Modulation of growth, differentiation and glycoprotein synthesis by β‐ALL‐trans retinoic acid in a multicellular tumor spheroid model for squamous carcinoma of the head and neck

Abstract

Cell line MDA 886Ln was established from a laryngeal lymph node metastasis. When grown as a multicellular tumor spheroid (MTS), it exhibits squamous differentiation. We studied the effects of ß‐all‐trans retinoic acid (RA) on the growth, differentiation and glycoprotein content of this MTS model for squamous carcinomas of the head and neck. The growth of MTSs was inhibited in a dose‐dependent manner by 10⁻⁶ to 10⁻¹⁰ M RA. Growth inhibition occurred between 3 and 5 days of RA treatment (10⁻⁶ M). Immunohistochemical and electrophoretic analyses revealed that RA suppressed the morphological markers of squamous differentiation (squames), involucrin expression, and keratin expression. Glycoprotein expression was examined by metabolic labelling using ³H‐glucosamine, in situ labelling of polyacrylamide gels with ¹²⁵l‐labelled wheat‐germ agglutinin (WGA), localization of fluorescein isothionate‐WGA in frozen sections, and determination of sialyltransferase activity. Treatment using 10⁻⁶ M RA altered glycoprotein expression both biochemically and morphologically, and WGA was shown to bind preferentially to sialic acid residues. The sensitivity of this MTS model to RA treatment and its ability to be analyzed through morphological, immunohistochemical and biochemical techniques suggest that it will prove useful in studying the relationships between growth, differentiation and RA‐induced alterations in squamous carcinomas.