Targeted imaging of Ewing sarcoma in preclinical models using a 64Cu-labeled anti-CD99 antibody

Current Role of Topoisomerase I Inhibitors for the Treatment of Mesenchymal Malignancies and Their Potential Future Use as Payload of Sarcoma-Specific Antibody-Drug Conjugates

BACKGROUND

Topoisomerase I is an enzyme that plays a crucial part in DNA replication and transcription by the relaxation of supercoiled double-stranded DNA. Topoisomerase I inhibitors bind to the topoisomerase I cleavage complex, thereby stabilizing it and preventing the religation of the DNA strands, leading to DNA damage, cell cycle arrest, and apoptosis. Various topoisomerase I inhibitors have been evaluated in solid tumors, and irinotecan and topotecan have been approved for the treatment of epithelial malignancies. None of them have been approved for sarcoma, a diverse group of rare solid tumors with an unmet need for effective treatments.

SUMMARY

Topoisomerase I inhibitors have been evaluated in preclinical studies as single agents or in combination in solid tumors, some of which have included sarcomas where activity was observed. Clinical trials evaluating topoisomerase I inhibitors for the treatment of sarcoma have shown limited efficacy as monotherapy. In combination with other cytotoxic agents, topoisomerase I inhibitors have become part of clinical routine in selected sarcoma subtypes. Regimens such as irinotecan/vincristine/temozolomide are used in relapsed rhabdomyosarcoma, irinotecan/temozolomide and vincristine/topotecan/cyclophosphamide are commonly given in refractory Ewing sarcoma, and topotecan/carboplatin showed some activity in advanced soft tissue sarcoma. This review provides an overview of key studies with topoisomerase I inhibitors for the treatment of sarcoma. Topoisomerase I inhibitors are currently also being assessed as "payloads" for antibody-drug conjugates (ADCs), allowing for the targeting of specific antigen-expressing tumor cells and the delivery of the inhibitor directly to the tumor cells with the potential of enhancing therapeutic efficacy while minimizing systemic toxicity. Here, we also provide a brief overview on topoisomerase I-ADCs.

KEY MESSAGE

Topoisomerase I inhibitors are an important component of some systemic therapies for selected sarcomas and have potent cytotoxic properties and pharmacological characteristics that make them relevant candidates as payloads for the development of sarcoma-specific ADCs. ADCs are antibody-based targeted agents allowing for efficient and specific delivery of a given drug to the tumor cell. Topoisomerase I-ADCs are a novel targeted delivery approach which may have the potential to improve the therapeutic index of topoisomerase I inhibitors in the treatment of sarcoma and warrants investigation in a broad variety of mesenchymal malignancies.

Imaging Hallmarks of Sarcoma Progression Via X-ray Computed Tomography: Beholding the Flower of Evil

Simple Summary

Sarcomas represent the largest group of rare solid tumors that arise from mesenchymal stem cells and are a leading cause of cancer death in individuals younger than 20 years of age. There is an immediate need for the development of an algorithm for the early accurate diagnosis of sarcomas due to the high rate of diagnostic inaccuracy, which reaches up to 30%. X-ray computed tomography is a non-invasive imaging technique used to obtain detailed internal images of the human or animal body in clinical practice and preclinical studies. We summarized the main imaging features of soft tissue and bone sarcomas, and noted the development of new molecular markers to reach tumor type-specific imaging. Also, we demonstrated the possibility of the use X-ray computed microtomography for non-destructive 3D visualization of sarcoma progression in preclinical studies. Finding correlations between X-ray computed tomography modalities and the results of the histopathological specimen examination may significantly increase the accuracy of diagnostics, which leads to the initiation of appropriate management in a timely manner and, consequently, to improved outcomes.

