Glioblastoma is a rare form of aggressive brain cancer that affects over 10,000 individuals in the US alone each year. The average survival rate of the disease sits at about 14.6 months for adults and 25% of children live for five years or more. One of the difficulties in treating the disease is due to the cancer cells’ lack of response to chemotherapy.

A recent experimental study published in the Open Access journal Biomedicines carried out by researchers at Brain Chemistry Labs in Jackson Wyoming, USA, found that molecules extracted from the violet flower called cyclotides increase the activity and effectiveness of chemotherapy drugs targeting glioblastoma cells.

“(cyclotides) have been found active against certain types of human cancer cells”- Dr. Samantha L. Gerlach, a violet researcher at Brain Chemistry Labs

Cancer cells resistance to chemotherapy

The researchers in the study wanted to test a few different, naturally occurring violets as well as synthetic cyclotides, and their role in chemotherapy treatment for glioblastoma. They did this by testing the effects on cultured glioblastoma cell lines (U-87 MG and T-98G) and using Temozolomide (TMZ), a chemotherapy drug commonly used for the treatment of glioblastoma.

The authors of the paper explain how TMZ is ineffective in 50% of patients with the disease. Drug resistance occurs in many different cancers, and is due to the molecular complexities of the cancer cells. When a part of the cancer is resistant to the type of therapy due to molecular advantages, it makes it difficult to treat the disease. Sometimes, the cancer is insensitive even before treatment and sometimes it acquires changes that make it resistant over time. This is cancer’s way of ‘adapting’ to the drug, ensuring it is able to survive and grow.

Because of this tricky phenomenon, medical treatment for resistant cancers often involves combination therapy, which means that different types of drugs are used at the same time. This aims to target all the cancer cells that might be resistant to one type of treatment but not the other.

Testing natural and synthetic cyclotides to induce cytotoxicity

In previous studies, the researchers tested natural cyclotides and their cytotoxicity on glioblastoma cells, breast cancer cells and HIV-infected cells. These studies confirmed that the compounds were able to induce sufficient cytotoxicity and make the cancer cells more chemosensitive.

The present study tested some of the same naturally occurring cyclotides and their  cytotoxicity on glioblastoma cell lines with and without TMZ treatment, confirming findings from previous studies. The researchers show that the molecules demonstrated dose-dependent cytotoxicity.

Importantly, the main novel finding of the present study is that the synthetic cyclotide Kalata B1 was able to enhance the sensitivity of the glioblastoma cells to TMZ, by exposing the cells to both the cyclotide and TMZ at the same time. They showed that by doing this, there was an increase the cytotoxic effects on the glioblastoma cells. Furthermore, they concluded that using cyclotides from violets reduces the amount of TMZ required to kill glioblastoma cells by ten-fold.

 Kalata B1 cyclotide for future research

This study supported the findings of previous research that cyclotides have proven effective at inducing cytotoxicity in glioblastoma cell lines. Using synthetic cyclotides, such as synthetic Kalata B1, may prove more beneficial for research and future treatment as the scientists were able to generate large quantities of the synthetic molecule.

“While Kalata B1 commonly occurs in violet species, extraction from plant material yields only minuscule amounts…working day and night for months, the minimal qualities we obtain are insufficient for clinical research” – Dr. Samantha L. Gerlach

In the study, the researchers confirmed that the synthetic cyclotide was stable in human serum and confirmed the structural sequence of the peptide using mass and NMR spectrometry. The mechanism of action of the molecule is yet to be fully understood, as the researchers do not fully understand how it can enhance the toxicity of TMZ.

The authors of the study speculate various mechanisms of action for the molecules. However, it is evident that much more research is needed to be carried out to fully understand how Kalata B1 can exert cytotoxic effects on glioblastoma cells and enhance chemosensitivity.

Future research

As the study was carried out on human cell lines, naturally, the next step is to carry out animal studies. This suggestion is supported by researchers at the Brain Chemistry Lab

‘Our cell data suggest that we can now move forward with the synthetic version in mice models’ – Dr. Rachael Dunlop, a researcher at the Brain Chemistry Lab.

In vitro research carried out on cell lines is vital for early research, especially for initial proof-of-concept studies. However, they are not able to fully recapitulate how the drug would work in the natural biological environment, involving critical aspects like immune-cell responses to the drug and toxic side effects.

In vivo animal studies are required to confirm whether synthetic cyclotide Kalata B1 can indeed exert the same cytotoxic effects on glioblastoma cells as they do in cell lines. Additionally, further research is needed to confirm the extent to which the plant peptide is able to enhance the effectiveness of TMZ, or other chemotherapy drugs in vivo.

Dr. Paul Alan Cox comments on the enlightening and hopeful research, and its future aims:

“We are still a long way from clinical trials, but now the way is clear to determine if it might be safe for further testing” – Dr. Paul Alan Cox, director of Brain Chemistry Labs

If you would like to read previous research like this, you can look at the recent Special Issue: Glioblastoma: Recent Advances and Challenges, published in Cancers, or have a look at more research published in Biomedicines.