Drug allows for treatment-free periods in PV
ATLANTA—Results of a phase 1 study suggest patients with polycythemia vera (PV) can achieve extended treatment-free periods after receiving idasanutlin.
Six of 12 patients who received the drug were able to have a treatment holiday—4 patients for 1 month, 1 for 2 to 3 consecutive months, and 1 for more than 3 consecutive months.
Four patients achieved a complete response (CR) and 3 a partial response (PR), for an overall response rate (ORR) of 58%.
There were no dose-limiting toxicities (DLTs) in the trial.
John Mascarenhas, MD, of Icahn School of Medicine at Mount Sinai in New York, New York, reported these results at the 2017 ASH Annual Meeting as abstract 254.*
The study was supported by Roche and funded by the National Cancer Institute, PDRC, and a grant from the Leukemia and Lymphoma Society.
Study rationale
Patients with PV have higher levels of MDM2 in their CD34+ cells compared to normal CD34+ cells. Nutlins block the interaction between p53 and MDM2, thus activating the p53 pathway.
Investigators previously found that low doses of nutlin and pegylated IFNα 2a promoted apoptosis in PV CD34+ cells.
And treatment with the combination reduced the numbers of JAK2V617-positive cells transplanted into immune-deficient NOD/SCID mice.
So Dr Mascarenhas and his colleagues undertook a study (NCT02407080) to evaluate the toxicity, safety, and tolerability of the MDM2 antagonist idasanutlin in patients with PV and essential thrombocythemia (ET).
The investigators hypothesized that since overexpression of MDM2 negatively regulates wild-type p53 function in primary PV cells, idasanutlin therapy, either alone or in combination with low-dose peg-IFN, could result in selective reduction or elimination of the myeloproliferative neoplasm cells in PV patients.
Study design
The investigators evaluated 2 dose levels of idasanutlin—100 mg daily and 150 mg daily on days 1 to 5, repeated every 28 days. The first cycle was 56 days to allow investigators to evaluate any DLTs.
Dr Mascarenhas pointed out that the dose is 1/6 of that being evaluated in acute myeloid leukemia.
Investigators defined a DLT as a non-hematologic adverse event (AE) of grade 3 or higher or a hematologic AE of grade 2 or higher thrombocytopenia or grade 3 or higher neutropenia or anemia.
If patients did not achieve at least a PR by the end of cycle 3 of single-agent therapy, they could proceed to Part B of the study and receive idasanutlin with pegylated IFN.
After cycle 3, dosing was dependent upon patients hitting a hematocrit greater than 42% and/or platelet counts greater than 400,000.
“So you had to meet parameters, which means that if you did meet parameters, you could get a treatment holiday,” Dr Mascarenhas explained.
Patients were eligible if they had JAK2V617F-positive PV or ET confirmed by WHO diagnostic criteria.
They had to have high-risk disease, be older than 60, and have a history of thrombosis. They also had to be either intolerant or resistant to at least one prior treatment, including hydroxyurea, interferon, or anagrelide.
Patients were excluded if they had post-ET/PV myelofibrosis, blast phase disease, acute thrombosis within 3 months of screening, or uncontrolled inter-current illness.
Baseline patient characteristics
Eleven of the 12 patients enrolled had PV, and 1 had ET. Their median age was 63.5, and 7 were female. Their median duration of disease was 43.9 months (range, 14.9–154.3), 3 had previous thrombosis, and 10 had prior hydroxyurea therapy.
They had a median leukocyte count of 11.3 x 109/L, median hemoglobin levels of 13.6 g/dL, median hematocrit of 42.3%, and median platelet levels of 443.5 x 109/L.
