DNA-directed alkylating agents. 3. Structure-activity relationships for acridine-linked aniline mustards: consequences of varying the length of the linker chain

Four series of acridine-linked aniline mustards have been prepared and evaluated for in vitro cytotoxicity, in vivo antitumor activity, and DNA cross-linking ability. The anilines were attached to the DNA-intercalating acridine chromophores by link groups (-O-, -CH2-, -S-, and -SO2-) of widely varying electronic properties, providing four series of widely differing mustard reactivity where the alkyl chain linking the acridine and mustard moieties was varied from two to five carbons. Relationships were sought between chain length and biological properties. Within each series, increasing the chain length did not alter the reactivity of the alkylating moiety but did appear to position it differently on the DNA, since cross-linking ability (measured by agarose gel assay) altered with chain length, being maximal with the C4 analogue. The in vivo antitumor activities of the compounds depended to some extent on the reactivity of the mustard, with the least reactive SO2 compounds being inactive. However, DNA-targeting did appear to allow the use of less reactive mustards, since the S-linked acridine mustards showed significant activity whereas the parent S-mustard did not. Within each active series, the most active compound was the C4 homologue, suggesting some relationship between activity and extent of DNA alkylation.     

Early cytokine responses during intestinal parasitic infections.

Infections with gastro-intestinal nematodes elicit immune and inflammatory responses mediated by cytokines released from T-helper type-2 (Th2) cells. In vitro assays of cells from the mesenteric lymph nodes (MLN) of experimentally infected rodents confirm that, after about 1 week, the dominant cytokine responses to mitogens and antigens are those associated with this Th-cell subset. Polarization of the Th response in this way implies an initial local cytokine environment that favours Th2 development. However, experimental infections with Trichinella spiralis and Nippostrongylus brasiliensis show that, within 2 days of worms reaching the intestine, MLN cells (MLNC) respond with a Th1 rather than a Th2 response [i.e. there is an increase in mRNA for the type 1 cytokine interferon-gamma (IFN-gamma), and mitogen-stimulated MLNC release IFN-gamma rather than interleukin-5 (IL-5)]. Antigen stimulation at this time does not elicit IFN-gamma release and the MLNC cannot adoptively transfer immunity. Within a few days the MLNC phenotype changes. There is a Th2 response (IL-5 release) to both mitogen and antigen stimulation and MLNC can adoptively transfer immunity. Early release of IFN-gamma is T-cell dependent, with CD4+ T cells playing the major role. The data are discussed in relation to factors regulating the mucosal response to invasion by parasites.     

Genetic control of eosinophilia. Mouse strain variation in response to antigens of parasite origin

Strain variation in capacity to develop peripheral blood eosinophilia was observed in inbred NIH and C57BL/10 (B10) mice exposed to parasite antigens by infection or by parenteral injection in Freund's complete adjuvant. NIH mice were good responders, showing rapid development of high eosinophil counts, B10 mice were low responders. The difference in response phenotype was independent of the parasite used for infection (Trichinella spiralis or Nematospiroides dubius) and of the antigen used for injection (T. spiralis larval antigen or Limulus haemocyanin). Pre-treatment of T. spiralis infected mice with low doses of cyclophosphamide (150 mg/kg) or restriction of the duration of infection to 7 days by anthelmintic treatment did not enhance the response of B10 mice. Thus no evidence was found that the poor response phenotype of B10 during T. spiralis infection reflected any active suppressive mechanisms developed during the adult or muscle larval phases of infection. Demonstration that eosinophilia is induced primarily by the intestinal phase allows comparison with other parameters of the immune response induced by the adult worms, namely intestinal mastocytosis and worm expulsion. From this comparison it is concluded that the low eosinophil response phenotype of B10 mice may reflect a generalized deficiency in the response of bone marrow derived precursor cells to factors of T lymphocyte origin. The significance of genetically determined variation in eosinophil responsiveness is discussed in relation to the development of protective immune or pathological responses to parasite infection.     

Genetic control of eosinophilia. Analysis of production and response to eosinophil-differentiating factor in strains of mice infected with Trichinella spiralis.

