This new form of treatment for metastatic prostate cancer is being used in Europe, Australia and elsewhere, and being tested in clinical trials in the U.S.  As part of my series on PSMA-targeting, here’s more of the story:

We have talked a lot about the amazing results in some men with metastatic prostate cancer of PSMA-targeting radionuclides, being used in Europe, Australia, and elsewhere, but still in clinical trials here in the U.S.  Now, I’m all for moving drugs right along, damn the torpedoes, and giving anyone who wants to take the risk a chance to beat a terrible disease.  But there’s a good reason that the U.S. is taking this cautiously:  because some of these PSMA-targeting treatments – not all – can harm the salivary glands and tear ducts.  When these treatments become FDA-approved in this country, I believe the side effects will not be so severe.  Scientists like Neil Bander and Martin Pomper are developing agents that have much milder side effects.

The whole time I’ve been writing about PSMA, I have been thinking of Nathan (I changed his name to protect his privacy), a remarkable, tough and courageous man I interviewed in 2018.  He is one of the pioneer patients of PSMA-targeting treatment.  I want to tell you his story now.

On a dark day in 2013, Nathan was diagnosed at age 57, with stage 4 prostate cancer that had spread to his lymph nodes, his spine and hip.   His cancer was very aggressive: Gleason 9.  The prognosis was grim, and Nathan had a choice to make:  do what his initial urologist suggested, start on androgen deprivation therapy (ADT), hope it works for a long time and wait until the cancer gets worse, or go into “high-gear mode.”  He chose option B.  “If I have an aggressive cancer, I want to deal with it aggressively.”

So, in addition to starting on ADT and an androgen receptor blocker, abiraterone (Zytiga), plus prednisone – a combination that is now FDA-approved, but was about five years ahead of its time in 2013 – Nathan underwent a radical prostatectomy.  The surgery did not cure him, but eliminating the primary tumor dealt the cancer a severe blow and bought him more time.  “The plan all along was, kick the can down the road until science can catch up,” he says.  He assembled a team of doctors who had the same philosophy.

Next, Nathan got radiation:  high-intensity radiation to the spots of cancer in his spine, followed by 40 radiation treatments over two months to his pelvis and prostate bed.  Despite a change to a different androgen receptor blocker, enzalutamide (Xtandi), his cancer picked up steam.   Soon, his PSA was doubling every three weeks.  A PET scan showed new metastases, including a big one in his elbow.  In 2016, Nathan learned about the PSMA-targeted radionuclide treatment being done in Heidelberg, Germany.  He talked to his oncologist, who expressed concern about the side effects.  Nathan decided to go to Heidelberg.

The most worrisome side effect of this treatment was damage to the salivary gland.  As it turns out, PSMA doesn’t quite live up to its name; it is not entirely “prostate-specific.”  This molecule normally exists in small amounts in the salivary glands and a few other places of the body.  The drugs that target the PSMA-containing cancer cells don’t know the difference, and they can kill or damage these normal cells, too; there is also a risk of kidney toxicity.  “The salivary gland problem happens right away,” Nathan says.  “But the treatment also works right away.  They give you an infusion and the cancer cells are dying within hours.”

Despite the risks and the unknowns, Nathan wanted to go ahead – sooner, rather than later.  “I knew they had done this treatment on no more than 30 to 40 patients.  But I also didn’t want to get to a point where I was going to be in bad shape,” before the cancer burden grew bigger and began causing pain, “and then get the treatment.”

Before he could undergo the treatment in Germany, Nathan had to have a PSMA-PET scan.  “My body lit up like a Christmas tree with PSMA-PET: it showed cancer in my ribs, sternum, manubrium, scapulas, upper extremities, femur, and numerous places on my spine.”

Nathan weighed the risks of side effects against the possibility of getting a true remission of his cancer.  The hope of remission won.

What’s it like?  The treatment itself is given by infusion and only takes 10 minutes – and in 10 minutes, prostate cancer cells throughout Nathan’s body started to die.  Before and after his treatment, he drank “tremendous amounts of electrolyte fluids,” to minimize the risk of kidney damage:  “The more you drink, the more you can flush out the radioactive materials.” Nathan was given ice packs to put around his neck to help protect the salivary glands.  He was supposed to use them for six hours; he kept icing his neck for 12 hours, and also drank as much water as he could.  “I think in those two days, I drank between 10 and 12 liters of electrolyte water.

“This treatment was only approved by the German government on a humanitarian basis,” he notes, “basically, to treat people in extensive pain, who were far along in the disease, and who didn’t have much time to live.”  Nathan was the only man on the ward who was not taking morphine.  “One guy came in in a wheelchair, in bad shape.  He got discharged before me.  He walked out – didn’t use the wheelchair.  That’s how quickly it alleviated his pain and was killing the cancer cells.”  The man in the next room had an exceptional response, as well:  “He was from the Netherlands.  He told me he came in when his PSA was 964, got his first treatment, and his PSA went down to 11, then his second treatment was two months later, and his PSA was down to 3.5, and now he was there for his third treatment.”

Two weeks later, when Nathan went to see his oncologist back in New York, his PSA was undetectable.  A second treatment was scheduled.  “I was already experiencing significant salivary gland problems,” Nathan says, “and we thought he might reduce the dosage.”  However, he doesn’t know whether the dosage was reduced for the second round.

