Somatostatin enhances neurofilament expression and neurite outgrowth in cultured rat cerebellar granule cells

Somatostatin and its receptors are transiently expressed at a high level in the cerebellum around birth, before declining to adult levels by 2-3 weeks postnatally. We therefore investigated the neurotrophic effects of somatostatin (SS) on rat cerebellar granule cells in culture by measuring the percentage of cells with processes, the content of mRNA and protein for neurofilament (NF) and mRNA for glutaminase, and the number of viable cells (MTS assay). SS increased the percentage of cells with processes at 8 h after plating. After 1 day in vitro (DIV), SS caused a 2-fold increase in NF mRNA, and a 23% increase in NF protein. The mRNA increase was maximal at DIV1 whereas by DIV7 the NF protein content of control cells reached that of SS-treated cells. SS had no effect on glutaminase mRNA or on the number of viable neurons from either postnatal day 5 or 8 animals. These results demonstrated that SS has a neurotrophic effect on neurite production, including initiation of neurite outgrowth, but no effect on neuronal survival, cell proliferation, or phenotype differentiation (glutaminase expression), and support the possibility that SS plays a role in the differentiation of immature cerebellar granule cells during central nervous system development.

Genetic damage and the inhibition of 7,12-dimethylbenz[a]anthracene-induced genetic damage by the phytoestrogens, genistein and daidzein, in female ICR mice

Populations consuming soybeans have reduced rates of breast, colon and prostate cancer possibly due, in part, to the presence in soybeans of two estrogenic isoflavones, genistein and daidzein. This study investigated the genotoxicity of these soya isoflavones and their interactions with 7,12-dimethylbenz[a]anthracene (DMBA)-induced sister chromatid exchanges (SCE) in bone marrow cells and DNA adduct formations in liver and mammary glands of mice. Groups of female ICR mice were pretreated i.p. with daidzein and/or genistein (10-20 mg/kg per day for 6 days or 50 mg/kg per 12 h for 3 days) or with the solvent, dimethylsulfoxide (DMSO). The mice were implanted with bromodeoxyuridine (BrdU) tablets s.c., and treated with DMBA (50 mg/kg) i.p. and colchicine (4 mg/kg) i.p. 24, 23, and 2 h before sacrifice, respectively. In bone marrow cells. DMBA alone induced 11.73 +/- 1.42 SCE/cell compared to 4.35 +/- 0.83 SCE/cell in the DMSO treated controls (P = 0.001). DMBA induced 20% fewer SCE (P < 0.05) in mice pretreated with daidzein, genistein or a combination of genistein and daidzein (6 x 20 mg/kg per day for 6 days) when compared to mice that received no pretreatments. Genistein at 50 mg/kg per 12 h for 3 days also inhibited DMBA-induced SCE by 20%. However, treatment for 3 days with 50 mg/kg per 12 h of genistein or daidzein alone, or a combination of daidzein plus genistein (without DMBA treatment) also induced more SCE than treatment with only the solvent (DMSO, P < 0.05). Pretreatment with both the low and the high doses of daidzein plus genistein or the high dose of genistein reduced the replication index of bone marrow cells when compared to pretreatment with DMSO (P < 0.05). Pretreatment with genistein reduced DMBA-induced DNA adduct formation by 34%, but this was only marginally significant (P = 0.08) due to the large inter-individual variability in adduct levels. These results show that genistein and daidzein suppress SCE and possibly DNA adduct formation induced by the known carcinogen, DMBA. This response to a low dose isoflavone exposure may be partly responsible for the protective effect against endocrine cancers of soya consumption.

Pro-transforming growth factor-alpha processing in human colon carcinoma cells: role of protein kinase C

The human colon cancer cell lines HCT 116 (poorly differentiated) and GEO (well differentiated) express the mitogenic peptide transforming growth factor alpha (TGF-alpha). The secretion of TGF-alpha was enhanced by phorbol 12-myristate 13-acetate (PMA), indicating the possible role of protein kinase C (PKC) in the formation of mature TGF-alpha. Cells were metabolically labeled with 35S-cysteine and the formation of the mature 6 kDa TGF-alpha polypeptide from the 17 kDa pro-TGF-alpha precursor was determined. The conversion of pro-TGF-alpha was complete in 2-4 hr with the HCT 116 cells showing faster kinetics of TGF-alpha formation than GEO cells. HCT 116 cells secreted more TGF-alpha than GEO cells and the rate and extent of formation of TGF-alpha was enhanced by PMA in both cell lines. The expression of several PKC isozymes by HCT 116 and GEO cells was examined by immunoblotting. The expression of all isozymes examined was higher in HCT 116 cells compared with GEO cells. Calphostin C, an inhibitor of PKC, reduced the enzyme activity and significantly inhibited the PMA-induced secretion of TGF-alpha by both cell lines. Two agonists of PKC that act on specific PKC isozymes, thymeleatoxin and 12-deoxyphorbol 13-phenylacetate 20-acetate (dPPA), stimulated the release of TGF-alpha into the medium to the same extent as PMA. Since dPPA has been reported to stimulate PKC-beta 1 specifically, our results suggest a potential role for PKC-beta in the processing of pro-TGF-alpha by these 2 human colon carcinoma cell lines.

Quercetin: synergistic action with carboxyamidotriazole in human breast carcinoma cells

Quercetin, a plant flavonoid, blocks signal transduction pathways by inhibiting 1-phosphatidylinositol 4-kinase (EC 2.7.1.67, PI kinase) and 1-phosphatidylinositol 4-phosphate 5-kinase (EC 2.7.1.68, PIP kinase), resulting in a reduction of inositol 1,4,5-trisphosphate (IP3) concentration which decreases the release of calcium from intracellular sources. Carboxyamidotriazole (CAI), a novel anticancer agent, inhibits calcium entry into cells. Because both drugs reduce cytosolic calcium levels, we tested the action of quercetin and CAI in human carcinoma cells. Human breast carcinoma MDA-MB-435 cells were grown in minimum essential medium with 10% fetal bovine serum. In growth inhibition assay the IC50s for quercetin and CAI were 55 and 4.8 microM, respectively; in clonogenic assay, 28 and 1.4 microM, respectively. When quercetin and CAI were added to the cultures, synergism was observed in isobolograms in growth inhibition and clonogenic assays. In growth inhibition assay, the best combination was 20 microM quercetin with 4 microM CAI; in clonogenic assay, 30 microM quercetin with 1.2 microM CAI. Since these drugs are in phase I trials the synergistic action of quercetin and CAI may be of interest in clinical trials for breast carcinoma.

In vitro drug sensitivity of leukemic progenitors and P-glycoprotein expression in adult acute myeloid leukemia: correlation with induction treatment outcome

We have investigated the self-renewal capacity (PE2) and in vitro sensitivity to cytosine-arabinoside (ara-C) and daunorubicine (DNR) of leukemic progenitors (CFU-AML) to determine the significance of these tests for predicting induction treatment outcome in 75 adult acute myeloid leukemia (AML) patients. In addition, in a part of this group of patients (n = 46) we determined the expression of P-glycoprotein (P-gp) immunocytochemically and correlated those results with the therapeutic response. We have evaluated 66 patients who showed the following responses: 28/66 complete remissions (CR), 16/66 resistant leukemias (RL) and 22/66 early deaths (ED). The PE2 value was significantly higher in patients with RL than in patients with CR (p < 0.00375). CFU-AML sensitivity to ara-C and DNR alone was not different between response groups, but the difference in CFU-AML sensitivity to the combination of drugs between patients with CR and RL was not significant, although a trend was noted (p < 0.06). P-gp expression was found in only 1/18 patients who achieved CR but in 9/11 patients with RL and 7/11 patients with ED, which is a highly significant difference (p < 0.0006). We concluded that both PE2 and P-gp expression in AML cells are valuable predictors of therapeutic response in adult AML and should be included in creating the best therapeutic approach to AML patients.

