Phase 1/2 Study of TP-3654, a Selective PIM1 Kinase Inhibitor: Preliminary Data Showed Clinical Activity and Cytokine Reductions in Relapsed/Refractory Myelofibrosis Patients

Background: PIM1 expression is significantly upregulated in hematologic malignancies including myelofibrosis (MF) and has been shown to play a role in modulating the activity of cytokine induced PI3K/AKT and JAK/STAT pathways. The distinct clinical features of MF are partly attributed to the elevated circulating cytokines; a subset of which are shown to correlate with poor prognosis. TP-3654, an oral investigational highly selective PIM1 kinase inhibitor, is currently being evaluated in a phase 1/2 study in patients (pts) with relapsed/refractory MF. In preclinical studies, TP-3654 alone and in combination with ruxolitinib showed spleen size and bone marrow (BM) fibrosis reduction in murine MF models. Importantly, TP-3654 also showed reduction of cytokine response genes and serum TGF-β in progenitor cells and JAK2V617F murine MF model, respectively.

Methods: This phase 1/2 study evaluates the safety and efficacy of TP-3654 monotherapy in pts with MF (NCT04176198). Key eligibility criteria include primary or secondary MF; previously treated with or ineligible for JAK inhibitor treatment; DIPSS intermediate 1, 2 or high-risk MF; platelet ≥25x10 ⁹/L; splenomegaly (≥450 cm ³ by imaging); and ≥2 measurable symptoms per MFSAF v4. The study aims to identify the MTD and/or RP2D of TP-3654 monotherapy and to assess safety, clinical activity (spleen volume reduction [SVR], total symptom score [TSS] improvement), PK, and PD markers (cytokine profile, BM fibrosis etc.). We investigated the patterns of similarity of 43 cytokines changes after 12 weeks of TP-3654 treatment using principal component analysis (PCA).

Results: As of 20 June 2023, a total of 23 pts enrolled across 5 dose levels in the phase 1 dose escalation part. At baseline, median age 73 years (range 61, 80), spleen volume 2008.2 cm ³ (range 609, 6006), TSS 20.8 (range 4, 62), platelet 115 x10 ⁹/L (range 64, 520), hemoglobin 10.1 g/dL (range 5.9, 13.7; 5 pts requiring transfusion). All pts, except one, had received ≥1 prior JAK inhibitor treatment (median 12.9 months [range 2.3, 81.0]). Median duration of TP-3654 treatment was 14.9 weeks (range 2, 96). No DLT occurred. Treatment-related adverse events (TRAEs) occurring in ≥20% of pts included grade 1/2 nausea, vomiting, and diarrhea. Grade 3 TRAEs were diarrhea (n=1) and platelet count decreased (n=2). Mean hemoglobin and platelet counts remained stable throughout the 24-week treatment period. SVR observed in 10 of 13 evaluable pts treated for ≥12 weeks (median best change -11%, range +97% to -63%); 3 pts showed ≥35% SVR. TSS improvement were observed in 12 of 13 evaluable pts (median best change -70%, range +9 to -100%); 7 pts showed ≥50% TSS response (Fig 1A); 5 pts had durable response for ≥12 weeks. Broad reductions in cytokines observed as early as within the first 24 hours after TP-3654 treatment. At week 12, pts with higher cytokine reductions correlated with greater TSS improvement. Two components of the PCA, PC1 and PC7, include MF associated cytokines such as IL-8, IL-18, CD40, ENRAGE amongst others, were reduced with TP-3654 treatment and these reductions correlated with symptom improvement (Fig 1B). BM fibrosis was reduced in one pt who also achieved spleen and symptom responses, showed MF associated cytokine reductions, and is on active treatment for 2 years.

Conclusions: This preliminary data of TP-3654 in relapsed/refractory MF pts showed early signs of clinical activity including spleen volume reduction, TSS improvement, and correlating cytokine reductions. TP-3654 is well tolerated with limited myelosuppressive adverse events. Enrollment is ongoing as monotherapy and current data support the development of TP-3654 in combination with JAK inhibitors given the preliminary clinical activity and minimal cytopenia.