PARP1 allows proper telomere replication through TRF1 poly (ADP-ribosyl)ation and helicase recruitment

Telomeres are nucleoprotein structures at eukaryotic chromosome termini. Their stability is preserved by a six-protein complex named shelterin. Among these, TRF1 binds telomere duplex and assists DNA replication with mechanisms only partly clarified. Here we found that poly (ADP-ribose) polymerase 1 (PARP1) interacts and covalently PARylates TRF1 in S-phase modifying its DNA affinity. Therefore, genetic and pharmacological inhibition of PARP1 impairs the dynamic association of TRF1 and the bromodeoxyuridine incorporation at replicating telomeres. Inhibition of PARP1 also affects the recruitment of WRN and BLM helicases in TRF1 containing complexes during S-phase, triggering replication-dependent DNA-damage and telomere fragility. This work unveils an unprecedented role for PARP1 as a "surveillant" of telomere replication, which orchestrates protein dynamics at proceeding replication fork.

Targeted therapy for brain tumours: role of PARP inhibitors

The prognosis of malignant glioma and metastatic brain tumours is still extremely poor, despite recent advances in therapeutic strategies with molecular-targeted agents. Poly(ADP-ribose) polymerase (PARP) inhibitors are a promising, novel class of anticancer drugs to be used either as single agents or in combination with chemotherapy and radiotherapy. PARP-1 and PARP-2 are the only PARP proteins that bind to DNA single strand breaks (SSBs), facilitating the repair process by the base excision repair. For this reason, PARPs have been extensively investigated as targets of novel drugs that may be used to enhance the antitumour activity of SSBs inducing agents, such as the methylating compound temozolomide, which is the drug of choice for glioblastoma, or ionizing radiations. Moreover, PARP inhibitors exert cytotoxic effects in monotherapy in BRCA mutated tumours, which are defective in the homologous recombination (HR) repair. Finally, recent studies have shown that inhibition of PARP function might also induce anti-angiogenic effects which might contribute to impair tumour growth. Many clinical trials with PARP inhibitors are ongoing for the treatment of a variety of advanced solid tumours, including primary or secondary brain tumours. This review discusses the implications of targeting PARP on the design of new treatment regimens.

Smad-interacting protein-1 and microRNA 200 family define a nitric oxide-dependent molecular circuitry involved in embryonic stem cell mesendoderm differentiation

OBJECTIVE

Smad-interacting protein-1 (Sip1/ZEB2) is a transcriptional repressor of the telomerase reverse transcriptase catalytic subunit (Tert) and has recently been identified as a key regulator of embryonic cell fate with a phenotypic effect similar, in our opinion, to that reported for nitric oxide (NO). Remarkably, SIP1/ZEB2 is a known target of the microRNA 200 (miR-200) family. In this light, we postulated that Sip1/ZEB2 and the miR-200 family could play a role during the NO-dependent differentiation of mES.

METHODS AND RESULTS

The results of the present study show that Sip1/ZEB2 expression is downregulated during the NO-dependent expression of mesendoderm and early cardiovascular precursor markers, including Flk1 and CXCR4 in mES. Coincidently, members of the miR-200 family, namely miR-429, -200a, -200b, and -200c, were transcriptionally induced in parallel to mouse Tert. This regulation occurred at the level of chromatin. Remarkably, miR-429/miR-200a overexpression or Sip1/ZEB2 knockdown by short hairpin RNA interference elicited a gene expression pattern similar to that of NO regardless of the presence of leukemia inhibitory factor.

CONCLUSIONS

These results are the first demonstrating that the miR-200 family and Sip1/ZEB2 transcription factor are regulated by NO, indicating an unprecedented molecular circuitry important for telomerase regulation and early differentiation of mES.