Abstract

Sarcomas are a leading cause of cancer death in individuals younger than 20 years of age and represent the largest group of rare solid tumors. To date, more than 100 morphological subtypes of sarcomas have been described, among which epidemiology, clinical features, management, and prognosis differ significantly. Delays and errors in the diagnosis of sarcomas limit the number of effective therapeutic modalities and catastrophically worsen the prognosis. Therefore, the development of an algorithm for the early accurate diagnosis of sarcomas seems to be as important as the development of novel therapeutic advances. This literature review aims to summarize the results of recent investigations regarding the imaging of sarcoma progression based on the use of X-ray computed tomography (CT) in preclinical studies and in current clinical practice through the lens of cancer hallmarks. We attempted to summarize the main CT imaging features of soft-tissue and bone sarcomas. We noted the development of new molecular markers with high specificity to antibodies and chemokines, which are expressed in particular sarcoma subtypes to reach tumor type-specific imaging. We demonstrate the possibility of the use of X-ray computed microtomography (micro-CT) for non-destructive 3D visualization of solid tumors by increasing the visibility of soft tissues with X-ray scattering agents. Based on the results of recent studies, we hypothesize that micro-CT enables the visualization of neovascularization and stroma formation in sarcomas at high-resolution in vivo and ex vivo, including the novel techniques of whole-block and whole-tissue imaging. Finding correlations between CT, PET/CT, and micro-CT imaging features, the results of the histopathological specimen examination and clinical outcomes may significantly increase the accuracy of soft-tissue and bone tumor diagnostics, which leads to the initiation of appropriate histotype-specific management in a timely manner and, consequently, to improved outcomes.

Systemic Treatment of Ewing Sarcoma: Current Options and Future Perspectives

Ewing sarcoma (ES) is an uncommon malignant neoplasm, mostly affecting young adults and adolescents. Surgical excision, irradiation, and combinations of multiple chemotherapeutic agents are currently used as a multimodal strategy for the treatment of local and oligometastatic disease. Although ES usually responds to the primary treatment, relapsed and primarily refractory disease remains a difficult therapeutic challenge. The growing understanding of cancer biology and the subsequent development of new therapeutic strategies have been put at the service of research in recurrent and refractory ES, generating a great number of ongoing studies with compounds that could find superior clinical outcomes in the years to come. This review gathers the current available information on the treatment and clinical investigation of ES and aims to be a point of support for future research.

Rapid Flow-Based System for Separation of Radioactive Metals by Selective Complex Formation

Short-lived radioactive metals are important tracers in clinical diagnosis. Radioactive metals for clinical use are produced from suitable target metals in cyclotrons. The trace amount of radioactive metal produced is contained in a relatively large amount of target metal. A rapid and effective method is required to isolate the radioactive metal. In the present study, selective complex formation followed by cation-exchange adsorption was performed in a continuous flow-based system. Ethylenediamine-N,N,N',N'-tetraacetic acid (EDTA) was selected as the ligand after simulation of the separation of radioactive Ga from the target (Zn). Selectively, the Ga-EDTA complex passed through the cation trap, while Zn²⁺ was trapped. This separation principle is opposite to that of typical solid-phase extraction, which captures the target ion. The proposed separation was performed in a flow-based system with a parallel, open-channel ion trap. The performance was optimized by altering the channel dimensions, channel-filling mesh, and flow rate. Finally, the target radioactive metal, Ga, was selectively and effectively (>99%) separated from a mixture of 50 fg Ga/L and 100 mg Zn/L. The concentration of Zn remaining in the Ga solution was 2.3 μg/L. The complexed Ga was converted to free Ga³⁺ by a simple UV irradiation method. The proposed method effectively and rapidly separates trace amounts of radioactive metals contained in larger amounts of target metals using a simple flow system that can be operated on site.

EWS-FLI1-targeting peptide identifies Ewing sarcoma tumor boundaries and lymph node metastasis via near-infrared imaging

Ewing sarcoma (ES) is one of the most aggressive types of pediatric tumors. The lack of tools for the identification of ES has largely hindered clinical diagnosis and the improvement of treatment. To address this challenge, we synthesized a near‐infrared (NIR) fluorescent probe (CS2‐N‐E9R) that targets the ES‐specific fusion protein EWS–FLI1 (E/F). This probe exhibited specific and high binding affinity to E/F. Further studies in animal models showed that CS2‐N‐E9R can be used to identify the boundaries of ES and lymph node metastases under a complex biological environment. These results demonstrate that CS2‐N‐E9R is a promising probe for early diagnosis and surgical guidance of ES through molecularly targeted NIR imaging.