Going Off Enzalutamide

Enzalutamide may have helped make the treatment more effective:  some studies have suggested that enzalutamide enhances PSMA.  Otherwise, Nathan wasn’t sure how helpful it was.  Six months after his second treatment in Germany, he asked his doctor: “What do you think about me getting off enzalutamide, and staying on Lupron?  He said, ‘I don’t know if it ever really worked on you; it only lowered the PSA for a few weeks.’”  So Nathan tapered off, then stopped taking it altogether – which led him to another milestone:  “I said, ‘So, am I still castrate-resistant?”  His doctor told him, “’From a scientific standpoint, once you’re castrate-resistant, that’s it.  They don’t change that.’  But I don’t think they’ve ever come across a situation where people start dialing back their medicines.”

“Not for the Faint of Heart”

About a year after the treatment in Germany, Nathan got a PET scan.  “There was no evidence of cancer, which is great news,” he says.  However, “they said I had a compression fracture in my spine.”  Previously, when he had the high-dose radiation to his spine, he asked about side effects.  The radiation oncologist told him, “In rare cases, people can get compression fractures.  Don’t jump out of any planes.”  But back then, this was a new treatment, and there was no long-term follow-up.  To treat the fracture, he underwent a procedure called kyphoplasty, done by an interventional radiologist.  It involves a balloon – like angioplasty – that restores space in the collapsed vertebra, which then is filled in with glue and cement to restore the bone and relieve pain.

In 2018, Nathan got another PSMA-PET scan at Weill Cornell.  “Thankfully, I was PSMA negative.”  But Nathan cautions that the radionuclide treatment he received is “not for the faint of heart.”  The loss of salivary gland function “has not been pleasant.  It encompasses many things.  I can swallow, and I can taste, but I get a tremendous amount of dry mouth.”  A CT scan showed esophagitis – inflammation of his esophagus from lack of salivation, and thyroiditis.  “I have to constantly keep lubrication going.  It has gotten slightly better, and they told me it’s possible that if the treatment didn’t burn off all my salivary glands and there were some cells left, they could possibly regenerate, but it would take a long time.   I think I’ve gotten about 20 percent back over the two years.”  Nathan uses gels in his mouth every night.  “Otherwise, I wake up choking.”  He also uses prescription toothpaste and extra fluoride to protect the enamel on his teeth.

He is trying to limit scans that will subject his body to more radiation (MRI, for example, has no radiation; CT does).  “Over the last couple months, my creatine level (reflecting kidney function) has slowly increased.   It’s not out of the range of normal, but at the high end.  I’m conscious that these radioligand therapies can produce kidney damage.”

“It’s an amazing age we’re living in,” Nathan says.  “I’m happy to be here, grateful that I was able to kick the can long enough to have gotten this treatment.”  Whenever he sees his oncologist, the conversation ends with the doctor saying, “Grow old.”  And Nathan says:  “I plan to.”

Note:  If you are seeing this as a solo story, click here for more.

 

In addition to the book, I have written much more about prostate cancer on the Prostate Cancer Foundation’s website, pcf.org. The stories I’ve written are under the categories, “Understanding Prostate Cancer,” and “For Patients.”  As Patrick Walsh and I have said for years in our books, Knowledge is power: Saving your life may start with you going to the doctor, and knowing the right questions to ask. I hope all men will put prostate cancer on their radar. Get a baseline PSA blood test in your early 40s, and if you are of African descent, or if cancer and/or prostate cancer runs in your family, you need to be screened regularly for the disease. Many doctors don’t do this, so it’s up to you to ask for it.

 ©Janet Farrar Worthington

This new form of treatment for metastatic prostate cancer is being used in Europe, Australia and elsewhere, and being tested in clinical trials in the U.S.  As part of my series on PSMA-targeting, here’s more of the story:

With the dramatic results in some men, why aren’t radionuclides a done deal here in the U.S?  Because – just like the use of magic in fairy tales – they come with a price.

Neil Bander, M.D., Director of Urological Oncology Research at Weill Cornell and a pioneer in the study of PSMA (prostate-specific membrane antigen), developed an antibody that targets this molecule that sits on the surface of prostate cancer cells.  He later characterized PSMA, and found many reasons why it is an excellent way to target prostate cancer.  The alpha particle radioligands (using the small molecule delivery system) target the salivary glands, where a small amount of PSMA is made.  Beta particles such as Lu177, used in the Novartis compound, generally cause only minor salivary gland toxicity, Bander says.  But “since alpha particles are at least 1,000 times more potent than beta particles, when you put the alpha particle on the ligand, it targets the salivary glands and the tear glands, and they get destroyed.”

Now, you might be thinking, losing my salivary glands is a small price to pay for really knocking back and maybe even curing my prostate cancer.  But Bander would suggest that you think very carefully about this.  “When you destroy the salivary glands, the result is absence of saliva, inability to taste, difficulty swallowing, and tooth decay and loss.  Affected patients report that it’s a pretty miserable existence.  So that has proven to be a major impediment to using the small ligands to target the alpha particles.  Despite some amazing responses with the alpha particle, “it can be intolerable for the patient.”

