amit tiwari - Academia.edu (original) (raw)
Papers by amit tiwari
Journal of Colloid and Interface Science, 2010
The dipolar nature of trans-2-[4-(dimethylamino)styryl]benzothiazole (DMASBT) in its twisted intr... more The dipolar nature of trans-2-[4-(dimethylamino)styryl]benzothiazole (DMASBT) in its twisted intramolecular charge transfer (TICT) excited state makes it useful as a surface probe for phenomena such as premicellar and micellar aggregation of non-ionic Brij surfactants. The process of micellization of Brij 35, Brij 58, Brij 78, and Brij 98 through the formation of smaller premicellar aggregates results in a progressive change in the nature of the DMASBT molecule and its location in the aggregates, reflecting the changes in its photophysical properties, which have been studied using steady-state fluorescence, fluorescence anisotropy, and time-correlated single-photon counting measurements. The microenvironment polarity around the DMASBT probe in the micellar phase is greater than that in corresponding premicellar phases. The orders of premicellar as well as micellar concentrations are Brij 35 > Brij 58 > Brij 98 > Brij 78. The lower fluorescence anisotropies observed in the case of Brij 78 aggregates compared to those in other Brijs studied could be due to the accessibility of a nonrigid environment as a result of a folded conformation of a part of the nonpolar long chain of surfactant molecules near the core of aggregates. Three different locations of DMASBT were noted for Brijs 35, Brij 78, and Brij 98, whereas for Brij 58 only two locations are observed. The micropolarity of the environment around DMASBT in aggregation states has been determined.
![Research paper thumbnail of Characterization of guest molecule concentration dependent nanotubes of β-cyclodextrin and their secondary assembly: Study with trans-2-[4(dimethylamino)styryl]benzothiazole, a TICT-fluorescence probe](https://attachments.academia-assets.com/49873524/thumbnails/1.jpg)
](Journal of Photochemistry and Photobiology A-chemistry, 2009
The formation of nanotubes of -cyclodextrins (-CD) and their secondary assembly induced by tran... more The formation of nanotubes of -cyclodextrins (-CD) and their secondary assembly induced by trans-2-[4-(dimethylamino)styryl]benzothiazole (DMASBT) as a guest molecule has been explained using twisted intramolecular charge transfer (TICT) fluorescence, steady state fluorescence anisotropy, time-correlated single-photon counting fluorescence decay of DMASBT, atomic force microscopy and also transmission electron microscopy. It has been demonstrated that although at lower concentration of -CD, DMASBT molecules form simple adduct of 1:1 stoichiometry but they form extended nanotubes at relatively high concentration of -CD which further lead to the secondary assembly through intertubular hydrogen bondings forming rod-like structures. The changes in fluorescence properties of DMASBT yield critical aggregation concentration (CAC) of -CD very close to 2.5 mM. The extent of formation of these supramolecular structures is dependent on the concentration of guest molecule. It has been observed that perchlorate ion (ClO 4 − ) reduces the stability of supramolecular structures at higher concentration of it but at low concentration (<7 mM) it enhances the stability by providing the anchor sites for intermolecular hydrogen bonding between neighboring -CD molecules. The polarity and viscosity dependent TICT fluorescence characteristics of DMASBT are exploited to determine the micropolarity and microviscosity of environment around it inside the nanotubes.
Journal of Photochemistry and Photobiology A-chemistry, 2011
The aggregation properties of two gemini surfactants, 12-3(OH)-12,2Br − and 12-4(OH) 2 -12,2Br − ... more The aggregation properties of two gemini surfactants, 12-3(OH)-12,2Br − and 12-4(OH) 2 -12,2Br − with hydroxyl substituted spacer group have been studied. The changes in photophysical properties of a single probe, trans-2-[4-(dimethylamino)styryl]benzothiazole (DMASBT) showing dipolar nature in its twisted intramolecular charge transfer (TICT) excited state have been exploited rather than using multiple probes to describe various properties of micellar aggregates. Formation of a number of premicellar aggregates has been demonstrated in addition to the description of the micropolarity and the microviscosity of environment using steady-state fluorescence spectroscopy and fluorescence anisotropy of DMASBT. Conductometric measurements have been carried out to determine degree of micellar ionization (˛) and to verify critical micelle concentration (CMC) values estimated by fluorescence method. Hydroxyl substituted spacer group induces the formation of premicellar aggregates. The micropolarity of environment around probe molecules increases on going from premicellar to micellar aggregates. The growth of micellar aggregates has been demonstrated by a continuous increase in the microviscosity of environment. The micropolarity of micellar environment of 12-4(OH) 2 -12 is found to be less than that of 12-3(OH)-12. The microviscosity of premicellar and micellar aggregates of 12-4(OH) 2 -12 are higher than that of 12-3(OH)-12. CMC increases, whereas ˛ decreases with increasing spacer chain length as well as number of hydroxyl substitution of a spacer group.
