PET/CT is not only the most sensitive diagnosis tool in many cancers, but it also has the potential to open a new era in drug development. It can help physicians to select the right dose and the right combination for the right patient. By combining anatomy and function, PET/CT has become the most sensitive diagnosis tool in many cancers. It provides whole-body investigation in 30 to 60 minutes with sensitivity of up to 95 per cent depending on the cancer. It can also be used for treatment monitoring, helping physicians to make decisions on treatment continuation.

"But FDG only works for some drugs and some tumours. PET can do so much more", says Mats Bergstrom, director of biology at the GSK Clinical Imaging Centre in London, whose work has a focus on translational imaging and ensuring exploratory PET components in early oncology trials.

Cancers are driven by multiple signalling cascades - each unique for a certain tumour type and certain individual. To stop cancer, it's essential to

- know the right target;
- know this target is expressed in the chosen patient;
- ensure the right dose and schedule.

According to Bergstrom, PET imaging will open a new era in drug development. In the old/current model, the approval process starts with preclinical testing, followed by clinical trials (phases I, II and III). In the new model, registration will be preceded by three different steps: learning, optimising, and confirming. The middle step guarantees that the right dose and the right combination are selected for the right patient.

"Imaging allows us to be more rational before affirming we know the drug", Mats Bergstrom points out. "Does the drug reach the target tissue? Does it sufficiently bind to its primary target? Does it affect cellular physiology? The answers are not 'yes' or 'no' - we can look at quantification."

The use of PET in drug development already makes it possible to image enzymes. The next step is to image signalling cascades. "The beauty of PET is the versatility of chemistry. You can produce custom-made PET tracers for different tasks", says Bergstrom.

The technique enables researchers to image the pharmacodynamic effects of anticancer drugs and to observe adverse effects. Equally important, molecular imaging improves scheduling drug administration. "Drugs have transient effects that can last periods as long as one month and as short as one hour, and that's when non-invasive techniques come in", Bergstrom explains. "No biopsy can be planned for the right time."

While PET provides data on early cellular response, contrast-enhanced MR imaging brings the vascular response. Anatomical response can be accessed with computed tomography or MRI. With these tools, Bergstrom believes, drug development will see the advent of adequate characterisation, response monitoring and effective screening. "Imaging combined with soluble and tissue biomarkers are key elements in personalised medicine", he says.

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