Actinium-225 Theranostics for Advanced Prostate Cancer:

 A Patient's Guide to the State of the Science

An IPCSG patient-education feature — April 2026

BLUF (Bottom Line Up Front): 

Actinium-225 (Ac-225) PSMA-targeted alpha therapy is producing some of the most striking PSA response numbers ever seen in heavily pretreated mCRPC — about 65% of men achieve a PSA50 response across pooled studies, a figure that exceeds what beta-emitting Lu-177 PSMA delivers in the same setting. It is showing meaningful activity even in men who have already progressed through Pluvicto (Lu-177 PSMA-617). However, Ac-225 PSMA therapy is not a finished product: it remains investigational only — no Ac-225 drug has FDA approval for prostate cancer as of April 2026 — and the dominant problem is severe, often permanent, dry mouth (xerostomia) from off-target damage to the salivary glands, which is reported in roughly 80–85% of treated patients. A wave of randomized phase 2/3 trials (PSMAcTION, CONVERGE-01, AcTION, TATCIST, ACCEL, AlphaBreak, SatisfACtion, and others) is now under way to nail down the right dose, the right ligand, and the right place in the treatment sequence. A parallel battle — building enough Ac-225 supply to actually treat patients — is being fought in DOE national labs, at SpectronRx, and through a $450 million TerraPower investment announced in March 2026. For an mCRPC patient today, the realistic path to Ac-225 therapy is a clinical trial.

Why Patients and Doctors Are Excited About Alpha Therapy

Most IPCSG members already know about Pluvicto (the brand name for lutetium-177 PSMA-617), which the FDA approved in March 2022 and again, with an expanded indication, on March 28, 2025. Pluvicto uses a small molecule that homes in on prostate-specific membrane antigen (PSMA) — a protein parked on the surface of nearly all prostate cancer cells — to deliver a beta-radiation payload directly to the tumor. It has extended lives, but it doesn't cure mCRPC, and a substantial number of men either don't respond or eventually progress.

Actinium-225 therapy uses the same PSMA homing principle but swaps the radioactive payload. Instead of a beta-emitter, it carries an alpha-emitter. The physics matters:

• Alpha particles hit harder. They deliver about 100 keV/µm of energy — roughly 1,000 times the energy density of beta particles. They tend to break both strands of the DNA double helix at once, a kind of damage cancer cells struggle to repair.
• Alpha particles travel a much shorter distance. Their range in tissue is only about 47–85 micrometers — a few cell diameters. In theory, that means a tumor cell catches the lethal dose while the cell next door gets nothing.
• Ac-225 has a 9.92-day half-life. That's long enough to manufacture, ship, and inject the drug, and short enough that it doesn't linger in the body for months. As Ac-225 decays, it produces a chain of four net alpha emissions before reaching stable bismuth-209.

Put plainly: the same delivery vehicle, but a more potent, more focused warhead. That is the promise of Ac-225 PSMA theranostics.

What the Clinical Data Actually Show

The "Big Number" — A 65% PSA50 Response Rate

The most comprehensive recent analysis is a systematic review and meta-analysis published in the journal Theranostics in February 2025 by Ninatti and colleagues. Pooling 18 studies and 1,155 patients, the researchers found:

• A pooled PSA50 response rate (the share of men whose PSA falls by half or more) of 65% — appreciably higher than the roughly 49% rate reported in the same kind of meta-analysis for Lu-177 beta therapy.
• Response rates were tied to how heavily pretreated the patient was: 82% in men with no prior lines of treatment, 72% after one prior line, and 55% after more than one prior line.
• Progression-free survival (PFS) ranged from 3 to 15 months, and overall survival (OS) from 8 to 31 months across the included studies.
• Severe (grade ≥3) hematologic toxicity was relatively uncommon: anemia in 11% and thrombocytopenia in 6%.

The largest single dataset feeding into that picture is the WARMTH Act study, a multicenter retrospective study published in Lancet Oncology in February 2024 by Sathekge and colleagues. It examined 488 men with mCRPC who received 1,174 cycles of Ac-225 PSMA radioligand therapy between 2016 and 2023. The headline numbers:

• Median overall survival: 15.5 months (95% CI 13.4–18.3).
• Median progression-free survival: 7.9 months.
• Grade 3 or higher anemia in 13%, leukopenia in 4%, thrombocytopenia in 7%, renal toxicity in 5%.
• And the catch: 68% of patients reported xerostomia after just the first cycle, and every patient who received more than seven cycles ended up with dry mouth.

