Phase I Study of DMOT4039A, an Antibody-Drug Conjugate Targeting Mesothelin, in Patients with Unresectable Pancreatic or Platinum-Resistant Ovarian Cancer

Clinical translation of antibody drug conjugate dosing in solid tumors from preclinical mouse data

Antibody drug conjugates (ADCs) have made impressive strides in the clinic in recent years with 11 Food and Drug Administration approvals, including 6 for the treatment of patients with solid tumors. Despite this success, the development of new agents remains challenging with a high failure rate in the clinic. Here, we show that current approved ADCs for the treatment of patients with solid tumors can all show substantial efficacy in some mouse models when administered at a similar weight-based [milligrams per kilogram (mg/kg)] dosing in mice that is tolerated in the clinic. Mechanistically, equivalent mg/kg dosing results in a similar drug concentration in the tumor and a similar tissue penetration into the tumor due to the unique delivery features of ADCs. Combined with computational approaches, which can account for the complex distribution within the tumor microenvironment, these scaling concepts may aid in the evaluation of new agents and help design therapeutics with maximum clinical efficacy.

A tumor-restricted glycoform of podocalyxin is a highly selective marker of immunologically cold high-grade serous ovarian carcinoma

Introduction

Targeted-immunotherapies such as antibody-drug conjugates (ADC), chimeric antigen receptor (CAR) T cells or bispecific T-cell engagers (eg, BiTE®) all aim to improve cancer treatment by directly targeting cancer cells while sparing healthy tissues. Success of these therapies requires tumor antigens that are abundantly expressed and, ideally, tumor specific. The CD34-related stem cell sialomucin, podocalyxin (PODXL), is a promising target as it is overexpressed on a variety of tumor types and its expression is consistently linked to poor prognosis. However, PODXL is also expressed in healthy tissues including kidney podocytes and endothelia. To circumvent this potential pitfall, we developed an antibody, named PODO447, that selectively targets a tumor-associated glycoform of PODXL. This tumor glycoepitope is expressed by 65% of high-grade serous ovarian carcinoma (HGSOC) tumors.

Methods

In this study we characterize these PODO447-expressing tumors as a distinct subset of HGSOC using four different patient cohorts that include pre-chemotherapy, post-neoadjuvant chemotherapy (NACT) and relapsing tumors as well as tumors from various peritoneal locations.

Results

We find that the PODO447 epitope expression is similar across tumor locations and negligibly impacted by chemotherapy. Invariably, tumors with high levels of the PODO447 epitope lack infiltrating CD8+ T cells and CD20+ B cells/plasma cells, an immune phenotype consistently associated with poor outcome.

Discussion

We conclude that the PODO447 glycoepitope is an excellent biomarker of immune "cold" tumors and a candidate for the development of targeted-therapies for these hard-to-treat cancers.

Preclinical assessment of a novel human antibody VH domain targeting mesothelin as an antibody-drug conjugate

Mesothelin (MSLN) has been a validated tumor-associated antigen target for several solid tumors for over a decade, making it an attractive option for therapeutic interventions. Novel antibodies with high affinity and better therapeutic properties are needed. In the current study, we have isolated and characterized a novel heavy chain variable (VH) domain 3C9 from a large-size human immunoglobulin VH domain library. 3C9 exhibited high affinity (KD [dissociation constant] <3 nM) and binding specificity in a membrane proteome array (MPA). In a mouse xenograft model, 3C9 fused to human IgG1 Fc was detected at tumor sites as early as 8 h post-infusion and remained at the site for over 10 days. Furthermore, 3C9 fused to a human Fc domain drug conjugate effectively inhibited MSLN-positive tumor growth in a mouse xenograft model. The X-ray crystal structure of full-length MSLN in complex with 3C9 reveals interaction of the 3C9 domains with two distinctive residue patches on the MSLN surface. This newly discovered VH antibody domain has a high potential as a therapeutic candidate for MSLN-expressing cancers.

Understanding the promising role of antibody drug conjugates in breast and ovarian cancer

A nascent category of anticancer therapeutic drugs called antibody-drug conjugates (ADCs) relate selectivity of aimed therapy using chemotherapeutic medicines with high cytotoxic power. Progressive linker technology led to the advancement of more efficacious and safer treatments. It offers neoteric as well as encouraging therapeutic strategies for treating cancer. ADCs selectively administer a medication by targeting antigens which are abundantly articulated on the membrane surface of tumor cells. Tumor-specific antigens are differently expressed in breast and ovarian cancers and can be utilized to direct ADCs. Compared to conventional chemotherapeutic drugs, this approach enables optimal tumor targeting while minimizing systemic damage. A cleavable linker improves the ADCs because it allows the toxic payload to be distributed to nearby cells that do not express the target protein, operating on assorted tumors with dissimilar cell aggregation. Presently fifteen ADCs are being studied in breast and ovarian carcinoma preclinically, and assortment of few have already undergone promising early-phase clinical trial testing. Furthermore, Phase I and II studies are investigating a wide variety of ADCs, and preliminary findings are encouraging. An expanding sum of ADCs will probably become feasible therapeutic choices as solo agents or in conjunction with chemotherapeutic agents. This review accentuates the most recent preclinical findings, pharmacodynamics, and upcoming applications of ADCs in breast and ovarian carcinoma.

Value of Antibody Drug Conjugates for Gynecological Cancers: A Modern Appraisal Following Recent FDA Approvals

Antibody drug conjugates (ADCs) are a new class of targeted anti-cancer therapies that combine a monoclonal tumor surface receptor-targeting antibody with a highly cytotoxic molecule payload. They enable delivery of cytotoxic therapy more directly to tumor cells and minimize delivery to healthy tissues. This review summarizes the existing literature about ADC therapies approved for use in gynecologic malignancies, relevant preclinical studies, as well as ongoing clinical trials.

Mesothelin-targeting T cell receptor fusion construct cell therapy in refractory solid tumors: phase 1/2 trial interim results

The T cell receptor fusion construct (TRuC) gavocabtagene autoleucel (gavo-cel) consists of single-domain anti-mesothelin antibody that integrates into the endogenous T cell receptor (TCR) and engages the signaling capacity of the entire TCR upon mesothelin binding. Here we describe phase 1 results from an ongoing phase1/2 trial of gavo-cel in patients with treatment-refractory mesothelin-expressing solid tumors. The primary objectives were to evaluate safety and determine the recommended phase 2 dose (RP2D). Secondary objectives included efficacy. Thirty-two patients received gavo-cel at increasing doses either as a single agent (n = 3) or after lymphodepletion (LD, n = 29). Dose-limiting toxicities of grade 3 pneumonitis and grade 5 bronchioalveolar hemorrhage were noted. The RP2D was determined as 1 × 108 cells per m2 after LD. Grade 3 or higher pneumonitis was seen in 16% of all patients and in none at the RP2D; grade 3 or higher cytokine release syndrome occurred in 25% of all patients and in 15% at the RP2D. In 30 evaluable patients, the overall response rate and disease control rate were 20% (13% confirmed) and 77%, respectively, and the 6-month overall survival rate was 70%. Gavo-cel warrants further study in patients with mesothelin-expressing cancers given its encouraging anti-tumor activity, but it may have a narrow therapeutic window. ClinicalTrials.gov identifier: NCT03907852 .

High mesothelin expression by immunohistochemistry predicts improved survival in pleural mesothelioma

AIMS

Mesothelin (MSLN) is a cancer-associated antigen that is overexpressed in malignancies such as mesothelioma, pancreatic and ovarian cancer. It is also a target for novel personalised therapies, including antibodies, antibody-drug conjugates and chimeric antigen receptor T cells. Immunohistochemistry may predict those who would best respond to anti-mesothelin therapies and guide decisions in therapeutic strategy. This study aimed to assess the intensity and distribution of MSLN immunostaining in mesothelioma, and to determine the prognostic value of MSLN expression by histochemical-score (H-score).