![Research paper thumbnail of Study on intramolecular charge transfer fluorescence properties of trans-4-[4′-(N,N′-dimethylamino)styryl]pyridine: Effect of solvent and pH](https://attachments.academia-assets.com/49873508/thumbnails/1.jpg)
](Journal of Photochemistry and Photobiology A-chemistry, 2011
Photophysical characterization of a molecule, trans-4- [4 -(N,N -dimethylamino)styryl]pyridine (4... more Photophysical characterization of a molecule, trans-4- [4 -(N,N -dimethylamino)styryl]pyridine (4-DMASP) containing donor and acceptor moieties has been done experimentally as well as theoretically. Upon single excitation a charge-transfer state with high dipole moment is formed through rapid relaxation of a locally excited (LE) state in polar medium. A complete charge transfer process occurs as a result of twisting of donor group with respect to the acceptor part of the molecule resulting in the highly stabilized twisted state in polar medium giving fluorescence from LE state as well as from twisted state. However, in a nonpolar solvent emission occurs explicitly from a LE state. Hydrogen bond donor ability of solvents rather than dipolar interactions contributes more to the stability of ground state. However, dipolar interactions have greater contribution towards the stability of an excited state. All such interactions have higher contribution towards the stability of excited state than that of ground state. Very low fluorescence quantum yield in water is because of high rate of nonradiative processes as a result of high degree of stabilization of charge transfer state thereby making closer proximity of this state to triplet as well as ground charge transfer states. Monocation of 4-DMASP formed due to the protonation of pyridine nitrogen atom is more stable than neutral and dication species at ground as well as excited states because of greater extent of flow of charge from donor to acceptor part in monocation. Basicity of pyridine nitrogen atom being greater at excited state than that in ground state results in higher extent of pulling of charge from donor to acceptor part of monocation at excited state. Theoretical calculations suggest donor twisting as a possible path for creation of a charge transfer state rather than acceptor twisting. Excited state dipole moment value obtained from theoretical calculation corroborates well with the value determined experimentally. Theoretical calculation suggests no cis-trans photoisomerization in the ground state as well as excited state at room temperature.
Clinical Nutrition, 2011
Background & aims: This study was aimed to assess the desirable and undesirable effects of iron (... more Background & aims: This study was aimed to assess the desirable and undesirable effects of iron (100 mg/ day as ferrous sulphate) and folic acid (500 mg/day) supplementation in iron deficient anemic women.
Indian Journal of Clinical Biochemistry, 2010
The present study was conducted to investigate the oxidant–antioxidant status in iron deficient p... more The present study was conducted to investigate the oxidant–antioxidant status in iron deficient pregnant anemic women. One hundred thirty pregnant women with iron deficiency anemia (IDA) were divided into three groups, namely mild (50), moderate (50) and severe (30) anemic along with pregnant healthy women as controls (50). The complete blood count, plasma lipid peroxidation products, enzymatic and non-enzymatic antioxidants were measured according to respective protocols. The levels of complete blood count, iron, ferritin along with antioxidant enzymes namely catalase, superoxide dismutase, glutathione peroxidase, glutathione reductase and reduced glutathione were significantly reduced in all IDA groups. However, the level of oxidized glutathione, lipid peroxides, protein carbonyls, conjugated dienes were found significantly increased in all anemic patients. Antioxidant vitamins, namely C, E and A were also found significantly decreased in IDA patients. On the basis of our results, it may be concluded that IDA tends to increase the pro-oxidant components, which may result in various complications including peroxidation of vital body molecules resulting in increased risk for pregnant women as well as fetus.
Biochemical Pharmacology, 2009
The tyrphostin 4-(3-chloroanilino)-6,7-dimethoxyquinazoline (AG1478) is a potent and specific EGF... more The tyrphostin 4-(3-chloroanilino)-6,7-dimethoxyquinazoline (AG1478) is a potent and specific EGFR tyrosine kinase inhibitor (TKI); its promising pre-clinical results have led to clinical trials. Overexpression of ATP-binding cassette (ABC) transporters such as ABCB1, ABCC1 and ABCG2 is one of the main causes of multidrug resistance (MDR) and usually results in the failure of cancer chemotherapy. However, the interaction of AG1478 with these ABC transporters is still unclear. In the present study, we have investigated this interaction and found that AG1478 has differential effects on these transporters. In ABCB1-overexpressing cells, non-toxic doses of AG1478 were found to partially inhibit resistance to ABCB1 substrate anticancer drugs as well as increase intracellular accumulation of [ 3 H]-paclitaxel. Similarly, in ABCG2-overexpressing cells, AG1478 significantly reversed resistance to ABCG2 substrate anticancer drugs and increased intracellular accumulation of [ 3 H]-mitoxantrone as well as fluorescent compound BODIPY-prazosin. AG1478 also profoundly inhibited the transport of [ 3 H]-E 2 17βG and [ 3 H]-methotrexate by ABCG2. We also found that AG1478 slightly stimulated ABCB1 ATPase activity and significantly stimulated ABCG2 ATPase activity. Interestingly, AG1478 did not inhibit the photolabeling of ABCB1 or ABCG2 with [ 125 I]iodoarylazidoprazosin. Additionally, AG1478 did not alter the sensitivity of parental, ABCB1-or ABCG2-overexpressing cells to non-ABCB1 and non-ABCG2 substrate drug and had no effect on the function of ABCC1. Overall, we conclude that AG1478 is able to inhibit the function of ABCB1 and ABCG2, with a more pronounced effect on ABCG2. Our findings provide valuable contributions to the development of safer and more effective EGFR TKIs for use as anticancer agents in the clinic.