Bone marrow cultures were established from mice undergoing parasitic eosinophilia after infection with Trichinella spiralis. In the presence of eosinophil-differentiation factor (EDF/IL-5) eosinophil precursor cells differentiated and could be identified and counted after a 7-day in vitro culture period. The EDF-bone marrow assay system was used to determine differences in bone marrow eosinophil precursor capacity between a number of inbred strains of mice. Bone marrow cultures from high peripheral eosinophil-response phenotype strains of mice (NIH, SWR & SJL) contained significantly greater numbers of eosinophil precursor cells than the low response strain C57BL/10. All congenic strains of mice with the B10 background, i.e. C57BL/10, B10.S, B10.BR and B10.G were found to have low eosinophil precursor capacity. Bone marrow cultures obtained from F1 hybrids (NIH x C57/BL10, SJL x C57/BL10 and SWR x C57BL/10) demonstrated high precursor numbers, indicating that low responsiveness is inherited as a recessive characteristic. When spleen cells from T. spiralis-infected, high and low responder strains of mice were stimulated in vitro with concanavalin A (Con A) or with parasite antigen, it was found that low responder phenotype strains produced quantities of two eosinophilopoietic lymphokines EDF and IL3, which were similar to, if not greater than high responder strains. This suggests that bone marrow precursor capacity and not T cell lymphokine release is an important limiting factor in determining strain-dependent eosinophilia.     

L3T4-positive T lymphoblasts are responsible for transfer of immunity to Trichinella spiralis in mice

The characteristics of lymphocyte subpopulations involved in mediating immunity to the intestinal nematode Trichinella spiralis in vivo have been examined using adoptive transfer in conjunction with accurate cell-sorting and cell-depletion techniques. Positive selection of cell subsets, using FACS sorting and velocity sedimentation at unit gravity, confirm that rapidly dividing T blasts are the major population that mediates expulsion of the worm from the gut. Furthermore, cell-depletion studies demonstrated that the T-cell subset involved is of the L3T4 + ve Lyt 2-ve phenotype. This phenotype suggests class II MHC restriction in recognition of T. spiralis antigens by T cells in vivo. The roles that such T cells play in immunity to T. spiralis are discussed in terms of lymphokine release.     

Kinetic studies of the binding of acridinecarboxamide topoisomerase poisons to DNA: implications for mode of binding of ligands with uncharged chromophores

We have used stopped-flow spectrophotometry and the sodium dodecyl sulfate sequestration technique to study the kinetics of dissociation of DNA complexes of the mixed topoisomerase I/II poison N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (termed DACA) and a range of related linear tricyclic carboxamides with neutral chromophores. Complexes of DACA and related acridine and phenazinecarboxamides bearing an N,N-dimethylaminoethyl side chain dissociate from calf thymus DNA by a kinetic pathway involving four discernible steps in a manner similar to complexes of N-[(2-dimethylamino)ethyl]-9-aminoacridine-4-carboxamide (termed 9-amino-DACA). We infer from these findings that the side chains of DACA, its phenazine homologue, and 9-amino-DACA make comparable interactions with the DNA base pairs. In the case of 9-amino-DACA, a selective topoisomerase II poison, these are known, by crystallographic analysis, to involve hydrogen-bonding interactions between the protonated dimethylammonium group of the side chain and the O6/N7 atoms of guanine and to include a bridging water molecule hydrogen bonded to the carboxamide group and a phosphate oxygen. By contrast, we find that other linear tricyclic carboxamides with neutral chromophores which lack a peri nitrogen atom and are biologically inactive dissociate from DNA by a different mechanism in which it appears their side chains fail to interact with guanine. We conclude that the ability of the carboxamide group to lie preferentially in the plane of the chromophore, so facilitating the dimethylammonium-guanine hydrogen bond and ensuring maintenance of the water-bridged carboxamide-phosphate interaction, is a critical requirement for antitumor activity among ligands of the linear tricyclic carboxamide class. However, unlike the situation for 9-amino-DACA, for ligands with uncharged chromophores containing peri nitrogen atoms such as DACA, this outcome is possible with the 4-carboxamide group rotated cis or trans with respect to the ring nitrogen. This difference may have relevance to the ability of DACA to be a dual poison of both topoisomerases I and II.