Modification of growth related enzymatic pathways and apparent loss of tumorigenicity of a ras-transformed bovine endothelial cell line by treatment with 5-iodo-6-amino-1,2-benzopyrone (INH2BP)

Bovine aortic endothelial cells were converted to a highly tumorigenic cell line by transfection with Ha-ras and stimulation with thrombin. Sustained pretreatment with a non-cytotoxic concentration (600 mu M) of 5-iodo-6-amino-1,2-benzopyrone (INH2BP), a lipophilic ligand of poly(ADP-ribose) polymerase, abrogated in vivo tumorigenicity, of 10(5) cells per inoculum an effect which developed progressively during 2 to 6 weeks of drug treatment. The initial action of the drug was cytostasis, consisting of an arrest in prophase, extreme cell enlargement consistent with cytoplasmic hypertrophy, as seen by EM, and dramatic morphologic changes. Although neither DNA, RNA or protein syntheses are directly affected by INH2BP, apparently newly synthesized cellular DNA is degraded by endonucleases, which are upregulated by the inhibition of their poly-ADP-ribosylation. The drug treated cells exhibited greatly increased respiration and aerobic glycolysis, due to an augmentation of,glycolytic and respiratory enzymes in enlarged cells. These responses to the drug were reversible in cell cultures following drug removal, within 5-10 days drug exposure but the progressive loss of tumorigenicity in nude mice that developed after 3-6 weeks of drug exposure of cells, prior to inoculation to nude mice, was not reversible in vivo. Drug treatment produced a sustained 70-80% inhibition of pADPRT in intact cells at 600 mu M extracellular concentration of INH2BP. The prerequisite for the abrogation of tumorigenicity was the maintenance of pADPRT inhibition. The arrest of cell multiplication and a large decrease of Topo I, especially of Topo II and MAP kinase activities occurred without loss of enzyme protein as assayed in cell extracts of drug-treated cells. However INH2BP had no direct effect on these enzymes. Drug treatment down-regulated DNA-methyltransferase, PKC, ODC proteins, diminished cyclin A protein, but the hypophosphorylated form of Rb protein was significantly augmented. None of the enzymatic components of signal pathways so far studied, were directly affected by INH2BP. The inhibition of pADPRT by INH2BP coincided with an induction or activation of alkaline phosphatase and leucyl and glutamyl peptidase. The pADPRT content or the expression of pADPRT gene were not influenced by drug treatment, but the expression of ras gene was completely absent in nontumorigenic drug-treated cells, without a loss of ras gene from genomic DNA. Telomerase activity was not directly influenced by INH2BP treatment when assayed in diluted cell extracts, but the addition of homogeneous pADPRT to cell extracts, to approach physiological concentration of this protein in the cell, inhibited telomerase activity by binding of the polymer-free pADPRT to telomer templates. We conclude that inhibition of pADPRT indirectly down-regulates growth stimulatory signal pathways and sustains growth-arrested cells in culture at a pre-apoptotic threshold which explains the absence of tumorigenicity in vivo.     

Enhancement of alkylating agent activity in vitro by PD 128763, a potent poly(ADP-ribose) synthetase inhibitor.

The ability of DNA repair inhibitors to potentiate alkylating agent cytotoxicity was explored with PD 128763, a dihydroisoquinolinone known to effectively inhibit poly(ADP-ribose) synthetase. The cytotoxic activity of streptozotocin in L1210 leukemia cells was maximally potentiated (7-fold decrease in IC50) under conditions of 24 hr exposure to PD 128763 following treatment with the alkylating agent for 1 hr. Similar treatment conditions resulted in a much greater effect (36-fold enhancement in activity) for the 2-nitroimidazole RSU 1069. In contrast, 3-aminobenzamide was only weakly effective at enhancing activity of either streptozotocin or RSU 1069 (2-3 fold potentiation). However, PD 128763 was ineffective at potentiating the cytotoxicity of the bifunctional alkylating agents carmustine (BCNU) and lomustine (CCNU). Our results are consistent with a role for (poly-ADP) ribosylation in the repair of monofunctional alkylating agent damage. This study supports further exploration of the combination of PD 128763 and RSU 1069 as a potentially useful chemotherapeutic regimen.     

