The in vitro activity of the tyrosine kinase inhibitor STI571 in BCR-ABL positive chronic myeloid leukaemia cells: synergistic interactions with anti-leukaemic agents

Synergistic activity of nilotinib and established chemotherapeutic drugs in imatinib-sensitive and -resistant BCR-ABL-positive cells

We investigated various combination treatment regimens employing nilotinib with established chemotherapeutic agents (daunorubicin, mitoxantrone, etoposide and cytarabine) in imatinib-sensitive and -resistant BCR-ABL-positive cells. Mitoxantrone or cytarabine showed synergism (CI < 1) in combination with nilotinib in imatinib-sensitive LAMA84 cells, whereas in imatinib-resistant LAMA84-R cells synergistic effects could be assessed for daunorubicin, mitoxantrone and etoposide when combined with nilotinib. In both imatinib-sensitive and -resistant K562 cells daunorubicin, mitoxantrone and etoposide demonstrated synergism in combination with nilotinib. Moreover, both daunorubicin and mitoxantrone led to synergistic antiproliferative effects when combined with nilotinib in imatinib-resistant Ba/F3 cells carrying point mutations in the ABL TK domain (E255K, E255V and T315I). Annexin V/propidium iodide staining revealed a significant enhancement of nilotinib-induced apoptosis in imatinib-resistant Ba/F3T315I and LAMA84-R cells upon combination with daunorubicin and mitoxantrone, respectively. Our results demonstrate the efficacy of combination treatment regimens employing nilotinib and established chemotherapeutic agents in improving antileukemic effects in imatinib-sensitive and imatinib-resistant cells. This may be the foundation for further study on the potential of the applied combinations in a clinical setting.

A pilot study of imatinib, low-dose cytarabine and idarubicin for patients with chronic myeloid leukemia in myeloid blast phase

Imatinib is the single most effective agent in chronic myelogenous leukemia (CML) in blast phase (BP), inducing hematologic responses in 30 - 50% of patients. However, only a few of these are complete (CHR) and durable. Imatinib is synergistic with idarubicin and cytarabine. We administered imatinib 600 mg/day, cytarabine 10 mg/day subcutaneous, and idarubicin 12 mg/m2 intravenous every 14 days in 19 patients with CML in myeloid BP. Fourteen patients (74%) achieved a hematologic response: CHR in 9 (47%) (3 with complete and 1 with minor cytogenetic responses) and return to chronic phase (RTC) in 5 (26%). Median duration of response was 10 weeks (range, 2 - 89). Six patients received allogeneic stem cell transplantation: 4 CHR, 1 chronic phase and 1 BP. Median survival was 5 months (range, 2 - 20 months). This outpatient regimen is effective and well tolerated and perhaps superior to single-agent imatinib for patients in myeloid BP.

Enhancing the in vitro cytotoxic activity of Delta9-tetrahydrocannabinol in leukemic cells through a combinatorial approach

Delta(9)-Tetrahydrocannabinol (THC) is the active metabolite of cannabis, which has demonstrable cytotoxic activity in vitro. In support of our previously published data, we have investigated the interactions between THC and anti-leukemia therapies and studied the role of the signalling pathways in mediating these effects. Results showed clear synergistic interactions between THC and the cytotoxic agents in leukemic cells. Additionally, exposure of cells to sub lethal levels of THC (1 microM) sensitised cells to these cytotoxic agents, by reducing IC(50) values by approximately 50%. Sensitisation appeared to be dependent upon the ability of THC to down regulate phosphorylated ERK, as cells dominantly expressive of MEK were not sensitised to the cytotoxic drugs by equi-molar amounts of THC. Overall, these results demonstrate for the first time that a combination approach with THC and established cytotoxic agents may enhance cell death in vitro. Additionally the MAPK/ERK pathway appears responsible in part for these effects.

A comparison of the platinum analogues in bladder cancer cell lines

BACKGROUND

Oxaliplatin is a 3rd generation platinum analogue, which is active in a broad spectrum of tumours. Clinical trials using this drug in bladder cancer are underway, but not yet reported. There are currently no in vitro data regarding oxaliplatin in bladder cancer. Therefore, this study compares the efficacy of oxaliplatin with cisplatin and carboplatin, which are both used widely in this tumour type, in bladder cancer cell lines.

