Transcriptomic profiles of tissues from rats treated with anticancer drug combinations.

To achieve therapeutic goals, many cancer chemotherapeutics are used at doses close to their maximally tolerated doses. Thus, it may be expected that when therapies are combined at therapeutic doses, toxicity profiles may change. In many ways, prediction of synergistic toxicities for drug combinations is similar to predicting synergistic efficacy, and is dependent upon building hypotheses from molecular mechanisms of drug toxicity. The key objective of this initiative was to generate and make publicly available key high-content data sets for mechanistic hypothesis generation as it pertains to a unique toxicity profile of a drug pair for several anticancer drug combinations. The expectation is that tissue-based genomic information that are derived from target tissues will also facilitate the generation and testing of mechanistic hypotheses. The view is that availability of these data sets for bioinformaticians and other scientists will contribute to analysis of these data and evaluation of the approach.

Toxicogenomics profiling of bone marrow from rats treated with topotecan in combination with oxaliplatin: a mechanistic strategy to inform combination toxicity.

Combinations of anticancer agents may have synergistic anti-tumor effects, but enhanced hematological toxicity often limit their clinical use. We examined whether "microarray profiles" could be used to compare early molecular responses following a single dose of agents administered individually with that of the agents administered in a combination. We compared the mRNA responses within bone marrow of Sprague-Dawley rats after a single 30 min treatment with topotecan at 4.7 mg/kg or oxaliplatin at 15 mg/kg alone to that of sequentially administered combination therapy or vehicle control for 1, 6, and 24 h. We also examined the histopathology of the bone marrow following all treatments. Drug-related histopathological lesions were limited to bone marrow hypocellularity for animals dosed with either agent alone or in combination. Lesions had an earlier onset and higher incidence for animals given topotecan alone or in combination with oxaliplatin. Severity increased from mild to moderate when topotecan was administered prior to oxaliplatin compared with administering oxaliplatin first. Notably, six patterns of co-expressed genes were detected at the 1 h time point that indicate regulatory expression of genes that are dependent on the order of the administration. These results suggest alterations in histone biology, chromatin remodeling, DNA repair, bone regeneration, and respiratory and oxidative phosphorylation are among the prominent pathways modulated in bone marrow from animals treated with an oxaliplatin/topotecan combination. These data also demonstrate the potential for early mRNA patterns derived from target organs of toxicity to inform toxicological risk and molecular mechanisms for agents given in combination.

Nonclinical safety assessment of a synthetic peptide thrombopoietin agonist: effects on platelets, bone homeostasis, and immunogenicity and the implications for clinical safety monitoring of adverse bone effects.

RWJ-800088 is a novel, potent polyethylene glycol (PEG)-conjugated thrombopoietin (TPO) mimetic that increases platelet levels and protects against thrombocytopenia. A nonclinical safety program was customized for this peptide that takes into account its protein-like structure, synthetic chemical nature, agonist pharmacologic activity, and mode of administration. In repeat-dose toxicity studies, the salient findings were dose-related increases in circulating platelet counts, mean platelet volume, and megakaryocytes in the bone marrow with no antibody formation. Reversible myelofibrosis and hyperostosis were observed in rats, but not dogs, when the circulating platelet levels exceeded 3× those of vehicle controls. The bone effects were due to the exaggerated pharmacologic effect and excessive stimulation and elevation of megakaryocytes by TPO, which results in intramedullary proliferation of fibroblasts and mesenchymal cells followed by osseous metaplasia. These findings support the use of platelet elevations of >3× as a stopping criterion to prevent potential adverse bone-related effects in humans.

Unexpected nasal changes in rats related to reflux after gavage dosing.

In a three-week oral gavage toxicity study in rats, a high incidence of respiratory symptoms and high mortality was noted in compound-dosed rats only. Because of audible respiration, an effect in the upper respiratory tract was suspected and the nasal cavity was included for examination. Histology revealed extensive necrosis and purulent inflammation within the nasal passages, indicative of direct irritation. Since posterior nasal regions were most affected, with food material present within the inflammatory exudates, reflux and retrograde aspiration of irritant material (possibly stomach contents with test formulation) into the nasal cavity were suspected. Lowering the dose volume and fasting the rats prior to gavage dosing substantially reduced the respiratory effects and mortality. The current article focuses on the histological changes in the nasal cavity indicative of gavage-related reflux and provides guidance on differentiation between technical gavage error and gavage-related reflux.

Gavage-related reflux in rats: identification, pathogenesis, and toxicological implications (review).

After oral gavage dosing of rats, reflux may occur, resulting in serious respiratory effects and mortality. Published information on gavage-related reflux is limited, as it has not yet been a focus of research. Nevertheless, it represents a recurrent challenge in daily toxicology practice of oral gavage dosing. The absence of clear guidance and criteria for the identification and management of reflux-induced effects can limit the ability to properly interpret toxicity study results. The review presented herein includes an overview of experimental data from gavage studies in rats, in which reflux was observed, and provides a comprehensive analysis of the literature on reflux in general and the different potential pathways contributing to gavage-related reflux in rats. The article aims to increase the awareness and understanding of the pathogenesis of gavage-related reflux and provides guidance on identification of potential risk factors, as well as interpretation of histological changes and their toxicological relevance. Furthermore, differentiation of reflux-induced effects from direct compound-related toxicity and from gavage errors is addressed in particular, and the importance of nasal histology is discussed.