Fractionation of an extract from American sycamore leaves produced the small molecule, kaempferol-3- O-alpha-L-(2″,3″-di- p-coumaroyl)rhamnoside (KCR), which exists in four stereoisomeric forms ( EE, EZ, ZE, and ZZ) at the olefin in the p-coumaroyl; all four isomers exhibit potent anti-MRSA activity in vitro. As part of the preclinical development of KCR, we set out to investigate the metabolites of KCR in mouse plasma as a prelude of ADME studies and therapeutic assessment. When KCR was added to mouse plasma at 37 °C, two new HPLC peaks appeared with increasing intensity as the incubation time increased; their retention times were shorter than that of KCR indicating that KCR was metabolized to produce two compounds that were more polar. HPLC results indicated that the two metabolites mainly came from the ZE and EE isomers and that the ZZ isomer was the most stable. Based on their respective HPLC retention times and UV spectra, these two metabolites were tentatively identified as p-coumaric acid and afzelin; both of which are more polar than KCR. The molecular weights of both metabolites were then confirmed by a Waters Acquity UPLC system with a QDa mass detector. UPLC chromatograms and molecular ions of metabolites 1 and 2 match well with those of reference materials, p-coumaric acid and afzelin, thus confirming the identities of the two major metabolites of KCR. In summary, KCR was metabolized in mouse plasma and two major metabolites ( p-coumaric acid and afzelin) were identified; the metabolites were mainly converted from the ZE and EE isomers.

UTL-5g is a novel small-molecule TNF-alpha modulator. It reduces cisplatin-induced side effects by protecting kidney, liver, and platelets, thereby increasing tolerance for cisplatin. UTL-5g also reduces radiation-induced acute liver toxicity. The mechanism of action for UTL-5g is not clear at the present time. A phosphoproteomic analysis to a depth of 4943 phosphopeptides and a luminescence-based transcription factor activity assay were used to provide complementary analyses of signaling events that were disrupted by UTL-5g in RAW 264.7 cells. Transcriptional activity downstream of the interferon gamma, IL-6, type 1 Interferon, TGF-β, PKC/Ca2+ and the glucocorticoid receptor pathways were disrupted by UTL-5g. Phosphoproteomic analysis indicated that hyperphosphorylation of proteins involved in actin remodeling was suppressed by UTL-5g (gene set analysis, FDR < 1%) as was phosphorylation of Stat3, consistent with the IL-6 results in the transcription factor assay. Neither analysis indicated that LPS-induced activation of the NF-kB, cAMP/PKA and JNK signaling pathways were affected by UTL-5g. This global characterization of UTL-5g activity in a macrophage cell line discovered that it disrupts selected aspects of LPS signaling including Stat3 activation and actin remodeling providing new insight on how UTL-5g acts to reduce cisplatin-induced side effects.

UTL-5g is a small-molecule TNF-α modulator that is anti-inflammatory in a carrageenan-induced edema animal model and chemoprotective against anticancer drug-induced side effects. Recently, it was shown that UTL-5g is a prodrug and its active metabolite is 5-methylisoxazole-3-carboxylic acid (Isox). We set out to investigate the anti-inflammatory and cardioprotective effects of Isox, and two of its esterified analogues, methyl ester (Isox-Me), and ethyl ester (Isox-Et). First, the carrageenan-induced edema animal model was employed to compare their anti-inflammatory effects. Briefly, Wistar rats were randomly divided into 5 groups and pretreated with vehicle, leflunomide, Isox, Isox-Me, and Isox-Et respectively before carrageenan treatment. The results showed that the anti-inflammatory effect of Isox was essentially the same as that of leflunomide. However, the anti-inflammatory effects of Isox-Me and Isox-Et were lower than that of Isox. In the second study, cardioprotective effects of Isox, Isox-Me, and Isox-Et on doxorubicin (DOX)induced toxicity were investigated. SD rats were randomly divided into five groups. Rats in groups 1 and 2 were pretreated with vehicle; rats in groups 3-5 were pretreated with Isox, Isox-Me, and Isox-Et respectively for 5 consecutive days. One hr after the last treatment, animals in group 2-5 were treated with DOX. Twenty four hr later, effects of test compounds on cardioprotection were examined. The results showed that Isox significantly reduced the cardiotoxicity, but Isox-Me and Isox-Et did not show much cardioprotective effect. A subsequent in vitro MTT study confirmed that Isox, but not Isox-Me or Isox-Et, protected cardiomyocytes from the injury induced by DOX. In summary, Isox is anti-inflammatory against carrageenan-induced edema and the anti-inflammatory effect of Isox is at least partially responsible for its chemoprotective effect against DOX-induced cardiac injury; esterification of Isox significantly reduces its anti-inflammatory effect and cardioprotective effect.

