Antineoplastic drug activity in the mitotic cycle--effects of six agents on macromolecular synthesis in synchronous mammalian leukemic cells

The mechanism of transglutaminase 2 inhibition with glucosamine: implications of a possible anti-inflammatory effect through transglutaminase inhibition

PURPOSE

Although many efforts on revealing mechanism of the constitutive activation of NF-κB in cancer cells contributed to understanding canonical pathways, largely it remains to be determined for therapeutic approaches. Recently, we found that increased expression of transglutaminase 2 (TGase 2) appears to be responsible for constitutive activation of NF-κB in certain types of cancer cells. In previous studies, we demonstrated that TGase 2 inhibition markedly increases anti-cancer drug sensitivity in drug resistance cancer cells. Therefore, we develop safe and effective TGase 2 inhibitors for therapeutic approach.

METHODS

We screened a chemical library of natural compounds using in vitro TGase 2 activity assay. The salient discovery was that glucosamine (GlcN), a known anti-inflammatory substance, inhibited the cross-linking activity of TGase 2. We tested, through a biochemical analysis including kinetics, whether the GlcN and GlcN analogs specifically inhibit TGase 2. We also determined the inhibitory mechanism using conformational change of TGase 2.

RESULTS

We found that the primary amine of GlcN plays a key role in TGase 2 inhibition. We also demonstrated that GlcN reversed TGase 2-mediated I-κBα polymerization in vitro. Interestingly, the metabolite of GlcN, glucosamine-6-phosphate (GlcN6P), inhibited TGase 2 activity via binding to the GTP-binding site with better efficiency than GlcN. In the native gel electrophoresis, it was clearly observed that GlcN6P binds to TGase 2 directly as an allosteric inhibitor.

CONCLUSIONS

We concluded that GlcN inhibits TGase 2 activity by direct contact. GlcN and its metabolite GlcN6P can down-regulate constitutive activation of NF-κB in vivo via inhibition of TGase 2.

Immunosuppressive effects of glucosamine

Glucosamine is a naturally occurring derivative of glucose and is an essential component of glycoproteins and proteoglycans, important constituents of many eukaryotic proteins. In cells, glucosamine is produced enzymatically by the amidation of glucose 6-phosphate and can then be further modified by acetylation to result in N-acetylglucosamine. Commercially, glucosamine is sold over-the-counter to relieve arthritis. Although there is evidence in favor of the beneficial effects of glucosamine, the mechanism is unknown. Our data demonstrate that glucosamine suppresses the activation of T-lymphoblasts and dendritic cells in vitro as well as allogeneic mixed leukocyte reactivity in a dose-dependent manner. There was no inherent cellular toxicity involved in the inhibition, and the activity was not reproducible with other amine sugars. More importantly, glucosamine administration prolonged allogeneic cardiac allograft survival in vivo. We conclude that, despite its documented effects on insulin sensitivity, glucosamine possesses immunosuppressive activity and could be beneficial as an immunosuppressive agent.

Sodium salicylate facilitates calcium-dependent release of transmitter at mouse neuromuscular junctions

1. The effects of sodium salicylate on the frequency of miniature endplate potentials (m.e.p.ps) and on the quantal content of endplate potentials (e.p.ps) in mouse diaphragm muscles at 36 degrees C and 24 degrees C were studied by conventional microelectrode techniques. 2. At 36 degrees C, salicylate (10 mM) elevated the frequency of m.e.p.ps in a manner which was insensitive to [Mg2+]0 and independent of the presence of [Ca2+]0. Lowering the temperature to 24 degrees C abolished the stimulating effect. 2,4-Dinitrophenol (10 microM) had similar effects at 36 degrees C and these disappeared at 24 degrees C. All subsequent experiments were performed at 24 degrees C. 3. Salicylate (10 mM) further increased the frequency (F) of m.e.p.ps stimulated by [Ca2+]0 in a depolarizing solution. When [Ca2+]0 was varied in the absence of salicylate, a linear relationship between ln(F) and ln([ CA2+]0) was obtained. Salicylate shifted this relationship to the left, with respect to the control, without altering the slope. 4. Salicylate (5 mM) also increased the quantal content (m) of e.p.ps in a solution that contained 5 mM Mg2+, in a concentration-dependent fashion. As [Ca2+]0 was varied in the absence of salicylate, a linear relationship between ln(m) and ln[(Ca2+]0) was observed. Salicylate shifted this linear relationship to the left, with respect to the control, without altering the slope. Doubling the concentration of [Mg2+]0 antagonized this effect of salicylate on the quantal content of e.p.ps. 5. These results indicate that salicylate enhances the effect of changing [Ca2+]0. Salicylate probably facilitates the entry of Ca2+ into the nerve terminal or sensitizes the process that is regulated by Ca2 , thereby stimulating the release of transmitter. Surface negative charges may have an important role in the effect of [Ca22]0.

Experimental investigations on a sequential combination chemotherapy protocol

This paper deals with experimental investigations concerning the composition of a cytostatic three-drug-protocol in diploid Ehrlich-Ascites-Tumor (EAT) cells in vivo at a far advanced stage of the disease. Hydroxyurea (HU) and vincristine (VCR) were used in very low doses to induce a modification of the growth pattern of tumor cells alike partial synchronization. Adriamycin (ADM) was selected as cytocidal drug during DNA synthesis of the partially synchronized cells. It was found that the sequential combination of HU and VCR (first HU and 12 h thereafter VCR) caused the greatest alteration of growth pattern compared with other combination protocols. A further statistically significant increase of the degree of synchrony was observed after a second VCR administration -- 22 h after HU. By means of this protocol the EAT was subdivided into two proliferating subpopulations, a diploid and tetraploid one. The tetraploid population resulted from surviving cells being not able to perform dytokinesis correctly, so that polynuclear cells and cells with a large single nucleus containing tetraploid DNA values were created. With respect to therapy, the administation of ADM at the time of DNA synthesis of the partially synchronized cells resulted in a statistically significant prolongation of the mean survival time and in 30% of cures of the animals. The dosage of ADM was 2.6 mg/kg, i.e., a nonlethal dose (50% of the LD10). Other combinations, i.e., simultaneous or reversed sequential combinations, did not show any therapeutic improvement compared to single drug therapy of ADM.

Hydroxyurea

Hydroxyurea (HU) is an anti-leukaemia and anti-tumour drug which has also found limited application in the treatment of dermatological disorders. It is a potent inhibitor of DNA synthesis in many organisms from viruses to man and in cell culture systems. To a lesser degree it can also inhibit RNA and protein synthesis. It is anti-mitotic and cytotoxic depending on the concentration used, the duration of exposure, and the sensitivity of the organism. In most cells HU is active mainly in the S-phase of the cycle and because of the easy reversibility of its action it has been used as a synchronising agent in cell cultures with some success. There is conflicting evidence about the ability of HU to act as an inhibitor of the natural DNA repair mechanisms in cells exposed to radiation or alkylating agents. HU has, however, been shown to induce chromosome damage in a number of organisms including man. It is clearly teratogenic in mammals and can cross the placental barrier at least in rats and the golden hamster, but it is believed to have only a limited mutagenic activity. Studies involving a direct comparison of the action of HU with other compounds suggest that the = C--NHOH moiety is responsible for its biological activity.