Dictyostelium differentiation-inducing factor-1 induces glucose transporter 1 translocation and promotes glucose uptake in mammalian cells

Research on a Minor Organism can also be Benefit the World: The Fascinating Cellular Slime Mold Dictyostelium discoideum

In 1985, when I entered the Graduate School of Science at Kyoto University, I began my research on cellular slime molds, a group of soil microorganisms. The cellular slime mold Dictyostelium discoideum is studied globally as a model organism for cell and developmental biology. I was conducting basic biological research into cell differentiation and migration using D. discoideum, and during this process, our research group made a discovery with potential implications for drug development. Specifically, we found that a chlorinated polyketide named differentiation-inducing factor 1 (DIF-1), derived from D. discoideum, exhibits antitumor activity. Based on this discovery, I began elucidating the mechanism of the antitumor action of DIF-1 and developing anticancer drugs using DIF-1 as a lead compound. During this period, in 1991, I obtained my Ph.D. in research related to D. discoideum cell differentiation, and subsequently served as a Japan Society for the Promotion of Science (JSPS) Special Research Fellow before joining the Institute for Molecular and Cellular Regulation (IMCR) at Gunma University in 1993. I then joined the Graduate School of Health and Sports Sciences at Juntendo University in 2015, where I have been until 2024. Throughout this period, I continued my research on DIF-1 and discovered that DIF-1 and its derivatives possess various biological activities ─ such as anti-diabetic, immunoregulatory, anti-bacterial, and anti-malarial activities ─ that could be applicable in drug development. In this review, I aim to present a segment of both our fundamental and applied research on D. discoideum and DIF-1.

Mammalian target of differentiation-inducing factor-1 is mitochondrial malate dehydrogenase for activation of AMP-activated protein kinase and induction of mitochondrial fission

AIMS

Differentiation-inducing factor-1 (DIF-1) is a polyketide produced by Dictyostelium discoideum that inhibits growth and migration, while promoting the differentiation of Dictyostelium stalk cells through unknown mechanisms. DIF-1 localizes in stalk mitochondria. In addition to its effect on Dictyostelium, DIF-1 also inhibits growth and migration, and induces mitochondrial fission followed by mitophagy in mammalian cells, at least in part by activating AMP-activated protein kinase (AMPK). In a previous study, we found that DIF-1 binds to mitochondrial malate dehydrogenase (MDH2) and inhibits its activity in HeLa cells. In the present study, we investigated whether MDH2 serves as a pharmacological target of DIF-1 in mammalian cells.

MAIN METHODS

To examine the enzymatic activity of MDH, mitochondrial morphology, and molecular mechanisms of DIF-1 action, we conducted an MDH reverse reaction assay, immunofluorescence staining, western blotting, and RNA interference using mammalian cells such as human umbilical vein endothelial cells, human cervical cancer cells, mouse endothelial cells, and mouse breast cancer cells.

KEY FINDINGS

DIF-1 inhibited mitochondrial but not cytoplasmic MDH activity. Similar to DIF-1, LW6, an authentic MDH2 inhibitor, induced phosphorylation of AMPK, resulting in the phosphorylation of acetyl-CoA carboxylase (ACC) and the dephosphorylation of p70 S6 kinase with approximately the same potency. DIF-1 and LW6 induced mitochondrial fission. Furthermore, MDH2 knockdown using siRNA reproduced the DIF-1 action on the AMPK signaling and mitochondrial morphology. Conversely, an AMPK inhibitor prevented DIF-1-induced mitochondrial fission.

SIGNIFICANCE

We propose that MDH2 is a mammalian target of DIF-1 for the activation of AMPK and induction of mitochondrial fission.

