The antiproliferative activity of the heat shock protein 90 inhibitor IPI-504 is not dependent on NAD(P)H:quinone oxidoreductase 1 activity in vivo.
IPI-504, a water-soluble ansamycin analogue currently being investigated in clinical trials, is a potent inhibitor of the protein chaperone heat shock protein 90 (Hsp90). Inhibition of Hsp90 by IPI-504 triggers the degradation of important oncogenic client proteins. In cells, the free base of IPI-504 hydroquinone exists in a dynamic redox equilibrium with its corresponding quinone (17-AAG); the hydroquinone form binding 50 times more tightly to Hsp90. It has been proposed recently that the NAD(P)H:quinone oxidoreductase NQO1 can produce the active hydroquinone and could be essential for the activity of IPI-504. Here, we have devised a method to directly measure the intracellular ratio of hydroquinone to quinone (HQ/Q) and have applied this measurement to correlate NQO1 enzyme abundance with HQ/Q ratio and cellular activity of IPI-504 in 30 cancer cell lines. Interestingly, the intracellular HQ/Q ratio was correlated with NQO1 levels only in a subset of cell lines and overall was poorly correlated with the growth inhibitory activity of IPI-504. Although artificial overexpression of NQO1 is able to increase the level of hydroquinone and cell sensitivity to IPI-504, it has little effect on the activity of 17-amino-17-demethoxy-geldanamycin, the major active metabolite of IPI-504. This finding could provide an explanation for the biological activity of IPI-504 in xenograft models of cell lines that are not sensitive to IPI-504 in vitro. Our results suggest that NQO1 activity is not a determinant of IPI-504 activity in vivo and, therefore, unlikely to become an important resistance mechanism to IPI-504 in the clinic.
Douglas
Mark
M
Infinity Pharmaceuticals, 780 Memorial Drive, Cambridge, MA 02139, USA.
Lim
Alice R
AR
Porter
James R
JR
West
Kip
K
Pink
Melissa M
MM
Ge
Jie
J
Wylie
Andrew A
AA
Tibbits
Thomas T
TT
Biggs
Kurtis
K
Curtis
Michael
M
Palombella
Vito J
VJ
Adams
Julian
J
Fritz
Christian C
CC
Normant
Emmanuel
E
D000818:Animals; D016227:Benzoquinones / Q000378:metabolism / Q000494:pharmacology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D045325:HCT116 Cells; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D019073:HT29 Cells; D006801:Humans; D006873:Hydroquinones / Q000378:metabolism; D015151:Immunoblotting; D020014:K562 Cells; D047029:Lactams, Macrocyclic / Q000378:metabolism / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009154:Mutation; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000235:genetics / Q000378:metabolism*; D009369:Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D011485:Protein Binding; D047368:Tumor Burden / Q000187:drug effects; D023041:Xenograft Model Antitumor Assays
D016227:Benzoquinones; D018841:HSP90 Heat-Shock Proteins; D006873:Hydroquinones; D047029:Lactams, Macrocyclic; C004532:quinone; C112765:tanespimycin; D016660:NAD(P)H Dehydrogenase (Quinone); C447479:NQO1 protein, human; C031927:hydroquinone