Novartis actinium drug shows promise in prostate cancer, even after prior treatment

Novartis announced early trial results on Sunday for an experimental cancer drug that works differently from anything the company has sold before. The new treatment uses actinium-225, a radioactive isotope that delivers energy in a tighter, more concentrated burst than the lutetium-based drug the company already markets under the name Pluvicto. In a study of 101 patients, the actinium drug showed it could shrink tumors even in men who had already failed treatment with Pluvicto—a finding that suggests the two drugs might work in sequence, or that the newer one might simply be more powerful.

The numbers tell the story. Among patients who had previously received Pluvicto, just over half saw their prostate-specific antigen levels drop by at least half, which is the standard measure of response in prostate cancer. That's meaningful, because these were patients whose cancer had already resisted one radioligand therapy. But the real signal came from patients who had never received Pluvicto at all. More than 85 percent of treatment-naive patients saw their PSA levels fall by half. Among those who had received chemotherapy first, the response rate was 58.8 percent. The data were presented at the American Society of Clinical Oncology meeting in Chicago.

What makes this drug work is physics. Actinium-225 is an alpha emitter, meaning it releases particles that travel only a short distance but pack enormous energy into that small space. Lutetium-177, which Pluvicto uses, is a beta emitter—it spreads its energy over a longer path. Shreeram Aradhye, Novartis's Chief Medical Officer, explained that the concentrated energy delivery of actinium could mean greater killing power against cancer cells. The company is betting heavily on this approach. Radioligand therapies now account for nearly 40 percent of Novartis's cancer research and development spending, a dramatic shift in where the company is placing its bets.

But the early promise comes with a cost. Patients in the trial experienced notable side effects. Dry mouth was common. More concerning was severe anemia—a dangerous drop in red blood cells. TD Cowen analysts, reviewing the data, noted that managing these toxicities would be crucial to the drug's eventual success. Aradhye acknowledged that larger trials will be needed to understand how severe these side effects are and whether they reverse once treatment stops, especially if the company wants to use the drug earlier in the treatment sequence, when patients are healthier and might tolerate it differently.

Novartis is already moving forward. Two late-stage studies of the experimental drug are underway. The company's existing radioligand therapies—Pluvicto and another drug called Lutathera—generated $2.8 billion in combined sales last year, a sign that the market for these targeted radiation treatments is real and growing. Competitors have noticed. Eli Lilly, Bristol Myers Squibb, Bayer, and AstraZeneca have all acquired radioligand therapy companies in recent years, sensing the same opportunity.

One constraint looms: supply. Actinium-225 is not abundant. The isotope must be produced, and current production capacity may not keep pace with clinical demand if the drug reaches the market and is used widely. Analysts have flagged this as a potential bottleneck. Novartis is thinking ahead. In February, the company signed a long-term supply agreement with Niowave, a U.S.-based medical isotope producer, to secure actinium for future trials and, if the drug is approved, for commercial use. The company is essentially betting that the science will work and that the supply chain can be built to match.