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PubMed2007

Material surfaces affect the protein expression patterns of human macrophages: A proteomics approach.

Monocyte-derived macrophages (MDM) are key inflammatory cells and are central to the foreign body response to implant materials. MDM have been shown to exhibit changes in actin cytoskeleton, multinucleation, cell size, and function in response to small alterations in polycarbonate-urethane (PCNU) surface chemistry. Although PCNU chemistry has an influence on de novo protein synthesis, no assessments of the protein expression profiles of MDM have yet been reported. The rapid emerging field of expression proteomics facilitates the study of changes in cellular protein profiles in response to their microenvironment. The current study applied proteomic techniques, 2-dimensional electrophoresis (2-DE) combined with MALDI-ToF (matrix assisted laser desorption ionization-time of flight) mass spectrometry, to determine differences in MDM protein expression influenced by PCNU. Results indicated that MDM responded to material chemistry by modulation of structural proteins (i.e. actin, vimentin, and tubulin). Additionally, intracellular protein modulation which requires proteins responsible for trafficking (i.e. chaperone proteins) and protein structure modification (i.e. bond rearrangement and protein folding) were also altered. This study demonstrated for the first time that a proteomics approach was able to detect protein expression profile changes in MDM cultured on different material surfaces, forming the basis for utilizing further quantitative proteomics techniques that could assist in elucidation of the mechanisms involved in MDM-material interaction.

Biocompatible Materials↗
PubMed1992

Modulation of gamma-actin and alpha 1-tubulin expression by corticosterone during neuronal plasticity in the hippocampus.

Evidence is given for altered gene expression of gamma-actin in the hippocampus in response to entorhinal cortex lesion (ECL). Time course analysis reveals a progressive repression of gamma-actin expression between 4 and 14 days post-lesion, coinciding with the early and middle phases of the hippocampal reinnervation process. RNA prevalence returns to near control values at 30 days post-lesion. Corticosterone administration, which is known to impair the reinnervation process in ECL rats, prevents the lesion-induced reduction in gamma-actin expression and blocks the induction of alpha 1-tubulin in the deafferented hippocampus. The timing of response of gamma-actin to ECL and its modulation by glucocorticoid administration support suggestions that gamma-actin has an important role to play in neuronal cytoarchitecture remodelling during hippocampal reinnervation.

Actins↗
PubMed1995

Beta-tubulin genes from the parasitic nematode Haemonchus contortus modulate drug resistance in Caenorhabditis elegans.

Resistance to antimitotic chemotherapeutics in pathogenic nematodes, fungi and mammalian cells is closely associated with structural changes in cytoskeletal beta-tubulin. We investigated the possibility of using the well-characterised free-living nematode Caenorhabditis elegans as a model for studying the mechanism of resistance against benzimidazole (BZ) drugs in the parasitic nematode Haemonchus contortus. Functional analysis of a conserved beta-tubulin isotype (tub-1) mutation near GTP-binding domain II, which is linked to BZ resistance, was carried out in C. elegans by heterologous expression of: (1) parasite BZ-sensitive alleles; (2) BZ-resistant alleles; and (3) in vitro mutagenised beta-tubulin gene constructs. The injected heterologous gene constructs were not only stably maintained, but also expressed as shown by reverse transcriptase-polymerase chain reaction analysis. The degree of BZ drug susceptibility of the transformants was assayed and quantified by incubation with both benomyl and thiabendazol. All H. contortus tub-1 constructs, which encoded Phe at position 200, conferred susceptibility to thiabendazole in BZ-resistant C. elegans ben-1 mutants. In contrast, constructs carrying Tyr200 did not alter the BZ drug phenotype. From these experiments we conclude that: (1) C. elegans can be used as an expression host, since injected parasite genes were biologically active; and (2) the single Phe to Tyr mutation at position 200 in beta-tubulin isotype 1 is the cause of BZ resistance in H. contortus.

Amino Acid Sequence↗
PubMed1981

Ca2+- and calmodulin-stimulated endogenous phosphorylation of neurotubulin.