A longer-chain acylated derivative of Dictyostelium differentiation-inducing factor-1 enhances the antimalarial activity against Plasmodium parasites

The spread of malarial parasites resistant to first-line treatments such as artemisinin combination therapies is a global health concern. Differentiation-inducing factor 1 (DIF-1) is a chlorinated alkylphenone (1-(3,5-dichloro-2,6-dihydroxy-4-methoxyphenyl) hexan-1-one) originally found in the cellular slime mould Dictyostelium discoideum. We previously showed that some derivatives of DIF-1, particularly DIF-1(+2) (1-(3,5-dichloro-2,6-dihydroxy-4-methoxyphenyl) octan-1-one), exert potent antimalarial activities. In this study, we synthesised DIF-1(+3) (1-(3,5-dichloro-2,6-dihydroxy-4-methoxyphenyl) nonan-1-one). We then evaluated the effects of DIF-1(+3) in vitro on Plasmodium falciparum and in vivo over 7 days (50-100 mg/kg/day) in a mouse model of Plasmodium berghei. DIF-1(+3) exhibited a half-maximal inhibitory concentration of approximately 20-30 % of DIF-1(+2) in three laboratory strains with a selectivity index > 263, including in strains resistant to chloroquine and artemisinin. Parasite growth and multiplication were almost completely suppressed by treatment with 100 mg/kg DIF-1(+3). The survival time of infected mice was significantly increased (P = 0.006) with no apparent adverse effects. In summary, addition of an acyl group to DIF-1(+2) to prepare DIF-1(+3) substantially enhanced antimalarial activity, even in drug-resistant malaria, indicating the potential of applying DIF-1(+3) for malaria treatment.

Dictyostelium Differentiation-Inducing Factor 1 Promotes Glucose Uptake via Direct Inhibition of Mitochondrial Malate Dehydrogenase in Mouse 3T3-L1 Cells

Differentiation-inducing factor 1 (DIF-1), found in Dictyostelium discoideum, has antiproliferative and glucose-uptake-promoting activities in mammalian cells. DIF-1 is a potential lead for the development of antitumor and/or antiobesity/antidiabetes drugs, but the mechanisms underlying its actions have not been fully elucidated. In this study, we searched for target molecules of DIF-1 that mediate the actions of DIF-1 in mammalian cells by identifying DIF-1-binding proteins in human cervical cancer HeLa cells and mouse 3T3-L1 fibroblast cells using affinity chromatography and liquid chromatography-tandem mass spectrometry and found mitochondrial malate dehydrogenase (MDH2) to be a DIF-1-binding protein in both cell lines. Since DIF-1 has been shown to directly inhibit MDH2 activity, we compared the effects of DIF-1 and the MDH2 inhibitor LW6 on the growth of HeLa and 3T3-L1 cells and on glucose uptake in confluent 3T3-L1 cells in vitro. In both HeLa and 3T3-L1 cells, DIF-1 at 10-40 μM dose-dependently suppressed growth, whereas LW6 at 20 μM, but not at 2-10 μM, significantly suppressed growth in these cells. In confluent 3T3-L1 cells, DIF-1 at 10-40 μM significantly promoted glucose uptake, with the strongest effect at 20 μM DIF-1, whereas LW6 at 2-20 μM significantly promoted glucose uptake, with the strongest effect at 10 μM LW6. Western blot analyses showed that LW6 (10 μM) and DIF-1 (20 μM) phosphorylated and, thus, activated AMP kinase in 3T3-L1 cells. Our results suggest that MDH2 inhibition can suppress cell growth and promote glucose uptake in the cells, but appears to promote glucose uptake more strongly than it suppresses cell growth. Thus, DIF-1 may promote glucose uptake, at least in part, via direct inhibition of MDH2 and a subsequent activation of AMP kinase in 3T3-L1 cells.

