Iodine-131 Tositumomab: (131)I-anti-B1 antibody, (131)I-tositumomab, anti-CD20 murine monoclonal antibody-I-131, B1, Bexxar, (131)I-anti-B1 antibody, iodine-131 tositumomab, iodine-131 anti-B1 antibody, tositumomab

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BioDrugs: Clinical Immunotherapeutics, Biopharmaceuticals and Gene Therapy 2003, 17 (4): 290-5
Iodine-131 tositumomab [B1, Bexxar , iodine-131 anti-B1 antibody] is a murine antibody conjugated to iodine 131 that recognises and binds to the B1 (CD20) antigen which is found specifically on B lymphocytes. Iodine-131 tositumomab has a dual mechanism of action. It is capable of initiating a host immune response to those B cells to which it is attached, and it also triggers apoptosis in a significant proportion of the cells to which it binds. The product was first discovered by Coulter Corporation, Miami, in collaboration with the Dana-Farber Cancer Institute and the University of Michigan. The spin-off company Coulter Pharmaceutical, upon its formation, obtained worldwide rights to iodine-131 tositumomab. (Coulter Corporation was acquired subsequently by Beckman Instruments in October 1997. The union of the two companies produced Beckman Coulter.) In December 2000, Coulter Pharmaceutical was acquired by, and merged into, Corixa Corporation.Iodine-131 tositumomab is available for licencing in Japan. Corixa Corporation and GlaxoSmithKline signed an agreement to jointly develop and commercialise iodine-131 tositumomab. The total agreement has a potential value of up to $US132 million, plus shared profits and royalties. The two companies will jointly market the antibody in the US following regulatory approval. Corixa Corporation has announced it expects iodine-131 tositumomab to be approved in the US for non-Hodgkin's lymphoma (NHL). Under the terms of the original agreement, GlaxoSmithKline will receive exclusive marketing rights outside the US, excluding Japan. However, an amended agreement between the two companies will allow Corixa Corporation to also market the product outside the US. In February 2003, the European Commission granted iodine-131 tositumomab orphan-drug designation. Corixa Corporation and GlaxoSmithKline also intend to jointly investigate the use of the product in other indications. GlaxoSmithKline may also receive access to second generation anti-CD20 compounds under its agreement with Corixa Corporation. In May 2003, Corixa Corporation entered into an agreement that will see GlaxoSmithKline market Bexxar in Canada. Under the terms of the agreement, Corixa Corporation will manufacture and supply the product to GlaxoSmithKline, who will register, market and sell it in Canada. In October 2001, Amersham PLC, a supplier of medical equipment, announced that its Amersham Health unit had signed a marketing agreement with Corixa Corporation. The agreement allows Amersham Health to market iodine-131 tositumomab in Europe. Corixa Corporation formed agreements with Boehringer Ingelheim Pharma KG and Lonza Biologics to produce the B1 antibody and radiolabelling of the antibody has been contracted out to MDS Nordion.Iodine-131 tositumomab has received orphan drug and fast track designation for the treatment of NHL. Corixa Corporation submitted a Biologics Licence Application (BLA) to the US FDA in 1999, seeking permission to market Bexxar in the US for the treatment of relapsed or refractory, low grade or transformed low grade B-cell NHL. Following a priority review, the US FDA requested that Corixa Corporation reformat certain sections and perform additional analyses of existing data in its BLA. Corixa Corporation and GlaxoSmithKline resubmitted their BLA to the US FDA in September 2000. The BLA was subsequently accepted by the US FDA in November 2000. However, in March 2001, the US FDA requested additional information in its complete review letter to Corixa Corporation and marketing partner GlaxoSmithKline. The two companies submitted data pertaining to the chemistry, manufacturing and controls section of the BLA, and to the majority of the questions regarding the clinical section of the BLA in August 2001. Corixa Corporation and GlaxoSmithKline submitted the remainder of the response to the US FDA in September 2001, following an independent review of clinical trial data. In March 2002, Corixa Corporation received another complete review letter from the US FDA, which stated that additional clinical trials would have to be conducted in order to provide adequate evidence of the safety and clinical benefit of Bexxa. The US FDA also denied Corixa Corporation's request for