Synergism through direct covalent bonding between agents: a strategy for rational design of chemotherapeutic combinations

Self-assembling chemotherapeutic agents are mixtures of relatively nontoxic precursors that can combine chemically under physiological conditions to form products with greater cytotoxic and/or antimicrobial activity than either of the precursors. Combinations that form products more rapidly in or near the target (tumor, pathogen, virally infected cell) than in normal tissues will exhibit target-selective synergism, thus exhibiting an antitarget selectivity that is greater than the selectivities of the product (e.g., a hydrazone) and of either precursor (e.g., a hydrazine derivative or ketone) used singly. This paper describes the target-selective cytotoxic synergism of a cationic aldehyde (A) and a cationic acylhydrazine (B) containing a triarylalkylphosphonium moiety against Ehrlich ascites carcinoma cells (ELA) in culture, in addition to reviewing previous work on self-assembling cytotoxins. The synergism between A and B is carcinoma selective when the ELA cells (the target) are compared to CV-1, an untransformed African green monkey kidney epithelial line. Like tetraphenylphosphonium and rhodamine 123, which are selectively concentrated in ELA cells relative to CV-1, A, B and the hydrazone C resulting from their reaction are lipophilic delocalized cations that selectively inhibit ELA growth relative to CV-1 growth. The hydrazone C is more growth inhibitory than either A or B for both cell lines. A combination of A with an unreactive analogue of B and a combination of B with an unreactive analogue of A did not synergistically inhibit ELA proliferation. The degree of synergism is greater against the ELA cells than against the CV-1 cells. These data, together with hydrazone formation kinetics, suggest that A and B are both concentrated together selectively inside the ELA due to the transmembrane potentials, reacting inside the ELA cells at a higher velocity than inside the CV-1 cells to form the more growth-inhibitory hydrazone C.     

The contribution of N2O3 to the cytotoxicity of the nitric oxide donor DETA/NO: an emerging role for S-nitrosylation

The relationship between the biological activity of NO and its chemistry is complex. The objectives of this study were to investigate the influence of oxygen tension on the cytotoxicity of the NO^• donor DETA/NO and to determine the effects of oxygen tension on the key RNS (reactive nitrogen species) responsible for any subsequent toxicity. The findings presented in this study indicate that the DETA/NO-mediated cytotoxic effects were enhanced under hypoxic conditions. Further investigations revealed that neither ONOO⁻ (peroxynitrite) nor nitroxyl was generated. Fluorimetric analysis in the presence of scavengers suggest for the first time that another RNS, dinitrogen trioxide may be responsible for the cytotoxicity with DETA/NO. Results showed destabilization of HIF (hypoxia inducible factor)-1α and depletion of GSH levels following the treatment with DETA/NO under hypoxia, which renders cells more susceptible to DETA/NO cytotoxicity, and could account for another mechanism of DETA/NO cytotoxicity under hypoxia. In addition, there was significant accumulation of nuclear p53, which showed that p53 itself might be a target for S-nitrosylation following the treatment with DETA/NO. Both the intrinsic apoptotic pathway and the Fas extrinsic apoptotic pathway were also activated. Finally, GAPDH (glyceraldehyde-3-phosphate dehydrogenase) is another important S-nitrosylated protein that may possibly play a key role in DETA/NO-mediated apoptosis and cytotoxicity. Therefore this study elucidates further mechanisms of DETA/NO mediated cytotoxicity with respect to S-nitrosylation that is emerging as a key player in the signalling and detection of DETA/NO-modified proteins in the tumour microenvironment.     

