PT2399

An AAV targeting Vhl, Pbrm1, Keap1, and Tsc1 reproducibly caused macroscopic ccRCCs that partially resembled human ccRCC tumors with respect to transcriptome and cell of origin and responded to a ccRCC standard-of-care agent, axitinib. Unfortunately, these tumors, like those produced by earlier genetically engineered mouse ccRCCs, are HIF2 independent.

We show that BMAL1-HIF2α is more sensitive than ARNT-HIF2α to suppression by PT2399, and increasing BMAL1 sensitizes 786O cells to growth inhibition by PT2399. Together, these findings indicate that an alternate HIF2α heterodimer containing the circadian partner BMAL1 contributes to HIF2α activity, growth, and sensitivity to HIF2α antagonist drugs in ccRCC cells.

We show that BMAL1-HIF2α is more sensitive than ARNT-HIF2α to suppression by PT2399, and increasing BMAL1 sensitizes 786O cells to growth inhibition by PT2399. Together, these findings indicate that an alternate HIF2α heterodimer containing the circadian partner BMAL1 contributes to HIF2α activity, growth, and sensitivity to HIF2α antagonist drugs in ccRCC cells.

Furthermore, pharmaceutical inhibition of HIF-2α by PT2399 attenuates disease progression and improves the efficacy of TKI treatment in both mouse and human CML. Overall, our findings highlight the role of HIF-2α in controlling the metabolic state and vascular niche remodeling in CML, suggesting it is a potential therapeutic target to enhance TKI therapy.

Nanocarrier-loaded PT2399 prevented radiation-induced bone loss in mice while reducing drug accumulation in the kidney. Targeted inhibition of HIF-2α may represent a therapeutic approach for protecting bone during radiation therapy.

In conclusion, HIF-2α knockout could inhibit the function of LSCs by affecting their metabolic pattern and vascular microenvironment in CML. Therefore, targeting HIF-2α may become a new strategy, and its specific inhibitor PT2399 may be a candidate drug for clinical application in CML treatment.

Inhibition of HIF2α with the small-molecule PT2399 prevented prostate cancer cell proliferation. Inhibition of HIF2α with the small molecule PT2399 prevented prostate cancer cell proliferation. These results thus identify HIF2α as a regulator of androgen synthesis and potential therapeutic target in prostate cancer.

Together, these data suggest that stromal HIF2 is an essential component of PDAC pathobiology and is a druggable therapeutic target that could relieve tumor microenvironment immunosuppression and enhance immune responses in this disease.

Referring herein to both first- and second-generation (ARO-HIF2) siRNA drugs, siHIF2 is specifically taken up by human ccRCC tumors transplanted in mice, where it depletes HIF2a inhibiting target gene expression and tumor growth...siHIF2 has activity against both wild-type and drug-resistant mutant HIF2a and is expected to be active in patients progressing on PT2977 (belzutifan), a PT2399-related drug recently approved by the FDA. To our knowledge, this is the first example of functional inactivation of an oncoprotein with a tumor-directed siRNA in humans. In summary, these studies provide unique insight into HIF2a (the only known core dependency in ccRCC), illustrate how it can be effectively inhibited by an siRNA drug, and establish a paradigm for the development of tumor directed siRNA-based therapeutics.

While as a transcription factor HIF2a had escaped drug targeting, structural studies revealed an unusual cavity, which became the foundation for the development of small molecule inhibitors such as PT2385 (a first-in-class drug), or the related PT2399 tool compound and the recently FDA-approved PT2977 (also called belzutifan). Reporting on a hypoxia sensor, a HIF2a radiotracer may be a useful ischemia probe. In summary, we report the development of a novel radiotracer with extensive potential applications currently being evaluated in humans.

Here we investigated the effects on tumor growth and on the tumor microenvironment of three different direct and indirect HIF-α inhibitors, namely the HIF-2α-specific inhibitor PT2399, the dual HIF-1α/HIF-2α inhibitor Acriflavine, and the S1P signaling pathway inhibitor FTY720, in the autochthonous Vhl/Trp53/Rb1 mutant ccRCC mouse model and validated these findings in human ccRCC cell culture models. We also identify that HIF-2α inhibition strongly suppresses T cell activation in ccRCC. These findings suggest prioritization of sphingosine pathway inhibitors for clinical testing in ccRCC patients and also suggest that HIF-2α inhibitors may inhibit anti-tumor immunity and might therefore be contraindicated for combination therapies with immune checkpoint inhibitors.