Ara-C treatment leads to differentiation and reverses the transformed phenotype in a human rhabdomyosarcoma cell line

Rhabdomyosarcoma (RMS) is an embryonal tumor of childhood that arises from primitive skeletal muscle-forming cells (rhabdomyoblasts) probably arrested and transformed along the normal myogenic pathway to maturation. Since Ara-C is an antitumor agent known to induce differentiation in human acute myelogenous leukemia, also presumably a disorder of cellular maturation, we treated RD, a human embryonal RMS cell line, with Ara-C and evaluated its effect on growth and differentiation. Ara-C treatment of RD cells in vitro caused a dose-dependent growth inhibition in the absence of cytotoxicity. Interestingly, RD cells treated with 5 x 10(-7) M Ara-C for 4 days were able to recover logarithmic growth after the removal of the drug from the media. A reexposure of these cells to Ara-C led to morphological and biochemical changes related to differentiation, including the appearance of an increased number of multinucleated cells that expressed muscle-specific actin and skeletal muscle myosin heavy chain (MHC) (fast). In vivo studies demonstrated that RD cells pretreated with 5 x 10(-7) M Ara-C lost their ability to form tumors in nude mice. We conclude that treatment of this human embryonal RMS cell line with Ara-C results in marked growth inhibition in vitro, loss of tumorigenicity in vivo, and the expression of biochemical markers present in a more differentiated phenotype. These data suggest a potential role for differentiation therapy as a therapeutic approach in RMS.

Frequency and diversity of p53 mutations in childhood rhabdomyosarcoma

The p53 gene was examined in primary or metastatic tumors from six patients with rhabdomyosarcoma (RMS) and in five RMS cell lines by screening methods including single-strand conformation polymorphism analysis, the RNase protection assay, sequencing of complementary DNA subclones, and Southern blotting. Six original tumors were of embryonal histology, four alveolar, and one mixed. p53 mutations were identified in four of the six tumors or cell lines derived from tumors with embryonal histology and in one of the four with alveolar histology. Consistent with p53 allele loss, each mutation was found in the homo- or hemizygous state. One tumor showed a G to C transversion at p53 codon 213 (arginine to proline), and another showed deletion of the entire gene. The p53 mutations in cell lines included a codon 248 C to T transition (arginine to tryptophan) in RD and a codon 280 A to T transversion (arginine to serine) in RH30. The cell line CTR contained a 4-base pair deletion at codons 219/220 in exon 6 with resultant frame shift and premature termination in exon 7. These data support the role of diverse types of p53 mutations in the pathogenesis and/or progression of a significant proportion of cases of childhood RMS.

All-trans-retinoic acid inhibits the growth of human rhabdomyosarcoma cell lines

We have been evaluating the role of all-trans-retinoic acid (RA) in the differentiation and growth of human rhabdomyosarcoma (RMS) cell lines. Treatment of both embryonal (RD) and alveolar (RH30) human RMS cell lines with all-trans-RA resulted in a dose-dependent inhibition of cell growth with a maximal inhibition of 92 and 66%, respectively, at 5 x 10(-6) M. When 13-cis-RA was used under identical experimental conditions, maximal growth inhibition was 41 and 37%, respectively. This stereo-specific growth inhibition was not associated with morphological or biochemical evidence of myogenic differentiation. Furthermore, all-trans-RA demonstrated no evidence of competition with binding of insulin-like growth factor II (IGF-II), an autocrine growth factor in RMS, to its membrane receptor as evaluated by an [125I]IGF-I-receptor-binding assay. Attempts to rescue all-trans-RA growth-inhibited RMS cells with exogenous IGF-II resulted in no increase in growth compared to cells treated with all-trans-RA alone. We conclude that RA inhibits the growth of human RMS cell lines in a dose-dependent, stereo-specific manner, is not associated with differentiation, and does not appear to be directly related to IGF-II.