Inhibition of PARP activity by PJ-34 leads to growth impairment and cell death associated with aberrant mitotic pattern and nucleolar actin accumulation in M14 melanoma cell line

The capability of PARP activity inhibitors to prevent DNA damage recovery suggested the use of these drugs as chemo- and radio-sensitisers for cancer therapy. Our research, carried out on cultured human M14 melanoma cells, was aimed to examine if PJ-34, a potent PARP activity inhibitor of second generation, was per se able to affect the viability of these cancer cells without any DNA damaging agents. Using time-lapse videomicroscopy, we evidenced that 10 microM PJ-34 treatment induced severe mitotic defects leading to dramatic reduction of cell proliferation and to cell death. PJ-34 cytotoxic effect was further confirmed by analysis of cell viability and clonogenic assay. Absence of canonic apoptosis markers allowed us to exclude this kind of cell death. No single and/or double stranded DNA damage was evidenced. Immunofluorescence analysis showed an aberrant mitotic scenario in several cells and subsequent multinucleation suggesting an atypical way for cells to die: the mitotic catastrophe. The detection of aberrant accumulation of polymerised actin inside the nucleolus was noteworthy. Taken together, our results demonstrate that, targeting PARP activity by PJ-34, cancer cell survival is affected independently of DNA damage repair. Two findings are remarkable: (a) cisplatin concentration can be reduced by three quarters if it is followed by treatment with 10 microM PJ-34 for 24 h to obtain the same cytotoxic effect; (b) effects dependent on PJ-34 treatment are reversible. Our data suggest that, to reduce the harm done to non-tumour cells during chemotherapy with cisplatin, the latter could be coupled with PJ-34 treatment.

Involvement of hTERT in apoptosis induced by interference with Bcl-2 expression and function

Here, we investigated the role of telomerase on Bcl-2-dependent apoptosis. To this end, the 4625 Bcl-2/Bcl-xL bispecific antisense oligonucleotide and the HA14-1 Bcl-2 inhibitor were used. We found that apoptosis induced by 4625 oligonucleotide was associated with decreased Bcl-2 protein expression and telomerase activity, while HA14-1 triggered apoptosis without affecting both Bcl-2 and telomerase levels. Interestingly, HA14-1 treatment resulted in a profound change from predominantly nuclear to a predominantly cytoplasmic localization of hTERT. Downregulation of endogenous hTERT protein by RNA interference markedly increased apoptosis induced by both 4625 and HA14-1, while overexpression of wild-type hTERT blocked Bcl-2-dependent apoptosis in a p53-independent manner. Catalytically and biologically inactive hTERT mutants showed a similar behavior as the wild-type form, indicating that hTERT inhibited the 4625 and HA14-1-induced apoptosis regardless of telomerase activity and its ability to lengthening telomeres. Finally, hTERT overexpression abrogated 4625 and HA14-1-induced mitochondrial dysfunction and nuclear translocation of hTERT. In conclusion, our results demonstrate that hTERT is involved in mitochondrial apoptosis induced by targeted inhibition of Bcl-2.

Telomerase activity, apoptosis and cell cycle progression in ataxia telangiectasia lymphocytes expressing TCL1

Individuals affected by ataxia telangiectasia (AT) have a marked susceptibility to cancer. Ataxia telangiectasia cells, in addition to defects in cell cycle checkpoints, show dysfunction of apoptosis and of telomeres, which are both thought to have a role in the progression of malignancy. In 1-5% of patients with AT, clonal expansion of T lymphocytes carrying t(14;14) chromosomal translocation, deregulating TCL1 gene(s), has been described. While it is known that these cells can progress with time to a frank leukaemia, the molecular pathway leading to tumorigenesis has not yet been fully investigated. In this study, we compared AT clonal cells, representing 88% of the entire T lymphocytes (AT94-1) and expressing TCL1 oncogene (ATM(-) TCL1(+)), cell cycle progression to T lymphocytes of AT patients without TCL1 expression (ATM(-) TCL1(-)) by analysing their spontaneous apoptosis rate, spontaneous telomerase activity and telomere instability. We show that in ATM(-) TCL1(+) lymphocytes, apoptosis rate and cell cycle progression are restored back to a rate comparable with that observed in normal lymphocytes while telomere dysfunction is maintained.

