Longitudinal efficacy and safety modeling and simulation framework to aid dose selection of belantamab mafodotin for patients with multiple myeloma

Belantamab mafodotin, a monomethyl auristatin F (MMAF)-containing monoclonal antibody-drug conjugate (ADC), demonstrated deep and durable responses in the DRiving Excellence in Approaches to Multiple Myeloma (DREAMM)-1 and pivotal DREAMM-2 studies in patients with relapsed/refractory multiple myeloma. As with other MMAF-containing ADCs, ocular adverse events were observed. To predict the effects of belantamab mafodotin dosing regimens and dose-modification strategies on efficacy and ocular safety end points, DREAMM-1 and DREAMM-2 data across a range of doses were used to develop an integrated simulation framework incorporating two separate longitudinal models and the published population pharmacokinetic model. A concentration-driven tumor growth inhibition model described the time course of serum M-protein concentration, a measure of treatment response, whereas a discrete time Markov model described the time course of ocular events graded with the GSK Keratopathy and Visual Acuity scale. Significant covariates included baseline β2 -microglobulin on growth rate, baseline M-protein on kill rate, extramedullary disease on the effect compartment rate constant, and baseline soluble B cell maturation antigen on maximal effect. Efficacy and safety end points were simulated for various doses with dosing intervals of 1, 3, 6, and 9 weeks and various event-driven dose-modification strategies. Simulations predicted that lower doses and longer dosing intervals were associated with lower probability and lower overall time with Grade 3+ and Grade 2+ ocular events compared with the reference regimen (2.5 mg/kg every 3 weeks), with a less-than-proportional reduction in efficacy. The predicted improved benefit-risk profiles of certain dosing schedules and dose modifications from this integrated framework has informed trial designs for belantamab mafodotin, supporting dose-optimization strategies.

First-in-human phase I study of the OX40 agonist GSK3174998 with or without pembrolizumab in patients with selected advanced solid tumors (ENGAGE-1)

BACKGROUND

The phase I first-in-human study ENGAGE-1 evaluated the humanized IgG1 OX40 agonistic monoclonal antibody GSK3174998 alone (Part 1 (P1)) or in combination with pembrolizumab (Part 2 (P2)) in patients with advanced solid tumors.

METHODS

GSK3174998 (0.003-10 mg/kg) ± pembrolizumab (200 mg) was administered intravenously every 3 weeks using a continuous reassessment method for dose escalation. Primary objectives were safety and tolerability; secondary objectives included pharmacokinetics, immunogenicity, pharmacodynamics, and clinical activity.

RESULTS

138 patients were enrolled (45 (P1) and 96 (P2, including 3 crossovers)). Treatment-related adverse events occurred in 51% (P1) and 64% (P2) of patients, fatigue being the most common (11% and 24%, respectively). No dose-toxicity relationship was observed, and maximum-tolerated dose was not reached. Dose-limiting toxicities (P2) included Grade 3 (G3) pleural effusion and G1 myocarditis with G3 increased troponin. GSK3174998 ≥0.3 mg/kg demonstrated pharmacokinetic linearity and >80% receptor occupancy on circulating T cells; 0.3 mg/kg was selected for further evaluation. Limited clinical activity was observed for GSK3174998 (P1: disease control rate (DCR) ≥24 weeks 9%) and was not greater than that expected for pembrolizumab alone (P2: overall response rate 8%, DCR ≥24 weeks 28%). Multiplexed immunofluorescence data from paired biopsies suggested that increased infiltration of natural killer (NK)/natural killer T (NKT) cells and decreased regulatory T cells (Tregs) in the tumor microenvironment may contribute to clinical responses: CD16+CD56-CD134+ NK /NKT cells and CD3+CD4+FOXP3+CD134+ Tregs exhibited the largest magnitude of change on treatment, whereas CD3+CD8+granzyme B+PD-1+CD134+ cytotoxic T cells were the least variable. Tumor gene expression profiling revealed an upregulation of inflammatory responses, T-cell proliferation, and NK cell function on treatment with some inflammatory cytokines upregulated in peripheral blood. However, target engagement, evidenced by pharmacologic activity in peripheral blood and tumor tissue, did not correlate with clinical efficacy. The low number of responses precluded identifying a robust biomarker signature predictive of response.

CONCLUSIONS

GSK3174998±pembrolizumab was well tolerated over the dose range tested and demonstrated target engagement. Limited clinical activity does not support further development of GSK3174998±pembrolizumab in advanced cancers.

TRIAL REGISTRATION NUMBER

NCT02528357.