The effect of 3-aminobenzamide, inhibitor of poly(ADP-ribose) polymerase, on human osteosarcoma cells

This study demonstrates that in human osteosarcoma cells treatment with 3-aminobenzamide (3-AB), a potent inhibitor of poly(ADP-ribose) polymerase (PARP), induces morphological and biochemical features of differentiation, the duration of which depends on whether or not the normal RB gene is expressed. In Saos-2 cells expressing a non-functional Rb protein, 3-AB treatment induced the formation of transient, short dendritic-like protrusions. In RB-transfected-Saos-2 cells (a clone previously generated in our laboratory that shows stable expression of wild-type Rb protein), 3-AB induced marked and prolonged changes with the formation of long dendritic-like protrusions and the appearance of stellate (osteocyte-like) cells. In MG-63 cells producing a wild-type Rb protein, 3-AB treatment had more marked effects, with a larger number of cells assuming the stellate appearance of osteocytes, which were connected to each other via junctions resembling small channels. Regardless of cell type, at some point after 3-AB treatment the differentiative attempt failed and the cells died. Death was apoptotic, as demonstrated by chromatin condensation and fragmentation, specific cleavage of PARP and Lamin-B, processing of caspase-3 and the appearance of Bax immunoreactive species. Enzymatic assay and RT-PCR of alkaline phosphatase (ALP) - an enzyme whose levels markedly decrease when osteoblasts undergo terminal differentiation into osteocytes - showed that 3-AB treatment markedly lowered ALP expression. Simultaneously, 3-AB treatment markedly increased the expression of CD44, a transmembrane multifunctional adhesion molecule and sensitive marker of osteocytic differentiation. This study hypothesizes a cross-talk between pRb and PARP and suggests that PARP may be a useful target for anticancer drugs.     

Enhancement of bleomycin activity by 3-aminobenzamide, a poly (ADP-ribose) synthesis inhibitor, in vitro and in vivo

A series of poly (ADP-ribose) synthesis inhibitors was evaluated for their ability to potentiate the cytotoxicity of bleomycin compared with their inhibition of poly(ADP-ribose) synthesis in L1210 cultured cells. Theophylline, nicotinamide, 3-aminobenzamide and thymidine inhibited 70 to 80% of poly(ADP-ribose) synthesis in L1210 cells. The degree of inhibition of poly(ADP-ribose) synthesis by these inhibitors corresponded in general with their potentiating ability of bleomycin cytotoxicity. Among these inhibitors, 3-aminobenzamide significantly potentiated the cytotoxic activity of bleomycin (3.6 fold), but it could not potentiate the cytotoxic activity of other antitumor agents, including nitrosourea and Cis-DDP, in L1210 cells in vitro. Treatment of Ehrlich ascites tumor bearing mice with bleomycin and 3-aminobenzamide produced a synergistic effect. 6-Aminonicotinamide also potentiated the antitumor activity of bleomycin against Ehrlich ascites tumor.     

Radiosensitization of human and rodent cell lines by INO-1001, a novel inhibitor of poly(ADP-ribose) polymerase

Inhibition of poly(ADP-ribose) polymerase (PARP) by a novel, potent inhibitor, INO-1001, was examined in two rodent and one human fibroblast cell lines, after single and fractionated radiation treatments. Since PARP plays a role in the early events following DNA damage and influences the effectiveness of DNA repair, its inhibition has been proposed to constitute a drug target for the development of novel radiosensitizers. We found that INO-1001 effectively inhibited PARP activity at non-cytotoxic concentrations. Combination treatment of 10 microM INO-1001 and a single dose of radiation resulted in significant radiosensitization of all three cells lines (enhancement ratios 1.4-1.6). This radioenhancement was even greater when the drug and radiation were given as fractionated treatments (enhancement ratio 8.0). Apoptosis (as evaluated by TUNEL staining) was not enhanced by the treatments, suggesting that inhibiting PARP enzyme activity by INO-1001 enhanced radiation-induced cell killing by interfering with DNA repair mechanisms, resulting in necrotic cell death. INO-1001 therefore, appears to have potential as a potent enhancer of radiation sensitivity, without any intrinsic cytotoxicity from the drug alone.     

