Dimethylthiourea inhibition of B16 melanoma growth and induction of phenotypic alterations; relationship to ATP levels

Identification and cloning of genes displaying elevated expression as a consequence of metastatic progression in human melanoma cells by rapid subtraction hybridization

Although extensively investigated, the complete repertoire of genes associated with and causative of metastasis remain largely unknown. We developed an efficient approach for identifying differentially expressed genes that involves rapid subtraction hybridization (RaSH) of cDNA clones prepared from two cell populations, a driver and a tester. This RaSH approach has previously documented high sensitivity and effectiveness in identifying genes that are differentially expressed as a function of induction of terminal differentiation in human melanoma cells, resistance or sensitivity to human immunodeficiency virus-1 (HIV-1) infection of human T cells and perturbation in gene expression in normal human fetal astrocytes infected with HIV-1 or treated with HIV-1 gp120 viral envelope glycoprotein or tumor necrosis factor-alpha (TNF-alpha). In the present study, RaSH has been applied to a metastatic melanoma model, which mimics the early events of metastasis in humans, comprising weakly metastatic vs. immunosuppressed newborn rat-selected highly metastatic variants. This has now resulted in the identification of eight genes displaying elevated expression in the high metastatic variants vs. normal immortal melanocytes or weakly metastatic parental clones. These include six known genes, 67-kDa laminin receptor (67LR), endothelin receptor B (ENDRB), Na+/K+-ATPase, Ku antigen, interleukin-receptor-associated kinase-1 (IRAK-1) and ribosomal protein RPLA, which may contribute to the complex process of melanoma metastasis. Additionally, two unknown genes (not reported in current databases) that may also impact on the metastatic phenotype have also been identified. These studies provide additional support of the use of the RaSH approach, in this application in the context of closely related variant cell lines with different metastatic potential, for effective differential gene identification and elucidate eight previously unrecognized genes whose role in melanoma progression to metastatic competence can now be scrutinized.

The myocardial profile of the cytosolic isozymes of creatine kinase is apparently not related to cyanosis in congenital heart disease

BACKGROUND

CKMB, the cardiac-specific heterodimer of cytosolic creatine-kinase (CK), is developmentally and physiologically regulated, tissue hypoxia being a proposed regulator. In patients with cyanotic heart disease the myocardium is perfused with partially saturated blood. We questioned whether the myocardium of cyanotic subjects contains higher proportions of CKMB.

MATERIALS AND METHODS

CK activity, the distribution of cytosolic CK isozymes, activity of lactic dehydrogenase (LDH), and tissue protein content were determined in obstructive tissues removed at corrective surgery of patients with congenital heart defects. Cyanotic (n = 13) and acyanotic (n = 12) subjects were compared.

RESULTS

In cyanotic and acyanotic patients, CK activity was 8.4 +/- 0.6 and 7.6 +/- 0.6 IU/mg protein and the proportion of CKMB was 21 +/- 1.4 and 22 +/- 2. 0% (mean +/- S.E.M), respectively. In the two groups of patients, the activity related to the B subunit corresponded to the steady-state level of the CKBmRNA. The tissue content of protein and the activities of CK and LDH were similar in cyanotic and acyanotic subjects and increased with the age.

CONCLUSIONS

The lack of difference in CKMB distribution between the cyanotic and acyanotic patients may either indicate that hypooxygenation is not a regulator of CK isozyme expression, or may be attributed to the already high proportion of this isozyme in hypertrophied, obstructive tissues. Recruitment of additional CKMB, in the cyanotic hearts, may thus not be required.

Antiproliferative and differentiating effects of benzodiazepine receptor ligands on B16 melanoma cells

In this study, we evaluated the effect of several ligands active at the central-type and peripheral-type benzodiazepine receptor (BzR) (clonazepam, diazepam, PK11195 and Ro5-4864) on the growth and differentiation of B16 melanoma cells. All tested BzR ligands were able to suppress proliferation of the cells at the micromolar range and in a concentration-dependent manner. However, agents selectively active at the peripheral-type BzR (PK11195 and Ro5-4864) exhibited more potent antiproliferative activity. In addition, the BzR ligands were demonstrated to affect the cell cycle by reducing the percent of cells in the S phase and increasing the percent in the G2/M phase. BzR ligands induced cellular phenotypic alterations, which have been previously shown to be associated with melanoma cell differentiation. These alterations included: marked morphological changes, enhancement of melanogenesis, lipid accumulation and increase in the activity of gamma glutamyl transpeptidase. All BzR ligands induced a marked reduction in the concentration of UTP and most of them did the same in GTP and CTP, while ATP levels were not significantly altered. In summary, BzR ligands (clonazepam, diazepam, PK11195 and Ro5-4864) were found to exert antitumor effects in B16 melanoma cells. These findings encourage further studies of a possible therapeutic potential of BzR ligands in treatment of melanoma.

