‘Engineered’ virus slows stubborn cancers



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February 14, 2008  
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CM NEWS – A lab-engineered virus has been proved to slow the growth of two particularly stubborn solid tumour cancers – neuroblastoma and peripheral nerve sheath tumours – without harming healthy tissues, according to study results published in the Cancer Research.

A team of researchers in a multi-institutional study was led by Cincinnati Children’s Hospital Medical Centre. They were able to insert “instructions to inhibit tissue growth into an engineered virus.”

“Malignant solid tumours are still very difficult to treat effectively, especially without causing harm to normal tissues, so we need to find innovative therapeutic approaches,” said Timothy Cripe, M.D., Ph.D., a physician and researcher at Cincinnati Children’s.

“In our study, this tumour-targeting viral therapy enhanced anti-tumour activity by stimulating multiple biological processes, including directly killing the cancer cells and reducing the formation of blood vessels that fed the tumours. These data support continuing development and study of our tumour-targeted viral therapy to fight cancer.”

Previous research has documented that oncolytic herpes simplex virus (oHSV) and similar viruses can infect and kill human cancer cells without harming normal, healthy cells or causing disease.

What is oncolytic herpes simplex virus? An oncolytic virus is a virus that is able to infect and lyse cancer cells, while leaving normal cells unharmed, making them potentially useful in cancer therapy.

Replication of oncolytic viruses both facilitates tumour cell destruction and also produces dose amplification at the tumour site. They may also act as vectors for anticancer genes, allowing them to be specifically delivered to the tumour site.

The virus should be able to tolerate storage, and production at high titres. A double stranded DNA genome is advantageous because it has greater stability during storage, and reduces the chances of hazardous mutations. Viruses like adenoviruses and herpes simplex virus are the most suitable, and have been the most extensively studied.

In their study, Dr. Cripe and his colleagues genetically armed oHSV with a gene that carries instructions for a cancer-fighting protein, human tissue inhibitor of metalloproteinase 3 (TIMP3). TIMP3 blocks enzymes that aid the development and progression of cancer, called matrix of metalloproteinases (MMP). Specifically, MMPs help break down molecules that are important for the structural support and normal development of cells, organs and maintenance of tissues. When MMP activity becomes unbalanced, the enzyme plays a well-documented role in the formation of invasive and metastatic cancers, including pediatric neuroblastoma, the most common solid cancer tumour in childhood.

Researchers dubbed the tumour-targeted viral therapy created by combining of TIMP and oHSV as rQT3. In laboratory studies involving human cancer cells and mice designed to develop neuroblastoma or peripheral nerve sheath tumours, rQT3 reduced new blood vessel development and increased toxicity to both kinds of tumour cells. In addition, rQT3 treatment resulted in longer life spans in mice compared to mouse models receiving just saline or other treatments.

Dr. Cripe said the researchers also discovered that rQT3 reduced the number of circulating endothelial progenitors (CEP). CEPs are derived from blood marrow and circulate in the blood. They have the ability to become cells that line blood vessels to promote blood flow.

“Our findings suggest that therapeutic viruses can act systemically by limiting the mobilization and recruitment of bone-barrow derived progenitors, both CEPs and others, that contribute to the tumour microenvironment and growth, resulting in the restriction of new blood vessel growth that can feed tumours,” Dr. Cripe said.

Neuroblastoma is a solid tumour cancer that begins in the sympathetic nervous system and most often strikes children younger than 5 years old. For children younger than 2, or those with a single mass tumour, the combination of surgery and chemotherapy has led to cure rates of 90 to 95%. In older children or those with metastatic disease, neuroblastoma is a much harder to fight.

Tumour cells are often able to survive ordinary doses of chemotherapy and radiation, leading to relapses that are difficult to cure. During the last three decades, Cincinnati Children’s has been a leader in developing high-dose chemotherapy used in combination with bone marrow transplants and other drug treatments to help improve outcomes for patients with high-risk neuroblastoma. Malignant peripheral nerve sheath tumours are cancers affecting the connective tissue surrounding nerves. The first-line treatment is surgical removal with chemotherapy or radiotherapy used as auxiliary therapies.

CM NEWS reports that a special can help fight neuroblastoma; or other cancer related articles.