Receptor Occupancy Research Articles

A phase 1 study to evaluate the safety, pharmacokinetics (PK), and pharmacodynamics (PD), and to determine the recommended phase 2 dose (RP2D) of subcutaneous (SC) cetrelimab (CET) in patients (pts) with advanced solid malignancies.

e14602 Background: In part (P) 1 and P2 of LUC1001 (NCT02908906), the RP2D of intravenous (IV) CET was established as 240 mg IV once every 2 weeks (Q2W) or 480 mg IV Q4W, and the PK/PD characteristics, safety profile, and clinical activity were consistent with known and approved PD-1 inhibitors (Felip et al. Cancer Chemother Pharmacol 2022). CET administered SC was investigated in P3 and P4 of LUC1001. Methods: In P3 and P4 of LUC1001, safety, PK, PD, and clinical activity of low- (30 mg/mL [CET-LC]) and high- (150 mg/mL [CET-HC]) concentration SC CET formulations, respectively, were evaluated. Key entry criteria were advanced or refractory solid tumors, previous receipt of or ineligibility for standard treatment, and being anti-PD-1/PD-L1/2–naïve. In P3, SC CET-LC injection was administered at a dose level of 600 mg with a 6-week dosing interval between doses 1 and 2, then Q3W dosing after dose 2. In P4, SC CET-HC injection was administered as a single loading dose of 900 mg, followed by 600 mg Q3W. Results: Among 30 enrolled pts (P3: n = 11; P4: n = 19), median age was 54.5 years; 17 (57%) were male; most (29 [97%]) were White and heavily pretreated, with a median of 3 (range, 1-8) prior lines of therapy. Most common tumor types were colorectal cancer (6 [20%]), breast cancer (4 [13%]), cholangiocarcinoma and NSCLC (3 [10%] each). Most commonly reported adverse events (AE) were fatigue (11 [37%]), ALT increased (7 [23%]), abdominal pain, constipation and AST increased (6 [20%] each). Overall, 20 (67%) pts had CET-related AEs, 1 (3%) of which led to CET discontinuation. Eight (27%) pts had ≥1 CET-related ≥Grade 3 AE. Immune-related AEs were reported in 9 (30%) pts. No pts experienced systemic-administration–related reactions, and 2 (6%) pts experienced Grade 1 administration-site reactions. No CET-related serious AEs were reported. Durable responses were observed in 2 (7%) patients (cholangiocarcinoma in P3 and thymoma in P4). Stable disease ≥24 weeks was observed in 4 (13% [P3, 0 (0%); P4, 4 (21%)]) pts. According to PK data, the 900-mg SC CET loading dose followed by 600-mg SC CET Q3W would likely result in comparable exposure as observed at steady state with IV RP2Ds. No differences in PK, including absorption, were observed between CET-LC and CET-HC formulations. Maximum PD-1 receptor occupancy was achieved, consistent with historical IV and SC data. Incidence of anti-CET antibodies (P3, 3/11 [27%]; P4, 0/13 [0%]) was low, and no neutralizing antibodies (0/24 [0%]) were detected. Conclusions: SC CET demonstrated a safety profile similar to IV CET. Based on safety, PK, and PD data, the RP2D of SC CET was established as a loading dose of 900 mg followed by 600 mg Q3W. Studies are planned to further evaluate the safety and efficacy of SC CET in combination with other agents. Clinical trial information: NCT02908906 .

Discovery and Model-Informed Drug Development of a Controlled-Release Formulation of Nonracemic Amisulpride that Reduces Plasma Exposure but Achieves Pharmacodynamic Bioequivalence in the Brain.

Nonracemic amisulpride (SEP-4199) is aninvestigational 85:15 ratio of aramisulpride to esamisulpride and currently in clinical trials for the treatment of bipolar depression. During testing of SEP-4199, a pharmacokinetic/pharmacodynamic (PK/PD) disconnect was discovered that prompted the development of a controlled-release (CR) formulation with improved therapeutic index for QT prolongation. Observations that supported the development of a CR formulation included (i) plasma concentrations of amisulpride enantiomers were cleared within 24-hours, but brain dopamine D2 receptor (D2R) occupancies, although achieving stable levels during this time, required 5 days to return to baseline; (ii) nonracemic amisulpride administered to non-human primates produced significantly greater D2R occupancies during a gradual 6-hour administration compared with a single bolus; (iii) concentration-occupancy curves were left-shifted in humans when nonracemic amisulpride was gradually administered over 3 and 6 hours compared with immediate delivery; (iv) CR solid oral dose formulations of nonracemic amisulpride were able to slow drug dissolution in vitro and reduce peak plasma exposures in vivo in human subjects. By mathematically solving for a drug distribution step into an effect compartment, and for binding to target receptors, the discovery of a novel PK/PD model (termed here as Distribution Model) accounted for hysteresis between plasma and brain, a lack of receptor saturation, and an absence of accumulation of drug occupancy with daily doses. The PK/PD disconnect solved by the Distribution Model provided model-informed drug development to continue in Phase III using the non-bioequivalent CR formulation with diminished QT prolongation as dose-equivalent to the immediate release (IR) formulation utilized in Phase II.

Population pharmacokinetics and CD20 binding dynamics for mosunetuzumab in relapsed/refractory B-cell non-Hodgkin lymphoma.

Mosunetuzumab (Mosun) is a CD20xCD3 T-cell engaging bispecific antibody that redirects T cells to eliminate malignant B cells. The approved step-up dose regimen of 1/2/60/30 mg IV is designed to mitigate cytokine release syndrome (CRS) and maximize efficacy in early cycles. A population pharmacokinetic (popPK) model was developed from 439 patients with relapsed/refractory B-Cell Non-Hodgkin lymphoma receiving Mosun IV monotherapy, including fixed dosing (0.05-2.8 mg IV every 3 weeks (q3w)) and Cycle 1 step-up dosing groups (0.4/1/2.8-1/2/60/30 mg IV q3w). Prior to Mosun treatment, ~50% of patients had residual levels of anti-CD20 drugs (e.g., rituximab or obinutuzumab) from prior treatment. CD20 receptor binding dynamics and rituximab/obinutuzumab PK were incorporated into the model to calculate the Mosun CD20 receptor occupancy percentage (RO%) over time. A two-compartment model with time-dependent clearance (CL) best described the data. The typical patient had an initial CL of 1.08 L/day, transitioning to a steady-state CL of 0.584 L/day. Statistically relevant covariates on PK parameters included body weight, albumin, sex, tumor burden, and baseline anti-CD20 drug concentration; no covariate was found to have a clinically relevant impact on exposure at the approved dose. Mosun CD20 RO% was highly variable, attributed to the large variability in residual baseline anti-CD20 drug concentration (median = 10 μg/mL). The 60 mg loading doses increased Mosun CD20 RO% in Cycle 1, providing efficacious exposures in the presence of the competing anti-CD20 drugs. PopPK model simulations, investigating Mosun dose delays, informed treatment resumption protocols to ensure CRS mitigation.

