AMG 531, a thrombopoiesis-stimulating protein, for chronic ITP.
BACKGROUND
Most current treatments for chronic immune thrombocytopenic purpura (ITP) act by decreasing platelet destruction. In a phase 1-2 study, we administered a thrombopoiesis-stimulating protein, AMG 531, to patients with ITP.


METHODS
In phase 1, 24 patients who had received at least one treatment for ITP were assigned to escalating-dose cohorts of 4 patients each and given two identical doses of AMG 531 (0.2 to 10 microg per kilogram of body weight). In phase 2, 21 patients were randomly assigned to receive six weekly subcutaneous injections of AMG 531 (1, 3, or 6 microg per kilogram) or placebo. The primary objective was to assess the safety of AMG 531; the secondary objective was to evaluate platelet counts during and after treatment.


RESULTS
No major adverse events that could be attributed directly to AMG 531 occurred during the treatment period; 4 of 41 patients had transient post-treatment worsening of thrombocytopenia. In phase 1, a platelet count that was within the targeted range (50,000 to 450,000 per cubic millimeter) and at least twice the baseline count was achieved in 4 of 12 patients given 3, 6, or 10 mug of AMG 531 per kilogram. Overall, a platelet count of at least 50,000 per cubic millimeter was achieved in 7 of 12 patients, including 3 with counts exceeding 450,000 per cubic millimeter. Increases in the platelet count were dose-dependent; mean peak counts were 163,000, 309,000, and 746,000 per cubic millimeter with 3, 6, and 10 microg of AMG 531 per kilogram [corrected], respectively. In phase 2, the targeted platelet range was achieved in 10 of 16 patients treated with 1 or 3 mug of AMG 531 per kilogram per week for 6 weeks. Mean peak counts were 135,000, 241,000, and 81,000 per cubic millimeter in the groups that received the 1-mug dose, the 3-mug dose, and placebo, respectively.


CONCLUSIONS
AMG 531 caused no major adverse events and increased platelet counts in patients with ITP. (ClinicalTrials.gov number, NCT00111475 [ClinicalTrials.gov].).
Bussel
James B
JB
New York Presbyterian Hospital, New York, USA. jbussel@med.cornell.edu
Kuter
David J
DJ
George
James N
JN
McMillan
Robert
R
Aledort
Louis M
LM
Conklin
George T
GT
Lichtin
Alan E
AE
Lyons
Roger M
RM
Nieva
Jorge
J
Wasser
Jeffrey S
JS
Wiznitzer
Israel
I
Kelly
Reggie
R
Chen
Chien-Feng
CF
Nichol
Janet L
JL
D000305:Adrenal Cortex Hormones / Q000627:therapeutic use; D000328:Adult; D000368:Aged; D000906:Antibodies / Q000097:blood; D002352:Carrier Proteins / Q000008:administration & dosage* / Q000009:adverse effects / Q000276:immunology; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D007279:Injections, Subcutaneous; D008297:Male; D008875:Middle Aged; D010976:Platelet Count; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000097:blood / Q000188:drug therapy*; D011961:Receptors, Fc / Q000008:administration & dosage* / Q000276:immunology; D011993:Recombinant Fusion Proteins; D034061:Thrombopoiesis / Q000187:drug effects*; D013926:Thrombopoietin / Q000097:blood / Q000276:immunology
D000305:Adrenal Cortex Hormones; D000906:Antibodies; D002352:Carrier Proteins; D011961:Receptors, Fc; D011993:Recombinant Fusion Proteins; D013926:Thrombopoietin; C488777:romiplostim