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PubMed1991

Modulation of alkylating agents by lonidamine in vivo.

We are searching for relatively nontoxic compounds that can positively modulate the efficacy of antitumor alkylating agents. Lonidamine inhibits cellular energy metabolism and could potentially increase damage by alkylating agents if cellular defenses are energy-requiring. In the FSaIIC murine fibrosarcoma tumor system, 5 intraperitoneal (IP) injections of 50 mg/kg of lonidamine over 36 hours increased the tumor cell kill by cisplatin, carboplatin, D-tetraplatin, melphalan and BCNU approximately two- to threefold over the dosage ranges of each drug tested when the antitumor agents were given IP immediately after the third lonidamine injection. When cyclophosphamide and thiotepa were given in the same schedule, 10-fold increases in tumor cell killing were evident on tumor excision assay over the dosage ranges for each drug. The increase in bone marrow toxicity caused by lonidamine in addition to the alkylating agents, cisplatin, carboplatin, and BCNU was less than for tumor cells. Dose modifying effects were observed in the killing of bone marrow colony forming units-granulocyte-macrophage progenitors (CFU-GM) by cyclophosphamide, thiotepa and melphalan but at standard doses of cyclophosphamide and thiotepa there was no increase in the killing of bone marrow CFU-GM with the addition of lonidamine to treatment with these drugs. The results suggest that lonidamine can positively modulate tumor cell killing by some antitumor alkylating agents and may be a clinically useful adjunctive therapy with these drugs.

Alkylating Agents↗
PubMed1989

Influence of schedule on alkylating agent cytotoxicity in vitro and in vivo.

High dose, multiple alkylating agent chemotherapy is being employed in conjunction with autologous marrow transplantation in the clinic. We have investigated the scheduling of several alkylating drugs in an effort to optimize their antitumor effects. In vitro modeling of "continuous" (up to 72 h) versus "bolus" (1 h) exposure in MCF-7 cells showed that for N,N',N"-triethylenethiophosphoramide (thiotEPA), cis-diamminedichloroplatinum(II) (CDDP), 4-hydroperoxycyclophosphamide, carboplatin, and L-phenylalanine mustard (L-PAM) "continuous" exposure yielded essentially the same killing kinetics as "bolus" exposure. For N,N'-bis(2-chloroethyl)-N-nitrosourea (BCNU), however, even with fresh drug additions every 30 min, "bolus" exposure produced superior cytotoxicity. In vivo modeling of "continuous" (three i.p. injections over 9 h) versus "bolus" (single dose) administration of the alkylating agents cyclophosphamide, BCNU, thiotEPA, melphalan, CDDP, and carboplatin was conducted in mice bearing EMT6 tumors, and tumor cell killing as measured by tumor cell survival in vitro was compared with killing of bone marrow (CFU-GM) measured in culture as a representative sensitive normal tissue. With cyclophosphamide there was a considerable increase in the therapeutic index (killing of tumor cells/killing of CFU-GMs) when the same total dose of drug was administered in multiple injections versus a single injection. For BCNU and thiotEPA, smaller increases in therapeutic index were observed. With L-PAM and CDDP, some advantage to multiple versus single dose administration was observed, and for carboplatin a decrease in the therapeutic index was seen. In conclusion, for all six alkylating agents examined, the multiple dose schedule was at least as effective against the tumor as the single dose schedule at all dose levels.

Adenocarcinoma↗
PubMedDate not supplied

Potent long-acting alkylated analogs of growth hormone-releasing factor.

Analogs of growth hormone-releasing factor-(1-29)-NH2 (GRF-29) involving derivatization with alkyl substituents at the N-terminus, with or without concomitant alkylation of basic amino acids within the peptide chain (lysine in positions 12 and 21), were synthesized using solid-phase methodology and tested for their ability to stimulate growth hormone release in pentobarbital and urethane-anesthetized rats and in 4-day primary cultures of rat anterior pituitary cells. N alpha-MeTyr1-GRF-29 was 40% as potent as GRF-29 15 min after injection of peptide into pentobarbital-anesthetized rats; N alpha-EtTyr1, Nle27-GRF-29 was 5 times more potent and N alpha-iPrTyr1-GRF-29 was 35 times more potent. Combining this latter modification with our previously reported superactive analog modification, D-Ala2, did not appreciably change potency. Analogs with larger alkyl groups, N alpha-cyclohexyl-Tyr1-GRF-29 were not superactive. However, N alpha-benzyl-Tyr1-GRF-29 was 73 times more potent than GRF-29. Most strikingly, the triisopropylated analog N alpha-iPrTyr1, N epsilon-iPr-Lys12,21-GRF-29 was 106 times more active. Several analogs were tested in time course assays. All were long-acting as compared to GRF-29, with the triisopropylated analog having the longest duration of activity. In vitro potencies among the analogs with the higher in vivo activities were only slightly increased (2-4 X) with respect to GRF-29. The observed increases in in vivo potencies presumably occur due to enhanced resistance to enzymatic degradation following alkylation or through some other pharmacokinetic effect due to the increased lipophilicity of these analogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkylation↗
PubMed1989