Ca2+ plays a major role in the functional use of tubulin in brain and other tissues. It activates an endogenous tubulin kinase system in brain cytosol, tubulin, and presynaptic nerve terminal fractions prepared from rat brain. Activation of the Ca2+ tubulin kinase system was modulated by the Ca2+ receptor protein calmodulin. The concentrations of Ca2+ and calmodulin required to produce a half-maximal stimulation of the tubulin kinase were 0.8 microM and 0.4 micrograms, respectively. Ca2+ -calmodulin tubulin kinase activity was very unstable after death, and procedures were developed to stabilize the activity of this enzyme system. Evidence is presented demonstrating that the Ca2+ -calmodulin tubulin kinase system is distinct from the previously described cyclic AMP-Mg2+ tubulin kinase. The results suggest that Ca2+- and calmodulin-stimulated phosphorylation of tubulin may be a major biochemical mechanism modulating some of calcium's effects on tubulin and may play a significant role in mediating some of calcium's actions on cell functions.

Animals↗
PubMed1991

Effects of antimitotic agents on tubulin-nucleotide interactions.

The interaction of antimitotic drugs with guanine nucleotides in the tubulin-microtubule system is reviewed. Antimitotic agent-tubulin interactions can be covalent, entropic, allosteric or coupled to other equilibria (such as divalent cation binding, alternate polymer formation, or the stabilization of native tubulin structure). Antimitotics bind to tubulin at a few common sites and alter the ability of tubulin to form microtubules. Colchicine and podophyllotoxin compete for a common overlapping binding site but only colchicine induces GTPase activity and large conformational changes in the tubulin heterodimer. The vinca alkaloids, vinblastine and vincristine, the macrocyclic ansa macrolides, maytansine and ansamitocin P-3, and the fungal antimitotic, rhizoxin, share and compete for a different binding site near the exchangeable nucleotide binding site. The macrocyclic heptapeptide, phomopsin A, and the depsipeptide, dolastatin 10, bind to a site adjacent to the vinca alkaloid and nucleotide sites. Colchicine, vinca alkaloids, dolastatin 10 and phomopsin A induce alternate polymer formation (sheets for colchicine, spirals for vinblastine and vincristine and rings for dolastatin 10 and phomopsin A). Maytansine, ansamitocin P-3 and rhizoxin inhibit vinblastine-induced spiral formation. Taxol stoichiometrically induces microtubule formation and, in the presence of GTP, assembly-associated GTP hydrolysis. Analogs of guanine nucleotides also alter polymer morphology. Thus, sites on tubulin for drugs and nucleotides communicate allosterically with the interfaces that form longitudinal and lateral contacts within a microtubule. Microtubule associated proteins (MAPs), divalent cations, and buffer components can alter the surface interactions of tubulin and thus modulate the interactions between antimitotic drugs and guanine nucleotides.

Animals↗
PubMedDate not supplied

Effects of lithium gammalinolenate on the perfusion of liver and pancreatic tissues in pancreatic cancer.

Because of its poor prognosis, new modalities to treat pancreatic cancer are highly welcome. Gammalinolenate (GLA) has been shown to possess antitumor activity on various human cancer cell lines in vitro and some evidence has been found of its modulative activity on tubulin active agents, such as vinca alkaloids. GLA treatment is thought to change the penetration and distribution of chemotherapeutic agents in pancreatic tumor tissue. The in vivo effects of GLA are widely unknown. This is the first study on the modulation effects of both oral or intravenous GLA on blood perfusion in vivo. We analysed tissue perfusion prior to treatment and on the 10th day of GLA treatment in patients with pancreatic cancer. Dynamic gamma imaging was performed for 20 minutes after Tc-99m-MIBI injection, and the whole body was scanned after the dynamic study and at 4 hours. Half-lives in liver, left kidney, spleen, pancreas and tumor were recorded using a developed macro program for background corrected geometric mean data from irregular region of interests. Half-lives in the liver did not change due to oral GLA treatment, but they decreased dramatically in two of three patients after i.v. GLA treatment. Additionally, individual changes were observed in pancreatic half-lives, as in four out of five cases the half-life increased and in one case it decreased. No major changes were observed in kidney and spleen half-lives. GLA treatment had no effects on the blood brain barrier. This technique demonstrates perfusion in salivary glands, thyroid, lungs, heart, spleen, kidneys, muscles, spine and bladder, but no changes in perfusion could be detected due to GLA treatment. However, qualitatively enhanced blood flow through the pancreatic tumor was observed. In all patients irrespective of the route of administration of GLA, the organ-to-background ratios in liver decreased. The effect is, however, smallest after oral dosing. The pancreas-to-background ratio was increased in 3/5 patients, these patients exhibited stabilized disease. In a patient with large liver metastases the pancreas-to-background ratio decreased, and she showed a rapid disease progression during GLA therapy. The change in the pancreatic uptake was inversely proportional to the change in CA 19-9 concentration. Our results indicate the that GLA treatment dramatically changes tissue perfusion, especially in liver and pancreatic tumors, even at low doses, and these changes may predict response to GLA therapy.

