Activity Of Antibody-drug Conjugate Research Articles

Antibody drug conjugates as targeted cancer therapy: past development, present challenges and future opportunities.

Antibody drug conjugates (ADCs) are promising cancer therapeutics with minimal toxicity as compared to small cytotoxic molecules alone and have shown the evidence to overcome resistance against tumor and prevent relapse of cancer. The ADC has a potential to change the paradigm of cancer chemotherapeutic treatment. At present, 13 ADCs have been approved by USFDA for the treatment of various types of solid tumor and haematological malignancies. This review covers the three structural components of an ADC-antibody, linker, and cytotoxic payload-along with their respective structure, chemistry, mechanism of action, and influence on the activity of ADCs. It covers comprehensive insight on structural role of linker towards efficacy, stability & toxicity of ADCs, different types of linkers & various conjugation techniques. A brief overview of various analytical techniques used for the qualitative and quantitative analysis of ADC is summarized. The current challenges of ADCs, such as heterogeneity, bystander effect, protein aggregation, inefficient internalization or poor penetration into tumor cells, narrow therapeutic index, emergence of resistance, etc., are outlined along with recent advances and future opportunities for the development of more promising next-generation ADCs.

Abstract LB218: Developing a bispecific anti-ROR1 antibody drug conjugate for hematological and solid tumor treatment

Abstract Developing a bispecific anti-ROR1 Antibody Drug Conjugate for hematological and solid tumor treatment Receptor tyrosine kinase ROR1 is a type I transmembrane protein belongs to the ROR family members. ROR1 is a receptor for Wnt family signaling molecules Wnt5a and is a key regulator of normal cellular process, including cell proliferation, survival, and migration. It is also involved in the development and progression of many types of cancer. Although being an oncofetal protein with limited expression in most of the normal tissues, ROR1 is expressed abnormally in various hematological and solid cancers, making it a highly attractive target for antibody-drug conjugate (ADC) therapy. The current clinical results of ROR1 ADC have been promising in treating patients with relapsed and/or refractory (R/R) hematologic malignancies. Utilizing our unique and innovated linker platform, we screened many anti-ROR1 ADCs, with defined DAR=4. Those unique ADCs consist of a humanized monoclonal antibody (mAb against single epitope) or a bispecific antibody (BsAb against two epitopes), stably conjugated to an antimitotic agent. The bispecific mAbs that target to two different epitopes of ROR1, are superior to those antibodies that target to single epitope in the binding to ROR1-expressing tumor cells, the induction of tumor cell death and anti-tumor immunity. Our novel linker structure prevents payloads from coming off of the antibody during the circulation, significantly reduced the off-target toxicity. In vitro and In vivo studies demonstrated the antitumor activity of anti-ROR1 ADCs outperformed the lead anti-ROR1 ADC currently in phase II/IIl trial, providing a promising treatment for hematological and solid cancers with a better safety profile and a larger therapeutic window. The lead candidate molecule, BR111A will start the preclinical studies soon. Citation Format: Xiaobei Zhao, Jie Zhu, Zhenhua Wu, Jing Li, yaqiong zhou, Lei Nie, Gang Chen. Developing a bispecific anti-ROR1 antibody drug conjugate for hematological and solid tumor treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB218.

Pharmacokinetics and Pharmacodynamics of Antibody-Drug Conjugates Administered via Subcutaneous and Intratumoral Routes.

We hypothesize that different routes of administration may lead to altered pharmacokinetics/pharmacodynamics (PK/PD) behavior of antibody-drug conjugates (ADCs) and may help to improve their therapeutic index. To evaluate this hypothesis, here we performed PK/PD evaluation for an ADC administered via subcutaneous (SC) and intratumoral (IT) routes. Trastuzumab-vc-MMAE was used as the model ADC, and NCI-N87 tumor-bearing xenografts were used as the animal model. The PK of multiple ADC analytes in plasma and tumors, and the in vivo efficacy of ADC, after IV, SC, and IT administration were evaluated. A semi-mechanistic PK/PD model was developed to characterize all the PK/PD data simultaneously. In addition, local toxicity of SC-administered ADC was investigated in immunocompetent and immunodeficient mice. Intratumoral administration was found to significantly increase tumor exposure and anti-tumor activity of ADC. The PK/PD model suggested that the IT route may provide the same efficacy as the IV route at an increased dosing interval and reduced dose level. SC administration of ADC led to local toxicity and reduced efficacy, suggesting difficulty in switching from IV to SC route for some ADCs. As such, this manuscript provides unprecedented insight into the PK/PD behavior of ADCs after IT and SC administration and paves the way for clinical evaluation of these routes.

