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Paras N Prasad

Publications and source records attributed to Paras N Prasad.

35 records · Page 2Linked to original sources
PubMed2004

Detection of trophic factor activated signaling molecules in cells by a compact fiber-optic sensor.

This paper describes a highly sensitive method to detect trophic factor activated signaling molecules in cells using a compact fiber optic biosensor. The method is demonstrated by quantitative detection of phosphorylation of signal transducers and activators of transcription 3 (STAT3) in neuroblastoma cells. A single fiber-optic probe based on total internal reflection fluorescence sensing system is used. A 405 nm diode laser is used for evanescent wave excitation of immobilized labelled analyte on the probe surface. A compact charged coupled device (CCD) based spectrometer is used for recording the fluorescence signal. The method is two orders of magnitude more sensitive than the Western blotting technique.

Biomarkers, Tumor↗
PubMed2004

Synthesis, properties, and photodynamic properties in vitro of heavy-chalcogen analogues of tetramethylrosamine.

Thio and seleno analogues of tetramethylrosamine were prepared by the directed-metalation/cyclization of the corresponding N,N-diethyl 2-(3-dimethylaminophenylchalcogeno)-4-dimethylaminobenzamide to the 2,7-bis-(N,N-dimethylamino)-9H-chalcogenoxanthen-9-one followed by the addition of phenylmagnesium bromide, dehydration, and ion exchange to the chloride salt. The thio and seleno tetramethylrosamines had longer wavelengths of absorption and higher quantum yields for the generation of singlet oxygen than tetramethylrosamine. Both the thio and selenoanalogues of tetramethylrosamine were efficient photosensitizers against R3230AC rat mammary adenocarcinoma cells in vitro.

Animals↗
PubMed2004

Singlet oxygen generation via two-photon excited FRET.

A new approach to two-photon excited photodynamic therapy has been developed. A dendritic array of eight donor chromophores capable of two-photon absorption (TPA) was covalently attached to a central porphyrin acceptor. Steady-state fluorescence measurements demonstrated that the donor chromophores transfer excited-state energy to the porphyrin with 97% efficiency. Two-photon excitation of the donor chromophores at 780 nm resulted in a dramatic increase in porphyrin fluorescence relative to a porphyrin model compound. Enhanced singlet oxygen luminescence was observed from oxygen-saturated solutions of the target compound under two-photon excitation conditions.

Journal Article↗
PubMed2004

Degenerate two-photon-absorption spectral studies of highly two-photon active organic chromophores.

Degenerate two-photon absorption (TPA) spectral properties of five AFX chromophore solutions have been studied using a single and spectrally dispersed sub-picosecond white-light continuum beam. In a specially designed optical configuration, optical pathways inside the sample solution for different spectral components of the focused continuum beam were spatially separated from each other. Thus, the nondegenerate TPA processes coming from different spectral components can be eliminated, and the direct nonlinear absorption spectrum attributed to degenerate TPA processes can be readily obtained. Using this new technique, the complete TPA spectra for these five highly two-photon-active compounds (AF-380, AF-350, AF-295, AF-270, and AF-50) were obtained in the spectral range from 600 to 950 nm on an absolute scale of TPA cross section. The relationship between the molecular structures and their TPA spectral behaviors are discussed. In general the measured TPA spectra are not identical with the linear absorption spectra on the scale of absorbed photon(s) energy. Moreover, for some sample (such as AF-380), the TPA spectrum is totally different from the linear spectrum, which implies the difference of molecular transition pathways and selection rules for one- and two-photon excitation processes. At high excitation intensity levels (>or=15 GW/cm(2)), the saturation behavior of TPA transition can be observed obviously in AF-350 and AF-380 solutions that exhibit much higher nonlinear absorptivity than the other chromophores investigated.

Journal Article↗
PubMed2004

Dramatic enhancement of third-harmonic generation in three-dimensional photonic crystals.

We have observed a dramatic enhancement of third-harmonic generation in 3D polystyrene-air photonic crystals pumped by a near infrared laser beam. As the pump wavelength is tuned, the peak of the enhancement occurs when the third-harmonic wavelength approaches the short-wavelength edge of the band gap. We show that the origin of the enhancement is phase matching provided by the periodic structure of the photonic crystals.

Journal Article↗
PubMed2003

Ceramic-based nanoparticles entrapping water-insoluble photosensitizing anticancer drugs: a novel drug-carrier system for photodynamic therapy.