Manufacturing-dependent change in biological activity of the TLR4 agonist GSK1795091 and implications for lipid A analog development

A phase I trial (NCT03447314; 204686) evaluated the safety and efficacy of GSK1795091, a Toll-like receptor 4 (TLR4) agonist, in combination with immunotherapy (GSK3174998 [anti-OX40 monoclonal antibody], GSK3359609 [anti-ICOS monoclonal antibody], or pembrolizumab) in patients with solid tumors. The primary endpoint was safety; other endpoints included efficacy, pharmacokinetics, and pharmacodynamics (PD). Manufacturing of GSK1795091 formulation was modified during the trial to streamline production and administration, resulting in reduced PD (cytokine) activity. Fifty-four patients received GSK1795091 with a combination partner; 32 received only the modified GSK1795091 formulation, 15 received only the original formulation, and seven switched mid-study from the original to the modified formulation. Despite the modified formulation demonstrating higher systemic GSK1795091 exposure compared with the original formulation, the transient, dose-dependent elevations in cytokine and chemokine concentrations were no longer observed (e.g., IP-10, IL10, IL1-RA). Most patients (51/54; 94%) experienced ≥1 treatment-emergent adverse event (TEAE) during the study. Safety profiles were similar between formulations, but a higher incidence of TEAEs associated with immune responses (chills, fatigue, pyrexia, nausea, and vomiting) were observed with the original formulation. No conclusions can be made regarding GSK1795091 anti-tumor activity due to the limited data collected. Manufacturing changes were hypothesized to have caused the change in biological activity in this study. Structural characterization revealed GSK1795091 aggregate size in the modified formulation to be twice that in the original formulation, suggesting a negative correlation between GSK1795091 aggregate size and PD activity. This may have important clinical implications for future development of structurally similar compounds.

Reductions in circulating B cell subsets and immunoglobulin G levels with long-term belimumab treatment in patients with SLE

Objective

To examine the long-term changes in circulating B cell subsets and IgG levels at 5+ years of continuous belimumab treatment and their correlations with efficacy and safety measures.

Methods

This was a post hoc analysis of a continuation study (BEL112233; NCT00724867) of eligible US patients who completed the 76-week BLISS-76 Study (BEL110751; NCT00410384), with up to eight calendar-years of follow-up and median (IQR) belimumab exposure of 310 (209, 364) weeks. From week 76, patients initially randomised to intravenous belimumab 1 mg/kg or 10 mg/kg every 4 weeks in BLISS-76 continued to receive the same dose in the continuation study, while those initially randomised to placebo received belimumab 10 mg/kg intravenous every 4 weeks during continuation. All patients continued to receive standard SLE therapy. Biomarker data were collected, and the effects on baseline and early changes (weeks 0–24 after starting belimumab) from baseline in biomarkers on SLE Responder Index (SRI-4) and infection rate were evaluated.

Results

Of the 819 patients from BLISS-76, 268 self-selecting patients entered BEL112233. Compared with baseline, B cell subset counts decreased by 40%–99% after 312 weeks (6 years), and serum IgG levels decreased by 28% after 284 weeks. Higher baseline naïve B cell counts were associated with greater SRI-4 response rates (p<0.05), whereas higher baseline SLE subset plasma and short-lived plasma B cell counts were associated with lower SRI-4 response rates (p<0.05). Elevated baseline IgG levels were associated with increased infection rates over the treatment period (p<0.05), and early greater decreases in IgG levels were associated with higher SRI-4 response rates (p<0.05).

Conclusions

Belimumab treatment up to 312 weeks (6 years) resulted in substantial decreases in several circulating B cell subsets and IgG levels. Higher baseline naïve B cell counts and IgG levels were associated with improved SRI-4 response and increased infection rates, respectively.

Exposure-Response Analyses for Therapeutic Dose Selection of Belantamab Mafodotin in Patients With Relapsed/Refractory Multiple Myeloma

Belantamab mafodotin is an antibody–drug conjugate comprising a humanized anti‐B‐cell maturation antigen (BCMA) monoclonal antibody conjugated to monomethyl auristatin F (MMAF) via a protease‐resistant maleimidocaproyl linker. Single‐agent belantamab mafodotin showed clinically meaningful activity and manageable safety in patients with heavily pretreated relapsed/refractory multiple myeloma (RRMM) in the phase I DREAMM‐1 and phase II DREAMM‐2 studies and is approved by the US Food and Drug Administration and European Medicines Agency for RRMM treatment. To support monotherapy dose selection, the relationship between Cycle 1 exposure (derived using a population pharmacokinetic model) and clinical response (for multiple efficacy and safety end points) was explored. In DREAMM‐2, efficacy end points (probability of response (PoR) and progression‐free survival (PFS)) were associated with exposure in univariate evaluation; however, once disease burden factors were included in the model (e.g., baseline soluble BCMA, ß₂‐microglobulin), exposure was no longer significant. Patients with higher disease burden had lower exposure. In DREAMM‐1, belantamab mafodotin exposure was the only variable to correlate with PoR and PFS. Probability of corneal events (keratopathy), but not dry eye or blurred vision, was strongly associated with belantamab mafodotin exposure (DREAMM‐2). Higher cys‐mcMMAF maximum plasma drug concentration (C_max) and lower baseline platelet count were associated with increased probability of thrombocytopenia (DREAMM‐1 and DREAMM ‐2). In general, safety end points were more strongly associated with belantamab mafodotin exposure than efficacy end points, particularly after disease factors and patient characteristics were taken into account. Overall, these findings supported the monotherapy dose recommendation of belantamab mafodotin as 2.5 mg/kg every 3 weeks in patients with RRMM who have received four or more prior therapies.

