This blog discusses radiohybrids, theranostics and radioisotope theranostic pairs, which are the concepts in nuclear medicine focused on combining diagnostic imaging and therapeutic treatment using radioactive materials.
POSLUMA (flotufolastat F 18) injection (Bracco, Blue Earth Diagnostics), approved as a prostate cancer specific PET imaging agent by FDA in May 2023, is an example of a radiohybrid drug product.
The active ingredient of POSLUMA is flotufolastat F 18 gallium. The molecular structure of Posluma includes a covalently bound F18 radioisotope and a nonradioactive Gallium as DOTA complexed Ga+3.
If DOTA chelator includes radioisotopes e.g. 68Ga3+ or 177Lu3+, such compounds would be examples of radiohybrids. E.g., Posluma molecule containing nonradioactive fluorine and 68Ga3+ radioisotope, a β+ emitter, the product would function as a PET imaging agent. A schematic of a hybride molecule is shown below:
In the above example, if along with nonradioactive fluorine, 177Lu3+ is chelated instead of 68Ga3+, this product would be a radiotherapeutic for prostate cancer owing to β– emission of Lu177. A molecule which could act either as an imaging agent or a radiotherapeutic, depending on the type of the radioisotope chosen, would be an example of a theranostic compound.
On theranostic pairs, let us consider Pb-203 and Pb-212: This is a promising theranostic pair in nuclear medicine, where Pb-203, a γ emitter, functions as a SPECT imaging agent, and Pb-212, an α emitter, functions as a radiotherapeutic. This pair is advantageous because both isotopes are chemically identical, allowing for matched imaging and therapy, ensuring precision delivery of radiotherapeutic to the imaged lesions. Some oncology clinical trials of this theranostic pair are in progress.