Administration, Oral↗
PubMed2002

Resistance to arsenite modulates expression of beta- and gamma-tubulin and sensitivity to paclitaxel during differentiation of Leishmania donovani.

Differentiation of Leishmania donovani promastigotes into infectious amastigotes is accompanied by differential tubulin gene expression. Tubulin is one of the proposed targets of clinically useful antileishmanial agents and its expression is known to alter due to drug resistance. In this study, beta- and gamma-tubulin expression under various stages of differentiation was measured in an in vitro generated arsenite-resistant L. donovani strain. Results showed higher constitutive expression of beta-tubulin in the arsenite-resistant promastigotes and amastigotes compared with the wild-type. beta-Tubulin expression in the resistant promastigotes increased on paclitaxel treatment. Significant differences in gamma-tubulin expression were observed only between the amastigotes, but not between promastigotes, of wild-type and resistant strains. Paclitaxel did not produce any significant change in the expression profile of gamma-tubulin in either of the strains, neither before nor after differentiation. Data suggest that the beta- and gamma-tubulin expression and the response to paclitaxel is affected due to arsenite resistance.

Animals↗
PubMed1996

Interaction of kinesin motor domains with alpha- and beta-tubulin subunits at a tau-independent binding site. Regulation by polyglutamylation.

Interaction of rat kinesin and Drosophila nonclaret disjunctional motor domains with tubulin was studied by a blot overlay assay. Either plus-end or minus-end-directed motor domain binds at the same extent to both alpha- and beta-tubulin subunits, suggesting that kinesin binding is an intrinsic property of each tubulin subunit and that motor directionality cannot be related to a preferential interaction with a given tubulin subunit. Binding features of dimeric versus monomeric rat kinesin heads suggest that dimerization could drive conformational changes to enhance binding to tubulin. Competition experiments have indicated that kinesin interacts with tubulin at a Tau-independent binding site. Complementary experiments have shown that kinesin does not interact with the same efficiency with the different tubulin isoforms. Masking the polyglutamyl chains with a specific monoclonal antibody leads to a complete inhibition of kinesin binding. These results are consistent with a model in which polyglutamylation of tubulin regulates kinesin binding through progressive conformational changes of the whole carboxyl-terminal domain of tubulin as a function of the polyglutamyl chain length, thus modulating the affinity of tubulin for kinesin and Tau as well. These results indicate that microtubules, through tubulin polymorphism, do have the ability to control microtubule-associated protein binding.

Animals↗
PubMed1999

Dynamic interaction between soluble tubulin and C-terminal domains of N-methyl-D-aspartate receptor subunits.

The cytoplasmic C-terminal domains (CTs) of the NR1 and NR2 subunits of the NMDA receptor have been implicated in its anchoring to the subsynaptic cytoskeleton. Here, we used affinity chromatography with glutathione S-transferase-NR1-CT and -NR2B-CT fusion proteins to identify novel binding partner(s) of these NMDA receptor subunits. Upon incubation with rat brain cytosolic protein fraction, both NR1-CT and NR2B-CT, but not glutathione S-transferase, specifically bound tubulin. The respective fusion proteins also bound tubulin purified from brain, suggesting a direct interaction between the two binding partners. In tubulin polymerization assays, NR1-CT and NR2B-CT significantly decreased the rate of microtubule formation without destabilizing preformed microtubules. Moreover, only minor fractions of either fusion protein coprecipitated with the newly formed microtubules. Consistent with these findings, ultrastructural analysis of the newly formed microtubules revealed a limited association only with the CTs of the NR1 and NR2B. These data suggest a direct interaction of the NMDA receptor channel subunit CTs and tubulin dimers or soluble forms of tubulin. The efficient modulation of microtubule dynamics by the NR1 and NR2 cytoplasmic domains suggests a functional interaction of the receptor and the subsynaptic cytoskeletal network that may play a role during morphological adaptations, as observed during synaptogenesis and in adult CNS plasticity.

Animals↗
PubMed1996

Mg2+ antagonism on Ni(2+)-induced changes in microtubule assembly and cellular thiol homeostasis.