Population pharmacokinetics of belantamab mafodotin, a BCMA-targeting agent in patients with relapsed/refractory multiple myeloma

Belantamab mafodotin (belamaf) is an antibody-drug conjugate (ADC) targeting B-cell maturation antigen (BCMA). Nonlinear mixed-effects models were developed to characterize the population pharmacokinetics (PopPK) of ADC, total monoclonal antibody (mAb), and cysteine-maleimidocaproyl-MMAF (cys-mcMMAF) after 0.03-4.6 mg/kg dosing every 3 weeks in heavily pretreated patients with relapsed/refractory multiple myeloma (RRMM; DREAMM-1, n = 73; DREAMM-2, n = 218). Sequential modeling methodology was used. Individual post hoc parameter estimates from the final ADC model were used to develop total mAb and cys-mcMMAF models. Formal covariate selection used a modified stepwise forward inclusion method with backward elimination. A linear, two-compartment PopPK model with a time-varying clearance (CL) described ADC PK. Initial ADC typical value for CL for a DREAMM-2 patient was 0.936 L/day with a half-life of 11.5 days, over time CL was reduced by 28% resulting in a half-life of 14.3 days. Time to 50% maximal CL change was ~ 50 days. Baseline soluble BCMA (sBCMA), immunoglobulin (IgG), albumin, and bodyweight impacted ADC CL. Cys-mcMMAF concentrations were described with a linear two-compartment model linked to ADC; input rate was governed by deconjugation/intracellular proteolytic degradation of ADC represented by an exponentially decreasing MMAF:mAb (drug antibody ratio [DAR]) after each dose. Time to 50% DAR reduction was 10.3 days. Baseline sBCMA and IgG impacted cys-mcMMAF central volume of distribution. In conclusion, ADC, total mAb, and cys-mcMMAF concentration-time profiles in RRMM were well-described by PopPK models, and exposure was most strongly impacted by disease-related characteristics.

Pharmacokinetics of Belimumab in Children With Systemic Lupus Erythematosus

The phase 2 placebo-controlled, double-blind PLUTO trial characterized the pharmacokinetics of belimumab plus standard systemic lupus erythematosus (SLE) therapy in patients with childhood-onset SLE (cSLE) and demonstrated similar efficacy and safety to that in adult SLE. Patients with active cSLE aged 5-17 years were randomized to intravenous belimumab 10 mg/kg every 4 weeks (n = 53). A linear 2-compartment population pharmacokinetics (popPK) model with first-order elimination was developed, and an exploratory exposure-response analysis assessed the impact of between-patient exposure variability on clinical response (SLE Responder Index 4 [SRI4]) in week 52, and occurrence of serious adverse events during the study. The popPK model estimated clearance of 158 mL/day, steady-state volume of distribution of 3.5 L, terminal half-life of 16.3 days, and distribution half-life of 0.8 days in the overall population. Fat-free mass (FFM) better characterized the pharmacokinetics than total body weight and was more consistent with allometric scaling theory; belimumab pharmacokinetics were largely determined by FFM. Age, sex, disease activity, and concomitant medication had no impact on pediatric belimumab exposure after accounting for body size. Individual and median steady-state pediatric pharmacokinetic profiles were similar to known adult profiles and pediatric exposure estimates for belimumab 10 mg/kg intravenously were consistent with adult exposures. Exposures were similar between SRI4 responders and nonresponders, and patients who did or did not experience a serious adverse event. There was no clinically relevant correlation between exposure and efficacy or safety, confirming belimumab 10 mg/kg intravenous dose every 4 weeks as appropriate for pediatric patients with cSLE.

Opportunities for Quantitative Translational Modeling in Oncology

A 2-day meeting was held by members of the UK Quantitative Systems Pharmacology Network () in November 2018 on the topic of Translational Challenges in Oncology. Participants from a wide range of backgrounds were invited to discuss current and emerging modeling applications in nonclinical and clinical drug development, and to identify areas for improvement. This resulting perspective explores opportunities for impactful quantitative pharmacology approaches. Four key themes arose from the presentations and discussions that were held, leading to the following recommendations: Evaluate the predictivity and reproducibility of animal cancer models through precompetitive collaboration. Apply mechanism of action (MoA) based mechanistic models derived from nonclinical data to clinical trial data. Apply MoA reflective models across trial data sets to more robustly quantify the natural history of disease and response to differing interventions. Quantify more robustly the dose and concentration dependence of adverse events through mathematical modelling techniques and modified trial design.

Abstract CT150: A first-in-human phase I study of the OX40 agonist GSK3174998 (GSK998) +/- pembrolizumab in patients (Pts) with selected advanced solid tumors (ENGAGE-1)