Pharmacological Evidence That Dictyostelium Differentiation-Inducing Factor 1 Promotes Glucose Uptake Partly via an Increase in Intracellular cAMP Content in Mouse 3T3-L1 Cells

Differentiation-inducing factor 1 (DIF-1) isolated from the cellular slime mold Dictyostelium discoideum can inhibit mammalian calmodulin-dependent cAMP/cGMP phosphodiesterase (PDE1) in vitro. DIF-1 also promotes glucose uptake, at least in part, via a mitochondria- and AMPK-dependent pathway in mouse 3T3-L1 fibroblast cells, but the mechanism underlying this effect has not been fully elucidated. In this study, we investigated the effects of DIF-1 on intracellular cAMP and cGMP levels, as well as the effects that DIF-1 and several compounds that increase cAMP and cGMP levels have on glucose uptake in confluent 3T3-L1 cells. DIF-1 at 20 μM (a concentration that promotes glucose uptake) increased the level of intracellular cAMP by about 20% but did not affect the level of intracellular cGMP. Neither the PDE1 inhibitor 8-methoxymethyl-3-isobutyl-1-methylxanthine at 10-200 μM nor the broad-range PDE inhibitor 3-isobutyl-1-methylxanthine at 40-400 μM had any marked effects on glucose uptake. The membrane-permeable cAMP analog 8-bromo-cAMP at 200-1000 μM significantly promoted glucose uptake (by 20-25%), whereas the membrane-permeable cGMP analog 8-bromo-cGMP at 3-100 μM did not affect glucose uptake. The adenylate cyclase activator forskolin at 1-10 μM promoted glucose uptake by 20-30%. Thus, DIF-1 may promote glucose uptake by 3T3-L1 cells, at least in part, via an increase in intracellular cAMP level.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Derivatives of Dictyostelium differentiation-inducing factors suppress the growth of Plasmodium parasites in vitro and in vivo

Malaria, which is caused by protozoa of the genus Plasmodium, remains a major endemic public health problem worldwide. Since artemisinin combination therapies are used as a first-line treatment in all endemic regions, the emergence of parasites resistant to these regimens has become a serious problem. Differentiation-inducing factor 1 (DIF-1) is a chlorinated alkylphenone originally found in the cellular slime mold Dictyostelium discoideum. DIF-1 and its derivatives exhibit a range of biological activities. In the present study, we investigated the effects of 41 DIF derivatives on the growth of Plasmodium falciparum in vitro using four laboratory strains and 12 field isolates. Micromolar concentrations of several DIF derivatives strongly suppressed the growth of the four laboratory strains, including strains that exhibited resistance to chloroquine and artemisinin, as well as strains that were susceptible to these drugs. In addition, DIF-1(+2), the most potent derivative, strongly suppressed the growth of 12 field isolates. We also examined the effects of DIF-1(+2) on the activity of the rodent malarial parasite Plasmodium berghei in mice. Intraperitoneal administration of DIF-1(+2) over 4 days (50 or 70 mg/kg/day) significantly suppressed the growth of the parasite in the blood with no apparent adverse effects, and a dose of 70 mg/kg/day significantly prolonged animal survival. These results suggest that DIF derivatives, such as DIF-1(+2), could serve as new lead compounds for the development of antimalarial agents.

Dictyostelium Differentiation-Inducing Factor-1 Promotes Glucose Uptake, at Least in Part, via an AMPK-Dependent Pathway in Mouse 3T3-L1 Cells

Differentiation-inducing factor-1 (DIF-1) is a chlorinated alkylphenone (a polyketide) found in the cellular slime mold Dictyostelium discoideum. DIF-1 and its derivative, DIF-1(3M) promote glucose consumption in vitro in mammalian cells and in vivo in diabetic rats; they are expected to be the leading antiobesity and antidiabetes compounds. In this study, we investigated the mechanisms underlying the actions of DIF-1 and DIF-1(3M). In isolated mouse liver mitochondria, these compounds at 2-20 μM promoted oxygen consumption in a dose-dependent manner, suggesting that they act as mitochondrial uncouplers, whereas CP-DIF-1 (another derivative of DIF-1) at 10-20 μM had no effect. In confluent mouse 3T3-L1 fibroblasts, DIF-1 and DIF-1(3M) but not CP-DIF-1 induced phosphorylation (and therefore activation) of AMP kinase (AMPK) and promoted glucose consumption and metabolism. The DIF-induced glucose consumption was reduced by compound C (an AMPK inhibitor) or AMPK knock down. These data suggest that DIF-1 and DIF-1(3M) promote glucose uptake, at least in part, via an AMPK-dependent pathway in 3T3-L1 cells, whereas cellular metabolome analysis revealed that DIF-1 and DIF-1(3M) may act differently at least in part.