Leukemia Research, 2008
To investigate the mechanism of cellular resistance to 6-MP, we established a 6-MP resistant cell... more To investigate the mechanism of cellular resistance to 6-MP, we established a 6-MP resistant cell line (CEM-MP5) by stepwise selection of the human T-lymphoblastic leukemia cell line (CEM). CEM-MP5 cells were about 100-fold resistant to 6-MP compared with parental CEM cells. Western blot analysis demonstrated that multidrug resistant protein 4 (MRP4) was increased in CEM-MP5 cells, whereas the levels of the nucleoside transporters hENT1, hCNT2 and hCNT3 were decreased compared with those of parental CEM cells. Consistent with the operation of an efflux pump, accumulation of [14C]6-MP and/or its metabolites was reduced, and ATP-dependent efflux was increased in CEM-MP5 cells. Taken together these results showed that up-regulation of MRP4 and down-regulation of influx transporters played a major role in 6-MP resistance of CEM-MP5 cells.
Biochemical Pharmacology, 2009
Nilotinib, a BCR-Abl tyrosine kinase inhibitor (TKI), was developed to surmount resistance or int... more Nilotinib, a BCR-Abl tyrosine kinase inhibitor (TKI), was developed to surmount resistance or intolerance to imatinib in patients with Philadelphia positive chronic myelogenous leukemia. Recently, it was shown that several human multidrug resistance (MDR) ATP-binding cassette (ABC) proteins could be modulated by specific TKIs. MDR can produce cancer chemotherapy failure, typically due to overexpression of ABC transporters, which are involved in the extrusion of therapeutic drugs. Here, we report for the first time that nilotinib potentiates the cytotoxicity of widely used therapeutic substrates of ABCG2, such as mitoxantrone, doxorubicin, and ABCB1 substrates including colchicine, vincristine, and paclitaxel. Nilotinib also significantly enhances the accumulation of paclitaxel in cell lines overexpressing ABCB1. Similarly, nilotinib significantly increases the intracellular accumulation of mitoxantrone in cells transfected with ABCG2. Furthermore, nilotinib produces a concentration-dependent inhibition of the ABCG2-mediated transport of methotrexate (MTX), as well as E 2 17bG a physiological substrate of ABCG2. Uptake studies in membrane vesicles overexpressing ABCG2 have indicated that nilotinib inhibits ABCG2 similar to other established TKIs as well as fumitremorgin C. Nilotinib is a potent competitive inhibitor of MTX transport by ABCG2 with a K i value of 0.69 AE 0.083 mM as demonstrated by kinetic analysis of nilotinib.
Lapatinib is active at the ATP-binding site of tyrosine kinases that are associated with the huma... more Lapatinib is active at the ATP-binding site of tyrosine kinases that are associated with the human epidermal growth factor receptor (Her-1 or ErbB1) and Her-2. It is conceivable that lapatinib may inhibit the function of ATP-binding cassette (ABC) transporters by binding to their ATP-binding sites. The aim of this study was to investigate the ability of lapatinib to reverse tumor multidrug resistance (MDR) due to overexpression of ABC subfamily B member 1 (ABCB1) and ABC subfamily G member 2 (ABCG2) transporters. Our results showed that lapatinib significantly enhanced the sensitivity to ABCB1 or ABCG2 substrates in cells expressing these transporters, although a small synergetic effect was observed in combining lapatinib and conventional chemotherapeutic agents in parental sensitive MCF-7 or S1 cells. Lapatinib alone, however, did not significantly alter the sensitivity of non-ABCB1 or non-ABCG2 substrates in sensitive and resistant cells. Additionally, lapatinib significantly increased the accumulation of doxorubicin or mitoxantrone in ABCB1-or ABCG2-overexpressing cells and inhibited the transport of methotrexate and E 2 17BG by ABCG2. Furthermore, lapatinib stimulated the ATPase activity of both ABCB1 and ABCG2 and inhibited the photolabeling of ABCB1 or ABCG2 with [ 125 I]iodoarylazidoprazosin in a concentration-dependent manner. However, lapatinib did not affect the expression of these transporters at mRNA or protein levels. Importantly, lapatinib also strongly enhanced the effect of paclitaxel on the inhibition of growth of the ABCB1-overexpressing KBv200 cell xenografts in nude mice. Overall, we conclude that lapatinib reverses ABCB1-and ABCG2-mediated MDR by directly inhibiting their transport function. These findings may be useful for cancer combinational therapy with lapatinib in the clinic.
Biochemical Pharmacology, 2010
In recent years, a number of TKIs (tyrosine kinase inhibitors) targeting epidermal growth factor ... more In recent years, a number of TKIs (tyrosine kinase inhibitors) targeting epidermal growth factor receptor (EGFR) family have been synthesized and some have been approved for clinical treatment of cancer by the FDA. We recently reported a new pharmacological action of the 4-anilinoquinazoline derived EGFR TKIs, such as lapatinib (Tykerb®) and erlotinib (Tarceva®), which significantly affect the drug resistance patterns in cells expressing the multidrug resistance (MDR) phenotype. Previously, we showed that lapatinib and erlotinib could inhibit the drug efflux function of Pglycoprotein (P-gp, ABCB1) and ABCG2 transporters. In this study, we determined if these TKIs have the potential to reverse MDR due to the presence of the multidrug resistance protein 7 (MRP7, ABCC10). Our results showed that lapatinib and erlotinib dose-dependently enhanced the sensitivity of MRP7-transfected HEK293 cells to several established MRP7 substrates, specifically docetaxel, paclitaxel, vinblastine and vinorelbine, whereas there was no or a lesser effect on the control vector transfected HEK293 cells. [ 3 H]-paclitaxel accumulation and efflux studies demonstrated that lapatinib and erlotinib increased the intracellular accumulation of [ 3 H]-paclitaxel and inhibited the efflux of [ 3 H]-paclitaxel from MRP7 transfected cells but not in the control cell line. Lapatinib is a more potent inhibitor of MRP7 than erlotinib. In addition, the Western blot analysis revealed that both lapatinib and erlotinib did not significantly affect MRP7 expression. We conclude that the EGFR TKIs, lapatinib and erlotinib reverse MRP7-mediated MDR through inhibition of the drug efflux function, suggesting that an EGFR TKI based combinational therapy may be applicable for chemotherapeutic practice clinically.
