Dextran-based nanoparticles with 5-FU-conjugated polymethacrylate segments for drug delivery: Synthesis of amphiphilic graft copolymers by mechanochemical solid-state polymerization and characterization.

Dextran (Dx) is a biodegradable and biocompatible polysaccharide, thus promising as a drug delivery carrier for tumor therapy. Herein, we applied mechanical energy to a high molecular weight Dx to control its molecular weight and simultaneously generate mechanoradicals. The solid-state polymerization of methacrylate- or methacrylamide derivatives initiated with Dx mechanoradicals showed polymer conversion of >95 %, yielding Dx-based graft copolymers with molecular weights of approximately 30,000 g mol-1. The Dx-based graft copolymers with hydrophobic segments formed nanoparticles with a particle size of 25-35 nm in an aqueous solution. The anti-pancreatic tumor drug 5-fluorouracil (5-FU) was covalently conjugated onto the hydrophobic segments of the amphiphilic Dx, and the nanoparticles were also prepared. The drug release profile from 5-FU-conjugated nanoparticles corresponded well to the Korsmeyer-Peppas model applied to drug release from matrix substrates, and was also immensely predicted by the Logistic and Gompertz curves. The 5-FU-conjugated nanoparticles showed cytotoxicity against the pancreatic adenocarcinoma cell lines (BxPC-3) that were not significantly inferior to the 5-FU positive group. Furthermore, the fluorescein-labeled nanoparticles internalized into BxPC-3 within 6 h and actively migrated into the cytosol. These results suggest that Dx-based graft copolymers with hydrophobic segments might be used to enhance therapeutic activity.

Celecoxib-Loaded Self-micellizing Solid Dispersion Suppresses Its Delayed Absorption in Rats with Impaired Gastrointestinal Motility.

The aim of this study was to develop a self-micellizing solid dispersion of celecoxib (SMSD/CEL) with enhanced dissolution to suppress a delay in absorption under impairment of gastrointestinal (GI) secretion and motility induced by severe pain. Soluplus®-based SMSD/CEL was prepared by lyophilization and physiochemically characterized. A pharmacokinetic study of orally-dosed CEL samples was carried out in rats with propantheline (PPT)-induced the impairment of GI secretion and motility. SMSD/CEL was micellized in aqueous media with a mean diameter of 153 nm, and it showed improved dissolution behavior of CEL under acidic conditions with 2.1-fold higher dissolved CEL at 120 min than crystalline CEL. SMSD/CEL was found to be in an amorphous state, and there was no significant crystallization even after storage under accelerated conditions for 8 weeks, indicating relatively high storage stability of the amorphous form. Orally-dosed crystalline CEL in PPT-treated rats showed a delayed mean absorption time (MAT) and area under the curve of plasma concentration versus time from 0 to 4 h (AUC0-4) was reduced to 12% compared with that in normal rats, whereas SMSD/CEL suppressed the delay and decrease of absorption in PPT-treated rats. From these findings, SMSD/CEL might be efficacious to suppress poor and delayed absorption of CEL for better pain medication in the presence of impaired GI secretion and motility associated with severe pain.

Characterization of a novel polymeric prodrug of an antibacterial agent synthesized by mechanochemical solid-state polymerization.

Polycrystalline methacryloyl monomers of the antibacterial drug nalidixic acid with an anhydride bond to the drug carboxyl group were prepared. The physicochemical properties of the synthesized vinyl monomer were characterized using X-ray powder diffraction, thermal analysis, and polarized light microscopy measurements. Mechanochemical solid-state polymerization of the resulting monomers was carried out to yield a novel polymeric prodrug. The in vitro hydrolysis behavior of the polymeric prodrug indicated that the release rate of drug from the polymeric prodrug was clearly dependent on the pH value of the hydrolysis solution. Moreover, sustained release of the drug at an almost constant rate for more than 10 hr was shown in both neutral and alkaline solutions. The results suggest that anhydride-based polymeric prodrugs could be potentially useful in colon targeted drug delivery systems.

Amorphous Solid Dispersion of Meloxicam Enhanced Oral Absorption in Rats With Impaired Gastric Motility.

