Clear cell renal cell carcinoma represents the most common form of kidney cancer, accounting for 70 to 90% of cases, and remains largely incurable at the metastatic stage. Approximately 30% of patients present with already metastatic disease at the time of diagnosis, and nearly half of the remainder will subsequently develop metastases. The vast majority of these tumors carry biallelic inactivation of the pVHL (von Hippel-Lindau) gene, a component of a ubiquitin ligase complex responsible for the degradation of the hypoxia-inducible factors HIF-1α and HIF-2α. Loss of pVHL therefore leads to the accumulation of HIF-2α, a central oncogenic event. Although several agents targeting the VHL-HIF pathway, notably antiangiogenic tyrosine kinase inhibitors such as sunitinib, have been approved, their benefit remains limited because tumors eventually progress, which justifies the search for combinations acting on complementary pathways.
To identify relevant therapeutic targets, the authors combined genetic and chemical approaches within a high-throughput screen. A multiplexed assay was used to evaluate the viability of a panel of isogenic VHL-deficient 786-O cell lines exposed to a collection of targeted therapies, including kinase inhibitors, thereby interrogating more than 2880 drug-gene pairs. Among the sensitivities observed, one combination was selected and then mechanistically characterized in tumor spheroids and ex vivo cultures of renal tumor slices. These models showed that VHL-deficient cells were more vulnerable to combined inhibition of the kinases CK2 and ATM than cells expressing functional VHL.
The mechanism relies on synthetic lethality. Used alone, the CK2 inhibitor (CX-4945) induces only moderate cell death but triggers strong overexpression of ATM, suggesting a link between these two survival pathways. In contrast, simultaneous targeting of CK2 and ATM (with the inhibitor KU-60019) curbs migration and induces reactive oxygen species (ROS)-dependent apoptosis. The NOX4 isoform emerges as a key modulator: in NOX4-knockout cells, the ROS production and apoptosis induced by CK2/ATM blockade are significantly reduced. Importantly, HIF-2α acts as a decisive mediator that potentiates this response, with its genetic disruption markedly decreasing the sensitivity of spheroids. The basal expression level of HIF-2α could therefore constitute a predictive biomarker of response.
In tumor slices derived from six patients, the KU-60019/CX-4945 combination proved more effective than sunitinib in five out of six cases, while exhibiting low toxicity toward normal tissues. Given the safety of CX-4945 already demonstrated in early human studies, these preclinical data provide a mechanistic rationale for the combined use of CK2 and ATM inhibitors in a subgroup of patients with VHL-deficient, HIF-2α-expressing metastatic renal carcinoma, a prospect currently being evaluated within a preclinical trial.