Hairy cell leukaemia: effects of phorbol ester on cell morphology and adherence and comparison with other B-cell neoplasias

12-0-Tetradecanoyl Phorbol-13-Acetate (TPA) and Its Effect on Leukaemic Cells, In-vitro-A Review

The action of the promoting agent 12-0-tetradecanoyl phorbol-13-acetate (TPA), an active component of croton oil, on the cell membrane, is described. TPA primarily acts on Protein Kinase C (PKC), which is the prime target for this agent. PKC activation and calcium mobilization are the basic pathways for signal transduction and the regulation of differentiation, explaining how TPA affects cell growth and proliferation in some cell types. The effects of TPA on leukaemic cells in-vitro, is reviewed and the changes in cell surface features, membrane phenotype, regulation of growth and differentiation in leukaemic cells and particularly in B-cell neoplasias are described and discussed in detail. The importance of incubation of leukaemic cells with TPA, as a routine in-vitro test in leukaemia is emphasized, in the light of information reported in this review.

Interferon alpha and intracytoplasmic free calcium in hairy cell leukemia cells

Hairy cell leukemia (HCL) is a B-cell tumor affecting the pre-plasma stage of B cell differentiation. One of the most striking characteristics of this disease is its remarkable responsiveness to alpha-interferon (IFN-alpha) therapy. Interferons constitute a heterologous family of multifunctional cytokines displaying anti-viral, anti-proliferative and immunoregulatory properties. These activities have been extensively studied in hairy cells, but the mechanism of action of IFN-alpha in hairy cell leukemia remains unknown. Our approach to investigate the mode action of IFN-alpha in HCL has been to identify abnormalities which occur in these tumor cells and then to ascertain whether these abnormalities can be rectified by IFN-alpha treatment. A high level of free Ca2+ in the cytoplasm of hairy cells was identified. Increases in cytosolic Ca2+ are believed to be a pivotal signal in regulating cell proliferation, cell differentiation and cell death. These high Ca2+ levels in hairy cells could be reduced upon treatment with IFN-alpha either in vitro or in vivo, probably acting by reducing Ca2+ influx into the leukemic cells. Moreover, the effect of IFN-alpha on [Ca2+]i seems to be correlated with down-regulation of CD20 phosphorylation, a B cell specific phosphoprotein involved in Ca2+ influx across the plasma membrane. The possible origins and implications of Ca2+ deregulation and the possible mechanisms or sites of action of IFN-alpha in tumor cells from HCL are explored in this review.

Induction of plasmacytoid and hairy cell features by phorbol esters (TPA) in B-lymphoma cells: attempted correlation with disease activity

Mononuclear cells concentrated from the blood of 16 non-Hodgkin's lymphoma (NHL) patients in the leukemic phase, were exposed to 10 ng/ml of TPA in an attempt to induce differentiation. Immunoglobulin (Ig) secretion, surface markers (SmIg, GP-70), tartrate resistant acid phosphatase (TRAP) and surface features were followed for up to six days in vitro. TPA induced 'hairy cell' like features in NHL cells as defined by cell morphology, ultrastructure, cell surface markers and the presence of TRAP. Unlike the results obtained in patients with CLL, cells from different patients at the same stage of disease reacted in a similar way. Differences were evident between NHL mononuclear cells obtained from patients in partial remission and active disease when compared with those derived from patients in complete remission. In the former group, NHL cells were maximally induced by TPA to secrete Ig and higher proportions of TRAP positive cells. In addition hairy cell features as seen by light and scanning electron microscopy were also more pronounced. TPA also induced the maximal expression of SmIg and GP-70 in cells derived from patients in this group. Patients with NHL in leukemic phase in complete remission did not express surface membrane GP-70 before or after TPA treatment while SmIg was expressed to some degree before TPA treatment and further induced following treatment with TPA. GP-70 appears to be a more reliable marker for follow-up of NHL patients than any other marker studied here.

Expression of tartrate-resistant acid phosphatase in B-CLL treated with phorbol ester or phorbol ester plus calcium ionophore

Cells from 3 patients with B-chronic lymphocytic leukaemia (B-CLL) and 1 with B-prolymphocytic leukaemia (B-PLL) were treated in vitro with the phorbol ester 12-0-tetradecanoylphorbol (TPA), the calcium ionophore A23187, or a combination of TPA and A23187. TPA induced the cells to adhere to the culture flask or to clump in dense clusters; single cells became enlarged, often with cytoplasmic elongations. Cells treated with TPA plus A23187 acquired a plasmacytoid morphology and formed regular aggregates in culture. Only TPA alone induced the expression of tartrate-resistant acid phosphatase (TRAP) as documented by isoelectric focusing on horizontal thin-layer gels. The TRAP isoenzyme was first detected after 24 h of TPA treatment; its intensity increased during further TPA exposure, being maximally expressed at 72/96 h. The results suggest that, while TPA triggers B-CLL cells to convert to hairy cell leukaemia (HCL)-type cells, the double stimulus which more closely imitates physiological activation initiates a 'normal' differentiation programme which leads to plasma cells.

Hairy cell leukemia: in-vitro proliferation and pseudo-colony formation

In an established double layer clonogenic assay, the PHA-leukocyte feeder colony assay, hairy cell leukemia (HCL) cells formed strong aggregates simulating colonies. After irradiation with 50 Gy, colony formation persisted. Even in a modified colony assay consisting of agar 0.5% overlayered by methylcellulose 0.9%, cell aggregation was still possible due to increasing fluidity of the methylcellulose during the culture period. Time-lapse video recordings confirmed prominent cell motility leading to pseudo-colony formation. Studies with bromodeoxyuridine incorporation showed a low proliferation index (up to 13%) of hairy cells. In conclusion, any assay that facilitates cell motility is unsuitable to study HCL colony growth.