Mechanism of activation of a human oncogene

RAS oncogenes: the first 30 years

From the pioneering work with acute transforming retroviruses to the current post-genomic era, RAS genes have always been at the leading edge of signal transduction and molecular oncology. Yet, a complete understanding of RAS function and dysfunction - mainly in human cancer - is still to come. The knowledge that has accumulated since their discovery 30 years ago has, however, been remarkable, and should pave the way for not only solving the outstanding issues regarding RAS biology, but also for developing efficacious drugs that could have a significant impact on cancer treatment.

Oncogenes in melanoma

Transformation of normal melanocytes into melanoma cells is accomplished by the activation of growth stimulatory pathways, typically leading to cellular proliferation, and the inactivation of apoptotic and tumor suppressor pathways. Small molecule inhibitors of proteins in the growth stimulatory pathways are under active investigation, and their application to melanoma patients would represent a new treatment strategy to inhibit cell proliferation or induce cell death. We provide a general overview of the mechanisms of oncogene activation and the functions of oncogenes. Lastly, we review oncogenic events in melanoma.

Unexpected induction of the human connexin 43 promoter by the ras signaling pathway is mediated by a novel putative promoter sequence

Connexin 43 (Cx43) is essential for survival and is tightly regulated at the transcriptional and post-transcriptional levels. A number of previous studies have demonstrated altered expression in malignant tissues, and in the presence of carcinogenic factors. We examined the effect of protooncogenes of Cx43 expression, and found no effect on Cx43 promoter activity in cells transformed with Src or erbB2. On the other hand, we identified and characterized a novel sequence that mediates Cx43 promoter regulation in cell lines engineered to overexpress H-Ras. Compared with wild-type NIH3T3 cells, both Cx43 mRNA and protein levels are increased in NIH3T3-Ras cells. The H-Ras+ cells also have enhanced Cx43 promoter activation, which is inhibited by the MEK1 inhibitor 2'-amino-3'-methoxyflavone (PD98059), suggesting that Ras-mediated Cx43 overexpression is via the mitogen activated protein kinase kinase/extracellular signal-regulated pathway. Deletion analysis of the Cx43 promoter revealed a 200-bp region downstream of the Cx43 transcription start site as the minimal sequence essential for the Ras-mediated Cx43 up-regulation. Using this 200-base pair fragment in electrophoretic mobility shift assays, we identified one main protein complex that binds efficiently and is more abundant in nuclear extracts from NIH3T3-Ras and MCF7-Ras cells compared with their matched controls. This complex selectively recognizes a consensus sequence, AGTTCAATCA, located at positions +149 to +158 of the Cx43 promoter. Supershift assays identified the 90-kDa heat shock protein (HSP90) and c-Myc as constituents of this DNA-binding complex. Treatment of cells with the HSP90 inhibitor geldanamycin resulted in repression of the Cx43 promoter activity, and inhibits binding of the complex to the Cx43 promoter. Coimmunoprecipitation studies confirmed the interaction between endogenous HSP90 and c-Myc. This study provides evidence that the transcriptional up-regulation of Cx43 by Ras-Raf-MAPK is mediated via the interaction of a novel Cx43 promoter element with a protein complex that contains both HSP90 and c-Myc.

Recombinant adenovirus encoding H-ras ribozyme induces apoptosis in laryngeal cancer cells through caspase- and mitochondria-dependent pathways

Previously, we designed a ribozyme that targets the H-ras oncogene at the 12th codon mutation site (Chang et al., 1997). Ribozymes have antisense molecule and site-specific ribonuclease potential. In this study, an adenoviral vector was used to transduce the H-ras ribozyme into laryngeal cancer cells (HEp-2). This served to downregulate the H-ras gene expression in which this ribozyme performed antisense activity due to HEp-2 cells containing wild-type alleles in the 12th H-ras codon. Together, our data demonstrated that the recombinant adenovirus encoding H-ras ribozyme can be broadly regarded as a cytotoxic gene therapy in laryngeal cancer cells regardless of containing wild-type or mutant ras gene. In addition, the mechanism through which the H-ras ribozyme inhibited tumor growth was apoptosis and involved both caspase- and mitochondria-mediated pathways. The activators caspase-8 and -9 as well as the effector caspase-3 in the induction phase of apoptosis and the substrate PARP of caspase-3 in the execution phase were activated 48h following the H-ras ribozyme treatment. Mitochondrial events characterized by the production of superoxide anion and the release of cytochrome c started at 24h. Mitochondrial transmembrane potential loss occurred 48h after the ribozyme treatment. However, Bcl-2 delayed cytochrome c release to the cytosol, but it could not protect the apoptosis effect, suggesting that cytochrome c release from mitochondria may not play a role in H-ras ribozyme-induced apoptosis.

Hammerhead ribozymes as therapeutic agents for bladder cancer

Hammerhead ribozymes have been investigated extensively as therapeutic agents against cancer. Aberrant or overexpression of genes related to tumorigenicity or cancer growth might be the appropriate targets for ribozyme strategies. Ribozyme-mediated gene therapy should be applied to those diseases that have no successful conventional therapy such as advanced or treatment-resistant bladder cancer. Many genetic alterations have been identified in bladder cancer related to both tumorigenesis and disease progression. Mutated H-ras, fos, and erb-B2 genes have been chosen as targets for ribozymes in previous studies, and antitumor efficacy has been demonstrated by reversion of the malignant phenotypes and by inhibition of tumor growth both in vitro and in vivo. The efficiency of various delivery systems has also been evaluated. An overview of ribozyme strategies, especially for therapeutic applications against bladder cancer, is described here.

Inhibitors of the ras oncogene as therapeutic targets

Advances in our understanding of the molecular pathways and genetic mutations that control tumor cell proliferation and metastasis present an opportunity to develop novel, mechanism-based therapeutic strategies. Ras mutations are the most frequently activated oncogenes in human tumors, with over 30% expressing ras mutations. Molecular dissection of the signaling pathway and the mechanisms of ras anchorage, post-translational modification, and downstream effector signaling of ras now under intensive investigation will help us to design additional methods for ras-directed therapy in an effort to reach an optimal treatment for human tumors that will most likely comprise a combination of modalities targeted at the different underlying genetic defects. The successes and limitations of ras-targeted therapies must be viewed in light of the increasing understanding of the complexity of the ras-signaling pathway. Only now are we beginning to discover the many functions of this integrated pathway, such as the differences between the actions of various ras isoforms that may affect our choice of therapeutic approach. Many of these Ras therapeutic targets have shown success in preclinical studies, and some have shown efficacy in clinical trials with minimal toxicities. Compounds that block ras-transforming activity without affecting normal ras function seem more attractive for the future development of ras-targeted therapy. FTIs may partially fulfill such requirements. Based on their specific, novel, and mechanism-based action; minimal toxicity; and encouraging responses in clinical trials, the development of Ras therapeutic targets as single agents or in combination with conventional chemotherapy and radiotherapy should be pursued.

