CGP57148B (STI-571) induces differentiation and apoptosis and sensitizes Bcr-Abl–positive human leukemia cells to apoptosis due to antileukemic drugs

Blood ◽  
2000 ◽  
Vol 96 (6) ◽  
pp. 2246-2253 ◽  
Author(s):  
Guofu Fang ◽  
Caryn Naekyung Kim ◽  
Charles L. Perkins ◽  
Nimmanapalli Ramadevi ◽  
Elliott Winton ◽  
...  
Keyword(s):  
Myeloid Leukemia ◽  
Fas Ligand ◽  
Ectopic Expression ◽  
K562 Cells ◽  
Parp Cleavage ◽  
Human Leukemia ◽  
Sti 571 ◽  
Tnf Α ◽  
Cyt C ◽  
Induced Apoptosis

The differentiation and apoptosis-sensitizing effects of the Bcr-Abl–specific tyrosine kinase inhibitor CGP57148B, also known as STI-571, were determined in human Bcr-Abl–positive HL-60/Bcr-Abl and K562 cells. First, the results demonstrate that the ectopic expression of the p185 Bcr-Abl fusion protein induced hemoglobin in the acute myeloid leukemia (AML) HL-60 cells. Exposure to low-dose cytosine arabinoside (Ara-C; 10 nmol/L) increased hemoglobin levels in HL-60/Bcr-Abl and in the chronic myeloid leukemia (CML) blast crisis K562 cells, which express the p210 Bcr-Abl protein. As compared with HL-60/neo, HL-60/Bcr-Abl and K562 cells were resistant to apoptosis induced by Ara-C, doxorubicin, or tumor necrosis factor-α (TNF-α), which was associated with reduced processing of caspase-8 and Bid protein and decreased cytosolic accumulation of cytochrome c (cyt c). Exposure to CGP57148B alone increased hemoglobin levels and CD11b expression and induced apoptosis of HL-60/Bcr-Abl and K562 cells. CGP57148B treatment down-regulated antiapoptotic XIAP, cIAP1, and Bcl-xL, without affecting Bcl-2, Bax, Apaf-1, Fas (CD95), Fas ligand, Abl, and Bcr-Abl levels. CGP57148B also inhibited constitutively active Akt kinase and NFκB in Bcr-Abl–positive cells. Attenuation of NFκB activity by ectopic expression of transdominant repressor of IκB sensitized HL-60/Bcr-Abl and K562 cells to TNF-α but not to apoptosis induced by Ara-C or doxorubicin. Importantly, cotreatment with CGP57148B significantly increased Ara-C– or doxorubicin-induced apoptosis of HL-60/Bcr-Abl and K562 cells. This was associated with greater cytosolic accumulation of cyt c and PARP cleavage activity of caspase-3. These in vitro data indicate that combinations of CGP57148B and antileukemic drugs such as Ara-C may have improved in vivo efficacy against Bcr-Abl–positive acute leukemia.

CGP57148B (STI-571) induces differentiation and apoptosis and sensitizes Bcr-Abl–positive human leukemia cells to apoptosis due to antileukemic drugs

Blood ◽  
2000 ◽  
Vol 96 (6) ◽  
pp. 2246-2253 ◽  
Author(s):  
Guofu Fang ◽  
Caryn Naekyung Kim ◽  
Charles L. Perkins ◽  
Nimmanapalli Ramadevi ◽  
Elliott Winton ◽  
...  
Keyword(s):  
Myeloid Leukemia ◽  
Fas Ligand ◽  
Ectopic Expression ◽  
K562 Cells ◽  
Parp Cleavage ◽  
Human Leukemia ◽  
Sti 571 ◽  
Tnf Α ◽  
Cyt C ◽  
Induced Apoptosis

