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T-cell engagers (TCE), a therapeutic class of cancer immunotherapy (CIT), offer a novel approach to cancer treatment by harnessing and reactivating the patient's immune system to eradicate tumor cells. However, the use of TCE in the clinic can lead to severe side effects, including cytokine release syndrome (CRS). Therefore, innovative dosing strategies need to be implemented to mitigate the risk of developing CRS. In the presented work, a mechanistic pharmacokinetics/pharmacodynamics (PKPD) model describing cytokine release following TCE therapy has been developed combining literature knowledge and preclinical data. The model was developed to explore and test hypotheses regarding the mechanisms behind the decrease of cytokine release following two repeated TCE administrations. The model is able to successfully reproduce the observed dynamics of cytokine levels associated with the initial and subsequent TCE doses, accounting for different dosing intervals. In addition, the model suggests a mechanism of action that uncouples cytokine release from tumor cell killing. This model provides an initial mechanistic framework to support the design of experiments and paves the way for the application of mathematical modeling to support clinical dosing regimen selection of any TCE.

BackgroundT cell engagers are bispecific antibodies recognizing, with one moiety, the CD3ε chain of the T cell receptor and, with the other moiety, specific tumor surface antigens. Crosslinking of CD3 upon simultaneous binding to tumor antigens triggers T cell activation, proliferation and cytokine release, leading to tumor cell killing. Treatment with T cell engagers can be associated with safety liabilities due to on-target on-tumor, on-target off-tumor cytotoxic activity and cytokine release syndrome (CRS). Tyrosine kinases such as SRC, LCK or ZAP70 are involved in downstream signaling pathways after engagement of the T cell receptor and blocking these kinases might serve to abrogate T cell activation when required (online supplemental material 1). Dasatinib was previously identified as a potent kinase inhibitor that switches off CAR T cell functionality.MethodsUsing an in vitro model of target cell killing by human peripheral blood mononuclear cells, we assessed the effects of dasatinib combined with 2+1 T cell bispecific antibodies (TCBs) including CEA-TCB, CD19-TCB or HLA-A2 WT1-TCB on T cell activation, proliferation and target cell killing measured by flow cytometry and cytokine release measured by Luminex. To determine the effective dose of dasatinib, the Incucyte system was used to monitor the kinetics of TCB-mediated target cell killing in the presence of escalating concentrations of dasatinib. Last, the effects of dasatinib were evaluated in vivo in humanized NSG mice co-treated with CD19-TCB. The count of CD20+ blood B cells was used as a readout of efficacy of TCB-mediated killing and cytokine levels were measured in the serum.ResultsDasatinib concentrations above 50 nM prevented cytokine release and switched off-target cell killing, which were subsequently restored on removal of dasatinib. In addition, dasatinib prevented CD19-TCB-mediated B cell depletion in humanized NSG mice. These data confirm that dasatinib can act as a rapid and reversible on/off switch for activated T cells at pharmacologically relevant doses as they are applied in patients according to the label.ConclusionTaken together, we provide evidence for the use of dasatinib as a pharmacological on/off switch to mitigate off-tumor toxicities or CRS by T cell bispecific antibodies.

Rationale Hypofunction of NMDA receptors has been implicated in neuropsychiatric disorders including schizophrenia. NMDA receptor neurotransmission can be enhanced through inhibition of glycine reuptake by the glycine transporter type 1 (GlyT1). Objectives The primary objective of these studies was to explore the relationship between plasma exposure and glycine cerebrospinal fluid (CSF) concentrations following administration of bitopertin and RG7118 in healthy volunteers. Methods The bitopertin study comprised four dose levels (3, 10, 30 and 60 mg) administered once daily for 10 days. In the RG7118 study, placebo, 15 or 30 mg RG7118 was administered once daily for 28 days. CSF samples were taken on day −2 and day 10, and day −1 and day 26 for bitopertin and RG7118, respectively. Results Twenty-two and 24 subjects participated in the bitopertin and RG7118 study, respectively. In the bitopertin study, CSF glycine concentrations showed a dose-dependent increase from baseline to day 10. The geometric mean ratios (coefficient of variation) of AUC 0–12 h on day 10 over baseline were 1.3 (17 %), 1.3 (49 %), 1.7 (18 %) and 2.3 (14 %) after 3, 10, 30 and 60 mg, respectively. In the RG7118 study, the geometric mean ratio of glycine concentration (CV) on day 26 at 6 h post-dose over time-matched baseline was approx. 1.9 (24 and 15 %) for 15 and 30 mg. Conclusions The mechanism of action of bitopertin and RG7118, i.e. inhibition of glycine reuptake in the brain, was confirmed. The maximal increase observed in healthy volunteers was similar to the one observed in animals showing the good translatability of this biomarker.

