Development of an Improved Guanidine-Based Rac1 Inhibitor with in vivo Activity against Non-Small Cell Lung Cancer

The Rho GTPase Rac1 is involved in the control of cytoskeleton reorganization and other fundamental cellular functions. Aberrant activity of Rac1 and its regulators is common in human cancer. In particular, deregulated expression/activity of Rac GEFs, responsible for Rac1 activation, has been associated to a metastatic phenotype and drug resistance. Thus, the development of novel Rac1-GEF interaction inhibitors is a promising strategy for finding new preclinical candidates. Here, we studied structure-activity relationships within a new family of N,N'-disubstituted guanidine as Rac1 inhibitors. We found that compound 1D-142, presents superior antiproliferative activity in human cancer cell lines and higher potency as Rac1-GEF interaction inhibitor in vitro than parental compounds. In addition, 1D-142 reduces Rac1-mediated TNFα-induced NF-κB nuclear translocation during cell proliferation and migration in NSCLC. Notably, 1D-142 allowed us to show for the first time the application of a Rac1 inhibitor in a lung cancer animal model.

Anti-Selective Organocatalytic Michael Addition between Phenylacetaldehyde and Nitrostyrene

Using the reaction between phenylacetaldehyde and nitrostyrene catalyzed by pyrrolidine as a simple model, we have studied the diastereochemical outcome of the organocatalytic Michael reactions between benzylic aldehydes and nitrostyrenes. We found that the anti adduct was obtained in high yield and diastereoselection as was demonstrated by the X-ray structure of the product. In situ NMR studies showed a different reaction pathway when compared to aliphatic aldehydes that yield the syn adduct as major isomer.

Preclinical development of novel Rac1-GEF signaling inhibitors using a rational design approach in highly aggressive breast cancer cell lines

Rho GTPases play a key role in the regulation of multiple essential cellular processes, including actin dynamics, gene transcription and cell cycle progression. Aberrant activation of Rac1, a member of Rho family of small GTPases, is associated with tumorigenesis, cancer progression, invasion and metastasis. Particularly, Rac1 is overexpressed and hyperactivated in highly aggressive breast cancer. Thus, Rac1 appears to be a promising and relevant target for the development of novel anticancer drugs. We identified the novel Rac1 inhibitor ZINC69391 through a docking-based virtual library screening targeting Rac1 activation by GEFs. This compound was able to block Rac1 interaction with its GEF Tiam1, prevented EGF-induced Rac1 activation and inhibited cell proliferation, cell migration and cell cycle progression in highly aggressive breast cancer cell lines. Moreover, ZINC69391 showed an in vivo antimetastatic effect in a syngeneic animal model. We further developed the novel analog 1A-116 by rational design and showed to be specific and more potent than the parental compound in vitro and interfered Rac1-P-Rex1 interaction. We also showed an enhanced in vivo potency of 1A-116 analog. These results show that we have developed novel Rac1 inhibitors that may be used as a novel anticancer therapy.

New human papilloma virus E2 transcription factor mimics: a tripyrrole-peptide conjugate with tight and specific DNA-recognition

Background

Human papillomavirus (HPV) is the main causative agent of cervical cancer, particularly high risk strains such us HPV-16, -18 and -31. The viral encoded E2 protein acts as a transcriptional modulator and exerts a key role in viral DNA replication. Thus, E2 constitutes an attractive target for developing antiviral agents. E2 is a homodimeric protein that interacts with the DNA target through an α-helix of each monomer. However, a peptide corresponding to the DNA recognition helix of HPV-16 E2 binds DNA with lower affinity than its full-length DNA binding domain. Therefore, in an attempt to promote the DNA binding of the isolated peptide, we have designed a conjugate compound of the E2 α-helix peptide and a derivative of the antibiotic distamycin, which involves simultaneous minor- and major-groove interactions.

Methodology/Principal Findings

An E2 α-helix peptide-distamycin conjugate was designed and synthesized. It was characterized by NMR and CD spectroscopy, and its DNA binding properties were investigated by CD, DNA melting and gel shift experiments. The coupling of E2 peptide with distamycin does not affect its structural properties. The conjugate improves significantly the affinity of the peptide for specific DNA. In addition, stoichiometric amounts of specific DNA increase meaningfully the helical population of the peptide. The conjugate enhances the DNA binding constant 50-fold, maintaining its specificity.