Methicillin-resistant Staphylococcus aureus (MRSA) is a serious pathogen that is resistant to current antibiotic therapy. Thus, there is an urgent need for novel antimicrobial agents that can effectively combat these new strains of drug-resistant “superbugs”. Recently, fractionation of an extract from Platanus occidentalis (American sycamore) leaves produced an active kaempferol molecule, 3- O-alpha-L-(2″,3″-di- p-coumaroyl)rhamnoside (KCR), in four isomeric forms; all four isomers exhibit potent anti-MRSA activity. In order to further the preclinical development of KCR as a new antibiotic class, we developed and validated a simple analytical method for assaying KCR plasma concentration. Because KCR will be developed as a new drug, although comprising four stereoisomers, the analytical method was devised to assay the total amount of all four isomers. In the present work, both a plasma processing procedure and an HPLC method have been developed and validated. Mouse plasma containing KCR was first treated with ethanol and then centrifuged. The supernatant was dried, suspended in ethanol, centrifuged, and the supernatant was injected into an HPLC system comprising a Waters C18, a mobile phase composing methanol, acetonitrile, and trifluoroacetic acid and monitored at 313 nm. The method was validated by parameters including a good linear correlation, a limit of quantification of 0.27 μg/mL, and high accuracy. In summary, this method allows a rapid analysis of KCR in the plasma samples for pharmacokinetics studies.

UTL-5g is a novel small-molecule chemoprotective agent against cisplatin-induced host cytotoxicity.Recent studies showed that UTL-5g increased the blood platelet count, which was reduced in cisplatintreated mice.In order to have a better understanding about the mechanism of action by which UTL-5g promotes platelet production, BDF1 mice were treated with or without UTL-5g after cisplatin treatment; several hematological analyses were conducted.The results showed that treatment of mice with UTL-5g alone by either i.p. injection or oral gavage markedly increased platelet counts.UTL-5g also restored bone marrow cell counts that were reduced by cisplatin treatment.Flow cytometric analysis showed that bone marrow CD41+ megakaryocytic cells were significantly increased in animals pretreated with UTL-5g before cisplatin.Measurement of secreted cytokines showed that pretreatment of UTL-5g lowered blood levels of both TNF- and IL-12 (p70) elevated by cisplatin treatment.On the other hand, pretreatment of UTL-5g raised blood levels of IL-5 that were lowered by cisplatin treatment.The results also showed that 60 mg/kg is the optimal dose of UTL-5g by oral route for the protection of bone marrow cells, CD41+ megakaryocytes, and platelets.In conclusion, this study suggests that UTL-5g (by i.p. injection or oral gavage) enhances the production of platelets by either protecting or increasing bone marrow CD41+ megakaryocytic cells at least in part; UTL-5g also modulates TNF-, IL-12 (p70), and IL-5.Taken together, these observed effects of UTL-5g on megakaryocytes and cytokines play important roles in the chemoprotective properties of UTL-5g.

