Methionine redox regulation of actin-interacting proteins primarily governs antioxidative signaling and response to the salvianolic acid B treatment in EA.hy926 cells.

Actin-interacting proteins are important molecules for filament assembly and cytoskeletal signaling within vascular endothelium. Disruption in their interactions causes endothelial pathogenesis through redox imbalance. Actin filament redox regulation remains largely unexplored, in the context of pharmacological treatment. This work focused on the peptidyl methionine (M) redox regulation of actin-interacting proteins, aiming at elucidating its role on governing antioxidative signaling and response. Endothelial EA.hy926 cells were subjected to treatment with salvianolic acid B (Sal B) and tert-butyl-hydroperoxide (tBHP) stimulation. Mass spectrometry was employed to characterize redox status of proteins, including actin, myosin-9, kelch-like erythroid-derived cap-n-collar homology-associated protein 1 (Keap1), plastin-3, prelamin-A/C and vimentin. The protein redox landscape revealed distinct stoichiometric ratios or reaction site transitions mediated by M sulfoxide reductase and reactive oxygen species. In comparison with effects of tBHP stimulation, Sal B treatment prevented oxidation at actin M325, myosin-9 M1489/1565, Keap1 M120, plastin-3 M592, prelamin-A/C M187/371/540 and vimentin M344. For Keap1, reaction site was transitioned within its scaffolding region to the actin ring. These protein M oxidation regulations contributed to the Sal B cytoprotective effects on actin filament. Additionally, regarding the Keap1 homo-dimerization region, Sal B preventive roles against M120 oxidation acted as a primary signal driver to activate nuclear factor erythroid 2-related factor 2 (Nrf2). Transcriptional splicing of non-POU domain-containing octamer-binding protein was validated during the Sal B-mediated overexpression of NAD(P)H dehydrogenase [quinone] 1. This molecular redox regulation of actin-interacting proteins provided valuable insights into the phenolic structures of Sal B analogs, showing potential antioxidative effects on vascular endothelium.

Bidirectional crosstalk of the cAMP/ROS-dependent signaling pathways in inflammatory macrophage: An activation of formononetin.

Bacterial lipopolysaccharide (LPS) is a toxic stimulant to macrophage inflammation. Inflammation intersects cell metabolism and often directs host immunopathogenesis stress. We aim here at pharmacological discovering of formononetin (FMN) action, to which anti-inflammatory signaling spans across immune membrane receptors and second messenger metabolites. In ANA-1 macrophage stimulated by LPS, and simultaneous treatment with FMN, results show the Toll-like receptor 4 (TLR4) and estrogen receptor (ER) signals, in concert with reactive oxygen species (ROS) and cyclic adenosine monophosphate (cAMP), respectively. LPS stimulates inactivation of the ROS-dependent nuclear factor erythroid 2-related factor 2 (Nrf2) by upregulating TLR4, but it does not affect cAMP. However, FMN treatment not only activates Nrf2 signaling by TLR4 inhibition, but also it activates cAMP-dependent protein kinase activities by upregulating ER. The cAMP activity gives rise to phosphorylation (p-) of protein kinase A, liver kinase B1 and 5'-AMP activated protein kinase (AMPK). Moreover, bidirectional signal crosstalk is amplified between p-AMPK and ROS, as FMN combinational validation with AMPK activator/inhibitor/target small-interfering RNA or ROS scavenger. The signal crosstalk is well positioned serving as the 'plug-in' knot for rather long signaling axis, and the immune-to-metabolic circuit via ER/TLR4 signal transduction. Collectively, convergence of the FMN-activated signals drives significant reduction of cyclooxygenase-2, interleukin-6 and NLR family pyrin domain-containing protein 3, in LPS-stimulated cell. Although anti-inflammatory signaling is specifically related to the immune-type macrophage, the p-AMPK antagonizing effect arises from FMN combination with ROS scavenger H-bond donors. Information of our work assists in predictive traits against macrophage inflammatory challenges, using phytoestrogen discoveries.

Bleeding the Excited State Energy to the Utmost: Single-Molecule Iridium Complexes for In Vivo Dual Photodynamic and Photothermal Therapy by an Infrared Low-Power Laser.

