Medical use
The pharmaceutical product and medical use of radium-223 against skeletal metastases was invented by Roy H. Larsen, Gjermund Henriksen and Øyvind S. Bruland and has been developed by the former Norwegian company Algeta ASA, in a partnership with Bayer, under the trade name Xofigo (formerly Alpharadin), and is distributed as a solution containing radium-223 chloride (1100 kBq/ml), sodium chloride, and other ingredients for intravenous injection. Algeta ASA was later acquired by Bayer who is now the sole owner of Xofigo. The recommended regimen is six treatments of 55 kBq/kg (1.5 μCi/kg), repeated at 4-week intervals. Mechanism of action
The use of radium-223 to treat metastatic bone cancer relies on the ability of alpha radiation from radium-223 and its short-lived decay products to kill cancer cells. Radium is preferentially absorbed by bone by virtue of its chemical similarity to calcium, with most radium-223 that is not taken up by the bone being cleared, primarily via the gut, and excreted. Although radium-223 and its decay products also emit beta and gamma radiation, over 95% of the decay energy is in the form of alpha radiation. Alpha radiation has a very short range in tissues compared to beta or gamma radiation: around 2-10 cells. This reduces damage to surrounding healthy tissues, producing an even more localized effect than the beta-emitter strontium-89, also used to treat bone cancer.
Taking account of its preferential uptake by bone and the alpha particles short range, radium-223 is estimated to give targeted osteogenic cells a radiation dose at least eight times higher than other non-targeted tissues. Clinical trials and FDA and EMA approval
The phase II study of radium-223 in castration-resistant prostate cancer (CRPC) patients with bone metastases showed minimum myelotoxicity and good tolerance for the treatment.223Ra successfully met the primary endpoint of overall survival in the phase III ALSYMPCA (ALpharadin in SYMptomatic Prostate CAncer patients) study for bone metastases resulting from CRPC in 922 patients.The ALSYMPCA study was stopped early after a pre-planned efficacy interim analysis, following a recommendation from an Independent Data Monitoring Committee, on the basis of achieving a statistically significant improvement in overall survival (two-sided p-value = 0.0022, HR = 0.699, the median overall survival was 14.0 months for 223Ra and 11.2 months for placebo). Earlier phase II of the trial showed a median increased survival of 18.9 weeks (around 4.4 months). The lower figure of 2.8 months increased survival in interim phase III results is a probable result of stopping the trial; median survival time for patients still alive could not be calculated. A 2014 update indicates a median increased survival of 3.6 months.In May 2013, 223Ra received marketing approval from the U.S. Food and Drug Administration (FDA) as a treatment for CRPC with bone metastases in patients with symptomatic bone metastases and without known visceral disease.