Anti-Endosialin Antibody-Drug Conjugate: Potential in Sarcoma and Other Malignancies

Endosialin-directed CAR-T cell therapy: A promising approach for targeting triple-negative breast cancer

In triple-negative breast cancer, this review article explores into the utilization of Chimeric antigen receptor T-cell (CAR-T) cell therapy to target cells expressing endosialin. Even with all the new treatments available, breast cancer still kills more women than any other disease. Drug resistance and ineffective cancer cell targeting are two major problems with targeted medications, chemotherapy, and surgery. Among cancer treatments, CAR-T cell therapy stands out. To identify endosialin as a therapeutic target, it is essential to understand its molecular structure and its involvement in tumor angiogenesis and progression. An effective target for CAR-T cells is breast cancer, which overexpresses endosialin. The development of CARs that are specific to endosialin and the results of early trials are covered in relation to CAR-T cell therapy that targets endosialin. Perhaps the most effective cancer treatment is endosialin targeting, since it is expressed only in tumors and plays a crucial role in the course of cancer. This article reviews endosialin-directed CAR-T cell breast cancer treatments' safety and efficacy from current and completed clinical trials. Despite promising results, these trials reveal that clinical translation must overcome significant challenges. The report suggests further research and combination tactics to improve endosialin-targeted CAR-T cell treatment.

Group XIV C-type lectins: emerging targets in tumor angiogenesis

C-type lectins, distinguished by a C-type lectin binding domain (CTLD), are an evolutionarily conserved superfamily of glycoproteins that are implicated in a broad range of physiologic processes. The group XIV subfamily of CTLDs are comprised of CD93, CD248/endosialin, CLEC14a, and thrombomodulin/CD141, and have important roles in creating and maintaining blood vessels, organizing extracellular matrix, and balancing pro- and anti-coagulative processes. As such, dysregulation in the expression and downstream signaling pathways of these proteins often lead to clinically relevant pathology. Recently, group XIV CTLDs have been shown to play significant roles in cancer progression, namely tumor angiogenesis and metastatic dissemination. Interest in therapeutically targeting tumor vasculature is increasing and the search for novel angiogenic targets is ongoing. Group XIV CTLDs have emerged as key moderators of tumor angiogenesis and metastasis, thus offering substantial therapeutic promise for the clinic. Herein, we review our current knowledge of group XIV CTLDs, discuss each's role in malignancy and associated potential therapeutic avenues, briefly discuss group XIV CTLDs in the context of two other relevant lectin families, and offer future direction in further elucidating mechanisms by which these proteins function and facilitate tumor growth.

TEM1 up-regulates MMP-2 and promotes ECM remodeling for facilitating invasion and migration of uterine sarcoma

OBJECTIVES

To explore the correlation between tumor endothelial marker 1 (TEM1) and matrix metalloproteinase 2 (MMP-2) in uterine sarcoma and their roles in the progression of uterine sarcoma.

METHODS

Uterine leiomyosarcoma (uLMS, n = 25) and uterine leiomyoma (n = 25) specimens were collected from a total of 50 patients. Immunohistochemistry assay was conducted to determine the expression of TEM1, MMP-2 and MMP-9. TEM1 over expression (hTEM1) and low expression (shRNA-TEM1) MES-SA cell lines were established as in vitro uterine sarcoma models. MMP-2 mRNA, protein expression and enzymatic activity were verified using qPCR, Western blot and gelatin zymography respectively. MMP-2 expression was downregulated using MMP-2 siRNA in hTEM1 MES-SA cells to better study the role of MMP-2. The invasive and migratory capacities of hTEM1, shRNA-TEM1, and hTEM1 treated with MMP-2 siRNA MES-SA cells were determined using transwell assays. Extracellular matrix (ECM) remodeling mediated by TEM1 was examined using cell-ECM adhesion and fluorescent gelatin-ECM degradation assays. The immunofluorescence of F-actin was examined to analyze the formation of invadopodia. Subcutaneous and intraperitoneal xenografts were established to validate the role of TEM1 in promoting uterine sarcoma metastasis.

RESULTS

TEM1 and MMP-2 were expressed in 92% (n = 23) and 88% (n = 22) of uterine leiomyosarcoma specimens, respectively. Both TEM1 and MMP-2 were highly expressed in 100% (n = 17) of high stage (III-IV) uterine leiomyosarcoma specimens. In addition, TEM1 expression was positively correlated with MMP-2 expression in uterine leiomyosarcoma. The successful establishment of in vitro uterine sarcoma models was confirmed with qPCR and Western blotting tests. TEM1 promoted the invasion and metastasis of uterine sarcoma in vivo and in vitro. MMP-2 expression and activity were up-regulated in hTEM1 cells but down-regulated in shRNA-TEM1 cells. Importantly, MMP-2 knockdown impaired the invasive and migratory capacity of hTEM1 cells. TEM1 promoted ECM remodeling by increasing cell-ECM adhesion and ECM degradation. TEM1 overexpression also induced the formation of invadopodia.

CONCLUSION

TEM1 was co-expressed and positively correlated with MMP-2 in uterine leiomyosarcoma specimens. In addition, both TEM1 and MMP-2 were associated with tumor development. TEM1 promoted uterine sarcoma progression by regulating MMP-2 activity and ECM remodeling.