A series of cyclometalated Ir(III) complexes with morpholine and piperazine groups are designed as dual photosensitizers and photothermal agents for more efficient antitumor phototherapy via infrared low-power laser. Their ground and excited state properties, as well as the structural effect on their photophysical and biological properties, are investigated by spectroscopic, electrochemical, and quantum chemical theoretical calculations. They target mitochondria in human melanoma tumor cells and trigger apoptosis related to mitochondrial dysfunction upon irradiation. The Ir(III) complexes, particularly Ir6, demonstrate high phototherapy indexes to melanoma tumor cells and a manifest photothermal effect. Ir6, with minimal hepato-/nephrotoxicity in vitro, significantly inhibits the growth of melanoma tumors in vivo under 808 nm laser irradiation by dual photodynamic therapy and photothermal therapy and can be efficiently eliminated from the body. These results may contribute to the development of highly efficient phototherapeutic drugs for large, deeply buried solid tumors.

More-Is-Better Strategy for Constructing Homoligand Polypyridyl Ruthenium Complexes as Photosensitizers for Infrared Two-Photon Photodynamic Therapy.

Photodynamic therapy (PDT) uses a combination of photosensitizers (PSs), light sources, and reactive oxygen species (ROS) to damage only the desired target and keep normal tissues from being hurt. The dark cytotoxicity (chemotoxicity) of PSs, leading to whole-body damage in the absence of irradiation, is a major limiting factor in PDT. How to simultaneously increase ROS generation and decrease dark cytotoxicity is an essential challenge that must be resolved in PS research. In this study, a series of homoligand polypyridyl ruthenium complexes (HPRCs) containing three singlet oxygen (1O2)-generating ligands (L) in a single molecule ([Ru(L)3]2+) have been constructed. Compared to the heteroligand complexes [Ru(bpy)2(L)]2+ where bpy is 2,2'-bipyridine, the 1O2 quantum yield under infrared two-photon irradiation and the DNA photocleavage effect of the HPRCs are significantly enhanced with two more ligands L. The intraligand triplet excited states transition played an important role in the activation of oxygen. The HPRCs target the mitochondria but not the nuclei, generating 1O2 intracellularly under irradiation of visible or infrared light. Ru1 exhibits high phototoxicity and low dark cytotoxicity toward human malignant melanoma cells in vitro. Moreover, HPRCs have minimal cytotoxicity to human normal liver cells, suggesting their potential as antitumor PDT reagents with more security. This study may provide inspiration for the structural design of potent PS for PDT.

Dinuclear osmium complexes as mitochondrion-targeting antitumor photothermal agents in vivo.

Four dinuclear osmium complexes have been constructed for antitumor phototherapy. The most potent Os4 has extremely high photothermal conversion capability under irradiation of an 808 nm low-power laser, targets mitochondria in human melanoma cells without nucleus affinity, and acts as an antitumor photothermal therapy agent in vitro and in vivo.

Efficacy and safety of raltitrexed plus S-1 versus regorafenib in patients with refractory metastatic colorectal cancer: a real-world propensity score matching study.

Background: Raltitrexed plus S-1 (RS) and regorafenib both showed considerable efficacy for metastatic colorectal cancer (mCRC) patients. This study aims to compare the effectiveness and safety of two different regimens in patients with refractory mCRC. Methods: This retrospective cohort study included mCRC patients who were treated with RS or regorafenib from February 2017 to June 2021. A propensity score matching (PSM) analysis was conducted to balance the baseline characteristics of all patients. Progression-free survival (PFS), overall survival (OS), tumor response, and safety of two regimens were evaluated. Results: A total of 187 patients were included in our study, with 107 patients in the RS group and 80 patients in the regorafenib group. After PSM, 78 pairs were recognized. Patients treated with RS had a semblable PFS compared to those treated with regorafenib before PSM (4.8 months vs 5.5 months, p = 0.400) and after PSM (4.7 months vs 5.4 months, p = 0.430). Patients in the RS group were associated with a longer OS than those in the regorafenib group (13.4 months vs 10.1 months, p = 0.010). A similar trend of OS was also obtained in the matched cohort (13.3 months vs 10.0 months, p = 0.024). Both objective response rate (12.8% vs 5.1%, p = 0.093) and disease control rate (53.8% vs 46.2%, p = 0.337) in the RS cohort were higher than those in the regorafenib group, without significant differences. Adverse events (AEs) of each group were well tolerated. Conclusion: Patients treated with RS demonstrated a longer OS than those treated with regorafenib and had manageable AEs, which could be recognized as a primary choice for refractory mCRC. Plain Language Summary: Efficacy and Safety of Raltitrexed plus S-1 Versus Regorafenib in Patients with Refractory Metastatic Colorectal Cancer: A Real-world Propensity Score Matching StudyBoth raltitrexed plus S-1 (RS) and regorafenib showed considerable efficacy for metastatic colorectal cancer (mCRC) patients. No study has compared the two regimens yet. Therefore, we compare the efficacy and safety between RS and regorafenib to provide an optimal treatment option. We retrospectively included patients with mCRC who failed at least two standard treatments. All enrolled patients received RS or regorafenib treatments. We conducted a propensity score matching to eliminate differences in the enrolled patients. After the analysis, we found no significant differences in progression-free survival in patients between the two groups. However, patients treated with RS had a longer OS than those treated with regorafenib, whether before matching (13.4 months vs 10.1 months, p = 0.010) or after matching (13.3 months vs 10.0 months, p = 0.024). In addition, the adverse effects caused by cancer-related therapy were tolerable for the patient. Certainly, this is a non-randomized retrospective study with a small sample size, so we conducted a propensity score matching to minimize potential bias. Importantly, this is the first research comparing the two treatments, and we believe that the results of this article could present a primary choice for clinical doctors dealing with patients with standard treatments that failed mCRC.

