Cell type-specific anti-cancer properties of valproic acid: independent effects on HDAC activity and Erk1/2 phosphorylation.

BACKGROUND: The anti-epileptic drug valproic acid (VPA) has attracted attention as an anti-cancer agent. METHODS: The present study investigated effects of VPA exposure on histone deacetylase (HDAC) inhibition, cell growth, cell speed, and the degree of Erk1/2 phosphorylation in 10 cell lines (BT4C, BT4Cn, U87MG, N2a, PC12-E2, CSML0, CSML100, HeLa, L929, Swiss 3T3). RESULTS: VPA induced significant histone deacetylase (HDAC) inhibition in most of the cell lines, but the degree of inhibition was highly cell type-specific. Moreover, cell growth, motility and the degree of Erk1/2 phosphorylation were inhibited, activated, or unaffected by VPA in a cell type-specific manner. Importantly, no relationship was found between the effects of VPA on HDAC inhibition and changes in the degree of Erk1/2 phosphorylation, cell growth, or motility. In contrast, VPA-induced modulation of the MAPK pathway downstream of Ras but upstream of MEK (i.e., at the level of Raf) was important for changes in cell speed. CONCLUSIONS: These results suggest that VPA can modulate the degree of Erk1/2 phosphorylation in a manner unrelated to HDAC inhibition and emphasize that changes in the degree of Erk1/2 phosphorylation are also important for the anti-cancer properties of VPA.

Enhanced antitumor efficacy of clinical-grade vasculature-targeted liposomal doxorubicin.

PURPOSE: In vivo evaluation of good manufacturing practice-grade targeted liposomal doxorubicin (TVT-DOX), bound to a CD13 isoform expressed on the vasculature of solid tumors, in human tumor xenografts of neuroblastoma, ovarian cancer, and lung cancer. EXPERIMENTAL DESIGN: Mice were implanted with lung, ovarian, or neuroblastoma tumor cells via the pulmonary, peritoneal, or orthotopic (adrenal gland) routes, respectively, and treated, at different days post inoculation, with multiple doses of doxorubicin, administered either free or encapsulated in untargeted liposomes (Caelyx) or in TVT-DOX. The effect of TVT-DOX treatment on tumor cell proliferation, viability, apoptosis, and angiogenesis was studied by immunohistochemical analyses of neoplastic tissues and using the chick embryo chorioallantoic membrane assay. RESULTS: Compared with the three control groups (no doxorubicin, free doxorubicin, or Caelyx), statistically significant improvements in survival was seen in all three animal models following treatment with 5 mg/kg (maximum tolerated dose) of TVT-DOX, with long-term survivors occurring in the neuroblastoma group; increased survival was also seen at a dose of 1.7 mg/kg in mice bearing neuroblastoma or ovarian cancer. Minimal residual disease after surgical removal of neuroblastoma primary mass, and the enhanced response to TVT-DOX, was visualized and quantified by bioluminescence imaging and with magnetic resonance imaging. When treated with TVT-DOX, compared with Caelyx, all three tumor models, as assayed by immunohistochemistry and chorioallantoic membrane, showed statistically significant reductions in cell proliferation, blood vessel density, and microvessel area, showing increased cell apoptosis. CONCLUSION: TVT-DOX should be evaluated as a novel angiostatic strategy for adjuvant therapy of solid tumors.

Binding and internalization of NGR-peptide-targeted liposomal doxorubicin (TVT-DOX) in CD13-expressing cells and its antitumor effects.