Targeted Delivery of Chemotherapeutic Agents for Osteosarcoma Treatment

Since osteosarcoma (OS) is an aggressive bone cancer with unknown molecular pathways of etiology and pathophysiology, improving patient survival has long been a challenge. The conventional therapy is a complex multidisciplinary management that include radiotherapy, chemotherapy which followed by surgery and then post-operative adjuvant chemotherapy. However, they have severe side effects because the majority of the medicines used have just a minor selectivity for malignant tissue. As a result, treating tumor cells specifically without damaging healthy tissue is currently a primary goal in OS therapy. The coupling of chemotherapeutic drugs with targeting ligands is a unique therapy method for OS that, by active targeting, can overcome the aforementioned hurdles. This review focuses on advances in ligands and chemotherapeutic agents employed in targeted delivery to improve the capacity of active targeting and provide some insight into future therapeutic research for OS.

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.

CD248+ Cancer-Associated Fibroblasts: A Novel Prognostic and Therapeutic Target for Renal Cell Carcinoma

BACKGROUND

The tumor microenvironment (TME) plays an important role in the progression of renal cell carcinoma (RCC). Cancer-associated fibroblasts (CAFs) are considered to constitute a major component of the TME and participate in various tumor-promoting molecular events. We have previously confirmed that CD248 represents a promising biomarker of CAFs, which may provide insight into CAF-based tumor-promoting effects. However, CAF-mediated tumor progression and the potential mechanism of CD248 remain largely unknown in RCC patients.

METHODS

Expression profiling and clinical data of RCC patients were obtained from The Cancer Genome Atlas (TCGA) database. An MCP-counter algorithm and Kaplan-Meier survival analysis were performed to explore the prognostic value of CAFs and CD248, respectively. A Pearson correlation coefficient test and Student's t-test were employed to evaluate the relationship between immunosuppressive TME and CD248 or CAFs. Immunohistochemistry and immunofluorescence staining were performed to confirm CD248 expression within CAFs. CD248-specific siRNA was used to investigate the potential function of CD248 in CAF tumor promotion. Differentially expressed genes (DEGs), weighted gene co-expression network analysis (WGCNA), and enrichment analysis were conducted to clarify the function of CD248+ CAFs in RCC progression and the associated regulatory mechanism.

RESULTS

CD248 overexpression and CAF infiltration could predict poor RCC prognosis, which may involve the immunosuppressive TME. CD248 may serve as a promising CAFs biomarker and be involved with the tumor-promoting effect of CAFs. Moreover, CD248+ CAF infiltration may contribute to RCC progression and an immunosuppressive TME through cell-extracellular matrix (ECM) interactions and metabolism regulation.

CONCLUSION

CD248+ CAFs participate in the regulation of RCC progression and immunosuppressive TME, which may represent a novel prognostic and therapeutic target for RCC.

Copper-64-Labeled 1C1m-Fc, a New Tool for TEM-1 PET Imaging and Prediction of Lutetium-177-Labeled 1C1m-Fc Therapy Efficacy and Safety

Simple Summary

The prevalence of TEM-1 in the vasculature and the stroma of solid tumors and in malignant cells of sarcomas suggests that targeting TEM-1 could have therapeutic benefit. In this context, an anti-TEM-1 companion diagnostic may assist in the personalized medicine approach, whereby TEM-1 expression is exploited as a biomarker to select patients that would most benefit from a treatment directed toward the TEM-1 antigen. In our previous works, we have selected 1C1m-Fc, a fusion protein antibody, radiolabeled it with ¹⁷⁷Lu and demonstrated that [¹⁷⁷Lu]Lu-1C1m-Fc has interesting therapeutic performance. To define a suitable radiopharmaceutical companion for theranostic applications, ⁶⁴Cu was chosen to radiolabel the fusion protein antibody. The aim of this work was thus to determine if [⁶⁴Cu]Cu-1C1m-Fc can be considered for TEM-1 PET imaging and to predict the dosimetry of the [¹⁷⁷Lu]Lu-1C1m-Fc companion therapy.

Abstract

1C1m-Fc, a promising anti-TEM-1 DOTA conjugate, was labeled with ⁶⁴Cu to target cancer cells for PET imaging and predicting the efficacy and safety of a previously studied [¹⁷⁷Lu]Lu-1C1m-Fc companion therapy. DOTA-conjugated 1C1m-Fc was characterized by mass spectrometry, thin layer chromatography and immunoreactivity assessment. PET/CT and biodistribution studies were performed in human neuroblastoma xenografted mice. Absorbed doses were assessed from biodistribution results and extrapolated to ¹⁷⁷Lu based on the [⁶⁴Cu]Cu-1C1m-Fc data. The immunoreactivity was ≥ 70% after 48 h of incubation in serum, and the specificity of [⁶⁴Cu]Cu-1C1m-Fc for the target was validated. High-resolution PET/CT images were obtained, with the best tumor-to-organ ratios reached at 24 or 48 h and correlated with results of the biodistribution study. Healthy organs receiving the highest doses were the liver, the kidneys and the uterus. [⁶⁴Cu]Cu-1C1m-Fc could be of interest to give an indication of ¹⁷⁷Lu dosimetry for parenchymal organs. In the uterus and the tumor, characterized by specific TEM-1 expression, the ¹⁷⁷Lu-extrapolated absorbed doses are overestimated because of the lack of later measurement time points. Nevertheless, 1C1m-Fc radiolabeled with ⁶⁴Cu for imaging would appear as an interesting radionuclide companion for therapeutic application with [¹⁷⁷Lu]Lu-1C1m-Fc.

