Cisplatin Resistance May Be Caused by Domino Effect of Hyperactive Signals

Cisplatin is a mainstay chemotherapeutic agent used to treat major tumors, but the eventuality that a patient will develop treatment resistance is high. Emergent findings from a study conducted by investigators in the Republic of Korea and the United States showed that cisplatin resistance in tumor cells may be caused by hyperactive signaling of the EGFR/AKT pathway.

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“It is important to identify the cause of EGFR hyperactivation to overcome the clinical limitations of cisplatin treatment in [patients with cervical cancer] with hyperactivated EGFR signaling,” the authors wrote in the study published in Nature Communications.

To expound on the components and pathways that lead to EGFR hyperactivity and eventual cisplatin resistance, investigators began by looking at the magnitude of EGFR signaling (high vs low) in patients with cervical cancer who were either treated or not treated with cisplatin. During the study, investigators observed that patients who had received prior cisplatin treatment had markedly higher (hyperactive) EGFR signaling than patients who never received cisplatin.

The team also noticed that cells with hyperactive EGFR signaling were more likely to resist apoptosis (programmed cell death) induced by chemotherapy. Further, these treated cells (CaSki CR) became even more resistant to cisplatin with each subsequent treatment, whereas the treatment-naïve parent line (CaSki P) of cervical cancer cells remained sensitive to cisplatin. Ergo, both hyperactive EGFR signaling and continuous cisplatin treatment appear to increase the risk of treatment resistance.

The current analysis also confirms that autophagosomes promote epidermal growth factor (EGF) secretion, which occurs when EGF binds to its ligand, EGFR, and will eventually mediate fatal hyperactive EGFR signaling. Investigators realized this when they neutralized EGF secretion—which hyperactivates the EGFR signaling pathway via phosphorylation of EGFR—in cancer-resistant CaSki CR cells. The team observed both a significant reduction in phosphorylation levels and the number of CaSki CR cells resistant to apoptotic cell death.

However, it was important to assess what led to the mediation of EGF secretion. Previous findings suggest that mediation is caused by a transcription factor called NANOG, associated with metastatic, antiapoptotic, and therapy-resistant cancer cells. For this reason, investigators looked to compare NANOG expression in the treatment-resistant CaSki CR cells and treatment-sensitive CaSki P cells. Ultimately, they observed a dramatic increase in NANOG expression in only the treatment-resistant cells (13.9%-91.0%).

“These results demonstrate that cisplatin depletes tumor cells lacking NANOG while enriching tumor cells containing NANOG, suggesting that NANOG expression in tumor cells could confer a survival advantage [of tumor cells] under the selection pressure imposed by cisplatin,” the study authors wrote.

Furthermore, the molecular pathway of NANOG can be an actionable target to overcoming cisplatin resistance. However, to understand more about NANOG’s role, investigators needed to focus on the NANOG-TRPV1 axis.

TRPV1—a nonselective cation channel mediated by NANOG—regulates intracellular calcium ions (Ca2 +). Past studies have shown that increased levels of Ca2+ promote autophagosome formation that leads to secretory autophagy, or the secretion of tumorpromoting proteins. The increase in autophagosome abundance “increased the secretion of EGF, which activated the EGFR/AKT signaling and, consequentially, the acquisition of cisplatin resistance,” the study authors wrote.

Upon comparing TRPV1 expression in treatment-resistant vs treatment-naïve tumor cells, TRPV1 was significantly overexpressed in the treatment-resistant tumor cells compared with treatment-naïve tumor cells. This suggests that NANOG-mediated TRPV1 expression may start the chain of events leading to cisplatin resistance.

But to better understand whether (and how) NANOG regulates TRPV1 expression, investigators used the TRPV1 inhibitor AMG9810 to block downstream TRPV1 gene expression in tumor cells containing the NANOG gene; the results showed an increased tumor sensitivity to cisplatin. Notably, blocking TRPV1 activation with AMG9810 reduced this intracellular Ca2+, which overall reduced NANOG-mediated autophagic EGF secretion. “TRPV1 activation…elicited [an] increase in intracellular Ca2+ influx, which [was] abolished by TRPV1-specific inhibitor AMG9810, in CaSki NANOG cells,” the study authors wrote.

Anecdotally, a Kaplan-Meier graph shows that high expression of NANOG/TRPV1 decreased the overall survival (OS) rate of patients with cervical cancer to 60.0% as opposed to 100.0% in patients with low NANOG/TRPV1 expression and treated with chemotherapy, according to the study authors. The disparate OS highlights the significance of chemotherapy resistance on survival outcomes and the need for targeted treatment to overcome resistance.

TRVP1-targeted therapy could be effective for overcoming chemotherapy resistance because of its role in EGF secretory autophagy and apoptosis of tumor cells. Inhibiting TRPV1 can control the number of cancer cells that have high NANOG expression, thus sensitizing treatment-resistant cancer cells to chemotherapy.

Additionally, TRVP1-targeted therapies could have the added benefit of reducing chemotherapy-induced neuropathic pain, a severe adverse event associated with treatment; aside from autophagy and apoptosis, TRPV1 is involved in pain sensations.

It is important to note that different pathways could also be stimulating cisplatin resistance. For instance, ErbB family members (like EGFR) may activate TRPV1-mediated EGF secretion to induce cisplatin resistance. Other stemness factors or tumor microenvironmental factors could activate TRPV1 expression, or TRPV1 may activate itself in its own TRPV1 channel, but more research is needed.

“Notably, we found that the NANOGTRPV1 axis could be a major molecular pathway inducing autophagosome abundance in cisplatin-resistant cancer cells,” the study authors wrote. “Our results propose that the NANOG-TRPV1 axis could be used as one of [the] molecular markers to predict the outcome of autophagosome abundance in cisplatin-resistant cancer cells.”

Reference

Oh SJ, Lim JY, Son MK, et al. TRPV1 inhibition overcomes cisplatin resistance by blocking autophagy-mediated hyperactivation of EGFR signaling pathway. Nat Commun. 2023;14(1):2691. doi:10.1038/s41467-023-38318-7