Abstract The differentiation and apoptosis-sensitizing effects of the Bcr-Abl–specific tyrosine kinase inhibitor CGP57148B, also known as STI-571, were determined in human Bcr-Abl–positive HL-60/Bcr-Abl and K562 cells. First, the results demonstrate that the ectopic expression of the p185 Bcr-Abl fusion protein induced hemoglobin in the acute myeloid leukemia (AML) HL-60 cells. Exposure to low-dose cytosine arabinoside (Ara-C; 10 nmol/L) increased hemoglobin levels in HL-60/Bcr-Abl and in the chronic myeloid leukemia (CML) blast crisis K562 cells, which express the p210 Bcr-Abl protein. As compared with HL-60/neo, HL-60/Bcr-Abl and K562 cells were resistant to apoptosis induced by Ara-C, doxorubicin, or tumor necrosis factor-α (TNF-α), which was associated with reduced processing of caspase-8 and Bid protein and decreased cytosolic accumulation of cytochrome c (cyt c). Exposure to CGP57148B alone increased hemoglobin levels and CD11b expression and induced apoptosis of HL-60/Bcr-Abl and K562 cells. CGP57148B treatment down-regulated antiapoptotic XIAP, cIAP1, and Bcl-xL, without affecting Bcl-2, Bax, Apaf-1, Fas (CD95), Fas ligand, Abl, and Bcr-Abl levels. CGP57148B also inhibited constitutively active Akt kinase and NFκB in Bcr-Abl–positive cells. Attenuation of NFκB activity by ectopic expression of transdominant repressor of IκB sensitized HL-60/Bcr-Abl and K562 cells to TNF-α but not to apoptosis induced by Ara-C or doxorubicin. Importantly, cotreatment with CGP57148B significantly increased Ara-C– or doxorubicin-induced apoptosis of HL-60/Bcr-Abl and K562 cells. This was associated with greater cytosolic accumulation of cyt c and PARP cleavage activity of caspase-3. These in vitro data indicate that combinations of CGP57148B and antileukemic drugs such as Ara-C may have improved in vivo efficacy against Bcr-Abl–positive acute leukemia.

scholarly journals Albendazole-Induced SIRT3 Upregulation Protects Human Leukemia K562 Cells from the Cytotoxicity of MCL1 Suppression

2020 ◽  
Vol 21 (11) ◽  
pp. 3907 ◽  
Author(s):  
Liang-Jun Wang ◽  
Li-Ren Liou ◽  
Yi-Jun Shi ◽  
Jing-Ting Chiou ◽  
Yuan-Chin Lee ◽  
...  
Keyword(s):  
Ectopic Expression ◽  
K562 Cells ◽  
Human Leukemia ◽  
Cancer Therapies ◽  
Microtubule Targeting Agents ◽  
Induced Apoptosis ◽  
Benzimidazole Anthelmintic ◽  
Sirt3 Expression ◽  
Human Leukemia K562 Cells

Previous studies have shown that MCL1 stabilization confers cancer cells resistance to microtubule targeting agents (MTAs) and functionally extends the lifespan of MTA-triggered mitotically arrested cells. Albendazole (ABZ), a benzimidazole anthelmintic, shows microtubule-destabilizing activity and has been repositioned for cancer therapies. To clarify the role of MCL1 in ABZ-induced apoptosis, we investigated the cytotoxicity of ABZ on human leukemia K562 cells. Treatment with ABZ for 24 h did not appreciably induce apoptosis or mitochondrial depolarization in K562 cells, though it caused the mitotic arrest of K562 cells. ABZ-evoked p38 MAPK activation concurrently suppressed Sp1-mediated MCL1 expression and increased SIRT3 mRNA stability and protein expression. ABZ and A-1210477 (an MCL1 inhibitor) enhanced the cytotoxicity of ABT-263 (a BCL2/BCL2L1 inhibitor) to their effect on MCL1 suppression. Unlike ABZ, A-1210477 did not affect SIRT3 expression and reduced the survival of K562 cells. Overexpression of SIRT3 attenuated the A-1210477 cytotoxicity on K562 cells. ABZ treatment elicited marked apoptosis and ΔΨm loss in ABT-263-resistant K562 (K562/R) cells, but did not alter SIRT3 expression. Ectopic expression of SIRT3 alleviated the cytotoxicity of ABZ on K562/R cells. Collectively, our data demonstrate that ABZ-induced SIRT3 upregulation delays the apoptosis-inducing effect of MCL1 suppression on apoptosis induction in K562 cells.

scholarly journals Apoptosis Induced by Tanshinone IIA and Cryptotanshinone Is Mediated by Distinct JAK/STAT3/5 and SHP1/2 Signaling in Chronic Myeloid Leukemia K562 Cells

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Ji Hoon Jung ◽  
Tae-Rin Kwon ◽  
Soo-Jin Jeong ◽  
Eun-Ok Kim ◽  
Eun Jung Sohn ◽  
...  
Keyword(s):  
Chronic Myeloid Leukemia ◽  
Myeloid Leukemia ◽  
Biological Effects ◽  
K562 Cells ◽  
Tanshinone Iia ◽  
Anticancer Activities ◽  
Caspase 9 ◽  
Anticancer Effects ◽  
Induced Apoptosis ◽  
Better Than

