Mode of action of neocarzinostatin: inhibition of DNA synthesis and degradation of DNA in Sarcina lutea

Changes in calpain-2 expression during glioblastoma progression predisposes tumor cells to temozolomide resistance by minimizing DNA damage and p53-dependent apoptosis

BACKGROUND

Glioblastoma multiforme (GBM) is characterized by an unfavorable prognosis for patients affected. During standard-of-care chemotherapy using temozolomide (TMZ), tumors acquire resistance thereby causing tumor recurrence. Thus, deciphering essential molecular pathways causing TMZ resistance are of high therapeutic relevance.

METHODS

Mass spectrometry based proteomics were used to study the GBM proteome. Immunohistochemistry staining of human GBM tissue for either calpain-1 or -2 was performed to locate expression of proteases. In vitro cell based assays were used to measure cell viability and survival of primary patient-derived GBM cells and established GBM cell lines after TMZ ± calpain inhibitor administration. shRNA expression knockdowns of either calpain-1 or calpain-2 were generated to study TMZ sensitivity of the specific subunits. The Comet assay and ɣH2AX signal measurements were performed in order to assess the DNA damage amount and recognition. Finally, quantitative real-time PCR of target proteins was applied to differentiate between transcriptional and post-translational regulation.

RESULTS

Calcium-dependent calpain proteases, in particular calpain-2, are more abundant in glioblastoma compared to normal brain and increased in patient-matched initial and recurrent glioblastomas. On the cellular level, pharmacological calpain inhibition increased the sensitivities of primary glioblastoma cells towards TMZ. A genetic knockdown of calpain-2 in U251 cells led to increased caspase-3 cleavage and sensitivity to neocarzinostatin, which rapidly induces DNA strand breakage. We hypothesize that calpain-2 causes desensitization of tumor cells against TMZ by preventing strong DNA damage and subsequent apoptosis via post-translational TP53 inhibition. Indeed, proteomic comparison of U251 control vs. U251 calpain-2 knockdown cells highlights perturbed levels of numerous proteins involved in DNA damage response and downstream pathways affecting TP53 and NF-κB signaling. TP53 showed increased protein abundance, but no transcriptional regulation.

CONCLUSION

TMZ-induced cell death in the presence of calpain-2 expression appears to favor DNA repair and promote cell survival. We conclude from our experiments that calpain-2 expression represents a proteomic mode that is associated with higher resistance via "priming" GBM cells to TMZ chemotherapy. Thus, calpain-2 could serve as a prognostic factor for GBM outcome.

Changes in cellular composition induced by neocarzinostatin pretreatment in Meth A-bearing mice and the responsible antitumor effector cells

We previously reported that tumor eradication was induced by a single injection of neocarzinostatin (NCS) between 1 day and 4 weeks before Meth A transplantation in Balb/c mice via augmenting host-mediated antitumor activity. In order to elucidate the mechanism of this tumor eradication, the cellular components of spleen and regional lymph nodes, tumor infiltrating cells and antitumor effector cells were investigated. Pretreatment with NCS on day -3 caused an increase in the percentage of T-cell subsets, a decrease in the percentage of B-cells, Mac-1+ cells and asialo GM1+ cells and a decrease of the total cell number in the spleen. These changes were observed before but not during the period of tumor regression and were also observed in non-transplanted mice with NCS treatment. In the lymph nodes, while B-cells increased on Meth A transplantation, this was suppressed by NCS pretreatment. Although histological examination of tumor nodules showed the presence of only a few host immune cells in the tumor tissue, the area of necrosis was already extensive on day 7 and expanded thereafter. In vivo depletion of whole T-cells, T-cell subsets or asialo GM1+ cells by antibody treatment suggests that the antitumor effector cells in tumor eradication were Thy1,2+/Lyt2+, and at least some of which also express asialo GM1 antigen and that L3T4+ T-cells were also involved in tumor eradication.

Crystal structure of apo-neocarzinostatin at 0.15-nm resolution

The three-dimensional structure of apo-neocarzinostatin, an antitumour antibiotic protein isolated from Streptomyces carzinostaticus, has been determined by X-ray diffraction at 0.15-nm resolution and refined to R = 17.2%. The crystal structure of neocarzinostatin is similar to that of the related proteins actinoxanthin and macromomycin. It is also in good agreement with the solution structure determined by NMR spectroscopy. The protein molecule consists of a seven-stranded antiparallel beta-sandwich and a smaller lobe formed by two beta-ribbons. A deep cleft between the two lobes is a putative chromophore binding site. Side chains of Trp39, Leu45, Phe52, Phe78 and the disulphide Cys37-Cys47 aligning the binding cleft in neocarzinostatin suggest the importance of hydrophobic interactions in stabilizing the chromophore molecule. Comparison of the atomic models of neocarzinostatin, actinoxanthin and macromomycin reveals functional residues which might determine specificity towards different chromophores.

