The ABC of ADCs (Antibody-Drug Conjugates): A Comprehensive Review of Technical, Regulatory, and Clinical Challenges

Over the past several decades, there has been a significant surge in the development of Antibody-Drug Conjugates (ADCs). Designing an ideal ADC presents a multifaceted challenge, requiring the precise orchestration of various elements such as antigens, antibodies, linkers, and payloads. While ADCs aim to target tumor cells specifically, several antigens can also be found in regular tissues, potentially compromising the specificity of ADCs in therapeutic applications. The complexity extends to antibody selection, necessitating effective targeting of the desired antigen and ensuring compatibility with linkers for effective payload delivery. Additionally, the linker and payload combination are critical for the ADC’s therapeutic efficiency, balancing stability in circulation and timely payload release upon target binding. ADC doses must be safe for normal tissues while ensuring the released payloads are effective. The success of ADCs is attributed to their unmatched efficacy compared to traditional chemotherapy agents. The current research article aims to provide a technical review of Antibody-Drug Conjugates (ADCs) for cancer therapies. A brief discussion on the basics of ADCs, regulatory approach, overview, and technical complexities for quantification is presented. This review also summarizes recently approved ADCs and introduces the concepts of antibodies, linkers, and payloads. The article also outlines cancer-specific ADCs currently in late-stage clinical trials for cancer treatment.

Bispecific antibody drug conjugates:Making 1+1>2

Bispecific antibody‒drug conjugates(BsADCs)represent an innovative therapeutic category amalgamating the merits of antibody‒drug conjugates(ADCs)and bispecific antibodies(BsAbs).Positioned as the next-generation ADC approach,BsADCs hold promise for ameliorating extant clinical challenges associated with ADCs,particularly pertaining to issues such as poor internalization,off-target toxicity,and drug resistance.Presently,ten BsADCs are undergoing clinical trials,and initial findings underscore the imperative for ongoing refinement.This review initially delves into specific design considerations for BsADCs,encompassing target selection,antibody formats,and the linker–payload complex.Subsequent sections delineate the extant progress and challenges encountered by BsADCs,illustrated through pertinent case studies.The amalgamation of BsAbs with ADCs offers a prospective solution to prevailing clinical limitations of ADCs.Nevertheless,the symbiotic interplay among BsAb,linker,and payload necessitates further optimizations and coordination beyond a simplistic“1+1”to effectively surmount the extant challenges facing the BsADC domain.

Bispecific antibodies targeting immunomodulatory checkpoints for cancer therapy

Advances in antibody engineering have led to the generation of more innovative antibody drugs,such as bispecific antibodies(bs Abs).Following the success associated with blinatumomab,bs Abs have attracted enormous interest in the field of cancer immunotherapy.By specifically targeting two different antigens,bs Abs reduce the distance between tumor and immune cells,thereby enhancing tumor killing directly.There are several mechanisms of action upon which bs Abs have been exploited.Accumulating experience on checkpoint-based therapy has promoted the clinical transformation of bs Abs targeting immunomodulatory checkpoints.Cadonilimab(PD-1×CTLA-4)is the first approved bs Ab targeting dual inhibitory checkpoints,which confirms the feasibility of bs Abs in immunotherapy.In this review we analyzed the mechanisms by which bs Abs targeting immunomodulatory checkpoints and their emerging applications in cancer immunotherapy.

TCR-mimic antibody-drug conjugates targeting intracellular tumor-specific mutant antigen KRAS G12V mutation

Limited clinical application of antibody-drug conjugates(ADCs)targeting tumor associated antigens(TAAs)is usually caused by on-target off-tumor side effect.Tumor-specific mutant antigens(TSMAs)only expressed in tumor cells which are ideal targets for ADCs.In addition,intracellular somatic mutant proteins can be presented on the cell surface by human leukocyte antigen class I(HLA I)molecules forming tumor-specific peptide/HLA I complexes.KRAS G12 V mutation frequently occurred in varied cancer and was verified as a promising target for cancer therapy.In this study,we generated two TCR-mimic antibodydrug conjugates(TCRm-ADCs),2E8-MMAE and 2 A5-MMAE,targeting KRAS G12 V/HLAA*0201 complex,which mediated specific antitumor activity in vitro and in vivo without obvious toxicity.Our findings are the first time validate the strategy of TCRm-ADCs targeting intracellular TSMAs,which improves the safety of antibody-based drugs and provides novel strategy for precision medicine in cancer therapy.