Meloxicam (MEL) shows a slow onset of action in severe pain patients on account of delayed gastric motility. This study aimed to develop an amorphous solid dispersion (ASD) of MEL to achieve rapid oral absorption in severe pain patients. ASD formulations of MEL with hydroxypropylmethylcellulose (ASD-MEL/HPMC) and polyacrylates and polymethacrylates (ASD-MEL/EUD) were prepared and physicochemically characterized. Oral absorption behavior of MEL samples was also clarified in both normal and propantheline (PPT)-pretreated rats with impaired gastric motility. MEL in the formulations was amorphous, and ASD formulations of MEL exhibited high dissolution behavior in acidic solution. After oral administration of crystalline MEL (1 mg-MEL/kg), a 69% reduction in AUC0-4 was observed between normal and PPT-pretreated rats. For orally dosed ASD-MEL/HPMC (1 mg-MEL/kg), there were approximately 9- and 12-fold increases of AUC0-4 in normal and PPT-pretreated rats, respectively, in comparison with crystalline MEL (1 mg-MEL/kg). However, the oral absorption behavior of ASD-MEL/EUD (1 mg-MEL/kg) was low and similar to that of crystalline MEL. The infrared spectroscopic study revealed potent interactions between MEL and EUD, possibly leading to marked attenuation of MEL absorption. This ASD approach might provide rapid oral absorption of MEL in severe pain patients, possibly leading to better clinical outcomes.

Kinetic analysis of mechanoradical formation during the mechanolysis of dextran and glycogen.

A detailed electron spin resonance (ESR) analysis of mechanically induced free radicals (mechanoradicals) formation of glucose-based polysaccharides, dextran (Dx) and glycogen (Gly) was performed in comparison with amylose mechanoradicals. The ESR spectra of the samples mechanically fractured at room temperature were multicomponent. The radical concentration of Dx and Gly mechanoradicals gradually decreased during vibratory milling after reaching the maximum value. Although the molecular weight of Dx or the particle diameter of Gly steeply diminished until reaching the each maximum value of radical concentration, after that the molecular weight or the particle diameter slowly decreased. These results suggested that Dx and Gly mechanoradicals might be more unstable than amylose radicals possessing an intramolecular helical structure due to the branched structure.

Improved Dissolution of Dipyridamole with the Combination of pH-Modifier and Solid Dispersion Technology.

The aim of this study was to develop a pH-independent release formulation of dipyridamole (DP) by the combined use of pH-modifier technology and solid dispersion (SD) technology employing enteric polymer, Eudragit® S100 (Eud). Tartaric acid (TA) was selected as an appropriate pH-modifier in terms of improving the dissolution behavior of DP under neutral conditions. Upon optimization of the ratio of TA to DP, SD of DP with Eud and TA (SD-Eud/DP/TA) was prepared by a freeze-drying method. Scanning electron microscopic images revealed that DP was dispersed in the polymer in SD-Eud/DP/TA, and DP in SD-Eud/DP/TA was in an amorphous state, supported by powder X-ray diffraction and differential scanning calorimetry analyses. The dissolution behavior of SD-Eud/DP/TA was not dependent on the pH of the medium, although SD-Eud/DP exhibited very limited dissolution behavior under neutral conditions. Spectroscopic analysis suggested that there might be inter-molecular interaction among DP, TA and enteric polymer in SD-Eud/DP/TA, possibly leading to the stable pH-independent dissolution behavior of SD-Eud/DP/TA. TA in SD-Eud/DP/TA promoted the degradation of DP, suggesting that improving the stability of DP in SD-Eud/DP/TA might be key for its practical use. From these results, pH-independent dissolution behavior of SD-Eud/DP/TA could be achieved by an enteric polymer-based solid dispersion with a pH-modifier.

Development of Novel Polymeric Prodrugs Synthesized by Mechanochemical Solid-State Copolymerization of Hydroxyethylcellulose and Vinyl Monomers.

Novel polymeric prodrugs were synthesized by mechanochemical solid-state copolymerization of hydroxyethylcellulose and the methacryloyloxy derivative of 5-fluorouracil (5-FU). Copolymerization was about 94% complete after 4 h, and the polymeric prodrug was quantitatively obtained after 14 h of reaction. The number average molecular weight (Mn) and polydispersity (H) of the polymeric prodrug were 39000 g/mol and 6.20, respectively. Mechanical fracturing of the polymer in a stainless steel twin-shell blender improved these properties (Mn=16000 g/mol and H=1.94). 5-FU was sustainably released from the polymeric prodrugs, and the rate was not affected by the molecular weight or molecular weight distribution of the prodrug under the experimental conditions used. These results suggest that novel polymeric prodrugs composed of a polysaccharide and a synthetic polymer can be fabricated by mechanochemical solid-state copolymerization under anaerobic conditions.