So:  Is there any way to protect the salivary gland?  As it turns out, there is.  “While the small molecule ligand targets the salivary glands and lachrymal glands, antibodies do not,” says Bander.  “Antibodies are much larger molecules than the ligands.”  With the small ligands, the radioisotope “can easily pass through normal tissue barriers.  But when we deliver the radioisotope by use of the antibody, we see no targeting of the salivary or lachrymal glands.”

In fact, “we recently completed a trial at Weill Cornell using our J591 antibody to target the alpha particle, Ac225.  Based on an interim analysis, we have seen minor salivary gland toxicity in six of 27 patients, five of whom previously had been treated with the small ligand.  We found that the antibody-targeted alpha particle was well tolerated and very effective against the prostate cancer, even in patients who previously had progressed after treatment with the ligand Lu177.”  This Phase 1 trial was funded by the Prostate Cancer Foundation.

Another key difference between the antibody and ligand: “The ligand is excreted from the body through the kidney and bladder,” says Bander, and there is a risk of kidney toxicity.  “It has not yet been a significant problem, although there have been a few reports of kidney toxicity from the ligand with an alpha particle on it, and it may take a while to develop.  With the antibody, the path of excretion is through the liver, so the kidney is less likely to be subject to damage from the alpha particle.  The liver is pretty resistant to radiation.”

So… no to the ligands, then?  Not so fast, says Bander.  “Here at Cornell, we have data that suggests the best way to target prostate cancer is actually using a dual-targeted combination of the antibody and the ligand.  Our data show that with the combination, we can deliver a substantially higher dose to the tumor without increasing side effects.”  That’s because these agents each behave differently in the body.  “Dual targeting also allows us to use both the beta and the alpha emitters simultaneously, and our research shows this combination of alpha and beta isotopes to be very complementary.  Ultimately, the dual-targeting approach, with both antibody and small ligand, provides a substantial increase in the dose to the tumor without additive toxicity.  At Cornell, we are beginning to treat mCRPC patients with the ligand-Lu177 plus the antibody-Ac225.  Our laboratory data and our understanding of the biology of how these agents interact suggest a substantial benefit to this dual targeting/dual isotope approach.  The ability to substantially increase the dose to the tumor offers, I think, significant potential benefit for improved survival.”

This is what Bander envisioned 30 years ago, when he first began investigating PSMA.  And, he says, “it’s going to get a lot better.”   At the 2019 ASCO international oncology meeting, a session on PSMA “filled a 4,000-seat auditorium.  I was joking that a few years ago, we could have had that meeting in my hotel room and there would have been room for housekeeping!  It’s just like somebody flipped a switch.  Leveraging the ability to target PSMA for imaging and treatment is in the process of dramatically changing everything about how we approach prostate cancer – how patients are diagnosed, how they’re monitored, and how they’re treated.  If serial PSMA imaging can be shown to reflect tumor response, it has the potential to be used in the development of all prostate cancer drugs going forward to provide rapid insight into drug efficacy.  That will make new drug development in this disease much more rapid and efficient.  It’s a game-changer.  I’m confident that the best is yet to come.”

Note: If you are seeing this as a solo story, click here for more.

 

In addition to the book, I have written much more about prostate cancer on the Prostate Cancer Foundation’s website, pcf.org. The stories I’ve written are under the categories, “Understanding Prostate Cancer,” and “For Patients.”  As Patrick Walsh and I have said for years in our books, Knowledge is power: Saving your life may start with you going to the doctor, and knowing the right questions to ask. I hope all men will put prostate cancer on their radar. Get a baseline PSA blood test in your early 40s, and if you are of African descent, or if cancer and/or prostate cancer runs in your family, you need to be screened regularly for the disease. Many doctors don’t do this, so it’s up to you to ask for it.

 ©Janet Farrar Worthington

 

 

 

 

This new form of treatment for metastatic prostate cancer is being used in Europe, Australia and elsewhere, and being tested in clinical trials in the U.S.  As part of my series on PSMA-targeting, here’s more of the story:

As we have discussed here, Neil Bander, M.D., Director of Urological Oncology Research at Weill Cornell and a pioneer in the study of PSMA (prostate-specific membrane antigen), developed an antibody that targets this molecule that sits on the surface of prostate cancer cells.  He later characterized PSMA, and found many reasons why it is an excellent way to target prostate cancer.  Results from work by Bander and others generated worldwide interest – particularly in Germany.

Bander made an antibody that targets PSMA, and linked it to a radioisotope called lutetium 177 (Lu 177), a beta emitter.  With colleagues at Weill Cornell and “with a nod from the FDA,” in 2000, Bander began a series of prospectively designed clinical trials that showed “excellent targeting of metastatic prostate cancers wherever the disease was located in the body.  These treatments resulted in PSA d eclines and improvement of pain.”  At the time, however, he notes, the pharmaceutical industry was not interested in radioactive drugs, and the prostate cancer field was more focused on the development of Taxotere chemotherapy.

In Germany around 2013, physicians began using different agents that bind to PSMA: small molecules, called ligands, instead of antibodies.  Some of these had been developed in the U.S. by John Babich, Ph.D., (now at Weill-Cornell), and Martin Pomper, M.D., Ph.D., of Johns Hopkins.  The Germans tested Lu177 as well as a different radioisotope, actinium 225 (Ac225), “which is an alpha emitter,” says Bander.  “Ac225 is several thousand times more potent than Lu 177,” which, again, is a beta-emitting particle.  (I have to be honest here, I don’t fully understand alpha vs. beta particles, but this article might help those who are motivated understand more.)

