Poly(ADP-ribose) polymerase (PARP-1) is not involved in DNA double-strand break recovery

BACKGROUND

The cytotoxicity and the rejoining of DNA double-strand breaks induced by gamma-rays, H2O2 and neocarzinostatin, were investigated in normal and PARP-1 knockout mouse 3T3 fibroblasts to determine the role of poly(ADP-ribose) polymerase (PARP-1) in DNA double-strand break repair.

RESULTS

PARP-1-/- were considerably more sensitive than PARP-1+/+ 3T3s to induced cell kill by gamma-rays and H2O2. However, the two cell lines did not show any significant difference in the susceptibility to neocarzinostatin below 1.5 nM drug. Restoration of PARP-1 expression in PARP-1-/- 3T3s by retroviral transfection of the full PARP-1 cDNA did not induce any change in neocarzinostatin response. Moreover the incidence and the rejoining kinetics of neocarzinostatin-induced DNA double-strand breaks were identical in PARP-1+/+ and PARP-1-/- 3T3s. Poly(ADP-ribose) synthesis following gamma-rays and H2O2 was observed in PARP-1-proficient cells only. In contrast neocarzinostatin, even at supra-lethal concentration, was unable to initiate PARP-1 activation yet it induced H2AX histone phosphorylation in both PARP1+/+ and PARP-1-/- 3T3s as efficiently as gamma-rays and H2O2.

CONCLUSIONS

The results show that PARP-1 is not a major determinant of DNA double-strand break recovery with either strand break rejoining or cell survival as an endpoint. Even though both PARP-1 and ATM activation are major determinants of the cell response to gamma-rays and H2O2, data suggest that PARP-1-dependent poly(ADP-ribose) synthesis and ATM-dependent H2AX phosphorylation, are not inter-related in the repair pathway of neocarzinostatin-induced DNA double-strand breaks.

Gene rearrangements induced by the DNA double-strand cleaving agent neocarzinostatin: conservative non-homologous reciprocal exchanges in an otherwise stable genome

Among a collection of 74 aprt mutations induced by treatment of plateau phase Chinese hamster ovary CHO cells with the radiomimetic DNA double-strand cleaving agent neocarzinostatin, nine were large-scale rearrangements. Molecular analysis indicated that all nine were highly conservative, non-homologous reciprocal exchanges, most of which were intrachromosomal as determined by fluorescence in situ hybridization. All but one of the parental sequences contained potential double-strand cleavage sites positioned such that the observed rearrangements could be explained by drug-induced double-strand breakage followed by trimming, templated patching and ligation of the exchanged ends. Predicted non-complementary 3' overhangs were often preserved in the newly formed junctions, suggesting alignment-based fill-in of the overhangs. Banding of metaphase spreads of these mutants, and of a number of mutants induced by the functionally similar compound bleomycin, revealed that bleomycin-induced reciprocal exchange mutants had multiple additional chromosome alterations and considerable chromosomal heterogeneity within each mutant line. In contrast, neocarzinostatin-induced reciprocal exchange mutants, as well as bleomycin-induced base substitution and single base deletion mutants, retained stable pseudodiploid karyotypes similar to that of the parent line. Thus, some reciprocal exchanges arising from misjoining of double-strand breaks were associated with global chromosomal instability, while other ostensibly similar events were not.

Delocalized electronic structure of the thiol sulfur substantially prevents nucleic acid damage induced by neocarzinostatin

Neocarzinostatin is a potent antitumor antibiotic and is a prodrug, which induces genome damage after activation by a thiol. The prodrug is stored as a protein-bound chromophore that contains an enediyne nucleus. A thiolate attack on the chromophore cyclizes the nucleus and produces radicals that abstract hydrogen from DNA. Because thiol is the only cofactor in the vital activation process, the structure of the thiol plays an important role in the activity of the drug. Here we systematically examine the effect of the electronic structure of some thiols on the efficiency of the drug, and compare particularly aromatic with aliphatic thiols. The values of drug-induced base release from DNA are remarkably different between thiophenol (3.6%) and benzyl mercaptan (12.5%), the activity of which is comparable with those of aliphatic thiols. Cleavage results determined by DNA electrophoresis are consistent with the results of base release; they show that the total number of DNA lesions is more than 3-fold lower for thiophenol than for aliphatic thiols or benzyl mercaptan. We conclude that among aromatic thiols, only those that have delocalized thiol sulfur electrons can substantially reduce the DNA cleavage activity. This result suggests that the effect of an aromatic ring arises from an inductive effect imposed on the thiol sulfur electron through pi-resonance rather than through effects such as aromatic stacking, steric hindrance, or hydrophobic interaction. Replacing thiophenol with substituted derivatives with electron-releasing or -withdrawing groups changes the drug activity and supports the important role of the electronic structure of the thiol sulfur in determining the drug activity.

The cellular response to DNA damage induced by the enediynes C-1027 and neocarzinostatin includes hyperphosphorylation and increased nuclear retention of replication protein a (RPA) and trans inhibition of DNA replication

This study examined the cellular response to DNA damage induced by antitumor enediynes C-1027 and neocarzinostatin. Treatment of cells with either agent induced hyperphosphorylation of RPA32, the middle subunit of replication protein A, and increased nuclear retention of RPA. Nearly all of the RPA32 that was not readily extractable from the nucleus was hyperphosphorylated, compared to < or =50% of the soluble RPA. Enediyne concentrations that induced RPA32 hyperphosphorylation also decreased cell-free SV40 DNA replication competence in extracts of treated cells. This decrease did not result from damage to the DNA template, indicating trans-acting inhibition of DNA replication. Enediyne-induced RPA hyperphosphorylation was unaffected by the replication elongation inhibitor aphidicolin, suggesting that the cellular response to enediyne DNA damage was not dependent on elongation of replicating DNA. Neither recovery of replication competence nor reversal of RPA effects occurred when treated cells were further incubated in the absence of drug. C-1027 and neocarzinostatin doses that caused similar levels of DNA damage resulted in equivalent increases in RPA32 hyperphosphorylation and RPA nuclear retention and decreases in replication activity, suggesting a common response to enediyne-induced DNA damage. By contrast, DNA damage induced by C-1027 was at least 5-fold more cytotoxic than that induced by neocarzinostatin.

Differential responses of Chinese hamster mutagen sensitive cell lines to low and high concentrations of calicheamicin and neocarzinostatin

To shed light on the mechanism underlying the cellular response to the radiomimetic agents calicheamicin Y(1)(1) (CAL) and neocarzinostatin (NCS), several hamster cell mutants defective in different DNA repair pathways were used. Two X-ray sensitive Chinese hamster V79 mutant cell lines, XR-V9B and V-E5 were studied for their response to the induction of cell killing, micronuclei, and G2-chromosomal aberrations relative to that of parental wild-type cells. In addition, effects of CAL and NCS on bleomycin sensitive BL-V40 cells and on UV sensitive V-H1 cells were analyzed. In general, the radiosensitive cell lines showed the highest sensitivities to CAL and NCS, but also the other mutants demonstrated differences in their responses compared to wild-type cells. With respect to cell killing, expressed as D(10)-value, enhanced sensitivities of mutants with factors up to 4.4 were recorded. For the induction of micronuclei (MN) and chromosomal aberrations (CA) all cell lines, including the parental cells, show a steep increase in the frequencies at the lowest tested doses and a leveling off at higher concentrations. Probably toxic effects at the higher exposure levels are responsible for these biphasic dose effect curves. Enhanced sensitivities of the various mutants were primarily observed at the higher exposure levels. With respect to the induction of MN increased sensitivities up to a factor of 18.1 were observed for the radiosensitive mutants, whereas for CA the mutant cell lines showed a variation from resistance (0.3) of VH-1 cells up to a 3.8-fold higher sensitivity to the radiomimetic agents. However, at the lowest tested concentrations for both MN and CA, the differences between the sensitive mutants and wild-type clearly diminished, suggesting the existence of residual and/or alternative DNA repair pathways in these mutants.