Comparison of dose selection based on target engagement versus inhibition of receptor-ligand interaction for checkpoint inhibitors.

Immune checkpoint inhibitors block the interaction between a receptor on one cell and its ligand on another cell, thus preventing the transduction of an immunosuppressive signal. While inhibition of the receptor-ligand interaction is key to the pharmacological activity of these drugs, it can be technically challenging to measure these intercellular interactions directly. Instead, target engagement (or receptor occupancy) is commonly measured, but may not always be an accurate predictor of receptor-ligand inhibition, and can be misleading when used to inform clinical dose projections for this class of drugs. In this study, a mathematical model explicitly representing the intercellular receptor-ligand interaction is used to compare dose prediction based on target engagement or receptor-ligand inhibition for two checkpoint inhibitors, atezolizumab and magrolimab. For atezolizumab, there is little difference between target engagement and receptor-ligand inhibition, but for magrolimab, the model predicts that receptor-ligand inhibition is significantly less than target engagement. The key variables explaining the difference between these two drugs are the relative concentrations of the target receptors and their ligands. Drug-target affinity and receptor-ligand affinity can also have divergent effects on target engagement and inhibition. These results suggest that it is important to consider ligand-receptor inhibition in addition to target engagement and demonstrate the impact of using modeling for efficacious dose estimation.

Total-body imaging of mu-opioid receptors with [11C]carfentanil in non-human primates

PurposeMu-opioid receptors (MORs) are widely expressed in the central nervous system (CNS), peripheral organs, and immune system. This study measured the whole body distribution of MORs in rhesus macaques using the MOR selective radioligand [11C]carfentanil ([11C]CFN) on the PennPET Explorer. Both baseline and blocking studies were conducted using either naloxone or GSK1521498 to measure the effect of the antagonists on MOR binding in both CNS and peripheral organs.MethodsThe PennPET Explorer was used for MOR total-body PET imaging in four rhesus macaques using [11C]CFN under baseline, naloxone pretreatment, and naloxone or GSK1521498 displacement conditions. Logan distribution volume ratio (DVR) was calculated by using a reference model to quantitate brain regions, and the standard uptake value ratios (SUVRs) were calculated for peripheral organs. The percent receptor occupancy (%RO) was calculated to establish the blocking effect of 0.14 mg/kg naloxone or GSK1521498.ResultsThe %RO in MOR-abundant brain regions was 75–90% for naloxone and 72–84% for GSK1521498 in blocking studies. A higher than 90% of %RO were observed in cervical spinal cord for both naloxone and GSK1521498. It took approximately 4–6 min for naloxone or GSK1521498 to distribute to CNS and displace [11C]CFN from the MOR. A smaller effect was observed in heart wall in the naloxone and GSK1521498 blocking studies.Conclusion[11C]CFN total-body PET scans could be a useful approach for studying mechanism of action of MOR drugs used in the treatment of acute and chronic opioid use disorder and their effect on the biodistribution of synthetic opioids such as CFN. GSK1521498 could be a potential naloxone alternative to reverse opioid overdose.

The physiological and biochemical basis of potency thresholds modeled using human estrogen receptor alpha: implications for identifying endocrine disruptors

The endocrine system functions by interactions between ligands and receptors. Ligands exhibit potency for binding to and interacting with receptors. Potency is the product of affinity and efficacy. Potency and physiological concentration determine the ability of a ligand to produce physiological effects. The kinetic behavior of ligand-receptor interactions conforms to the laws of mass action. The laws of mass action define the relationship between the affinity of a ligand and the fraction of cognate receptors that it occupies at any physiological concentration. We previously identified the minimum ligand potency required to produce clinically observable estrogenic agonist effects via the human estrogen receptor-alpha (ERα). By examining data on botanical estrogens and dietary supplements, we demonstrated that ERα ligands with potency lower than one one-thousandth that of the primary endogenous hormone 17β-estradiol (E2) do not produce clinically observable estrogenic effects. This allowed us to propose a Human-Relevant Potency Threshold (HRPT) for ERα ligands of 1 × 10–4 relative to E2. Here, we test the hypothesis that the HRPT for ERα arises from the receptor occupancy by the normal metabolic milieu of endogenous ERα ligands. The metabolic milieu comprises precursors to hormones, metabolites of hormones, and other normal products of metabolism. We have calculated fractional receptor occupancies for ERα ligands with potencies below and above the previously established HRPT when normal circulating levels of some endogenous ERα ligands and E2 were also present. Fractional receptor occupancy calculations showed that individual ERα ligands with potencies more than tenfold higher than the HRPT can compete for occupancy at ERα against individual components of the endogenous metabolic milieu and against mixtures of those components at concentrations found naturally in human blood. Ligands with potencies less than tenfold higher than the HRPT were unable to compete successfully for ERα. These results show that the HRPT for ERα agonism (10–4 relative to E2) proposed previously is quite conservative and should be considered strong evidence against the potential for disruption of the estrogenic pathway. For chemicals with potency 10–3 of E2, the potential for estrogenic endocrine disruption must be considered equivocal and subject to the presence of corroborative evidence. Most importantly, this work demonstrates that the endogenous metabolic milieu is responsible for the observed ERα agonist HRPT, that this HRPT applies also to ERα antagonists, and it provides a compelling mechanistic explanation for the HRPT that is grounded in basic principles of molecular kinetics using well characterized properties and concentrations of endogenous components of normal metabolism.

