Safety and efficacy of everolimus, a mTOR inhibitor, as single agent in a phase 1/2 study in patients with myelofibrosis

Abstract

In addition to dysregulated JAK/STAT signaling, activation of the AKT/mTOR pathway occurs in myelofibrosis, a myeloproliferative neoplasm with no approved therapies. We conducted a phase 1/2 study with everolimus, an mTOR inhibitor, in 39 high- or intermediate-risk primary or postpolycythemia vera/postessential thrombocythemia myelofibrosis subjects. Responses were evaluated in 30 patients of phase 2. No dose-limiting toxicity was observed in phase 1 up to 10 mg/d. When this dose was used in phase 2, grade ≥ 3 toxicities were infrequent; the commonest toxicity was grade 1-2 stomatitis. Rapid and sustained splenomegaly reduction of > 50% and > 30% occurred in 20% and 44% of subjects, respectively. A total of 69% and 80% experienced complete resolution of systemic symptoms and pruritus. Response in leukocytosis, anemia, and thrombocytosis occurred in 15%-25%. Clinical responses were not associated with reduced JAK2V617F burden, circulating CD34(+) cells, or cytokine levels, whereas CCDN1 mRNA and phospho-p70S6K level, known targets of mTOR, and WT1 mRNA were identified as possible biomarkers associated with response. Response rate was 60% when European Network for Myelofibrosis criteria were used (8 major, 7 moderate, 3 minor responses) or 23% when IWG-MRT criteria (1 partial response, 6 clinical improvements) were used. These results provide proof-of-concept that targeting mTOR pathway in myelofibrosis may be clinically relevant.

Figure 1

Responses of splenomegaly, constitutional symptoms, and pruritus to RAD001 therapy. The proportion of patients who presented variable reduction of splenomegaly at 1 and 4 months of therapy, expressed as percent change from the baseline, is shown in panel A. The decrease of spleen enlargement was already maximal at 1 month, and it was maintained up to the end of treatment. Panel B and C represent the proportion of patients who presented constitutional symptoms (B) or pruritus (C) at baseline and their response to therapy at each month. Only patients who reported complete disappearance of night sweats, fever (B), or pruritus (C) were considered as responders.

Figure 2

The phosphorylation status of the mTOR target, p70S6K, measured at 1 month of treatment, correlates with obtainment of clinical response. Proteins extracted from peripheral blood cells, collected at baseline (D0) and at 1 month of treatment (D30), were subjected to SDS-PAGE electrophoresis and Western blotting and probed with antibodies against the total and phosphorylated form of p70S6K; tubulin was used for loading normalization. Top, 5 patients who showed a major-to-moderate clinical response; bottom, 5 patients who were defined as nonresponders.

Figure 3

Changes in plasma levels of selected cytokines and inflammatory markers in patients included in phase 2 of the study. Plasma levels of 46 cytokines and inflammatory proteins were evaluated in samples obtained at baseline and after 1 month of therapy. The HumanMAP Version 1.6 panel (Rules-Based Medicine), was used for this analysis. Results are shown as heat map, with each row indicating the plasma marker and the columns corresponding to individual patients. In the left part of the plot, corresponding to baseline samples, the green and red denote proteins that were present in the patients at lower or higher levels, respectively, relative to normal control subjects. In the columns on the right, corresponding to 1 month of treatment, red and green indicate the proteins whose levels increased or decreased, respectively, compared with the baseline level for the same patient.