Background: Claudin18.2 (CLDN18.2), a tight junction protein normally expressed only on gastric mucosa, is overexpressed in gastric, pancreatic, esophageal, ovarian, lung and other solid tumors. Unlike in normal tissue, CLDN18.2 is exposed on epithelial surfaces in malignancy. There are no approved targeted therapies for CLDN18.2-expressing cancers. An antibody-drug conjugate (ADC) composed of a monoclonal antibody (mAb) targeting CLDN18.2 with a monomethyl auristatin E (MMAE) payload site-specifically conjugated via a cleavable linker at a drug-antibody ratio (DAR) of 2, EO-3021/SYSA1801, was developed to target CLDN18.2-expressing cancer cells, minimize toxicities and maximize therapeutic index. Methods: HEK293-CLDN18.2 cells were used to evaluate CLDN18.2-dependent EO-3021 endocytosis, MMAE payload release, inhibition of proliferation and antibody dependent cellular cytotoxicity (ADCC). Cell cycle distribution and caspase-3/7 activity were measured 24 hours after treating BxPC3-CLDN18.2 pancreatic cells with EO-3021 or the unconjugated antibody, EO-3021 mAb. Inhibition of proliferation by EO-3021 was measured on cell lines ectopically expressing medium to high CLDN18.2 and on cell lines with endogenous low to medium CLDN18.2 expression. Xenograft studies evaluating tumor growth inhibition by EO-3021, EO3021 mAb, and cisplatin or gemcitabine were done in gastric (NUGC4; NUGC4-CLDN18.2), pancreatic (Patu8988S; BxPC3-CLDN18.2), and lung (NCI-H460) cancer models. Results: EO-3021 binding to cancer cells, endocytosis, MMAE release, and inhibition of proliferation were dependent on CLDN18.2 expression. EO-3021 (EC50: 172 ng/ml) and EO-3021 mAb (EC50: 130 ng/ml) demonstrated similar levels of ADCC. EO-3021 but not EO-3021 mAb promoted G2/M cell cycle arrest and apoptosis and exhibited potent activity across cell lines with low, medium, and high CLDN18.2 expression (IC50: 7-456 ng/mL). EO-3021 induced tumor regressions with a single dose across low, medium, and high CLDN18.2-expressing in vivo models derived from pancreatic (2-10 mg/kg), gastric (0.5-10 mg/kg), and lung cancers (4 mg/kg), respectively. In contrast, standard of care (SOC) chemotherapies and EO-3021 mAb did not induce tumor regressions across in vivo models. Conclusions: EO-3021 demonstrated profound in vivo antitumor activity and outperformed SOC in gastric, pancreatic, and lung cancer models. Results from in vitro and in vivo studies highlight the promising therapeutic potential of EO-3021/SYSA1801 for patients with CLDN18.2-expressing cancers. A Phase 1 study is ongoing to evaluate the safety, tolerability, pharmacokinetics and preliminary anti-tumor activity of SYSA1801 in patients with CLDN18.2 positive advanced solid tumors (NCT05009966). Citation Format: Mo Dan, Xiwu Hui, Yancui Wang, Can Yuan, Thomas O'Hare, Valerie Malyvanh Jansen, Shawn M. Leland, Yang Zhang, David Dornan, Xiaoyan Wang. Therapeutic potential of EO-3021/SYSA1801, a Claudin18.2 antibody-drug conjugate, for the treatment of CLDN18.2-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 6300.

