monensin and Carcinoma--Small-Cell

Possible involvement of cell membrane ion transport systems in the uptake and extrusion of Tc-99m-MIBI was investigated by using various buffers with or without Na+ and Ca++, and ion transport inhibitors in a tumor cell line. The ion transport modulators dimethyl amiloride (DMA), verapamil, flunarizine and monensin were used. The uptake of Tc-99m-MIBI was significantly increased in all buffers containing either Na+ or Ca++ alone or none of them. There was significantly increased uptake of Tc-99m-MIBI especially in buffers without Na+. Verapamil, a L-type Ca++ channel blocker, increased Tc-99m-MIBI uptake in all buffers. Flunarizine, which inhibits Na+/ Ca++ channels, caused significantly increased accumulation of Tc-99m-MIBI only in buffer containing both Na+ and Ca++. Monensin, a sodium ionophore, significantly increased uptake of Tc-99m-MIBI. DMA, a potent Na+/H+ antiport inhibitor, significantly inhibited the uptake of Tc-99m-MIBI in all buffers. In conclusion, Tc-99m-MIBI behaves like Na+ during its uptake and extrusion. Extrusion of Tc-99m-MIBI may involve both verapamil- and flunarizine-sensitive pathways.

Topics: Adrenal Cortex Neoplasms; Amiloride; Calcium; Calcium Channel Blockers; Calcium Channels; Carcinoma, Small Cell; Flunarizine; Humans; Monensin; Sodium; Sodium Channels; Technetium Tc 99m Sestamibi; Tumor Cells, Cultured; Verapamil

A ricin A chain immunotoxin, SEN36-ricin A chain, directed against the neural cell adhesion molecule (N-CAM) had no selective cytotoxic activity against three different small cell lung cancer (SCLC) cell lines in tissue culture despite expression of the target antigen on more than 98% of cells in each line detected by indirect immunofluorescence. Treatment of the SW2 SCLC cell line with suramin and interferons alpha and gamma increased the level of N-CAM expression only slightly and had no significant effect on the cytotoxic activity of the SEN36 immunotoxin. In the presence of the carboxylic ionophore monensin at a concentration of 0.1 microM, the toxicity of SEN36-ricin A chain to the SW2 cell line was enhanced by 12,000-fold. In contrast, lysosomotropic amines showed little or no potentiation of activity, suggesting that lysosomal degradation was not the major factor limiting the action of the anti-N-CAM immunotoxin. The findings of this study indicate that ricin A chain immunotoxins directed against N-CAM on SCLC are unlikely to have sufficient activity to be useful therapeutic agents in the absence of potentiating agents such as monensin, which can interfere with the normal intracellular pathways of antigen routing.

Topics: Carcinoma, Small Cell; Cell Adhesion Molecules, Neuronal; Cytotoxicity, Immunologic; Drug Synergism; Humans; Immunotoxins; Lung Neoplasms; Macromolecular Substances; Monensin; Ricin; Tumor Cells, Cultured

The cytotoxic activity profile of an immunotoxin, SWA11-ricin A chain, recognising a cell-surface antigen associated with human small cell lung cancer (SCLC), was examined in detail using a panel of SCLC, non-SCLC and non lung tumour cell lines in tissue culture. SWA11-ricin A chain was potently and selectively active against three SCLC cell lines of both classic and variant morphologies, inhibiting the incorporation of 3H-leucine with an IC50 of 5 x 10(-11) M. At a concentration of 1 x 10(-8) M, the SWA11 immunotoxin could selectively eliminate in excess of 99.9% of clonogenic tumour cells. Intoxication proceeded rapidly following a 4 h lag phase; the initial rate of protein synthesis inhibition occurred with a t50 of 2 h and a t10 of 7 h. The cytotoxic activity of SWA11-ricin A chain was potentiated by 100-fold in the presence of the carboxylic ionophore monensin at 1 x 10(-7) M. Kinetic studies revealed that monensin enhanced the rate of protein synthesis inhibition by two-fold and eliminated the lag phase suggesting a rapid effect on either the rate or route of internalisation. Studies with SWA11 could detect no influence of monensin on the rate of antibody internalisation and a transient delay in the delivery of internalised antibody to lysosomes was observed by immunoelectron microscopy.

Topics: Antibodies, Monoclonal; Carcinoma, Non-Small-Cell Lung; Carcinoma, Small Cell; Drug Synergism; Humans; Immunotoxins; Lung Neoplasms; Microscopy, Immunoelectron; Monensin; Neoplasm Proteins; Ricin; Tumor Cells, Cultured