Removal by human apurinic/apyrimidinic endonuclease 1 (Ape 1) and Escherichia coli exonuclease III of 3'-phosphoglycolates from DNA treated with neocarzinostatin, calicheamicin, and gamma-radiation

DNA strand breaks with terminal 3'-phosphoglycolate groups are produced by agents that can abstract the hydrogen atom from the 4'-carbon of DNA deoxyribose groups. Included among these agents are gamma-radiation (via the OH radical) and enediyne compounds, such as neocarzinostatin and calicheamicin. However, while the majority of radiation-induced phosphoglycolates are found at single-strand breaks, most of the phosphoglycolates generated by these two enediynes are found at bistranded lesions, including double-strand breaks. Using a 32P-post-labelling assay, we have compared the enzyme-catalyzed removal of phosphoglycolates induced by each of these agents. Both human apurinic/apyrimidinic endonuclease 1 (Ape 1) and its Escherichia coli homolog exonuclease III rapidly removed over 80% of phosphoglycolates from gamma-irradiated DNA, although there appeared to be a small resistant subpopulation. The neocarzinostatin-induced phosphoglycolates were removed more slowly, though not to completion, while the calicheamicin-induced phosphoglycolates were extremely refractory to both enzymes. These data suggest that unless other enzymes are capable of acting upon the phosphoglycolate termini at enediyne-induced double-strand breaks, such termini will be resistant to end rejoining repair pathways.

Thiopronin reduces the frequencies of neocarzinostatin-induced chromosomal aberrations and sister chromatid exchanges in Chinese hamster ovary cells

Chinese hamster ovary (CHO) cells were treated in the G1 phase of the cell cycle with different concentrations of neocarzinostatin (NCS) alone or in combination with N-(2-mercaptopropionyl)-glycine (thiopronin; TP). TP reduces the frequencies of NCS-induced chromosomal aberrations (CA) and of sister chromatid exchanges (SCE) significantly when added to the cultures simultaneously (TPsim), 1 min (TP1) or 10 min (TP10) after the addition of NCS. The addition of TP 30 min (TP30) or 60 min (TP60) after NCS reduces the frequencies of SCE, but not of CA. Our results indicate that the induction of CA and SCE by NCS is partially based on different mechanisms.

DNA effects in repair-deficient V79 Chinese hamster cells studied with the comet assay

Using the alkaline comet assay (single cell gel electrophoresis), we studied the induction and persistence of DNA damage induced by methyl methanesulfonate (MMS) and neocarzinostatin (NCS) in the repair-deficient Chinese hamster cell lines V-E5 and XR-V15B. Effects in the comet assay were analyzed directly after treatment as well as after a postincubation period in mutagen-free medium to gain insight into the DNA repair capacities of the mutant cell lines in relation to different primary DNA lesions. Both mutagens caused a concentration-related increase in DNA strand breakage in both mutant cell lines and in the normal parental cell lines. Repair of MMS-induced DNA damage during postincubation was similar in normal and mutant cell lines, while diminished repair was seen after NCS treatment in XR-V15B cells. Our data show that XR-V15B cells only repaired about 30% of NCS-induced DNA damage within 1 h, while the parental V79 cell line repaired about 70%. Since this cell line is defective in the repair of DNA double-strand breaks (DSB), the results indicate that NCS-induced DSB significantly contribute to the genotoxic effects seen in the comet assay. However, compared to previously studied induction of gene mutations and chromosome aberrations, detection of NCS-induced DNA effects with the comet assay was less sensitive and increased DNA migration only occurred under strong cytotoxic conditions.

Micronucleus induction by neocarzinostatin and methyl methanesulfonate in ionizing radiation--sensitive Chinese hamster V79 cell mutants

Two mutant V79 Chinese hamster cell lines (V-E5, XR-V15B) which show hypersensitivities to DNA damage and their two parental cell lines (V79-LE, V79-B) were used for micronucleus studies. The characteristics of V-E5 strongly resemble those of cells derived from patients suffering from the genomic instability syndrome ataxia telangiectasia, whereas XR-V15B has a decreased ability to rejoin double-strand breaks. The two cell lines V-E5 and XR-V15B showed increased spontaneous micronucleus frequencies and higher sensitivity for micronucleus induction by methyl methanesulfonate (MMS) and neocarzinostatin (NCS) both with and without the use of cytochalasin B in the micronucleus assay. Thus, defects in cellular responses to DNA damage are modulating factors in micronucleus formation.

Mechanism of free and conjugated neocarzinostatin activity: studies on chromophore and protein uptake using a transferrin-neocarzinostatin conjugate

Targeting studies using the anti-cancer agent neocarzinostatin (NCS), conjugated to anti-bodies have shown relatively poor specificity. From the literature, it is unclear whether NCS mediates its effects either in conjugated or unconjugated form. In the present work we have used a conjugate of NCS with transferrin, a biological ligand with a well defined endocytic route, to probe these mechanisms. NCS was covalently coupled to transferrin using the heterobifunctional reagent sulfo-4-(N-maleimidomethyl)cyclohexane-1-carboxylate (SMCC) and 2-iminothiolane to give a stable thioether-linked conjugate with a ratio of 1.6 mol of NCS per mole of transferrin. The binding activity of transferrin was completely retained. Conjugation of NCS to transferrin resulted in an apparent enhancement of cytotoxicity. However, incubation with excess transferrin had no influence on the observed enhanced toxicity, indicating that endocytosis is not responsible. Further experiments demonstrated that the apparent enhancement was dependent on incubation conditions and not an effect due to endocytosis of ligand. Studies where apo-NCS competed with holo-NCS and transferrin strongly indicated that the cytotoxicity of both NCS and conjugate is mediated by direct entry of the dissociated chromophore into the cell.

DNA damage and mutagenesis by radiomimetic DNA-cleaving agents: bleomycin, neocarzinostatin and other enediynes

Bleomycin and the enediyne antibiotics effect concerted, simultaneous site-specific free radical attack on sugar moieties in both strands of DNA, resulting in double-strand breaks of defined geometry and chemical structure, as well as abasic sites with closely opposed strand breaks. The hypersensitivity of several mammalian double-strand break repair-deficient mutants to these agents confirms the role of these double-strand breaks in mediating cytotoxicity. In bacteria, mutagenesis by both bleomycin and neocarzinostatin appears to result from replicative bypass of abasic sites, the repair of which is blocked by the presence of closely opposed strand breaks. However, in mammalian cells, such abasic sites decompose to form double-strand breaks, and mutagenesis consists primarily of small deletions, large deletions, and gene rearrangements, all of which probably result from errors in double-strand break repair by a nonhomologous end-joining mechanism. Studies with the radiomimetic antibiotics emphasize the importance of this end-joining repair pathway, and these agents provide useful probes of its mechanistic details, particularly the effects of chemically modified DNA termini on repair.

