ORLANDO – Treatments targeted to the neonatal Fc receptor are showing promise in phase 2 studies in primary immune thrombocytopenia, investigators reported at the annual meeting of the American Society of Hematology.
Encouraging outcomes support the continued phase 3 development of these agents, which are designed to block the neonatal Fc receptor (FcRn) in patients with this IgG-mediated disease.
Blocking FcRN is intended to prevent recycling of IgG, resulting in IgG degradation, according to the authors of studies evaluating rozanolixizumab, a subcutaneously administered monoclonal antibody, and efgartigimod, an intravenously administered antibody fragment, in primary immune thrombocytopenia (ITP).
Rozanolixizumab
Results of the phase 2 study of rozanolixizumab demonstrated that this agent reduced IgG levels and improved platelet counts at all doses tested, according to the investigators, led by Tadeusz Robak, MD, of the department of hematology at the Medical University of Lodz (Poland).
Efficacy endpoints were seen more quickly – by day 8 of treatment – with single subcutaneous infusions at higher doses, according to the researchers.
Headaches of mild to moderate severity were noted at higher doses, and no patients left the study because of adverse events, they reported.
“These safety, tolerability, and efficacy data support phase 3 development of rozanolixizumab in patients with primary ITP,” wrote Dr. Robak and coauthors in the abstract for their study.
A total of 66 adult patients with primary ITP were enrolled and treated with single or multiple subcutaneous doses of rozanolixizumab administered at 1-week intervals.
Baseline characteristics suggested a “difficult-to-treat” patient cohort that had a median ITP duration of nearly 6 years and a median of four prior therapies, including thrombopoietin receptor agonists in about one-third of patients, according to the investigators.
Platelet counts of at least 50 x 109/L were achieved by day 8 in more than half of patients who received single doses of rozanolixizumab at higher dose levels of 15 mg/kg (58.3%) and 20 mg/kg (54.5%), Dr. Robak and colleagues reported.
Mild to moderate headaches were seen in about 40% of patients over an 8-week observation period. There were no serious infections and, of four serious adverse events occurring during the study, none were deemed to be treatment related, according to the investigators.
“People who have primary ITP may experience low platelet count that can put them at risk for severe bleeding, and there are limited options that provide a rapid increase in platelet count to reduce this risk,” Dr. Robak said in an interview. “These data build on the growing body of evidence that suggest targeting the FcRn pathway could have the potential to transform the treatment experience for people with rare IgG autoantibody–mediated diseases such as primary ITP.”
Efgartigimod
Substantial reductions in IgG levels and clinically relevant increases in platelet counts were seen following a 3-week treatment cycle with efgartigimod in patients with treatment-refractory ITP, according to investigator Adrian C. Newland, MB, BCh, of the Royal London Hospital and coinvestigators.
The human IgG1 antibody Fc-fragment, a natural ligand of FcRN, is engineered to have increased affinity to FcRn, while preserving its pH‐dependent binding, according to the investigators.
Efgartigimod treatment was well tolerated and reduced the proportion of patients with bleeding in the phase 2 study presented at ASH 2019.
“This suggests that targeted IgG reduction with efgartigimod is a potential new treatment modality in primary ITP, and warrants evaluation of longer-term treatment in a larger phase 3 study,” the investigators reported in the abstract for their study.
The report described 38 patients randomized to four weekly intravenous infusions of placebo or efgartigimod at one of two dosing levels. Patients had long-standing ITP, with a median 4.8 years disease duration, and all had either failed splenectomy or had inadequate response to prior treatment.
Efgartigimod treatment rapidly reduced total IgG in all patients who received it, with a mean change from baseline of up to 63.7%, according to investigators.
Platelet counts favored the investigational treatment over placebo by several measures. Platelet counts of at least 50 x 109/L on two or more occasions were seen in 46% of efgartigimod-treated patients and 25% of the placebo group; that platelet count was achieved for 10 or more days in 38% and 0% of the efgartigimod and placebo groups, respectively.
Treatment was well tolerated, according to the investigators, who said there were “no dose-related safety observations.” Full results of the phase 2 investigation were published in the American Journal of Hematology, concurrent with the meeting (2019 Dec 10. doi.org/10.1002/ajh.25680).
The study of rozanolixizumab was supported by UCB; Dr. Robak reported disclosures related to UCB (honoraria, research funding), as well as Takeda, Janssen, Amgen, Roche, AbbVie, Gilead, BeiGene, Acerta, and MorphoSys. The study of efgartigimod was supported by argenx; Dr. Newland reported disclosures related to argenx, Novartis, Angle, Amgen, Ono Pharmaceutical, Shionogi, Rigel, and Dova Pharmaceuticals.
SOURCEs: Robak T et al. ASH 2019, Abstract 897; Newland AC et al. ASH 2019, Abstract 895.