A novel nanoparticle-based drug carrier for photodynamic therapy is reported which can provide stable aqueous dispersion of hydrophobic photosensitizers, yet preserve the key step of photogeneration of singlet oxygen, necessary for photodynamic action. A multidisciplinary approach is utilized which involves (i) nanochemistry in micellar cavity to produce these carriers, (ii) spectroscopy to confirm singlet oxygen production, and (iii) in vitro studies using tumor cells to investigate drug-carrier uptake and destruction of cancer cells by photodynamic action. Ultrafine organically modified silica-based nanoparticles (diameter approximately 30 nm), entrapping water-insoluble photosensitizing anticancer drug 2-devinyl-2-(1-hexyloxyethyl) pyropheophorbide, have been synthesized in the nonpolar core of micelles by hydrolysis of triethoxyvinylsilane. The resulting drug-doped nanoparticles are spherical, highly monodispersed, and stable in aqueous system. The entrapped drug is more fluorescent in aqueous medium than the free drug, permitting use of fluorescence bioimaging studies. Irradiation of the photosensitizing drug entrapped in nanoparticles with light of suitable wavelength results in efficient generation of singlet oxygen, which is made possible by the inherent porosity of the nanoparticles. In vitro studies have demonstrated the active uptake of drug-doped nanoparticles into the cytosol of tumor cells. Significant damage to such impregnated tumor cells was observed upon irradiation with light of wavelength 650 nm. Thus, the potential of using ceramic-based nanoparticles as drug carriers for photodynamic therapy has been demonstrated.

Antineoplastic Agents↗
PubMed2003

Two-photon excited intramolecular energy transfer and light-harvesting effect in novel dendritic systems.

Two-photon absorption excited intramolecular energy transfer and light-harvesting effects are demonstrated in three novel dendritic systems. These systems contain both an antenna structure that can effectively absorb two-photon energy at approximately 800 nm and emit fluorescence at approximately 515 nm and a core moiety that can absorb one-photon energy at approximately 520 nm and emit at approximately 590 nm. Covalently combining the core and antenna functionalities intrinsically changes the optical behavior of the component pieces. The two-photon energy absorbed by the antenna structure is resonantly transferred to the core, where the core's emission intensity is enhanced by 8, 20, and 34 times for the three dendritic systems.

Journal Article↗
PubMed2003

Ultrashort 1.5-microm laser excited upconverted stimulated emission based on simultaneous three-photon absorption.

Simultaneous three-photon excited stimulated emission at (cavityless lasing) approximately 610 nm has been achieved in an organic chromophore solution pumped by approximately 1.5-microm ultrashort coherent radiation. The stimulated emission can be observed only in the forward and backward directions and is characterized by its high directionality and spectral narrowing. The divergence angle for the backward stimulated emission is considerably smaller than that for the forward stimulated emission, which resembles optical phase conjugation.

Lasers↗
PubMed2003

Fluorescence resonance energy transfer in a novel two-photon absorbing system.

A novel fluorescence resonance energy transfer (FRET) system containing a two-photon absorbing dye and a nile red chromophore has been synthesized. Upon two-photon excitation by laser at 815 nm this molecule displays efficient energy transfer from the two-photon absorbing dye to the nile red moiety, with an 8-fold increase in emission compared to the model compound. Similarly, single-photon excitation of the two-photon absorbing moiety at 405 nm results in >99% energy-transfer efficiency, along with a 3.4-fold increase in nile red emission compared to direct excitation of the nile red chromophore at 540 nm. This system provides an effective way to use IR radiation to excite molecules that, by themselves, have little or no two-photon absorption.

Journal Article↗
PubMed2003

A monomethine cyanine dye Cyan 40 for two-photon-excited fluorescence detection of nucleic acids and their visualization in live cells.

Monomethine cyanine dye 4-((1-methylbenzothiazolyliliden-2)methyl)-1,2,6-trimethylpyridinium perchlorate (Cyan 40) was investigated as a two-photon-excited fluorescence probe for nucleic acids (NA). Cyan 40 has been shown to demonstrate efficient two-photon-excited fluorescence in the presence of NA in vitro in contrast to solutions without NA. Two-photon confocal laser scanning microscopy (TPCLSM) and two-photon laser scanning microspectrofluorometry were used to check the possibility of using Cyan 40 as two-photon-excited fluorescence label for NA in living cells. Study of dye effect on viability of cells was also carried out. We ascertained that Cyan 40 is a cell-permeant dye, manifesting efficient two-photon-excited fluorescence when bound to NA in living cells, without any significant influence on viability of cells. TPCLSM images obtained from stained cells indicate preferential RNA staining by Cyan 40 compared with DNA.