Detection of neocarzinostatin-induced translocations in human sperm chromosomes using fluorescence in situ hybridization of chromosome 2

Mature sperm and late spermatid are known to be sensitive stages to clastogens in mammalian spermatogenesis. Certain types of chromosomal damage induced in these stages will pass to successive generations as heritable translocations. In the present study, we employed whole chromosome 2 painting with the fluorescence in situ hybridization (FISH) technique to detect the chemically induced translocations in human sperm. Mature human sperm were treated in vitro with an antitumor drug, neocarzinostatin (NCS), and fertilized in vitro with golden hamster oocytes. Sperm pronuclear chromosome slides were prepared at the first cleavage metaphase. To compare the characteristics of translocations between somatic and germ cells, human lymphocytes in peripheral blood treated with NCS in vitro were analyzed at first round metaphase after PHA-stimulation. From the analysis of translocations by whole chromosome 2 painting, frequencies of the haploid genomic translocations (FhG) were predicted for both sperm and lymphocytes. At 1.0 micrograms/ml, the actual percentages of sperm and lymphocytes with chromosome 2 translocations were almost identical (11.9% and 12.0%). At the same dose, however, the FhG of the sperm (1.15) was considerably higher than that of the lymphocytes (0.58), indicating that complex translocations having two or more rearranged sites were induced by NCS more frequently in sperm than in lymphocytes.

The effect of defective DNA double-strand break repair on mutations and chromosome aberrations in the Chinese hamster cell mutant XR-V15B

The radiosensitive Chinese hamster cell line XR-V15B was used to study the effect of decreased rejoining of DNA double-strand breaks (DSBs) on gene mutations and chromosome aberrations. XR-V15B cells are hypersensitive to the cytotoxic effects of neocarzinostatin (NCS) and methyl methanesulfonate (MMS). Both mutagens induced more chromosome aberrations in XR-V15B cells than in the parental cell strain. The clastogenic action of NCS was characterized by the induction of predominantly chromosome-type aberrations in cells of both strains, whereas MMS induced mainly chromatid aberrations. The frequency of induced gene mutations at the hprt locus was not increased compared to the parental V79 cells when considering the same survival level. Molecular analysis by multiplex polymerase chain reaction (PCR) of mutants induced by NCS revealed a high frequency of deletions in cells of both cell lines. Methyl methane-sulfonate induced mainly mutations without visible changes in the PCR pattern, which probably represent point mutations. Our findings suggest a link between a defect in DNA DSB repair and increased cytotoxic and clastogenic effects. However, a decreased ability to rejoin DNA DSBs does not seem to influence the incidence and types of gene mutations at the hprt locus induced by NCS and MMS.

The pattern of mutations induced by neocarzinostatin and methyl methanesulfonate in the ataxia telangiectasia-like Chinese hamster cell line V-E5

The Chinese hamster cell line V-E5 is a mutant cell line isolated from V79 cells. The phenotypic characteristics of V-E5 strongly resemble those of cells from patients suffering from the genomic instability syndrome ataxia telangiectasia. In order to further characterize the mutant cell line and to get insight into the underlying genetic defect we compared the clastogenic and mutagenic effects of neocarzinostatin (NCS) and methyl methanesulfonate (MMS) in V-E5 and V79 wild-type cells (V79-LE). V-E5 cells were 2-3 times more sensitive to the cytotoxic effect of NCS or MMS. The clastogenic action of NCS was characterized by the predominant induction of chromosome breaks and dicentrics in both cell lines, whereas MMS mainly induced chromatid-type aberrations. The frequency of mutations induced by NCS as well as MMS was slightly enhanced in V-E5 cells compared to V79 cells treated with the same dose. However, the mutant cell line was found to be hypomutable when considering the same survival level as in the parental cell line. Molecular analysis of mutants induced by NCS revealed a high frequency of total deletions of the hprt gene in both cell lines. In contrast, among MMS-induced mutations only 11% deletion mutations were found in V79-LE, whereas in V-E5 MMS-induced deletions were seen in 52% of the hprt-deficient mutants. These results are discussed with respect to a possible relation between genomic instability, cell cycle control and mutational spectra.

Neocarzinostatin induces chromosomal aberrations and sister chromatid exchanges in Chinese hamster ovary cells

Chinese hamster ovary (CHO) cells were treated with neocarzinostatin (NCS) and analyzed for chromosomal aberrations and sister chromatid exchanges (SCE). After treatment the cells were recovered for 9, 20, 26 or 30 h. NCS induces chromosomal aberrations and SCE. SCE were much more frequent in cells with chromosome type aberrations at 20 h recovery time than in those with chromatid type aberrations at 9 h recovery time. In second post-treatment cells at 26 or 30 h recovery time NCS induced chromosomal aberrations but only few SCE.

The enhancement of cell lethality and changes in production and repair of DNA damage by hypertonic treatment after exposure to X rays, bleomycin, and neocarzinostatin

Chinese hamster ovary cells were treated with hypertonic 0.5 M NaCl solution after exposure to X rays or the radiomimetic drugs bleomycin or neocarzinostatin. The cytotoxicity of these agents was greatly enhanced by the hypertonic treatment. On the other hand, no effect was observed after exposure to ultraviolet light, and a significant effect was obtained with mitomycin C (MMC), adriamycin (ADR), and ethyl methanesulfonate (EMS). Assays by filter elution revealed that hypertonicity had various effects on the damage produced by the different agents. Strand breaks resulting from exposure to X rays and radiomimetic agents were sensitive to hypertonic treatment. Hypertonicity caused the production of new lesions and inhibited the rejoining of DNA strand breaks, both of which may be responsible for the enhanced cytotoxicity. On the other hand, the formation of crosslinks by MMC or protein-associated double-strand breaks by ADR, the major forms of damage by which these agents cause cytotoxicity, was not affected by hypertonic treatment. As strand breaks are known to be produced by MMC or ADR, they could account at least partly for the sensitization. However, various kinds of damage are produced by MMC, and any of these could be involved in the sensitization. To our knowledge EMS produces only base damage. Thus hypertonic treatment may have an effect on various types of damage.

The scid mutation in mice causes defects in the repair system for both double-strand DNA breaks and DNA cross-links

The sensitivity of scid fibroblasts established from C.B17-scid/scid fetuses to the DNA-damaging agents bleomycin, neocarzinostatin, mechlorethamine, mitomycin C, methyl methanesulfonate, and ultraviolet light, all of which induce different types of DNA damage, was examined. Scid fibroblasts were 2.8-, 3.7-, and 3.0-fold more sensitive to bleomycin, neocarzinostatin, and mechlorethamine, respectively, than wild-type fibroblasts derived from C.B17-+/+ fetuses. These findings indicate that the scid mutation in mice causes defects in repairing both double-strand DNA breaks and DNA cross-links.

