Studies In Cynomolgus Monkeys Research Articles

Abstract 5085: Preclinical development of NaPi2b-PL2202, a novel camptothecin-based antibody-drug conjugate targeting solid tumors expressing NaPi2b

Abstract NaPi2b, encoded by the SLC34A2 gene, is a multi-transmembrane, sodium-dependent phosphate transporter expressed at high levels in tumors and low levels in normal tissues. Functionally, it is involved in trans-cellular flux of phosphate in the small intestine and in the synthesis of surfactant in lung alveoli. NaPi2b is reported to be expressed at a high frequency in ovarian carcinoma as well as in NSCLC, bladder, endometrial and papillary thyroid carcinoma1, and its expression is associated with poor prognosis 2, 3. The purpose of this study was to characterize the in vitro and in vivo anti-tumor activity and tolerability of NaPi2b-PL2202, an antibody-drug conjugate (ADC) composed of a humanized, Fc-silenced IgG1 antibody directed against human NaPi2b, to which PL2202, a novel payload containing a valine-alanine cleavable linker and a camptothecin warhead, has been site-specifically conjugated with a drug to antibody ratio of 6. In addition, the level of NaPi2b expression in selected human tumor specimens was evaluated by immunohistochemistry (IHC). In vitro, NaPi2b-PL2202 showed good binding affinity for mouse, rat, cynomolgus monkey and human NaPi2b, and displayed highly potent, targeted cytotoxicity against various NaPi2b-expressing tumor cell lines. NaPi2b-PL2202 also exhibited strong in vitro bystander activity. In vivo, intravenous (IV) administration of a single dose of NaPi2b-PL2202 at 6.6 mg/kg resulted in substantial tumor regression in the OVCAR-3 ovarian carcinoma xenograft model, with 3/10 partial responders (PR) and 7/10 complete responders (CR), and all CRs being tumor-free at the end of the study (Day 44). In the G-402 renal leiomyoblastoma xenograft model, administration of a single IV dose of NaPi2b-PL2202 at 3.3 mg/kg was associated with durable antitumor activity and resulted in 1/10 CR, with this animal remaining tumor-free by the end of the study (Day 42). With respect to toxicity, in single dose studies in male rats, NaPi2b-PL2202 was tolerated up to 300 mg/kg IV. Furthermore, in a dose-range finding study in male cynomolgus monkeys, NaPi2b-PL2202 was well tolerated up to 40 mg/kg IV given on Day 1 and 22. Finally, cell membranous NaPi2b expression was confirmed by IHC in a panel of tissue microarrays including ovarian, lung, bladder and endometrial cancers. In conclusion, NaPi2b-PL2202 demonstrated specific and potent in vitro and in vivo anti-tumor activity, and was tolerated at high doses in toxicity studies in rats and cynomolgus monkeys, indicating a good therapeutic index. Together, these observations support future clinical development of NaPi2b-PL2202 for the treatment of NaPi2b-expressing cancers. 1- Bodyak N. D. et al., 2021 2- Valsenkova R. et al., 2021 3- Hakim S. A. et al., 2021 Citation Format: Elizabeth Horsley, Asma Jabeen, Nicolas Veillard, Karin Havenith, Narinder Janghra, Pedro Alves, Cecile Oblette, Ian Kirby, Paul W. Hogg, Francesca Zammarchi, Lolke de Haan, Patrick van Berkel. Preclinical development of NaPi2b-PL2202, a novel camptothecin-based antibody-drug conjugate targeting solid tumors expressing NaPi2b [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 5085.

Abstract 1892: KK2260: A fully human tetravalent bispecific antibody targeting TfR1 and EGFR for the treatment of EGFR-expressing tumors

Abstract Background: TfR1 is a transmembrane glycoprotein involved in iron uptake and regulation of cell growth. High TfR1 expression has been reported in different types of cancers, therefore recognized as a target molecule for cancer therapy. Despite the promise of potent efficacy of TfR1-targeted agents, there is a risk of side effects (i.e., severe anemia), since TfR1 is also highly expressed in certain normal cells (e.g., reticulocytes). KK2260 is a fully human tetravalent bispecific antibody (bsAb) based on REGULGENTTM technology targeting TfR1 and EGFR. This bsAb was designed for EGFR-expressing cell selective anti-cancer drug which could not be achieved by conventional monospecific Ab. In this study, we evaluated the mechanism of action (MOA), anti-cancer effect, and toxicity of KK2260. Methods: Binding activity of KK2260 to TfR1 and EGFR was evaluated by surface plasmon resonance method. Ligand blocking activity was evaluated by binding competition on esophageal squamous cell carcinoma (ESCC) OE21 cells. Growth inhibitory activity of KK2260 on cancer cells or hematopoietic progenitor cells was evaluated by proliferation inhibition assay. In some studies, excessive iron or anti-EGFR parent Ab was added. Effect on the cell surface target expression levels was evaluated by flow cytometry. The intracellular iron level was evaluated by cell imaging. Effect on EGF induced EGFR phosphorylation was evaluated by Western blotting. The in vivo efficacy of KK2260 was evaluated in cell line-derived and patient-derived xenograft (PDX) models of ESCC selected for high EGFR expression level. The toxicity of KK2260 was evaluated in cynomolgus monkeys. Results: KK2260 bound to TfR1 and EGFR with no ligand binding inhibition. KK2260 inhibited cell growth of moderate to high EGFR-expressing cancer cells, but not against EGFR-negative cancer cells or hematopoietic progenitor cells. KK2260 downregulated TfR1 expression on OE21 cells and the intracellular iron level decreased, but no effect was observed on EGFR phosphorylation. The growth inhibitory activity of KK2260 was abolished by adding excessive amounts of iron or reduced by inhibiting the binding to EGFR. Potent anti-tumor activity was observed in the ESCC PDX models with tumor regression. In the intermittent-dose toxicity study of cynomolgus monkeys, KK2260 was well-tolerated. Conclusions: KK2260 demonstrated potent anti-cancer effect both in vitro and in vivo. Intriguingly, KK2260 did not inhibit EGFR phosphorylation while EGFR-binding dependent TfR1 downregulation resulted in intracellular iron deficiency, which was considered as the MOA of KK2260. KK2260 was well tolerated in non-human primates. These preclinical data suggest the unique property of KK2260 is expected to provide significant benefit to patients with advanced ESCC and other EGFR-expressing tumors and Phase 1 study is currently on going in Japan (jRCT2031230372). Citation Format: Keisuke Mitamura, Hironori Otsuki, Keiko Nakahashi, Ayaka Kitagawa, Masayo Kamigaki, Yohei Kurio, Miho Inoue, Yasunori Uemura. KK2260: A fully human tetravalent bispecific antibody targeting TfR1 and EGFR for the treatment of EGFR-expressing tumors [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 1892.