Conclusions/Significance

These results demonstrate that peptide-distamycin conjugates are a promising tool to obtain compounds that bind the E2 target DNA-sequences with remarkable affinity and suggest that a bipartite major/minor groove binding scaffold can be a useful approach for therapeutic treatment of HPV infection.

Membrane anchoring of diacylglycerol lactones substituted with rigid hydrophobic acyl domains correlates with biological activities

Synthetic diacylglycerol lactones (DAG lactones) are effective modulators of critical cellular signaling pathways downstream of the lipophilic second messenger diacylglycerol that activate a host of protein kinase C (PKC) isozymes as well as other non-kinase proteins that share with PKC similar C1 membrane-targeting domains. A fundamental determinant of the biological activity of these amphiphilic molecules is the nature of their interactions with cellular membranes. This study characterizes the membrane interactions and bilayer anchoring of a series of DAG lactones in which the hydrophobic moiety is a 'molecular rod', namely a rigid 4-[2-(R-phenyl)ethynyl]benzoate moiety in the acyl position. Use of assays employing chromatic biomimetic vesicles and biophysical techniques revealed that the mode of membrane anchoring of the DAG lactone derivatives was markedly affected by the presence of the hydrophobic diphenyl rod and by the size of the functional unit at the terminus of the rod. Two primary mechanisms of interaction were observed: surface binding of the DAG lactones at the lipid/water interface and deep insertion of the ligands into the alkyl core of the lipid bilayer. These membrane-insertion properties could explain the different patterns of the PKC translocation from the cytosol to membranes that is induced by the molecular-rod DAG lactones. This investigation emphasizes that the side residues of DAG lactones, rather than simply conferring hydrophobicity, profoundly influence membrane interactions, and thus may further contribute to the diversity of biological actions of these synthetic biomimetic ligands.

Conformationally constrained analogues of diacylglycerol (DAG). 31. Modulation of the biological properties of diacylgycerol lactones (DAG-lactones) containing rigid-rod acyl groups separated from the core lactone by spacer units of different lengths

Diacylglycerol lactones built with a rigid 4-[(methylphenyl)ethynyl]phenyl rod that is separated from the exocyclic acylcarbonyl of the DAG-lactone core by a spacer unit of variable length were synthesized and studied. Binding affinities for a panel of classical and novel PKC isozymes in two different phospholipid environments, one corresponding to the plasma membrane of cells, were determined. The kinetics and site of translocation for the PKC isozymes α and δ upon treatment with the compounds were also studied as well as the early response of ERK phosphorylation and the late response of induction of apoptosis in the human prostatic carcinoma cell line LNCaP. Finally, the compounds were evaluated in terms of their interaction with biomimetic lipid/polydiacetylene membranes by the associated chromatic response. The different spatial disposition of the rigid structural motif on the DAG-lactones contributes to differential activity.

Self-assembly and lipid interactions of diacylglycerol lactone derivatives studied at the air/water interface

Synthetic diacylglycerol lactones (DAG-lactones) have been shown to be effective modulators of critical cellular signaling pathways. The biological activity of these amphiphilic molecules depends in part upon their lipid interactions within the cellular plasma membrane. This study explores the thermodynamic and structural features of DAG-lactone derivatives and their lipid interactions at the air/water interface. Surface-pressure/area isotherms and Brewster angle microscopy revealed the significance of specific side-groups attached to the terminus of a very rigid 4-(2-phenylethynyl)benzoyl chain of the DAG-lactones, which affected both the self-assembly of the molecules and their interactions with phospholipids. The experimental data highlight the formation of different phases within mixed DAG-lactone/phospholipid monolayers and underscore the relationship between the two components in binary mixtures of different mole ratios. Importantly, the results suggest that DAG-lactones are predominantly incorporated within fluid phospholipid phases rather than in the condensed phases that form, for example, by cholesterol. Moreover, the size and charge of the phospholipid headgroups do not seem to affect DAG-lactone interactions with lipids.

