Uracil mustard revisited

BACKGROUND

A patient with diffuse large cell lymphoma who had a complete response lasting 35 years following a 3-day course of uracil mustard stimulated a recall review of patients treated with this oral alkylating agent.

METHODS

Records of patients treated with uracil mustard between 1958 and 1970 were reviewed. A current histologic review according to the International Formulation was performed when possible. Total doses of uracil mustard were similar to those of mechlorethamine, although there were variations in the dose schedule.

RESULTS

Employing criteria used over 25 years ago to evaluate patients' responses, the overall regression rate for 94 non-Hodgkin lymphoma patients was 69.2% (complete response [CR] 23.4%). Of 62 patients with Hodgkin disease, 69.4% responded (CR 9.7%). For 39 patients with chronic lymphatic leukemia, the combined complete and partial response rate was 74% (CR 7.7%). Thrombocytopenia was the primary toxicity.

CONCLUSIONS

Uracil mustard is an unmarketed, inexpensive oral alkylating agent that has been effective in the treatment of patients with lymphoma, chronic lymphatic leukemia, and thrombocythemia. Perhaps it should be reevaluated.

DNA sequence selectivity of guanine-N7 alkylation by nitrogen mustards is preserved in intact cells

Nitrogen mustard alkylating agents react with isolated DNA in a sequence selective manner, and the substituent attached to the drug reactive group can impose a distinct sequence preference. It is not clear however to what extent the observed DNA sequence preferences are preserved in intact cells. The highly reiterated sequence of human alpha DNA has been used to determine the sites of guanine-N7 alkylation following treatment of cells with three nitrogen mustards, mechlorethamine, uracil mustard and quinacrine mustard, known to react in isolated DNA with distinctly different sequence preferences. Alpha DNA from drug treated cells was extracted, purified, end-labeled, and a 296 base pair, singly end-labelled, fragment isolated. Following the quantitative conversion of alkylation sites to strand breaks the fragments were separated on DNA sequencing gels. Clear differences were observed between the alkylation patterns of the three compounds, and the selectivities were qualitatively similar to those predicted and observed in the same sequence alkylated in vitro. In particular the unique preferences of uracil and quinacrine mustards for 5'-PyGC-3' and 5'-GT/GPu-3' sequences, respectively, were preserved in intact cells suggesting that the pattern of sequence dependent reactivity is not grossly affected by the nuclear milieu.

Comparative pharmacokinetics of DNA lesion formation and removal following treatment of L1210 cells with nitrogen mustards

The kinetics of formation and removal of DNA interstrand crosslinks (ISC), DNA-protein crosslinks (DPC), and single strand breaks (SSB) by several nitrogen mustards were compared in order to determine the degree to which lesion selectivity may vary. The kinetic measurements using DNA alkaline elution methodology were obtained in mouse L1210 cells treated with mechlorethamine (HN2), phenylalanine mustard (L-PAM), uracil mustard (UM), 6-methyl-UM, and quinacrine mustard (QM). The ISC or DPC challenge delivered to cells was gauged on the basis of the kinetics as either total ISC or DPC produced, or as the area under the lesions versus time curve (AUC). By either measure (excepting QM), ISC correlated well with loss of colony survival, whereas DPC did not. The ISC/DPC ratio may therefore be a useful index of lesion selectivity. This ratio was significantly greater for 6-methyl-UM than for HN2. The ratio was also greater for L-PAM than for HN2 but only when gauged by AUC; this was attributable to an unusually slow rate for ISC removal in the case of L-PAM. The preferential reaction of UM at some 5'-GC-3' sites in purified DNA had suggested that UM might produce ISC with increased efficacy. UM, however, was somewhat less efficacious in ISC production than was 6-methyl-UM, which lacked selectivity for alkylation at 5'-GC-3'. QM was the only compound that produced detectable SSB, and the SSB were so numerous that ISC could not be quantitated.(ABSTRACT TRUNCATED AT 250 WORDS)