The nonclinical development of T-cell receptor (TCR)–based therapeutics is uniquely challenged by the human-exclusive specificity of the peptide-HLA target, rendering conventional animal models unsuitable for safety assessment. To support first-in-human (FIH) studies in patients with solid tumors with the novel TCR-like T Cell Bispecific (TCB) antibody MAGE-A4-TCB, targeting the MAGE-A4 peptide presented by HLA-A*02:01 and engaging T-cells via the CD3ϵ chain, we implemented a comprehensive, prediction-independent safety strategy relying on New Approach Methodologies (NAMs). This approach utilized 21 human cellular systems, including 2D and 3D in vitro models of vital organs (such as liver, heart, kidney, and lung), co-cultured with allogeneic peripheral blood mononuclear cells to identify potential off-target toxicity and a whole blood assay for cytokine release risk assessment. The concentration-effect relationship and Minimal Anticipated Biological Effect Level (MABEL) were established using the A375 cancer cell line, chosen for its comparable sensitivity to ovarian carcinoma organoids, which were the most sensitive out of 22 tested tumor organoids. Nonclinical testing demonstrated an absence of off-target reactivity in vital organs, though the whole blood assay predicted cytokine release syndrome as the primary risk. The calculated FIH starting dose was safe in the subsequent Phase I study (NCT05129280), and the most commonly reported adverse events were treatment-related skin and subcutaneous tissue disorders (73% of patients). These skin-related adverse events, which appeared in contradiction to the initial in vitro results in skin co-culture models, were hypothesized to be driven by the target-independent activation capability of the UCHT1-based CD3 binder, potentially enhanced in patients with a systemic pro-inflammatory profile. This study provides a translational framework for TCR-based immunotherapies, demonstrating the successful application of NAMs to define a safe starting dose while highlighting the critical need for refining these methodologies to accurately predict complex, systemic immune-related adverse events, particularly those involving barrier organs.

Intratumoral regulatory T (Treg) cell abundance associates with diminished antitumor immunity and poor prognosis in human cancers. Recent work demonstrates that CD25, the high-affinity receptor subunit for interleukin (IL)-2, is a selective target for Treg depletion in mouse and human malignancies; however, anti-human CD25 antibodies have failed to deliver clinical responses against solid tumors due to bystander IL-2 receptor signaling blockade on effector T cells, which limits their antitumor activity. Here we demonstrate potent single-agent activity of anti-CD25 antibodies optimized to deplete Treg cells, while preserving IL-2-STAT5 signaling on effector T cells and show synergy with immune checkpoint blockade in vivo. Pre-clinical evaluation of an anti-human CD25 (RG6292) antibody with equivalent features demonstrates, in both nonhuman primates and humanized mouse models, efficient Treg cell depletion with no overt immune-related toxicities. Our data support the clinical development of RG6292 and evaluation of new combination therapies incorporating non-IL-2-blocking anti-CD25 antibodies in clinical studies.Quezada and colleagues develop improved anti-CD25 antibodies that preserve IL-2 signaling and enhance single-agent antitumor immunity and immunotherapy through specific and efficient Treg cell depletion.

Objective To assess the effect of strong and moderate cytochrome P450 (CYP) 3A4 inhibition on exposure of bitopertin, a glycine reuptake inhibitor primarily metabolized by CYP3A4, and to compare the results with predictions based on physiologically based pharmacokinetic (PBPK) modelling. Methods The effects of ketoconazole and erythromycin were assessed in two male volunteer studies with open-label, two-period, fixed-sequence designs. Twelve subjects were enrolled in each of the studies. In period 1, a single dose of bitopertin was administered; in period 2, 400 mg ketoconazole was administered once daily for 17 days or 500 mg erythromycin was administered twice daily for 21 days. A single dose of bitopertin was coadministered on day 5. Pharmacokinetic parameters were derived by non-compartmental methods. Simulated bitopertin profiles using dynamic PBPK modelling for a typical healthy volunteer in GastroPlus ® were used to predict changes in pharmacokinetic parameters. Results In healthy volunteers, coadministration of ketoconazole increased the bitopertin area under the plasma concentration–time curve (AUC) from 0 to 312 h (AUC 0–312h ) 4.2-fold (90 % confidence interval [CI] 3.5–5.0) and erythromycin increased the AUC from time zero to infinity (AUC 0–inf ) 2.1-fold (90 % CI 1.9–2.3). The peak concentration ( C max ) increased by <25 % in both studies. Simulated bitopertin profiles using PBPK modelling showed good agreement with the observed AUC ratios in both studies. The predicted AUC 0–inf ratios for the interaction with ketoconazole and erythromycin were 7.7 and 1.9, respectively. Conclusion Strong CYP3A4 inhibitors increase AUC 0–inf of bitopertin 7- to 8-fold and hence should not be administered concomitantly with bitopertin. Moderate CYP3A4 inhibitors double AUC 0–inf .

