Role of a small molecular weight phosphoprotein in the mechanism of action of CI-994 (N-acetyldinaline).

The mechanism of action of the novel anti-cancer compound CI-994 was studied in C26 murine colon tumor and HCT-8 human colon adenocarcinoma cells. Treatment of either cell line resulted in the specific loss of a 16-kDa phosphoprotein in a time- and concentration-dependent manner. Treatment with salicylanilide, CI-940, mimosine, aphidicolin, quercetin or ciclopirolxalamine, which, like CI-994, block cells in the G1-S phase of the cell cycle, did not affect the production of this protein. Loss of the 16-kDa protein preceded the block in cell proliferation induced by CI-994 treatment, and recovery of this protein was evident prior to the resumption of cell growth. Cellular fractionation studies demonstrated that the 16 kDa phosphoprotein is confined to the nuclear compartment. Our data indicate that loss the 16-kDa nuclear phosphoprotein appears to be a direct effect of CI-994 treatment and that the inhibition of this phosphoprotein may play a critical role in the mechanism of action of CI-994.

Future paradigm for autologous bone marrow transplantation: tumor purging and ex vivo production of normal stem and progenitor cells.

A major concern in autologous bone marrow transplantation (ABMT) is the possible contamination of the graft with tumor cells. Transplantation of malignant cells, along with normal hematopoietic stem and progenitor cells, may contribute to relapse of disease. Therefore, a growing strategy is to subject autologous marrow to some type of purging procedure to eliminate tumor cells selectively. Transplantation of purged marrow, however, often results in a delayed engraftment associated with (specific or nonspecific) loss of normal stem and progenitor cells during manipulations related to the purging process. A new and burgeoning field in the area of clinical bone marrow transplantation is the ex vivo production of stem and progenitor cells. Several advantages accrue to this strategy. First, this technology makes it possible to expand the stem and progenitor cell population of a small volume of bone marrow or mobilized peripheral blood (MPB), thus lessening the initial tumor burden to be purged. Secondly, ex vivo marrow or MPB expansion may overcome the significant problem of delayed engraftment by rebuilding the numbers of normal stem and progenitor cells necessary for both early and durable engraftment. To accomplish these and other objectives, an automated and closed, clinical-scale bioreactor system, based on continuous perfusion technology, is being developed and will soon enter clinical trials.

Expansion in bioreactors of human progenitor populations from cord blood and mobilized peripheral blood.

Umbilical cord blood (UCB) and mobilized peripheral blood (MPB) provide an alternate source to bone marrow for transplantation. Expansion in vitro of stem/progenitor cell populations from these sources may provide adult-sized grafts otherwise not attainable because of the limited cell numbers available in the case of UCB or because of numerous rounds of apheresis required for sufficient MPB cells. We asked whether continuous perfusion culture could be employed in ex vivo expansion to produce clinically relevant numbers of stem/progenitor cells from these sources. To evaluate MPB, 1-10 million leukocytes, from patients who had received either granulocyte colony-stimulating factor (G-CSF) or cyclophosphamide and granulocyte-macrophage colony-stimulating factor (GM-CSF), were inoculated into bioreactors, with or without irradiated, allogeneic stroma. The growth factor combination in the perfusion medium consisted of interleukin-3 (IL-3), stem cell factor (SCF), GM-CSF and erythropoietin (Epo). Under the best conditions tested, total cell numbers, granulocyte-macrophage colony-forming units (CFU-GM), and long-term culture-initiating cell (LTC-IC) populations were expanded by about 50-, 80-, and 20-fold, respectively, over 14 days. At low cell inocula (1 million), the presence of stroma enhanced the expansion of total cells and CFU-GM but not of LTC-IC. When SCF was not included in the medium, both total cells and CFU-GM expanded to a much lesser extent, but again the expansion of LTC-IC was not affected. At the higher cell inoculum (10 million), expansions of total cells and CFU-GM were equivalent with or without stroma. To evaluate UCB, cells were placed into bioreactors with or without irradiated, allogeneic stroma, and the bioreactors were perfused with medium containing the four standard growth factors. After 6-14 days, in several independent experiments, 20-24 million cells were harvested from bioreactors perfused with SCF-containing medium, irrespective of the presence or absence of preformed stroma. Similarly, in reactors perfused with SCF-containing medium (with or without stroma), an average 40- to 60-fold expansion of CFU-GM was obtained, yielding an average of 1.5-1.8 x 10(5) CFU-GM per reactor. Harvested cells were thus up to 40-fold enriched in CFU-GM in comparison to the inoculum. In the absence of SCF, cell expansions averaged 1.5- to 2-fold, and CFU-GM were expanded only 10- to 14-fold by day 14. As before, the presence of preformed stroma did not affect either cell or CFU-GM yields, provided the cell inoculum was at least 4.5 million cells.(ABSTRACT TRUNCATED AT 400 WORDS)

N-methyl-N-nitrosourea alters thymocyte subset distribution and targets immature CD4-8+ cells for lymphoma development.

The majority of N-methyl-N-nitrosourea (MNU)-induced lymphomas in AKR/J mice express a CD4-8+ phenotype. The CD4-8+ subset in normal thymus contains functionally mature medullary cells and immature cycling cells. This study demonstrates that MNU-induced lymphomas correspond to the immature CD4-8+ subset. In addition, specific changes in the distribution of thymocyte subsets defined by CD4 and CD8 expression were observed after MNU treatment. Cortical thinning and selective depletion of immature CD4-8+ and CD4+8+ subsets occur immediately after treatment. In contrast, immature CD4-8- progenitors and mature medullary CD4+8- and CD4-8+ subsets are relatively resistant to cytotoxicity. Normal thymic architecture and subset distribution are restored within 2 weeks after which selective expansion of the immature CD4-8+ subset occurs. The data suggest that MNU induces neoplastic conversion in progenitor cells corresponding to the CD4-8- or immature CD4-8+ stages of thymocyte maturation.

Coated vesicles from developing and adult rat skeletal muscles contain multiple molecular forms of acetylcholinesterase.

The main purpose of this work was to determine which of the multiple isoforms of acetylcholinesterase (AChE) are associated with clathrin-coated vesicles (CVs) from developing and adult rat skeletal muscles. CV-enriched preparations were obtained by subcellular fractionation/equilibrium sedimentation and further purified by immunoadsorption to anti-clathrin IgG-coated Staphylococcus aureus cells. Analysis of individual AChE isoforms by velocity sedimentation ultracentrifugation showed that a) while both globular (G-forms) and asymmetric (A-forms) AChE were detected in all subcellular fractions evaluated, the CV-enriched fraction contained a higher proportion of A-forms (mainly the A12 species); b) most of the AChE activity contained in such a CV fraction was recovered following immunoadsorption; c) alkaline extraction conditions (pH 8.5) which depolymerize clathrin were necessary to detect a large proportion of A-forms in both the CV-enriched and immunoprecipitated preparations, while most of the G-forms (especially G1 + G2 AChE) were detected following extraction at pH 6.8; and d) comparison of AChE isoform profiles from neonate and adult muscle CV-enriched fractions showed a greater concentration of A-forms in the former. These data suggest that considerable amounts of A12 and, to a lesser extent, G4 AChE are sequestered within muscle CVs which may be destined for the plasmalemma. Our findings also indicate that the relative proportions of AChE isoenzymes in rat muscle CVs vary according to the extent of muscle development and lend support to the contention that CVs participate in the externalization of functionally important AChE isoenzymes.