Discovery of targeted expression data for novel antibody-based and chimeric antigen receptor-based therapeutics in soft tissue sarcomas using RNA-sequencing: clinical implications

Recent failure of phase 3 trials and paucity of druggable oncogenic drivers hamper developmental therapeutics in sarcomas. Antibody-based therapeutics, like antibody-drug conjugates (ADCs) and chimeric antigen receptor (CAR)-based therapeutics, have emerged as promising strategies for anticancer drug delivery. The efficacy of these novel therapies is highly dependent on expression of the antibody target. We used RNA sequencing data from Cancer Genome Atlas (TCGA) to analyze expression of target antigens in sarcoma subtypes including dedifferentiated liposarcoma (DDLPS; n = 50), uterine leiomyosarcoma (ULMS; n = 27), leiomyosarcoma (STLMS; n = 53), undifferentiated pleomorphic sarcoma (UPS; n = 44), myxofibrosarcoma (MFS; n = 17), synovial sarcoma (SS; n = 10), and malignant peripheral nerve sheath tumor (MPNST; n = 5). We searched published literature and clinicaltrial.gov for ADC targets, bispecific antibodies, immunotoxins, radioimmunoconjugates, SPEAR T-cells, and CAR's that are in clinical trials. CD70 expression was significantly higher in DDLPS, UPS, and MFS than SS and STLMS. CDH3 expression was greater in LMS and ULMS than UPS (P < 0.001), MFS (P < 0.001), and DDLPS (P < 0.001). ERBB2 expression was low; however, it was overexpressed in MPNST when compared with UPS (P < 0.001), and MFS (P < 0.01). GPNMB was highly expressed in most sarcomas, with the exception of SS. LRRC15 also appeared to be a relevant target, especially in UPS. MSLN expression was relatively low except in SS and MPNST. PDGFRA was also highly expressed in most sarcomas with the exception of ULMS and STLMS. TNFRSF8 seems to be most appropriate in DDLPS, as well as MFS. AXL was expressed especially in MFS and STLMS. Sarcoma subtypes express multiple target genes relevant for ADCs, SPEAR T-cells and CAR's, warranting further clinical validation and evaluation.

Soluble trivalent engagers redirect cytolytic T cell activity toward tumor endothelial marker 1

Tumor endothelial marker 1 (TEM1) is an emerging cancer target with a unique dual expression profile. First, TEM1 is expressed in the stroma and neo-vasculature of many human carcinomas but is largely absent from healthy adult tissues. Second, TEM1 is expressed by tumor cells of mesenchymal origin, notably sarcoma. Here, we present two fully human anti-TEM1 single-chain variable fragment (scFv) reagents, namely, 1C1m and 7G22, that recognize distinct regions of the extracellular domain and possess substantially different affinities. In contrast to other, well-described anti-TEM1 binders, these fragments confer cytolytic activity when expressed as 2^nd generation chimeric antigen receptors (CARs). Moreover, both molecules selectively redirect human T cell effector functions toward TEM1⁺ tumor cells when incorporated into experimental soluble bispecific trivalent engagers that we term TriloBiTEs (tBs). Furthermore, systemic delivery of 1C1m-tB prevents the establishment of Ewing sarcoma tumors in a xenograft model. Our observations confirm TEM1 as a promising target for cancer immunotherapy and illustrate the prospective translational potential of certain scFv-based reagents.

Antibody Conjugates for Sarcoma Therapy: How Far along Are We?

Sarcomas are one of the most difficult type of cancer to manage and treat because of their extremely heterogeneous molecular and morphological features. Despite the progress made over the years in the establishment of standard protocols for high and low grading/staging sarcoma patients, mostly with chemotherapy and/or radiotherapy, 50% of treated patients experience relapse episodes. Because of this, in the last 20 years, new therapeutic approaches for sarcoma treatment have been evaluated in preclinical and clinical studies. Among them, antibody-based therapies have been the most studied. Immunoconjugates consist of a carrier portion, frequently represented by an antibody, linked to a toxic moiety, i.e., a drug, toxin, or radionuclide. While the efficacy of immunoconjugates is well demonstrated in the therapy of hematological tumors and more recently also of epithelial ones, their potential as therapeutic agents against sarcomas is still not completely explored. In this paper, we summarize the results obtained with immunoconjugates targeting sarcoma surface antigens, considering both preclinical and clinical studies. To date, the encouraging results obtained in preclinical studies allowed nine immunoconjugates to enter clinical trials, demonstrating the validity of immunotherapy as a promising pharmacological tool also for sarcoma therapy.