Abstract PO1-05-07: Circulating tumor DNA dynamics in acelERA Breast Cancer: a Phase II study of giredestrant for estrogen receptor-positive, HER2-negative, previously treated advanced breast cancer

Abstract BACKGROUND Giredestrant (GIR) is a highly potent, oral, selective estrogen receptor antagonist and degrader (SERD) that exhibits robust estrogen receptor (ER) occupancy. The Phase II, randomized, open-label acelERA Breast Cancer (BC) study (NCT04576455) assessed GIR vs physician’s choice of endocrine therapy (PCET) in second- or third-line ER-positive, HER2-negative advanced BC (ER+, HER2– aBC). The study did not reach statistical significance for the primary endpoint of investigator-assessed progression-free survival (PFS); however, the benefit of GIR was of larger magnitude among patients (pts) with ESR1-mutated tumors (ESR1m; a common cause of acquired resistance to endocrine therapy [ET]). We present an exploratory biomarker analysis of circulating tumor (ct)DNA dynamics. METHODS Pts (n = 303) were randomized 1:1 to GIR or PCET (75% of pts had fulvestrant [FUL]; 25%, an aromatase inhibitor). Partial response (PR), stable disease (SD), and progressive disease (PD) were categorized by RECIST v1.1. Plasma samples taken at Cycle 1, Day 1 (C1D1; n = 229), while on treatment (tx) at C2D1 (n = 220), and at the end of therapy (EOT; n = 155) were evaluated with the FoundationOne Liquid CDx next-generation sequencing assay. Gene mutations were defined as variants with known or likely impact on protein function. Composite tumor fraction (cTF) was defined as the total estimated tumor ctDNA content in each sample, and was only evaluable for a subset of samples (137 C1D1; 136 C2D1; 99 EOT). cTF or ESR1 mutant allele frequency (MAF) changes were calculated as a percent change from C1D1. ESR1m clonality was estimated as variant tumor fraction/estimated tumor fraction. Statistical significance was evaluated using the Mann–Whitney test. RESULTS The overall mutation landscape remained relatively unchanged with GIR tx at C2D1 or EOT, except for ESR1m prevalence, which declined from 43% at C1D1 to 26% on tx and 27% at EOT. With PCET, ESR1m prevalence decreased from 34% at C1D1 to 29% on tx, but increased to 43% by EOT. There were no concordant changes for other top mutated genes in this study, including PIK3CA, TP53, or DNMT3A. cTF decreased on tx in 38/65 (59%) and 32/59 (54%) of evaluable pts with GIR and PCET, respectively; the median change from C1D1 was –23% with GIR compared with –5% with PCET or –15% with FUL. The median change in cTF levels on tx with GIR was significantly greater in pts with a PR (–88%) vs PD (+6%, p = 0.002) or SD (–19%, p = 0.004). The degree of cTF decline on tx with GIR was significantly higher in pts with baseline ESR1m (median change –58%) vs no ESR1m detected (+5%, p = 0.012). Pts with a clonal ESR1m had higher levels of cTF decline on tx vs pts with subclonal ESR1m, suggesting cTF dynamics are a function of tumor heterogeneity. ESR1 MAF decreased on tx in 93% of pts with baseline ESR1m on GIR, vs 60% with PCET and 70% with FUL. ESR1 MAF decline on tx was significantly higher with GIR vs PCET at both C2D1 and EOT (p < 0.0001). The average ESR1 MAF decline on tx with GIR was greater in pts with a PR (–97%) vs PD (–54%, p = 0.025) or SD (–48%, p = 0.051), and all seven GIR-treated pts with a PR showed a near or total loss of ESR1 MAF by C2D1. The ESR1m variants D538G and Y537X had a significantly greater decline in MAF on tx with GIR vs PCET or FUL (p < 0.0001). CONCLUSIONS Data show that cTF and ESR1m ctDNA dynamics were associated with clinical response to GIR in ER+, HER2– aBC. ESR1 MAF decline was significantly greater with GIR vs PCET or FUL. ESR1 MAF declined to a greater degree with GIR compared with cTF, which is consistent with the larger magnitude of PFS benefit seen with GIR in pts with ESR1m tumors. The specific ESR1 variants D538G and Y537X showed greater sensitivity to GIR compared with PCET or FUL. Citation Format: Ann Collier, Aditya Bardia, Joo Hyuk Sohn, Elgene Lim, Marianna Chavez, Miguel Martín, Jorge Martinalbo, Pablo Perez-Moreno, Heather Moore. Circulating tumor DNA dynamics in acelERA Breast Cancer: a Phase II study of giredestrant for estrogen receptor-positive, HER2-negative, previously treated advanced breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-05-07.

Development of simultaneous determination of dopamine 2, histamine 1, and muscarinic acetylcholine receptor occupancies by antipsychotics using liquid chromatography with tandem mass spectrometry

Receptor occupancy is an indicator of antipsychotic efficacy and safety. It is desirable to simultaneously determine the occupancy of multiple brain receptors as an indicator of the efficacy and central side effects of antipsychotics because many of these drugs have binding affinities for various receptors, such as dopamine 2 (D2), histamine 1 (H1), and muscarinic acetylcholine (mACh) receptors. The purpose of this study was to develop a method for the simultaneous measurement of multiple receptor occupancies in the brain by the simultaneous quantification of unlabeled tracer levels using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Rats were pre-administered with a vehicle, displacer, or olanzapine, and mixed solutions of raclopride, doxepin, and 3-quinuclidinyl benzilate (3-QNB) were administered (3, 10, and 30 μg/kg). The brain tissue and plasma tracer concentrations were quantified 45 min later using LC-MS/MS, and the binding potential was calculated. The highest binding potential was observed at 3 μg/kg raclopride, 10 μg/kg doxepin, and 30 μg/kg 3-QNB. Tracer-specific binding at these optimal tracer doses in the cerebral cortex was markedly reduced by pre-administration of displacers. D2, H1, and mACh receptor occupancy by olanzapine increased in a dose-dependent manner, reaching 70–95%, 19–43%, and 12–45%, respectively, at an olanzapine dose range of 3–10 mg/kg. These results suggest that simultaneous determination of in vivo D2, H1, and mACh receptor occupancy is possible using LC-MS/MS.

Preclinical Pharmacokinetics and Pharmacology Study of RC98: A Programmed Cell Death Ligand 1 Monoclonal Antibody in Cynomolgus Monkeys.

RC98 is the monoclonal antibody against Programmed Cell Death Ligand 1 (PD-L1). Relevant reports have confirmed that the influence of PD-L1 expressed by tumor cells on antitumor CD8+ T cell responses is well characterized, but the impact of PD-L1 expressed by immune cells has not been well defined. This study aimed to design a Pharmacokinetics/Pharmacology (PK/PD) study of RC98 in normal cynomolgus monkeys to research the effect on the immune system. RC98 and vehicle were administered to cynomolgus monkeys at 15 mg/kg via intravenous infusion once a week for 4 weeks to evaluate the relationship between PK and PD. The pharmacodynamic activity was measured by the PD-L1 receptor occupancy (RO) in CD3+ T cells, A T-cell-dependent antibody response (TDAR), and the concentration of soluble PD-L1. The pharmacokinetic result showed that the exposure from the last administration was lower than that of the first administration, probably due to immunogenicity production. There was a strong correlation between systemic exposure and RO in CD3+ T cells but decreased RO levels after the last dose, which indirectly reflected the activation of T cells. The keyhole limpet hemocyanin (KLH)-induced TDAR in the RC98 group was higher than in the vehicle group. The concentration of soluble PD-L1 had increased feedback with RC98, and the concentration of soluble PD-L1 was maintained at a higher level after multiple doses than before dosing. These data indicate that the immune system was clearly activated. In addition, the non-clinical data could provide a basis for its efficacy evaluation in clinical trials.

