Overcoming HSP27-mediated resistance by altered dimerization of HSP27 using small molecules

Abstract

Heat shock protein 27 (HSP27, HSPB1) is an anti-apoptotic protein characterized for its tumorigenic and metastatic properties, and now referenced as a major therapeutic target in many types of cancer. The biochemical properties of HSP27 rely on a structural oligomeric and dynamic organization that is important for its chaperone activity. Down-regulation by small interfering RNA or inhibition with a dominant-negative mutant efficiently counteracts the anti-apoptotic and protective properties of HSP27. However, unlike other HSPs such as HSP90 and HSP70, small molecule approaches for neutralization of HSP27 are not well established because of the absence of an ATP binding domain. Previously, we found that a small molecule, zerumbone (ZER), induced altered dimerization of HSP27 by cross linking the cysteine residues required to build a large oligomer, led to sensitization in combination with radiation. In this study, we identified another small molecule, a xanthone compound, more capable of altering dimeric HSP27 than ZER and yielding sensitization in human lung cancer cells when combined with HSP90 inhibitors or standard anticancer modalities such as irradiation and cytotoxic anticancer drugs. Therefore, altered dimerization of HSP27 represents a good strategy for anticancer therapy in HSP27-overexpressing cancer cells.

Sensitization of lung cancer cells by altered dimerization of HSP27

“…Our previous study showed that SW15 promotes cross-linking of HSP27 to form altered dimers, inhibiting oligomerization of HSP27 [ 13 ]. For sequential further studies for screening of more potent HSP27 cross linkers using synthetic compounds ( Supplementary Figure 1A ) in NCI-H460 cells, we selected 3 chromenone compounds with differing side chain structures, J2, J4 and YK-598-2 because they promoted different amounts of altered cross-linking of HSP27 in both cells and HSP27 protein system (Figure 1A and Supplementary Figure 1B and 1C ).…”

“…Small molecule, J2, which promotes altered cross-linking of HSP27, offer a promising approach for inhibition of HSP27, although further research is needed to evaluate the safety and efficacy of this compound in a clinical setting. However, one thing that J2 is more advanced than the previous ones such as SW15 or zerumbone [ 12 , 13 ] is that it can be used for i.p. injection in combined with conventional anticancer drugs.…”

“…Compounds were synthesized as described previously [ 13 , 24 ] or as in Supplementary Information . Taxol (Santa Cruz, sc-201439A), and tanespimycin (17-N-allylamino-17-demethoxygeldanamycin, 17-AAG) (Selleckchem, S1141) were dissolved in DMSO and diluted in cell culture medium.…”

“…We previously demonstrated that zerumbone (ZER), a cytotoxic component isolated from a natural product, Zingiber zerumbet , and SW15 a synthetic xanthone compound, induced cross-linking of the HSP27 protein by insertion between the disulfide bonds of HSP27. Altered cross-linking of HSP27 modified normal HSP27 dimerization, which resulted in a sensitizing effect to tumors after treatment with radiation (IR) [ 12 , 13 ]. Therefore, altered cross-linking strategy was suggested as a novel strategy for inhibition of HSP27-mediated resistance.…”

HSP27 inhibitor attenuates radiation-induced pulmonary inflammation

“…We have previously demonstrated that synthetic compounds zerumbone and SW-15 could induce abnormal cross-linking of the HSP27 protein. Altered crosslinking of HSP27 modifies normal HSP27 dimerization resulting in functional inhibition of HSP27, thereby sensitizing tumors to conventional radiation and chemotherapies 10 , 11 . As an continuous study to further optimize HSP27 inhibitors through abnormal dimerization of HSP27, we have additionally designed and synthesized a small number of chrome-4-one derivatives and found J2 (Supplementary Fig.…”