Biological evaluation of new TEM1 targeting recombinant antibodies for radioimmunotherapy: In vitro, in vivo and in silico studies

The tumour endothelial marker 1 (TEM1/endosialin/CD248) is a receptor overexpressed in several human solid tumours and silenced in normal adult tissues, representing a suitable and potentially safe target for radioimmunotherapy of sarcoma. To develop new tools with improved TEM1 targeting properties, a new panel of antibody fragments was for the first time evaluated preclinically following ¹²⁵I radiolabelling. The antibody fragment 1C1m-Fc, with the highest human/murine TEM1 binding affinity, was extensively characterized in vitro and in vivo in a Ewing's sarcoma human xenograft mouse model. In silico studies were also performed to elucidate the influence of a single amino acid mutation in the complementarity-determining region (CDR3) of the heavy chain, upon affinity maturation of the parental clone 1C1-Fc. From this study, 1C1m-Fc emerged as a promising candidate for the development of TEM1-targeted radioimmunoconjugates, namely to be further explored for theranostic applications with other suitable medical radionuclides.

177Lu radiolabeling and preclinical theranostic study of 1C1m-Fc: an anti-TEM-1 scFv-Fc fusion protein in soft tissue sarcoma

PURPOSE

TEM-1 (tumor endothelial marker-1) is a single-pass transmembrane cell surface glycoprotein expressed at high levels by tumor vasculature and malignant cells. We aimed to perform a preclinical investigation of a novel anti-TEM-1 scFv-Fc fusion antibody, 1C1m-Fc, which was radiolabeled with ¹⁷⁷Lu for use in soft tissue sarcomas models.

METHODS

1C1m-Fc was first conjugated to p-SCN-Bn-DOTA using different excess molar ratios and labeled with ¹⁷⁷Lu. To determine radiolabeled antibody immunoreactivity, Lindmo assays were performed. The in vivo behavior of [177Lu]Lu-1C1m-Fc was characterized in mice bearing TEM-1 positive (SK-N-AS) and negative (HT-1080) tumors by biodistribution and single-photon emission SPECT/CT imaging studies. Estimated organ absorbed doses were obtained based on biodistribution results.

RESULTS

The DOTA conjugation and the labeling with ¹⁷⁷Lu were successful with a radiochemical purity of up to 95%. Immunoreactivity after radiolabeling was 86% ± 4%. Biodistribution showed a specific uptake in TEM-1 positive tumor versus liver as critical non-specific healthy organ, and this specificity is correlated to the number of chelates per antibody. A 1.9-fold higher signal at 72 h was observed in SPECT/CT imaging in TEM-1 positive tumors versus control tumors.

CONCLUSION

TEM-1 is a promising target that could allow a theranostic approach to soft-tissue sarcoma, and 1C1m-Fc appears to be a suitable targeting candidate. In this study, we observed the influence of the ratio DOTA/antibody on the biodistribution. The next step will be to investigate the best conjugation to achieve an optimal tumor-to-organ radioactivity ratio and to perform therapy in murine xenograft models as a prelude to future translation in patients.

Preclinical Evaluation and Dosimetry of [111In]CHX-DTPA-scFv78-Fc Targeting Endosialin/Tumor Endothelial Marker 1 (TEM1)

PURPOSE

Endosialin/tumor endothelial marker-1 (TEM1) is an attractive theranostic target expressed by the microenvironment of a wide range of tumors, as well as by sarcoma and neuroblastoma cells. We report on the radiolabeling and preclinical evaluation of the scFv78-Fc, a fully human TEM1-targeting antibody fragment cross-reactive with mouse TEM1.

PROCEDURES

The scFv78-Fc was conjugated with the chelator p-SCN-Bn-CHX-A"-DTPA, followed by labeling with indium-111. The number of chelators per molecule was estimated by mass spectrometry. A conventional saturation assay, extrapolated to infinite antigen concentration, was used to determine the immunoreactive fraction of the radioimmunoconjugate. The radiopharmaceutical biodistribution was assessed in immunodeficient mice grafted with Ewing's sarcoma RD-ES and neuroblastoma SK-N-AS human TEM1-positive tumors. The full biodistribution studies were preceded by a dose-escalation experiment based on the simultaneous administration of the radiopharmaceutical with increasing amounts of unlabeled scFv78-Fc. Radiation dosimetry extrapolations to human adults were obtained from mouse biodistribution data according to established methodologies and additional assumptions concerning the impact of the tumor antigenic sink in the cross-species translation.

RESULTS

[111In]CHX-DTPA-scFv78-Fc was obtained with a radiochemical purity > 98 % after 1 h incubation at 42 °C and ultrafiltration. It showed good stability in human serum and > 70 % immunoreactive fraction. Biodistribution data acquired in tumor-bearing mice confirmed fast blood clearance and specific tumor targeting in both xenograft models. The radiopharmaceutical off-target uptake was predominantly abdominal. After a theoretical injection of [111In]CHX-DTPA-scFv78-Fc to the reference person, the organs receiving the highest absorbed dose would be the spleen (0.876 mGy/MBq), the liver (0.570 mGy/MBq) and the kidneys (0.298 mGy/MBq). The total body dose and the effective dose would be 0.058 mGy/MBq and 0.116 mSv/MBq, respectively.

CONCLUSIONS

[111In]CHX-DTPA-scFv78-Fc binds specifically to endosialin/TEM1 in vitro and in vivo. Dosimetry estimates are in the range of other monoclonal antibodies radiolabeled with indium-111. [111In]CHX-DTPA-scFv78-Fc could be potentially translated into clinic.