METHODS AND RESULTS

The MN1 anti-MSLN antibody was used to stain a formalin-fixed paraffin-embedded tissue microarray of histologically confirmed mesothelioma from 75 consecutive patients who had undergone pleurectomy with or without decortication. MSLN positivity, the staining intensity, distribution of staining and H-score were evaluated. The correlation of H-score with prognosis was investigated. Sixty-six per cent of epithelioid tumours were MSLN-positive (with expression in > 5% tumour cells). Of MSLN-expressing epithelioid tumours, 70.4% had moderate (2+) or strong (3+) intensity MSLN immunostaining, although only 37% of samples had staining in ≥ 50% of tumour cells. In multivariate analysis, MSLN H-score as a continuous variable and an H-score ≥ 33 were independent predictors of improved survival (P = 0.04 and P < 0.001, respectively).

CONCLUSIONS

MSLN expression was more heterogenous in epithelioid mesothelioma than reported previously. Therefore, it would be appropriate to perform an immunohistochemical assessment of MSLN expression to stratify and assess patient suitability for mesothelin-targeted personalised therapies, such as chimeric antigen receptor T cells.

Mass Spectrometry-based Proteomics of Epithelial Ovarian Cancers: a Clinical Perspective

Increasing proteomic studies focused on epithelial ovarian cancer (EOC) have attempted to identify early disease biomarkers, establish molecular stratification, and discover novel druggable targets. Here we review these recent studies from a clinical perspective. Multiple blood proteins have been used clinically as diagnostic markers. The ROMA test integrates CA125 and HE4, while the OVA1 and OVA2 tests analyze multiple proteins identified by proteomics. Targeted proteomics has been widely used to identify and validate potential diagnostic biomarkers in EOCs, but none has yet been approved for clinical adoption. Discovery proteomic characterization of bulk EOC tissue specimens has uncovered a large number of dysregulated proteins, proposed new stratification schemes, and revealed novel targets of therapeutic potential. A major hurdle facing clinical translation of these stratification schemes based on bulk proteomic profiling is intra-tumor heterogeneity, namely that single tumor specimens may harbor molecular features of multiple subtypes. We reviewed over 2500 interventional clinical trials of ovarian cancers since 1990, and cataloged 22 types of interventions adopted in these trials. Among 1418 clinical trials which have been completed or are not recruiting new patients, about 50% investigated chemotherapies. Thirty-seven clinical trials are at phase 3 or 4, of which 12 focus on PARP, 10 on VEGFR, 9 on conventional anti-cancer agents, and the remaining on sex hormones, MEK1/2, PD-L1, ERBB, and FRα. Although none of the foregoing therapeutic targets were discovered by proteomics, newer targets discovered by proteomics, including HSP90 and cancer/testis antigens, are being tested also in clinical trials. To accelerate the translation of proteomic findings to clinical practice, future studies need to be designed and executed to the stringent standards of practice-changing clinical trials. We anticipate that the rapidly evolving technology of spatial and single-cell proteomics will deconvolute the intra-tumor heterogeneity of EOCs, further facilitating their precise stratification and superior treatment outcomes.

Targeting Mesothelin in Solid Tumours: Anti-mesothelin Antibody and Drug Conjugates

PURPOSE OF REVIEW

This review aims to summarise the pathobiological role of mesothelin and the current data on therapeutic antibodies targeting mesothelin in solid tumours.

RECENT FINDINGS

High mesothelin expression is restricted to the pericardium, pleura, peritoneum and tunica vaginalis. Mesothelin does not seem to have any normal biological function in adult normal tissues. Mesothelin is highly expressed in mesothelioma, serous ovarian cancer, pancreatic cancer and some gastric cancer and adenocarcinoma of the lung and is responsible for tumour proliferation, metastasis, resistance to chemotherapy or radiation and evasion of immune system. To date, antibody, antibody drug conjugates and bispecific antibodies with immune checkpoints have been investigated in mesothelin expressing malignancies. After a couple of decades of clinical investigation in antibody targeting mesothelin, the therapeutic benefit is relatively modest. Novel delivery of mesothelin targeting agents, more potent payload in antibody drug conjugates and immune checkpoint inhibitor, may improve therapeutic benefit.

High Homogeneity of Mesothelin Expression in Primary and Metastatic Ovarian Cancer

To study the extent of heterogeneity of mesothelin overexpression in primary ovarian cancers and their peritoneal and lymph node metastases, a tissue microarray (TMA) was constructed from multiple sites of 220 ovarian cancers and analyzed by immunohistochemistry. One tissue core each was taken from up to 18 different tumor blocks per cancer, resulting in a total of 2460 tissue spots from 423 tumor sites (188 primary cancers, 162 peritoneal carcinosis, and 73 lymph node metastases). Positive mesothelin expression was found in 2041 of the 2342 (87%) arrayed tissue spots and in 372 of the 392 (95%) tumor sites that were interpretable for mesothelin immunohistochemistry. Intratumoral heterogeneity was found in 23% of 168 primary cancer sites interpretable for mesothelin and decreased to 12% in 154 peritoneal carcinosis and to 6% in 71 lymph node metastases ( P <0.0001). Heterogeneity between the primary tumor and matched peritoneal carcinosis was found in 16% of 102 cancers with interpretable mesothelin results. In these cancers, the mesothelin status switched from positive in the primary tumor to negative in the peritoneal carcinosis (3 cancers) in or vice versa (2 cancers), or a mixture of positive and negative peritoneal carcinoses was found (11 cancers). No such switch was seen between the mesothelin-interpretable primary tumors and their nodal metastases of 59 cancers, and only 1 mesothelin-positive tumor had a mixture of positive and negative lymph node metastases. In conclusion, mesothelin expression is frequent and highly homogeneous in ovarian cancer.

NAV-001, a high-efficacy antibody-drug conjugate targeting mesothelin with improved delivery of a potent payload by counteracting MUC16/CA125 inhibitory effects

Subsets of tumor-produced cell surface and secreted proteins can bind to IgG1 type antibodies and suppress their immune-effector activities. As they affect antibody and complement-mediated immunity, we call these proteins humoral immuno-oncology (HIO) factors. Antibody-drug conjugates (ADCs) use antibody targeting to bind cell surface antigens, internalize into the cell, then kill target cells upon liberation of the cytotoxic payload. Binding of the ADC antibody component by a HIO factor may potentially hamper ADC efficacy due to reduced internalization. To determine the potential effects of HIO factor ADC suppression, we evaluated the efficacy of a HIO-refractory, mesothelin-directed ADC (NAV-001) and a HIO-bound, mesothelin-directed ADC (SS1). The HIO factor MUC16/CA125 binding to SS1 ADC was shown to have a negative effect on internalization and tumor cell killing. The MUC16/CA125 refractory NAV-001 ADC was shown to have robust killing of MUC16/CA125 expressing and non-expressing tumor cells in vitro and in vivo at single, sub-mg/kg dosing. Moreover, NAV-001-PNU, which contains the PNU-159682 topoisomerase II inhibitor, demonstrated good stability in vitro and in vivo as well as robust bystander activity of resident cells while maintaining a tolerable safety profile in vivo. Single-dose NAV-001-PNU demonstrated robust tumor regression of a number of patient-derived xenografts from different tumor types regardless of MUC16/CA125 expression. These findings suggest that identification of HIO-refractory antibodies to be used in ADC format may improve therapeutic efficacy as observed by NAV-001 and warrants NAV-001-PNU's advancement to human clinical trials as a monotherapy to treat mesothelin-positive cancers.

Preclinical safety profile of RC88-ADC：a novel mesothelin-targeted antibody conjugated with Monomethyl auristatin E

Mesothelin (MSLN) is an attractive therapeutic target for antibody drug conjugates (ADC) because of significant differences in expression pattern between diseased and normal tissues. RC88-ADC is a novel ADC, targeting MSLN, and inhibits tumor growth significantly in mice xenograft models. We performed an 11-week repeated dose toxicity study of RC88-ADC via intravenous injection in Cynomolgus Monkeys with an 8-Week recovery period according to International Conference on Harmonization (ICH) S9 and S6(R1). RC88-ADC was administered to groups of 5 male and 5 female monkeys at dose levels of 2.5, 5, and 10 mg/kg/2 weeks, meanwhile vehicle, naked antibody, small molecule groups were set up as the control. 4 animals died in 10 mg/kg group of RC88-ADC. The clinical symptoms mainly included ocular toxicity, weight loss and food intake decrease in the middle and high dose groups of RC88-ADC. RC88-ADC caused dose-related reversible myelosuppression, manifested as hematologic toxicity, which was consistent with the small molecule toxicity profile of its coupling. The highest non-severely toxic dose of RC88-ADC was 5 mg/kg in monkeys after repeated dosing. Nonetheless, the integrated analysis showed that RC88-ADC demonstrated an acceptable safety profile and provided an improved treatment window. These results pave the way for further investigation of RC88-ADC in humans.