Persistence of microscopic human cancers in mice: alterations in the angiogenic balance accompanies loss of tumor dormancy

Some human tumor lines do not form visible tumors when inoculated into immunosuppressed mice. The fate of these human tumor lines was followed by transfecting them with green fluorescence protein before inoculating them into mice. Although the tumor lines failed to grow progressively, they formed small dormant microscopic foci maintained at constant mass by balanced proliferation and apoptosis. Transfecting the cells with either VEGF165 or activated c-Ha-ras induced loss of dormancy, which correlated with a shift in the angiogenic balance toward increased vascularity with reduced tumor cell apoptosis. These results support a model in which loss of dormancy is controlled in part by a switch to an angiogenic phenotype. These tumor lines may serve as models for investigating the cellular mechanisms controlling dormancy and identifying those factors that promote the loss of balanced proliferation and apoptosis. Finally, these models may prove useful in the design and testing of therapies directed toward eradicating dormant tumors and preventing tumor recurrence.

Differentiation and stromal-induced growth promotion of murine prostatic tumors

BACKGROUND

We have derived a panel of p53-null prostatic "basal" and "luminal" epithelial cell lines and their ras transformed counterparts to study stromal/epithelial interactions and the properties of tumors arising from "basal" and "luminal" cells.

METHODS

Previously derived normal murine prostatic "basal" epithelial (PE-B-1) and "luminal" epithelial (PE-L-1) cell lines were transformed with N-Ras. These lines and a spontaneously transformed "luminal" cell line were inoculated subcutaneously or orthotopically into athymic mice, alone or in combination with normal prostatic smooth muscle cells (SMC).

RESULTS

All transformed lines formed subcutaneous tumors. SMC significantly enhanced the growth rate of the tumors arising from the "basal" and one of the "luminal" cell lines. The transformed "basal" line gave rise to tumors expressing both "basal" and "luminal" cytokeratins.

CONCLUSIONS

Prostatic SMC promote the growth of transformed epithelial cells, suggesting that prostatic stroma may promote tumor development. Furthermore, transformed "basal" cells give rise to tumors containing "luminal" cells, suggesting that although most human tumors have a "luminal" phenotype, they may originate from transformed "basal" cells.

CDC42 is required for polarized growth in human pathogen Candida albicans

Cdc42p is a member of the RAS superfamily of GTPases and plays an essential role in polarized growth in many eukaryotic cells. We cloned the Candida albicans CaCDC42 by functional complementation in Saccharomyces cerevisiae and analyzed its function in C. albicans. A double deletion of CaCDC42 was made in a C. albicans strain containing CaCDC42 under the control of the PCK1 promoter. When expression of the heterologous copy of CaCDC42 was repressed in this strain, the cells ceased proliferation. These arrested cells were large, round, and unbudded and contained predominantly two nuclei. The PCK1-mediated overexpression of wild-type CaCdc42p had no effect on cells. However, in cells overexpressing CaCdc42p containing the dominant-negative D118A substitution, proliferation was blocked and the arrested cells were large, round, unbudded, and multinucleated, similar to the phenotype of the cdc42 double-deletion strain. Cells overexpressing CaCdc42p containing the hyperactive G12V substitution also ceased proliferation in yeast growth medium; in this case the arrested cells were multinucleated and multibudded. An intact CAAX box is essential for the phenotypes associated with either CaCdc42p(G12V) or CaCdc42p(D118A) ectopic expression, suggesting that membrane attachment is involved in CaCdc42p function. In addition, the lethality caused by ectopic expression of CaCdc42p(G12V) was suppressed by deletion of CST20 but not by deletion of CaCLA4. CaCdc42p function was also examined under hypha-inducing conditions. Cdc42p depletion prior to hyphal induction trapped cells in a round, unbudded state, while depletion triggered at the same time as hyphal induction permitted the initiation of germ tubes that failed to be extended. Ectopic expression of either the G12V or D118A substitution protein modified hyphal formation in a CAAX box-dependent manner. Thus, CaCdc42p function appears important for polarized growth of both the yeast and hyphal forms of C. albicans.

Cancer genetics: from Boveri and Mendel to microarrays

The human genome has now been sequenced, a century after the re-discovery of Mendel's Laws, and the publication of Theodor Boveri's chromosomal theory of heredity. Tracing the historical landmarks of cancer genetics from these early days to the present time not only gives us an appreciation of how far we have come, but also emphasizes the challenges that we face if we are to unravel the genetic basis of hereditary and sporadic cancers in the next century.

Searching new targets for anticancer drug design: the families of Ras and Rho GTPases and their effectors

The Ras superfamily of low-molecular-weight GTPases are proteins that, in response to diverse stimuli, control key cellular processes such as cell growth and development, apoptosis, lipid metabolism, cytoarchitecture, membrane trafficking, and transcriptional regulation. More than 100 genes of this superfamily grouped in six subfamilies have been described so far, pointing to the complexities and specificities of their cellular functions. Dysregulation of members of at least two of these families (the Ras and the Rho families) is involved in the events that lead to the uncontrolled proliferation and invasiveness of human tumors. In recent years, the cloning and characterization of downstream effectors for Ras and Rho proteins have given crucial clues to the specific pathways that lead to aberrant cellular growth and ultimately to tumorigenesis. A direct link between the functions of some of these effectors with the appearance of transformed cells and their ability to proliferate and invade surrounding tissues has been made. Accordingly, drugs that specifically alter their functions display antineoplasic properties, and some of these drugs are already under clinical trials. In this review, we survey the progress made in understanding the underlying molecular connections between carcinogenesis and the specific cellular functions elicited by some of these effectors. We also discuss new drugs with antineoplastic or antimetastatic activity that are targeted to specific effectors for Ras or Rho proteins.

A new verdict for an old convict

Certain human cancers and carcinogen-induced rodent tumors commonly contain Kras2 mutations. This activated form of ras has always been described as a dominant oncogene. A new study indicates that wildtype Kras2 has properties of a tumor suppressor gene and may have the capacity to reduce the transforming potential of oncogenically activated ras.