Phage display screening of therapeutic peptide for cancer targeting and therapy

Recently, phage display technology has been announced as the recipient of Nobel Prize in Chemistry 2018. Phage display technique allows high affinity target-binding peptides to be selected from a complex mixture pool of billions of displayed peptides on phage in a combinatorial library and could be further enriched through the biopanning process; proving to be a powerful technique in the screening of peptide with high affinity and selectivity. In this review, we will first discuss the modifications in phage display techniques used to isolate various cancer-specific ligands by in situ, in vitro, in vivo, and ex vivo screening methods. We will then discuss prominent examples of solid tumor targeting-peptides; namely peptide targeting tumor vasculature, tumor microenvironment (TME) and over-expressed receptors on cancer cells identified through phage display screening. We will also discuss the current challenges and future outlook for targeting peptide-based therapeutics in the clinics.

C-type lectin domain group 14 proteins in vascular biology, cancer and inflammation

The C‐type lectin domain (CTLD) group 14 family of transmembrane glycoproteins consist of thrombomodulin, CD93, CLEC14A and CD248 (endosialin or tumour endothelial marker‐1). These cell surface proteins exhibit similar ectodomain architecture and yet mediate a diverse range of cellular functions, including but not restricted to angiogenesis, inflammation and cell adhesion. Thrombomodulin, CD93 and CLEC14A can be expressed by endothelial cells, whereas CD248 is expressed by vasculature associated pericytes, activated fibroblasts and tumour cells among other cell types. In this article, we review the current literature of these family members including their expression profiles, interacting partners, as well as established and speculated functions. We focus primarily on their roles in the vasculature and inflammation as well as their contributions to tumour immunology. The CTLD group 14 family shares several characteristic features including their ability to be proteolytically cleaved and engagement of some shared extracellular matrix ligands. Each family member has strong links to tumour development and in particular CD93, CLEC14A and CD248 have been proposed as attractive candidate targets for cancer therapy.

Linking myofibroblast generation and microvascular alteration: The role of CD248 from pathogenesis to therapeutic target (Review)

Fibrosis is characterized by excessive extracellular matrix (ECM) deposition, and is the pathological outcome of tissue injury in a number of disorders. Accumulation of the ECM may disrupt the structure and function of native tissues and organs, including the lungs, heart, liver and skin, resulting in significant morbidity and mortality. On this basis, multiple lines of evidence have focused on the molecular pathways and cellular mechanisms involved in fibrosis, which has led to the development of novel antifibrotic therapies. CD248 is one of several proteins identified to be localized to the stromal compartment in cancers and fibroproliferative disease, and may serve a key role in myofibroblast generation and accumulation. Numerous studies have supported the contribution of CD248 to tumour growth and fibrosis, stimulating interest in this molecule as a therapeutic target. In addition, it has been revealed that CD248 may be involved in pathological angiogenesis. The present review describes the current understanding of the structure and function of CD248 during angiogenesis and fibrosis, supporting the hypothesis that blocking CD248 signalling may prevent both myofibroblast generation and microvascular alterations during tissue fibrosis.

Potential drugs used in the antibody-drug conjugate (ADC) architecture for cancer therapy

Cytotoxic small-molecule drugs have a major influence on the fate of antibody-drug conjugates (ADCs). An ideal cytotoxic agent should be highly potent, remain stable while linked to ADCs, kill the targeted tumor cell upon internalization and release from the ADCs, and maintain its activity in multidrug-resistant tumor cells. Lessons learned from successful and failed experiences in ADC development resulted in remarkable progress in the discovery and development of novel highly potent small molecules. A better understanding of such small-molecule drugs is important for development of effective ADCs. The present review discusses requirements making a payload appropriate for antitumor ADCs and focuses on the main characteristics of commonly-used cytotoxic payloads that showed acceptable results in clinical trials. In addition, the present study represents emerging trends and recent advances of payloads used in ADCs currently under clinical trials.

A phase 1 and randomized controlled phase 2 trial of the safety and efficacy of the combination of gemcitabine and docetaxel with ontuxizumab (MORAb-004) in metastatic soft-tissue sarcomas

Background

Ontuxizumab, a humanized monoclonal antibody, targets endosialin (tumor endothelial marker 1 [TEM‐1] or CD248), which is expressed on sarcoma cells and is believed to be involved in tumor angiogenesis. This is the first trial to evaluate ontuxizumab in patients with sarcoma.

Methods

Part 1 was an open‐label, dose‐finding, safety lead‐in: 4, 6, or 8 mg/kg with gemcitabine and docetaxel (G/D; 900 mg/m² gemcitabine on days 1 and 8 and 75 mg/m² docetaxel on day 8). In part 2, patients were randomized in a double‐blind fashion in 2:1 ratio to ontuxizumab (8 mg/kg) or a placebo with G/D. Randomization was stratified by 4 histological cohorts.

Results

In part 2 with 209 patients, no significant difference in progression‐free survival between ontuxizumab plus G/D (4.3 months; 95% confidence interval [CI], 2.7‐6.3 months) and the placebo plus G/D (5.6 months; 95% CI, 2.6‐8.3 months) was observed (P = .67; hazard ratio [HR], 1.07; 95% CI, 0.77‐1.49). Similarly, there was no significant difference in median overall survival between the 2 groups: 18.3 months for the ontuxizumab plus G/D group (95% CI, 16.2‐21.1 months) and 21.1 months for the placebo plus G/D group (95% CI, 14.2 months to not reached; P = .32; HR, 1.23; 95% CI, 0.82‐1.82). No significant differences between the treatment groups occurred for any efficacy parameter by sarcoma cohort. The combination of ontuxizumab plus G/D was generally well tolerated.