Does It Still Work After Pluvicto?

For many patients reading this newsletter, that's the question that matters. Several studies say yes:

• A landmark German study from Feuerecker and colleagues treated 26 men whose disease had progressed after Lu-177 PSMA. 17 of 26 (65%) achieved a PSA decline of 50% or more on Ac-225 PSMA-617, with median overall survival of 7.7 months — in a population whose median was 6 prior lines of mCRPC treatment.
• The phase 2 TATCIST trial of FPI-2265 (Ac-225 PSMA-I&T), reported at the 2024 AACR Annual Meeting and updated since, showed a 50% PSA50 rate overall, a 61% rate in men who had not received prior Lu-PSMA, and a still-respectable 42% rate in men who had received it. Patients with higher PSMA expression on PET (SUVmean > 6) responded best, with 69% achieving PSA50.

What this means clinically: progression on Pluvicto does not appear to "burn out" the PSMA target. Many patients still have PSMA-expressing disease that an alpha emitter can reach.

The Major Trials You'll Hear About

Trial / Drug	Sponsor	Setting	Status (April 2026)
AcTION (NCT04597411) Ac-225 PSMA-617	Novartis	Phase 1, with or without prior Lu-PSMA	Enrolling; up to 6 cycles at 100 kBq/kg every 8 weeks
PSMAcTION Ac-225 PSMA-617	Novartis	Phase 2/3 randomized vs. standard of care, post-Lu-PSMA	13 sites, 7 countries; ~420 patients planned in phase 3 (TiP presented ESMO 2025)
TATCIST (NCT05219500) FPI-2265 (Ac-225 PSMA-I&T)	Fusion Pharmaceuticals (now AstraZeneca)	Phase 2, mCRPC including post-Lu	Phase 2/3 follow-on initiated
CONVERGE-01 (NCT06549465) CONV01-α / Ac-225 rosopatamab tetraxetan (formerly Ac-225-J591)	Convergent Therapeutics	Phase 2, three-part: dosimetry, dose optimization, dose escalation; both Lu-naïve and post-Lu	Enrolling at multiple US sites including UCSD; Lu-pretreated cohort data to be presented at ASCO 2026 (June 1, abstract 5011)
ACCEL (NCT06229366) LY4181530 / Ac-225 PSMA-62	Eli Lilly (POINT Biopharma)	Phase 1a/1b/2, oligometastatic HSPC and mCRPC	Next-generation ligand designed to reduce salivary/renal toxicity
SatisfACtion Ac-225 PSMA-R2	Novartis	Phase 1/2	Development halted in late 2025 due to high xerostomia rates
JNJ-69086420 Ac-225 anti-hK2 antibody	Janssen / J&J	Phase 1, post-ARPI mCRPC	First-in-human results presented ASCO 2024; targets human kallikrein 2, a non-PSMA target
AZD2284 Ac-225 anti-STEAP2	AstraZeneca	Phase 1, mCRPC	First-in-human dose escalation; explores a new, non-PSMA target

Members at IPCSG who have been tracking the CONVERGE-01 trial at UCSD will want to note: Convergent Therapeutics announced on April 21, 2026 that Phase 2 data from CONVERGE-01 Part 3 in Lu-PSMA pretreated patients will be presented as an oral presentation by Dr. Michael Morris of Memorial Sloan Kettering at ASCO on June 1, 2026 (abstract 5011). The radioantibody approach is meaningfully different from small-molecule PSMA ligands: because the antibody is too large to penetrate the tight junctions of the salivary glands, the Ac-225-J591 phase 1 trial reported dry mouth in only 38% of patients, far below the 80%+ rate seen with small-molecule PSMA-617.

