A single chain immunotoxin, targeting the melanoma-associated chondroitin sulfate proteoglycan, is a potent inducer of apoptosis in cultured human melanoma cells

Immunohistochemical detection of the chondroitin sulfate proteoglycan 4 protein in primary and metastatic melanoma

Treatment of malignant melanoma, the most aggressive form of skin cancer, continues to be a major challenge for clinicians. New targeted therapies with kinase inhibitors or drugs which modify the immune response are often accompanied by the development of resistance or severe side effects. In this context, chondroitin sulfate proteoglycan 4 (CSPG4), a highly immunogenic melanoma tumor antigen, could be a potential target for alternative therapeutic approaches. The aim of the present study was to identify differences in the levels of CSPG4 protein expression in primary and metastatic melanomas as well as to analyze correlations between CSPG4 expression and histopathological data and patient characteristics. A total of 189 melanoma tissue samples from Lower Austria, including primary melanomas and melanoma metastases, were immunohistochemically stained for the expression of CSPG4 and statistical analyses were performed. A total of 65.6% of melanoma tissue samples stained positive for the expression of CSPG4. Primary nodular and primary superficial spreading melanomas demonstrated a significantly higher number of positively stained tissue samples for CSPG4 compared with primary lentigo maligna melanomas. No significant differences in the expression of CSPG4 were demonstrated between primary melanomas and melanoma metastases. The present study supports the advancement of the understanding of CSPG4 tissue expression patterns in melanoma patients and provides additional information for further investigation of CSPG4 as a potential therapeutic target.

Antibody-Based Targeted Interventions for the Diagnosis and Treatment of Skin Cancers

BACKGROUND

Cutaneous malignancies most commonly arise from skin epidermal cells. These cancers may rapidly progress from benign to a metastatic phase. Surgical resection represents the gold standard therapeutic treatment of non-metastatic skin cancer while chemo- and/or radiotherapy are often used against metastatic tumors. However, these therapeutic treatments are limited by the development of resistance and toxic side effects, resulting from the passive accumulation of cytotoxic drugs within healthy cells.

OBJECTIVE

This review aims to elucidate how the use of monoclonal Antibodies (mAbs) targeting specific Tumor Associated Antigens (TAAs) is paving the way to improved treatment. These mAbs are used as therapeutic or diagnostic carriers that can specifically deliver cytotoxic molecules, fluorophores or radiolabels to cancer cells that overexpress specific target antigens.

RESULTS

mAbs raised against TAAs are widely in use for e.g. differential diagnosis, prognosis and therapy of skin cancers. Antibody-Drug Conjugates (ADCs) particularly show remarkable potential. The safest ADCs reported to date use non-toxic photo-activatable Photosensitizers (PSs), allowing targeted Photodynamic Therapy (PDT) resulting in targeted delivery of PS into cancer cells and selective killing after light activation without harming the normal cell population. The use of near-infrared-emitting PSs enables both diagnostic and therapeutic applications upon light activation at the specific wavelengths.

CONCLUSION

Antibody-based approaches are presenting an array of opportunities to complement and improve current methods employed for skin cancer diagnosis and treatment.

Clinical-Scale Production of CAR-T Cells for the Treatment of Melanoma Patients by mRNA Transfection of a CSPG4-Specific CAR under Full GMP Compliance

Chimeric antigen receptor (CAR)-T cells already showed impressive clinical regressions in leukemia and lymphoma. However, the development of CAR-T cells against solid tumors lags behind. Here we present the clinical-scale production of CAR-T cells for the treatment of melanoma under full GMP compliance. In this approach a CAR, specific for chondroitin sulfate proteoglycan 4 (CSPG4) is intentionally transiently expressed by mRNA electroporation for safety reasons. The clinical-scale protocol was optimized for: (i) expansion of T cells, (ii) electroporation efficiency, (iii) viability, (iv) cryopreservation, and (v) potency. Four consistency runs resulted in CAR-T cells in clinically sufficient numbers, i.e., 2.4 × 10⁹ CAR-expressing T cells, starting from 1.77x10⁸ PBMCs, with an average expansion of 13.6x, an electroporation efficiency of 88.0% CAR-positive cells, a survival of 74.1% after electroporation, and a viability of 84% after cryopreservation. Purity was 98.7% CD3⁺ cells, with 78.1% CD3⁺/CD8⁺ T cells and with minor contaminations of 1.2% NK cells and 0.6% B cells. The resulting CAR-T cells were tested for cytolytic activity after cryopreservation and showed antigen-specific and very efficient lysis of tumor cells. Although our work is descriptive rather than investigative in nature, we expect that providing this clinically applicable protocol to generate sufficient numbers of mRNA-transfected CAR-T cells will help in moving the field of adoptive cell therapy of cancer forward.