Downregulation of mdr-1 expression by 8-Cl-cAMP in multidrug resistant MCF-7 human breast cancer cells

8-Cl-cAMP, a site-selective analogue of cAMP, decreased mdr-1 expression in multidrug-resistant human breast cancer cells. A sixfold reduction of mdr-1 mRNA expression by 8-Cl-cAMP began within 8 h of treatment and was associated with a decrease in the synthesis of P-glycoprotein and with an increase in vinblastine accumulation. A reduction in mdr-1 expression after 8-Cl-cAMP treatment was also observed in multidrug-resistant human ovarian cancer cell lines. 8-Cl-cAMP is known to change the ratio between the two regulatory subunits, RI and RII, of protein kinase A (PKA). We observed that RI alpha decreased within 24 h of 8-Cl-cAMP treatment, that RII beta increased after as few as 3 h of treatment, and that PKA catalytic activity remained unchanged during 48 h of 8-Cl-cAMP treatment. The results are consistent with the hypothesis that mdr-1 expression is regulated in part by changes in PKA isoenzyme levels. Although 8-Cl-cAMP has been used to differentiate cells in other model systems, the only differentiating effect that could be detected after 8-Cl-cAMP treatment in the MCF-7TH cells was an increase in cytokeratin expression. Evidence that the reduction of mdr-1 mRNA occurred at the level of gene transcription was obtained by measuring chloramphenicol acetyltransferase (CAT) mRNA in MCF-7TH cells transfected with an mdr-1 promoter-CAT construct prior to 8-Cl-cAMP treatment. Thus, 8-Cl-cAMP is able to downregulate mdr-1 expression and suggests a new approach to reversal of drug resistance in human breast cancer.

Growth-inhibitory effects of serotonin uptake inhibitors on human prostate carcinoma cell lines

Growth stimulation of a variety of cell types by the neurotransmitter serotonin has been reported. We have examined the effects of three serotonin-uptake inhibitors, 6-nitroquipazine, zimelidine and fluoxetine (Prozac, Eli Lilly Co., Indianapolis, Indiana) on human prostate carcinoma cell lines. In vitro, all 3 of these compounds inhibited the proliferation of PC-3, DU-145 and LNCaP cells in a dose-dependent manner. Also, all 3 compounds blocked the uptake of a radiolabeled analog of serotonin by the prostate carcinoma cell lines. The order of potency for inhibition of growth as well as for serotonin uptake was fluoxetine > zimelidine > 6-nitroquipazine. The growth of subcutaneous, PC-3 xenografts in athymic nude mice was significantly inhibited by fluoxetine. These results implicate biogenic amines such as serotonin in the growth of prostate carcinoma cells and indicate the potential use of serotonin-uptake inhibitors for the treatment of prostate cancer.

New aspects of cell biology in osteosarcoma

Among the solid tumors of childhood and adolescence, osteosarcoma (OS) represents the most prominent example of efficient aggressive chemotherapy with secondary surgical therapy. A specific subclassification of the tumor is indispensable and must include recent results of cell biology. The co-distribution of different collagen types I-VI reflects the diverse differentiation of osteosarcoma cells, supporting the concept of a pluripotent mesenchymal cell to be the stem cell of the tumor. In contrast, osteonectin (SPARC) may not be considered as a reliable marker for osteosarcoma. The experience of special proteins being secreted by osteosarcoma cells is rather limited. Detailed molecular biological studies are still lacking. A loss of alleles on chromosome 17, particularly in the defined region 17p 13, can be observed in more than 75% of all OS, suggesting the contribution of a tumor suppressor gene, p53, located in that region. It is a 53 kd nucleophosphoprotein binding the major transforming protein, the large T antigen of Simian Virus 40. Immunohistological results showed positive staining with the antibody Pab 240 in 13 of 18 cases. In one osteoblastic OS, a novel splice mutation resulting in a fusing of exon 5 directly to exon 7 was detected. RB1 gene is also of major importance for the tumorigenesis of OS. The multidrug resistance (mdr) is associated with a membrane-bound channel-forming transport protein, the P-glycoprotein. It is a conserved plasma membrane component of about 170 kd. Both the human isoforms mdr 1 and mdr 3 are localised in the long arm of chromosome 7.(ABSTRACT TRUNCATED AT 250 WORDS)

Antitumor effects of liposomal IL1 alpha and TNF alpha against the pulmonary metastases of the B16F10 murine melanoma in syngeneic mice

Interleukin 1 alpha (IL1 alpha) and tumor necrosis factor alpha (TNF alpha) have been successfully incorporated into specific phosphatidylcholine (PC) and phosphatidylserine (PS) multilamellar vesicle (MLV) liposomes by modifying the concentration of calcium ion and pH of the encapsulation buffer. Under these conditions, some of the cytokines may attach to the exterior surface of the MLV and therefore be readily accessible to target cells for receptor binding and signal transduction. These cytokine-associated liposomes are stable for up to 2 weeks in serum-free buffer, and leakage of cytokines into medium containing 10% fetal bovine serum was about 50% at the end of a 3-day incubation period at 37 degrees C. The biological activities mediated by liposomal IL1 alpha and TNF alpha were specific: the stimulation of thymidine uptake in T-helper D10 lymphocytes and the cytolysis of TNF alpha-sensitive L929 target cells could be blocked by specific neutralizing antibodies in a dose-dependent fashion. When administered intravenously into C57BL/6 mice bearing the syngeneic B16F10 murine melanoma cells, dual entrapment of liposomal IL1 alpha and TNF alpha significantly reduced the number of metastatic tumor nodules in the lungs and prolonged the life span of the animals. Thus, liposomal IL1 alpha and TNF alpha displayed significant in vivo antitumor activity against the IL1 alpha- and TNF alpha-resistant B16F10 metastatic murine melanoma.

Modulation of resistance to cisplatin by amphotericin B and aphidicolin in human larynx carcinoma cells

The aim of this study was to examine whether resistance to cisplatin [cis-diamminedichloroplatinum (II)] (CDDP) could be overcome by amphotericin B, cyclosporin A and aphidicolin in two sublines of human larynx carcinoma HEp2 cells. The sensitivity of parental and cisplatin-resistant CA3 and CK2 cells to amphotericin B, cyclosporin A and aphidicolin, and also the effects of these drugs (given in maximal nontoxic concentrations) on cisplatin sensitivity were determined by clonogenic survival assay. CA3 and CK2 cells were sensitive to amphotericin B, and resistant to cyclosporin A and aphidicolin, compared with their parental cells. Amphotericin B increased cisplatin toxicity 2-fold in CA3 cells and 2.7-fold in CK2 cells, while it had no effect in parental HEp2 cells. Cyclosporin A did not influence the sensitivity of examined cells to cisplatin. The sensitizing effect of aphidicolin was more obvious in cisplatin-resistant cells. Cisplatin toxicity was increased by aphidicolin: 1.5-fold in HEp2 cells, 2-fold in CA3 cells, and 1.9-fold in CK2 cells. Therefore, the resistance to cisplatin in human larynx carcinoma CA3 and CK2 cells can be partially reversed by amphotericin B and aphidicolin.

Molecular genetics of dysplasia in ulcerative colitis

Numerous molecular genetic events occurring in the development of sporadic colorectal neoplasia have been previously defined. The most frequent genetic alterations are mutations of the APC, KRAS, and TP53 genes, as well as loss of the DCC gene and of the second TP53 allele. The data from several groups indicate that these genes play an important role in ulcerative colitis-associated dysplasias and cancer, as they do in sporadic colorectal adenomas and carcinomas. KRAS and TP53 mutations were detected in dysplasia, but also in villous regeneration and active colitis, and affect a subpopulation of the cells composing these lesions. We conclude that in histologically defined dysplasia, clones can be found that genetically represent precancerous lesions in ulcerative colitis. Seen in this way, part of the active colitis and villous regeneration lesions might be considered as preneoplastic. When present, KRAS mutation is an excellent genetic marker to map populations of preneoplastic cells.

