Agent reduces fibrosis, improves platelet counts in MF
VIENNA—The immunotherapeutic agent PRM-151, when given alone or in combination with ruxolitinib, can reduce bone marrow fibrosis and improve platelet counts in patients with myelofibrosis (MF), results of a phase 2 trial suggest.
Using a novel assessment technique known as computer-assisted image analysis (CIA), researchers found that PRM-151, with or without ruxolitinib, prompted fibrosis responses in nearly three-quarters of patients studied.
And nearly 60% of thrombocytopenic patients saw improvements in their platelet counts.
“Thrombocytopenia remains a significant problem for many patients with myelofibrosis, and a new treatment that is not myelosuppressive and actually increases platelet counts would be of great benefit to patients,” said Srdan Verstovsek, MD, PhD, of the University of Texas MD Anderson Cancer Center in Houston.
He and his colleagues presented this research—the first part of a 2-stage study—at the 20th Congress of the European Hematology Association (abstract P677*). The trial is sponsored by Promedior, the company developing PRM-151.
Stage 1 of the study included 27 patients with a median age of 67 (range, 51-85). They had been diagnosed with primary MF, post-polycythemia vera MF, or post-essential thrombocythemia MF.
The patients received PRM-151 at 10 mg/kg IV dosed weekly (n=8) or monthly (n=7), or ruxolitinib plus PRM-151 at 10 mg/kg IV dosed weekly (n=6) or monthly (n=6). The patients who received ruxolitinib were already taking the drug, and doses varied. The mean duration of ruxolitinib treatment was 1.6 years (range, 0.6-3 years).
Patients were set to receive study treatment for 24 weeks but could continue beyond that if they experienced clinical improvement.
Response assessment: Using CIA
Hematopathologists who were blinded to the patient, treatment, and time point performed morphologic analysis on bone marrow specimens taken at baseline and at 12, 24, and 36 weeks (if available).
The pathologists also performed CIA on whole-slide scans from specimens taken at the same time points. The idea to use CIA came after morphologic analyses revealed some surprising findings.
“[The pathologists] were really struck by the fact that, in the patients who had reductions in fibrosis, there were other elements in the bone marrow that showed improvements,” said Beth Trehu, MD, Chief Medical Officer at Promedior. “There were trends toward normalization of the red cells and of the megakaryocytes.”
“They also remarked that, whereas the baseline samples were totally homogeneous—a grade 3 was a grade 3 throughout the bone marrow—after treatment, the samples became very heterogeneous. There were areas of grade 3, grade 2, grade 1, and 0, all in one sample.”
To solve this problem, the pathologists decided that a sample’s WHO grade would be defined as whatever grade was present in at least 50% of the sample. But the team still thought these grades weren’t accurately quantifying the effects of PRM-151.
So they turned to CIA, which allowed them to quantify the volume of collagen or reticulin fibers in the bone marrow.
Fibrosis and platelet responses
According to CIA, 73% of evaluable patients (19/26) experienced reductions in bone marrow fibrosis at any time during the trial.
Of the 23 evaluable patients who had grade 2 or 3 fibrosis at baseline, 11 patients had a reduction of 1 grade or more during the study period, according to morphologic analysis. Nine patients had a fibrosis response by morphology at the last time point they were assessed.
Reductions in fibrosis correlated with increased platelet counts in thrombocytopenic patients. Fifty-seven percent of thrombocytopenic patients (8/14) saw an improvement in platelet counts after treatment.
Results across treatment groups were as follows:
