Understanding the Role Theranostics Plays in Treating Prostate Cancer

There’s a tremendous amount of excitement surrounding a new therapeutic option for patients with advanced prostate cancer, according to Dr. Phillip J. Koo.

Koo, the chief of diagnostic imaging at Banner MD Anderson Cancer Center in Phoenix, recently provided an overview of the field of theranostics during CURE®’s Educated Patient® Prostate Cancer Summit, which was held virtually on Sept. 26.

In an interview with CURE®, Koo defined theranostics, which involves using one radiopharmaceutical to diagnose a patient’s disease and a second radioactive drug to treat the cancer, discussed the potential of the strategy and assured patients about its safety.

CURE: What is theranostics?

Koo: Theranostics is a play on words. It combines the term therapy, or therapeutics, with diagnostics. And basically, what it's trying to represent is this idea of combining both diagnostics and therapeutics to help identify patients who might benefit from a treatment and then using that information directly to treat a patient with that specific therapy. And this is very relevant, because in prostate cancer, the protein prostate-specific membrane antigen (PSMA) is very specific for those prostate cancer cells (and can be targeted with theranostics).

How has the field developed over the years in terms of treating patients with prostate cancer?

This field of theranostics, and its use in prostate cancer, has been around for a while. It was initiated by a group in Germany that really advanced the field. And then it started to become much more prevalent in Europe.

And we've recently seen that Australia is taking the lead with regards to clinical development. Access has increased globally, to include South America as well.

In the United States, availability has been much more limited as it is not FDA approved. (Here), the main access has been through a clinical trial, the VISION trial, which is sponsored by Advanced Accelerator Applications, which is owned by Novartis. And that was the first opportunity to give access to patients in the U.S.

Does theranostics involve one specific therapy or a class of multiple therapies?

Currently, it's all being studied with a lutetium-177 labeled PSMA-617 molecule. Whether it's lutetium-177, or something like actinium, that really talks about the radioactive material that is being delivered to the cancer cells. So, for the time being, lutetium-177 is what everyone is really focusing on.

It's a radioactive material that emits a radiation particle that can kill the prostate cancer cells. The trial from Australia and the VISION trial are focused on lutetium-177-PSMA. And the great thing about that radioisotope is it can kill the prostate cancer cells and you can image patients with that, as well.

There are other trials currently in process that are looking at other radioisotopes such as thorium or actinium, as these isotopes may have higher energy, but there might be side effects that we need to learn about, as well. So, it really has to be studied very closely before it gets approval.

What is the potential of this treatment option?

I think there's a lot of excitement because many single-site trials have shown in some patients this amazing response on imaging, and amazing response with regards to their PSA (prostate-specific antigen) levels. Their PSA values might go from hundreds or thousands to even undetectable, or their imaging scans might go from seeing all these different metastases throughout the body, to then no longer seeing them.

Visually, it creates a lot of hope that something like this can really make a huge difference. And again, that's why we need to see the data to understand the outcomes and where the treatment best fits.

For the time being, the existing studies have looked at it in later-stage patients, patients who have metastatic castration-resistant disease and have received two to three lines of therapy already. And, there are patients who will respond, (but) there (also) might be some patients who don't.

And that's another question we need to figure out: How do we know who the patients who will respond are and who the patients who won't respond are? That's another important piece as well, because we do not want to have patients undergo this therapy and potentially suffer from any side effects if it's not going to benefit them.

How does this treatment differ from what’s currently available to treat patients with prostate cancer?

There are currently so many different therapies available, and in Dr. Alan Bryce's lecture that he gave during CURE®'s Educated Patient Summit, he talked about this era of warp-speed development in research and prostate cancer.

There are various mechanisms of action; so, various ways drugs are helping patients to perhaps live longer or live a better life. The great thing about theranostics is it's very different from the therapies we've had in the past for prostate cancer.

I like to group radiopharmaceuticals into one big bucket. And within that we've had radium-223. It's an alpha particle, a radiation particle that we inject into patients, that distributes throughout the body, goes to the bones and kills the prostate cancer cells. And it focuses just on the bones. Lu177-PSMA takes it a step further; it focuses on all of the prostate cancer cells themselves, wherever they might be (bones or soft tissues), because it's targeting PSMA. And to take it beyond that, we can pair that therapy with an imaging test.

We could do an imaging test in a patient, see where all the sites of disease are, give them that radiopharmaceutical, and then after we give it to them, we can image the patient and confirm that all those sites of disease that we saw on the diagnostic test are taking up the radiopharmaceutical. It provides this confirmation that adds a level of security and comfort in knowing that it's getting to where it needs to and hopefully will do what it needs to, as well to kill those prostate cancer cells. It's a completely new type of therapy that just gives us even more weapons to help someone who has metastatic prostate cancer fight their disease.

How do you see the field of theranostics developing over the next several years?

We're hoping that the data from the VISION trial gets presented in mid-2021. And if that data turns out to be positive, it clearly proves that it's good for patients. We're hoping that maybe it receives FDA approval soon after that, and then it could be distributed to patients perhaps in late 2021, or at some point in 2022.

That would be just the beginning. That is what allows for this drug to get FDA approval. But that's just only step one. There would need to be more trials, testing this in a variety of different disease states, testing it in combination with other drugs, testing it perhaps earlier in disease. Maybe testing it earlier when a patient is initially diagnosed with metastatic prostate cancer, and maybe they would benefit from this and you might be able to cure a patient. So, you could imagine that there are going to be even more questions that need to be answered. The potential applications of this could increase exponentially in the future, as well.

How does safety play a role in theranostics?

Radiation safety is a topic that I think oftentimes brings a lot of fear in patients, since theranostics involves radiation. And oftentimes, radiation sort of creates just some general fear in the patient population. I think what we've discovered with lutetium therapies that we're using for other diseases is that it is a very safe drug.

And in terms of restrictions for the patient, and people around them, it isn’t too restrictive. There are global and state level differences in how officials manage radiation exposure to the public.

There are some countries out there that will require patients to be admitted to the hospital to get this therapy, whereas other countries will have these patients discharged four to six hours after receiving the therapy. It's important just to follow the directions of the radiation safety officer and the physicians who are providing this therapy. Overall, it's a very safe and tolerable drug and the radiation exposure to family members is relatively low and can be controlled and not harmful to the public, if we follow the provided directions.

For more news on cancer updates, research and education, don’t forget to subscribe to CURE®’s newsletters here.