Neocarzinostatin-mediated DNA damage in a model AGT.ACT site: mechanistic studies of thiol-sensitive partitioning of C4' DNA damage products

Double-strand (DS) DNA damage caused by neocarzinostatin (NCS) has been studied in the trinucleotide AGT-ACT sequence in an AP-1 transcription factor binding site. There are strong similarities between bistranded lesions produced at AGT.ACT and AGC-GCT, including the fact that DS lesions outnumber SS lesions on the AGT and AGC strands, while SS exceed DS on the ACT and GCT strands. Structure-function studies revealed that a variety of different thiols produced bistranded lesions in this model by predominantly C4'-hydrogen atom abstraction (84-93%) at the T of AGT and C5'-hydrogen atom abstraction (87-91%) at the T of ACT. Single-strand (SS) lesions were found to represent a variable mixture of C4' and C5' chemistry. The C4'-hydroxylated abasic site occurred in both SS and DS lesions at both sites and accounted for most of the DS damage at AGT (60-83%); the remaining damage consisted of 3'-phosphoglycolate- and 3'-phosphate-ended fragments. The nature of the thiol was found to affect the partitioning of the breakdown products arising from C4' and, to a lesser extent, C5' hydrogen atom abstraction. Production of 3'-phosphoglycolate residues, restricted mainly to the T of AGT in bistranded lesions, correlated with the incidence of direct DS breaks in the AGT.ACT model and in plasmid DNA and appeared to be influenced by the reducing power of the thiol activator. Furthermore, hydrazine and sodium borohydride both inhibited the formation of glycolate, an effect that was exploited to determine the rate constant for 3'-phosphoglycolate formation: 0.06 min-1 at 0 degree C, pH 7.4. Under anaerobic conditions, the nitroaromatic radiation sensitizer misonidazole caused a large increase in glycolate production in both SS and DS lesions formed by NCS, which suggests that the formation of 3'-phosphoglycolate, like 3'-formylphosphate generated by C5' chemistry, involves an oxyradical intermediate. The pathways for DNA damage involving C4' and C5' hydrogen atom abstraction thus share many common features, several of which are consistent with a mechanism for the production of NCS-mediated bistranded lesions at AGT.ACT that involves a tetraoxide bridge joining the lesions on opposite strands of DNA.

Influence of thiol structure on neocarzinostatin activation and expression of DNA damage

Neocarzinostatin (NCS) is an enediyne antitumor antibiotic that cleaves DNA following a thiol-induced electronic rearrangement to a diradical form. Structure-function studies with 11 thiol-containing compounds were undertaken to clarify the role of the thiol in NCS-mediated DNA damage. The rates of activation of NCS in the presence of DNA with the various thiols approximated a Brønsted relation (beta = 0.43, r2 = 0.86), which suggests that the basicity/nucleophilicity of the thiol is important to NCS activation. However, an additional contribution to NCS activation may arise from the affinity of the thiol for DNA, since there is a correlation between the concentration of thiol producing maximal DNA damage, assessed by quantitating the topologic forms of plasmid pBR322 following treatment with NCS, and the apparent ability of the thiol to bind to DNA by hydrophobic or electrostatic interactions. The overall second-order rate constants for the activation of NCS were found to be inversely correlated with the thiol optima; a plot of the former versus the reciprocal of the optimal thiol concentration revealed a first-order rate constant of activation of 0.013 s-1 in the presence of DNA. This indicates that maximal DNA damage occurs when NCS is activated with a half-life of 52 s, a relatively slow rate of activation that suggests that NCS binds to DNA before undergoing activation by thiol. Finally, an analysis of strand breaks in pBR322 shows that thiols possessing a carboxylate moiety produce larger quantities of bistranded DNA lesions than their esterified or non-carboxylate-containing counterparts.

Antitumor effects of SMANCS on rat mammary tumor induced by 7,12-dimethylbenz[a]anthracene

We previously found that a high-molecular-weight anticancer agent, polystyrene-co-maleic acid conjugated neocarzinostatin (SMANCS), in which two chains of styrene/maleic acid copolymer are conjugated to the anticancer protein neocarzinostatin (NCS), accumulated more selectively in tumor tissue than in normal tissue and was more stable than NCS in blood. These results indicate that SMANCS should have less systemic toxicity and a better therapeutic effect than NCS. In this study, the antitumor activity and adverse effects of SMANCS were compared with those of NCS by using rat mammary tumor induced by 7,12-dimethylbenz[a]anthracene. When tumors of rats, that had received 7,12-dimethylbenz[a]anthracene (20 mg/kg, one dose, p.o. in oily formulation), became palpable usually after 4-20 weeks, SMANCS treatment was initiated. Thirty days after i.v. administration of SMANCS (0.1 mg/kg 3 times and 0.3 mg/kg 3 times), tumors had shrunk in 35 of 37 rats (a mean weight was about 10% of control value; or decreased to about 30% of the value of before treatment in tumor weight); tumor size had not changed in 1 rat, and in the remaining 1 rat the tumor had enlarged. Thirty days after i.v. administration of NCS, tumors had shrunk in 8 of 14 rats, but the tumor size was unchanged in 1 rat and was enlarged in 5. In the control group, all tumors had enlarged. Development of new tumors was completely prevented by the administration of SMANCS. Histological examination of sequential slices of tumor revealed clear finding of degeneration and tumor encapsulation at 30 days after initial administration of SMANCS, with an accompanying fatty degeneration, but these effects were not observed for tumors treated with NCS. Although red blood cell counts and hemoglobin amounts decreased significantly in rats receiving NCS, no such effects were apparent in the SMANCS group.

Combined effect of radiation and YM-881 (SMANCS) on murine tumors and bone marrow

The combined effect of radiation and YM-881 (SMANCS) was studied in vitro and in vivo. When 0.25 microgram/ml of YM-881 was simultaneously combined with radiation, during and after irradiation for 30 min in total, Dq decreased from 3.3 Gy to 1.4 Gy without changing D0 in the dose-survival curve of exponentially growing SCC VII tumor cells. Five or ten times administrations of 0.1 mg/kg YM-881 at an interval of 24 h did not inhibit tumor growth. However, administration of 0.1 mg/kg YM-881 just before every irradiation which was repeated five times at an interval of 24 h yielded dose modifying factors (DMFs) of 1.8-1.2 when the tumor response to treatment was evaluated by the time for the tumors to regrow to three times the original volume. Administration of YM-881 ten times just before every irradiation yielded DMFs of 1.3-1.2. Adverse effects of the combination on bone marrow were examined by spleen colony assay. After five injections of 0.1 mg/kg YM-881, the mean number of CFU-S per femur decreased to 77% of the pretreatment level, but this was not significant statistically (0.1 greater than p greater than 0.05). The slope of radiation response curve for CFU-S per femur was not affected by the combination.

Differential neutralizing effect of tiopronin on the toxicity of neocarzinostatin and SMANCS: a new rescue cancer chemotherapy

The toxic effect and antitumor activity of neocarzinostatin (NCS) and SMANCS [copoly(styrenemaleic acid)-conjugated NCS] were greatly affected by N-(2-mercaptopropionyl)-glycine [tiopronin] both in vitro and in vivo, in cultured HeLa cells and RL male 1 tumor-bearing mice. The cytotoxicity of NCS and SMANCS against HeLa cells was remarkably reduced by the addition of tiopronin during drug treatment. Interestingly, the neutralizing effect of tiopronin on the toxicity of SMANCS was greater than that in the case of NCS. In the continuous presence of 10 mM tiopronin during a 1 h drug treatment, the 50% cell-killing doses of NCS and SMANCS were increased 72 and 208 times as compared to those without tiopronin, respectively, whereas tiopronin itself has no cytotoxicity to HeLa cells up to 100 mM. Furthermore, more effective reduction of the lethal toxicity of SMANCS was observed by the intraperitoneal (ip) administration of tiopronin after ip injection of a lethal dose of SMANCS as compared to the same protocol in the case of NCS in mice. Therapeutic studies on RL male 1 tumor-bearing mice revealed that delayed (time lag) ip administration of tiopronin after high-dose SMANCS administration ip was much superior to the combination of NCS with tiopronin, or SMANCS alone. In this time-lag combination chemotherapy of SMANCS with tiopronin, 60% of treated mice survived more than 60 days after tumor inoculation, while all the untreated control mice died within 20 days.