Abstract P6-04-03: Computational pathology based HER2 expression quantification in HER2-low breast cancer

Abstract Background HER2 directed therapies for breast cancer (BC) rely on accurate estimation of HER2 expression by pathologist scoring of immunohistochemically (IHC) stained tissue according to ASCO/CAP guidelines Emerging HER2-targeted antibody drug conjugates (ADCs) like trastuzumab deruxtecan (T-DXd), have demonstrated efficacy in the HER2-low (IHC 1+ or IHC 2+/ISH-) population (Modi, NEJM 2022). A deeper understanding of the spectrum of HER2 expression and its spatial distribution could provide insights about the mode of action of ADCs, including potential bystander activity. Computational pathology-based methods like Quantitative Continuous Scoring (QCS) can help here by objectively quantifying HER2 expression levels on a per cell basis from digitized HER2 IHC slides (Gustavson, SABCS 2020). We applied QCS to a cohort of HER2-negative (HER2-neg) patients (pts) from a retrospective study (NCT04807595) to quantify the prevalence of HER2 expression in this population and investigate the relationship with manual scoring. Methods To analyze the prevalence of HER2 expression in the HER2-neg population, we used available digital images (N=207 pts) from retrospectively rescored HER2 slides from tumors categorized as HER2-low or IHC 0 (IHC 0 or >0< 1+). QCS algorithm was applied to perform an instance segmentation of each tumor cell into the membrane, cytoplasmic and nuclear sub-compartments. HER2 expression levels on the membrane were estimated from a Hue-Saturation-Density model (Van der Laak, JQCS 2000) in terms of optical density (OD). Descriptive statistics and spatial modelling were used to aggregate cell-level information to a slide level score using the membrane OD values and tumor cell locations. A novel Spatial Proximity Score (SPS) was used to mathematically model the proportion of tumor cells that could potentially be targeted either directly or via bystander activity of ADCs. The analysis is ongoing, complete results with additional patient data to be presented. Analytical validation of the QCS algorithm demonstrated high correlation between OD values as measured on the automatically detected membranes from QCS and those measured on consolidated manual membrane annotations (N=2157 cells) from three pathologists (R = 0.993). This is very similar to the correlation observed between individual pathologists (R = 0.995). Results In the analyzed cohort (N=207), median OD of HER2-low tumors was significantly higher compared to IHC 0 tumors (one-sided Wilcoxon p-value < 0.001). A significant increase of OD values was observed for increasing IHC categories from 0 through >0 < 1+ and 1+ to 2+/ISH- (one-sided Jonckheere-Terpstra p-value < 0.001). OD values within each IHC category showed considerable variability, particularly in IHC 1+ and IHC 2+. In 49% of pts (N=101), greater than 88% of tumor cells expressed HER2 at any intensity (OD≥10). Among the remaining 106 pts, the number of potentially ADC-susceptible cells (within 25μm radius of HER2 expressing cells) as estimated by SPS was at least double the amount estimated by single cell-based scores alone in 45 cases (42%) and increased by at least 50% in another 12 cases (11%). Conclusions Computational approaches such as QCS can help us to objectively characterize the spectrum and spatial distribution of HER2 expression. These mathematical models contribute to our understanding of potential mechanisms of action of ADCs. While this study confirmed a general association of QCS-based scores with manual IHC categories, we also saw considerable variation, as some IHC 1+ or 2+ samples had low OD. Building on these and other promising initial results (Gustavson et al, SABCS 2020), we will further explore clinical relevance of QCS-based scoring. Eventually, digital scoring may be able to define data-driven signatures to select HER2-low pts that might benefit from HER2 targeted therapies. Citation Format: Andreas Spitzmüller, Ansh Kapil, Anatoliy Shumilov, Jessica Chan, Lemonia Konstantinidou, Zonera Hassan, Mark Gustavson, Danielle Carroll, Della Varghese, Gareth D. James, Akira Moh, Andrew Livingston, Victoria de Giorgio-Miller. Computational pathology based HER2 expression quantification in HER2-low breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-04-03.

Stability assessment of Polatuzumab vedotin and Brentuximab vedotin using different analytical techniques

Antibody-drug conjugates (ADC) are considered to be fast-growing innovative biopharmaceuticals. The science used for conjugating potent cytotoxic payload to the targeted monoclonal antibody through a chemical linker has played a great value in the area of oncology treatment. In this study; Polatuzumab vedotin (POLA) and Brentuximab vedotin (SGN-35) were subjected to various stress conditions enclosing different pH, thermal stress, agitation, and successive cycles of freeze and thaw in order to produce potential degradation by-products and guarantee the appropriateness of the applied testing protocol. Different analytical techniques were established and validated to be used in the quantitation of the degraded products from different perspectives. The formation of ADC aggregates and fragments was monitored using SE-HPLC as well as dynamic light scattering (DLS). The drug antibody ratio (DAR) and ADC conjugation profile were determined using hydrophobic interaction chromatography (HIC-HPLC). In addition to performing a statistical interpretation of HIC-HPLC results by principal component analysis (PCA) to explicate the obtained data. Also, the quantity of the unconjugated toxic drug was quantified using RP-HPLC. Testing the binding activity of ADC to their target receptor ADC was conducted using ELISA. Results presented that used assay protocol had worked as a complementary design for characterization and stability assessment of the used ADC. Variances in the stability profile of both products were observed which could be attributed to the usage of different formulation buffers. This highlighted the importance of using multiple techniques for the assessment of the quality attributes of such sophisticated products. The analytical assay protocol should be used for the evaluation of the quality and stability of several ADC.