Novel pH-responsive polymeric micelles prepared through self-assembly of amphiphilic block copolymer with poly-4-vinylpyridine block synthesized by mechanochemical solid-state polymerization.

We fabricated polymeric micelles containing 5-fluorouracil (5-FU) or fluorescein using the amphiphilic block copolymer, poly-4-vinylpyridine-b-6-O-methacryloyl galactopyranose. Although the polymeric micelles were stable at pH 7.4, they readily decomposed at pH 5, resulting in near complete release of 5-FU. Uptake of polymeric micelles containing fluorescein by HepG2 and HCT116 cells was also investigated. With both cell types, strong fluorescence was observed after a 12-h incubation, but the fluorescence weakened after 24 h of incubation. The fluorescein incorporated into the polymeric micelles was released into acidic organelles (endosome and/or lysosome), from which it diffused throughout the cell. The cytotoxicity of polymeric micelles containing 5-FU was evaluated against HepG2 cells using a CCK-8 assay. The results suggest that polymeric micelles containing 5-FU are more cytotoxic to HepG2 cells than free 5-FU.

Development of novel solid dispersion of tranilast using amphiphilic block copolymer for improved oral bioavailability.

The present study aimed to develop novel solid dispersion (SD) of tranilast (TL) using amphiphilic block copolymer, poly[MPC-co-BMA] (pMB), to improve the dissolution and pharmacokinetic behavior of TL. pMB-based SD of TL (pMB-SD/TL) with drug loading of 50% (w/w) was prepared by wet-mill technology, and the physicochemical properties were characterized in terms of morphology, crystallinity, dissolution, and hygroscopicity. Powder X-ray diffraction and polarized light microscopic experiments demonstrated high crystallinity of TL in pMB-SD/TL. The pMB-SD/TL exhibited immediate micellization when introduced to aqueous media, forming fine droplets with a mean diameter of ca. 122 nm. There was marked improvement in the dissolution behavior for the pMB-SD/TL even under acidic conditions, although the supersaturated TL concentration gradually decreased. NMR analyses demonstrated interaction between TL and pMB, as evidenced by the chemical shift drifting and line broadening. Pharmacokinetic behaviors of orally dosed TL formulations were evaluated in rats using UPLC/ESI-MS. After oral administration of pMB-SD/TL (10mg TL/kg) in rats, enhanced TL exposure was observed with increases of Cmax and AUC by 125- and 52-fold, respectively, compared with those of crystalline TL. From these findings, pMB-based SD formulation approach might be an efficacious approach for enhancing the therapeutic potential of TL.

Development of meloxicam salts with improved dissolution and pharmacokinetic behaviors in rats with impaired gastric motility.

PURPOSE: Because of its poor solubility in acidic solution, oral absorption and efficacy of meloxicam (MEL) may be reduced in severe pain patients with impaired gastric motility. The present study aimed to develop salt forms to overcome these drawbacks. METHOD: Upon MEL salt screening with eight counterions, five MEL salts were obtained. The physicochemical properties of these MEL salts were characterized with a focus on morphology, crystallinity, thermal behavior, dissolution, and chemical/photo-stability. Pharmacokinetic profiling of an orally administered MEL salt was also carried out in both normal rats and rats treated with propantheline for the suppression of gastric motility. RESULTS: Dissolution behaviors for all obtained MEL salts were markedly better than that of crystalline MEL; in particular, the initial dissolution rate of arginine MEL dihydrate (MEL/Arg) was ca. 14-fold higher than that of crystalline MEL. MEL/Arg was found to be chemically and physically stable. There was ca. 18-fold reduction of AUC(0-4) for orally dosed crystalline MEL (1.0 mg-MEL/kg) in propantheline-treated rats compared with that in normal rats. In contrast, there was only a ca. 3-fold difference in AUC(0-4) between normal and propantheline-treated rats after oral administration of MEL/Arg (1.0 mg-MEL/kg). CONCLUSION: From these findings, MEL/Arg may provide improved oral absorption in severe pain patients.

Novel formulations of dipyridamole with microenvironmental pH-modifiers for improved dissolution and bioavailability under hypochlorhydria.