Ras biochemistry and farnesyl transferase inhibitors: a literature survey

Over the last decades, knowledge on the genetic defects involved in tumor formation and growth has increased rapidly. This has launched the development of novel anticancer agents, interfering with the proteins encoded by the identified mutated genes. One gene of particular interest is ras, which is found mutated at high frequency in a number of malignancies. The Ras protein is involved in signal transduction: it passes on stimuli from extracellular factors to the cell nucleus, thereby changing the expression of a number of growth regulating genes. Mutated Ras proteins remain longer in their active form than normal Ras proteins, resulting in an overstimulation of the proliferative pathway. In order to function, Ras proteins must undergo a series of post-translational modifications, the most important of which is farnesylation. Inhibition of Ras can be accomplished through inhibition of farnesyl transferase, the enzyme responsible for this modification. With this aim, a number of agents, designated farnesyl transferase inhibitors (FTIs), have been developed that possess antineoplastic activity. Several of them have recently entered clinical trials. Even though clinical testing is still at an early stage, antitumor activity has been observed. At the same time, knowledge on the biochemical mechanisms through which these drugs exert their activity is expanding. Apart from Ras, they also target other cellular proteins that require farnesylation to become activated, e.g. RhoB. Inhibition of the farnesylation of RhoB results in growth blockade of the exposed tumor cells as well as an increase in the rate of apoptosis. In conclusion, FTIs present a promising class of anticancer agents, acting through biochemical modulation of the tumor cells.

Membrane localization of Raf assists engagement of downstream effectors

We have previously described a small molecule-directed protein dimerization strategy, using coumermycin to juxtapose Raf fusion proteins containing the coumermycin-binding domain GyrB. Oligomerization of cytoplasmically localized Raf-GyrB fusion proteins leads to an increase in the kinase activity of both Raf and its substrate Mek. Surprisingly, more distal targets, such as Erk1 and Erk2, are not activated using this approach. Here we report that coumermycin-induced oligomerization of a membrane-localized Raf-GyrB fusion protein potently activated Erk1 and Erk2, up-regulated Fos protein levels, and induced expression of many immediate-early response genes. Thus, both membrane localization and oligomerization of Raf-GyrB are required to target Raf signals to downstream effectors. The ability to activate the entire Raf signal transduction cascade conditionally, using coumermycin-induced oligomerization, should prove useful for dissecting Raf-mediated effects on gene expression and cellular differentiation.

Reduced G-protein-coupled-receptor kinase 2 activity results in impairment of osteoblast function

Rapid phosphorylation of many G-protein-coupled receptors (GPCRs) by G-protein-coupled receptor kinases (GRKs) accompanies stimulus-driven desensitization. Recent evidence suggests that GRKs and their associated arresting proteins, beta-arrestins, function as essential elements in the GPCR-mediated mitogen-activated protein (MAP) kinase signaling cascade. We investigated the interaction between GRKs and MAP kinase activation by growth factors in UMR 106-H5 osteoblastic cells stably expressing a dominant negative mutant of GRK2 (K220R). Expression of K220R in osteoblastic cells results in reduced cellular proliferation, both basally and in response to insulin-like growth factor-1 (IGF-1), and blunting of IGF-1- and EGF-induced MAP kinase activation. Reduced MAP kinase activation is not associated with alterations in IGF-1-receptor autophosphorylation. Both a constitutively active Ras mutant and PMA fully activate MAP kinase in K220R cells. We found that disruption of the GRK2 gene results in: (1) reduced osteoblast proliferation in response to growth factors, and (2) impaired receptor tyrosine kinase activation of mitogenic signaling pathways. Thus, GRK2 may regulate growth factor responsiveness in osteoblasts by modulating multiprotein complex formation following receptor tyrosine kinase activation.

Molecular basis of cancer and clinical applications

This article attempts to show the vertiginous advances that exist today in the concept of what cancer is. The authors chose some multiple biologic concepts that have enabled the progress in the knowledge of this disease to occur at a speed no one could imagine until recently. Although the areas and biologic problems that remain to be solved are more numerous and complex than they expected, the basic fundamentals already partially understood and the multidisciplinary integration of the various medical specialties with biomolecular research enable physicians to face the next millennium with great optimism about the possibilities of therapeutic success, prevention, and effective early diagnosis.

Mutation of cell cycle regulators and their impact on superficial bladder cancer

Early cytogenetic studies in bladder cancer identify regions of chromosomal gain or loss that can be candidate loci for oncogenes and tumor suppressor genes. Oncogenes with potential prognostic significance identified in bladder cancer the RAS family, epidermal growth factor receptor, ERBB-2, MDM2, and cyclin D1. The TP53 gene has been the most thoroughly characterized tumor suppressor gene in bladder cancer, with correlation of TP53 alterations with type of carcinogenic exposure, tumor stage and grade, as well as prognosis. Studies evaluating alterations of the retinoblastoma pathway have identified the retinoblastoma gene, RB, p161NK4A/CDKN2, and E2F-1 as tumor suppressor genes with potential prognostic significance in patients with bladder cancer. Better understanding of the genetic mechanisms underlying bladder tumor development and progression will allow better prevention, diagnosis, and treatment strategies.

Relationship between Ras pathways and cell cycle control

The ordered execution of the two main events of cellular reproduction, duplication of the genome and cell division, characterize progression through the cell cycle. Cultured cells can be switched between cycling and non-cycling states by alteration of extracellular conditions and the notion that a critical cellular control mechanism presides on this decision, whose temporal location is known as the restriction point, has become the focus for the study of how extracellular mitogenic signalling impinges upon the cell cycle to influence proliferation. This review attempts to cover the disparate pathways of Ras-mediated mitogenic signal transduction that impact upon restriction point control.

