Targeting of HIF2-driven cachexia in kidney cancer

The most common type of renal cell carcinoma, clear cell renal cell carcinoma (ccRCC), shows aberrant activation of HIF2 due to loss of pVHL.
HIF2 directly activates transcription of the PTHLH gene, located in the amplified region of chromosome 12p, leading to PTHrP overexpression.
PTHrP is a central factor that drives tumor-associated cachexia and humoral hypercalcemia.
This study proposes that the HIF2–PTHrP axis forms the common molecular basis of two paraneoplastic syndromes (cachexia and hypercalcemia) in ccRCC.

In VHL-mutant ccRCC xenograft mouse models such as OSRC-2 and RXF393, severe body weight loss and depletion of fat and muscle occur.
Upon treatment with the HIF2 inhibitor PT2399:
Rapid recovery of body weight and fat mass is observed with no change in food intake → indicating that reduced energy expenditure is key.
Preservation of white adipose tissue (iWAT, eWAT), brown adipose tissue, and some skeletal muscles (soleus).
Suppression of Ucp1 expression and inhibition of ‘browning’ of white fat (conversion to thermogenic brown/beige fat).
At the same time points, tumor mass is not markedly reduced and can be similar or even increased → the effect is a pharmacologic action independent of tumor shrinkage.

BirA–ER–based biotin labeling plus LC–MS/MS (TMT quantification) was used to compare secreted proteins before and after HIF2 inhibition.
Secreted factor candidates specifically reduced by PT2399 in OSRC-2 included PTHrP, GDF15, and IL-6.
Validation by RT–qPCR/ELISA showed:
PTHLH/PTHrP is highly expressed in OSRC-2 and is strongly suppressed by PT2399.
GDF15 and IL6 show weak HIF2 dependency and little variation across cell lines, so they were excluded as primary factors.
ChIP–seq, RNA-seq, PRO-seq, and polysome-seq analyses revealed:
HIF2α directly binds to regulatory regions of PTHLH.
Upon PT2399 treatment or EPAS1 CRISPR KO, both transcription and translation of PTHLH drop sharply → indicating it is a direct HIF2 target.
In other cancers such as head and neck squamous cell carcinoma, HIF1α/HIF2α were also found to cooperatively regulate PTHLH under hypoxic conditions.

Necessity
When PTHLH is knocked out by CRISPR in OSRC-2 and RXF393:
Cachexia and hypercalcemia disappear, and survival is prolonged.
Tumors are actually larger or similar in size → suppression of cachexia is not simply a consequence of tumor reduction.
Even when hypercalcemia alone is corrected with a calcium-lowering drug (zoledronic acid), cachexia persists → hypercalcemia is not a sufficient condition for cachexia.
Sufficiency
Doxycycline (DOX)-inducible PTHLH cDNA was introduced into 786-O, a line that normally does not strongly induce cachexia.
DOX treatment causes rapid body weight loss, fat wasting, hypercalcemia, and early death.
Conversely, re-expression of sgRNA-resistant PTHLH in PTHLH KO OSRC-2 reinduces cachexia and hypercalcemia, which are reversed upon DOX withdrawal.

In patients with ccRCC:
Baseline plasma PTHrP is higher than in healthy individuals and positively correlates with corrected calcium and reduced skeletal muscle index.
Belzutifan
Significantly reduces PTHrP and corrected calcium, and an increase in BMI is observed within one month.
ICI and VEGF TKIs show little to no effect on PTHrP suppression or weight gain, and can even cause weight loss.
Weight recovery occurs regardless of tumor response → indicating a cachexia-correcting effect independent of tumor shrinkage.
NKT2152
Rapidly and durably suppresses plasma PTHrP.
Patients with high baseline PTHrP derive the greatest benefit in terms of weight gain and calcium normalization.
Here again, tumor response rate and weight recovery are uncoupled → suggesting potential as a cachexia therapy.
The main trends remain consistent in sex-stratified analyses.

PTHLH strongly correlates with HIF transcriptional signatures across many cancer types, and is highly expressed particularly in KIRC, HNSC, and lung squamous cell carcinoma.
In ccRCC, PTHrP serves as:
a mechanistic driver of cachexia and hypercalcemia, and
a potential pharmacodynamic biomarker of HIF2 inhibitors (falls rapidly after dosing).
Future strategies:
Prevent cachexia in the pre-onset and early stages by directly targeting PTHrP or HIF2.
Through combined analysis of other secreted factors such as GDF15, develop tumor-type- and patient-tailored cachexia therapies based on PTHrP and GDF15.
In other cancers (pancreatic cancer, head and neck cancer, lung cancer, etc.), test activation of the hypoxia–HIF–PTHrP axis and dissect the respective roles of HIF1 and HIF2.