Preparation of¹²⁵I labeled PKCδ-V5 Heptapeptide and evaluation of its targeting heat shock protein 27 in NCI-H1299 and H460 cells

PKCδ-catalytic V5 Heptapeptide (FEQFLDI, FP7) interacts with heat shock protein 27 (HSP27) and inhibits HSP27-mediated resistance to cell death against various stimuli including radiation therapy. Here, we prepared radio-iodinated heptapeptide and further investigated its uptake properties in HSP27 expression cells. Peptide sequence of FP7 and a negative control peptide (WSLLEKR, QP7) was modified by substituting their C-terminus residue to tyrosine (FP6Y and QP6Y) to label radio-iodine. Iodinated peptides were confirmed by LC mass analysis with cold iodine reaction mixture. Accumulation of [ ¹²⁵I]iodo-FP6Y and [¹²⁵I]iodo-QP6Y in NCI-H1299 cell line, with higher level of HSP27, and NCI-H460 cell line, with lower level of HSP27, was measured by NaI(Tl) scintillation counter. The modification of substituting C-terminus residue of FP7 to tyrosine (FP6Y) did not affect its interaction with HSP27. Accumulation of [¹²⁵I]iodo-FP6Y in NCI-H1299 cells was 3 fold higher than in NCI-H460 cells. The novel radio-iodinated FP6Y would be used as a tracer for targeting HSP27 protein.