Efficacy of two-route chemotherapy using intraperitoneal neocarzinostatin and its antidote, intravenous tiopronin, for peritoneally disseminated tumors in mice

We assessed the efficacy of "two-route chemotherapy (TRC)" using neocarzinostatin (NCS) given ip and its antidote, N-(2-mercaptopropionyl)-glycine (tiopronin), given iv for peritoneally disseminated tumors in mice. Whether or not the single iv administration of tiopronin (800 mg/kg) at various times after NCS ip would decrease the lethal toxicity induced by NCS ip was given attention. When compared with the LD50 (4.4 mg/kg) of NCS ip alone, simultaneous or postadministration of tiopronin together with NCS ip increased the LD50 of NCS ip by 2.8 to 7.6 fold in a time-dependent manner. Chemotherapy experiments on ip disseminated tumors in mice were done to compare the antitumor effects of the following treatments, at two dose levels (75 and 100% of LD10) of NCS, with or without tiopronin: treatment with NCS ip alone and combined chemotherapy using NCS ip plus tiopronin iv, simultaneously or postadministered. Based on the survival time of the treated mice, the groups given NCS plus tiopronin (postadministration, 15 or 25 min later) showed a significantly superior survival time to that of the group given NCS ip alone. The side effects, evaluated in terms of the changes in body weight and number of WBC of the mice, were not significantly different among the groups treated with 100% of LD10 of NCS.

Cytotoxicity of smancs in comparison with other anticancer agents against various cells in culture

The cytoxicity of neocarzinostatin (NCS) and smancs [copoly(styrene maleic acid)-conjugated NCS] to various cultured cells was compared with that of several other antitumor agens in clinical use on various malignant and non-malignant cells as regards to their effect on colony formation of cells. Both NCS and smancs showed the most potent cytotoxicity against all tumor cell lines tested; the IC50s (colony inhibitory concentration 50%) of these drugs were 3.2-20 nM, 10-1000 times lower than those of other drugs. In contrast, NCS and smancs exhibited relatively lower toxicity to normal cells such as human skin fibroblasts and chick embryonic fibroblasts (IC50, about 50 and 100 nM, respectively). Normal rat hepatocytes were found to be very resistant to NCS and smancs (both IC50s were about 500 nM). Moreover, the minimum exposure time of smancs to cultured tumor cells required to achieve effective cytotoxic activity was much shorter than that of NCS and other drugs. Namely, at 30 nM more than 80% cells were killed by exposure to smancs for only a few minutes, whereas with NCS more than 80 min of exposure time was required. It was also found that smancs inhibited the uptake of 3H-thymidine into DNA as expected. These results clearly indicate that smancs is an unique antitumor agent with a broad antitumor spectrum which exhibits some characteristics similar to, but also some very different from NCS.

Defective repair of DNA single- and double-strand breaks in the bleomycin- and X-ray-sensitive Chinese hamster ovary cell mutant, BLM-2

Using filter elution techniques, we have measured the level of induced single- and double-strand DNA breaks and the rate of strand break rejoining following exposure of two Chinese hamster ovary (CHO) cell mutants to bleomycin or neocarzinostatin. These mutants, designated BLM-1 and BLM-2, were isolated on the basis of hypersensitivity to bleomycin and are cross-sensitive to a range of other free radical-generating agents, but exhibit enhanced resistance to neocarzinostatin. A 1-h exposure to equimolar doses of bleomycin induces a similar level of DNA strand breaks in parental CHO-K1 and mutant BLM-1 cells, but a consistently higher level is accumulated by BLM-2 cells. The rate of rejoining of bleomycin-induced single- and double-strand DNA breaks is slower in BLM-2 cells than in CHO-K1 cells. BLM-1 cells show normal strand break repair kinetics. The level of single- and double-strand breaks induced by neocarzinostatin is lower in both BLM-1 and BLM-2 cells than in CHO-K1 cells. The rate of repair of neocarzinostatin-induced strand breaks is normal in BLM-1 cells but retarded somewhat in BLM-2 cells. Thus, there is a correlation between the level of drug-induced DNA damage in BLM-2 cells and the bleomycin-sensitive, neocarzinostatin resistant phenotype of this mutant. Strand breaks induced by both of these agents are also repaired with reduced efficiency by BLM-2 cells. The neocarzinostatin resistance of BLM-1 cells appears to be a consequence of a reduced accumulation of DNA damage. However, the bleomycin-sensitive phenotype of BLM-1 cells does not apparently correlate with any alteration in DNA strand break induction or repair, as analysed by filter elution techniques, suggesting an alternative mechanism of cell killing.

Facilitated internalization of neocarzinostatin and its lipophilic polymer conjugate, SMANCS, into cytosol in acidic pH

The effects of environmental pH on the binding and cytotoxicity of the antitumor proteins neocarzinostatin (NCS) and SMANCS [copoly(styrene-maleic acid)-conjugated NCS] to cultured cells were studied by using their fluorescent-labeled derivatives (F-drugs). At 37 degrees C the binding of these drugs to HeLa cells was pH dependent: The amount of cell-bound drugs increased with an increase in the acidity of the medium. The pH-dependent change in the binding of the drugs was not as evident at 0 degree C. The cytotoxic action of these drugs was much more rapid at acidic pH compared with that at neutral or slightly alkaline pH. Furthermore, F-drugs could be utilized to probe the microenvironmental pH in Meth-A cells, in which the drug was located by the ratio of fluorescent intensities at 450 and 490 nm. The environment of the cell-bound F-drugs became acidic with incubation time at 37 degrees C but not at 0 degree C. Inasmuch as these drugs directly attack DNA, these results suggest that NCS and SMANCS are translocated across the membrane of acidic vesicles into the cytosol after endocytotic uptake. This hypothesis is also supported by the finding that NH4Cl and chloroquine protected HeLa cells against the cytotoxicity of the drugs. Data also showed that the hydrophobic polyanion conjugate SMANCS had a much greater cell binding (10 times) and more rapid internalization compared with NCS. Taken together, our results show that acidic pH of tumor tissue is preferable for effective binding and internalization into cytosol for NCS and SMANCS.

A role of oxidative DNA sugar damage in mutagenesis by neocarzinostatin and bleomycin

The anti-tumor antibiotics neocarzinostatin and bleomycin specifically oxidize deoxyribose in DNA at the C-5' and C-4' positions, respectively. The resulting DNA lesions include strand breaks and apyrimidinic sites. Both agents are broad specificity mutagens, inducing, in various systems, base substitutions, frameshifts and deletions. Sequencing studies in bacterial systems have suggested that the base substitutions may result primarily from replicative bypass of the oxidized apyrimidinic sites.

