title: An immunoconjugate of anti-CD24 and Pseudomonas exotoxin selectively kills human colorectal tumors in mice.
abstract: OBJECTIVE
  Effective and selective treatment options are needed for patients with colorectal cancer (CRC). The CD24 mucin-like glycoprotein is overexpressed in CRCs; monoclonal antibodies (mAbs) against CD24 inhibit tumor cell growth in vitro and in vivo. Based on the tumor-specific expression of CD24, we investigated the potential of anti-CD24 SWA11 mAb, to deliver a cytotoxic agent into CRC cells.
  
  
  METHODS
  We conjugated SWA11 to a Pseudomonas exotoxin derivative (PE38) via an Fc-binding ZZ domain from Staphylococcal protein A (which binds the Fc domain of mouse IgG2a immunoglobulins) to generate the immunotoxin SWA11-ZZ-PE38; IgG-ZZ-PE38 was used as control. Human HT-29 and COLO320 (CD24-positive) and HCT116 (CD24-negative) CRC cell lines were assayed for immunotoxin binding, cytotoxicity, viability, and apoptosis. Toxicity and antitumor efficacy were tested in mice.
  
  
  RESULTS
  The immunotoxin preserved the affinity and specificity of SWA11, bound and selectively killed CD24-expressing CRC cells via apoptosis. IC(50) values ranged from 20 to 50 ng/mL-several orders of magnitude lower than that of the mAb alone. The immunotoxins were not toxic to mice at the maximum dose of 0.75 mg/kg. Growth of HT-29 xenograft tumors was significantly reduced in mice given SWA11-ZZ-PE38 (by 78%) compared to untreated mice.
  
  
  CONCLUSIONS
  Anti-CD24 SWA11 mAb can deliver a PE exotoxin derivative to CRC cells and cause them to undergo apoptosis, without toxicity to normal tissues. This immunotoxin might be developed as a therapeutic treatment for patients with CRC.
authors.affiliation: The Integrated Cancer Prevention Center, Tel Aviv, Israel.
authors.forename: Shiran
authors.initials: S
authors.lastname: Shapira
authors.forename: Assaf
authors.initials: A
authors.lastname: Shapira
authors.forename: Alex
authors.initials: A
authors.lastname: Starr
authors.forename: Dina
authors.initials: D
authors.lastname: Kazanov
authors.forename: Sarah
authors.initials: S
authors.lastname: Kraus
authors.forename: Itai
authors.initials: I
authors.lastname: Benhar
authors.forename: Nadir
authors.initials: N
authors.lastname: Arber
mesh_terms: D036002:ADP Ribose Transferases / Q000494:pharmacology*; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001427:Bacterial Toxins / Q000494:pharmacology*; D051927:CD24 Antigen / Q000276:immunology*; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000276:immunology / Q000473:pathology; D004305:Dose-Response Relationship, Drug; D005098:Exotoxins / Q000494:pharmacology*; D045325:HCT116 Cells; D019073:HT29 Cells; D006801:Humans; D018796:Immunoconjugates / Q000494:pharmacology*; D020128:Inhibitory Concentration 50; D051379:Mice; D008819:Mice, Nude; D011993:Recombinant Fusion Proteins / Q000494:pharmacology; D013205:Staphylococcal Protein A / Q000494:pharmacology*; D013997:Time Factors; D047368:Tumor Burden / Q000187:drug effects; D037521:Virulence Factors / Q000494:pharmacology*; D023041:Xenograft Model Antitumor Assays; D000097668:Pseudomonas aeruginosa Exotoxin A
chemical_list: D036002:ADP Ribose Transferases; D000911:Antibodies, Monoclonal; D001427:Bacterial Toxins; D051927:CD24 Antigen; D005098:Exotoxins; D018796:Immunoconjugates; D011993:Recombinant Fusion Proteins; D013205:Staphylococcal Protein A; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A; C497889:CD24 protein, human