CSPG4-Specific CAR T Cells for High-Risk Childhood B Cell Precursor Leukemia

The advent of CD19-specific chimeric antigen receptor (CAR) T cells has proven to be a powerful asset in the arsenal of cancer immunotherapy of acute lymphoblastic leukemia and certain B cell lymphomas. However, a sizable portion of patients treated with CD19-CAR T cells relapse with CD19-negative cancer cells, necessitating the quest for back-up antigens. Chondroitin sulfate proteoglycan 4 (CSPG4) expression has been reported on leukemic blasts bearing the ill-fated MLL 11q23 rearrangement. We aimed at exploring the use of CSPG4-specific CAR T cells against mixed-lineage leukemia (MLL)-rearranged leukemic blasts, using the precursor B cell leukemia cell line KOPN8 (MLL–MLLT1 translocation) as a model. First, we confirmed CSPG4 expression on KOPN8 cells. Bulk T cells electroporated with mRNA encoding a CSPG4-specific CAR upregulated activation markers and secreted the Th1 cytokines TNF and IFNγ in an antigen-specific manner upon co-culture with KOPN8 cells. More importantly, CSPG4-specific CAR T cells evinced specific degranulation towards KOPN8 cells and specifically lysed KOPN8 target cells in chromium lysis experiments. CSPG4 is a well-established CAR target in cutaneous melanoma. Here, we provide proof-of-principle data for the use of CSPG4-specific CAR T cells against MLL-translocated leukemias.

Efficient targeting of CD13 on cancer cells by the immunotoxin scFv13-ETA' and the bispecific scFv [13xds16]

PURPOSE

Treatment of cancer using standard chemotherapy still offers a poor prognosis combined with severe side effects. Novel antibody-based therapies have been shown to overcome low efficiency and lack of selectivity by targeting cancer-associated antigens, such as aminopeptidase CD13.

METHODS

We isolated a high-affinity CD13-specific single-chain fragment variable (scFv13) from a phage display library of V-genes from mice immunized with soluble antigen. An immunotoxin comprising the scFv13 and a truncated version of the exotoxin A of Pseudomonas aeruginosa (ETA', scFv13-ETA') and a bispecific scFv targeting CD13 and CD16 simultaneously (bsscFv[13xds16]) was generated and investigated for their therapeutic potential.

RESULTS

Both fusion proteins bound specifically to target cells with high affinity. Furthermore, scFv13-ETA' inhibited the proliferation of human cancer cell lines efficiently at low concentrations (IC50 values of 408 pM-7 nM) and induced apoptosis (40-85% of target cells). The bsscFv triggered dose-dependent antibody-dependent cell-mediated cytotoxicity, resulting in the lysis of up to 23.9% A2058 cells, 18.0% MDA-MB-468 cells and 19.1% HL-60 cells.

CONCLUSION

The provided data demonstrate potent therapeutic activity of the scFv13-ETA' and the bsscFv[13xds16]. The CD13-specific scFv is therefore suitable for the direct and specific delivery of both cytotoxic agents and effector cells to cancer-derived cells, making it ideal for further therapeutic evaluation.