"Two-route chemotherapy" using high-dose intra-arterial neocarzinostatin and systemic tiopronin, its antidote, for rat limb tumor

We studied the effect of "two-route chemotherapy" (TRC) with intra-arterial (IA) neocarzinostatin (NCS) and IV N-(2-mercaptopropionyl)-glycine (tiopronin), its antidote, on rat limb tumors. Chemotherapy experiments were carried out on day 9 after the inoculation of 10(6) syngeneic transitional carcinoma cells into the hind limb in female Wistar King A rats. In the group given TRC, 3500 units/kg NCS and 800 mg/kg tiopronin were given via the femoral artery and the femoral vein, respectively. The antitumor effect was evaluated by the tumor weight on day 12 after the treatment. Compared with the weight of tumors in untreated controls, TRC reduced tumor weight to one-tenth, while 700 units/kg IA NCS alone reduced tumor weight to one-third and 700 units/kg systemic NCS alone reduced tumor weight to three-fourths of the control weight. In the group given TRC, WBC and nucleated bone marrow cells were completely protected and loss of body weight was slight.

Auromomycin-induced DNA damage and repair in human leukemic lymphoblasts (CCRF-CEM cells)

An alkaline elution procedure was used to study the nature of DNA damage induced by auromomycin, an antitumor protein, in human leukemic lymphoblasts (CCRF-CEM cells). The filter elution of drug-treated cells at pH 12.2 and 9.6 showed induction of both single and double strand DNA breaks. The DNA strand scission activities were linear in relation to drug concentration. The frequency of single strand breaks was higher than that of the double strand breaks. Protein-associated DNA single strand breaks were also detected in alkaline elution of drug-treated cells when a proteinase K digestion step was included in the assay protocol. The auromomycin-induced single strand breaks were repaired to almost completion within 8 h of postincubation of DNA-damaged cells whereas the repair of double strand breaks was not detected.

Glutathione dependence of neocarzinostatin cytotoxicity and mutagenicity in Chinese hamster V-79 cells

Neocarzinostatin (NCS) is mutagenic in bacteria, yeast, fungi, and mammalian cells. In cell-free systems, DNA strand breakage induced by NCS requires a reducing agent like 2-mercaptoethanol, unless very high (greater than 100 micrograms/ml) concentrations of NCS are used. In this study, we have investigated the role of the sulfhydryl compound glutathione (GSH), which is usually the most common intracellular thiol, in the bioactivation of NCS to a toxic and mutagenic species. Chinese hamster V79 cells were pretreated with one of two GSH depleting agents, buthionine sulfoximine or diethyl maleate. These agents deplete GSH via different mechanisms, but both will lower GSH levels within the cell to less than 5% of control (untreated) values. GSH-depleted cells and control cells were then exposed to NCS concentrations of 0.5-2.5 micrograms/ml for 1 h, assayed for survival, and plated for expression of hypoxanthine-guanine phosphoribosyltransferase-negative (HGPRT-) mutants. After an expression period of 7 days, during which the cultures were subcultured twice, HGPRT- mutants were selected by plating in hypoxanthine-free medium containing 5 micrograms of 6-thioguanine per ml, at a density of 2 X 10(5) cells per 100 mm dish. NCS alone decreased the surviving fraction to about 1% at 2.5 micrograms/ml and produced dose-related increases in HGPRT-mutants that reached greater than 10 times the spontaneous mutation frequency at 2.5 micrograms NCS per ml. In GSH-depleted cells, however, NCS was only mildly cytotoxic (60-80% surviving fraction) and did not produce dose-related increases in HGPRT- mutants over cells treated only with diethyl maleate or buthionine sulfoximine. Thus, GSH appears to be the main reducing agent for the bioactivation of NCS to a toxic and mutagenic species in Chinese hamster V79 cells.

The response of normal and ataxia-telangiectasia cells to bleomycin: relationships between chromosome damage, cell cycle delay and cell killing

In agreement with our earlier observation (Scott and Zampetti-Bosseler, 1982) on X-irradiated normal and ataxia-telangiectasia (A-T) fibroblasts, we now report that after bleomycin or neocarzinostatin treatment also, A-T cells exhibit less G2 delay than normal cells. We confirm that A-T cells sustain more chromosome damage and lethality than normal cells after bleomycin. These observations support the hypothesis (Painter and Young, 1980) that A-T cells are defective in the recognition of certain lesions which normally lead to delays in progression through the cell cycle, during which they are repaired, and which, if unrepaired, lead to cell-lethal chromosome damage. However, we find that after bleomycin, as opposed to X-rays, the contribution of this type of lesion to cell death is minimal. The predominant lesions leading to cell death after bleomycin are not manifested at chromosome aberrations and do not lead to G2 delay or DNA-synthesis inhibition. A-T cells are defective in the recognition and/or repair of both types of lesion.

Glutathione depletion greatly reduces neocarzinostatin cytotoxicity in Chinese hamster V79 cells

The role of the intracellular thiol glutathione in the reductive activation of neocarzinostatin was investigated in Chinese hamster V79 cells. The cells were pretreated with agents that either lower (buthionine sulfoximine or diethyl maleate) or elevate (oxothiazolidine carboxylate) intracellular glutathione levels. These cells were then exposed to 1-5 micrograms/ml neocarzinostatin for 1 h and assayed for survival. Depletion of glutathione to levels at or below the limit of detection resulted in a marked reduction in neocarzinostatin cytotoxicity, while increasing glutathione levels to 250% of control values had little or no effect on neocarzinostatin toxicity. High performance liquid chromatography analysis of cysteine in untreated and glutathione-depleted cells showed cysteine levels lower than 0.2 microM, indicating that cysteine does not play a major role in the reductive activation of neocarzinostatin in untreated or glutathione-depleted cells. When intracellular cysteine levels were artificially elevated by oxothiazolidine carboxylate treatment of glutathione-depleted cells, neocarzinostatin toxicity was about two-thirds that seen in cells with normal glutathione levels. In cell-free systems, others have shown that reducing agents such as 2-mercaptoethanol are necessary for the activation of neocarzinostatin to a species that will cleave DNA. In this study, we have identified glutathione as the major cellular reducing agent for the activation of neocarzinostatin in a mammalian cell line.

Endonuclease-resistant apyrimidinic sites formed by neocarzinostatin at cytosine residues in DNA: evidence for a possible role in mutagenesis

When defined-sequence DNA from the lacl region of plasmid pMC1 was treated with the nonprotein chromophore of neocarzinostatin in the presence of various thiols, the predominant lesions were direct strand breaks, occurring primarily at thymine and adenine residues. In the presence of glutathione, however, alkali-dependent strand breaks, occurring at certain cytosine residues, were also detected but were virtually absent when other thiols were used. Chromophore-induced release of free cytosine base from [3H]cytosine-labeled DNA was 2- to 3-fold greater with glutathione than with the other thiols. These results suggest that the alkali-dependent strand break is some form of apyrimidinic site. These sites were substrates for endonuclease IV of Escherichia coli, although a 5-fold greater concentration of enzyme was required for their cleavage than was required for cleavage of apurinic sites in depurinated DNA. These sites were also less sensitive to E. coli endonuclease VI (exonuclease III) by a factor of at least 5 and less sensitive to E. coli endonuclease III by a factor of at least 10. These and other results suggest that these sites are chemically different from normal apurinic/apyrimidine sites. When chromophore-induced apyrimidinic sites were quantitated as alkali-dependent breaks at 11 specific sites in the lacl gene, a correlation was found between occurrences of these lesions and the reported frequencies of G-C to A X T transitions at the same sites. All occurrences of the trinucleotide sequence A-G-C, including the ochre 21 mutational hot spot, were particularly prominent sites. The selective formation of endonuclease-resistant apyrimidinic sites at specific cytosine residues may explain the high frequency of G X C to A X T transitions in the mutational spectrum of neocarzinostatin.

