[Show abstract][Hide abstract] ABSTRACT: Imatinib mesylate (IM) induces clinical remissions in chronic-phase chronic myeloid leukemia (CML) patients but IM resistance remains a problem. We recently identified several features of CML CD34(+) stem/progenitor cells expected to confer resistance to BCR-ABL-targeted therapeutics. From a study of 25 initially chronic-phase patients, we now demonstrate that some, but not all, of these parameters correlate with subsequent clinical response to IM therapy. CD34(+) cells from the 14 IM nonresponders demonstrated greater resistance to IM than the 11 IM responders in colony-forming cell assays in vitro (P < .001) and direct sequencing of cloned transcripts from CD34(+) cells further revealed a higher incidence of BCR-ABL kinase domain mutations in the IM nonresponders (10%-40% vs 0%-20% in IM responders, P < .003). In contrast, CD34(+) cells from IM nonresponders and IM responders were not distinguished by differences in BCR-ABL or transporter gene expression. Interestingly, one BCR-ABL mutation (V304D), predicted to destabilize the interaction between p210(BCR-ABL) and IM, was detectable in 14 of 20 patients. T315I mutant CD34(+) cells found before IM treatment in 2 of 20 patients examined were preferentially amplified after IM treatment. Thus, 2 properties of pretreatment CML stem/progenitor cells correlate with subsequent response to IM therapy. Prospective assessment of these properties may allow improved patient management.
[Show abstract][Hide abstract] ABSTRACT: Ahi-1 (Abelson helper integration site 1) is a novel gene frequently activated by provirus insertional mutagenesis in murine leukemias and lymphomas. Its involvement in human leukemogenesis is demonstrated by gross perturbations in its expression in human leukemia cells, particularly in cutaneous T-cell lymphoma cell lines where increases in AHI-1 transcripts of 40-fold are seen. To test directly whether deregulated expression of AHI-1 contributes to their transformed properties, knockdown of AHI-1 expression in Hut78 cells, a cell line derived from a patient with Sezary syndrome (SS), was performed using retroviral-mediated RNA interference. Retroviral-mediated suppression specifically inhibited expression of AHI-1 and its isoforms in transduced cells by 80% and also reduced autocrine production of interleukin (IL)-2, IL-4 and tumor necrosis factor-alpha (TNFalpha) by up to 85%. It further significantly reduced their growth factor independence in vitro and the ability to produce tumors in immunodeficient mice. Interestingly, aberrant expression of AHI-1, particularly truncated isoforms, was present in CD4+CD7- Sezary cells from some patients with SS. Elevated expression of IL-2 and TNFalpha was also found in these cells. These findings provide strong evidence of the oncogenic activity of AHI-1 in human leukemogenesis and demonstrate that its deregulation may contribute to the development of SS.
[Show abstract][Hide abstract] ABSTRACT: Xenograft models of chronic phase human chronic myeloid leukemia (CML) have been difficult to develop because of the persistence of normal hematopoietic stem cells in most chronic phase CML patients and the lack of methods to selectively isolate the rarer CML stem cells. To circumvent this problem, we first identified nine patients' samples in which the long-term culture-initiating cells were predominantly leukemic and then transplanted cells from these samples into sublethally irradiated NOD/SCID and NOD/SCID-beta2microglobulin-/- mice. This resulted in the consistent and durable (>5 months) repopulation of both host genotypes with similar numbers of BCR-ABL+/Ph+ cells. The regenerated leukemic cells included an initial, transient population derived from CD34+CD38+ cells as well as more sustained populations derived from CD34+CD38- progenitors, indicative of a hierarchy of transplantable leukemic cells. Analysis of the phenotypes produced revealed a reduced output of B-lineage cells, enhanced myelopoiesis with excessive production of erythroid and megakaropoietic cells and the generation of primitive (CD34+) leukemic cells displaying an autocrine IL-3 and G-CSF phenotype, all characteristics of primary CML cells. These findings demonstrate the validity of this xenograft model of chronic phase human CML, which should enable future investigation of disease pathogenesis and new approaches to therapy.