Hepatitis A Virus Infection in Cynomolgus Monkeys Confounds the Safety Evaluation of a Drug Candidate.

In a 3-month toxicity study in cynomolgus monkeys at a European contract laboratory, animals were infected with HAV, initially resulting in hepatic injury being incorrectly attributed to the test compound. Elevated serum ALT/AST/GLDH (5- to 10-fold) were noted in individual animals from all groups including controls, with no apparent dose, exposure, or time-related relationship. Liver histopathology revealed minimal to slight inflammatory cell accumulation in periportal zones of most animals, and minimal to slight hepatocyte degeneration/necrosis in 10/42 animals from all groups. As these findings were more pronounced in 6 drug-treated animals, including 2/6 in the low dose group, the draft report concluded: "treatment-related hepatotoxicity at all dose levels precluded determination of a NOAEL." However, the unusual pattern of hepatotoxicity suggested a factor other than drug exposure might have caused the hepatic effects. Therefore, snap-frozen liver samples were tested for hepatitis viruses using a PCR method. Tests for hepatitis B, C, and E virus were negative; however, 20/42 samples were positive for hepatitis A virus (HAV). Infection was strongly associated with increased serum ALT/GLDH, and/or hepatocyte degeneration/necrosis. Re-evaluation of the study in light of these data concluded that the hepatic injury was not drug-related. A subsequent 6-month toxicology study in HAV-vaccinated cynomolgus monkeys confirmed the absence of hepatotoxicity. Identification of HAV infection supported progression of the drug candidate into later clinical trials. Although rarely investigated, subclinical HAV infection has occasionally been reported in laboratory primates, including those used for toxicology studies and it may be more prevalent than the literature indicates.

Development and Validation of an ADA-Tolerant Assay for Quantification of an Exatecan-Based ADC in Monkey Plasma.

The development of an anti-drug antibody (ADA)-tolerant pharmacokinetic (PK) assay is important when the drug exposure is irrelevant to toxicity in the presence of ADA. We aimed to develop and validate an ADA-tolerant assay for an exatecan-based antibody-drug conjugate (ADC) in monkey plasma. The assay tolerated 5.00 µg/mL of ADA at 12 µg/mL of ADC. Its accuracy and precision results satisfied the acceptance criteria. Furthermore, the assay was free from hook and matrix effects and exhibited good dilutional linearity. Additionally, the ADC in plasma samples was stable under different storage conditions. An ADA-tolerant ADC assay was configured with an anti-payload antibody for capture, and a drug-target protein combined with a horseradish peroxidase (HRP)-labeled antibody against a drug-target-protein tag for detection. Samples were firstly acidified to dissociate drug and ADA complexes, and to convert the carboxylate form to the lactone form of exatecan molecules; then, the ADAs in the samples were removed with a naked antibody-coated microplate. The treated samples were further incubated with coated anti-payload antibody and captured ADC molecules were quantified by the detection reagent. The developed assay was optimized and validated against regulatory guidelines. The assay met both methodological and sample-related ADA tolerance requirements, and was applicable to a nonclinical study in cynomolgus monkeys.

Repeat-Dose and Embryo-Fetal Developmental Toxicity of Zinpentraxin Alfa

Zinpentraxin alfa is a recombinant human pentraxin-2 (PTX-2) developed for the treatment of various fibrotic diseases with the hypothesis that supplementing endogenous PTX-2 levels through intravenous administration should increase its regulatory capacity in circulation and at the site of disease, thereby promoting healing and reducing fibrosis. Zinpentraxin alfa has been studied in various clinical trials, particularly in patients with idiopathic pulmonary fibrosis, where it has demonstrated efficacy in slowing decline in lung function in a phase 2 study. In the present investigation, we summarize findings from 14-day repeat-dose toxicity studies in rats and cynomolgus monkeys supporting early clinical development of zinpentraxin alfa. In addition, we also describe the findings from the embryo-fetal developmental (EFD) studies conducted in rats and rabbits, since the intended fibrosis patient population may include patients of childbearing potential. Zinpentraxin alfa was well tolerated by rats and monkeys in general toxicity studies with no treatment-related adverse effects, as well as by pregnant rats over the same dose range in a definitive EFD study. In contrast, substantial toxicity was observed in a rabbit dose-range-finder EFD study. Zinpentraxin alfa was poorly tolerated by pregnant rabbits and effects on the dams correlated with post-implantation fetal losses. The disparate effects of zinpentraxin alfa on embryo-fetal development between the two species suggests a potential unknown biological function of PTX-2 in pregnancy in the rabbit, which may be relevant to humans. Our findings warrant the consideration for highly effective contraceptive measures to avoid pregnancy in patients enrolled in clinical studies with zinpentraxin alfa.

A highly potent anti-VISTA antibody KVA12123 -a new immune checkpoint inhibitor and a promising therapy against poorly immunogenic tumors.

Immune checkpoint therapies have led to significant breakthroughs in cancer patient treatment in recent years. However, their efficiency is variable, and resistance to immunotherapies is common. VISTA is an immune-suppressive checkpoint inhibitor of T cell response belonging to the B7 family and a promising novel therapeutic target. VISTA is expressed in the immuno-suppressive tumor microenvironment, primarily by myeloid lineage cells, and its genetic knockout or antibody blockade restores an efficient antitumor immune response. Fully human monoclonal antibodies directed against VISTA were produced after immunizing humanized Trianni mice and single B cell sequencing. Anti-VISTA antibodies were evaluated for specificity, cross-reactivity, monocyte and T cell activation, Fc-effector functions, and antitumor efficacy using in vitro and in vivo models to select the KVA12123 antibody lead candidate. The pharmacokinetics and safety profiles of KVA12123 were evaluated in cynomolgus monkeys. Here, we report the development of a clinical candidate anti-VISTA monoclonal antibody, KVA12123. KVA12123 showed high affinity binding to VISTA through a unique epitope distinct from other clinical-stage anti-VISTA monoclonal antibodies. This clinical candidate demonstrated high specificity against VISTA with no cross-reactivity detected against other members of the B7 family. KVA12123 blocked VISTA binding to its binding partners. KVA12123 induced T cell activation and demonstrated NK-mediated monocyte activation. KVA12123 treatment mediated strong single-agent antitumor activity in several syngeneic tumor models and showed enhanced efficacy in combination with anti-PD-1 treatment. This clinical candidate was engineered to improve its pharmacokinetic characteristics and reduce Fc-effector functions. It was well-tolerated in preclinical toxicology studies in cynomolgus monkeys, where hematology, clinical chemistry evaluations, and clinical observations revealed no indicators of toxicity. No cytokines associated with cytokine release syndrome were elevated. These results establish that KVA12123 is a promising drug candidate with a distinct but complementary mechanism of action of the first generation of immune checkpoint inhibitors. This antibody is currently evaluated alone and in combination with pembrolizumab in a Phase 1/2 open-label clinical trial in patients with advanced solid tumors.