In Germany, a “compassionate use” program is often used to allow the use of new, previously untested therapies in patients who don’t have much other hope.  This means that, for a patient with a serious illness who has no other medical options and who agrees to take the risk, doctors can try promising – but unproven – treatments outside of a formally designed clinical trial.  “So in Germany, they were able to give these radiolabeled ligands (small-molecule radionuclides) to patients on an ad hoc basis, not as part of a formally designed and specified treatment protocol.  A number of centers in Germany started to make their own radiolabeled ligands.  They started treating patients and started publishing the results, sometimes on just one or two patients, sometimes on small groups, sometimes on large retrospective series of patients,” in various nuclear medicine journals.

“The other thing they did,” Bander continues, “was, they would only treat patients whose cancers showed up well on PSMA-PET scans.  They selected their patients, which helped them achieve high response rates.”  Notably, a report of two patients treated with a PSMA-Ac225 ligand showed spectacular results.  “To say they were dramatic would be an understatement.  These two patients had already had their cancer progress despite treatment of every kind of therapy then available for prostate cancer.   Everyone was blown away by those two cases.”  The “before and after” images showed that widely metastatic cancer had melted away from the pelvis, ribs, spine, liver and brain.  PSAs that were in the hundreds in one man, and thousands in the other, became undetectable.

Those ligands became readily available in Germany, Austria, Australia, India, South Africa, and “other countries that have more liberal regulatory policies than the U.S.,” Bander says.  “It was just an onslaught of publications, all showing excellent results.  That’s what really flipped the switch and got Big Pharma interested; among them, Novartis and Bayer.”

At the June 2021 meeting of the American Society of Clinical Oncology (ASCO), results from the Phase 3 trial of LuPSMA (Lu177), run by Novartis, confirmed a significant delay in tumor progression and improved survival in men with metastatic castrate-resistant prostate cancer.

Note:  If you are seeing this as a solo story, click here for more.

 

In addition to the book, I have written much more about prostate cancer on the Prostate Cancer Foundation’s website, pcf.org. The stories I’ve written are under the categories, “Understanding Prostate Cancer,” and “For Patients.”  As Patrick Walsh and I have said for years in our books, Knowledge is power: Saving your life may start with you going to the doctor, and knowing the right questions to ask. I hope all men will put prostate cancer on their radar. Get a baseline PSA blood test in your early 40s, and if you are of African descent, or if cancer and/or prostate cancer runs in your family, you need to be screened regularly for the disease. Many doctors don’t do this, so it’s up to you to ask for it.

 ©Janet Farrar Worthington

 

 

 

This new form of treatment for metastatic prostate cancer is being used in Europe, Australia and elsewhere, and being tested in clinical trials in the U.S.  As part of my series on PSMA-targeting, here’s more of the story:

Neil Bander, M.D., Director of Urological Oncology Research at Weill Cornell and a pioneer in the study of PSMA, saw the potential of targeting PSMA, a molecule that sits on the surface of prostate cancer cells, soon after it was discovered more than 30 years ago.  His research shed light on why PSMA was such a promising target, and in 2000 his team began clinical trials with J591, a PSMA-targeting antibody he made.

“We were interested in two different approaches,” Bander says.  “One was putting a radioactive isotope on the antibody” – a molecular grenade of cancer-killing radiation – “and the other was putting a drug on the antibody.”  This “antibody-drug conjugate” approach was very new; fewer than a handful of drugs were available to attach to antibodies, “and all of them were owned by drug companies.  We didn’t have ready access to those,” so instead, Bander’s team focused on linking a “radioactive payload” to the antibody.

 The other benefit of using a radioactive isotope as a weapon:  it could be seen on imaging!  “Because of the radioactivity, we could see where this antibody-isotope was actually going,” says Bander.

Think of an old movie, where as a B-52 plane travels, it’s superimposed on a map, and an arrow connects Point A – California, let’s say – to Point B – Guam on our plane’s journey – and all points in between.  Bander didn’t have an arrow, but he could plot the progress of the radioactive isotope just the same.  “We could see immediately that the antibody was going right to the tumor cells.  Wherever we saw tumor sites – on the patient’s bone scan, CT scan, or MRI – we could see those sites lighting up after we gave the radioactive antibody.  So right from day one, we knew we were hitting the target!  We knew we were actually delivering the radioactivity to the tumor sites.”

But Bander and colleagues noticed something odd:  the radioactive isotope was also going to other sites where there was no apparent cancer.  They soon realized what was happening:  the PSMA-targeting isotope was finding cancer that was too small to show up on conventional imaging!  “We knew very early on that this could potentially be a very potent imaging modality.”