Rabies, caused by the rabies virus (RABV), is the most fatal zoonotic disease. It is a neglected tropical disease which remains a major public health problem, causing approximately 59,000 deaths worldwide annually. Despite the existence of effective vaccines, the high incidence of human rabies is mainly linked to tedious vaccine immunisation procedures and the overall high cost of post-exposure prophylaxis. Therefore, it is necessary to develop an effective vaccine that has a simple procedure and is affordable to prevent rabies infection in humans. RABV belongs to the genus Lyssavirus and family Rhabdoviridae. Previous phylogenetic analyses have identified seven major clades of RABV in China (China I-VII), confirmed by analysing nucleotide sequences from both the G and N proteins. This study evaluated the immunogenicity and protective capacity of SYS6008, an mRNA rabies vaccine expressing rabies virus glycoprotein, in mice and cynomolgus macaques. We demonstrated that SYS6008 induced sufficient levels of rabies neutralising antibody (RVNA) in mice. In addition, SYS6008 elicited strong and durable RVNA responses in vaccinated cynomolgus macaques. In the pre-exposure prophylaxis murine model, one or two injections of SYS6008 at 1/10 or 1/30 of dosage provided protection against a challenge with a 30-fold LD50 of rabies virus (China I and II clades). We also demonstrated that in the post-exposure prophylaxis murine model, which was exposed to lethal rabies virus (China I-VII clades) before vaccination, one or two injections of SYS6008 at both 1/10 and 1/30 dosages provided better protection against rabies virus challenge than the immunization by five injections of commercial vaccines at the same dosage. In addition, we proved that SYS6008-induced RVNAs could neutralise RABV from the China I-VII clades. Finally, 1/10 of the dosage of SYS6008 was able to stimulate significant RABV-G specificity in the T cell response. Furthermore, we found that SYS6008 induced high cellular immunity, including RABV-G-specific T cell responses and memory B cells. Our results imply that the SYS6008 rabies vaccine, with a much simpler vaccination procedure, better immunogenicity, and enhanced protective capacity, could be a candidate vaccine for post-exposure prophylaxis of rabies infections.

The development of vaccines that can efficiently prevent the infection of SARS-CoV-2 is necessary to fight the COVID-19 epidemic. mRNA vaccine has been proven to induce strong humoral and cellular immunity against SARS-CoV-2. Here, we studied the immunogenicity and protection efficacy of a novel mRNA vaccine SYS6006. High expression of mRNA molecules in 293T cells was detected. The initial and boost immunization with a 21-day interval was determined as an optimal strategy for SYS6006. Two rounds of immunization with SYS6006 were able to induce the neutralizing antibodies against the SARS-CoV-2 wild-type (WT) strain, and Delta and Omicron BA.2 variants in mice or non-human primates (NHPs). A3rd round of vaccination could further enhance the titers of neutralization against Delta and Omicron variants. In vitro ELISpot assay showed that SYS6006 could induce memory B cell and T cell immunities specifically against SARS-CoV-2 in mice. FACS analysis indicated that SYS6006 successfully induced SARS-CoV-2-specific activation of T follicular helper cell (Tfh) and Th1 cell, and did not induce CD4+Th2 response in NHPs. SYS6006 vaccine could significantly reduce the viral RNA loads and prevent lung lesions in Delta variant infected hACE2 transgenic mice. Therefore, SYS6006 could provide significant immune protection against SARS-CoV-2.

Abstract CRB-701 (SYS6002) is a clinical stage, next generation ADC targeting Nectin-4 wherein two monomethyl auristatin E (MMAE) moieties are site-specifically conjugated to a novel Nectin-4 targeting IgG1 antibody via a cleavable linker. Nectin proteins are cell adhesion molecules belonging to the immunoglobulin (Ig) superfamily that participate in cell-to-cell interactions and form adhesion junctions between cells. Nectin-4 is widely expressed in epithelial cancers including bladder, breast, lung, colorectal, pancreatic, and ovarian. By contrast the expression level of Nectin-4 is very low in healthy adult human tissues. Due to this differential expression, Nectin-4 has emerged as a robust tumor associated antigen (TAA) that has been clinically validated in urothelial carcinoma by Enfortumab Vedotin (EV). While approved, EV carries associated toxicity concerns including skin rash, peripheral neuropathy and ocular toxicities that can lead to EV discontinuations and lasting adverse effects. CRB-701 (SYS6002) has demonstrated high affinity Nectin-4 binding (~2ng/ml) across species and has selectivity for Nectin-4 among the Nectin family of proteins (>5000 ng/ml). The antibody retains potent in vitro activity against FcgRI and C1q (<10nM) conferring antibody dependent cellular cytotoxicity (ADCC) and complement dependent cytotoxicity (CDC) activity in vitro. Compared to EV, CRB-701 (SYS6002) reduces free MMAE exposure by 4.8-9.7-fold when adjusted to ADC exposure (AUC) and there is a 2.2-7.4-fold reduction in MMAE in circulation based on Cmax in rats and non-human primates. Collectively these data reflect lower free MMAE in plasma, reducing the risk of MMAE-induced toxicities observed with EV in the clinic. This improved PK and safety profile coincides with a longer half-life of the ADC in plasma potentially reducing the frequency of administration to achieve efficacy. The internalization rate of CRB-701 (SYS6002) was 2-fold faster than EV when assessed in nectin-4 expressing cells. These data may explain the statistically significant reduction in tumor growth observed in a BL0597 patient derived xenograft model (PDX) of bladder cancer with low Nectin-4 protein expression by IHC (H score =50) when compared to EV at the same dose and frequency. Collectively these data suggest that CRB-701 (SYS6002) could demonstrate an improved therapeutic index and PK profile relative to EV and as such could achieve higher tolerated concentrations at lower dose frequency. The stability of the site-specific linker and the reduction in the drug-antibody ratio (DAR) could lead to a differentiated profile clinically that enables higher doses, longer treatment duration and a greater potential in drug combinations in nectin-4 positive tumors. CRB-701 (SYS6002) is currently being explored clinically in a phase 1 dose escalation with an anticipated completion date mid-2024. Citation Format: Rachael Brake, Zhaopeng Sun, Mo Dan, Lu Lv, Congcong Niu, Yang Zhang, Mingyue Shen, XiXin Hu, Xiwu Hui, Andrew Kolodziej. Development of CRB-701 (SYS6002): A novel site-specific, Nectin-4 targeting ADC [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C121.