The role of interferon-alpha as a modulator of fluorouracil and leucovorin

Several preclinical studies have demonstrated that interferon-alpha (IFN-alpha) may enhance the cytotoxicity of fluoropyrimidines in a greater-than-additive manner in a variety of human cancer cell lines. The underlying mechanism(s) have varied in different cancer cell lines, and include increased fluorouracil anabolism to fluorodeoxyuridine monophosphate, further inhibition of thymidylate synthase, stimulation of thymidine and uridine phosphorylase activities, greater DNA damage, and enhanced natural killer cell-mediated lysis of tumour targets. These preclinical studies stimulated clinical evaluation of IFN-alpha in combination with 5-fluorouracil (5-FU) with and without leucovorin (LV), and the initial clinical results appeared promising. We summarise preclinical research concerning the interaction of 5-FU and IFN-alpha. The rationale for combining 5-FU with IFN-alpha and LV is discussed, and we describe our clinical experience with the combination of 5-FU, LV and IFN-alpha-2a. The insights and unresolved questions concerning the clinical application of this combination are also discussed.

Enhanced hepatocyte colony growth in soft agar after in vivo treatment with a genotoxic carcinogen: a potential assay for hepatocarcinogens?

We have shown previously that approximately 1 in 10,000 primary hepatocytes isolated from untreated rats undergo clonal growth in soft agar in vitro in response to the synergistic action of nafenopin, a peroxisome proliferator (PP) and epidermal growth factor (EGF), a naturally occurring liver growth regulator. Here, we demonstrate that prior treatment of the animals with the genotoxic hepatocarcinogen diethylnitrosamine (DEN) caused a dose-dependent increase in soft agar colony numbers formed in vitro. These data suggest that the colony assay may offer a method of detecting in vitro hepatocytes transformed in vivo by DEN. It is known that rats treated with DEN develop enzyme altered foci prior to the development of tumours. The majority of these foci express high levels of gamma-glutamyl transpeptidase (GGT). However, foci promoted by PPs do not show this increased enzyme activity. In the present study, the colonies we have generated in vitro mimicked this pattern since the majority (approximately 80%) of the spontaneous colonies expressed GGT whereas colonies promoted by the synergistic action of nafenopin and EGF were mainly (75%) GGT negative. The proportion of colonies positive for GGT were similar using either hepatocytes isolated from control or from DEN-initiated rats. Further studies are required to assess if the hepatocytes selected for clonal expansion by this EGF/nafenopin regime reflect the presumed pre-neoplastic cells induced by genotoxin in vivo and associated with an increased propensity to cancer.

Low affinity binding of phorbol esters to protein kinase C and its recombinant cysteine-rich region in the absence of phospholipids

Binding of phorbol esters to protein kinase C (PKC) has been regarded as dependent on phospholipids, with phosphatidylserine being the most effective for reconstituting binding. By using a purified single cysteine-rich region from PKC delta expressed in Escherichia coli we were able to demonstrate that specific binding of [3H]phorbol 12,13-dibutyrate to the receptor still takes place in the absence of the phospholipid cofactor. However, [3H]phorbol 12,13-dibutyrate bound to the cysteine-rich region with 80-fold lower affinity in the absence than in the presence of 100 micrograms/ml phosphatidylserine. Similar results were observed with the intact recombinant PKC delta isolated from insect cells. When different phorbol derivatives were examined, distinct structure-activity relations for the cysteine-rich region were found in the presence and absence of phospholipid. Our results have potential implications for PKC translocation, for inhibitor design, and for PKC structural determination.

Contribution of O6-methylguanine-DNA methyltransferase to resistance to 1,3-(2-chloroethyl)-1-nitrosourea in human brain tumor-derived cell lines

To assess the possible role of the DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT) in resistance of brain neoplasms to the clinically important chloroethylating agent 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), we quantitated MGMT activity, BCNU survival, and the effect of ablating MGMT activity on the sensitivity of 14 human medulloblastoma- and glioma-derived cell lines. BCNU resistance, measured as 10% survival dose (LD10), differed eightfold among the lines. Elimination of measurable MGMT activity with the substrate analogue inhibitor O6-benzylguanine (O6-BG) revealed a variable but limited contribution of MGMT to survival. In no case did O6-BG reduce LD10 by more than 3.4-fold. In contrast, O6-BG reduced the LD10 for N-methyl-N'-nitro-N-nitrosoguanidine up to 31-fold in the same cell lines (Bobola MS, Blank A, Berger MS, Silber JR, Mol Carcinog 13:70-80, 1995). Variability in BCNU survival, manifested as a sevenfold range of LD10, persists after measurable MGMT was eliminated, indicating that another mechanism or mechanisms is operating to limit cytotoxicity. Cells alkylated while suspended in growth medium are more resistant to BCNU and display less dependence on MGMT than cells treated while proliferating on a plastic substratum. When alkylated in suspension, most of the lines are either unresponsive to O6-BG or contain a subpopulation that did not respond to O6-BG. Our results demonstrate that BCNU resistance is multifactorial and that MGMT makes a modest contribution to resistance in our lines.

EO9: relationship between DT-diaphorase levels and response in vitro and in vivo

EO9 [3-hydroxy-5-aziridinyl-1-methyl-2(1H-indole-4,7-dione)-prop-beta-en- alpha-ol] was selected for clinical trial in Europe because of its preclinical profile but also because of its distinct mechanism of bioactivation. Several studies have shown that cells rich in DT-diaphorase may be particularly sensitive to EO9. The present study examined the relationship between DT-diaphorase activity and sensitivity to EO9 in a panel of cell lines largely derived from human and rodent leukaemias/lymphoma and solid tumours. A possible relationship between chemosensitivity and enzyme activity was demonstrated (correlation coefficient 0.796). A number of the human cell lines were established as xenografts in nude mice but, with the exception of HT29, DT-diaphorase specific activity was greatly reduced compared with the corresponding cell lines. These data suggest that in vitro studies of bioactivation of drugs by specific enzymes is unlikely to be relevant for the same tumour in vivo. Except for HCLO, all xenografts failed to respond to EO9 as a single dose. HT29 tumours in vivo had similar DT-diaphorase activity [359 nmol of 2,6-dichlorophenol-indophenol (DCPIP) reduced per min per mg of protein] to the cell line (337) but failed to respond to a single dose or daily dose schedule. A preliminary attempt to investigate an hourly dose schedule demonstrated a modest anti-tumour effect accompanied by enhanced toxicity. Attempts to optimise EO9 exposure parameters to potentiate activity in tumours with high DT-diaphorase activity are under way, but as yet the relevance of this particular enzyme for in vivo EO9 activity requires further investigation.

trans-dominant inhibition of poly(ADP-ribosyl)ation sensitizes cells against gamma-irradiation and N-methyl-N'-nitro-N-nitrosoguanidine but does not limit DNA replication of a polyomavirus replicon

Poly(ADP-ribosyl)ation is a posttranslational modification of nuclear proteins catalyzed by poly(ADP-ribose) polymerase (PARP; EC 2.4.2.30), with NAD+ serving as the substrate. PARP is strongly activated upon recognition of DNA strand breaks by its DNA-binding domain. Experiments with low-molecular-weight inhibitors of PARP have led to the view that PARP activity plays a role in DNA repair and possibly also in DNA replication, cell proliferation, and differentiation. Accumulating evidence for nonspecific inhibitor effects prompted us to develop a molecular genetic system to inhibit PARP in living cells, i.e., to overexpress selectively the DNA-binding domain of PARP as a dominant negative mutant. Here we report on a cell culture system which allows inducible, high-level expression of the DNA-binding domain. Induction of this domain leads to about 90% reduction of poly(ADP-ribose) accumulation after gamma-irradiation and sensitizes cells to the cytotoxic effect of gamma-irradiation and of N-methyl-N'-nitro-N-nitrosoguanidine. In contrast, induction does not affect normal cellular proliferation or the replication of a transfected polyomavirus replicon. Thus, trans-dominant inhibition of the poly(ADP-ribose) accumulation occurring after gamma-irradiation or N-methyl-N'-nitro-N-nitrosoguanidine is specifically associated with a disturbance of the cellular recovery from the inflicted damage.