PLOS One, 2009
Background: One of the major mechanisms that could produce resistance to antineoplastic drugs in ... more Background: One of the major mechanisms that could produce resistance to antineoplastic drugs in cancer cells is the ATP binding cassette (ABC) transporters. The ABC transporters can significantly decrease the intracellular concentration of antineoplastic drugs by increasing their efflux, thereby lowering the cytotoxic activity of antineoplastic drugs. One of these transporters, the multiple resistant protein 7 (MRP7, ABCC10), has recently been shown to produce resistance to antineoplastic drugs by increasing the efflux of paclitaxel. In this study, we examined the effects of BCR-Abl tyrosine kinase inhibitors imatinib, nilotinib and dasatinib on the activity and expression of MRP7 in HEK293 cells transfected with MRP7, designated HEK-MRP7-2.
PLOS One, 2011
One of the major causes of chemotherapy failure in cancer treatment is multidrug resistance (MDR)... more One of the major causes of chemotherapy failure in cancer treatment is multidrug resistance (MDR) which is mediated by the ABCB1/P-glycoprotein. Previously, through the use of an extensive screening process, we found that vardenafil, a phosphodiesterase 5 (PDE-5) inhibitor significantly reverses MDR in ABCB1 overexpressing cancer cells, and its efficacy was greater than that of tadalafil, another PDE-5 inhibitor. The present study was designed to determine the reversal mechanisms of vardenafil and tadalafil on ABC transporters-mediated MDR. Vardenafil or tadalafil alone, at concentrations up to 20 mM, had no significant toxic effects on any of the cell lines used in this study, regardless of their membrane transporter status. However, vardenafil when used in combination with anticancer substrates of ABCB1, significantly potentiated their cytotoxicity in ABCB1 overexpressing cells in a concentration-dependent manner, and this effect was greater than that of tadalafil. The sensitivity of the parenteral cell lines to cytotoxic anticancer drugs was not significantly altered by vardenafil. The differential effects of vardenafil and tadalafil appear to be specific for the ABCB1 transporter as both vardenafil and tadalafil had no significant effect on the reversal of drug resistance conferred by ABCC1 (MRP1) and ABCG2 (BCRP) transporters. Vardenafil significantly increased the intracellular accumulation of [ 3 H]-paclitaxel in the ABCB1 overexpressing KB-C2 cells. In addition, vardenafil significantly stimulated the ATPase activity of ABCB1 and inhibited the photolabeling of ABCB1 with [ 125 I]-IAAP. Furthermore, Western blot analysis indicated the incubation of cells with either vardenafil or tadalafil for 72 h did not alter ABCB1 protein expression. Overall, our results suggest that vardenafil reverses ABCB1-mediated MDR by directly blocking the drug efflux function of ABCB1.
PLOS One, 2009
Background: One of the major mechanisms that could produce resistance to antineoplastic drugs in ... more Background: One of the major mechanisms that could produce resistance to antineoplastic drugs in cancer cells is the ATP binding cassette (ABC) transporters. The ABC transporters can significantly decrease the intracellular concentration of antineoplastic drugs by increasing their efflux, thereby lowering the cytotoxic activity of antineoplastic drugs. One of these transporters, the multiple resistant protein 7 (MRP7, ABCC10), has recently been shown to produce resistance to antineoplastic drugs by increasing the efflux of paclitaxel. In this study, we examined the effects of BCR-Abl tyrosine kinase inhibitors imatinib, nilotinib and dasatinib on the activity and expression of MRP7 in HEK293 cells transfected with MRP7, designated HEK-MRP7-2.
Cancer Letters, 2009
Sunitinib is an ATP-competitive multi-targeted tyrosine kinase inhibitor. In this study, we evalu... more Sunitinib is an ATP-competitive multi-targeted tyrosine kinase inhibitor. In this study, we evaluated the possible interaction of sunitinib with P-glycoprotein (P-gp, ABCB1), multidrug resistance protein 1 (MRP1, ABCC1), breast cancer resistance protein (BCRP, ABCG2) and lung-resistance protein (LRP) in vitro. Our results showed that sunitinib completely reverse drug resistance mediated by ABCG2 at a non-toxic concentration of 2.5muM and has no significant reversal effect on ABCB1-, ABCC1- and LRP-mediated drug resistance, although a small synergetic effect was observed in combining sunitinib and conventional chemotherapeutic agents in ABCB1 overexpressing MCF-7/adr and parental sensitive MCF-7 cells, ABCC1 overexpressing C-A120 and parental sensitive KB-3-1 cells. Sunitinib significantly increased intracellular accumulation of rhodamine 123 and doxorubicin and remarkably inhibited the efflux of rhodamine 123 and methotrexate by ABCG2 in ABCG2-overexpressing cells, and also profoundly inhibited the transport of [(3)H]-methotrexate by ABCG2. However, sunitinib did not affect the expression of ABCG2 at mRNA or protein levels. In addition, sunitinib did not block the phosphorylation of Akt and Erk1/2 in ABCG2-overexpressing or parental sensitive cells. Overall, we conclude that sunitinib reverses ABCG2-mediated MDR through inhibiting the drug efflux function of ABCG2. These findings may be useful for cancer combinational therapy with sunitinib in the clinic.