Clinicopathologic features, treatment, survival, and prognostic factors of combined hepatocellular and cholangiocarcinoma: A nomogram development based on SEER database and validation in multicenter study.

PURPOSE: The aim of the study was to comprehensively understand the combined hepatocellular and cholangiocarcinoma (CHC) and develop a nomogram for prognostic prediction of CHC. METHODS: Data were collected from the Surveillance, Epidemiology and End Results (SEER) database (year 2004-2014). Propensity-score matching (PSM) was used to match the demographic characteristic of the CHC versus hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC). A nomogram model was established to predict the prognosis in terms of cancer specific survival (CSS). The established nomogram was externally validated by a multicenter cohort. RESULTS: A total of 71,756 patients enrolled in our study including 62,877 HCC patients, 566 CHC patients, and 8303 ICC patients. The CHC, HCC, and ICC are not exactly similar in clinical characteristic. After PSM, the CSS of CHC was better than HCC but comparable to ICC. Tumor size, M stage, surgery, chemotherapy, and surgery were independently prognostic factors of CHC and were included in the establishment of novel nomogram. The c-index of the novel nomogram in SEER training set and multicenter validation was 0.779 and 0.780, respectively, which indicated that the model was with better discrimination power. In addition, decision curve analyses proved the favorable potential clinical effect of the predictive model. Lastly, a risk classification based on nomogram also verified the reliability of the model. CONCLUSION: CHC had better survival than HCC but was comparable to ICC. The nomogram was established based on tumor size, M stage, chemotherapy, surgery, and radiotherapy and well validated by external multicenter cohort.

Ultra-high hydrogen storage capacity of holey graphyne.

Holey graphyne (HGY), a novel two-dementional 2D single-crystalline carbon allotrope, was recently synthesized by Castro-Stephens coupling reaction. The naturally existing uniform periodic holes in the 2D carbon-carbon network demonstrate its promising potential in the energy storage. Herein, we conducted density functional theory (DFT) calculation to predict the hydrogen storage capacity of HGY sheet. It is found the Li-decorated single-layer HGY can serve as a promising candidate for hydrogen storage. Our DFT calculations demonstrate that Li atoms can bind strongly to the HGY sheet without the formation of Li clusters, and each Li atom can anchor four H2 molecules with the average adsorption energy about 0.22 eV/H2. The largest hydrogen storage capacity of the doped HGY sheet can reach as high as 12.8 wt%, largely surpassing the target of the U. S. DOE (9 wt%), showing the Li/HGY complex is an ideal hydrogen storage material at ambient conditions. In addition, we investigate the polarization mechanism of the storage media and find that the polarization is originated from both the electric field induced by the ionic Li decorated on the HGY and the weak polarized hydrogen molecules dominated the H2 adsorption process.

Arginine deprivation inhibits pancreatic cancer cell migration, invasion and EMT via the down regulation of Snail, Slug, Twist, and MMP1/9.