Cerebral Anoxia in an 18-year-old Patient Being Treated for Major Depressive Disorder: How Forensic Detective Work Uses Medical Knowledge Including Clinical Pharmacology to Solve Cases.

This column is the first of a 3-part series illustrating the importance of medical knowledge, including clinical pharmacology, in a forensic context. This first case involved an 18-year-old high school student who suffered an anoxic brain injury and remained in a state of permanent decorticate posture, unresponsive except for grunts and primitive movements until he died several years later. Our investigation began by ruling out plausible causes that were suggested by the defense in the malpractice suit. Once those possibilities were eliminated, the focus was on what accounted for the damage to the patient using general medical knowledge and clinical pharmacology. The 4 Ds of forensic psychiatry (duty, damages, dereliction, and direct cause) are the 4 elements that the plaintiff is required to prove in civil court to prevail in a malpractice suit and are applied to this case with a special focus on dereliction and direct cause. This catastrophic outcome was due to 3 factors. First, the patient had physiologically significant dehydration to the point that he had developed a reflex tachycardia to maintain his blood pressure. Second, the patient had been switched from extended to immediate-release quetiapine, resulting in a doubling of the peak concentration of the drug, which produced higher occupancy of alpha-1 adrenergic, histamine-1, and dopamine-2 receptors, causing a further drop in his blood pressure as well as increased sedation and impairment of his gag reflex. These effects occurred quickly because of the faster absorption of the IR formulation of the drug. Third, the patient had gone to sleep in a reclining chair so that his brain was above his heart and his lower extremities were below his heart, resulting in an increased "steal" of cardiac output going to his brain. These 3 factors together led the patient to aspirate and suffer a hypoxic brain injury after an episode of vomitus. This column explains the process by which the cause of this sad outcome was determined, how it was related to a dereliction of duty to the patient, and how other proposed causes were ruled out.

Non-linear blood-brain barrier transport and dosing strategies influence receptor occupancy ratios of morphine and its metabolites in pain matrix.

Morphine is important for treatment of acute and chronic pain. However, there is high interpatient variability and often inadequate pain relief and adverse effects. To better understand variability in the dose-effect relationships of morphine, we investigated the effects of its non-linear blood-brain barrier (BBB) transport on μ-receptor occupancy in different CNS locations, in conjunction with its main metabolites that bind to the same receptor. CNS exposure profiles for morphine, M3G and M6G for clinically relevant dosing regimens based on intravenous, oral immediate- and extended-release formulations were generated using a physiology-based pharmacokinetic model of the CNS, with non-linear BBB transport of morphine. The simulated CNS exposure profiles were then used to derive corresponding μ-receptor occupancies at multiple CNS pain matrix locations. Simulated CNS exposure profiles for morphine, M3G and M6G, associated with non-linear BBB transport of morphine resulted in varying μ-receptor occupancies between different dose regimens, formulations and CNS locations. At lower doses, the μ-receptor occupancy of morphine was relatively higher than at higher doses of morphine, due to the relative contribution of M3G and M6G. At such higher doses, M6G showed higher occupancy than morphine, whereas M3G occupancy was low throughout the dose ranges. Non-linear BBB transport of morphine affects the μ-receptor occupancy ratios of morphine with its metabolites, depending on dose and route of administration, and CNS location. These predictions need validation in animal or clinical experiments, to understand the clinical implications.

Abstract CT068: Interim results of the ongoing phase 1-2 clinical trial of KVA12123, an engineered IgG1 targeting VISTA, as monotherapy and in combination with pembrolizumab in patients with advanced solid tumors

Abstract V-domain Ig Suppressor of T-cell Activation (VISTA), a promising immuno-oncology target, is primarily expressed by immunosuppressive myeloid cells that infiltrate solid tumors. VISTA may contribute to resistance to anti-PD-(L)1 and anti-CTLA-4 therapies and correlates with a poor prognosis. KVA12123 is a human IgG1 monoclonal antibody that specifically binds to VISTA at neutral and acidic pHs. It was designed to improve pharmacokinetic (PK) characteristics as well as reduce the risk of cytokine release syndrome (CRS). KVA12123 exhibited strong anti-tumor activity alone and in combination with anti-PD1 in preclinical studies. It demonstrated an excellent safety profile in non-human primates. The VISTA-101 clinical trial is a first-in-human, Phase 1/2, multicenter, open-label, safety, PK and pharmacodynamic (PD) evaluation of KVA12123, both as monotherapy and in combination with pembrolizumab, in adult patients with advanced solid tumors (NCT05708950). METHODS: The phase 1 of VISTA-101 is an accelerated Bayesian Optimal Interval Design consisting of two arms: Part A) KVA12123 monotherapy dose escalation from 3 mg to 1000 mg including 6 cohorts and Part B) KVA12123 dose escalation from 30 mg to 1000 mg in combination with 400 mg fixed dosing of pembrolizumab including 4 cohorts. The primary objectives are safety, tolerability and to define a recommended phase 2 dose. Safety, PK and receptor occupancy data were considered during dose escalation. VISTA-101 is also assessing PD and predictive biomarkers of response. Patient tumor response is evaluated by iRECIST. RESULTS: Forty-two patients have been enrolled in the dose escalation monotherapy arm of the study. KVA12123 was administered at doses ranging from 3 to 1000 mg every 2 weeks over a 6-week cycle. KVA12123 was well tolerated at all dose levels and no DLTs were observed. The most frequently observed adverse events were grade 1 or 2 transient infusion-related reactions. No evidence of CRS-associated cytokines were detected. PK analysis demonstrated greater than dose-proportional exposure consistent with target-mediated metabolism. A VISTA receptor occupancy assay demonstrated full target engagement at doses of 30 mg and above. PD analysis indicated a dose-dependent induction of pro-inflammatory myeloid derived cytokines and chemokines involved in immune cell activation and recruitment to the tumor microenvironment including CCL2, CCL3, CCL4 and CXCL10. Increases in nonclassical monocytes, NK cells, CD4+ and CD8+ T cells were also demonstrated, consistent with observations made in preclinical models and indicative of VISTA target engagement. Patient tumor response evaluations in the monotherapy arm will be reported. The study continues to evaluate KVA12123 both as a monotherapy and in combination with pembrolizumab to define the recommended phase 2 dose. Citation Format: Evan Y. Yu, Jason Henry, Manish R. Patel, Paul Swiecicki, Ida Micaily, Benjamin Garmezy, Kalyan Banda, Vinny Hayreh, Kurt Lustig, Yulia Ovechkina, Shawn P. Iadonato, Thierry Guillaudeux, Lee Rosen. Interim results of the ongoing phase 1-2 clinical trial of KVA12123, an engineered IgG1 targeting VISTA, as monotherapy and in combination with pembrolizumab in patients with advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT068.