Spontaneous regeneration of free muscarinic receptor after alkylation by BM 123. II. Recovery in broken cell preparations.

Muscarinic receptors from rat cerebral cortex were found to recover from alkylation by the specific ligand N-[-(2-chloroethyl-methylamino)-2-butynyl]-2-pyrrolidone (BM 123) without the benefit of cellular integrity, i.e., in washed membranes incubated at 37 degrees C for relatively long times (days). Unalkylated receptor number increased in alkylated preparations whether viewed as femtomoles per milligram of protein or as a percentage of the atropine-protected control. The rate of recovery was independent of pH over the range 6 to 9 and it was slowed but not eliminated by incubation at 4 degrees C. Muscarinic receptor recovery from BM 123 was linearly dependent on the concentration of alkylated receptors, indicating first-order kinetics and yielding a rate constant 0.026/hr. Of the other chloroethylamines examined for evidence of in vitro muscarinic receptor recovery from alkylation, only one, phenoxybenzamine, exhibited irreversible receptor blockade under these conditions. Each of the others showed different rates for regeneration of free receptors.

Alkylation↗
PubMed1986

Cytotoxic, cell cycle, and chromosomal effects of methylxanthines in human tumor cells treated with alkylating agents.

Human tumor cells, like rodent cells, are sensitive to effects of methylxanthines (MEX) on lethality, cell cycle delays, and chromosome aberrations after DNA damage by anticancer drugs. Enhanced cytotoxicity of alkylating agents was observed when T24 human bladder tumor cells in culture were exposed to nontoxic concentrations of MEX such as caffeine or pentoxifylline. Tumor cell lethality was increased up to 10-fold by either caffeine or pentoxifylline (1 mM) present during the first cell cycle (16-24 h) after exposure to nitrogen mustard (HN2) or thiotepa. Cycloheximide, a protein synthesis inhibitor, abolished the enhanced lethality produced by MEX. In these synchronized human tumor cells further kinetic studies revealed that HN2 (0.5 microM X 1 h) delayed transit through S phase by about 1-2 h, and this delay was prevented by MEX. After completion of S phase, HN2-treated cells were delayed 3-6 h in G2, and MEX also prevented this delay, leading to mitoses at the rate of controls. Chromosome analysis of these mitotic cells revealed dramatic increases in aberrations induced by alkylator + MEX combinations. The greatest number of aberrations was seen in HN2-treated cells exposed briefly to MEX in late S-G2. In contrast, no increased chromosome damage was seen in cells exposed to MEX in mid-S phase. Taken together, our results are consistent with the model that MEX enhance lethality of alkylator-treated human tumor cells by preventing delays in cell cycle transit through G2, leading to chromosome aberrations which are lethal. G2 delays in human tumor cells may provide time for repair processes that are critical for survival after sublethal DNA damage by HN2 or other anticancer alkylating agents.

Alkylating Agents↗
PubMed1987

Leukemia after therapy with alkylating agents for childhood cancer.

The risk of leukemia was evaluated in 9,170 2-or-more-year survivors of childhood cancer in the 13 institutions of the Late Effects Study Group. Secondary leukemia occurred in 22 nonreferred individuals compared to 1.52 expected, based on general population rates [relative risk (RR) = 14; 95% confidence interval (CI), 9-22]. The influence of therapy for the first cancer on subsequent leukemia risk was determined by a case-control study conducted on 25 cases and 90 matched controls. Treatment with alkylating agents was associated with a significantly elevated risk of leukemia (RR = 4.8; 95% CI, 1.2-18.9). A strong dose-response relationship was also observed between leukemia risk and total dose of alkylating agents, estimated by an alkylator score. The RR of leukemia reached 23 in the highest dose category. Radiation therapy, however, did not increase risk. Although doxorubicin was also identified as a possible risk factor, the excess risk of leukemia following treatment for childhood cancer appears almost entirely due to alkylating agents.