Amelioration of ferric nitrilotriacetate (Fe-NTA) induced renal oxidative stress and tumor promotion response by coumarin (1,2-benzopyrone) in Wistar rats

In this study, we report the modulatory effect of coumarin (1,2-benzopyrone) on Ferric nitrilotriacetate (Fe-NTA) induced renal oxidative stress and tumor promotion response in rats. Fe-NTA (9 mg Fe/kg body weight, intraperitoneally) enhances renal lipid peroxidation, xanthine oxidase, gamma-glutamyl transpeptidase and hydrogen peroxide (H2O2) generation with reduction in antioxidant enzymes and renal glutathione content. It also enhances blood urea nitrogen, serum creatinine, ornithine decarboxylase (ODC) activity and thymidine [3H] incorporation into renal DNA. Prophylactic treatment of rats with coumarin (10 and 20 mg/kg body weight) resulted in significant recovery of antioxidant enzymes (P < 0.001) and renal glutathione content (P < 0.01). There was also significant decrease in gamma-glutamyl transpeptidase, lipid peroxidation, xanthine oxidase, H2O2 generation, blood urea nitrogen, serum creatinine, renal ODC activity and DNA synthesis (P < 0.001) Thus, our results show that coumarin is a potent chemopreventive agent and suppresses Fe-NTA induced nephrotoxicity in Wistar rats.     

Regulation of phosphoglucose isomerase/autocrine motility factor activities by the poly(ADP-ribose) polymerase family-14

Phosphoglucose isomerase (PGI; EC 5.3.1.9) is a ubiquitous cytosolic enzyme essential for glycolysis and gluconeogenesis. PGI is a multifunctional dimeric protein that extracellularly acts as a cytokine [autocrine motility factor (AMF)] eliciting mitogenic, motogenic, and differentiation functions through binding to its cell surface receptor gp78/AMF receptor (AMFR). AMFR contains a seven-transmembrane domain with RING-H2 and leucine zipper motifs showing ubiquitin protein ligase (E3) activity and is exposed on the endoplasmic reticulum surface. Augmented expressions of both PGI/AMF and AMFR have been implicated in tumor progression and metastasis, and an intracellular binding partner of PGI/AMF is expected to regulate in part its diverse biological functions. Thus, we screened a cDNA library using a yeast two-hybrid system to search for interacting protein(s) and report on the finding of poly(ADP-ribose) polymerase-14 (PARP-14) to be a binding partner with PGI/AMF. PARP-14-PGI/AMF interaction was confirmed by coimmunoprecipitation and immunolocalization. We also report that PGI/AMF degradation is mainly regulated by the ubiquitin-lysosome system and RNA interference experiments revealed that PARP-14 inhibits PGI/AMF ubiquitination, thus contributing to its stabilization and secretion. This newly characterized PARP-14 protein should assist in understanding the regulation of PGI/AMF intracellular function(s) and may provide a new therapeutic target for inhibition of PGI/AMF inducing tumor cell migration and invasion during metastasis.     

Differential radiosensitization by the poly(ADP-ribose) transferase inhibitor 3-aminobenzamide in human tumor cells of varying radiosensitivity

Four newly-established human tumor cell lines, have been irradiated at dose rates of 150 and 3.2 cGy/min to compare their capacity to repair radiation damage. They included a neuroblastoma, a germ-cell carcinoma of the testis, a large cell carcinoma of the lung, and a carcinoma of the cervix. The four lines varied in their sensitivity to high dose-rate irradiation, with the neuroblastoma being most radiosensitive and the lung and cervix tumors the most radioresistant. The extent of dose sparing associated with lowering the dose rate to 3.2 cGy/min was similar in three of the lines but somewhat greater in the case of the cervix carcinoma cell line. The presence of non-toxic concentrations of the poly(ADP-ribose) transferase inhibitor, 3-aminobenzamide (3-AB), enhanced the response of 3 of the 4 tumors to irradiation; it failed to modify the sensitivity of a lung carcinoma cell line. The extent of sensitization was generally similar at high and low dose rate. Measurement of poly(ADP-ribose) transferase activity in control and irradiated cells showed the neuroblastoma cells to contain much higher initial levels than the other three lines but there were no significant differences in the extent of stimulation in enzyme levels after irradiation. Survival curves obtained at low dose-rate help define the initial slope of the acute curve and it appears that 3-AB may exert a differential effect among human tumors in modifying this component.     

