FIGURE SUMMARY
Title

Light-controllable dithienylethene-modified cyclic peptides: photoswitching the in vivo toxicity in zebrafish embryos

Authors
Afonin, S., Babii, O., Reuter, A., Middel, V., Takamiya, M., Strähle, U., Komarov, I.V., Ulrich, A.S.
Source
Full text @ Beilstein J Org Chem

DAE photoswitch and photoswitchable peptides explored in this study. (A) The reversible photoisomerization of the dithienylethene photoswitch core. (B) Photoconversion between ring-open and ring-closed photoforms of DAE-derived peptides. (C) Structures of the non-photoswitchable cytotoxic peptide GS (1), and one of our first photoswitchable prototypes 2 in the ring-open photoform.

Two versions of the D. rerio embryotoxicity assay for DAE-modified peptides: timelines, peptide photostates, ages of larvae, and definitions of the measured characteristics. (A) Direct application of the non-photoswitchable parent GS 1 or of the ring-open photoform of our prototype 2, and the corresponding killing curves for 1 (C, top, black) and 2 (C, bottom, red). (B) “Photoactivation” assay: initial application of the ring-closed photoform, incubation in darkness, followed by in situ photoconversion into the ring-open(ed) photoform, with the corresponding killing curves for 1 (D, top) and 2 (D, bottom, green for ring-closed, red for ring-open isomers). The latter panel illustrates the “phototherapeutic safety window” (green arrow) as the difference in toxicity between the ring-closed and the ring-open isomers upon photoactivation.

The in vivo toxicity against D. rerio embryos appears to be correlated with the empirical hydrophobicities of GS 1 and its photoswitchable analogues 220. LD50 values are plotted against the HPLC (C18) retention times upon elution with a standardized linear water/acetonitrile gradient: both, for the ring-closed photoforms (A, filled circles), as well as for the ring-open photoforms (B, open circles). The compound numbers are shown next to the data points. Values for the parent peptide 1 are shown as black filled circles; the original prototype 2 is color-coded in black; the data points for peptides of series i (35) are shown in grey, series ii (69) in blue, series iii (1015) in red, series iv (1618) in green, and series v (19, 20) in purple.

D. rerio embryotoxicity of GS 1 and the photoswitchable analogues 220 correlated with their in vitro hemolysis [30] for the ring-closed photoforms (A, filled circles), and for the ring-open photoforms (B, open circles). The compound numbers are shown next to the data points, and the color code is the same as in Fig. 3.

Phototherapeutic cytotoxic action against HeLa cells of GS 1 and its photoswitchable analogues 220, correlated with the new in vivo results and earlier in vitro data. For each peptide, the HeLa cytotoxic concentrations of the ring-open photoforms (IC50(open)) are plotted against the corresponding in vivo toxicities to D. rerio embryos (A, LD50(closed)24h), or against the in vitro hemolytic activities (B, HC50(closed), i.e., 50% hemolysis]) of the ring-closed photoforms. The compound numbers are shown next to the data points. The in vitro data is from [30]. Values for the parent peptide 1 are marked black, and a white filling highlights the initial prototype 2. Color codes for the remaining peptides are the same as in Fig. 3.

Acknowledgments
This image is the copyrighted work of the attributed author or publisher, and ZFIN has permission only to display this image to its users. Additional permissions should be obtained from the applicable author or publisher of the image. Full text @ Beilstein J Org Chem