Preclinical characterization of CG53135 (FGF-20) in radiation and concomitant chemotherapy/radiation-induced oral mucositis

PURPOSE

The purpose of this study was to evaluate the activity of CG53135 (FGF-20), a protein with in vitro mitogenic activity on epithelial and mesenchymal cells, in two in vivo models of oral mucositis (OM).

EXPERIMENTAL DESIGN

Radiation or concomitant chemotherapy/radiation-induced OM was elicited in hamsters. Activity of CG53135 was assessed at different doses and regimens in the models. Bromodeoxyuridine (BrdUrd) incorporation and pharmacokinetic studies were also performed to correlate in vivo activity of CG53135 with exposure.

RESULTS

In the hamster radiation model, administration of CG53135 (600 or 1200 micro g/day, i.p.) on days 3-15 resulted in a statistically significant (P < 0.001) reduction in days spent with severe mucositis. CG53135 administered at 12 mg/kg, i.p. (days 1-2 or 1-8) in the concomitant chemotherapy/radiation model resulted in a statistically significant (P < 0.001) reduction in severe mucositis. Maximal BrdUrd incorporation was observed in cheek pouch and jejunal tissues at 8 h, and peak plasma levels of CG53135 were reached 1 h after administration.

CONCLUSIONS

CG53135 demonstrates potent, regimen-dependent activity in hamster models of OM. The activity was regimen dependent. BrdUrd incorporation studies confirmed that CG53135 had proliferative activity in vivo with a favorable pharmacokinetic profile. Based in part on work described herein, CG53135 has received approval from the United States Food and Drug Administration to be evaluated in a Phase I clinical trial of cancer patients at risk for developing OM.

Technical report. Intra-operative ultrasound-guided needle localization for impalpable testicular lesions

AIMS

To describe a new technique of intra-operative ultrasound-guided needle localization of impalpable intratesticular lesions.

MATERIALS AND METHODS

Three patients with impalpable testicular lesions identified on ultrasound underwent needle localization under ultrasound guidance. The procedure was performed in the operating theatre under general anaesthetic using a 7.5-8 MHz linear array probe and a portable ultrasound machine. Under direct guidance, a 21 G needle was placed through the centre of the lesion allowing resection and immediate frozen section analysis.

RESULTS

In two patients malignancy was confirmed and an orchidectomy was performed. In one patient a benign lesion was detected obviating the need for orchidectomy.

CONCLUSION

Patients presenting with impalpable testicular lesions can pose a diagnostic dilemma and orchidectomy is often performed. We describe an ultrasound-guided intra-operative localization technique enabling direct pathological examination so surgical approach can be re-evaluated in the presence of a benign lesion. This is particularly important in the case of a solitary testicle in order to preserve testicular function.

A novel human fibroblast growth factor treats experimental intestinal inflammation

BACKGROUND & AIMS

We recently identified a novel member of the human fibroblast growth factor (FGF) family of signaling molecules, designated FGF-20. In the present study, we examined the activity of this protein in 2 animal models of acute intestinal inflammation and in mechanistic studies in vitro.

METHODS

In vivo experiments consisted of a murine dextran sulfate sodium (DSS) model of colitis and a rat indomethacin model of small intestinal ulceration/inflammation. Cell growth, restitution, gene expression (cyclooxygenase-2 [COX-2] and intestinal trefoil factor [ITF]), and prostaglandin E2 (PGE2) levels were examined in vitro.

RESULTS

In the DSS-colitis model, prophylactic administration of FGF-20 significantly reduced the severity and extent of mucosal damage as indicated by a 55%-93% reduction in luminal blood loss, distal colonic edema, histologic inflammation, and epithelial cell loss relative to animals administered vehicle control. No toxicity was noted during administration of FGF-20 to normal controls. In addition, therapeutic administration of FGF-20 enhanced survival in this model. In the indomethacin-small bowel ulceration/inflammation model, administration of FGF-20 reduced small intestinal weight gain, necrosis, inflammation, and weight loss (36%-53% relative to vehicle control). In vitro studies demonstrated that FGF-20 stimulates growth, restitution, mRNA expression of COX-2 and ITF, and PGE2 levels in human intestinal epithelial cells and enhances the growth of human intestinal fibroblasts.

CONCLUSIONS

FGF-20, having demonstrated therapeutic activity in 2 experimental models of intestinal inflammation, represents a promising new candidate for the treatment of human inflammatory bowel disease.