TSL-1502, a glucuronide prodrug of a poly (ADP-ribose) polymerase (PARP) inhibitor,exhibits potent anti-tumor activity in preclinical models

Poly (ADP-ribose) polymerase (PARP) enzymes play an important role in the cellular response to DNA damage and the inhibition of PARP causes synthetic lethality in homologous recombination (HR)-deficient cancer. Multiple PARP inhibitors have been developed and have shown remarkable clinical benefits. However, treatment-related toxicities, especially the hematologic toxicities, are common and restrict the clinical applications of PARP inhibitors. In this study, we designed the first glucuronide prodrug of PARP inhibitor, TSL-1502, based on a novel and highly potent PARP inhibitor TSL-1502M. TSL-1502M exhibited promising inhibitory activity on PARP1/2, significantly induced DNA double strand breaks, G2/M arrest and apoptosis in HR-deficient cells, selectively inhibited the proliferation of HR-deficient cancer cells and sensitized both HR-deficient and HR-proficient cancer cells to conventional chemotherapy. Notably, TSL-1502M was superior to olaparib, the first-in-class PARP inhibitor, in all these processes. TSL-1502 had no inhibitory effects on PARP1/2 itself, but could selectively liberate the active drug TSL-1502M in tumor after administration in nude mice. Moreover, TSL-1502 elicited significant more potent inhibitory effects than olaparib in HR-deficient tumors, and sensitized chemotherapy in both HR-deficient and HR-proficient tumors. No severe toxicities were caused by TSL-1502 in this study. Based on the encouraging preclinical antitumor activity and the selective decomposition characteristic of TSL-1502, a clinical phase I study was initiated in China, and an Investigational New Drug (IND) was granted by the US FDA. TSL-1502 could represent a new potential therapeutic choice of PARP inhibitors.     

Inhibition of methylazoxymethanol acetate initiation of colon carcinogenesis in rats by treatment with the poly(ADP-ribose)polymerase inhibitor 3-aminobenzamide

To clarify the biological role of poly(ADP-ribose) in cancerinduction in vivo, the influence of the poly(ADP-ribose) polymeraseinhibitor, 3-aminobenzamide (3-AB), on initiation of carcinogenesisin the colon and liver by a single application of methylazoxymethanol(MAM) acetate was investigated. Since 3-AB is rapidly metabolizedand excreted in vivo when injected as a single dose, rats weregiven a continuous i.v. infusion of the compound (1200 mg/kg/day) for 4 days and injected with a single dose (35 mg /kg)of MAM acetate 4 h after the start of the experiment. Rats werekilled 70 weeks after the beginning of the experiment. The incidenceof colon tumors was significantly lower (t < 0.025) in the3-AB-treated group than in the carcinogen-only controls. Althoughsignificant numbers of glutathione S-transferase placental formpositive foci were also induced in the liver of MAM-acetatetreatedanimals, 3-AB administration had no effect on their number andsize. The results thus clearly demonstrated that continuousinfusion of 3-AB during the initiation phase inhibited the developmentof MAM-acetate-induced colon tumors, but was not effective forthe formation of preneoplastic foci in the liver.     

Central nervous system penetration and enhancement of temozolomide activity in childhood medulloblastoma models by poly(ADP-ribose) polymerase inhibitor AG-014699

Background:

Temozolomide shows activity against medulloblastoma, the most common malignant paediatric brain tumour. Poly(ADP-ribose) polymerase (PARP) inhibitors enhance temozolomide activity in extracranial adult and paediatric human malignancies.

Methods:

We assessed the effect of AG-014699, a clinically active PARP inhibitor, on temozolomide-induced growth inhibition in human medulloblastoma models. Pharmacokinetic, pharmacodynamic and toxicity assays were performed in tumour-bearing mice.