Cisplatin increases sensitivity of human leukemic blasts to triazene compounds

High levels of O6-alkylguanine-DNA-alkyltransferase (OGAT) can, at least in part, account for tumor cell resistance to O6-alkylguanine alkylating agents, including triazene compounds. A pilot clinical study indicates that dacarbazine can induce a marked decrease of leukemic blasts in patients affected by acute myelogenous leukemia (AML) with low pretreatment levels of OGAT activity. In this study we show a synergistic antitumor effect between cisplatin (CDDP) and temozolomide (an in vitro active analog of dacarbazine), following combined in vitro treatment of leukemic blasts. Synergistic effect appears to be CDDP-dose dependent. In vivo treatment of leukemic patients with CDDP was followed by a reduction of OGAT activity in 2 out 3 cases. These data point out that CDDP could be a good candidate for depleting OGAT protein of leukemic cells, thus reversing tumor cell resistance to dacarbazine.

Inhibition of Head and Neck Squamous Cell Carcinoma Cell Lines by Transforming Growth Factor-β

Transforming growth factor-β is known to be a potent autocrine growth inhibitor produced by a wide variety of cells, including cells of the immune system. Other investigators have noted that the growth of nontransformed keratinocytes is inhibited by transforming growth factor-β, whereas various carcinoma cell lines are resistant to these effects. Head and neck squamous cell carcinoma cells are known to have surface receptors for this cytokine. We thus assessed the effect of transforming growth factor-β on the growth of head and neck squamous cell carcinoma cell lines. Four head and neck squamous cell carcinoma cell lines were incubated with varying concentrations of transforming growth factor-β, and cytotoxicity was evaluated with a methylene blue colorimetric assay. After culturing in transforming growth factor-β for 4 days, inhibition of growth was detected in CAL-27 (maximal inhibition at 5.0 ng/ml), UMSCC-1, and UMSCC-19 (maximal inhibition at 50 ng/ml) cell lines. One other cell line, UMSCC-8 was found resistant to the inhibitory effects of transforming growth factor-β. Kinetics analysis experiments revealed minimal inhibition before day 2 of incubation, at which time inhibition increased linearly to day 4. Assessment of double-stranded DNA fragmentation suggested that DNA fragmentation occurs before significant cytotoxicity. Electron microscopic analysis and gel electrophoresis of extracted DNA revealed morphologic features consistent with apoptotic cell death. Our findings indicate that transforming growth factor-β significantly inhibits the growth of head and neck squamous cell carcinoma cell lines by inducing apoptotic cell death.

Striatal TGF-alpha: postnatal developmental expression and evidence for a role in the proliferation of subependymal cells

Transforming growth factor alpha (TGF-alpha) is expressed in the brain and affects cells by binding to the epidermal growth factor receptor (EGF-R). Using a ribonuclease protection assay, we found that TGF-alpha steady state mRNA levels in the mouse striatum peak during the first week of postnatal life. Temporally this peak correlates with the height of gliogenesis in the subependymal layer (SEL), which lies along the striatal border of the lateral ventricle. In vitro studies demonstrate that TGF-alpha can stimulate the proliferation of astrocytes, so glial fibrillary acidic protein (GFAP) mRNA levels were measured as well and it was observed that the peak of GFAP expression followed that of TGF-alpha by 1 week. Furthermore, in a TGF-alpha deficient mouse, waved-1 (wa-1), a significant reduction of GFAP mRNA levels and immunostaining for GFAP was found in the striatum. Bromodeoxyuridine labeling combined with immunohistochemistry of normal postnatal day 6 brain showed that the proliferating cells in the SEL are EGF-R immunoreactive. In the waved-1 SEL, there were fewer BrdU positive cells and there was a reduced level of [3H]thymidine incorporation. EGF-R immunoreactive cells were found in the SEL of the adult mouse brain. Taken together, our data suggest that the TGF-alpha/EGF-R signaling pathway is involved in postnatal mitogenic events in the brain.

The urokinase inhibitor p-aminobenzamidine inhibits growth of a human prostate tumor in SCID mice

Malignant cells possess a high degree of proteolytic activity in which the plasminogen activator system plays an important role. An increased expression of urokinase type plasminogen activator (uPA) is of significance for degradation of the extracellular tumor matrix, facilitating invasiveness and growth. Inhibition of the active site of uPA makes it possible to evaluate the significance of uPA in tumor growth. We report here experiments on a uPA-producing human prostate xenograft (DU 145) using a competitive inhibitor of uPA, p-aminobenzamidine. In vitro experiments with DU 145 cells showed that p-aminobenzamidine caused a dose-dependent inhibition of uPA activity. DU 145 cells were inoculated s.c. in SCID mice and, once tumors were established, treatment with p-aminobenzamidine added to drinking water was started and lasted for 23 days. Mice receiving 250 mg/kg/day of p-aminobenzamidine showed a clear decrease in tumor-growth rate compared to the non-treated mice, resulting in 64% lower final tumor weight. In addition, uPA-antigen levels in the membrane fractions of DU 145 tumors from p-aminobenzamidine-treated mice were found to be decreased by 59%. We also show that p-aminobenzamidine has an anti-proliferative effect in cell culture at low cell number, correlating with a dose-dependent decrease in uPA production. In conclusion, we show that a low-molecular-weight uPA-inhibitor, p-aminobenzamidine, has a growth-inhibitory effect on a solid uPA-producing tumor.

Specific inhibition of DNA polymerase beta by its 14 kDa domain: role of single- and double-stranded DNA binding and 5'-phosphate recognition

DNA polymerase beta (beta-polymerase) has been implicated in short-patch DNA synthesis in the DNA repair pathway known as base excision repair. The native 39 kDa enzyme is organized into four structurally and functionally distinct domains. In an effort to examine this enzyme as a potential therapeutic target, we analyzed the effect of various beta-polymerase domains on the activity of the enzyme in vitro. We show that the 14 kDa N-terminal segment of beta-polymerase, which binds to both single- and double-stranded DNA, but lacks DNA polymerase activity, inhibits beta-polymerase activity in vitro. Most importantly, the 8, 27 and 31 kDa domains of beta-polymerase do not inhibit beta-polymerase activity, demonstrating that the inhibition by the 14 kDa domain is specific. The inhibition of beta-polymerase activity in vitro is abolished by increasing the concentrations of both of the substrates (template-primer and deoxynucleoside triphosphate). In contrast, an in vitro base excision repair assay is inhibited in a domain specific manner by the 14 kDa domain even in the presence of saturating substrates. The inhibition of beta-polymerase activity by the 14 kDa domain appears specific to beta-polymerase as this domain does not inhibit either mammalian DNA polymerase alpha or Escherichia coli polymerase I (Klenow fragment). These data suggest that the 14 kDa domain could be used as a potential inhibitor of intracellular beta-polymerase and that it may provide a means for sensitizing cells to therapeutically relevant DNA damaging agents.