[Screening for the antagonizing agents against lethal toxicity of neocarzinostatin. I. Inhibitory effects of various drugs on the toxicity of neocarzinostatin in vitro and in vivo]

Neocarzinostatin (NCS) used for the chemotherapy of leukemia and cancers such as stomach, pancreas and bladder, has been pointed out to have the side effects mainly causing leukopenia. In order to prevent these side effects of NCS by systemic administration, we have attempted to inject NCS directly into the tumor tissues and to inactivate NCS leaked from the tissues by the treatment of antidotes for NCS. The present report deals with the influence of some antidotes on the toxicity of NCS in vitro and in vivo. The results demonstrated that; Four SH-compounds, such as thiopronin, glutathione (reduced form), sodium thioglycolate and L-cysteine monohydrochloride monohydrate were effective to inactivate antibacterial activity of NCS against M. luteus ATCC 9341 in vitro. It was recognized that acute toxicity of NCS was reduced by pretreatment of these SH-compounds and its action was dose related. The LD50 values of NCS intravenous administration in mice increased 5.8- to 24-fold when 150, 300, 500 and 1,000 mg/kg of thiopronin were administered intravenously 2 minutes prior to NCS. And 2.3- to 4.2-fold by 500 and 1,000 mg/kg of glutathione (reduced form), 1.6- to 4.2-fold by 50, 100 and 200 mg/kg of sodium thioglycolate, 1.9- to 4.2-fold by 100, 200 and 400 mg/kg of L-cysteine monohydrochloride monohydrate respectively. On the other hand, pretreatment of NCS didn't affect the acute toxicity of thiopronin.

Mutagenicity of neocarzinostatin in Neurospora crassa

Neocarzinostatin (NCS) is an acidic, single-chain polypeptide of 109 amino acids that has shown some antitumor activity in clinical trials. NCS is mutagenic in recA+ strains of Escherichia coli, but not in recA strains; on the other hand, a defect in the nucleotide-excision-repair pathway has no effect on the mutagenicity of NCS in E. coli. Similar results are seen in mammalian cells. Excision-repair-deficient xeroderma pigmentosum (XP) cells repair NCS-induced DNA damage at the same rate as repair-proficient XP heterozygotes, and X-ray-sensitive ataxia telangiectasia fibroblasts are also sensitive to NCS. I have investigated the mutagenicity of NCS in the ad-3 forward-mutation test in nucleotide excision-repair-sufficient and -deficient heterokaryons of Neurospora crassa. Resting conidia from a repair-sufficient strain, H-12, and a nucleotide-excision-repair-deficient strain (uvs-2) H-59, were exposed to NCS. These conidia were assayed for survival and ad-3 forward mutation. The results show that H-59 is more sensitive to the killing and mutagenic activities of NCS than is H-12. These data indicate, in contrast to E. coli and mammalian cells, that the nucleotide-excision-repair pathway of N. crassa does repair NCS-induced lesions. In other experiments, ad-3 mutants induced by NCS in H-59 were characterized to determine the spectrum of NCS-induced mutation. The results show that NCS induces both intracistronic mutations and multilocus deletions in H-59.

Neocarzinostatin-mediated DNA damage and repair in wild-type and repair-deficient Chinese hamster ovary cells

The formation and repair of neocarzinostatin (NCS)-mediated DNA damage were examined in two strains of Chinese hamster ovary cells. The response in strain EM9, a mutant line selected for its sensitivity to ethyl methanesulfonate and shown to have a defect in the repair of X-ray-induced DNA breaks, was compared with that observed in the parental strain (AA8). The DNA strand breaks and their subsequent rejoining were measured using the method of elution of DNA from filters under either alkaline (for single-strand breaks), or nondenaturing conditions (for double-strand breaks). Colony survival assays showed that the mutant was more sensitive to the action of NCS than was the parental strain by a factor of approximately 1.5. Elution analyses showed that the DNA from both strains was damaged by NCS; the mutant displayed more damage than the parent under the same treatment conditions. Single-strand breaks were produced with a frequency of about 10 to 15 times the frequency of double-strand breaks. Both strains were able to rejoin both single-strand breaks and double-strand breaks induced by NCS treatment. The strand break data suggest that the difference in NCS-mediated cytotoxicity between EM9 and AA8 cells may be directly related to the enhanced production of DNA strand breaks in EM9. However, the fact that much higher doses of NCS were required in the DNA studies compared to the colony survival assays implies that either a small number of DNA breaks occur in a critical region of the genome, or that lesions other than DNA strand breaks are partly responsible for the observed cytotoxicity.

Induction of chromosome aberrations and specific locus mutation but not sister chromatid exchanges in Chinese hamster ovary cells by neocarzinostatin

The induction of chromosome aberrations, sister chromatid exchanges (SCE), cytotoxicity, and 6-thioguanine-resistant mutation by neocarzinostatin (NCS) in Chinese hamster ovary cells was analyzed. It was observed that within the same concentration range of 0.01-0.1 mu/ml NCS, the drug induced a significant increase in all analyzed end-points except in SCE frequencies. There was no increase in SCE frequencies even when the cells were treated at the G1/S border in the first cell cycle and when aberrations were observed in the same cell showing a second cycle differential staining pattern. Our study indicates that the cellular damage induced by NCS leads to expression in chromosome aberrations, cytotoxicity, and mutagenicity but not in sister chromatid exchanges.

Antitumor activity of trioxacarcin C

The novel antitumor antibiotic, trioxacarcin C, was studied for antitumor activities against murine tumor systems. When mice with i.p.-inoculated B16 melanoma were given intraperitoneal injections of trioxacarcin C, the maximal T/C% was 164 by successive administration of 0.125 mg/kg/day (day 1 approximately 10). It also gave the prolongation of life span of mice bearing i.p. P388 leukemia (T/C 141%) by i.p. injection for 10 days, and inhibited the growth of sarcoma 180 (T/C 42%) and Lewis lung carcinoma implanted s.c. (T/C 23%) by i.v. administration for 6 or 7 days. It inhibited the growth of P388 leukemia cells in vitro and showed significant inhibition on the colony formation of HeLa S3 cells. DNA and RNA synthesis were more strongly inhibited than protein synthesis by trioxacarcin C. Also, it induced strand scission of PM-2 DNA without reducing agents or metals. It did not effect the number of white blood cells and blood urea nitrogen value of the peripheral blood.