Selection of novel affinity-matured human chondroitin sulfate proteoglycan 4 antibody fragments by yeast display

Chondroitin sulfate proteoglycan 4 (CSPG4) is a promising target for cancer immunotherapy due to its high level of expression in a number of malignant tumors, and its essential role in tumor growth and progression. Clinical application of CSPG4-targeting immunotherapies is hampered by the lack of fully human high-affinity CSPG4 antibodies or antibody fragments. To overcome this limitation, we performed affinity maturation on a novel human CSPG4 single-chain Fv fragment (scFv) using the random mutagenesis approach and screened for improved variants from a yeast display library using a modified whole-cell panning method followed by fluorescence-activated cell sorting. After six rounds of panning and sorting, the top seven mutant scFvs were isolated and their binding affinities were characterized by flow cytometry and surface plasmon resonance. These highly specific, affinity-matured variants displayed nanomolar to picomolar binding affinities to the CSPG4 antigen. While each of the mutants harbored only two to six amino acid substitutions, they represented ~270-3000-fold improvement in affinity compared to the parental clone. Our study has generated affinity-matured scFvs for the development of antibody-based clinical therapeutics targeting CSPG4-expressing tumors.

Granzyme B-based cytolytic fusion protein targeting EpCAM specifically kills triple negative breast cancer cells in vitro and inhibits tumor growth in a subcutaneous mouse tumor model

Triple-negative breast cancer (TNBC) is associated with poor prognosis and high prevalence among young premenopausal women. Unlike in other breast cancer subtypes, no targeted therapy is currently available. Overexpression of epithelial cell adhesion molecule (EpCAM) in 60% of TNBC tumors correlates with poorer prognosis and is associated with cancer stem cell phenotype. Thus, selective elimination of EpCAM(+) TNBC tumor cells is of clinical importance. Therefore, we constructed a fully human targeted cytolytic fusion protein, designated GbR201K-αEpCAM(scFv), in which an EpCAM-selective single-chain antibody fragment (scFv) is genetically fused to a granzyme B (Gb) mutant with reduced sensitivity to its natural inhibitor serpin B9. In vitro studies confirmed its specific binding, internalization and cytotoxicity toward a panel of EpCAM-expressing TNBC cells. Biodistribution kinetics and tumor-targeting efficacy using MDA-MB-468 cells in a human TNBC xenograft model in mice revealed selective accumulation of GbR201K-αEpCAM(scFv) in the tumors after i.v. injection. Moreover, treatment of tumor-bearing mice demonstrated a prominent inhibition of tumor growth of up to 50 % in this proof-of-concept study. Taken together, our results indicate that GbR201K-αEpCAM(scFv) is a promising novel targeted therapeutic for the treatment of TNBC.

Stability and activity of MCSP-specific chimeric antigen receptors (CARs) depend on the scFv antigen-binding domain and the protein backbone

Chimeric antigen receptor (CAR)-modified T cells emerged as effective tools in the immunotherapy of cancer but can produce severe on-target off-tissue toxicities. This risk can conceivably be overcome, at least partially, by transient transfection. The design of CARs, however, has so far not been optimized for use in non-permanent T cell modification. Here we compared the performance of T cells modified with three different first- and second-generation CARs, each specific for MCSP (HMW-MAA) which is commonly expressed by melanoma cells. Upon RNA transfer, the expression of all receptors was limited in time. The second-generation CARs, which combined CD28-CD3ζ signaling, were expressed at higher levels and more prolonged than first-generation CARs with CD3ζ only. The CD28 domain increased the cytokine production, but had only an indirect effect on the lytic capacity, by prolonging the CAR expression. Especially for the second-generation CARs, the scFv clearly impacted the level and duration of CAR expression and the T cell performance. Thus, we identified a CAR high in both expression and anti-tumor cell reactivity. T cells transfected with this CAR increased the mean survival time of mice after challenge with melanoma cells. To facilitate clinical application, this CAR was used to redirect T cells from late-stage melanoma patients by RNA transfection. These T cells mediated effective antigen-specific tumor cell lysis and release of pro-inflammatory cytokines, even after cryoconservation of the transfected T cells. Taken together, the analysis identified a CAR with superior anti-melanoma performance after RNA transfer which is a promising candidate for clinical exploration.