Leflunomide is a disease-modifying antirheumatic drug (DMARD) for the treatment of rheumatoid arthritis (RA). Structurally, it is a derivative of 5-methylisoxazole-4-carboxamide. Upon metabolism, the N-O bond in the isoxazole ring is cleaved to form the active metabolite, teriflunomide, which was recently approved by the FDA for the treatment of multiple sclerosis. Both leflunomide and teriflunomide inhibit dihydroorotate dehydrogenase (DHODH) thereby inhibiingt the synthesis of pyrimidine. For both drugs, the two major concerns are potential liver toxicity and teratogenicity. It was suspected that these undesirable effects might be related to the cleavage of the N-O bond. We herein summarize the metabolites-toxicity issues related to leflunomide/teriflunomide and discuss two related molecular platforms, UTL-4 and UTL-5. UTL-4 compounds are based on the same scaffold of leflunomide; their toxicological and pharmacological effects are not significantly different from those of leflunomide/teriflunomide. In UTL-5 series, the leflunomide scaffold is changed into 5-methylisoxazole-3-carboxamide. Unlike leflunomide, the N-O bond of a UTL-5 compound, UTL-5b, is not cleaved upon metabolism; instead, the peptide bond is cleaved to form its major metabolites. UTL-5b and its metabolites do not inhibit DHODH in vitro. In addition, UTL-5b and all other UTL-5 compounds have lower acute toxicity than leflunomide/teriflunomide. Furthermore, from leflunomide to UTL-5b/UTL-5g, the potential liver toxicity becomes liver protective effect. With the reduced toxicity, UTL-5 compounds still maintain significant pharmacological effects including anti-inflammatory and antiarthritic effects. In summary, our observations provide a valuable direction in drug optimization based on the modification of the leflunomide scaffold.

UTL-5g is a small-molecule TNF- inhibitor having chemoprotective and liver radioprotective effects.We investigated the effects of UTL-5g on lung irradiated mice and whether UTL-5g affects tumor responses to radiotherapy.C57BL/6 mice were individually treated with UTL-5g at 15, 30, and 60 mg/kg and amifostine (200 mg/kg) by i.p. injection 30 min prior to lung irradiation of 6 Gy (daily x 5).Two mice in the amifostine group died within 8 wks.At the first time point (8 wks), the plasma levels of TGF-β elevated by irradiation were significantly reduced by UTL-5g at 60 mg/kg (p<0.05).For the second time point (5 months), elevated levels of TNF-α in lung tissue from the irradiated group were suppressed by UTL-5g in a dose-dependent manner and was statistically significant at 60 mg/kg (p<0.05).Amifostine also showed a similar effect but at a much higher dose, 200 mg/kg (p <0.05).Incidentally, it was observed that UTL-5g delayed the radiation-induced hair-discoloration significantly ( >60 days after lung irradiation).The results indicate that UTL-5g may protect melanocytes against radiation-induced injury.Next, the effects of UTL-5g on tumor response were investigated in CD-1 nu/nu athymic nude mice bearing intramuscular A549 tumors (human non-small cell lung carcinoma) implanted in the right gastrocnemius muscle.Animals were treated with UTL-5g (30 mg/kg i.p.) 30 min prior to or after irradiation (5 Gy) daily for five days.The results showed that UTL-5g did not protect tumor from radiation damage.These observations suggest that UTL-5g may be lung radioprotective and thus, warranted further investigation.