Current LC-MS-based strategies for characterization and quantification of antibody-drug conjugates

The past few years have witnessed enormous progresses in the development of antibody-drug conjugates(ADCs).Consequently,comprehensive analysis of ADCs in biological systems is critical in supporting discovery,development and evaluation of these agents.Liquid chromatography-mass spectrometry(LC-MS)has eme rged as a promising and versatile tool for ADC analysis across a wide range of scenarios,owing to its multiplexing ability,rapid method development,as well as the capability of analyzing a variety of targets ranging from small-molecule payloads to the intact protein with a high,molecular resolution.However,despite this tremendous potential,challenges persist due to the high complexity in both the ADC molecules and the related biological systems.This review summarizes the up-to-date LC-MS-based strategies in ADC analysis and discusses the challenges and opportunities in this rapidly-evolving field.

Preparation and Characterization for Bispecific Antibodies of Anti-CD3×Anti-Idiotype to BCellLym phocytic Leukem ia

Bispecific antibodies (BsAbs) of anti CD3×anti idiotype (Id) to B cell lymphocytic leukemia (CLL) were prepared by chemical conjugation and direct hybridization technique of hybridoma and hybridoma without screening markers. The specificity of BsAbs from culture supernatants or ascites was assayed by indirect ELISA and indirect immunoflurescence (IF). The results showed that BsAbs could specifically react with homologous serum IgM from patients with B CLL and cells carrying CD3 marker respectively. Cell combination test and LDH assay demonstrated that BsAb significantly increased the conjugate formation between lymphocyte activated kill (LAK) cells and Daudi cells, and enhanced the cytotoxic activity of LAK cells against Daudi cells.

Enzyme-linked immunosorbent assays for quantification of MMAE-conjugated ADCs and total antibodies in cynomolgus monkey sera

Antibody-drug conjugates(ADCs)are commonly heterogeneous and require extensive assessment of exposure-efficacy and exposure-safety relationships in preclinical and clinical studies.In this study,we report the generation of a monoclonal antibody against monomethyl auristatin E(MMAE)and the development,validation,and application of sensitive and high-throughput enzyme-linked immunosorbent assays(ELISA)to measure the concentrations of MMAE-conjugated ADCs and total antibodies(tAb,antibodies in ADC plus unconjugated antibodies)in cynomolgus monkey sera.These assays were successfully applied to in vitro plasma stability and pharmacokinetic(PK)studies of SMADC001,an MMAE-conjugated ADC against trophoblast cell surface antigen 2(TROP-2).The plasma stability of SMADC001 was better than that of similar ADCs coupled with PEG4-Val-Cit,Lys(m-dPEG24)-Cit,and Val-Cit linkers.The developed ELISA methods for the calibration standards of ADC and tAb revealed a correlation between serum concentrations and the OD450 values,with R2 at 1.000,and the dynamic range was 0.3-35.0 ng/mL and 0.2-22.0 ng/mL,respectively;the intra-and inter-assay accuracy bias%ranged from -12.2% to -5.2%,precision ranged from -12.4% to -1.4%,and the relative standard deviation(RSD)was less than 6.6% and 8.7%,respectively.The total error was less than 20.4%.The development and validation steps of these two assays met the acceptance criteria for all addressed validation parameters,which suggested that these can be applied to quantify MMAE-conjugated ADCs,as well as in PK studies.Furthermore,these assays can be easily adopted for development of other similar immunoassays.

Resistance to antibody-drug conjugates in breast cancer:mechanisms and solutions

Antibody-drug conjugates(ADCs)are a rapidly developing therapeutic approach in cancer treatment that has shown remarkable activity in breast cancer.Currently,there are two ADCs approved for the treatment of human epidermal growth factor receptor 2-positive breast cancer,one for triple-negative breast cancer,and multiple investigational ADCs in clinical trials.However,drug resistance has been noticed in clinical use,especially in trastuzumab emtansine.Here,the mechanisms of ADC resistance are summarized into four categories:antibodymediated resistance,impaired drug trafficking,disrupted lysosomal function,and payload-related resistance.To overcome or prevent resistance to ADCs,innovative development strategies and combination therapy options are being investigated.Analyzing predictive biomarkers for optimal therapy selection may also help to prevent drug resistance.

