The genetic properties of beta-propiolactone

β-Propiolactone (BPL)-inactivation of SARS-Co-V-2: in vitro validation with focus on saliva from COVID-19 patients for scent dog training

β-Propiolactone (BPL) is an organic compound widely used as an inactivating agent in vaccine development and production, for example for SARS-CoV, SARS-CoV-2 and Influenza viruses. Inactivation of pathogens by BPL is based on an irreversible alkylation of nucleic acids but also on acetylation and cross-linking between proteins, DNA or RNA. However, the protocols for BPL inactivation of viruses vary widely. Handling of infectious, enriched SARS-CoV-2 specimens and diagnostic samples from COVID-19 patients is recommended in biosafety level (BSL)-3 or BSL-2 laboratories, respectively. We validated BPL inactivation of SARS-CoV-2 in saliva samples with the objective to use saliva from COVID-19 patients for training of scent dogs for the detection of SARS-CoV-2 positive individuals. Therefore, saliva samples and cell culture medium buffered with NaHCO₃ (pH 8.3) were comparatively spiked with SARS-CoV-2 and inactivated with 0.1% BPL for 1hour (h) or 71h (± 1h) at 2-8°C, followed by hydrolysis of BPL at 37°C for 1 or 2h, converting BPL into non-toxic beta-hydroxy-propionic acid. SARS-CoV-2 inactivation was demonstrated by a titre reduction of up to 10^4 TCID₅₀/ml in the spiked samples for both inactivation periods using virus titration and virus isolation, respectively. The validated method was confirmed by successful inactivation of pathogens in saliva samples from COVID-19 patients. Furthermore, we reviewed the currently available literature on SARS-CoV-2 inactivation by BPL. Accordingly, BPL-inactivated, hydrolysed samples can be handled in a non-laboratory setting. Furthermore, our BPL inactivation protocols can be adapted to validation experiments with other pathogens.

Role of viral RNA and lipid in the adverse events associated with the 2010 Southern Hemisphere trivalent influenza vaccine

In Australia, during the 2010 Southern Hemisphere (SH) influenza season, there was an unexpected increase in post-marketing adverse event reports of febrile seizures (FS) in children under 5 years of age shortly after vaccination with the CSL 2010 SH trivalent influenza vaccine (CSL 2010 SH TIV) compared to previous CSL TIVs and other licensed 2010 SH TIVs. In an accompanying study, we described the contribution to these adverse events of the 2010 SH influenza strains as expressed in the CSL 2010 SH TIV using in vitro cytokine/chemokine secretion from whole blood cells and induction of NF-κB activation in HEK293 reporter cells. The aim of the present study was to identify the root cause components that elicited the elevated cytokine/chemokine and NF-κB signature. Our studies demonstrated that the pyrogenic signal was associated with a heat-labile, viral-derived component(s) in the CSL 2010 SH TIV. Further, it was found that viral lipid-mediated delivery of short, fragmented viral RNA was the key trigger for the increased cytokine/chemokine secretion and NF-κB activation. It is likely that the FS reported in children <5 years were due to a combination of the new influenza strains included in the 2010 SH TIV and the CSL standard method of manufacture preserving strain-specific viral components of the new influenza strains (particularly B/Brisbane/60/2008 and to a lesser extent H1N1 A/California/07/2009). These combined to heighten immune activation of innate immune cells, which in a small proportion of children <5 years of age is associated with the occurrence of FS. The data also demonstrates that CSL TIVs formulated with increased levels of splitting agent (TDOC) for the B/Brisbane/60/2008 strain can attenuate the pro-inflammatory signals in vitro, identifying a potential path forward for generating a CSL TIV indicated for use in children <5 years.

Reactions of beta-propiolactone with nucleobase analogues, nucleosides, and peptides: implications for the inactivation of viruses