A Novel Antibody-Drug Conjugate Targeting CCR7 in Hematologic Malignancies

Introduction: CC-chemokine receptor 7 (CCR7) is expressed in lymphoid malignancies and is therefore an attractive target for antibody-drug conjugates (ADCs). JBH492 is a novel, CCR7-targeting ADC, comprised of a humanized anti-CCR7 IgG1 antibody, conjugated in a site-specific manner to the maytansinoid microtubule inhibitor DM4 via a cleavable linker. Methods: CCR7 expression was investigated in human and cynomolgus monkey normal tissue microarrays (TMA) by in situ hybridization (ISH). CCR7 expression across multiple malignancies was investigated by RNA sequencing (RNAseq). The cytotoxic ADC activity of JBH492 was evaluated in vitro in a CellTiter-Glo viability assay. To characterize the impact of the ADC on the CCL19/CCR7 axis, p-ERK was measured as a downstream signaling event of CCL19-mediated CCR7 pathway activation. The in vivo efficacy of JBH492 was investigated in multiple preclinical models of lymphoid malignancies, chosen to cover a range of various CCR7 expression levels, including a panel of 11 DLBCL patient derived xenograft (PDX) models. The safety of JBH492 was assessed in repeat dose toxicity studies conducted in cynomolgus monkeys. Results: RNAseq and flow cytometry reveal high CCR7 expression in lymphoid neoplasms, including chronic lymphocytic leukemia (CLL), B-cell and T-cell non-Hodgkin's lymphoma (NHL), with very limited expression in healthy tissues. Preclinical characterization of JBH492 demonstrates potent, target-dependent cytotoxic activity. In vitro binding studies support avidity-driven binding of JBH492 to CCR7-high tumor cells compared to CCR7-low healthy immune cells. Mechanistic studies of JBH492 suggest a dual mechanism of action, including payload-mediated cytotoxicity, and blockade of ligand-induced CCR7 signaling through antibody antagonistic functionality. In vivo studies showed robust and durable efficacy in multiple clinically relevant lymphoma models. JBH492 achieved PR or CR in 7/11 DLBCL PDX models (response rate ~64%). Nonclinical toxicology studies indicate a favorable safety profile with no notable changes in circulating immune cell populations. Conclusions: Our translational data support the hypothesis that JBH492 may have the potential to become a promising first-in-class ADC for the treatment of CCR7-expressing lymphoid malignancies. The first-in-human clinical trial in patients with refractory/relapsed CLL and non-Hodgkin's lymphoma is currently ongoing (NCT04240704).

Abstract 1755: IKS03, a CD19-targeted antibody drug conjugate with enhanced efficacy and tolerability for treatment of B-cell lymphomas

Abstract Background: Lymphoma is the most common hematological malignancy with non-Hodgkin B-cell lymphomas (NHL), including those with high unmet clinical need such as relapsed/refractory Diffuse Large B Cell Lymphoma (DLBCL), and Mantle-Cell Lymphoma (MCL), representing 90% of all lymphoma cases. CD19 is an attractive target for antibody-directed lymphoma therapies as it is expressed in most B cell malignancies, with normal tissue expression limited to B-cells thus reducing any on-target toxicity concerns. Antibody Drug Conjugates (ADCs) are the focus of intense interest as a means to provide selective tumor killing with increased efficacy and less toxicity than standard of care chemotherapies. IKS03 is an ADC comprised of an anti-CD19 antibody conjugated to a proprietary DNA-crosslinking PBD prodrug and includes a tumor-selective glucuronide-trigger technology for payload release and activation. ADC activity requires processing by beta-glucuronidase, a lysosomal enzyme often upregulated in tumor cells, while normal tissues with low levels of the enzyme are less able to process the ADC and are differentially spared. Methods: IKS03 was generated via chemo-enzymatic bioconjugation at defined sites on the antibody yielding an ADC with a drug to antibody ratio of 2. In vivo efficacy was evaluated in CD19-expressing cell line-derived xenograft models in mice including Farage (DLBCL, Germinal Centre B-cell subtype), OCI-LY10 (DLBCL, Activated B-Cell subtype), Granta-519 (MCL) and Ramos (Burkitt’s lymphoma). Activity was compared to benchmark ADCs known to have demonstrated clinical efficacy. Efficacy was also assessed in low passage DLBCL patient-derived xenograft models of known genomic profile. Toxicology studies were conducted in cynomolgus monkeys with immunophenotyping by flow cytometry included to quantify the level of normal B-cells following IKS03 administration. Results: IKS03 is highly effective in causing tumor regressions in DLBCL models at doses that are well tolerated. Complete regressions were observed with a single dose of 0.1 mg/kg in the Farage xenograft model. IKS03 is also highly active in the Granta-519 MCL model, with complete regressions observed with a single dose of 0.1 mg/kg. Tumor regression was observed in a high-grade triple-hit lymphoma PDX model with a single 0.3 mg/kg dose. IKS03 was tolerated in monkeys at the highest dose tested of 1.5 mg/kg (single dose). IKS03 cross reacts with monkey CD19 and reduced B-cell depletion was observed in relation to comparator agents, even at doses much greater (1.5 mg/kg) than that needed for complete responses in B-cell lymphoma mouse models (0.1 mg/kg). Conclusion: Preclinical data demonstrates that IKS03’s advanced ADC design results in an increased therapeutic margin compared to traditional ADCs with DNA-crosslinking payloads, with increased efficacy and decreased toxicity. Citation Format: Jenny Thirlway, Adam Lodge, Daniel J. Williamson, Justyna Mysliwy, Jutta Deckert, Xavier Chauchet, Laura Cons, Yun-Hee Park, Hyun-Min Ryu, Na Ra Han, Ho Young Song, Chul-Woong Chung, Robert J. Lutz. IKS03, a CD19-targeted antibody drug conjugate with enhanced efficacy and tolerability for treatment of B-cell lymphomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1755.