Though tanshinone IIA and cryptotanshinone possess a variety of biological effects such as anti-inflammatory, antioxidative, antimetabolic, and anticancer effects, the precise molecular targets or pathways responsible for anticancer activities of tanshinone IIA and cryptotanshinone in chronic myeloid leukemia (CML) still remain unclear. In the present study, we investigated the effect of tanshinone IIA and cryptotanshinone on the Janus activated kinase (JAK)/signal transducer and activator of transcription (STAT) signaling during apoptotic process. We found that both tanshinone IIA and cryptotanshinone induced apoptosis by activation of caspase-9/3 and Sub-G1 accumulation in K562 cells. However, they have the distinct JAK/STAT pathway, in which tanshinone IIA inhibits JAK2/STAT5 signaling, whereas cryptotanshinone targets the JAK2/STAT3. In addition, tanshinone IIA enhanced the expression of both SHP-1 and -2, while cryptotanshinone regulated the expression of only SHP-1. Both tanshinone IIA and cryptotanshinone attenuated the expression of bcl-xL, survivin, and cyclin D1. Furthermore, tanshinone IIA augmented synergy with imatinib, a CML chemotherapeutic drug, better than cryptotanshinone in K562 cells. Overall, our findings suggest that the anticancer activity of tanshinone IIA and cryptotanshinone is mediated by the distinct the JAK/STAT3/5 and SHP1/2 signaling, and tanshinone IIA has the potential for combination therapy with imatinib in K562 CML cells.

Mitomycin Induced Apoptosis in Human Leukemia K562 Cells

2012 ◽  
Vol 599 ◽  
pp. 71-75
Author(s):  
Shu Li Shao ◽  
Bin Zhao ◽  
Wei Wei Zhang ◽  
Wei Zhao ◽  
Guang Hui Wu ◽  
...  
Keyword(s):  
Flow Cytometry ◽  
Gel Electrophoresis ◽  
Light Microscope ◽  
Previous Experiment ◽  
K562 Cells ◽  
S Phase ◽  
Fluorescence Microscope ◽  
Human Leukemia ◽  
Induced Apoptosis ◽  
Human Leukemia K562 Cells

Objective: The research aimed to study the effects of mitomycin on human leukemic K562 cells, and to explore the mechanism of mitomycin induced apoptosis．In order to provide previous experiment basis for mitomycin applying clinical treatments Methods: The multiplication and apoptosis status of K562 cells treated different time by different concentration mitomycin were observed by light microscope, fluorescence microscope, TEM, agrose gel electrophoresis of DNA and flow cytometry. Results: The results showed that mitomycin could induce K562 cells apoptosis, and the best concentration was 12.5μg/ml for 48 h. The optimal concentration of apoptosis induced by apoptosis rate is （28.8±1.04）% （P<0.01）. Mitomycin could affect the S phase among cellular multiplication, cell could be blocked by mitomycin and then apoptosis in this phase. Conclusions: Mitomycin can induce the apoptosis of human leukemic K562 cells. It is of great significance to guide clinical medication.

scholarly journals Combination therapy using TGF-β1 and STI-571 can induce apoptosis in BCR-ABL oncogene-expressing cells

2021 ◽  
Vol 12 (1) ◽  
pp. 144-155
Author(s):  
Masoome Bakhshayesh ◽  
Ladan Hosseini Gohari ◽  
Mahmood Barati ◽  
Majid Safa
Keyword(s):  
Combination Therapy ◽  
Tyrosine Kinase ◽  
Cell Signaling ◽  
Signaling Pathway ◽  
Kinase Inhibitor ◽  
K562 Cells ◽  
Parp Cleavage ◽  
Kinase Gene ◽  
Sti 571 ◽  
Tgf Β1