β-Propiolactone is often applied for inactivation of viruses and preparation of viral vaccines. However, the exact nature of the reactions of β-propiolactone with viral components is largely unknown. The purpose of the current study was to elucidate the chemical modifications occurring on nucleotides and amino acid residues caused by β-propiolactone. Therefore, a set of nucleobase analogues was treated with β-propiolactone, and reaction products were identified and quantified. NMR revealed at least one modification in either deoxyguanosine, deoxyadenosine, or cytidine after treatment with β-propiolactone. However, no reaction products were found from thymidine and uracil. The most reactive sides of the nucleobase analogues and nucleosides were identified by NMR. Furthermore, a series of synthetic peptides was used to determine the conversion of reactive amino acid residues by liquid chromatography-mass spectrometry. β-Propiolactone was shown to react with nine different amino acid residues. The most reactive residues are cysteine, methionine, and histidine and, to a lesser degree, aspartic acid, glutamic acid, tyrosine, lysine, serine, and threonine. Remarkably, cystine residues (disulfide groups) do not react with β-propiolactone. In addition, no reaction was observed for β-propiolactone with asparagine, glutamine, and tryptophan residues. β-Propiolactone modifies proteins to a larger extent than expected from current literature. In conclusion, the study determined the reactivity of β-propiolactone with nucleobase analogues, nucleosides, and amino acid residues and elucidated the chemical structures of the reaction products. The study provides detailed knowledge on the chemistry of β-propiolactone inactivation of viruses.

Frequencies of mutagen-induced coincident mitotic recombination at unlinked loci in Saccharomyces cerevisiae

Frequencies of coincident genetic events were measured in strain D7 of Saccharomyces cerevisiae. This diploid strain permits the detection of mitotic gene conversion involving the trp5-12 and trp5-27 alleles, mitotic crossing-over and gene conversion leading to the expression of the ade2-40 and ade2-119 alleles as red and pink colonies, and reversion of the ilv1-92 allele. The three genes are on different chromosomes, and one might expect that coincident (simultaneous) genetic alterations at two loci would occur at frequencies predicted by those of the single alterations acting as independent events. Contrary to this expectation, we observed that ade2 recombinants induced by bleomycin, beta-propiolactone, and ultraviolet radiation occur more frequently among trp5 convertants than among total colonies. This excess among trp5 recombinants indicates that double recombinants are more common than expected for independent events. No similar enrichment was found among Ilv(+) revertants. The possibility of an artifact in which haploid yeasts that mimic mitotic recombinants are generated by a low frequency of cryptic meiosis has been excluded. Several hypotheses that can explain the elevated incidence of coincident mitotic recombination have been evaluated, but the cause remains uncertain. Most evidence suggests that the excess is ascribable to a subset of the population being in a recombination-prone state.

Tissue-specific induction of mutations by acute oral administration of N-methyl-N'-nitro-N-nitrosoguanidine and beta-propiolactone to the Muta Mouse: preliminary data on stomach, liver and bone marrow

We used the positive selection Muta Mouse model to detect organ-specific activity of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and beta-propiolactone (BPL), two highly reactive alkylating agents known to induce genetic damage and tumors in rodent stomach when administered orally. Seven days after a single oral administration of MNNG (100 mg/kg) or BPL (150 mg/kg), the mutation frequency in the Muta Mouse stomach increased significantly by 6.4-fold and 8.8-fold, respectively. A slight (1.8-fold) but significant increase in mutation frequency was also observed in the livers of BPL-treated mice, but not in the livers of MNNG-treated mice or the bone marrow of MNNG- and BPL-treated animals. These data indicate that the Muta Mouse model can be used to predict the gastric specificity of genotoxic carcinogens.

Mutagenicity of acridines in a reversion assay based on tetracycline resistance in plasmid pBR322 in Escherichia coli

The mutagenicity of a series of acridine compounds was studied in an assay based on the reversion of mutations in the tetracycline-resistance gene (tet) of plasmid pBR322 in Escherichia coli. Mutations that restore the tetracycline-resistant phenotype were detected in tetracycline-sensitive strains carrying mutant plasmids. Mutations that revert by +2, +1, -1 and -2 frameshift mutations and by base-pair substitutions were used to analyze the mutagenicity of two simple acridines, two acridine mustards, and a nitroacridine. The simple acridines (9-aminoacridine and quinacrine) effectively induced -1 frameshifts and weakly induced +1 frameshifts. The acridine mustards (quinacrine mustard and ICR-191) were more potent inducers of -1 and +1 frameshifts than the simple acridines. Reactive acridines, including both the mustards and the nitroacridine Entozon, were effective inducers of -2 frameshifts but the simple acridines were not. The two classes of reactive acridines differed from one another, in that the mustards were better inducers of +1 frameshifts than Entozon, whereas Entozon was a particularly potent inducer of -2 frameshifts. None of the compounds induced +2 frameshifts, and the induction of base-pair substitutions was negligible. These results confirm and extend studies showing that adduct-forming acridines are stronger frameshift mutagens than simple intercalating acridines and that the acridines differ from one another not only in overall mutagenic potency but also in the prevalence of different classes of frameshift mutations.