Phase 2 trial of tucatinib plus trastuzumab deruxtecan in patients with HER2+ locally advanced or metastatic breast cancer with and without brain metastases (HER2CLIMB-04, trial in progress).

TPS1111 Background: Tucatinib is an oral reversible small-molecule tyrosine kinase inhibitor highly selective for human epidermal growth factor receptor 2 (HER2). Tucatinib is approved in the US for use in combination with trastuzumab and capecitabine in adult patients with HER2+ metastatic breast cancer (MBC), with and without brain metastases, who have received ≥1 prior anti–HER2-based regimens in the metastatic setting. Trastuzumab deruxtecan (T-DXd), an antibody–drug conjugate (ADC) comprising a HER2-directed monoclonal antibody conjugated to a topoisomerase I inhibitor payload, is also approved in the US for patients with HER2+ MBC. In HER2+ breast cancer (BC) xenograft models, tucatinib increased the antitumor activity of a HER2-directed ADC comprising a HER2-directed monoclonal antibody conjugated with 8 exatecan moieties (T-Ex) when compared to T-Ex alone (Kulukian et al 2019). While significant advances have been made in the treatment of patients with HER2+ BC, treatment of metastatic disease remains a clinical challenge due to limited treatment options. Methods: HER2CLIMB-04 (NCT04539938) is a single-arm, open-label, multicenter, phase 2 study evaluating the efficacy and safety of tucatinib plus T-DXd in previously treated patients aged ≥18 years with unresectable, locally advanced, or metastatic (LA/M) HER2+ BC. Patients must have prior treatment with a taxane and trastuzumab (with or without pertuzumab) in the LA/M setting or progressed within 6 months after neoadjuvant or adjuvant treatment involving a regimen including a taxane and trastuzumab (with or without pertuzumab). Patients with brain metastases, including active brain metastases, may be enrolled. A safety lead-in portion of the study with 10 patients who were followed for at least 1 cycle has been completed. This portion of the study demonstrated a manageable safety profile so the trial will enroll approximately 60 response-evaluable patients (including the 10 patients from the safety lead-in), evenly distributed between patients with and without brain metastases. The primary endpoint is confirmed objective response rate (cORR) by investigator assessment per RECIST 1.1. Secondary endpoints are progression-free survival (PFS), duration of response (DOR), disease control rate (DCR) by investigator assessment per RECIST 1.1, overall survival, and safety. Exploratory endpoints will include cORR, PFS, DCR, and DOR by independent central review per RECIST 1.1, pharmacokinetic analyses, biomarker analyses, and changes in patient-reported outcomes. Efficacy and safety will be summarized with descriptive statistics. Enrollment in the US began in late 2020. Clinical trial information: NCT04539938.

Bystander effect of antibody-drug conjugates: fact or fiction?

Summarizing the current preclinical and clinical evidence about bystander effect of antibody-drug conjugates (ADCs) in solid tumors. One of the main challenges of treating solid tumors with ADCs is the heterogeneous expression of the target antigen (Ag), which however may be overcome by the so-called bystander killing effect. This unique, but still debated, feature of certain ADCs is represented by the unintentional payload diffusion from Ag-positive tumor cells to adjacent Ag-negative tumor cells. Some pharmacological characteristics, such as a hydrophobic payload or a cleavable linker, seem to play a major role in this effect. Abundant preclinical evidence of the bystander effect has emerged, and the clinical activity of ADCs in tumors with a heterogeneous Ag expression suggests the relevance of this feature. Additional studies are required to investigate if the bystander effect is necessary for achieving a solid activity with ADCs.

Abstract OT1-13-01: HER2CLIMB-04: phase 2 trial of tucatinib + trastuzumab deruxtecan in patients with HER2+ locally advanced or metastatic breast cancer with and without brain metastases (trial in progress)