Arginine deprivation is currently being evaluated for its efficacy and safety in clinical trials aimed at combating tumors. However, the cellular signaling and molecular changes in response to such deprivation have not been systematically deciphered. Here, we evaluate the effect of arginine deprivation on human pancreatic cancer cells, with respect to their migratory and invasive potentials and their ability to undergo epithelial-mesenchymal transition (EMT). The transcription factors Snail, Slug, and Twist are regulators of EMT, as indicated by the suppression of E-cadherin and other epithelial markers and adhesion molecules. Our data indicated that arginine starvation inhibited the migration and impaired the adhesion and invasion of the pancreatic cancer cells, decreased Snail, Slug, and Twist expression, and increased E-cadherin expression without altering the expression of vimentin. It is well known that matrix metalloproteinases (MMPs) are important for the events that underlie tumor dissemination. Arginine starvation inhibited the expression of MMP-1 and MMP-9. Furthermore, the PI3K/Akt pathway was altered when the pancreatic cancer cells underwent arginine deprivation as exhibited by the decreased Akt phosphorylation. Thus, these data reveal that arginine deprivation has the potential to decrease the metastatic ability of pancreatic cancer cells.

Identification of novel 1-indolyl acetate-5-nitroimidazole derivatives of combretastatin A-4 as potential tubulin polymerization inhibitors.

Microtubules are essential for the mitotic division of cells and have become an attractive target for anti-tumour drugs due to the increased incidence of cancer and significant mitosis rate of tumour cells. In this study, a total of six indole 1-position modified 1-indolyl acetate-5-nitroimidazole derivatives were designed, synthesized, and evaluated for their ability to inhibit tubulin polymerization caused by binding to the colchicine-binding site of tubulin. Among them, compound 3 displayed the best ability to inhibit tubulin polymerization; it also exhibited better anti-proliferative activities than colchicine against a panel of human cancer cells (with IC50 values ranging from 15 to 40nM), especially HeLa cells (with IC50 values of 15nM), based on the cellular cytotoxicity assay results. Moreover, cellular mechanism studies indicated that compound 3 could induce G2/M phase arrest and apoptosis of HeLa and MCF-7 cells, which were associated with alterations in the expression of cell cycle-checkpoint related proteins (Cyclin B1, Cdc2, and P21) and a reduction in the mitochondrial membrane potential as well as alterations in the levels of apoptosis-related proteins (PARP, Caspase 9, Bcl-2, and Bax) of these cells, respectively. Importantly, in vivo studies further revealed that compound 3 could dramatically suppress HeLa cell xenograft tumour growth compared with vehicle and CA-4 phosphate (CA-4P), and no signs of toxicity were observed in these mice. Collectively, these in vitro and in vivo results indicated that compound 3 might be a promising lead compound for further development as a potential anti-cancer drug.

Preparation of Optically Active cis-Cyclopropane Carboxylates: Cyclopropanation of α-Silyl Stryenes with Aryldiazoacetates and Desilylation of the Resulting Silyl Cyclopropanes.

Optically active cis-cyclopropane carboxylates are prepared via the Rh2(S-PTAD)4-catalyzed cyclopropanation of α-silyl styrenes with aryl diazoacetates followed by desilylation of the resulting silyl cyclopropane carboxylates. The conjugation of the aryl ring with C═C bond and π stacking are proposed for the stereoselectivity of cyclopropanation, and configuration inversion is observed with the desilylation process.

G protein pathway suppressor 2 (GPS2) acts as a tumor suppressor in liposarcoma.

Liposarcoma(LPS) is the most common type of soft tissue sarcoma accounting for 20 % of all adult sarcomas. However, the molecular pathogenesis of this malignancy is still poorly understood. Here, we showed that GPS2 expression was downregulated in LPS and correlated with the prognosis of this disease. In vitro study showed that knockdown of GPS2 resulted in enhanced proliferation and migration of LPS cell line SW872, without significant influence of cell death. Conclusively, our results suggest that GPS2 may act as a tumor suppressor in LPS and serve as a potential prognosis marker for this disease.

Changes in spatial patterns of Caragana stenophylla along a climatic drought gradient on the Inner Mongolian Plateau.