Increased angiogenesis in bone marrow of children with acute lymphoblastic leukaemia has no prognostic significance

The importance of angiogenesis for the growth and viability of solid tumours has been established. Similarly, prognostic information may be gained from the extent of angiogenesis in these tumours. Haematopoietic malignancies should have equal requirements for angiogenesis and important prognostic information may be derived from quantification of bone marrow angiogenic activity. We retrospectively investigated 82 bone marrow trephine biopsies from 41 children with acute lymphoblastic leukaemia (ALL) at diagnosis and following treatment. Nine normal bone marrow trephines from age-matched children were also analysed as controls. The microvessels were stained immunohistochemically with anti-Factor VIII-related antigen (antivWF) and antithrombomodulin (anti-THR). Angiogenesis was quantified manually by two independent observers and was highly reproducible (Pearson's r = 0.91). Staining with anti-vWF and anti-THR was highly specific for microvessels and thetwo stains closely correlated (r = 0.68). Microvessel densities (MVD) at presentation were significantly increased in the majority of patients in comparison with controls (P < 0.0001) and MVD dropped towards normal in remission (P < 0.0001). Of interest, the difference in total vessel counts between leukaemic and normal/remission marrows was contributed solely by small microvessels. There was no significant difference in MVD at presentation or remission from children in poor prognostic groups or those who subsequently relapsed. Similarly, we could not find an association with age, sex, cytogenetic abnormality or disease phenotype.

Fibroblast growth factors in cancer: therapeutic possibilities

The fibroblast growth factor (FGF) family of signalling molecules and its receptors (FGFRs) contribute to normal developmental and physiological processes. However, the subversion of this powerful growth stimulatory pathway has been implicated in the generation of a variety of pathological conditions. This review focuses on the role of FGF/FGFRs in cancer. The case will be made that this signalling pathway is associated with and functionally important for the growth of some human tumours. As such, FGF/FGFRs can be viewed as rational therapeutic oncology targets and strategies used to inhibit these molecules are discussed. The therapeutic exploitation of tumour-associated FGFR expression to deliver toxins or antiproliferative signals to tumour cells is also reviewed, as is the use of FGFs as protein therapeutics to alleviate the side effects of cancer therapy.

Angioarrestin: an antiangiogenic protein with tumor-inhibiting properties

The angiopoietins comprise a family of proteins that have pro or antiangiogenic activities. Through a proprietary technology designed to identify transcripts of all expressed genes, we isolated a cDNA encoding an angiopoietin-related protein that we designate angioarrestin. The mRNA expression profile of angioarrestin was striking in that it was down-regulated in many tumor tissues when compared with adjacent nontumor tissue, suggesting a role for this protein in tumor inhibition. To test this hypothesis, we ectopically expressed angioarrestin in HT1080 tumor cells and measured pulmonary tumor nodule formation in nude mice. HT1080 cells expressing angioarrestin showed a marked reduction in the number and size of tumor nodules. In vitro, the recombinant protein was systematically tested in a number of endothelial cell assays and found to block critical processes involved in the angiogenic cascade, such as vascular endothelial growth factor/basic fibroblast growth factor-mediated endothelial cell proliferation, migration, tubular network formation, and adhesion to extracellular matrix proteins. These findings reveal a novel function for angioarrestin as an angiogenesis inhibitor and indicate that the molecule may be a potential cancer therapeutic.

Platelet-derived growth factor D: tumorigenicity in mice and dysregulated expression in human cancer

Platelet-derived growth factor (PDGF) has been directly implicated in developmental and physiological processes, as well as in human cancer and other proliferative disorders. We have recently isolated and characterized a novel protease-activated member of the PDGF family, PDGF D. PDGF D has been shown to be proliferative for cells of mesenchymal origin, signaling through PDGF receptors. Comprehensive and systematic PDGF D transcript analysis revealed expression in many cell lines derived from ovarian, renal, and lung cancers, as well as from astrocytomas and medulloblastomas. beta PDGF receptor profiling further suggested autocrine signaling in several brain tumor cell lines. PDGF D transforming ability and tumor formation in SCID mice was further demonstrated. Exploiting a sensitive PDGF D sandwich ELISA using fully human monoclonal antibodies, PDGF D was detected at elevated levels in the sera of ovarian, renal, lung, and brain cancer patients. Immunohistochemical analysis confirmed PDGF D localization to ovarian and lung tumor tissues. Together, these data demonstrate that PDGF D plays a role in certain human cancers.