Principles of selective inactivation of viral genome. VIII. The influence of beta-propiolactone on immunogenic and protective activities of influenza virus

The influence of beta-propiolactone action on the immunogenic and protective activity of the influenza virus A/WSN/33 (H1N1) has been studied. The production of antibodies against virion surface antigens in mice immunized intramuscularly by the modified virus was enhanced with the increase of inoculating dose from 6 x 10(7) to 1.5 x 10(8) viral particles per animal. The immunizing dose of 6 x 10(7) produced complete protection of immunized animals against a lethal challenge of A/WSN/33 virus. The inhibition of virus reproduction in animal lungs was increased with the increase of the virus immunizing dose up to 6 x 10(8). At a constant dose the inhibition of virus reproduction decreases with the increase of the virus modification extent.

Beta-propiolactone treatment impairs the biological activity of residual DNA from BHK-21 cells infected with rabies virus

The effects of beta-propiolactone (BPL), an alkylating and virus inactivating agent, on the structural and in vitro biological properties of different DNA preparations from BHK-21 cells were investigated. Both uninfected and rabies virus-infected cells were used. Purified cellular DNA (celDNA) was used as the reference, and supernatants from infected cells were treated with BPL. For structural and biological studies three types of DNA preparation were tested: celDNA; purified DNA from cell (infected or uninfected) supernatant (pcsDNA) with or without BPL treatment; and residual cell DNA present in purified rabies virus (inactivated or not) preparations. Rabies infection and BPL (diluted 1:4000) treatment induced modifications in the structure of the three DNA types, including strand breaks and nicks. The damage to the DNA structure by BPL modifies the biological properties of the pcsDNA appraised by its ability to serve as the template in vitro for different polymerases. When rabies virus was inactivated with BPL diluted 1:1000 the DNA damage increased dramatically: small double-stranded DNA fragments (50-200 base pairs) were generated which could not function as templates for polymerases.

The genotoxic effect of beta-propiolactone on mammalian oocytes

beta-Propiolactone (beta PL) has been tested on preimplantation mouse embryos for possible genotoxic effects. Tests were performed at different stages of meiosis (late prophase I, diakinesis/metaphase I, anaphase I, telophase I/prophase II and metaphase II) by injecting females at various times after the induction of superovulation. Male and female derived chromosome complements from first-cleavage embryos were analysed before syngamy for cytogenetic abnormalities. A higher proportion of diploid oocytes, produced by the non-extrusion of the first or second polar body, was found after fertilization when the compound was administered immediately before metaphase I or II. No obvious effect was detected at any other time of beta PL exposure. Based on these results, several possible modes of action for beta PL are postulated.

Potential carcinogenic and mutagenic industrial chemicals. I. Alkylating agents

A variety of alkylating agents, acylating agents, peroxides, halogenated derivatives, and nitrogen derivatives have been reviewed, principally in terms of their synthesis, areas of utility, stability, distribution, reactivity, levels of exposure, population at risk, metabolism, carcinogenicity, and mutagenicity.

Chromosomal analysis in bone-marrow cells of Chinese hamsters after treatment with mycotoxins

Mycotoxins are ubiquitously occurring metabolites of moulds that grow on foodstuffs. They are able to cause toxic diseases in man and animals. Aflatoxin B1 (AFB1), aflatoxin G1 (AFG1) and platulin (PA) induce chromosomal damage in Chinese hamster bone-marrow cells. With respect to the number of induced aberrant mitoses the 3 mycotoxins can be ranked in the order PA greater than AFB1 greater than AFG1.