Exploration of the antibody-drug conjugate clinical landscape

The antibody-drug conjugate (ADC) field has undergone a renaissance, with substantial recent developmental investment and subsequent drug approvals over the past 6 y. In November 2022, ElahereTM became the latest ADC to be approved by the US Food and Drug Administration (FDA). To date, over 260 ADCs have been tested in the clinic against various oncology indications. Here, we review the clinical landscape of ADCs that are currently FDA approved (11), agents currently in clinical trials but not yet approved (164), and candidates discontinued following clinical testing (92). These clinically tested ADCs are further analyzed by their targeting tumor antigen(s), linker, payload choices, and highest clinical stage achieved, highlighting limitations associated with the discontinued drug candidates. Lastly, we discuss biologic engineering modifications preclinically demonstrated to improve the therapeutic index that if incorporated may increase the proportion of molecules that successfully transition to regulatory approval.

A review of recent advances on single use of antibody-drug conjugates or combination with tumor immunology therapy for gynecologic cancer

Immune checkpoint inhibitors have made significant progress in the treatment of various cancers. However, due to the low ICI responsive rate for the gynecologic cancer, ICI two-drug combination therapy tends to be a predominant way for clinical treatment. Antibody-drug conjugates, a promising therapeutic modality for cancer, have been approved by the FDA for breast cancer, lymphoma, multiple myeloma and gastric cancer. On September 2021, the FDA granted accelerated approval to tisotumab vedotin for patients with recurrent or metastatic cervical cancer. Currently, the role of therapy of ADCs on gynecologic tumors was also included in medication regimens. Now more than 30 ADCs targeting for 20 biomarkers are under clinical trials in the field, including monotherapy or combination with others for multiple lines of therapy. Some ADCs have been proved to enhance the antitumor immunity effect on both pre-clinical models and clinical trials. Therefore, combination of ADCs and ICIs are expected in clinical trials. In this review, we discuss current development of ADCs in gynecologic oncology and the combination effects of ICIs and ADCs.

Characterization of Mesothelin Glycosylation in Pancreatic Cancer: Decreased Core Fucosylated Glycoforms in Pancreatic Cancer Patients’ Sera

Currently, there are no reliable biomarkers for the diagnosis of pancreatic cancer (PaC). Glycoproteomic approaches that analyze the glycan determinants on specific glycoproteins have proven useful to develop more specific cancer biomarkers than the corresponding protein levels. In PaC, mesothelin (MSLN) is a neo-expressed glycoprotein. MSLN glycosylation has not been described and could be altered in PaC. In this work, we aimed to characterize MSLN glycans from PaC cells and serum samples to assess their potential usefulness as PaC biomarkers. First, we analyzed MSLN glycans from PaC cell lines and then we developed an enzyme-linked lectin assay to measure core fucosylated-MSLN (Cf-MSLN) glycoforms. MSLN glycans from PaC cells were analyzed by glycan sequencing and through Western blotting with lectins. All of the cell lines secreted MSLN, with its three N-glycosylation sites occupied by complex-type N-glycans, which were mainly α2,3-sialylated, core fucosylated and highly branched. The Cf-MSLN glycoforms were quantified on PaC serum samples, and compared with MSLN protein levels. The Cf-MSLN was significantly decreased in PaC patients compared to control sera, while no differences were detected by using MSLN protein levels. In conclusion, Cf-MSLN glycoforms were differently expressed in PaC, which opens the way to further investigate their usefulness as PaC biomarkers.

Mesothelin: An Immunotherapeutic Target beyond Solid Tumors

Simple Summary

This review summarizes the current knowledge on mesothelin’s function, its role in cancer, and opportunities for immunotherapeutic targeting of mesothelin. Immunotherapies including monoclonal antibodies, antibody–drug conjugates, chimeric antigen receptor T and NK-cells, targeted alpha therapies, and bispecific T cell engaging molecules are reviewed. We show future directions for mesothelin targeting in hematological malignancies, including acute myeloid leukemia.

Abstract

Modern targeted cancer therapies rely on the overexpression of tumor associated antigens with very little to no expression in normal cell types. Mesothelin is a glycosylphosphatidylinositol-anchored cell surface protein that has been identified in many different tumor types, including lung adenocarcinomas, ovarian carcinomas, and most recently in hematological malignancies, including acute myeloid leukemia (AML). Although the function of mesothelin is widely unknown, interactions with MUC16/CA125 indicate that mesothelin plays a role in the regulation of proliferation, growth, and adhesion signaling. Most research on mesothelin currently focuses on utilizing mesothelin to design targeted cancer therapies such as monoclonal antibodies, antibody–drug conjugates, chimeric antigen receptor T and NK cells, bispecific T cell engaging molecules, and targeted alpha therapies, amongst others. Both in vitro and in vivo studies using different immunotherapeutic modalities in mesothelin-positive AML models highlight the potential impact of this approach as a unique opportunity to treat hard-to-cure AML.

Antibody-Drug Conjugate Targets, Drugs and Linkers

Antibody-drug conjugates offer the possibility of directing powerful cytotoxic agents to a malignant tumor while sparing normal tissue. The challenge is to select an antibody target expressed exclusively or at highly elevated levels on the surface of tumor cells and either not all or at low levels on normal cells. The current review explores 78 targets that have been explored as antibody-drug conjugate targets. Some of these targets have been abandoned, 9 or more are the targets of FDA-approved drugs, and most remain active clinical interest. Antibody-drug conjugates require potent cytotoxic drug payloads, several of these small molecules are discussed, as are the linkers between the protein component and small molecule components of the conjugates. Finally, conclusions regarding the elements for the successful antibody-drug conjugate are discussed.

Antibody-drug conjugates: Resurgent anticancer agents with multi-targeted therapeutic potential

Antibody-drug conjugates (ADCs) constitute a relatively new group of anticancer agents, whose first appearance took place about two decades ago, but a renewed interest occurred in recent years, following the success of anti-cancer immunotherapy with monoclonal antibodies. Indeed, an ADC combines the selectivity of a monoclonal antibody with the cell killing properties of a chemotherapeutic agent (payload), joined together through an appropriate linker. The antibody moiety targets a specific cell surface antigen expressed by tumor cells and/or cells of the tumor microenvironment and acts as a carrier that delivers the cytotoxic payload within the tumor mass. Despite advantages in terms of selectivity and potency, the development of ADCs is not devoid of challenges, due to: i) low tumor selectivity when the target antigens are not exclusively expressed by cancer cells; ii) premature release of the cytotoxic drug into the bloodstream as a consequence of linker instability; iii) development of tumor resistance mechanisms to the payload. All these factors may result in lack of efficacy and/or in no safety improvement compared to unconjugated cytotoxic agents. Nevertheless, the development of antibodies engineered to remain inert until activated in the tumor (e.g., antibodies activated proteolytically after internalization or by the acidic conditions of the tumor microenvironment) together with the discovery of innovative targets and cytotoxic or immunomodulatory payloads, have allowed the design of next-generation ADCs that are expected to possess improved therapeutic properties. This review provides an overview of approved ADCs, with related advantages and limitations, and of novel targets exploited by ADCs that are presently under clinical investigation.

Phase I/IIa Trial of BMS-986148, an Anti-mesothelin Antibody-drug Conjugate, Alone or in Combination with Nivolumab in Patients with Advanced Solid Tumors

PURPOSE

To assess the safety and tolerability of BMS-986148, a mesothelin-directed antibody-drug conjugate (ADC) ± nivolumab, in patients with selected tumors.

PATIENTS AND METHODS

In an international phase I/IIa study [NCT02341625 (CA008-002)], patients received BMS-986148 monotherapy (0.1-1.6 mg/kg intravenously (i.v.) every 3 weeks or 0.4 or 0.6 mg/kg i.v. once weekly; n = 96) or BMS-986148 0.8 mg/kg + nivolumab 360 mg i.v. every 3 weeks (n = 30). The primary endpoint was safety and tolerability.

