Biochem. Soc. Trans (2007) 35, 1347-1351 - H.G. Jorgensen and T.L. Holyoake

Medline/PubMed Citation | Related Articles in PubMed | Download to Citation Manager

Biochemical Society Transactions (2007) 35, (1347–1351) (Printed in Great Britain)

Enhanced Full Text

PDF

Legacy HTML

Send to a friend

Add a comment

Focus Topics at Life Sciences 2007

Characterization of cancer stem cells in chronic myeloid leukaemia

H.G. Jørgensen and T.L. Holyoake¹

Section of Experimental Haematology, Division of Cancer Sciences and Molecular Pathology, University of Glasgow, Level 3 Queen Elizabeth Building, Royal Infirmary, 10 Alexandra Parade, Glasgow G31 2ER, U.K.

Key words: BCR-ABL, farnesyl transferase, myeloid leukaemia, quiescence, stem cell, tyrosine kinase.

Abbreviations used: BC, blast crisis; CFSE, carboxyfluorescein succinimidyl ester; CML, chronic myeloid leukaemia; CP, chronic phase; FISH, fluorescence in situ hybridization; FTI, farnesyl transferase inhibitor; HSC, haemopoietic stem cell; IM, imatinib mesylate; LTC-IC, long-term culture-initiating cell; Ph, Philadelphia chromosome; TKI, tyrosine kinase inhibitor; QPCR, quantitative PCR.

¹To whom correspondence should be addressed (email tlh1g@clinmed.gla.ac.uk).

CML (chronic myeloid leukaemia) is a myeloproliferative disease that originates in an HSC (haemopoietic stem cell) as a result of the t(9;22) translocation, giving rise to the Ph (Philadelphia chromosome) and bcr-abl oncoprotein. The disease starts in CP (chronic phase), but as a result of genomic instability, it progresses over time to accelerated phase and then to BC (blast crisis), becoming increasingly resistant to therapy. bcr-abl is a constitutively active tyrosine kinase that has been targeted by TKIs (tyrosine kinase inhibitors), including IM (imatinib mesylate), nilotinib and dasatinib. We have developed various flow cytometry techniques to enable us to isolate candidate CML stem cells from CP patients at diagnosis that efflux Hoechst dye, express CD34, lack CD38 and are cytokine-non-responsive in culture over periods of up to 12 days in growth factors. These stem cells have been shown to regenerate bcr-abl-positive haemopoiesis in immunocompromised mice upon transplantation. We previously demonstrated that IM was antiproliferative for CML stem cells but did not induce apoptosis. Clinical experience now confirms that IM may not target CML stem cells in vivo with few patients achieving complete molecular remission and relapse occurring rapidly upon drug withdrawal. Our recent efforts have focused on understanding why CML stem cells are resistant to IM and on trying to find novel ways to induce apoptosis of this population. We have shown that CML stem cells express very high levels of functional wild-type bcr-abl; no kinase domain mutations have been detected in the stem cell population. Dasatinib, a more potent multitargeted TKI than IM, inhibits bcr-abl activity more efficiently than IM but still does not induce apoptosis of the stem cell population. Most recently, we have tested a number of novel drug combinations and found that FTIs (farnesyl transferase inhibitors) have activity against CML. BMS-214662 is the most effective of these and induces apoptosis of phenotypically and functionally defined CML stem cells in vitro, as a single agent and in combination with IM or dasatinib. The effect against CML stem cells is selective with little effect on normal stem cells. The drug is also effective against BC CML stem cells and equally effective against wild-type and mutant bcr-abl, including the most resistant mutant T315I. In association with apoptosis, there is activation of caspase 8 and caspase 3, inhibition of the MAPK pathway, IAP-1 (inhibitor of apoptosis protein-1), NF-kB (nuclear factor kB) and iNOS (inducible nitric oxide synthase). Furthermore, BMS-214662 synergizes with MEK1/2 [MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase 1/2] inhibitors, suggesting a second mechanism other that RAS inhibition for induction of apoptosis. Our intentions are now to explore the activity of BMS-214662 in other cancer stem cell disorders and to move this preclinical work to a clinical trial combining dasatinib with BMS-214662 in CML.