Abstract The BCR-ABL oncogene is a tyrosine kinase gene that is over-expressed in CML. It inhibits the TGF-β1 signaling pathway. Due to resistance of cells to the tyrosine kinase inhibitor, STI-571, the combined effect of STI-571 and TGF-β1 on K562 cells was studied in the present research. Results revealed that the TGF-β1 cell signaling pathway, which is activated in K562 cells treated with TGF-β1, activates collective cell signaling pathways involved in survival and apoptosis. It is noteworthy that treating K562 cells with STI-571 triggered apoptotic pathways, accompanied by a reduction in proteins such as Bcl-xL, Bcl-2, p-AKT, p-Stat5, p-FOXO3, and Mcl-1 and an increase in the pro-apoptotic proteins PARP cleavage, and p27, leading to an increase in sub-G1 phase-arrested and Annexin-positive cells. Interestingly, the proliferation behavior of TGF-β1-induced cells was changed with the combination therapy, and STI-571-induced apoptosis was also prompted by this combination. Thus, combination treatment appears to promote sub-G1 cell cycle arrest compared to individually treated cells. Furthermore, it strongly triggered apoptotic signaling. In conclusion, TGF-β1 did not negatively impact the effect of STI-571, based on positive annexin cells, and AKT protein phosphorylation remains effective in apoptosis.

Differential protective effects of Bcl-xL and Bcl-2 on apoptotic liver injury in transgenic mice

1999 ◽  
Vol 277 (3) ◽  
pp. G702-G708 ◽  
Author(s):  
Alix de la Coste ◽  
Monique Fabre ◽  
Nathalie McDonell ◽  
Arlette Porteu ◽  
Helène Gilgenkrantz ◽  
...  
Keyword(s):  
Liver Injury ◽  
Transgenic Mice ◽  
Fas Ligand ◽  
Dependent Manner ◽  
Protective Effects ◽  
Tnf Α ◽  
Apoptotic Pathways ◽  
Induced Apoptosis ◽  
Factor Α

Fas ligand (CD95L) and tumor necrosis factor-α (TNF-α) are pivotal inducers of hepatocyte apoptosis. Uncontrolled activation of these two systems is involved in several forms of liver injury. Although the broad antiapoptotic action of Bcl-2 and Bcl-xL has been clearly established in various apoptotic pathways, their ability to inhibit the Fas/CD95- and TNF-α-mediated apoptotic signal has remained controversial. We have demonstrated that the expression of BCL-2 in hepatocytes protects them against Fas-induced fulminant hepatitis in transgenic mice. The present study shows that transgenic mice overexpressing[Formula: see text]in hepatocytes are also protected from Fas-induced apoptosis in a dose-dependent manner. Bcl-xL and Bcl-2 were protective without any change in the level of endogenous[Formula: see text]or Bax and inhibited hepatic caspase-3-like activity. In vivo injection of TNF-α caused massive apoptosis and death only when transcription was inhibited. Under these conditions,[Formula: see text]mice were partially protected from liver injury and death but PK-BCL-2 mice were not. A similar differential protective effect of Bcl-xL and Bcl-2 transgenes was observed when Fas/CD95 was activated and transcription blocked. These results suggest that apoptosis triggered by activation of both Fas/CD95 and TNF-α receptors is to some extent counteracted by the transcription-dependent protective effects, which are essential for the antiapoptotic activity of Bcl-2 but not of Bcl-xL. Therefore, Bcl-xL and Bcl-2 appear to have different antiapoptotic effects in the liver whose characterization could facilitate their use to prevent the uncontrolled apoptosis of hepatocytes.

Bcr-Abl-Mediated Suppression of Normal Hematopoiesis in Chronic Myeloid Leukemia: Involvement of a Modified Form of NGAL.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 2869-2869
Author(s):  
Hui Lin ◽  
Xiaohong Leng ◽  
Tong Sun ◽  
Giuseppe Monaco ◽  
Clifton Stephens ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Chronic Myeloid Leukemia ◽  
Myeloid Leukemia ◽  
Hematopoietic Cells ◽  
K562 Cells ◽  
Soft Agar ◽  
Leukemia Cells ◽  
Active Process ◽  
Culture Studies ◽  
Induced Apoptosis

