Two main types of radiopharmaceutical treatments can be distinguished, each with specific indications and modes of action.
1. PSMA-targeting agents
These treatments use a targeting molecule, called a ligand, which specifically binds to a protein found on the surface of cancer cells: PSMA (prostate-specific membrane antigen). This protein is highly expressed on prostate cancer cells, particularly when the cancer has metastasized.
The drug acts like a key that finds the “lock” on the diseased cells expressing PSMA.
Once bound, the drug delivers a radioactive isotope that emits a highly targeted dose of radiation to destroy the cancer cells from within, while sparing healthy tissue.
If a patient’s cells have enough PSMA receptors, they may be eligible for this type of treatment, which increases the likelihood of effectiveness.
Examples of radioactive isotopes:
- Lutetium-177-PSMA (Lu-177-PSMA-617 / Pluvicto®)
Used for men with metastatic castration-resistant prostate cancer after hormone therapy and chemotherapy have failed. It is administered via slow intravenous infusion under medical supervision.
Each dose is custom-made for the patient. Because the radioactivity decreases quickly, the drug must be administered within five days of production, requiring precise coordination between medical, pharmacy, and nuclear medicine teams.
- Actinium-225-PSMA (Ac-225-PSMA-617)
Still under development, this experimental treatment emits ultra-precise alpha particles that directly target PSMA-expressing cells. It is currently being tested in clinical trials in Canada and worldwide.
These approaches represent a breakthrough in nuclear oncology.
How radioactive isotopes work
A radioligand combines:
- a targeting molecule that recognizes the PSMA protein
- a radioactive isotope that emits targeted radiation to destroy cancer cells
It is often compared to a guided missile that delivers its payload directly to the target.
2. Bone-targeting agents
Bone metastases are common in advanced prostate cancer. These agents localize in areas of the bone with the highest cancer activity.
Example:
-
Radium-223 (Xofigo®)
This drug is used to specifically target bone metastases in prostate cancer. Because of its chemical similarity to calcium, radium is naturally attracted to cancer-affected bone regions. Once deposited, radium emits powerful radiation that kills cancer cells in bone metastases while preserving healthy bone.
This treatment may be offered to men with metastatic castration-resistant prostate cancer who have painful bone metastases but no liver or lung metastases.
How bone-targeting agents work
Radium-223 mimics calcium and binds to areas of bone affected by cancer.
It then emits short-range alpha radiation, which:
- slows disease progression
- relieves bone pain
- improves quality of life
Who are these treatments for?
Radiopharmaceutical treatments are intended for men with metastatic castration-resistant prostate cancer when standard treatments are no longer effective and depending on the type of metastases:
- Lutetium-177-PSMA (Pluvicto®): for patients whose cancer cells express PSMA and who no longer respond to hormone therapy or chemotherapy.
- Radium-223 (Xofigo®): for patients with painful bone metastases who no longer respond to hormone therapy.
These treatments require specialized facilities and are only available in certain authorized hospitals.
Note: Indications and usage of radiopharmaceutical treatments may vary by country.
