Publications by authors named "Krishnankutty C Sivakumar"

5 Publications

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Binding of alpha-fodrin to gamma-tubulin accounts for its role in the inhibition of microtubule nucleation.

FEBS Lett 2019 06 17;593(11):1154-1165. Epub 2019 May 17.

Cancer Research Programme, Rajiv Gandhi Centre for Biotechnology, Trivandrum, India.

Non-erythroid spectrin or fodrin is present as part of the γ-tubulin ring complex (γ-TuRC) in brain tissue and brain derived cells. Here, we show that fodrin, which is otherwise known for providing structural support to the cell membrane, interacts directly with γ-tubulin within the γ-TuRC through a GRIP2-like motif. Turbidometric analysis of microtubule polymerization with nucleation-potent γ-TuRC isolated from HEK-293 cells that lack fodrin and the γ-TuRC from goat brain that contains fodrin shows inefficiency of the latter to promote nucleation. The involvement of fodrin was confirmed by the reduction in the microtubule polymerization efficiency of HEK-293 derived γ-TuRCs upon addition of purified brain fodrin. Thus, the interaction of fodrin with gamma-tubulin is responsible for its inhibitory effect on γ-tubulin mediated microtubule nucleation.
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http://dx.doi.org/10.1002/1873-3468.13425DOI Listing
June 2019

Self-assembling peptide nanofibers containing phenylalanine for the controlled release of 5-fluorouracil.

Int J Nanomedicine 2016;11:5583-5594. Epub 2016 Oct 25.

Chemical Biology, Nano Drug Delivery Systems, Bio-Innovation Center.

The study shows that RADA-F6 peptide with pH-responsive self-assembling nature can be effectively used as a drug delivery system for the sustained release of a potent anticancer drug 5-fluorouracil (5-FU) at basic pH. As 5-FU contains the aromatic pyrimidine ring, RADA-F6 system is suitable for entrapping an aromatic drug due to effective π-π stacking with phenylalanine and be able to show better controlled release behavior. The stability and controlled release nature of RADA-F6 in different conditions followed by 5-FU entrapment at in silico conditions was confirmed by molecular dynamics simulation taking RADA-16 as control. Cytotoxicity of the drug-loaded RADA-F6 was measured by MTT assay and cellular uptake by confocal microscopy. Physicochemical characterization and further Western blot analysis and flow cytometric studies confirm that RADA-F6 can be successfully used as an efficient vector for pH-sensitive, controlled 5-FU delivery system.
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http://dx.doi.org/10.2147/IJN.S104707DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5087806PMC
February 2017

Diaminothiazoles evade multidrug resistance in cancer cells and xenograft tumour models and develop transient specific resistance: understanding the basis of broad-spectrum versus specific resistance.

Carcinogenesis 2015 Aug 25;36(8):883-93. Epub 2015 May 25.

Division of Cancer Research and Distributed Information Sub-Centre, Rajiv Gandhi Centre for Biotechnology, Trivandrum, India and Department of Chemistry, University of Kerala, Trivandrum, India

Acquired drug resistance poses a challenge in cancer therapy. Drug efflux is the most common mechanism of resistance displayed by hydrophobic drugs beyond a certain size. However, target specific changes and imbalance between the pro- and anti-apoptotic proteins are also found quite often in many tumours. A number of small antimitotic agents show high potential for multidrug resistant tumours, mainly because they are able to evade the efflux pumps. However, these compounds are also likely to suffer from resistance upon prolonged treatment. Thus, it is important to find out agents that are sensitive to resistant tumours and to know the resistance mechanisms against small molecules so that proper combinations can be planned. In this report, we have studied the efficiency of diaminothiazoles, a novel class of tubulin targeting potential anticancer compounds of small size, in multidrug resistant cancer. Studies in model cell lines raised against taxol and the lead diaminothiazole, DAT1 [4-amino-5-benzoyl-2-(4-methoxy phenyl amino) thiazole], and the xenograft tumours derived from them, show that diaminothiazoles are highly promising against multidrug resistant cancers. They were able to overcome the expression of efflux protein MDR1 and certain tubulin isotypes, could sensitize improper apoptotic machinery and ablated checkpoint proteins Bub1 and Mad2. Further, we have found that the resistance against microtubule binding compounds with higher size is broad-spectrum and emerges due to multiple factors including overexpression of transmembrane pumps. However, resistance against small molecules is transient, specific and is contributed by target specific changes and variations in apoptotic factors.
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http://dx.doi.org/10.1093/carcin/bgv072DOI Listing
August 2015

Reversible action of diaminothiazoles in cancer cells is implicated by the induction of a fast conformational change of tubulin and suppression of microtubule dynamics.

Mol Cancer Ther 2014 Jan 5;13(1):179-89. Epub 2013 Nov 5.

Corresponding Author: Suparna Sengupta, Division of Cancer Research, Rajiv Gandhi Centre for Biotechnology, Thiruvananthapuram 695014, India.

Diaminothiazoles are novel cytotoxic compounds that have shown efficacy toward different cancer cell lines. They show potent antimitotic and antiangiogenic activity upon binding to the colchicine-binding site of tubulin. However, the mechanism of action of diaminothiazoles at the molecular level is not known. Here, we show a reversible binding to tubulin with a fast conformational change that allows the lead diaminothiazole DAT1 [4-amino-5-benzoyl-2-(4-methoxy phenyl amino)thiazole] to cause a reversible mitotic block. DAT1 also suppresses microtubule dynamic instability at much lower concentration than its IC(50) value in cancer cells. Both growth and shortening events were reduced by DAT1 in a concentration-dependent way. Colchicine, the long-studied tubulin-binding drug, has previously failed in the treatment of cancer due to its toxicity, even though it generates a strong apoptotic response. The toxicity is attributable to its slow removal from the cell due to irreversible tubulin binding caused by a slow conformational change. DAT1 binds to tubulin at an optimal pH lower than colchicine. Tubulin conformational studies showed that the binding environments of DAT1 and colchicine are different. Molecular dynamic simulations showed a difference in the number of H-bonding interactions that accounts for the different pH optima. This study gives an insight of the action of compounds targeting tubulin's colchicine-binding site, as many such compounds have entered into clinical trials recently.
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http://dx.doi.org/10.1158/1535-7163.MCT-13-0479DOI Listing
January 2014

Three dimensional structure of the closed conformation (active) of human merlin reveals masking of actin binding site in the FERM domain.

Int J Bioinform Res Appl 2009 ;5(5):516-24

Bioinformatics Centre, Rajiv Gandhi Centre for Biotechnology, Thycaud PO, Poojappura, Thiruvananthapuram, India.

We modelled the structure of human merlin using the structure of moesin from Spodoptera frugiperda as the template. The present model suggests an interaction of its extreme C-terminal region with the subdomains B and C of FERM domain, masking the binding site of beta II spectrin. Modelling the complete structure of merlin revealed a novel central alpha helical domain with a helix-coil-helix. The actin binding site in the carboxy terminal is absent in merlin and in its closed conformation the indirect actin binding site in the FERM domain is also not available for the interaction of other proteins with it.
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http://dx.doi.org/10.1504/IJBRA.2009.02868DOI Listing
January 2010
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