Journal of Colloid and Interface Science, 2010
The dipolar nature of trans-2-[4-(dimethylamino)styryl]benzothiazole (DMASBT) in its twisted intr... more The dipolar nature of trans-2-[4-(dimethylamino)styryl]benzothiazole (DMASBT) in its twisted intramolecular charge transfer (TICT) excited state makes it useful as a surface probe for phenomena such as premicellar and micellar aggregation of non-ionic Brij surfactants. The process of micellization of Brij 35, Brij 58, Brij 78, and Brij 98 through the formation of smaller premicellar aggregates results in a progressive change in the nature of the DMASBT molecule and its location in the aggregates, reflecting the changes in its photophysical properties, which have been studied using steady-state fluorescence, fluorescence anisotropy, and time-correlated single-photon counting measurements. The microenvironment polarity around the DMASBT probe in the micellar phase is greater than that in corresponding premicellar phases. The orders of premicellar as well as micellar concentrations are Brij 35 &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; Brij 58 &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; Brij 98 &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; Brij 78. The lower fluorescence anisotropies observed in the case of Brij 78 aggregates compared to those in other Brijs studied could be due to the accessibility of a nonrigid environment as a result of a folded conformation of a part of the nonpolar long chain of surfactant molecules near the core of aggregates. Three different locations of DMASBT were noted for Brijs 35, Brij 78, and Brij 98, whereas for Brij 58 only two locations are observed. The micropolarity of the environment around DMASBT in aggregation states has been determined.
Journal of Photochemistry and Photobiology A-chemistry, 2009
The formation of nanotubes of -cyclodextrins (-CD) and their secondary assembly induced by tran... more The formation of nanotubes of -cyclodextrins (-CD) and their secondary assembly induced by trans-2-[4-(dimethylamino)styryl]benzothiazole (DMASBT) as a guest molecule has been explained using twisted intramolecular charge transfer (TICT) fluorescence, steady state fluorescence anisotropy, time-correlated single-photon counting fluorescence decay of DMASBT, atomic force microscopy and also transmission electron microscopy. It has been demonstrated that although at lower concentration of -CD, DMASBT molecules form simple adduct of 1:1 stoichiometry but they form extended nanotubes at relatively high concentration of -CD which further lead to the secondary assembly through intertubular hydrogen bondings forming rod-like structures. The changes in fluorescence properties of DMASBT yield critical aggregation concentration (CAC) of -CD very close to 2.5 mM. The extent of formation of these supramolecular structures is dependent on the concentration of guest molecule. It has been observed that perchlorate ion (ClO 4 − ) reduces the stability of supramolecular structures at higher concentration of it but at low concentration (<7 mM) it enhances the stability by providing the anchor sites for intermolecular hydrogen bonding between neighboring -CD molecules. The polarity and viscosity dependent TICT fluorescence characteristics of DMASBT are exploited to determine the micropolarity and microviscosity of environment around it inside the nanotubes.
Journal of Photochemistry and Photobiology A-chemistry, 2011
The aggregation properties of two gemini surfactants, 12-3(OH)-12,2Br − and 12-4(OH) 2 -12,2Br − ... more The aggregation properties of two gemini surfactants, 12-3(OH)-12,2Br − and 12-4(OH) 2 -12,2Br − with hydroxyl substituted spacer group have been studied. The changes in photophysical properties of a single probe, trans-2-[4-(dimethylamino)styryl]benzothiazole (DMASBT) showing dipolar nature in its twisted intramolecular charge transfer (TICT) excited state have been exploited rather than using multiple probes to describe various properties of micellar aggregates. Formation of a number of premicellar aggregates has been demonstrated in addition to the description of the micropolarity and the microviscosity of environment using steady-state fluorescence spectroscopy and fluorescence anisotropy of DMASBT. Conductometric measurements have been carried out to determine degree of micellar ionization (˛) and to verify critical micelle concentration (CMC) values estimated by fluorescence method. Hydroxyl substituted spacer group induces the formation of premicellar aggregates. The micropolarity of environment around probe molecules increases on going from premicellar to micellar aggregates. The growth of micellar aggregates has been demonstrated by a continuous increase in the microviscosity of environment. The micropolarity of micellar environment of 12-4(OH) 2 -12 is found to be less than that of 12-3(OH)-12. The microviscosity of premicellar and micellar aggregates of 12-4(OH) 2 -12 are higher than that of 12-3(OH)-12. CMC increases, whereas ˛ decreases with increasing spacer chain length as well as number of hydroxyl substitution of a spacer group.
