Fragment-based hit discovery and structure-based optimization of aminotriazoloquinazolines as novel Hsp90 inhibitors.

In the last decade the heat shock protein 90 (Hsp90) has emerged as a major therapeutic target and many efforts have been dedicated to the discovery of Hsp90 inhibitors as new potent anticancer agents. Here we report the identification of a novel class of Hsp90 inhibitors by means of a biophysical FAXS-NMR based screening of a library of fragments. The use of X-ray structure information combined with modeling studies enabled the fragment evolution of the initial triazoloquinazoline hit to a class of compounds with nanomolar potency and drug-like properties suited for further lead optimization.

Discovery of NMS-E973 as novel, selective and potent inhibitor of heat shock protein 90 (Hsp90).

Novel small molecule inhibitors of heat shock protein 90 (Hsp90) were discovered with the help of a fragment based drug discovery approach (FBDD) and subsequent optimization with a combination of structure guided design, parallel synthesis and application of medicinal chemistry principles. These efforts led to the identification of compound 18 (NMS-E973), which displayed significant efficacy in a human ovarian A2780 xenograft tumor model, with a mechanism of action confirmed in vivo by typical modulation of known Hsp90 client proteins, and with a favorable pharmacokinetic and safety profile.

Covalent and allosteric inhibitors of the ATPase VCP/p97 induce cancer cell death.

VCP (also known as p97 or Cdc48p in yeast) is an AAA(+) ATPase regulating endoplasmic reticulum-associated degradation. After high-throughput screening, we developed compounds that inhibit VCP via different mechanisms, including covalent modification of an active site cysteine and a new allosteric mechanism. Using photoaffinity labeling, structural analysis and mutagenesis, we mapped the binding site of allosteric inhibitors to a region spanning the D1 and D2 domains of adjacent protomers encompassing elements important for nucleotide-state sensing and ATP hydrolysis. These compounds induced an increased affinity for nucleotides. Interference with nucleotide turnover in individual subunits and distortion of interprotomer communication cooperated to impair VCP enzymatic activity. Chemical expansion of this allosteric class identified NMS-873, the most potent and specific VCP inhibitor described to date, which activated the unfolded protein response, interfered with autophagy and induced cancer cell death. The consistent pattern of cancer cell killing by covalent and allosteric inhibitors provided critical validation of VCP as a cancer target.

NMS-E973, a novel synthetic inhibitor of Hsp90 with activity against multiple models of drug resistance to targeted agents, including intracranial metastases.

PURPOSE: Recent developments of second generation Hsp90 inhibitors suggested a potential for development of this class of molecules also in tumors that have become resistant to molecular targeted agents. Disease progression is often due to brain metastases, sometimes related to insufficient drug concentrations within the brain. Our objective was to identify and characterize a novel inhibitor of Hsp90 able to cross the blood-brain barrier (BBB). EXPERIMENTAL DESIGN: Here is described a detailed biochemical and crystallographic characterization of NMS-E973. Mechanism-based anticancer activity was described in cell models, including models of resistance to kinase inhibitors. Pharmacokinetics properties were followed in plasma, tumor, liver, and brain. In vivo activity and pharmacodynamics, as well as the pharmacokinetic/pharmacodynamic relationships, were evaluated in xenografts, including an intracranially implanted melanoma model. RESULTS: NMS-E973, representative of a novel isoxazole-derived class of Hsp90 inhibitors, binds Hsp90α with subnanomolar affinity and high selectivity towards kinases, as well as other ATPases. It possesses potent antiproliferative activity against tumor cell lines and a favorable pharmacokinetic profile, with selective retention in tumor tissue and ability to cross the BBB. NMS-E973 induces tumor shrinkage in different human tumor xenografts, and is highly active in models of resistance to kinase inhibitors. Moreover, consistent with its brain penetration, NMS-E973 is active also in an intracranially implanted melanoma model. CONCLUSIONS: Overall, the efficacy profile of NMS-E973 suggests a potential for development in different clinical settings, including tumors that have become resistant to molecular targeted agents, particularly in cases of tumors which reside beyond the BBB.

Alkylsulfanyl-1,2,4-triazoles, a new class of allosteric valosine containing protein inhibitors. Synthesis and structure-activity relationships.