O6-methylguanine-DNA methyltransferase activity in breast and brain tumors

The DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT) is a main determinant of resistance of tumor cells to the cytostatic activity of chemotherapeutic alkylating agents (methylating and chloroethylating nitrosoureas) and is effective in protecting normal cells against genotoxic and carcinogenic effects resulting from DNA alkylation. Therefore, the level of expression of MGMT is significance for the response of both the tumor and the non-target tissue following application of nitrosoureas in tumor therapy. To determine the expression of MGMT in tumor tissue, we have assayed MGMT activity in 68 breast carcinomas and 38 brain tumors. There was a wide variation of MGMT expression in breast carcinomas ranging from below the level of detection up to 863 fmol/mg protein. About 4% of breast tumors did not display detectable MGMT, 15% had activity lower than 100 fmol/mg protein, and 26% expressed more than 500 fmol/mg. The mean level of expression was 321 fmol/mg. In brain tumors (astrocytoma WHO grade I, II, and III, and glioblastoma WHO grade IV) the MGMT activity was generally lower than in breast tumors, ranging from below the level of detection up to 238 fmol/mg. The mean level of expression was 55 fmol/mg. Five percent of the brain tumors had no detectable MGMT activity. The MGMT repair activity correlated well with the amount of MGMT protein present in tumor samples, as shown by Western-blot analysis, indicating that loss of MGMT repair activity is due to inability of these tumor cells to synthesize the protein.

O6-methylguanine-DNA methyltransferase in tumors and cells of the oligodendrocyte lineage

BACKGROUND

Oligodendrogliomas respond to nitrosourea-based chemotherapy and are induced in rats following transplacental exposure to ethylnitrosourea, observations suggesting that neoplastic and normal cells of the oligodendrocyte lineage are "sensitive" to nitrosoureas. Nitrosoureas alkylate DNA at O6-guanine with repair mediated by O6-methylguanine-DNA methyltransferase (MGMT). The cytotoxic and carcinogenic properties of the nitrosoureas appear related to MGMT activity.

METHODS

To explore why oligodendrogliomas respond to chemotherapy, we measured MGMT activity in five chemosensitive human oligodendrogliomas and in rat oligodendrocyte lineage cells. We also measured MGMT activity in rat astrocytes and compared the cytotoxic effects of carmustine (BCNU) on oligodendrocyte lineage cells and astrocytes.

RESULTS

Low levels of MGMT activity were found in five of five human oligodendrogliomas. Cultures of neonatal rat glia enriched for oligodendrocyte lineage cells also had low levels of MGMT activity, approximately one-third that found in astrocytes (p < 0.02), and oligodendrocyte lineage cells were more sensitive to BCNU than astrocytes.

CONCLUSIONS

Low MGMT activity may contribute to the chemosensitivity of some human oligodendrogliomas and rat oligodendrocyte lineage cells also have low levels. If drug resistance mechanisms in tumors reflect the biochemical properties of their cells of origin, then normal glia may serve as a laboratory substitute for human glioma.

Establishment and characterization of non-small cell lung cancer cell lines resistant to mitomycin C under aerobic conditions

To elucidate the mechanisms of acquired resistance to mitomycin C (MMC) in non-small cell lung cancer (NSCLC), we established two MMC-resistant NSCLC sublines by continuous exposure to MMC, using PC-9 as a parent cell line. The sublines, PC-9/MC2 and PC-9/MC4, were 6.4- and 10-fold more resistant to MMC than their parent cell line, respectively, at the IC50 value as determined by MTT assay. They exhibited cross-resistance to EO9, but were not resistant to cisplatin, vindesine, etoposide, carboquone, or KW-2149, a novel MMC derivative. They were collaterally sensitive to adriamycin and menadione. Accumulation of the drug was decreased in the resistant sublines to about 60% of that in the parent cells. Cytosolic DT-diaphorase (DTD) activities were decreased to 13.5 +/- 3.2 in PC9/MC2 and 1.3 +/- 0.6 in PC-9/MC4 from 261.5 +/- 92.7 nmol/min/mg protein in the parent PC-9. NADH:cytochrome b5 reductase activities in both of the resistant cell lines were significantly decreased as compared to that in the parent cell line. Addition of dicumarol resulted in a two-fold increase in IC50 value in PC-9, whereas the IC50 value showed no change in PC-9/MC4. Moreover, dicumarol did not affect the sensitivities to KW-2149 but decreased the sensitivities to EO9 in both the parent and the resistant cell lines. Formation of an alkylating metabolite was significantly decreased in the resistant cells, in parallel to the degree of resistance. We concluded that deficient drug activation due to decreased DTD activity was important as a mechanism of resistance to MMC in PC-9, a relatively DTD-rich NSCLC cell line.

Expression of gap junction protein connexin 32 and E-cadherin in human hepatocellular carcinoma

The expression of connexin 32, a major gap junction protein, and E-cadherin, an intercellular adhesion molecule that is supposed to be involved in the regulation of gap junctional intercellular communications, was examined immunohistochemically in seven specimens of human hepatocellular carcinoma and surrounding non-carcinomatous tissues. We found that the number of connexin 32-positive spots per mm2 was significantly less in hepatocellular carcinoma tissues than in the surrounding non-carcinomatous cirrhotic tissues (4360 +/- 3390/mm2 vs 10,030 +/- 3690/mm2; p < 0.01). The number in the latter was also significantly less than that in normal controls (23,560 +/- 4170/mm2). E-cadherin was expressed in all non-carcinomatous hepatocytes as well as carcinomatous cells, except for one case of Edmondson's grade III hepatocellular carcinoma. These results suggest an impairment of cell-to-cell communications in human hepatocellular carcinomas.

The lesions of locoweed (Astragalus mollissimus), swainsonine, and castanospermine in rats

To better characterize and compare the toxicity of and lesions produced by locoweed (Astragalus mollissimus) with those of swainsonine and a related glycoside inhibitor, castanospermine, 55 Sprague-Dawley rats were randomly divided into 11 groups of five animals each. The first eight groups were dosed via subcutaneous osmotic minipumps with swainsonine at 0, 0.1, 0.7, 3.0, 7.4, or 14.9 mg/kg/day or with castanospermine at 12.4 or 143.6 mg/kg/day for 28 days. The last three groups were fed alfalfa or locoweed pellets with swainsonine doses of 0, 0.9, or 7.2 mg/kg/day for 28 days. Swainsonine- and locoweed-treated rats gained less weight, ate less, and showed more signs of nervousness than did controls. Histologically, these animals developed vacuolar degeneration of the renal tubular epithelium, the thyroid follicular cells, and the macrophage-phagocytic cells of the lymph nodes, spleen, lung, liver, and thymus. Some rats also developed vacuolation of neurons, ependyma, adrenal cortex, exocrine pancreas, myocardial epicytes, interstitial cells, and gastric parietal cells. No differences in lesion severity or distribution were detected between animals dosed with swainsonine and those dosed with locoweed. Rats dosed with castanospermine were clinically normal; however, they developed mild vacuolation of the renal tubular epithelium, the thyroid follicular epithelium, hepatocytes, and skeletal myocytes. Special stains and lectin histochemical evaluation showed that swainsonine- and castanospermine-induced vacuoles contained mannose-rich oligosaccharides. Castanospermine-induced vacuoles also contained glycogen. These results suggest that 1) swainsonine causes lesions similar to those caused by locoweed and is probably the primary locoweed toxin; 2) castanospermine at high doses causes vacuolar changes in the kidney and thyroid gland; and 3) castanospermine intoxication results in degenerative vacuolation of hepatocytes and skeletal myocytes, similar to genetic glycogenosis.