Antimicrobial Activities of Dictyostelium Differentiation-Inducing Factors and Their Derivatives

At the end of its life cycle, the cellular slime mold Dictyostelium discoideum forms a fruiting body consisting of spores and a multicellular stalk. Originally, the chlorinated alkylphenone differentiation-inducing factors (DIFs) -1 and -3 were isolated as stalk cell inducers in D. discoideum. Later, DIFs and their derivatives were shown to possess several biologic activities including antitumor and anti-Trypanosoma properties. In this study, we examined the antibacterial activities of approximately 30 DIF derivatives by using several bacterial species. Several of the DIF derivatives strongly suppressed the growth of the Gram-positive bacteria Staphylococcus aureus, Bacillus subtilis, and Enterococcus faecalis and Enterococcus faecium, at minimum inhibitory concentrations (MICs) in the sub-micromolar to low-micromolar range. In contrast, none of the DIF derivatives evaluated had any noteworthy effect on the growth of the Gram-negative bacterium Escherichia coli (MIC, >100 µM). Most importantly, several of the DIF derivatives strongly inhibited the growth of methicillin-resistant S. aureus and vancomycin-resistant E. faecalis and E. faecium. Transmission electron microscopy revealed that treatment with DIF derivatives led to the formation of distinct multilayered structures consisting of cell wall or plasma membrane in S. aureus. The present results suggest that DIF derivatives are good lead compounds for developing novel antimicrobials.

Dictyostelium: An Important Source of Structural and Functional Diversity in Drug Discovery

The cellular slime mold Dictyostelium discoideum is an excellent model organism for the study of cell and developmental biology because of its simple life cycle and ease of use. Recent findings suggest that Dictyostelium and possibly other genera of cellular slime molds, are potential sources of novel lead compounds for pharmacological and medical research. In this review, we present supporting evidence that cellular slime molds are an untapped source of lead compounds by examining the discovery and functions of polyketide differentiation-inducing factor-1, a compound that was originally isolated as an inducer of stalk-cell differentiation in D. discoideum and, together with its derivatives, is now a promising lead compound for drug discovery in several areas. We also review other novel compounds, including secondary metabolites, that have been isolated from cellular slime molds.

Biological Activities of Novel Derivatives of Differentiation-Inducing Factor 3 from Dictyostelium discoideum

Differentiation-inducing factor-3 (DIF-3; 1-(3-chloro-2,6-dihydroxy-4-methoxyphenyl)hexan-1-one), which is found in the cellular slime mold Dictyostelium discoideum, is a potential candidate compound for the development of new medicines; DIF-3 and its derivatives possess several beneficial biological activities, including anti-tumor, anti-Trypanosoma cruzi, and immunoregulatory effects. To assess the relationship between the biological activities of DIF-3 and its chemical structure, particularly in regard to its alkoxy group and the length of the alkyl chains at the acyl group, we synthesized two derivatives of DIF-3, 1-(3-chloro-2,6-dihydroxy-4-methoxyphenyl)octan-1-one (DIF-3(+3)) and 1-(3-chloro-2,6-dihydroxy-4-butoxyphenyl)-hexan-1-one (Hex-DIF-3), and investigated their biological activities in vitro. At micro-molar levels, DIF-3(+3) and Hex-DIF-3 exhibited strong anti-proliferative effects in tumor cell cultures, but their anti-T. cruzi activities at 1 µM in vitro were not as strong as those of other known DIF derivatives. In addition, Hex-DIF-3 at 5 µM significantly suppressed mitogen-induced interleukin-2 production in vitro in Jurkat T cells. These results suggest that DIF-3(+3) and Hex-DIF-3 are promising leads for the development of anti-cancer and immunosuppressive agents.

