Síntesis química, actividad antitumoral modo de acción de la neurostatina y sus análogos sobre el crecimiento de gliomas

Resumen

In spite of their low incidence, the central nervous system tumors are responsible of about 2,3% of total cancer deaths; these tumors have an elevated morbidity and mortality. Unless several molecular targets have been described to attack glioma growth, the therapeutic strategies remain partially uneffective. The ganglioside 9-O-Ac-GD1b or neurostatin, present in the mammalian brain, is a potent astroblast and astrocytoma cell division inhibitor, appearing as a possible candidate for treatment of nervous system tumours. Because the purification of neurostatin from brain is highly laborious, we designed its preparation by chemical O-acetylation of GD1b. Moreover, searching for a more stable compound with higher inhibitory activity, we also tested O-butyrylation or multi-Osubstitution of GD1b. The semi-synthetic compounds efficiently inhibited the in-vitro division of rat and human glioma cells (C6 and U373 cell lines), with no toxic effect over neural cells. Growth inhibition in culture correlated with inhibition of the growth of xenotransplants of both rat and human glioma cells (C6 and U373) in Foxn1nu/nu nude mice and alotransplants of C6 cells in the striatum of Sprague-Dawley rats. Neurostatin and O-But GD1b efficiently inhibited the in vivo cell cycle progression of glioma cells, reducing its proliferation, and induced apoptosis of intracranial gliomas. Additionally, intracranial gliomas, when treated with the compounds, were infiltrated of immune cells, to collaborate to resume the tumor. The molecular mechanisms of growth inhibition of neurostatin were also assessed. Using an in vitro model of human glioma cells (U373MG), we observed that neurostatin inhibited the expression of the ciclins and CDK¿s that control cell cycle progression and increased the expression of the inhibitors p21 and p27, further blockin Rb inactivation. The main consequence of neurostatin action was the arrest of the glioma cell cycle in G1, as evidenced by flow cytometry, western blotting and PCR arrays techniques. These effects were exerted through the inhibition of the epidermal growth factor receptor (EGFR) activation and the consequent blockade of its intracellular signalling pathways, like the MAPKs or PI3K, the main regulatory pathways of tumor cell growth. The overall effect of neurostatin over glioma cells, analyzed by PCR arrays, was the regulation of the expression of the proteins responsible of the control of proliferation, angiogenesis, invasion, metastasis or apoptosis, key mechanisms determining the tumor final growth. The results presented here indicate that semi-synthetic O-acetylated and O-butyrylated GD1b derivatives (neurostatin and O-But GD1b) are potent antitumoral compounds that block glioma cells growth, angiogenesis and invasion, also inducing its apoptosis, making them potential strategies for brain tumor treatment.