Esolation of 3-(2-carboxyethyl)thymine following in vitro reaction of beta-propiolactone with calf thymus DNA

3-(2-Carboxyethyl)thymine (3-CET) was synthesized from beta-propiolactone (BPL) and dThd 5'P at pH 9.0--9.5 via the intermediate 3-(2-carboxyethyl)-thymidine-5'-monophosphoric acid (3-CEdThd5'P). 3-CEdThd5'P was converted to 3-CET by hydrolysis in 1.5 N HCl at 100 degrees C for 2 h. The structure of 3-CET was assigned on the basis of UV spectra, electron impact (EI) and isobutane chemical ionization mass spectra and the EI mass spectrum of a trimethylsilyl derivative of 3-CET. BPL was reacted in vitro with calf thymus DNA at pH 7.5. 100 A units of BPL-reacted DNA yielded, following perchloric acid hydrolysis and preparative paper chromatography, 3 A units of 3-CET. Reaction of BPL with the phosphodiester thymidylyl-(3'-5')-thymidine gave 3-(2-carboxyethyl)thymidylyl-(3'-5')-3-(2-carboxyethyl)-thymidine (approximately 3%). Phosphotriester formation was not detected.

The influence of ethanol treatment of cytogenetic effects in bone marrow cells of Chinese hamsters by cyclophosphamide, aflatoxin B1 and patulin

Chromosomes were investigated from the bone marrow of Chinese hamsters which received 10% (v/v) ethanol as the only liquid supply for a period of 9 weeks. At the end of the ethanol drinking period 1 group of animals received 2 oral doses of 80 mg/kg cyclophosphamide (CP), a second group received 2 oral doses of 25 mg/kg aflatoxin B1 (AFB1), a third group 2 oral doses of 20 mg/kg patulin (PA). The 2 applications were separated by 24 h. The intake of ethanol had no effect on the bone marrow chromosomes, and had no potentiating effect on CP induced aberrations. 9 weeks consumption of 10% (v/v) ethanol revealed likewise no influence on the frequencies of chromosomal aberrations induced by the indirect mutagen AFB1. However, the rate of chromosomal aberrations induced by the direct mutagen PA was clearly suppressed in ethanol drinking animals.

Induction of sex-linked recessive lethals and autosomal translocations by beta-propiolactone in Drosophila: influence of the route of administration on mutagenic activity

Beta-propiolactone (BPL) was tested for the induction of sex-linked recessive lethals and autosomal translocations in Drosophila melanogaster. The compound was administered to adult males either by oral application or by abdominal injection. When injected, BPL was a potent inducer of sex-linked recessive lethals. When BPL was given by feeding, its mutagenic activity was detectable only when the flies were starved and when the BPL-containing solutions were renewed several times. Nevertheless, the recessive-lethal frequency was one order of magnitude higher with injection. This difference in effects is attributed to (1) rapid decomposition of the compound in aqueous feeding solutions, and to (2) rapid degradation in vivo which restricts the activity of BPL mainly to the site of application. These data are compared with other studies in which both routes of application were applied. BPL induced translocations in stored spermatozoa when injected, but not when fed. This finding seems a logical consequence of (1) the difference in effectiveness of the two routes of application for BPL, and (2) the existence of different LECs for mutation induction (recessive lethals) and for chromosome breakage (translocations). In Drosophila, the breakage capacity of BPL was one order of magnitude lower than that of MMS, when a comparison was made on the basis of equal recessive-lethal frequencies.

Forward mutations to arabinose resistance in Salmonella typhimurium strains: a sensitive assay for mutagenicity testing

The forward-mutation assay using the L-arabinose-sensitive strain SV3 of Salmonella typhimurium has been calibrated against a selected set of mutagens. Strain SV3 is sensitive to chemicals causing base-pair substitutions, frameshift mutations and deletions. New strains deficient for the excision-repair system or the lipopolysaccharide barrier or both have been selected from strain SV3. The additional mutations do not affect the independence of the assay from experimental artifacts due to physiological or lethal damage or differences in plating density. The new strains are more sensitive than SV3 to certain mutagens. Techniques for using this set of strains are presented and their relative advantages discussed.

Alterations in Bacillus subtilis transforming DNA induced by beta-propiolactone and 1,3-propane sultone, two mutagenic and carcinogenic alkylating agents