Valosine containing protein (VCP), also known as p97, is a member of AAA ATPase family that is involved in several biological processes and plays a central role in the ubiquitin-mediated degradation of misfolded proteins. VCP is an ubiquitously expressed, highly abundant protein and has been found overexpressed in many tumor types, sometimes associated with poor prognosis. In this respect, VCP has recently received a great deal of attention as a potential new target for cancer therapy. In this paper, the discovery and structure-activity relationships of alkylsulfanyl-1,2,4-triazoles, a new class of potent, allosteric VCP inhibitors, are described. Medicinal chemistry manipulation of compound 1, identified via HTS, led to the discovery of potent and selective inhibitors with submicromolar activity in cells and clear mechanism of action at consistent doses. This represents a first step toward a new class of potential anticancer agents.

Benzodipyrazoles: a new class of potent CDK2 inhibitors.

The synthesis and the preliminary expansion of this new class of CDK2 inhibitors are presented. The synthesis was accomplished using a solution-phase protocol amenable to rapid parallel expansion and suitable to be scaled-up in view of possible lead development. Following a medicinal chemistry program aimed at improving cell permeability and selectivity, a series of compounds with nanomolar activity in the biochemical assay and able to efficiently inhibit tumor cell proliferation has been obtained.

Catecholic flavonoids acting as telomerase inhibitors.

In recent years telomerase has been identified as a new promising target in oncology and consequently new telomerase inhibitors have been intensely explored as anticancer agents. Focused screening of several polyhydroxylated flavonoids has allowed us to identify 7,8,3',4'-tetrahydroxyflavone 1 as a new telomerase inhibitor with an interesting in vitro activity in a Flash-Plate assay (IC50 = 0.2 microM) that has been confirmed in the classical TRAP assay. Starting from this compound, we developed a medicinal chemistry program to optimize our lead, and in particular to replace one of the two catechols with potential bioisosteres. From this study, new structural analogues characterized by submicromolar potencies have been obtained. Their synthesis and biological activity are described.

Rational design, synthesis, and biological evaluation of bis(pyrimido[5,6,1-de]acridines) and bis(pyrazolo[3,4,5-kl]acridine-5-carboxamides) as new anticancer agents.

The good results obtained with pyrimido[5,6,1-de]acridines 7 and with pyrazolo[3,4,5-kl]acridinecarboxamides 8 prompted us to the synthesis of two new series of bis acridine derivatives: the bis(pyrimidoacridines) 5 and the bis(pyrazoloacridinecarboxamides) 6. Compounds 5 can be regarded also as cyclized derivatives of bis(acridine-4-carboxamides) 3 and compounds 6 as cyclized derivatives of bis(acridine-4-carboxamides) 4. The noncovalent DNA-binding properties of these compounds have been examined using fluorometric techniques. The results indicate that (i) the target compounds are excellent DNA ligands; (ii) the bis derivatives 5 and 6 are more DNA-affinic than corresponding monomers 7 and 8; (iii) the new bis 5 and 6 result always less efficient in binding than related bis(acridine-4-carboxamides) 3 and 4; and (iv) in both series 5 and 6 a clear, remarkable in some cases, preference for binding to AT rich duplexes can be noted. In vitro cytotoxic potency of these derivatives toward the human colon adenocarcinoma cell line (HT29) is described and compared to that of reference drugs. Structure-activity relationships are discussed. We could identify six very potent cytotoxic compounds for further in vitro studies: a cytotoxic screening against six human cancer cell lines and the National Cancer Institute (NCI) screening on 60 human tumor cell lines. Finally, compound 6a was selected for evaluation in a NCI in vivo hollow fiber assay.

Design, synthesis, and biological properties of new bis(acridine-4-carboxamides) as anticancer agents.

To enhance the outstanding biological response shown by the corresponding monomers 4 and 5, two classes of bis-acridine-4-carboxamides, 9, with a linker between the 4,4' positions, and 13, with a linker between the 1,1' positions, have been prepared as DNA-binding and potential antitumor agents. The noncovalent DNA-binding properties of these compounds have been examined using gel-electrophoresis and fluorometric techniques. The results indicate that (i). target compounds intercalate DNA; (ii). the bis derivatives with the optimal linker are considerably more DNA-affinic than corresponding monomers; (iii). overall affinity is sensitive to the nature of the linker, of the chromophores, and of the substituents at 7,7'; (iv). often, the bis derivatives show a marked AT-preferential binding. In vitro cytotoxic potency of these derivatives toward the human colon adenocarcinoma cell line (HT29) is described and compared to that of reference drugs. Structure-activity relationships are discussed. Some highly DNA-affinic and potent cytotoxic compounds, 9b,f and 13b,c, have been selected for the National Cancer Institute (NCI) screening on 60 human tumor cell lines and identified as new leads in the antitumor strategies.