Few studies have investigated the influence of water availability on plant population spatial patterns. We studied changes in the spatial patterns of Caragana stenophylla along a climatic drought gradient within the Inner Mongolian Plateau, China. We examined spatial patterns, seed density, "nurse effects" of shrubs on seedlings, transpiration rates and water use efficiency (WUE) of C. stenophylla across semi-arid, arid, and intensively arid zones. Our results showed that patches of C. stenophylla populations shifted from a random to a clumped spatial pattern towards drier environments. Seed density and seedling survival rate of C. stenophylla decreased from the semi-arid zone to the intensively arid zone. Across the three zones, there were more C. stenophylla seeds and seedlings underneath shrub canopies than outside shrub canopies; and in the intensively arid zone, there were almost no seeds or seedlings outside shrub canopies. Transpiration rates of outer-canopy leaves and WUE of both outer-canopy and inner-canopy leaves increased from the semi-arid zone to the intensively arid zone. In the intensively arid zone, transpiration rates and WUE of inner-canopy leaves were significantly lower and higher, respectively, than those of outer-canopy leaves. We conclude that, as drought stress increased, seed density decreased, seed proportions inside shrubs increased, and "nurse effects" of shrubs on seedlings became more important. These factors, combined with water-saving characteristics associated with clumped spatial patterns, are likely driving the changes in C. stenophylla spatial patterns.

[Effect of microRNA-17-92 cluster on the biological characteristics of K562 cells and its mechanisms].

The objective of this study was to explore the effects of microRNA-17-92 on the biological characteristics of K562 cells. The expression of miR-17-92 in K562 cells transfected with miRNA-17-92 mimic was detected by real time PCR. The effect of microRNA-17-92 on K562 cell proliferation was detected by CCK-8 method. Apoptosis of K562 cells was detected by Annexin V-PI labeling. Cell cycle distribution was determined by using flow cytometry. Western blot was performed to determine the protein levels of Crk. The results indicated that the transfection with miR-17-92 mimic increased expression of mature miR-17-92 in K562 cells. Compared with control group, cell proliferation and cell amount in S-phase of miR-17-92 mimic transfected group significantly increased, cell apoptosis decreased. The expression of signal connector protein Crk was greatly up-regulated in miR-17-92-mimic-transfected K562 cells. It is concluded that miR-17-92 can promote proliferation, inhibit apoptosis and regulate the cell cycle of K562 cells.

Electronic structure and optical properties of Cu-doping and Zn vacancy impurities in ZnTe.

The geometric structures of perfect ZnTe, that with Zn vacancy (Zn0.875Te), and Cu-doped ZnTe (Zn0.875Cu0.125Te) were optimized using the pseudopotential plane wave (PP-PW) method based on the density functional theory (DFT) within generalized gradient approximation (GGA). The cohesive energy, band structure, density of states, and Mulliken populations were calculated and discussed in detail. On the other hand, an accurate calculation of linear optical functions (the dielectric function, refraction index, reflectivity, conductivity function, and energy-loss spectrum) was performed. The results demonstrated that compared to the perfect ZnTe, the lattice parameters of Zn0.875Te and Zn0.875Cu0.125Te were changed and the cell volumes decreased to some extent due to the vacancy and introduction of impurity. A vacancy acceptor level and an acceptor impurity level were produced in Zn0.875Te and Zn0.875Cu0.125Te, respectively. By comparison, Cu doping in the ZnTe system is relatively stable while the monovacancy system is not.

Novel metal(II) coordination polymers based on N,N'-bis-(4-pyridyl)phthalamide as supercapacitor electrode materials in an aqueous electrolyte.

Based on the redox-active L (N,N'-bis-(4-pyridyl)phthalamide) ligand, two porous MOFs formulated as Zn(6)(BPC)(6)(L)(3)·9DMF (H(2)BPC = 4,4'-biphenyldicarboxylic acid) (1) and Cd(2)(TDC)(2)(L)(2)·4H(2)O (H(2)TDC = 2,5-thiophenedicarboxylic acid) (2) were synthesized and structurally characterized by single-crystal X-ray diffractions. Complex 1 features a uninodal 5-connected 3-fold interpenetrated 3D framework with {4(6).6(4)}-bnn hexagonal BN topology. Complex 2 displays a uninodal 6-connected 2-fold interpenetrated 3D framework with {4(12).6(3)}-pcu topology. When complexes 1 and 2 are used as supercapacitor electrode materials, they can provide a large voltage window as high as 2.6 V in an aqueous electrolyte, and their specific capacitances are much more than the value for the bare carbon glassy electrode. It is observed that the more the current density, the less the specific capacitance for the two kinds of supercapacitor electrode materials. The two complexes show different thermal stabilities, UV absorption and photoluminescence properties.

Methyl-ß-cyclodextrin induces programmed cell death in chronic myeloid leukemia cells and, combined with imatinib, produces a synergistic downregulation of ERK/SPK1 signaling.