Oral administration of Dictyostelium differentiation-inducing factor 1 lowers blood glucose levels in streptozotocin-induced diabetic rats

AIMS

Differentiation-inducing factor 1 (DIF-1), originally discovered in the cellular slime mold Dictyostelium discoideum, and its derivatives possess pharmacological activities, such as the promotion of glucose uptake in non-transformed mammalian cells in vitro. Accordingly, DIFs are considered promising lead candidates for novel anti-diabetic drugs. The aim of this study was to assess the anti-diabetic and toxic effects of DIF-1 in mouse 3T3-L1 fibroblast cells in vitro and in diabetic rats in vivo. Main methods We investigated the in vitro effects of DIF-1 and DIF-1(3M), a derivative of DIF-1, on glucose metabolism in 3T3-L1 cells by using capillary electrophoresis time-of-flight mass spectrometry (CE-TOF-MS). We also examined the effects of DIF-1 on blood glucose levels in streptozotocin (STZ)-induced rats.

KEY FINDINGS

CE-TOF-MS revealed that 20μM DIF-1 and 20μM DIF-1(3M) promoted glucose uptake and metabolism in 3T3-L1 cells. Oral administration of DIF-1 (30mg/kg) significantly lowered basal blood glucose levels in STZ-treated rats and promoted a decrease in blood glucose levels after oral glucose loading (2.5g/kg) in the rats. In addition, daily oral administration of DIF-1 (30mg/kg/day) for 1wk significantly lowered the blood glucose levels in STZ-treated rats but did not affect their body weight and caused only minor alterations in the levels of other blood analytes.

SIGNIFICANCE

These results indicate that DIF-1 may be a good lead compound for the development of anti-diabetic drugs.

Synthesis and SAR of 4-methyl-5-pentylbenzene-1,3-diol (MPBD), produced by Dictyostelium discoideum

4-Methyl-5-pentylbenzene-1,3-diol (MPBD) is a secondary metabolite of SteelyA polyketide synthase, which controls cell aggregation and spore maturation of Dictyostelium discoideum. In this study, chemical synthesis of MPBD and its derivatives was achieved. Structure-activity relationship (SAR) studies for antimicrobial activities against Escherichia coli and Bacillus subtilis were also conducted.

Development of novel DIF-1 derivatives that selectively suppress innate immune responses

The multiple pharmacological activities of differentiation-inducing factor-1 (DIF-1) of the cellular slime mold Dictyostelium discoideum led us to examine the use of DIF-1 as a 'drug template' to develop promising seed compounds for drug discovery. DIF-1 and its derivatives were synthesized and evaluated for their regulatory activities in innate immune responses. We found two new derivatives (4d and 5e) with highly selective inhibitory activities against production of the antimicrobial peptide attacin in Drosophila S2 cells and against production of interleukin-2 in Jurkat cells.

Novel chlorinated dibenzofurans isolated from the cellular slime mold, Polysphondylium filamentosum, and their biological activities

Cellular slime molds are expected to have the huge potential for producing secondary metabolites including polyketides, and we have studied the diversity of secondary metabolites of cellular slime molds for their potential utilization as new biological resources for natural product chemistry. From the methanol extract of fruiting bodies of Polysphondylium filamentosum, we obtained new chlorinated benzofurans Pf-1 (4) and Pf-2 (5) which display multiple biological activities; these include stalk cell differentiation-inducing activity in the well-studied cellular slime mold, Dictyostelium discoideum, and inhibitory activities on cell proliferation in mammalian cells and gene expression in Drosophila melanogaster.