N-(2,4-dichlorophenyl)-5-methyl-1,2-oxazole-3-carboxamide (UTL-5g) is a small-molecule chemoprotector against cisplatin and radioprotector against radiation.To further investigate its protective effects, we evaluated whether UTL-5g protects mice in a septic shock animal model.The two metabolites of UTL-5g, 5-methylisoxazole-3-carboxylic acid (Isox) and 2,4-dichloroaniline (DCA) were also evaluated side-by-side with UTL-5g.First, mice were pretreated with UTL-5g, Isox, and DCA before the i.p. injection of lipopolysaccharide (LPS)/D-(+)-galactosamine hydrochloride (D-Gal), respectively.Oral administration of both UTL-5g and Isox increased mouse survival while DCA did not, indicating that Isox is an active metabolite of UTL-5g while DCA is not.In the second study, mice were pretreated with UTL-5g or Isox individually by i.p. injection each at 30 mg/kg before LPS/D-Gal injection.The survival rates for both UTL-5g and Isox were better than those found for oral administration.In the third study, the same molar dose of UTL-5g and Isox by i.p. injection was used respectively and the results showed that UTL-5g had a better protective effect than Isox.In the fourth study, a protocol similar to the third study was used but blood samples were collected from the orbital plexus two hr after LPS/D-gal treatment.The results showed that UTL-5g lowered blood levels of both TNF- and TGF- elevated by LPS/D-gal.In summary, pretreatment of UTL-5g protected mice treated with LPS/D-Gal and the protection was related to the lowering of TNF- and TGF- levels elevated by LPS/D-Gal.In addition, UTL-5g appeared to be both an active drug and a prodrug wherein Isox is the active metabolite.

UTL-5g is a novel small-molecule chemoprotector that lowers hepatotoxicity, nephrotoxicity, and myelotoxicity induced by cisplatin through TNF-α inhibition among other factors. As a prelude to investigating the metabolites of UTL-5g, we set out to identify the enzymatic products of UTL-5g under the treatment of both porcine liver esterase (PLE) and rabbit liver esterase (RLE). First, a number of mixtures made by UTL-5g and PLE were incubated at 25°C. At predetermined time points, individual samples were quenched by acetonitrile, vortexed, and centrifuged. The supernatants were then analyzed by reversed-phase HPLC (using a C18 column). The retention times and UV/vis spectra of individual peaks were compared to those of UTL-5g and its two postulated enzymatic products; thus the enzymatic products of UTL-5g were tentatively identified. Secondly, a different HPLC method (providing different retentions times) was used to cross-check and to confirm the identities of the two enzymatic products. Based on the observations, it was concluded that under the treatment of PLE, the major enzymatic products of UTL-5g were 5-methyliosxazole-3-carboxylic acid (ISOX) and 2,4-dichloroaniline (DCA). Treatment of UTL-5g by RLE also provided the same enzymatic products of UTL-5g from esterase. These results indicate that the peptide bond in UTL-5g was cleaved by PLE/RLE. Michaelis-Menten kinetics showed that the Km values of UTL-5g were 2.07mM with PLE and 0.37mM with RLE indicating that UTL-5g had a higher affinity with RLE. In summary, by a simple HPLC approach, we have concluded that the peptide bond in UTL-5g was cleaved by esterase from either porcine liver or rabbit liver in vitro and afforded DCA (at a mole ratio of 1:1) and ISOX. However, further studies are needed in order to determine whether UTL-5g is metabolized by microsomal enzymes to produce ISOX and DCA.

UTL-5g is a novel small-molecule chemoprotector that lowers hepatotoxicity, nephrotoxicity, and myelotoxicity induced by cisplatin through TNF-α inhibition among other factors. The objective of this study was to investigate whether UTL-5g can reduce the overall acute toxicity of cisplatin and increase cisplatin tolerability in mice.

Radiation-induced liver toxicity is a major limitation to the use of radiation in the treatment of intrahepatic cancers.The purpose of this study was to evaluate the potential radioprotective effect of a smallmolecule tumor necrosis factor alpha (TNF-) inhibitor, UTL-5g, against radiation-induced acute liver injury.Mice were pre-treated by i.p. injection with UTL-5g and control vehicle one hr prior to liver irradiation at 15 Gy.Blood and liver were collected 2 hr after irradiation and analyzed for levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities in serum and TNF- in liver tissue extracts.Both AST and ALT in serum and TNF- in liver induced by irradiation were significantly reduced by UTL-5g in a drug dose-dependent manner.The reductions of AST, ALT and TNF- appeared to correlate with the reduction of liver apoptosis detected by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay.A radiation dose escalation study (5, 15 and 25 Gy) showed that UTL-5g at 60 mg/kg was effective as a radioprotective agent at 5 and 15 Gy; the protection was only modest at 25 Gy.In summary, our results suggest that the TNF- inhibitor, UTL-5g, is potentially radioprotective against acute phase of radiation-induced liver injury.