The Phase One trials were for men with metastatic castrate-resistant prostate cancer (CRPC).  These were men whose cancer had progressed despite all the standard treatments of the day.  In about 10 to 20 percent of participants, “we did not see their tumors light up.”  Is this because their tumors somehow don’t make PSMA?  Bander doesn’t think so.  (Note: Martin Pomper of Johns Hopkins does, and is working on ways to target those non-PSMA-making cells.)  “If you remove prostate cancer, say in surgery or biopsy, and do a test to see if there’s PSMA – and this has been done in many thousands of patients – almost 95 percent are PSMA-positive.”  Nonetheless, in some men, the PSMA-targeting agent does not show up much on imaging.  “In our studies, we found about 15 percent did not image, and another 5 to 10 percent imaged weakly, but we treated all those patients anyway.  We found that if you are PSMA-negative or PSMA-weak, you are significantly less likely to have a good response to the treatment.”  However:  “If your imaging study lit up like a neon sign, you had a very high likelihood of responding.  It was a pretty clear distinction.”

Bander’s group tested two different isotopes and found that lutetium 177 (Lu 177) was the most effective.  “Responses varied, from no response to PSA stabilization to 95-percent decreases in PSA levels that could last many months,” says Bander.  “We also saw that as we increased the dose, the responses got better.”  Other centers reported success in some animal tumor models with breaking up the dose of radiation.  “Instead of giving just one big dose, if you split it up into two or more smaller doses, you could deliver an even higher cumulative dose.  So we did a phase 1 study of fractionated J591-Lu 177, gave higher doses and got better and more durable responses.”

This was 2007.  Why hasn’t this become mainstream therapy?  One big reason:  the pharmaceutical industry is like a freight train.  Once it gets going on a particular track, it picks up steam and generates huge momentum.  Until that happens, however, momentum can be very slow.  Twenty years ago, Bander says, “pharmaceutical companies had no interest in radiopharmaceuticals.”  Instead, their model was for literal shelf life: drugs put into a tablet or capsule and shipped to sit either at a pharmacy or in a patient’s medicine cabinet.  “Making drugs from living cells was a whole new area,” but the industry has evolved to “this greater willingness to make very complicated products.”

PSMA-targeting radioisotopes have reached a crucial tipping point, says Bander.  “When we characterized PSMA – its specificity for prostate cancer, the fact that 95 percent of prostate cancers were PSMA-positive, that cancer internalizes the PSMA-targeting antibody, that it’s upregulated by hormonal therapy, and that it’s a potential target in other types of tumors – interest started to build.  Then when we showed that if we administered a PSMA-targeting agent, we could actually validate in a patient that it was reaching the cancer, it increased even more.”

A big kick in the pants to the world of PSMA-targeting treatment came from striking results achieved overseas, discussed here.

Note: This is one of a series of stories I’ve just written on PSMA-targeting.  If you are seeing this as a solo story, click here for more.

 

In addition to the book, I have written much more about prostate cancer on the Prostate Cancer Foundation’s website, pcf.org. The stories I’ve written are under the categories, “Understanding Prostate Cancer,” and “For Patients.”  As Patrick Walsh and I have said for years in our books, Knowledge is power: Saving your life may start with you going to the doctor, and knowing the right questions to ask. I hope all men will put prostate cancer on their radar. Get a baseline PSA blood test in your early 40s, and if you are of African descent, or if cancer and/or prostate cancer runs in your family, you need to be screened regularly for the disease. Many doctors don’t do this, so it’s up to you to ask for it.

 ©Janet Farrar Worthington

 

 

 

 

There’s some bright hope on the horizon for men with metastatic prostate cancer:  it’s PSMA-targeting therapy. This is different from PSMA-targeted imaging, which shows where small bits of prostate cancer are hiding in the body.  But it uses the very same building blocks.  Think of molecular LEGOS:  Instead of attaching the tracer molecule that can “see” prostate cancer, a different isotope (chemical brick), called a radionuclide, can be attached: one that can kill cancer.

PSMA stands for prostate-specific membrane antigen (PSMA), a protein that sits on the surface of 95 percent of prostate cancer cells.  Briefly, to recap the PSMA story so far, we have talked about how PSMA-targeting came to be, covered the first PSMA-imaging agent to get limited FDA approval, and the second imaging agent, which will be used more widely.  Now it’s time to talk about radionuclides.

“With the same chemical scaffold serving as both a diagnostic and therapeutic agent, the field of ‘theranostics’ has recently gained traction,” Martin G. Pomper, M.D, Ph.D., Director of Nuclear Medicine and Molecular Imaging at Johns Hopkins, told me in a recent interview.  Pomper’s team developed the small molecule PSMA tracer that is now the FDA-approved agent, PYLARIFY.  “Recent advances have really lit this form of treatment on fire.”

In Europe and Australia, and in international clinical trials, PSMA-targeting radionuclides such as 177Lu-PSMA-617 (called lutetium-177-PSMA-617, or LuPSMA), are being used to kill metastatic prostate cancer.  “In Australia, 177Lu-PSMA-617  proved superior to cabazitaxel in terms of PSA response and lack of significant adverse effects when compared head-to-head in the TheraP trial,” says Pomper.  “We are working with Novartis on a similar agent, called 177Lu-PSMA-R2, which has even fewer side effects, including lack of uptake in salivary and lachrymal glands.  We are hoping that agents using this molecular scaffold will be able to be outfitted with a variety of even more potent radionuclides than 177Lu.  It is anticipated that 177Lu-PSMA-617 will be FDA-approved at the end of this calendar year.”