Bcl-2 has differing effects on the sensitivity of breast cancer cells depending on the antineoplastic drug used

The aim of this paper was to evaluate the role of bcl-2 in the susceptibility of the MCF7 ADR human breast carcinoma line overexpressing the P-170 glycoprotein (P-170) to various drugs. The sensitivity to four multidrug resistance (MDR)-related drugs (doxorubicin (ADR), vincristine (VCR), vinblastine (VBL), actinomycin D (ACTD)) and three MDR-non-related drugs (cisplatin (DDP), bischloroethylnitrosourea (BCNU), 5-fluorouracil (5-FU)) was evaluated by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay in three bcl-2-overexpressing clones obtained from the MCF7 ADR line. We found that the bcl-2-overexpressing clones show increased resistance to DDP and BCNU, while no difference to 5-FU were observed between the control cells and bcl-2 transfectants. Surprisingly, bcl-2-overexpressing clones displayed an increased sensitivity compared with the control cells to the MDR-related drugs ADR, VCR, VBL and ACTD. Focusing on DDP and ADR, we found that the increased resistance of the bcl-2 transfectants to DDP was correlated to their ability to prevent apoptosis, while the enhanced sensitivity to ADR was associated with an increased ADR accumulation and a decreased ADR efflux. Moreover, while bcl-2 overexpression does not induce changes in P-170 glycoprotein expression, it did induce a reduction of the adenosine triphosphate (ATP) levels and basal protein kinase C (PKC) activity, both of which have a crucial role in the regulation of the MDR phenotype. In conclusion, the effect of bcl-2 on antineoplastic sensitivity observed in this study underscores the idea that bcl-2 may have distinct biological effects depending on the anticancer drug used.

relA over-expression reduces tumorigenicity and activates apoptosis in human cancer cells

We previously demonstrated that bcl-2 over-expression increases the malignant behaviour of the MCF7 ADR human breast cancer cell line and enhances nuclear factor-kappa B (NF-kappa B) transcriptional activity. Here, we investigated the direct effect of increased NF-kB activity on the tumorigenicity of MCF7 ADR cells by over-expressing the NF-kappa B subunit relA/p65. Surprisingly, our results demonstrated that over-expression of relA determines a considerable reduction of the tumorigenic ability in nude mice as indicated by the tumour take and the median time of tumour appearance. In vitro studies also evidenced a reduced cell proliferation and the activation of the apoptotic programme after relA over-expression. Apoptosis was associated with the production of reactive oxygen species, and the cleavage of the specific substrate Poly-ADP-ribose-polymerase. Our data indicate that there is no general role for NF-kappa B in the regulation of apoptosis and tumorigenicity. In fact, even though inhibiting NF-kappa B activity has been reported to be lethal to tumour cells, our findings clearly suggest that an over-induction of nuclear NF-kappa B activity may produce the same effect.

Bcl-2 overexpression decreases BCNU sensitivity of a human glioblastoma line through enhancement of catalase activity

The aim of this study was to evaluate the role of bcl-2 in 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) sensitivity of the ADFS human glioblastoma cell line in vitro and in vivo. To this end, the ADFS line expressing a low level of the bcl-2 protein was transfected with a bcl-2 expression vector. We found that bcl-2 overexpressing clones were less sensitive to in vitro BCNU treatment than the control clone. Cell cycle analysis demonstrated that while BCNU induced a consistent block in S/G2-M phases of the cell cycle in the control clone, it did not affect the cell cycle phase distribution of the two bcl-2 transfectants. The different sensitivity to BCNU was unrelated to the ability of bcl-2 to inhibit apoptosis, while bcl-2 appeared to protect bcl-2 transfectants from BCNU toxicity through an increase of catalase activity. The ability of the catalase inhibitor, sodium azide, to increase the BCNU sensitivity of the bcl-2 transfectants to levels of the BCNU-treated control clone substantiated the role of the catalase activity. The effect of bcl-2 in reducing sensitivity to BCNU was also confirmed by in vivo experiments. Xenografts of bcl-2 overexpressing tumors were less sensitive to BCNU treatment than xenografts originating from control cells.

c-Myc down-regulation increases susceptibility to cisplatin through reactive oxygen species-mediated apoptosis in M14 human melanoma cells