Background: OX40 is a costimulatory receptor transiently expressed on the surface of activated T cells and some innate immune cells (e.g. NK cells). OX40 agonists have been shown to increase antitumor immunity and improve tumor-free survival in preclinical models, demonstrating increased efficacy when given in combination with a PD-1 inhibitor. GSK998 is a humanized IgG1 agonistic OX40 monoclonal antibody. Methods: ENGAGE-1 (NCT02528357) is a Phase 1 dose escalation study evaluating safety, PK, PD, and clinical activity of GSK998 (0.003-10 mg/kg IV Q3W) alone (Part 1) and in combination with pembrolizumab 200 mg IV Q3W (Part 2) in pts with previously treated advanced solid tumors: non-small cell lung cancer (NSCLC), squamous cell carcinoma of the head and neck, renal cell carcinoma, melanoma (MEL), bladder cancer, soft tissue sarcoma (STS), triple-negative breast cancer, and MSI-high colorectal carcinoma. Dose escalation used a continuous reassessment method and 4-week DLT period. Results: A total of 138 pts were enrolled (45 Part 1, 96 Part 2; 3 crossed over from Part 1). Two DLTs occurred in Part 2 only (G3 non-malignant pleural effusion 0.03 mg/kg; G1 myocarditis 10 mg/kg); MTD was not established. Most common (≥10%) treatment-related AEs (mostly G1-2) were diarrhea, fatigue (Part 1) and fatigue, nausea (Part 2). GSK998 demonstrated target engagement in the periphery as evidenced by PK and receptor occupancy (RO); a dose of 0.3 mg/kg was the threshold for linear PK & peripheral RO saturation over the 3-wk dose interval and was selected for further clinical evaluation in MEL, STS, and NSCLC in Part 2 expansion. Clinical responses and SD ≥24 weeks were observed in both PD-1/L1 naïve and experienced pts: Part 1 (1 PR, 1 SD; both 0.3 mg/kg) and Part 2 (2 CR, 7 PR, 9 SD; 0.01-3 mg/kg); Part 2 clinical responses were not correlated with baseline tumor PD-L1 expression levels; including one MEL pt with PD-L1 TPS=0 who progressed on prior CTLA-4/PD-1 treatment and had a CR (&gt;18mo). Overall, peripheral and tumor expression of OX40 was low (&lt;2% total cells in tumor were OX40 +ve). MultiOmyxTM data from tumor biopsies suggested increased NK/decreased Treg involvement in some responders. Conclusions: GSK998 +/- pembrolizumab was well tolerated, with evidence of target engagement; monotherapy clinical activity was limited. While combination responses may not be significantly greater than expected for pembrolizumab alone, responses were observed in some PD-1/L1 experienced pts and some with low PD-L1 expression. Given the low OX40 expression observed and preclinical evidence that increased expression improves activity of OX40 agonism, ongoing clinical evaluation of GSK998 will assess whether concurrent immune-stimulation or immunogenic cell death impacts OX40 expression and increases the efficacy of this agent. Combinations with TLR4 and ICOS agonists and an anti-BCMA antibody-drug conjugate are ongoing.

Citation Format: Sophie Postel-Vinay, Vincent K. Lam, Willeke Ros, Todd M. Bauer, Aaron R. Hansen, Daniel C. Cho, F. Stephen Hodi, Jan H.M. Schellens, Jennifer K. Litton, Sandrine Aspeslagh, Karen A. Autio, Frans L. Opdam, Meredith McKean, Neeta Somaiah, Stephane Champiat, Mehmet Altan, Anna Spreafico, Osama Rahma, Elaine M. Paul, Christoph M. Ahlers, Helen Zhou, Herbert Struemper, Shelby A. Gorman, Maura Watmuff, Kaitlin M. Yablonski, Niranjan Yanamandra, Michael J. Chisamore, Emmett V. Schmidt, Axel Hoos, Aurélien Marabelle, Jeffrey S. Weber, John V. Heymach. A first-in-human phase I study of the OX40 agonist GSK3174998 (GSK998) +/- pembrolizumab in patients (Pts) with selected advanced solid tumors (ENGAGE-1) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT150.

Safety, Pharmacokinetics, and Pharmacodynamics of the TLR4 Agonist GSK1795091 in Healthy Individuals: Results from a Randomized, Double-blind, Placebo-controlled, Ascending Dose Study

PURPOSE

Interest in Toll-like receptor (TLR) agonists for cancer treatment has been renewed after promising preliminary clinical data in combination with checkpoint inhibitors. This first-in-human study assessed the safety, tolerability, and pharmacokinetic (PK) and pharmacodynamic (PD) properties of intravenous GSK1795091, a synthetic TLR4 agonist, in healthy volunteers as a precursor to evaluation in patients with cancer.

METHODS

Healthy participants were randomized (1:3; double-blinded manner) to receive placebo or a single intravenous injection of GSK1795091 at doses of 7-100 ng. The primary objective was to evaluate the safety and tolerability of GSK1795091; secondary and exploratory objectives were to characterize GSK1795091 PK and PD properties.

FINDINGS

Forty participants received study treatment (10 received placebo and 30 received GSK1795091). Overall, 3 of the 10 participants (30%) who received placebo and 16 of the 30 (53%) who received GSK1795091 experienced ≥1 adverse event (AE). The most common AEs were influenza-like illness, headache, back pain, and increased body temperature. One participant experienced late-occurring AEs (alanine aminotransferase and aspartate aminotransferase increases), considered possibly related to GSK1795091. No serious AEs were reported. GSK1795091 PK properties were characterized by dose proportional increase in exposure. Transient and dose-dependent changes in induced cytokine and chemokine concentrations and immune cell counts were observed 1-4 h after GSK1795091 administration and returned to baseline within 24 h.

IMPLICATIONS

Intravenously administered GSK1795091 was acceptably tolerated in healthy volunteers, had favorable PK properties, and stimulated immune cell changes in a dose-dependent manner, providing evidence of target engagement and downstream pharmacology. These results supported the design and initiation of a repeat-dose study of intravenous GSK1795091 in combination with other immunotherapies in patients with advanced cancer. ClinicalTrials.gov identifier: NCT02798978.