In the international Phase 3 VISION trial, reported in June 2021, 831 men with PSMA-positive cancer (cancer that shows up on PSMA-PET) were randomly assigned either to receive LuPSMA plus standard of care, or standard of care alone.  Men who received LuPSMA were about 40 percent less likely to die and 60 percent less likely to have disease progression on scans, compared to the men who received standard of care alone.  After 21 months, cancer progression was delayed for longer: 8.7 months vs. 3.4 months among controls, and men in the LuPSMA group had better median overall survival: 15.3 months compared to 11.3 months in the control group.  Side effects of LuPSMA included fatigue, bone marrow suppression, dry mouth, and nausea/vomiting.

Note:  The TheraP trial compared LuPSMA to chemotherapy (cabazitaxel), but the VISION study did not include chemotherapy, immunotherapy, or other therapies that oncologists would otherwise try.  Oncologists will tell you that  any one therapy may not ever become the magic weapon for beating metastatic prostate cancer – but along with other weapons, PSMA-targeting radionuclides will be part of a pretty impressive arsenal.  Also, as LuPSMA and similar agents get FDA approval, you can bet that doctors will start giving them to patients at earlier stages, when cancer is more vulnerable and easier to kill, and that’s going to boost survival, too.

You might also be wondering about the cancer cells that don’t make PSMA.  New methods of treating them are on the horizon, too.  Pomper is developing new molecules and therapies to target “PSMA-invisible” forms of prostate cancer.  “We are working on agents that work through different mechanisms and can complement the PSMA-targeted agents,” he says.  “I believe that combining theranostics with immunotherapy, PARP inhibitors and other emerging agents – in addition to further optimization of dosage, dose rate and type of isotope of the PSMA-targeting agents – will be able to stave off progression of the disease for years, and that these patients will eventually succumb to ailments other than their prostate cancer.”  In other words, that one day, maybe not too far away, these new forms of therapy will allow men to die with, and not of, prostate cancer.

There are even wider implications, too:  “It took a long time, but now we’re seeing many exciting offshoots of our work in other forms of cancer, as well.  Some pretty amazing things are happening.”

We’re not done here.  I’ve got a lot more on PSMA-targeting therapy.  I want to put it in context, and also break it up into reasonably-sized chunks.  So bear with me: I’m doing this as a series, but to get it to you ASAP, I will post it all at once. Note:  If you are seeing this as a solo story, click here for more.

 

In addition to the book, I have written much more about prostate cancer on the Prostate Cancer Foundation’s website, pcf.org. The stories I’ve written are under the categories, “Understanding Prostate Cancer,” and “For Patients.”  As Patrick Walsh and I have said for years in our books, Knowledge is power: Saving your life may start with you going to the doctor, and knowing the right questions to ask. I hope all men will put prostate cancer on their radar. Get a baseline PSA blood test in your early 40s, and if you are of African descent, or if cancer and/or prostate cancer runs in your family, you need to be screened regularly for the disease. Many doctors don’t do this, so it’s up to you to ask for it.

 ©Janet Farrar Worthington

 

 

Imagine looking at a very young Ian McKellen, the knighted British actor, and thinking, “Half a century from now, if they ever film the Lord of the Rings trilogy, he could be the best Gandalf ever!”

That kind of vision is rare – but scientist Neil Bander, M.D., has it.  Nearly three decades ago, Bander, now Director of Urological Oncology Research at Weill Cornell, saw the potential of a newly discovered molecule called PSMA to be used in two ways:  for imaging and also for precisely targeted treatment of prostate cancer.  Over the last few years, both aspects of his vision have been coming true – in clinical trials and newly in practice in the U.S., and in practice in Europe, Australia, South Africa and elsewhere – for a growing number of men with prostate cancer.

You’re going to be hearing a lot more about PSMA, a protein that sits on the surface of 95 percent of prostate cancer cells, and about strategies for targeting it.  One of the most promising tactics involves an antibody developed by Bander and colleagues, and it is no exaggeration to say that without funding from the Prostate Cancer Foundation (PCF, which has invested $28 million into PSMA-targeting research over the last nearly 30 years), the antibody wouldn’t be nearly as far along as it is today.   Briefly, here’s how it came to be:

The late 1980s-early 1990s saw the dawn of monoclonal antibodies, lab-developed clones of B cells that make antibodies designed to zero in on one specific target, like molecular homing pigeons.  Scientists studying cancer were using this technology like gangbusters, “trying to find tumor-specific antigens on cancer cells that could be a way to distinguish cancer cells from normal cells at the molecular level,” says Bander.  (An antigen is a foreign substance, like a toxin, bacteria, or cancer; when the body detects it, the immune system makes a very specific antibody to identify and kill this intruder.)  The hope, if they could find a way to target just cancer, and not normal cells, was to develop more precise treatment – unlike systemic chemotherapy, which takes a toll on the rest of the body.

In 1987, a urologist named Gerald Murphy, who directed the Roswell Park Memorial Institute for cancer research and treatment – and who developed the original PSA test –made a monoclonal antibody, called 7E-11. “Not much happened with that antibody until 1993, when a group at Memorial Sloan Kettering Cancer Center, headed by Skip Heston, used Murphy’s antibody as a way to clone the gene for the antigen that was detected by the antibody,” says Bander.  “When they cloned the gene, their analysis indicated that it was very specific for prostate cancer.  They also found it was actually present in the cell membrane of prostate cancer cells,” and called it PSMA, for prostate-specific membrane antigen.

