Actinium Reports Early Safety Findings in 3 Prostate Cancer Patients
Key Facts
Actinium Pharmaceuticals reported preliminary safety findings for its experimental treatment for metastatic castration-resistant prostate cancer in a detailed results statement issued on October 20, 2026. The first clinical cohort comprised 3 patients who received a dose of 1.0 microcuries per kilogram in the ongoing study of the drug candidate. The company said it observed no "dose-limiting toxicities" during the toxicity assessment window and the reported follow-up of participating patients. The data were presented in Vienna on October 19, 2026, during a session scheduled between 4:45 and 6:15 p.m. Central European Summer Time. The findings form part of the assessment of the candidate's safety and tolerability in patients, ahead of determining the recommended dose for phase two clinical development.
On imaging, Actinium said serial scans showed uptake of the targeted imaging agent within tumor lesions and continued retention "through day seven." The observation concerns the imaging agent within the lesions, as part of the program's early evaluation in patients with metastatic castration-resistant prostate cancer. On liver monitoring, the company added that it observed no "elevation in liver enzymes" during the reported follow-up period. The drug candidate links the antibody baristamab to the radioactive isotope actinium-225, according to the company's description of the treatment it is developing. The antigen targeted by the program is involved in a pathway that contributes to tumor survival and treatment resistance, according to Actinium's announcement of the program.
The program's target patient population includes those whose tumors have low or negative expression of prostate-specific membrane antigen, according to the company. It also includes patients who do not respond to therapies targeting this antigen, or whose disease progresses after receiving those treatments. This places the program within the treatment landscape for metastatic castration-resistant prostate cancer, targeting groups that differ in antigen expression and response to therapies directed at it. In the regulatory pathway for treatments targeting the same antigen, approval of Pluvicto was based on a trial involving 831 patients, according to the U.S. Food and Drug Administration. The trial supporting Pluvicto's approval was limited to patients positive for this antigen, defining the context of that trial when considered alongside Actinium's development program.
Actinium first announced the program on March 27, 2025, when the company disclosed early results in preclinical prostate cancer models. In that announcement, it said the candidate achieved 99.8% tumor growth inhibition in the experimental models used. That result followed a single dose, according to the statement launching the company's announcement of its drug program. Those experiments involved preclinical prostate cancer models, while the results announced in October concern a human cohort with metastatic castration-resistant disease. Development has thus moved from reporting tumor growth inhibition in experimental models to assessing safety, tolerability and dose selection in the ongoing human study.
Alongside clinical development in prostate cancer, Actinium presented preclinical results for the candidate in other tumor types at the 2026 European Association of Nuclear Medicine congress. In a colorectal cancer model, adding the candidate to oxaliplatin and bevacizumab increased tumor growth inhibition to 72%. The company compared that with 25% for the two drugs alone in the same preclinical experiment, which tested adding the candidate to this treatment combination. In a separate ovarian cancer model, Actinium said the candidate alone achieved 93% tumor growth inhibition. The preclinical lung cancer experiments included models driven by multiple molecular alterations, which the company said support studying the program across different forms of the disease.
On the financial front, Actinium's cash and cash equivalents totaled 36,473 thousand dollars at the end of June 2026, according to its quarterly report. That compares with 47,998 thousand dollars at the end of December 2025, according to the comparative figures in the same report. The cash balance thus declined between the end of December and the end of June, in the period preceding the clinical program update presented in October. Regarding the company's listing, a regulatory filing issued in August 2026 disclosed that Actinium had been granted a period to implement a compliance plan. The deadline under that plan extends to November 27, 2027, according to the filing with the U.S. Securities and Exchange Commission.
As the study's next step, Actinium said in its October 2026 update that it had advanced to a dose of 1.5 microcuries per kilogram, with dose escalation continuing. The protocol calls for intravenous treatment every 6 weeks, for a maximum of 4 treatment cycles per patient. Alongside safety and tolerability, the assessment of antitumor activity includes monitoring prostate-specific antigen response and the objective response rate. It also includes monitoring radiographic progression-free survival and overall survival as measures for subsequent efficacy assessment. The study will use this follow-up to determine the recommended phase two dose, the next stated objective in the candidate's clinical development.