Over the past few decades, extensive research has been conducted on cancer and a myriad of compounds have been developed. Despite significant progress for some cancers, the overall efficiency of these drugs remains limited by the emergence of resistance. Cancer cells often acquire resistance to targeted therapies by gaining further oncogenic alterations, reactivating feedback loops, and becoming more aggressive and refractory to subsequent treatments. We recently proposed an unconventional approach for cancer therapy involving the activation of oncogenic signaling along with the inhibition of stress responses. The underlying rationale is that in cancer cells, the aberrant oncogenic signaling is accompanied by cellular stress which increases the necessity for stress responses to maintain cell viability. Therefore, the overactivation of oncogenic signaling can overload cancer cells with cellular stress and be highly toxic to them, especially when combined with stress-response inhibitors. We have recently shown that the inhibition of protein phosphatase 2A (PP2A) led to hyperactivation multiple oncogenic signaling pathways in colon cancer models and was associated with engagement of multiple stress response pathways. Compound and CRISPR screens revealed that the inhibition of the mitosis gatekeeper kinase WEE1 as the major vulnerability of such hyperactivated cells. The combination of PP2A and WEE1 inhibitors proved very efficient in killing different cancer cell in vitro and in vivo. As for any other treatment, resistance to this approach can also emerge. Given the fundamentally different mechanism of toxicity, we aimed to explore how cancer cells acquire resistance to overactivation therapy.

The experiments were performed on colorectal cancer cell lines. We performed viability, invasion and seahorse assays, genome-wide screens, RNA sequencing and animal experiments.

Our study showed that the resistance to the combination of PP2A and WEE1 inhibitors led to transcriptional suppression of oncogenic signaling and cellular stresses. Moreover, the resistant cells switched from glycolysis to oxidative phosphorylation for their metabolic needs. In line with the in vitro data, the acquired resistance restrained the ability of cancer cells to form tumors in vivo. Altogether, our data suggest that the acquired resistance, developed to evade the stressful state caused by the activation therapy, is related with reduced tumorigenicity.

These data suggest that the combination of overactivation of oncogenic signaling together with suppression of stress responses can force cancer cells to give up their malignant traits. Our study proposes that this unconventional approach targets the pathological behavior of cancer cells and can be explored therapeutically as it may provide unforeseen ways to suppress oncogenic signaling.