Antitumor Activity And Mechanism Of Antibody-drug Conjugates Targeting Cell Adhesion Molecules

Antibody-drug conjugates（ADCs）,a novel targeted drug delivery strategy,combine highly potent cytotoxic molecules with monoclonal antibodies targeting specific antigens on the surface of tumor cells through chemical linkers.Based on specificity and affinity of antigen-antibody interactions,ADCs can selectively deliver payloads to tumor cells while sparing normal cells.This strategy,with specificity and efficacy that traditional chemotherapy drugs cannot achieve,drastically solves the problems of systemic exposure and dose-limiting toxicity of chemotherapy drugs and overcomes the main clinical obstacles of chemotherapy.In the past,the development of ADCs mainly focused on hematological tumors with clear antigenic characteristics and human epidermal growth factor receptor 2（HER2）positive solid tumors.With a more comprehensive understanding of tumor biology and the rapid development of pathological analysis technology,more and more cell surface antigens with significant differential expression characteristics have been identified.As a result,the layout of ADCs is gradually diversified.Both Claudin 18.2 and Nectin-4,which belong to cell adhesion molecules,are important transmembrane proteins that constitute cell junctions and are promising drug targets for ADCs.In this study,a variety of tumor cell models with stable expression of human Claudin 18.2 or human Nectin-4 were constructed.And based on this,we evaluated the antitumor effect and mechanism of LZ1904 and LMA282,novel ADCs targeting Claudin 18.2 and Nectin-4 respectively.Claudins,with different tissue-specific expression patterns,are a family of transmembrane proteins that is important for the structure and function of tight junctions（TJs）.Claudin 18.2,a member of the Claudin family,is only widely expressed in differentiated gastric cells and is retained during malignant transformation.Meanwhile,studies have revealed that Claudin 18.2 is frequently ectopic activated in a variety of human malignancies of epithelial origin.This significant differential expression pattern between normal cells and tumor cells makes Claudin 18.2 a potential target for tumor targeted therapy.As the earliest reported and the fastest-advanced drug in the field of drugs targeting Claudin 18.2,whether used as a single agent or in combination with chemotherapy,IMAB362（a monoclonal antibody targeting Claudin18.2）has shown powerful antitumor activity in clinical trials.Therefore,the development of Claudin 18.2-targeted drugs has great clinical significance.LZ1904 is a new ADC formed by combining the monoclonal antibody LZ1903targeting Claudin 18.2 and topoisomerase I inhibitor 9106-IM-2 through a cleavable linker.It was found that LZ1904 could selectively bind to Claudin 18.2-positive cells and be transported into lysosomes after internalization.Thereby,it could induce G₂/M-phase cell cycle arrest and apoptosis,thus significantly and selectively inhibit the proliferation of Claudin 18.2-positive gastric or pancreatic cancer cells.Meanwhile LZ1904 could also kill neighboring Claudin 18.2-negative tumor cells through bystander effect and kill Claudin 18.2-positive tumor cells through antibody-dependent cell-mediated cytotoxicity（ADCC）.In general,LZ1904 showed significant selective antitumor activity in vitro,which deserves further evaluation in vivo.Nectin is an intercellular adhesion molecule belonging to the immunoglobulin superfamily（Ig SF）,and is an important transmembrane protein family that constitutes Adherens Junction（AJs）.Unlike other family members of Nectin,which are widely expressed in adult normal tissues,Nectin-4 tissue distribution is restricted to placenta and almost not detected in adult healthy tissues.However,studies have found that Nectin-4 is abnormally overexpressed in a variety of human cancers,especially bladder cancer,breast cancer and lung cancer,in which more than 50%of patients show positive expression.Meanwhile,as a receptor mediating the invasion of measles virus into cells,Nectin-4 has a significant internalization ability.Given the above two characteristics,Nectin-4 is a potential drug target for ADCs.In fact,PADCEV^?,a novel ADC targeting Nectin-4,was successfully approved in 2019 for the treatment of urothelial carcinoma（UC）.And this further validates the feasibility and great clinical potential of this target.LMA282 is an ADC comprising the anti-Nectin-4 antibody（LM282）conjugated to the microtubule-disrupting agent MMAE.In vitro,we found that LMA282 could selectively bind to Nectin-4-positive cells and then be transported into lysosomes after internalization,causing the inhibition of microtubule aggregation,G₂/M arrest and apoptosis.Based on the above-mentioned mechanisms,LMA282 finally achieved a significant and selective proliferation inhibitory effect on the Nectin-4-positive cells.Treatment of mouse xenograft models of human breast,bladder and lung cancer with LMA282 significantly inhibited the growth of tumors,showing comparable or even superior antitumor effect than that of PADCEV^?in vivo.These results suggested that LMA282 had significant antitumor activity in a variety of potential indications,providing support for clinical applications.In summary,LZ1904 and LMA282 have shown significant and highly selective antitumor effect in a variety of indications and are promising ADCs with great clinical application potential.In addition,the antitumor effect and mechanism of TSL-1502,a PARP inhibitor,were also studied.PARP enzymes play an important role in DNA damage response and the inhibition of PARP causes synthetic lethality in homologous recombination（HR）-deficient cancers.Currently,6 PARP inhibitors have been approved for the treatment of various HR-deficient cancers,however,the hematologic toxicities inhibitors greatly restrict their clinical applications.TSL-1502 is a highly effective glucuronide prodrug of PARP inhibitor,which can be hydrolyzed byβ-glucuronidase rich in tumor tissues to release TSL-1502M,the active compound.In this study,TSL-1502M exhibited strong inhibitory activity on PARP1/2,significantly induced double strand breaks（DSBs）,G₂/M arrest and apoptosis in HR-deficient cells,and selectively inhibited the proliferation of HR-deficient cancer cells.Notably,TSL-1502M was more superior than Olaparib.Meanwhile,TSL-1502 had no inhibitory effects on PARP1/2 itself,but selectively liberated the active metabolite TSL-1502M in tumor,showing a stronger antitumor effect than that of Olaparib in HR-deficient xenograft models.Overall,TSL-1502 is a novel PARP inhibitor with great innovation and clinical application potential.Based on the impressive preclinical efficacy and the unique decomposition characteristic of TSL-1502,a clinical phase I study was initiated in China.