Pim-1 expression and monoclonal antibody targeting in human leukemia cell lines.
OBJECTIVE
Based on our previous findings that Pim-1 was expressed on the cell surface and could be targeted with a highly specific anti-Pim-1 monoclonal antibody (P9), this study aims to evaluate the possibility that Pim-1 could be targeted for the treatment of human leukemia.


METHODS
Pim-1 expression was investigated in a series of human leukemia cell lines with immunohistochemistry and flow cytometry. The inhibitory effect of P9 on cell proliferation was evaluated with (3)H-thymidine incorporation assay. Cell apoptosis was assayed with Annexin-V/propidium iodide dual staining. The in vivo effect of P9 was evaluated with xenograft tumor models in severe combined immunodeficient mice.


RESULTS
Pim-1 expression varied depending on the cell lines and correlated with the inhibitory effects mediated by P9. An association between Pim-1 expression and drug resistance was observed. Although the drug-resistant CEM/A7R cells were highly resistant to cytotoxic P-glycoprotein substrates, their growth was inhibited by P9 as demonstrated by in vitro proliferation assay and in vivo inhibition of xenograft tumors. P9 had little effect on P-glycoprotein expression and intracellular Rhodamine 123 accumulation, but it inhibited the phosphorylation of Bad and induced apoptosis.


CONCLUSIONS
Pim-1 is variably expressed in leukemia cell lines and associated with drug resistance. Targeting Pim-1 with monoclonal antibody could be explored for the treatment of leukemia and may represent a novel strategy to overcome drug resistance.
Li
Jie
J
Cancer Immunotherapy Laboratory, Burnet Institute Incorporating Austin Research Institute, Heidelberg, Victoria, Australia. jieli6688@hotmail.com
Hu
Xiu Feng
XF
Loveland
Bruce E
BE
Xing
Pei Xiang
PX
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology* / Q000627:therapeutic use; D000912:Antibodies, Neoplasm / Q000276:immunology / Q000494:pharmacology* / Q000627:therapeutic use; D000970:Antineoplastic Agents / Q000378:metabolism / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor / Q000187:drug effects / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007938:Leukemia / Q000473:pathology*; D007942:Leukemia, Experimental / Q000188:drug therapy; D051379:Mice; D016513:Mice, SCID; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology; D010766:Phosphorylation / Q000187:drug effects; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D051573:Proto-Oncogene Proteins c-pim-1 / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology; D014410:Tumor Stem Cell Assay; D014700:Verapamil / Q000494:pharmacology; D023041:Xenograft Model Antitumor Assays; D051025:bcl-Associated Death Protein / Q000378:metabolism
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000911:Antibodies, Monoclonal; D000912:Antibodies, Neoplasm; D000970:Antineoplastic Agents; C494819:BAD protein, human; D009363:Neoplasm Proteins; D051025:bcl-Associated Death Protein; D014700:Verapamil; C496634:PIM1 protein, human; D051573:Proto-Oncogene Proteins c-pim-1