METHOD

The efficacy of oxaliplatin, carboplatin and cisplatin were compared in 4 bladder cancer cell lines (5637, J82, HT1197 and 253J). Cell parameters including cell number, viability and apoptosis were assessed after 3 days of drug exposure. The effects of the drugs on the cell cycle were also observed.

RESULTS

Overall cisplatin was the most potent at inducing cell death (IC(50) 11.5-70.6 microM). Oxaliplatin was the 2nd most potent drug (IC(50 )15.2-126.3 microM) and carboplatin the least effective (IC(50 )75.4-137.8 microM). Carboplatin was significantly less potent at inducing cell death than the other two drugs in all 4 cell lines. Carboplatin was also inferior at inducing apoptosis in 3 of the 4 cell lines. All three drugs had a similar effect on the cell cycle, causing an initial G2 block.

CONCLUSIONS

These data suggest that oxaliplatin is a potent agent in bladder cancer cell lines and is superior to carboplatin in this in vitro setting. It justifies the clinical studies using oxaliplatin that are underway.

Effect of cytarabine and decitabine in combination in human leukemic cell lines

PURPOSE

1-beta-D-Arabinofuranosylcytosine (cytarabine; ara-C) is the most active agent in myeloid leukemia. 5-Aza-2'-deoxycytidine (DAC) is a cytosine analogue that inhibits DNA methylation and also has activity in myeloid leukemia. Therefore, we investigated combining these two drugs in human leukemia cell lines in vitro.

EXPERIMENTAL DESIGN

We initially examined the effects of ara-C and DAC on human leukemia cell lines HL60, ML-1, RAji, and Jurkat. We measured IC(50) of DAC and ara-C in these cell lines and calculated a combination index of these two drugs given either simultaneously or sequentially. In searching for mechanisms relative to epigenetic regulation for this effect, we examined DNA methylation of LINE and Alu repetitive elements as a surrogate for global genomic DNA methylation. In addition, we sorted Annexin V positive and negative cells and measured differences in LINE methylation between them.

RESULTS

The combination of DAC and ara-C showed additive induction of cell death in ML-1 and synergistic induction in HL60, Raji, and Jurkat. Sequentially, DAC followed by ara-C was a synergistic combination in all cell lines. Low-dose DAC induced more hypomethylation than high doses of the drug, whereas ara-C had no effects on methylation. The combination of ara-C with DAC either together or DAC followed by ara-C resulted in inhibition of LINE demethylation in HL60. The RIL gene, which is silenced by DNA hypermethylation, was activated by DAC, but the addition of ara-C to DAC reduced RIL gene activation. DAC treatment increased H3 Lys(9) acetylation of Alu elements, whereas ara-C had no effect, and the addition of ara-C to DAC inhibited this effect. Finally, we showed that after DAC exposure, Annexin V positive cells were more hypomethylated than Annexin V negative cells.

CONCLUSION

The combination of DAC and ara-C showed additive or synergistic effects on cell death in four human leukemia cell lines in vitro, but antagonism in terms of epigenetic effects. One possible explanation for these paradoxical observations is that hypomethylated cells are sensitized to cell killing by ara-C. These data suggest that DAC used in combination with ara-C has clinical potential in the treatment of acute myeloid leukemia.

Comparison between molecularly defined and conventional therapeutics in a conditional BCR-ABL cell culture model

Accumulating knowledge about the molecular mechanisms causing human diseases can support the development of targeted therapies such as imatinib, a BCR-ABL-specific tyrosine kinase inhibitor to treat chronic myeloid leukemia (CML). Here, we use lentivirus-mediated RNA interference (RNAi) targeting BCR-ABL and the downstream signaling molecules SHP2, STAT5, and Gab2 to compare the efficacy and specificity of molecularly defined therapeutics with that of conventional cytotoxic drugs (cytarabine, doxorubicin, etoposide) in a conditional BCR-ABL cell culture model. IC(50) values were determined for each drug in TonB cells cultured either with interleukin-3 (IL-3) or BCR-ABL, and molecularly defined therapies were studied using lentivirally expressed shRNAs. We demonstrate that conventional anti-leukemic drugs have small or no differential effects under different cell culture conditions, whereas both imatinib and specific RNAi significantly inhibit proliferation of TonB cells in the presence of BCR-ABL but not IL-3. To study molecularly defined combination therapy, we evaluated either imatinib in TonB cells with target-specific RNAi or we used lentiviral vectors to induce combinatorial RNAi through simultaneous expression of two shRNAs. These combination therapies result in increased efficacy without loss in specificity. Interestingly, combinatorial RNAi can specifically deplete TonB cell cultures in the presence of BCR-ABL, even without targeting the oncogene itself. This model provides a tool to evaluate potential therapeutic targets and to quantify efficacy and specificity preclinically of new combination therapies in BCR-ABL-positive cells.

