Clear cell Renal Cell Carcinoma (ccRCC) is characterized by
VHL inactivation1,2. Because no
other gene is mutated as frequently, and VHL mutations are
truncal3,
VHL inactivation is regarded as the governing
event4.
VHL loss activates HIF-2, and constitutive HIF-2 restores
tumorigenesis in VHL-reconstituted ccRCC cells5. HIF-2 is implicated in
angiogenesis and multiple other processes6–9, but
angiogenesis is the main target of drugs like sunitinib10. HIF-2, a transcription
factor, has been regarded as undruggable11. A structure-based design approach identified a
selective HIF-2 antagonist (PT2399) that we evaluate using a tumorgraft (TG)/PDX
platform12,13. PT2399 dissociated HIF-2 (an
obligatory heterodimer [HIF-2α/HIF-1β])14 in human ccRCC suppressing
tumorigenesis in 56% (10/18) lines. PT2399 had greater activity than
sunitinib, was active in sunitinib-progressing tumors, and was better tolerated.
Unexpectedly, some VHL-mutant ccRCCs were resistant. Resistance
occurred despite HIF-2 dissociation in tumors and evidence of Hif-2 inhibition
in the mouse as determined by suppression of circulating erythropoietin, a HIF-2
target15 and possible
pharmacodynamic marker. We identified a HIF-2-dependent gene signature in
sensitive tumors. Illustrating drug specificity, gene expression was largely
unaffected by PT2399 in resistant tumors. Sensitive tumors exhibited a
distinguishing gene expression signature, and generally higher HIF-2α
levels. Prolonged PT2399 treatment led to resistance. We identified a binding
site and second site suppressor mutation in HIF-2α and HIF-1β
respectively. Both mutations preserved HIF-2 dimers despite treatment with
PT2399. Finally, an extensively pretreated patient with a sensitive TG had
disease control for >11 months with the close analogue PT2385. We
validate HIF-2 as a target in ccRCC, show that some ccRCC are, unexpectedly,
HIF-2 independent, and set the stage for biomarker-driven clinical trials.