DNA sequence selectivity of guanine-N7 alkylation by nitrogen mustards

Nitrogen mustards alkylate DNA primarily at the N7 position of guanine. Using an approach analogous to that of the Maxam-Gilbert procedure for DNA sequence analysis, we have examined the relative frequencies of alkylation for a number of nitrogen mustards at different guanine-N7 sites on a DNA fragment of known sequence. Most nitrogen mustards were found to have similar patterns of alkylation, with the sites of greatest alkylation being runs of contiguous guanines, and relatively weak alkylation at isolated guanines. Uracil mustard and quinacrine mustard, however, were found to have uniquely enhanced reaction with at least some 5'-PyGCC-3' and 5'-GT-3' sequences, respectively. In addition, quinacrine mustard showed a greater reaction at runs of contiguous guanines than did other nitrogen mustards, whereas uracil mustard showed little preference for these sequences. A comparison of the sequence-dependent variations of molecular electrostatic potential at the N7-position of guanine with the sequence dependent variations of alkylation intensity for mechlorethamine and L-phenylalanine mustard showed a good correlation in some regions of the DNA, but not others. It is concluded that electrostatic interactions may contribute strongly to the reaction rates of cationic compounds such as the reactive aziridinium species of nitrogen mustards, but that other sequence selectivities can be introduced in different nitrogen mustard derivatives.

Mutagenicity of cancer chemotherapeutic agents in the Salmonella/microsome test

Seventeen cancer chemotherapeutic agents were tested for their ability to mutate Salmonella typhimurium tester strains in the Salmonella/microsome mutagenicity test. There was a high correlation between the mutagenicity and carcinogenicity of a given agent. Carcinogens positive in the test were Adriamycin, daunomycin, 1-propanol-3,3'-iminodimethanesulfonate, cyclophosphamide, isophosphamide, hycanthone, chlornaphazin, nitrogen mustard, uracil mustard, melphalan, and thio-tepa. Two carcinogesn, actinomycin D and bleomycin, were not detected as mutagens. The presumptive noncarcinogen, methotrexate, was negative in the test. Tilorone and 6-mercaptopurine, tentatively classified as noncarcinogens, were mutagenic. The carcinogenicity of cis-dichlorodiammineplatinum(II), which was positive in the test, has not been determined.

5-Aminouracil treatment. A method for estimating G2

Treatment of Vicia faba lateral roots with a range of concentrations of 5-aminouracil (5-AU) indicate that cells are stopped at a particular point in interphase. The timing of the fall in mitotic index suggests that cells are held at the S - G(2) transition. When cells are held at this point, treatments with 5-AU can be used to estimate the duration of G(2) + mitosis/2 of proliferating cells. Treatment with 5-AU can also be used to demonstrate the presence of subpopulations of dividing cells that differ in their G(2) duration. Using this method, 5-AU-induced inhibition, we have confirmed that in V. faba lateral roots there are two populations of dividing cells: (a) a fast-dividing population, which makes up approximately 85% of the proliferating cell population and has a G(2) + mitosis/2 duration of 3.3 hr, and (b) a slow-dividing population, which makes up approximately 15% of dividing cells and has a G(2) duration in excess of 12 hr. These estimates are similar to those obtained from percentage labeled mitosis (PLM) curves after incorporation of thymidine-(3)H.

Effect of immunosuppressive agents on normal phage-neutralizing antibody in the mouse

The actions of three immunosuppressive drugs on normal antibody synthesis in the adult mouse were determined. Inbred mice were given daily intraperitoneal injections of actinomycin D, uracil mustard, or cyclophosphamide for extended periods. The sera of treated and untreated mice were assayed for phage-neutralizing activity to monitor the effect of each drug on the amount of circulating normal antibody. Except for an initial decrease in titer of normal anti-phage MSP2 activity, actinomycin D had no significant effect on normal antibody activity. Uracil mustard caused alternating elevation and depression of normal antibody titers. Cyclophosphamide caused a prolonged depression of normal antibody. The response patterns to the three immunosuppressive agents were the same for both induced and normal antibody.