Experimental Treatment for Chronic ITP Patients

These experimental treatments will be discussed in alphabetical order since their relative merit is not known at this time.

Stem Cell Transplantation.

In patients with chronic ITP who have: (1) failed to respond to all forms of standard therapy and (2) who have severe thrombocytopenia with associated mucosal bleeding (nosebleeds, bleeding from the stomach or bowel, etc.), consideration may be given to stem cell transplantation.

In this treatment, blood stem cells are obtained from the patient and frozen. In some cases, the stem cells are treated to remove the cells which may be involved in producing the antiplatelet antibody. After the stem cells have been obtained and frozen, very high doses of chemotherapy (about 5-10 times the doses described in the standard treatment section) are given. After this treatment has been completed, the blood stem cells are thawed and given back to the patient to allow more rapid recovery from the effects of the chemotherapy on the bone marrow.

Mortality from the complications of this procedure in other diseases (leukemia, lymphoma, etc.) ranges from 1-5%; the mortality in severe chronic ITP patients is not known, although results thus far suggest that it will be very low. The treatment at most transplant centers is very expensive ($100-150,000) and, since it is experimental, insurance companies may be unwilling to pay for it. If transplantation is done at the National Institutes of Health, there is no cost to the patient.

Results. The group at the National Institutes of Health has transplanted 14 patients with refractory ITP. Of these 14 patients, 6 have attained a complete response (platelet counts >100,000 off all medications); 2 patients had 'partial' responses (platelet counts increased from less than 5000 to the 15-30,000 range on either no medication or reduced doses of steroids/other medicines); and the remaining 6 patients did not respond or had only very transient responses. Followup times range from 9-42 months. There were no deaths associated with the procedure and no major complications, although 3 patients died several months later of unrelated diseases. Further followup will be required to see if these initial responses persist.

Patients who feel that the severity of their disease may qualify them for this treatment should discuss this with their physician. If their physician agrees that this is a reasonable treatment alternative, the doctor should contact Dr. Cynthia Dunbar at the Clinical Center of the National Institutes of Health (301-496-1434 or dunbarc@nhlbi.nih.gov) to obtain more information.

 

Thrombopoietin Receptor Stimulators.

Thrombopoietin (TPO) is the major platelet growth factor that is responsible for stimulating platelet production under normal circumstances. This factor has been cloned which provided sufficient quantitites for clinical testing. TPO has been tested in several animals, including baboons, where its administration results in a marked increase in the platelet count. In early clinical studies, TPO or agents which contained the active portion of the TPO molecule were used successfully in humans to stimulate platelet production in patients who had received chemotherapy, in normal subjects to increase the platelet count prior to platelet donation and in a few ITP patients. However, it soon became obvious that, in some cases, the recipient started to make antibodies against TPO which also reacted with and inactivated their native TPO, resulting in thrombocytopenia. For this reason, the use of these products was abandoned. More recently, small molecules that have no structural similarity to TPO have been identified that stimulate the TPO receptor, resulting in increased platelet production in both normal subjects and some patients with ITP. Three of these agents, AMG531, eltrombopag and AKR-501 are being studied in FDA-approved clinical trials in ITP patients.

AMG531. This agent, which is given by subcutaneous injection, was shown to stimulate platelet production in normal subjects. It is now being tested in a phase III clinical trial of ITP patients with baseline platelet counts of <30,000. Periodic injections are given (usually each week) aiming to increase the platelet count to >50,000 and at least twice the pre-treatment platelet count. At present, 27 ITP patients who completed 48 weeks of therapy have been studied, with the following results: (1) a platelet increase to the target level (>50,000 and twice baseline) was noted in 86% of patients with an average time to a response of 3.1 weeks; (2) patients with platelet counts >150,000 at any time- 81%; (3) patients with platelet counts >400,000 at any time- 42%; and (4) average platelet count: weeks 1 to 24- 100,000; weeks 25 to 48- 131,000.

For information about participating in an AMG531 clinical trial, call 1-866-572-6436. Their most recent trial is: "AMG531 versus medical standard of care for ITP."

Eltrombopag. This agent, which is given as an oral medication, also stimulates platelet production in normal subjects and is being tested in clinical trials on ITP patients. In a dose-finding study, average platelet counts after 43 days of therapy using different doses were: eltrombopag (30 mg per day)- 26,000; eltrombopag (50 mg per day)- 128,000 and eltrombopag (75 mg per day)- 183,000. An ITP phase III study is starting.

For information about participating in an eltrombopag clinical trial, contact the following website: http://www.itpstudy.com.

AKR-501 Phase 1 studies show that this orally administered drug stimulates platelet production in normal subjects. An ITP phase II study is ongoing.

For information about participating in an AKR-501 clinical trial, contact the following website: http://www.PlateletStudies.com/acitp

Comment. The development of these agents that stimulate platelet production in ITP patients provides another treatment approach. Their role in ITP therapy remains to be determined.