Podocalyxin enhances breast tumor growth and metastasis and is a target for monoclonal antibody therapy.

INTRODUCTION: Podocalyxin (gene name PODXL) is a CD34-related sialomucin implicated in the regulation of cell adhesion, migration and polarity. Upregulated expression of podocalyxin is linked to poor patient survival in epithelial cancers. However, it is not known if podocalyxin has a functional role in tumor progression. METHODS: We silenced podocalyxin expression in the aggressive basal-like human (MDA-MB-231) and mouse (4T1) breast cancer cell lines and also overexpressed podocalyxin in the more benign human breast cancer cell line, MCF7. We evaluated how podocalyxin affects tumorsphere formation in vitro and compared the ability of podocalyxin-deficient and podocalyxin-replete cell lines to form tumors and metastasize using xenogenic or syngeneic transplant models in mice. Finally, in an effort to develop therapeutic treatments for systemic cancers, we generated a series of antihuman podocalyxin antibodies and screened these for their ability to inhibit tumor progression in xenografted mice. RESULTS: Although deletion of podocalyxin does not alter gross cell morphology and growth under standard (adherent) culture conditions, expression of PODXL is required for efficient formation of tumorspheres in vitro. Correspondingly, silencing podocalyxin resulted in attenuated primary tumor growth and invasiveness in mice and severely impaired the formation of distant metastases. Likewise, in competitive tumor engraftment assays where we injected a 50:50 mixture of control and shPODXL (short-hairpin RNA targeting PODXL)-expressing cells, we found that podocalyxin-deficient cells exhibited a striking decrease in the ability to form clonal tumors in the lung, liver and bone marrow. Finally, to validate podocalyxin as a viable target for immunotherapy, we screened a series of novel antihuman podocalyxin antibodies for their ability to inhibit tumor progression in vivo. One of these antibodies, PODOC1, potently blocked tumor growth and metastasis. CONCLUSIONS: We show that podocalyxin plays a key role in the formation of primary tumors and distant tumor metastasis. In addition, we validate podocalyxin as potential target for monoclonal antibody therapy to inhibit primary tumor growth and systemic dissemination.

An Oncofetal Glycosaminoglycan Modification Provides Therapeutic Access to Cisplatin-resistant Bladder Cancer.

BACKGROUND: Although cisplatin-based neoadjuvant chemotherapy (NAC) improves survival of unselected patients with muscle-invasive bladder cancer (MIBC), only a minority responds to therapy and chemoresistance remains a major challenge in this disease setting. OBJECTIVE: To investigate the clinical significance of oncofetal chondroitin sulfate (ofCS) glycosaminoglycan chains in cisplatin-resistant MIBC and to evaluate these as targets for second-line therapy. DESIGN, SETTING, AND PARTICIPANTS: An ofCS-binding recombinant VAR2CSA protein derived from the malaria parasite Plasmodium falciparum (rVAR2) was used as an in situ, in vitro, and in vivo ofCS-targeting reagent in cisplatin-resistant MIBC. The ofCS expression landscape was analyzed in two independent cohorts of matched pre- and post-NAC-treated MIBC patients. INTERVENTION: An rVAR2 protein armed with cytotoxic hemiasterlin compounds (rVAR2 drug conjugate [VDC] 886) was evaluated as a novel therapeutic strategy in a xenograft model of cisplatin-resistant MIBC. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Antineoplastic effects of targeting ofCS. RESULTS AND LIMITATIONS: In situ, ofCS was significantly overexpressed in residual tumors after NAC in two independent patient cohorts (p<0.02). Global gene-expression profiling and biochemical analysis of primary tumors and cell lines revealed syndican-1 and chondroitin sulfate proteoglycan 4 as ofCS-modified proteoglycans in MIBC. In vitro, ofCS was expressed on all MIBC cell lines tested, and VDC886 eliminated these cells in the low-nanomolar IC50 concentration range. In vivo, VDC886 effectively retarded growth of chemoresistant orthotopic bladder cancer xenografts and prolonged survival (p=0.005). The use of cisplatin only for the generation of chemoresistant xenografts are limitations of our animal model design. CONCLUSIONS: Targeting ofCS provides a promising second-line treatment strategy in cisplatin-resistant MIBC. PATIENT SUMMARY: Cisplatin-resistant bladder cancer overexpresses particular sugar chains compared with chemotherapy-naïve bladder cancer. Using a recombinant protein from the malaria parasite Plasmodium falciparum, we can target these sugar chains, and our results showed a significant antitumor effect in cisplatin-resistant bladder cancer. This novel treatment paradigm provides therapeutic access to bladder cancers not responding to cisplatin.

Identification and Characterization of MEDI4736, an Antagonistic Anti-PD-L1 Monoclonal Antibody.