Alkylating Agents↗
PubMed1987

The effects of 6-benzyl-1,3-benzodioxole derivatives on the alkylation of tubulin.

Derivatives of 6-benzyl-1,3-benzodioxole are known to bind to tubulin and inhibit tubulin polymerization. For a better understanding of the mechanism of action of the 6-benzyl-1,3-benzodioxole derivatives, we have examined their effect on the alkylation of tubulin sulfhydryls by iodo[14C]acetamide and N,N'-ethylene(bis)iodoacetamide. We have found that the 6-benzyl-1,3-benzodioxole derivatives with an intact dioxole ring affect alkylation to an extent proportional to their ability to inhibit tubulin polymerization. Those derivatives with the strongest resemblance to podophyllotoxin have the weakest effects. However, derivatives with a disrupted dioxole ring show little or no ability to inhibit polymerization, but their effect on alkylation is directly related to the degree of resemblance they bear to the trimethoxy ring of podophyllotoxin. It thus appears that the relatively simple approach of using alkylating agents can generate a significant amount of information on the mechanism by which various drugs interact with tubulin.

Alkylation↗
PubMedDate not supplied

Electrochemistry of potential bioreductive alkylating quinones: its use in the development of new aziridinylquinones.

The concept of bioreductive alkylation as a mechanism of action of quinone-containing anticancer agents was investigated, using electrochemical techniques. According to this concept, an electrochemical step (reduction of the quinone ring) is followed by one or more chemical steps, leading to formation of the actual alkylating species. The proper use of electrochemical analysis of potential bioreductive alkylating quinones in the design of new analogs is limited. Up to now, the only electrochemical parameter frequently used in structure-activity relationship studies, is the half-wave potential of the quinone reduction. However, reliable information can only be obtained from the found value of this parameter when the reduction mechanism has been elucidated. Furthermore, it only gives information about the first step of the model. More detailed electrochemical analysis of potential bioreductive alkylating quinones, in combination with a biological evaluation, is required to gain more insight in their mechanism of action and to yield quantitative information about substituent effects on both the electrochemical and the chemical step(s) of the model. Results of such studies of a series of aziridinylquinones indicate, that the biological activity in vitro is correlated with the ease of protonation of the aziridines after quinone reduction, which is in accordance with the concept of bioreductive activation. No correlation with the ease of protonation of the aziridines prior to quinone reduction or with the quinone reduction step itself can be found.

Alkylating Agents↗
PubMed1985

Mutagenic and chemotherapeutic activity in L1210 leukemia of several monofunctional alkylating agents.

The mutagenic and chemotherapeutic activities of the following monofunctional alkylating agents were compared in vivo: beta-chloroethylamine, dimethyl- and diethylaminoethyl chloride; methyl- and ethylmethanesulfonate; methyl- and ethylnitrosourea; and procarbazine. The bifunctional alkylating agent diethylamine 2,2'-dichloro-N-methyl-hydrochloride was used as reference. The alkylating activity was assessed by reacting with 4-(p-nitrobenzyl)pyridine, and antitumor activity was determined against L1210 in vitro and in vivo. The L1210 response, which is consistent with useful alkylating reactivity, was very marked with the two nitrosoureas and procarbazine. The nitrosoureas and, to some extent, procarbazine decreased the tumorigenicity of L1210 leukemia as evidenced by the increase in survival times with increasing numbers of treatment generations. After treatment for about five transfers (10(6) cells i.p.) with methylnitrosourea (40 mg/kg i.p. on Days 1, 3, and 5), the untreated control mice consistently survived free of tumor, whereas the treated mice died before Day 30. After treatment with ethylnitrosourea (80 mg/kg), the survival times also increased but more in the treated than in the corresponding control groups. Methylnitrosourea was most efficient in increasing the survival times and abolishing tumor transplantability. Antigenic change and loss of growth potential presumably were the reason for this increase in survival time, as indicated by tests in X-irradiated and nude mice. The fact that nitrosoureas and triazenes, besides reducing tumorigenicity, have similarities in their chemistry in that they decompose or are metabolically converted into diazohydroxides and then to carbonium ions is possibly of significance.

Alkylating Agents↗
PubMed1985

Effect of phenobarbital and other liver monooxygenase modifiers on dimethylnitrosamine-induced alkylation of rat liver macromolecules.