Location of the disulfide bonds in the antitumor protein neocarzinostatin

Two disulfide bonds in the antitumor antibiotic neocarzinostatin were determined chemically. The peptic and peptic/thermolytic peptides from the native protein were isolated by gel filtration and ion-exchange chromatography followed by reverse-phase HPLC. The cystine peptides obtained were oxidized separately by performic acid treatment and further separated by HPLC into cysteic acid peptides. Sequence analyses of the isolated peptides revealed the location of the disulfide bonds at Cys37-Cys47 and Cys88-Cys93.

Characterization of intracellular DNA strand breaks induced by neocarzinostatin in Escherichia coli cells

DNA strand breaks induced by Neocarzinostatin in Escherichia coli cells have been characterized. Radioactively labeled phage lambda DNA was introduced into lysogenic host bacteria allowing the phage DNA to circularize into superhelical molecules. After drug treatment DNA single- and double-strand breaks were measured independently after neutral sucrose gradient sedimentation. The presence of alkali-labile lesions was measured in parallel in alkaline sucrose gradients. The cell envelope provided an efficient protection towards the drug, since no strand breaks were detected unless the cells were made permeable with toluene or with hypotonic Tris buffer. In permeable cells, no double strand breaks could be detected, even at high NCS concentration (100 micrograms/ml). Induction of single-strand breaks leveled off after 15 min at 20 degrees C in the presence of 2 mM mercaptoethanol. Exposure to 0.3N NaOH doubled the number of strand breaks. No enzymatic repair of the breaks could be observed.

Gamma-radiolysis study of the reductive activation of neocarzinostatin by the carboxyl radical

The activation of the antitumor protein antibiotic neocarzinostatin (NCS) by the carboxyl radical CO-2, a one-electron donor obtained selectively from gamma-ray irradiation of nitrous oxide-saturated formate buffer, has been investigated in the presence and in the absence of DNA at pH 4.7 and pH 7.0. The reaction of NCS with CO-2 in the absence of DNA is followed by a marked red shift (420----441 nm) and a pronounced increase (X 8.8) of the fluorescence emission corresponding to the naphthalene moiety of the NCS chromophore. The light absorption spectrum shows in parallel a hypochromic change with considerable fine structure throughout the 250-400 nm wavelength range. When DNA is present, the fluorescence intensity at completion of the reaction is slightly reduced (by 5 to 15 per cent) and the maximum emission wavelength shifted to 436-438 nm. However, the bulk rate of reaction is not altered by DNA and is independent of the pH, of the temperature and of the concentration of NCS. The NCS concentration-independence of the reaction rate is consistent with a high intrinsic rate (k greater than 10(8)M-1 . s-1) for the reaction of CO-2 with the NCS chromophore. Complete reduction of the NCS chromophore involves a total of three electron-equivalents. The final product does not react with oxygen, shows no odd electron spin, and is unable to induce DNA strand scission. Its molecular state, however, is fundamentally different when gamma-ray irradiations are performed with DNA. This bears evidence of short-lived one electron or two-electrons reduced intermediates decaying via non-identical routes depending on the presence of the acceptor DNA. Actually, dose-related strand breaks appear in DNA exposed to the action of NCS and CO-2. Some NCS chromophore-DNA covalent adducts are also found. DNA strand breakage by CO-2-activated NCS is correlated with thymine release and is inhibited by a redox-stable intercalating agent. The DNA-nicking process thus bears resemblance to that reported by other authors using mercaptans to initiate reductive activation of the NCS chromophore. However, some spectral differences are observed between the CO-2-reacted and the thiol-treated chromophores. Moreover, thymine release and strand scission in DNA incubated with CO-2 and NCS proceed under anaerobic conditions. It is proposed that the strict oxygen requirement for DNA damage by NCS in the presence of mercaptans is due, at least partly, to competition between oxygen and thiols for reaction with the same primary deoxyribose radical resulting from DNA attack by the reductively activated NCS chromophore.

