A two-headed compound caused the death of treatment-resistant cancer cells

Researchers at the Technion have developed a family of molecules called R4VPs, which simultaneously degrade two proteins that help cancer cells survive. The compounds damaged resistant melanoma cells and sarcoma cells from patients, with little damage to non-cancerous cells. The research is still in the preclinical stage.

Researchers from the Technion have developed a family of experimental compounds that cause the breakdown of two proteins inside the cell, thereby pushing cells cancer Violent and resistant to treatment for a type of iron-dependent cell death. In cell culture experiments, the compounds damaged cells Melanoma Resistant to treatment and cells Sarcoma which originated from patients' tumors, but had less effect on non-cancerous cells.

The study, published in the journal oncogene, was jointly led by Dr. Avital Oknin-Weissman and Dr. Diphanjan Panda, from the laboratories of Prof. Amir Orin, head of the Rappaport Cancer Research Center and member of the Ruth and Baruch Rappaport Faculty of Medicine at the Technion, and Prof. Ashraf Barik from the Schulich Faculty of Chemistry at the Technion. ([Nature][1])

Not blocking the protein – but breaking it down

Many targeted cancer drugs work by blocking the activity of a protein that is necessary for growth. However, not every protein is suitable for inhibition by a drug, andCancer cells They may also develop alternative pathways and become resistant to treatment.

The approach tested in the study is based on targeted protein degradation. Instead of attaching an inhibitor to a protein and trying to stop its action, the researchers designed a molecule that recruits the cell's natural protein clearance mechanism and causes it to degrade the target protein.

Compounds of this type are called PROTAC – Abbreviation for Proteolysis-Targeting Chimera. In Hebrew, the Technion researchers suggested calling them OpenersThese are bifunctional molecules: one side of them binds to the target protein, and the other side binds to an enzyme from the ubiquitin ligase family. Bringing the two proteins together causes the target protein to be tagged with ubiquitin and transferred for degradation by the proteasome – the cell’s protein recycling system. ([Nature][1])

Two target proteins

The compounds the researchers developed are called R4VPs. They link two proteins: RNF4 and VHL, both of which are enzymes from the ubiquitin ligase family.

RNF4 plays a complex role in the cell. In some tumors, it helps stabilize cancer-promoting proteins, participates in DNA damage repair, and strengthens mechanisms that help cancer cells survive. High levels of RNF4 have been found in some melanoma, sarcoma, and carcinoma samples, and have been linked to a worse prognosis in previous studies.

The researchers wanted to induce the cell to break down RNF4 rather than try to block its enzymatic activity. However, the compounds they developed acted in an unusual way: they not only caused RNF4 to be broken down, but also reduced the amount of VHL.

This result weakened two survival mechanisms simultaneously. Knocking down RNF4 reduced the levels of cancer-promoting proteins that it helps stabilize, including active forms of c-Myc and beta-catenin. Reducing VHL contributed to increasing the cells’ susceptibility to apoptosis. Proptosis. ([Nature][1])

Iron-dependent cell death

Ferroptosis is a type of controlled cell death that results from the accumulation of oxidative damage in the lipids that make up the cell membrane. The process is iron-dependent and distinct from apoptosis, the more familiar mechanism of programmed cell death.

Certain cancer cells, especially those that are resistant to treatment, develop mechanisms that protect them from oxidative damage and apoptosis. One important defense system involves the protein GPX4, which prevents the accumulation of harmful oxides in cell lipids.

According to the study, R4VP compounds also bound to and altered anti-proptosis proteins, including GPX4. The combination of RNF4 and VHL degradation and the weakening of oxidative defenses led to the accumulation of damage in cell membranes and their rapid death.

Preferential damage to cancer cells

The researchers tested the compounds in several cell systems. They caused rapid death of human melanoma cells that had developed resistance to receptor tyrosine kinase inhibitors and of various types of sarcoma cells.

The compounds were also tested on primary sarcoma cells isolated directly from patient tumors. Significant damage was also observed in these cells.

In contrast, the compounds had little effect on several types of non-cancerous cells and primary cells tested in the trials. The researchers found a particularly high sensitivity in cells carrying tumor-promoting alterations in the EGFR pathway, while cells transformed by certain alterations in the PI3K pathway did not respond as well. This finding suggests that future treatments, if they are developed, will not necessarily be suitable for every tumor and will need to be tailored to its molecular characteristics. ([Nature][1])

The term "selectivity" in this context requires caution. It describes the difference found between cancer cells and non-cancer cells in the laboratory. It is not yet known how the compounds will distribute in the body, which tissues will be exposed to them, and what their effects on whole systems will be.

From target protein to combined reaction

In most PROTAC compounds, one enzyme is recruited to break down another target protein. In this case, the two linked proteins – RNF4 and VHL – break down themselves. In this way, the compound creates a dual response and simultaneously weakens several mechanisms that help the cancer cell.

The approach may be particularly important against tumors that are "addicted" to high levels of RNF4. The researchers describe the protein as a kind of weak point in certain cancer cells: it is not the only factor that causes the cell to become cancerous, but once the tumor has developed, it may need it to continue to survive.

However, RNF4 does not always act as a cancer-promoting protein. In some types of leukemia, it may actually participate in the breakdown of a cancer protein. Therefore, any treatment targeting it will need to take into account the tumor type and molecular context.

The road to clinical trials is still long.

The current study does not prove that the compounds are safe or effective as a drug. Most of the experiments were conducted in cancer cell cultures, including cells from patient tumors. The researchers note that the next step should include animal experiments to examine the distribution of the compounds in the body, dosage, efficacy against whole tumors and possible side effects.

Only after further preclinical studies can human trials be considered. A compound capable of killing a cancer cell in a lab dish may break down quickly in the body, not reaching the tumor or damaging tissues not tested in the cell experiment.

For the scientific article: Opening the scientific article

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