D-(+)-iso-methanocarbathymidine: a high-affinity substrate for herpes simplex virus 1 thymidine kinase

The stereoselective syntheses of the (+)-D and (-)-L enantiomers of iso-methanocarbathymidine (iso-MCT) was achieved through two independent linear approaches that converged on two antipodal enantiomers, common to a key precursor used in the synthesis of racemic iso-MCT. In the study reported herein we identified (+)-3 [D-(+)-iso-MCT] as the active enantiomer that was exclusively recognized by the herpes simplex virus 1 thymidine kinase (HSV1-tk), as was predicted by molecular modeling. For this purpose, a human osteosarcoma (HOS) cell line modified to contain and express HSV1-tk from herpes simplex virus 1 (HSV1) was used to determine the cytotoxicity of the compounds by an assay that measures the level of ATP in the cells. The work demonstrates that changes in the substitution pattern of rigid bicyclo[3.1.0]hexane nucleosides, which, relative to normal nucleosides, appear unconventional, can lead to the spatial optimization of pharmacophores and vastly improved substrate recognition.

Rearranging the bicyclo[3.1.0]hexane template of carbocyclic nucleosides to improve binding recognition by kinases

A novel bicyclo[3.1.0]hexane carbocyclic nucleoside (4) with a south-like conformation amenable to interact with the herpes thymidine kinase (HSV-tk) was synthesized with an endo-hydroxyl group positioned at the tip of the bicyclo[3.1.0]hexane ring system opposite to the tip of the fused cyclopropane ring. The introduction of the hydroxymethyl chain through a Baylis-Hillman type reaction and the regioselective opening of a cyclic sulfite intermediate to introduce the nitrogen functionality at the correct position are highlighted.

Sculpting the bicyclo[3.1.0]hexane template of carbocyclic nucleosides to improve recognition by herpes thymidine kinase

The replacement of the furanose ring by a cyclopentane in nucleosides generates a group of analogues known generically as carbocyclic nucleosides. These compounds have increased chemical and enzymatic stability due to the absence of a true glycosyl bond that characterizes conventional nucleosides. The additional fusion of a cyclopropane ring to the cyclopentane produces a bicyclo[3.1.0]hexane system that depending on its location relative to the nucleobase is able to lock the embedded cyclopentane ring into conformations that mimic the typical north and south conformations of the furanose ring in conventional nucleosides. These bicyclo[3.1.0]hexane templates have already provided important clues to differentiate the contrasting conformational preferences between kinases and polymerases. Herein, we describe the design, synthesis, and phosphorylation pattern of a new bicyclo[3.1.0]hexane thymidine analogue that seems to possess an ideal spatial distribution of pharmacophores for an optimal interaction with herpes simplex 1 thymidine kinase. The bicyclo[3.1.0]hexane template represents a privileged rigid template for sculpting other carbocyclic nucleosides to meet the demands of specific receptors.

Synthesis of Bicyclo[3.1.0]hexanes Functionalized at the Tip of the Cyclopropane Ring. Application to the Synthesis of Carbocyclic Nucleosides

[reaction: see text] A general synthetic strategy for the preparation of functionalized bicyclo[3.1.0]hexanes is described. The new approach employs a cross metathesis step designed to functionalize the appropriate terminal olefin of the bicyclo[3.1.0]hexane precursor and a carbene-mediated intramolecular cyclopropanation reaction on the corresponding diazo intermediate. This combined methodology allowed the diastereoselective introduction of chemically diverse substituents at the tip of the cyclopropane group, except in cases where the substituents consisted of electron-withdrawing groups where a competing [3 + 2] cycloaddition predominated.

Structural determinants of efficacy at A3 adenosine receptors: modification of the ribose moiety

We have found previously that structural features of adenosine derivatives, particularly at the N6- and 2-positions of adenine, determine the intrinsic efficacy as A3 adenosine receptor (AR) agonists. Here, we have probed this phenomenon with respect to the ribose moiety using a series of ribose-modified adenosine derivatives, examining binding affinity and activation of the human A3 AR expressed in CHO cells. Both 2'- and 3'-hydroxyl groups in the ribose moiety contribute to A3 AR binding and activation, with 2'-OH being more essential. Thus, the 2'-fluoro substitution eliminated both binding and activation, while a 3'-fluoro substitution led to only a partial reduction of potency and efficacy at the A3 AR. A 5'-uronamide group, known to restore full efficacy in other derivatives, failed to fully overcome the diminished efficacy of 3'-fluoro derivatives. The 4'-thio substitution, which generally enhanced A3 AR potency and selectivity, resulted in 5'-CH2OH analogues (10 and 12) which were partial agonists of the A3 AR. Interestingly, the shifting of the N6-(3-iodobenzyl)adenine moiety from the 1'- to 4'-position had a minor influence on A3 AR selectivity, but transformed 15 into a potent antagonist (16) (Ki = 4.3 nM). Compound 16 antagonized human A3 AR agonist-induced inhibition of cyclic AMP with a K(B) value of 3.0 nM. A novel apio analogue (20) of neplanocin A, was a full A3 AR agonist. The affinities of selected, novel analogues at rat ARs were examined, revealing species differences. In summary, critical structural determinants for human A3 AR activation have been identified, which should prove useful for further understanding the mechanism of receptor activation and development of more potent and selective full agonists, partial agonists and antagonists for A3 ARs.