Degradation of HeLa cell chromatin by neocarzinostatin and its chromophore

Chromatin is the in vivo target site for neocarzinostatin, a DNA strand scission antitumor drug. The effect of neocarzinostatin and its active chromophore component on HeLa cell chromatin is described here. Chromatin consisting of a mixture of mono-, di-, tri- and larger nucleosome fragments is prepared by micrococcal nuclease digestion of HeLa cell nuclei. Drug-induced conversion of chromatin to smaller sized fragments is measured by electrophoresis of the DNA on non-denaturing 4% polyacrylamide gels. Chromatin breakdown measured under these conditions is double-stranded in nature. In the presence of 2 mM dithiothreitol, neocarzinostatin causes degradation of large chromatin fragments and a loss of distinct nucleosome peaks. Detection of chromatin breakdown by neocarzinostatin is dependent upon the concentration of chromatin in the assay. When chromatin is increased from 14 to 70 micrograms/ml, changes in the larger fragments caused by 100 micrograms/ml neocarzinostatin become less obvious are are almost undetectable at 140 micrograms/ml chromatin. No change is observed when chromatin is treated with either neocarzinostatin or its chromophore in the absence of dithiothreitol. For detectable levels of chromatin degradation, 10 micrograms/ml neocarzinostatin is required compared to only 2.5 microgram/ml chromosome (expressed in microgram equivalent neocarzinostatin). Such degradation also occurs more rapidly with chromophore than with neocarzinostatin. Digestion of chromatin with neocarzinostatin continues for at least 30 min at 37 degrees C, while similar degradation caused by chromophore is complete in 1 min. Neocarzinostatin levels which actively degrade isolated chromatin can also effect release of soluble chromatin from intact nuclei. The released chromatin can serve as a substrate for micrococcal nuclease digestion. Such chromatin studies should prove useful in characterizing the mechanism of action of DNA reactive drugs such as neocarzinostatin.

A pharmacokinetic simulation model for chemotherapy of brain tumor with an antitumor protein antibiotic, neocarzinostatin. Theoretical considerations behind a two-compartment model for continuous infusion via an internal carotid artery

A pharmacokinetic two-compartment model for the treatment of brain tumors in man was simulated with the aid of a computer. The parameters necessary for the simulations such as inactivation rate constant, elimination rate constant, distribution volume, blood volume, cerebral blood flow, and cytotoxic drug concentration were either determined in this study or obtained from the literature. A proteinaceous antitumor antibiotic, neocarzinostatin (NCS), was utilized as a prototype drug because it has features making it advantageous in the treatment of brain tumor. In particular, NCS has an extremely short half-life in serum (t 1/2 less than or equal to 3 s), while it is relatively stable in the cerebrospinal fluid (CSF) (t 1/2 approximately 50 s). Therefore, the drug level in the cerebral compartment can be made adequately high with an appropriate infusion velocity into the cerebral compartment; however, it was possible to keep the plasma level of the drug much lower than the toxic level. Thus, few side-effects should result. In an in vitro study, NCS was found to exhibit its cytotoxicity to glioblastoma cells at a concentration as low as 0.005 microgram/ml. In contrast, the cytotoxicity was not apparent for the normal glia cells at 0.1 microgram/ml. The model being considered in this investigation is a two-compartment model, which consists of the cerebral compartment and the rest of the circulatory system of the body. In this case the drug is infused via an internal carotid artery. The results of pharmacokinetic simulation and dose regimens for NCs are presented, based on the effective concentration of the drug to glioblastoma cells in culture and the available pharmacological parameters.

Contrasts in the actions of protein antibiotics on deoxyribonucleic acid structure and function

The protein antibiotics neocarzinostain (NCS), macromomycin (MCR), and auromomycin (AUR), which is closely related to MCR, have been compared for their in vitro and in vivo actions on deoxyribonucleic acid (DNA). NCS, markedly stimulated by 2-mercaptoethanol, is much more active in inducing strand scissions in superhelical pMB9 and linear duplex lambda DNA than AUR, which is slightly inhibited by 2-mercaptoethanol. Purified MCR, even at very high levels, does not give any significant amount of cutting with either DNA substrate. 2-Propanol stimulates the activity of NCS but inhibits that of AUR. On the other hand, the antioxidant alpha-tocopherol strongly inhibits DNA breakage by both drugs. The intercalating drugs ethidium bromide, daunorubicin, proflavin, and actinomycin D at low concentrations inhibit DNA scission by AUR. The levels of intercalators required to inhibit NCS activity to comparable levels are about 10 times higher than those for AUR. Although MCR has virtually no in vitro DNA cutting activity, it is, like AUR and NCS, cytotoxic, as measured by the inhibition of DNA synthesis and induction of DNA strand breakage in HeLa cells.