An evaluation of the prognostic significance of vascular endothelial growth factor in node positive primary breast carcinoma

Angiogenesis is intimately related to the growth and progression of tumours and must be induced to facilitate growth beyond a minimum size. It has been implicated in the development of metastases and survival in breast carcinoma. VEGF is a cytokine that plays an important role in angiogenesis. Its expression is increased in solid tumours during induction of angiogenesis and it has been implicated as a prognostic marker in patients with node negative breast carcinoma. We studied VEGF expression, in a series of patients with node positive breast carcinoma and examined histopathological parameters of the tumour and the prognostic value of VEGF expression. Specimens from 108 cases of node positive breast cancer were stained for VEGF using an antibody suitable for use on formalin fixed tissue. VEGF staining was cytoplasmic and was scored by intensity and the percent positive cells. Patients with positive VEGF staining (n=48) were compared with patients with negative VEGF staining (n=60). Demographic criteria were similar in both groups. Only one (12%) patient with lobular carcinoma and one (14%) patient with medullary carcinoma expressed VEGF compared with 46 (49%) patients with ductal carcinoma (NOS). DCIS was present in 60 tumours. There was a strong correlation between staining in DCIS and the adjacent invasive tumours. There was no significant association between VEGF staining and T stage, tumour size or the number of positive lymph nodes. VEGF expression had no prognostic significance either for disease-free or overall survival in patients with node positive disease. This study failed to support a role for VEGF as a prognostic marker in patients with node positive breast carcinoma.

An immunohistochemical study of p21 and p53 expression in primary node-positive breast carcinoma

AIMS

p21, an inhibitor of cyclin-dependent kinase, is involved in the p53 pathway of growth control. Its expression has been linked to cellular differentiation. It has been implicated in p53-mediated growth arrest following DNA damage and in terminally differentiated cells. This study analysed p21 and p53 expression, in a series of node-positive patients with breast carcinoma and examined histopathological parameters of the tumour and the prognostic implications of p21 and p53 expression.

METHODS

One hundred and five consecutive patients with node-positive disease and at least 3 years follow-up were identified. Sections were stained for p53 and p21 using monoclonal antibodies. Results were expressed as percentage positive cells, and over 20% considered positive for p53 and over 10% considered for p21.

RESULTS

p21 was overexpressed (>10% of cells positive) in 65% of patients and p53 was overexpressed (>20% of cells positive in 68%. The mean (SEM) level of p21 staining was 5.7(0.8)% and was 54.9(4.0)% for p53. There was no correlation between p21 and p53 expression (r=0.071 P=0.5). There were no significant differences in demographic criteria between patients that were p21 positive or negative and p53 positive or negative. There were no significant differences in tumour type, grade or stage between the groups. p21 expression did not have prognostic significance; however, p53 positivity was associated with a worse prognosis, which remained when controlled for stage.

CONCLUSIONS

This study demonstrated p21 overexpression in 65% of patients with node-positive breast carcinoma. Levels did not correlate with p53 status and unlike p53 failed to have prognostic significance.

PDGF-D, a new protease-activated growth factor

Platelet-derived growth factor (PDGF) has been directly implicated in developmental and physiological processes, as well as in human cancer, fibrotic diseases and arteriosclerosis. The PDGF family currently consists of at least three gene products, PDGF-A, PDGF-B and PDGF-C, which selectively signal through two PDGF receptors (PDGFRs) to regulate diverse cellular functions. After two decades of searching, PDGF-A and B were the only ligands identified for PDGFRs. Recently, however, database mining has resulted in the discovery of a third member of the PDGF family, PDGF-C, a functional analogue of PDGF-A that requires proteolytic activation. PDGF-A and PDGF-C selectively activate PDGFR-alpha, whereas PDGF-B activates both PDGFR-alpha and PDGFR-beta. Here we identify and characterize a new member of the PDGF family, PDGF D, which also requires proteolytic activation. Recombinant, purified PDGF-D induces DNA synthesis and growth in cells expressing PDGFRs. In cells expressing individual PDGFRs, PDGF-D binds to and activates PDGFR-beta but not PDGFR-alpha. However, in cells expressing both PDGFRs, PDGF-D activates both receptors. This indicates that PDGFR-alpha activation may result from PDGFR-alpha/beta heterodimerization.