RESULTS

In CA008-002, the most common (≥ 10%) treatment-related adverse events (TRAEs) included increased aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase. Grade 3/4 TRAEs occurred in 42 patients (49%) receiving BMS-986148 every 3 weeks monotherapy, three (25%) receiving BMS-986148 once-weekly monotherapy, and 10 (33%) receiving BMS-986148 + nivolumab every 3 weeks. Overall, 17 of 126 patients (13%) discontinued because of a TRAE. The MTD of BMS-986148 was 1.2 mg/kg i.v. every 3 weeks. The safety profile of BMS-986148 + nivolumab was similar to that of BMS-986148 monotherapy (0.8 mg/kg). Active ADC exposures increased in a dose-proportional manner with both dosing regimens (every 3 weeks and once weekly). Preliminary clinical activity was observed with BMS-986148 ± nivolumab. No association between mesothelin expression and response was detected.

CONCLUSIONS

BMS-986148 ± nivolumab demonstrated a clinically manageable safety profile and preliminary evidence of clinical activity, supporting additional studies combining directed cytotoxic therapies with checkpoint inhibitors as potential multimodal therapeutic strategies in patients with advanced solid tumors.

Revisiting antibody-drug conjugates and their predictive biomarkers in platinum-resistant ovarian cancer

Until to date, platinum derived drugs are still the backbone of treating ovarian cancer (OC). Most patients treated with platinum-based chemotherapy develop resistance during the course of their management. The treatment of platinum-resistant ovarian cancer (PROC) is challenging. Few therapeutic options are available for patients with this aggressive disease. Besides, there are liminal advances regarding new anticancer drugs as well as validated predictive biomarkers of clinical outcomes in this setting. The enrollment of PROC patients in interventional studies is limited as compared to newly launched clinical trials for platinum-sensitive OC. Enthusiastically, the emergence of antibody-drug conjugates (ADCs) has provided promising findings for further clinical development in PROC. ADCs have the advantage to selectively deliver cytotoxic drugs to cancer cells expressing several of antigens using specific monoclonal antibodies based on the concept of immune bioconjugation. This innovative class of therapeutics showed encouraging early signs of clinical efficacy in PROC particularly mirvetuximab soravtansine that has been successfully introduced into three randomized and controlled phase III studies. In this review, the evidence from clinical trials supporting the development of ADCs targeting folate receptor alpha, sodium-dependent phosphate transporter 2B, dipeptidase 3, mesothelin, mucin 16, and tissue factor using various cytotoxic payloads in PROC is reviewed.

Host Mesothelin Expression Increases Ovarian Cancer Metastasis in the Peritoneal Microenvironment

Mesothelin (MSLN), a glycoprotein normally expressed by mesothelial cells, is overexpressed in ovarian cancer (OvCa) suggesting a role in tumor progression, although the biological function is not fully understood. OvCa has a high mortality rate due to diagnosis at advanced stage disease with intraperitoneal metastasis. Tumor cells detach from the primary tumor as single cells or multicellular aggregates (MCAs) and attach to the mesothelium of organs within the peritoneal cavity producing widely disseminated secondary lesions. To investigate the role of host MSLN in the peritoneal cavity we used a mouse model with a null mutation in the MSLN gene (MSLN^KO). The deletion of host MSLN expression modified the peritoneal ultrastructure resulting in abnormal mesothelial cell surface architecture and altered omental collagen fibril organization. Co-culture of murine OvCa cells with primary mesothelial cells regardless of MSLN expression formed compact MCAs. However, co-culture with MSLN^KO mesothelial cells resulted in smaller MCAs. An allograft tumor study, using wild-type mice (MSLN^WT) or MSLN^KO mice injected intraperitoneally with murine OvCa cells demonstrated a significant decrease in peritoneal metastatic tumor burden in MSLN^KO mice compared to MSLN^WT mice. Together, these data support a role for host MSLN in the progression of OvCa metastasis.

Emerging targeted drug delivery strategies toward ovarian cancer

Ovarian cancer is a high-mortality malignancy in women. The contemporary clinical chemotherapy with classic cytotoxic drugs, targeted molecular inhibitors would mostly fail when ovarian cancer cells become drug-resistant or metastasize through the body or when patients bare no more toleration because of strong adverse effects. The past decade has spotted varying targeted delivery systems including antibody-drug conjugates (ADCs), peptide/folate/aptamer-drug conjugates, polymer-drug conjugates, ligand-functionalized nanomedicines, and dual-targeted nanomedicines that upgrade ovarian cancer chemo- and molecular therapy effectively in preclinical/clinical settings via endowing therapeutic agents selectivity and bypassing drug resistance as well as lessening systemic toxicity. The targeted delivery approaches further provide means to potentiate emergent treatment modalities such as molecular therapy, gene therapy, protein therapy, photodynamic therapy, dual-targeting therapy and combination therapy for ovarian cancer. This review highlights up-to-date development of targeted drug delivery strategies toward advanced, metastatic, relapsed, and drug resistant ovarian cancers.

The Collagen Receptor uPARAP in Malignant Mesothelioma: A Potential Diagnostic Marker and Therapeutic Target

Malignant mesothelioma (MM) is a highly aggressive cancer with limited therapeutic options. We have previously shown that the endocytic collagen receptor, uPARAP, is upregulated in certain cancers and can be therapeutically targeted. Public RNA expression data display uPARAP overexpression in MM. Thus, to evaluate its potential use in diagnostics and therapy, we quantified uPARAP expression by immunohistochemical H-score in formalin-fixed paraffin-embedded bioptic/surgical human tissue samples and tissue microarrays. We detected pronounced upregulation of uPARAP in the three main MM subtypes compared to non-malignant reactive mesothelial proliferations, with higher expression in sarcomatoid and biphasic than in epithelioid MM. The upregulation appeared to be independent of patients’ asbestos exposure and unaffected after chemotherapy. Using immunoblotting, we demonstrated high expression of uPARAP in MM cell lines and no expression in a non-malignant mesothelial cell line. Moreover, we showed the specific internalization of an anti-uPARAP monoclonal antibody by the MM cell lines using flow cytometry-based assays and confocal microscopy. Finally, we demonstrated the sensitivity of these cells towards sub-nanomolar concentrations of an antibody-drug conjugate formed with the uPARAP-directed antibody and a potent cytotoxin that led to efficient, uPARAP-specific eradication of the MM cells. Further studies on patient cohorts and functional preclinical models will fully reveal whether uPARAP could be exploited in diagnostics and therapeutic targeting of MM.

Antibody drug conjugates in gastrointestinal cancer: From lab to clinical development

The antibody-drug conjugates (ADCs) are one the fastest growing biotherapeutics in oncology and are still in their infancy in gastrointestinal (GI) cancer for clinical applications to improve patient survival. The ADC based approach is developed with tumor specific antigen, antibody carrying cytotoxic agents to precisely target and deliver chemotherapeutics at the tumor site. To date, 11 ADCs have been approved by US-FDA, and more than 80 are in the clinical development phase for different oncological indications. However, The ADCs based therapies in GI cancers are still far from having high-efficient clinical outcomes. The limited success of these ADCs and lessons learned from the past are now being used to develop a newer generation of ADC against GI cancers. In this review, we did a comprehensive assessment of the key components of ADCs, including tumor marker, antibody, cytotoxic payload, and linkage strategy, with a focus on technical improvement and some future trends in the pipeline for clinical translation. The various preclinical and clinical ADCs used in gastrointestinal malignancies, their target, composition and bioconjugation, along with preclinical and clinical outcomes, are discussed. The emphasis is also given to new generation ADCs employing novel mAb, payload, linker, and bioconjugation methods are also included.

Antibody-Antineoplastic Conjugates in Gynecological Malignancies: Current Status and Future Perspectives

In the last decade, antibody-drug conjugates (ADCs), normally formed by a humanized antibody and a small drug via a chemical cleavable or non-cleavable linker, have emerged as a potential treatment strategy in cancer disease. They allow to get a selective delivery of the chemotherapeutic agents at the tumor level, and, consequently, to improve the antitumor efficacy and, especially to decrease chemotherapy-related toxicity. Currently, nine antibody-drug conjugate-based formulations have been already approved and more than 80 are under clinical trials for the treatment of several tumors, especially breast cancer, lymphomas, and multiple myeloma. To date, no ADCs have been approved for the treatment of gynecological formulations, but many formulations have been developed and have reached the clinical stage, especially for the treatment of ovarian cancer, an aggressive disease with a low five-year survival rate. This manuscript analyzes the ADCs formulations that are under clinical research in the treatment of gynecological carcinomas, specifically ovarian, endometrial, and cervical tumors.

