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Breaking Barriers: How Oncolytic Viruses Penetrate Brain Tumors

August 17, 2023
Shimon Slavin
Oncolytic Viruses Penetrate Brain Tumors

Treating brain tumors is one of medicine’s biggest challenges. Their surgical removal is often associated with a high risk of complications, as they may impair or damage a patient’s physical or cognitive abilities. In addition, many anti-cancer drugs do not pass through the blood-brain barrier, which protects the brain from various agents. This also greatly complicates therapy.

All these factors make it very difficult to treat brain cancer and increase the risk of recurrence or tumor re-growth. Currently, there is a great scientific interest in the clinical application of the most promising innovative technologies for the treatment of malignant brain tumors – that of oncolytic viruses.

The Potential of Oncolytic Viruses for Brain Malignancies

One of the most promising therapies for incurable brain cancer, as well as solid brain tumor metastases, is based on the use of oncolytic viruses. Currently, cancer treatment with oncolytic viruses is administered intravenously or intranasally (through the nose). Once the oncolytic virus targets and penetrates malignant cells, it activates the mechanism of apoptosis (the process of programmed cell death), which leads to the death of cancer cells.

Furthermore, any residual non-immunogenic malignant cells, which are not visible to the immune system, are “tagged” with viral antigens. This makes them more likely to be recognized as foreign by the immune system, and open to immune attack.

However, the brain’s protective natural barrier, the so-called blood-brain barrier (BBB), may make it difficult for oncolytic viruses to enter the tumor. Therefore, there is no 100% guarantee that when oncolytic viruses are administered intravenously or through the nose, their concentration within the tumor mass will reach sufficient levels for effective treatment.
On the other hand, intratumoral administration of oncolytic viruses ensures that the entire dose penetrates directly inside the tumor.

Building on Past Experiences with Oncolytic Viruses

Recent studies used adenoviruses (a type of oncolytic virus) for intratumoral administration in children with diffuse intrinsic brainstem glioma (DIPG).

However, the use of oncolytic viruses such as infectious bursal disease virus (IBD) or Newcastle disease virus (ND), which are used by Biotherapy International, have demonstrated a more pronounced anti-cancer effect in preclinical studies.

By injecting oncolytic viruses directly into the brain tumor or into brain metastasis, in the case of solid tumors, we can turn an existing visible tumor mass into an in-situ internal anti-cancer vaccine. Now, brain gliomas are almost always confined to the central nervous system. However, if we activate an immune response against targeted metastases of solid tumors, we can trigger a systemic immune reaction that can work against distant metastases.

The use of oncolytic viruses may offer new hope to patients considered incurable or inoperable. It unlocks the potential to apply immunotherapy to a new group of patients, many of whom have unsuccessfully undergone repeated cycles of standard treatment.

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