Abstract CT173: Preliminary results from a phase I study of IMM0306 in patients with relapsed or refractory CD20-positive B-cell non-Hodgkin's lymphoma

Abstract Background: IMM0306 is a fusion protein of CD20 monoclonal antibody with the CD47 binding domain of SIRPα on both heavy chains. It exerts excellent cancer killing efficacy by activating both macrophages and NK cells via blockade of CD47-SIRPα interaction and FcɣR engagement. Here, we report the safety, pharmacokinetics (PK), pharmacodynamics (PD), and efficacy results of phase I in patients (pts) with relapsed or refractory (R/R) CD20-positive B-cell non-Hodgkin's lymphoma (B-NHL). Methods: Eligible pts with R/R CD20-positive B-NHL were enrolled in this open-label, multicenter phase I/II study (NCT05805943). IMM0306 was administered as monotherapy at escalating doses of 0.04, 0.1, 0.25, 0.5, 0.8, 1.2, 1.6, 2.0 mg/kg intravenously once a week after a 2-week single-dose observation period, until disease progression or intolerable toxicity. Dose-limiting toxicity (DLT) was evaluated in the first 28 days. Safety was evaluated per CTCAE 5.0, PK and PD analysis were also assessed, tumor assessments performed once every 8 weeks by Lugano 2014. Results: As of Nov 21, 2023, 48 pts were enrolled. The median age was 56 years with 30 (62.5%) males. The median prior lines of therapy was 2. All pts received previous anti-CD20 therapy. No DLTs were observed. Recommended phase II dose (RP2D) was determined as 2.0 mg/kg. The most frequent treatment related adverse events (TRAEs) were WBC decreased (66.7%), anemia (64.6%), lymphocyte decreased (58.3%), ANC decreased (47.9%), PLT decreased (45.8%), infusion-related reactions (35.4%). Grade ≥3 TRAEs occurred in 33 (68.8%) pts, the most frequent grade ≥ 3 TRAEs were lymphocyte decreased (56.3%), WBC decreased (18.8%), ANC decreased (18.8%). Eight (16.7%) pts experienced treatment related serious adverse event, including PLT decreased, chest pain and pneumonia. Drug discontinuation due to AEs occurred in 1 pt (G4 PLT decreased occurred at 1.6mg/kg without any bleeding). No AE led to death. IMM0306 exhibited approximate dose-proportional increase in PK exposure from 0.5 to 2.0 mg/kg and no obvious accumulation was observed after repeated dosing. At 1.2 mg/kg, CD47 receptor occupancy on peripheral lymphocytes was saturated, suggesting IMM0306 is well tolerated from perspective of CD47 engagement in high dose cohorts. B-cell counts depleted rapidly at doses ≥ 0.8 mg/kg. Elevated cytokines levels were observed after first dosing of IMM0306, but multiple dosing did not stimulate further cytokine activation. Among 33 pts who received active doses ≥ 0.8 mg/kg, 5 CR (4 follicular lymphoma [FL], 1 marginal zone lymphoma [MZL]), 5 PR (3 FL, 1 MZL, 1 diffuse large B cell lymphoma) and 11 SD were seen. Among 17 FL pts, 7 (41%) responded including 4 CR and 3 PR; among 6 MZL pts, 2 (33.3%) responded including 1 CR and 1 PR. Conclusions: IMM0306 was well-tolerated and with a robust preliminary anti-tumor activity especially in pts with R/R FL and MZL. The phase II study is ongoing. Citation Format: Yuankai Shi, Jianliang Yang, Yongping Song, Keshu Zhou, Zhiming Li, Mingzhi Zhang, Hongmei Jing, Zhen Wang, Li Yu, Qiying Lu, Frank Gan, Wenzhi Tian. Preliminary results from a phase I study of IMM0306 in patients with relapsed or refractory CD20-positive B-cell non-Hodgkin's lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT173.

Abstract CT185: A phase I clinical trial to evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics and preliminary anti-tumor activity of BC3402 in advanced solid malignancies

Abstract Background: BC3402, an IgG4 monoclonal antibody (mAb) that targets TIM-3, is being developed for solid and hematological malignancies. In preclinical studies in immunocompetent cancers, BC3402 demonstrated synergy when combined with mAbs to PD-1 and/or CTLA-4, supporting a rationale for combination strategies in the clinic. As a first step, the safety, tolerability, pharmacokinetics (PK), pharmacodynamics, and preliminary anti-tumor activity of BC3402 monotherapy was evaluated in patients (pts) with advanced solid malignancies. Methods: In this phase I, open-label study, multiple doses of BC3402 were explored in pts with advanced solid cancers who had been previously treated with standard therapies to evaluate its safety and tolerability and recommend doses for further development. An accelerated titration design was used to select doses in the first two dose levels (0.02 and 0.2mg/kg IV Q3W) followed by a standard “3+3” design in the remainder of the study (1, 5, 10, 20 and 30 mg/kg IV Q3W). Results: Nineteen pts (median [range] age: 59 [29-73]; 63.2% male; 94.7% ECOG 1) were treated with at least one 3-week cycle of BC3402. DLT was not observed, and adverse events (AEs) were not dose related. The most common TEAEs (incidence ≥20%) and TRAEs (incidence ≥10%) were grade 1-2. The most common (incidence ≥10%) TEAE ≥ grade 3 was dysphagia (2/19 pts, 10.5%), which occurred in the 5 mg/kg and 10 mg/kg dose cohorts. Two pts reported grade 3 or above TRAEs – grade 3 hypertension (5 mg/kg) and grade 3 gamma-glutamyl transferase increase (10 mg/kg), There were neither dose interruptions nor treatment discontinuation due to AEs. There were no objective responses. Seven of 18 pts who were evaluable for tumor assessment had stable disease as best response with one pt (20 mg/kg dose cohort) with NSCLC having sustained reductions (32 weeks) in target lesions. Median Tmax values ranged from 1.08 to 2.96 hours, and mean T1/2 values ranged from 119 to 182 hours at doses ranging from 5-30 mg/kg. Exposure was linear in the dose range of 1 -30 mg/kg, and there was no drug accumulation after the second cycle. Receptor occupancy saturation was observed within the tested dose range. Based on these data, the RP2D was determined as 20mg/kg every 2 weeks or 30mg/kg every 3 weeks. Conclusions: BC3402 exhibited favorable safety profile and PK characteristics when administered as single infusion at doses ranging from 0.02 mg/kg to 30 mg/kg Q3W in pts with advanced solid cancers, and its safety profile supports further disease-directed studies in combination with other immune checkpoint inhibitors and/or rational therapeutic modalities. Citation Format: Yi-Long Wu, Huajun Chen, Sheng Wang, Rui Zhang, En-Tzu Tang, Weiwei Zhang, Kaicun Gu, Yiwei Wang, Yongjiang Hei. A phase I clinical trial to evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics and preliminary anti-tumor activity of BC3402 in advanced solid malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT185.