Neocarzinostatin: a phase I clinical trial with five-day intermittent and continuous infusions

Neocarzinostatin, a polypeptide antibiotic, was administered by both continuous and intermittent intravenous infusion to 76 patients with a variety of malignant diseases. Doses ranged from 500 to 6500 units/m2 X 5 days. With levels greater than or equal to 1800 units/m2, bone marrow suppression (particularly thrombocytopenia) was the dose-limiting toxicity. Delayed bone marrow recovery was less dose-dependent and occurred in 58% of initial treatment courses in solid tumor patients. Allergic reactions were more frequent with intermittent than with continuous infusions (20% vs. 2% of courses). No complete or partial remissions were observed among solid tumor patients although clinical improvement was noted in one patient with mycosis fungoides and one patient with multiple myeloma. One complete and two partial remissions were noted among 21 patients with acute leukemia. There was one complete remission in a patient with chronic leukemia. Leukemic patients on intermittent therapy evidenced greater change in bone marrow cellularity than those treated by continuous infusion. Although neocarzinostatin has some activity in the treatment of acute leukemia, continuous infusion offers no advantage over intermittent therapy.

DNA damage and repair in relation to cell killing in neocarzinostatin-treated HeLa cells

To elucidate the mechanism of the cell killing activity of neocarzinostatin on mammalian cells, the drug-induced damage of DNA and its repair were examined. Very low doses of neocarzinostatin, at which high survival of cells was observed, clearly produced single-strand breaks of DNA and decomposition of the 'DNA complex', but these damages appeared to be repaired almost completely. At higher doses of neocarzinostatin, single-strand breaks were repaired to a considerable extent while double-strand breaks seemed not to be repaired. The number of non-repairable single-strand breaks was about twice that of double-strand breaks. This implies that single-strand breaks are repaired except for those constituting double-strand breaks. Although at low levels of neocarzinostatin repair of double-strand breaks may occur, the correlation existing between the colony-forming ability of cells treated with neocarzinostatin and non-repairable DNA breakage suggests that production of a small number of critical non-repairable double-strand breaks per cell may be responsible for the cell killing activity of the drug.

Suppression of graft-versus-host reaction by preincubation of the graft with an antitumor protein, neocarzinostatin

The immunosuppressive activity of neocarzinostatin, an antitumor antibiotic with a high molecular weight, was demonstrated, as measured by the local and systemic graft-versus-host reaction in rats. The preincubation of parental strain lymphocytes with doses more than 1 micrograms/ml of neocarzinostatin for at least 10 min at 37 degrees C resulted in the marked suppression of the popliteal lymph node enlargement, when injected subcutaneously into the hind footpads of F1 hybrid rats. The suppressive effect was temperature-dependent and irreversible, because the neocarzinostatin (1 microgram/ml) pretreatment of parental lymphocytes at 4 degrees C was not effective in the suppressive activity, and the reincubation of cells after the removal of the drug from the culture did not result in demonstrable changes in the degree of suppression. The neocarzinostatin pretreatment does not result in visible changes in the oxygen consumption rate and viability of cells in vitro or in the distribution pattern within a regional lymph node, indicating that treated cells may retain the same viability and migration capacity in vivo as do untreated cells. Furthermore, the drug pretreatment resulted in the complete prevention of runting syndrome, when treated parental lymphocytes were injected intravenously into F1 hybrid rats.

Neocarzinostatin induction of DNA repair synthesis in HeLa cells and isolated nuclei

The antitumor antibiotic neocarzinostatin that causes DNA strand breaks in vivo and in vitro is shown to induce DNA repair synthesis in HeLa S3 cells. In the repair assay, the parental DNA was prelabeled with 32P and a density label (bromodeoxyuridine) was introduced into the new synthesized DNA. Quantitation of the repair synthesis as measured by the incorporation of [3H]thymidine into the light parental DNA at varying doses of the drug indicate that there is a significant repair response at low levels of the drug (0.2--0.5 microgram/ml) which cause DNA strand breakage and inhibition of DNA synthesis. In isolated HeLa nuclei neocarzinostatin stimulates the incorporation of dTMP many-fold. This enhancement of dTMP incorporation, which requires the presence of a sulfhydryl agent, is a consequence of the drug-induced DNA strand breakage and is in the parental DNA. These results suggest that an intact cell membrane is not required for DNA strand breakage and its subsequent repair.

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.

Activation and inactivation of neocarzinostatin-induced cleavage of DNA

The possible role of free radicals in the mechanism of neocarzinostatin (NCS) action was studied. While mercaptene markedly stimulate the ability of NCS to degrade DNA, they also rapidly inactivate the antibiotic in a preincubation and at higher concentration inhibit the degradation reaction. The radiation protector S,2-aminoethylisothiuronium bromide-HBr is the most potent compound tested. Scavengers of diffusible OH radicals, O2- or H2O2 do not result in significant inhibition of the oxygen-dependent cleavage of DNA by NCS; in fact, alcohols and other organic solvents stimulate the reaction several-fold. By contrast, the potent peroxyl free radical scavenger, alpha-tocopherol, blocks the reaction 50% at 50 micron.