Spontaneous regression of human melanoma/nonmelanoma skin cancer: association with infiltrating CD4+ T cells

Spontaneous regression occurs in some human malignant melanomas and basal cell carcinomas (BCCs). We have compared the cellular infiltrate in regressing and nonregressing tumors in order to analyze the mechanism by which regression occurs. Regressing primary melanomas and BCCs were infiltrated with a larger number of CD4+, but not CD8+, T lymphocytes than were seen in nonregressing tumors. The number of interleukin 2 receptor-positive (early activation marker) but not transferrin receptor-positive (intermediate activation marker) T cells was increased, indicating that the infiltrating T cells were activated. Large numbers of Langerhans cells, macrophages, and other class II major histocompatibility complex (MHC)-expressing cells were present but were not increased in the regressing tumors. There were no detectable B lymphocytes, and the regressing tumor cells displayed levels of HLA-DR expression similar to those of the nonregressing tumors. Comparison of squamous cell carcinoma (SCCs) with keratoacanthomas (KAs), which are likely to be a spontaneously regressing form of SCC, also showed increased infiltration of activated CD4+, but not CD8+, T cells within the KA. A murine ultraviolet (UV)-induced squamous tumor that spontaneously regresses when transplanted into immunocompetent syngeneic mice was also infiltrated with increased numbers of activated CD4+, but not CD8+, T cells prior to and during rejection. These results indicate that spontaneous regression of human skin tumors is likely to be immunologically mediated, and that CD4+ T lymphocytes seem to mediate this regression.

Mammalian glutathione S-transferase: regulation of an enzyme system to achieve chemotherapeutic efficacy

The glutathione S-transferases are a family of Phase II detoxication enzymes that catalyze the conjugation of glutathione to a large variety of electrophilic compounds. In the 1990s, there have been many advances regarding the function of these enzymes in protecting a cell from the toxic effects of these electrophiles. The complexity of this enzyme family has been realized and much work has been performed to identify the specific roles played by individual isozymes in resistance to a variety of agents. Likewise, the determination of the crystal structure of these enzymes has allowed the identification of specific amino acid residues that are involved in the catalysis of important reactions. The important role that these enzymes play in carcinogenesis and in drug resistance has warranted an attempt to bring together these different subfields of glutathione S-transferase biology to investigate possible ways that this system could be regulated in therapeutically useful ways. In this report, we have reviewed the recent advances and ways in which this knowledge could be utilized in the advancement of the treatment of cancer.

Interferon-alpha does not improve the antineoplastic efficacy of high-dose infusional 5-fluorouracil plus folinic acid in advanced colorectal cancer. First results of a randomized multicenter study by the Association of Medical Oncology of the German Cancer Society (AIO)

BACKGROUND

High-dose 5-FU given weekly as a 24-h infusion in combination with folinic acid (FA) has been associated with low toxicity and a high response rate. Interferon-alpha (IFN) either alone or in combination with FA has also improved treatment results by modulating 5-FU activity. We therefore initiated a randomized multicenter trial comparing the ability of FA or IFN to modulate infusional 5-FU. The statistical design using a sequential analysis allows us to report on the comparison of 5-FU/FA vs. 5-FU/FA/IFN while randomization of patients into 5-FU/FA vs. 5 FU/IFN continues.

METHODS

Chemotherapy-naive patients with advanced progressive colorectal cancer and measurable metastatic lesions were randomized to receive 5-FU 2600 mg/m2 i.v. as a 24-h infusion, combined with either FA 500 mg/m2 as a 2-h infusion (A), or IFN 3 x 10(6) U s.c. 3 x/week (B), or the combination of FA plus IFN as in arms A and B (C). Treatment arms were repeated weekly for 6 weeks followed by a 2-week rest period. These 8-week cycles were administered until tumor progression. Because of the occurrence of 2 toxic deaths among the first 17 patients treated in arm C, 5-FU was reduced to 2000 mg/m2 for all patients in arm C. Sequential analysis according to Whitehead for objective response was planned with alpha = 0.05/3 and a power of 80% (beta = 0.2) to detect a difference of > or = 25% (delta = 0.25) or equivalence of response rates. For pairwise comparison of treatment arms a minimum of 30 patients per arm and a maximum of 90 patients per arm were expected in case of equivalence or difference.

RESULTS

An interim analysis was performed after the first 93 of 149 randomized patients were evaluable for response and toxicity (A 31 pts, B 33 pts, C 29 pts). Despite the 5-FU dose reduction in arm C, 28% of patients experienced grade 3/4 toxicity (CTC) including diarrhea, mucositis and handfoot syndrome compared to 16% in arm A and 12% in arm B (not significant). No treatment related toxic death occurred in arms A or B, but 3 patients (10%) in arm C died of diarrhea and septicemia. Among patients treated with 5-FU/FA objective tumor response occurred in 12/31 patients (39%) (21%-56%, 95% confidence interval) (3 CR, 9 PR), no change in 13/31 (42%) and PD in 6/31 (19%) patients. Eleven of 29 patients (38%) (20%-56%, 95% confidence interval) receiving 5-FU/FA/IFN achieved complete (3 patients) or partial (8 patients) remissions, 10/29 patients (34%) had stable disease and 8/29 patients (28%) tumor progression. According to the sequential analysis the rates of objective responses observed in patients treated with 5-FU/FA or 5-FU/FA/IFN were equivalent.

CONCLUSION

This interim analysis allows the conclusion that infusional 5-FU plus FA/IFN is no more active than infusional 5-FU plus FA alone. However, 5-FU/FA/IFN despite 5-FU dose reduction was associated with unacceptably high toxicity, including 10% deaths. Therefore, further investigation of this regimen is not justified. The study is continued with the comparison of 5-FU/FA vs. 5-FU/IFN.

Characterization of cross-resistance to methotrexate in a human breast cancer cell line selected for resistance to melphalan

We have demonstrated previously decreased melphalan accumulation in a human breast cancer cell line selected for resistance to melphalan (MelR MCF-7). Cross-resistance studies of MelR MCF-7 cells revealed that this cell line was 6.7-fold cross-resistant to methotrexate, but only 2-fold resistant to trimetrexate. Methotrexate transport studies in MelR MCF-7 cells showed a 2-fold decrease in initial methotrexate uptake and a 2-fold decrease in the Vmax for methotrexate uptake in the resistant cells. Methotrexate resistance in MelR MCF-7 cells was also associated with a decrease in non-effluxable methotrexate following incubation with radiolabeled drug for 24 hr. Characterization of intracellular methotrexate after accumulation for 24 hr demonstrated decreased levels of free methotrexate in MelR MCF-7 cells. Analysis of methotrexate polyglutamate formation in MelR MCF-7 cells indicated that the decrease in non-effluxable, non-protein-bound methotrexate was associated with a 3-fold decrease in higher order methotrexate polyglutamate formation. No difference was noted in folylpolyglutamate synthetase activity between the resistant and parental cell lines. Therefore, the observed decrease in methotrexate polyglutamate formation in MelR MCF-7 cells appeared to result from decreased availability of substrate. There was no evidence of any alteration in the amount of the catalytic activity of dihydrofolate reductase in MelR MCF-7 cells compared with parental MCF-7 (WT MCF-7) cells; moreover, the binding affinity of dihydrofolate reductase for methotrexate and the percentage of protein-bound methotrexate were similar in both cell lines. In addition, the total amounts of thymidylate synthase protein and thymidylate synthase catalytic activity in MelR MCF-7 cells were unchanged. Thus, acquired methotrexate resistance in MCF-7 cells selected for resistance to melphalan appears to result from down-regulation of methotrexate uptake.