A conformationally locked analogue of the anti-HIV agent stavudine. An important correlation between pseudorotation and maximum amplitude

The synthesis and biological evaluation of a bicyclo[3.1.0]hexene nucleoside designed as a conformational mimic of the anti-HIV agent stavudine (1, D4T) is described. The unsaturated methanocarbocyclic pseudosugar of N-MCD4T (2) was constructed from an iodo-substituted precursor by a DBU-catalyzed olefination reaction. Mitsunobu coupling with N(3)-benzoylthymine afforded the desired target after deprotection. Both D4T and N-MCD4T are in the North (N) hemisphere of the pseudorotational cycle but 70 degrees away from a perfect N (P = 0 degrees ) conformation toward the East and West hemispheres, respectively. Despite this large difference, the double bond reduces the puckering amplitude (nu(max)) of N-MCD4T to 6.81 degrees, and the superposition of both structures showed a RMS deviation of only 0.039 A. The combined structural analysis of P and nu(max) shows that while the value of P may differ substantially, the low nu(max) resolves the differences and becomes the dominant pseudorotational parameter. N-MCD4T is active against HIV-1 and HIV-2 in CEM, MT-2, and MT-4 cells, and while it is somewhat less potent than D4T, it also appears to be less toxic. The triphosphate (N-MCD4TTP) inhibits HIV reverse transcriptase with a 10-fold higher IC(50) than D4TTP. By virtue of its carbocyclic nature, N-MCD4T (2) is a more robust molecule stable to conditions that would cleave D4T.

Synthesis of C-5'-nor-dideoxycarbanucleosides structurally related to neplanocin C

Purine carbanucleosides built on a 6-oxabicyclo[3.1.0]hexane template were synthesized from readily available 2-cyclopentenone employing a Mitsunobu reaction to incorporate the base onto the carbocyclic ring. Both adenosine and guanosine analogues exhibited moderate antiviral activity.

Evaluation of the antiviral activity of natural sulfated polyhydroxysteroids and their synthetic derivatives and analogs

Disodium 3beta,21-dihydroxypregn-5-en-20-one disulfate (2), sodium 3beta,21-dihydroxypregn-5-en-20-one 3-sulfate (3), sodium 3beta,21-dihydroxypregn-5-en-20-one 21-sulfate (4), and disodium 3beta,6alpha-dihydroxy-5alpha-pregnan-20-one disulfate (6) have been synthesized and completely characterized for the first time from readily available materials. Sulfation was performed using triethylamine-sulfur trioxide complex in dimethylformamide as the sulfating agent. Selective sulfation of 3beta,21-dihydroxypregn-5-en-20-one rendered sodium 3beta,21-dihydroxypregn-5-en-20-one 3-sulfate (3) as the major compound. The synthetic sulfated steroids as well as natural disulfated polyhydroxysteroids (7-9) isolated by us from the antarctic ophiuroid Astrotoma agassizii and the synthetic derivatives disodium 2beta,3alpha,21-trihydroxy-(20R)-cholesta-5,24-diene 3-acetate, 2,21-disulfate (7a) and 2beta,3alpha,21-trihydroxy-(20R)-cholesta-5,24-diene (7b) were comparatively evaluated for their inhibitory effect on the replication of one DNA (HSV-2) and two RNA (PV-3, JV) viruses. In general, steroids with sulfate groups at C-21 and C-2 or C-3 were the most effective in their inhibitory action against HSV-2 and also proved to be active against PV-3 and JV.