SGN-B6A: A New Vedotin Antibody-Drug Conjugate Directed to Integrin Beta-6 for Multiple Carcinoma Indications.

Integrin beta-6, a component of the heterodimeric adhesion receptor alpha-v/beta-6, is overexpressed in numerous solid tumors. Its expression has been shown by multiple investigators to be a negative prognostic indicator in diverse cancers including colorectal, non-small cell lung, gastric, and cervical. We developed SGN-B6A as an antibody-drug conjugate (ADC) directed to integrin beta-6 to deliver the clinically validated payload monomethyl auristatin E (MMAE) to cancer cells. The antibody component of SGN-B6A is specific for integrin beta-6 and does not bind other alpha-v family members. In preclinical studies, this ADC has demonstrated activity in vivo in models derived from non-small cell lung, pancreatic, pharyngeal, and bladder carcinomas spanning a range of antigen expression levels. In nonclinical toxicology studies in cynomolgus monkeys, doses of up to 5 mg/kg weekly for four doses or 6 mg/kg every 3 weeks for two doses were tolerated. Hematologic toxicities typical of MMAE ADCs were dose limiting, and no significant target-mediated toxicity was observed. A phase I first-in-human study is in progress to evaluate the safety and antitumor activity of SGN-B6A in a variety of solid tumors known to express integrin beta-6 (NCT04389632).

Phase 1/2 study of PRO1160, a CD70-directed antibody-drug conjugate, in patients with advanced solid tumors and hematologic malignancies

Abstract Background: PRO1160 is a novel antibody-drug conjugate (ADC) directed to CD70, an antigen mediating immuno-suppression that is overexpressed in multiple solid tumors and hematologic malignancies, with limited distribution in normal tissues. PRO1160 comprises (1) a human monoclonal antibody specific for CD70, (2) a protease-cleavable proprietary hydrophilic linker, and (3) exatecan, a topoisomerase 1 inhibitor. Comprehensive prior work demonstrated that the hydrophilic linker confers excellent physicochemical properties and pharmacokinetics (PK) across a range of payload mechanisms and is superior to conventional linkers on these critical parameters for ADCs. In addition, exatecan is broadly active in many tumor types, is membrane permeable, and is not a substrate of multidrug resistance pumps, thus likely lending strong bystander effects and durable treatment responses. PRO1160 is highly potent in cell-derived xenograft models of renal cell carcinoma (RCC), non-Hodgkin lymphoma (NHL), and nasopharyngeal carcinoma (NPC). PRO1160 also demonstrates marked antitumor activity in patient-derived xenograft models of diverse tumor sites, histologies, molecular subtypes, target expression levels, and Epstein Barr Virus status. PRO1160 is stable in circulation and displays PK characteristics indistinguishable from the parent antibody in rats. In a GLP toxicity study in cynomolgus monkeys, the primary PRO1160-related toxicity resided in the thymus and bone marrow, was consistent with exatecan toxicities, and was reversible. PRO1160-001 is an ongoing, open-label Phase 1/2 study to evaluate the safety, tolerability, PK, and antitumor activity of PRO1160 in patients with metastatic RCC, metastatic or relapsed NPC, or advanced relapsed/refractory NHL. Patients must have measurable disease per the Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 or the Lugano Classification for NHL. Patients must also have previously received therapies known to confer clinical benefit unless considered ineligible, refused by the patient, or not available in the region. PRO1160 is given by intravenous infusion on Day 1 of a 21-day cycle and treatment may continue until disease progression, unacceptable toxicity, or other reason for discontinuation. The primary objectives are to evaluate the safety and tolerability of PRO1160 and to identify the maximum tolerated dose, if reached, and recommended phase 2 dose (RP2D). This study consists of 2 parts, Part A: dose-escalation and dose-level expansion, and Part B: 3 tumor-specific expansion cohorts (metastatic RCC, metastatic or relapsed NPC, or advanced relapsed/refractory NHL) treated at the RP2D. PK, immunogenicity, and antitumor activity will also be evaluated. The study is currently enrolling at sites in the US, with future enrollment in China planned (Clinicaltrials.gov: NCT05721222).

