Prostate cancer is a disease that affects the male reproductive system when the cells of the prostate start to grow out of control. It is the second most common type of cancer among American men, but there are treatment options for patients with the disease. Depending on each case, these include watchful waiting or active surveillance, surgery, radiation therapy, cryotherapy or cryosurgery, hormone therapy, chemotherapy, vaccine treatment, and bone-directed treatment.
Radiation therapy consists of the use of high-energy rays or particles to kill cancer cells. It is particularly used as the first course of treatment for cancer that is still limited to the prostate gland and is low grade, as part of the first treatment together with hormone therapy to treat tumors that have spread outside the prostate gland and into nearby tissues, before or after surgery to improve the results and kill any remaining cancerous cells, or in the case of advanced prostate cancer to keep the cancer under control for as long as possible and to help prevent or relieve symptoms.
How Radium 223 Dichloride Works
There are two different types of radiation therapy, which are known as external beam radiation and brachytherapy (internal radiation). Radium 223 dichloride is a mildly radioactive form of the metal radium and it is one of the drugs used in brachytherapy. “A radiopharmaceutical composed of the dichloride salt of the alpha-emitting isotope radium Ra 223, with antineoplastic activity,” defines the NCI Drug Dictionary. “Like calcium, radium targets bone tissue and preferentially accumulates in osteoblastic lesions, such as those seen in areas of bone metastases. Radium Ra 223 forms complexes with hydroxyapatite and becomes incorporated into the bone matrix. The radioisotope Ra 223 kills bone cancer cells through local emission of high energy alpha particles, causing DNA double-strand breaks and tumor regression in the skeleton. The short range effects of alpha emission allows for localized DNA damage with limited toxicity to nearby healthy bone tissue.”
Radium and calcium are similar compounds, being both able to pick up active bone cells. Therefore, radium 223 dichloride can target bone cancer cells, which are more active than healthy bone cells. It is released into the bones as radiation, which travels only short distances of two to 10 cells. This means that cancer cells receive a high dose of radiation, while healthy cells receive only a low dose or no radiation. In the case of prostate cancer, the drug is used for the treatment of patients whose tumor have spread to the bones. Due to its mechanism of action, radium 223 dichloride is known to be effective in treating metastasized cancer to the bones and decrease pain. It is, however, not available in every hospital and patients may need to seek it in a different medical center. Previously known as Alpharadin, radium 223 dichloride is the generic name of the brand medication Xofigo.
Radium 223 Dichloride to Treat Prostate Cancer
“On May 15, 2013, the Food and Drug Administration (FDA) approved radium 223 dichloride (Xofigo Injection, made by Bayer HealthCare Pharmaceuticals Inc.) for the treatment of patients with castration-resistant prostate cancer, symptomatic bone metastases, and no known visceral metastatic disease,” stated the National Cancer Institute. “Radium 223 dichloride, also known as Radium Ra 223 dichloride, is an alpha-particle emitting radiotherapeutic drug that mimics calcium and forms complexes with hydroxyapatite at areas of increased bone turnover, such as bone metastases.” The FDA also defines as a recommended dose and schedule 50 kBq/kg (1.35 microcuries/kg) radium 223 dichloride, slowly and intravenously administered, over a minute every four weeks for six cycles.
The compound was approved after a double-blind, randomized placebo-controlled trial confirmed the effectiveness of radium 223 dichloride. Patients with metastatic castration-resistant prostate cancer were randomly treated with receive radium 223 dichloride, 50 kBq/kg, intravenously, every four weeks for six cycles plus best standard of care, or a matching placebo. The first group registered an overall survival of 14.0 months, while the placebo group registered 11.2 months of overall survival. However, there are also adverse events associated to the treatment. At least 10% of the patients experienced nausea, diarrhea, vomiting, peripheral edema, anemia, lymphocytopenia, leukopenia, thrombocytopenia, and neutropenia, while 2% of the patients suffered bone marrow failure or ongoing pancytopenia as adverse events.
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