Abstract The BCR-ABL oncogene plays an essential role in chronic myeloid leukemia (CML). In NOD/scid mice injected with soft agar clones of a human CML cell line (K562), we observed a leukemia syndrome involving not only leukemia but also a severe reduction of normal mouse hematopoiesis (Lin et al., Oncogene, 2001). Some of these mice died of a wasting syndrome that involved suppression of hematopoiesis without extensive tumor cell invasion of the spleen and marrow. In CML patients, since normal hematopoietic cells in marrow and spleen are replaced with proliferating leukemic blasts, we postulate that this is an active process mediated by the leukemia cells. The lipocalin 24p3 is secreted by mouse hematopoietic cells deprived of IL-3, resulting in apoptosis induction in a variety of hematopoietic cells including bone marrow cells (Devireddy et al., Science, 2001). We found that BCR-ABL+ mouse hematopoietic cells induce a persistent secretion of a modified form of 24p3 (21 kDa). Co-culture studies show that BCR-ABL+ cells induced apoptosis in BCR-ABL negative cells. Importantly, BCR-ABL+ hematopoietic cells are resistant to apoptosis under the same conditions. Conditioned medium (CM) from BCR-ABL+ cells expressing anti-sense/siRNA 24p3 or CM mixed with 24p3 antibody have reduced apoptotic activity for target cells. We also found that the expression of the Bcr-Abl oncoprotein and its tyrosine kinase are required for induction of 24p3 expression. Leukemic mice induced by BCR-ABL+ cells expressing anti-sense/siRNA 24p3 have increased levels of normal hematopoiesis (marrow and spleen erythropoiesis and blood platelet levels) and reduced invasion of leukemia cells in marrow and spleen tissues, but the leukemia cells readily invade liver and the abdomen as ascites (Lin et al, Oncogene, 2005). These findings indicate that suppression of normal hematopoiesis in BCR-ABL induced leukemia is an active process involving the apoptotic factor 24p3, raising the possibility that similar factors are involved in BCR-ABL+ CML patients. We have found that the K562 clones (Lin et al. 2001) have enhanced expression of NGAL (neutrophil gelatinase-associated lipocalin, human homologue of 24p3) transcripts compared to uncloned K562 cells. We generated additional soft agar K562 clones, each with different expression levels of NGAL transcripts. NOD/scid mice injected with the clone (C5) of K562 cell line expressing a high level of NGAL had severe depression of hematopoiesis and significantly shorter survival time as compared with mice injected with parental K562 cells and a clone (C6) expressing a low level of NGAL. Co-culture studies showed that the C5 K562 clone also induced apoptosis in BCR-ABL negative cells. We detected two glycosylated forms of NGAL/24p3 migrating at 24 kDa and 21 kDa on SDS-PAGE. The 21 kDa form is the major form in CM from mouse BCR-ABL+ cells and K562 clones. Our preliminary data with CML patient samples showed that levels of 21 kDa NGAL protein in bone marrow fluid correlated with BCR-ABL/ABL ratio. Further studies with more patient samples are ongoing to confirm the role of NGAL in suppressing normal hematopoiesis in CML patients and to determine the structural change(s) that leads to the modified form of 24p3/NGAL secreted by CML cells.

Myeloperoxidase Is Required for the Combined Apoptotic Effects of Arsenic Trioxide with Ascorbic Acid or Epigallocatechin-3-Gallate in Myeloid Leukemia Cells.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 3474-3474
Author(s):  
Lijuan Xia ◽  
Min Lu ◽  
Duo Chen ◽  
Samuel Waxman ◽  
Yongkui Jing
Keyword(s):  
Ascorbic Acid ◽  
Nadph Oxidase ◽  
Arsenic Trioxide ◽  
Myeloid Leukemia ◽  
K562 Cells ◽  
H2o2 Production ◽  
Nb4 Cells ◽  
Combination Treatments ◽  
Induced Apoptosis ◽  
High Level

Abstract Arsenic trioxide (As2O3) is a drug used world-wide that selectively causes the death of acute promyelocytic leukemia (APL) cells by novel mechanisms and induces complete clinical remission in 90% of patients without significant toxicity. The outstanding success of As2O3 therapy in relapsed APL patients has not been replicated by an equivalent success in other types of acute myeloid leukemia (AML). We have studied As2O3 mechanism(s) of action and identified agents to use in combination to improve the use of As2O3 as a treatment for other types of AML. As2O3 produces higher levels of H2O2 and apoptosis in APL NB4 cells than in other AML cells at therapeutic concentrations of 1-2 uM. As2O3 does not induce apoptosis in HL-60 cells but is synergistic with ascorbic acid (AA) or epigallocatechin-3-gallate (EGCG). Both AA and EGCG produce H2O2 which is augmented by the addition of As2O3. Apoptosis induction by As2O3 in combination with AA or EGCG is inhibited by catalase and the antioxidant N-acetylcysteine. Myeloperoxidase (MPO), a major neutrophil enzyme, augments H2O2-induced apoptosis by converting it into more potent reactive oxygen species. HL-60, NB4, SKNO-1 and PLB985 cells which express high level of MPO, but not U937 and K562 cells without expression of MPO, are responsive to As2O3 plus AA or EGCG-induced apoptosis. HP-100 cells, a subclone of HL-60 cells without MPO expression, are resistant to both combination treatments. MPO stable transfection sensitizes K562 cells to apoptosis following treatment with As2O3 and AA or EGCG. NADPH oxidase is an enzyme complex which generates O2− and H2O2 in neutrophils. In APL NB4 cells, As2O3 induces expression of NADPH oxidase members and is thought to participate in H2O2 production required for As2O3 response. X-CGD cells, a subclone of PLB-985 with targeted disruption of the gp91phox gene (Zhen et al, PNAS90:9832, 1993) and loss of NADPH oxidase activity but with high levels of MPO activity, are responsive to treatment with As2O3 and AA or EGCG. These results suggest that AA and EGCG enhance As2O3-induced apoptosis through a synergistic production of H2O2 which is independent NADPH oxidase activation in non-APL AML cells. MPO augments the apoptotic effect of H2O2 produced by As2O3 plus AA or EGCG and it could be used as a marker to predict the sensitivity of AML cells to both combination treatments.