The effects of phenobarbital (PB) and other liver monooxygenase modifiers on dimethylnitrosamine (DMN)-induced alkylation of rat liver DNA and protein were investigated at different carcinogen doses. In rats given single injections of radioactively labeled DMN, pretreatment with PB (80 mg/kg body weight, administered for 5 days) resulted in a small but significant decrease in the formation of 7-methylguanine and O6-methylguanine per mole of guanine in liver DNA associated with a decrease in the O6/N7-methylguanine ratio. The specific radioactivity of liver protein was also lowered in PB-pretreated rats. The degree of PB interference was independent of DMN dose within a carcinogen dose range of 0.5 microgram to 10 mg/kg body weight. In parallel experiments, the effects of pretreatment with PB, Aroclor 1254, pregnenolone-16 alpha-carbonitrile, butylated hydroxytoluene, beta-naphthoflavone, and ethanol on DMN-induced alkylation of liver DNA were studied at a DMN dose of 5 micrograms/kg body weight. In general, pretreatment with these modifiers of liver monooxygenase resulted in a decrease in specific alkylation of DNA and in the ratio of 7-methylguanine to guanine. If, however, 7-methylguanine levels were related to total liver DNA, these differences in DNA alkylation between controls and pretreated rats became substantially smaller, partially being negligible, since these inducers led to an increase in relative liver weight with concomitant increase in the content of liver DNA. Thus, when expressed per total liver, no significant changes in the overall extent of metabolic activation of DMN were evident. These findings are not consistent with the results of in vitro studies on DMN metabolism in microsomal systems which favored the hypothesis that changes in the metabolism of hepatocarcinogens are responsible for the reduction of liver tumor response in animals treated simultaneously with inducers of the liver monooxygenase system and hepatocarcinogens. Our findings suggest that these effects might rather be related to drug-mediated changes on the cellular level.

Alkylation↗
PubMed1985

Direct alkylation of 2'-deoxynucleosides and DNA following in vitro reaction with acrylamide.

Reaction of the rodent carcinogen acrylamide (AM) at pH 7.0 and 37 degrees C for 10 and 40 days with 2'-deoxyadenosine (dAdo), 2'-deoxycytidine (dCyd), 2'-deoxyguanosine (dGuo), and thymidine (dThd) resulted in the formation of 2-formamidoethyl and 2-carboxyethyl adducts via Michael addition. The alkylated 2'-deoxynucleoside adducts isolated (% yield after 40 days) were 1-(2-carboxyethyl)-dAdo (1-CE-dAdo) (8%), N6-CE-dAdo (21%) (via Dimroth rearrangement of 1-CE-dAdo), 1-CE-dGuo (4%), 7-(2-formamidoethyl)-Gua (7-FAE-Gua) (6%), 7, 9-bis-FAE-Gua (1%) (formed by reaction of AM with depurinated 7-FAE-Gua during the course of the reaction), and 3-FAE-dThd (4%). The products isolated following in vitro reaction of AM with calf thymus DNA at pH 7.0 and 37 degrees C for 40 days were (nmol/mg DNA) 1-CE-dAdo (5.5), N6-CE-dAdo (1.4), 3-CE-dCyd (2.8), 1-CE-dGuo (0.3), and 7-FAe-Gua (1.6). Compound 3-FAE-dThd was not detected. Structures were assigned on the basis of chemical properties, UV spectra, and electron impact, chemical ionization, desorption chemical ionization, Californium-252 fission fragment ionization, and fast atom bombardment mass spectra. A facile hydrolysis of the amide group to a carboxylic acid was observed when AM alkylated a ring nitrogen adjacent to an exocyclic nitrogen atom. In previous studies, we had observed an analogous phenomenon when studying the in vitro reactions of acrylonitrile with DNA, i.e., a facile hydrolysis of nitrile to carboxylic acid when acrylonitrile alkylated (via Michael addition) a ring nitrogen adjacent to an exocyclic nitrogen. Since the nitrile group hydrolyzes to a carboxylic acid via an amide intermediate, we had hypothesized in the present study that the same facile hydrolysis of amide to carboxylic acid would occur under identical stereochemical conditions as had occurred with the nitrile group. Thus, in vitro alkylation of calf thymus DNA by both acrylonitrile and, in the present study, AM, resulted in mixed adduct formation.

Acrylamide↗
PubMedDate not supplied

[Selective alkylation of G24 residue in tRNAPhe].