SP70-Targeted Imaging for the Early Detection of Lung Adenocarcinoma

NJ001 is a monoclonal antibody that can specifically recognize the SP70 antigen on lung adenocarcinoma cells. The goal of this study was to explore its utility in targeted imaging. Subcutaneous xenograft and orthotopic lung tumor implantation BALB/c mouse models were established. Near-infrared fluorescent CF750-labeled NJ001 was injected into two tumor mouse models. Mice that received orthotopic lung tumor implantation were also injected with NJ001-conjugated nanomagnetic beads intravenously, and then underwent micro-CT scanning. Meanwhile, mice with lung tumor were intravenously injected with normal saline and bare nanomagnetic beads as a control. Fluorescence could be monitored in the mice detected by anti-SP70 fluorescence imaging, which was consistent with tumor burden. Signal intensities detected with SP70-targeted micro-CT scans were greater than those in control mice. More importantly, orthotopic tumor lesions could be found on the fourth week with SP70-targeted imaging, which was 2 weeks earlier than detection in the control. Our results suggest that SP70 is a promising target for molecular imaging, and molecularly targeted imaging with an NJ001-labeled probe could be applied for the early detection of lung adenocarcinoma.

Nrf2 induced cisplatin resistance in ovarian cancer by promoting CD99 expression

Cisplatin resistance is a vital obstacle for the prognosis of ovarian cancer. However, the mechanism of cisplatin resistance is still unknown. This research was performed to explore the role of Nrf2 (nuclear factor, erythroid 2 like 2) and CD99 (CD99 molecule) in cisplatin resistance in ovarian cancer. QRT-PCR and Western blot were used to detect the expression of CD99 in ovarian cancer cells and tissues with different cisplatin sensitivities. Cell viability was analyzed by the Cell Counting Kit-8 (CCK8). The relationship of Nrf2 and CD99 was assessed by dual-luciferase reporter gene assay and chromatin immunoprecipitation (ChIP). Bioinformatics analysis was performed to search for the downstream gene of CD99. In this study, it was revealed that CD99 was highly expressed in cisplatin-resistant ovarian cancer cells and tissues, while lower CD99 expression was found in cisplatin-sensitive ovarian cancer cells and tissues. In addition, the overexpression of CD99 resulted in cisplatin resistance; on the other hand, knockdown of CD99 sensitized ovarian cancer to cisplatin. Furthermore, survival analysis indicated that overall survival (OS) and progression-free survival (PFS) of patients with higher CD99 expression were shorter than those with lower CD99 expression. It was also found that when Nrf2 was upregulated in cisplatin-sensitive ovarian cells, CD99 expression and cell viability increased after cisplatin treatment. Knockdown of CD99 could reverse cisplatin resistance induced by Nrf2. Conversely, when Nrf2 was knocked down in cisplatin-resistant ovarian cancer cells, CD99 expression and cell viability with cisplatin treatment decreased, while simultaneously upregulating CD99 reactivated cisplatin resistance in ovarian cancer cells. The dual-luciferase reporter gene assay and ChIP analysis suggested CD99 was a downstream gene of Nrf2, and Nrf2 positively regulated the expression of CD99 at the transcriptional level. In conclusion, Nrf2 induced cisplatin resistance in ovarian cancer cells by promoting CD99 expression. Targeted CD99 might be an effective way to reverse cisplatin resistance in ovarian cancer.