Therapeutic Targeting of Mesothelin with Chimeric Antigen Receptor T Cells in Acute Myeloid Leukemia

PURPOSE

We previously identified mesothelin (MSLN) as highly expressed in a significant fraction of acute myeloid leukemia (AML) but entirely silent in normal hematopoiesis, providing a promising antigen for immunotherapeutic targeting that avoids hematopoietic toxicity. Given that T cells genetically modified to express chimeric antigen receptors (CAR) are effective at eradicating relapsed/refractory acute lymphocytic leukemia, we developed MSLN-directed CAR T cells for preclinical evaluation in AML.

EXPERIMENTAL DESIGN

The variable light (VL) and heavy (VH) sequences from the MSLN-targeting SS1P immunotoxin were used to construct the single-chain variable fragment of the standard CAR containing 41-BB costimulatory and CD3Zeta stimulatory domains. The preclinical efficacy of MSLN CAR T cells was evaluated against AML cell lines and patient samples expressing various levels of MSLN in vitro and in vivo.

RESULTS

We demonstrate that MSLN is expressed on the cell surface of AML blasts and leukemic stem cell-enriched CD34⁺CD38^- subset, but not on normal hematopoietic stem and progenitor cells (HSPC). We further establish that MSLN CAR T cells are highly effective in eliminating MSLN-positive AML cells in cell line- and patient-derived xenograft models. Importantly, MSLN CAR T cells can target and eradicate CD34⁺CD38^- cells without impacting the viability of normal HSPCs. Finally, we show that CAR T-cell functionality can be improved by inhibition of the ADAM17 metalloprotease that promotes shedding of MSLN.

CONCLUSIONS

These findings demonstrate that MSLN is a viable target for CAR T-cell therapy in AML and that inhibiting MSLN shedding is a promising approach to improve CAR T-cell efficacy.

Biological basis for novel mesothelioma therapies

Mesothelioma is an aggressive cancer that is associated with exposure to asbestos. Although asbestos is banned in several countries, including the UK, an epidemic of mesothelioma is predicted to affect middle-income countries during this century owing to their heavy consumption of asbestos. The prognosis for patients with mesothelioma is poor, reflecting a failure of conventional chemotherapy that has ultimately resulted from an inadequate understanding of its biology. However, recent work has revolutionised the study of mesothelioma, identifying genetic and pathophysiological vulnerabilities, including the loss of tumour suppressors, epigenetic dysregulation and susceptibility to nutrient stress. We discuss how this knowledge, combined with advances in immunotherapy, is enabling the development of novel targeted therapies.

Mesothelin is Commonly Expressed in Pancreatic Adenocarcinoma but Unrelated to Cancer Aggressiveness

Data on Mesothelin (MSLN) expression in human normal and cancerous tissues is controversial. We employed immunohistochemistry (IHC) on a tissue microarray (TMA) from 599 pancreatic cancers and 12 large tissue sections of pancreatitis. MSLN expression was highest in pancreatic adenocarcinomas (89%) and adenocarcinomas of the ampulla Vateri (79%), infrequent in pancreatitis and absent in 6 acinus cell carcinomas and normal pancreas. MSLN expression was unrelated to pathological tumor stage, grade, metastasis, and tumor-infiltrating CD8+ lymphocytes. In conclusion, pancreatic cancer may be ideally suited for putative anti- MSLN therapies, and MSLN may represent a suitable biomarker for pancreatic cancer diagnosis, especially on small biopsies.

Eradicating mesothelin-positive human gastric and pancreatic tumors in xenograft models with optimized anti-mesothelin antibody-drug conjugates from synthetic antibody libraries

Mesothelin (MSLN) is an attractive candidate of targeted therapy for several cancers, and hence there are increasing needs to develop MSLN-targeting strategies for cancer therapeutics. Antibody–drug conjugates (ADCs) targeting MSLN have been demonstrated to be a viable strategy in treating MSLN-positive cancers. However, developing antibodies as targeting modules in ADCs for toxic payload delivery to the tumor site but not to normal tissues is not a straightforward task with many potential hurdles. In this work, we established a high throughput engineering platform to develop and optimize anti-MSLN ADCs by characterizing more than 300 scFv CDR-variants and more than 50 IgG CDR-variants of a parent anti-MSLN antibody as candidates for ADCs. The results indicate that only a small portion of the complementarity determining region (CDR) residues are indispensable in the MSLN-specific targeting. Also, the enhancement of the hydrophilicity of the rest of the CDR residues could drastically increase the overall solubility of the optimized anti-MSLN antibodies, and thus substantially improve the efficacies of the ADCs in treating human gastric and pancreatic tumor xenograft models in mice. We demonstrated that the in vivo treatments with the optimized ADCs resulted in almost complete eradication of the xenograft tumors at the treatment endpoints, without detectable off-target toxicity because of the ADCs’ high specificity targeting the cell surface tumor-associated MSLN. The technological platform can be applied to optimize the antibody sequences for more effective targeting modules of ADCs, even when the candidate antibodies are not necessarily feasible for the ADC development due to the antibodies’ inferior solubility or affinity/specificity to the target antigen.

Progress in Gynecologic Cancers with Antibody Drug Conjugates

PURPOSE OF REVIEW

This article provides a comprehensive review of antibody-drug conjugates (ADCs) under investigation in gynecologic cancers. The structure and function of ADCs are reviewed with a focus on clinical benefit as well as toxicity profiles.

RECENT FINDINGS

Several ADCs with various target antigens have been investigated in ovarian, cervical, and endometrial cancer. ADCs have consistently demonstrated favorable safety/tolerability profiles both as monotherapy and in combination therapy. In ovarian cancer, response rates have ranged from 9 to 46% for monotherapy with response rates as high as 83% in combination therapy. In patients with cervical cancer with progressive disease despite doublet therapy and bevacizumab, response rates as high as 24% have been observed. ADCs represent a rapidly evolving field of targeted therapy which have demonstrated notable clinical benefit both as monotherapy but also in combination therapy with an overall favorable toxicity profile. With continued refinement of the target biomarkers utilized, improved clinical benefit is likely to be observed.

Mesothelin is a novel cell surface disease marker and potential therapeutic target in acute myeloid leukemia

In an effort to identify acute myeloid leukemia (AML)-restricted targets for therapeutic development in AML, we analyzed the transcriptomes of 2051 children and young adults with AML and compared the expression profile with normal marrow specimens. This analysis identified a large cohort of AML-restricted genes with high expression in AML, but low to no expression in normal hematopoiesis. Mesothelin (MSLN), a known therapeutic target in solid tumors, was shown to be highly overexpressed in 36% of the AML cohort (range, 5-1077.6 transcripts per million [TPM]) and virtually absent in normal marrow (range, 0.1-10.7 TPM). We verified MSLN transcript expression by quantitative reverse transcription polymerase chain reaction, confirmed cell surface protein expression on leukemic blasts by multidimensional flow cytometry, and demonstrated that MSLN expression was associated with promoter hypomethylation. MSLN was highly expressed in patients with KMT2A rearrangements (P < .001), core-binding factor fusions [inv(16)/t(16;16), P < .001; t(8;21), P < .001], and extramedullary disease (P = .001). We also demonstrated the presence of soluble MSLN in diagnostic serum specimens using an MSLN-directed enzyme-linked immunosorbent assay. In vitro and in vivo preclinical efficacy of the MSLN-directed antibody-drug conjugates (ADCs) anetumab ravtansine and anti-MSLN-DGN462 were evaluated in MSLN+ leukemia cell lines in vitro and in vivo, as well as in patient-derived xenografts. Treatment with ADCs resulted in potent target-dependent cytotoxicity in MSLN+ AML. In this study, we demonstrate that MSLN is expressed in a significant proportion of patients with AML and holds significant promise as a diagnostic and therapeutic target in AML, and that MSLN-directed therapeutic strategies, including ADCs, warrant further clinical investigation.

Significance of mesothelin and CA125 expression in endometrial carcinoma: a retrospective analysis

Background

This study aimed to investigate the association between clinicopathologic factors, mesothelin, and cancer antigen (CA) 125 in endometrial carcinoma.

