A naturally-occurring harmless human virus given in combination with radiotherapy has shown significant benefit in patients with advanced cancer, according to results of an early trial published online today in the journal Clinical Cancer Research.

Reolysin is a new drug developed by Oncolytics Biotech Inc with preclinical and clinical studies conducted at The Institute of Cancer Research (ICR) and The Royal Marsden Hospital that can be injected directly into patients’ tumours. It is based on a virus (reovirus type 3 Dearing) that is commonly found in humans’ respiratory and gastrointestinal tracts without causing any symptoms.

Until now, trials of virus treatments injected in cancer patients have found them to be safe but with only limited effectiveness. Meanwhile, scientists have been looking for approaches that would amplify the effects of radiotherapy in a process known as radiation sensitisation, giving a greater effect than simply the sum of the two treatments.

Laboratory tests on tumour cells showed Reolysin appeared to magnify the effects of radiotherapy, so researchers began a Phase I study on 23 patients with a range of solid tumours, including lung, colorectal, ovarian and skin cancer. They were given between two and six injections of Reolysin in escalating doses, in combination with either a low dose (20Gy) or high dose (36Gy) of radiotherapy, at either The Royal Marsden Hospital in London or St James University Hospital in Leeds.

The study primarily assessed whether the treatment combination was safe, and found side-effects were generally mild and typical of patients receiving radiotherapy alone. However clinicians were also able to measure tumour response for 14 patients, and found tumours for all 14 patients either shrank or stabilised.

Of the seven patients who received low dose radiotherapy and were able to be evaluated, tumours shrank in two cases and stabilised in five. In seven patients on high-dose radiotherapy, tumours shrank in five cases and stabilised in two. One patient had a large tumour mass of his parotid gland and it shrank enough to be surgically removed. Another patient with metastatic melanoma was still alive 17 months after treatment commenced.

The study also tested patients’ blood, stools, urine and sputum for viral RNA, and found the virus was not shed after treatment. This means people could be given the drug as outpatients as no risk was found that they could transmit the virus to others.

Patients in this trial had advanced disease that had stopped responding to traditional drugs, but for which radiotherapy could provide some pain relief. Dr Kevin Harrington from the ICR and The Royal Marsden said the next step was to investigate the treatment combination in patients with newly-diagnosed cancers that would normally be treated with radiotherapy alone, to see whether it could improve cure rates.

“The absence of any significant side-effects in this study is extremely reassuring for future trials in patients receiving radiotherapy with the aim of curing their cancer,” Dr Harrington said.

Dr Brad Thompson, President and CEO of Oncolytics, added: “We believe that this study clearly demonstrates that the combination of low dose radiation and Reolysin is well tolerated and that the very high response rate warrants further investigation.”

The study was funded by Oncolytics Biotech Inc.

Source: The Institute of Cancer Research