First-in-man, first-in-class phase I study with the monopolar spindle 1 kinase inhibitor S81694 administered intravenously in adult patients with advanced, metastatic solid tumours.

BACKGROUND: S81694 is an inhibitor of monopolar spindle 1 kinase, a target expressed in proliferating cells. CL1-81694-001 was the first-in-human study aiming at identifying a safe dosing schedule in solid tumour patients. PATIENTS AND METHODS: This trial was based on inter-individual dose-escalation of single agent S81694 in cohorts of ≥3 patients to assess the safety and tolerability and determine dose-limiting toxicities (DLTs), maximum tolerated dose (MTD) and recommended phase II dose (RP2D), with S81694 given on days 1,8,15 of a 28-day cycle as 1-h infusion. RESULTS: 38 patients were treated at doses ranging from 4 to 135 mg/m2/week; 144 cycles were administered (median 2/patient; range 1-32 cycles). Patients discontinued treatment for disease progression (78.9%), adverse events (AE; 18.4%) or withdrawal of consent (2.6%). Treatment modifications occurred in 22 patients (57.9%; 49 cycles). Common treatment-emergent AEs were fatigue (22 patients;57.9%), anaemia (17;44.7%) and nausea (12;31.6%). Haematological toxicity was mild, with Grade 3 anaemia observed in three patients and neutropenia mainly seen at the 135 mg/m2 dose level. Three first cycle DLTs included G3 anaemia (4 mg/m2 dose), G4 hypertension (20 mg/m2), G3 fatigue (135 mg/m2). MTD was not reached due to premature discontinuation of enrolment based on a sponsor decision. Among 35 patients evaluable for response, one (renal cell carcinoma) had a complete response, one (hepatocellular carcinoma) had a transient decrease of target lesions and 13 had stable disease. Seven patients remained on study for ≥6 cycles, two at the 135 mg/m2 dose. CONCLUSIONS: S81694 can be administered safely as a single agent in adults with solid tumours on days 1,8,15 of a 28-day cycle up to a dose of 135 mg/m2/week without reaching MTD. The RP2D was not defined due to the prioritization of the use of S81694 in combination with cytotoxic agents, based on emerging preclinical data. TRIAL REGISTRATION: EudraCT number: 2014-002023-10; ISRCTN registry ISRCTN35641359.

Nkx2-5(+)islet1(+) mesenchymal precursors generate distinct spleen stromal cell subsets and participate in restoring stromal network integrity.

Secondary lymphoid organ stromal cells comprise different subsets whose origins remain unknown. Herein, we exploit a genetic lineage-tracing approach to show that splenic fibroblastic reticular cells (FRCs), follicular dendritic cells (FDCs), marginal reticular cells (MRCs), and mural cells, but not endothelial cells, originate from embryonic mesenchymal progenitors of the Nkx2-5(+)Islet1(+) lineage. This lineage include embryonic mesenchymal cells with lymphoid tissue organizer (LTo) activity capable also of supporting ectopic lymphoid-like structures and a subset of resident spleen stromal cells that proliferate and regenerate the splenic stromal microenvironment following resolution of a viral infection. These findings identify progenitor cells that generate stromal diversity in spleen development and repair and suggest the existence of multipotent stromal progenitors in the adult spleen with regenerative capacity.