Conclusions

Ontuxizumab plus G/D showed no enhanced activity over chemotherapy alone in soft‐tissue sarcomas, whereas the safety profile of the combination was consistent with G/D alone.

Endosialin is involved in tumor blood vessel formation and is expressed on sarcoma tumor cells. This phase 1/2 randomized controlled trial shows that ontuxizumab, an endosialin‐directed monoclonal antibody, does not enhance efficacy in sarcomas when it is combined with chemotherapy (gemcitabine and docetaxel), although the combination is generally well tolerated.

CD248: A therapeutic target in cancer and fibrotic diseases

CD248/endosialin/TEM1 is a type 1 transmembrane glycoprotein found on the plasma membrane of activated mesenchymal cells. CD248 functions during embryo development and is either not expressed or found at very low levels in adult tissues. CD248 is expressed at high levels by malignant sarcoma cells, by the pericyte component of tumor vasculature and by mesenchymal cells in some fibrotic diseases. CD248 is being targeted by several experimental therapeutics including antibodies, antibody drug conjugates, as an antigen for CART cells and in therapeutic vaccines. Although the function of CD248 has yet to be fully elucidated, this protein is a potential broad scope therapeutic target.

Small animal models for the study of bone sarcoma pathogenesis:characteristics, therapeutic interests and limitations

Osteosarcoma, Ewing sarcoma and chondrosarcoma are the three main entities of bone sarcoma which collectively encompass more than 50 heterogeneous entities of rare malignancies. In contrast to osteosarcoma and Ewing sarcoma which mainly affect adolescents and young adults and exhibit a high propensity to metastasise to the lungs, chondrosarcoma is more frequently observed after 40 years of age and is characterised by a high frequency of local recurrence. The combination of chemotherapy, surgical resection and radiotherapy has contributed to an improved outcome for these patients. However, a large number of patients still suffer significant therapy related toxicities or die of refractory and metastatic disease. To better delineate the pathogenesis of bone sarcomas and to identify and test new therapeutic options, major efforts have been invested over the past decades in the development of relevant pre-clinical animal models. Nowadays, in vivo models aspire to mimic all the steps and the clinical features of the human disease as accurately as possible and should ideally be manipulable. Considering these features and given their small size, their conduciveness to experiments, their affordability as well as their human-like bone-microenvironment and immunity, murine pre-clinical models are interesting in the context of these pathologies. This chapter will provide an overview of the murine models of bone sarcomas, paying specific attention for the models induced by inoculation of tumour cells. The genetically-engineered mouse models of bone sarcoma will also be summarized.

Immunoconjugates for Osteosarcoma Therapy: Preclinical Experiences and Future Perspectives

Osteosarcoma (OS) is an aggressive osteoid-producing tumor of mesenchymal origin, which represents the most common primary bone malignancy. It is characterized by a complex and frequently uncertain etiology. The current standard care for high-grade OS treatment is neoadjuvant chemotherapy, followed by surgery and post-operative chemotherapy. In order to ameliorate survival rates of patients, new therapeutic approaches have been evaluated, mainly immunotherapy with antibody-drug conjugates or immunoconjugates. These molecules consist of a carrier (frequently an antibody) joined by a linker to a toxic moiety (drug, radionuclide, or toxin). Although several clinical trials with immunoconjugates have been conducted, mainly in hematological tumors, their potential as therapeutic agents is relatively under-explored in many types of cancer. In this review, we report the immunoconjugates directed against OS surface antigens, considering the in vitro and in vivo studies. To date, several attempts have been made in preclinical settings, reporting encouraging results and demonstrating the validity of the idea. The clinical experience with glembatumumab vedotin may provide new insights into the real efficacy of antibody-drug conjugates for OS therapy, possibly giving more information about patient selection. Moreover, new opportunities could arise from the ongoing clinical trials in OS patients with unconjugated antibodies that could represent future candidates as carrier moieties of immunoconjugates.

Tumour endothelial marker 1/endosialin-mediated targeting of human sarcoma

BACKGROUND

Tumour endothelial marker 1 (TEM1/endosialin/CD248) is a tumour-restricted cell-surface protein expressed by human sarcomas. We previously developed a high-affinity human single-chain variable fragment (scFv)-Fc fusion protein (78Fc) against TEM1 and demonstrated its specific binding to human and mouse TEM1.

PATIENT AND METHODS

Clinical sarcoma specimens were collected between 2000 and 2015 at the Hospital of the University of Pennsylvania, as approved by the institutional review board and processed by standard formalin-fixed paraffin embedded techniques. We analysed TEM1 expression in 19 human sarcoma subtypes (n = 203 specimens) and eight human sarcoma-cell lines. Near-infrared (NIR) imaging of tumour-bearing mice was used to validate 78Fc binding to TEM1⁺ sarcoma in vivo. Finally, we tested an immunotoxin conjugate of anti-TEM1 78Fc with saporin (78Fc-Sap) for its therapeutic efficacy against human sarcoma in vitro and in vivo.