Transforming DNA was exposed to either beta-propiolactone or 1,3-propane sultone and then used for transformation of competent bacteria to nutritional independence from tyrosine and tryptophan (linked markers) and leucine (an unlinked marker). The ability to transform was progressively lost by the DNA during incubation with either of these two chemicals. For all three markers the inactivation curve was biphasic, with a short period of rapid inactivation followed by one characterized by a much slower rate. The overall rate of inactivation was different for all three markers and presumably was related to the size of the marker. The decrease in the transforming activity was in part due to the slower rate of penetration of alkylated DNA through the cellular membrane and its inability to enter the recipient bacteria. This decrease in the rate of cellular uptake, even for DNA eventually destined to enter the cell, began almost immediately after its exposure to the chemical and ended up with an almost complete lack of recognition of the heavily alkylated DNA by the specific surface receptors of competent cells. Such DNA attached to sites on the surface of competent bacteria which were different from receptors specific for the untreated nucleic acid. This attachment was not followed by uptake of the altered DNA. Presence of albumin during the incubation with a carcinogen further increased the degree of inactivation, indicating that the artificial nucleoproteins produced under such conditions were less efficient in the transformation assay than was the naked DNA. Cotransfomration of close markers progressively decreased, beginning immediately after the start of incubation of DNA with the chemicals. Extensively alkylated DNA fractionated by sedimentation through sucrose density gradients showed a peculiar distribution of cotransforming activity for such markers; namely, molecules larger than the bulk of DNA ("megamolecules") showed less ability to transform the second marker than did some of the apparently smaller molecules which sedimented more slowly through the gradient. An increase in cotransformation of distant markers was evident in DNA molecules after a short exposure to an alkylating agent, but cotransformation of such markers was absent in DNA treated for longer periods. The observed changes in the transforming and cotransforming activities of the alkylated DNA can be explained by what is known about the physicochemistry of such DNA and in particular about the propensity of the alkylated and broken molecules to form complexes with themselves and with other macromolecules.

The nucleotide-permeable Escherichia coli cell, a sensitive DNA repair indicator for carcinogens, mutagens, and antitumor agents binding covalently to DNA

Ether-permeabilized (nucleotide-permeable) Escherichia coli cells respond to alkylating and arylalkylating carcinogens with DNA excision repair, as assessed by their stimulation of DNA repair synthesis. In the present work, we have investigated whether DNA repair synthesis in ether-treated E. coli cells can serve as a general indicator to monitor the DNA-binding of carcinogens, mutagens and antitumor agents. Therefore, a standard assay was developed and comparative analyses were performed on 11 ultimate carcinogens, 10 proximate carcinogens, 2 tumor promoters, 6 mutagens, and 12 antitumor agents. All ultimate carcinogens (alkylating, acylating, arylalkylating agents) and mutagens (e.g., hydrogeen peroxide, acridine derivatives) caused DNA excision repair in wild type cells as measured by [3H] dTMP incorporation and simultaneously inhibited replicative DNA synthesis to various extents. Control experiments with the mutant cells uvrA and uvrB were performed to determine whether the pyrimidine-dimer-specific UV-endonuclease was involved in the removal of DNA damage. This was found to be true for the ultimate carcinogens (Ac)2 ONFln, mitomycin C, and for very reactive alkylating carcinogens. None of the ultimate carcinogens induced repair polymerization in mutant cells lacking the 5'-3' exonucleolytic activity of DNA polymerase I. Proximate carcinogens, such as Me2NNO, 4-nitroquinoline-1-oxide and aflatoxins, did not induce excision repair in the standard assay, probably because of the inability of E. coli to perform the activation steps necessary for covalent DNA-binding. However, Me2NNO, when pretreated with Udenfriend's hydroxylating mixture, gave rise to a low level of repair polymerization in ether-treated cells. Intercalating mutagens, such as quinacrine and ethidum bromide, inhibited replicative DNA synthesis. However, they were not found to be repair-inducers. THE TUMOR PROMOters TPA and phorbol-12,13-didecanoate did not cause excision repair, even when applied at high concentrations, nor did they inhibit repair synthesis stimulated by MeNOUr or (Ac)2 ONFln. The antitumor agents may be classified into two groups on the basis of the influence they exert on DNA synthesis: members of the first group (involving BCNU and bleomycin) stimulate repair polymerization and, in addition, inhibit DNA replication. These compounds are known to bind covalently to DNA. The second group of drugs (including adriamycin and cis-Pt(II)diammine complexes) inhibits DNA replication without stimulating repair synthesis. The predominant DNA-interaction of these compounds is known to be a non-covalent (i.e., intercalative, electrostatic) binding. Our experiments show that the ether-permeabilized E. coli cell can be successfully used to test ultimate carcinogens, mutagens and antitumor agents for repair-inducing and replication-inhibiting activity. The standard test might be extended to pre- and proximate carcinogens, provided these can be suitably activated.