Sanat K. Mandal

Rational drug design

In this article, current knowledge of drug design is reviewed and an approach of rational drug design is presented. The process of drug development is challenging, expensive, and time consuming, although this process has been accelerated due to the development of computational tools and methodologies. The current target based drug design approach is incomplete because most of the drugs developed by structure guided approaches have been shown to have serious toxic side effects. Otherwise these drugs would have been an ideal choice for the treatment of diseases. Hence, rational drug design would require a multidisciplinary approach. In this regard, incorporation of gene expression technology and bioinformatics tools would be indispensable in the structure based drug design. Global gene expression data and analysis of such data using bioinformatics tools will have numerous benefits such as efficiency, cost effectiveness, time saving, and will provide strategies for combination therapy in addition to overcoming toxic side effects. As a result of incorporation of gene expression data, partial benefit of the structure based drug design is slowly emerging and rapidly changing the approach of the drug development process. To achieve the full benefit of developing a successful drug, multidisciplinary approaches (approaches such as computational chemistry and gene expression analysis, as discussed in this article) would be necessary. In the future, there is adequate room for the development of more sophisticated methodologies.

Apoptin, a tumor-selective killer

Apoptin, a small protein from chicken anemia virus, has attracted great attention, because it specifically kills tumor cells while leaving normal cells unharmed. The subcellular localization of apoptin appears to be crucial for this tumor-selective activity. In normal cells, apoptin resides in the cytoplasm, whereas in cancerous cells it translocates into the nucleus. The nuclear translocation of apoptin is largely controlled by its phosphorylation. In tumor cells, apoptin causes the nuclear accumulation of survival kinases including Akt and is phosphorylated by CDK2. Thereby, apoptin redirects survival signals into cell death responses. Apoptin also binds as a multimeric complex to DNA and interacts with several nuclear targets, such as the anaphase-promoting complex, resulting in a G2/M phase arrest. The proapoptotic signal of apoptin is then transduced from the nucleus to cytoplasm by Nur77, which triggers a p53-independent mitochondrial death pathway. In this review, we summarize recent discoveries of apoptins mechanism of action that might provide intriguing insights for the development of novel tumor-selective anticancer drugs.

The S100A7-c-Jun Activation Domain Binding Protein 1 Pathway Enhances Prosurvival Pathways in Breast Cancer

S100A7 is among the most highly expressed genes in preinvasive breast cancer, is a marker of poor survival when expressed in invasive disease, and promotes breast tumor progression in experimental models. To explore the mechanism of action, we examined the role of S100A7 in cell survival and found that overexpression of S100A7 in MDA-MB-231 cell lines promotes survival under conditions of anchorage-independent growth. This effect is paralleled by increased activity of nuclear factor-kappaB (3-fold) and phospho-Akt (4-fold), which are known to mediate prosurvival pathways. S100A7 and phospho-Akt are also correlated in breast tumors examined by immunohistochemistry (n = 142; P < 0.0001; r = 0.34). To explore the underlying mechanism, we examined the role of a putative c-Jun activation domain-binding protein 1 (Jab1)-binding domain within S100A7 using a panel of MDA-MB-231 breast cell lines stably transfected with either S100A7 or S100A7 mutated at the Jab1 domain. Structural analysis by three-dimensional protein modeling, immunoprecipitation, and yeast two-hybrid assay and functional analysis using transfected reporter gene and Western blot assays revealed that the in vitro effects of S100A7 on phospho-Akt and the nuclear factor-kappaB pathway are dependent on the Jab1-binding site and the interaction with Jab1. Enhanced epidermal growth factor receptor signaling was also found to correlate with the increased phospho-Akt. Furthermore, the Jab1-binding domain is also necessary for the enhanced tumorigenicity conferred by S100A7 expression in murine xenograft tumors in vivo. We conclude that the S100A7-Jab1 pathway acts to enhance survival under conditions of cellular stress, such as anoikis, which may promote progression of breast cancer.