Pharmacological Basis of Differences in Dose Response, Dose Equivalence, and Duration of Action of Inhaled Corticosteroids.

Asthma treatment guidelines classify inhaled corticosteroid (ICS) regimens as low, medium, or high dose. However, efficacy and safety are not independently assessed accordingly. Moreover, differences in ICS duration of action are not considered when a dose regimen is selected. We investigated the efficacy and safety implications of these limitations for available ICS molecules. Published pharmacodynamic and pharmacokinetic parameters were used, alongside physiological and pharmacological principles, to estimate the efficacy and safety of available ICS molecules. Extent and duration of glucocorticoid receptor (GR) occupancy in the lung (efficacy) and cortisol suppression (systemic exposure and safety) were estimated. Some ICS regimens (e.g., fluticasone furoate, fluticasone propionate, and ciclesonide) rank high for efficacy but low for systemic exposure, contrary to how ICS dose equivalence is currently viewed. Differences in dose-response relationships for efficacy and systemic exposure were unique for each ICS regimen and reflected in their therapeutic indices. Notably, even low doses of most ICSs can generate high GR occupancy (≥ 90%) across the entire dose interval at steady state, which may explain previously reported difficulties in obtaining dose responses within the clinical dose range and observations that most clinical benefit typically occurs at low doses. The estimated post dose duration of lung GR occupancy for ICS molecules was categorized as 4-6h (short), 14-16h (medium), 25-40h (long), or > 80h (ultra-long), suggesting potentially large differences in anti-inflammatory duration of action. In a real-world clinical setting where there may be poor adherence to prescribed therapy, our findings suggest a significant therapeutic advantage for longer-acting ICS molecules in patients with asthma.

Abstract 2577: Analyzing specific and nonspecific tissue uptake of antibodies by SPECT imaging and non-linear compartmental modeling

Abstract Understanding the mechanisms driving specific target engagement versus off-target nonspecific cellular uptake of antibodies can help inform design and/or delivery strategies that maximize therapeutic indices. Receptor binding kinetics, rates of receptor-mediated internalization and nonspecific pinocytosis are often measured through in vitro cell culture models, but there have been fewer efforts to collectively measure these cellular parameters in vivo. Single photon emission computed tomography (SPECT) imaging is a powerful method of estimating these parameters by quantifying both free/bound (intact) and internalized/catabolized antibody using non-residualizing halogen labels and residualizing radiometal-chelates, respectively. Modeling longitudinal in vivo imaging data of non-residualizing antibody can inform receptor occupancy (RO), while residualizing tracer kinetics can provide additional insights into catabolism due to pinocytosis and receptor-mediated internalization in the intracellular spaces. Here, we describe SPECT imaging of tumor-targeting trastuzumab (anti-HER2) and non-targeting anti-glycoprotein D (anti-gD) antibody, each labeled with non-residualizing ([125I]SIB) and residualizing radiometal-chelate (111In-DOTA) radionuclides in HER2+ xenograft-bearing mice. A non-linear compartmental model was fitted to SPECT imaging data to characterize RO of 10 mg/kg of anti-HER2 out to 7 days post dosing as well as to estimate rate constants of pinocytosis and receptor-mediated internalization of anti-HER2 in tumor. Longitudinal SPECT imaging demonstrated statistically significant differences in tumor drug exposure between 125I- and 111In-labeled anti-HER2 relative to anti-gD (p < 0.01). Tracer kinetics of anti-HER2 and associated RO simulations in tumor showed rapid extravasation from blood to tumor with peak RO of 25% at 13 hours post administration followed by a reduction in RO, reaching ~10% by day 7. Simulations for free, bound and catabolized tracer kinetics from our fitted model showed that anti-HER2 in the tumor interstitium was primarily receptor-bound with minimal pinocytosis of unbound anti-HER2 as well as gradual receptor-mediated catabolism, reaching a peak concentration of 113 µg/mL 7 days post dosing. Rate constants of nonspecific pinocytosis and HER2-mediated receptor internalization were estimated to be 0.0145 and 0.036 hours−1, respectively. Our model allowed us to successfully capture anti-HER2 antibody receptor binding and specific and nonspecific internalization over time in vivo. These data and analyses demonstrate the power of SPECT imaging using both non-residualizing and residualizing radiolabels combined with compartmental modeling to better characterize the different biological states (free, bound, and catabolized) of antibody within interstitial and intracellular compartments. Citation Format: Nicholas Cho, Phillip Spinosa, Danielle Mandikian, Geoffrey Del Rosario, Shang-Fan Yu, Jason Ho, Greg Ferl, Charles A. Boswell. Analyzing specific and nonspecific tissue uptake of antibodies by SPECT imaging and non-linear compartmental modeling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2577.