RESULTS

TEM1 expression was identified by immunohistochemistry in 96% of human sarcomas, of which 81% expressed TEM1 both on tumour cells and the tumour vasculature. NIR imaging revealed specific in vivo targeting of labelled 78Fc to TEM1⁺ sarcoma xenografts. Importantly, 78Fc-Sap was effective in killing in vitro TEM1⁺ sarcoma cells and eliminated human sarcoma xenografts without apparent toxicity in vivo.

CONCLUSION

TEM1 is an important therapeutic target for human sarcoma, and the high-affinity TEM1-specific scFv fusion protein 78Fc is suitable for further clinical development for therapeutic applications in sarcoma.

Development of 89Zr-Ontuxizumab for in vivo TEM-1/endosialin PET applications

PURPOSE

The complexity of sarcoma has led to the need for patient selection via in vivo biomarkers. Tumor endothelial marker-1 (TEM-1) is a cell surface marker expressed by the tumor microenvironment. Currently MORAb-004 (Ontuxizumab), an anti-TEM-1 humanized monoclonal antibody, is in sarcoma clinical trials. Development of positron emission tomography (PET) for in vivo TEM-1 expression may allow for stratification of patients, potentially enhancing clinical outcomes seen with Ontuxizumab.

RESULTS

Characterization of cell lines revealed clear differences in TEM-1 expression. One high expressing (RD-ES) and one low expressing (LUPI) cell line were xenografted, and mice were injected with 89Zr-Ontuxizumab. PET imaging post-injection revealed that TEM-1 was highly expressed and readily detectable in vivo only in RD-ES. In vivo biodistribution studies confirmed high radiopharmaceutical uptake in tumor relative to normal organs.

EXPERIMENTAL DESIGN

Sarcoma cell lines were characterized for TEM-1 expression. Ontuxizumab was labeled with 89Zr and evaluated for immunoreactivity preservation. 89Zr-Ontuxizumab was injected into mice with high or null expressing TEM-1 xenografts. In vivo PET imaging experiments were performed.

CONCLUSION

89Zr-Ontuxizumab can be used in vivo to determine high versus low TEM-1 expression. Reliable PET imaging of TEM-1 in sarcoma patients may allow for identification of patients that will attain the greatest benefit from anti-TEM-1 therapy.

A Randomized, Double-Blind, Placebo-Controlled Phase II Study of the Efficacy and Safety of Monotherapy Ontuxizumab (MORAb-004) Plus Best Supportive Care in Patients with Chemorefractory Metastatic Colorectal Cancer

Purpose: The purpose of this study was to evaluate the safety and efficacy of ontuxizumab (MORAb-004), a monoclonal antibody that interferes with endosialin (tumor endothelial marker-1) function, in patients with chemorefractory metastatic colorectal cancer and to identify a responsive patient population based on biomarkers.Experimental Design: This was a randomized, double-blind, placebo-controlled, phase II study. Patients were randomly assigned in a 2:1 ratio to receive weekly intravenous ontuxizumab (8 mg/kg) or placebo plus best supportive care until progression or unacceptable toxicity. Tissue and blood biomarkers were evaluated for their ability to identify a patient population that was responsive to ontuxizumab.Results: A total of 126 patients were enrolled. No significant difference between the ontuxizumab and placebo groups was evident for the primary endpoint of progression-free survival (PFS), with a median PFS of 8.1 weeks in each group (HR, 1.13; 95% confidence interval, 0.76-1.67; P = 0.53). There were no significant differences between groups for overall survival (OS) or overall response rate (ORR). The most common treatment-emergent adverse events (TEAEs) in the ontuxizumab group (vs. the placebo group, respectively) were fatigue (53.7% vs. 47.5%), nausea (39.0% vs. 35.0%), decreased appetite (34.1% vs. 27.5%), and constipation (28.0% vs. 32.5%). The most common grade 3/4 TEAE in the ontuxizumab group versus placebo was back pain (11.0% vs. 0%). No single biomarker clearly identified patients responsive to ontuxizumab.Conclusions: No benefit with ontuxizumab monotherapy compared with placebo for clinical response parameters of PFS, OS, or ORR was demonstrated. Ontuxizumab was well tolerated. Clin Cancer Res; 24(2); 316-25. ©2017 AACR.

Generation of a novel Antibody-Drug Conjugate targeting endosialin: potent and durable antitumor response in sarcoma

The endosialin/CD248/TEM1 receptor is expressed on the cell surface of tumor-associated stroma cells as well as in sarcoma and neuroblastoma cells. This receptor is emerging as an attractive molecule in diagnostics and therapeutics because of its expression across the stroma of many human tumors, the low to absent expression in normal tissues and accessibility from the vascular circulation. In this study, we present evidence of the preclinical efficacy of a novel Antibody-Drug Conjugate (ENDOS/ADC). It consists of a humanized endosialin monoclonal antibody, named hMP-E-8.3, conjugated to a potent duocarmycin derivative. In endosialin expressing cancer cell lines, this ENDOS/ADC showed a powerful, specific and target-dependent killing activity. High expression levels of endosialin in cells correlated with efficient internalization and cytotoxic effects in vitro. Efficacy studies demonstrated that ENDOS/ADC treatment led to a long-lasting tumor growth inhibition of a cell line-based model of human osteosarcoma. Taken together, our results demonstrate that endosialin is an attractive target in sarcoma and suggest that ENDOS/ADC has the potential to be developed into a bio-therapeutic agent for these malignancies.