Bitopertin (RG1678) is a glycine reuptake inhibitor in phase 3 trials for treatment of schizophrenia. Its clinical oral pharmacokinetics is sensitive to changes in drug substance particle size and dosage form. Physiologically based pharmacokinetic (PBPK) absorption model simulations of the impact of changes in particle size and dosage form (either capsules, tablets, or an aqueous suspension) on oral pharmacokinetics was verified by comparison to measured plasma concentrations. Then, a model parameter sensitivity analysis was applied to set limits on the particle sizes included in tablets for the market. The model was also used to explore the in vitro to in vivo correlation. Simulated changes in oral pharmacokinetics caused by differences in particle size and dosage form were confirmed in two separate relative bioavailability studies. Model parameter sensitivity analyses predicted that AUCinf was hardly reduced as long as particle diameter (D50) remained smaller than 30 μm, and >20% reduced Cmax is anticipated only when particle diameter exceeds 15 μm. An exploration of the sensitivity to the presence of larger particles within a polydisperse distribution showed that simulated Cmax is again more affected than AUC but is less than 20% reduced as long as D50 is less than 8 μm and D90 is smaller than 56 μm. PBPK absorption modelling can contribute to a quality by design (QbD) approach for clinical formulation development and support the setting of biorelevant specifications for release of the product.

Simlukafusp alfa (FAP-IL2v) was engineered to preferentially activate CD8+ T and natural killer (NK) cells in tumor microenvironments overexpressing fibroblast activation protein (FAP). Checkpoint inhibitors combined with antiangiogenic agents are standard therapy for metastatic renal cell carcinoma (mRCC), which overexpresses FAP. Here, we explored the efficacy, safety, and pharmacodynamic effects of FAP-IL2v in combination with atezolizumab with or without bevacizumab in patients with mRCC. Patients with treatment-naïve or pretreated clear cell and/or sarcomatoid mRCC were eligible. Dose escalation explored FAP-IL2v every 2 weeks (Q2W) with atezolizumab Q2W (doublet, arm A), and with atezolizumab and bevacizumab Q2W (triplet, arm B) in patients treated with up to one prior systemic therapy. Dose extension explored in untreated patients the recommended FAP-IL2v dose administered Q2W (doublet, arm A; and triplet, arm B) or 3-weekly (doublet, arm C; and triplet, arm D). Primary objectives were the recommended FAP-IL2v dose and antitumor activity. Secondary objectives included safety, pharmacodynamics, and exploratory biomarkers in peripheral blood and paired biopsies. By the data cut-off date (31 August, 2021), 66 patients were enrolled. The median duration of treatment was 11.0 months. Objective response rates (ORRs) were 25% for the doublet and 47% for the triplet, and median progression-free survival was 6.3 and 18.3 months, respectively. Safety profiles were consistent with the individual drugs, including expected interleukin-2 (IL-2) class-specific adverse events (AEs). Two deaths were recorded caused by AEs related to study treatment (acute kidney injury, n=1; pancytopenia, n=1). Expansion and activation of NK and T cells, but not regulatory T cells, was observed in peripheral blood, leading to increased tumor infiltration and inflammation in paired biopsies. The addition of bevacizumab led to a reduced angiogenesis signature score and reduced vessel density. The combination of FAP-IL2v plus atezolizumab with or without bevacizumab was consistent with the known safety profile of the individual drugs. The maximum tolerated dose was not reached, with a recommended FAP-IL2v dose of 10 mg. ORR was higher among patients receiving the triplet therapy compared with the doublet. Pharmacodynamic results were consistent with the mechanism of action of IL-2, supporting further research in this field.