Repair of potentially lethal and sublethal damage induced by neocarzinostatin in normal and ataxia-telangiectasia skin fibroblasts

Neocarzinostatin is a radiomimetic antibiotic with a potent cytotoxic effect which elicits a hypersensitive response in human cells homozygous or heterozygous for the gene for ataxia-telangiectasia. The extent and the time course of potentially lethal damage repair and sublethal damage repair following neocarzinostatin treatment were investigated in human skin fibroblast strains and were found to be remarkably similar to those obtained following X-irradiation. Ataxia-telangiectasia homozygous cells essentially lacked potentially lethal damage repair, but were able to perform some degree of sublethal damage repair following neocarzinostatin treatment. Ataxia-telangiectasia heterozygous cells which show an intermediate degree of neocarzinostatin sensitivity could perform both processes but with somewhat reduced efficiency as compared to normal cells. These observations provide further evidence for a DNA repair defect in ataxia-telangiectasia cells.

Induction and repair of DNA damage in normal and ataxia-telangiectasia skin fibroblasts treated with neocarzinostatin

Cells from patients with the hereditary multisystem disorder ataxia-telangiectasia (A-T) are hypersensitive to the cytotoxic action of DNA-breaking agents, such as X-rays, bleomycin and neocarzinostatin (NCS). A defect in the repair of a certain DNA lesion induced by all three agents may underlie this hypersensitivity. This DNA lesion may be a certain type of DNA strand break. Most of the previous experiments done with X-rays and bleomycin failed to show any retardation in the rejoining of DNA strand breaks in A-T cells. However, since both A-T homozygous and heterozygous cells are particularly hypersensitive to NCS, we studied the time course of strand breakage induction and repair in A-T skin fibroblast strains treated with NCS, using the sensitive method of alkaline or neutral elution. A linear dose response was obtained for the induction by NCS of single-strand breaks and double-strand breaks. A-T cells did not respond with a higher initial extent of strand breakage compared with normal cells. NCS is an appropriate agent for studying the kinetics of rejoining strand breaks, due to its rapid action in the cells; this action, which is completed within 2--4 min, was studied by monitoring strand break induction, inhibition of DNA synthesis and decrease in cellular survival. The time course of strand break rejoining found after NCS treatment was very similar to that found following X-irradiation: with both single- and double-strand breaks, a rapid phase of rejoining was first noticed (t 1/2 approximately 5 min for single-strand breaks and 20--25 min for double-strand breaks). This was followed by a second, slow phase that continued for several hours. No difference could be detected between normal and A-T cells either with regard to the time course of rejoining or the fraction of non-rejoined breaks remaining several hours after treatment.

Phase II trial of neocarzinostatin in patients with bladder and prostatic cancer: toxicity of a five-day iv bolus schedule

Neocarzinostatin (NCZ), a new antitumor antibiotic, was administered to 19 patients with bladder cancer, 16 patients with prostatic cancer, and 3 patients with hepatoma. All patients had objectively measurable metastatic lesions including 21 with palpable nodes or subcutaneous nodules, 10 with pulmonary nodules as demonstrated by chest x-ray, 4 with malignant hepatomegaly, and 3 with bidimensional pelvic masses as demonstrated by CT scanning. Sixty-five courses of NCZ were administered via an intravenous bolus daily for five days with dosages ranging from 1500 to 3000 U/m2. Immediate toxicity was not dose-limiting except for 1 episode of anaphylaxis and 1 of acute renal failure. Myelotoxicity was delayed, dose-dependent, noncumulative, and dose-limiting. Thrombocytopenia was prolonged or irreversible in 5 cases. The maximally tolerated dose was 2750 U/m2. One patient with NCZ-associated pulmonary fibrosis and 1 with biopsy-proven hepatitis are discussed in detail. Neocarzinostatin demonstrated minimal therapeutic activity (1 partial remission) in patients with bladder cancer. There was no response in patients with prostatic cancer or hepatoma.

Phase I study of neocarzinostatin in children with cancer

Twenty-three children with advanced cancer refractory to conventional therapy received weekly iv doses of neocarzinostatin for 5 weeks. Doses were escalated from 500 to 6750 units/m2/week. Four types of toxic manifestations occurred: acute reactions consisting of shaking chills with or without fever and cyanosis (rigor), hypersensitivity, vomiting, and marrow depression. Evidence of oncolytic activity was limited to patients with acute leukemia in whom phase II trials at doses between 3000 and 4500 units/m2 appear warranted.

Phase I and preliminary phase II study of neocarzinostatin

Neocarzinostatin is a protein antitumor antibiotic isolated from cultures of Streptomyces carzinostaticus var.F41. The drug has undergone extensive clinical trial in Japan, and has been reported active against a variety of human tumors. A phase I and preliminary phase II evaluation of the drug has been performed, using an iv bolus daily x 5 schedule. Ninety-six patients have been treated at doses from 500 to 2250 units/m2/day. Courses were repeated at 4-week intervals if allowed by bone marrow recovery. Dose-limiting toxicity was myelosupppression, which occurred late (median nadir, Day 27). Myelosuppression was more pronounced in patients who had received previous chemotherapy. In nine patients (9%) thrombocytopenia was prolonged (greater than or equal to 45 days) or irreversible. Acute administration of the drug was associated with rigors in approximately half the patients. Gastrointestinal side effects were mild. Three patients had a severe acute reaction resembling anaphylaxis. The maximally tolerated dose for this dose schedule is approximately 2250 units/m2/day. Antitumor activity has been seen in hepatoma and hematologic malignancies. Activity in lung and colorectal carcinoma appears limited with this dose schedule.

Phase I study with neocarzinostatin: tolerance to two hour infusion and continuous infusion

Neocarzinostatin (NCZ), an acidic polypeptide antibiotic, was given to 47 patients with cancer and leukemia, and tolerance to two schedules, a single dose given as a 2 hour infusion and a continuous infusion over 5 days was investigated. Immediate reactions, including fever, chills, rigor, hypertension and mental confusion, were dose-limiting for the 2 hour infusion schedule, occurring at 3000 U/m2 and higher. Continuous administration for 5 days eliminated the immediate reactions and then hematological toxicity--often prolonged leukopenia and thrombocytopenia--became dose-limiting. Other toxicities of NCZ at both dose schedules included anemia, fever and chills, anorexia, nausea and vomiting, hepatic dysfunction, azotemia, hypophosphatemia, aminoaciduria, stomatitis, phlebitis and/or cellulitis at the venous infusion site and pruritus. Patients with solid tumors who had received little or no prior chemotherapy and had good bone marrow reserve tolerated up to 6000 U/m2/24 hours X 5 days. One patient with previously treated acute myelocytic leukemia was induced into a good partial remission lasting 10 weeks.

Evaluation of succinyl neocarzinostatin in vivo

The toxicity of the bis-succinyl derivative of the protein antibiotic, neocarzinostatin, was compared with the parent compound, neocarzinostatin (NCS), in rats. The derivative was found to be about two to five fold more active than NCS in vivo. The antitumor activity in rats bearing eleven distinct Yoshida hepatoma ascitic cell lines was tested under four possible combinations with regard to sites of drug and tumor cell administration. The results indicate that the antitumor spectrum of the derivative had changed slightly. Antitumor activity in mice was also tested with L1210 and P388 lymphatic leukemia, and with B16 melanocarcinoma. When the effect of the derivative was compared with parental NCS at the molecular level with respect to the inhibition of DNA synthesis in vitro, the specific activities of the two were found to be almost identical. These results were interpreted to indicate that the succinyl derivative of NCS was more stable to inactivation and proteolytic break-down in vivo than NCS as observed previously in in vitro studies.