Modeling of Molecular Interaction between Apoptin, BCR-Abl and CrkL - An Alternative Approach to Conventional Rational Drug Design

In this study we have calculated a 3D structure of apoptin and through modeling and docking approaches, we show its interaction with Bcr-Abl oncoprotein and its downstream signaling components, following which we confirm some of the newly-found interactions by biochemical methods. Bcr-Abl oncoprotein is aberrantly expressed in chronic myelogenous leukaemia (CML). It has several distinct functional domains in addition to the Abl kinase domain. The SH3 and SH2 domains cooperatively play important roles in autoinhibiting its kinase activity. Adapter molecules such as Grb2 and CrkL interact with proline-rich region and activate multiple Bcr-Abl downstream signaling pathways that contribute to growth and survival. Therefore, the oncogenic effect of Bcr-Abl could be inhibited by the interaction of small molecules with these domains. Apoptin is a viral protein with well-documented cancer-selective cytotoxicity. Apoptin attributes such as SH2-like sequence similarity with CrkL SH2 domain, unique SH3 domain binding sequence, presence of proline-rich segments, and its nuclear affinity render the molecule capable of interaction with Bcr-Abl. Despite almost two decades of research, the mode of apoptins action remains elusive because 3D structure of apoptin is unavailable. We performed in silico three-dimensional modeling of apoptin, molecular docking experiments between apoptin model and the known structure of Bcr-Abl, and the 3D structures of SH2 domains of CrkL and Bcr-Abl. We also biochemically validated some of the interactions that were first predicted in silico. This structure-property relationship of apoptin may help in unlocking its cancer-selective toxic properties. Moreover, such models will guide us in developing of a new class of potent apoptin-like molecules with greater selectivity and potency.

Dinuclear metal complexes. Part 4. Electrochemical studies of macrocyclic dicopper(II) complexes. Investigation of the effect of solvents, donor groups, and steric constraints on the stability of mixed-valence copper(II)–copper(I) complexes

Two series of macrocyclic dicopper(II) complexes of stoicheiometry [Cu2L][ClO4]2·2H2O have been synthesized and characterized. Compounds belonging to series (1) are derived from the 6,12,18,24-substituted (H,H,Me,Me; H,H,Me,Ph; Me,Me,Me,Ph; Me,Me,Ph,Ph) macrocycie 7,11;19,23-dimetheno-9,21-dimethyl-1,5,13,17-tetra-azacyclotetracosa-5,7,9,12,17,19,21,24-octaene-25,26-diol (H2L). Complexes belonging to series (2) are related to those of series (1) by replacement of two of the –CHN– linkages by –CH2–NH– groups and the segment containing two azomethine linkages having the 6,12-substituents H,H; Me,Me; Me,Ph; Ph,Ph. The electrochemistry of these compounds has been investigated in MeCN and CH2Cl2 solvents using platinum and glassy carbon electrodes. In all cases cyclic voltammograms show sequential one-electron transfers at two different potentials, and from these data the conproportionation constant (Kc) and free energy of the mixed-valent species (ΔGc) have been evaluated. Electrochemical results have been analysed in terms of the effect due to solvent, donor groups, and steric constraints. Values of Kc for all of the compounds are greater in MeCN than those in CH2Cl2, and the Kc value for any compound belonging to series (1) is greater than its analogue in series (2). Factors affecting stability and intramolecular electron-transfer rates of CuIICuIL+ species are discussed.

Binuclear copper(II) complexes of tetradentate (Ne) diazine ligands. Crystal structures of [μ-1,4-Bis(4,6-dimethyl-2-pyridylamino)phthalazine-N,μ-N3,μN3,N]-(μ-Dichloro)dichlorodicopper(II), [μ-3,6-Bis(2-pyridylthio)pyridazine-N,μ-N1,μ-N2,N] (μ-dichloro)dichlorodicopper(II) ethanol, and 3,6-Bis(2-pyridylthio)-pyridazine

Abstract The X-ray structures of two binuclear copper(II) chloride complexes of the tetradentate ligands 1,4- bis(4,6-dimethyl-2-pyridylamino)phthalazine (PAP46Me) and 3,6-bis(2-pyridylthio)pyridazine are reported. [Cu2(PAP46Me)Cl4] (1) and [Cu2(PTP)Cl4]· CH3CH2OH (2) contain triply bridged binuclear centres involving a diazine (NN) and two chlorobridges with copper-copper separations in the fange 3.19–3.25 A and distorted square pyramidal copper stereochemistry. The reduced room temperature magnetic moments indicate antiferromagnetically coupled binuclear copper(II) centres. Complex 1 forms green crystals with a= 15.795(3), b=10.661(3), c=16.155(4) A, β= 113.82(3)°, C2/c, Z = 4, Rf=0.031. Complex (2) forms green crystals with a=33.9022(8), b= 9.1626(5), c= 15.7885(5) A,β= 114.853(2)°, C2/c, Z=8, Rf=0.047. The structure of the ligand PTP is also reported and compared with that of 2.

Synthesis and cytotoxic activity of benzopyran-based platinum(II) complexes.