Rational design, synthesis and biological evaluation of thiadiazinoacridines: a new class of antitumor agents.

A series of potential DNA-binding antitumor agents, 3-[omega-(alkylamino)alkyl]-6-nitro-thiadiazino[3,4,5-kl]acridines 12 and 1,3-di[omega-(alkylamino)alkyl]-6-nitro-thiadiazino[3,4,5-kl]acridines 13, has been prepared by cyclization with SOCl(2) of 1-[[omega-(alkylamino)alkyl]amino]-9-imino-4-nitro-9,10-dihydroacridines 16 or 1-[[omega-(alkylamino)alkyl]amino]-9-[omega-(alkylamino)alkyl]imino-4-nitro-9,10-dihydroacridines 17, respectively. The non-covalent DNA-binding properties of 12, 13 have been examined using a fluorometric technique. In vitro cytotoxic potencies of these derivatives toward six tumor cell lines, including human colon adenocarcinoma (HT29) and human ovarian carcinoma (A2780 sensitive, A2780cisR cisplatin-resistant, CH1, CH1cisR cisplatin-resistant, and SKOV-3) cells, are described and compared to that of reference drugs. In vivo antitumor activity of some selected derivatives, endowed with relevant cytotoxic activity against murine leukemia P388 are reported. The 3-[2-(dimethylamino)ethyl]-6-nitro-2,7-dihydro-3H-2 lambda(4)-thiadiazino[3,4,5-kl]acridin-2-one (12d) has been identified as a new lead in the development of anticancer tetracyclic acridine derivatives.

Binding free energy of selected anticancer compounds to DNA--theoretical calculations.

Many studies have elucidated structures and thermodynamics of complexes formed by different ligands with DNA. However, in most cases structural and free energy binding studies were not correlated with each other because of the problem of identifying which experimental free energy of binding corresponds to which experimental DNA-ligand structure. In the present work, Poisson-Boltzmann and solvent-accessible surface area methods were used to predict unknown modes of interaction between DNA and three different ligands: mitoxantrone and two pyrimidoacridine derivatives. In parallel, experimental measurements of binding free energy for the studied complexes were performed to compare experimental and calculated values. Our studies showed that the calculated values of free energy are only close to experimental data for some models of interaction between ligands and DNA. Based on this correlation, the most likely models of DNA-ligand complexes were postulated: (i) mitoxantrone and one derivative of pyrimidoacridine, both with two charged side chains, intercalate from the minor groove of DNA and bind with both chains in this groove; (ii) pyrimidoacridine, with only one side chain, very likely does not intercalate into DNA at all. Additionally, the non-electrostatic and electrostatic parts of the calculated binding free energy for the DNA-ligands studied are discussed.

2,6-Di(omega-aminoalkyl)-2,5,6,7-tetrahydropyrazolo[3,4,5-mn]pyrimido[5,6,1-de]acridine-5,7-diones: novel, potent, cytotoxic, and DNA-binding agents.

DNA-binding agents with potential antitumor activities bearing two cationic side chains, the 2,6-di(omega-aminoalkyl)-2,5,6,7-tetrahydropyrazolo[3,4,5-mn]pyrimido[5,6,1-de]acridine-5,7-diones (4a-r), have been prepared either by reaction of the appropriate 2-(omega-aminoalkyl)-6-chloro-2,3-dihydro-1H,7H-pyrimido[5,6,1-de]acridine-1,3,7-trione with the appropriate (omega-aminoalkyl)hydrazine or by cyclization of the requisite N-6,2-di(omega-aminoalkyl)-2,6-dihydropyrazolo[3,4,5-kl]acridine-6-carboxamide with phosgene. In vitro cytotoxic properties of these derivatives against three human colon adenocarcinoma cell lines (HT29, LoVo, and LoVo/Dx) and against some cell lines of the NCI panel are described and compared to that of reference drugs. Some of the new compounds showed outstanding potency while lacking cross-resistance with anthracyclines. Structure-activity relationships are discussed, and a mechanistic analysis is performed using the COMPARE procedure. The mechanism and efficiency of noncovalent DNA binding of these compounds are examined using gel electrophoresis and fluorometric techniques. The 2,6-di(omega-aminoalkyl)-2,5,6,7-tetrahydropyrazolo[3,4,5-mn]pyrimido[5,6,1-de]acridine-5,7-diones (4) constitute a new class of potent, cytotoxic DNA-binding agents not cross-resistant with doxorubicin.