A mild phenoxysilyl linker for self-immolative release of antibody-drug conjugates

Self-immolative linkers have been widely used to construct prodrugs to improve their efficacy and safety.In this study,we report the use of phenoxysilyl linker as a self-immolative unit to prepare antibody-drug conjugates(ADCs).Phenoxysily based ADC Ate-PPS-CA4 was prepared and its release was systematically investigated by mass spectrometry.Biological evaluation showed that Ate-PPS-CA4 displayed the ability to target delivery and self-immolative release the active payload CA4 on PD-L1 positive cells MDA-MB-231.As the same with its payload CA4,it could arrest the cell cycle to the G2/M phase and induced changes in cell morphology at the dose of its IC_(50).The development of this linker with novel drug release mechanisms will expand the methodology to construct ADCs,especially for non-internalizing ADCs by extracellular cleavage.

HER3-targeted therapeutic antibodies and antibody-drug conjugates in non-small cell lung cancer refractory to EGFR-tyrosine kinase inhibitors

Human epidermal growth factor receptor 3(HER3)is a unique member of the human epidermal growth factor receptor(HER/EGFR)family,since it has negligible kinase activity.Therefore,HER3 must interact with a kinase-proficient receptor to form a heterodimer,leading to the activation of signaling cascades.Overexpression of HER3 is observed in various human cancers,including non-small cell lung cancer(NSCLC),and correlates with poor clinical outcomes in patients.Studies on the underlying mechanism demonstrate that HER3-initiated signaling promotes tumor metastasis and causes treatment failure in human cancers.Upregulation of HER3 is frequently observed in EGFR-mutant NSCLC treated with EGFR-tyrosine kinase inhibitors(TKIs).Increased expression of HER3 triggers the so-called EGFR-independent mechanism via interactions with other receptors to activate“by-pass signaling pathways”,thereby resulting in resistance to EGFR-TKIs.To date,no HER3-targeted therapy has been approved for cancer treatment.In both preclinical and clinical studies,targeting HER3 with a blocking an-tibody(Ab)is the only strategy being examined.Recent evaluations of an anti-HER3 Ab-drug conjugate(ADC)show promising results in patients with EGFR-TKI-resistant NSCLC.Herein,we summarize our understanding of the unique biology of HER3 in NSCLC refractory to EGFR-TKIs,with a focus on its dimerization partners and subsequent activation of signaling pathways.We also discuss the latest development of the therapeutic Abs and ADCs targeting HER3 to abrogate EGFR-TKI resistance in NSCLC.

多发性骨髓瘤新型治疗方案的研究进展

多发性骨髓瘤(MM)是一种无法治愈的浆细胞恶性肿瘤,其典型病程特点是对最初治疗有所反应,随后产生耐药性。尽管在引入新药(如蛋白酶体抑制剂、免疫调节剂)的推动下,多发性骨髓瘤的临床治疗虽然取得了重大进展,但是仍然无法完全治愈。然而只要患者有可用的新疗法,即可实现疾病的缓解,提高患者生存质量。这一现实促进了许多新型疗法的发展,在过去15年中批准了12种MM新型药物,还有更多的药物在临床试验中,极大地改变了MM的治疗格局,并提高了患者的生存率。本文就多发性骨髓瘤新型治疗的进展进行综述。

Targeting triple-negative breast cancer:A clinical perspective

Triple-negative breast cancer(TNBC)is a disease with often an aggressive course and a poor prognosis compared to other subtypes of breast cancer.TNBC accounts for approximately 10%–15%of all diagnosed breast cancer cases and represents a high unmet need in the field.Up to just a few years ago,chemotherapy was the only systemic treatment option for this subtype(1).To date,TNBC is considered a heterogeneous disease.One of the existing classifications is based on the analysis of mRNA expression in 587 TNBC cases,in which Lehman et al.proposed six subtypes of TNBC as follows:two basal-like(BL1 and BL2)subtypes,a mesenchymal(M)subtype,a mesenchymal stem-like(MSL)subtype,an immunomodulatory(IM)subtype,and a luminal androgen receptor(LAR)subtype(2).Later studies have demonstrated that the IM and MSL subtypes do not correlate with independent subtypes but reflect background expression by dense infiltration of tumor-infiltrating lymphocytes(TILs)or stromal cells.According to this finding,the classification of TNBC has been revised into the following four subtypes:basal 1,basal 2,LAR,and mesenchymal subtypes(3).Over the last years,several new strategies have been investigated for the treatment of patients with TNBC.Among them,immunotherapy,antibody drug conjugates,new chemotherapy agents,and targeted therapy have been and are currently being developed.The present article aims to provide an updated overview on the different treatment options that are now available or are still under investigation for patients with TNBC.