Activation of K-p21ras and N-p21ras, but not H-p21ras, is necessary for mitogen-induced human airway smooth-muscle proliferation

Ras proteins (H-, K-, and N-p21ras) play critical roles in the control of normal and neoplastic cell growth. To date, however, little is known about the role of p21ras in regulating mitogen-induced smooth muscle and, specifically, human airway smooth-muscle (HASM) cell growth. We postulate that p21ras is a critical signaling event regulating mitogen-induced HASM cell proliferation. Growth-arrested, confluent HASM cells were treated for 1 h with 10 ng/ml epidermal growth factor (EGF), 1 U/ml thrombin, or 5 microM bradykinin, then cell lysates were immunoprecipitated using anti-p21ras antibody. Immunoblot analysis using a pan p21ras antibody, which recognizes H-, K-, and N-p21ras, found no significant difference in p21ras expression in HASM after stimulation with either agent, as compared with control. In parallel experiments, we characterized that HASM cells express K- and N-p21ras, but not H-p21ras. Further, there was no difference between the levels of each p21ras isoform after stimulation with any of the agonists. The time course of p21ras activation, however, was markedly different among agonists. EGF rapidly activated p21ras within 30 s and was sustained for up to 30 min. Although thrombin also induced a rapid rise in p21ras activity after 2.5 min, the activation was transient. In contrast, bradykinin, which is nonmitogenic for HASM cells, did not activate p21ras. Using single-cell microinjection, the role of p21ras activation in modulating mitogen-induced HASM DNA synthesis was determined by 5-bromo-2'-deoxyuridine (BrdU) incorporation and anti-BrdU immunofluorescent staining. Thrombin- and EGF-induced DNA synthesis in cells microinjected with Y13-259, a neutralizing p21ras antibody, was significantly inhibited as compared with those microinjected with isotype-matched rat immunoglobulin G(1) or a vehicle control. These data suggest that activation of p21ras appears to be necessary for EGF and thrombin-induced HASM cell proliferation and that activation of K- and N-p21ras, but not H-p21ras, mediates smooth-muscle cell growth.

Diminished energy metabolism and enhanced apoptosis in livers of B6C3F1 mice treated with the antihepatocarcinogen rotenone

Rotenone decreases the incidence of hepatocellular carcinoma and lowers rates of hepatocellular proliferation. In an effort to delineate mechanisms involved, the in vivo effect of rotenone on liver mitochondrial metabolism, apoptotic machinery as well as elements of the hepatic signal transduction pathways were investigated. Mitochondria from livers of male B6C3F1 mice fed a standard diet containing 600 ppm rotenone for 7 days were uncoupled or inhibited when succinate or glutamate plus malate were used as the substrate, respectively. These livers also showed a significant increase in apoptosis compared with control livers. Furthermore, rotenone increased the expression of c-myc mRNA to 5-fold of control values within 3 days, an effect which was still observed (3-fold) after 7 days. Levels of p53 mRNA were also increased 3-fold after 1 day, but declined to control levels by 7 days. Rotenone also caused a transient, yet marked increase in liver particulate glyceraldehyde phosphate dehydrogenase (GAPDH) protein expression, while it did not alter the expression of the cytosolic form of the enzyme. Conversely, mRNA of the proto-oncogene H-ras showed a decline of 35% after 3 days of rotenone treatment, and remained diminished for the duration of the experiment. These data suggest that rotenone may act as an anticancer agent by diminishing mitochondrial bioenergetics which prevents basal hepatocyte proliferation and lowers the threshold for liver cells with DNA damage to undergo apoptosis.

Combination of the novel farnesyltransferase inhibitor RPR130401 and the geranylgeranyltransferase-1 inhibitor GGTI-298 disrupts MAP kinase activation and G(1)-S transition in Ki-Ras-overexpressing transformed adrenocortical cells

To test the Kirsten-Ras (Ki-Ras) alternative prenylation hypothesis in malignant transformation, we used a novel farnesyltransferase inhibitor competitive to farnesyl-pyrophosphate, RPR130401, and a CaaX peptidomimetic geranylgeranyltransferase-1 inhibitor GGTI-298. In Ki-Ras-overexpressing transformed adrenocortical cells, RPR130401 at 1-10 microM inhibited very efficiently the [(3)H]farnesyl but not [(3)H]geranylgeranyl transfer to Ras. However, proliferation of these cells was only slightly sensitive to RPR130401 (IC(50)=30 microM). GGTI-298 inhibited the growth of these cells with an IC(50) of 11 microM but cell lysis was observed at 15 microM. The combination of 10 microM RPR130401 and 10 microM GGTI-298 inhibited efficiently (80%) cell proliferation. These combined inhibitors but not each inhibitor alone blocked the cell cycle in G(0)/G(1) and disrupted MAP kinase activation. Thus, combination of two inhibitors, at non-cytotoxic concentrations, acting on the farnesyl-pyrophosphate binding site of the farnesyltransferase and the CaaX binding site of the geranylgeranyltransferase-1 respectively is an efficient strategy for disrupting Ki-Ras tumorigenic cell proliferation.

Estrogen inducibility of c-Ha-ras transcription in breast cancer cells. Identification of functional estrogen-responsive transcriptional regulatory elements in exon 1/intron 1 of the c-Ha-ras gene

Although mutation of ras gene is rare in human breast cancer, overexpression of normal c-Ha-ras gene is frequently observed. Using a mouse mammary metastasis model consisting of genetically related mammary tumor sublines with variant metastatic potential, we have previously (i) demonstrated a direct correlation between c-Ha-ras mRNA and protein levels and metastatic potential and (ii) identified a novel hormone-responsive transcriptional regulatory element in intron 1 of the mouse c-Ha-ras gene that contains the consensus half-site of a glucocorticoid response element and flanking consensus half-sites for estrogen response element. Here, we have examined the functionality of intron 1 sequence in context of upstream sequences by using transient transfection assays with plasmids expressing chloramphenicol acetyltransferase. Intron 1 sequence and sequences similar to intron 1 element located in exon 1 function as transcriptional regulatory elements that confer hormonal inducibility to chloramphenicol acetyltransferase gene expression both independently and in context of 5'-flanking sequences. Measurement of c-Ha-ras transcription rates and protein expression by nuclear run-on and metabolic labeling assays showed a 5-12-fold enhancement, respectively, following treatment with 17beta-estradiol that was blunted by ICI 182,780 in the nonmetastatic variant. In contrast, constitutive overexpression of c-Ha-ras transcripts and protein in the metastatic subline was unaffected by estrogen and ICI 182,780. Gel shift assays demonstrated specific interaction of c-Ha-ras exon 1 sequence with nuclear proteins of human breast cancer MCF-7 cells with formation of two complexes, one of which contains estrogen receptor. Our data demonstrate a direct (i) interaction of c-Ha-ras sequence with estrogen receptor and (ii) stimulatory effect of estrogen on c-Ha-ras gene transcription and suggest that alteration in transcriptional regulation of c-Ha-ras gene by estrogen may play an important role in progression of breast cancer.

