What's my name?

As a boxing fan, I am reminded of the famous line from Muhammad Ali: “What’s my name?”. It was a moment that transcended sport. It was dramatic, theatrical, impossible to forget, and incredibly significant for a host of reasons. That moment meant many things to many people, and the point about names was probably the least important of them. Still, it offers a simple reminder:

Names matter.

Like any good modality in pharmaceutical development, radiopharmaceuticals have a long list of terms used to describe the various forms of the drugs we make and the treatments we develop. So, while this is not unique to radiopharmaceuticals, if this modality does not own the championship for number of names, it is certainly coming for the belt.

Taking it from the top

There are terms used to describe the program that includes both the imaging and therapy components together. A short list includes:

• Radiopharmaceutical pair

• Radioligand pair

• Theragnostic pair

• Theranostic pair

• Diagnostic–therapeutic pair

• Imaging–therapy pair

These terms have been used in everything from technical presentations to investor pitch decks to regulatory filings. They are generally regarded as interchangeable, but if you dig into them, there is some nuance.

“g” or no “g”?

A theranostic pair describes two related molecules: one used for imaging and one used for therapy, typically using the same targeting molecule but different isotopes.

A theragnostic pair is often used to describe the same concept, but sometimes implies a targeting molecule is used for therapy and a different targeting molecule for imaging.

While there are subtle differences among these terms, using any of them will usually communicate the general concept. Pick a term, be consistent, and you will not go too far wrong. If there is an exception to that rule, it would be the word “diagnostic”—more on that below.

Individual radiopharmaceuticals

Next are the terms used for the individual compounds. To keep the list manageable we will limit the examples to antibody-based programs. A short list for antibodies includes:

• RIC: radioimmunoconjugate

• RIT: radioimmunotherapy

• ARC: antibody radioconjugate

• AIC: antibody isotope conjugate

• RAC: radiopharmaceutical antibody conjugate

• ANC: antibody radionuclide conjugate

All the same.

It could be argued that RIT describes the treatment rather than the drug, but do the various names really matter for antibodies? Not much. Pick a term, and be consistent.

The imaging radiopharmaceutical

If there were to be any real concerns raised about the meaning behind the terms that are selected, they would likely be here. A short list includes:

• Imaging agent

• Diagnostic agent

• Radiotracer

• Tracer

• PET tracer

• SPECT tracer

• Molecular imaging agent

• Companion diagnostic

• Imaging companion

• Diagnostic radiopharmaceutical

Diagnostic carries specific meaning. It is defined as “an article intended for use in the diagnosis or monitoring…...” In most, but not all, therapeutic radiopharmaceutical development programs, the imaging radiopharmaceutical is used to support dosimetry and as a patient selection tool. In early human studies, it is not being developed to diagnose or monitor disease. Is there room for robust discussion on the similarities and differences between the terms imaging and diagnostic? Absolutely.

Names matter.

But you are not going to find that discussion here. The term imaging is general enough that it does not misrepresent what the compound is, whereas diagnostic may, depending on the context and the people involved, carry meaning that was not intended. Unlike most of the terms in this space—which can be used interchangeably (but best to select one and be consistent)—these are terms that are often best kept separate.

I will leave you with a question. For your

• RLT: radioligand therapy

• TRT: targeted radiotherapy

• MRT: molecular radiotherapy

• RPT: radiopharmaceutical therapy

• TRNT: targeted radionuclide therapy

What’s your name?