Exploiting Signaling Pathways and Immune Targets Beyond the Standard of Care for Ewing Sarcoma

Ewing sarcoma (ES) family of tumors includes bone and soft tissue tumors that are often characterized by a specific translocation between chromosome 11 and 22, resulting in the EWS-FLI1 fusion gene. With the advent of multi-modality treatment including cytotoxic chemotherapy, surgery, and radiation therapy, the prognosis for patients with ES has substantially improved. However, a therapeutic plateau is now reached for both localized and metastatic disease over the last two decades. Burdened by the toxicity limits associated with the current frontline systemic therapy, there is an urgent need for novel targeted therapeutic strategies. In this review, we discuss the current treatment paradigm of ES, and explore preclinical evidence and emerging treatments directed at tumor signaling pathways and immune targets.

Targeting Tumor Vascular CD99 Inhibits Tumor Growth

CD99 (MIC2; single-chain type-1 glycoprotein) is a heavily O-glycosylated transmembrane protein (32 kDa) present on leukocytes and activated endothelium. Expression of CD99 on endothelium is important in lymphocyte diapedesis. CD99 is a diagnostic marker for Ewing's Sarcoma (EWS), as it is highly expressed by these tumors. It has been reported that CD99 can affect the migration, invasion and metastasis of tumor cells. Our results show that CD99 is also highly expressed in the tumor vasculature of most solid tumors. Furthermore, we found that in vitro CD99 expression in cultured endothelial cells is induced by starvation. Targeting of murine CD99 by a conjugate vaccine, which induced antibodies against CD99 in mice, resulted in inhibition of tumor growth in both a tumor model with high CD99 (Os-P0109 osteosarcoma) and low CD99 (CT26 colon carcinoma) expression. We demonstrated that vaccination against CD99 is safe, since no toxicity was observed in mice with high antibody titers against CD99 in their sera during a period of almost 11 months. Targeting of CD99 in humans is more complicated due to the fact that the human and mouse CD99 protein are not identical. We are the first to show that growth factor activated endothelial cells express a distinct human CD99 isoform. We conclude that our observations provide an opportunity for specific targeting of CD99 isoforms in human tumor vasculature.

Production and characterization of monoclonal antibodies against recombinant extracellular domain of CD99

BACKGROUND AND OBJECTIVE

CD99/MIC2 gene product is a heavily glycosylated transmembrane protein which plays a major role in homotypic cell adhesion, apoptosis of double positive T cells and vesicular protein trafficking. It is over expressed in various cancers and has been considered as an ideal therapeutic target. The present study focused at developing monoclonal antibodies against the extracellular domain (ECD) of CD99 using hybridoma technology.

MATERIALS AND METHODS

In order to generate monoclonal antibodies, the recombinant ECD of CD99 was used for immunizing the mice. Resulting hybridomas were screened through indirect ELISA. Clones which gave high absorbance values were sub cloned by limiting dilution followed by isotype determination, IP, WB and FACS. The monoclonal antibody 547F2 4F12 was purified from culture supernatant using FPLC and further screened using IF. Finally, the antibodies were validated for specificity using siRNA knock-down.

RESULTS

We were able to establish stable hybridoma clones secreting CD99 antibodies. The antibodies reacted with both the recombinant ECD as well as the wild type CD99 and their isotype's were determined as IgM.

CONCLUSION

Based on these results, we propose that the purified monoclonal antibody 547F2 4F12 could be possibly used for targeting tumors which over express CD99.

Introducing fluorescence guided surgery into orthopedic oncology: A systematic review of candidate protein targets for Ewing sarcoma

Ewing sarcoma (ES), an aggressive bone and soft‐tissue tumor, is treated with chemotherapy, radiotherapy, and surgery. Intra‐operative distinction between healthy and tumorous tissue is of paramount importance but challenging, especially after chemotherapy and at complex anatomical locations. Near infrared (NIR) fluorescence‐guided surgery (FGS) is able to facilitate the determination of tumor boundaries intra‐operatively, improving complete resection and therefore survival. This review evaluates potential ES‐specific proteins from the literature as targets for NIR FGS.