Therapeutic efficacy of an adenovirus-mediated anti-H-ras ribozyme in experimental bladder cancer

Ras oncogenes are thought to play a critical role in cellular proliferation and tumorigenesis. Reversal of the malignant phenotype, inhibition of tumor growth, and decreased tumorgenicity have been demonstrated with the use of anti-H-ras ribozymes. In this study, the therapeutic efficacy of a hammerhead ribozyme targeting the mutated H-ras oncogene was investigated in an experimental bladder cancer model using a recombinant adenovirus as delivery vehicle. Tumors were established in nude mice by subcutaneous injection of EJ human bladder carcinoma cells harboring a point mutation of the H-ras gene. The tumors were treated with intralesional injections of an adenovirus expressing an anti-H-ras ribozyme (rAd-Hras Rz) by different schedules at serial titers, and the tumor inhibition efficacy was analyzed. The viral infection efficacy and kinetics of ribozyme expression were also evaluated. Intralesional injection of rAd-Hras Rz resulted in significant antineoplastic effects in a dose-dependent fashion. Complete regression of the tumor was achieved by rAd-Hras Rz in several cases without recurrence during the 50-day observation period. Although there was moderate vector-associated cytotoxicity in this cell line, complete regressions were not observed in the cases treated with control adenovirus vectors or vectors expressing an inactive anti-H-ras ribozyme or anti-H-ras antisense oligonucleotides. These results suggest the efficacy of a ribozyme-encoding adenovirus in the experimental gene therapy of human bladder cancer.

p21Waf1/Cip1/Sdi1 induces permanent growth arrest with markers of replicative senescence in human tumor cells lacking functional p53

We have shown previously that wild type p53 can rapidly induce replicative senescence in EJ human bladder carcinoma cells lacking functional p53. A major effector of p53 functions is p21Waf1/Cip1/Sdi1, a potent cyclin-dependent kinase inhibitor. p21Waf1/Cip1/Sdi1 has been shown to be involved in both p53 dependent and independent control of cell proliferation, differentiation and death. To directly investigate the effects of p21Waf1/Cip1/Sdi1 in the p53 response observed in EJ tumor cells, we established p21Waf1/Cip1/Sdi1 inducible lines using the tetracycline-regulatable vector system. p21Waf1/Cip1/Sdi1 induction caused irreversible cell cycle arrest in both G1 and G2/M, and diminished Cdk2 kinase activity. In addition, p21Waf1/Cip1/Sdi1 induction led to morphological alterations characteristic of cells undergoing replicative senescence with morphological, biochemical and ultrastructural markers of the senescent phenotype. Furthermore, sustained p21Waf1/Cip1/Sdi1 induction sensitized EJ cells to apoptotic cell death induced by mitomycin C, a cross-linking DNA damaging agent. These findings support the function of p21Waf1/Cip1/Sdi1 as an inducer of replicative senescence and a major mediator of this phenomenon in response to p53. Moreover, our results imply that therapeutic intervention in human cancers might be aimed at sustained elevation of p21Waf1/Cip1/Sdi1 expression.

Nerve growth factor induces survival and differentiation through two distinct signaling cascades in PC12 cells

Nerve growth factor induces differentiation and survival of rat PC12 pheochromocytoma cells. The activation of the erk cascade has been implicated in transducing the multitude of signals induced by NGF. In order to explore the role of this signaling cascade in NGF mediated survival, differentiation and proliferation, we generated recombinant adenoviruses which express the intermediates of the erk cascade in their wild type, dominant negative and constitutively activated forms. We show that differentiation of PC12 cells requires activity of the ras/erk pathway, whereas inhibition of this pathway had no effect on survival or proliferation. Constitutively active forms of ras, raf and mek induced PC12 cell differentiation, while dominant interfering forms inhibited differentiation. Survival of PC12 cells in serum-free medium did not require activity of the ras/erk pathway. Instead, PI3 Kinase signaling was necessary for PC12 cell survival. Interestingly, constitutively activated versions of raf and mek were able to promote survival, but again this was dependent on activation of PI3 Kinase. Therefore, at least two distinct signaling pathways are required in PC12 cells for mediation of NGF functions.

p21 ras and phosphatidylinositol-3 kinase are required for survival of wild-type and NF1 mutant sensory neurons

Nerve growth factor (NGF) is a required differentiation and survival factor for sympathetic and a majority of neural crest-derived sensory neurons in the developing vertebrate peripheral nervous system. Although much is known about the function of NGF, the intracellular signaling cascade that it uses continues to be a subject of intense study. p21 ras signaling is considered necessary for sensory neuron survival. How additional intermediates downstream or in parallel may function has not been fully understood yet. Two intracellular signaling cascades, extra cellular regulated kinase (erk) and phosphatidylinositol-3 (PI 3) kinase, transduce NGF signaling in the pheochromocytoma cell line PC12. To elucidate the role these cascades play in survival and differentiation, we used a combination of recombinant adenoviruses and chemical inhibitors to perturb these pathways in sensory neurons from wild-type mice and mice deficient for neurofibromin in which the survival and differentiation pathway is constitutively active. We demonstrate that ras activity is both necessary and sufficient for the survival of embryonic sensory neurons. Downstream of ras, however, the erk cascade is neither required nor sufficient for neuron survival or overall differentiation. Instead, the activity of PI 3 kinase is necessary for the survival of the wild-type and neurofibromin-deficient neurons. Therefore, we conclude that in sensory neurons, NGF acts via a signaling pathway, which includes both ras and PI 3 kinase.

Notch inhibition of E47 supports the existence of a novel signaling pathway

E47 is a widely expressed transcription factor that activates B-cell-specific immunoglobulin gene transcription and is required for early B-cell development. In an effort to identify processes that regulate E47, and potentially B-cell development, we found that activated Notch1 and Notch2 effectively inhibit E47 activity. Only the intact E47 protein was inhibited by Notch-fusion proteins containing isolated DNA binding and activation domains were unaffected-suggesting that Notch targets an atypical E47 cofactor. Although overexpression of the coactivator p300 partially reversed E47 inhibition, results of several assays indicated that p300/CBP is not a general target of Notch. Notch inhibition of E47 did not correlate with its ability to activate CBF1/RBP-Jkappa, the mammalian homolog of Suppressor of Hairless, a protein that associates physically with Notch and defines the only known Notch signaling pathway in drosophila. Importantly, E47 was inhibited independently of CBF1/RPB-Jkappa by Deltex, a second Notch-interacting protein. We provide evidence that Notch and Deltex may act on E47 by inhibiting signaling through Ras because (i) full E47 activity was found to be dependent on Ras and (ii) both Notch and Deltex inhibited GAL4-Jun, a hybrid transcription factor whose activity is dependent on signaling from Ras to SAPK/JNK.

A stochastic model of cellular transformation and its relevance to chemical carcinogenesis

A mathematical model is presented which determines the relationship of cellular mutation to cellular survival and transformation. The basis for this model is the hypothesis that the entropy associated with changes of genotype are linearly proportional to the entropy associated with changes in phenotype. This hypothesis leads to a mathematical derivation relating cellular survival, mutation and transformation. The relevance of this model to data derived from experiments in chemical carcinogenesis is presented.