This study was undertaken to develop new dipyridamole (DP) formulations with acidic microenvironmental pH-modifiers for improving dissolution and absorption under hypochlorhydric conditions. Dipyridamole granules (DPG) with ten acidic pH-modifiers were prepared with conventional wet granulation, and their manufacturability, stability and dissolution behavior were characterized. Pharmacokinetic profiling of the optimized DPG with acid was carried out in omeprazole-treated rats as a hypochlorhydric model. On the basis of the manufacturability, stability and dissolution behavior of new DPG formulations, p-toluenesulfonic acid (TS) was found to be a suitable acidic pH-modifier for DPG formulation. Although DPG showed pH-dependent dissolution behavior, DPG with TS exhibited a high rate and extent of dissolution in both acidic and neutral media. After oral administration of DPG (10mg DP/kg) in omeprazole-treated hypochlorhydric rats, there was ca. 40% reduction of the area under the curve of plasma concentration vs. time from zero to 3h (AUC(0-3)) for DPG compared with that in normal rats. However, AUC(0-3) for DPG/TS under hypochlorhydria was almost identical to that of DPG in normal rats. From these findings, the addition of TS as a microenvironmental pH-modifier in DP formulation might be beneficial in expanding the therapeutic potential of DP in hypochlorhydric patients.

Comparative studies on physicochemical stability of cyclosporine A-loaded amorphous solid dispersions.

The present study aimed to evaluate the physical stability on amorphous solid dispersion (SD) of cyclosporine A (CsA) employing hydroxypropyl cellulose (HPC). SD formulations (5-30% CsA) of CsA such wet-milled SD (WM/SD) and freeze-dried SD (FD/SD) were prepared, and both SD formulations were stored at 40 °C/75% relative humidity for 8 weeks. Transitions in morphology, dissolution behavior, crystallinity and thermal behavior of CsA were evaluated. There was at least 84-fold improvement in initial dissolution rate of SD formulations compared with that of amorphous CsA powder, although their dissolution rate was gradually decreased under accelerated conditions. In particular, aged FD/SD with a drug load of 30% exhibited highly limited dissolution as evidenced by 40% reduction of solubility after 8 weeks of storage. In contrast, aged WM/SD exhibited less reduction in dissolution rate compared with FD/SD. No significant changes were seen in crystallinity and thermal behavior after aging of SD formulations for 8 weeks; however, electron microscopic observations revealed aggregation of drug molecules/particles in the aged FD/SD, possibly leading to the reduced dissolution. From these findings, stability on CsA-loaded SD might be variable depending on the preparation methodology, and the wet-milling approach could be a viable option for preparing efficacious SD formulations with improved stability.

Physicochemical and pharmacokinetic characterization of amorphous solid dispersion of tranilast with enhanced solubility in gastric fluid and improved oral bioavailability.

In the present study, amorphous solid dispersion (ASD) formulations of tranilast (TL) with 8 hydrophilic polymers were prepared by a solvent evaporation method with the aim of improving dissolution behavior in gastric fluid and thereby enhancing oral bioavailability. The physicochemical properties were characterized with a focus on morphology, crystallinity, thermal behavior, dissolution, drug-polymer interaction, and stability. Of all TL formulations, ASD formulation with Eudragit EPO exhibited the highest improvement in dissolution behavior with a 3,000-fold increase in the first-order dissolution rate under acidic conditions (pH 1.2). Spectroscopic studies using infrared and near-infrared analyses revealed the drug-polymer interaction in the Eudragit EPO-based ASD formulation. On the basis of dissolution, crystallinity, and stability data, the maximum allowable drug load in the Eudragit EPO-based ASD formulation was deduced to be ca. 50%. Pharmacokinetic profiling of orally dosed TL formulations in rats was also carried out using UPLC/ESI-MS. After oral administration of the Eudragit EPO-based ASD formulation in rats, enhanced TL exposure was observed with an increase of oral bioavailability by 19-fold, and the variation of AUC was ca. 4 times lower than that with crystalline TL. With these data, the ASD approach could be a viable formulation strategy for enhancing the wettability and oral bioavailability of TL, resulting in improved therapeutic potential of TL for the treatment of inflammatory diseases.

Improved dissolution and pharmacokinetic behavior of dipyridamole formulation with microenvironmental pH-modifier under hypochlorhydria.

