Pharmacologic characterization of the antiinflammatory properties of a new dual inhibitor of lipoxygenase and cyclooxygenase.

SK&F 86002 [6-(4-fluorophenyl)2,3-dihydro-5-(4-pyridinyl)imidazo (2,1-b)thiazole], a dual inhibitor of arachidonic acid metabolism, administered orally to rats prevented the development of carrageenan-induced edema, immune- and nonimmune-mediated inflammation of adjuvant-induced arthritis (AA) and reduced established inflammation in AA and collagen type II-induced arthritis. A similar profile of activity was observed following treatment with the cyclooxygenase inhibitor, indomethacin. However, unlike other nonsteroidal antiinflammatory drugs, SK&F 86002 exhibited antiinflammatory activity in inflammation models that are insensitive to cyclooxygenase inhibitors such as the established inflammation in carrageenan-induced edema and the edema induced by arachidonic acid and platelet activating factor. Moreover, SK&F 86002, but not indomethacin, inhibited the immune-mediated inflammatory responses evoked in sensitized animals by challenge with purified protein derivative. In addition, SK&F 86002 produced dose-related analgesia in mice, which was not reversed by the narcotic antagonist, naltexone. SK&F 86002 thus represents an orally active antiarthritic and analgesic compound with novel antiinflammatory properties.

Pathogenesis of metastatic disease: implications for current therapy and for the development of new therapeutic strategies.

Different tumor cell subpopulations coexisting within the same tumor exhibit varied susceptibilities to antineoplastic agents. Tumor cell heterogeneity is now recognized as the principal cause of treatment failure in cancer, and is a formidable obstacle to effective therapy and to the development of drug delivery systems for selective targeting of antineoplastic agents to tumor cells. Recent insights into the genesis of tumor cell heterogeneity during progressive tumor growth reveal new complexities that raise challenging questions about the adequacy of certain approaches to the current therapy of metastatic disease and impose challenging criteria for the development of improved therapeutic strategies. Many of the experimental approaches used in the search for new antineoplastic agents and targeted drug delivery systems ignore the pathogenesis of metastasis and the problem of tumor cell heterogeneity. The adoption of more relevant assay systems is an urgent priority. These include the greater use of metastatic tumor models and the increased use of human tumor cells to replace rodent cell systems which have been of limited predictive value in identifying effective anticancer agents. In contrast to current strategies for the development of new antineoplastic drugs which seek to identify agents with activity against a broad range of histologically diverse tumors, greater success may be achieved by seeking agents active only against specific cell lineages. Many established human tumor cell lines may not be suitable for this purpose because of extensive phenotypic change produced by prolonged passage ex vivo. Development of histiotype-specific human tumor cell screens will require an extensive research effort to identify target cells that display demonstrable phenotypic relatedness to tumor cells in neoplastic lesions. Major advances in the therapy of metastatic disease are considered unlikely in the next few years, and progress will stem from improved use of existing agents in refined combination therapy protocols in which greater attention is given to the duration, frequency, and sequence of therapy with different agents to limit emergence of tumor cell variants resistant to one or more antineoplastic agents. Advances in molecular biology offer exciting prospects for the identification of new therapeutic targets in human tumor cells, for the induction of alterations in tumor cells that could serve as therapeutic targets, and for the elucidation of the mechanisms responsible for the rapid phenotypic diversification of tumor cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Experimental systems for analysis of the malignant phenotype.

Identification of the cellular and subcellular alterations responsible for the metastatic behavior of malignant tumor cells and development of reliable screening programs for detecting new therapeutic agents for improved treatment of metastatic disease both depend crucially on the availability of experimental systems that can serve as relevant models of human cancer. Recent advances in our understanding of the pathogenesis of cancer metastasis have raised serious doubts about the usefulness of many of the experimental approaches that have long been used in the study of metastasis. Recent findings showing that metastases are caused by specific subpopulations of metastatic tumor cells, and that not all cells in a malignant primary tumor possess metastatic properties, are of profound importance for experimental efforts to understand the mechanism of metastatic phenotype among cells from the same tumor means that the traditional, and widely used, approach of analyzing primary tumors and cultured cell lines containing multiple, phenotypically heterogeneous, subpopulations of cells may provide little or no insight into the properties of the metastatic subpopulations, particularly if they represent only a minor fraction of the entire population. Similarly, the practice of screening potential therapeutic modalities for their ability to reduce the mass and/or growth rate of a primary tumor may be inadequate in predicting the responsiveness of metastatic lesions. Solution of these problems requires that new methods must be devised to isolate and characterize the specific subpopulations of tumor cells endowed with metastatic potential. In addition, knowledge of how the extraordinary phenotypic diversity found in tumor cell subpopulations from the same tumor is generated and how subpopulation diversity is regulated during progressive growth of both the primary tumor and its metastases are of fundamental importance if we are to design meaningful experimental systems for studying the metastatic process. This article reviews our current understanding of these complex issues and their implications for the experimental analysis of the malignant phenotype. The merits and shortcomings of different experimental systems are discussed in detail together with the identification of areas in which new experimental strategies and models are now needed.'

On the genesis and regulation of cellular heterogeneity in malignant tumors.

The growing body of evidence showing that malignant tumors are heterogeneous and contain diverse subpopulations of cells with different metastatic abilities is reviewed. The factors that may influence the evolution of cellular diversity at different stages in the progression of malignant neoplasms are discussed. Particular emphasis is given to the possibility that interactions occurring between the constituent subpopulations of a malignant tumor may influence the rate at which new variant subpopulations emerge. Metastatic heterogeneity poses significant problems for experimental efforts to identify the cellular features that correlate with metastatic behavior and for the therapy of metastatic disease.