A first-in-man phase I study of R306465, a histone deacetylase (HDAC) inhibitor exploring pharmacokinetics (PK) and pharmacodynamics (PD) utilizing an electrochemiluminescent immunoassay in patients (p) with advanced tumours
3578 Background: R306565 is an aromatic hydroxamic acid with predominant inhibitory effects on Class 1 HDAC enzymes (with IC50 ∼10 nM). HDAC inhibitors (HDACi) affect gene expression at the transcriptional level, leading to cell cycle arrest and induction of apoptosis. Methods: P with solid tumours or lymphoma were given R306465 orally daily for 3 weeks (w) out of 4 in an escalating schedule. Objectives include safety, tolerability, PK (including food effect exploration), PD evaluation and circulating tumour cell (CTC) quantitation. Results: Four dose levels (100, 200, 300 and 400 mg) have been evaluated involving 15 p (7 male), age range 29–72 (median 59 y) and ECOG PS 0–2. A total of 37 cycles have been administered. Most common adverse events (AE) were Grade (G) 1–3 fatigue (87%), G1–2 nausea (66%), G1–2 vomiting (33%), G1–2 diarrhoea (40%), and G1–2 anorexia (40%). Dose limiting toxicity of G3 fatigue was seen in 1/6 p in the 400mg cohort. PK parameters were approximately dose proportional. Plasma concentrations increased in the fed state. PD effect of histone H3 acetylation (AcH3) in peripheral blood mononuclear cells (PBMC) was determined quantitatively with a novel validated electrochemiluminescent immunoassay developed in-house (applying Mesoscale Discovery technology). Although some interpatient variability exists, increased AcH3 was observed in 2/6 p in the 400 mg cohort, while the percentage rise in AcH3 was minimal for cohorts 1–3. Peak AcH3 achieved in 2 p dosed at 400 mg was approximately 5–10 fold increase over baseline. Using CellSearch technology for quantitation of CTCs, 8/14 p had detectable CTCs at baseline; the CTC trend will be presented. 4 p had stable disease (SD) for = 4 months. Conclusions: R306465 could be safely administered on a daily dosing schedule for 3 of 4 w up to 400 mg. Common toxicities seen were gastrointestinal and fatigue. Maximum tolerated dose has not been reached. PK suggests dose proportionality. Promising PD data showing increased acetylation in PBMC at 400 mg, further supports the utilization of the immunoassay platform in HDACi clinical trials. No significant financial relationships to disclose.