Methods

Between 1989 and 2017, patients with endometrial carcinoma who underwent total hysterectomy and bilateral salpingo-oophorectomy at our hospital were identified. The association between either or both immunochemical expression of mesothelin and CA125 and clinicopathological features were retrospectively examined.

Results

Among 485 patients, 171 were positive for mesothelin, 368 were positive for CA125, and 167 were positive for mesothelin and CA125. The expression of mesothelin and CA125 was positively correlated (p < 0.01). More patients with mesothelin expression showed myometrial invasion of more than 50% (p = 0.028) and positive lymphovascular invasion (p = 0.027). Similarly, more patients with co-expression of mesothelin and CA125 had myometrial invasion of more than 50% (p = 0.016) and positive lymphovascular invasion (p = 0.02). Patients with mesothelin expression and co-expression of mesothelin and CA125 demonstrated worse progression-free survival (PFS) and overall survival (OS). In the multivariate analysis, mesothelin expression and co-expression were poor prognostic factors for PFS (mesothelin expression: hazard ratio [HR] = 2.14, p < 0.01; co-expression: HR = 2.19, p < 0.01) and OS (mesothelin expression: HR = 2.18, p < 0.01; co-expression: HR = 2.22, p < 0.01).

Conclusions

Mesothelin expression and co-expression might be associated with tumor aggressiveness and poor prognosis in patients with endometrial carcinoma. Persons with mesothelin-expressing endometrial cancers present a particularly high medical unmet need.

Mesothelin Expression in Human Tumors: A Tissue Microarray Study on 12,679 Tumors

Mesothelin (MSLN) represents an attractive molecule for targeted cancer therapies. To identify tumors that might benefit from such therapies, tissue microarrays including 15,050 tumors from 122 different tumor types and 76 healthy organs were analyzed for MSLN expression by immunohistochemistry. Sixty-six (54%) tumor types showed at least occasional weak staining, including 50 (41%) tumor types with at least one strongly positive sample. Highest prevalence of MSLN positivity had ovarian carcinomas (serous 97%, clear cell 83%, endometrioid 77%, mucinous 71%, carcinosarcoma 65%), pancreatic adenocarcinoma (ductal 75%, ampullary 81%), endometrial carcinomas (clear cell 71%, serous 57%, carcinosarcoma 50%, endometrioid 45%), malignant mesothelioma (69%), and adenocarcinoma of the lung (55%). MSLN was rare in cancers of the breast (7% of 1138), kidney (7% of 807), thyroid gland (1% of 638), soft tissues (0.3% of 931), and prostate (0 of 481). High expression was linked to advanced pathological tumor (pT) stage (p < 0.0001) and metastasis (p < 0.0001) in 1619 colorectal adenocarcinomas, but unrelated to parameters of malignancy in 1072 breast-, 386 ovarian-, 174 lung-, 757 kidney-, 171 endometrial-, 373 gastric-, and 925 bladder carcinomas. In summary, numerous important cancer types with high-level MSLN expression might benefit from future anti-MSLN therapies, but MSLN’s prognostic relevance appears to be limited.

Clinical pharmacology of vc-MMAE antibody-drug conjugates in cancer patients: learning from eight first-in-human Phase 1 studies

vc-MMAE antibody–drug conjugates (ADCs) consist of a monoclonal antibody (mAb) covalently bound with a potent anti-mitotic toxin (MMAE) through a protease-labile valine-citrulline (vc) linker. The objective of this study was to characterize the pharmacokinetics (PK) and explore exposure–response relationships of eight vc-MMAE ADCs, against different targets and for diverse tumor indications, using data from eight first-in-human Phase 1 studies. PK parameters of the three analytes, namely antibody-conjugated MMAE (acMMAE), total antibody, and unconjugated MMAE, were estimated using non-compartmental approaches and compared across the eight vc-MMAE ADCs. Relationships between analytes were assessed by linear regression. Exposure–response relationships were explored with key efficacy (objective response rate) and safety (Grade 2+ peripheral neuropathy) endpoints. PK profiles of acMMAE, total antibody and unconjugated MMAE following the first dose of 2.4 mg/kg were comparable across the eight ADCs; the exposure differences between molecules were small relative to the inter-subject variability. acMMAE exposure was strongly correlated with total antibody exposure for all the eight ADCs, but such correlation was less evident between acMMAE and unconjugated MMAE exposure. For multiple ADCs evaluated, efficacy and safety endpoints appeared to correlate well with acMMAE exposure, but not with unconjugated MMAE over the doses tested. PK of vc-MMAE ADCs was well characterized and demonstrated remarkable similarity at 2.4 mg/kg across the eight ADCs. Results from analyte correlation and exposure–response relationship analyses suggest that measurement of acMMAE analyte alone might be adequate for vc-MMAE ADCs to support the clinical pharmacology strategy used during late-stage clinical development.

Novel mesothelin antibody-drug conjugates: current evidence and future role in the treatment of ovarian cancer

Introduction: Ovarian cancer is the deadliest gynecologic malignancy in the United States, and effective therapies for recurrent, advanced, and progressive disease are limited. Mesothelin is known to be expressed in ovarian cancers, and antibody-drug conjugates targeting mesothelin are a promising novel therapeutic agent.Areas Covered: This article reviews the currently available literature of anti-mesothelin antibody-drug conjugates as a novel treatment for ovarian cancer. Preclinical in vitro and in vivo data as well as clinical results are reviewed for each available agent. Additionally, adverse effects are covered.Expert Opinion: Anti-mesothelin antibody-drug conjugates and their combination with chemotherapeutic agents have undergone phase II trials with encouraging results and demonstrated favorable adverse effect profiles. Phase III data will be necessary to establish its role in ovarian cancer, particularly in recurrent, advanced, or progressive disease.

Preclinical Characterization of HPN536, a Trispecific, T-Cell-Activating Protein Construct for the Treatment of Mesothelin-Expressing Solid Tumors

PURPOSE

Mesothelin (MSLN) is a glycophosphatidylinositol-linked tumor antigen overexpressed in a variety of malignancies, including ovarian, pancreatic, lung, and triple-negative breast cancer. Early signs of clinical efficacy with MSLN-targeting agents have validated MSLN as a promising target for therapeutic intervention, but therapies with improved efficacy are still needed to address the significant unmet medical need posed by MSLN-expressing cancers.

EXPERIMENTAL DESIGN

We designed HPN536, a 53-kDa, trispecific, T-cell-activating protein-based construct, which binds to MSLN-expressing tumor cells, CD3ε on T cells, and to serum albumin. Experiments were conducted to assess the potency, activity, and half-life of HPN536 in in vitro assays, rodent models, and in nonhuman primates (NHP).

RESULTS

HPN536 binds to MSLN-expressing tumor cells and to CD3ε on T cells, leading to T-cell activation and potent redirected target cell lysis. A third domain of HPN536 binds to serum albumin for extension of plasma half-life. In cynomolgus monkeys, HPN536 at doses ranging from 0.1 to 10 mg/kg demonstrated MSLN-dependent pharmacologic activity, was well tolerated, and showed pharmacokinetics in support of weekly dosing in humans.

CONCLUSIONS

HPN536 is potent, is well tolerated, and exhibits extended half-life in NHPs. It is currently in phase I clinical testing in patients with MSLN-expressing malignancies (NCT03872206).

Mesothelin-targeted CAR-T cell therapy for solid tumors

Introduction: Mesothelin (MSLN) is a tumor differentiation antigen normally restricted to the body's mesothelial surfaces, but significantly overexpressed in a broad range of solid tumors. For this reason, MSLN has emerged as an important target for the development of novel immunotherapies. This review focuses on anti-MSLN chimeric antigen receptor (CAR) T cell immunotherapy approaches.Areas covered: A brief overview of MSLN as a therapeutic target and existing anti-MSLN antibody-based drugs and vaccines is provided. A detailed account of anti-MSLN CAR-T cell approaches utilized in preclinical models is presented. Finally, a comprehensive summary of currently ongoing and completed anti-MSLN CAR-T cell clinical trials is discussed.Expert opinion: Initial trials using anti-MSLN CAR-T cells have been safe, but efficacy has been limited. Employing regional routes of delivery, introducing novel modifications leading to enhanced tumor infiltration and persistence, and improved safety profiles and combining anti-MSLN CAR-T cells with standard therapies, could render them more efficacious in the treatment of solid malignancies.