Safety and efficacy of intravenous belimumab in children with systemic lupus erythematosus: results from a randomised, placebo-controlled trial

OBJECTIVES

This ongoing Phase-2, randomised, placebo-controlled, double-blind study evaluated the efficacy, safety and pharmacokinetics of intravenous belimumab in childhood-onset systemic lupus erythematosus (cSLE).

METHODS

Patients (5 to 17 years) were randomised to belimumab 10 mg/kg intravenous or placebo every 4 weeks, plus standard SLE therapy. Primary endpoint: SLE Responder Index (SRI4) response rate (Week 52). Key major secondary endpoints: proportion of patients achieving the Paediatric Rheumatology International Trials Organisation/American College of Rheumatology (PRINTO/ACR) response using 50 and '30 alternative' definitions (Week 52), and sustained response (Weeks 44 to 52) by SRI4 and Parent Global Assessment of well-being (Parent-global). Safety and pharmacokinetics were assessed. Study not powered for statistical testing.

RESULTS

Ninety-three patients were randomised (belimumab, n=53; placebo, n=40). At Week 52, there were numerically more SRI4 responders with belimumab versus placebo (52.8% vs 43.6%; OR 1.49 (95% CI 0.64 to 3.46)). PRINTO/ACR 30 alternative (52.8% vs 27.5%; OR 2.92 (95% CI 1.19 to 7.17)) and PRINTO/ACR 50 (60.4% vs 35.0%; OR 2.74 (95% CI 1.15 to 6.54)) responses were more frequent with belimumab than placebo, as were sustained responses for SRI4 (belimumab, 43.4%; placebo, 41.0%; OR 1.08 (95% CI 0.46 to 2.52)) and Parent-global (belimumab, 59.1%; placebo, 33.3%; OR 3.49 (95% CI 1.23 to 9.91)). Serious adverse events were reported in 17.0% of belimumab patients and 35.0% of placebo patients; one death occurred (placebo). Week-52, geometric mean (95% CI) belimumab trough concentration was 56.2 (45.2 to 69.8) µg/mL.

CONCLUSION

The belimumab intravenous pharmacokinetics and benefit-risk profile in cSLE are consistent with adult belimumab studies and the 10 mg/kg every 4 weeks dose is appropriate.

TRIAL REGISTRATION NUMBER

NCT01649765.

Efficacy and safety of intravenous belimumab in Japanese patients with systemic lupus erythematosus: A subgroup analysis of a phase 3 randomized placebo-controlled trial

OBJECTIVES

To assess the efficacy and safety of intravenous (IV) belimumab plus standard systemic lupus erythematosus (SLE) therapy standard of care (SoC) in Japanese patients with SLE.

METHODS

A Phase 3, multicenter, double-blind, placebo-controlled, 52-week study (BEL 113750; NCT01345253) in patients with SLE, randomized 2:1 to belimumab 10 mg/kg plus SoC or placebo plus SoC to Week 48.

RESULTS

Sixty of 707 randomized patients were enrolled from study centers in Japan (belimumab, n = 39; placebo, n = 21). In this cohort, more patients achieved SLE Responder Index 4 response at Week 52 in the belimumab group compared with placebo (46.2% [18/39] vs. 25.0% [5/20]; odds ratio, 2.57 [95% confidence interval: 0.78, 8.47]; p=.1204). Fewer patients receiving belimumab experienced a severe flare through Week 52, with longer median time to flare compared with placebo. More patients with baseline prednisone dose >7.5 mg/d receiving belimumab had a dose reduction of ≥25% from baseline to ≤7.5 mg/d during Weeks 40-52, compared with placebo. No new safety issues were identified within the Japanese cohort.

CONCLUSION

In Japanese patients with SLE, belimumab improved disease activity, with efficacy and safety results similar and consistent to the pivotal Phase 3 trials, suggesting that belimumab is a potential treatment option in this population.

Abstract CT027: A phase I, open-label study of GSK3174998 administered alone and in combination with pembrolizumab in patients (pts) with selected advanced solid tumors (ENGAGE-1)

Background: OX40 (CD134) belongs to the tumor necrosis factor receptor (TNFR) family, and transduces a costimulatory signal during T-cell activation. In the periphery, OX40 expression is limited to recently activated CD4+ and CD8+ cells. In tumors, infiltrating T lymphocytes are enriched for OX40, where it augments T-cell activation, proliferation and survival. OX40 is also expressed on tumor infiltrating regulatory T cells (Tregs). Intratumoral Treg depletion is critical for the in vivo antitumor activity of immune checkpoint antibodies. OX40 can also be found on natural killer (NK) cells, mediating antibody-dependent cellular cytotoxicity. Together, these mechanisms make stimulation of OX40 with agonistic agents an attractive target for a novel anti-cancer immunotherapy. GSK3174998 is a humanized IgG1 anti-OX40 agonistic monoclonal antibody identified through collaboration with MD Anderson Cancer Center and is currently in phase I development.