Our aim in this work was to define the role of c-Myc in the susceptibility to cisplatin [cis-diamminedichloroplatinum(II) (CDDP)] in human melanoma cells. Two M14 melanoma cell clones obtained by transfection and expressing six to ten times lower c-Myc protein levels than the parental cells and the control clone were employed. Analysis of survival curves demonstrates an increase in CDDP sensitivity in c-Myc low-expressing clones if compared with the control clone and the parental line. The enhanced sensitivity is unrelated to the impairment in enzymatic DNA repair activity. Cell cycle analysis demonstrates that although the control clone is able to completely recover from the CDDP-induced S-G(2)/M block, this arrest is prolonged in c-Myc low-expressing clones and a fraction of cells undergoes apoptosis. Although no changes in P53, Bax, Bcl-2, and Bcl-x(L/S) protein levels are observed, apoptosis is associated with the formation of reactive oxygen species (ROS), activation of caspase-1, caspase-3 and cleavage of the specific caspase substrate poly-ADP-ribose polymerase. The use of the antioxidant N-acetyl cysteine and caspase inhibitors prevents CDDP-induced apoptosis in c-Myc low-expressing clones, demonstrating that ROS, caspase-1, and caspase-3 are required for apoptotic cell death. Moreover, ROS generation depends on caspase-1-like activation because the Ac-YVAD-cho inhibitor abrogates CDDP-induced ROS in the c-Myc low-expressing clones.

Encapsulation of c-myc antisense oligodeoxynucleotides in lipid particles improves antitumoral efficacy in vivo in a human melanoma line

Phosphorothioate c-myc antisense oligodeoxynucleotides [S]ODNs (free INX-6295) were encapsulated in a new liposome formulation and the antitumor activity was compared to the unencapsulated antisense in a human melanoma xenograft. The systemic administration of INX-6295 encapsulated in stabilized antisense lipid particles (SALP INX-6295) improved plasma AUC (area under the plasma concentration-time curve) and initial half-life of free INX-6295, resulting in a significant enhancement in tumor accumulation and improvement in tumor distribution of antisense oligodeoxynucleotides. Animals treated with SALP INX-6295 exhibited a prolonged reduction of c-myc expression, reduced tumor growth and increased mice survival. When administered in combination with cisplatin (DDP), SALP INX-6295 produced a complete tumor regression in approximately 30% of treated mice, which persisted for at least 60 days following the first cycle of treatment. Finally, the median survival of mice treated with DDP/SALP INX-6295 increased by 105% compared to 84% for animals treated with the combination DDP/free INX-6295. These data indicate that the biological activity and the therapeutic efficacy of c-myc antisense therapy may be improved when these agents are administered in lipid-based delivery systems.

bcl-2 over-expression enhances NF-kappaB activity and induces mmp-9 transcription in human MCF7(ADR) breast-cancer cells

bcl-2 expression is often associated with poor prognosis in several types of tumors; however, the role of this molecule in breast cancer is still controversial. We found earlier that over-expression of bcl-2 in a human breast-cancer cell line (MCF7(ADR)) enhances its tumorigenicity and metastatic potential by inducing metastasis-associated properties such as increased secretion of the matrix metalloproteinase-9 (mmp-9). In the present study, we investigated the effect of bcl-2 over-expression on the activity of the transcription factor NF-kappaB, an important regulator of genes involved in tumor progression and invasion. Transient transfection experiments indicate that over-expression of bcl-2 in the MCF7(ADR) cell line, enhances NF-kappaB-dependent transcriptional activity. Mobility-shift analysis revealed an increase of NF-kappaB DNA-binding in bcl-2-over-expressing clones that correlated with lower levels of the NF-kappaB cytoplasmic inhibitor IkappaBalpha. Moreover, point mutations of 2 highly conserved residues within the BH1 and BH2 domains that abrogate the interaction of bcl-2 with bax, or deletion of the N-terminal BH4 domain, completely eliminate the ability of this molecule to up-regulate NF-kappaB-dependent transactivation. Since mmp-9 is a NF-kappaB-regulated gene, we also investigated whether bcl-2 over-expression up-regulated mmp-9 transcription. We found that induction of mmp-9 mRNA correlates with the activation of an mmp-9-promoter-reporter-gene construct in transient transfection assay, and a mutation of the (-600)mmp-9-NF-kappaB binding element abolishes this effect. The overall data indicate that bcl-2-mediated regulation of NF-kappaB-transcription-factor activity may represent an important mechanism for the promotion of malignant behavior in MCF-7(ADR) cells.