Journal of Photochemistry and Photobiology A-chemistry, 2011
Photophysical characterization of a molecule, trans-4- [4 -(N,N -dimethylamino)styryl]pyridine (4... more Photophysical characterization of a molecule, trans-4- [4 -(N,N -dimethylamino)styryl]pyridine (4-DMASP) containing donor and acceptor moieties has been done experimentally as well as theoretically. Upon single excitation a charge-transfer state with high dipole moment is formed through rapid relaxation of a locally excited (LE) state in polar medium. A complete charge transfer process occurs as a result of twisting of donor group with respect to the acceptor part of the molecule resulting in the highly stabilized twisted state in polar medium giving fluorescence from LE state as well as from twisted state. However, in a nonpolar solvent emission occurs explicitly from a LE state. Hydrogen bond donor ability of solvents rather than dipolar interactions contributes more to the stability of ground state. However, dipolar interactions have greater contribution towards the stability of an excited state. All such interactions have higher contribution towards the stability of excited state than that of ground state. Very low fluorescence quantum yield in water is because of high rate of nonradiative processes as a result of high degree of stabilization of charge transfer state thereby making closer proximity of this state to triplet as well as ground charge transfer states. Monocation of 4-DMASP formed due to the protonation of pyridine nitrogen atom is more stable than neutral and dication species at ground as well as excited states because of greater extent of flow of charge from donor to acceptor part in monocation. Basicity of pyridine nitrogen atom being greater at excited state than that in ground state results in higher extent of pulling of charge from donor to acceptor part of monocation at excited state. Theoretical calculations suggest donor twisting as a possible path for creation of a charge transfer state rather than acceptor twisting. Excited state dipole moment value obtained from theoretical calculation corroborates well with the value determined experimentally. Theoretical calculation suggests no cis-trans photoisomerization in the ground state as well as excited state at room temperature.
Clinical Nutrition, 2011
Background & aims: This study was aimed to assess the desirable and undesirable effects of iron (... more Background & aims: This study was aimed to assess the desirable and undesirable effects of iron (100 mg/ day as ferrous sulphate) and folic acid (500 mg/day) supplementation in iron deficient anemic women.
Indian Journal of Clinical Biochemistry, 2010
The present study was conducted to investigate the oxidant–antioxidant status in iron deficient p... more The present study was conducted to investigate the oxidant–antioxidant status in iron deficient pregnant anemic women. One hundred thirty pregnant women with iron deficiency anemia (IDA) were divided into three groups, namely mild (50), moderate (50) and severe (30) anemic along with pregnant healthy women as controls (50). The complete blood count, plasma lipid peroxidation products, enzymatic and non-enzymatic antioxidants were measured according to respective protocols. The levels of complete blood count, iron, ferritin along with antioxidant enzymes namely catalase, superoxide dismutase, glutathione peroxidase, glutathione reductase and reduced glutathione were significantly reduced in all IDA groups. However, the level of oxidized glutathione, lipid peroxides, protein carbonyls, conjugated dienes were found significantly increased in all anemic patients. Antioxidant vitamins, namely C, E and A were also found significantly decreased in IDA patients. On the basis of our results, it may be concluded that IDA tends to increase the pro-oxidant components, which may result in various complications including peroxidation of vital body molecules resulting in increased risk for pregnant women as well as fetus.
Biochemical Pharmacology, 2009
The tyrphostin 4-(3-chloroanilino)-6,7-dimethoxyquinazoline (AG1478) is a potent and specific EGF... more The tyrphostin 4-(3-chloroanilino)-6,7-dimethoxyquinazoline (AG1478) is a potent and specific EGFR tyrosine kinase inhibitor (TKI); its promising pre-clinical results have led to clinical trials. Overexpression of ATP-binding cassette (ABC) transporters such as ABCB1, ABCC1 and ABCG2 is one of the main causes of multidrug resistance (MDR) and usually results in the failure of cancer chemotherapy. However, the interaction of AG1478 with these ABC transporters is still unclear. In the present study, we have investigated this interaction and found that AG1478 has differential effects on these transporters. In ABCB1-overexpressing cells, non-toxic doses of AG1478 were found to partially inhibit resistance to ABCB1 substrate anticancer drugs as well as increase intracellular accumulation of [ 3 H]-paclitaxel. Similarly, in ABCG2-overexpressing cells, AG1478 significantly reversed resistance to ABCG2 substrate anticancer drugs and increased intracellular accumulation of [ 3 H]-mitoxantrone as well as fluorescent compound BODIPY-prazosin. AG1478 also profoundly inhibited the transport of [ 3 H]-E 2 17βG and [ 3 H]-methotrexate by ABCG2. We also found that AG1478 slightly stimulated ABCB1 ATPase activity and significantly stimulated ABCG2 ATPase activity. Interestingly, AG1478 did not inhibit the photolabeling of ABCB1 or ABCG2 with [ 125 I]iodoarylazidoprazosin. Additionally, AG1478 did not alter the sensitivity of parental, ABCB1-or ABCG2-overexpressing cells to non-ABCB1 and non-ABCG2 substrate drug and had no effect on the function of ABCC1. Overall, we conclude that AG1478 is able to inhibit the function of ABCB1 and ABCG2, with a more pronounced effect on ABCG2. Our findings provide valuable contributions to the development of safer and more effective EGFR TKIs for use as anticancer agents in the clinic.
Leukemia Research, 2008
To investigate the mechanism of cellular resistance to 6-MP, we established a 6-MP resistant cell... more To investigate the mechanism of cellular resistance to 6-MP, we established a 6-MP resistant cell line (CEM-MP5) by stepwise selection of the human T-lymphoblastic leukemia cell line (CEM). CEM-MP5 cells were about 100-fold resistant to 6-MP compared with parental CEM cells. Western blot analysis demonstrated that multidrug resistant protein 4 (MRP4) was increased in CEM-MP5 cells, whereas the levels of the nucleoside transporters hENT1, hCNT2 and hCNT3 were decreased compared with those of parental CEM cells. Consistent with the operation of an efflux pump, accumulation of [14C]6-MP and/or its metabolites was reduced, and ATP-dependent efflux was increased in CEM-MP5 cells. Taken together these results showed that up-regulation of MRP4 and down-regulation of influx transporters played a major role in 6-MP resistance of CEM-MP5 cells.
