Newswise  Researchers at the University of California, San    Diego School of Medicine have discovered that hard-to-reach,    drug-resistant leukemia stem cells (LSCs) that overexpress    multiple pro-survival protein forms are sensitive  and thus    vulnerable  to a novel cancer stem cell-targeting drug    currently under development.  
    The findings, published in the January 17 online issue of    Cell Stem Cell, open the possibility that diseases like    chronic myeloid leukemia (CML) and some solid tumor cancers    might  in combination with other therapies  be more    effectively treated with this drug, and with a lower chance of    relapse.  
    Led by principal investigator Catriona H. M. Jamieson, MD, PhD,    associate professor of medicine and director of stem cell    research at UC San Diego Moores Cancer Center, the researchers    found that a compound called sabutoclax appears to selectively    target LSCs that express particular protein isoforms through    alternatively splicing, a fundamental process in which a gene    is able to code for multiple proteins.  
    An emerging class of drugs called tyrosine kinase inhibitors    (TKI)  such as imitinib (Gleevec), gifitinib (Iressa) and    sunitinib (Sutent)  has become a popular anti-cancer    treatment. However, current TKIs are not 100 percent effective.    In cases of CML, for example, some LSCs tucked protectively    within bone marrow elude destruction, develop resistance to    therapy, self-renew and eventually cause the leukemia to    dramatically return.  
    Jamieson and colleagues found that alternative splicing of BCL2    genes, which code for proteins involved in apoptosis or    programmed cell death, specifically promoted malignant    transformation of dormant white blood cell precursors into    blast crisis LSCs. The blast crisis is the final phase of CML    when overabundant, abnormal white blood cells crowd out healthy    cells, causing serious dysfunction.  
    Of clinical importance, they noted that sabutoclax, which    suppresses all BCL2 anti-apoptotic proteins, renders these    marrow-dwelling blast crisis LSCs sensitive  and more    susceptible  to TKI-based therapeutics at doses that do not    harm normal progenitor cells.  
    Our findings show that pan-BCL2 inhibition will be critical    for the eradication of cancer stem cells in CML and that there    is an essential link between cancer stem cell dormancy,    pro-survival BCL2 isoform expression and therapeutic    resistance, Jamieson said. By using a novel pan-BCL2    inhibitor, we may be able to prevent therapeutic resistance by    sensitizing malignant stem cell clones to TKIs.  
    The findings may have implications for treating solid tumor    cancers, such as colon, prostate, breast, and brain cancers,    noted Daniel J. Goff, the studys first author.    With many of these tumor types being shown to harbor cancer    stem cells, it raises the question of whether BCL2 family    expression as well as isoform-switching may be crucial for the    maintenance of cancer stem cells in these diseases as well, he    said. If so, they may also be candidates for treatment with a    BCL2 inhibitor like sabutoclax.  
    Co-authors are Angela Court Recart, Anil Sadarangani, Heather    Leu, Janine Low-Marchelli, Wenxue Ma, Alice Y. Shih, Ifat    Geron, Minya Pu, Lei Bao, Ryan Chuang, Larisa Balaian, Peggy    Wentworth, Kristen M. Smith, Christina A.M. Jamieson, Sheldon    R. Rorris and Karen Messer, UCSD Department of Medicine and    UCSD Moores Cancer Center; Hye-Jung Chun and Marco Marra,    Michael Smith Genome Sciences Center, Vancouver, BC, Canada;    Christian L. Barrett and Kelly A. Frazer, UCSD Department of    Pediatrics; Maryla Krajewska, Jun Wei, Dayong Zhai, Maurizio    Pellecchia and John C. Reed, Sanford-Burnham Medical Research    Institute; Jason Gotlib, Stanford Medical Center; Mark Minden,    Princess Margaret Hospital, Toronto, Canada; Giovanni    Martinelli, Institute of Hematology and Medical Oncology,    University of Bologna, Italy; Jessica Rusert and Lawrence S.B.    Goldstein, UCSD Department of Cellular and Molecular Medicine    and Howard Hughes Medical Institute; Kim-Hien Dao, Oregon    Health and Science University, Portland; Kamran Shazand and    Thomas J. Hudson, Ontario Institute for Cancer Research,    Toronto, Canada.  
    Funding for this research was provided by a California    Institute for Regenerative Medicine (CIRM) early Translational    II grant (TR2-1789), a CIRM HALT leukemia disease team grant    (DR1-01430), the UCSD CIRM Training Grant (TG2-01154), the    Ratner Family Foundation, the National Cancer Institute    (CA-55164), the National Institutes of Health (CA-149668), the    Ontario Institute for Cancer Research, Genome Canada, Ontario    Genomics Institute and the Canadian Institute of Health    Research.  
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Drug Targets Hard-to-Reach Leukemia Stem Cells Responsible for Relapses