As an essential metal for cell metabolism, Mg2+ is known to exert antagonism on Ni2+ genotoxic and other effects. This study examined the influence of Mg2+ on Ni(2+)-induced changes in microtubule (MT) assembly in vitro, cytoplasmic MT organization, cellular glutathione (GSH), and cytoskeletal and cytosolic protein sulfhydryls (PSH). As determined by a turbidity assay at 27 degrees C, Ni2+ enhanced the in vitro MT assembly in a Pipes buffer by shortening the initial lag (nucleation phase) and increasing the rate of polymerization with a higher final plateau. However, presence of 1 mM exogenous MgCl2 abolished the Ni2+ enhancing effect. Exposure of 3T3 cells to 2 mM NiCl2 for 20 hr resulted in perinuclear bundling of MTs and decreases in cytoskeletal and cytosolic PSH and cellular GSH levels. However, coincubation of cells with MgCl2 (1.25-20 mM) added to the culture medium markedly diminished the Ni2+ injury to MT organization. Under these conditions the Ni2+ interference with PSH was blocked such that both the cytoskeletal and cytosolic PSH levels returned to the range of control cells without metal treatment. Treatment of cells with Mg2+ (1.25-5 mM) for 20 hr slightly increased, while with higher Mg2+ doses (> 10 mM) decreased, cellular GSH content. Importantly, in Ni(2+)-treated cultures, addition of Mg2+ (1.25-10 mM) elevated GSH levels to > or = 200% of that in cells treated with Ni2+ alone. Furthermore, these Ni2+ and Mg2+ (1.25-10 mM) treated cells actually maintained GSH levels which were essentially unchanged from the basal level of control cells with no metal treatment. Although Mg2+ replacement of Ni2+ bound to MT proteins could be an important mechanism, cellular GSH may also be a critical factor in Mg2+ antagonism on Ni(2+)-enhanced MT assembly in view of the essential role of tubulin PSH in modulating MT assembly and, in turn, the GSH modulation of PSH.

3T3 Cells↗
PubMed1991

Cell-cycle specific cytotoxicity mediated by stizophyllin (2 alpha,3 beta,12 beta-trihydroxypregna-4,7,16-trien-20-one), a novel electrophilic pregnane isolated from Stizophyllum riparium.

A structurally-novel pregnane derivative, 2 alpha,3 beta,12 beta-trihydroxypregna-4,7,16-trien-20-one (stizophyllin), was isolated from an extract of Stizophyllum riparium (H.B.K.) Sandw. on the basis of bioactivity-guided fractionation and confirmed to mediate a potent cytotoxic response with cultured P-388 cells. We presently report a detailed isolation procedure and the results of studies designed to examine its mechanism of action. By means of a Michael-type addition, stizophyllin formed adducts with nucleophilic substances such as L-cysteine and beta-mercaptoethanol. The adduct with beta-mercaptoethanol was isolated, structurally characterized, and found to be 20-fold less cytotoxic than stizophyllin. Stizophyllin interacted with DNA, but no mutagenicity was observed with Salmonella typhimurium strain TM677 or cultured Chinese hamster ovary cells, and no in vitro reaction occurred with guanosine. Relative to control cell cultures, the total biosynthesis of DNA, RNA or protein was reduced when P-388 cells were treated with stizophyllin. However, the cell number did not increase in the presence of inhibitory stizophyllin concentrations (e.g., 4 micrograms/ml), and the DNA content (per cell) actually doubled after approximately 48 h. Consistent with this, stizophyllin blocked the cells in the G2 + M compartment of the cycle, and the block appeared to be specific for the G2 phase. Accordingly, stizophyllin did not modulate in vitro tubulin polymerization reactions nor did it affect the morphology of dibutyryl cAMP-treated astrocytoma cells in culture. These data suggest that the cytotoxic activity of stizophyllin is mediated by covalent reaction with a cellular component (such as a sulfhydryl-containing protein) by means of a Michael-type addition. Based on the cell-cycle specificity of the response, it appears that this interaction prevents the cells from progressing through mitosis.

Animals↗
PubMed1995

[Colchicine: recent data on pharmacokinetics and clinical pharmacology].

