A novel, small molecule inhibitor of Hsc70/Hsp70 potentiates Hsp90 inhibitor induced apoptosis in HCT116 colon carcinoma cells.
OBJECTIVE
The anti-apoptotic function of the 70 kDa family of heat shock proteins and their role in cancer is well documented. Dual targeting of Hsc70 and Hsp70 with siRNA induces proteasome-dependent degradation of Hsp90 client proteins and extensive tumor specific apoptosis as well as the potentiation of tumor cell apoptosis following pharmacological Hsp90 inhibition.


METHODS
We have previously described the discovery and synthesis of novel adenosine-derived inhibitors of the 70 kDa family of heat shock proteins; the first inhibitors described to target the ATPase binding domain. The in vitro activity of VER-155008 was evaluated in HCT116, HT29, BT474 and MDA-MB-468 carcinoma cell lines. Cell proliferation, cell apoptosis and caspase 3/7 activity was determined for VER-155008 in the absence or presence of small molecule Hsp90 inhibitors.


RESULTS
VER-155008 inhibited the proliferation of human breast and colon cancer cell lines with GI(50)s in the range 5.3-14.4 microM, and induced Hsp90 client protein degradation in both HCT116 and BT474 cells. As a single agent, VER-155008 induced caspase-3/7 dependent apoptosis in BT474 cells and non-caspase dependent cell death in HCT116 cells. VER-155008 potentiated the apoptotic potential of a small molecule Hsp90 inhibitor in HCT116 but not HT29 or MDA-MB-468 cells. In vivo, VER-155008 demonstrated rapid metabolism and clearance, along with tumor levels below the predicted pharmacologically active level.


CONCLUSIONS
These data suggest that small molecule inhibitors of Hsc70/Hsp70 phenotypically mimic the cellular mode of action of a small molecule Hsp90 inhibitor and can potentiate the apoptotic potential of a small molecule Hsp90 inhibitor in certain cell lines. The factors determining whether or not cells apoptose in response to Hsp90 inhibition or the combination of Hsp90 plus Hsc70/Hsp70 inhibition remain to be determined.
Massey
Andrew J
AJ
Vernalis (R&D) Ltd, Granta Park, Cambridge, CB21 6GB, UK. a.massey@vernalis.com
Williamson
Douglas S
DS
Browne
Helen
H
Murray
James B
JB
Dokurno
Pawel
P
Shaw
Terry
T
Macias
Alba T
AT
Daniels
Zoe
Z
Geoffroy
Stephanie
S
Dopson
Melanie
M
Lavan
Paul
P
Matassova
Natalia
N
Francis
Geraint L
GL
Graham
Christopher J
CJ
Parsons
Rachel
R
Wang
Yikang
Y
Padfield
Antony
A
Comer
Mike
M
Drysdale
Martin J
MJ
Wood
Mike
M
D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000188:drug therapy / Q000473:pathology; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000473:pathology; D016503:Drug Delivery Systems; D004357:Drug Synergism; D005260:Female; D050883:HSC70 Heat-Shock Proteins / Q000037:antagonists & inhibitors*; D018840:HSP70 Heat-Shock Proteins / Q000037:antagonists & inhibitors*; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006801:Humans; D011684:Purine Nucleosides / Q000493:pharmacokinetics / Q000494:pharmacology*
D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins; D011684:Purine Nucleosides; C550733:VER 155008; D053148:Caspase 3; D053179:Caspase 7