JSKN003, A NOVEL BIPARATOPIC ANTI-HER2 ANTIBODY-DRUG CONJUGATE, EXHIBITS POTENT ANTITUMOR EFFICACY

Abstract In human advanced solid tumors, expression of HER2 protein has been reported in various tumor tissues and a variety of cultured tumor cell lines including breast cancer, gastric cancer, pancreatic cancer, lung cancer, colorectal cancer, and ovarian cancer. Due to the critical roles of HER2 in carcinogenesis, two main targeted therapies have been developed in the past two decades to block the HER2-driven pathways, which include small molecule compounds that inhibit the tyrosine kinase activity of the intracellular domain, and mono-antibodies (mAbs) that target the extracellular domain (ECD) of the receptors. JSKN003 is an antibody-drug conjugate (ADC) comprised of a recombinant, humanized anti-human epidermal growth factor receptor 2 (HER2) bispecific antibody conjugated to a topoisomerase I inhibitor via a dibenzocyclooctyne tetrapeptide linker. The anti-HER2 component, KN026, is a recombinant, humanized bispecific antibody that targets both extra-cellular domains II (pertuzumab binding site) and IV (trastuzumab binding site) of HER2. JSKN003 showed high affinity binding to human HER2 with KDs of 2.209 E-10M, which is comparable to its parental antibody KN026 and bound to NCI-N87 and BxPC-3 cells in a concentration-dependent manner. At the same time JSKN003 showed more extensive and faster internalization than DS8201 on NCI-N87 cells. As expected, JSKN003 showed directly inhibits growth by targeting HER2 positive tumor model (NCI-N87 and BT474 cell models). The single dose and multiple dose pharmacokinetics study in cynomolgus monkey indicated that JSKN003, total antibody and DXd had general linear dynamic characteristics, and pharmacokinetics parameters showed no significant differences between males and females in the range 0.3-30 mg/kg. The HNSTD (highest non-severely toxic dose) of JSKN003 was determined as 30mg/kg in cynomolgus monkeys. These preclinical data suggest that JSKN003 could potentially benefit patients with tumors co-expressing HER2 through improved drug selectivity and efficacy. JSKN003’s safety, tolerability and preliminary anti-tumor activity are currently being evaluated in a first-in-human phase I study in advanced stage solid tumors in Australia (NCT05494918) using a BOIN design. This ADC is targeted on the subjects who has HER2 expression and/or HER2-gene mutation and may address an unmet medical need for these patients.

Abstract ND06: AMG 305, a dual targeting BiTE®molecule with selective activity for solid tumors that co-express CDH3 and MSLN

Abstract T cell engager (TCE) molecules are a targeted immune therapy that redirect a patient’s T cells to kill tumor cells. While several TCE molecules have now advanced to approval, clinical development has been challenging, especially in the solid tumor setting. There are few solid tumor surface antigens that are tumor-specific, and antigens with even low levels of expression in normal tissue can be recognized by a TCE and result in on-target off-tumor toxicity. To overcome this challenge, we have developed AMG 305, a first-in-class, dual targeting BiTE® (bispecific T cell engager) molecule that requires binding to both P-cadherin (CDH3) and mesothelin (MSLN) for potent cytotoxic activity. Immunohistochemistry analysis shows that CDH3 and MSLN are co-expressed in multiple solid tumor types. In normal tissues, immunostaining shows fewer tissues have overlapping co-expression than expression of just one or the other target. AMG 305 relies on an avidity-based approach to engage T cells to preferentially kill CDH3+MSLN+ tumor cells, with limited activity against normal cells that express only one of the target antigens. In vitro, AMG 305 induces potent cytotoxicity against tumor cells co-expressing CDH3 and MSLN, with greatly attenuated activity against cells expressing only CDH3 or MSLN. In vivo, AMG 305 demonstrates dose-dependent antitumor activity in a CDH3+MSLN+ xenograft tumor model. AMG 305 was clinically well-tolerated in a nonclinical safety study in cynomolgus monkey. Data from IND-enabling preclinical studies support initiation of the first-in-human study of AMG 305 in CDH3+MSLN+ solid tumors in 2023. Citation Format: Elizabeth Pham, Petra Lutterbuese, Petra Deegen, Natalie Mariano, Katja Matthes, Joachim Wahl, Pamela Bogner, Joan Lane, Kristin Lewis Wilson, Rodolfo Yabut, Virginie Naegele, Ines Ullrich, Stephanie Everts, Markus Muenz, Thomas Boehm, Sabine Stienen, Angela Coxon, Peter Kufer, Tobias Raum, Julie M. Bailis. AMG 305, a dual targeting BiTE®molecule with selective activity for solid tumors that co-express CDH3 and MSLN [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr ND06.

Abstract ND01: ABBV-319: A first-in-class Glucocorticoid Receptor Modulator (GRM) agonist ADC for the treatment of B-cell malignancies

Abstract ABBV-319 is a novel CD19-targeting multi-modal antibody drug conjugate (ADC) for the treatment of B-cell malignancies. The ADC is engineered to have 3 distinct mechanisms of action to maximize anti-cancer activity while reducing systemic toxicities: (1) targeted GRM payload delivery, (2) signaling inhibition of CD19/BCR and (3) enhanced ADCC via afucosylation. Unlike traditional cytotoxic ADCs, the GRM payload is a high potency agonist (sub nM EC50) of the intracellular glucocorticoid receptor (GR) which then traffics to the nucleus resulting in sustained GR-driven transcriptional events leading to cancer cell death. CD19 is a clinically validated B-cell target (approved antibodies, ADCs, CARTs) known to be highly expressed even following multiple lines of therapy, making it an appropriate target for this novel approach. The CD19 antibody in ABBV-319 is an optimized high affinity IgG1 that can inhibit CD19/BCR downstream signaling events including AKT, leading to inhibition of growth in certain B-cell lines. Given ADCC/ADCP is a highly effective mechanism in B-cell malignancies (e.g., rituximab, tafasitamab) the CD19 antibody was engineered to have increased FcγR binding via afucosylation, that retains its enhanced ADCC activity as a GRM drug conjugate. By engineering the molecule in this way, the multi-modal ADC is not solely reliant on one mechanism of action for activity and therefore has the potential for broader activity. Sustained regressions/cures have been observed in multiple B-cell malignancy xenograft model systems (cell-line, PDX, humanized) after a single ADC dose that compares favorably against approved benchmark antibodies, systemic steroids and ADCs. ABBV-319 targets clinically validated mechanisms of action that are known to combine well with multiple standard-of-care agents. This combination potential together with its favorable safety profile, suggests ABBV-319 will be a highly effective combination treatment for B-cell malignancies. ABBV-319 was well tolerated in cynomolgus monkey studies with favorable drug-like properties and antibody-like pharmacokinetics, enabling a high mg/kg clinical starting dose. A first in-human Phase 1 clinical trial evaluating ABBV-319 in B-cell malignancies (DLBCL, FL, CLL) was recently initiated in late 2022 (clinicaltrials.gov, NCT05512390). Citation Format: James W. Purcell. ABBV-319: A first-in-class Glucocorticoid Receptor Modulator (GRM) agonist ADC for the treatment of B-cell malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr ND01.

A fully human neutralizing monoclonal antibody targeting a highly conserved epitope of the human cytomegalovirus glycoprotein B.