Novel EGFR-specific immunotoxins based on panitumumab and cetuximab show in vitro and ex vivo activity against different tumor entities

PURPOSE

The epidermal growth factor receptor (EGFR) is overexpressed in many solid tumors. EGFR-specific monoclonal antibodies (mAbs), such as cetuximab and panitumumab, have been approved for the treatment of colorectal and head and neck cancer. To increase tissue penetration, we constructed single-chain fragment variable (scFv) antibodies derived from these mAbs and evaluated their potential for targeted cancer therapy. The resulting scFv-based EGFR-specific immunotoxins (ITs) combine target specificity of the full-size mAb with the cell-killing activity of a toxic effector domain, a truncated version of Pseudomonas exotoxin A (ETA').

METHODS

The ITs and corresponding imaging probes were tested in vitro against four solid tumor entities (rhabdomyosarcoma, breast, prostate and pancreatic cancer). Specific binding and internalization of the ITs scFv2112-ETA' (from cetuximab) and scFv1711-ETA' (from panitumumab) were demonstrated by flow cytometry and for the scFv-SNAP-tag imaging probes by live cell imaging. Cytotoxic potential of the ITs was analyzed in cell viability and apoptosis assays. Binding of the ITs was proofed ex vivo on rhabdomyosarcoma, prostate and breast cancer formalin-fixed paraffin-embedded biopsies.

RESULTS

Both novel ITs showed significant pro-apoptotic and anti-proliferative effects toward the target cells, achieving IC50 values of 4 pM (high EGFR expression) to 460 pM (moderate EGFR expression). Additionally, rapid internalization and specific in vitro and ex vivo binding on patient tissue were confirmed.

CONCLUSIONS

These data demonstrate the potent therapeutic activity of two novel EGFR-specific ETA'-based ITs. Both molecules are promising candidates for further development toward clinical use in the treatment of various solid tumors to supplement the existing therapeutic regimes.

Utilization of Glycosaminoglycans/Proteoglycans as Carriers for Targeted Therapy Delivery

The outcome of patients with cancer has improved significantly in the past decade with the incorporation of drugs targeting cell surface adhesive receptors, receptor tyrosine kinases, and modulation of several molecules of extracellular matrices (ECMs), the complex composite of collagens, glycoproteins, proteoglycans, and glycosaminoglycans that dictates tissue architecture. Cancer tissue invasive processes progress by various oncogenic strategies, including interfering with ECM molecules and their interactions with invasive cells. In this review, we describe how the ECM components, proteoglycans and glycosaminoglycans, influence tumor cell signaling. In particular this review describes how the glycosaminoglycan hyaluronan (HA) and its major receptor CD44 impact invasive behavior of tumor cells, and provides useful insight when designing new therapeutic strategies in the treatment of cancer.

A CSPG4-specific immunotoxin kills rhabdomyosarcoma cells and binds to primary tumor tissues

The treatment of rhabdomyosarcoma (RMS) remains challenging, with metastatic and alveolar RMS offering a particularly poor prognosis. Therefore, the identification and evaluation of novel antigens, which are suitable targets for immunotherapy, is one attractive possibility to improve the treatment of this disease. Here we show that chondroitin sulfate proteoglycan 4 (CSPG4) is expressed on RMS cell lines and RMS patient material. We evaluated the immunotoxin (IT) αMCSP-ETA', which specifically recognizes CSPG4 on the RMS cell lines RD, FL-OH1, TE-671 and Rh30. It is internalized rapidly, induces apoptosis and thus kills RMS cells selectively. We also demonstrate the specific binding of this IT to RMS primary tumor material from three different patients.

