Abstract: NMS-P088 is a potent and selective inhibitor of FLT3 and KIT kinases, including variants with both primary as well as secondary resistance mutations, in particular retaining potent activity against residue 691 gatekeeper mutation which still represents an unmet medical need. Different form most clinically advanced selective FLT3 inhibitors, NMS-P088 was also shown to strongly inhibit CSF1R in biochemical assays (Ki= 4.5 nM; Kd 0.88nM). FLT3, KIT and CSF1R are members of the class III receptor tyrosine kinase family. Activating rearrangements of the JM domain of FLT3 (FLT3 ITD) occur in 20-25% of Acute Myeloid Leukemia (AML) and represent a driver of disease and a negative prognostic factor. Another 5-7% of AML cases harbor an activating D835 mutation in the activation loop of the kinase domain. KIT is also found mutated in circa 8.0% of AML, primarily in core binding factor (CBF) AML. CSF1R has been shown to polarize macrophages towards an immunosuppressive and tumor-promoting phenotype. CSF1 and/or CSF1R genes are expressed in AML blasts and CSF1R mediates supportive interactions between AML and stromal cells in the AML microenvironment. CSF1R has also been found to be highly expressed in blast samples from chronic myelomonocytic leukemia (CMML), a clonal hematopoietic stem cell disorder with poor survival rates post- blast transformation. Hypomethylating agents or standard induction with chemotherapy are the most commonly used therapeutic intervention for CMML and no targeted therapy is currently approved. We found that in vitro NMS-P088 has potent activity on CSF1-dependent macrophages, inhibiting CSF1-stimulated proliferation and cell signalling. In mice NMS-P088 efficiently and dose-dependently decreased tissue infiltration of CSF1R expressing macrophages in liver, consistent with potent in vivo inhibition of this kinase. Furthermore, it showed single agent efficacy in a syngeneic mouse tumor model, with robust reduction of CSF-1R positive intratumoral macrophages. Importantly, we observed high expression of CSF1R in blast samples derived from CMML patients, and the compound was able to inhibit their proliferation and CSF1R signalling. It has been reported that treatment with CSF1R inhibitors induces upregulation of circulating CSF1 ligand as compensatory feedback modulation. Accordingly, during preclinical studies of NMS-088 conducted in non-human primates, a dose-related increase of circulating CSF1 levels was consistently observed. These data confirm in vivo CSF1R inhibition by NMS-P088 and support the opportunity to monitor CSF1 levels as a pharmacodynamic biomarker of CSF1R modulation in the clinical setting. Based on its original kinase targets profile, including FLT3 and KIT gatekeeper resistance mutations as well as CSF1R, preclinical efficacy and safety NMS-P088 was selected to initiate in a clinical trial to potentially address unmet medical needs in AML and CMML. Citation Format: Marina Ciomei, Elena Ardini, Laura Gianellini, GianMaria Borleri, Gemma Texido Romero, Roberta Ceruti, Wilma Pastori, Nilla Avanzi, Daniele Casero, Paola Gnocchi, Andrea Lombardi Borgia, Federico Lussana, Alessandro Rambaldi, Arturo Galvani, Antonella Isacchi. NMS-P088, a novel FLT3, KIT and CSF1R inhibitor, is a promising clinical candidate for AML and CMML treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1324.