Methods: The primary objective of this open-label non-randomized multicenter phase I study is to evaluate the safety of GSK3174998, as monotherapy in escalating doses every 3 weeks IV for up to 48 weeks (Part 1) or

in combination with 200 mg pembrolizumab administered every 3 weeks IV for up to 2 years (Part 2). Secondary objectives include assessment of antitumor activity, pharmacokinetics, pharmacodynamics and immunogenicity. Adverse events will be monitored using NCI CTCAE v. 4.0. Radiographic imaging will be obtained every 12 weeks to assess clinical response defined by immune-related RECIST. Exploratory objectives include examination of changes in genomic DNA, RNA, protein, measures of immune function in tumor, and the association of these with antitumor activity. The study will enroll up to approximately 180 pts; eligible pts will have measurable disease with documentation of metastatic non-small cell lung cancer, squamous cell carcinoma of the head and neck, renal cell carcinoma, melanoma, bladder, soft tissue sarcoma, triple-negative breast cancer, and colorectal carcinoma displaying microsatellite instability that has progressed after standard therapy, or for which standard therapy is ineffective, intolerable, or inappropriate. A pre-treatment biopsy is requested of all pts. Matched pre-treatment and on-treatment biopsies will be performed in expansion cohorts to allow investigation of candidate biomarkers which may predict clinical response. As of Feb 1, 2016, monotherapy cohorts 1 and 2 have completed without DLT and enrollment to Cohort 3 is ongoing. This study (NCT02528357) is funded by GlaxoSmithKline.

Citation Format: Jeffrey Infante, Christoph M. Ahlers, F Stephen Hodi, Sopie Postel-Vinay, Jan HM Schellens, John V. Heymach, Karen Autio, Mary Barnette, Herbert Struemper, Maura Watmuff, Elaine M. Paul, David R. Kaufman, Jeffrey S. Weber, Axel Hoos. A phase I, open-label study of GSK3174998 administered alone and in combination with pembrolizumab in patients (pts) with selected advanced solid tumors (ENGAGE-1). [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr CT027.

Comparison of intravenous and subcutaneous exposure supporting dose selection of subcutaneous belimumab systemic lupus erythematosus Phase 3 program

Background Belimumab is a recombinant, human, IgG1λ monoclonal antibody that targets B-lymphocyte stimulator. The intravenous formulation is indicated for the treatment of active, autoantibody-positive systemic lupus erythematosus (SLE). Belimumab has been formulated for subcutaneous (SC) administration to improve patient convenience. This post-hoc modeling and simulation analysis characterizes the population pharmacokinetics (PK) of SC belimumab, and compares the exposure profiles of the approved belimumab IV dose-10 mg/kg every four weeks-to the 200 mg SC weekly dose in SLE patients, highlighting key pharmacological differences relevant for clinicians. Methods Data from two Phase 1 studies in US American and Japanese healthy subjects were analyzed with a non-linear mixed effects modeling approach. The resulting SC population PK model and a previously developed IV population PK model were used to conduct simulation trials in a Phase 3 IV belimumab SLE patient population, comparing chronic exposure profiles and exposure ranges stratified by body weight tertiles for IV vs SC dosing. Results The PK of belimumab following SC administration was best described by a linear two-comment model. The estimates for clearance, steady-state volume of distribution, and bioavailability were 208 mL/day, 5250 mL, and 76%, respectively. After four weeks of SC dosing, simulated belimumab concentrations exceeded the steady-state trough concentrations of the IV dosing regimen. At steady state simulated serum profiles demonstrated comparable average belimumab concentrations (C_avg,ss) after IV and SC dosing. Simulated belimumab exposures demonstrated largely overlapping concentration ranges following 200 mg SC weekly and 10 mg/kg IV every four weeks dosing. Discussion The predicted C_avg,ss of belimumab in SLE patients was comparable following 200 mg SC weekly and 10 mg/kg IV every four weeks dosing. The simulated belimumab accumulation following SC weekly dosing indicated that administration of a loading dose was not required. Similar C_avg,ss ranges were predicted for fixed dose SC and weight-proportional IV regimens in the simulated SLE population, albeit with a reversed body-size-to-exposure relationship for the SC regimen. These findings provide rheumatologists with a better understanding of expected differences in belimumab exposure when comparing IV and SC dosing regimens.

Methods and strategies for assessing uncontrolled drug-drug interactions in population pharmacokinetic analyses: results from the International Society of Pharmacometrics (ISOP) Working Group

The purpose of this work was to present a consolidated set of guidelines for the analysis of uncontrolled concomitant medications (ConMed) as a covariate and potential perpetrator in population pharmacokinetic (PopPK) analyses. This white paper is the result of an industry-academia-regulatory collaboration. It is the recommendation of the working group that greater focus be given to the analysis of uncontrolled ConMeds as part of a PopPK analysis of Phase 2/3 data to ensure that the resulting outcome in the PopPK analysis can be viewed as reliable. Other recommendations include: (1) collection of start and stop date and clock time, as well as dose and frequency, in Case Report Forms regarding ConMed administration schedule; (2) prespecification of goals and the methods of analysis, (3) consideration of alternate models, other than the binary covariate model, that might more fully characterize the interaction between perpetrator and victim drug, (4) analysts should consider whether the sample size, not the percent of subjects taking a ConMed, is sufficient to detect a ConMed effect if one is present and to consider the correlation with other covariates when the analysis is conducted, (5) grouping of ConMeds should be based on mechanism (e.g., PGP-inhibitor) and not drug class (e.g., beta-blocker), and (6) when reporting the results in a publication, all details related to the ConMed analysis should be presented allowing the reader to understand the methods and be able to appropriately interpret the results.

