A phase I study of ruxolitinib in combination with abemaciclib for patients with primary or post-polycythemia vera/essential thrombocythemia myelofibrosis.

Abstract

TPS7086 Background: Patients (pts) with myelofibrosis (MF) have a reduced life-expectancy compared to age-matched controls. Several oral Janus Kinase (JAK) inhibitors such as ruxolitinib (RUX) have been approved by the US FDA based on improvements in symptom burden and spleen volume reduction compared to physician’s choice of best available therapy. However, duration of response to these agents is generally time-limited and treatment with JAK inhibitors is not considered to have disease-modifying potential. Additionally, median overall survival after RUX discontinuation is only 11-14 months. Thus, novel mechanism-based therapies for pts with disease progression on RUX are needed. JAK2 V617F mutations promote transition from G1 to S-phase of the cell cycle via increased expression of CDC25A, which is also upregulated in primary MPN patient samples. Additional cell cycle regulators such as CDK6 and Cyclin D have also been implicated in MF pathogenesis. Finally, we and others have shown that combination of the CDK4/6 inhibitors and RUX had synergistic effects in murine models of MF (Rampal et al., CCR 2021) providing the preclinical rationale for this trial. Methods: This multicenter, phase I dose-escalation trial (NCT05714072) evaluates the safety of RUX + the CDK4/6 inhibitor abemaciclib in pts with primary or secondary MF with intermediate-1/2 or high-risk disease by DIPSS who require treatment and had an inadequate response to RUX. Among the currently FDA-approved CDK4/6 inhibitors, abemaciclib was chosen for combination therapy due to less myelosuppressive effects compared with other CDK4/6 inhibitors. Inadequate response to RUX is defined by (I) palpable splenomegaly ≥5 cm below the left costal margin at study entry AND/OR (II) active MPN symptoms, as defined by the presence of one symptom score ≥5 or two symptom scores ≥3 using the screening MPN-SAF TSS. Following a conventional “3+3” dose-escalation design, pts will be treated with increasing doses of abemaciclib and stable doses of RUX (10mg or 15mg BID). The primary endpoint is to determine the maximum tolerated dose of RUX + abemaciclib. Secondary endpoints include measures of efficacy. Exploratory endpoints include changes in allele fraction of driver mutations, gene expression profiling, and clonal architecture to identify biomarkers of response, mechanisms of resistance, and to assess for any disease-modifying effects of the combination therapy. This trial is open to enrollment at Memorial Sloan Kettering Cancer Center and MD Anderson Cancer Center. Clinical trial information: NCT05714072 .