Abstract: Background: NMS-03592088 is a novel, potent inhibitor of the FLT3, CSF1R and KIT receptor tyrosine kinases (KD 〈 1 nM for all three targets). The compound demonstrated high preclinical efficacy following oral administration in all tested target-dependent tumor models, including those harboring kinase domain secondary resistance mutations, such us the FLT3 residue 691 gatekeeper mutation and the KIT residue 670 and exon 17 mutations. In a FLT3-ITD model of disseminated AML, efficacy observed following single agent treatment with NMS-03592088 was further significantly increased when administered in combination with cytarabine, with excellent tolerability. In preclinical studies conducted in non-human primates, a dose-related increase of circulating CSF1 levels was observed in association with the administration of NMS-03592088, consistent with in vivo inhibition of CSF1R by the compound, thus providing the opportunity for the use of CSF1 levels as a potential pharmacodynamic biomarker of CSF1R modulation in the clinical setting. All three targets of NMS-03592088 are relevant in different settings of hematologic malignancies and solid tumors. In particular, FLT3 mutations occur in approximately 30% of acute myeloid leukemia patients (AML), and are associated with a poor prognosis; KIT mutations are reported in patients with the core-binding factor (CBF) subtype of AML and the CSF1 and/or CSF1R genes are frequently expressed in AML blasts. Recent experimental evidence suggests a potential therapeutic rationale for CSF1R blockade in AML, possibly due to interference with microenvironmental support [Edwards DK et al, Blood, 2019, 133: 588]. Furthermore, chronic myelomonocytic leukemia (CMML) blasts express high levels of CSF1R and NMS-03592088 was able to effectively inhibit their proliferation, concomitant with the suppression of intracellular CSF1R dependent signalling. A clinical trial exploring safety, tolerability and efficacy of NMS-03592088 in patients with AML and CMML is therefore warranted. Trial design: This first-in-human study (EudraCT Number: 2018-002793-47) is designed as an open-label multicenter Phase I/II trial including patients with relapsed or refractory AML or CMML who have exhausted standard treatment options, or for whom standard therapy is considered unsuitable. The study is designed to characterize the safety, tolerability, pharmacokinetics, pharmacodynamics and to explore the preliminary anticancer activity of NMS-03592088 administered orally as single agent once daily for 21 consecutive days, followed by a 7-day break within a 28 day cycle. The study includes an initial conventional phase I part with an accelerated dose titration design in subsequent cohorts of 3+3 patients aimed at defining the maximal tolerated dose (MTD) and the recommended phase 2 dose (RP2D), followed by a limited dose expansion to confirm the RP2D. Once the RP2D is confirmed, a single-stage exploratory Phase II part will start comprising two parallel cohorts, one cohort will consist of AML FLT3 mutated patients and one of patients with CMML. Patients previously treated with FLT3 inhibitors are allowed to participate. The primary endpoint of the Phase II portion of the study is Overall Response Rate. Efficacy will be assessed according to standard criteria [Döhner H et al, Blood 2017, 129: 424; Savona MR et al., Blood, 2015, 125: 1857]. Exploratory endpoints are included to evaluate the potential effects of treatment with NMS-03592088 on circulating levels of CSF1 in plasma, the potential correlation of cellular CSF1R expression levels with clinical outcome in both AML and CMML, and the mutational status of a panel of leukemia-related genes, not limited to FLT3. The Phase I part started in Italy in March, 2019 and is currently ongoing. Disclosures Ciomei: NMS: Employment. Zanetta:Clioss: Employment. Fiorentini:Accelera: Employment. Bosotti:NMS: Employment. Ardini:NMS: Employment. Lombardi Borgia:NMS: Employment. Pulci:Accelera: Employment. Gatto:Clioss: Employment. Di Sanzo:Clioss: Employment. Colajori:Clioss: Consultancy. Davite:Clioss: Employment. Galvani:NMS: Employment. Gan:NMS: Employment. Rossi:Janssen: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Jazz: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria; Mundipharma: Honoraria; BMS: Honoraria; Sandoz: Honoraria; Daiichi-Sankyo: Consultancy; Roche: Membership on an entity's Board of Directors or advisory committees. Rambaldi:Jazz: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau, travel support; Novartis: Membership on an entity's Board of Directors or advisory committees, Other: travel support, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees, Other: travel support, Speakers Bureau; Roche: Membership on an entity's Board of Directors or advisory committees, Other: travel support, Research Funding, Speakers Bureau; Amgen: Membership on an entity's Board of Directors or advisory committees, Other: travel support, Research Funding, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Italfarmaco: Membership on an entity's Board of Directors or advisory committees, Other: travel support, Research Funding, Speakers Bureau; Gilead: Membership on an entity's Board of Directors or advisory committees, Other: travel support, Speakers Bureau; Omeros: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Isacchi:NMS: Employment.