Biochemical Pharmacology, 2009
Nilotinib, a BCR-Abl tyrosine kinase inhibitor (TKI), was developed to surmount resistance or int... more Nilotinib, a BCR-Abl tyrosine kinase inhibitor (TKI), was developed to surmount resistance or intolerance to imatinib in patients with Philadelphia positive chronic myelogenous leukemia. Recently, it was shown that several human multidrug resistance (MDR) ATP-binding cassette (ABC) proteins could be modulated by specific TKIs. MDR can produce cancer chemotherapy failure, typically due to overexpression of ABC transporters, which are involved in the extrusion of therapeutic drugs. Here, we report for the first time that nilotinib potentiates the cytotoxicity of widely used therapeutic substrates of ABCG2, such as mitoxantrone, doxorubicin, and ABCB1 substrates including colchicine, vincristine, and paclitaxel. Nilotinib also significantly enhances the accumulation of paclitaxel in cell lines overexpressing ABCB1. Similarly, nilotinib significantly increases the intracellular accumulation of mitoxantrone in cells transfected with ABCG2. Furthermore, nilotinib produces a concentration-dependent inhibition of the ABCG2-mediated transport of methotrexate (MTX), as well as E 2 17bG a physiological substrate of ABCG2. Uptake studies in membrane vesicles overexpressing ABCG2 have indicated that nilotinib inhibits ABCG2 similar to other established TKIs as well as fumitremorgin C. Nilotinib is a potent competitive inhibitor of MTX transport by ABCG2 with a K i value of 0.69 AE 0.083 mM as demonstrated by kinetic analysis of nilotinib.
Lapatinib is active at the ATP-binding site of tyrosine kinases that are associated with the huma... more Lapatinib is active at the ATP-binding site of tyrosine kinases that are associated with the human epidermal growth factor receptor (Her-1 or ErbB1) and Her-2. It is conceivable that lapatinib may inhibit the function of ATP-binding cassette (ABC) transporters by binding to their ATP-binding sites. The aim of this study was to investigate the ability of lapatinib to reverse tumor multidrug resistance (MDR) due to overexpression of ABC subfamily B member 1 (ABCB1) and ABC subfamily G member 2 (ABCG2) transporters. Our results showed that lapatinib significantly enhanced the sensitivity to ABCB1 or ABCG2 substrates in cells expressing these transporters, although a small synergetic effect was observed in combining lapatinib and conventional chemotherapeutic agents in parental sensitive MCF-7 or S1 cells. Lapatinib alone, however, did not significantly alter the sensitivity of non-ABCB1 or non-ABCG2 substrates in sensitive and resistant cells. Additionally, lapatinib significantly increased the accumulation of doxorubicin or mitoxantrone in ABCB1-or ABCG2-overexpressing cells and inhibited the transport of methotrexate and E 2 17BG by ABCG2. Furthermore, lapatinib stimulated the ATPase activity of both ABCB1 and ABCG2 and inhibited the photolabeling of ABCB1 or ABCG2 with [ 125 I]iodoarylazidoprazosin in a concentration-dependent manner. However, lapatinib did not affect the expression of these transporters at mRNA or protein levels. Importantly, lapatinib also strongly enhanced the effect of paclitaxel on the inhibition of growth of the ABCB1-overexpressing KBv200 cell xenografts in nude mice. Overall, we conclude that lapatinib reverses ABCB1-and ABCG2-mediated MDR by directly inhibiting their transport function. These findings may be useful for cancer combinational therapy with lapatinib in the clinic.
Biochemical Pharmacology, 2010
In recent years, a number of TKIs (tyrosine kinase inhibitors) targeting epidermal growth factor ... more In recent years, a number of TKIs (tyrosine kinase inhibitors) targeting epidermal growth factor receptor (EGFR) family have been synthesized and some have been approved for clinical treatment of cancer by the FDA. We recently reported a new pharmacological action of the 4-anilinoquinazoline derived EGFR TKIs, such as lapatinib (Tykerb®) and erlotinib (Tarceva®), which significantly affect the drug resistance patterns in cells expressing the multidrug resistance (MDR) phenotype. Previously, we showed that lapatinib and erlotinib could inhibit the drug efflux function of Pglycoprotein (P-gp, ABCB1) and ABCG2 transporters. In this study, we determined if these TKIs have the potential to reverse MDR due to the presence of the multidrug resistance protein 7 (MRP7, ABCC10). Our results showed that lapatinib and erlotinib dose-dependently enhanced the sensitivity of MRP7-transfected HEK293 cells to several established MRP7 substrates, specifically docetaxel, paclitaxel, vinblastine and vinorelbine, whereas there was no or a lesser effect on the control vector transfected HEK293 cells. [ 3 H]-paclitaxel accumulation and efflux studies demonstrated that lapatinib and erlotinib increased the intracellular accumulation of [ 3 H]-paclitaxel and inhibited the efflux of [ 3 H]-paclitaxel from MRP7 transfected cells but not in the control cell line. Lapatinib is a more potent inhibitor of MRP7 than erlotinib. In addition, the Western blot analysis revealed that both lapatinib and erlotinib did not significantly affect MRP7 expression. We conclude that the EGFR TKIs, lapatinib and erlotinib reverse MRP7-mediated MDR through inhibition of the drug efflux function, suggesting that an EGFR TKI based combinational therapy may be applicable for chemotherapeutic practice clinically.