[Show abstract][Hide abstract] ABSTRACT: Ahi-1/AHI-1 (Abelson helper integration site-1) encodes a family of protein isoforms containing one Src homology 3 (SH3) domain and multiple tryptophan-aspartic acid 40 (WD40)-repeat domains. The function of these proteins is unknown, but involvement in leukemogenesis has been suggested by the high frequency of Ahi-1 mutations seen in certain virus-induced murine leukemias. Here we show that in both mice and humans, Ahi-1/AHI-1 expression is highest in the most primitive hematopoietic cells with specific patterns of down-regulation in different lineages. Cells from patients with chronic myeloid leukemia (CML; n = 28) show elevated AHI-1 transcripts in all disease phases and, in chronic phase, in the leukemic cells at all stages of differentiation, including quiescent (G(0)) CD34(+) cells as well as terminally differentiating cells. In the most primitive lin(-)CD34(+)CD38(-) CML cells, transcripts for the 2 shorter isoforms of AHI-1 are also increased. Although 15 of 16 human lymphoid and myeloid leukemic cell lines showed aberrant control of AHI-1 expression, this was not seen in blasts obtained directly from patients with acute Philadelphia chromosome-negative (Ph(-)) leukemia (n = 15). Taken together, our results suggest that down-regulation of AHI-1 expression is an important conserved step in primitive normal hematopoietic cell differentiation and that perturbations in AHI-1 expression may contribute to the development of specific types of human leukemia.
[Show abstract][Hide abstract] ABSTRACT: Transplantation of sublethally irradiated NOD/SCID or NOD/SCID-beta2microglobulin (beta2m) null mice with cells from most chronic phase chronic myeloid leukemia (CML) patients results in the regeneration in the mice of primarily normal human hematopoietic cells. This is due to the usual predominance of normal cells within the most primitive subsets of bone marrow or blood cells in these patients. To date, no markers that allow the most primitive normal and leukemic cells to be differentially isolated from chronic phase CML samples have been identified except those reflecting an increased turnover of the leukemic cells. As an alternative approach to characterizing chronic phase CML stem cells, we have identified particular patient samples that contain predominantly leukemic LTC-ICs and have found that transplants of these samples regenerate a predominance of leukemic cells in both NOD/SCID and NOD/SCID-beta2m null mice. To investigate the biological and phenotypic properties of CML cells that have short- and longterm repopulating activity, we transplanted sublethally irradiated NOD/SCID and NOD/SCID-beta2m null mice with FACS-sorted subsets of lin- CML cells from 2 such samples and then monitored their output of cells in the bone marrow of the mice for up to 12 weeks. The CD34+CD38+ CML cells produced a rapid but transient wave of mainly myeloid progeny that peaked at 3 weeks whereas the CD34+CD38- cells produced a more delayed but persistent wave of cells in both types of mice that included some lymphoid progeny although the latter represented a markedly reduced proportion of the total relative to the cells produced by normal human bone marrow. These patterns were seen in both recipient genotypes but cell output was enhanced in NOD/SCID-beta2m null mice as expected for short-term repopulating cells. In additional studies with 3 patients' samples, both types of repopulating cells were found primarily in the aldehyde dehydrogenase-positive fraction based on their staining with BODIPY-labeled amino acetaldehyde. To test the feasibility of the CML xenograft model for evaluating novel treatments in vivo, groups of NOD/SCID mice repopulated to high levels with leukemic cells (49+/-8%) 7 weeks after being transplanted with 3x107 CD34+ CML cells, were injected with 50 mg/kg imatinib mesylate (or not) i.p. twice daily for 10 days. Bone marrow samples obtained from the imatinib mesylate-treated mice 2, 4, 12 and 22 weeks after initiation of this treatment, initially showed a more rapid and greater decline of human leukemic cells (>2-fold as assessed by both FACS and quantitative real-time PCR); however by 5 months after completion of the treatment, the level of human cells in the bone marrow of both the imatinib mesylate-treated and untreated mice was the same. Taken together, these findings demonstrate that the CML clone in chronic phase patients contains a similar hierarchy of short and longterm repopulating cells as is found in normal adult bone marrow, and that the CML repopulating cells have, in addition to their ability to sustain the clone, a greater innate resistance to the toxic effects that imatinib mesylate has in vivo on the majority population of more differentiated CML cells.