A Phase I Study of DLYE5953A, an Anti-LY6E Antibody Covalently Linked to Monomethyl Auristatin E, in Patients with Refractory Solid Tumors

PURPOSE

DLYE5953A is an antibody-drug conjugate consisting of an anti-LY6E antibody covalently linked to the cytotoxic agent monomethyl auristatin E. This study characterized the safety, pharmacokinetics, immunogenicity, potential biomarkers, and antitumor activity of DLYE5953A in patients with metastatic solid tumors.

PATIENTS AND METHODS

This was a phase I, open-label, 3+3 dose-escalation, and dose-expansion study of DLYE5953A administered intravenously every 21 days (Q3W) in patients with locally advanced or metastatic solid malignancies.

RESULTS

Sixty-eight patients received DLYE5953A (median, four cycles; range, 1-27). No dose-limiting toxicities were identified during dose escalation (0.2-2.4 mg/kg; n = 20). The recommended phase II dose (RP2D) of 2.4 mg/kg Q3W was based on overall safety and tolerability. Dose-expansion cohorts for HER2-negative metastatic breast cancer (HER2-negative MBC; n = 23) and non-small cell lung cancer (NSCLC; n = 25) patients were enrolled at the RP2D. Among patients receiving DLYE5953A 2.4 mg/kg (n = 55), the most common (≥30%) related adverse events (AEs) included alopecia, fatigue, nausea, and peripheral neuropathy. Grade ≥3 related AEs occurred in 14 of 55 (26%) patients, with neutropenia being the most common (13%). DLYE5953A demonstrated linear total antibody pharmacokinetics at doses of ≥0.8 mg/kg with low unconjugated monomethyl auristatin E levels in blood. Partial response was confirmed in eight of 68 (12%) patients, including three of 29 patients with MBC (10%) and five of 25 patients with NSCLC (20%) at the RP2D. Stable disease was the best response for 37 of 68 (54%) patients.

CONCLUSIONS

DLYE5953A administered at 2.4 mg/kg has acceptable safety. Preliminary evidence of antitumor activity in patients with HER2-negative MBC and NSCLC supports further investigation of LY6E as a therapeutic target.

Insights Into the Role of Mesothelin as a Diagnostic and Therapeutic Target in Ovarian Carcinoma

Ovarian malignancies remain the leading cause of death in female gynecological tumors. More than 70% of patients are diagnosed with advanced stage with extensive metastatic lesions in abdominal cavity due to lack of symptoms in early stage and sensitive diagnostic approaches. Mesothelin (MSLN), a glycosylphosphatidylinositol-anchored membrane glycoprotein, participates in cell adhesion, tumor progression, metastasis, and drug resistance. Despite this, the mechanism is still poorly understood. The differential expression pattern of MSLN in normal and cancer tissues makes it a promising target for diagnosis and therapeutic applications. Several clinical trials are underway to evaluate the safety and efficacy of MSLN-targeted drugs, including CAR T cells, immunotoxin, antibody-drug conjugates, and vaccine. This review is aimed to briefly discuss the characteristics of MSLN and the latest progress in MSLN targeting therapies.

Antibody-Drug Conjugates: A Promising Novel Therapy for the Treatment of Ovarian Cancer

Antibody-drug conjugates (ADCs) represent a novel and promising therapeutic strategy for the treatment of cancer patients. ADCs target antigens highly expressed on the membrane surface of tumor cells to selectively deliver a cytotoxic drug. Ovarian tumors differentially express tumor-specific antigens, which can be used to guide ADCs. This strategy allows for optimizing tumor targeting while minimizing systemic toxicity compared to classical chemotherapeutic agents. ADCs can be improved by using a cleavable linker allowing the delivery of the toxic payload in surrounding cells not expressing the target protein, therefore acting on heterogeneous tumors with different cell populations. Currently, more than 15 ADCs are under preclinical investigation in ovarian cancer, and some of them have already been tested in early-phase clinical trials with promising results. In this review, we summarize the mechanism of action and the toxicity profile of ADCs and discuss the latest preclinical discoveries and forthcoming applications in ovarian cancer.

Histoepigenetic analysis of the mesothelin network within pancreatic ductal adenocarcinoma cells reveals regulation of retinoic acid receptor gamma and AKT by mesothelin

To enable computational analysis of regulatory networks within the cancer cell in its natural tumor microenvironment, we develop a two-stage histoepigenetic analysis method. The first stage involves iterative computational deconvolution to estimate sample-specific cancer-cell intrinsic expression of a gene of interest. The second stage places the gene within a network module. We validate the method in simulation experiments, show improved performance relative to differential expression analysis from bulk samples, and apply it to illuminate the role of the mesothelin (MSLN) network in pancreatic ductal adenocarcinoma (PDAC). The network analysis and subsequent experimental validation in a panel of PDAC cell lines suggests AKT activation by MSLN through two known activators, retinoic acid receptor gamma (RARG) and tyrosine kinase non receptor 2 (TNK2). Taken together, these results demonstrate the potential of histoepigenetic analysis to reveal cancer-cell specific molecular interactions directly from patient tumor profiles.

Mesothelin-Targeted Recombinant Immunotoxins for Solid Tumors

Mesothelin (MSLN) is a cell surface glycoprotein normally expressed only on serosal surfaces, and not found in the parenchyma of vital organs. Many solid tumors also express MSLN, including mesothelioma and pancreatic adenocarcinoma. Due to this favorable expression profile, MSLN represents a viable target for directed anti-neoplastic therapies, such as recombinant immunotoxins (iToxs). Pre-clinical testing of MSLN-targeted iTox’s has yielded a strong body of evidence for activity against a number of solid tumors. This has led to multiple clinical trials, testing the safety and efficacy of the clinical leads SS1P and LMB-100. While promising clinical results have been observed, neutralizing anti-drug antibody (ADA) formation presents a major challenge to overcome in the therapeutic development process. Additionally, on-target, off-tumor toxicity from serositis and non-specific capillary leak syndrome (CLS) also limits the dose, and therefore, impact anti-tumor activity. This review summarizes existing pre-clinical and clinical data on MSLN-targeted iTox’s. In addition, we address the potential future directions of research to enhance the activity of these anti-tumor agents.

Patient Selection Strategies to Maximize Therapeutic Index of Antibody-Drug Conjugates: Prior Approaches and Future Directions

Antibody-drug conjugates (ADC) are targeted agents that have shown promise in treating cancer. A central challenge in development of ADCs is the relatively narrow therapeutic index observed in clinical studies. Patient selection strategies based on expression of the target in tumors have the potential to maximize benefit and provide the best chance of clinical success; however, implementation of biomarker-driven trials can be difficult both practically and scientifically. We conducted a survey of recent clinical experience from early-phase ADC trials completed between 2000 and 2019 to evaluate the different approaches to patient selection currently being used and assess whether there is evidence that target expression is associated with clinical activity. Our analysis of patient selection strategies indicates that optimal trial design for early-stage trials should be based on multiple factors, including prevalence and heterogeneity of target expression among intent-to-treat patients, as well as biological factors influencing expression of cell surface and soluble target. To ensure a high probability of success, early implementation of patient selection strategies centered around target expression are pivotal to development of ADCs. In this review, we propose a strategic approach that can be applied for optimization of trial design.

Antibody-drug conjugates for the treatment of ovarian cancer

INTRODUCTION

Ovarian cancer typically presents at an advanced stage and while initial chemotherapy response rates are favorable, a majority of patients experience recurrence with the subsequent development of chemoresistance. Recurrent, platinum-resistant disease is associated with a very poor prognosis as treatment in this setting is often limited by systemic toxicity. Antibody-drug conjugates (ADCs) are novel therapeutic agents designed to target antigens specific to ovarian tumor cells with direct delivery of cytotoxic agents to combat recurrent, platinum-resistant disease while limiting systemic toxicity.

AREAS COVERED

The basic structure and function of ADCs will be reviewed as well as the current data on ADCs under investigation in ovarian cancer.

EXPERT OPINION

ADCs represent a promising class of targeted therapy in recurrent ovarian cancer with excellent response rates particularly when utilized as combination therapy. While mirvetuximab soravtansine is the only ADC that has been evaluated in a phase 3 trial, many other ADCs and trials are on the horizon. As the field of targeted therapy continues to evolve, continued development of target antigens and ADCs are likely to represent a key development in treatment of recurrent, platinum-resistant disease.

