title: Markers of tumor-initiating cells predict chemoresistance in breast cancer.
abstract: OBJECTIVE
  Evidence is lacking whether the number of breast tumor-initiating cells (BT-ICs) directly correlates with the sensitivity of breast tumors to chemotherapy. Here, we evaluated the association between proportion of BT-ICs and chemoresistance of the tumors.
  
  
  METHODS
  Immunohistochemical staining(IHC) was used to examine the expression of aldehyde dehydrogenase 1 (ALDH1) and proliferating cell nuclear antigen, and TUNEL was used to detect the apoptosis index. The significance of various variables in patient survival was analyzed using a Cox proportional hazards model. The percentage of BT-ICs in breast cancer cell lines and primary breast tumors was determined by ALDH1 enzymatic assay, CD44(+)/CD24(-) phenotype and mammosphere formation assay.
  
  
  RESULTS
  ALDH1 expression determined by IHC in primary breast cancers was associated with poor clinical response to neoadjuvant chemotherapy and reduced survival in breast cancer patients. Breast tumors that contained higher proportion of BT-ICs with CD44(+)/CD24(-) phenotype, ALDH1 enzymatic activity and sphere forming capacity were more resistant to neoadjuvant chemotherapy. Chemoresistant cell lines AdrR/MCF-7 and SK-3rd, had increased number of cells with sphere forming capacity, CD44(+)/CD24(-) phenotype and side-population. Regardless the proportion of T-ICs, FACS-sorted CD44(+)/CD24(-) cells that derived from primary tumors or breast cancer lines were about 10-60 fold more resistant to chemotherapy relative to the non- CD44(+)/CD24(-) cells and their parental cells. Furthermore, our data demonstrated that MDR1 (multidrug resistance 1) and ABCG2 (ATP-binding cassette sub-family G member 2) were upregulated in CD44(+)/CD24(-) cells. Treatment with lapatinib or salinomycin reduced the proportion of BT-ICs by nearly 50 fold, and thus enhanced the sensitivity of breast cancer cells to chemotherapy by around 30 fold.
  
  
  CONCLUSIONS
  These data suggest that the proportion of BT-ICs is associated with chemotherapeutic resistance of breast cancer. It highlights the importance of targeting T-ICs, rather than eliminating the bulk of rapidly dividing and terminally differentiated cells, in novel anti-cancer strategies.
authors.affiliation: Breast Tumor Center, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, Guangzhou, People's Republic of China.
authors.forename: Chang
authors.initials: C
authors.lastname: Gong
authors.forename: Herui
authors.initials: H
authors.lastname: Yao
authors.forename: Qiang
authors.initials: Q
authors.lastname: Liu
authors.forename: Jingqi
authors.initials: J
authors.lastname: Chen
authors.forename: Junwei
authors.initials: J
authors.lastname: Shi
authors.forename: Fengxi
authors.initials: F
authors.lastname: Su
authors.forename: Erwei
authors.initials: E
authors.lastname: Song
mesh_terms: D000328:Adult; D000080924:Aldehyde Dehydrogenase 1 Family; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D051927:CD24 Antigen / Q000378:metabolism; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism; D007150:Immunohistochemistry / Q000379:methods; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008875:Middle Aged; D010641:Phenotype; D050697:Retinal Dehydrogenase / Q000235:genetics / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D051927:CD24 Antigen; C497483:CD44 protein, human; D018960:Hyaluronan Receptors; D007527:Isoenzymes; D000080924:Aldehyde Dehydrogenase 1 Family; C510223:ALDH1A1 protein, human; D050697:Retinal Dehydrogenase