Programmed cell-death 1 ligand 1 (PD-L1) is a member of the B7/CD28 family of proteins that control T-cell activation. Many tumors can upregulate expression of PD-L1, inhibiting antitumor T-cell responses and avoiding immune surveillance and elimination. We have identified and characterized MEDI4736, a human IgG1 monoclonal antibody that binds with high affinity and specificity to PD-L1 and is uniquely engineered to prevent antibody-dependent cell-mediated cytotoxicity. In vitro assays demonstrate that MEDI4736 is a potent antagonist of PD-L1 function, blocking interaction with PD-1 and CD80 to overcome inhibition of primary human T-cell activation. In vivo MEDI4736 significantly inhibits the growth of human tumors in a novel xenograft model containing coimplanted human T cells. This activity is entirely dependent on the presence of transplanted T cells, supporting the immunological mechanism of action for MEDI4736. To further determine the utility of PD-L1 blockade, an anti-mouse PD-L1 antibody was investigated in immunocompetent mice. Here, anti-mouse PD-L1 significantly improved survival of mice implanted with CT26 colorectal cancer cells. The antitumor activity of anti-PD-L1 was enhanced by combination with oxaliplatin, which resulted in increased release of HMGB1 within CT26 tumors. Taken together, our results demonstrate that inhibition of PD-L1 function can have potent antitumor activity when used as monotherapy or in combination in preclinical models, and suggest it may be a promising therapeutic approach for the treatment of cancer. MEDI4736 is currently in several clinical trials both alone and in combination with other agents, including anti-CTLA-4, anti-PD-1, and inhibitors of IDO, MEK, BRAF, and EGFR.

Targeting Human Cancer by a Glycosaminoglycan Binding Malaria Protein.

Plasmodium falciparum engineer infected erythrocytes to present the malarial protein, VAR2CSA, which binds a distinct type chondroitin sulfate (CS) exclusively expressed in the placenta. Here, we show that the same CS modification is present on a high proportion of malignant cells and that it can be specifically targeted by recombinant VAR2CSA (rVAR2). In tumors, placental-like CS chains are linked to a limited repertoire of cancer-associated proteoglycans including CD44 and CSPG4. The rVAR2 protein localizes to tumors in vivo and rVAR2 fused to diphtheria toxin or conjugated to hemiasterlin compounds strongly inhibits in vivo tumor cell growth and metastasis. Our data demonstrate how an evolutionarily refined parasite-derived protein can be exploited to target a common, but complex, malignancy-associated glycosaminoglycan modification.

A pan-cancer analysis of alternative splicing events reveals novel tumor-associated splice variants of matriptase.

High-throughput transcriptome sequencing allows identification of cancer-related changes that occur at the stages of transcription, pre-messenger RNA (mRNA), and splicing. In the current study, we devised a pipeline to predict novel alternative splicing (AS) variants from high-throughput transcriptome sequencing data and applied it to large sets of tumor transcriptomes from The Cancer Genome Atlas (TCGA). We identified two novel tumor-associated splice variants of matriptase, a known cancer-associated gene, in the transcriptome data from epithelial-derived tumors but not normal tissue. Most notably, these variants were found in 69% of lung squamous cell carcinoma (LUSC) samples studied. We confirmed the expression of matriptase AS transcripts using quantitative reverse transcription PCR (qRT-PCR) in an orthogonal panel of tumor tissues and cell lines. Furthermore, flow cytometric analysis confirmed surface expression of matriptase splice variants in chinese hamster ovary (CHO) cells transiently transfected with cDNA encoding the novel transcripts. Our findings further implicate matriptase in contributing to oncogenic processes and suggest potential novel therapeutic uses for matriptase splice variants.

Generation and characterization of human monoclonal neutralizing antibodies with distinct binding and sequence features against SARS coronavirus using XenoMouse.

Passive therapy with neutralizing human monoclonal antibodies (mAbs) could be an effective therapy against severe acute respiratory syndrome coronavirus (SARS-CoV). Utilizing the human immunoglobulin transgenic mouse, XenoMouse, we produced fully human SARS-CoV spike (S) protein specific antibodies. Antibodies were examined for reactivity against a recombinant S1 protein, to which 200 antibodies reacted. Twenty-seven antibodies neutralized 200TCID(50) SARS-CoV (Urbani). Additionally, 57 neutralizing antibodies were found that are likely specific to S2. Mapping of the binding region was achieved with several S1 recombinant proteins. Most S1 reactive neutralizing mAbs bound to the RBD, aa 318-510. However, two S1 specific mAbs reacted with a domain upstream of the RBD between aa 12 and 261. Immunoglobulin gene sequence analyses suggested at least 8 different binding specificities. Unique human mAbs could be used as a cocktail that would simultaneously target several neutralizing epitopes and prevent emergence of escape mutants.

Recognition of human cytomegalovirus by human primary immunoglobulins identifies an innate foundation to an adaptive immune response.

Most primates, including humans, are chronically infected with cospecifically evolved, potentially pathogenic CMV. Abs that bind a 10-aa linear epitope (antigenic determinant 2 site 1) within the extracellular domain of human CMV glycoprotein B neutralize viral infectivity. In this study, we show that genes generated by recombinations involving two well-conserved human germline V elements (IGHV3-30 and IGKV3-11), and IGHJ4, encode primary Ig molecules that bind glycoprotein B at this key epitope. These particular V(H), J(H), and V(kappa) genes enable humans to generate through recombination and N nucleotide addition, a useful frequency of primary Igs that efficiently target this critical site on human CMV and thus confer an innate foundation for a specific adaptive response to this pathogen.