Soon afterward, Bander received PCF funding to develop antibodies that were specific to prostate cancer cells.  He studied 7E-11, and realized that “if you were looking to target PSMA, this antibody had a significant flaw:  it binds to a part of the PSMA protein that is inside the cell membrane, a site that antibodies can’t readily reach.  In fact, the 7E-11 antibody could only bind to dead prostate cancer cells.   But fortunately, PSMA spans the cell membrane; a short region of it is inside the cell, another region traverses the membrane, and the largest part of the molecule is outside the cell.  Because the antibody is administered through the bloodstream, he notes, “the only thing it sees is what’s on the outside of the cell.  We set out to make a series of antibodies to the part of the molecule that’s on the outside.  A few other groups, including Skip Heston’s group, also set out to do the same thing.  We happened to get there first.”

In 1997, Bander and colleagues published in Cancer Research their development of four antibodies, the first antibodies that could stick to the part of PSMA on the outside of the cell, and the first antibodies that could attach to living prostate cancer cells.  Their most promising antibody was called J591.  Over the next few years, “we did a pretty thorough analysis of these antibodies – where they bound on PSMA and how specific they were for prostate cancer cells vs. normal tissues.”  Then, “because our goal from the outset was to develop this into a therapeutic,” they “humanized” it, genetically re-engineering it from a mouse-derived antibody into a sequence that the human body would not see as a foreign protein.

Bander and colleagues also spent years “really trying to understand more about PSMA, how good a target it was.  They learned that PSMA was very highly overexpressed in cancer; that although normal prostate cells are PSMA-positive, prostate cancer cells are PSMA-loaded.  “We also found that as prostate cancer cells get more aggressive and are more likely to kill a patient, they have more and more PSMA on them.  The more dangerous the prostate cancer is, generally speaking, the more PSMA there is.”

And, they found, the amount of PSMA on the cell surface is affected by male hormones (androgens).  In fact, “when you put a patient on hormonal therapy (androgen deprivation therapy, ADT) you actually upregulate the amount of PSMA on the cell surface by five- to ten-fold.”  The result is “enormous amounts of PSMA sitting on the surface of prostate cancer cells.”  So in effect, ADT, the mainstay of treatment for advanced prostate cancer, makes the bullseye on the cancer cell bigger:  on a tiny scale, from the size of a golf ball to that of a three-foot-wide crater!

But wait!  There’s more!  Bander’s team looked at other types of cancers, and found that the blood supply in almost every other type of solid tumor was PSMA-positive!   For example, a kidney tumor itself does not make PSMA – but its blood supply sure does.  In fact, “the blood supply is pretty strongly PSMA-positive.  We were surprised by this,” but the finding was independently noted by the Heston group.  “We did not and still do not understand why that is the case, but this means a PSMA-targeted drug is potentially useful not just in prostate cancer, but in other types of cancer, where the approach could be to basically eliminate the blood supply to the tumor.  We’ve done some clinical trials to show that this is a real possibility.”

One more early finding, something “we didn’t anticipate,” says Bander:  “When you bind the antibody to PSMA on a living prostate cancer cell, that cell swallows the PSMA and whatever’s attached to it!”  Like a fish gulping a fat worm with a hook, the cancer cell takes in the PSMA antibody and the cancer-killing payload.  This discovery, he continues, “opened up the door to develop antibody drug conjugates: you put a very potent drug on the antibody, direct it specifically to the prostate cancer cells, and the prostate cancer cell swallows up the drug, whereas PSMA-negative cells don’t.  This was, in effect, a door opening to developing chemotherapeutic agents that are only taken up by the cancer cells.”

The door keeps opening wider.  “If you look at PubMed today,” says medical oncologist and molecular biologist Jonathan Simons, M.D., CEO of PCF, “there are now 3,707 research papers on PSMA discoveries.  That’s a paradigm-changing impact.”

Coming up soon: we’ve talked all around the subject of killing prostate cancer by targeting PSMA.  Now how, exactly, does that work?

In addition to the book, I have written about this story and much more about prostate cancer on the Prostate Cancer Foundation’s website, pcf.org. The stories I’ve written are under the categories, “Understanding Prostate Cancer,” and “For Patients.”  As Patrick Walsh and I have said for years in our books, Knowledge is power: Saving your life may start with you going to the doctor, and knowing the right questions to ask. I hope all men will put prostate cancer on their radar. Get a baseline PSA blood test in your early 40s, and if you are of African descent, or if cancer and/or prostate cancer runs in your family, you need to be screened regularly for the disease. Many doctors don’t do this, so it’s up to you to ask for it.

 ©Janet Farrar Worthington

Maybe you’ve been diagnosed with high-risk prostate cancer.   Maybe you have already been treated for prostate cancer, but your PSA is starting to creep back up, which means that the treatment didn’t get all of the cancer – but maybe it’s just right there in the prostate area, easily targetable with radiation.  Or maybe it’s just in one lymph node, or it’s in a transition state called oligometastasis: not widespread, but in just a few isolated spots outside the prostate.  In other words, maybe the cancer can still be cured – if you can just find it.