Anti-apoptotic signaling by hepatocyte growth factor/Met via the phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase pathways

Hepatocyte growth factor (HGF) is a ligand of the receptor tyrosine kinase encoded by the c-Met protooncogene. HGF/Met signaling has multifunctional effects on various cell types. We sought to determine the role of HGF/Met in apoptosis and identify signal transducers involved in this process. In experiments with human SK-LMS-1 leiomyosarcoma cells, we show that the Akt kinase is activated by HGF in a time- and dose-dependent manner by phosphatidylinositol 3-kinase (PI3-kinase). Akt is also activated by active tumorigenic forms of Met, i.e., ligand-independent Tpr-Met, a truncated and constitutively dimerized form of Met, and a mutationally activated version of Met corresponding to that found in human hereditary papillary renal carcinoma. In NIH 3T3 cells transfected with wild-type Met, HGF inhibits apoptosis induced by serum starvation and UV irradiation. HGF-induced survival correlates with Akt activity and is inhibited by the specific PI3-kinase inhibitor LY294002, indicating that HGF inhibits cell death through the PI3-kinase/Akt signal transduction pathway. Furthermore, transiently transfected Tpr-Met activates Akt (both Akt1 and Akt2) and protects cells from apoptosis. Mitogen-activated protein kinase (MAPK) also is activated by HGF and rescues cells from apoptosis, although the cytoprotective effect is less marked than for PI3-kinase/Akt. Blocking MAPK with the specific MAPK kinase inhibitor PD098059 impairs the ability of HGF to promote cell survival. Similar results were obtained with NIH 3T3 cells expressing the fusion protein Trk-Met and stimulated with nerve growth factor, the Trk ligand. These results demonstrate that HGF/Met is capable of protecting cells from apoptosis by using both PI3-kinase/Akt and, to a lesser extent, MAPK pathways.

Identification of a novel human fibroblast growth factor and characterization of its role in oncogenesis

The fibroblast growth factor (FGF) family of signaling molecules has been implicated in normal developmental and physiological processes, as well as in human malignancy. Using a homology-based genomic DNA mining process, we identified a human gene encoding a novel member of the FGF family, that we designate FGF-20. The FGF-20 cDNA was isolated, and its sequence confirmed the gene prediction. FGF-20 is expressed in normal brain, particularly the cerebellum, and in some cancer cell lines. Recombinant FGF-20 protein induces DNA synthesis in a variety of cell types and is recognized by multiple FGF receptors. Ectopic expression of FGF-20 in NIH 3T3 cells renders the cells transformed in vitro and tumorigenic in nude mice. These results underscore the utility of mining genomic DNA databases and reveal FGF-20 to be a novel oncogene that may play a role in human cancer.

Efficacy of hydroquinone cream (USP 4%) used alone or in combination with salicylic acid peels in improving photodamage on the neck and upper chest

BACKGROUND

Salicylic acid, hydroquinone, and glycolic acid have been proved effective in the treatment of photodamaged facial skin. Few reports are available on the treatment of photodamage on the neck and upper chest.

OBJECTIVE

This study's purpose was to evaluate the efficacy of a cream containing 4% hydroquinone and 2% glycolic acid (LUSTRA) used alone or with salicylic acid peels in reversing actinic damage on the neck and upper chest.

METHODS

Nineteen women with moderate to advanced photodamage on the neck and upper chest applied a cream containing 4% hydroquinone and 2% glycolic acid twice daily on photodamaged areas for 12 weeks. Nine of these subjects had salicylic acid peels every 3 weeks. Improvements were assessed by the investigator, the subjects, and Mexameter readings measuring melanin and erythema levels.

RESULTS

The result shows that there was a 33-71% improvement in photodamage, hyperpigmentation, texture, fine lines, dryness, tone, and clarity in both groups. There were no significant differences between the two treatments.

CONCLUSION

Hydroquinone 4% cream with 2% glycolic acid is safe and effective in improving photodamage on the neck and upper chest when used alone or in combination with salicylic acid peels.

