ABSTRACT:With efforts to reduce cytochrome P450-mediated clearance (CL) during the early stages of drug discovery, transporter-mediated CL mechanisms are becoming more prevalent. However, the prediction of plasma concentration-time profiles for such compounds using physiologically based pharmacokinetic (PBPK) modeling is far less established in comparison with that for compounds with passively mediated pharmacokinetics (PK). In this study, we have assessed the predictability of human PK for seven organic aniontransporting polypeptide (OATP) substrates (pravastatin, cerivastatin, bosentan, fluvastatin, rosuvastatin, valsartan, and repaglinide) for which clinical intravenous data were available. In vitro data generated from the sandwich culture human hepatocyte system were simultaneously fit to estimate parameters describing both uptake and biliary efflux. Use of scaled active uptake, passive distribution, and biliary efflux parameters as inputs into a PBPK model resulted in the overprediction of exposure for all seven drugs investigated, with the exception of pravastatin. Therefore, fitting of in vivo data for each individual drug in the dataset was performed to establish empirical scaling factors to accurately capture their plasma concentration-time profiles. Overall, active uptake and biliary efflux were under-and overpredicted, leading to average empirical scaling factors of 58 and 0.061, respectively; passive diffusion required no scaling factor. This study illustrates the mechanistic and model-driven application of in vitro uptake and efflux data for human PK prediction for OATP substrates. A particular advantage is the ability to capture the multiphasic plasma concentration-time profiles for such compounds using only preclinical data. A prediction strategy for novel OATP substrates is discussed.

Purpose: Selective inhibition of cyclin-dependent kinases 4 and 6 (CDK4/6) represents a promising therapeutic strategy. However, despite documented evidence of clinical activity, limited information is available on the optimal dosing strategy of CDK4/6 inhibitors. Here, we present an integrated semimechanistic pharmacokinetic/pharmacodynamic model to characterize the quantitative pharmacology of LY2835219, a CDK4/6 inhibitor, in xenograft tumors.Experimental Design: LY2835219 plasma concentrations were connected to CDK4/6 inhibition and cell-cycle arrest in colo-205 human colorectal xenografts by incorporating the biomarkers, phospho-(ser780)-Rb, topoisomerase II a, and phosphohistone H3, into a precursor-dependent transit compartment model. This biomarker model was then connected to tumor growth inhibition (TGI) by: (i) relating the rate of tumor growth to mitotic cell density, and (ii) incorporating a concentration-dependent mixed cytostatic/ cytotoxic effect driving quiescence and cell death at high doses. Model validation was evaluated by predicting LY2835219-mediated antitumor effect in A375 human melanoma xenografts.Results: The model successfully described LY2835219-mediated CDK4/6 inhibition, cell-cycle arrest, and TGI in colo-205, and was validated in A375. The model also demonstrated that a chronic dosing strategy achieving minimum steady-state trough plasma concentrations of 200 ng/mL is required to maintain durable cell-cycle arrest. Quiescence and cell death can be induced by further increasing LY2835219 plasma concentrations.Conclusions: Our model provides mechanistic insight into the quantitative pharmacology of LY2835219 and supports the therapeutic dose and chronic dosing strategy currently adopted in clinical studies.

Background and ObjectivesAbemaciclib, a dual inhibitor of cyclin-dependent kinases 4 and 6, has demonstrated clinical activity in a number of different cancer types. The objectives of this study were to characterize the pharmacokinetics of abemaciclib in cancer patients using population pharmacokinetic (popPK) modeling, and to evaluate target engagement at clinically relevant dose levels.MethodsA phase I study was conducted in cancer patients which incorporated intensive pharmacokinetic sampling after single and multiple oral doses of abemaciclib. Data were analyzed by popPK modeling, and patient demographics contributing to pharmacokinetic variability were explored. Target engagement was evaluated by combining the clinical popPK model with a previously developed pre-clinical pharmacokinetic/pharmacodynamic model.ResultsThe pharmacokinetic analysis incorporated 4012 plasma concentrations from 224 patients treated with abemaciclib at doses ranging from 50 to 225 mg every 24 h and 75 to 275 mg every 12 h. A linear one-compartment model with time- and dose-dependent relative bioavailability (F rel) adequately described the pharmacokinetics of abemaciclib. Serum albumin and alkaline phosphatase were the only significant covariates identified in the model, the inclusion of which reduced inter-individual variability in F rel by 10.3 percentage points. By combining the clinical popPK model with the previously developed pre-clinical pharmacokinetic/pharmacodynamic model, the extent of target engagement in skin in cancer patients was successfully predicted.ConclusionThe proportion of abemaciclib pharmacokinetic variability that can be attributed to patient demographics is negligible, and as such there are currently no dose adjustments recommended for adult patients of different sex, age, or body weight.Trial registrationNCT01394016 (ClinicalTrials.gov).Electronic supplementary materialThe online version of this article (doi:10.1007/s40262-017-0559-8) contains supplementary material, which is available to authorized users.

LY2874455 has an RP2D of 16 mg BID and demonstrated good tolerability and activity in solid-organ cancer patients. The role of FGFR inhibition on tumor growth in patients requires further study. (NCT01212107).