Differential oligonucleotide activity in cell culture versus mouse models

The usual course of drug discovery begins with the demonstration of compound activity in cells and, usually, a lower level of activity in animals. Successive rounds of drug design may result in a compound with sufficient activity in animals to justify clinical trials. The basic endpoints of therapeutic oligonucleotide experiments include target antigen reduction, target messenger reduction and inhibition of transformed cell proliferation or viral replication. However, one should expect oligonucleotides to exhibit pleiotropic behaviour, as do all other drugs. In an animal oligonucleotides will necessarily bind to and dissociate from all macromolecules encountered in the blood, in tissues, on cell surfaces and within cellular compartments. Contrary to expectations, oligonucleotides designed to be complementary to certain transcripts have sometimes been found moderately effective in cell-free extracts, more effective in cell culture and most effective in animal models. If greater potency against standard endpoints is reported in mouse models than was observed in cell culture, critical examination must consider alternate modes of action in animals that may not apply in cell culture. This counterintuitive paradox will be examined, based on studies of Ha-ras expression in bladder cancer, Ki-ras expression in pancreatic cancer, erbB2 expression in ovarian cancer and c-myc expression in B cell lymphoma.

Polyamines induce malignant transformation in cultured NIH 3T3 fibroblasts

Previous studies have demonstrated that polyamines accumulate in cancer cells and that overproduction of ornithine decarboxylase (ODC), which catalyzes polyamine synthesis, elicits the acquisition of the transformed phenotype. However, it was not clear whether the overexpression of ODC and the accumulation of polyamines are only innocent by-products of the transformation process. In this study we demonstrate that polyamines as such, may play a crucial role in malignant transformation. The system used consisted of NIH 3T3 fibroblasts transfected with a construct (pATMras) in which Ha-ras was under the transcriptional control of the mouse mammary tumor virus long terminal repeat (MMTV-LTR) promoter (MMTVras cells). Dexamethasone, which activates the promoter, triggered phenotypic transformation. This was accompanied by an increase in ODC activity and polyamine accumulation. Cells, thus transformed, grew in soft agar and formed typical foci. alpha-Difluoromethylornithine (DFMO), which blocks polyamine synthesis, inhibited the dexamethasone-enhanced transformation. This inhibition was reversed by polyamines. Polyamines caused transformation of MMTVras cells in the absence of dexamethasone. Under these conditions, cells became anchorage independent. This phenomenon is not explained by the leakiness of ras, since normal, immortalized NIH 3T3 fibroblasts, also grew in soft agar in the presence of polyamines. Taken together, these observations suggest that polyamines may stimulate malignant transformation of immortalized cells, in cooperation with other factors, such as oncogenes or genetic defects.

Aneuploidy correlated 100% with chemical transformation of Chinese hamster cells

Aneuploidy or chromosome imbalance is the most massive genetic abnormality of cancer cells. It used to be considered the cause of cancer when it was discovered more than 100 years ago. Since the discovery of the gene, the aneuploidy hypothesis has lost ground to the hypothesis that mutation of cellular genes causes cancer. According to this hypothesis, cancers are diploid and aneuploidy is secondary or nonessential. Here we reexamine the aneuploidy hypothesis in view of the fact that nearly all solid cancers are aneuploid, that many carcinogens are nongenotoxic, and that mutated genes from cancer cells do not transform diploid human or animal cells. By regrouping the gene pool-as in speciation-aneuploidy inevitably will alter many genetic programs. This genetic revolution can explain the numerous unique properties of cancer cells, such as invasiveness, dedifferentiation, distinct morphology, and specific surface antigens, much better than gene mutation, which is limited by the conservation of the existing chromosome structure. To determine whether aneuploidy is a cause or a consequence of transformation, we have analyzed the chromosomes of Chinese hamster embryo (CHE) cells transformed in vitro. This system allows (i) detection of transformation within 2 months and thus about 5 months sooner than carcinogenesis and (ii) the generation of many more transformants per cost than carcinogenesis. To minimize mutation of cellular genes, we have used nongenotoxic carcinogens. It was found that 44 out of 44 colonies of CHE cells transformed by benz[a]pyrene, methylcholanthrene, dimethylbenzanthracene, and colcemid, or spontaneously were between 50 and 100% aneuploid. Thus, aneuploidy originated with transformation. Two of two chemically transformed colonies tested were tumorigenic 2 months after inoculation into hamsters. The cells of transformed colonies were heterogeneous in chromosome number, consistent with the hypothesis that aneuploidy can perpetually destabilize the chromosome number because it unbalances the elements of the mitotic apparatus. Considering that all 44 transformed colonies analyzed were aneuploid, and the early association between aneuploidy, transformation, and tumorigenicity, we conclude that aneuploidy is the cause rather than a consequence of transformation.

Role of heparin-binding EGF-related peptides in proliferation and apoptosis of activated ras-stimulated intestinal epithelial cells

The ras mutation is a common and critical step in carcinogenesis. Autocrine growth factors are also known to play an important role in cancer cell growth and transformation. However, the contribution of autocrine growth factors in regulation of proliferation and apoptosis of activated ras-stimulated intestinal epithelium is not fully understood. Therefore, we constructed activated ras-transfected intestinal epithelial cell clones (IEC-ras) to examine the role of epidermal growth factor (EGF)-related peptides in the behavior of IEC-ras. Overexpression of EGF family growth factors (transforming growth factor alpha, heparin-binding EGF-like growth factor, amphiregulin and betacellulin) and stronger phosphorylation of the EGF receptor was observed in IEC-ras compared with control cells. IEC-ras proliferated more rapidly than control cells, and a specific EGF receptor kinase inhibitor, AG 1478, abolished the increased proliferation of IEC-ras. Heparitinase and chlorate also prevented increased proliferation of IEC-ras. Additionally, IEC-ras expressed more bcl-2 and was more resistant to apoptosis induction by UV radiation and mitomycin C. AG 1478 suppressed bcl-2 expression and inhibited resistance to apoptosis of IEC-ras. Heparitinase and chlorate had effects similar to those of AG 1478. Our data indicate that heparin-binding EGF family growth factors play an important role in both increased proliferation and resistance to apoptosis of ras-stimulated intestinal epithelial cells.

