Heat shock protein 27 (HSP27), which is highly expressed in human lung and breast cancer tissues, induced resistance to cell death against various stimuli. Treatment of NCI-H1299 cells, which express a high level of HSP27, with small interference RNA specifically targeting HSP27 resulted in inhibition of their resistance to radiation or cisplatin, suggesting that HSP27 contributed to cellular resistance in these lung cancer cells. Furthermore, because HSP27 interacts directly with the COOH terminus of the protein kinase Cδ (PKCδ)-V5 region with ensuing inhibition of PKCδ activity and PKCδ-mediated cell death, we wished to determine amino acid residues in the V5 region that mediate its interaction with HSP27. Investigation with various deletion mutants of the region revealed that amino acid residues 668 to 674 of the V5 region mediate its interaction with HSP27. When NCI-H1299 cells were treated with biotin or with FITC-tagged heptapeptide of the residues 668 to 674 (E-F-Q-F-L-D-I), the cells exhibited dramatically increased cisplatin or radiation-induced cell death with the heptapeptide having efficient interaction with HSP27, which in turn restored the PKCδ activity that had been inhibited by HSP27. In vivo nude mice grafting data also suggested that NCI-H1299 cells were sensitized by this heptapeptide. The above data strongly show that the heptapeptide of the PKCδ-V5 region sensitized human cancer cells through its interaction with HSP27, thereby sequestering HSP27. The heptapeptide may provide a novel strategy for selective neutralization of HSP27.