We identified an insect
neuropeptide, namely,
allatostatin 1 from Drosophila melanogaster, that transfects living NIH 3T3 and A431 human
epidermoid carcinoma cells and transports
quantum dots (QDs) inside the cytoplasm and even the nucleus of the cells. QD-conjugated biomolecules are valuable resources for visualizing the structures and functions of
biological systems both in vivo and in vitro. Here, we selected
allatostatin 1,
Ala-Pro-Ser-Gly-Ala-Gln-Arg-Leu-Tyr-Gly-Phe-Gly-Leu-NH2, conjugated to
streptavidin-coated CdSe-ZnS QDs. This was followed by investigating the transfection of live mammalian cells with QD-
allatostatin conjugates, the transport of QDs by
allatostatin inside the nucleus, and the proliferation of cells in the presence of
allatostatin. Also, on the basis of dose-dependent proliferation of cells in the presence of
allatostatin we identified that
allatostatin is not cytotoxic when applied at nanomolar levels. Considering the sequence similarity between the receptors of
allatostatin in D. melanogaster and
somatostatin/
galanin in mammalian cells, we expected interactions and localization of
allatostatin to
somatostatin/
galanin receptors on the membranes of 3T3 and A431 cells. However, with QD conjugation we identified that the
peptide was delivered inside the cells and localized mainly to the cytoplasm, microtubules, and nucleus. These results indicate that
allatostatin is a promising candidate for high-efficiency cell transfection and nucleus-specific cell labeling. Also, the transport property of
allatostatin is promising with respect to label/
drug/gene delivery and high contrast imaging of live cells and cell organelles. Another promising application of
allatostatin is that the transport of QDs inside the nucleus would lift the limit of general
photodynamic therapy to nucleus-specific
photodynamic therapy, which is expected to be more efficient than
photosensitization at the cell membrane or in the cytoplasm as a result of the short lifetime of
singlet oxygen.