The geldanamycins are potent inhibitors of the hepatocyte growth factor/scatter factor-met-urokinase plasminogen activator-plasmin proteolytic network

The Met receptor tyrosine kinase and its ligand, hepatocyte growth factor/scatter factor (HGF/SF), have been implicated in human tumor development and metastasis. HGF/SF induces the expression of urokinase plasminogen activator (uPA) and the uPA receptor (uPAR), important mediators of cell invasion and metastasis. We have developed a cell-based assay to screen for inhibitors of this signaling system using the induction of endogenous uPA and uPAR and the subsequent conversion of plasminogen to plasmin as the biological end point. Assay validation was established using a neutralizing antiserum to HGF/SF and a uPA inhibitor (B428), as well as inhibitors of the MKK-MAPK1/2 pathway, shown previously to be important in the induction of uPA and uPAR. Using this assay, we found several classes of molecules that exhibited inhibition of HGF/SF-dependent plasmin activation. However, we discovered that certain members of the geldanamycin family of anisamycin antibiotics are potent inhibitors of HGF/SF-mediated plasmin activation, displaying inhibitory properties at femtomolar concentrations and nine orders of magnitude below their growth inhibitory concentrations. At nanomolar concentrations, the geldanamycins down-regulate Met protein expression, inhibit HGF/SF-mediated cell motility and invasion, and also revert the phenotype of both autocrine HGF/SF-Met transformed cells as well as those transformed by Met proteins with activating mutations. Thus, the geldanamycins may have important therapeutic potential for the treatment of cancers in which Met activity contributes to the invasive/metastatic phenotype.

The von Hippel-Lindau tumor suppressor gene inhibits hepatocyte growth factor/scatter factor-induced invasion and branching morphogenesis in renal carcinoma cells

Loss of function in the von Hippel-Lindau (VHL) tumor suppressor gene occurs in familial and most sporadic renal cell carcinomas (RCCs). VHL has been linked to the regulation of cell cycle cessation (G(0)) and to control of expression of various mRNAs such as for vascular endothelial growth factor. RCC cells express the Met receptor tyrosine kinase, and Met mediates invasion and branching morphogenesis in many cell types in response to hepatocyte growth factor/scatter factor (HGF/SF). We examined the HGF/SF responsiveness of RCC cells containing endogenous mutated (mut) forms of the VHL protein (VHL-negative RCC) with that of isogenic cells expressing exogenous wild-type (wt) VHL (VHL-positive RCC). We found that VHL-negative 786-0 and UOK-101 RCC cells were highly invasive through growth factor-reduced (GFR) Matrigel-coated filters and exhibited an extensive branching morphogenesis phenotype in response to HGF/SF in the three-dimensional (3D) GFR Matrigel cultures. In contrast, the phenotypes of A498 VHL-negative RCC cells were weaker, and isogenic RCC cells ectopically expressing wt VHL did not respond at all. We found that all VHL-negative RCC cells expressed reduced levels of tissue inhibitor of metalloproteinase 2 (TIMP-2) relative to the wt VHL-positive cells, implicating VHL in the regulation of this molecule. However, consistent with the more invasive phenotype of the 786-0 and UOK-101 VHL-negative RCC cells, the levels of TIMP-1 and TIMP-2 were reduced and levels of the matrix metalloproteinases 2 and 9 were elevated compared to the noninvasive VHL-positive RCC cells. Moreover, recombinant TIMPs completely blocked HGF/SF-mediated branching morphogenesis, while neutralizing antibodies to the TIMPs stimulated HGF/SF-mediated invasion in vitro. Thus, the loss of the VHL tumor suppressor gene is central to changes that control tissue invasiveness, and a more invasive phenotype requires additional genetic changes seen in some but not all RCC lines. These studies also demonstrate a synergy between the loss of VHL function and Met signaling.

Activation mechanisms of the urokinase-type plasminogen activator promoter by hepatocyte growth factor/scatter factor

