Alpha Emitter Radium 223 in High-Risk Osteosarcoma: First Clinical Evidence of Response and Blood-Brain Barrier Penetration

Osteosarcoma is the most common primary malignant condition of the bone in children, adolescents, and young adults. We have reached a therapeutic plateau with standard chemotherapy.¹ Patients with relapsed disease have a dismal prognosis. There have been no new therapies for osteosarcoma approved by the US Food and Drug Administration (FDA) in the last 3 decades.

Radium 223 dichloride (²²³RaCl₂) is an alpha-emitting radiopharmaceutical and calcimimetic that has intrinsic bone-targeting properties.² It recently received FDA approval for prostate cancer with bone metastases.^2,3 Preclinical studies in mice with human osteosarcoma xenografts and in dogs with osteosarcoma have shown that ²²³RaCl₂ is a potentially low-toxicity, high-efficacy targeted agent for osteosarcoma, which is an osteoblastic bone-forming tumor.⁴ Knowing this, we hypothesized that ²²³RaCl₂ could be safely administered to patients with osteosarcoma and that early response or resistance signals could be assessed by quantitative or qualitative correlative imaging studies.

We designed a phase 1 clinical trial for patients with progressive, locally recurrent, or metastatic osteosarcoma with no standard curative options available with at least one indicator lesion avid on technetium Tc 99m–methylene diphosphate scan. The protocol was approved by the University of Texas MD Anderson Cancer Center institutional review board, and all participants provided written informed consent. The trial is ongoing and registered (NCT01833520).

A man in his 20s with lung and brain metastatic osteosarcoma had been initially diagnosed with left femur osteosarcoma and had undergone standard osteosarcoma chemotherapy, surgery, and rotationplasty. A pathologic analysis showed less than 90% necrosis. He received preadjuvant and adjuvant high-dose methotrexate, cisplatin + doxorubicin, and ifosfamide + etoposide. While on surveillance, he developed sudden left hip pain and chest pain. Imaging revealed recurrence in the left ischium, a large calcific right lung mass, and cerebellar metastases. Biopsy confirmed osteosarcoma.

The patient was enrolled in the ²²³RaCl₂ osteosarcoma clinical trial. Baseline imaging studies were performed, including a positron emission tomography–computed tomography (PET-CT) bone scan using fluoride 18 (¹⁸F) (Na¹⁸F-PET–CT) and brain magnetic resonance imaging (MRI). Serum markers of bone turnover were also obtained. The patient received 3 infusions of ²²³RaCl₂, 75 kBq/kg, at 4-week intervals, with a total administered dose of 14.44 MBq (0.390 mCi). Posttreatment imaging showed positive response to therapy at most sites (Table), including the dominant left cerebellar metastasis. On MRI, the cerebellar lesion decreased from 1.5 cm at baseline to 1.2 cm after treatment, with resolution of perilesional edema (Figure). On Na¹⁸F-PET–CT, the cerebellar metastasis decreased significantly in intensity following radium therapy (Figure). However, both MRI and Na¹⁸F-PET–CT showed interval development of new cerebellar metastases smaller than 5 mm, and the patient was disenrolled from the clinical trial because of progressive disease. Patient reported a clinical reduction in bone pain after 3 doses of ²²³RaCl₂ and had no grade 3 or 4 toxic effects related to ²²³RaCl_2.

This is the first clinical evidence of an alpha particle with blood-brain barrier (BBB) penetration and early evidence of ²²³RaCl₂ activity in osteosarcoma. Interestingly, review of the literature revealed BBB penetration of a beta particle, Yttrium Y 90 (⁹⁰Y) ibritumomab tiuxetan, given intravenously to a patient with primary central nervous system lymphoma.^5,6 After ⁹⁰Y ibritumomab tiuxetan administration, there was complete response in enhancing tumor where the BBB was leaky, but lesions occurred in other brain regions, where the BBB was intact.⁶

Once a radionuclide is deposited in or near a cancer cell, the rate (half-life), range, and energy of radioactive particle emissions (MeV) are quite different within the target zone for alpha vs beta emitters.¹ The charged alpha particles from ²²³Ra have far more mass and energy than beta particles (electrons).¹ In the present patient, both imaging and biomarkers showed a definite ²²³RaCl₂ response signal. A dose-escalation study is underway to further define the role of single-agent ²²³RaCl₂ in osteosarcoma. An adjuvant trial with combined chemotherapy–targeted therapy and ²²³RaCl₂ is warranted.

Corresponding Author: Vivek Subbiah, MD, Department of Investigational Cancer Therapeutics, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd, FC8.3038, PO Box 0455, Houston, TX 77030 (vsubbiah@mdanderson.org).

Published Online: February 19, 2015. doi:10.1001/jamaoncol.2014.289.

Conflict of Interest Disclosures: None reported.

Funding/Support: This research was supported the Shannon Wilkes Foundation; The University of Texas MD Anderson Cancer Center; and grant CA016672 from the National Institutes of Health. Bayer AG donated the radioactive isotopes.

Role of the Funder/Sponsor: The funding/sponsoring institutions had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Trial Registration: clinicaltrials.gov Identifier: NCT01833520

Additional Contributions: We thank Eugenie Kleinerman, MD, for her support for this study.