A therapeutic role of
STI571 (
imatinib mesylate) has been anticipated in patients with c-Kit positive
neuroectodermal tumors. We examined the efficacy of
STI571 to inhibit expansion of c-Kit positive
neuroectodermal tumor cell lines in vitro and in a mouse model inoculated with ES (
Ewing sarcoma) derived
tumor cells, and investigated the molecular mechanism of
STI571 action. Eleven
tumor lines of ES,
PNET (
primitive neuroectodermal tumors) and NB (
neuroblastoma) were assayed in the presence of 1, 5, 10, 15, 20 or 30 micro M
STI571 for 24, 48, 72 h and 7 days. The mechanism of
STI571 action was investigated using a microphysiometer cytosensor that determines cellular metabolic rates in the presence of
STI571. c-Kit and global
protein phosphorylation was assayed by immunoprecipitation and a direct
enzyme-linked
immunoadsorbent assay after 72 h of 10 micro M
STI571. Apoptosis was investigated by
propidium iodide (PI),
Annexin V staining and by enzymatic activity of
caspase-3. Moreover, apoptotic gene expression was investigated using microarray technology. In nude mice,
tumor volume and histology were analyzed in
STI571 treated and untreated mice, and apoptotic gene expression analysis was performed on
tumor masses. A decrease in cell proliferation and increase of cell apoptosis was caused by
STI571 in a concentration- and time-dependent manner. Cytosensor microphysiometer and immunoprecipitation experiments demonstrated a time- and concentration-dependent decrease of cellular metabolic activity and global
protein dephosphorylation after
STI571 exposure. The inhibition by
STI571 appeared at least to some extent independent of c-Kit inhibition since cells remained sensitive to SCF stimulation.
Tumor volume was significantly reduced in STI571-treated mice compared to
tumors from control inoculated non-treated mice. The apoptosis pathway in response to
STI571 appeared not to be dependent on
caspase activation, while gene expression profiles suggested accumulation of
reactive oxygen species (ROS) resulting in cell death after exposure to
STI571. The results point to the potential relevance of STI157 for
neuroectodermal tumor therapy in view of its inhibitory effect on
tumor cell growth, in spite of the observation that the inhibition of the c-Kit signaling pathway is not critically involved.