A new series of isoxazole derivatives, N-phenyl-5-carboxamidyl isoxazoles, was investigated for their anticancer activity with solid tumor selectivity. Six N-phenyl-5-carboxamidylisoxazoles were chemically synthesized and evaluated by the in vitro disk-diffusion assay and IC50 cytotoxicity determination. The results showed that one of the derivatives, compound 3,N-(4-chlorophenyl)-5-carboxamidyl isoxazole, was the most active against colon 38 and CT-26 mouse colon tumor cells with an IC50 of 2.5 μg/mL for both cell lines. Western blot analysis showed that compound 3 significantly down-regulated the expression of phosphorylated STAT3 in both human and mouse colon cancer cells indicating that the mechanism of action for compound 3 may involve the inhibition of JAK3/STAT3 signaling pathways. Flow cytometric analysis with Annexin V staining showed that the death induced by compound 3 is mediated through cell necrosis and not apoptotic pathway. In summary, our results show that compound 3 is a new N-phenyl-5-carboxamidyl isoxazole with potential anticancer activity. Compound 3 inhibits the phosphorylation of STAT3, a novel target for chemotherapeutic drugs, and is worthy of further investigation as a potential chemotherapeutic agent for treating colon cancer.

UTL-5b is an anti-inflammatory and anti-arthritic small-molecule tumor necrosis factor-alpha inhibitor and a structural analogue of the anti-arthritic drug, leflunomide. Leflunomide is known to be metabolized to teriflunomide, but the metabolites of UTL-5b have not been reported. The objective of this study was to investigate whether UTL-5b has a similar metabolic behavior as leflunomide. Preliminary studies showed that when exposed to microsomes in vitro with or without NADPH, UTL-5b disappeared within 30 min. To further investigate the microsomal metabolism, liquid chromatography-ultraviolet (LC-UV) and LC/tandem mass spectrometry (LC–MS/MS) were employed to, respectively, monitor the microsomal metabolites and identify the structure of the metabolites using LC-full scan MS and LC combined with multiple-ion monitoring MS. Fragmentation determination was analyzed by two types of scans: product ion scans and precursor ion scan. The in vitro microsomal treatment of UTL-5b resulted in two major metabolites: 5-methylisoxazole-3-carboxylic acid and 2-chloroaniline. Thus, the in vitro metabolic behavior of UTL-5b appears to be different from that of leflunomide in that the isoxazole ring is cleaved.

Colorectal cancer is the leading cause of cancer-related mortality in the western world. It is also the third most common cancer diagnosed in both men and women in the United States with a recent estimate for new cases of colorectal cancer in the year 2012 being around 103,170. Various risk factors for colorectal cancer include life-style, diet, age, personal and family history, and racial and ethnic background. While a few cancers are certainly preventable but this does not hold true for colon cancer as it is often detected in its advanced stage and generally not diagnosed until symptoms become apparent. Despite the fact that several options are available for treating this cancer through surgery, chemotherapy, radiation therapy, immunotherapy, and nutritional-supplement therapy, but the success rates are not very encouraging when used alone where secondary complications appear in almost all these therapies. To maximize the therapeutic-effects in patients, combinatorial approaches are essential. In this review we have discussed the therapies previously and currently available to patients diagnosed with colorectal-cancer, focus on some recent developments in basic research that has shaded lights on new therapeutic-concepts utilizing macrophages/dendritic cells, natural killer cells, gene delivery, siRNA-, and microRNA-technology, and specific-targeting of tyrosine kinases that are either mutated or over-expressed in the cancerous cell to treat these cancer. Potential strategies are discussed where these concepts could be applied to the existing therapies under a comprehensive approach to enhance the therapeutic effects.