Abstract 7179: OBI-992, a novel TROP2 targeting antibody drug conjugate demonstrates superior in vivo PK/PD properties and a favorable safety profile

Abstract Background: TROP2 targeting antibody-drug conjugates (ADC) have demonstrated promising clinical responses for the treatment of various solid tumors. However, these ADCs still exhibit serious safety issues, such as hematologic toxicities and interstitial lung disease. OBI-992, a novel TROP2 targeting ADC, which is derived from the conjugation of an anti-TROP2 antibody with a topoisomerase I inhibitor, exatecan, via an enzyme-cleavable linker. OBI-992 is designed to have high serum stability and broad therapeutic index. Herein, we describe the results from preclinical studies of OBI-992, including in vitro and in vivo stability, pharmacokinetics/pharmacodynamics (PK/PD) profile, and safety evaluation. Material and Methods: To characterize OBI-992, the linker stability was evaluated by ex vivo serum stability and rat PK studies. PK/PD properties, including systemic and tumor exposures as well as receptor occupancy, were evaluated in a human lung cancer xenograft model. In vitro toxicity testing, including ADC toxicity on differentiating neutrophils and FcγR mediated toxicity, was evaluated using human monocyte THP-1 cells. A 6-week repeat dose toxicity study in cynomolgus monkeys was conducted to evaluate the safety and toxicokinetics of OBI-992. Results: Ex vivo serum stability demonstrated that OBI-992 exhibited better linker stability than the benchmark datopotamab deruxtecan (Dato-DXd). In vivo PK evaluation in rats showed that OBI-992 had lower Cmax and AUC of free payload than Dato-DXd, indicating a better PK profile of OBI-992 in rats. A PK/PD study in tumor-bearing mice revealed that OBI-992 exhibited higher tumor exposure of free payload than Dato-DXd, resulting in a better antitumor efficacy. In addition, the antitumor effect positively correlated with percentage of receptor occupancy in a dose-dependent manner. In vitro cytotoxicity testing demonstrated that OBI-992 had lower toxicity in differentiating neutrophils and THP-1 cells compared to Dato-DXd, suggesting that OBI-992 may cause less off-target toxicity. Toxicokinetics of OBI-992 in cynomolgus monkeys revealed that the systemic exposure of ADC was similar to that of total antibody. Furthermore, the systemic exposure of ADC and total antibody were found to increase in a dose-proportional manner. Major toxicities in monkeys were target-related skin lesions. The highest non-severely toxic dose (HNSTD) was determined to be 60 mg/kg. Conclusions: OBI-992 exhibits remarkable antitumor efficacy and a favorable safety profile, supporting further clinical development of OBI-992 in TROP2 positive cancers. Citation Format: Chi-Sheng Shia, Shih-Ni Wen, Ren-Yu Hsu, Jyy-Shiuan Tu, Hui-Wen Chang, Wan-Fen Li, Ming-Tain Lai. OBI-992, a novel TROP2 targeting antibody drug conjugate demonstrates superior in vivo PK/PD properties and a favorable safety profile [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7179.

Abstract 1905: The ROR1 antibody-drug conjugate, MK-2140, enhances the efficacy of established drugs in preclinical models of pediatric acute lymphoblastic leukemia

Abstract Introduction: Children diagnosed with acute lymphoblastic leukemia (ALL) experience ~90% likelihood of cure. However, the outcome for high-risk ALL and children who relapse remains poor. Receptor tyrosine kinase like orphan 1 receptor (ROR1) is a cell surface antigen primarily expressed in embryonic tissue, but also overexpressed in hematological malignancies. UC961 is a humanized IgG monoclonal antibody with high affinity for ROR1. MK-2140 (Zilovertamab vedotin/VLS-101) and VLS-211 are antibody-drug conjugates (ADCs) of UC961 with monomethyl auristatin-E or PNU payloads, respectively. This study evaluated the in vivo efficacy of MK-2140 and VLS211 against pediatric ALL patient derived xenografts (PDXs). Methods: PDXs were selected based on ROR1 mRNA (RNA-seq) and cell surface (flow cytometry) expression and grown as orthotopic disease in immune-deficient NSG mice. Engraftment and drug responses were assessed by flow cytometric enumeration of the proportion of human versus mouse CD45+ cells in peripheral blood (%huCD45+). Events were defined a priori as the %huCD45+ exceeding 25% or leukemia-related morbidity. MK-2140 (2.5 and 5.0 mg/kg) and VLS-211 (0.25 and 0.5 mg/kg) were administered intravenously, weekly x 3 weeks. Vincristine (0.15 mg/kg once weekly), dexamethasone (5 mg/kg daily x 5) and Lasparaginase (1,250 U/kg daily x 5) (VXL) were administered intraperitoneally for 3 weeks, followed by MK-2140 (5 mg/kg weekly x 3 weeks). Drug efficacy was assessed by event-free survival of treated (T) and control (C) groups and by stringent objective response criteria. In receptor occupancy/pharmacokinetic studies, a single dose of MK-2140 was administered and samples collected for analysis at discrete timepoints thereafter. Results: ROR1 mRNA and cell surface expression showed a significant correlation (R=0.83, P=0.021). MK-2140 significantly delayed disease progression in 4/7 PDXs compared to vehicle control (T-C, -2.6 to 20.0 days). At the highest dose, MK-2140 elicited objective responses (remissions) in two PDXs. VLS-211 significantly delayed disease progression in 5/7 PDXs (TC, -1.8 to 70.5 days), including 3 objective responses. Prior treatment with VXL followed by MK-2140 significantly delayed disease progression compared to VXL alone (T-C, 56.8 versus 35.2 days). MK-2140 bound to ROR1+ cells with near 100% occupancy within two hours of treatment, which was sustained for up to 96 h. Consistent with the receptor occupancy data, plasma levels of MK-2140 were maintained at >100 nM for at least 96 h after a single dose (5 mg/kg). Conclusions: MK-2140 and VLS-211 exerted significant single-agent in vivo activity against a panel of pediatric ALL PDXs. MK-2140 significantly enhanced the efficacy of an induction-type regimen and should be considered for further evaluation in a minimal residual disease setting. Citation Format: Richard B. Lock, Kathryn Evans, Ben Watts, Edward P. Bowman, Steven Neuhauser, Timothy Stearns, Jeffrey H. Chuang, Vivek M. Phillip, Katti A. Jessen, Emily L. Jocoy, Carol J. Bult, Beverly A. Teicher, Malcolm A. Smith. The ROR1 antibody-drug conjugate, MK-2140, enhances the efficacy of established drugs in preclinical models of pediatric acute lymphoblastic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1905.