Antibody-drug conjugates： recent advances in conjugation and linker chemistries

The antibody-drug conjugate （ADC）, a humanized or human monoclonal antibody conjugated with highly cytotoxic small molecules （payloads） through chemical linkers, is a novel therapeutic format and has great potential to make a paradigm shift in cancer chemother- apy. This new antibody-based molecular platform enables selective delivery of a potent cytotoxic payload to target cancer cells, resulting in improved efficacy, reduced systemic toxicity, and preferable pharmacokinetics （PK）I pharmacodynamics （PD） and biodistribution compared to traditional chemotherapy. Boosted by the successes of FDA-approved Adcetris~ and Kadcyla~, this drug class has been rapidly growing along with about 60 ADCs cur- rently in clinical trials. In this article, we briefly review molecular aspects of each component （the antibody, payload, and linker） of ADCs, and then mainly discuss traditional and new technologies of the conjugation and linker chemistries for successful construction of clini- cally effective ADCs. Current efforts in the conjugation and linker chemistries will provide greater insights into molecular design and strategies for clinically effective ADCs from medicinal chemistry and pharmacology standpoints. The development of site-specific conjuga- tion methodologies for constructing homogeneous ADCs is an especially promising path to improving ADC design, which will open the way for novel cancer therapeutics.

抗体靶向治疗在弥漫性大B细胞淋巴瘤中的研究进展

弥漫性大B细胞淋巴瘤(diffuse large B-cell lymphoma,DLBCL)是一种侵袭性淋巴瘤,通常采用含CD20单克隆抗体(利妥昔单抗)的免疫化疗方案,然而仍有部分复发难治(relapsed/refractory,R/R)患者无法获得临床治愈。近年来,不少新开发的单抗类药物用于治疗DLBCL,显著改善了R/R DLBCL的预后。本综述系统讨论这些单抗类药物,包括传统简单结构的单克隆抗体、双特异性抗体(bispecific antibodies,bsAb)及抗体-药物偶联物(antibody-drug conjugates,ADCs)。首先介绍除利妥昔单抗以外的其他传统单抗,主要涉及单抗结构上的改进及针对更多的靶点。接着详细阐述bsAb的基本结构和作用机制,以及各种不同双抗结合位点带来的多种可能及尝试。最后对ADCs的作用机制及结构各部分做详细的分析比较。文中还介绍这些单抗类药物用于治疗DLBCL的最新临床试验数据,包括反应率、无进展生存期等疗效结果,以及主要的不良反应。

Antibody-drug conjugates:Recent advances in linker chemistry

Antibody-drug conjugates(ADCs)are gradually revolutionizing clinical cancer therapy.The antibody-drug conjugate linker molecule determines both the efficacy and the adverse effects,and so has a major influence on the fate of ADCs.An ideal linker should be stable in the circulatory system and release the cytotoxic payload specifically in the tumor.However,existing linkers often release payloads nonspecifically and inevitably lead to off-target toxicity.This defect is becoming an increasingly important factor that restricts the development of ADCs.The pursuit of ADCs with optimal therapeutic windows has resulted in remarkable progress in the discovery and development of novel linkers.The present review summarizes the advance of the chemical trigger,linker-antibody attachment and linker-payload attachment over the last 5 years,and describes the ADMET properties of ADCs.This work also helps clarify future developmental directions for the linkers.