Relative Bioavailability of a Single Dose of Belimumab Administered Subcutaneously by Prefilled Syringe or Autoinjector in Healthy Subjects

Intravenous belimumab is approved for the treatment of systemic lupus erythematosus; subcutaneous self‐administration would enable greater patient access. This study assessed relative bioavailability, tolerability, and safety of 1 subcutaneous dose of self‐administered belimumab by healthy subjects using a single‐use autoinjector or prefilled syringe. Subjects (randomized 1:1:1:1) self‐administered belimumab 200 mg subcutaneously (abdomen or thigh) by prefilled syringe or autoinjector. Pharmacokinetics, adverse events (AEs), injection‐site pain, and administration errors were recorded. Of 81 subjects, 5 experienced administration errors and were excluded from pharmacokinetic analyses. Mean serum belimumab concentration profiles were similar for both devices, with a weak trend toward higher concentrations for thigh injection compared with abdominal injections. Maximum observed serum concentration was slightly higher with the autoinjector (27.0 vs 25.3 µg/mL) and area under the concentration–time curve slightly lower (701 vs 735 day · μg/mL), compared with the prefilled syringe. Incidence of AEs was 51% (41 of 81 subjects; headache was most common), with no serious or severe AEs. Median injection‐site pain scores were low (0 after 1 hour). Device handling was reported as acceptable by ≥95% of autoinjector users and ≥90% of prefilled syringe users for each characteristic assessed. These results support the use of either device for belimumab subcutaneous administration.

Preclinical Modeling of Tumor Growth and Angiogenesis Inhibition to Describe Pazopanib Clinical Effects in Renal Cell Carcinoma

The objective was to leverage tumor size data from preclinical experiments to propose a model of tumor growth and angiogenesis inhibition for the analysis of pazopanib efficacy in renal cell carcinoma (RCC) patients. We analyzed tumor data in mice with RCC CAKI‐2 cell line treated with pazopanib. Clinical tumor size data obtained in a subset of patients with RCC were also analyzed. A model accounting for the processes of tumor growth, angiogenesis, and drug effect was developed. The final tumor model was composed of two variables: the tumor and its vasculature. Our results show that, both in mice and in humans, pazopanib exhibits a dual mechanism of action, and parameter estimation values highlight the inherent difference between mice and humans on the time scale of tumor size response. We developed a semimechanistic tumor growth inhibition model that takes into account tumor angiogenesis in order to describe the effects of pazopanib in mice. Analyzing rich preclinical data with a semimechanistic model may be a relevant approach to facilitate the description of sparse clinical longitudinal tumor size data and to provide insights for the understanding of the drug mechanisms of action in patients.

Population pharmacokinetics of ofatumumab in patients with chronic lymphocytic leukemia, follicular lymphoma, and rheumatoid arthritis

Ofatumumab is a human monoclonal antibody directed at CD20 approved for treatment of chronic lymphocytic leukemia. The population pharmacokinetics of intravenous ofatumumab were characterized in patients with relapsed/refractory chronic lymphocytic leukemia, relapsed/refractory follicular lymphoma, and rheumatoid arthritis, diseases with widely varying CD20⁺ B-cell counts in blood. Serum concentration data from a total of 477 patients who received ofatumumab doses ranging from 100 mg to 2000 mg in different dosing regimens were analyzed to determine the pharmacokinetic characteristics of ofatumumab across different patient groups and to identify factors contributing to the pharmacokinetic variability. Ofatumumab pharmacokinetics were well described by a linear two-compartment model component to represent non-specific monoclonal antibody clearance from the central compartment interacting with a model component representing the target-mediated clearance of ofatumumab by binding to CD20 expressed on B cells. The clearance (7.5 mL/h) and steady-state volume of distribution (5.3 L) for the linear, non-specific component were consistent with results obtained for other monoclonal antibodies. The target-mediated clearance component was related to the disease-specific number of circulating B cells, which will allow simulation of the contribution of target-mediated clearance to ofatumumab pharmacokinetics in untested disease states with data on B-cell counts and turnover.

Chemoimmunotherapy using pegylated liposomal Doxorubicin and interleukin-18 in recurrent ovarian cancer: a phase I dose-escalation study

Recombinant interleukin (IL)-18 (SB-485232) is an immunostimulatory cytokine, with shown antitumor activity in combination with pegylated liposomal doxorubicin (PLD) in preclinical models. This phase I study evaluated the safety, tolerability, and biologic activity of SB-485232 administered in combination with PLD in subjects with recurrent ovarian cancer. The protocol comprised four cycles of PLD (40 mg/m(2)) on day 1 every 28 days, in combination with SB-485232 at increasing doses (1, 3, 10, 30, and 100 μg/kg) on days 2 and 9 of each cycle, to be administered over five subject cohorts, followed by discretionary PLD monotherapy. Sixteen subjects were enrolled. One subject withdrew due to PLD hypersensitivity. Most subjects (82%) were platinum-resistant or refractory, and had received a median of three or more prior chemotherapy regimens. SB-485232 up to 100 μg/kg with PLD had an acceptable safety profile. Common drug-related adverse events were grade 1 or 2 (no grade 4 or 5 adverse events). Concomitant PLD administration did not attenuate the biologic activity of IL-18, with maximal SB-485232 biologic activity already observed at 3 μg/kg. Ten of 16 enrolled subjects (63%) completed treatment, whereas five (31%) subjects progressed on treatment. A 6% partial objective response rate and a 38% stable disease rate were observed. We provide pilot data suggesting that SB-485232 at the 3 μg/kg dose level in combination with PLD is safe and biologically active. This combination warrants further study in a phase II trial.

