Novel photochromic inhibitor for mitotic kinesin Eg5 which forms multiple isomerization states.

The mitotic kinesin Eg5 is a plus-end directed homotetrameric molecular motor essential for the formation of bipolar spindles during cell division. Kinesin Eg5 is overexpressed in cancer cells and hence considered as a target for cancer therapy; the inhibitors specific for Eg5 have been developed as anticancer drugs. In this study, we synthesized a novel functional photoresponsive inhibitor composed of spiropyran and azobenzene derivatives to control Eg5 function with multistage inhibitory activity accompanied by the formation of different isomerization states. The photochromic inhibitor spiropyran-sulfo-azobenzene (SPSAB) exhibited three isomerization states: spiro (SP)-trans, merocyanine (MC)-cis and MC-trans, upon exposure to visible light, ultraviolet and in the dark, respectively. SPSAB-induced reversible changes in the inhibitory activity of ATPase and motor activities correlating with photoisomerization among the three states. Among the three isomerization states of SPSAB, the SP-trans isomer showed potent inhibitory activity at an IC50 value of 30 µM in the basal ATPase assay. MC-trans and MC-cis exhibited less inhibitory activity at IC50 values of 38 and 86 µM, respectively. The results demonstrated that the novel photochromic inhibitor enabled precise control of Eg5 function at three different levels using light irradiation.

Time-resolved detection of SDS-induced conformational changes in α-synuclein by a micro-stopped-flow system.

An intrinsically disordered protein, α-synuclein (αSyn), binds to negatively charged phospholipid membranes and adopts an α-helical structure. This conformational change is also induced by interaction with sodium dodecyl sulfate (SDS), which is an anionic surfactant used in previous studies to mimic membrane binding. However, while the structure of the αSyn and SDS complex has been studied widely by various static measurements, the process of structural change from the denatured state to the folded state remains unclear. In this study, the interaction dynamics between αSyn and SDS micelles was investigated using time-resolved measurements with a micro-stopped-flow system, which has been recently developed. In particular, the time-resolved diffusion based on the transient grating technique in combination with a micro-stopped-flow system revealed the gradual change in diffusion triggered by the presence of SDS micelles. This change is induced not only by binding to SDS micelles, but also by an intramolecular conformational change. It was interesting to find that the diffusion coefficient decreased in an intermediate state and then increased to the final state in the binding reaction. We also carried out stopped-flow-kinetic measurements of circular dichroism and intramolecular fluorescence resonance energy transfer, and the D change was assigned to the formation of a compact structure derived from the helix bending on the micelle.

Morelloflavone as a novel inhibitor of mitotic kinesin Eg5.

Among 40 plant-derived biflavonoids with inhibitory potential against Eg5, morelloflavone from Garcinia dulcis leaves was selected for further testing based on in silico analysis of binding modes, molecular interactions, binding energies and functional groups that interact with Eg5. Computational models predicted that morelloflavone binds the putative allosteric pocket of Eg5, within the cavity surrounded by amino acid residues of Ile-136, Glu-116, Glu-118, Trp-127, Gly-117, Ala-133, Glu-215, Leu-214 and Tyr-211. Binding energy was -8.4 kcal/mol, with a single hydrogen bond formed between morelloflavone and Tyr-211. The binding configuration was comparable to that of a reference inhibitor, S-trityl-L-cysteine. Subsequent biochemical analysis in vitro confirmed that morelloflavone inhibited both the basal and microtubule-activated ATPase activity of Eg5 in a manner that does not compete with ATP binding. Morelloflavone also suppressed Eg5 gliding along microtubules. These results suggest that morelloflavone binds the allosteric binding site in Eg5 and thereby inhibits ATPase activity and motor function of Eg5.

Highly efficient photocontrol of mitotic kinesin Eg5 ATPase activity using a novel photochromic compound composed of two azobenzene derivatives.

Mitotic kinesin Eg5 plays an important physiological role in cell division. Several small-molecule inhibitors of Eg5 are the focus of cancer therapies. Azobenzene is a photochromic compound exhibiting cis-trans isomerization upon ultraviolet (UV) and visible (VIS) light irradiation. Photochromic compounds of azobenzene derivatives, mimicking Eg5-specific inhibitors of STLC, indicated photoreversible inhibitory effects on Eg5 ATPase activity; however, the photoreversible switching efficiency was not significant. This study presents a novel synthesized photochromic Eg5 inhibitor 2, 3-bis[(2,5-dioxo-1-{4-[(E)-2-phenyldiazen-1-yl]phenyl}pyrrolidin-3-yl)sulfanyl] butanedioic acid (BDPSB), which is composed of two azobenzenes. BDPSB exhibited cis-trans isomerization with UV and VIS light irradiation. The trans form of BDPSB significantly inhibited microtubule-dependent ATPase activity of Eg5, with an IC50 of 74 µM. Cis BDPSB showed weak effects on the microtubule-dependent ATPase activity. The results suggest that the novel photochromic Eg5 inhibitor BDPSB, which exhibits highly efficient photoswitching, shows a switch 'ON' and 'OFF' behaviour with VIS and UV light irradiation.

Photo-control of the mitotic kinesin Eg5 using a novel photochromic inhibitor composed of a spiropyran derivative.

In this study, we synthesized a novel photochromic inhibitor of the mitotic kinesin Eg5, which is composed of the photochromic compound spiropyran to photo-control the function of Eg5. The compound (S)-2, 3-dispiropyran propionic acid (DSPPA) exhibits reversible spiropyran-merocyanine photo-isomerization upon irradiation with visible or ultra-violet light. DSPPA induced reversible changes in the inhibitory effect on Eg5 ATPase and motor activities, which correlates with the spiropyran-merocyanine photo-isomerization. Microtubule-dependent ATPase activity was significantly more inhibited by the spiropyran isomer of DSPPA than by the merocyanine isomer. Additionally, an in vitro motility assay revealed that the microtubule gliding velocity was reduced more by the spiropyran isomer than by the merocyanine isomer. This indicates that the spiropyran derivative may be useful in regulating the function of the mitotic kinesin.

Low-power 808-nm laser irradiation inhibits cell proliferation of a human-derived glioblastoma cell line in vitro.

It has been reported that low-power laser irradiation (LLI) can modulate various biological processes including cell proliferation. Some reports suggest that LLI interferes with the cell cycle and inhibits cell proliferation, while others suggest that LLI has a stimulatory effect. Mechanisms underlying the effects of LLI remain unclear. Since the effects of LLI on cancer cells are not well understood, with the aim of developing an LLI therapy for malignant glioblastoma, we investigated the effects of LLI on the cell proliferation of the human-derived glioblastoma cell line A-172. Glioblastoma cell cultures were irradiated with a diode laser at a wavelength of 808 nm and the effects on cell viability and proliferation were examined. Cell counting at 24 and 48 h after irradiation showed that LLI (at 18, 36 and 54 J/cm(2)) suppressed proliferation of A-172 cells in a fluence-dependent manner (irradiation for 20, 40 and 60 min). A reduction in the number of viable cells was also demonstrated by a fluorescent marker for viable cells, calcein acetoxymethylester (calcein-AM). The reduction in cell viability was not associated with morphological changes in the cells or with necrotic cell death as demonstrated by propidium iodide staining. LLI also had little effect on cell proliferation as shown by 5-bromo-2'-deoxyuridine staining. We discuss possible mechanisms underlying the suppressive effect of 808-nm LLI on the viability of human-derived glioblastoma A-172 cells.