Carbocyanines↗
PubMed2002

Observation of stimulated emission by direct three-photon excitation.

Multiphoton processes, predicted theoretically in 1931, were for a long time considered to be mainly of academic interest. This view changed when it was shown that a two-photon absorption process could, because of a quadratic dependence of excitation on intensity, produce a spatially confined excitation useful for three-dimensional data storage and imaging. Two-photon absorption has received considerable attention recently because of the development of highly efficient two-photon-sensitive materials, leading to numerous technological applications. These successes have created interest in exploring applications based on three-photon excitations. For a three-photon process, a longer excitation wavelength such as those common in optical communications can be used. Also, the cubic dependence of the three-photon process on the input light intensity provides a stronger spatial confinement, so that a higher contrast in imaging can be obtained. Here we report the observation of a highly directional and up-converted stimulated emission as an amplified spontaneous emission, produced in an organic chromophore solution by a strong simultaneous three-photon absorption at 1.3 microm. This achievement suggests opportunities for a three-photon process in frequency-upconversion lasing, short-pulse optical communications, and the emerging field of biophotonics.

Coloring Agents↗
PubMed2002

A conjugate of doxorubicin and an analog of Luteinizing Hormone-Releasing Hormone shows increased efficacy against oral and laryngeal cancers.

A doxorubicin and [D-Lys(6)]Luteinizing Hormone-Releasing Hormone (LH-RH) conjugate, AN-152, was designed to target LH-RH receptor positive cells. AN-152 is more potent against a specific group of cancers than doxorubicin and has less peripheral toxicity. This therapy is potentially efficacious against many other types of malignancies. Here, AN-152 was tested on oral (KB) and laryngeal (HEp-2) carcinoma cells. LH-RH receptor presence was demonstrated by displacement binding assays. Cells were treated with 10 nM EGF or left untreated, then exposed to 0-10 microM AN-152. Cytotoxicity was assessed by MTT assay to determine ED(50) values. AN-152 association with the cells was monitored using two-photon laser scanning microscopy. AN-152 was more potent than doxorubicin in both KB and HEp-2 cell lines (P<0.05). Up-regulation of LH-RH receptors by epidermal growth factor (EGF) increased the entry and potency of AN-152 in KB cells, but not in HEp-2 cells. This novel approach may be effective against a variety of cancers.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2002

Bombesin and epidermal growth factor potentiate the effect of cytotoxic LH-RH analog AN-152 in vitro.

The conjugation of doxorubicin with [D-Lys6] Luteinizing Hormone-Releasing Hormone (LH-RH), yields AN-152, a cytotoxic analog that can be targeted to tumor cells expressing LH-RH receptors. This conjugate is more potent against LH-RH receptor positive cancer cells and has less peripheral toxicity than free doxorubicin. The proliferation of MCF-7 human breast cancer cells in vitro is inhibited by AN-152 and this effect can be augmented by the up-regulation of LH-RH receptor expression through stimulation of tyrosine phosphorylation with epidermal growth factor (EGF). Bombesin and gastrin releasing peptide increase tyrosine phosphorylation and can act synergistically with EGF, as well as independently. The aim of this study was to demonstrate that bombesin enhances cytotoxic sensitivity of MCF-7 cells to AN-152 and that a significantly higher efficacy of the drug can be achieved in cells exposed to both bombesin and EGF. The cells were pretreated with bombesin and/or EGF, and then exposed to 0-10 micro M AN-152 for 96 h for determination of cytotoxicity. In addition, cells pretreated with bombesin and/or EGF were exposed for 1 h to 0.6 micro M AN-152 labeled with a two-photon fluorophore (AN-152:C625) for fluorescent imaging of drug entry. Bombesin as well as EGF increased the uptake and cytotoxicity of AN-152 in MCF-7 cells. The exposure of the cells to both EGF and bombesin produces a synergistic effect and results in increased cellular entry and cytotoxicity of AN-152. These results suggest that the activation of LH-RH receptors by compounds that increase tyrosine phosphorylation could further improve the response to targeted chemotherapy with AN-152.