Population pharmacokinetics of belimumab following intravenous administration in patients with systemic lupus erythematosus

The population pharmacokinetics (PK) of belimumab were characterized in 1,603 patients with systemic lupus erythematosus receiving belimumab 1, 4, 10, or 20 mg/kg doses in Phase 1-3 trials. Belimumab PK were well described with a linear two-compartment model, with clearance from the central compartment (CL). Belimumab exposure was approximately dose-proportional. The estimated population terminal half-life was 19.4 days and steady-state volume of distribution (Vss) was 5.29 L for the currently approved 10 mg/kg dose used in the Phase 3 trials, with an estimated CL of 215 mL/day. No effects of age, sex, race, disease activity, co-medications, or baseline characteristics on belimumab PK were found to alter exposure in a manner requiring dose adjustment. An association observed between increasing baseline proteinuria and increasing CL may be clinically relevant in nephropathy with very high proteinuria levels. No evidence of target-mediated clearance was observed. Clinically relevant effects of body size (increased CL and V1 with increased body weight, and reduced V1 with increased body mass index) have been accounted for in current weight-normalized belimumab dosing.

A phase I, dose escalation trial to assess the safety and biological activity of recombinant human interleukin-18 (SB-485232) in combination with pegylated liposomal doxorubicin in platinum-resistant recurrent ovarian cancer

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Background: SB-485232, a recombinant human form of interleukin-18 (IL-18), is being studied as a novel cytokine for tumor immunotherapy. IL-18 has been shown to increase the anti-tumor activity of doxorubicin in other cancer mouse models. Methods: This multi-center study enrolled 16 patients (pts), and evaluated four cycles (28 days each) of standard pegylated liposomal doxorubicin (PLD) (40 mg/m2 day 1) in combination with increasing doses of IL-18 (1, 3, 10, 30, and 100 mg/kg) on days 2 and 9 of each cycle with a 1 yr follow-up to further evaluate safety and efficacy. Results: Of the 16 pts, 10 (63%) completed study treatment and 6 (37%) did not because of disease progression (5 pts) and PLD hypersensitivity (1 pt). Thirteen (82%) were platinum resistant/refractory having received a median of > 3 prior lines of therapy. SB-485232 up to 100 mg/kg in combination with PLD had an acceptable safety profile. All 16 pts experienced at least 1 AE including chills (81%), nausea (75%), anemia (63%), fatigue (56%), hyperglycemia, and pyrexia (50% each). Eight of 16 pts had Grade 3 AEs including anemia (19%), and 6% each for abdominal pain, asthenia, dehydration, PLD hypersensitivity, edema, fatigue, hyperglycemia, hyperkalemia, jaundice, pain, nausea, vomiting, and pyelonephritis. There were no grade 4/5 AEs. Four subjects experienced 10 non-fatal SAEs with 3 related to study drug: anemia, PLD hypersensitivity, and cytokine release syndrome. Maximal SB-485232 biological activity, assessed by peripheral blood NK and T cell markers, was observed at 10mg/kg-100mg/kg. This drug combination resulted in a 6% partial response rate (RR) and a 38% stable disease rate using RECIST 1.0. Median (95% CI) time of progression-free survival (PFS) was 4.50 (3.52,--) months. Conclusions: The SB-485232/PLD combination was tolerable with minimal toxicity. These preliminary efficacy data are comparable to the historical RR and PFS observed with PLD monotherapy in platinum-resistant ovarian cancer. However, given the small sample size, this combination warrants further investigation.

Systems biology for battling rheumatoid arthritis: Application of the Entelos PhysioLab platform

A large-scale mathematical model, the Entelos Rheumatoid Arthritis (RA) PhysioLab platform, has been developed to describe the inflammatory and erosive processes in afflicted joints of people suffering from RA. The platform represents the life cycle of inflammatory cells, endothelium, synovial fibroblasts, and chondrocytes, as well as their products and interactions. The interplay between these processes culminates in clinically relevant measures for inflammation and erosion. The simulation model is deterministic, which allows tracing back the mechanism of action for a particular simulation result. Different patient phenotypes are represented by different virtual patients. The RA PhysioLab platform has been used to systematically and quantitatively study the predicted therapeutic effect of modulating several molecular targets, which resulted in a ranking of putative drug targets and a workflow to confirm the simulations experimentally. In addition, critical pathways were identified that drive the predicted disease outcome. Within these pathways, targets were identified from public literature that were not previously associated with arthritis. The model provides insights into the biology of RA and can be used as a platform for hypothesis-driven research. Case studies of therapies directed against IL-12 and IL-15 illustrate the approach, with emphasis on the analysis of system dynamics.