Distinguishing between folate receptor-alpha-mediated transport and reduced folate carrier-mediated transport in L1210 leukemia cells

L1210 leukemia cells transport reduced folates and methotrexate via a well defined reduced folate carrier system and, in the absence of low folate selective pressure, do not express an alternate endocytotic route mediated by cell surface folate receptors. This laboratory previously described an L1210 leukemia cell line, MTXrA, with acquired resistance to methotrexate (MTX) due to the loss of mobility of the reduced folate carrier. We now report on the transfection of MTXrA with a cDNA encoding the murine homolog of the human folate receptor isoform of KB cells to produce MTXrA-TF1, which constitutively expresses high levels of FR-alpha. MTXrA-TF1 and L1210 cells were utilized to compare transport of methotrexate mediated by FR-alpha and the reduced folate carrier, respectively. Methotrexate influx in the two lines was similar when the extracellular level was 0.1 microM, but as the methotrexate concentration increased, influx via the reduced folate carrier increased in comparison to influx mediated by FR-alpha. Transport kinetics indicated both a approximately 20-fold lower influx Kb and Vmax for MTXrA-TF1 as compared to L1210 cells. The two cell lines exhibited distinct influx properties. Methotrexate influx in MTXrA-TF1 was markedly inhibited by 50 nM folic acid and metabolic poisons. In L1210 cells, 1.0 microM folic acid did not affect MTX influx, and metabolic poisons either had no effect on or increased methotrexate influx. Removal of extracellular chloride markedly inhibited transport in MTXrA-TF1 but stimulated influx in L1210 cells. When the pH was decreased to 6.2, methotrexate influx was not altered in MTXrA-TF1 but was reduced in L1210 cells. Probenecid and sulfobromophthalein inhibit methotrexate influx in both L1210 and MTXrA-TF1 cell lines; however, inhibition in MTXrA-TF1 could be accounted for on the basis of inhibition of methotrexate binding to FR-alpha. The data indicate that the reduced folate carrier and FR-alpha function independently and exhibit distinct properties. FR-alpha expressed at sufficient levels can mediate influx of MTX and folates into cells at rates comparable to the reduced folate carrier and hence has pharmacologic and physiologic importance.

MCF-7 breast cancer cells transfected with protein kinase C-alpha exhibit altered expression of other protein kinase C isoforms and display a more aggressive neoplastic phenotype

Increased protein kinase C (PKC) activity in malignant breast tissue and positive correlations between PKC activity and expression of a more aggressive phenotype in breast cancer cell lines suggest a role for this signal transduction pathway in the pathogenesis and/or progression of breast cancer. To examine the role of PKC in the progression of breast cancer, human MCF-7 breast cancer cells were transfected with PKC-alpha, and a group of heterogenous cells stably overexpressing PKC-alpha were isolated (MCF-7-PKC-alpha). MCF-7-PKC-alpha cells expressed fivefold higher levels of PKC-alpha as compared to parental or vector-transfected MCF-7 cells. MCF-7-PKC-alpha cells also displayed a substantial increase in endogenous expression of PKC-beta and decreases in expression of the novel delta- and eta-PKC isoforms. MCF-7-PKC-alpha cells displayed an enhanced proliferative rate, anchorage-independent growth, dramatic morphologic alterations including loss of an epithelioid appearance, and increased tumorigenicity in nude mice. MCF-7-PKC-alpha cells exhibited a significant reduction in estrogen receptor expression and decreases in estrogen-dependent gene expression. These findings suggest that the PKC pathway may modulate progression of breast cancer to a more aggressive neoplastic process.

Role of protein kinase beta isozyme in multidrug resistance in murine leukemia P388/ADR cells

To define a role of protein kinase C (PKC) in multidrug resistance (MDR), we examined the influence of PKC isozyme specific antibodies delivered intracellularly, on drug sensitivity and drug accumulation in P388/ADR cells. Drug sensitive (P388) and drug resistant (P388/ADR) cells were permeabilized at 4 degrees C with L-lysolecithin and were incubated with rabbit anti-PKC, alpha, beta antibodies, or normal rabbit serum for 10 minutes at 37 degrees C. Daunorubicin (DNR) accumulation and drug sensitivity were studied by flow cytometry and MTT assay, respectively. Anti-PKC beta antibody partially corrected drug accumulation defect and completely reversed resistance to DNR. Anti-PKC alpha antibody had no effect on either parameter of MDR. These results suggest that PKC beta plays an important role in MDR in P388/ADR cells. Furthermore, the technique of intracellular delivery of antibodies provides a new approach to discern the role of PKC isoforms in multidrug resistance in various tumor cells.

The genetic basis of resistance to cancer chemotherapy

The Goldie-Coldman hypothesis of how tumours develop resistance to chemotherapy predicts that random mutations occur within a tumour cell population that bestows cytotoxic resistance. These resistance mechanisms may be specific to a certain class of cytotoxic drug, such as changes the enzymes topoisomerase II and dihydrofolate reductase, or may affect many drugs simultaneously, such as increased expression of P-glycoprotein. Knowledge of the genetic basis of these resistance mechanisms will have fundamental clinical importance in individual cases by allowing cytotoxic regimes that are unaffected to be chosen. Moreover, it will allow the development of more effective modulators of resistance.

Comparison of ability of protein kinase C inhibitors to arrest cell growth and to alter cellular protein kinase C localisation

Inhibitors of protein kinase C (PKC) such as the staurosporine analogues UCN-01 and CGP 41251 possess antineoplastic properties, but the mechanism of their cytostatic action is not understood. We tested the hypothesis that the ability of these compounds to arrest growth is intrinsically linked with their propensity to inhibit PKC. Compounds with varying degrees of potency and specificity for PKC were investigated in A549 and MCF-7 carcinoma cells. When the log values of drug concentration which arrested cell growth by 50% (IC50) were plotted against the logs of the IC50 values for inhibition of cytosolic PKC activity, two groups of compound could be distinguished. The group which comprised the more potent inhibitors of enzyme activity (calphostin C, staurosporine and its analogues UCN-01, RO 31-8220, CGP 41251) were the stronger growth inhibitors, whereas the weaker enzyme inhibitors (trimethylsphingosine, miltefosine, NPC-15437, H-7, H-7I) affected proliferation less potently. GF 109203X was exceptional in that it inhibited PKC with an IC50 in the 10(-8) M range, yet was only weakly cytostatic. To substantiate the role of PKC in the growth inhibition caused by these agents, cells were depleted of PKC by incubation with bryostatin 1 (1 microM). The susceptibility of these enzyme-depleted cells towards growth arrest induced by staurosporine, RO 31-8220, UCN-01 or H-7 was studied. The drug concentrations which inhibited incorporation of [3H]thymidine into PKC-depleted A549 cells by 50% were slightly, but not significantly, lower than significantly, lower than those observed in control cells. These results suggest that PKC is unlikely to play a direct role in the arrest of the growth of A549 and MCF-7 cells mediated by these agents. Staurosporine is not only a strong inhibitor of PKC but also mimics activators of this enzyme in that it elicits the cellular redistribution of certain PKC isoenzymes. The ability of kinase inhibitors other than staurosporine to exert a similar effect was investigated. Calphostin C, H-7, H-7I, miltefosine, staurosporine, UCN-01, RO 31-8220, CGP 41251 or GF 109203X were incubated for 30 min with A549 cells in the absence or presence of the PKC activator 12-O-tetradecanoyl phorbol-13-acetate. The subcellular distribution of PKC-alpha-, -epsilon and -zeta was measured by Western blot analysis. None of the agents affected PKC-alpha or -zeta.(ABSTRACT TRUNCATED AT 400 WORDS)

Indoloquinone EO9: DNA interstrand cross-linking upon reduction by DT-diaphorase or xanthine oxidase

We report DNA interstrand cross-linking caused by the anti-tumour indoloquinone EO9 following reductive activation with purified rat liver DT-diaphorase or xanthine oxidase. Reduction was a necessary event for cross-linking to occur. DNA cross-link formation by EO9 following DT-diaphorase reduction was completely inhibited by addition 10 microM dicoumarol, whereas only a minor effect of dicoumarol on xanthine oxidase-mediated DNA cross-linking by EO9 was observed. DNA cross-linking was pH dependent, with increasing cross-link formation from pH 5.5 to 7.0 for both DT-diaphorase and xanthine oxidase mediated reactions. Also, conversion of EO9 upon reduction was pH dependent. However, in contrast to DNA cross-linking, conversion rates of EO9 decreased at higher pH. EO9 was shown to be more efficient in DNA cross-linking than mitomycin C under identical conditions, using both DT-diaphorase and xanthine oxidase reductive activation at pH 5.5 and 7.0. This study indicates that the anti-tumour activity of EO9 may be at least partly mediated by interstrand DNA cross-link formation, and that various reducing enzymes may be important for activation of EO9 in vitro and in vivo.

