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Inhibitory Effects of Phytohemagglutinin Isolectins L₄ and E₄ on L1210 Cells

Laboratory of Clinical Biochemistry, Baltimore Cancer Research Center, Division of Cancer Treatment, National Cancer Institute, Baltimore, Maryland 21211

Phytohemagglutinin isolectins L₄ and E₄ inhibit the growth and proliferation of cultured L1210 murine leukemia cells. L1210 cells were incubated with L₄ or E₄, and the metabolic and morphological characteristics of the cells were assessed. Dose-dependent inhibition of up to 90% occurs for [³H]thymidine and [¹⁴C]uridine incorporation. L₄ is 30 to 50 times more potent an inhibitor than is E₄. Inhibition begins 2 to 3 hr after exposure of L1210 cells to L₄ and persists for as long as the cells are exposed to this isolectin. Total DNA and oxygen consumption in L₄-treated cultures is also decreased. Whereas protein synthesis assessed by [¹⁴C]valine incorporation is less affected, glucose utilization remains unchanged. The binding of L₄ and E₄ to L1210 cells and human lymphocytes is similar and is reversible by porcine thyroglobulin. Porcine thyroglobulin also reverses L₄-induced inhibition of nucleotide incorporation. Cell aggregation is the major morphological consequence of isolectin treatment observed by light or electron microscopy. L1210 cells are agglutinated at lower doses of isolectins than are normal murine lymphocytes. No evidence of cell death as estimated by ⁵¹Cr release or trypan blue uptake has been noted. Our data indicate that L₄ and E₄ have cytostatic properties and demonstrate that the reversible binding of a macromolecule to the surface of a malignant cell can modulate synthetic pathways and the rate of proliferation.

¹ To whom requests for reprints should be addressed.

Received 7/29/77. Accepted 3/14/78.