Colchicine is widely used in the treatment of acute goutty arthritis. Recently, colchicine was shown to be effective in inflammatory diseases such as familial Mediterranean fever. Two proteins can modulate its pharmacokinetics: tubulin, the specific intracellular receptor for colchicine which determines the plasma half-life, and P-glycoprotein, an active efflux pump towards some anticancer drugs which regulates colchicine absorption, distribution, and elimination. Therapeutic dosage is monitored empirically, by the control of the balance between the occurrence of side effects and the clinical efficacy. Recently, using a specific and sensitive radioimmunoassay, the investigation of plasma concentrations during single and multiple dose studies has allowed to define the colchicine pharmacokinetic parameters. Following oral route, colchicine bioavailability is extremely variable (from 24 to 88% of the administered dose), the distribution volume is elevated (7 l/kg) but the binding to albumin is moderate. Colchicine elimination occurred mainly via hepatic pathways and the elimination half-life ranged from 20 to 40 hours. In multiple dose study (1 mg/d), the steady-state is reached 8 days after the first oral administration and plasma concentrations ranged from 0.3 to 2.5 ng/ml. Pharmacokinetic/pharmacodynamic studies show that the biological effects of colchicine were not related to plasma concentrations but with intraleukocyte concentrations. Drug interactions may occur when colchicine is associated to drugs which interact with cytochrome P450 and/or P-glycoprotein and modify renal and/or hepatic clearances. The therapeutic drug monitoring of colchicine during these circumstances could allow to prevent the observation of side effects.

Biological Availability↗
PubMed2004

Double-stranded RNA mediates homology-dependent gene silencing of gamma-tubulin in the human parasite Entamoeba histolytica.

Approaches that eliminate mRNA are a powerful tool for reverse genetics applications in eukaryotic microbes for which gene replacement techniques have not yet been developed. Here, for the first time, we demonstrate that RNA duplexes efficiently inhibit gene expression when introduced into the human parasite Entamoeba histolytica. Chemically synthesized, small interfering RNA (siRNA) were highly specific and efficient in silencing parasite gamma-tubulin mRNA. Use of specific antibodies revealed that microtubules and gamma-tubulin were intra-nuclear in E. histolytica. The RNAi approach to modulation of gamma-tubulin mRNA resulted in loss of the highly organized microtubule array an observation that correlates with a significant reduction of gamma-tubulin as well as of the specific mRNA. Our results suggest that gamma-tubulin is essential for microtubule nucleation in E. histolytica.

Animals↗
PubMed2004

Modulation of kinesin binding by the C-termini of tubulin.

The flexible tubulin C-terminal tails (CTTs) have recently been implicated in the walking mechanism of dynein and kinesin. To address their role in the case of conventional kinesin, we examined the structure of kinesin-microtubule (MT) complexes before and after CTT cleavage by subtilisin. Our results show that the CTTs directly modulate the motor-tubulin interface and the binding properties of motors. CTT cleavage increases motor binding stability, and kinesin appears to adopt a binding conformation close to the nucleotide-free configuration under most nucleotide conditions. Moreover, C-terminal cleavage results in trapping a transient motor-ADP-MT intermediate. Using SH3-tagged dimeric and monomeric constructs, we could also show that the position of the kinesin neck is not affected by the C-terminal segments of tubulin. Overall, our study reveals that the tubulin C-termini define the stability of the MT-kinesin complex in a nucleotide-dependent manner, and highlights the involvement of tubulin in the regulation of weak and strong kinesin binding states.

Adenosine Diphosphate↗
PubMed1996

Effect of transient overexpression of Gq alpha on soluble and polymerized tubulin pools in GH3 and AtT-20 cells.

In order to study Gq-tubulin interaction in the cytosol, GH3 and AtT-20 cells (stably expressing TRH receptor) were transiently transfected with Gq alpha cDNA. Forty-eight hours after transfection, thyrotropin-releasing hormone (TRH)-stimulated prolactin (PRL) secretion by Gq alpha-transfected GH3 cells increased by 90% compared to mock-transfected cells. In addition, using immunocytochemistry it was observed that Gq alpha-specific staining was much more prominent in Gq alpha-transfected GH3 and AtT-20 cells (also transfected with Gq alpha) compared to mock-transfected cells. Thus, transfection resulted in successful overexpression of functional Gq alpha. Forty-eight hours after transfection, cells were processed to obtain soluble and polymerized tubulin fractions. Tubulin levels were determined in these fractions by immunoblotting using polyclonal anti-tubulin antibodies. Compared to mock-transfected cells soluble tubulin levels decreased in Gq alpha-transfected GH3 and AtT-20 cells, by 33 and 52%, respectively. Moreover, compared to mock-transfected cells a 50% reduction in the ratio (an index of the flux between tubulin pools) of soluble and polymerized tubulin levels was observed in Gq alpha-transfected GH3 and AtT-20 cells. To determine whether these effects on tubulin were mediated by Gq directly, we examined the influence of purified Gq on tubulin polymerization. Gq (0.5 microM) inhibited polymerization of crude tubulin (present in GH3 cell cytosol) by 53%. In contrast to its effects on GH3 cell cytosol tubulin, Gq stimulated purified tubulin polymerization by 160%. These results suggest that Gq modulates the polymerization and depolymerization cycles of tubulin and that this modulation is in turn influenced by other unknown cellular components.