The present study aimed to develop and characterize new formulations of dipyridamole (DP), a pH-dependent poorly soluble drug, employing an acidic pH-modifier for improving dissolution and absorption under hypochlorhydric condition. Granule formulations of DP (DPG) with and without fumaric acid (FA) were prepared with wet granulation, physicochemical properties of which were characterized focusing on morphology, dissolution and stability. Pharmacokinetic profiling of orally dosed DPG or DPG with 60% loading of FA (DPG/FA60) was carried out in omeprazole-treated rats as a hypochlorhydric model. Although pH-dependent dissolution behavior was observed in DPG, DPG/FA exhibited high rate and extent of dissolution in both acidic and neutral media. Complete supersaturation was achieved with a 2 h testing period in pH6.8 medium, and co-existing fumaric acid had no impact on the chemical/photochemical stability of DP in solid-state. After oral administration of DPG or DPG/FA60 (10 mg-DP/kg), there was ca. 40% reduction of AUC(0-3) for DPG in omeprazole-treated rats as compared to that in normal rats; however, AUC(0-3) for DPG/FA60 under hypochlorhydria was almost identical to that of DPG in normal rats. Given the improved systemic exposure early after oral administration in hypochlorhydric rats, the DPG/FA might provide better clinical outcomes in hypochlorhydric patients.

Characterization of novel pH-sensitive polymeric micelles prepared by the self-assembly of amphiphilic block copolymer with poly-4-vinylpyridine block synthesized by mechanochemical solid-state polymerization.

We fabricated novel pH-sensitive polymeric micelles consisting of amphiphilic block copolymer containing pyridyl groups as side chains in the hydrophobic block. The number average particle diameter of the polymeric micelles at pH 7 was approximately 200 nm. A decrease in pH resulted in deformation of the polymeric micelles over a very narrow pH range (between pH 5.7 and 5.6). Interestingly, micellization and demicellization occurred reversibly in this narrow pH range. Polymeric micelles incorporating 5-fluorouracil (5FU) were also prepared. Decreasing the pH of this polymeric micelle solution from 7 to 5.5 resulted in the rapid release of 5FU at pH 5.6; the drug was completely released within 30 min. These results suggest that deformation of the polymeric micelles caused the rapid release of 5FU.

Development of inhalable nanocrystalline solid dispersion of tranilast for airway inflammatory diseases.

Tranilast (TL), an antiallergic agent, has been clinically used in the treatment of bronchial asthma, although the clinical use of TL is limited because of its poor solubility and systemic side effects. To overcome these drawbacks, a novel respirable powder (RP) of TL for inhalation therapy was developed using nanocrystal solid dispersion of TL (CSD/TL). In the CSD/TL, wet-milled crystalline TL particles with a mean diameter of 122 nm were dispersed, and there was a marked improvement in dissolution behavior of the CSD/TL-RP compared with that of a physical mixture of TL and carrier. Laser diffraction and cascade impactor analyses on the CSD/TL-RP demonstrated high dispersibility and deposition in the respiratory organs with emitted dose and fine particle fraction of ca. 98 and 60%, respectively. Inhaled CSD/TL-RP could attenuate antigen-induced inflammatory events in rats, as evidenced by histochemical analyses and inflammatory biomarkers such as lactate dehydrogenase, eosinophil peroxidase, and myeloperoxidase. The CSD/TL-RP seemed to be more potent than the physical mixture in inhibiting inflammatory responses, possibly due to the improved dissolution behavior. Systemic exposure of TL after intratracheal administration of CSD/TL-RP at a pharmacologically effective dose (100 µg of TL/rat) was found to be fivefold less than that of the oral TL dosage form at clinical dose (1.67 mg/kg). Given the improved pharmacodynamics and lower systemic TL concentration, the inhalable TL formulation might provide an interesting alternative to oral therapy with a better safety margin for the treatment of asthma and other airway inflammatory diseases.

High-throughput screening system for identifying phototoxic potential of drug candidates based on derivatives of reactive oxygen metabolites.

PURPOSE: The present study aimed to develop a high-throughput screening strategy for predicting the phototoxic potential of pharmaceutical substances, using a derivatives-of-reactive-oxygen-metabolites (D-ROM) assay. METHODS: The assay conditions of the D-ROM assay were optimized with a focus on screening run time, sensitivity, solvent system, and reproducibility. The phototoxic potentials of 25 model compounds were assessed by the D-ROM assay, as well as by other screening systems for comparison, including the reactive oxygen species (ROS) assay, the DNA-photocleavage assay, and the 3T3 neutral red uptake phototoxicity test (3T3 NRU PT). RESULTS: Some phototoxic drugs tended to yield D-ROM when exposed to simulated sunlight (250 W/m(2)), whereas D-ROM generation was negligible for non-phototoxic chemicals. Compared with the ROS assay, the assay procedure for the D-ROM assay was highly simplified with a marked reduction in screening run time. Comparative experiments also demonstrated that D-ROM data were related to the outcomes of the DNA-photocleavage assay and the 3T3 NRU PT, with prediction accuracies of 76 and 72%, respectively. CONCLUSION: The D-ROM assay has potential for identifying the phototoxic potential of a large number of new drugs as a 1st screening system in the early stages of drug discovery.