Melanoma-associated Chondroitin Sulfate Proteoglycan (MCSP)-targeted delivery of soluble TRAIL potently inhibits melanoma outgrowth in vitro and in vivo

BACKGROUND

Advanced melanoma is characterized by a pronounced resistance to therapy leading to a limited patient survival of ~6 - 9 months. Here, we report on a novel bifunctional therapeutic fusion protein, designated anti-MCSP:TRAIL, that is comprised of a melanoma-associated chondroitin sulfate proteoglycan (MCSP)-specific antibody fragment (scFv) fused to soluble human TRAIL. MCSP is a well-established target for melanoma immunotherapy and has recently been shown to provide important tumorigenic signals to melanoma cells. TRAIL is a highly promising tumoricidal cytokine with no or minimal toxicity towards normal cells. Anti-MCSP:TRAIL was designed to 1. selectively accrete at the cell surface of MCSP-positive melanoma cells and inhibit MCSP tumorigenic signaling and 2. activate apoptotic TRAIL-signaling.

RESULTS

Treatment of a panel of MCSP-positive melanoma cell lines with anti-MCSP:TRAIL induced TRAIL-mediated apoptotic cell death within 16 h. Of note, treatment with anti-MCSP:sTRAIL was also characterized by a rapid dephosphorylation of key proteins, such as FAK, implicated in MCSP-mediated malignant behavior. Importantly, anti-MCSP:TRAIL treatment already inhibited anchorage-independent growth by 50% at low picomolar concentrations, whereas > 100 fold higher concentrations of non-targeted TRAIL failed to reduce colony formation. Daily i.v. treatment with a low dose of anti-MCSP:TRAIL (0.14 mg/kg) resulted in a significant growth retardation of established A375 M xenografts. Anti-MCSP:TRAIL activity was further synergized by co-treatment with rimcazole, a σ-ligand currently in clinical trials for the treatment of various cancers.

CONCLUSIONS

Anti-MCSP:TRAIL has promising pre-clinical anti-melanoma activity that appears to result from combined inhibition of tumorigenic MCSP-signaling and concordant activation of TRAIL-apoptotic signaling. Anti-MCSP:TRAIL alone, or in combination with rimcazole, may be of potential value for the treatment of malignant melanoma.

Novel conjugates of single-chain Fv antibody fragments specific for stem cell antigen CD123 mediate potent death of acute myeloid leukaemia cells

Four new single-chain Fv antibody fragments (scFvs) specific for the human leucocyte surface antigen CD123 (interleukin-3 receptor alpha) were generated to achieve preferential targeting of leukaemia stem cells (LSCs) in acute myeloid leukaemia (AML). The scFvs were isolated from a phage display library generated with spleen RNA from mice, immunized with a fusion protein consisting of the extracellular domain of CD123 and the Fc domain of a human immunoglobulin G1. The scFvs displayed CD123-specific binding on tumour cells (binding constants (K(D)) 4.5-101 nmol/l). The scFv with the highest affinity was used to design two cell death-inducing molecules. First, an immunotoxin, a fusion protein with truncated Pseudomonas Exotoxin A, induced potent apoptosis of AML-derived MOLM-13 and SKNO-1 cells at nanomolar concentrations. Second, the fusion to another scFv, specific for the low affinity Fcgamma-receptor III (CD16), created a bispecific single chain Fv (bsscFv). This bsscFv [123 x ds16] mediated potent lysis of AML-derived MOLM-13, THP-1 and SKNO-1 cells in antibody-dependent cellular cytotoxicity (ADCC) reactions at picomolar concentrations. The recruitment of CD16-positive effector cells for the lysis of AML cells via CD123 represents a novel combination with attractive prospects for future clinical testing.

Immunotoxins: a promising treatment modality for metastatic melanoma?

The incidence of melanoma is rising in the Western population, and melanoma is the most aggressive form of skin cancer with a very poor prognosis once it has progressed to metastatic stages. Patients with stage IV melanoma (metastases to distant lymph nodes and other areas of the body) are treated with the chemotherapeutic drug dacarbazine (DTIC). However, fewer than 5% of the patients treated with DTIC sustain long-term complete responses; hence, DTIC is administered with palliative purposes. New therapy is urgently needed. We are developing another therapeutic strategy, specifically targeting melanoma cells with the 9.2.27PE immunotoxin (IT). ITs bind to antigens overexpressed on cancer cells and are therefore tumor selective. This targeted approach may potentially cause fewer side effects in a clinical situation compared to conventional approaches like chemotherapy and radiotherapy.