A Phase 2 Consortium (P2C) Trial of R115777 (Tipifarnib) in Myelofibrosis with Myeloid Metaplasia.
Authors: Mesa Ruben A. , Camoriano John K. , Geyer Susan M. , Kaufmann Scott H. , Rivera Candido E. , Erlichman Charles , Tefferi Ayalew 
Published: October 2019

Background: Myelofibrosis with myeloid metaplasia (MMM) is a progressive and fatal myeloproliferative disorder with limited therapeutic options. R115777 is a non-peptidomimetic enzyme-specific inhibitor of farnesyl protein transferase (FT) which we recently reported has in vitro activity against aberrant myeloid progenitors from MMM patients (Leukemia2003;17:849). This observation, coupled with the clinical activity demonstrated in high risk acute myeloid leukemia (Blood2001;97:3361) and chronic myeloid disorders (Blood2003;101:1692) led us to perform a Phase II trial in patients (pts) with MMM.

Methods: Eligible pts had histologically confirmed MMM and were symptomatic, defined by anemia (hemoglobin<10g/dL or transfusion dependent) or palpable hepatosplenomegaly. Pts received 300 mg of R115777 orally twice daily for the first 21 days of a 28 day cycle. Dose escalations (up to 1200mg/day) and reductions (down to 100mg/day) were allowed based on activity and toxicity. The primary endpoint was response as defined by improvement in either anemia or organomegaly.

Results: 34 pts (median age 65 yrs, range 55–80; 71% male) were enrolled in the trial. All pts displayed symptomatic disease at enrollment, with 10 who were erythrocyte transfusion dependent; and 19 (56%) had a Lille MMM prognostic score ≥1; no pts were significantly thrombocytopenic at entry by enrollment criteria. Median pre-study spleen and liver sizes were 12 cm (range: 0–35) and 2 cm (range: 0–15) below the left and right costal margin, respectively. Median time to discontinuation of therapy was 5.5 months (95% CI:2.9–6.4). Reasons for early termination were progression (7), adverse reactions (5), co-morbidities (2), refusal of further treatment (2), and death on study (1). One pt died of grade 5 pneumonitis two weeks after study enrollment, which was felt to be unrelated to study treatment. Significant toxicities (≥ grade 3) were seen for myelosuppression (n=13), neuropathy (n=2), fatigue (n=1), rash (n=1) and hyponatremia (n=1). Overall, R115777 resulted in little improvement in anemia, with the exception of one anemia-based partial response. However, the myelosuppressive aspects of the agent may have masked improvements in cytopenias. In contrast, R115777 did result in clinically relevant decreases in organomegaly in 11 pts (33%) (splenomegaly in 3 pts, hepatomegaly in 5 pts, and both in an additional 3 pts.) Across all pts who had some reduction in splenomegaly, the median maximal reduction was 42.5% (of palpable component; range: 8–100%). Likewise, all patients with baseline hepatomegaly had resolution of this problem at some point during therapy. Four pts remain on the agent (from 14 to 22 months) for continued and sustained improvement in organomegaly. Responses observed did not significantly correlate with reductions in bone marrow fibrosis, osteosclerosis, neoangiogenesis, or resolution of baseline karyotypic abnormalities.

Conclusions: R115777 has demonstrated preliminary activity against MMM associated organomegaly. Whether this latter benefit is independent of R115777 induced myelosuppression is unclear. The myelosuppression observed was generally mild and without clinical consequence, although it was difficult to differentiate between myelosuppression versus disease progression. Pts continue to be followed to evaluate durability of observed responses, long term effects on anemia and intramedullary manifestations of the disease.