accelerated approval, stating that the data provided was inadequate to show that Bexxar filled an unmet medical need. Corixa Corporation has met formally with the US FDA but the two were unable to resolve their differences. Corixa Corporation will now file a formal request for dispute resolution under the Food and Drug Administration Modernisation Act. Corixa Corporation also requested a presentation of Bexxa data to the US FDA's scientific advisors. In June 2002, the US FDA granted the company's appeal for additional regulatory review. In December 2002, the US FDA's Oncologic Drugs Advisory Committee agreed that Bexxar has clinical benefit for patients with NHL. In May 2003, Corixa Corporation and GlaxoSmithKline announced that they had fulfilled many of the steps required for US FDA approval, however the US FDA has extended its review of the application for another 3 months. This extension will allow for further refinement of post marketing commitments and package insert language, and to ensure they are consistent with an updated safety database requested by the US FDA and submitted by Corixa Corporation in early April. GlaxoSmithKline was waiting for the outcome of the situation before deciding on marketing plans for Bexxar. Corixa Corporation and GlaxoSmithKline will conduct a head-to-head study of Bexxar and Idec's Zevalin, planned for mid-2003. The trial will likely be one of three phase IV studies that the US FDA requires for accelerated approval of Bexxar. Corixa Corporation initiated its Expanded Access Program for Bexxar in response to requests from physicians and patients for continued access to Bexxar during the period prior to potential US FDA marketing approval.A phase II multicentre trial of Bexxar in combination with CHOP chemotherapy is underway in the US as first-line therapy in patients with intermediate-grade NHL. Corixa Corporation has initiated a phase II trial of iodine-131 tositumomab in combination with cyclophosphamide, vincristine and prednisone for the treatment of previously untreated low-grade NHL. The trial was initiated while the company was preparing its BLA for Bexxar for use as a single agent for relapsed or refractory NHL. Corixa Corporation intends to pursue additional trials to expand the potential use of iodine-131 tositumomab to other indications, including chronic lymphocytic leukaemia. The agent is also in a clinical trial for preparation in autologous bone marrow transplant patients. The trial is designed to test the combination of iodine-131 tositumomab and chemotherapy. The trial began in 1995 and has so far enrolled 40 patients. In addition, a phase II dose-escalation trial has begun at the University of Nebraska for the combined use of iodine-131 tositumomab and chemotherapy as preparation for autologous bone marrow transplant. Corixa Corporation has received an issued US patent covering methods for administering and dosing radioimmunotherapy for the treatment of B-cell lymphomas. The patent covers iodine-131 tositumomab and other anti-CD20 antibodies used to aid in selective tumour targeting. Corixa Corporation has exclusive rights to the patent.A February 2000 media release from GlaxoSmithKline and Corixa Corporation stated that they had been issued a composition patent relating to radiolabelled monoclonal antibodies (including Bexxar) for the treatment of B-cell lymphomas. On 11 September 2001, IDEC announced that it had filed two separate lawsuits. The first lawsuit is against Corixa Corporation and the University of Michigan on six patents pertaining to products and processes related to radioimmunotherapy. They seek a declaration that Zevalin does not infringe Corixa Corporation's issued US patents. The second lawsuit involves two patents relating to cell culture media, and is against GlaxoSmithKline. IDEC's lawsuit in this case, seeks a declaration that its manufacture of Zevalin does not infringe GlaxoSmithKline's issued US patents. Corixa Corporation and GlaxoSmithKline have also filed a complaint for patent infringement against IDEC. These actions however, should have no effect on the regulatory process that Zevalin is completing, or prevent IDEC from launching the drug before iodine-131 tositumomab.A year earlier, in March 2001, the Financial Times reported that Bexxar could reach peak sales of $US120 million. In 1998, Coulter Pharmaceutical received a licencee fee payment of $US34 million from SmithKline Beecham (now GSK) in the fourth quarter of the year, as part of the joint development and commercialisation agreement for Bexxar.


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