Effect of anti-alkaline phosphatase monoclonal antibody on B lymphocyte function

Effect of levamisole on expression of CD138 and interleukin-6 in human multiple myeloma cell lines

INTRODUCTION

Multiple myeloma (MM) is a B-cell malignancy accounting for 0.8% of all cancer deaths globally. This malignancy is characterized by lytic bone disease renal insufficiency, anemia, hypercalcemia, and immunodeficiency. The myeloma cells have enhanced expression of CD138. CD138 is a transmembrane heparin sulfate glycoprotein expressed on different types of adherent and nonadherent cells.CD138 is used as a standard marker for identification of tumor cells.

AIMS AND OBJECTIVES

Despite introduction of many therapeutic agents, the management of multiple myeloma (MM) remains a challenge and search for new therapeutic agents is in progress. In this study, we attempted to evaluate the effect of an alkaline phosphatase inhibitor, levamisole on expression of CD138, and level of interleukin-6 (IL-6) in human MM cell lines RPMI 8226 and U266 B1.

MATERIAL AND METHODS

U266B1 and RPMI 8226 cell lines were obtained from the National Centre for Cell Sciences, Pune. Alkaline phosphatase assay, Interleukin-6 assay and CD138 expression on myeloma cells by flow cytometry were investigated when the cells were exposed to Levamisole.

RESULTS

Levamisole-mediated growth inhibition of myeloma cells in vitro is associated with a loss of CD138 and increased IL-6 secretion. The increased secretion of IL-6 by myeloma cells could be an attempt to protect themselves from apoptosis.

CONCLUSION

Levamisole inhibited CD138 expression and affected the levels of IL-6 in a dose-dependent manner. The results of the present study add new dimension to levamisole's mode of action as inhibitor of CD138 and IL-6 and as an antiapoptotic agent.

Anti-proliferative effect of levamisole on human myeloma cell lines in vitro

Levamisole has been employed as an immunomodulatory agent in conjunction with 5-fluorouracil in the treatment of colon cancer relapse. At high doses, levamisole has been shown to have both anti-cancer and immunosuppressive activities. In vitro, levamisole has been shown to potentiate the anti-proliferative effect of 5-fluorouracil in several types of tumor cell lines; however, its mechanism of cytotoxic action and its molecular targets in cells remains to be elucidated. Here, the effect of levamisole on the proliferative response of the human multiple myeloma cell lines RPMI 8226 and U266B1 was studied in vitro. Treatment of both lines with varying concentrations of levamisole for 48 and 72 h in culture resulted in a significant inhibition of proliferation (unstimulated) in a dose-dependent manner, as assessed by an 3-[(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide dye assay. Furthermore, measurements of cell viability (using a trypan blue dye exclusion assay) clearly showed that the levamisole was cytotoxic. The preliminary evaluation of the mechanism of this cytotoxic effect revealed that this drug induced apoptosis in the myeloma cells, as evidenced by increases in the levels of DNA fragmentation, release of cytochrome c into the cytoplasm, and the activation of caspase-3 activity in the cells. The results of these studies strongly suggest that levamisole could be a potent anti-myeloma agent and might be considered in the treatment of multiple myeloma in the future.

Age-associated modulation of apoptosis and activation in murine B lymphocytes

We have investigated the influence of age on B-cell responsiveness. The present study showed that the B-cell mitogen, lipopolysaccharide (LPS), similarly stimulated the proliferation of purified B lymphocytes obtained from either young mice (3 months) or old mice (24 months). In contrast, expression of the differentiation marker, alkaline phosphatase (ALP), was about fourfold higher in young mice than in older mice upon stimulation with LPS or with dextran sulfate (DXS) and interleukin-5 (IL-5). The occurrence of apoptosis during aging was then studied: unexpectedly, spontaneous cell death was double in B lymphocytes from young mice compared to older animals. Stimulation with DXS with or without IL-5 rescued B lymphocytes from cell death in young mice but protection decreased with aging, and no longer occurred in 24-month-old mice B cells. Meanwhile, the protective activity conferred by IL-4 was maintained at similar levels throughout aging. However, B cells from old mice were more responsive to apoptosis induction with cycloheximide, dibutyryl cAMP and dexamethasone. Together, the present results indicate an age-associated alteration in apoptosis and activation of B lymphocytes which could contribute to the age-related decline of the immune response.

Alkaline phosphatase activity is expressed in murine splenic B-lymphocytes sensitized in vivo with Tetanus toxoid

Alkaline phosphatase (APase) activity and proliferative response to Tetanus toxoid (TT) were measured in murine splenic lymphocytes immunized in vivo with TT. APase activity was enhanced in TT-stimulated B-lymphocytes concomitant with an increase in the proliferative response in a dose-dependent manner. Cytochemical staining for APase using beta-naphthyl phosphate also showed an increase in APase positive cells in TT-stimulated lymphocyte population. The results suggest that membrane APase expression is a physiological phenomenon occurring in antigen-stimulated B-lymphocytes.

UV irradiation of a B-cell hybridoma increases expression of alkaline phosphatase: involvement in apoptosis

Expression of alkaline phosphatase (APase) by 7TD1 B-cell hybridoma was amplified by ultraviolet irradiation; cell growth was inhibited and cell death by apoptosis was increased. Irradiation induced high levels of APase activity in cycling as well as in apoptotic cells. In contrast, APase activity faded with time in nonirradiated cells and was no longer expressed in spontaneous apoptotic cells appearing after several days in culture. This was demonstrated by cell morphology, DNA fragmentation, and flow cytometry after simultaneous staining of DNA with Hoechst 33342 and APase with naphthol AS-TR phosphate - fast red RC fluorescent reagent. Levamisole, a specific inhibitor of APase activity, almost totally abrogated apoptosis induced by ultraviolet irradiation at doses that failed to affect 7TD1 cell survival. These data suggest that APase could play a role in the signalling cascade that mediates apoptosis in irradiated cells. Key words: alkaline phosphatase, apoptosis, flow cytometry, levamisole, UV irradiation.

Expression of alkaline phosphatase by a B-cell hybridoma and its modulation during cell growth and apoptosis

The 7TD1 B-cell hybridoma was found to spontaneously express alkaline phosphatase (ALP), an enzyme which is produced by splenic B lymphocytes once optimally activated. Determination of ALP levels during cell growth and departure to apoptosis showed fluctuations. Following a temporary increase within the first 24 h, enzyme expression was maintained at high levels during the early proliferation stage, and then declined from 3 to 4 days in mid-exponential phase to basal levels at day 6 when living cells were no longer detectable and the apoptotic process was completed. The protein synthesis inhibitor, cycloheximide (1 microg/ml), decreased ALP production while stimulating a strong apoptosis of 7TD1 cells, within 4 h. Aphidicolin (1 microg/ml) maintained ALP production and provoked a release of ALP activity into the surrounding medium; it also induced apoptosis, but with a 24 h delay. Quantification of apoptosis and ALP expression by flow cytometry, after simultaneous staining of DNA with Hoechst 33342 and ALP with naphthol AS-TR phosphate/Fast Red RC fluorescent reagent, revealed cell cycle modulation of ALP expression, its activity increasing as 7TD1 cells progressed from G1 phase into S and G2/M phases of the cell cycle in control as well as in drug-treated cells. Kinetics of drug-induced apoptosis and higher expression of ALP associated preferentially with active cell growth during the prevention stage of apoptosis suggested a possible link between cellular ALP expression and cell survival.