From Malignant Progression to Therapeutic Targeting: Current Insights of Mesothelin in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC), accounting for 90% of all pancreatic tumors, is a highly devastating disease with poor prognosis and rising incidence. The lack of available specific diagnostics tests and the limited treatment opportunities contribute to this pejorative issue. Over the last 10 years, a growing interest pointing towards mesothelin (MSLN) as a promising PDAC-associated antigen has emerged. The limited expression of MSLN in normal tissues (peritoneum, pleura and pericardium) and its overexpression in 80 to 90% of PDAC make it an attractive candidate for therapeutic management of PDAC patients. Moreover, its role in malignant progression related to its involvement in tumor cell proliferation and resistance to chemotherapy has highlighted the relevance of its targeting. Hence, several clinical trials are investigating anti-MSLN efficacy in PDAC. In this review, we provide a general overview of the different roles sustained by MSLN during PDAC progression. Finally, we also summarize the different MSLN-targeted therapies that are currently tested in the clinic.

Generation of a Transgenic BALB/c Mouse Line With Selective Expression of Human Mesothelin in Thyroid Gland: Application in Mesothelin-targeted Immunotherapy

Despite encouraging clinical results with immune checkpoint inhibitors and other types of immunotherapies, the rate of failure is still very high. The development of proper animal models which could be applied to the screening of effective preclinical antitumor drugs targeting human tumor antigens, such as mesothelin (MSLN), is a great need. MSLN is a 40 kDa cell-surface glycoprotein which is highly expressed in a variety of human cancers, and has great value as a target for antibody-based therapies. The present study reports the establishment of an immunocompetent transgenic mouse expressing human MSLN (hMSLN) only in thyroid gland by utilizing an expression vector containing a thyroid peroxidase (TPO) promoter. These mice do not reject genetically modified tumor cells expressing hMSLN on the cell membrane, and tolerate high doses of hMSLN-targeted immunotoxin. Employing this TPO-MSLN mouse model, we find that the combination treatment of LMB-100 and anti-CTLA-4 induces complete tumor regression in 91% of the mice burdened with 66C14-M tumor cells. The combination therapy provides a significant survival benefit compared with both LMB-100 and anti-CTLA-4 monotherapy. In addition, the cured mice reject tumor cells when rechallenged, indicating the development of long-term antitumor immunity. This novel TPO-MSLN mouse model can serve as an important animal tool to better predict tumor responses to any immunomodulatory therapies that target MSLN.

Molecular Interaction Characterization Strategies for the Development of New Biotherapeutic Antibody Modalities

The characterization of target binding interactions is critical at each stage of antibody therapeutic development. During early development, it is important to design fit-for-purpose in vitro molecular interaction characterization (MIC) assays that accurately determine the binding kinetics and the affinity of therapeutic antibodies for their targets. Such information enables PK/PD (pharmacokinetics/pharmacodynamics) modeling, estimation of dosing regimens, and assessment of potency. While binding kinetics and affinities seem to be readily obtained, there is little discussion in the literature on how the information should be generated and used in a systematic manner along with other approaches to enable key drug development decisions. The introduction of new antibody modalities poses unique challenges to the development of MIC assays and further increases the need to discuss the impact of developing context-appropriate MIC assays to enable key decision making for these programs. In this paper, we discuss for the first time the challenges encountered when developing MIC assays supporting new antibody modalities. Additionally, through the presentation of several real case studies, we provide strategies to overcome these challenges to enable investigational new drug (IND) filings.

ADCs, as Novel Revolutionary Weapons for Providing a Step Forward in Targeted Therapy of Malignancies

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Antibody drug conjugates (ADCs), as potent pharmaceutical trojan horses for cancer treatment, provide superior efficacy and specific targeting along with low risk of adverse reactions compared to traditional chemotherapeutics. In fact, the development of these agents combines the selective targeting capability of monoclonal antibody (mAb) with high cytotoxicity of chemotherapeutics for controlling the neoplastic mass growth. Different ADCs (more than 60 ADCs) in preclinical and clinical trials were introduced in this novel pharmaceutical field. Various design-based factors must be taken into account for improving the functionality of ADC technology, including selection of appropriate target antigen and high binding affinity of fragment (miniaturized ADCs) or full mAbs (preferentially use of humanized or fully human antibodies compared to murine and chimeric ones), use of bispecific antibodies for dual targeting effect, linker engineering and conjugation method efficacy to obtain more controlled drug to antibody ratio (DAR). Challenging issues affecting therapeutic efficacy and safety of ADCs, including bystander effect, on- and off-target toxicities, multi drug resistance (MDR) are also addressed. 4 FDA-approved ADCs in the market, including ADCETRIS ®, MYLOTARG®, BESPONSA ®, KADCYLA®. The goal of the current review is to evaluate the key parameters affecting ADCs development.

Single-Cell RNA Sequencing Identifies Yes-Associated Protein 1-Dependent Hepatic Mesothelial Progenitors in Fibrolamellar Carcinoma

Fibrolamellar carcinoma (FLC) is characterized by in-frame fusion of DnaJ heat shock protein family (Hsp40) member B1 (DNAJB1) with protein kinase cAMP-activated catalytic subunit α (PRKACA) and by dense desmoplasia. Surgery is the only effective treatment because mechanisms supporting tumor survival are unknown. We used single-cell RNA sequencing to characterize a patient-derived FLC xenograft model and identify therapeutic targets. Human FLC cells segregated into four discrete clusters that all expressed the oncogene Yes-associated protein 1 (YAP1). The two communities most enriched with cells coexpressing FLC markers [CD68, A-kinase anchoring protein 12 (AKAP12), cytokeratin 7, epithelial cell adhesion molecule (EPCAM), and carbamoyl palmitate synthase-1] also had the most cells expressing YAP1 and its proproliferative target genes (AREG and CCND1), suggesting these were proliferative FLC cell clusters. The other two clusters were enriched with cells expressing profibrotic YAP1 target genes, ACTA2, ELN, and COL1A1, indicating these were fibrogenic FLC cells. All clusters expressed the YAP1 target gene and mesothelial progenitor marker mesothelin, and many mesothelin-positive cells coexpressed albumin. Trajectory analysis predicted that the four FLC communities were derived from a single cell type transitioning among phenotypic states. After establishing a novel FLC cell line that harbored the DNAJB1-PRKACA fusion, YAP1 was inhibited, which significantly reduced expression of known YAP1 target genes as well as cell growth and migration. Thus, both FLC epithelial and stromal cells appear to arise from DNAJB1-PRKACA fusion in a YAP1-dependent liver mesothelial progenitor, identifying YAP1 as a target for FLC therapy.

Prevalence of DLL3, CTLA-4 and MSTN Expression in Patients with Small Cell Lung Cancer

Introduction

Immune-based and antibody-drug conjugate therapies have shown promise in the treatment of patients with small cell lung cancer (SCLC). However, better predictive biomarkers are needed for selection of the appropriate SCLC patients for these advanced therapies and also for evaluation of the efficacy of these treatments.

Objective

The aim of this study was to examine the expression of delta-like protein 3 (DLL3), cytotoxic T lymphocyte-associated protein 4 (CTLA-4), and mesothelin (MSTN) in patients with SCLC and compare them with those patients’ clinical characteristics.

Methods

Immunohistochemical analyses of DLL3, CTLA-4 and MSTN expression were performed in 38 samples from patients with SCLC.

Results

We found that positive expression in patients of the biomarkers was as follows: for DLL3, 100% (38/38), for CTLA-4, 89.5% (36/38) and for MSTN 81.5% (31/38). The median survival time was 17.9 months in the DLL3 high expression group and 23 months in the DLL3 low expression group. Patients with a high expression of DLL3 showed a poorer prognosis than those with a low expression of DLL3 (HR=3.4; 95% CI, 1.34–8.6; p=0.01).

Conclusion

The expression of DLL3, CTLA-4 and MSTN was not correlated with patients’ age, sex, smoking status, stage, and tumor metastasis. The fact that there was a higher expression of DLL3, CTLA-4, and MSTN in SCLC suggested that these molecules could be used as predictive biomarkers for SCLC.