Derivatives of Dictyostelium discoideum differentiation-inducing factor-3 suppress the activities of Trypanosoma cruzi in vitro and in vivo

Chagas disease (human American trypanosomiasis), which is caused by the protozoan parasite Trypanosoma cruzi, is responsible for numerous deaths each year; however, established treatments for the disease are limited. Differentiation-inducing factor-1 (DIF-1) and DIF-3 are chlorinated alkylphenones originally found in the cellular slime mold Dictyostelium discoideum that have been shown to possess pharmacological activities. Here, we investigated the effects of DIF-3 derivatives on the infection rate and growth of T. cruzi by using an in vitro assay system utilizing host human fibrosarcoma HT1080 cells. Certain DIF-3 derivatives, such as butoxy-DIF-3 (Bu-DIF-3), at micro-molar levels strongly suppressed both the infection rate and growth of T. cruzi in HT1080 cells and exhibited little toxicity for HT1080 cells. For example, the IC50 of DIF-3 and Bu-DIF-3 versus the growth of T. cruzi in HT1080 cells were 3.95 and 0.72μM, respectively, and the LD50 of the two compounds versus HT1080 cells were both greater than 100μM. We also examined the effects of DIF-3 and Bu-DIF-3 on T. cruzi activity in C57BL/6 mice. Intraperitoneally administered Bu-DIF-3 (50mg/kg) significantly suppressed the number of trypomastigotes in blood with no apparent adverse effects. These results strongly suggest that DIF-3 derivatives could be new lead compounds in the development of anti-trypanosomiasis drugs.

Derivatives of Dictyostelium differentiation-inducing factors promote mitogen-activated IL-2 production via AP-1 in Jurkat cells

AIMS

Differentiation-inducing factors (DIFs) are chlorinated alkylphenones found in the cellular slime mold Dictyostelium discoideum. DIF derivatives exhibit antiproliferative activities and promote glucose consumption in mammalian cells in vitro. Here, we assessed the ability of DIFs to regulate the immune system in a mammalian cell-line and investigated their mechanisms of action.

MAIN METHODS

We examined the effects of 30 DIF derivatives on concanavalin A-induced interleukin-2 (IL-2) production (CIIP) in Jurkat T-cells. We also examined the effects of these DIF derivatives on the activity of three transcription factors required for CIIP: namely, activator protein-1 (AP-1), nuclear factor of activated T-cells (NFAT), and nuclear factor kappa B (NFκB).

KEY FINDINGS

A reporter gene assay suggested that 2 DIF derivatives, termed DIF-1(+1) and DIF-3(3M), significantly promoted CIIP in Jurkat cells, at least in part, by enhancing the activity of AP-1. These 2 DIF derivatives had no significant effect on concanavalin A-induced interferon-γ production.

SIGNIFICANCE

The results suggest that DIF derivatives could be developed as novel drugs for the activation of IL-2 production and resultant stimulation of the immune system.

Preparation of an antibody that recognizes and neutralizes Dictyostelium differentiation-inducing factor-1

In the development of the cellular slime mold Dictyostelium discoideum, the differentiation-inducing factor-1 (DIF-1; 1-(3,5-dichloro-2,6-dihydroxy-4-methoxyphenyl)hexan-1-one) plays an important role in the regulation of cell differentiation and chemotaxis; however, the cellular signaling systems involving DIF-1 remain to be elucidated. To obtain a probe for DIF-1, we synthesized a DIF derivative (DIF-1-NH(2); 6-amino-1-(3,5-dichloro-2,6-dihydroxy-4-methoxyphenyl)hexan-1-one), and prepared an anti-DIF-1 antibody using a DIF-1-NH(2)-conjugated macromolecule as the immunogen. A 100-fold dilution of the antibody bound to DIF-1-NH(2)-conjugated resin, and this binding was inhibited by co-addition of 20 microM DIF-1 or DIF-1-NH(2). In a monolayer culture of HM44 cells, a DIF-deficient D. discoideum strain, 0.5 nM exogenous DIF-1 induced stalk cell formation in approximately 60% of the cells; this induction was dose-dependently inhibited by the antibody (diluted 12.5- or 25-fold). Furthermore, this inhibition by the antibody was recovered by co-addition of 2.5 or10 nM DIF-1. The results indicate that the anti-DIF-1 antibody recognizes DIF-1 and neutralizes its function.