Toxic Effects of Intracerebral PrP Antibody Administration During the Course of BSE Infection in Mice

The absence of specific immune response is a hallmark of prion diseases. However, in vitro and in vivo experiments have provided evidence that an anti-PrP humoral response could have beneficial effects. Prophylactic passive immunization performed at the time of infection delayed or prevented disease. Nonetheless, the potential therapeutic effect of PrP antibodies administered shortly before the clinical signs has never been tested in vivo. Moreover, a recent study showed the potential toxicity of PrP antibodies administered intracerebrally. We aimed at evaluating the effect of a prolonged intracerebral anti-PrP antibody administration at the time of neuroinvasion in BSE infected Tg20 mice. Unexpectedly, despite a good penetration of the antibodies in the brain parenchyma, the treatment was not protective against the development of BSE. Instead, it led to an extensive neuronal loss, strong astrogliosis and microglial activation. Since this effect was observed after injection of anti-PrP antibodies as whole IgGs, F(ab')2 or Fab fragments, the toxicity was directly related to the ability of the antibodies to recognize native PrP and to the intracerebral concentration achieved, and not to the Fc portion or the divalence of the antibodies. This experiment shows that a prolonged treatment with anti-PrP antibodies by the intracerebral route can induce severe side-effects and calls for caution with regard to the use of similar approaches for late therapeutic interventions in humans.     

Related base sequences in the DNA of simple and complex organisms. III. Variability in the base sequence of the reduplicated genes for ribosomal RNA in the rabbit

A comparative study has been made of the arrangement of base sequences in the ribosomal RNA cistrons of Escherichia coliand rabbit DNA. This was accomplished by examination of the thermal stability profiles of DNA/RNA hybrids formed by the two types of ribosomal RNA under various conditions. The thermal stabilities of ribosomal RNA hybrids of rabbit origin are more dependent on the conditions of reaction during the formation and are always lower than those of E. coli RNA. It is concluded that the rabbit ribosomal RNA hybrids are formed mainly from mismatching between RNA molecules and DNA sites other than those from which they were transcribed. Thus, the cluster of ribosomal RNA cistrons in a mammalian DNA, representing a historical series of tandem duplications, exhibits intercistronic base sequence divergence. This research was supported by a research grant from the National Science Foundation (GB 6099) and a predoctoral traineeship (to R.L.M.) from the U.S. Public Health Service.     

Lengthening the human mandible by gradual distraction.

Lengthening of the mandible by gradual distraction was performed on four young patients (average age 78 months). The amount of mandibular bone lengthening ranged from 18 to 24 mm; one patient with Nager's syndrome underwent bilateral mandibular expansion. Following the period of expansion, the patients were maintained in external fixation for an average of 9 weeks to allow ossification. The patients were followed for a minimum of 11 months to a maximum of 20 months with clinical and dental examinations as well as photographic and radiographic documentation. The technique holds promise for early reconstruction of craniofacial skeletal defects without the need for bone grafts, blood transfusion, or intermaxillary fixation.     

Matrix analysis to model the invasion of alligatorweed (Alternanthera philoxeroides) on Kentucky lakes

Aims Alligatorweed (Alternanthera philoxeroides (Mart.) Griseb.) is an invasive species indigenous to South America. With its rapid invasion of southeastern US waterways, understanding the invasiveness of this plant species is critical for providing possible mechanisms of prevention for resource managers. The aim of this project is to use a matrix model to study the invasion dynamics of alligatorweed under both terrestrial and aquatic environments. The use of this model allows for a deeper understanding of the invasiveness and life history–stage structure of alligatorweed. In particular, matrix analysis can further test the hypothesis that certain life stages of alligatorweed might be more sensitive to control and management.Methods A greenhouse experiment was conducted to study the spread of alligatorweed under both aquatic and terrestrial environments. Utilizing the growth data obtained during the summer of 2010, matrix analysis was used to model the growth of alligatorweed for six different treatments. Transition matrices were generated based on plant measurements taken at different life stages defined by the number of leaves or nodes. These matrices are population projection models whose eigenvalues represent the growth rate of alligatorweed. A high growth rate is a key feature of successful invaders. Residuals were calculated and sensitivity analysis was performed to test the accuracy of the model and importance of each life stage over the entire life cycle of alligatorweed.Important findings The results of this study indicate that in the aquatic habitat, plants at their early life cycle stage are most sensitive to potential control measures. Conversely, in the terrestrial habitat, the most sensitive stage of alligatorweed is at its late life cycle stage, characterized with large-sized plants, thus suggesting the best timing for management and eradication of this invasive species.