Background Imatinib mesylate (IM) induces clinical remission of chronic myeloid leukemia (CML). The Abelson helper integration site 1 (AHI-1) oncoprotein interacts with BCR-ABL and Janus kinase 2 (JAK2) to mediate IM response of primitive CML cells, but the effect of the interaction complex on the response to ABL and JAK2 inhibitors is unknown. Methods The AHI-1–BCR-ABL–JAK2 interaction complex was analyzed by mutational analysis and coimmunoprecipitation. Roles of the complex in regulation of response or resistance to ABL and JAK2 inhibitors were investigated in BCR-ABL + cells and primary CML stem/progenitor cells and in immunodeficient NSG mice. All statistical tests were two-sided. Results The WD40-repeat domain of AHI-1 interacts with BCR-ABL, whereas the N-terminal region interacts with JAK2; loss of these interactions statistically significantly increased the IM sensitivity of CML cells. Disrupting this complex with a combination of IM and an orally bioavailable selective JAK2 inhibitor (TG101209 [TG]) statistically significantly induced death of AHI-1–overexpressing and IM-resistant cells in vitro and enhanced survival of leukemic mice, compared with single agents (combination vs TG alone: 63 vs 53 days, ratio = 0.84, 95% confidence interval [CI] = 0.6 to 1.1, P = .004; vs IM: 57 days, ratio = 0.9, 95% CI = 0.61 to 1.2, P = .003). Combination treatment also statistically significantly enhanced apoptosis of CD34+ leukemic stem/progenitor cells and eliminated their long-term leukemia-initiating activity in NSG mice. Importantly, this approach was effective against treatment-naive CML stem cells from patients who subsequently proved to be resistant to IM therapy. Conclusions Simultaneously targeting BCR-ABL and JAK2 activities in CML stem/progenitor cells may improve outcomes in patients destined to develop IM resistance.

Long-term deregulated human hematopoiesis in goats transplanted in utero with BCR-ABL -transduced lin − CD34 + cord blood cells

Results: Cytogenetic data demonstrated that NCI-H460/R, DLD1-TxR and U87-TxR retained several karyotypic characteristics of their sensitive counterparts and also acquired novel structural or numerical chromosomal aberrations that may be related to resistance to chemotherapy.Gene expression analysis and flow cytometric analysis revealed that the most pronounced mechanism of MDR in resistant cell lines was the over-expression of P-gp associated with its activity.The homozygous mutations at position 2677G>T in mdr1 gene are present in all tested cancer cell lines.Only U87 and U87-TxR cell lines have the heterozygous mutations at the position 3435C>T.These mutations are involved in P-gp folding and may change the effects of P-gp inhibitors in MDR cancer cell lines.Indeed, our results showed that noncompetitive P-gp inhibitor tariquidar was less effective in the inhibition of the P-gp efflux activity in U87-TxR cells.Conclusions: Newly established resistant cancer cell lines represent models for studying the reasons for chemotherapy failure.Moreover, they are suitable for testing new therapeutics with the potential for overcoming MDR.

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 p210BCR-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.

AHI-1 is an oncogene often targeted by provirus insertional mutagenesis in murine leukemias and lymphomas. Aberrant expression of human AHI-1 occurs in cutaneous T-cell lymphoma (CTCL) cells and in CD4(+)CD7(-) Sezary cells from patients with Sezary syndrome. Stable knockdown of AHI-1 using retroviral-mediated RNA interference in CTCL cells inhibits their transforming activity in vitro and in vivo. To identify genes involved in AHI-1-mediated transformation, microarray analysis was performed to identify differentially expressed genes in AHI-1-suppressed CTCL cells. Fifteen up-regulated and 6 down-regulated genes were identified and confirmed by quantitative reverse transcription-polymerase chain reaction. Seven were further confirmed in a microarray analysis of CD4(+)CD7(-) Sezary cells from Sezary syndrome patients. HCK and BIN1 emerged as new candidate cooperative genes, with differential protein expression, which correlates with observed transcript changes. Interestingly, changes in HCK phosphorylation and biologic response to its inhibitor, dasatinib, were observed in AHI-1-suppressed or -overexpressed cells. The tumor suppressor BIN1 physically interacts with MYC in CTCL cells, which also exhibit differential MYC protein expression. In addition, aberrant expression of alternative splicing forms of BIN1 was observed in primary and transformed CTCL cells. These findings indicate that HCK and BIN1 may play critical roles in AHI-1-mediated leukemic transformation of human CTCL cells.