Novel dry powder formulation of ovalbumin for development of COPD-like animal model: Physicochemical characterization and biomarker profiling in rats.

This study was directed toward the development of novel ovalbumin dry powder inhalation system (OVA-DPI) for preparing experimental animal models of chronic obstructive pulmonary disease, with the aim of aiding the drug discovery. OVA-DPI, prepared with jet mill, showed high dispersion and emission from capsule as evaluated by cascade impactor. Based on the results from long term stability studies employing scanning electron microscopy, UPLC/ESI-MS analysis, powder X-ray diffraction and TG/DTA analyses, the OVA-DPI, stored at room temperature, was found to be stable for more than 3 years as evidenced by no significant degradation and crystal polymorphism. Intratracheal administration of OVA-DPI in OVA-sensitized rats resulted in 11-fold increase of infiltrated granulocytes, especially neutrophil, which would be characteristics of severe asthma/COPD symptoms. Of all plasma biomarkers monitored, myeloperoxidase activity and lactate dehydrogenase leakage into blood seemed to be sensitive indicators of lung injury in this model. In addition, biphasic increase of LDH was observed with peak responses at 3 and 24h after antigen challenge, suggesting that OVA-DPI could cause both acute and delayed inflammatory reactions. Upon these findings, OVA-DPI can be useful and reproducible research tool for the development of experimental asthma/COPD model.

Novel application of plasma treatment for pharmaceutical and biomedical engineering.

The nature of plasma-induced surface radicals formed on a variety of organic polymers has been studied by electron spin resonance (ESR), making it possible to provide a sound basis for future experimental design of polymer surface processing using plasma treatment. On the basis of the findings from such studies, several novel bio-applications in the field of drug- and biomedical- engineering have been developed. Applications for drug engineering include the preparation of reservoir-type drug delivery system (DDS) of sustained- and delayed-release, and floating drug delivery system (FDDS) possessing gastric retention capabilities, followed by preparation of "Patient-Tailored DDS". Furthermore, the preparation of composite powders applicable to matrix-type DDS was developed by making a mechanical application to the surface radical-containing polymer powders with drug powders. In applications for biomedical engineering, the novel method to introduce the durable surface hydrophilicity and lubricity on hydrophobic biomedical polymers was developed by plasma-assisted immobilization of carboxyl group-containing polymer on the polymer substrate. The surfaces thus prepared were further used for the covalent immobilization of oligo-nucleotides (DNA) onto the polymer surfaces applicable to constructing DNA diagnosis system, and also plasma-assisted preparation of functionalized chemo-embolic agent of vinyl alcohol-sodium acrylate copolymer (PVA- PAANa).

In vitro phototoxic potential and photochemical properties of imidazopyridine derivative: a novel 5-HT4 partial agonist.

Drug-induced phototoxic skin responses have been recognized as undesirable side effects, and as we previously proposed the determination of reactive oxygen species (ROS) from photo-irradiated compounds can be effective for the prediction of phototoxic potential. In this investigation, we evaluated the photosensitizing properties of imidazopyridine derivative, a novel 5-HT(4) partial agonist, using ROS assay and several analytical/biochemical techniques. Exposure of the compound to simulated sunlight resulted in the significant production of singlet oxygen, which is indicative of its phototoxic potential. In practice, an imidazopyridine derivative under UVA/B light exposure also showed significant photodegradation and even photobiochemical events; peroxidation of fatty acid and genetic damage after DNA-binding, which are considered as causative agents for phototoxic dermatitis. Interestingly, both photodegradation and lipoperoxidation were dramatically attenuated by the addition of radical scavengers, especially singlet oxygen quenchers, suggesting the possible involvement of ROS generation in the phototoxic pathways. In the 3T3 neutral red uptake phototoxicity test, imidazopyridine derivative also showed the phototoxic effect on 3T3 mouse fibroblast cells. These results suggest the phototoxic risk of newly synthesized imidazopyridine derivative and also verify the usefulness of ROS assay for phototoxicity prediction.