CD99: A Cell Surface Protein with an Oncojanus Role in Tumors

The cell surface molecule CD99 has gained interest because of its involvement in regulating cell differentiation and adhesion/migration of immune and tumor cells. However, the molecule plays an intriguing and dual role in different cell types. In particular, it acts as a requirement for cell malignancy or as an oncosuppressor in tumors. In addition, the gene encodes for two different isoforms, which also act in opposition inside the same cell. This review highlights key studies focusing on the dual role of CD99 and its isoforms and discusses major critical issues, challenges, and strategies for overcoming those challenges. The review specifically underscores the properties that make the molecule an attractive therapeutic target and identifies new relationships and areas of study that may be exploited. The elucidation of the spatial and temporal control of the expression of CD99 in normal and tumor cells is required to obtain a full appreciation of this molecule and its signaling.

Adult Primary Spinal Epidural Extraosseous Ewing's Sarcoma: A Case Report and Review of the Literature

Background. Extraosseous Ewing's sarcoma in the spinal epidural space is a rare malignancy, especially in adults. Case Presentation. A 40-year-old male presented with back pain and urinary hesitancy. MRI revealed a thoracic extradural mass with no osseous involvement. He underwent surgery for gross total resection of the mass, which was diagnosed as Ewing's sarcoma. He was subsequently treated with chemoradiotherapy. He remains disease-free 1 year after surgery. Review of the literature indicated only 45 previously reported cases of spinal epidural extraosseous Ewing's sarcoma in adults. Conclusions. Extraosseous Ewing's sarcoma in the spinal epidural space is a rare clinical entity that should be included in the differential for spinal epidural masses. Its treatment is multidisciplinary but frequently requires surgical intervention due to compressive neurologic symptoms. Gross total resection appears to correlate with improved outcomes.

Preclinical imaging and translational animal models of cancer for accelerated clinical implementation of nanotechnologies and macromolecular agents

The majority of animal models of cancer have performed poorly in terms of predicting clinical performance of new therapeutics, which are most often first evaluated in patients with advanced, metastatic disease. The development and use of metastatic models of cancer may enhance clinical translatability of preclinical studies focused on the development of nanotechnology-based drug delivery systems and macromolecular therapeutics, potentially accelerating their clinical implementation. It is recognized that the development and use of such models are not without challenge. Preclinical imaging tools offer a solution by allowing temporal and spatial characterization of metastatic lesions. This paper provides a review of imaging methods applicable for evaluation of novel therapeutics in clinically relevant models of advanced cancer. An overview of currently utilized models of oncology in small animals is followed by image-based development and characterization of visceral metastatic cancer models. Examples of imaging tools employed for metastatic lesion detection, evaluation of anti-tumor and anti-metastatic potential and biodistribution of novel therapies, as well as the co-development and/or use of imageable surrogates of response, are also discussed. While the focus is on development of macromolecular and nanotechnology-based therapeutics, examples with small molecules are included in some cases to illustrate concepts and approaches that can be applied in the assessment of nanotechnologies or macromolecules.

Targeted therapies for advanced Ewing sarcoma family of tumors

The prognosis of adolescent and young adult patients battling metastatic Ewing sarcoma family of tumors (ESFT) remains less than 30% despite the development of systemic therapies. In the era of personalized medicine, novel molecular targets have been tested in preclinical or clinical settings in ESFT. In this review, we focus on early clinical and translational research that identified multiple molecular targets, including IGF-1R; mTOR; tyrosine kinase inhibitors; EWS-FLI1-related targets, and others. Overall, novel targeted therapies demonstrated modest efficacy; however pronounced and durable antineoplastic responses have been observed in small subsets of treated patients, for example with IGF-1R antibodies. Identifying outcome-predicting biomarkers and overcoming treatment resistance remain major challenges. Due to the rarity of ESFT, multi-institutional collaboration efforts of clinicians, basic and translational scientists are needed in order to understand biology of therapeutic response or resistance, which can lead to development of novel therapeutic methods and improved patient outcomes.