Camptothecin acts synergistically with imatinib and overcomes imatinib resistance through Bcr-Abl independence in human K562 cells

In this study, we have tried to find new targets and effective drugs for imatinib-resistant chronic myelogenous leukemia (CML) cells displaying loss of Bcr-Abl kinase target dependence. The imatinib-resistant K562/R1, -R2 and -R3 cells showed profound declines of Bcr-Abl level and concurrently exhibited up-regulation of Bcl-2 and Ku70/80, and down-regulation of Bax, DNA-PKcs and BRCA1, suggesting that loss of Bcr-Abl after exposure to imatinib might be accompanied by other cell survival mechanism. K562/R3 cells were more sensitive to camptothecin (CPT)- and radiation-induced apoptosis than K562 cells, indicating hypersensitivity of imatinib-resistant cells to DNA damaging agents. Moreover, when K562 cells were treated with the combination of imatinib with CPT, the level of Bax and the cleavage of PARP-1 and DNA-PK were significantly increased in comparison with the effects of each drug. Therefore, our study suggests that CPT can be used to treat CML with loss of Bcr-Abl expression.

Betulinic acid induces apoptosis in human chronic myelogenous leukemia (CML) cell line K-562 without altering the levels of Bcr-Abl

Betulinic acid (BA), a plant derived triterpenoid, isolated from various sources shows cytotoxicity in cell lines of melanoma, neuroectodermal and malignant brain tumors. Chronic myelogenous leukemia (CML) is characterized by Philadelphia chromosome (Bcr-Abl), a molecular abnormality leading to the intrinsic tyrosine kinase activity that provides growth and survival advantage to the cells. Present study describes the cytotoxicity of BA on human CML cell line K-562, positive for Bcr-Abl. The decrease in the viability of K-562 cells treated with BA at different concentrations and time intervals was assessed using MTT assay. Cell death induced by BA was determined to be apoptotic as measured by FACS analysis of PI stained nuclei, PS externalization by Annexin-V fluorescence and characteristic DNA fragmentation. DiOC6(3) fluorescent probe determined alterations in the mitochondrial membrane potential (MMP). RT-PCR confirmed the expression levels of Bcr-Abl in controls and K-562 cells treated with BA. The rapid loss of MMP of K-562 cells upon treatment with BA shows the direct activation of apoptosis at the level of mitochondria, overcoming the resistance of the high levels of expression of Bcr-Abl.

Cannabis-induced cytotoxicity in leukemic cell lines: the role of the cannabinoid receptors and the MAPK pathway

Δ9-Tetrahydrocannabinol (THC) is the active metabolite of cannabis. THC causes cell death in vitro through the activation of complex signal transduction pathways. However, the role that the cannabinoid 1 and 2 receptors (CB1-R and CB2-R) play in this process is less clear. We therefore investigated the role of the CB-Rs in mediating apoptosis in 3 leukemic cell lines and performed microarray and immunoblot analyses to establish further the mechanism of cell death. We developed a novel flow cytometric technique of measuring the expression of functional receptors and used combinations of selective CB1-R and CB2-R antagonists and agonists to determine their individual roles in this process. We have shown that THC is a potent inducer of apoptosis, even at 1 × IC50 (inhibitory concentration 50%) concentrations and as early as 6 hours after exposure to the drug. These effects were seen in leukemic cell lines (CEM, HEL-92, and HL60) as well as in peripheral blood mononuclear cells. Additionally, THC did not appear to act synergistically with cytotoxic agents such as cisplatin. One of the most intriguing findings was that THC-induced cell death was preceded by significant changes in the expression of genes involved in the mitogen-activated protein kinase (MAPK) signal transduction pathways. Both apoptosis and gene expression changes were altered independent of p53 and the CB-Rs.

