Objective: AZD9150 (ISIS 481464) is a 16-nucleotide oligonucleotide antisense molecule designed to reduce expression of human STAT3 protein by targeted down-regulation of STAT3 messenger RNA and is currently in clinical development in advanced solid tumors. The recommended Phase 2 dose (RP2D) for AZD9150 is 3 mg/kg, dosed based on ideal body weight (IBW) with three loading doses on day 1, 3 and 5 in week 1 followed by weekly dosing thereafter. The objective of the current analysis was to assess the effect of body size on AZD9150 pharmacokinetics (PK) to determine the appropriate dosing approach using population PK modeling.

Methods: PK and demographics data from 3 phase I/II studies (481464-CS1 [NCT01563302], D5660C00001 [NCT01839604], D5660C00004 [NCT02499328]) in total of 126 patients with diffuse large B-cell lymphoma (DLBCL), hepatocellular carcinoma (HCC) and squamous-cell carcinoma in head and neck (SCCHN), receiving doses ranging from 1 to 4 mg/kg as monotherapy or in combination with durvalumab, were used in the population PK analysis. Both 2-compartment and 3-compartment structure PK models were tested in the analysis. Patient characteristics including age, ideal body weight (IBW), race and sex were explored as covariates on relevant AZD9150 PK parameters in an automated forward inclusion followed by backward elimination procedure through use of the stepwise covariate modelling. Once a final model was identified, simulations (n=1000, body weight distribution 30 to 100 kg) were conducted to compare AZD9150 exposures at the RP2D of 3 mg/kg versus a flat dose of 200 mg.

Results: A 2-compartment model with linear elimination well described the data. None of the covariates (inc. IBW) were found to significantly impact AZD9150 PK. The final PK model parameter estimate for clearance (CL), central volume of distribution (V1) and peripheral volume of distribution (V2) are 3.11 L/h, 5.56 L and 87.3 L, respectively. Model based simulations demonstrate that systemic exposure of AZD9150 was similar between 3 mg/kg versus 200 mg dose with slightly less overall between-patients variability with the flat dosing regimen.

Conclusion: Population PK modeling supports the potential switch of dosing approach from 3 mg/kg dose to a flat dose of 200 mg. The AZD9150 flat dosing rationale and schedule has been granted approval by FDA (for IND 137525) and also by MHRA (for BISCAY trial) as the first protocol / IMPD to be approved in the EU. Flat dose of 200 mg is currently being evaluated in ongoing clinical studies.

Citation Format: Xiao Tong, Ganesh Mugundu, Martin Scott, Carl Cook, Paul Lyne, Nidal Al-Huniti, Hongmei Xu. Rationale for flat dosing of AZD9150 by population pharmacokinetic analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr CT103.