Abstract 3627: Volrustomig a novel PD-1/CTLA-4 bispecific antibody leads to robust increase in peripheral and intra-tumoral pharmacodynamic biomarkers in solid tumors from FTiH study

Abstract Background: Volrustomig (MEDI5752) is designed to fully inhibit PD-1 while preferentially inhibiting CTLA-4 on activated PD-1+ T cells. In a FTiH trial, volrustomig demonstrated meaningful clinical activity in patients with solid tumors (including 1L RCC and NSCLC), acceptable safety profile, sustained PD-1 receptor occupancy, and T cell proliferation at levels greater than seen with clinically tolerable doses of CTLA-4 inhibitors with co-administration of anti-PD(L)-1. We sought to further characterize volrustomig pharmacodynamic effect in the periphery and tumor to demonstrate its biological activity and inform dose optimization. Methods: Pre- and on-treatment blood samples from 86 patients enrolled in dose exploration were collected. Peripheral T cell profiling was assayed by flow cytometry, RNAseq, TCRSeq and serum proteomics. Paired tumor biopsies (N=17), pre- and at week 6 on-treatment, were analyzed for T cell infiltration and function using RNAseq and computational image analysis of immune cell marker density detected by histochemistry and multiplex immune fluorescence assays. Results: Volrustomig achieved dose-dependent peripheral pharmacodynamic changes of biomarkers specific to CTLA-4 blockade at ≥ 225mg. At C1D8 with doses ≥ 500mg, increases in CD4 T cell proliferation (ki67), activation (ICOS), and memory T cells (1516%, 321% and 88%, respectively) were seen, each greater than observed with historical controls of patients treated with tremelimumab 3mg/kg (T3) in combination with durvalumab. Similarly, CD8 proliferation and activation were also higher than T3 at C1D8 with 300% and 161% increase respectively. Additional CD4 and CD8 T cell proliferation and activation was observed at C2D8 supporting the benefit of repeat dosing. Higher peripheral T cell clonal expansion at doses ≥ 500mg was seen and associated with PFS and OS benefit. In patients with paired biopsies, volrustomig achieved robust T cell mediated anti-tumor activity including increases in T cell infiltration (CD8+, 2.3 fold, p=0.04), proliferation (CD8+ Ki67+, 2.1 fold, p=0.04) and, T cell cytotoxicity and activation (GrB+, 2.2 fold, p=0.01; T cell effector and IFNg gene signatures, > 2-fold, p< 0.01). Additionally, volrustomig increased CD8 proliferation in tumor compared to historical control durvalumab alone (>2-fold increase in 70% vs 50% patients). Conclusion: Voltrustomig demonstrated robust peripheral and intra-tumoral T cell activation and proliferation, broadening the pool of antigen experienced T cells, at levels greater than seen with dual checkpoint blockade currently used in the clinic. Citation Format: Ikbel Achour, Michael Kuziora, Florian Song, Steven Eck, Lina Meinecke, Jorge Blando, Jennifer Pearson, Megha Saraiya, Christian Eisen, Felix Segerer, Markus Schick, Nicolas Triltsch, Michael Surace, Gisele Silva Boos, Harald Hessel, Mai Bui, Katrin Pratsch, Alma Andoni, Shelby Denise Gainer, Dan Freeman, Deepa Subramaniam, Ben Tran. Volrustomig a novel PD-1/CTLA-4 bispecific antibody leads to robust increase in peripheral and intra-tumoral pharmacodynamic biomarkers in solid tumors from FTiH study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3627.

Abstract 4071: The first-in-class PD1-IL18 conjugate BPT567 induces potent anti-tumor immunity by preferentially activating PD1+IL18R+ intratumoral effector T cells in cis

Abstract Antibody-cytokine conjugates leverage orthogonal mechanisms of action (MoA) in one molecule to induce potent antitumor immune responses. PD-1-targeting conjugates are of particular interest since they preferentially target antigen-experienced PD-1+ CD8+ T cells enriched in the tumor microenvironment (TME) while simultaneously blocking the PD-(L)1 pathway and inducing potent cytokine receptor stimulation in the same CD8+ T cell in cis (cis-signaling). Interleukin 18 (IL-18) is a proinflammatory cytokine able to integrate both innate and adaptive immunity resulting in profound anti-tumor immune responses mediated by T effector and NK cells. BPT567 has been generated via chemical conjugation of the anti-PD-1 Ab LipustobartTM to an enhanced human IL-18 variant of increased potency and reduced sensitivity to IL-18 binding protein (IL-18BP). BPT567 is designed to specifically target and activate a subset of tumor-infiltrating PD-1+ IL18R+ CD8+ T effector cells recently described to exhibit superior cytotoxic and proliferative activity (Codarri Deak et al., Nature 2022). Due to its ability to signal in cis, BPT567 shows enhanced potency as well as increased resistance to IL-18BP when analyzing IFNγ release in vitro in PD-1+ cells. Subsequent PD-1 receptor occupancy analyses showed that it is fully sufficient for BPT567 to engage a low number of PD-1 receptors to induce maximum IFNγ release in NK92 cells expressing human PD-1. Strikingly, despite addressing overlapping epitopes in PD-1, even a 200-fold excess of pembrolizumab has no impact on the in vitro potency of BPT567. In vivo, BPT567 exhibits strong anti-tumor efficacy at significantly lower IL-18 doses compared to the combination of an untargeted antibody-IL-18 conjugate and an anti-PD1 Ab further corroborating the importance of cis-signaling as a unique MoA of this PD1-IL18 conjugate. Detailed analyses of tumor-infiltrating immune leukocytes (TIL) revealed that BPT567 triggers a preferential expansion of CD8+ T effector memory cells within the TME. In line with this finding, activity in the MC38 tumor model is dependent on the presence of CD8+ T cells while depletion of other immune cell subsets (e.g. NK cells, CD4+ T cells, macrophages) had no impact on efficacy. Although not required for anti-tumor efficacy, CD4+ T cells are essential for proficient formation of an immunological memory. In an effort to confirm findings generated in murine models in relevant human ex vivo systems, we analyzed the release of cytokines and chemokines in dissociated cells isolated from primary human tumor explants. Also in this human model, BPT567 is able to induce significantly stronger IFNγ release compared to either single agents or the combination of untargeted IL-18 and an anti-PD1 Ab, thus confirming the unique MoA of the PD1-IL18 conjugate triggering superior TIL activation in cis. Citation Format: Kea Martin, Thuy Luu, Jean-Philippe Carralot, Lilian Gremlich, Petra Herzig, Caoimhe Herr, Roy Meoded, Philipp Moosmann, Arnaud Goepfert, Alfred Zippelius, Vijaya Pattabiraman, Bertolt Kreft. The first-in-class PD1-IL18 conjugate BPT567 induces potent anti-tumor immunity by preferentially activating PD1+IL18R+ intratumoral effector T cells in cis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4071.