br Competing interests br The authors
The authors declare that no competing interests exist.
 R.W. Rickards, J.M. Rothschild, A.C. Willis, N.M. de Chazal, J. Kirk, K. Kirk, et al., Calothrixins A and B, novel pentacyclic metabolites from Calothrix 1977535-33-3 with potent activity against malaria parasites and human cancer cells, Tetrahedron 55 (1999) 13513–13520.
30 Original Study
Anti-Mesothelin Recombinant Immunotoxin Therapy for Colorectal Cancer
Adam Cerise,1 Tapan K. Bera,1 Xiufen Liu,1 Junxia Wei,1 Ira Pastan1
Mesothelin is expressed at high levels on the surface of colorectal carcinoma cells, mesothelioma, and pancreatic, ovarian, and gastric cancer. Immunotoxins targeting Mesothelin can kill colorectal cancer cell lines in vitro and can inhibit growth and cause regressions in mice. Combination therapy with actinomycin D resulted in > 90% tumor volume reduction with 50% complete regressions.
Background: Mesothelin (MSLN) is a cell surface glycoprotein expressed at a high level on many malignancies, including pancreatic adenocarcinoma, serous ovarian cancer, and epithelioid mesothelioma. MSLN-targeted re-combinant immunotoxins (RITs) consist of an anti-MSLN Fv fused to the catalytic domain of Pseudomonas exotoxin A. Recent data has also shown that MSLN is expressed at clinically relevant levels on the surface of colorectal cancer (CRC). In this study, CRC cell lines were tested for MSLN expression and susceptibility to MSLN-targeted RITs. Materials and Methods: CRC cell lines were tested for membranous MSLN expression via flow cytometry. Cell lines expressing MSLN were tested by WST-8 cell viability assay for sensitivity to various RITs and chemotherapeutic agents. CRC cell line SW-48 was tested in a mouse model for response to RIT as a single agent or in combination with actinomycin D and oxaliplatin. Results: CRC cell lines were susceptible to anti-MSLN RITs at half maximal inhibitory concentration levels comparable with those previously described in pancreatic cancer cell lines. In a nude mouse model, MSLN-targeted RIT treatment of SW48 CRC tumors resulted in a significant decrease in tumor volume. Although combination therapy with standard of care chemotherapeutic oxaliplatin did not improve tumor regressions, combination therapy with actinomycin D resulted in > 90% tumor volume reduction with 50% complete regressions. Conclusions: These data support the development of anti-MSLN RITs as well as other MSLN-targeted therapies for CRC.
Clinical Colorectal Cancer, Vol. -, No. -, --- Published by Elsevier Inc.
A recombinant immunotoxin (RIT) is a chimeric protein con-sisting of the Fv or Fab portion of an antibody fused to a truncated bacterial toxin. In our laboratory, we use Pseudomonas exotoxin A (PE) as the toxin. To construct RITs, we replace domain I, the binding domain of PE, with an Fv or Fab portion of an antibody,
A.C. and T.K.B. contributed equally to this work as first authors.
Current affiliation: Adam Cerise, Department of Surgery, Indiana Univeristy School of Medicine, Indianapolis, IN.
1Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD
Address for correspondence: Ira Pastan, MD, Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, 37 Convent Dr, MSC 4264, Bldg 37, Room 5106, Bethesda, MD 20892 E-mail contact: [email protected]
which binds to a cancer cell-specific surface antigen. After binding to the cell, the toxin is internalized, arrests protein synthesis, and kills the cell. Because protein synthesis is necessary for cell survival, RIT therapy can kill both dividing and quiescent cells.1 An RIT containing an anti-CD22 Fv fragment, clinically iden-tified as Moxetumomab pasudotox, has shown considerable efficacy in phase I and phase III studies in drug-refractory hairy cell leu-kemia, including a 64% complete response rate and an 88% overall response rate.2,3 Moxetumomab pasudotox is now United States Food and Drug Administration-approved for the therapy of drug-resistant hairy cell leukemia. However, targeting solid organ epithelial cancers is more challenging than targeting leukemias. One attractive target is mesothelin (MSLN), a 71 kDa glycoprotein that is cleaved by furin into a 40 kDa membrane-bound form, expressed on the cell membrane of mesothelial cells lining the peritoneum, pleura, and pericardium, and a secreted 31 kDa megakaryocyte potentiating factor whose function has yet to be clearly elucidated. MSLN was originally found to be highly expressed on the cell