The human immunodeficiency virus(HIV) inhibitor 9-(2-phosphonylmethoxyethyl)adenine (PMEA) is a strong inducer of differentiation of several tumor cell lines

9-(2-phosphonylmethoxyethyl)adenine (PMEA) is the prototype compound of a series of acyclic nucleoside phosphonate derivatives endowed with potent and selective anti-retroviral activity in vitro and in vivo. We have now found that PMEA is also a potent inducer of differentiation of a number of tumor cells, including human erythroleukemia K562 cells, rat choriocarcinoma RCHO cells and human acute promyelocytic leukemic HL-60 cells. At 10 microM PMEA, rat RCHO cell cultures could be almost fully differentiated, and at 50 microM PMEA, approximately 50% of the K562 cells could be triggered to produce hemoglobin. The differentiating activity of butyric acid was at least partially additive to that of PMEA when both drugs were combined in K562 cell cultures. PMEA needs to be present for at least 2 or 3 days in the K562 cell cultures to achieve optimal differentiating activity. This suggests that either a PMEA metabolite and/or its anti-metabolic effects may be responsible for differentiation of the tumor cells.

Cisplatin inhibits chromatin remodeling, transcription factor binding, and transcription from the mouse mammary tumor virus promoter in vivo

The anticancer drug cis-diamminedichloro-platinum(II) (cisplatin) covalently modifies DNA, and these lesions are thought to lead to cell death by inhibiting DNA and RNA synthesis. By using in vivo analysis techniques, we have investigated the influence of cisplatin on hormone-induced transcription from the mouse mammary tumor virus (MMTV) promoter. Cisplatin substantially reduced glucocorticoid-induced expression from the MMTV promoter stably incorporated into mouse tumor cells. The glucocorticoid-receptor-dependent chromatin remodeling and loading of transcription factors that is a signature response of this promoter in the context of chromatin were significantly reduced by cisplatin but not by the clinically ineffective trans-isomer trans-diamminedichloroplatinum(II) (transplatin). Additional in vivo studies on transiently introduced nonchromatin MMTV templates demonstrated that cisplatin modification of DNA blocked binding of the transcription factor NF1. These results provide strong evidence that cisplatin influences transcription by interfering with the opening of repressive chromatin structures and by blocking transcription factor binding directly, each of which could contribute substantially to its toxicity.

Expression of transforming growth factor alpha and its receptor in human neuroendocrine tumours

Transforming growth-factor-alpha (TGF-alpha) is a 50-amino-acid polypeptide that binds to the epidermal growth factor (EGF) receptor and stimulates cell growth. It has been suggested that enhanced production of TGF-alpha and EGF receptors by tumour cells promote tumour-cell growth by autocrine mechanisms. In the present study we have investigated the expression of TGF-alpha and EGF receptors in human neuroendocrine tumours, including midgut carcinoid tumours, phaeochromocytomas and medullary thyroid carcinomas. TGF-alpha expression was demonstrated in biopsies of all tumours examined (n = 30) and EGF receptors in a majority of tumours by Northern analysis and/or immunocytochemistry. Expression of TGF-alpha and EGF receptors was also demonstrated in primary cultures of tumour cells. Carcinoid tumours and phaeochromocytomas in culture secreted detectable amounts of TGF-alpha into the culture medium (400-700 pM). The amount of secreted TGF-alpha could be suppressed by octreotide treatment in individual tumours. Administration of exogenous TGF-alpha stimulated carcinoid tumour growth in vitro as determined by the DNA contents of cell cultures. The growth-stimulatory effect of TGF-alpha could be partially blocked by the use of neutralizing anti-EGF receptor monoclonal antibodies (MAbs). In conclusion, several human neuroendocrine tumours express both TGF-alpha and EGF receptors in in vivo and in vitro, suggesting that TGF-alpha may regulate tumour-cell growth by autocrine mechanisms.

Effects of protein kinase C modulators on multidrug resistance in human glioma cells

To identify the role of protein kinase C (PKC) in multidrug resistance, the effects of phorbol-12-myristate-13-acetate (PMA), a PKC activator, or calphostin C, a PKC inhibitor, on intracellular vincristine accumulation and expression of P-glycoprotein phosphorylation were studied in one multidrug-resistant and three multidrug-sensitive human glioma cell lines. Basal PKC activities and immunoreactivities of PKC-alpha and -zeta were higher in multidrug-resistant cells than in multidrug-sensitive cells. There was no significant difference in the immunoreactivity of PKC-delta between multidrug-resistant and -sensitive cells, and immunoreactive PKC-beta, -gamma, and -epsilon were not detected in either multidrug-resistant or -sensitive cells. The treatment of multidrug-resistant cells with 100 nM PMA for 2 hours resulted in the activation not of PKC-zeta but of PKC-alpha, with concomitant decrease in vincristine accumulation and increase in P-glycoprotein phosphorylation. The exposure of multidrug-resistant cells to 100 nM PMA for 24 hours induced down-regulation not of PKC-zeta but of PKC-alpha, with concurrent decrease in vincristine accumulation, and reduced but still increased P-glycoprotein phosphorylation. The treatment of multidrug-resistant cells with 100 nM calphostin C for 2 hours decreased immunoreactive PKC-zeta and not immunoreactive PKC-alpha, inducing increase in vincristine accumulation, with concomitant decrease in P-glycoprotein phosphorylation. There was no evidence of significant change in vincristine accumulation in multidrug-sensitive cells treated with PMA or calphostin C. This may suggest that at least two isozymes of PKC, PKC-alpha and -zeta, are involved in P-glycoprotein phosphorylation and that vincristine efflux function in multidrug-resistant human glioma cells is closely associated with P-glycoprotein phosphorylation and is decreased by PKC inhibitor.

Mice lacking ADPRT and poly(ADP-ribosyl)ation develop normally but are susceptible to skin disease

Poly(ADP-ribosyl)ation is catalyzed by NAD+: protein(ADP-ribosyl) transferase (ADPRT), a chromatin-associated enzyme which, in the presence of DNA breaks, transfers ADP-ribose from NAD+ to nuclear proteins. This post-translational modification has been implicated in many fundamental processes, like DNA repair, chromatin stability, cell proliferation, and cell death. To elucidate the biological function of ADPRT and poly(ADP-ribosyl)ation in vivo the gene was inactivated in the mouse germ line. Mice homozygous for the ADPRT mutation are healthy and fertile. Analysis of mutant tissues and fibroblasts isolated from mutant fetuses revealed the absence of ADPRT enzymatic activity and poly(ADP-ribose), implying that no poly(ADP-ribosyl)ated proteins are present. Mutant embryonic fibroblasts were able to efficiently repair DNA damaged by UV and alkylating agents. However, proliferation of mutant primary fibroblasts as well as thymocytes following gamma-radiation in vivo was impaired. Moreover, mutant mice are susceptible to the spontaneous development of skin disease as approximately 30% of older mice develop epidermal hyperplasia. The generation of viable ADPRT-/-mice negates an essential role for this enzyme in normal chromatin function, but the impaired proliferation and the onset of skin lesions in older mice suggest a function for ADPRT in response to environmental stress.