Results:

Sensitivity to temozolomide in vitro was consistent with methylguanine methyltransferase (MGMT) and DNA mismatch repair (MMR) status; MGMT⁺ MMR⁺ D384Med cells (temozolomide GI₅₀=220 μ), representative of most primary medulloblastomas, were sensitised fourfold by AG-014699; MGMT⁻ MMR⁺ D425Med cells were hypersensitive (GI₅₀=9 μ) and not sensitised by AG-014699, whereas MGMT⁺ MMR⁻ temozolomide-resistant D283Med cells (GI₅₀=807 μ) were sensitised 20-fold. In xenograft models, co-administration of AG-014699 produced an increase in temozolomide-induced tumour growth delay in D384Med xenografts. Consistent with the in vitro data, temozolomide caused complete tumour regressions of D425Med xenografts, whereas D283Med xenografts were relatively resistant. AG-014699 was not toxic, accumulated and reduced PARP activity ⩾75% in xenograft and brain tissues.

Conclusion:

We show for the first time central nervous system penetration and inhibition of brain PARP activity by AG-014699. Taken together with our in vitro chemosensitisation and toxicity data, these findings support further evaluation of the clinical potential of AG-014699–temozolomide combinations in intra-cranial malignancies.     

Inhibitors of poly(adenosine diphosphoribose) synthetase, examination of metabolic perturbations, and enhancement of radiation response in Chinese hamster cells

3-Aminobenzamide, a specific inhibitor of poly(adenosine diphosphoribose) synthesis, has been shown to enhance the response of mammalian cells to ionizing radiation and alkylating agents. Observations such as these usually have been taken to be an indication of the involvement of poly(adenosine diphosphoribose) in the repair of DNA damage. It has been reported that some inhibitors of adenosine diphosphoribosyl transferase (ADPRT) affect cell viability, glucose metabolism, and DNA synthesis when present at low concentrations in the growth medium for extended periods (e.g., lymphoid cells exposed to a few millimolar for 24 h [Milam, K. M., and Cleaver, J. E. Science (Wash. DC), 223: 589, 1984]). The latter report questioned previous interpretations of radiation results based on the use of ADPRT inhibitors which enhance cell killing. We have studied the enhanced radiation lethality of Chinese hamster cells using higher concentrations of these inhibitors, but for shorter periods, in an effort to determine if metabolic perturbations are produced and if they are relatable to enhanced cell killing. The compounds used were 2-aminobenzamide, 3-aminobenzamide, 4-aminobenzamide, benzamide, and nicotinamide, compounds which show a large variation in their potency as inhibitors of ADPRT. It was found that none of the compounds was toxic at the highest doses used (20 mM for 2 h) and that, during a 2-h period, the potent inhibitor 3-aminobenzamide had little or no effect on DNA synthesis. Two h is long enough to yield a near-maximum radiosensitization with 3-aminobenzamide. Although glucose metabolism was affected to varying degrees (up to a 50% inhibition by 4-aminobenzamide in 2 h), there was no correlation between effectiveness in inhibiting ADPRT and effectiveness in inhibiting glucose metabolism. A correlation was observed, however, between the inhibitory potential of ADPRT and the enhancement of radiation response. When used for sufficiently short times, we conclude that the effects at even high concentrations of a potent inhibitor of ADPRT (e.g., 3-aminobenzamide) are consistent with an involvement of poly(adenosine diphosphoribose) synthesis in the expression of a radiation-induced end point like cell killing.     

Repair of O6-methylguanine, by mammalian cell extracts, in alkylated DNA and poly(dG-m5 dC).(poly dG-m5 dC) in B and Z forms

The ability of rat hepatoma cells extracts to repair O⁶-methylguaninewas measured using as substrate alkylated DNA and alkylatedpoly(dG-m⁵ dC).poly(dG-m⁵ dC) either in the B or in the Z conformation.The O⁶-methylguanine-DNA methyltransferase had similar activitieson DNA and on the right-handed polymer. However, when the polymerwas in the Z conformation, the protein activity represented10% of that measured on DNA. Therefore the efficiency of O⁶-methylguaninerepair is related to the DNA conformation and is markedly reducedduring the B to Z transition of the substrate.     

Systemic administration of GPI 15427, a novel poly(ADP-ribose) polymerase-1 inhibitor, increases the antitumor activity of temozolomide against intracranial melanoma, glioma, lymphoma.

