The expression of sphingosine-1 phosphate receptor-1 in chronic lymphocytic leukemia cells is impaired by tumor microenvironmental signals and enhanced by piceatannol and R406.

Chronic lymphocytic leukemia (CLL) is characterized by the progressive accumulation of clonal B lymphocytes. Proliferation occurs in lymphoid tissues upon interaction of leukemic cells with a supportive microenvironment. Therefore, the mobilization of tissue-resident CLL cells into the circulation is a useful therapeutic strategy to minimize the reservoir of tumor cells within survival niches. Because the exit of normal lymphocytes from lymphoid tissues depends on the presence of sphingosine-1 phosphate (S1P) and the regulated expression of S1P receptor-1 (S1PR1), we investigated whether the expression and function of S1PR1 can be modulated by key microenvironment signals. We found that activation of CLL cells with CXCL12, fibroblast CD40L(+), BCR cross-linking, or autologous nurse-like cells reduces their S1PR1 expression and the migratory response toward S1P. Moreover, we found that S1PR1 expression was reduced in the proliferative/activated subset of leukemic cells compared with the quiescent subset from the same patient. Similarly, bone marrow-resident CLL cells expressing high levels of the activation marker CD38 showed a lower expression of S1PR1 compared with CD38(low) counterparts. Finally, given that treatment with BCR-associated kinase inhibitors induces a transient redistribution of leukemic cells from lymphoid tissues to circulation, we studied the effect of the Syk inhibitors piceatannol and R406 on S1PR1 expression and function. We found that they enhance S1PR1 expression in CLL cells and their migratory response toward S1P. Based on our results, we suggest that the regulated expression of S1PR1 might modulate the egress of the leukemic clone from lymphoid tissues.

A fast, low cost, and highly efficient fluorescent DNA labeling method using methyl green.

The increasing need for multiple-labeling of cells and whole organisms for fluorescence microscopy has led to the development of hundreds of fluorophores that either directly recognize target molecules or organelles, or are attached to antibodies or other molecular probes. DNA labeling is essential to study nuclear-chromosomal structure, as well as for gel staining, but also as a usual counterstain in immunofluorescence, FISH or cytometry. However, there are currently few reliable red to far-red-emitting DNA stains that can be used. We describe herein an extremely simple, inexpensive and robust method for DNA labeling of cells and electrophoretic gels using the very well-known histological stain methyl green (MG). MG used in very low concentrations at physiological pH proved to have relatively narrow excitation and emission spectra, with peaks at 633 and 677 nm, respectively, and a very high resistance to photobleaching. It can be used in combination with other common DNA stains or antibodies without any visible interference or bleed-through. In electrophoretic gels, MG also labeled DNA in a similar way to ethidium bromide, but, as expected, it did not label RNA. Moreover, we show here that MG fluorescence can be used as a stain for direct measuring of viability by both microscopy and flow cytometry, with full correlation to ethidium bromide staining. MG is thus a very convenient alternative to currently used red-emitting DNA stains.

The cytotoxic activity of Aplidin in chronic lymphocytic leukemia (CLL) is mediated by a direct effect on leukemic cells and an indirect effect on monocyte-derived cells.

Aplidin is a novel cyclic depsipeptide, currently in Phase II/III clinical trials for solid and hematologic malignancies. The aim of this study was to evaluate the effect of Aplidin in chronic lymphocytic leukemia (CLL), the most common leukemia in the adult. Although there have been considerable advances in the treatment of CLL over the last decade, drug resistance and immunosuppression limit the use of current therapy and warrant the development of novel agents. Here we report that Aplidin induced a dose- and time-dependent cytotoxicity on peripheral blood mononuclear cells (PBMC) from CLL patients. Interestingly, Aplidin effect was markedly higher on monocytes compared to T lymphocytes, NK cells or the malignant B-cell clone. Hence, we next evaluated Aplidin activity on nurse-like cells (NLC) which represent a cell subset differentiated from monocytes that favors leukemic cell progression through pro-survival signals. NLC were highly sensitive to Aplidin and, more importantly, their death indirectly decreased neoplasic clone viability. The mechanisms of Aplidin-induced cell death in monocytic cells involved activation of caspase-3 and subsequent PARP fragmentation, indicative of death via apoptosis. Aplidin also showed synergistic activity when combined with fludarabine or cyclophosphamide. Taken together, our results show that Aplidin affects the viability of leukemic cells in two different ways: inducing a direct effect on the malignant B-CLL clone; and indirectly, by modifying the microenvironment that allows tumor growth.

Surface localization of high-mobility group nucleosome-binding protein 2 on leukemic B cells from patients with chronic lymphocytic leukemia is related to secondary autoimmune hemolytic anemia.

Chronic lymphocytic leukemia (CLL) is the main cause of autoimmune hemolytic anemia (AHA). However, the cellular basis underlying this strong association remains unclear. We previously demonstrated that leukemic B cells from patients with CLL recognize the erythrocyte protein Band 3, a prevalent autoantigen in AHA. Here we show that the major binding site of Band 3 on leukemic cells is an extrinsic protein identified as high-mobility group nucleosome binding protein 2 (HMGN2), a nucleosome-interacting factor which has not been previously reported at the cell surface. T lymphocytes do not express HMGN2 or bind Band 3. Removal of HMGN2 from the cell membrane abrogated the capacity of Band 3-pulsed CLL cells to induce CD4 + T cell proliferation. We conclude that surface HMGN2 in leukemic B cells is involved in Band 3 binding, uptake and presentation to CD4 + T lymphocytes, and as such may favor the initiation of AHA secondary to CLL.