Alkylation of E. coli tRNAPhe with 4-(N-2-chloroethyl-N-methylamino) benzyl-5'-phosphamide of oligonucleotide d(pAACCA) was studied. G24 residue located near the sequence C17GGDA21 partially complementary to the oligonucleotide moiety of the reagent was shown to be alkylated. Oligonucleotide d(pAACCA) inhibited the alkylation. Association constant of oligonucleotide derivative with tRNAPhe (10(3) M-1) was evaluated from the dependence of the extent of tRNA modification on the concentration of the reagent. The reported method for selective alkylation of tRNA may be used for preparing photoaffinity derivatives of tRNA bearing an arylazidogroups in desired position.

Alkylation↗
PubMed1981

Interaction of the alkylating antitumor agent 2,3,5-tris(ethyleneimino)benzoquinone with the plasma membrane of Ehrlich ascites tumor cells.

The effect of the alkylating agent 2,3,5-tris(ethyleneimino)benzoquinone (Trenimon) on the uptake of 2-aminoisobutyric acid, 1-aminocyclopentane-1-carboxylic acid (cycloleucine), 3-O-methyl-D-glucose, and 86Rb was studied. All transport studies were performed at nonsaturating conditions where the specific transport system was rate limiting for the uptake. The activities of all systems are reduced after treatment with the alkylating agent. The impairment of the plasma membrane is expressed 30 sec after exposure to the drug, as measured by the 86Rb uptake, and lasts for at least 12 hr according to the reduced 3-O-methyl-D-glucose uptake. Inhibition of protein synthesis by cycloheximide for 2 hr does not affect the uptake of 86Rb. The short interval which is necessary before an inhibition of 86Rb uptake can be registered and the resistance of the 86Rb transport system to an inhibition of protein synthesis are considered as indicative for a direct alkylation of a membrane constituent. Treatment with the alkylating agent increases the cyclic adenosine 3':5'-monophosphate of the cells. This effect is not due to an effect on adenylate cyclase or the membrane-bound cyclic adenosine 3':5'-monophosphate phosphodiesterase. In view of the known correlations between plasma membrane functions and the regulation of cell division, it is proposed that the growth inhibition by Trenimon of Ehrlich ascites tumor cells may be caused by its interaction with the plasma membrane.

Alkylating Agents↗
PubMed1981

The interaction of N alpha-alkylenkephalins with opiate receptors. Tissue-dependent shifts in the opiate activity of methionine-enkephalin following N alpha-alkylation.

Experimental conditions for the small scale alkylation of the alpha-amino group of the opioid peptide methionine-enkephalin using the method of reductive alkylation are described. The generality of the method is established by describing in detail the synthesis, purification, and structure elucidation of the N alpha-ethyl, isopropyl, phenethyl, and cyclopropylmethyl derivatives of methionine-enkephalin. By a combination of amino acid and mass spectral analysis it is possible to carry out the structure analysis of nanomole quantities of these modified peptides, making direct chemical modification and structure elucidation of carrier-free tritiated and radioiodinated enkephalins feasible. Using these chemical procedures, a homologous series of N alpha-n-alkyl derivatives of methionine-enkephalin has has been synthesized. It is shown that the relative binding and opiate activity of these N alpha-alkyl derivatives, using several standard in vitro assay systems, depends on the tissue source used. The results of this study are analyzed by considering recent reports indicating the existence of multiple opiate receptors.

Alkylation↗
PubMed1983

Induction of neoplastic transformation and DNA single-strand breaks in C3H/10T1/2 clone 8 cells by polycyclic hydrocarbons and alkylating agents.

The standard C3H/10T1/2 clone 8 (C3H/10T1/2 CL8) cell transformation assay was tested for its ability to identify a variety of polycyclic hydrocarbons and alkylating agents. Dose-dependent morphologic transformation occurred with benzo[a]pyrene (BaP), 3-methylcholanthrene (MCA), 7,12-dimethylbenz[a]anthracene, BaP-7,8-dihydroxy-7,8-dihydrodiol (BaP-7,8-diol), as well as with the relatively weak in vivo carcinogen benzo[e]pyrene. Dibenz[a,h]anthracene yielded a relatively weak response, whereas anthracene and phenanthrene were negative. In contrast, treatment of C3H/10T1/2 CL8 cells with two directly acting alkylating agents, N-nitroso-N-methylnitroguanidine (MNNG) and styrene oxide, gave no transformation, whereas a third alkylating agent, ethyl methanesulfonate (EMS), gave a weak response. Treatment with MCA (2.5 micrograms/ml) yielded a reproducible positive response and, therefore, served as a positive control for routine use of the C3H/10T1/2 CL8 assay. When cells treated with the hydrocarbons BaP, BaP-7,8-diol, or MCA were analyzed for nonspecific DNA damage (single-strand breaks or alkaline-labile sites) by alkaline elution techniques, little if any DNA damage was observed. In contrast, the alkylating agents MNNG, styrene oxide, and EMS yielded substantial numbers of single-strand breaks.