This is a problem nobody wants, but the good news is that there’s never been a better time to have it:  because now your doctor has a way to see exactly where the cancer is. 

It’s called PSMA-PET imaging, and it works kind of like a heat-seeking missile.  A radioactive tracer that lights up in a PET scan is molecularly engineered to find one very specific target:  PSMA (prostate-specific membrane antigen), a protein that lives in high concentrations on the surface of most prostate cancer cells.  Because the tracer is injected systemically, it can shine a virtual spotlight on whatever it tags – even tiny bits of prostate cancer as small as a grain of rice – anywhere in the body.  Several of these tracers have been studied, and one, called 68Ga-PSMA-11was recently FDA-approved for limited use at two hospitals in California: USLA and UCSF.  Another agent called 18F-DCFPyL (PyL, trade name  PYLARIFY®), developed at Johns Hopkins by a team led by Martin G. Pomper, M.D., Ph.D., Director of Nuclear Medicine and Molecular Imaging, is the latest to receive FDA approval and will be more widely available.

Pyl has proven itself in two important clinical trials:  CONDOR, published in Clinical Cancer Research, and OSPREY; published in the Journal of Urology.  In the OSPREY trial, PyL PET/CT was tested in two groups of patients: men just diagnosed with high-risk, locally advanced prostate cancer who were set to undergo radical prostatectomy with pelvic lymphadenectomy, and men with metastatic or recurrent cancer.  In the first group, the ability of PyL to detect metastases in the pelvic lymph nodes or beyond was determined, and in the second group, PyL was used to detect distant metastases.

In the CONDOR study, men with a rising PSA after treatment for prostate cancer with surgery, radiation, or cryotherapy, who had no visible cancer on standard imaging were scanned with PyL PET/CT, which accomplished what researchers hoped it would: “PyL successfully localized sites of disease in 85 percent of men with biochemical recurrence,” says Pomper, “even men with low PSA levels.  It detected disease in most men with biochemical recurrence presenting with negative or equivocal conventional (bone scan plus CT) imaging, and led to changes in management in the majority of patients.”

For many doctors and patients, this new FDA approval of PyL can’t come soon enough, says Pomper.  “I’ve had patients for years asking me when we are going to be able to use this.  It’s proven very difficult, and taken a long time, but we are finally there.”

In 1996, Pomper was the first to figure out how to engineer a small-molecule, harmless radioactive tracer to PSMA, and his team went on to test the first PSMA-targeted PET agent in a clinical trial.  This he refined into PyL, a more sensitive and specific second-generation agent that provides sharper images.  “With standard imaging (bone scans and CT), we may suspect there is cancer outside the prostate area, but we often just can’t see it in its earliest stages.  Standard imaging is not good enough for detecting and characterizing disease in men with biochemically recurrent prostate cancer, particularly in men with a low PSA (less than 2).  But 95 percent of prostate cancer has PSMA.”  And as Johns Hopkins radiation oncologist Phuoc Tran, M.D., Ph.D., and others are showing in clinical trials of oligometastasis, very small, isolated bits of prostate cancer are now being considered treatable – and possibly curable – targets.  

How is PyL different from 68Ga-PSMA-11?  Both are very good.  PyL may provide clearer images, but the main difference is that 68Ga-PSMA-11 requires special equipment to make, has a short half-life, and must made in small batches on site in the hospital.  18F-DCFPyL has a longer half-life, and can be made in a factory and shipped to any medical center able to perform PET imaging, so it will be widely available.  Although this is a radioactive compound, it is well-tolerated, says Pomper.  “It has no pharmacological effect, it’s given in trace doses.  It just binds to PSMA and goes away; it doesn’t do anything else to your body.”

PSMA-Targeting Can Kill Cancer, Too!

But wait!  This is not all that PSMA-targeting can do!  Think of molecular LEGOS:  Instead of attaching the tracer molecule that can “see” prostate cancer, a different chemical brick can be attached that can kill cancer.  In Europe and Australia, and in international clinical trials, PSMA-targeting radionuclides, such as 177Lu-PSMA-617, are being used to target and kill cancer in just those tiny outposts, leaving nearby cells undamaged.  This is killing prostate cancer cells at the level of hand-to-hand combat, and it is a bright spot on the horizon as a treatment option for men with metastatic prostate cancer. 

What about the cancer cells that don’t make PSMA?  This, too, is on the horizon, but Pomper is developing new molecules and therapies to target “PSMA-invisible” forms of prostate cancer.  “It took a long time, but now we’re seeing many exciting offshoots of our work in other forms of cancer, as well.  Some pretty amazing things are happening.”

In addition to the book, I have written about this story and much more about prostate cancer on the Prostate Cancer Foundation’s website, pcf.org. The stories I’ve written are under the categories, “Understanding Prostate Cancer,” and “For Patients.”  As Patrick Walsh and I have said for years in our books, Knowledge is power: Saving your life may start with you going to the doctor, and knowing the right questions to ask. I hope all men will put prostate cancer on their radar. Get a baseline PSA blood test in your early 40s, and if you are of African descent, or if cancer and/or prostate cancer runs in your family, you need to be screened regularly for the disease. Many doctors don’t do this, so it’s up to you to ask for it.

 ©Janet Farrar Worthington