Dominant transformation by mutated human ras genes in vitro requires more than 100 times higher expression than is observed in cancers

The gene-mutation-cancer hypothesis holds that mutated cellular protooncogenes, such as point-mutated proto-ras, "play a dominant part in cancer," because they are sufficient to transform transfected mouse cell lines in vitro [Alberts, B., Bray, D., Lewis, J., Raff, M., Roberts, K. & Watson, J. D. (1994) Molecular Biology of the Cell (Garland, New York)]. However, in cells transformed in vitro mutated human ras genes are expressed more than 100-fold than in the cancers from which they are isolated. In view of the discrepancy between the very low levels of ras transcription in cancers and the very high levels in cells transformed in vitro, we have investigated the minimal level of human ras expression for transformation in vitro. Using point-mutated human ras genes recombined with different promoters from either human metallothionein-IIA or human fibronectin or from retroviruses we found dominant in vitro transformation of the mouse C3H cell line only with ras genes linked to viral promoters. These ras genes were expressed more than 120-fold higher than are native ras genes of C3H cells. The copy number of transfected ras genes ranged from 2-6 in our system. In addition, nondominant transformation was observed in a small percentage (2-7%) of C3H cells transfected with ras genes that are expressed less than 20 times higher than native C3H ras genes. Because over 90% of cells expressing ras at this moderately enhanced level were untransformed, transformation must follow either a nondominant ras mechanism or a non-ras mechanism. We conclude that the mutated, but normally expressed, ras genes found in human and animal cancers are not likely to "play a dominant part in cancer." The conclusion that mutated ras genes are not sufficient or dominant for cancer is directly supported by recent discoveries of mutated ras in normal animals, and in benign human tissue, "which has little potential to progress" [Jen, J., Powell, S. M., Papadopoulos, N., Smith, K. J., Hamilton, S. R., Vogelstein, B. & Kinzler, K. W. (1994) Cancer Res. 54, 5523-5526]. Even the view that mutated ras is necessary for cancer is hard to reconcile with (i) otherwise indistinguishable cancers with and without ras mutations, (ii) metastases of the same human cancers with and without ras mutations, (iii) retroviral ras genes that are oncogenic without point mutations, and (iv) human tumor cells having spontaneously lost ras mutation but not tumorigencity.

Wild-type p53 triggers a rapid senescence program in human tumor cells lacking functional p53

The p53 tumor suppressor gene has been shown to play an important role in determining cell fate. Overexpression of wild-type p53 in tumor cells has been shown to lead to growth arrest or apoptosis. Previous studies in fibroblasts have provided indirect evidence for a link between p53 and senescence. Here we show, using an inducible p53 expression system, that wild-type p53 overexpression in EJ bladder carcinoma cells, which have lost functional p53, triggers the rapid onset of G1 and G2/M growth arrest associated with p21 up-regulation and repression of mitotic cyclins (cyclin A and B) and cdc2. Growth arrest in response to p53 induction became irreversible within 48-72 h, with cells exhibiting morphological features as well as specific biochemical and ultrastructural markers of the senescent phenotype. These findings provide direct evidence that p53 overexpression can activate the rapid onset of senescence in tumor cells.

Alternative signaling mechanism of leukemia inhibitory factor responsiveness in a differentiating embryonal carcinoma cell

Leukemia inhibitory factor (LIF) is a cytokine that plays an important role during mouse embryogenesis. We showed that adenovirus E1A represses the interleukin-6 signal transduction pathway that uses the same JAK tyrosine kinase and STAT (signal transducer and activator of transcription) transcription factor as LIF. Here, we report that the LIF-JAK-STAT signal transduction pathway is blocked in cellular E1A-expressing undifferentiated F9 cells, and that the block is overcome by retinoic acid-induced differentiation. LIF failed to stimulate the expression of the acute phase response element (APRE)-driven luciferase gene in undifferentiated F9 cells, whereas the luciferase activity was remarkably increased by LIF treatment in differentiated F9 (dF9) cells. We analyzed the mechanism of the APRE regulation and found that the LIF-induced APRE-binding activity was regulated in a differentiation-dependent manner. The protein levels and the tyrosine phosphorylation of JAK1, JAK2, and STAT3 in F9 cells were not different from those in dF9 cells. The exogenous expression of activated c-Ha-ras partially recovered the LIF responsiveness of the APRE-luciferase gene in F9 cells, but the dominant negative ras N-17 did not repress the LIF-induced activation of APRE-luciferase in dF9 cells. These results suggested that an unknown coactivation process that is partially compensated by Ras is required for STAT3-APRE binding in F9 cells.

An ADP-ribosylation-factor(ARF)-like protein involved in regulated secretion

A rat ADP-ribosylation factor(ARF)-like protein named ARL184 was identified by cDNA cloning. The corresponding recombinant protein had an apparent molecular mass of 22,000. The deduced amino acid sequence had 55% identity with the human ARL1 and four functional GTP-binding sites. Immunofluorescent confocal microscopy studies showed that ARL184 was present in the cytosol as well as in the Golgi apparatus, raising the possibility that it has a role in a secretory pathway. The involvement of this ARF-like protein in secretion was confirmed by demonstrating that ARL184 potentiated acetylcholine release in stably transfected PC12 cells. Collectively these results suggest that this ARL protein is a component of a regulated secretory pathway involved in Ca2(+)-dependent release of acetylcholine.

Identification of H, K, and N-ras point mutations in stage IB cervical carcinoma

OBJECTIVE

The ras oncogenes, Harvey (H), Kirsten (K), and neuroblastoma (N), are a family of genes coding for a membrane-associated protein (p21) which possesses inherent guanine triphosphatase (GTPase) activity. Point mutagenesis at codons 12, 13, and 61 has been implicated in ras activation and subsequent cellular transformation. Given the epidemiologic relationship of HPV infection with cervical carcinoma and the tumorigenic interaction of HPV and mutated ras oncogenes, this study was undertaken to identify if mutated ras oncogenes were present in early invasive cervical carcinomas.

METHODS

A combination of polymerase chain reaction (PCR) and dot-blot hybridization was used to determine the frequency and types of ras point mutants occurring in cervical carcinoma. Thirty-three patients with early-stage cervical carcinoma were identified. DNA was extracted from archival tumor samples. ras genes were PCR amplified using flanking primers and hybridized with a series of labeled allele-specific oligonucleotides corresponding to wild-type forms of K12,61, N12,13,61, and H12,61, as well as to all combinations of substitution mutations (7 wild-type, 45 mutants).

RESULTS

ras mutations were identified in 24.2% of specimens. The detected mutations in H, K, and N-ras all occurred at codon 61. This was not the result of PCR or hybridization artifact in that mutations were detected in position 12 and 13 in appropriate control samples.