Rheumatoid arthritis (RA) is a common disease characterized by chronic inflammation and irreversible destruction of articular cartilage and bone. In this report, we examined the anti-inflammatory and anti-arthritic effects of a novel leflunomide analogue, UTL-5b (also known as GBL-5b), for potential RA treatment. Using a carrageenan-induced edema study in rats, UTL-5b exhibited a better anti-inflammatory effect as compared with leflunomide and its metabolite. The chronic efficacy of UTL-5b was examined using type II collagen-induced arthritis (CIA) mouse model. UTL-5b exerted an anti-arthritic effect in a dose-dependant manner with mice given 30 mg/kg exhibiting amelioration of disease early in the trial, but losing statistical significance over time. In contrast, mice treated with 60 mg/kg showed reduced clinical disease parameters early in the trial and these effects were sustained over the ten week trial period. Mechanistic studies indicate that UTL-5b is an inhibitor of TNF-α production in vivo. Oral administration of UTL-5b prior to i.p. injection with lethal dose of lipopolysaccharide (LPS)/D-galactosamine markedly reduced the levels of serum TNF-α and increased survival rates of animals from septic shock-induced death. Acute toxicity study using mice receiving increasing doses of UTL-5b showed that no animals were killed by UTL-5b at 2,000 mg/kg (LD(50) >2,000 mg/kg). Our studies show that UTL-5b represents a novel anti-inflammatory and anti-arthritic agent with potential therapeutic application for RA treatment.

We investigated a small-molecule modulator of tumor necrosis factor alpha (TNF-alpha), UTL-5g (also referred to as GBL-5g), as a potential chemoprotective agent against cisplatin-induced side effects including nephrotoxicity, hepatotoxicity and hematotoxicity. Pretreatment of UTL-5g i.p. in BDF1 mice reduced the levels of blood urea nitrogen (BUN) and creatinine induced by cisplatin treatment. The levels of both aspartate transaminase (AST) and alanine transaminase (ALT) in these animals were also reduced by UTL-5g. Pretreatment of UTL-5g did not significantly affect the number of white blood cells (WBC) under current experimental conditions, yet it markedly increased blood platelet counts by more than threefold. Therapeutic assessment in SCID mice inoculated with human HCT-15 tumor cells showed that UTL-5g did not attenuate the anti-tumor effect of cisplatin but increased the therapeutic efficacy of cisplatin. The LD50 of UTL-5g was determined to be > 2,000 mg/kg by an acute toxicity study. In summary, our studies showed that 1) UTL-5g significantly reduces nephrotoxicity and hepatotoxicity induced by cisplatin in mice, presumably by lowering the levels of TNF-alpha, 2) UTL-5g markedly increased blood platelet counts in mice and 3) UTL-5g treatment increased the therapeutic efficacy of cisplatin against HCT-15 cells inoculated in SCID mice.

