A pharmacokinetic study of prednimustine as compared with prednisolone plus chlorambucil in cancer patients

Population pharmacokinetics identifies rapid gastrointestinal absorption and plasma clearance of oral chlorambucil administered to cats with indolent lymphoproliferative malignancies

OBJECTIVE

To establish the pharmacokinetics of a single 2-mg oral dose of chlorambucil in cats with indolent lymphoproliferative malignancies.

ANIMALS

24 client-owned cats.

PROCEDURES

Cats were assigned to 1 of 4 groups, with each group having a total of 3 sample collection time points over 12 hours after receiving a single 2-mg oral dose of chlorambucil. Each time point combined to generate 6 full patient plasma chlorambucil concentration-time curves from the 24 cats. Chlorambucil treatment was continued every other day and a single, variably timed sample collection was obtained on day 14. Population parameter estimates were obtained by nonlinear mixed-effects modeling. Covariates investigated included age, sex, baseline serum cobalamin, study location, weight, and body condition score.

RESULTS

Chlorambucil administered orally to cats was found to have a peak plasma concentration of approximately 170 ng/mL (SE, 31.1 ng/mL), percent coefficient of variation (%CV) of 18.4% within 15 minutes, and a terminal half-life of 1.8 hours (SE, 0.21 hour; %CV, 12.4). At the 4-hour mark, a smaller secondary peak in plasma chlorambucil was found. Day 14 samples were similar to those of the initial dose. No covariates showed a significant effect in the population model.

CLINICAL RELEVANCE

In these cats, chlorambucil at a 2-mg dose administered every other day undergoes rapid gastrointestinal absorption and plasma clearance with no drug accumulation between doses. These data are critical to inform future work investigating the association of chlorambucil drug exposure with adverse events and outcome of cats with lymphoproliferative diseases.

Reactions of {4-[Bis(2-chloroethyl)amino]phenyl}acetic Acid (Phenylacetic Acid Mustard) with 2′-Deoxyribonucleosides

Phenylacetic acid mustard (PAM; 2), a major metabolite of the anticancer agent chlorambucil (CLB; 1), was allowed to react with 2'-deoxyadenosine (dA), 2'-deoxyguanosine (dG), 2'-deoxycytidine (dC), 2'-deoxy-5-methylcytidine (dMeC), and thymidine (T) at physiological pH (cacodylic acid, 50% base). The reactions were followed by HPLC and analyzed by HPLC/MS and/or (1)H-NMR techniques. Although the predominant reaction observed was hydrolysis of PAM, 2 also reacted with various heteroatoms of the nucleosides to give a series of products: compounds 5-31. PAM (2) was found to be hydrolytically slightly more stable than CLB (1). The principal reaction sites of 2 with dA, dG, and with all pyrimidine nucleosides were N(1), N(7), and N(3), resp. Also, several other adducts were detected and characterized. There was no significant difference in the reactivity of 1 and 2 with dG, dA or T, but the N(3) dC-PAM adduct was deaminated easier than the corresponding CLB derivative. The role of PAM-2'-deoxyribonucleoside adducts on the cytotoxic and mutagenic properties of CLB (1) is discussed.

Polymyxin permeabilization as a tool to investigate cytotoxicity of therapeutic aromatic alkylators in DNA repair-deficient Escherichia coli strains

Chlorambucil (CLB; N,N-bis(2-chloroethyl)-p-aminophenylbutyric acid) and its biologically active beta-oxidation product phenylacetic acid mustard (PAM; N,N-bis(2-chloroethyl)-p-aminophenylacetic acid) are bifunctional aromatic alkylators. CLB is in wide clinical use as an anticancer drug and also as an immunosuppressant. The chemical structures indicate that CLB and PAM are mutagenic, teratogenic and carcinogenic, but the mode of action has remained obscure. We have investigated the biological effects of CLB and PAM with DNA repair-deficient Escherichia coli strains. In contrast to MNNG (N-methyl-N'-nitro-N-nitrosoguanine), CLB and PAM were not toxic to E. coli, but permeabilization of the outer membrane of the cells through use of polymyxin B nonapeptide (PMBN) rendered them susceptible to these compounds. The importance of DNA repair, shown by reversal of damage and attenuation of the toxicity of CLB and PAM, was indicated by the susceptibility of cells lacking O(6)-methylguanine-DNA methyltransferase I and II (ada ogt). Similarly, the protective role of base excision repair (BER) was substantiated by demonstration of an even more increased susceptibility to CLB and PAM of cells lacking 3-methyladenine-DNA glycosylase I and II (alkA1 tag-1). Cells deficient in mismatch repair (mutS) appeared to be slightly more sensitive than normal cells to CLB and PAM, although no such sensitivity to MNNG was observed. This implicates the role of mismatches in CLB- and PAM-related cytotoxicity. It is generally believed that bifunctional alkylating agents, like CLB and PAM, exert their cytotoxic action via DNA cross-linking. Our results with O(6)-methyltransferase- and 3-methyladenine-DNA glycosylase-deficient cells indicate that removal of the adducts prior to the formation of cross-links is an important mechanism maintaining cell viability. We conclude that PMBN permeabilization provides a valuable tool to investigate genetically engineered E. coli cells, whose outer membrane is not naturally permeable to mutagens or other interesting compounds.

Mitoxantrone, prednimustine, and vincristine for elderly patients with aggressive non-Hodgkin's lymphoma

Elderly patients with intermediate- or high-grade non-Hodgkin's lymphoma have a worse outcome than those who are younger than 60 years. It has been shown that aggressive combination chemotherapy is poorly tolerated in older patients resulting in a subsequent decrease in dose intensity. A phase II trial was conducted with mitoxantrone, prednimustine, and vincristine (NSO) in this group of patients. NSO consists of mitoxantrone 12 mg/M2 intravenously on day one, vincristine 1.4 mg/M2 intravenously on day 1 (maximum dose of two mg), and prednimustine 100 mg/M2 orally once a day for four days. NSO was repeated every 21 days. Thirty-six patients were able to be evaluated. There were 18 males and 18 females with the median age of 71 (range 60-85). NSO was well tolerated and nonhematological toxicities were uncommon. More than 80% of the patients received 90% or greater of the intended dose. The complete response rate was 60.6% and partial response was 21.8%. At 60 months the Kaplan-Meier estimate of progression-free survival was 47.9% (standard error 8.6%) and actual survival was 40.6% (standard error 8.8%). There were no differences in outcome between those with performance status (PS) of zero or one and those with PS > 1. NSO is well tolerated by elderly patients including those with PS > 1. These results compare favorably with other combinations in elderly patients with aggressive non-Hodgkin's lymphoma.