Human cytomegalovirus causes severe diseases in children (by congenital infection) and immunocompromised patients. Treatment with antiviral agents, such as ganciclovir, is limited by their toxicity. In this study, we investigated the effectiveness of a fully human neutralizing monoclonal antibody to inhibit human cytomegalovirus infection and viral cell-to-cell spread. We isolated a potent neutralizing antibody, EV2038 (IgG1 lambda), targeting human cytomegalovirus glycoprotein B using Epstein-Barr virus transformation. This antibody inhibited human cytomegalovirus infection by all four laboratory strains and 42 Japanese clinical isolates, including ganciclovir-resistant isolates, with a 50% inhibitory concentration (IC50) ranging from 0.013 to 0.105 μg/mL, and 90% inhibitory concentration (IC90) ranging from 0.208 to 1.026 μg/mL, in both human embryonic lung fibroblasts (MRC-5) and human retinal pigment epithelial (ARPE-19) cells. Additionally, EV2038 prevented cell-to-cell spread of eight clinical viral isolates, with IC50 values ranging from 1.0 to 3.1 μg/mL, and IC90 values ranging from 13 to 19 μg/mL, in ARPE-19 cells. EV2038 recognized three discontinuous sequences on antigenic domain 1 of glycoprotein B (amino acids 549-560, 569-576, and 625-632), which were highly conserved among 71 clinical isolates from Japan and the United States. Pharmacokinetics study in cynomolgus monkeys suggested the potential efficacy of EV2038 in vivo, the concentration of which in serum remained higher than the IC90 values of cell-to-cell spread until 28 days after intravenous injection of 10 mg/kg EV2038. Our data strongly support EV2038 as a promising candidate and novel alternative for the treatment of human cytomegalovirus infection.

Complex PK-PD of an engineered IL-15/IL-15Rα–Fc fusion protein in cynomolgus monkeys: QSP modeling of lymphocyte dynamics

XmAb24306 is a lymphoproliferative interleukin (IL)-15/IL-15 receptor α (IL-15Rα) Fc-fusion protein currently under clinical investigation as an immunotherapeutic agent for cancer treatment. XmAb24306 contains mutations in IL-15 that attenuate its affinity to the heterodimeric IL-15 receptor βγ (IL-15R). We observe substantially prolonged pharmacokinetics (PK) (half-life ∼ 2.5 to 4.5 days) in single- and repeat-dose cynomolgus monkey (cyno) studies compared to wild-type IL-15 (half-life ∼ 1 hour), leading to increased exposure and enhanced and durable expansion of NK cells, CD8+ T cells and CD4–CD8– (double negative [DN]) T cells. Drug clearance varied with dose level and time post-dose, and PK exposure decreased upon repeated dosing, which we attribute to increased target-mediated drug disposition (TMDD) resulting from drug-induced lymphocyte expansion (i.e., pharmacodynamic (PD)-enhanced TMDD). We developed a quantitative systems pharmacology (QSP) model to quantify the complex PKPD behaviors due to the interactions of XmAb24306 with multiple cell types (CD8+, CD4+, DN T cells, and NK cells) in the peripheral blood (PB) and lymphoid tissues. The model, which includes nonspecific drug clearance, binding to and TMDD by IL15R differentially expressed on lymphocyte subsets, and resultant lymphocyte margination/migration out of PB, expansion in lymphoid tissues, and redistribution to the blood, successfully describes the systemic PK and lymphocyte kinetics observed in the cyno studies. Results suggest that after 3 doses of every-two-week (Q2W) doses up to 70 days, the relative contributions of each elimination pathway to XmAb24306 clearance are: DN T cells > NK cells > CD8+ T cells > nonspecific clearance > CD4+ T cells. Modeling suggests that observed cellular expansion in blood results from the influx of cells expanded by the drug in lymphoid tissues. The model is used to predict lymphoid tissue expansion and to simulate PK-PD for different dose regimens. Thus, the model provides insight into the mechanisms underlying the observed PK-PD behavior of an engineered cytokine and can serve as a framework for the rapid integration and analysis of data that emerges from ongoing clinical studies in cancer patients as single-agent or given in combination.

Abstract 5667: CYT-303 FLEX-NKTM engager dose response efficacy mechanisms in HCC tumor model and safety in cynomolgus monkey toxicology studies support clinical evaluation in hepato-cellular carcinoma

Abstract BACKGROUND: CYT-303 is a multifunctional bispecific NK engager (NKE) targeting NK cell activating receptor NKp46 and tumor antigen Glypican-3 (GPC3) expressed in HCC (hepatocellular carcinoma). Cytovia’s proprietary FLEX-NKTM platform utilizes a novel FLEX-linker and human IgG1 back bone to allow for simultaneous binding to targeted cancer cells and NK cells. We evaluated CYT-303 dose response pharmacology efficacy mechanisms in HCC tumor models and conducted safety assessment studies in cynomolgus monkeys to support first in human clinical studies in HCC patients. METHODS: CYT-303 dose response pharmacology mechanistic studies were conducted in NSG-hIL-15 mice bearing Hep3B tumors and flow cytometry was used to assess bold and tumor NK cells. A 4-week CYT-303 repeat dose GLP toxicology study in cynomolgus monkeys at 6, 20 and 60 mg/kg dose was conducted following weekly intravenous infusions followed by a 6-week recovery period. CYT-303 toxicokinetic and anti-drug antibody (ADA) assessments were conducted using validated immunoassays. RESULTS: CYT-303 dose response in HCC tumor models showed increased tumor growth inhibition at the lower 2-3 mg/kg doses compared to higher 5-10 mg/kg doses consistent with the dose response previously reported in NK cell redirected cytotoxicity assays against HCC tumors. The increased anti- tumor efficacy observed at the lower doses were associated increased infiltration of PBNK’s to the tumor and corresponding reductions in PBNK’s in blood suggesting CYT-303 facilitates PBNK entry and retention in HCC tumors expressing GPC3 tumor antigen. CYT-303 safety assessment in the 4-week toxicology study in cynomolgous monkeys showed no treatment related toxicities or cytokine release and the NOAEL was determined to 60 mg/kg/week the highest dose administered in the study. No treatment related clinical signs, clinical pathology (hematology and clinical chemistry) and anatomic pathology (macroscopic, microscopic and organ weights) changes were observed. CYT-303 toxicokinetic analysis showed dose dependent increases in Cmax and AUC’s and no evidence for CYT-303 accumulation. CYT-303 anti-drug antibodies in monkeys were minimal and only observed in one low dose animal (1 out of 22) which also showed reduced CYT-303 exposures. Based on these pharmacology and toxicology results a pharmacologically active dose (PAD) based approach together with pharmacokinetic modeling would be utilized to estimate first in human dosing in HCC patients. CONCLUSIONS: CYT-303 efficacious doses identified in the HCC model together with safety in cynomolgus monkeys and planned human pharmacokinetic modeling studies support clinical evaluation of CYT-303 in first in human HCC clinical trials. Citation Format: Vishal Khairnar, Christine Waters, Solgalim Diaz, David De Franco, Jean Kadouche, Daniel Teper, Wei Li, Antonio Arulanandam. CYT-303 FLEX-NKTM engager dose response efficacy mechanisms in HCC tumor model and safety in cynomolgus monkey toxicology studies support clinical evaluation in hepato-cellular carcinoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5667.