The in vitro effects of CRE-decoy oligonucleotides in combination with conventional chemotherapy in colorectal cancer cell lines

The cAMP response element consensus sequence directs the transcription of a wide range of genes. A 24-mer single-stranded cAMP response element decoy oligonucleotide (CDO) has been shown to compete with these sequences for binding transcription factors and therefore interferes with cAMP-induced gene transcription. We have examined the effect of this CDO alone and in combination with a range of common chemotherapeutic agents in colorectal cancer cell lines. CDO had a potent anti-proliferative effect in colorectal cell lines, yet, a similar enhancement of cell death was not observed. Simple drug-drug interaction studies showed that combining CDO with chemotherapy resulted in an enhancement of the antiproliferative effects. Furthermore, this cytostatic effect was protracted and associated with an increase in senescence-associated beta-galactosidase activity at pH 6. There is a possible role for p21(waf1) in mediating this effect, as the enhancement of cell growth inhibition was not observed in cells lacking the ability to correctly upregulate this protein. Additionally, significant decreases in cyclin-dependent kinase (CDK) 1 and CDK 4 function were seen in the responsive cells. These data provide a possible model of drug interaction in colorectal cell lines, which involves the complex interplay of the molecules regulating the cell cycle. Clinically, the cytostatic ability of CDO could improve and enhance the antiproliferative effects of conventional cytotoxic agents.

Accelerated and blastic phases of chronic myelogenous leukemia

Chronic myelogenous leukemia (CML) may have a biphasic or triphasic course, whereby patients who were initially diagnosed in the chronic phase (CP) develop more aggressive disease, frequently pass through an intermediate or accelerated phase (AP), and finally evolve into an acute leukemia like blastic phase (BP). A slowing in the rate of development of AP or BP has accompanied successive improvements in therapy for patients who have CP CML. Variable diagnostic criteria for AP and BP are used in the literature, rendering comparisons difficult. The management of patients in AP or BP consistently has been less effective than the management of those inCP for all modalities of therapy. This article reviews the current diagnostic criteria, therapeutic strategies, outcomes, and investigational therapies for AP and BP CML.

Effect of haemopoietic growth factors on cancer cell lines and their role in chemosensitivity

The recombinant growth factors (GFs) erythropoietin (Epo) and granulocyte-macrophage colony stimulating factor (GM-CSF) have important roles in the management of cancer patients. However, the effects of these GFs at a cellular level are not well understood. We examined the effect of GFs alone, and in combination with cytotoxic chemotherapy, in a panel of seven cell lines. Flow cytometric analysis showed varying levels of receptor expression, which correlated with phosphorylated MAPK expression. Additionally, there were also concomitant increases in BCL-2 protein levels in those cells with high levels of MAPK activation. Although culturing cells with Epo or GM-CSF did not alter cell viability by themselves, GF pretreatment in cell lines expressing higher receptor levels resulted in a reduced magnitude of cell kill following exposure to cytotoxic IC50 concentrations of cisplatin. Subsequent co-culture with either the MEK inhibitor U0126 or the GM-CSF antagonist E21R negated this induced resistance to cytotoxic chemotherapy, confirming the importance of the GF receptor as well as MAPK in mediating these effects. These results suggest that the use of GFs during chemotherapy may be detrimental in those cancers expressing higher levels of the specific receptor. Conversely, our results also suggest that GFs are safe to use in chemotherapeutic regimens if the cancer cells do not overexpress the particular receptor.

DNA damage and repair in BCR/ABL-expressing cells after combined action of idarubicin, STI571 and amifostine

STI571 is a specific ABL family tyrosine kinases inhibitor approved for treatment of leukemias. It can differentially modulate the action of other antileukemic drugs. We have recently shown that deregulation of the mechanisms of DNA damage and repair in BCR/ABL-positive cells may be involved in drug resistance of these cells, and thus determine the response of cancer cells to therapy. In the present work we investigated DNA damage and repair induced by idarubicin in the presence of STI571 and amifostine, a normal cell protector, in the BCR/ABL fusion tyrosine kinase-expressing cell line. Amifostine increased the viability of both kinds of cells in the absence of STI571, but had no effect in the presence of the inhibitor. STI571 did not change the response of both BCR/ABL-expressing cells and their control counterparts to idarubicin in terms of DNA damage and repair. However, the presence of amifostine modulated the response of the cells. In the absence of STI571 amifostine decreased the DNA-damaging effect of idarubicin in normal cells and increased it in BCR/ABL-positive cells. STI571 at 2 M abolished the protective effect of amifostine against idarubicin in normal cells and diminished the magnitude of the amifostine-induce increase in cancer cells. These results suggest that amifostine should be applied with special caution in idarubicin-based chemotherapies of BCR/ABL-positive leukemias involving STI571 inhibitor.