CONCLUSIONS

Mutant ras has been shown to convert HPV immortalized keratinocytes to the tumorigenic state. Our results indicate that a significant percentage (24.2%) of these early-stage cervical cancers contain activated ras. Additional studies will be needed to evaluate whether codon 61 represents a characteristic "hot-spot" of ras mutation in a subset of cervical carcinoma.

Geranylgeranyl as well as farnesyl moiety is transferred to Ras p21 overproduced in adrenocortical cells transformed by c-Ha-rasEJ oncogene

The ras-transformed newborn rat adrenocortical (RTAC) cells were obtained by transfection with the mutated c-Ha-rasEJ oncogene. They are proliferative and tumorigenic cells characterized by expression of the c-Ha-rasEJ oncogene and overexpression of a wild-type ras oncogene. The overproduced Ras p21 was identified here as Ki-Ras p21 by western blotting using a specific anti-Ki-Ras monoclonal antibody. Radioactivity derived from [14C]mevalonolactone was strongly incorporated into Ras p21 overproduced in RTAC cells. RTAC cells pretreated with lovastatin and labeled with either [3H]geranylgeranyl-pyrophosphate or [3H]farnesyl-pyrophosphate incorporated also radioactivity into Ras p21. These results showed that overproduced Ras proteins were geranylgeranylated as well as farnesylated in RTAC cells. These findings suggest that the strategy for inhibiting proliferation of Ki-ras-dependent tumorigenic cells should be directed against not only farnesylation but also geranylgeranylation of Ras p21.

Evidence supporting a signal transduction pathway leading to the radiation-resistant phenotype in human tumor cells

A signal transduction pathway, involving oncogenes and their normal counterparts the proto-oncogenes, analogous to that for cell growth and differentiation has been proposed to lead to the phenotype of cellular radioresistance (RR). In this report we provide evidence demonstrating the existence of such a pathway by using antisense oligonucleotides (ASO) to reverse the RR phenotype. Utilizing ASO directed against the raf-1 gene, a central component of this proposed pathway, we were able to reverse the RR phenotype of human tumor cell lines having elevated HER-2 expression or a mutant form of Ha-ras, two genes upstream of raf-1 in signal transduction. Additionally, anti-ras ASO were able to radiosensitize HER-2 overexpressing cells. These results, which verify the presence of a signaling pathway leading to cellular RR, also have possible clinical implications for the use of ASO as a means to sensitize radioresistant tumors to radiation therapy.

Correlation of allelic loss of the P53 gene and tumor grade, stage, and malignant progression in bladder cancer

BACKGROUND

We examined loss of heterozygosity (LOH) of the P53 gene in bladder cancer, and investigated the role of the P53 gene on malignant progression of papillary tumors. In addition, the clonality of recurrent bladder cancer was examined.

METHODS

LOH of the P53 gene was analyzed in 67 bladder cancers from 47 patients. DNA was extracted from formalin-fixed, paraffin-embedded tissues, amplified by the polymerase chain reaction (PCR) at 3 polymorphic loci in the P53 gene, and analyzed with nonradioisotopic single-strand conformation polymorphism (Non-RI SSCP) analysis.

RESULTS

Out of 40 informative samples, LOH was detected in 13 samples, containing 4 of 7 in grade 3 (57%), 9 of 23 in grade 2 (39%), and none of 10 in grade 1 (10%). Statistical significance was observed between the LOH in grades 1 and 2, and in grades 1 and 3. An analysis of 5 cases showing malignant progression revealed that 3 (60%) showed an LOH in the primary tumor, and 2 showed LOH in recurrent tumors, in contrast to LOH found in 3 cases of 19 (16%) not showing malignant progression. Four cases with metachronous recurrence exhibited LOH; 2 at recurrent tumors, 1 only at the initial tumor, and 1 at both tumors.

CONCLUSIONS

The alterations of the P53 gene were considered to correlate with tumor grade, and contribute to the malignant progression of bladder cancer. LOH in the P53 gene may serve as a clinical indicator for prognosis in superficial bladder cancer.

A ribozyme specifically suppresses transformation and tumorigenicity of Ha-ras-oncogene-transformed NIH/3T3 cell lines

In this study, the efficacy of an anti-ras ribozyme in reversing a transformed phenotype was investigated. A murine NIH/3T3-derived cell line, designated 2-12, contains an inducible Ha-ras oncogene, which is regulated by the Escherichia coli (E. coli) lac operator/repressor system, and displays a transformed phenotype after isopropyl-beta-D-thiogalactoside induction. To reverse the transformed characteristics, the ribozyme, which specifically targets the Ha-ras oncogene at the codon 12 mutation site (GGC to GUC), was transfected into 2-12 cells. Two (ribZ4 and ribZ7) clones were subsequently selected and analyzed for their transforming features. Our results show that, in the transfectants, ribozyme gene expression was detected, and the target Ha-ras transgene was expressed at basal levels. Their phenotypic responses, including morphology, cell growth rate, colony-formation efficiency and tumorigenicity in mice with severe combined immunodeficiency were more similar to those of NIH/3T3 than 2-12 transformed cells. Directly injecting the ribozyme DNA into tumors induced by transformed 2-12 cells in BALB/c mice also caused tumor regression. The enzymatic cleavage products of the ribozyme acting on mutant Ha-ras mRNA in vivo were detected by primer-extension analysis. These results indicate that the ribozyme were designed exhibits a site-specific ribonuclease function that effectively abrogates Ha-ras-oncogene-induced transformation, and this unique anti-Ha-ras property should shed light on the development of strategies against the Ha-ras-oncogene-initiated malignancy.

Enhancing the effect of anticancer drugs against the colorectal cancer cell line with electroporation

Electroporation was applied in vitro and in vivo in the treatment of human colorectal cancer cell lines to study whether it can enhance the effect of bleomycin (BLM), 5-fluorouracil (5-FU) and cis-platinum (CDDP). We used LS174T and Colo320 cells derived from human colon cancer as target cells in this study. When the LS174T cells were used as target cells, the IC50 of BLM decreased to 10(-3) times, while that of 5-FU decreased to only about one fifth with the application of electric current. In the case of the Colo320 cells, the IC50 of BLM and 5-FU were about one hundredth and a half, respectively. The effect of CDDP was not enhanced with electric current. In vivo experiments were also performed using LS174T cells transplanted subcutaneously (s.c.) into nude mice. By treatment with intravenously (i.v.) administered BLM and simultaneous application of the electric current, tumors were markedly decreased in size after three weeks.