Chronic myeloid leukemia (CML) represents the first human malignancy successfully treated with a tyrosine kinase inhibitor (TKI; imatinib). However, early relapses and the emergence of imatinib-resistant disease are problematic. Evidence suggests that imatinib and other inhibitors may not effectively eradicate leukemic stem/progenitor cells, and that combination therapy directed to complimentary targets may improve treatment. Abelson helper integration site 1 (Ahi-1)/AHI-1 is a novel oncogene that is highly de-regulated in CML stem/progenitor cells where levels of BCR-ABL transcripts are also elevated. Here, we demonstrate that overexpression of Ahi-1/AHI-1 in murine and human hematopoietic cells confer growth advantages in vitro and induce leukemia in vivo, enhancing effects of BCR-ABL. Conversely, RNAi-mediated suppression of AHI-1 in BCR-ABL-transduced lin(-)CD34(+) human cord blood cells and primary CML stem/progenitor cells reduces their growth autonomy in vitro. Interestingly, coexpression of Ahi-1 in BCR-ABL-inducible cells reverses growth deficiencies exhibited by BCR-ABL down-regulation and is associated with sustained phosphorylation of BCR-ABL and enhanced activation of JAK2-STAT5. Moreover, we identified an AHI-1-BCR-ABL-JAK2 interaction complex and found that modulation of AHI-1 expression regulates phosphorylation of BCR-ABL and JAK2-STAT5 in CML cells. Importantly, this complex mediates TKI response/resistance of CML stem/progenitor cells. These studies implicate AHI-1 as a potential therapeutic target downstream of BCR-ABL in CML.

Abelson helper integration site 1 (Ahi-1) is a recently identified oncogene which is often the target of provirus insertional mutagenesis in murine leukemias and lymphomas. Ahi-1/AHI-1 encodes a unique cell signaling protein with a SH3 domain, multiple SH3 binding sites, seven WD40 repeats and a number of potential tyrosine kinase phosphorylation sites. Its involvement in human leukemogenesis is demonstrated by gross perturbations in its expression in several leukemic cells lines, particularly in cutaneous T-cell lymphoma (CTCL) cell lines (Hut 78 and Hut 102) where 40-fold up-regulation of AHI-1 transcripts is seen. Hut78 cells are derived from a patient with Sezary syndrome, a common leukemic variant of human CTCL. Interestingly, we have recently demonstrated that aberrant expression of AHI-1 at both RNA and protein levels is found in CD4+CD7− leukemic Sezary cells from patients with Sezary syndrome. Moreover, stable suppression of AHI-1 using retroviral-mediated RNA interference in Hut 78 cells reduces autocrine production of interleukin (IL)-2, IL-4 and tumor necrosis factor-alpha (TNFα) and normalizes their transforming activity both in vitro and in vivo. In an effort to identify genes involved in AHI-1-mediated leukemic transformation in CTCL, Microarray analysis was performed using the Affymetrix Human Genome U133 plus 2.0 Arrays which contains over 47,000 transcripts (54,330 probes). Comparative analysis of six RNA samples from AHI-1/sh4 cells (knockdown of AHI-1) and five samples from Hut 78 and Hut 78 cells transduced with a control vector (RPG) demonstrated that 101 genes (119 probes) were statistically differentially expressed with fold changes > or < 2 at p-values ≤ 0.001, using a DNA-Chip Analyzer (dChip). With the same selection criteria, the Linear Model for Microarray Data (Limma) analysis initially listed 239 genes (283 probes). Once the p-values for these genes were adjusted, using the approach of Benjamini and Hochberg, the list was refined to 27 genes (33 probes). After evaluation of differentially expressed genes selected by both dChip and Limma analyses, 15 up-regulated genes (fold change range: 2.2–11) and 6 down-regulated genes (fold change range: 2.1–8.3) in AHI-1 suppressed Hut 78 cells as compared to control cells, were chosen for further analysis. The expression patterns of these 21 genes identified by Microarray analyses were confirmed by quantitative real-time RT-PCR (fold change range: 6.7 higher to 33.3 lower, p≤0.001). Significant down-regulation of AHI-1 itself (p≤0.001) was confirmed in all six AHI-1/sh4 RNA samples studied. Interestingly, functional grouping of differentially expressed genes in AHI-1/sh4 cells shows several are involved in signal transduction (BRDG1, HCK, and REPS2), cell cycle control (CCNG2, CDKN1C, and PDCD6), cell proliferation and differentiation (BIN1 and MLLT11) and mRNA stability (ELAVL1). Additionally, our observed deregulated expression of NKG7 has also recently been documented in both Sezary syndrome and mycosis fungoides patient samples. Further, candidate tumor suppressor genes (BIN1 and CDKN1C) were found to be highly elevated in AHI-1/sh4 cells where AHI-1 expression is stably inhibited. These findings indicate that we have identified several new differentially expressed genes that may play critical roles in alteration of T-cell signaling in AHI-1 mediated leukemic transformation of human CTCL cells.