Abstract Background Tucatinib is an oral, reversible, small-molecule tyrosine kinase inhibitor highly selective for HER2 with minimal inhibition of the human epidermal growth factor receptor. Tucatinib is approved in the US for use in combination with trastuzumab and capecitabine in patients with HER2+ metastatic breast cancer, with and without brain metastases, who have received 1 or more prior anti-HER2-based regimens in the metastatic setting. Trastuzumab deruxtecan (T-DXd), an antibody-drug conjugate (ADC) comprising a HER2-directed monoclonal antibody conjugated to a topoisomerase I inhibitor payload, is approved in the US for patients with HER2+ metastatic breast cancer who have received 2 or more prior anti-HER2-based regimens in the metastatic setting. In HER2+ breast cancer xenograft models, tucatinib increased the antitumor activity of a HER2-directed ADC comprising a HER2-directed monoclonal antibody conjugated with 8 exatecan moieties (T-Ex) when compared to T-Ex alone (Kulukian, et al. (2019). Abstract P1-18-09. Proceedings of San Antonio Breast Cancer Symposium, December 10-14, 2019). While significant advances have been made in the treatment of patients with HER2+ breast cancer, treatment of metastatic disease remains a clinical challenge for which options are limited, particularly in patients with brain metastases. The HER2CLIMB-04 study is evaluating the efficacy and safety of tucatinib in combination with T-DXd in patients with HER2+ metastatic breast cancer following progression on 2 or more HER2-directed regimens in the metastatic setting. Trial Design HER2CLIMB-04 (NCT04539938) is a single-arm, open-label, multicenter, phase 2 study of tucatinib in combination with T-DXd in previously treated patients aged ≥18 years with unresectable, locally advanced, or metastatic HER2+ breast cancer. Patients with brain metastases, including active brain metastases, may be enrolled. A safety lead-in portion of the study will enroll 10 patients who will be followed for at least 1 cycle. If tucatinib combined with T-DXd has a manageable safety profile, the trial will enroll approximately 60 response-evaluable patients (including the 10 patients from the safety lead-in), approximately evenly distributed between patients with and without brain metastases. The primary endpoint is confirmed objective response rate (cORR) by investigator assessment per Response Evaluation Criteria in Solid Tumors (RECIST) 1.1. Secondary endpoints are progression-free survival (PFS), duration of response (DoR), disease control rate (DCR) by investigator assessment per RECIST 1.1, OS, and safety. Exploratory endpoints will include cORR, PFS, DCR, and DoR by independent central review per RECIST 1.1, pharmacokinetic analyses, biomarker analyses, and changes in patient-reported outcomes using the European Quality of Life 5-Dimension 5-Level instrument. Efficacy and safety will be summarized with descriptive endpoints to describe continuous variables. For response rates, the 2-sided exact confidence interval using the Clopper-Pearson method will be calculated. Enrollment began in late 2020 at approximately 30 study sites in the US. Citation Format: Erika Hamilton, Lisa Carey, Jorge Ramos, Yiyi Chen, Ian Krop. HER2CLIMB-04: phase 2 trial of tucatinib + trastuzumab deruxtecan in patients with HER2+ locally advanced or metastatic breast cancer with and without brain metastases (trial in progress) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT1-13-01.

Antibody-drug conjugates: beyond current approvals and potential future strategies.

The recent approvals for antibody-drug conjugates (ADCs) in multiple malignancies in recent years have fuelled the ongoing development of this class of drugs. These novel agents combine the benefits of high specific targeting of oncogenic cell surface antigens with the additional cell kill from high potency cytotoxic payloads, thus achieving wider therapeutic windows. This review will summarise the clinical activity of ADCs in tumour types not covered elsewhere in this issue, such as gastrointestinal (GI) and genitourinary (GU) cancers and glioblastoma (GBM). In addition to the ongoing clinical testing of existing ADCs, there is substantial preclinical and early phase testing of newer ADCs or ADC incorporating strategies. This review will provide selected insights into such future development, focusing on the development of novel ADCs against new antigen targets in the tumour microenvironment (TME) and combination of ADCs with immuno-oncology (IO) agents.

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.

Benefits and challenges of antibody drug conjugates as novel form of chemotherapy

Antibody drug conjugates (ADCs) are an emerging therapeutic modality for targeted cancer treatment. They represent the unique amalgamation of chemotherapy and immunotherapy. ADCs comprise of monoclonal antibodies linked with drugs (payloads) through a chemical linker designed to deliver the cytotoxic moiety to the cancer cells. The present paper is a review of recent clinical advances of each component of ADCs (antibody/linker/payload) and how the individual component influences the activity of ADCs. The review discusses opportunities for improving ADCs efficiency and ways to have a better antibody-based molecular platform, which could substantially increase chemotherapy outcomes. This review casts an outlook on how ADCs enhancement in terms of their pharmacokinetics, therapeutic indexes and safety profiles can overcome the prevailing challenges like drug resistance in cancer treatment. A novel strategy of augmenting antibodies with nanoparticles anticipates a huge success in terms of targeted delivery of drugs in several diseases. Antibody conjugated nanoparticles (ACNPs) are a very promising strategy for the cutting-edge development of chemo/immunotherapies for efficient delivery of payloads at the targeted cancer cells. The avenues of a high drug to antibody ratio (DAR) owing to the selection of broad chemotherapy payloads, regulating drug release eliciting higher avidity of ACNPs over ADCs will be the modern immunotherapeutics. ACNPs carry immense potential to mark a paradigm shift in cancer chemotherapy that may be a substitute for ADCs.

Antibody-drug conjugates: Smart chemotherapy delivery across tumor histologies.

As distinct cancer biomarkers have been discovered in recent years, a need to reclassify tumors by more than their histology has been proposed, and therapies are now tailored to treat cancers based on specific molecular aberrations and immunologic markers. In fact, multiple histology-agnostic therapies are currently adopted in clinical practice for treating patients regardless of their tumor site of origin. In parallel with this new model for drug development, in the past few years, several novel antibody-drug conjugates (ADCs) have been approved to treat solid tumors, benefiting from engineering improvements in the conjugation process and the introduction of novel linkers and payloads. With the recognition that numerous surface targets are expressed across various cancer histologies, alongside the remarkable activity of modern ADCs, this drug class has been increasingly evaluated as suitable for a histology-agnostic expansion of indication. For illustration, the anti-HER2 ADC trastuzumab deruxtecan has demonstrated compelling activity in HER2-overexpressing breast, gastric, colorectal, and lung cancer. Examples of additional novel and potentially histology-agnostic ADC targets include trophoblast cell-surface antigen 2 (Trop-2) and nectin-4, among others. In the current review article, the authors summarize the current approvals of ADCs by the US Food and Drug Administration focusing on solid tumors and discuss the challenges and opportunities posed by the multihistological expansion of ADCs.