Abstract 710: Preclinical development of ALD2510, a Next-Gen Fc-enhanced, TREG-selective and IL-2-sparing anti-CD25 antibody for the treatment of solid tumors

Abstract Within the tumor microenvironment (TME), TREGS have been associated with worse prognosis and/or resistance to checkpoint inhibitor (CPI) therapy in various cancer diseases, making these cells a promising target for the development of new immunotherapies. Here, we present recent preclinical development data about ALD2510, a next-gen low-fucose IL-2/TCONV-sparing anti-CD25 antibody designed for the selective depletion of CD25high TREGS and the boost of host anti-tumor immunity. Ultra-humanization of parental anti-CD25 antibody was achieved through phage display and, in parallel, all putative liability sequences were replaced for maximizing developability while minimizing off-target and immunogenicity risks. ALD2510 sequences were re-formatted and used for further CHO cell line development, using the GlymaxX™ technology which boosts Fc effector functions. Early tox ALD2510 material was produced following 10L fed-batch USP/DSP and analytical characterization, including a 6-month early stability study. Preliminary safety and pharmacokinetic/pharmacodynamic (PKPD) profile of ALD2510 were then determined through a non-GLP MTD/DRF study in cynomolgus monkey. ALD2510 demonstrated excellent potency (TREG depletion, ADCC, ADCP), manufacturability and stability together with very low immunogenicity potential. CHO productivity reached ~4g/L in 10L fed-batch bioreactor and characterization revealed excellent purity and activity in line with its low fucose content, together with very low levels of process- or cell-related impurities. This material showed a good behavior during the 6-month stability study and was therefore administered in cynomolgus monkeys during a non-GLP exploratory MTD/DRF study. Increasing doses of ALD2510 (from 0.3 to 100mg/kg) were given to four animals during MTD and same animals received three additional doses at 100mg/kg during DRF. Very good tolerability and safety were reported in animals. ALD2510 half-life and exposure were found consistent with that of humanized IgG1 in cynomolgus. Strong TREG depletion was monitored in the blood in all animals with, importantly, no drop was observed in CD4+ or CD8+ T-cells, confirming ALD2510 capacity to selectively target TREGS while sparing TCONV. Overall, ALD2510 demonstrated excellent potency, manufacturability and stability during the 1st phase of preclinical development. Very good tolerability and safety profile together with satisfying PKPD data were reported during exploratory MTD/DRF study in cynomolgus monkeys. Noteworthy, strong TREG depletion was confirmed while CD4+ or CD8+ T-cells were not impacted, confirming ALD2510 selectivity for TREGS while sparing TCONV. This makes ALD2510 a promising candidate for the treatment of solid tumors, in particular those where the presence of TREGS in the TME is associated with worse prognosis and/or resistance to CPI. Citation Format: Jemila Houacine, Riad Abes, Anne Marie-Cardine, Aude Le Roy, Bettina Serbin, Lucie Robert, Jérôme Giustiniani, Anne-Sophie Chrétien, Stéphane Fattori, Laurent Gorvel, Armand Bensussan, Daniel Olive, Arnaud Foussat. Preclinical development of ALD2510, a Next-Gen Fc-enhanced, TREG-selective and IL-2-sparing anti-CD25 antibody for the treatment of solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 710.

Abstract 1881: Pre-clinical evaluation of a novel antibody drug conjugate (ADC) LM-306 targeting IL-13Rα2 in immuno-oncology

Abstract Interleukin-13 receptor alpha 2 (IL-13Rα2) is overexpressed in various types of cancers including glioma and melanoma and is known to be associated with increased tumor invasiveness and metastases. Here, we present the preclinical efficacy and toxicity results for a novel, anti-IL-13Rα2 ADC-LM-306. In vitro binding activity and internalization of LM-306 and LM-106 (unconjugated antibody of LM-306) were assessed in human IL-13Rα2 overexpressing and endogenous cell lines using flow cytometry. The antibody-dependent cell-mediated cytotoxicity (ADCC) and direct cytotoxicity were assessed using viability assays. Cross-species reactivity of drug was assessed in cells expressing cynomolgus, rat and mouse IL-13Rα2. In vivo A375 CDX model was used to assess the effect of LM-306 anti-tumor activity. The toxicity of LM-306 was evaluated in repeated-dose intravenous dose range-finding (DRF) toxicity and single intravenous maximum tolerated dose (MTD) study in cynomolgus monkeys. Both LM-106 and LM-306 showed concentration dependent binding affinity to IL-13Rα2 in various cell lines (Table 1). In addition, LM-106 also showed a dose dependent internalization and ADCC and LM-306 showed significant cytotoxicity in all cell lines (Table 1). Furthermore, LM-306 showed comparable binding affinity to human IL-13Rα2 to its unconjugated counterpart LM-106 (KD:7.43E-10 vs 1.77E-9). LM-306 was also found to be cross-reactive toward cynomolgus IL-13Rα2. In vivo, LM-306 showed tumor growth inhibition at a dose of 1, 3, 10 mg/kg given intravenously once weekly, indicating its strong anti-tumor activity. The highest non-severely toxic dose of LM-306 was determined to be 9 mg/kg in the DRF study and MTD was determined to be 18mg/kg in MTD study for male monkey. In summary, LM-306 showed high binding affinity to human IL13Rα2 expressing cells with potent cytotoxicity in vitro and significant in vivo inhibition of tumor growth, suggesting its therapeutic benefit in immuno-oncology. Summary of parameters of LM-106 and LM-306 binding affinity, internalization, ADCC and cytotoxicity Assay Antibody EC50 (nM) HEK293/H_IL-13Rα2 U251 A375 SKMEL5 Binding affinity LM-106 0.99 0.21 0.57 0.1 LM-306 1.47 0.33 0.8 0.12 Internalization LM-106 2.22 - 0.43 - ADCC LM-106 0.16 - 0.03 - LM-306 0.31 - 0.03 - Cytotoxicity (IC50) LM-306 0.03 0.05 0.01 0.005 Citation Format: Wentao Huang, Zhifang Liu, Yifan Li, Heng Pan, Yuan Li, Xia Qin, Da Fei, Runsheng Li. Pre-clinical evaluation of a novel antibody drug conjugate (ADC) LM-306 targeting IL-13Rα2 in immuno-oncology [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1881.