淋巴瘤的免疫治疗进展

淋巴瘤的治疗经历了从传统的细胞毒药物化疗向免疫药物靶向治疗的转变,传统药物的研究和应用不断发展,新药的研究和开发更是人们关注的热点。许多免疫治疗药物如单克隆抗体、抗体-药物偶联物、双特异性抗体T细胞衔接器、嵌合抗原受体T细胞、免疫检查点抑制剂及小分子抑制剂等,无论是单药还是联合用药,在初治和复发/难治性霍奇金淋巴瘤及非霍奇金淋巴瘤的治疗中均展现出较好的疗效和安全性,为患者提供了更多的治疗选择。然而,免疫药物治疗淋巴瘤仍面临诸多挑战,需要进一步研究和优化。

Antibody-drug conjugates in HER2-positive breast cancer

Antibody-drug conjugates(ADCs)combine the high specificity of monoclonal antibodies with the high anti-tumor activity of small molecular cytotoxic payloads.The anti-tumor activity of ADCs is mainly achieved by the direct blocking of the receptor by monoclonal antibodies,direct action and bystander effect of cytotoxic drugs,and antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity.ADCs have been used in adjuvant therapy and rescue treatment of human epidermal receptor 2(HER2)-positive breast cancer,greatly improving the prognosis of breast cancer patients.Several ongoing clinical trials of ADC for breast cancer and other solid tumors proved the potential of ADCs will provide more promising treatment options for patients with malignant tumors.This review introduces the mechanism and latest clinical progress of ADC drugs approved for HER2-positive breast cancer to guide clinical practice and conduct research.

Advances in preclinical evaluation of experimental antibody-drug conjugates

The ability to chemically modify monoclonal antibodies with the attachment of specific functional groups has opened up an enormous range of possibilities for the targeted treatment and diagnosis of cancer in the clinic.As the number of such antibody-based drug candidates has increased,so too has the need for more stringent and robust preclinical evaluation of their in vivo performance to maximize the likelihood that time,research effort,and money are only spent developing the most effective and promising candidate molecules for translation to the clinic.Concurrent with the development of antibody-drug conjugate(ADC)technology,several recent advances in preclinical research stand to greatly increase the experimental rigor by which promising candidate molecules can be evaluated.These include advances in preclinical tumor modeling with the development of patient-derived tumor organoid models that far better recapitulate many aspects of the human disease than conventional subcutaneous xenograft models.Such models are amenable to genetic manipulation,which will greatly improve our understanding of the relationship between ADC and antigen and stringently evaluate mechanisms of therapeutic response.Finally,tumor development is often not visible in these in vivo models.We discuss how the application of several preclinical molecular imaging techniques will greatly enhance the quality of experimental data,enabling quantitative pre-and post-treatment tumor measurements or the precise assessment of ADCs as effective diagnostics.In our opinion,when taken together,these advances in preclinical cancer research will greatly improve the identification of effective candidate ADC molecules with the best chance of clinical translation and cancer patient benefit.

CLINICAL APPLICATION OF MONOCLONAL ANTIBODY-DRUG CONJUGATE TO IMMUNOTARGETING CHEMOTHERAPY OF BLADDER CANCER

Monoclonal antibody-drug conjugate was applied in a clinical trial for patients with bladder cancer, Monoclonal antibody HB7A from a mouse splenocyte immunized against human bladder cancer was used as a drug carrier, The anti-cancer drug adriamycin (ADR) was bound to HB7A through a dextran (DEX) bridge to form the conjugate HB7A-DEX-ADR. The in vitro cytotoxic effect of the conjugate on BIU-87 bladder cancer cells was similar to that of free ADR and the mixture of HB7A and ADR, Seven patients with bladder cancer were given HB7A-DEX-ADR intravenously. The immunoperoxidast studies of the resected specimens showed that HB7A was localized specifically in cancer, and histological studies revealed degenerative and necrotic changes of the tumor cells, Patients receiving the conjugate did not experience serious side effects, This study suggests that immunotargeting chemotherapy with HB7A-DEX-ADR is well tolerated by patients and its cytotoxicity on tumor is substantial.

单克隆抗体药物研发进展

目的:对单克隆抗体药物研发进展进行综述,为行业提供参考。方法:通过查阅文献和相关数据库,对经典的单克隆抗体药物,以及由此衍生的抗体偶联药物、双特异性抗体药物的研究进行汇总、梳理。结果与结论:自1986年第一个单克隆抗体药物上市以来,全球已有超过100种单抗药物获批上市。国内已获批的进口单抗药物达42个,国产单抗药物达31个。经过30多年的研究和发展,单抗药物以其高度特异性和疗效确切的特点,在肿瘤、自身免疫、代谢、病毒感染等疾病领域显示出独特的优势和广阔的应用前景。