Ahi-1 (Abelson helper integration site-1) is a novel gene that we recently identified based on its common activation in v-abl or myc-induced murine leukemias and lymphomas. It encodes a unique protein with known signaling features, including SH3 and WD40-repeat domains, but its function is largely unknown. We have recently demonstrated that Ahi-1/AHI-1 transcript levels are normally down-regulated during both early murine and human hematopoietic cell differentiation and are highly increased in human leukemic cells, particularly in highly enriched populations of primitive BCR-ABL+ leukemic stem cells (lin−CD34+CD38−) in patients with chronic myeloid leukemia (CML). To investigate the potential cooperative activity of Ahi-1 in BCR-ABL-mediated signal transduction and leukemogenesis, we transduced IL-3-dependent BaF3 cells with MSCV-Ahi-1-IRES-YFP and/or MSCV-BCR-ABL-IRES-GFP retroviruses and compared the biological behavior of these cells in vitro and in vivo. All Ahi-1-transduced clonal cell lines showed increased proliferative activity and reduced apoptosis in the absence of IL-3, compared to parental BaF3 cells or control GFP-transduced cells. Interestingly, overexpression of both Ahi-1 and BCR-ABL caused more enhanced perturbations when compared to cells transduced with either Ahi-1 or BCR-ABL alone. Strikingly, intravenous injection of NOD/SCID-β2microglobulin−/−mice with BaF3 cells induced to overexpress Ahi-1 alone induces a lethal leukemia within 70 days. These leukemogenic activities were further increased by introduction of co-transduced Ahi-1 and BCR-ABL cells, producing a shorter latency of 30 days. A disease latency of 40 days was revealed by introduction of BCR-ABL-transduced cells alone. Western blot analysis showed that both protein expression and the tyrosine kinase activity of p210BCR-ABL were highly increased in cells co-transduced with Ahi-1 and BCR-ABL compared to BaF3 cells transduced with BCR-ABL alone. Similarly, we also observed higher levels of Ahi-1 protein expression in the same dually transduced cells (Ahi-1+BCR-ABL+) than in those transduced with Ahi-1 alone. We further demonstrated a similarly perturbed proliferative activity, growth factor independence and colony-forming cell (CFC) output in long-term culture initiated cell (LTC-IC) assays of 5-fluorouracil (5-FU)-treated primitive murine BM cells (Lin−Sca1+ cells) transduced with Ahi-1 and BCR-ABL, either alone or in combination. To investigate directly the cooperating oncogenic role of AHI-1 in BCR-ABL-mediated malignant transformation of CML cells, knockdown of AHI-1 expression in K562 cells, a cell line that was derived from a patient with CML and that is characterized by highly increased expression of AHI-1, was performed using retroviral-mediated RNA interference. Retroviral-mediated suppression specifically inhibited endogenous AHI-1 expression in transduced cells by 70% as evaluated by Q-RT-PCR and Western blot analyses. It further caused a significant reduction in their growth factor independence in semi-solid cultures (up to 5-fold) and in single cell cultures (2-fold) by comparison to cells transduced with a control vector. Taken together, these findings provide strong evidence of the transforming potential of Ahi-1/AHI-1 in primitive hematopoietic cells. This effect is additive with those of BCR-ABL, suggesting that AHI-1 and BCR-ABL can play a cooperate role in the development of BCR-ABL-associated diseases like CML.

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 (TNF α ) 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 TNF α 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.