Endosialin-Expressing Pericytes Promote Metastatic Dissemination

Metastasis is a multistep process that is critically dependent on the interaction of metastasizing tumor cells with cells in the local microenvironment. Within this tumor stroma, vessel-associated pericytes and myofibroblasts share a number of traits, including the upregulated expression of the transmembrane receptor endosialin (CD248). Comparative experiments in wild-type and endosialin-deficient mice revealed that stromal endosialin does not affect primary tumor growth but strongly promotes spontaneous metastasis. Mechanistically, endosialin-expressing pericytes in the primary tumor facilitate distant site metastasis by promoting tumor cell intravasation in a cell contact-dependent manner, resulting in elevated numbers of circulating tumor cells. Corresponding to these preclinical experiments, in independent cohorts of primary human breast cancers, upregulated endosialin expression significantly correlates with increased metastasis and poorer patient survival. Together, the data demonstrate a critical role for endosialin-expressing primary tumor pericytes in mediating metastatic dissemination and identify endosialin as a promising therapeutic target in breast cancer. Cancer Res; 76(18); 5313-25. ©2016 AACR.

Athymic nude mice as an experimental model for cancer treatment

Athymic nude mice, a murine strain bearing spontaneous deletion in the Foxn1 gene that causes deteriorated or absent thymus (which results in inhibited immune system with reduction of number of T cells), represent a widely used model in cancer research having long lasting history as a tool for preclinical testing of drugs. The review describes three models of athymic mice that utilize cancer cell lines to induce tumors. In addition, various methods that can be applied in order to evaluate activity of anticancer agents in these models are shown and discussed. Although each model has certain disadvantages, they are still considered as inevitable instruments in many fields of cancer research, particularly in finding new drugs that would more effectively combat the cancer disease or enhance the use of current chemotherapy. Finally, the review summarizes strengths and weaknesses as well as future perspectives of the athymic nude mice model in cancer research.

Tumor rim cells: From resistance to vascular targeting agents to complete tumor ablation

Current vascular targeting strategies pursue two main goals: anti-angiogenesis agents aim to halt sprouting and the formation of new blood vessels, while vascular disrupting agents along with coaguligands seek to compromise blood circulation in the vessels. The ultimate goal of such therapies is to deprive tumor cells out of oxygen and nutrients long enough to succumb cancer cells to death. Most of vascular targeting agents presented promising therapeutic potential, but the final goal which is cure is rarely achieved. Nevertheless, in both preclinical and clinical settings, tumors tend to grow back, featuring a highly invasive, metastatic, and extremely resistant form. This review highlights the critical significance of tumor rim cells as the main factor, determining therapy success with vascular targeting agents. We present an overview of different single and combination treatments with vascular targeting agents that enable efficient targeting of tumor rim cells and long-lasting tumor cure. Understanding the nature of tumor rim cells, how they establish, how they manage to survive of vascular targeting agents, and how they contribute in tumor refractoriness, may open new avenues to the development of beneficial strategies, capable to eliminate residual rim cells, and enable tumor ablation once and forever.

Strategies and challenges for the next generation of antibody-drug conjugates

Antibody-drug conjugates (ADCs) are one of the fastest growing classes of oncology therapeutics. After half a century of research, the approvals of brentuximab vedotin (in 2011) and trastuzumab emtansine (in 2013) have paved the way for ongoing clinical trials that are evaluating more than 60 further ADC candidates. The limited success of first-generation ADCs (developed in the early 2000s) informed strategies to bring second-generation ADCs to the market, which have higher levels of cytotoxic drug conjugation, lower levels of naked antibodies and more-stable linkers between the drug and the antibody. Furthermore, lessons learned during the past decade are now being used in the development of third-generation ADCs. In this Review, we discuss strategies to select the best target antigens as well as suitable cytotoxic drugs; the design of optimized linkers; the discovery of bioorthogonal conjugation chemistries; and toxicity issues. The selection and engineering of antibodies for site-specific drug conjugation, which will result in higher homogeneity and increased stability, as well as the quest for new conjugation chemistries and mechanisms of action, are priorities in ADC research.

Diverse Mechanisms of Sp1-Dependent Transcriptional Regulation Potentially Involved in the Adaptive Response of Cancer Cells to Oxygen-Deficient Conditions

The inside of a tumor often contains a hypoxic area caused by a limited supply of molecular oxygen due to aberrant vasculature. Hypoxia-inducible factors (HIFs) are major transcription factors that are required for cancer cells to adapt to such stress conditions. HIFs, complexed with the aryl hydrocarbon receptor nuclear translocator, bind to and activate target genes as enhancers of transcription. In addition to this common mechanism, the induction of the unfolded protein response and mTOR signaling in response to endoplasmic reticulum stress is also known to be involved in the adaptation to hypoxia conditions. Sp1 is a ubiquitously-expressed transcription factor that plays a vital role in the regulation of numerous genes required for normal cell function. In addition to the well-characterized stress response mechanisms described above, increasing experimental evidence suggests that Sp1 and HIFs collaborate to drive gene expression in cancer cells in response to hypoxia, thereby regulating additional adaptive responses to cellular oxygen deficiency. However, these characteristics of Sp1 and their biological merits have not been summarized. In this review, we will discuss the diverse mechanisms of transcriptional regulation by Sp1 and their potential involvement in the adaptive response of cancer cells to hypoxic tumor microenvironments.