PLOS One, 2009
Background: One of the major mechanisms that could produce resistance to antineoplastic drugs in ... more Background: One of the major mechanisms that could produce resistance to antineoplastic drugs in cancer cells is the ATP binding cassette (ABC) transporters. The ABC transporters can significantly decrease the intracellular concentration of antineoplastic drugs by increasing their efflux, thereby lowering the cytotoxic activity of antineoplastic drugs. One of these transporters, the multiple resistant protein 7 (MRP7, ABCC10), has recently been shown to produce resistance to antineoplastic drugs by increasing the efflux of paclitaxel. In this study, we examined the effects of BCR-Abl tyrosine kinase inhibitors imatinib, nilotinib and dasatinib on the activity and expression of MRP7 in HEK293 cells transfected with MRP7, designated HEK-MRP7-2.
PLOS One, 2011
One of the major causes of chemotherapy failure in cancer treatment is multidrug resistance (MDR)... more One of the major causes of chemotherapy failure in cancer treatment is multidrug resistance (MDR) which is mediated by the ABCB1/P-glycoprotein. Previously, through the use of an extensive screening process, we found that vardenafil, a phosphodiesterase 5 (PDE-5) inhibitor significantly reverses MDR in ABCB1 overexpressing cancer cells, and its efficacy was greater than that of tadalafil, another PDE-5 inhibitor. The present study was designed to determine the reversal mechanisms of vardenafil and tadalafil on ABC transporters-mediated MDR. Vardenafil or tadalafil alone, at concentrations up to 20 mM, had no significant toxic effects on any of the cell lines used in this study, regardless of their membrane transporter status. However, vardenafil when used in combination with anticancer substrates of ABCB1, significantly potentiated their cytotoxicity in ABCB1 overexpressing cells in a concentration-dependent manner, and this effect was greater than that of tadalafil. The sensitivity of the parenteral cell lines to cytotoxic anticancer drugs was not significantly altered by vardenafil. The differential effects of vardenafil and tadalafil appear to be specific for the ABCB1 transporter as both vardenafil and tadalafil had no significant effect on the reversal of drug resistance conferred by ABCC1 (MRP1) and ABCG2 (BCRP) transporters. Vardenafil significantly increased the intracellular accumulation of [ 3 H]-paclitaxel in the ABCB1 overexpressing KB-C2 cells. In addition, vardenafil significantly stimulated the ATPase activity of ABCB1 and inhibited the photolabeling of ABCB1 with [ 125 I]-IAAP. Furthermore, Western blot analysis indicated the incubation of cells with either vardenafil or tadalafil for 72 h did not alter ABCB1 protein expression. Overall, our results suggest that vardenafil reverses ABCB1-mediated MDR by directly blocking the drug efflux function of ABCB1.
PLOS One, 2009
Background: One of the major mechanisms that could produce resistance to antineoplastic drugs in ... more Background: One of the major mechanisms that could produce resistance to antineoplastic drugs in cancer cells is the ATP binding cassette (ABC) transporters. The ABC transporters can significantly decrease the intracellular concentration of antineoplastic drugs by increasing their efflux, thereby lowering the cytotoxic activity of antineoplastic drugs. One of these transporters, the multiple resistant protein 7 (MRP7, ABCC10), has recently been shown to produce resistance to antineoplastic drugs by increasing the efflux of paclitaxel. In this study, we examined the effects of BCR-Abl tyrosine kinase inhibitors imatinib, nilotinib and dasatinib on the activity and expression of MRP7 in HEK293 cells transfected with MRP7, designated HEK-MRP7-2.
Cancer Letters, 2009
Sunitinib is an ATP-competitive multi-targeted tyrosine kinase inhibitor. In this study, we evalu... more Sunitinib is an ATP-competitive multi-targeted tyrosine kinase inhibitor. In this study, we evaluated the possible interaction of sunitinib with P-glycoprotein (P-gp, ABCB1), multidrug resistance protein 1 (MRP1, ABCC1), breast cancer resistance protein (BCRP, ABCG2) and lung-resistance protein (LRP) in vitro. Our results showed that sunitinib completely reverse drug resistance mediated by ABCG2 at a non-toxic concentration of 2.5muM and has no significant reversal effect on ABCB1-, ABCC1- and LRP-mediated drug resistance, although a small synergetic effect was observed in combining sunitinib and conventional chemotherapeutic agents in ABCB1 overexpressing MCF-7/adr and parental sensitive MCF-7 cells, ABCC1 overexpressing C-A120 and parental sensitive KB-3-1 cells. Sunitinib significantly increased intracellular accumulation of rhodamine 123 and doxorubicin and remarkably inhibited the efflux of rhodamine 123 and methotrexate by ABCG2 in ABCG2-overexpressing cells, and also profoundly inhibited the transport of [(3)H]-methotrexate by ABCG2. However, sunitinib did not affect the expression of ABCG2 at mRNA or protein levels. In addition, sunitinib did not block the phosphorylation of Akt and Erk1/2 in ABCG2-overexpressing or parental sensitive cells. Overall, we conclude that sunitinib reverses ABCG2-mediated MDR through inhibiting the drug efflux function of ABCG2. These findings may be useful for cancer combinational therapy with sunitinib in the clinic.