A flavin-dependent halogenase catalyzes the chlorination step in the biosynthesis of Dictyostelium differentiation-inducing factor 1

Differentiation-inducing factor 1 (DIF-1) is a polyketide-derived morphogen which drives stalk cell formation in the developmental cycle of Dictyostelium discoideum. Previous experiments demonstrated that the biosynthetic pathway proceeds via dichlorination of the precursor molecule THPH, but the enzyme responsible for this transformation has eluded characterization. Our recent studies on prokaryotic flavin-dependent halogenases and insights from the sequenced Dd genome led us to a candidate gene for this transformation. In this work, we present in vivo and in vitro evidence that chlA from Dd encodes a flavin-dependent halogenase capable of catalyzing both chlorinations in the biosynthesis of DIF-1. The results provide in vitro characterization of a eukaryotic oxygen-dependent halogenase and demonstrate a broad reach in biology for this molecular tailoring strategy, notably its involvement in the differentiation program of a social amoeba.

Dictyostelium differentiation-inducing factor-1 binds to mitochondrial malate dehydrogenase and inhibits its activity

We have reported that the differentiation-inducing factors (DIFs) DIF-1 and DIF-3, morphogens secreted from Dictyostelium discoideum, inhibit proliferation of several cancer cells via suppression of the Wnt/beta-catenin signaling pathway. However, the target molecules of DIFs involved in the anti-proliferative effects are still unknown. In the present study, DIF-1-tethered resins were synthesized to explore the target molecules of DIFs, and mitochondrial malate dehydrogenase (mMDH) was identified as one of the target molecules. In the in vitro assay, DIF-1 and other analogs including 2-MIDIF-1, DIF-3, and 6-MIDIF-3 were found to be capable of binding to mMDH but not to cytoplasmic MDH. However, only DIF-1 and 2-MIDIF-1 inhibited the enzymatic activity of mMDH. The effects of DIF analogs on ATP content and cell proliferation were then analyzed using HeLa cells. DIF-1 and 2-MIDIF-1 were found to lower the ATP content and both chemicals inhibited HeLa cell proliferation, suggesting that inhibition of mMDH activity affected cell energy production, probably leading to the inhibition of proliferation. These results suggest that the inhibition of mMDH activity by DIF-1 and 2-MIDIF-1 could be one of the mechanisms to induce anti-proliferative effects, independent of the inhibition of the Wnt/beta-catenin signaling pathway.

Biological activities of novel derivatives of DIF-1 isolated from Dictyostelium

The differentiation-inducing factor-1 (DIF-1) is a lipophilic signal molecule (chlorinated alkylphenone) that induces stalk cell differentiation in the cellular slime mold Dictyostelium discoideum. In addition, DIF-1 and its derivatives have been shown to possess anti-leukemic activity and glucose consumption-promoting activity in vitro in mammalian cells. In this study, to assess the chemical structure-effect relationship of DIF-1, we synthesized eight derivatives of DIF-1 and investigated their stalk cell-inducing activity in Dictyostelium cells and pharmacological activities in mammalian cells. Of the derivatives, two amide derivatives of DIF-1, whose hydrophobic indexes are close to that of DIF-1, induced stalk cell differentiation as strongly as DIF-1 in Dictyostelium cells. It was also found that some derivatives suppressed cell growth in human K562 leukemia cells and promoted glucose consumption in mouse 3T3-L1 cells. These results give us valuable information as to the chemical structure-effect relationship of DIF-1.