A series of benzopyran-based platinum complexes of types 4 and 5 were synthesized as potential anticancer agents. The novel compounds were synthesized in several steps using simple and efficient chemistry. The newly synthesized compounds were evaluated for their biological efficacy and showed significant in vitro cytotoxic activity in different hormone-dependent and -independent breast cancer cell lines. Docking and other molecular modeling experiments were also performed for one of the potent compounds, 5f, which showed that both the possible enantiomeric forms (5f with 3R,4R and 5f with 3S,4S) of the molecule have comparable lowest energy (for 5f with 3R,4R, -31.953 kcal/mol and for 5f with 3S,4S, -31.944 kcal/mol). The 3D QSAR was examined for the derivatives of both enantiomeric forms and a novel relationship for the 3S,4S derivatives is discussed.

Binuclear copper(II) complexes of some tetradentate (N4) diazine ligands with benzimidazole donor groups. Crystal structure of [μ-3,6-bis(N-ethyl-2-benzimidazolylthio)pyridazine-N, μ-N5, μ-N6, N]-(μ-hydroxo)(μ-chloro)dichlorodicopper(II) DMF

Abstract Binuclear copper(II) and copper(I) complexes and mononuclear copper(II) complexes of a series of N - alkyl substituted derivatives of the tetradentate ligand 3,6-bis(2-benzimidazolylthio)pyridazine (BITP) are reported. The complex [Cu 2 (EtBITP(OH)Cl 3 ]·DMF ( II ) contains a triply bridged binuclear centre with a diazine (N-N), a hydroxide and a chloride bridge. The two trigonal-bipyramidal copper(II) centres are separated by 3.017 A with a CuO(H)Cu bridge angle of 104.7° and are antiferromagnetically coupled (−2 J =260 cm −1 ). Cyclic voltammetric studies on several binuclear copper(II) complexes show quasi- reversible or essentially non-reversible redox waves at positive potentials (0.41-0.46 V versus SCE) associated with two electron reduction. Complex II forms green crystals with a=8.9198- (5), b =13.5738(8), c =13.7178(7) A,α=105.318- (5)°, β=105.255(5)°, γ=99.461(5)°, P 1 , Z=2, R f = 0.028.

Binuclear copper(II) complexes of some sexadentate phthalazine-hydrazone ligands with strong antiferromagnetic exchange

Abstract Sexadentate phthalazine-hydrazone ligands (N6), involving pyridine and N-methylimidazole as peripheral donor groups, form binuclear hydroxo-bridged copper(II) complexes which exhibit very strong antiferromagnetic exchange (−2J=885−1211 cm−1), which is propagated via a superexchange mechanism through the bridging diazine (NN) and hydroxide groups. When the hydroxide bridge in [Cu2(APHPH)(OH)(H2O)2](ClO4)2·H2O (APHP=1,4-dihydrazinophalazine-bis(2-pyridine) acetaldimine) (−2J=988 cm−1) is replaced by a pyrazolide bridge, a dramatic decrease in exchange is observed (−2J=521 cm−1) indicating the importance of hydroxide as a dominant superexchange bridge. The complexes are highly colored, exhibiting very intense visible absorptions (16 400–16 700 cm−1) associated with charge transfer transitions. The crystal and molecular structure of [Cu2(APHPH)(OH)(H2O)2](ClO4)2·H2O (VI) is reported. VI crystallized in the monoclinic system, space group P21/n, with a=8.0110(20), b=24.100(5), c=15.6750(20) A, β=100.240(20)° and four formula units per unit cell. Refinement by full-matrix least-squares gave final residuals of R=0.076 and Rw=0.038. This complex has a hydroxo-bridged suare-pyramidal structure with a CuCu separation of 3.296(2) A and a CuO(H)Cu angle of 117.8(3)°.

Thiopyridyl triazine derivatives and their platinum complexes: A new class of potential antitumor agents

Abstract A novel series of thiopyridyl triazine ligands and their metal(II) complexes have been synthesized. The X-ray structure of the mononuclear copper(II) complex of the ligand 6-thiopyridyl-2,4-bis(dimethylamino)-l,3,5-triazine (L5) has also been determined. The in vitro cytotoxic potency against the human colon cancer cell line (HT-29) has been determined for the ligands and their platinum complexes. All compounds including their ligands have been found to be highly potent against the HT-29 cell line. The ligand 2,4,6-trithiopyridyl-l,3,5-triazine (L2) and its platinum complex were found to be 10–30 times more potent than cisplatin.