Background:Resistance to BRAF inhibition is a major cause of treatment failure for BRAF-mutated metastatic melanoma patients. Abemaciclib, a cyclin-dependent kinase 4 and 6 inhibitor, overcomes this resistance in xenograft tumours and offers a promising drug combination. The present work aims to characterise the quantitative pharmacology of the abemaciclib/vemurafenib combination using a semimechanistic pharmacokinetic/pharmacodynamic modelling approach and to identify an optimum dosing regimen for potential clinical evaluation.Methods:A PK/biomarker model was developed to connect abemaciclib/vemurafenib concentrations to changes in MAPK and cell cycle pathway biomarkers in A375 BRAF-mutated melanoma xenografts. Resultant tumour growth inhibition was described by relating (i) MAPK pathway inhibition to apoptosis, (ii) mitotic cell density to tumour growth and, under resistant conditions, (iii) retinoblastoma protein inhibition to cell survival.Results:The model successfully described vemurafenib/abemaciclib-mediated changes in MAPK pathway and cell cycle biomarkers. Initial tumour shrinkage by vemurafenib, acquisition of resistance and subsequent abemaciclib-mediated efficacy were successfully captured and externally validated. Model simulations illustrate the benefit of intermittent vemurafenib therapy over continuous treatment, and indicate that continuous abemaciclib in combination with intermittent vemurafenib offers the potential for considerable tumour regression.Conclusions:The quantitative pharmacology of the abemaciclib/vemurafenib combination was successfully characterised and an optimised, clinically-relevant dosing strategy was identified.

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2548 Background: Tumor-associated macrophages (TAM) correlate with increased invasiveness, growth, and immunosuppression. Activation of CSF-1R results in proliferation, differentiation, and migration of monocytes/macrophages. CSF-1R inhibition with LY3022855 (LY), a human immunoglobulin G subclass 1 (IgG1) monoclonal antibody (mAB), may have favorable anti-tumor effects. We evaluated the safety and clinical response of LY monotherapy. Methods: Patients (pts) with advanced refractory MBC and MCRPC received LY intravenously in 6-week cycles in cohorts: A) 1.25 mg/kg every 2 weeks [Q2W]; B) 1.0 mg/kg on Weeks 1, 2, 4, and 5; C) 100 mg once weekly; D)100 mg Q2W. MCRPC pts were enrolled in cohorts A and B; MBC pts were enrolled in all cohorts. Anti-tumor activity was assessed using RECIST v1.1 by radiological imaging every 6 weeks. Results: Thirty-four pts (22 MBC; 12 MCRPC) received ≥1 dose of LY. Median age was 57.0 years (range: 32.0–81.0) for MBC pts and 72.5 years (range: 58.0–84.0) for MCRPC pts. Baseline Eastern Cooperative Oncology Group performance status was 0 (n = 13, 38.2%), 1 (n = 18, 52.9%), or 2 (n = 3, 8.8%). MBC pts were hormone receptor (HR) positive (n = 20), HR negative (n = 1), or unknown (n = 1); 3 MBC pts received concurrent hormone therapy. Common treatment-related adverse events of any grade were fatigue (38.2%), decreased appetite (26.5%), nausea (26.5%), increased lipase (23.5%), and increased creatine phosphokinase (20.6%). No complete or partial response was observed. Stable disease (SD) was observed in 5/22 MBC pts (duration 82–302 days) and 3/7 evaluable MCPRC pts (duration 50–124 days). Two MBC pts (9%; Cohort A) had durable SD > 9 months and 1 pt had palpable reduction in a nontarget neck mass. Circulating CSF1 and IL-34 increased at Day 8 suggestive of target engagement. Pharmacokinetics of LY were consistent with other IgG1 mAbs. Conclusions: LY3022855 was well tolerated and showed evidence of target engagement. Clinically meaningful SD > 9 months was observed in 2 MBC pts. Tumor biomarker analyses are underway. Clinical trial information: NCT02265536.

2523 Background: Binding of CSF-1 to the CSF-1 receptor (CSF-1R) results in proliferation, differentiation, and migration of monocytes/macrophages. Intratumoral infiltration with macrophages correlates with increased invasiveness, growth, and immunosuppression. LY3022855 (LY) is a human IgG1 antibody (mAb) targeting CSF-1R. Methods: Eligible pts (ECOG 0-2) with advanced solid tumors were enrolled. Mandatory pre and post-treatment biopsies were obtained. LY was given on a 6-week cycle. Two escalation regimens (Part A: weight-based dosing; Part B: flat dosing) were investigated in a 3+3 design. Primary objective was to establish the safety and characterize the pharmacokinetics (PK) of LY. Secondary objectives were to establish recommended phase 2 dose (RP2D) and to characterize pharmacodynamics (PD). Results: As of Sept 6, 2016, 35 cancer pts (colorectal 14; lung 4; pancreas 3; others 14) were treated (29 in Part A; 6 in Part B) with median treatment duration 4 weeks (range 1-21). Common treatment-emergent adverse events (TEAEs) were fatigue (54%), hypoalbuminemia (40%), nausea (37%), AST increase (37%), anemia (34%), anorexia (34%), creatine kinase elevation (29%), and constipation (23%). Most common grade (G) 3/4 TEAEs were anemia (11%), fatigue (11%), ascites (9%), and lymphocyte count decrease (9%). 3/28 evaluable pts had DLTs: G3 left ventricular systolic dysfunction (1), G4 rhabdomyolysis and G4 acute renal failure (1), and G3 pancreatitis (1). Eight treatment unrelated deaths were reported. One pt (adenoid cystic carcinoma) had stable disease (~3 mo as of last visit), 19 pts had progressive disease, and 15 pts were non-evaluable for response assessment. PK profile of LY was consistent with IgG1 mAbs. An interim analysis following completion of Part A demonstrated a lack of relationship between weight and clearance, prompting evaluation of non-weight based dosing. PD analyses revealed dose-dependent increases in serum CSF-1 levels as well as suppression of circulating non-classical monocytes (CD14dim CD16bright), indicating biologic activity at studied doses. Conclusions: RP2D for LY monotherapy has been determined. Detailed PK and PD data will be presented. Clinical trial information: NCT01346358.