6533b826fe1ef96bd12842de

RESEARCH PRODUCT

HSP70 inhibition : a new therapeutic target against cancer

subject

description

Heat shock proteins (HSPs) were first discovered in Drosophila by Ritossa in 1962. As stress proteins, HSPs are induced in response to a wide variety of physiological and environmental insults. HSPs have a cyto-protective function and act as molecular chaperones by assisting the folding of nascent or misfolded proteins and by preventing their aggregation. Mammalian HSPs have been classified into 5 families according to their molecular weight: HSP110, HSP90, HSP70, HSP60 and the family of small HSPs such as HSP27 (Kampinga et al., 2009). The most well-known inducible stress chaperone HSP70 is hardly detectable at basal level in normal “non-stressed” cells, but in cancer cells HSP70 is constitutively highly expressed. In that respect, this HSP play a key role in oncogenesis and in resistance to chemotherapeutic drugs (Goloudina et al., 2012).Until now, the cytoprotective properties of HSP70 were attributed to its intracellular functions mainly via its ability to block the apoptotic process at key points of the signal (Ravagnan et al., 2001). More recently, a membrane bound form of HSP70 was detected but also at the surface of exosomes derived from tumor cells but not non-cancerous cells (Kuppner et al., 2001). Moreover, growing evidence support the critical role of this membrane-bound HSP70 in the process of tumorigenesis (Pfister et al., 2007; Schmitt et al., 2007) via the activation of myeloid suppressor cells (MDSCs), which inhibit the anti-tumor immune response (Chalmin et al., 2010). Thereby, HSP70 by this dual action represents an attractive target for new anti-cancer therapy.In that aim, we developed specific inhibitors of HSP70, including peptide aptamers and peptides. In this work, we demonstrated that two aptamers A8, A17 (and the peptide P17), interact with different domains of HSP70 and, significantly sensitized cancer cells to apoptosis induced by chemotherapeutic drugs. Accordingly, in vivo studies in mice and rats showed a significant reduction of tumor growth by these inhibitors. Finally, we generate an A8 derived peptide called P8.1 that specifically neutralized the extracellular region of HSP70 at the surface of exosomes. Our results demonstrated that this peptide P8.1 inhibits MDSC activation and restored the antitumor immune response in vitro and in vivo, respectively.Overall, our work will help to develop and validate more effective cancer therapy based on the association of conventional chemotherapy with HSP70 inhibitors.