title: Podocalyxin enhances breast tumor growth and metastasis and is a target for monoclonal antibody therapy.
abstract: BACKGROUND
  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.
authors.affiliation: The Biomedical Research Centre, University of British Columbia, 2222 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada. ksnyder@brc.ubc.ca.
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Snyder
authors.affiliation: The Biomedical Research Centre, University of British Columbia, 2222 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada. mhughes@brc.ubc.ca.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Hughes
authors.affiliation: Centre for Drug Research and Development, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada. bhedberg@cdrd.ca.
authors.forename: Bradley
authors.initials: B
authors.lastname: Hedberg
authors.affiliation: Centre for Drug Research and Development, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada. jbrandon@cdrd.ca.
authors.forename: Jill
authors.initials: J
authors.lastname: Brandon
authors.affiliation: The Biomedical Research Centre, University of British Columbia, 2222 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada. dcanals@brc.ubc.ca.
authors.forename: Diana Canals
authors.initials: DC
authors.lastname: Hernaez
authors.affiliation: Centre for Drug Research and Development, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada. pbergqvist@cdrd.ca.
authors.forename: Peter
authors.initials: P
authors.lastname: Bergqvist
authors.affiliation: Centre for Drug Research and Development, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada. ecruz@cdrd.ca.
authors.forename: Frederic
authors.initials: F
authors.lastname: Cruz
authors.affiliation: Centre for Drug Research and Development, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada. kpo@cdrd.ca.
authors.forename: Kelvin
authors.initials: K
authors.lastname: Po
authors.affiliation: Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada. mgraves@mail.ubc.ca.
authors.forename: Marcia L
authors.initials: ML
authors.lastname: Graves
authors.affiliation: Centre for Molecular Pathology, School of Molecular & Biological Science, The University of Adelaide, Adelaide, SA, 5005, Australia. michelle.turvey@adelaide.edu.au.
authors.forename: Michelle E
authors.initials: ME
authors.lastname: Turvey
authors.affiliation: The Biomedical Research Centre, University of British Columbia, 2222 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada. jnielsen@bccancer.bc.ca.
authors.forename: Julie S
authors.initials: JS
authors.lastname: Nielsen
authors.affiliation: Department of Internal Medicine, Manitoba Centre for Proteomics and Systems Biology, University of Manitoba, Winnipeg, MB, Canada. john.wilkins@med.umanitoba.ca.
authors.forename: John A
authors.initials: JA
authors.lastname: Wilkins
authors.affiliation: Centre for Molecular Pathology, School of Molecular & Biological Science, The University of Adelaide, Adelaide, SA, 5005, Australia. shaun.mccoll@adelaide.edu.au.
authors.forename: Shaun R
authors.initials: SR
authors.lastname: McColl
authors.affiliation: Centre for Drug Research and Development, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada. jbabcook@cdrd.ca.
authors.forename: John S
authors.initials: JS
authors.lastname: Babcook
authors.affiliation: Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada. roskelly@mail.ubc.ca.
authors.forename: Calvin D
authors.initials: CD
authors.lastname: Roskelley
authors.affiliation: The Biomedical Research Centre, University of British Columbia, 2222 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada. kelly@brc.ubc.ca.
authors.forename: Kelly M
authors.initials: KM
authors.lastname: McNagny
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000008:administration & dosage / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000401:mortality / Q000473:pathology*; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism; D004195:Disease Models, Animal; D005260:Female; D006801:Humans; D015674:Mammary Neoplasms, Animal; D051379:Mice; D009362:Neoplasm Metastasis; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics; D012795:Sialoglycoproteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D018874:Spheroids, Cellular; D047368:Tumor Burden / Q000187:drug effects / Q000235:genetics; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays
chemical_list: D000911:Antibodies, Monoclonal; D000970:Antineoplastic Agents; D034741:RNA, Small Interfering; D012795:Sialoglycoproteins; C001643:podocalyxin