Meeting the challenges of PET-based molecular imaging in cancer

Abstract

As personalized medicine becomes a reality, there is a need for specific imaging agents that reflect molecular characteristics of a cancer. Fluorodeoxyglucose is an important advance because of its sensitivity. Newer molecular imaging probes offer higher specificity and are categorized as: radiolabeled biomimetics; antibody–antibody fragments and drug–drug-like compounds. Biomimetics have high sensitivity but tend to be less specific as they often engage natural transporters and metabolic pathways. Antibodies and their fragments are specific but may be limited by slow clearance. Labeled drugs and drug-like compounds offer good specificity but may be limited in sensitivity. There are numerous challenges facing molecular imaging related to their complexity. Additionally, fear of ionizing radiation and regulatory constraints have somewhat inhibited clinical translation. However, there is reason for optimism due to economies of scale and a changing health care system, which places a premium on diagnostic accuracy. Although molecular imaging is not likely to become mainstream in the near future, its long-term prospects for doing so are excellent.

Keywords::

• cancer
• FLT
• fluorodeoxyglucose
• fluoro-l-thymidine
• ionizing radiation
• medical costs
• molecular imaging
• PET
• positron emission tomography
• regulations
• single-photon emission-computed tomography
• SPECT

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.

Key issues

• • Molecular imaging is the next step after anatomic and functional imaging.

• • The growth of targeted therapies and personalized medicine motivates the development of molecular imaging probes.

• • Positron-based imaging probes represent the most sensitive imaging agents and, when combined with CT or MRI, result in high-resolution whole body images.

• • FDG has had remarkable success despite considerable obstacles to its early development.

• • FDG’s development has led to a commercially viable network of PET probe providers and PET/CT scanners in the developed world, paving the way for additional agents.

• • The success of FDG may inhibit the development of other agents in the near term.

• • New PET agents can be categorized as biomimetics, antibody–antibody fragments and drug–drug-like targeted agents.

• • Each category of agents has advantages and limitations, but the field is evolving toward highly specific compounds.

• • A major current obstacle to PET probe development is their complexity and hence their cost.

• • Other impediments include fear of ionizing radiation and stricter regulations.