The Catch: Salivary Gland Toxicity

The single biggest unsolved problem with Ac-225 PSMA therapy is what it does to the salivary glands. PSMA happens to be expressed at high levels on the parotid and submandibular glands, and the salivary acinar cells are exquisitely sensitive to the dense ionization tracks of alpha particles. Across the full clinical literature, the rate of any-grade xerostomia with Ac-225 PSMA-617 sits around 80–85%. Severe (grade 3+) dry mouth is uncommonly reported, but the meaningful clinical reality is that many patients live with permanently altered taste, painful eating, and disrupted sleep.

The dose-finding work has been telling. In Heidelberg's empiric dose-finding, treatment activity of 50 kBq/kg per cycle did not cause salivary toxicity, but pushing above 100 kBq/kg per cycle made severe xerostomia the dose-limiting toxicity. The standard regimen now is 100 kBq/kg every 8 weeks — right at the threshold — with "dynamic de-escalation" to 6 MBq and then 4 MBq in subsequent cycles for responders, popularized by the Pretoria group.

Strategies under active investigation include:

• Salivary gland cooling with ice packs during infusion.
• Sialendoscopy with steroid injection — an otolaryngology procedure that has shown some benefit but does not fully prevent damage.
• "TANDEM" therapy alternating Ac-225 with Lu-177 PSMA at lower alpha doses.
• Radioantibodies such as CONV01-α (Ac-225 rosopatamab) which appear to spare the salivary glands due to size exclusion.
• Next-generation ligands like PSMA-62 (in the ACCEL trial) and rhPSMA-10.1 (in ACTResolute, beginning April 2026 at University College London) that are engineered for lower gland uptake. Notably, a phase 1 trial of Ac-225 rhPSMA-10.1 reported salivary dose of just 0.130 Gy/GBq, versus 0.63 Gy/GBq in the VISION substudy with Lu-PSMA-617.
• The cautionary tale: Ac-225 PSMA-R2 was specifically designed to reduce salivary toxicity but its development was stopped in December 2025 because xerostomia rates in the SatisfACtion trial were still too high.

Other adverse events worth mentioning are anemia (in patients with extensive bone marrow disease), thrombocytopenia, and renal toxicity in those with pre-existing kidney issues. A March 2026 paper in Frontiers in Pharmacology using prostate cancer xenografts confirmed that, in the pre-clinical setting, salivary glands — not kidneys — are the true dose-limiting organ.

The Supply Problem — Why You Can't Just Walk In and Get Treated

Even if Ac-225 PSMA therapy were FDA-approved tomorrow, there isn't enough Ac-225 in the world to treat the patients who would want it. This is a real-world bottleneck and, for the past two years, it has shaped which trials open, which pause, and which patients can be enrolled.

Historically, almost all global Ac-225 has come from a single source: the U.S. Department of Energy's Oak Ridge National Laboratory, where it is "milked" from a 100-year-old stockpile of thorium-229. Two smaller international sources contributed; together, all three combined have produced enough Ac-225 to treat fewer than 100 patients per year worldwide. In 2024, Bristol Myers Squibb's RayzeBio paused a phase 3 trial because of the shortage.

That picture is changing fast in 2025–2026:

• DOE Tri-Lab Effort (Brookhaven, Los Alamos, Oak Ridge): accelerator-produced Ac-225 from thorium-232 spallation. The first U.S. clinical trial relying on accelerator-produced Ac-225 began in summer 2025.
• SpectronRx (Indiana): announced commercial-scale Ac-225 production in October 2025 using a proprietary accelerator-based method. Currently supplying 31 partners across 29 countries.
• TerraPower Isotopes: announced on March 17, 2026 a $450 million investment in a 250,000 sq ft Philadelphia facility, which combined with their Everett, Washington site, would increase production capacity 20-fold. The facility is scheduled to come online in 2029.
• Cardinal Health: shipped its first non-carrier-added Ac-225 to Convergent Therapeutics in November 2024 to support CONVERGE-01.
• Niowave: signed supply deals with Novartis (2026) and a 10-year agreement with AstraZeneca (December 2025).
• Eckert & Ziegler, NorthStar, Ionetix, PanTera, and ITM: all pursuing supply partnerships.

This sudden investment surge is the clearest sign that big pharma believes Ac-225 will be the next major class of cancer drug after Lu-177. Bayer, BMS, Eli Lilly, AstraZeneca, J&J, and Novartis have all bought biotechs or signed multi-year supply deals on Ac-225 since late 2023.