Effects of neocarzinostatin on mammalian nuclei: release of nucleosomes

When Chinese hamster cell nuclei (Line CHO) were reacted with neocarzinostatin and its DNA was analyzed on non-denaturing agarose gel electrophoresis, a series of bands with a multiplicity of 175 base pairs was obtained. A similar result was also obtained when the DNA samples were electrophoresed under denaturing gels. Our results suggest that the linker DNA between nucleosomes is the susceptible site to the drug and that neocarzinostatin can be used to study the chromatin structure.

The relationship between DNA strand-scission and DNA synthesis inhibition in HeLa cells treated with neocarzinostatin

Neocarzinostatin inhibits DNA synthesis in HeLa S3 cells and induces the rapid limited breakage of cellular DNA. The fragmentation of cellular DNA appears to precede the inhibition of DNA synthesis. Cells treated with drug at 37 degrees C for 10 min and then washed free of drug show similar levels of inhibition of DNA synthesis or cell growth, or of strand-scission of DNA as when cells were not washed. If cells are preincubated with neocarzinostatin at 0 degrees C before washing, the subsequent incubation of 37 degrees C results in no inhibition of DNA synthesis or cell growth, or cutting of DNA. Isolated nuclei or cell lysates derived from neocarzinostatin-treated HeLa S3 cells are inhibited in DNA synthesis but this can be overcome in cell lysates by adding activated DNA. A cytoplasmic fraction from drug-treated cells can stimulate DNA synthesis by nuclei isolated from untreated cells, whereas nuclei from drug-treated cells are not stimulated by the cytoplasmic fraction from untreated cells. By contrast, neocarzinostatin does not inhibit DNA synthesis when incubated with isolated nuclei, but it can be shown that under these conditions the DNA is already degraded and is not further fragmented by the drug. These data suggest that the drug's ability to induce breakage of cellular DNA in HeLa S3 cells is an essential aspect of its inhibition of DNA replication and may be responsible for the cytotoxic and growth-inhibiting actions of neocarzinostatin.

Single-strand nicking of DNA in vitro by neocarzinostatin and its possible relationship to the mechanism of drug action

Neocarzinostatin, a protein antibiotic with anti-tumor activity was found to place single-strand scissions in DNA in an in vitro reaction. The drug's cutting activity was strongly dependent on the presence of 2-mercaptoethanol or dithiothreitol but some cutting did take place in the absence of reducing agent at very high drug levels and prolonged incubation. The requirement for reducing agents could not be replaced with NAD+, FAD, NADH or H2O2 and the strand-scission reaction was not affected by Mg2+, EDTA or intercalating agents. Similar profiles of heat-inactivation of neocarzinostatin were found whether activity was measured by the scission of DNA strand either in vitro or in HeLa cells treated with the drug. Furthermore, both of these parameters corresponded closely with the ability of the modified drug to inhibit DNA synthesis and growth of HeLa cells. By column isoelectric focusing it was shown that all four activities are associated with the same protein band (pH 3.28). From these data we conclude that the cytotoxic activity of neocarzinostatin and the nicking of DNA strands in vitro appear to reside in the same protein.

Primary structure of neocarzinostatin, an antitumor protein

The antitumor protein neocarzinostatin is an acidic single-chain molecule, cross-linked by two disulfide bridges, and consists of 109 amino acid residues. Complete disulfide bond reduction and S-carboxymethylation was achieved in liquid ammonia. Sequence determination of five tryptic fragments led to the proposed primary structure.

Biogenesis of an antitumor antibiotic protein, neocarzinostatin

A study of the biogenesis of the antitumor protein antibiotic neocarzinostatin (NCS) was undertaken. The production of NCS, as well as the growth of Streptomyces carzinostaticus in a production medium, was sensitive to puromycin, chloramphenicol, and actinomycin D. However, when a 12-hr culture in production medium was transferred to a nongrowth medium consisting of a phosphate buffer with Mg(2+) and Ca(2+), rapid NCS synthesis and liberation occurred. NCS production in this medium was no longer sensitive to actinomycin D, but was sensitive to puromycin and chloramphenicol. The conversion of a precursor NCS to an active form was shown to occur in this medium. Subcellular analysis suggested that NCS synthesis occurred by a mechanism similar to that of protein synthesis by membrane polysomes.