A multimodal imaging approach uses a combination of different molecular imaging modalities. The approach has the potential to broaden the (pre)clinical pathway for new drugs and therapeutics. It allows drug developers to gather various types of in-human data that are vital to the drug development process.
Dual labeling – a multimodal imaging approach.
Dual labeling is an upcoming multimodal imaging approach that refers to the conjugation of two different reporter molecules. For example, a radionuclide and a fluorophore. Dual labeling can improve and accelerate the drug development process by combining the strengths of both nuclear and fluorescence imaging modalities.
Overcoming limitations of a single imaging modality.
Dual labeled targeting moieties have the potential to overcome the limitations of using a single imaging modality. For example, PET imaging non-invasively visualizes the whole body biodistribution with high sensitivity and has the ability of accurate quantification of drug accumulation. However, due to PET’s limited resolution the distribution and accumulation of the drug at a cellular level cannot be examined. By dual labeling the same targeting moiety with a radionuclide and a fluorophore this can be overcome. Namely, (ex vivo) fluorescence imaging can be used to examine the tissue distribution at a tissue and cellular level. In turn, PET imaging covers the low penetration depth of the fluorophore and the limitation of local/superficial imaging. Thus, a combination of imaging modalities uses “best of both worlds” and support more precise and faster decision making.
Executing a dual-labeling imaging approach.
In the past decade, the concept of dual labeled imaging agents for near-infrared and nuclear imaging is used more frequently in preclinical studies. Moreover, based on promising results of preclinical studies, the dual-label strategy is also used in (first-in-human) clinical trials. Additionally, dual-labeled targeting agents have a relatively simple manufacturing procedure. Altogether this shows the high potential of preclinical and clinical multimodal imaging in drug development.
For the optimal use of dual labeled drugs with a radionuclide and a fluorophore, the labeled drug should be evaluated ex vivo in tissue samples. Therefore, it is important to select a patient population expresses the target of interest and undergoes surgery or biopsy during the standard treatment. With nuclear imaging prior to surgery visualization of the tracer uptake and distribution can take place.
Case study dual modality imaging approach.
A dual modality imaging approach was used in a preclinical study with a novel antibody that targets a prostate-specific protein. The study shows great potential for highly selective cancer treatment using novel techniques such as fluorescence-guided excision and photodynamic therapy in one setting.  Due to this theranostic application, dual-labeled agents have the potential to improve diagnosis, staging, treatment planning, therapeutic monitoring, and surgical guidance in a variety of diseases.
The monoclonal antibody Girentuximab, targeting carbonic anhydrase-IX (CA-IX), was conjugated with indium-111 (nuclear) and IRDye800CW (fluorophore) to improve the detection of renal cell carcinoma. Researchers showed that this combination allowed adequate surgical guidance in 15 patients . Preclinical research has shown that this concept has the potential to be used in a variety of tumor types, such as prostate cancer. 
The collected clinical data does not only give surgical information, but also provides biological and morphological information about the tracer distribution. This distribution data is highly relevant for the development of novel drugs and therapeutics.
The advantages of using a multimodal imaging approach in your clinical trial.
By using bimodal nuclear and fluorescent molecular imaging in drug development, the advantage is that you simultaneously obtain whole body drug distribution and accumulation, while tissue- and cell-specific information is provided in combination with ex vivo histopathological and immunohistochemistry data after surgical excision of the tissue of interest. This complementary information can provide more insight in the potential of a drug/treatment and therefore decision making.
The disadvantages of using a multimodal imaging approach in your clinical trial.
The major disadvantage of multimodal fluorescence and nuclear imaging is the timing. PET/CT or SPECT imaging should be performed one or two days prior to surgery to enable representative fluorescence imaging of the tissue specimens. This requires accurate planning of the imaging procedures with various specialist in clinical molecular imaging and (radio)chemists. Obviously, the use of multiple labels and imaging equipment will lead to increased costs of the clinical trial. Nevertheless, it generates more information/knowledge from the same clinical trial.
Multimodality imaging has become an upcoming scientific imaging approach, both preclinically and in first-in-human studies. The information gained from multiple imaging modalities in one single clinical trial allows for faster, more efficient, and relatively cheaper trials for drug development.
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