Where This Fits in Real Treatment Decisions

For an IPCSG member with mCRPC today, here's the practical reality:

• Ac-225 PSMA therapy is not commercially available for prostate cancer. Period. It can only be obtained through a clinical trial or, in some non-U.S. centers, on a compassionate-use basis.
• If you have already received Pluvicto and progressed, you are exactly the population most of these trials want to enroll. CONVERGE-01, PSMAcTION, TATCIST, and AcTION all welcome post-Lu patients.
• Eligibility usually requires PSMA-positive disease confirmed by PSMA PET/CT (Locametz, Pylarify, or similar), adequate kidney and bone marrow reserve, and prior treatment with at least one androgen-receptor-pathway inhibitor (and, for most trials, taxane chemotherapy).
• The PSMAcTION phase 2/3 trial specifically excludes patients with grade 2 or higher xerostomia at baseline — which is itself an acknowledgment of the toxicity issue.
• San Diego patients have local options. UC San Diego is a CONVERGE-01 site under medical oncologist Dr. Yu-Wei Chen.

Questions Worth Asking Your Oncologist

• Has my PSMA PET shown adequate uptake (a higher SUVmean is associated with better response)?
• What is my baseline kidney function, blood counts, and salivary status?
• Am I a candidate for an antibody-based agent (like CONV01-α) rather than a small-molecule one, given my concern about dry mouth?
• If I respond and then progress, can I be re-treated? (Several trials are exploring this; it's not yet a settled question.)
• What is the trial's plan for managing toxicity, and what supportive care — sialendoscopy, gland cooling, hydration protocols — is built in?

Beyond PSMA: New Targets on the Horizon

An interesting wrinkle: not every prostate cancer cell loudly expresses PSMA, and PSMA expression can decrease in neuroendocrine-differentiated disease. Several new Ac-225 programs target other surface proteins:

• Janssen's JNJ-69086420: targets human kallikrein 2 (hK2), a protein expressed on prostate cancer cells with very limited expression elsewhere in the body — potentially translating to fewer off-target effects, including, possibly, less salivary toxicity.
• AstraZeneca's AZD2284: targets STEAP2, with a "cold antibody" pre-administration step to optimize biodistribution.
• Ac-225 hu11B6: another hK2-targeting agent in earlier development.
• Ac-225 YS5: targets CD46, a surface protein upregulated in many cancers.

And for patients with mixed neuroendocrine features, the NEPC study at UCLA is testing PSMA, somatostatin receptor (SSTR), and gastrin-releasing peptide receptor (GRPR) targeted therapies in combination — an explicit acknowledgment that one target is not enough for the heterogeneous late-stage disease.

The Honest Bottom Line

Ac-225 PSMA theranostics is one of the most genuinely promising new directions in mCRPC therapy in 20 years. The 65% pooled PSA50 rate is striking. The activity in Pluvicto-failure patients is striking. And for the first time, the manufacturing infrastructure is being built to actually deliver this drug at scale.

But "promising" is not "proven." There are no randomized, controlled phase 3 trials yet completed comparing Ac-225 to standard of care. Nearly all of the large datasets are retrospective. The xerostomia issue is severe enough that it has already killed one promising drug candidate (Ac-225 PSMA-R2). And no Ac-225 prostate cancer drug has FDA approval.

For a patient progressing through standard mCRPC therapy today, the rational move is to get evaluated for a clinical trial now, not later. The trial slots are limited, the supply is limited, and being an early enrollee may be the only practical way to access this class of drug for the next 2–4 years — until the phase 3 readouts (especially PSMAcTION) and the supply expansion (especially TerraPower's 2029 facility) finally bring it into routine practice.

Verified Sources

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Disclaimer: This article is patient-education content prepared for the Informed Prostate Cancer Support Group (IPCSG) audience. It is not medical advice. Treatment decisions about Ac-225 PSMA therapy or any clinical trial enrollment must be made together with your treating oncologist, after review of your specific medical history, imaging, and lab values. The trial and approval landscape is evolving rapidly; verify current trial status with ClinicalTrials.gov before acting on the information here.