PURPOSE: Temozolomide (TMZ) is a DNA methylating agent that has shown promising antitumor activity in recent clinical trials against high grade gliomas, metastatic melanoma, and brain lymphoma. In this study, we tested whether systemic administration of GPI 15427, a novel poly(ADP-ribose) polymerase (PARP-1) inhibitor capable of crossing the blood-brain barrier, could enhance the efficacy of TMZ against metastatic melanoma, glioblastoma multiforme, and lymphoma growing in the brain. EXPERIMENTAL DESIGN: Murine B16 melanoma or L5178Y lymphoma cells were injected intracranially in syngeneic mice. An orthotopic xenograft of the human SJGBM2 glioblastoma multiforme was implanted in nude mice. Animals were treated with TMZ + GPI 15427 using a schedule of 40 mg/kg/i.v. GPI 15427 + 100 mg/kg/i.p. TMZ for 3 days. The efficacy of drug treatment was assessed by: (a) the increase of mouse survival and life span; and (b) the suppression of melanoma metastases to lung after i.v. injection of B16 cells. RESULTS: In all models, systemic administration of GPI 15427 shortly before TMZ significantly increased life span of tumor-bearing mice with respect to untreated controls or to groups treated with either GPI 15427 or TMZ only. Moreover, GPI 15427 increased the antimetastatic effect of TMZ. CONCLUSIONS: These data indicate that systemic administration of the poly(ADP-ribose) polymerase-1 inhibitor GPI 15427 significantly enhances TMZ antitumor efficacy against solid or hematological neoplasias even when located at the central nervous system site.     

Characterization of cellular pathways involved in glioblastoma response to the chemotherapeutic agent 1, 3-bis(2-chloroethyl)-1-nitrosourea (BCNU) by gene expression profiling

The effectiveness of chemotherapy for human cancers is limited by pharmacokinetic parameters such as variation in metabolism and is determined by the cellular response. In this work, we aimed to gain a more holistic understanding of the molecular basis of glioma response to the DNA-alkylating agent 1, 3-bis(2-chloroethyl)-1-nitrosourea (BCNU) by using a systematic approach: we investigated the expression of 588 genes with various cellular functions in a BCNU-resistant glioblastoma cell line and a BCNU-sensitive subline before and after treatment with BCNU. Our gene expression profiling revealed major differences in gene expression between these two cell lines, especially after treatment with BCNU. One striking example was that BCNU decreased the expression of six DNA-repair genes in sensitive but not in resistant cells. In sensitive cells, BCNU treatment resulted in the induction of two MAP kinase genes; this finding suggests that the specific response to BCNU in sensitive cells may involve the Jun kinase signal transduction pathway. After BCNU treatment, marked induction of tumor necrosis factor was detected only in sensitive cells, suggesting that tumor necrosis factor is a mediator of BCNU-induced cell death. Bcl-2 family members were not altered by BCNU in sensitive cells, suggesting that BCNU-induced cell death may be independent of the bcl-2 pathway. Results of the present study demonstrate that gene expression profiling may facilitate identification of cellular pathways associated with specific responses to chemotherapeutic agents and contribute to an understanding of the molecular basis of drug action.     

Quantification of 2-amino-3-methylimidazo[4, 5-f]quinoline (IQ) and 2-amino-3, 8-dimethylimidazo[4, 5-f]quinoxaline (MeIQx) in beef extracts by liquid chromatography with electrochemical detection (LCEC)

A simple and sensitive method was developed for quantificationof mutagenic/carcinogenic aminoimidazoquinoline and aminoimidazoquinoxalinecompounds in heated materials. Samples were partially purifiedby blue-cotton treatment, 0.1 N HCI-methylene dichloride partitionand separation in a SEP-PAK silica cartridge. The recoveriesof aminoimidazoquinoline and aminoimidazoquinoxaline compoundsat the step of partial purification were estimated by spikingwith ¹⁴C-labeled compounds. The compounds in partially purifiedmaterials were analyzed by liquid chromatography with electrochemicaldetection using a combination of two columns of octadecyl silaneand cation exchange. Bacteriological-grade beef extract wasfound to contain 41.6 and 58.7 ng/g of 2-amino-3-methylimidazo[4,5-f]quinoline and 2-amino-3, 8-dimethylimidazo[4, 5-f]quinoxaline(MeIQx), respectively. MeIQx was also detected at a level of3.1 ng per g in food-grade beef extract.