A group of CNIO researchers headed by Manuel Valiente have found a new strategy that could be used in patients with brain metastasis to detect radioresistance.

They found that a simple blood test can help detect patients with resistance to brain radiotherapy and identified a drug that might reverse it.

A multi-centre clinical study is now under way to validate the predictive potential of this biomarker through the National Brain Metastasis Network (Spanish acronym: RENACER).

The study is being published in Nature Medicine.

“We are really happy, because we practically achieved a threefold result: we are beginning to understand the molecular mechanisms underlying radiotherapy resistance; we can stratify patients so as to enable personalised therapies; and we found a drug that reverses radioresistance,” Valiente said.

Between 20 and 40 per cent of solid tumours develop brain metastasis, mainly derived from the lung, the breast and the skin (melanoma).

As many drugs cannot cross the blood-brain barrier, systemic treatments are quite ineffective.

Radiotherapy is, thus, one of the most common treatment options for brain metastasis.

However, patients who undergo radiation, specifically whole-brain radiotherapy, rarely experience a significant impact on tumour progression while they are at high risk of side effects from the impact of the therapy on healthy tissue.

According to the authors of the study, the inefficacy of radiotherapy on metastases indicates the “emergence of radiation resistance.”

Resistance to radiotherapy in brain metastasis has not been thoroughly studied yet.

The Brain Metastasis Group at the CNIO, led by Manuel Valiente, carried out research using animal models and patient-derived 3D cell culture models that reproduce tumour tissue.

In addition, data from large patient cohorts were analysed for lung cancer, breast cancer and melanoma metastasis to the brain.

The study identified a pathway involved in the emergence of radiotherapy resistance, specifically, increased levels of S100A9 protein associated with limited sensitivity to this therapy.

According to the authors of the study, “endogenous levels of S100A9 are associated with the response to whole-brain radiotherapy in lung and breast adenocarcinoma and melanoma brain metastasis.”

To CNIO researchers’ surprise, S100A9 can be easily found in the blood of patients. “I did not expect it to be that simple,” said Valiente, “but there is a correlation between the levels of S100A9 in the blood of patients and their resistance to radiotherapy.”

Another promising result is that an existing drug known to inhibit the receptor that binds to S100A9 reverses radioresistance.

The drug has been previously tested in clinical trials for other disorders (Alzheimer’s disease), where it proved to be safe in patients and able to cross the blood-brain barrier and enter the brain.

With the help of the METPlatform tool, it was found that the drug could be used to transform radioresistant metastases from both mice and patient-derived organotypic cultures into sensitive ones.

In the article published in Nature Medicine, the authors of the study report “a comprehensive strategy that can be used to identify patients who might benefit from whole-brain radiotherapy as well as to design combined therapies to overcome radiation resistance.”

“Our findings could lead to a new approach to radiotherapy for cancer patients,” they added.

The expression of the S100A9 protein in the blood would enable them to “identify patients who might benefit from radiotherapy, preventing the neurocognitive decline that follows radiation therapy in patients with high radioresistance. Besides, S100A9 receptor inhibitors could enable the use of lower radiation doses to kill cancer cells, thus minimising collateral normal brain tissue damage and enhancing the benefits for patients.”

Source: Centro Nacional de Investigaciones Oncológicas (CNIO)