Alkylating Agents↗
PubMed1976

[Detection of alkylating air pollutants (author's transl)].

Occupational toxicological observations made during the last few years have shown that the respiratory intake of certain alkylating compounds entails a major carcinogenic risk even at concentrations below 1 ppm. Such inhalation carcinogens can also stem from photochemical and spontaneous chemical reactions in the atmosphere and not merely from direct emissions. For the examination of air samples for alkylating activities simple colorimetric test methods are available. Some of them must be considerably modified and matched to the reaction of the various alkylating compounds. In this manner colour reactions of, in part, high selectivity are obtained: thus, for example, carcinogenic alpha halogen ether can be detected in concentrations of 10 ng/ml test solution. By the use of sensitive colorimetric methods of analysis it was possible to fractionate the alkylating activity found in the exhaust gases of automobiles. It is now possible to enrich certain compounds, which react positively to the colour test, and to purify them for further chemical characterization.

Air Pollutants↗
PubMed1982

Alkylarylnitrosoureas--stability in aqueous solution, partition coefficient, alkylating activity and its relationship to SCE induction in Chinese hamster V 79-E cells.

The alkylating activity, chemical stability in aqueous solution (pH 7.0; 37 degrees C), and partition coefficient (octanol/water) of the following compounds were determined: 1-methyl-3-phenyl-1-nitrosourea (MPNU), 1-ethyl-3-phenyl-1-nitrosourea (EPNU), 1-isopropyl-3-phenyl-1-nitrosourea (i-PrPNU), 1-methyl-3-(p-fluorophenyl)-1-nitrosourea (F-MPNU), 1-methyl-3-(p-chlorophenyl)-1-nitrosourea (Cl-MPNU), 1-methyl-3-(p-bromophenyl)-1-nitrosourea (Br-MPNU), 1,3-dimethyl-3-phenyl-1-nitrosourea (DMPNU), and 1-methyl-3-naphthyl-1-nitrosocarbamate (NCA). 1-Methyl-1-nitrosourea (MNU) and 1-ethyl-1-nitrosourea (ENU) were used for the comparison. THe rate of decomposition in aqueous solution is discussed concerning the influences of the substituents at the 1- and 3-N-atom. The mono- and disubstituted N-nitrosoureas showed a coarse correlation between alkylating activity and SCE induction in Chinese hamster V 79-E cells. On the other hand, this correlation is missing in the case of NCA, which is a potent SCE inducer despite relatively low alkylating activity. DMPNU is the strongest SCE inducer, but this compound shows a high stability in aqueous solution and, consequently, we were not able to detect an alkylating activity.

Alkylating Agents↗
PubMed1981

Oncogenic transformation and mutation of C3H/10T 1/2 clone 8 mouse embryo fibroblasts by alkylating agents.

Two-hr treatments with N-methyl- and N-ethyl-N'-nitro-N-nitrosoguanidines and ethyl methanesulfonate induced ouabain-resistant mutants in C3H/10T 1/2 cells. The alkylnitronitroso-guanidines gave linear dose-response curves and were more potent mutagens than were ethyl methanesulfonate and methyl methanesulfonate. These differences in potency were largely due to differences in the half-lives of the alkylating agents in culture medium. Differences in mutation frequencies at equitoxic concentrations of the alkylating agents are considered to reflect differences in the chemical mechanisms of alkylation and mutagenesis by the compounds. However, the frequencies of mutations produced at equitoxic concentrations were not uniformly associated with the nucleophilic selectivities of the compounds as expressed by their published Swain-Scott substrate constants. Whether or not followed by repeated replating, the yield of oncogenically transformed foci of asynchronous cells after treatment with the alkylating agents was so low that we could not obtain dose-response curves, and the yield may not be significant. By contrast, in previous experiments with N-methyl-N'-nitro-N-nitrosoguanidines and polycyclic hydrocarbons in Syrian hamster embryo fibroblasts and with ultraviolet light and polycyclic hydrocarbons in C3H/10T 1/2 cells, transformation occurred to an equal or greater extent than mutation measured in the same cells.

Alkylating Agents↗