title: Immunotherapeutic potential of anti-human endogenous retrovirus-K envelope protein antibodies in targeting breast tumors.
abstract: BACKGROUND
  The envelope (env) protein of the human endogenous retrovirus type K (HERV-K) family is commonly expressed on the surface of breast cancer cells. We assessed whether HERV-K env is a potential target for antibody-based immunotherapy of breast cancer.
  
  
  METHODS
  We examined the expression of HERV-K env protein in various malignant (MDA-MB-231, MCF-7, SKBR3, MDA-MB-453, T47D, and ZR-75-1) and nonmalignant (MCF-10A and MCF-10AT) human breast cell lines by immunoblot, enzyme-linked immunosorbent assay, immunofluorescence staining, and flow cytometry. Anti-HERV-K env monoclonal antibodies (mAbs; 6H5, 4D1, 4E11, 6E11, and 4E6) were used to target expression of HERV-K, and antitumor effects were assessed by quantifying growth and apoptosis of breast cancer cells in vitro, and tumor growth in vivo in mice (n = 5 per group) bearing xenograft tumors. The mechanisms responsible for 6H5 mAb-mediated effects were investigated by microarray assays, flow cytometry, immunoblot, and immunofluorescence staining. The expression of HERV-K env protein was assessed in primary breast tumors (n = 223) by immunohistochemistry. All statistical tests were two-sided.
  
  
  RESULTS
  The expression of HERV-K env protein in malignant breast cancer cell lines was substantially higher than nonmalignant breast cells. Anti-HERV-K-specific mAbs inhibited growth and induced apoptosis of breast cancer cells in vitro. Mice treated with 6H5 mAb showed statistically significantly reduced growth of xenograft tumors compared with mice treated with control immunoglobulin (control [mIgG] vs 6H5 mAb, for tumors originating from MDA-MB-231 cells, mean size = 1448.33 vs 475.44 mm(3); difference = 972.89 mm(3), 95% CI = 470.17 to 1475.61 mm(3); P < .001). Several proteins involved in the apoptotic signaling pathways were overexpressed in vitro in 6H5 mAb-treated malignant breast cells compared with mIgG-treated control. HERV-K expression was detected in 148 (66%) of 223 primary breast tumors, and a higher rate of lymph node metastasis was associated with HERV-K-positive compared with HERV-K-negative tumors (43% vs 23%, P = .003).
  
  
  CONCLUSIONS
  Monoclonal antibodies against HERV-K env protein show potential as novel immunotherapeutic agents for breast cancer therapy.
authors.affiliation: Department of Veterinary Sciences, The University of Texas MD Anderson Cancer Center, Houston, TX, USA. fwangjoh@mdanderson.org
authors.forename: Feng
authors.initials: F
authors.lastname: Wang-Johanning
authors.forename: Kiera
authors.initials: K
authors.lastname: Rycaj
authors.forename: Joshua B
authors.initials: JB
authors.lastname: Plummer
authors.forename: Ming
authors.initials: M
authors.lastname: Li
authors.forename: Bingnan
authors.initials: B
authors.lastname: Yin
authors.forename: Katherine
authors.initials: K
authors.lastname: Frerich
authors.forename: Jeremy G
authors.initials: JG
authors.lastname: Garza
authors.forename: Jianjun
authors.initials: J
authors.lastname: Shen
authors.forename: Kevin
authors.initials: K
authors.lastname: Lin
authors.forename: Peisha
authors.initials: P
authors.lastname: Yan
authors.forename: Sharon A
authors.initials: SA
authors.lastname: Glynn
authors.forename: Tiffany H
authors.initials: TH
authors.lastname: Dorsey
authors.forename: Kelly K
authors.initials: KK
authors.lastname: Hunt
authors.forename: Stefan
authors.initials: S
authors.lastname: Ambs
authors.forename: Gary L
authors.initials: GL
authors.lastname: Johanning
mesh_terms: D000328:Adult; D000368:Aged; D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000494:pharmacology; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000276:immunology / Q000473:pathology / Q000821:virology*; D001973:Bromodeoxyuridine / Q000378:metabolism; D018270:Carcinoma, Ductal, Breast / Q000188:drug therapy / Q000821:virology; D045744:Cell Line, Tumor; D020077:Endogenous Retroviruses; D004797:Enzyme-Linked Immunosorbent Assay; D005240:Feasibility Studies; D005260:Female; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D015972:Gene Expression Regulation, Neoplastic; D015967:Gene Expression Regulation, Viral; D015686:Gene Products, env / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D007167:Immunotherapy / Q000379:methods*; D020287:In Situ Nick-End Labeling; D019394:Ki-67 Antigen / Q000032:analysis; D051379:Mice; D008819:Mice, Nude; D008875:Middle Aged; D058990:Molecular Targeted Therapy; D060787:Neoplasm Grading; D009367:Neoplasm Staging; D010865:Pilot Projects; D040081:Protein Array Analysis; D011897:Random Allocation; D012191:Retroviridae Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D015398:Signal Transduction; D014183:Transplantation, Heterologous; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D000888:Antibodies, Anti-Idiotypic; D000911:Antibodies, Monoclonal; D000970:Antineoplastic Agents; D015686:Gene Products, env; D019394:Ki-67 Antigen; D012191:Retroviridae Proteins; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D001973:Bromodeoxyuridine