Development of bifunctional anti-PD-L1 antibody MMAE conjugate with cytotoxicity and immunostimulation

In recent years, tumor immunotherapy, especially the combination of PD1/PD-L1 inhibitors and chemotherapy, has developed rapidly. However, the systemic side effects induced by chemotherapy remain a crucial problem that needs to be addressed. Antibody drug conjugates (ADCs) are exceptional target-specific prodrugs that greatly improve the therapeutic window of chemotherapy drugs. Therefore, designing PD-L1-targeting ADCs is an interesting research project. In this study, we confirmed for the first time that the commercial anti-PD-L1 antibody Atezolizumab has better endocytosis efficiencies than Avelumab, and was more suitable for ADC design. Then, the most popular cytotoxic payload MMAE was conjugated to Atezolizumab via a classical dipeptide (valine-alanine) linker to generate a bifunctional PD-L1 ADC (ADC 3). An in vitro cytotoxicity test indicated the potent tumor cell inhibitory activity of ADC 3, with EC50 values of 9.75 nM to 11.94 nM. In addition, a co-culture of PBMCs in vitro proved that ADC 3 retained the immune activation effect of the Atezolizumab antibody. Moreover, ADC 3 exhibited a higher tumor inhibition rate and tumor regression rate in humanized immune system mice. To the best of our knowledge, this is the most active PD-L1-ADC reported thus far, which may promote the development of immunotherapy and novel ADCs.

Abstract 1773: Tumor cell-intrinsic STING pathway activation leads to robust induction of Type III Interferons and contributes to the anti-tumor activity elicited by STING agonism

Abstract STING pathway plays a critical role in inducing anti-tumor immunity by upregulating Type 1 Interferon (IFN) and IFN-stimulated genes within the tumor microenvironment in response to cytosolic nucleic acid ligands. Therefore, the STING pathway agonism has emerged as a potential therapeutic mechanism to stimulate an anti-tumor innate immune response. Intratumorally injected free STING-agonists that are currently being evaluated in the clinic by others have shown limited effects in non-injected lesions. Antibody-drug conjugates (ADCs) constitute a proven therapeutic modality that enables tumor-targeted drug delivery with systemic administration. We have previously demonstrated that the tumor cell-intrinsic STING pathway is activated in the presence of cues from immune cells and contributes to the anti-tumor activity of tumor cell-targeted Immunosynthen STING-agonist ADCs, in which a STING-agonist payload is conjugated to a tumor cell-targeting antibody. Here we investigated the nature of the STING pathway activation in tumor cells and its contribution to the anti-tumor activity elicited by STING agonism. Leveraging ADCs with a wild type (wt) or mutant Fc (deficient in Fcγ receptor -FcγR- binding), we delivered a STING-agonist simultaneously to tumor-resident immune and cancer cells or only to cancer cells through FcγR-mediated and/or tumor antigen-mediated ADC internalization. We utilized these ADCs in in vivo human tumor xenograft models and STING wt or knock out (ko) cancer cell:immune cell co-cultures and evaluated gene expression, cytokine production, and anti-tumor activities induced by STING-agonist ADCs. Surprisingly, Nanostring analysis of the human tumor xenografts from mice treated with tumor cell-targeted STING-agonist ADCs revealed human tumor cell-specific activation of Type III IFNs. In human cancer cell:immune cell co-cultures, treatment with tumor cell-targeted STING-agonist ADCs also led to marked upregulation of Type III IFNs, which was significantly reduced in STING ko cancer cell:immune cell co-cultures, suggesting that the cancer cells may contribute majority of the Type III IFNs downstream of STING pathway activation. Blocking Type III IFNs with neutralizing antibodies in cancer cell:immune cell co-cultures inhibited the production of key cytokines, including Type I IFN, and nearly abolished tumor cell-killing in response to STING-agonist ADC treatment, indicating that the Type III IFNs play an important role in the anti-tumor activity induced by STING activation. These studies reveal a previously underappreciated mechanism of STING agonist anti-tumor activity. The ability of tumor cell-targeted STING-agonist ADCs to activate STING in both tumor cells and in tumor-resident immune cells may represent a significant therapeutic advantage of an Immunosynthen ADC approach to STING agonism. Citation Format: Naniye Malli Cetinbas, Travis Monnell, Kalli Catcott, Winnie Lee, Pamela Shaw, Kelly Slocum, Kenneth Avocetien, Keith Bentley, Susan Clardy, Brian Jones, Eoin Kelleher, Rebecca Mosher, Joshua D. Thomas, Dorin Toader, Jeremy Duvall, Raghida A. Bukhalid, Marc Damelin, Timothy B. Lowinger. Tumor cell-intrinsic STING pathway activation leads to robust induction of Type III Interferons and contributes to the anti-tumor activity elicited by STING agonism [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1773.

