. donovani amastigotes with a selectivity index (SI=265) twice than amphotericin B (SI=140).

4-arylcoumarin analogues of combretastatins stimulate apoptosis of leukemic cells from chronic lymphocytic leukemia patients.

OBJECTIVE: To investigate the proapoptotic capacities of four arylcoumarin analogues of combretastatins on leukemic cells from B-cell chronic lymphocytic leukemia (CLL), a malignancy characterized by apoptosis deficiency. MATERIALS AND METHODS: The effects of the four compounds on several nuclear, membrane, and mitochondrial events of apoptosis and on expression of proteins controlling the apoptosis were analyzed after treatment of cultured CLL patients' cells. RESULTS: Treatment with all four compounds resulted in a dose-dependent internucleosomal DNA fragmentation, in stimulation of phosphatidylserine externalization, disruption of the mitochondrial transmembrane potential and caspase-3 activation. DNA fragmentation was prevented in the presence of the pan-caspase inhibitor z-VAD-fmk. Two of the compounds downregulated the expression of Mcl-1, a protein thought to be crucial for the antiapoptotic state in CLL, while Bcl-2 expression was unaffected. No effects were observed on the expression of p27kip1 or the inducible nitric oxide synthase, two proteins, which are constitutively overexpressed by CLL cells and downregulated during the apoptosis induced by other plant-derived molecules (flavopiridol, polyphenols, or hyperforin). This suggests different mechanisms of action for the compounds studied here. Furthermore, normal B lymphocytes from healthy donors appeared less sensitive than CLL cells to the proapoptotic activity of the four compounds. CONCLUSION: The four arylcoumarin analogues were able to promote the apoptosis of CLL cells ex vivo through the caspase-dependent mitochondrial pathway. Therefore, these compounds may be of interest to develop new therapies of CLL based on apoptosis restoration.