Hepatocyte growth factor/scatter factor (HGF/SF) is a pleiotropic effector inducing invasion and metastasis of tumor cells that express the Met tyrosine kinase receptor. One of the effectors of HGF/SF is the urokinase-type plasminogen activator, a serine protease that facilitates tumor progression and metastasis by controlling the synthesis of the extracellular matrix degrading plasmin. Stimulation of NIH 3T3 cells that were stably transfected with the human Met receptor (NIH 3T3-Methum) with HGF/SF induced a trans-activation of the urokinase promoter and urokinase secretion. Induction of the urokinase promoter by HGF/SF via the Met receptor was blocked by co-expression of a dominant-negative Grb2 and Sos1 expression construct. Further, the expression of the catalytically inactive mutants of Ha-Ras, RhoA, c-Raf, and Erk2 or addition of the Mek1-specific inhibitor PD 098059 abrogated the stimulation of the urokinase promoter by HGF/SF. A sequence residing between -2109 and -1870 base pairs (bp) was critical for stimulation of the urokinase gene by HGF/SF. Mobility shift assays with oligonucleotides spanning an AP-1 site at -1880 bp or a combined PEA3/AP-1 site at -1967 bp showed binding of nuclear factors from NIH 3T3-Methum cells. Expression of an expression plasmid that inhibits DNA binding of AP-1 proteins (A-Fos) abrogated inducible and basal activation of the urokinase promoter. Nuclear extract from unstimulated NIH 3T3-Methum cells contained more JunD and showed a stronger JunD supershift with the AP-1 oligonucleotides, compared with HGF/SF-stimulated cells. Consistent with the levels of JunD expression being functionally important for basal expression of the urokinase promoter, we found that overexpression of wild type JunD inhibited the induction of the urokinase promoter by HGF/SF. These data suggest that the induction of urokinase by HGF/SF is regulated by a Grb2/Sos1/Ha-Ras/c-Raf/RhoA/Mek1/Erk2/c-++ +Jun-dependent mitogen-activated protein kinase pathway.

The unr gene: evolutionary considerations and nucleic acid-binding properties of its long isoform product

The unr transcription unit is located just upstream of the N-ras gene in the genome of mammals, in which unr, like N-ras, is ubiquitously expressed. To determine at what point in evolution the unr/N-ras linkage was created, analysis of nucleic acids by Southern and Northern blotting was performed, allowing us to track the presence of the unr gene to the start of vertebrate evolution and the unr/N-ras linkage to the time at which the reptilian and bird lines diverged. We have investigated, with specific anti-unr antibodies, a potential relation between unr protein levels and cellular processes in which N-ras is implicated. A positive correlation in the proliferation of 3T3 cells, but not differentiation of PC12 cells induced by nerve growth factor (NGF), was found. To study the nucleic acid-binding properties of unr, a protein with multiple repeats of a nucleic acid-binding motif, we expressed the long splicing isoform in a eukaryotic cell line and purified it in native form. The results obtained-a high affinity of unr for single-stranded DNA and RNA and lower affinity for double-stranded DNA without regard to nucleic acid sequence, and its intracellular localization in both the nuclear and non-nuclear compartments, together with its ubiquious expression in mammalian tissues-provide molecular information about the function of one of the closest gene tandems in mammalian cells (unr-N-ras).

The ras oncogene-mediated sensitization of human cells to topoisomerase II inhibitor-induced apoptosis

BACKGROUND

Among the inhibitors of the enzyme topoisomerase II (an important target for chemotherapeutic drugs) tested in the National Cancer Institute's In Vitro Antineoplastic Drug Screen, NSC 284682 (3'-hydroxydaunorubicin) and NSC 659687 [9-hydroxy-5,6-dimethyl-1-(N-[2(dimethylamino)ethyl]carbamoyl)-6H-pyrido -(4,3-b)carbazole] were the only compounds that were more cytotoxic to tumor cells harboring an activated ras oncogene than to tumor cells bearing wild-type ras alleles. Expression of the multidrug resistance proteins P-glycoprotein and MRP (multidrug resistance-associated protein) facilitates tumor cell resistance to topoisomerase II inhibitors. We investigated whether tumor cells with activated ras oncogenes showed enhanced sensitivity to other topoisomerase II inhibitors in the absence of the multidrug-resistant phenotype.

METHODS

We studied 20 topoisomerase II inhibitors and individual cell lines with or without activated ras oncogenes and with varying degrees of multidrug resistance.

RESULTS

In the absence of multidrug resistance, human tumor cell lines with activated ras oncogenes were uniformly more sensitive to most topoisomerase II inhibitors than were cell lines containing wild-type ras alleles. The compounds NSC 284682 and NSC 659687 were especially effective irrespective of the multidrug resistant phenotype. The ras oncogene-mediated sensitization to topoisomerase II inhibitors was far more prominent with the non-DNA-intercalating epipodophyllotoxins than with the DNA-intercalating inhibitors. This difference in sensitization appears to be related to a difference in apoptotic sensitivity, since the level of DNA damage generated by etoposide (an epipodophyllotoxin derivative) in immortalized human kidney epithelial cells expressing an activated ras oncogene was similar to that in the parental cells, but apoptosis was enhanced only in the former cells.