BackgroundT cell bispecific antibodies (TCBs) are extremely potent T cell engagers, harboring a 2+1 format with one binder to the CD3ε chain and two binders to specific tumor antigens. Crosslinking of CD3 with tumor antigens triggers T cell activation, proliferation and cytokine release, leading to tumor cell killing.1 2 TCB treatment is sometimes associated with safety liabilities due to on-target on-tumor, on-target off-tumor cytotoxic activity and cytokine release. Patients treated with TCBs may experience a Cytokine Release Syndrome (CRS), characterized by fever, hypotension and respiratory deficiency and associated with the release of pro-inflammatory cytokines such as IL-6, TNF-α, IFN-γ, and IL-1β.3 Off-tumor toxicity may occur if target antigens are expressed in healthy cells, which may potentially result in tissue damages and compromise the patient‘s safety. Rapid pharmacological blockade of T cell activation and proliferation is a promising approach to mitigate these life-threatening toxicities. Tyrosine kinases such as SRC, LCK or ZAP70 are involved in downstream signaling pathways after engagement of the T cell receptor and blocking these kinases might serve to abrogate T cell activation when required. Dasatinib was identified as a potent candidate that switches off CAR T cell functionality.4 5MethodsUsing an in vitro model of target cell killing by human peripheral blood mononuclear cells, we assessed the reversible effects of dasatinib combined with CEA-TCB or HLA-A2-WT1-TCB on T cell activation and proliferation, target cell killing and cytokine release. At assay endpoints, T cell phenotype and target cell killing were measured by flow cytometry and supernatants were analyzed by Luminex to assess cytokine release. To determine the effective dose of dasatinib, the Incucyte system was used to follow kinetics of target cells killing by TCB in the presence of a dose response of dasatinib concentrations.Results100 nM dasatinib prevented TCB-mediated target cell killing when added in the system upon restimulation of activated T cells (figure 1). Dasatinib concentrations above 50 nM fully switched off target cell killing (figure 2) which was restored upon removal of dasatinib. These data confirm that dasatinib act as a potent and reversible on/off switch for activated T cells at pharmacologically relevant doses as they are applied in patients according to the label.6ConclusionsTaken together, we provide evidence for the use of dasatinib as a pharmacological on/off switch to mitigate off-tumor toxicities or CRS by T cell engaging therapies. These data are being validated in vivo.ReferencesBacac M, Fauti T, Sam J, Colombetti S, Weinzierl T, Ouaret D, et al. A novel carcinoembryonic antigen T-Cell Bispecific Antibody [CEA TCB] for the treatment of solid tumors. Clin Cancer Res 2016;22(13):3286–97.Bacac M, Klein C, Umana P. CEA TCB: A novel head-to-tail 2:1 T cell bispecific antibody for treatment of CEA-positive solid tumors. Oncoimmunology 2016;5(8):e1203498.Shimabukuro-Vornhagen A, Gödel P, Subklewe M, Stemmler HJ, Schlößer HA, Schlaak M, et al. Cytokine release syndrome. J Immunother Cancer 2018;6(1):56.Weber EW, Lynn RC, Sotillo E, Lattin J, Xu P, Mackall CL. Pharmacologic control of CAR-T cell function using dasatinib. Blood Advances 2019;3(5):711–7.Mestermann K, Giavridis T, Weber J, Rydzek J, Frenz S, Nerreter T, et al. The tyrosine kinase inhibitor dasatinib acts as a pharmacologic on/off switch for CAR T cells. Science Translational Medicine 2019;11(499):eaau5907.Wang X, Roy A, Hochhaus A, Kantarjian HM, Chen TT, Shah NP. Differential effects of dosing regimen on the safety and efficacy of dasatinib: retrospective exposure-response analysis of a Phase III study. Clinical pharmacology : advances and applications 2013;5:85–97.Abstract 653 Figure 1Representative flow cytometry experiment reporting SKM-1 target cell viability upon first stimulation with 10 nM HLA-A2 WT-1-TCB in the absence of dasatinib (left pannel) and upon second stimulation with 10 nM HLA-A2 WT-1-TCB in the presence of 100 nM dasatinib (right pannel)[Figure omitted. See PDF]Abstract 653 Figure 2Real time killing (Incucyte) of red fluorescent A375 cells loaded with RMF peptides by 10 nM HLA-A2 WT-1-TCB (left pannel) and of red fluorescent MKN45 cells by 1 nM CEA-TCB (right pannel) in the presence of different dasatinib concentrations ranging from 100 nM to 0 nM. Mean of technical duplicates + SEM[Figure omitted. See PDF]

Intratumoral regulatory T cell (Treg) abundance associates with diminished anti-tumor immunity and poor prognosis in human cancers. Recent work demonstrates that CD25, the high affinity receptor subunit for IL-2, is a selective target for Treg depletion in mouse and human malignancies; however, anti-human CD25 antibodies have failed to deliver clinical responses against solid tumors due to bystander IL-2 receptor signaling blockade on effector T cells, which limits their anti-tumor activity. Here we demonstrate potent single-agent activity of anti-CD25 antibodies optimized to deplete Tregs whilst preserving IL-2-STAT5 signaling on effector T cells, and demonstrate synergy with immune checkpoint blockade in vivo. Pre-clinical evaluation of an anti-human CD25 (RG6292) antibody with equivalent features demonstrates, in both non-human primates and humanized mouse models, efficient Treg depletion with no overt immune-related toxicities. Our data supports the clinical development of RG6292 and evaluation of novel combination therapies incorporating non-IL-2 blocking anti-CD25 antibodies in clinical studies.