COX-2 expression in fibroblast aggregates as a functional indicator for the anti-inflammatory activity of leukemia patients' bone marrow-derived hematopoietic cells.

Reciprocal communication between hematopoietic cells and their surrounding bone marrow stroma is crucial for normal progression of hematopoiesis. This complex network of cell-to-cell signals in the microenvironment involves both cell contact-mediated and paracrine cues. In hematological malignancies the intricate balance is, however, disrupted to support cancer progression. In order to detect altered microenvironmental reactivity of a hematopoietic cell sample, cellular functional assays can be designed to measure the cells' capacity to modulate stromal stress reactions, such as inflammation.Recently, we showed that human leukemic cell lines of monocytic origin can actively participate in modulation of stromal inflammation. In order to further functionally evaluate the hematopoietic cells' capacity to modulate stromal inflammation, we utilized an in vitro model of nemosis-induced inflammation of fibroblasts in a three-dimensional culture setting. This process of stromal inflammation in fibroblast aggregates is consistent, requires both cell-contact and paracrine signals, and can be produced on a large scale to support dose-dependent analyses. To extend our previous observations, we evaluated the effect of a wide panel of leukemia cell lines on cyclooxygenase- 2 induction in fibroblast aggregates in co-culture. We also assessed the feasibility of the model to support clinical functional testing by utilizing the hematopoietic fraction of leukemia patients' bone marrow aspirates after immunophenotyping. Our results suggest that the stromal inflammation-modulating activity of these samples is differently modulated in cancer and in normal bone marrow. Moreover, differences in the samples' anti-inflammatory activity may reflect disease state.

Leukemic cells modulate induction of COX-2 in human stromal fibroblasts.

The interaction of cancer cells with surrounding normal tissue cells is of utmost importance for their survival and tumor progression. For these purposes the cancer cells exploit normal tissue responses associated with inflammation and tissue repair. In the immediate tumor microenvironment one of the early stromal markers is cyclooxygenase-2 (COX-2). In this study we evaluated the effect of leukemia cell lines on nemosis-induced COX-2 expression in stromal fibroblasts. We found that THP-1 cells were the most potent leukemic cells (IC50=746) to suppress COX-2 expression. The U-937 cell line exhibited similar suppressive potency (IC50=921), whereas the KG-1 cell line (IC50=3519) was the least potent to affect COX-2 expression in the stromal cells. Our study shows that human leukemic cells can actively participate in modulation of stromal inflammation via inhibition of COX-2 expression. In a co-culture model of leukemia cell lines and stromal fibroblasts, our data suggest that the tumor-stromal interactions are complexly regulated, and the straightforward association of COX-2 expression with tumor progression may require re-evaluation since some tumor cells, e.g. from hematologic malignancies, may differentially modulate inflammation and COX-2 expression.