UTL-5b (GBL-5b) is a novel analog of leflunomide with anti-inflammatory and antiarthritic effects. It has been shown to lower serum tumor necrosis factor-alpha (TNF-α) level induced by lipopolysaccharide (LPS) in an animal model. In this study, the effect of UTL-5b on nitric oxide (NO) and dihydroorotate dehydrogenase (DHODH) was investigated. Our in vitro studies showed that (1) UTL-5b is a stronger inhibitor of NO production as compared to leflunomide and its active metabolite, teriflunomide, and (2) Unlike leflunomide, a potent inhibitor of DHODH, UTL-5b does not inhibit DHODH activity. These findings show that UTL-5b acts in a manner different from that of leflunomide. To further investigate the mode of action of UTL-5b, an ex vivo gene array study was performed. C57BL/6 mice were injected subcutaneously with of UTL-5b 24 hr before injection of E. coli LPS. Mice were sacrificed 90 min later and the whole spleen mRNA was isolated for gene microarray analysis. The results showed that UTL-5b significantly suppressed three genes that are relevant to the TNF- pathway: Janus kinase 3 (JAK3), mitogen-activated protein kinase kinase kinase 2 (MAP3K2) and lipopolysaccharide-induced TNF- factor (LITAF). In summary, our results showed that UTL-5b has a stronger inhibitory effect on NO production than leflunomide; yet, unlike leflunomide, UTL-5b does not inhibit DHODH in vitro. In addition, gene array analysis showed that the biological effects of UTL-5b are attributed at least in part to the suppression of JAK3, MAP3K2 and LITAF gene expression.

The Protein kinase C (PKC) -associated signal pathway plays crucial roles in regulation of cell growth, differentiation and apoptosis. The present study focuses on conventional PKC (cPKC) expression and its regulation in primary cultures of bone marrow cells induced to undergo macrophage/granulocyte differentiation by macrophage colony-stimulating factor (M-CSF) or granular colony-stimulating factor (G-CSF). By performing western blot analysis with pan anti-PKC antibodies, we found that PKC is transiently induced by M-CSF, reaching a maximum level by day 2, and then declines and diminishes by day 9 in primary culture of bone marrow cells. In contrast, the expression of PKC along G-CSF induced granulocytic differentiation of bone marrow stem cells is low and increases gradually. Reverse transcription-PCR (RT-PCR) assay was utilized to investigate the expression of PKC isoforms. PKC-alpha is constitutively expressed in bone marrow cells independently of hematopoietic growth factors in cultures. PKC-gamma mRNA is undetectable. Similarly, the expression of PKC-beta is transiently induced by M-CSF, yet steadily increased by G-CSF, in agreement with results obtained from PKC protein expression. Furthermore, gel-shift assay showed that the activation of NF-kappaB is transiently induced by M-CSF but not by G-CSF. These data suggest that PKC expression is involved in both macrophage and granulocyte differentiation by bone marrow committed stem cells. Yet, NF-kappaB activation is only detected in macrophage and not granulocyte differentiation. Thus, we conclude that the PKC-mediated signaling pathway is distinctly involved in bone-marrow cell differentiation induced by M-CSF and G-CSF.

Histone acetylation plays an important role in the silencing and activation of genes involved in tumoregenesis. Trichostatin A, originally identified as an anti-fungal drug, is a potent inhibitor of histone deacetylase (HDAC) with potential anti-tumor activity. In this study, we investigated the effect of M344, an amide analogues of trichostatin A, on the growth and differentiation of THP-1 human leukemia cells. We showed that at low doses, (< 0.2 muM), M344 could inhibit the growth of THP-1 cells at G1 phase in vitro with low cytotoxic effect. Low dose of M344 exerted some differentiating effect on THP-1 cells as judged by the expression of c-fms proto-oncogene (M-CSF receptor) and appearance of adherent cells. Growth arrest induced by M344 is associated with increased levels of cyclin-dependent protein kinase inhibitor p21 and cyclin E, in agreement with G1 phase arrest. At higher doses (2 muM), M344 could induce THP-1 cells to undergo apoptosis, which was associated with the cleavage of PARP, cytochrome c release and activation of both caspases-8, -9, followed by the activation of caspase-3. In addition, M344 could increase the levels of pro-apoptotic protein Bax but decreased the levels of anti-apoptotic protein XIAP. M344 is a potent activator of NF-kappaB transcription factor. RT-PCR assay showed that the M344 could transiently increase IL-1 expression yet markedly decreased TNF-alpha expression. Our results show that M344 is a potent growth inhibitor and inducer of apoptosis in human leukemia cells and suggest potential therapeutic strategies of HDAC inhibitors for patients with leukemias.