Among the fluorescent proteins that emit light efficiently in the “optical window” (low absorbance of light by hemoglobin and low autofluorescence of body tissue) is the emerging Genelux technology TurboFP635 (scientific name “katushka”). TurboFP635 is derived from the sea anemone Entacmaea quadricolor and shows efficient light emission in this optical window.
When expressed by the oncolytic vaccinia virus, the detection of tumors (using fluorescent optical imaging techniques) improves significantly as can be seen in Figure 1. While GFP-imaging alone allowed detection of superficial parts of the tumor, presence of TurboFP635 resulted in delineation of a much higher proportion of the tumor tissue with much less background caused by autofluorescence. Therefore, expression of alternative fluorescent proteins like TurboFP635 allows detection of tumor cells with higher specificity (less autofluorescence “noise”) and sensitivity (less light absorption due to hemoglobin).
Figure 1: A mouse bearing two tumors (black and white image on the left, tumors encircled with yellow dotted line) was injected with a virus encoding GFP and TurboFP635. Both proteins are made in the same concentration, but the TurboFP635 signal is much stronger. On the colored images the mouse skin is blue, GFP green and TurboFP635 is red. When detected on the same spot (e.g. small spot on the tail), the expression of both proteins results in the yellow color (GFP+TurboFP635 image).