CONCLUSIONS

Activated ras oncogenes appear to enhance the sensitivity of human tumor cells to topoisomerase II inhibitors by potentiating an apoptotic response. Epipodophyllotoxin-derived topoisomerase II inhibitors should be more effective than the DNA-intercalating inhibitors against tumor cells with activated ras oncogenes.

Signaling requirements for oncogenic forms of the Met tyrosine kinase receptor

The Met tyrosine kinase receptor has been implicated in human cancer. Here we have examined the signaling requirements of three oncogenic forms of this molecule: wild type Met in response to ligand/autocrine stimulation, Met which has been mutationally activated, and Tpr-Met (a constitutively active truncated Met fusion protein). Previous studies have demonstrated the importance of a Grb2 binding site, and of specific tyrosine residues (i.e. Y8,9 and Y14,15) for Met function, and we have now explored the relevance of these and other sites for oncogenic Met signaling. Following substitution of various intracellular tyrosines for phenylalanine, we find that the transforming activity of each Met oncogene is dependent upon tyrosines Y8,9 and Y14,15, in addition to two novel tyrosines (Y6 and Y10) not previously implicated in Met signaling. Tyrosines Y6 and Y10 influence a variety of Met-mediated responses both in vitro (transformation, mitogenicity and invasion), and in vivo (tumorigenicity and metastasis). We also show that Tpr-Met is much more dependent on its Grb2 binding site for biological activity than are the other oncogenic forms of the Met receptor. Thus, although the three Met oncogenes examined are similar in their dependency on a number of specific tyrosines for activity, the signaling strategy employed by Tpr-Met can be differentiated from that of the other two.

The mutationally activated Met receptor mediates motility and metastasis

Mutations in Met have been identified in human papillary renal carcinomas. We have shown previously that these mutations deregulate the enzymatic activity of Met and that NIH 3T3 cells expressing mutationally activated Met are transformed in vitro and are tumorigenic in vivo. In the present investigation, we find that mutant Met induces the motility of Madin-Darby canine kidney cells in vitro and experimental metastasis of NIH 3T3 cells in vivo, and that the Ras-Raf-MEK-ERK signaling pathway, which has been implicated previously in cellular motility and metastasis, is constitutively activated by the Met mutants. We also report that transgenic mice harboring mutationally activated Met develop metastatic mammary carcinoma. These data confirm the tumorigenic activity of mutant Met molecules and demonstrate their ability to induce the metastatic phenotype.

Evidence for a role of Met-HGF/SF during Ras-mediated tumorigenesis/metastasis

Aberrations in Met-hepatocyte growth factor/scatter factor (HGF/SF) signaling have been implicated in the acquisition of tumorigenic and metastatic phenotypes. Here we show that murine NIH3T3 and C127 cells transformed by the Ras oncogene overexpress the Met receptor, resulting in enhanced HGF/SF-mediated responses in vitro including invasion through basement membrane. Accompanying the increase in Met in ras-transformed NIH3T3 cells, there is a decrease in endogenous HGF/SF expression as previously observed in cells exogenously overexpressing Met. However, subcutaneously grown tumors and experimental lung metastases derived from these cells express significantly higher levels of endogenous HGF/SF together with high levels of Met. These results suggest Met-HGF/SF signaling enhances tumor growth and metastasis of Ras-transformed NIH3T3 cells.

Decreased fibronectin expression in Met/HGF-mediated tumorigenesis

The tyrosine kinase receptor Met and its ligand, hepatocyte growth factor (HGF)/scatter factor are involved in the etiology and progression of a number of human cancers. Coexpression of Met and HGF in mesenchymal cells increases the tumorigenic and metastatic potential of the cells. In the studies described here, we used differential display screening to identify changes in gene expression that are initiated by Met/HGF, and that may lead to these phenotypes. We learned that Met/HGF signaling resulted in greatly decreased fibronectin mRNA production in three different human and mouse tumor cell lines; these decreases in fibronectin mRNA were paralleled by decreases in fibronectin protein. We also found a progressive decrease in fibronectin in tumor explants and metastases derived from the Met/HGF transformed cells. The absence of fibronectin expression is a frequent cancer phenotype; our results indicate that decreases in fibronectin correlate with, but are not essential for, MetHGF/SF-mediated tumorigenesis.