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Tositumomab is a murine monoclonal antibody which targets the CD20 antigen produced in mammalian cell.[1] It was combined with iodine-131 to produce a radiopharmaceutical for unsealed source radiotherapy, Iodine-131 Tositumomab (branded as Bexxar), for the treatment of non-Hodgkins lymphoma.[1] It is classified as a IgG2a lambda antibody.[1][2]
| Monoclonal antibody | |
|---|---|
| Type | Whole antibody |
| Source | Mouse |
| Target | CD20 |
| Clinical data | |
| Trade names | Bexxar |
| AHFS/Drugs.com | Monograph |
| MedlinePlus | a609013 |
| ATC code | |
| Identifiers | |
| CAS Number | |
| DrugBank | |
| ChemSpider |
|
| UNII | |
| KEGG | |
| ChEMBL | |
| Chemical and physical data | |
| Formula | C6416H9874N1688O1987S44 |
| Molar mass | 143860.04 g·mol−1 |
  (what is this?) (verify) | |
The drug combination was developed by Corixa which was purchased by GlaxoSmithKline in 2005.[3] It was sold for about $25,000 for one round of treatment.[4] Bexxar competed with Zevalin,[5] until the former's discontinuation in 2014.[6]
A personalized regimen using Bexxar was approved for the treatment of relapsed or chemotherapy/rituxan-refractory Non-Hodgkin lymphoma in 2003.[4][7][8]
The radioactive dose was adjusted for each patient in order to maximize the radiation delivered to the tumor and minimize the exposure of other organs.[1][9]: 14–15 Bexxar combined separate administration of unlabelled and iodine-labelled (i.e. covalently bonded to 131I) tositumomab. A first dose of labelled antibody was given once, and whole-body radiation was measured with a gamma camera over seven days. Analysis of that imaging data allowed an optimal dose of labelled antibody to be calculated, which was then administered once a day, for up to seven days.[1][9]: 14–15 Each time the labelled antibody was administered, it was always preceded by unlabelled (non-radioactive) antibody. Early clinical trials had shown that total body residence times of radioactivity were longer in people who first received unlabelled antibody, so that a lower dose of labelled antibody was needed to deliver the required total dose of radiation; additionally labelled antibody targeted tumors better in people pre-treated with unlabelled antibody.[9]: 21
United States
Following a first investigational new drug application in 1989 and biologics license application in 2000, Bexxar was approved by the FDA in 2003.[10][8] Sale of Bexxar was discontinued and marketing approval was withdrawn in February 2014 due to a decline in usage (fewer than 75 patients in 2012). One possible explanation for the lack of demand, despite a claimed 70% response rate, was that oncologists could not sell it directly to patients but had to refer patients to third party specialist centers, however a "muddled clinical trials strategy", supply chain issues, reimbursement problems, and emergence of non-radioactive competitors has also been blamed.[6][5][11]
Europe
The European Medicines Agency granted tositumomab and 131I-tositumomab orphan drug status, for the treatment of follicular lymphoma, to Amersham plc in 2003. This was withdrawn in October 2015 at the request of the new owner, GlaxoSmithKline.[12][13]
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