Ahi-1 (Abelson helper integration site 1) is a novel gene that is commonly activated by provirus insertional mutagenesis in v-abl and myc-induced murine leukemias and lymphomas. It encodes a unique protein with SH3 and WD40-repeat domains suggesting novel signaling activities. Involvement of Ahi-1 in leukemogenesis is suggested by the high frequency of Ahi-1 mutations seen in certain virus-induced murine leukemias and lymphomas and by the gross perturbations seen in the expression of human AHI-1 and its isoforms in several human leukemia cell lines, particularly in the cutaneous T-cell leukemia cell lines, Hut 78 and Hut 102, where increases in AHI-1 transcripts of 40-fold are seen. To test directly whether the deregulated expression of AHI-1 in leukemic cells contributes to their transformed properties, knockdown of AHI-1 expression in Hut 78 cells, a cell line derived from peripheral blood of a patient with Sezary syndrome, was performed using retroviral-mediated RNA interference (RNAi). In a screen of 9 constructs that produce specific short hairpin AHI-1 transcripts, one was found to specifically inhibit AHI-1 expression in transduced Hut 78 cells by 80%, as evaluated by quantitative real-time RT-PCR, Northern and Western blot analyses. Retroviral-mediated suppression of AHI-1 also reduced the autocrine production of IL-2, IL-4 and TNFalpha in Hut 78 cells by up to 85% and caused a significant reduction in their growth factor independence in semi-solid cultures (up to 10-fold) and in single cell cultures (4-fold) by comparison to cells transduced with a control vector. Interestingly, although addition of IL-4, TNFalpha or a combination of 3 growth factors restored colony formation from the shRNA-transduced Hut 78 cells in semi-solid cultures, this was not achieved if only IL-2 was added, even though AHI-1 expression was inhibited. The ability of Hut 78 cells to produce tumors in NOD/SCID-β2microglobulin−/− mice within 3 weeks was also lost when AHI-1 expression was suppressed. Microarray analysis on RNA from Hut 78 cells with the suppression of AHI-1, using the Affymetrix Human Genome U133 plus 2.0 Arrays, identified differentially expressed molecules critical in T-cell activation, signal transduction, as well as cell proliferation and differentiation. Q-RT-PCR analysis revealed that the transcript levels of AHI-1 and its isoforms were significantly increased in CD4+CD7− Sezary cells, in which more than 85% of these cells are leukemic cells, in 5 of 6 blood samples obtained from patients with Sezary syndrome as compared to T cells similarly isolated from 8 healthy individuals. Elevated AHI-1 transcript levels were not found in 3 patient samples containing less than 35% leukemic Sezary cells. Taken together, these findings provide strong evidence of the oncogenic activity of AHI-1 in human T-cell leukemic cells and its deregulation can contribute to the development of human cutaneous T-cell lymphomas, including Sezary syndrome.

Ahi-1 (Abelson helper integration site-1) is a novel gene that is commonly activated by proviral insertional mutagenesis in v-abl or myc-induced murine leukemias and lymphomas. Ahi-1 encodes a unique protein with known signaling features including SH3 and WD40-repeat domains but its normal function is unknown. Involvement of Ahi-1 in leukemogenesis is suggested by the high frequency of Ahi-1 mutations seen in certain virus-induced murine leukemias and by the gross perturbations seen in the expression of human AHI-1 and its isoforms in several human leukemic cell lines, as well as in the primary lin−CD34+CD38− leukemic stem cell-enriched population in patients with chronic phase CML. To further investigate the role of Ahi-1 as a potential co-operating oncogene relevant to BCR-ABL-mediated leukemogenesis, we compared the biological behavior of primitive murine hematopoietic cells from the bone marrow of 5-FU-treated adult C57BL/6 mice after their transduction with MSCV-Ahi-1-IRES-YFP, MSCV-BCR-ABL-IRES-GFP retroviruses, either alone or in combination. Quantitative real-time RT-PCR analysis of RNA from FACS-purified lin−YFP+ (Ahi-1+), lin−GFP+ (BCR-ABL+) and lin−YFP+GFP+ (Ahi-1+ + BCR-ABL+)-transduced bone marrow cells showed that Ahi-1 transcripts were present at 40-fold higher levels in the Ahi-1-transduced cells by comparison to the control cells transduced with the empty MIY vector. Immediately post-transduction, the Ahi-1-transduced cells produced a similar number of colonies as the MIY-transduced control cells in semi-solid cultures containing Steel factor (SF) + IL-3 + IL-6 + EPO, although a small proportion of the Ahi-1+ CFCs (~10%) were already growth factor-independent. In addition, the proliferative activity of the FACS-purified lin−YFP+ (Ahi-1+) cells (as indicated by the rate of expansion of viable cells in a week in liquid cultures containing SF, IL-3, and IL-6) was ~3-fold higher than in cultures initiated with control (lin−YFP+) cells. Moreover, after 4 weeks in longterm culture-initiating cell (LTC-IC) assays, the Ahi-1+ cells produced 2x more CFCs than the control cells. All of these endpoints (proliferative activity, growth factor-dependence and CFC output in LTC-IC assays) are also perturbed by BCR-ABL transduction. Interestingly, in cells that were co-transduced with Ahi-1 and BCR-ABL, all of these effects were further enhanced as compared to cells transduced with either BCR-ABL alone (2–4-fold) or Ahi-1 alone (3–6-fold). Thus, overexpression of Ahi-1 alone deregulates the proliferation control of primitive murine hematopoietic cells and this is additive with the effects of BCR-ABL, suggesting that Ahi-1 and BCR-ABL can cooperate to promote the progression of BCR-ABL-associated diseases like CML.