Abstract 5655: preclinical development of a novel anti-tslpr bispecific antibody 1b7/cd3 targeting crlf2-rearranged ph-like b-all

Abstract Acute lymphocytic leukemia (ALL) is the most common form of leukemia in childhood and adolescence. Outcomes of relapsed/refractory adult B-ALL remain dismal with long-term survival of less than 10%. Although targeted therapies such as blinatumomab, inotuzumab ozogamicin, and CD19 CAR T cell therapy are a significant treatment advance for patients with B-ALL, there is still an unmet medical need for novel therapies for B-ALL. CRLF2-rearranged B-ALL, a subtype of Philadelphia chromosome-like B-ALL, is a high-risk disease subset with poor long-term outcomes. In an effort to identify new therapeutic targets for B-ALL, we validated by flow cytometry that patients with CRLF2-rearranged Ph-like ALL overexpress thymic stromal lymphopoietin receptor (TSLPR) at levels comparable with CD19. We subsequently generated antibodies against TSLPR from immunized H2L2 Harbor mice through single B cell cloning technology. The lead antibody was further engineered to a CD3-redirecting bispecific antibody (BsAb) using Xencor’s CD3e bispecific antibody technology to create 1B7/CD3 BsAb with an Fc-silent region. 1B7/CD3 BsAb exhibits high affinity binding to both human and cynomolgus monkey CD3e and TSLPR by BLI. Additionally, UHPLC-SEC analysis of 1B7/CD3 shows that this BsAb is stable without any aggregation or degradation present after five weeks incubation at 37 °C. In cell-based analyses,1B7/CD3 BsAb demonstrate potent antigen-specific T cell activation and tumor lysis activity against TSLPR+-REH and MHH-CALL4 cell lines as well as a primary B-ALL patient sample, but none against human peripheral blood mononuclear cells (PBMC) collected from healthy donors. Animal tumor models suggest that 1B7/CD3 triggers a dose-dependent tumor regression or growth inhibition in PBMC humanized TSLPR-REH CDX and BOS-1 PDX models across donors. Correspondingly, T cell activation and expansion were examined by CD69 and CD3+ T cells with the best effect observed at the 1mg/kg dose. 1B7/CD3 exhibits durable PK with T1/2 in NSG mice of up to ten days. Finally, 1B7/CD3 BsAb demonstrated a tolerable safety margin in a two-dose exploratory toxicity study in cynomolgus monkeys with MTD equal to or less than 1mg/kg. Consistent with clinical observation, we observed a transient increase of six major cytokines (IFNγ, IL-6, IL-8, IL-10, MCP-1 and TNFα) 4hr post the initial dosing, but no notable induction of cytokine levels after the second dosing (except for IL-8). Thus, our preclinical data provide the framework for the clinical evaluation of 1B7/CD3 BsAb in patients with CRLF2-rearranged B-ALL. Citation Format: Ze Tian, chunhua shi, Amin AI-Shami, GuoJun Yong, Jason K Allen, Jill Wardell Olson, Melinda G Smith, Qing Chang, Qing Shi, Junping You, Michelle A Gonzalez, Timothy E Lofton, Jasbir Kaur, Qi Zhang, DongXing Zha, Nitin Jain, Marina Y Konopleva, Timothy Heffernan, Jeffrey J Molldrem. preclinical development of a novel anti-tslpr bispecific antibody 1b7/cd3 targeting crlf2-rearranged ph-like b-all. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5655.

Abstract 6337: Tri-specific CD3 x HER2 x HER2 antibodies in 1:2 format recognizing two different epitopes on HER2 demonstrate selective activity on human cancer cells with high HER2 expression

Abstract Human epidermal growth factor receptor 2 (HER2) is a membrane tyrosine kinase that was found to be amplified and overexpressed in various human cancers including breast cancer. Monoclonal antibodies targeting HER2 such as trastuzumab and pertuzumab provide good therapeutic benefits in patients with high HER2 expression tumors, however, not all patients respond to the treatment, and many suffer recurrence. There is still a large unmet need for targeted therapies to treat HER2 high expression tumors. T cell engaging antibodies that direct T cells to kill cancer cells by simultaneously binding to CD3 on T cells and tumor-associated antigens (TAA) on cancer cells have emerged as a promising new approach. Such therapeutics are potent, but safe use of them depends on selectivity of the TAA engaged. Though HER2 is highly overexpressed in ~ 20% of breast cancer, expression of HER2 is not restricted to cancer cells and present at low level in normal tissues. The capability of selectively targeting cancer cells over HER2 low expressing normal tissues is critical to the safety of CD3 x HER2 antibodies. It is noteworthy to mention that unlike antibody-drug conjugate (ADC) therapeutics, CD3 x HER2 antibodies might not be a good approach to target HER2 low/neg expression tumors due to the difference in mechanism of action. CMG6A19 is a 150 kD IgG-like tri-specific CD3 x HER2 x HER2 T cell-engaging antibody generated on Chimagen’s TRIAD platform. It is capable of simultaneously recognizing and binding to two different epitopes on HER2 proteins. Multiple human cell lines with different levels of HER2 expression were used as targets in the antibody-mediated hPBMC killing assays in vitro and in vivo, among which SK-BR-3, KPL-4 and BT474 have high HER2 expression as seen in HER2 positive cancers, HT55 and JIMT1 have medium level of HER2 expression, and PC3 and MCF7 have HER2 expression level that is close to in normal tissues. Conventional 1:1 IgG-like CD3 x HER2 bispecific antibodies were used as control. Results showed that CMG6A19 demonstrated higher tumor inhibition effect compared to control antibodies in SK-BR-3/KPL-4/BT474 models, meanwhile remarkably weaker effect in PC3/MCF7 models suggesting better safety in HER2 low expressing tissues. This selectivity of reactivity towards HER2 high expressing cells is likely due to the unique orientation of the antibody which allows better T cell activation when antigen abundance is high. Preliminary preclinical study in cynomolgus monkeys suggested that the antibody was well tolerated in monkeys at the dosage of 20 mpk and had a half-life that is comparable to conventional antibodies. CD3 x HER2 x HER2 tri-specific antibodies selectively showed potent anti-tumor activity on HER2 high expressing cells and good safety on HER2 low expressing cells. Current findings warrant further development in human. Citation Format: Jie Zhang, Xiaoqing Wang, Zhenhao Zhou. Tri-specific CD3 x HER2 x HER2 antibodies in 1:2 format recognizing two different epitopes on HER2 demonstrate selective activity on human cancer cells with high HER2 expression. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6337.