Decreased Proliferation of Myeloid Leukemia Cells through Down-Regulating LYL1 Expression with Small Interference RNA.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 4158-4158 ◽  
Author(s):  
Yuesheng Meng ◽  
Wei Liu ◽  
Xiaoxia Ma ◽  
Xiuqin Meng ◽  
Gongwen Ai ◽  
...  
Keyword(s):  
Growth Rates ◽  
Myeloid Leukemia ◽  
K562 Cells ◽  
Plating Efficiency ◽  
Leukemia Cell Line ◽  
Leukemia Cells ◽  
Human Leukemia ◽  
Small Interference Rna ◽  
Expression Levels ◽  
Interference Rna

Abstract Ectopic expression of the basic helix-loop-helix transcription factor LYL1 has been implicated in T-cell acute lymphoblastic leukemia (T-ALL). It has also been found to be over-expressed in cells of acute myeloid leukemia (AML). Myeloid leukemia cells over-expressing LYL1 cDNA had accelerated growth rates, increased plating efficiency and a blockade of differentiation. To further investigate its role in the pathogenesis of leukemia, we used small interference RNA (siRNA) to silence the expression of LYL1 in human leukemia cell line K562, which expresses a moderate level of endogenous LYL1 protein. Three LYL1-specific RNA oligos, the Stealth Select RNAi HSS142834, HSS142835, and HSS142836, purchased from Invitrogen, were introduced into K562 cells by using Invitrogen transfection reagent Lipofectamine RNAiMAX. Two successive transfections at day 1 and day 2 were made according to manufacturer’s manual. Expression levels of LYL1 in LYL1 siRNA transfected cells and control cells (transfected with the Stealth RNAi Negative Controls) were determined with fluorescence real-time quantitative polymerase chain reaction assay. Our result showed that the application of any single RNAi oligo achieved observable inhibition of LYL1 expression levels (30–40%) while a combination of the three RNAi oligos remarkable inhibition (70.4%). The growth rates of K562 cells were not affected by any single RNAi oligo. However, a combination of three RNAi oligos did induce noticeable growth inhibition of cells. Plating efficiency assay showed that the clonogenic recovery rate of K562 cells treated with a combination of thee RNAi oligos was inhibited by 32.5% (P<0.05). The reduced growth rate and clonogenicity of cells was supposed to be secondary to the repressed expression of LYL1 because all other factors were controlled in our experiments. Further experiments are underway to define the changes of other genes in the LYL1-suppressed cells. We also tested the effect of specific siRNA on the expression of LYL1 and clonogenecity of leukemia cells in patient samples. Mononuclear cells separated from nine newly-diagnosed AML patients whose cells expressed comparatively higher levels of LYL1 were transfected with a combination of three LYL1 specific siRNA oligos for twice. We found that the siRNA oligos suppressed the expression of LYL1 in leukemia cells in most of the patients (7/9, decreased by 2 times or more) when compared with controls. Remarkably, the clonogenicity of AML cells in 3 patients was also inhibited by siRNA (P<0.05). In conclusion, the specific siRNA was effective to downregulate the expression of LYL1 in myeloid leukemia cells. It was also effective to affect cell proliferation in some cases. The data demonstrates that LYL1 plays a role for the malignant genotypes of leukemia cells and suggests that the RNA interference therapy targeting specific oncogenes might be clinically useful in the management of hematological malignancies.

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