Purpose:Antibody-drug conjugates (ADCs) have emerged as a potent cancer therapeutic option in recent years. DP303c is a HER2-targeting ADC with a cleavable linker-MMAE payload. The current study aimed to evaluate the therapeutic potentials of DP303c in vitro as well as in vivo.Materials and Methods:Size exclusion chromatography (SEC), reverse-phase high-performance liquid chromatography (RP-HPLC), and liquid chromatography-tandem mass spectrometry (LC-MS/MS) were used to analyze the physicochemical characterization of DP303c. An enzyme-linked immunosorbent assay (ELISA), a cell-based assay, and bio-layer interferometry (BLI) were used to evaluate DP303c's affinity with HER2 and Fc receptors. A confocal laser scanning microscopy was used to observe the internalization of DP303c. Antibody-dependent cell-mediated cytotoxicity (ADCC) and cytotoxicity assays were used to investigate the activity of DP303c in vitro. The antitumor activity of DP303c was assessed in vivo in the HER2-positive cell-derived xenograft model.Results:DP303c was a site-specific anti-HER2 antibody-drug conjugate with a monomethyl auristatin E (MMAE) with an average drug-to-antibody ratio (DAR) of 2.0. DP303c showed a high affinity with HER2 and could be effectively internalized. In vitro and in vivo, DP303c showed stronger antitumor activity as compared to trastuzumab-DM1 (T-DM1) in a series of HER2-positive cancer cells and cell-derived xenograft (CDX) models, especially in the lower HER2-expressing cells. DP303c also exhibited high serum stability and a good PK profile.Conclusion:DP303c was a steady and homogenous DAR 2 ADC that was predicted to deliver MMAE inhibitor to tumor cells. DP303c demonstrated remarkable anticancer efficacy against T-DM1 in xenograft models. DP303c was a strong candidate for the treatment of patients with HER2-positive cancer.

The main objective of this work was to demonstrate which kind of payload is the suitable choice for antibody–drug conjugates directed to widely expressed tumor-associated antigen. Trop-2 is overexpressed in various solid tumors, but it is also present on the epithelium of several normal tissues. A well-designed anti-Trop-2 ADC demands a good balance of efficacy and toxicity. In this research, MMAE, SN-38, and DXd were selected as candidates for payloads of the anti-Trop-2 mAb SY02. The antitumor activities and safety profiles of these ADCs were investigated to compare the therapeutic windows. Robust in vitro cytotoxicity was observed on human pancreatic cancer cell CFPAC-1 and breast cancer cell MDA-MB-468 with IC50 generally in the subnanomolar range. Consistent with in vitro assay, SY02-DXd and SY02-SN-38 demonstrated superior efficacy in CFPAC-1 xenograft models with TGI rates of 98.2% and 87.3%, respectively. However, SY02-MMAE could hardly inhibit the tumor growth. Subsequently, antitumor activities of these ADCs were further compared in MDA-MB-468 xenograft model. Complete tumor regression was observed in SY02-DXd and SY02-MMAE groups, indicating their potent antitumor activities. In an exploratory safety and pharmacokinetic study, SY02-DXd demonstrated the best safety profile with minimal adverse events in cynomolgus monkeys, while SY02-MMAE exhibited severe on-target skin toxicity which caused death. In conclusion, SY02-DXd demonstrated superior efficacy and safety with the widest therapeutic window. Based on the efficacy and safety results, moderate cytotoxic payloads would be ideal choices for ADCs targeting ubiquitously expressed antigens.