Molecular and Structural Traits of Insulin Receptor Substrate 1/LC3 Nuclear Structures and Their Role in Autophagy Control and Tumor Cell Survival.

Insulin receptor substrate 1 (IRS-1) is a common cytosolic adaptor molecule involved in signal transduction from insulin and insulin-like growth factor I (IGF-I) receptors. IRS-1 can also be found in the nucleus. We report here a new finding of unique IRS-1 nuclear structures, which we observed initially in glioblastoma biopsy specimens and glioblastoma xenografts. These nuclear structures can be reproduced in vitro by the ectopic expression of IRS-1 cDNA cloned in frame with the nuclear localization signal (NLS-IRS-1). In these structures, IRS-1 localizes at the periphery, while the center harbors a key autophagy protein, LC3. These new nuclear structures are highly dynamic, rapidly exchange IRS-1 molecules with the surrounding nucleoplasm, disassemble during mitosis, and require a growth stimulus for their reassembly and maintenance. In tumor cells engineered to express NLS-IRS-1, the IRS-1/LC3 nuclear structures repress autophagy induced by either amino acid starvation or rapamycin treatment. In this process, IRS-1 nuclear structures sequester LC3 inside the nucleus, possibly preventing its cytosolic translocation and the formation of new autophagosomes. This novel mechanism provides a quick and reversible way of inhibiting autophagy, which could counteract autophagy-induced cancer cell death under severe stress, including anticancer therapies.

Anticancer potential of aminomethylidene-diazinanes I. Synthesis of arylaminomethylidene of diazinetriones and its cytotoxic effects tested in glioblastoma cells.

Diazinane and aryl moieties with vinylamine linkers were synthesized to investigate the importance of their structural variations as potential anti-glioblastoma agents. Structural variations incorporated on to the diazinane moiety included oxa and thio derivatives, each with a variety of nitrogen-bound substituents. The size and shape of the aromatic moiety was varied, with the final variation introducing two carbonyl groups, yielding a substituted anthraquinone. Readily available diazinanes and aryl amines were used asan advantageous foundation. Several parameters were calculated whilst engineering these compounds, including: ClogP, molecular polarizability, polar surface area, minimal molecular projected area, and pKa. In addition, a simple and efficient procedure was developed to synthesize these compounds. It was demonstrated that a vinylamine with 1,3-diazinane-2,4,6-trione and 1-anthraquinone moiety is the most promising drug candidate causing almost 70% of LN229 tumor cell death at 1µg/ml. In addition, its molecular polarizability, polar surface area and minimal molecular projected area indicate a possible potential of this molecule for crossing BBB.