bcl-2 over-expression enhances NF-kappaB activity and induces mmp-9 transcription in human MCF7(ADR) breast-cancer cells

bcl-2 expression is often associated with poor prognosis in several types of tumors; however, the role of this molecule in breast cancer is still controversial. We found earlier that over-expression of bcl-2 in a human breast-cancer cell line (MCF7(ADR)) enhances its tumorigenicity and metastatic potential by inducing metastasis-associated properties such as increased secretion of the matrix metalloproteinase-9 (mmp-9). In the present study, we investigated the effect of bcl-2 over-expression on the activity of the transcription factor NF-kappaB, an important regulator of genes involved in tumor progression and invasion. Transient transfection experiments indicate that over-expression of bcl-2 in the MCF7(ADR) cell line, enhances NF-kappaB-dependent transcriptional activity. Mobility-shift analysis revealed an increase of NF-kappaB DNA-binding in bcl-2-over-expressing clones that correlated with lower levels of the NF-kappaB cytoplasmic inhibitor IkappaBalpha. Moreover, point mutations of 2 highly conserved residues within the BH1 and BH2 domains that abrogate the interaction of bcl-2 with bax, or deletion of the N-terminal BH4 domain, completely eliminate the ability of this molecule to up-regulate NF-kappaB-dependent transactivation. Since mmp-9 is a NF-kappaB-regulated gene, we also investigated whether bcl-2 over-expression up-regulated mmp-9 transcription. We found that induction of mmp-9 mRNA correlates with the activation of an mmp-9-promoter-reporter-gene construct in transient transfection assay, and a mutation of the (-600)mmp-9-NF-kappaB binding element abolishes this effect. The overall data indicate that bcl-2-mediated regulation of NF-kappaB-transcription-factor activity may represent an important mechanism for the promotion of malignant behavior in MCF-7(ADR) cells.

Bcl-2 overexpression and hypoxia synergistically act to modulate vascular endothelial growth factor expression and in vivo angiogenesis in a breast carcinoma line

We have previously demonstrated that bcl-2 overexpression enhances the metastatic potential of the MCF7 ADR human breast cancer cell line resistant to adriamycin by inducing metastasis-associated properties. To further elucidate the relationship between bcl-2 expression and the metastatic potential of the MCF7 ADR line, we evaluated whether bcl-2 could be also involved in the modulation of the angiogenic phenotype. Four bcl-2-overexpressing clones, a control transfectant clone, and the MCF7 ADR parental line were used for in vitro and in vivo experiments. Bcl-2 overexpression enhanced the synthesis of the hypoxia-stimulated VEGF protein and mRNA. Northern blot analysis demonstrated an increased VEGF mRNA expression in bcl-2-overexpressing clones, and reverse transcription-polymerase chain reaction showed higher levels of the VEGF(121) and VEGF(165) mRNA isoforms, which are the most active in eliciting angiogenesis. When incorporated into matrigel, supernatants of bcl-2-transfected cells cultured under hypoxic conditions induced an increased angiogenic response in C57BL/6 mice compared with that of control clone. Tumors from bcl-2 transfectants demonstrated increased VEGF expression and neovascularization as compared to the parental line, whereas the apoptosis in in vivo xenografts was similar in control and bcl-2 transfectants. The effect of bcl-2 on angiogenesis was not mediated by p53 protein. These results demonstrate that bcl-2 and hypoxia can act synergistically to modulate VEGF expression and the in vivo angiogenic response in the MCF7 ADR line.