Abstract PS10-08: Tucatinib potentiates the activity of the antibody-drug conjugate T-DM1 in preclinical models of HER2-positive breast cancer

Abstract Background: Tucatinib is an orally administered, reversible, highly specific HER2 tyrosine kinase inhibitor recently approved by the FDA in combination with trastuzumab and capecitabine for adult patients with advanced unresectable or metastatic HER2-positive breast cancer (mBC), including patients with brain metastases, that have failed at least one anti-HER2 regimen in the metastatic setting. In a phase IB clinical trial, tucatinib in combination with the HER2-targeted antibody-drug conjugate (ADC) ado-trastuzumab emtansine (T-DM1) was well tolerated and demonstrated activity in heavily pre-pretreated patients with HER2-positive mBC (NCT01983501; Borges VF et al., 2018). We previously presented preclinical data that tucatinib increases the activity of trastuzumab-derived ADCs in HER2-positive breast cancer models. Here, we provide mechanistic insight that tucatinib potentiates the activity of T-DM1 by modulating HER2 protein dynamics and facilitating increased cytotoxic maytansinoid drug delivery. Methods: To assess changes to HER2 protein levels upon treatment with tucatinib, HER2-amplified breast cancer cell lines were analyzed by Western blot and quantitative FACS (qFACS). To probe the dynamics of HER2 at the cell surface upon binding to antibody therapeutics, SK-BR-3 cells were incubated with fluorescently labeled trastuzumab to mark HER2 at the cell surface. Cells were imaged over 72 hours to observe the internalization of surface-bound antibody. Concurrent experiments were conducted with trastuzumab labeled with QF01, a quenched fluor which fluoresces only upon lysosomal processing and can serve as a proxy for antibody catabolism. To directly measure the rates of ADC catabolism, lysates were generated from BT-474 cells treated with T-DM1 in the presence or absence of tucatinib over a 72 hour time course, and were analyzed by mass spectrometry for the T-DM1 adduct, Lys-MCC-DM1. Results: In HER2-amplified breast cancer cell lines, treatment with tucatinib increased overall and cell membrane-localized HER2 levels. As demonstrated by internalization assays, tucatinib had an initial effect that increased the dwell time of HER2 at the cell surface of SK-BR-3 cells. At later timepoints, HER2 bound to trastuzumab was internalized and directed towards lysosomes. These data were supported by parallel intracellular Lys-MCC-DM1 measurements, which demonstrated increased concentration of the adduct when TDM-1 was administered in combination with tucatinib. These data provide a mechanistic rationale as to why the co-administration of tucatinib with T-DM1 in vitro was synergistic by isobologram analysis, and why the combination of tucatinib with T-DM1 was more effective in vivo than either single agent alone in BT-474 xenografts and in PDX models tested, producing a higher proportion of partial or complete tumor regressions. Conclusions: The described preclinical in vitro and in vivo data of simultaneous dual HER2 inhibition with tucatinib and T-DM1, along with the results of the phase IB/2 clinical trial demonstrating preliminary safety and efficacy of the combination, warrant further clinical development of tucatinib in combination with T-DM1. These results also support the evaluation of tucatinib in combination with other HER2-targeted ADCs in patients with HER2-positive mBC. Citation Format: Anita Kulukian, Janelle Taylor, Nishi Jain, Devra Olson, Margo Zaval, Robert Thurman, Shawna Hengel, Lauren Farr, Thomas Pires, Scott R. Peterson. Tucatinib potentiates the activity of the antibody-drug conjugate T-DM1 in preclinical models of HER2-positive breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS10-08.

Abstract OT-03-03: SGNLVA-001: A phase 1 open-label dose escalation and expansion study of SGN-LIV1A administered weekly in breast cancer

Abstract Background: LIV-1 is a highly prevalent transmembrane protein in breast cancer cells. Ladiratuzumab vedotin (LV), SGN-LIV1A, is an investigational antibody-drug conjugate (ADC) that targets LIV-1 via a humanized IgG1 monoclonal antibody conjugated to monomethyl auristatin E (MMAE) by a protease-cleavable linker. LV is internalized when it binds LIV-1 on cell surfaces and MMAE is released, which binds tubulin and induces apoptosis. LV has been shown to be active and tolerable in metastatic breast cancer (mBC) at a recommended dose of 2.5 mg/kg every 21 days (Modi 2017). More frequent, fractionated dosing has improved the activity and/or safety of other ADCs. Thus, this study is actively accruing subjects with metastatic triple negative breast cancer (mTNBC; estrogen receptor (ER)/progesterone receptor (PR)/human epidermal growth factor receptor 2 (HER2) receptor-negative) and endocrine-resistant ER+ or PR+ (hormone receptor [HR+])/HER2-negative mBC to test weekly dosing of LV (Days 1, 8, and 15 of every 3-week cycle). Methods: This study is enrolling up to 82 subjects (42 HR+/HER2-negative and 40 mTNBC) into dose escalation and dose expansion cohorts (NCT01969643). Eligible subjects are females ≥18 years old with pathologically and radiologically confirmed metastatic HR+/HER2-negative or mTNBC with at least 1 measurable lesion per RECIST v1.1. Subjects with HR+/HER2-negative disease must have received no more than 1 prior line of cytotoxic chemotherapy in the locally advanced (LA)/mBC setting, either as single agent or combination therapy. Subjects with mTNBC must have received 1 prior line of cytotoxic chemotherapy in the LA/mBC setting. Progression within 6 months of completion of neoadjuvant or adjuvant therapy is considered an LA/mBC regimen. Subjects must have adequate organ function, ECOG status of ≤1, and no ≥ Grade 2 peripheral neuropathy. Subjects with brain lesions must have received definitive treatment of the lesions. Prior therapy with MMAE-containing agents is not allowed. Dose escalation follows the modified toxicity probability interval method (Ji 2010). Dose expansion cohorts will provide data about activity and tolerability. Tumor assessments will be conducted every 2 cycles per RECIST v1.1 and all subjects will be followed for safety. Pharmacokinetics and markers of pharmacodynamics will be assessed. Primary safety endpoint is the incidence of adverse events and dose-limiting toxicities. Key efficacy endpoints include confirmed overall response rate, duration of response, and progression-free survival. Citation Format: Heather C Beckwith, Diana C Medgyesy, Jame Abraham, Rita Nanda, Katherine HR Tkaczuk, Ian E Krop, Lajos Pusztai, Shanu Modi, Monica M Mita, Jennifer M Specht, Sara A Hurvitz, Hyo S Han, Kevin Kalinsky, Sharon Wilks, Joyce O’Shaughnessy, Lowell L Hart, Hope S Rugo, Zahi I Mitri, Phillip M Garfin, Howard A Burris III. SGNLVA-001: A phase 1 open-label dose escalation and expansion study of SGN-LIV1A administered weekly in breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr OT-03-03.

