A Phase 1/2 Study of RAD001, a mTOR Inhibitor, In Patients with Myelofibrosis: Final Results

Akt/mTOR activation has been found in association with dysregulated JAK2/STAT5 signaling due to JAK2V617F mutation. Increased phosphorylation of STAT5 and Akt was detected in patients (pts) with myeloproliferative neoplasms (MPN) (Grimwade LF, BJH 2009). We reported (Bogani C, ASH 2009) that RAD001, an oral inhibitor of mTOR, inhibited the proliferation of human and murine JAK2V617F-mutated cells and impaired colony formation by MPN progenitor cells, suggesting potential clinical activity.

We will report final data from an investigator-initiated, multicenter phase I/II trial with RAD001 in myelofibrosis, primary (PMF) and post-polycythemia vera/essential thrombocythemia (PPV/PET MF). Inclusion criteria were intermediate/high risk score (Lille criteria) or need of treatment because of progressing splenomegaly. Phase I involved a 3+3 pts scheme in 3 sequential cohorts at 5.0, 7.5, and 10 mg daily for 3 mo to establish maximum tolerated dose (MTD). Phase II was a two-stage Simon design involving 16+14 pts at MTD for 4 mo. The protocol was approved by IRBs and pts provided informed consent. The study was supported by Agenzia Italiana per il Farmaco (AIFA) and AIRC-Gruppo Italiano Malattie Mieloproliferative (AGIMM).

Phase I: there was no DLT at 10 mg daily, considered as MTD; there were 2 major (MR), 3 moderate (MO) and 1 minor (MI) and 3 no (NR) responses. In part 1 of Phase II, >1/16 pts achieved MR; according to study design, 14 additional pts were enrolled in part 2 (n=30). 20 patients had low and 10 intermediate Lille score; according to IWG-MRT criteria, 5, 10, 8 and 7 were low, int-I, int-II and high risk score, respectively. There were 16 PMF, 8 PPV- and 6 PET-MF. 20 pts were JAK2V617Fpos, 3 were MPLW515pos.

Patients evaluable for intention-to-treat (ITT) analysis as of aug 1^st were 26; the remaining 4 pts will be updated at meeting. Therapy was discontinued in 5 pts: 1 pt's decision at d60 without evidence of any >grade-2 toxicity, 2 at d60 and d90 for physician's decision due to grade-2 toxicity, 1 death due to respiratory failure at d60, 1 at d30 for grade-3 acute renal failure. 21/26 pts (81%) were available for per-protocol analysis. Therapy was generally well tolerated; commonest toxicities were grade-2 mouth ulcers and grade-1/2 hypertrigliceridemia. Hematological toxicities: 3 grade-2 and 4 grade-3 reversible anemia, one grade-2 neuthropenia, one grade-2 and 1 grade-3 reversible thrombocytopenia.

A reduction of spleen size consistent with CR, PR or NR was obtained in 8%, 46%, and 46% of the pts, respectively. 11 of 21 pts (52%) had complete resolution of systemic symptoms, and 14 of 19 pts (74%) reported disappearance of pruritus. Two pts achieved PR in anemia with decrease in transfusion requirement >50%, while in 3 pts Hb increased of 2g/dL. A CR in platelets was obtained in 3 of 19 pts and CR in leucocytes in 2 of 18 pts with abnormal blood count. Overall, according to ITT analysis: 6 major (23%), 6 moderate (23%), 2 minor (8%) and 12 NR (46%) (EUMNET criteria). According to IWG-MRT criteria, there were 6 (23%) clinical improvement. Per-protocol analysis: 33% major, 19% moderate, 5% minor, 43% NR; 24% clinical improvement. No disease progression.

Changes induced by RAD001 in some biological parameters were preliminary evaluated and will be finally updated at meeting. Blood levels of CCDN1 mRNA, a target of mTOR, significantly decreased in responders (MR+MO) versus non-responders (P=0.02). In the 13 JAK2-mutated pts who completed the treatment, the V617F allele burden was 61.6+/−15.8 versus 66.6+/−19.6% at baseline. There was a trend (P=0.07) towards a reduction of granulocyte WT1mRNA copy number in responders versus non-responders. We found no correlation of circulating CD34⁺ cells or CXCR4 expression with clinical response. A set of 46 inflammatory protein markers and cytokines were quantified before and at d30 of treatment. Some, including IL-10 and MIP-1beta, showed significant decrease while others increased, including Factor VII, IL-8 and MMP-2. Levels of MIP-1 beta were significantly lower in responders (P=0.006).

These data indicate that mTOR pathway targeting with RAD001 in MF pts induces an appreciable rate of response in splenomegaly, constitutional symptoms, and pruritus, with low-grade toxicity. However, effects on JAK2V617F mutational load were minimal, and should be better evaluated after longer trial duration.

Vannucchi:Novartis: Membership on an entity's Board of Directors or advisory committees. Off Label Use: This is an investigator-initiated, non-sponsored, clinical trial with RAD001 in myelofibrosis. Paratore:Novartis: Employment.