Increase of cisplatin sensitivity by c-myc antisense oligodeoxynucleotides in a human metastatic melanoma inherently resistant to cisplatin

In this study, we evaluated the role of the c-myc oncogene in response to cisplatin (DDP) treatment using two melanoma lines derived from the primary tumor (LP) and metastatic lymph node (LM) of the same patient. These cell lines, which retain the phenotypic profile of the original tumors, were studied for growth behavior, expression of c-Myc oncoprotein, and HLA-I antigen. The LM line shows a higher tumorigenic ability, an increased expression of c-Myc protein, and a lack of HLA-I antigen, compared with the LP line. In addition, LP tumor was relatively sensitive to DDP administration, whereas LM tumor was resistant to DDP treatment. To verify whether the increased c-Myc expression observed in the LM line might be responsible for DDP resistance, a c-myc antisense phosphorothioate oligodeoxynucleotide ([S]ODN) was used to down-regulate c-Myc expression. The administration of DDP plus c-myc antisense [S]ODNs produced a decrease in c-Myc protein levels of approximately 50%, accompanied by a tumor weight inhibition of 65%, similar to that obtained when the sensitive line was treated with DDP alone (tumor weight inhibition = 70%). Analysis of apoptosis demonstrated that the sensitivity to DDP of the LP line was related to the ability of tumor cells to undergo apoptosis. Conversely, DDP treatment was not able to induce apoptosis in the LM line, whereas apoptosis was evident both after treatment with c-myc antisense [S]ODNs alone and, more extensively, in combination with DDP. Taken together, these results clearly indicate an important role of c-myc oncogene in the resistance of melanoma to DDP and demonstrate that treatment with c-myc antisense [S]ODN sensitizes a human melanoma line to DDP treatment.

bcl-2 inhibits mitochondrial metabolism and lonidamine-induced apoptosis in adriamycin-resistant MCF7 cells

Lonidamine (LND), a selective inhibitor of the energy metabolism of tumor cells, induces apoptosis, independently of the p53 gene, in the adriamycin(ADR)-resistant MCF7 breast-cancer cell line (MCF7 ADR). On the contrary, LND fails to activate the apoptotic program in the parental MCF7-sensitive cell line (MCF7 WT). The extent of bcl-2 expression might account for the different effect of LND on these cell lines. In fact, the MCF7 ADR line shows a low level of bcl-2 protein, whereas MCF7 WT expresses a high level of bcl-2. We therefore investigated the relationship between the amount of bcl-2 and the ability of LND to induce apoptosis, using 4 clones over-expressing bcl-2. The effect of bcl-2 on the energy metabolism was also evaluated. We demonstrated that over-expression of bcl-2 inhibited LND-induced apoptosis, while reducing 14CO2 production, oxygen uptake and ATP content, whereas aerobic lactate production was essentially unaffected. In addition, LND decreased the oxidative metabolism of the MCF7 ADR cells to a greater extent than it did in the bcl-2 transfectants.

Increase of BCNU sensitivity by wt-p53 gene therapy in glioblastoma lines depends on the administration schedule

In this article, we investigated the effect induced by the reintroduction of wild-type p53 (wt-p53) protein on BCNU sensitivity in the ADF glioblastoma line. Using a wt-p53 recombinant adenovirus (Ad-p53), we demonstrated that exogenous wt-p53 expression was able to increase the sensitivity to BCNU in ADF cells. Interestingly, this effect was more evident when Ad-p53 infection was performed after BCNU treatment compared with the opposite sequence. To understand the biological basis of these different behaviors, we analyzed the cell cycle of the differently treated cells. We found that Ad-p53 infection induced a persistent accumulation of cells in the G0/G1 phase while, as expected, BCNU induced a block in the G2-M phase. Ad-p53-->BCNU sequence did not significantly modify the cell cycle profile in respect of Ad-p53 infected cells. In contrast, BCNU-->Ad-p53 sequence provoked G2-M arrest similar to that observed after treatment with BCNU alone, but prevented the later recovery of the cells through the cell cycle, by driving the cells to apoptotic death. These results demonstrate that the administration sequence is important to increase drug sensitivity. To generalize the phenomenon observed on ADF line, the antiproliferative effect of the two different schedules was analyzed on other glioblastoma lines (A172, CRS-A2, U373MG) with different BCNU sensitivity and p53 status. The data obtained confirm that the wt-p53 gene transfer enhances BCNU sensitivity in glioblastoma cells depending on the administration sequence.

