First experience with ²²⁴Radium-labeled microparticles (Radspherin®) after CRS-HIPEC for peritoneal metastasis in...

Peritoneal metastasis (PM) from colorectal cancer carries a dismal prognosis despite extensive cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS-HIPEC). With a median time to recurrence of 11-12 months, there is a need for novel therapies. Radspherin® consists of the α-emitting radionuclide radium-224 (²²⁴Ra), which has a half-life of 3.6 days and is adsorbed to a suspension of biodegradable calcium carbonate microparticles that are designed to give short-range radiation to the serosal peritoneal surface linings, killing free-floating and/or tumor cell clusters that remain after CRS-HIPEC.

A first-in-human phase 1 study (EudraCT 2018-002803-33) was conducted at two specialized CRS-HIPEC centers. Radspherin® was administered intraperitoneally 2 days after CRS-HIPEC. Dose escalation at increasing activity dose levels of 1-2-4-7-MBq, a split-dose repeated injection, and expansion cohorts were used to evaluate the safety and tolerability of Radspherin®. The aim was to explore the recommended dose and biodistribution using gamma-camera imaging. The results from the planned safety interim analysis after the completion of the dose-limiting toxicity (DLT) period of 30 days are presented.

Twenty-three patients were enrolled: 14 in the dose escalation cohort, three in the repeated cohort, and six in the expansion cohort. Of the 23 enrolled patients, seven were men and 16 were women with a median age of 64 years (28-78). Twelve patients had synchronous PM stage IV and 11 patients had metachronous PM [primary stage II; (6) and stage III; (5)], with a disease-free interval of 15 months (3-30). The peritoneal cancer index was median 7 (3-19), operation time was 395 min (194-515), and hospital stay was 12 days (7-37). A total of 68 grade 2 adverse events were reported for 17 patients during the first 30 days; most were considered related to CRS and/or HIPEC. Only six of the TEAEs were evaluated as related to Radspherin®. One TEAE, anastomotic leakage, was reported as grade 3. Accordion ≥3 grade events occurred in a total of four of the 23 patients: reoperation due to anastomotic leaks (two) and drained abscesses (two). No DLT was documented at the 7 MBq dose level that was then defined as the recommended dose. The biodistribution of Radspherin® showed a relatively even peritoneal distribution.

All dose levels of Radspherin® were well tolerated, and DLT was not reached. No deaths occurred, and no serious adverse events were considered related to Radspherin®.Clinical Trial Registration: Clinicaltrials.gov, NCT03732781.