Antineoplastic Agents↗
PubMedDate not supplied

A novel approach to a bifunctional photosensitizer for tumor imaging and phototherapy.

Optical imaging has attracted a great attention for studying molecular recognitions because minute fluorescent tracers can be detected in homogeneous and heterogeneous media with existing laboratory instruments. In our preliminary study, a clinically relevant photosensitizer (HPPH, a chlorophyll-a analog) was linked with a cyanine dye (with required photophysical characteristics but limited tumor selectivity), and the resulting conjugate was found to be an efficient tumor imaging (fluorescence imaging) and photosensitizing agent. Compared to HPPH, the presence of the cyanine dye moiety in the conjugate produced a significantly higher uptake in tumor than skin. At a therapeutic/imaging dose, the conjugate did not show any significant skin phototoxicity, a major drawback associated with most of the porphyrin-based photosensitizers. These results suggest that tumor-avid porphyrin-based compounds can be used as "vehicles" to deliver the desired fluorescent agent(s) to tumor. The development of tumor imaging or improved photodynamic therapy agent(s) by itself represents an important step, but a dual function agent (fluorescence imaging and photodynamic therapy) provides the potential for tumor detection and targeted photodynamic therapy, combining two modalities into a single cost-effective "see and treat" approach.

Animals↗
PubMedDate not supplied

Diacyllipid micelle-based nanocarrier for magnetically guided delivery of drugs in photodynamic therapy.

We report the design, synthesis using nanochemistry, and characterization of a novel multifunctional polymeric micelle-based nanocarrier system, which demonstrates combined function of magnetophoretically guided drug delivery together with light-activated photodynamic therapy. Specifically, the nanocarrier consists of polymeric micelles of diacylphospholipid-poly(ethylene glycol) (PE-PEG) coloaded with the photosensitizer drug 2-[1-hexyloxyethyl]-2-devinyl pyropheophorbide-a (HPPH), and magnetic Fe3O4 nanoparticles. The nanocarrier shows excellent stability and activity over several weeks. The physicochemical characterizations have been carried out by transmission electron micrography and optical spectroscopy. An efficient cellular uptake has been confirmed with confocal laser scanning microscopy. The loading efficiency of HPPH is practically unaffected upon coloading with the magnetic nanoparticles, and its phototoxicity is retained. The magnetic response of the nanocarriers was demonstrated by their magnetically directed delivery to tumor cells in vitro. The magnetophoretic control on the cellular uptake provides enhanced imaging and phototoxicity. These multifunctional nanocarriers demonstrate the exciting prospect offered by nanochemistry for targeting photodynamic therapy.

Chlorophyll↗
PubMedDate not supplied

Photosensitizers derived from 132-oxo-methyl pyropheophorbide-a: enhanced effect of indium(III) as a central metal in in vitro and in vivo photosensitizing efficacy.

The effects of an additional keto group on absorption wavelength and the corresponding metal complexes Zn(II), Cu(II) In(III) on singlet oxygen production and photodynamic efficacy were examined among the alkyl ether analogs of pyropheophorbide-a. For the preparation of the desired photosensitizers, the methyl 13(2)-oxo-pyropheophorbide-a obtained by reacting methyl pyropheophorbide-a with aqueous LiOH-THF was converted into a series of alkyl ether analogs. These compounds were evaluated for photophysical properties and in vitro (by means of the MTT assay and intracellular localization in RIF cells) and in vivo (in C3H mice implanted with RIF tumors) photosensitizing efficacy. Among the alkyl ether derivatives, the methyl 3-decyloxyethyl-3-devinyl-13(2)-oxo-pyropheophorbide-a was found to be most effective and the insertion of In(III) into this analog further enhanced its in vitro and in vivo photosensitizing efficacy. Fluorescence microscopy showed that, in contrast to the hexyl and dodecyl ether derivatives of HPPH (which localize in mitochondria and lysosomes, respectively), the diketo-analogs and their In(III) complexes localized in Golgi bodies. The preliminary in vitro and in vivo results suggest that, in both free-base and metalated analogs, the introduction of an additional keto group at the five-member exocyclic ring in pyropheophorbide-a diminishes its photosensitizing efficacy. This may be due to a shift in subcellular localization from mitochondria to the Golgi bodies. The further introduction of In(III) enhances photoactivity, but not by shifting the localization of the photosensitizer.

Animals↗