Cell Line↗
PubMed2005

Alterations of beta-tubulin isotypes in breast cancer cells resistant to docetaxel.

Docetaxel is one of the most active drugs used to treat breast cancer. The cellular target of docetaxel is the microtubule, specifically the beta-tubulin subunit, that comprises a series of isotypes and that can modulate function. This study has examined the role of alteration in beta-tubulin isotypes in vitro and has sequenced the beta-tubulin gene to determine if there were mutations, both of which may represent important mechanisms of acquired resistance to docetaxel. Breast cancer cells, MCF-7 (oestrogen-receptor positive) and MDA-MB-231, (oestrogen-receptor negative) were made resistant to docetaxel in vitro. Expression of beta-tubulin isotypes (class I, II, III, IVa, IVb, and VI) was determined at the RNA and protein level using RT-PCR and western analysis, respectively. DNA sequencing evaluated the beta-tubulin gene. At the mRNA level, class I, II, III, and IVa beta-tubulin mRNA isotypes were over-expressed in docetaxel-resistant MCF-7 cells when compared with the docetaxel-sensitive parental cells. However, class VI beta-tubulin mRNA isotype expression was decreased in resistant cells. In MDA-MB-231 cells, there was a decrease in expression of the class I and class IVa beta-tubulin mRNA. However, there were increased expressions in class II, IVb, and VI beta-tubulin mRNA isotypes in resistant cells. Western analysis has confirmed corresponding increases in beta-tubulin protein levels in MCF-7 cells. However, in MDA-MB-231 cells, there were decreased protein levels for class II and class III beta-tubulin. This study demonstrates that altered expression of mRNA beta-tubulin isotypes and modulation of beta-tubulin protein levels are associated with acquired docetaxel resistance in breast cancer cells. This allows further understanding and elucidation of mechanisms involved in resistance to docetaxel.

Antineoplastic Agents, Phytogenic↗
PubMed2005

Sulfonamide drugs binding to the colchicine site of tubulin: thermodynamic analysis of the drug-tubulin interactions by isothermal titration calorimetry.

The discovery of several sulfonamide drugs paved the way toward the synthesis of 6 (N-[2-[(4-hydroxyphenyl)amino]-3-pyridinyl]-4-methoxybenzenesulfonamide, E7010) and 7 (N-(3-fluoro-4-methoxyphenyl)pentafluorobenzenesulfonamide, T138067), both of which inhibit tubulin polymerization and are under clinical development. A series of diarylsulfonamides containing an indole scaffold was also found to have antimitotic properties, but their mode of interactions with tubulin has remained unidentified so far. In this study, we demonstrate that these sulfonamide drugs bind to the colchicine site of tubulin in a reversible manner. They quenched intrinsic tryptophan fluorescence of tubulin presumably due to drug-induced conformational changes in the protein, but were unable to modulate GTPase activity of tubulin in contrast to colchicine that enhances the same enzymatic activity. Further investigation using isothermal titration calorimetry (ITC) revealed that 5 (N-(5-chloro-7-indolyl)-4-methoxybenzenesulfonamide) afforded a large positive value of heat capacity change (DeltaC(p)() = +264 cal mol(-1) K(-1)) on binding to tubulin, suggesting a substantial conformational transition in the protein along with partial enthalpy-entropy compensation. On the other hand, the 2-chloro regioisomer 2 gave a large negative value of DeltaC(p)() (-589 cal mol(-1) K(-1)) along with complete enthalpy-entropy compensation. This thermodynamic profile was thought to be attributable to a prominent contribution of van der Waals interaction and hydrogen bonding between specific groups in the drug-tubulin complex. These results indicate that a mere alteration in the position of a single substituent chlorine on the indole scaffold has a great influence on the drug-tubulin binding thermodynamics.

Antineoplastic Agents↗