Exploitation of the derivatives of Dictyostelium differentiation-inducing factor-1, which promote glucose consumption in mammalian cells

AIMS

The differentiation-inducing factor-1 (DIF-1) is a signal molecule that induces stalk cell formation in the cellular slime mold Dictyostelium discoideum. DIF-1 has also been shown to possess pharmacological activities, such as the suppression of tumor cell growth and the promotion of glucose uptake in non-transformed mammalian cells. In this study, we tried to develop compounds that possess weaker anti-tumor activity and stronger glucose uptake-promoting activity than DIF-1.

MAIN METHODS

We investigated the in vitro effects of 12 derivatives of DIF-1 on glucose consumption in mouse 3T3-L1 cells and on cell growth in K562 human leukemia cells. We also examined the effect of a good compound on the blood glucose concentration in KK-Ay diabetic mice.

KEY FINDINGS

We found that some derivatives at 20 microM promoted glucose consumption more than twice as fast as the control. Of the derivatives, a compound named DIF-1(3M), which has a weaker anti-leukemic effect than DIF-1, promoted glucose consumption as strongly as DIF-1 in confluent 3T3-L1 cells. While DIF-1 at 20 microM was inhibitory to the cell growth of 3T3-L1, DIF-1(3M) at 20 microM exhibited no inhibitory effect on the growing cells. We also found that DIF-1(3M) injected (10-12.5 mg/kg body weight) intraperitoneally in mice tended to lower the blood glucose concentration.

SIGNIFICANCE

The present results open the possibility for the development of new agents that possess strong glucose-uptake-promoting activity but little anti-tumor activity and may have therapeutic potential for the treatment of diabetes and/or obesity.

Micellar structures of poly(styrene-b-4-vinylpyridine)s in THF/toluene mixtures and their functionalization with gold

The effects of the block copolymer composition and the solvent selectivity on the micellar morphologies of poly(styrene- b-4-vinylpyridine)s (PS- b-P4VPs) and their functionalizations with gold were studied in 10 mg/mL solutions using small-angle X-ray scattering and transmission electron microscopy (TEM). The solvent selectivity for the PS block was controlled by toluene/tetrahydrofuran (THF) mixtures in which toluene and THF are selective for PS and nonselective, respectively. The micellar structure was strongly dependent on phi (wt % toluene in toluene/THF mixture) and the composition of the block copolymers. PS(12K)- b-P4VP(11.8K) (symmetric) showed spherical micelles in the entire range of phi except phi = 0 (THF, nonselective solvent). PS(3.3K)- b-P4VP(18.7K) (asymmetric, longer P4VP) showed multiple morphologies with transitions from spheres to cylinders and finally to vesicles with an increase in phi. PS(19.6K)- b-P4VP(5.1K) (asymmetric, longer PS) showed spherical micelles only at the narrow ranges of 90 wt % <or= phi <or= 100 wt % and an isotropic state at the other ranges. The micelles formed a complex with HAuCl 4 and were reduced with hydrazine in the solvent mixtures. The morphologies of micelles, hybrid micelles, and gold nanoparticles were investigated by using TEM and UV/vis spectroscopy. The possible mechanisms leading to these morphological changes and the formation of the nanosized gold particles were also discussed.

[Novel biologically active compounds isolated from unexploited organisms, cellular sime molds]

Cellular slime molds are thought to be excellent model organisms for the study of cell and developmental biology because of their simple pattern of development. However, there have been few reports on secondary metabolites of them. We have focused on the utility of cellular slime molds as novel resources for natural product chemistry, and have studied the diversity of secondary metabolites produced by them as well as their physiological and pharmacological activities. We have recently isolated many novel compounds from the fruiting bodies of various species of Dictyostelium cellular slime molds. Total syntheses and biological evaluation of these compounds have been carried out. It was shown that dictyopyrones and dictyomedins may regulate Dictyostelium development. Amino sugar derivatives such as furanodictines and dictyoglucosamines induced neuronal differentiation of rat PC-12 cells. In addition, brefelamide inhibited the cellular proliferation of 1321N1 human astrocytoma cells. These results show that cellular slime molds are promising sources in natural product chemistry.