Novobiocin modulates colchicine sensitivity in parental and multidrug-resistant B16 melanoma cells

The effect of the antibiotic agent novobiocin on the sensitivity of melanoma cells to colchicine and vinblastine was examined in drug-sensitive and drug-resistant B16 melanoma cells. A cell line COL/R was selected for colchicine resistance. The COL/R cell line (resistant to 80 ng/ml colchicine) was found to possess the multidrug-resistant (MDR) phenotype. The cells were shown to be cross-resistant to vinblastine and Adriamycin and to overexpress P glycoprotein. P glycoprotein activity was assessed by using the rhodamine 123 accumulation test. Rhodamine accumulation was markedly decreased in COL/R cells as compared to the parental B16 cells. Verapamil reversed drug resistance and increased rhodamine accumulation in COL/R cells. Novobiocin in combination with colchicine or vinblastine synergistically inhibited the proliferation of parental B16 cells. In COL/R cells, novobiocin markedly decreased colchicine resistance and increased rhodamine accumulation. These data show that novobiocin increases the sensitivity of both parental and MDR melanoma cells to microtubule-disrupting cytotoxic drugs.

Nude mouse model to study passive humoral immunotherapy directed against B16 F10 murine melanoma

A model to study passive humoral immunotherapy of experimental melanoma was generated by subcutaneous injection of B16 F10 murine melanoma cells in the midtail of BALB/C nude (nu/nu) mice. Mice were challenged with melanoma cells pretreated: (1) with complete culture medium, (2) with 10% adjuvant control serum, (3) with 10% anti-fECA (formalinized extracellular antigens) immune serum, or (4) with a monoclonal antibody (mAB H2-3-3) specific for the B700 melanoma-associated antigen. All control mice challenged with melanoma cells pretreated either with culture medium or with medium containing adjuvant control serum (Groups I and II) died during the observation period of 84 days. At day 84, 60% of the mice challenged with melanoma cells pretreated with anti-fECA immune serum (Group III) survived, as did 100% of the mice challenged with cells pretreated with mAb H2-3-3 (Group IV). Injection of melanoma cells pretreated with mAb H2-3-3 was associated with the greatest reduction of subsequent local tumor growth and the lowest number of metastatic lung tumors. The inhibitory effects of immune sera in vivo also correlated with in vitro effects of anti-fECA immune serum and mAb H2-3-3, determined on B16 F10 melanoma target cells using assays for DNA synthesis and antibody dependent cellular cytotoxicity (ADCC). In sum, this nude mouse model for the study of passive humoral immunotherapy of experimental melanoma was utilized to demonstrate significant protective effects against B16 F10 melanoma cell challenge by treatment with anti-fECA immune sera or a melanoma-specific monoclonal antibody.

Expression of autocrine motility factor receptor in serum- and protein-independent fibrosarcoma cells: implications for autonomy in tumor-cell motility and metastasis

The motile response of serum-dependent (Gc-4 SD) and protein-independent (Gc-4 PF) murine fibrosarcoma cells to monoclonal antibody (MAb) that binds to gp78 a cell-surface receptor (M(r) 78,000) for an autocrine motility factor (AMF) was analyzed. The Gc-4 PF cells responded to the anti-gp78 by increased motility in vitro (3-fold) and increased lung colonization in vivo (8- to 20-fold), while the serum-dependent counterpart failed to respond to motile stimulation both in vitro and in vivo. Immuno-analysis of cell-surface expression and cell extracts revealed a smaller amount of gp78 in Gc-4 SD cells than in Gc-4 PF cells. Both cell lines secrete an equal amount of AMF to the culture media. Our results suggest that protein-free culture of Gc-4 PF cells is associated with high response to AMF and with high expression of its receptor, and that autonomous motile regulation may play a role in tumor dissemination.

Generation of cytotoxic antibodies to the B16 murine melanoma using a formalinized vaccine

The goal of our experiments was to determine the extent to which the humoral response to a melanoma vaccine elicits the production of cytotoxic antibodies in tumor-challenged mice. Mice were immunized with a vaccine produced from formalinized extracellular antigens (FECA) derived from B16 F10 melanomas. The production of antibodies that recognized the vaccine preparation was determined by ELISA, as was their cross-reactivity with the B700 melanoma antigen. The antibodies were shown to be anti-proliferative by inhibition of tritiated thymidine incorporation into the DNA of cultured target cells and cytotoxic by assays for complement-mediated and antibody-dependent cellular cytotoxicity. Flow cytometric analyses indicated that approximately 60% of the target cells specifically bound antibody from the immune sera. These results confirm that B700 is a significant antigenic component of the FECA vaccine, and provide encouragement for this approach to developing useful melanoma vaccines.

Novobiocin-induced anti-proliferative and differentiating effects in melanoma B16

The antibiotic drug novobiocin was evaluated for its anti-tumour properties in B16 melanoma cells. Novobiocin is shown to inhibit melanoma B16 cell proliferation. The anti-proliferative effect was gradually reversible upon removal of novobiocin from the culture medium. Growth inhibition by novobiocin was accompanied by phenotypic alterations, that included morphological changes, lipid accumulation and marked increases in the activities of NADPH cytochrome c reductase and gamma glutamyl transpeptidase. In vivo administration of repeated i.p. doses of novobiocin, to mice implanted with B16 melanoma cells resulted in growth retardation. The combined treatment of the B16 melanoma cells with novobiocin and other chemical inducers of differentiation was examined in a cell growth assay. Novobiocin and sodium butyrate inhibited cell growth in a near additive manner, while combination of novobiocin with the GTP-depleting agents, tiazofurin or mycophenolic acid resulted in a synergistic decrease in cell growth. Our results support the contention further that novobiocin and other differentiating agents might be of potential value in melanoma therapy.