Lipid rafts mediate several survival signals in the development of chronic myeloid leukemia (CML). Methyl-ß-cyclodextrin (MßCD) is an inhibitor specifically designed to disrupt lipid rafts in cells by depleting the cholesterol component. We hypothesize that treatment of CML cells with MßCD and imatinib could reduce imatinib resistance. Apoptotic and autophagic cell death was assayed using annexin V-propidium iodide double staining, immunoblotting, and immunocytochemistry. We next investigated whether MßCD could enhance the cytotoxicity of imatinib in imatinib-sensitive and imatinib-resistant K562 cells. Extracellular signal-regulated kinase/sphingosine kinase 1 signaling downstream of lipid raft-activated signaling pathways was significantly inhibited by treatment of cells with a combination of MßCD and imatinib compared with treatment with either agent alone. MßCD induces programmed cell death in CML cells, and its antileukemia action is synergistic with that of imatinib.

Overexpression of microRNA-29b induces apoptosis of multiple myeloma cells through down regulating Mcl-1.

MicroRNAs (miRNAs) are small, noncoding ribonucleic acids (ncRNAs), which regulate gene expression by targeting mRNAs for translational repression and degradation. Several lines of evidences have indicated that miRNAs act as tumor suppressors and oncogenes. However, the role of miRNAs in pathogenesis of multiple myeloma (MM) remains unclear. In this study, we examined the profile of miRNA expression of primary MM cells, using miRNA microarray and quantitative real-time polymerase chain reaction (qPCR) techniques. These results showed that in the bone marrow specimens analyzed, miRNA-29b was significantly downregulated. Similar results were also observed in human myeloma cell lines (HMCLs). Adenovirus-mediated overexpression of miR-29b induced apoptosis and elevated caspase-3 activation in HMCLs. Using a bioinformatics approach, we found a perfect complementarity between miRNA-29b and the 3'UTR of myeloid-cell-leukemia 1(Mcl-1). It is further confirmed that miRNA-29b downregulated the level of Mcl-1 without effect on the mRNA level using both qRT-PCR assays and Western blot analyses. Moreover, we observed that enforced miR-29b expression by using a retarget miRNA-29b expression vector (Ad5F11p-miR-29b) could induce apoptosis and elevate caspase-3 activation in HMCLs. Our results also indicated that miRNA-29b-induced apoptosis acted antagonistically with IL-6 in HMCLs. These findings suggest that miRNA-29b may play an important role in MM as a tumor suppressor.

Regulation of human hepatocellular carcinoma cells by Spred2 and correlative studies on its mechanism.

Members of the Spred gene family are negative regulators of the Ras/Raf-1/ERK pathway, which has been associated with several features of the tumor malignancy. However, the effect of Spred genes on hepatocellular carcinoma (HCC) remains uninvestigated. In the present work, we analyzed the in vitro and in vivo effects of Spred2 expression on the hepatic carcinoma cell line, SMMC-7721. In addition to attenuated ERK activation, which inhibited the proliferation and migration of unstimulated and HGF-stimulated SMMC-7721 cells. Adenovirus-mediated Spred2 overexpression induced the activation of caspase-3 and apoptosis, as well as reduced the expression level of Mcl-1. Most importantly, the knockdown of Spred2 markedly enhanced tumor growth in vivo. In conclusion, these results suggest that Spred2 could qualify as a potential therapeutic target in HCC.

Bortezomib and sphingosine kinase inhibitor interact synergistically to induces apoptosis in BCR/ABl+ cells sensitive and resistant to STI571 through down-regulation Mcl-1.

Interactions between the proteasome inhibitor, bortezomib, and the sphingosine kinase (SPK1) inhibitor, SKI, were examined in BCR/ABL human leukemia cells. Coexposure of K562 or chronic myeloid leukemia (CML) cells from patients to subtoxic concentrations of SKI (10 µM) and bortezomib (100 nM) resulted in a synergistic increase in caspase-3 cleavage and apoptosis. These events were associated with the downregulation of BCR-ABL and Mcl-1, and a marked reduction in SPK1 expression. In imatinib mesylate-resistant K562 cells that displayed decreased BCR-ABL expression, bortezomib/SKI treatment markedly increased apoptosis and inhibited colony-formation in association with the downregulation of Mcl-1. Finally, the bortezomib/SKI regimen also potently induced the downregulation of BCR/ABL and Mcl-1 in human leukemia cells. Collectively, these findings suggest that combining SKI and bortezomib may represent a novel strategy in leukemia, including apoptosis-resistant BCR-ABL(+) hematologic malignancies.