Improving Antibody-Tubulysin Conjugates through Linker Chemistry and Site-Specific Conjugation.

Tubulysins have emerged in recent years as a compelling drug class for delivery to tumor cells via antibodies. The ability of this drug class to exert bystander activity while retaining potency against multidrug‐resistant cell lines differentiates them from other microtubule‐disrupting agents. Tubulysin M, a synthetic analogue, has proven to be active and well tolerated as an antibody‐drug conjugate (ADC) payload, but has the liability of being susceptible to acetate hydrolysis at the C11 position, leading to attenuated potency. In this work, we examine the ability of the drug‐linker and conjugation site to preserve acetate stability. Our findings show that, in contrast to a more conventional protease‐cleavable dipeptide linker, the β‐glucuronidase‐cleavable glucuronide linker protects against acetate hydrolysis and improves ADC activity in vivo. In addition, site‐specific conjugation can positively impact both acetate stability and in vivo activity. Together, these findings provide the basis for a highly optimized delivery strategy for tubulysin M.

Open-label, phase II study of ladiratuzumab vedotin (LV) for advanced gastric and gastroesophageal junction adenocarcinoma (SGNLVA-005, Trial-in-Progress).

TPS256 Background: LIV-1 is a transmembrane protein expressed in a variety of cancer types. SGN-LIV1A, or ladiratuzumab vedotin (LV), is a novel investigational humanized IgG1 antibody-drug conjugate (ADC) directed against LIV-1. LV mediates delivery of monomethyl auristatin E (MMAE), which drives antitumor activity through cytotoxic cell killing and induces immunogenic cell death. In a phase 1 study, LV was tolerable and active in heavily pretreated patients with metastatic breast cancer at a recommended dose of 2.5 mg/kg every 21 days (Modi 2017). More frequent, fractionated dosing has improved the activity and/or safety of other ADCs. Thus, this study is currently evaluating the safety and efficacy of weekly LV dosing (Days 1, 8, and 15 of every 3-week cycle) in different advanced solid tumors with various LIV-1 expression, including advanced gastric and gastroesophageal junction (GEJ) adenocarcinoma, esophageal squamous cell carcinoma, small cell lung cancer (SCLC), non-small cell lung cancer (squamous and nonsquamous), head and neck squamous cell carcinoma, castration resistant prostate cancer, and melanoma. Methods: SGNLVA-005 (NCT04032704) is an open-label, phase 2 study evaluating LV monotherapy in patients with 8 different advanced solid tumors in two parts (administered as a 30 minute intravenous infusion [IV]: Part A LV 2.5 mg/kg IV every 3 weeks [up to n = 72 total]; Part B LV 1.0 or 1.25 mg/kg every 1 week [up to n = 252 total]). The study is enrolling previously treated patients with unresectable locally advanced or metastatic disease. Patients must have measurable disease per RECIST v1.1, an Eastern Cooperative Oncology Group (ECOG) score of 0 or 1, and adequate organ function. Cohort specific inclusion criteria require that patients in the gastric and GEJ adenocarcinoma and esophageal squamous cell carcinoma cohorts must have received and progressed during or after no more than 1 prior line of platinum based cytotoxic chemotherapy. Patients in the gastric and GEJ adenocarcinoma cohort may have received prior anti-programmed cell death (ligand) 1 (anti-PD[L]1) therapy (unless contraindicated), and patients with known human epidermal growth factor receptor 2 (HER2) overexpression must have received prior HER2-targeted therapy. Patients are not preselected based on tumor LIV-1 expression. Tumor samples will be analyzed for correlation between LIV-1 expression and tumor response. Safety and efficacy will be monitored throughout the study. Study objectives include objective response rate (primary); safety and tolerability, disease control rate, duration of response, progression-free and overall survival, and pharmacokinetics and immunogenicity (all secondary); and pharmacodynamics. Study accrual is ongoing in the USA, Italy, South Korea, Taiwan, Australia, and the UK. Clinical trial information: NCT04032704.