Abstract 5000: MYTX-011: A novel cMET-targeting antibody drug conjugate (ADC) engineered to increase on-target uptake in and efficacy against cMET expressing tumors

Abstract MET alterations can act as an oncogenic driver in non-small cell lung cancer (NSCLC) and elevated cMET expression occurs in many cancers. Antibody drug conjugates targeting cMET (cMET-ADCs) have been developed as a strategy to treat cMET+ tumors irrespective of dependency on cMET signaling. cMET- ADCs have shown promising clinical activity, but largely in a subset of NSCLC patients having the highest cMET levels, indicating tumor cMET levels may be limiting for efficacy. We sought to create an ADC with the potential to benefit a broader population of patients including those expressing moderate cMET levels. Here, we describe MYTX-011, an ADC incorporating the clinically validated vcMMAE linker-payload conjugated to a novel, pH-dependent anti-cMET antibody. We hypothesized that engineering the antibody to rapidly lose affinity at acidic endosomal pH would boost ADC uptake and efficacy in cMET+ tumor cells by avoiding non-productive ADC recycling. We conducted mutagenesis of anti-cMET antibodies, screening for variants that selectively lost binding under acidic conditions, and, in parallel, assessed antibody internalization in cell-based assays. The resulting lead humanized IgG1 antibody was conjugated to vcMMAE at engineered cysteine residues (DAR=2) to create MYTX-011, which exhibited rapid dissociation from cMET at pH5.4 but retained high affinity binding at pH7.4 and 6.4. MYTX-011 showed markedly higher (>3 fold) internalization in cMET+ tumor cells and broader, more potent cytotoxicity across a large panel of cMET+ cancer cell lines in vitro compared to a matched ADC based on the unmodified parent antibody lacking pH-dependent binding, or an in-house version of a clinical stage cMET ADC. These findings translated in vivo where MYTX-011 showed superior efficacy (>3 fold based on dose titration) in NSCLC xenograft models with high (EBC-1) or only moderate cMET expression levels (H1373, H1975) compared to the matched parent ADC or an in-house version of a clinical stage cMET ADC. PK and toxicity studies in cynomolgus monkeys revealed that MYTX-011 exhibited favorable PK characteristics, and a toxicity profile similar to previously described MMAE-based ADCs. Together, these findings highlight the potential of MYTX-011 as a therapeutic candidate for treating a broader range of cMET+ malignancies than other cMET-ADCs. Citation Format: Nimish Gera, Kyle Fitzgerald, Vijay Ramesh, Purvi Patel, Lena Kien, Deepak Kanojia, Simon Aoyama, Federico Colombo, Amit Deshpande, William Comb, Thomas Chittenden, Brian Fiske. MYTX-011: A novel cMET-targeting antibody drug conjugate (ADC) engineered to increase on-target uptake in and efficacy against cMET expressing tumors. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5000.

Abstract 6318: Preclinical characterization of ARX305, a next-generation anti-CD70 antibody drug conjugate for the treatment of CD70-expressing cancers

Abstract CD70 has emerged as an attractive tumor target with its over-expression in multiple solid and hematological cancers, yet tightly controlled and limited expression in normal cells. In the last decade, multiple anti-CD70 antibody drug conjugates (ADCs) have been developed, but most, if not all, of these ADC programs have been discontinued. Using an expanded genetic code to create Engineered Precision Biologics (EPBs), Ambrx has developed ARX305, a CD70-targeted next-generation antibody drug conjugate (ADC) to potentially overcome the challenges associated with earlier ADCs and treat patients with cancers over-expressing CD70. ARX305 is comprised of a proprietary, high-affinity, humanized anti-CD70 antibody stably and site-specifically conjugated to AS269, a potent microtubule inhibitor. After binding to CD70 expressed on target tumor cells, ARX305 internalizes and releases the cytotoxic payload pAF-AS269 which inhibits cellular proliferation. In vitro testing across a panel of solid and liquid tumor cell lines showed ARX305 elicited highly potent and specific cell killing across multiple tumor types with medium to high CD70 expression levels. In multiple in vivo CD70-expressing xenograft or disseminated models, ARX305 induced significant tumor growth inhibition or regression whereas unconjugated antibody exhibited poor activity. ARX305 utilizes stable oxime conjugation chemistry, a non-cleavable PEG linker, and a membrane-impermeable payload to minimize premature payload release in circulation and associated off-target toxicity. These properties of ARX305 result in high serum stability, with rodent pharmacokinetic studies confirming a similar exposure profile of ARX305 compared to unconjugated antibody and a long serum half-life. Repeat dose toxicokinetic studies in cynomolgus monkeys demonstrated ARX305 was tolerated at exposures well above therapeutic exposures in mouse pharmacology studies, indicating a wide therapeutic index. In summary, the highly potent anti-tumor activity in multiple tumor types and wide therapeutic index of ARX305 support clinical evaluation of this next generation anti-CD70 ADC. ARX305 is currently in a Phase 1 dose escalation study in China, and the IND in the United States is open. Citation Format: Lillian Skidmore, Jingjing Zhu, David Mills, Ting Jin, Suqin Li, Keith Tatsukawa, Nick A. Knudsen, Liying Gong, Jay Nelson, Kari Cox, Amha G. Hewet, Jianing Wang, Tim Buss, Feng Tian, Gang Xia, Shawn Zhang. Preclinical characterization of ARX305, a next-generation anti-CD70 antibody drug conjugate for the treatment of CD70-expressing cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6318.