In an effort to develop new agents and molecular targets for the treatment of cancer, aspargine-glycine-arginine (NGR)-targeted liposomal doxorubicin (TVT-DOX) is being studied. The NGR peptide on the surface of liposomal doxorubicin (DOX) targets an aminopeptidase N (CD13) isoform, specific to the tumor neovasculature, making it a promising strategy. To further understand the molecular mechanisms of action, we investigated cell binding, kinetics of internalization as well as cytotoxicity of TVT-DOX in vitro. We demonstrate the specific binding of TVT-DOX to CD13-expressing endothelial [human umbilical vein endothelial cells (HUVEC) and Kaposi sarcoma-derived endothelial cells (SLK)] and tumor (fibrosarcoma, HT-1080) cells in vitro. Following binding, the drug was shown to internalize through the endosomal pathway, eventually leading to the localization of doxorubicin in cell nuclei. TVT-DOX showed selective toxicity toward CD13-expressing HUVEC, sparing the CD13-negative colon-cancer cells, HT-29. Additionally, the nontargeted counterpart of TVT-DOX, Caelyx, was less cytotoxic to the CD13-positive HUVECs demonstrating the advantages of NGR targeting in vitro. The antitumor activity of TVT-DOX was tested in nude mice bearing human prostate-cancer xenografts (PC3). A significant growth inhibition (up to 60%) of PC3 tumors in vivo was observed. Reduction of tumor vasculature following treatment with TVT-DOX was also apparent. We further compared the efficacies of TVT-DOX and free doxorubicin in the DOX-resistant colon-cancer model, HCT-116, and observed the more pronounced antitumor effects of the TVT-DOX formulation over free DOX. The potential utility of TVT-DOX in a variety of vascularized solid tumors is promising.

Automated in vitro screening of teratogens.

We present a new in vitro assay for screening of potential teratogens, based on staining of cultured mouse fibroblastoid L929 cells for the determination of number of live and dead cells and of cell morphology, employing automatic video recording, followed by detection of the stained specimen and calculation of endpoint values by the use of a computerized microscope workstation. Ten different parameters were combined empirically into a single index describing general alterations in cell morphology, and, subsequently, measurements of alterations in morphology and proliferation were combined to produce a single empirical index aimed at predicting teratogenic potency. The assay was employed in two different laboratories on 10 coded compounds; 7 compounds that have demonstrated in vivo teratogenic potentials: valproic acid (VPA), pentyl-4-yn-VPA, retinoic acid (RA), 13-cis-RA, AM580, thalidomide, and alpha-EM12 and 3 compounds for which no teratogenic potential has been demonstrated: isobutyl-4-yn-VPA, phytanic acid, and beta-EM12. Within each of the three groups of compounds the nonteratogens generally caused smaller alterations in cell morphology than the teratogens, although the effects of thalidomide and related compounds generally were minor or insignificant. The data support the hypothesis that cell morphology and proliferation in combination with other endpoints may be employed for in vitro screenings of potential teratogens, although studies of additional compounds are needed in order to establish the general validity of the procedure.

NCAM regulates cell motility.

Cell migration is required during development of the nervous system. The regulatory mechanisms for this process, however, are poorly elucidated. We show here that expression of or exposure to the neural cell adhesion molecule (NCAM) strongly affected the motile behaviour of glioma cells independently of homophilic NCAM interactions. Expression of the transmembrane 140 kDa isoform of NCAM (NCAM-140) caused a significant reduction in cellular motility, probably through interference with factors regulating cellular attachment, as NCAM-140-expressing cells exhibited a decreased attachment to a fibronectin substratum compared with NCAM-negative cells. Ectopic expression of the cytoplasmic part of NCAM-140 also inhibited cell motility, presumably via the non-receptor tyrosine kinase p59(fyn) with which NCAM-140 interacts. Furthermore, we showed that the extracellular part of NCAM acted as a paracrine inhibitor of NCAM-negative cell locomotion through a heterophilic interaction with a cell-surface receptor. As we showed that the two N-terminal immunoglobulin modules of NCAM, which are known to bind to heparin, were responsible for this inhibition, we presume that this receptor is a heparan sulfate proteoglycan. A model for the inhibitory effect of NCAM is proposed, which involves competition between NCAM and extracellular components for the binding to membrane-associated heparan sulfate proteoglycan.