Abstract A69: Activation of PI3K p110α by minocycline leads to cell dysfunction and cell death in 9L glioma

Abstract

Abstract Minocycline is an FDA-approved tetracycline derivative and non-steroid anti-inflammatory drug. It has remarkable neuroprotective effect on different acute and chronic neurological diseases by inhibiting mitochondrial cytochrome c release (1). Several clinical trials of minocycline in neurodegeneration are ongoing. However, minocycline also has apoptosis-inducing effect in vitro and in vivo. Local delivery of minocycline in mice with intracranial 9L gliosarcoma at the time of tumor implantation resulted in 100% survival in contrast to untreated mice that died within 21 days (2). The detailed mechanism of apoptosis-inducing effect of minocycline in 9L glioma cells is not clear. We checked the effect of minocycline on 9L glioma cells under different conditions. Our experiments showed that in the presence of serum, minocycline at 50 µM induces aberrant vesicle trafficking with large membrane vesicles localized at the cell edge. And prolonged incubation of minocycline leads to cell rounding, detachment and eventually cell death after 72 hours. Minocycline also inhibits the 9L glioma cell migration by wound-healing assay. To our surprise, broad phosphoinositide 3-kinases (PI3K) inhibitor LY294002 can efficiently rescue the glioma cell dysfunction and cell death induced by minocycline. And protein level of caspase-8 and p85α regulatory subunit of PI3K was significantly up-regulated by minocycline. Caspase-8 also has non-apoptotic function involved in periphery localization of early endosome mediated by Rab5 (3). In addition, minocycline treatment leads to up-regulation of phospho-Akt level (ser473), but down-regulation of total Akt protein level. We further confirmed that selective PI3K p110α inhibitor PIK-75 (4) at 50 nM concentration, but not other PI3K isoform inhibitors used (TGX-221 for p110β and Furanyl-thiazolidinedione for p110γ), can rescue the glioma cell dysfunction and cell death, similar as LY294002. The Western blot results showed that PIK-75 restores the normal level of caspase-8, p85α regulatory subunit and total Akt protein level in cells treated with minocycline. The up-regulation of phospho-Akt (ser473) by minocycline treatment is also inhibited by PIK-75. Our results showed that PI3Kα activation is required for glioma cell dysfunction and cell death induced by minocycline. PI3K p110α belongs to Class I PI3K, an important kinase family for survival signaling (5). To our knowledge, this is the first evidence of PI3Kα serving as a death kinase. The result here raises the concerns to the development of PI3K inhibitors for cancer treatment. As minocycline has dual-role in apoptosis, dissecting the apoptosis-inducing and apoptosis-inhibitory effects of minocycline will pave the way for further drug development for the treatment of devastating diseases including neurodegeneration and malignant glioma, respectively. Note: Supported by Brain Science Foundation; Special thanks to Dr. Robert Friedlander and Neuroapoptosis Lab. Citation Information: Cancer Res 2009;69(23 Suppl):A69.