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New therapy for bone-marrow transplant gives hope to patients over 55

Bone_marrow_biopsyBy Kaushik J. Dave, Ph.D.

The fastest-growing hospital procedure might surprise you. It is not bariatric surgery, nor does it involve robotic machinery. In fact, bone marrow transplants are currently a $1.3 billion market representing the fastest-growing hospital procedure in the U.S. They are the only potential cure for many blood cancers such as acute myeloid leukemia (AML) in older patients.

The procedure is technically called hematopoietic stem cell transplantation (HSCT) and can be either a bone marrow transplant (BMT) or transplant of blood stem cells isolated from peripheral blood (PBSC). In either case, it involves transplanting cells capable of restoring normal bone marrow function into a patient.

An increasing number of HSCT patients are over age 55, but many in this group who need it are ruled ineligible. This is because the high-dose chemotherapy traditionally preceding HSCT—standard therapy for younger patients—is often deemed too harsh even for healthy looking older people. Indeed, in certain indications, less than 10 percent of those 55+ survive more than a year after conventional HSCT.

Since more than half of AML patients are over 65 years old, new tactics are needed. For example, what if a patient’s existing bone marrow could be “prepared” prior to the transplant in a way that eliminated the need for high-dose chemotherapy? This promising approach is being pursued by Actinium Pharmaceuticals, Inc., a New York City-based biotech company.

Actinium’s lead compound, Iomab-B, has been successfully harnessed as a “myeloconditioning” agent in Phase 1/2 trials involving more than 250 patients including cases of incurable blood cancers such as AML resistant to available therapies. It has demonstrated the ability to prepare such patients for bone marrow transplants when no other treatment was indicated.

Iomab-B is a radioimmunoconjugate consisting of BC8, a novel murine monoclonal antibody, and iodine 131 radioisotope. BC8 was developed by Fred Hutchinson Cancer Research Center to target CD45, a pan-leukocytic antigen widely expressed on white blood cells but not on other tissues. This antigen makes BC8 potentially useful in targeting white blood cells in preparation for HSCT in a number of blood cancer indications, including AML, chronic myeloid leukemia, acute lymphoblastic leukemia, chronic lymphocytic leukemia, Hodgkin disease, Non-Hodgkin lymphomas and multiple myeloma. When labeled with radioactive isotopes, BC8 carries radioactivity directly to the site of cancerous growth and bone marrow while avoiding effects of radiation on most healthy tissues.

With any cancer treatment, success is usually increased when treatment initiates soon after diagnosis. This is especially true when projected survival is only a few months. Waiting for half that time to initiate a therapy can have a serious impact. Very significantly, treatment with Iomab-B prepares a patient for bone marrow transplant in only 10 days, compared to approximately six weeks required with traditional care—a potentially vital difference in the face of a fast-evolving cancer.

The significance of this approach comes into focus in light of the fact that the only potentially curative treatment option for older AML patients is bone marrow transplant, but the majority of patients over age 55 are ineligible for conventional care due to health reasons and/or severity of their disease. Actinium believes Iomab™-B offers a positive step toward their continued treatment. Almost all patients are eligible, and preliminary studies indicate their survival rates are significantly higher. It also can help prepare older patients for bone marrow treatment who have survived chemo but whose AML either was not cured or returned.

On the strength of results showing its potential in Phase 1/2 trials, the company is poised to begin a Phase 3 trial during 2014. The primary endpoint will be the rate of durable complete remission among the treated patients. A series of physician-led trials involving Iomab™-B is also ongoing.

If Iomab-B continues to perform well in clinical trials, it could result in a potentially fresh approach to treatment for those over age 55 seeking bone marrow transplants.

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Kaushik J. Dave, Ph.D. is President and CEO of Actinium Pharmaceuticals, Inc., a biopharmaceutical company developing innovative targeted payload immunotherapeutics for the treatment of advanced cancers.

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