N-methylformamide induces changes on adhesive properties and lung-colonizing potential of M14 melanoma cells

We have studied whether N-methylformamide can affect the expression pattern of adhesion molecules and the attachment behaviour of M14 human melanoma cells. The role of N-methylformamide on experimental and spontaneous pulmonary metastases from M14 cells in nude mice was also investigated. We demonstrate that N-methylformamide in vitro pretreatment of M14 cells, although inducing a significant increase in the expression of alpha2beta1, alpha6beta1 and alpha(v)beta3 integrin receptors, slightly modifies alpha5beta1 heterodimer and beta1 subunit expression. After this modulation, enhancement of cell adhesion to laminin, collagen I, vitronectin and fibrinogen, which is blocked by specific anti-integrin antibodies, also occurs. No changes in binding to fibronectin are observed. In vitro N-methylformamide pretreatment also results in an increased number of experimental nodules and in a decrease in spontaneous metastases. Moreover, in vivo treatment with N-methylformamide significantly reduces the number of spontaneous metastases. Collectively, these data show that N-methylformamide modulates the expression of some adhesion receptors, cell adhesion to laminin, collagen I, vitronectin and fibrinogen as well as the metastatic behaviour of M14 cells. Our data also suggest that the effect of N-methylformamide might be evaluated in combination with antineoplastic agents for the treatment of human melanoma.

Bcl-2 overexpression enhances the metastatic potential of a human breast cancer line

Bcl-2 protein has been shown to contribute to oncogenesis because it can transform and immortalize cells in cooperation with c-myc, ras, or viral genes. However, in vivo studies have not yet established whether bcl-2 can play a role in metastasis. Here we investigate the potential metastatic role of bcl-2. We introduced the human bcl-2 gene into a low bcl-2 expressing human breast cancer cell line MCF7 ADR. We demonstrate that two bcl-2 overexpressing clones injected intravenously or intramuscularly into nude mice induce a significantly higher number of experimental and spontaneous lung metastases compared to the control transfectant clone. We demonstrate that bcl-2 overexpressing clones are more invasive and migratory in response to chemotactic stimuli than the control transfectant clone. Furthermore, zymographic analysis shows that secretion of 72 and 92 kDa gelatinases increases in the two bcl-2 overexpressing transfectants. Tumors originating from bcl-2 overexpressing clones also show a decrease in the latency period of tumor appearance. In conclusion, our data show that bcl-2 overexpression enhances both tumorigenicity and metastatic potential of MCF7 ADR cells by inducing metastasis-associated properties.

Lonidamine induces apoptosis in drug-resistant cells independently of the p53 gene

Lonidamine, a dichlorinated derivative of indazole-3-carboxylic acid, was shown to play a significant role in reversing or overcoming multidrug resistance. Here, we show that exposure to 50 microg/ml of lonidamine induces apoptosis in adriamycin and nitrosourea-resistant cells (MCF-7 ADR(r) human breast cancer cell line, and LB9 glioblastoma multiform cell line), as demonstrated by sub-G1 peaks in DNA content histograms, condensation of nuclear chromatin, and internucleosomal DNA fragmentation. Moreover, we find that apoptosis is preceded by accumulation of the cells in the G0/G1 phase of the cell cycle. Interestingly, lonidamine fails to activate the apoptotic program in the corresponding sensitive parental cell lines (ADR-sensitive MCF-7 WT, and nitrosourea-sensitive LI cells) even after long exposure times. The evaluation of bcl-2 protein expression suggests that this different effect of lonidamine treatment in drug-resistant and -sensitive cell lines might not simply be due to dissimilar expression levels of bcl-2 protein. To determine whether the lonidamine-induced apoptosis is mediated by p53 protein, we used cells lacking endogenous p53 and overexpressing either wild-type p53 or dominant-negative p53 mutant. We find that apoptosis by lonidamine is independent of the p53 gene.