PI3K inhibition synergizes with glucocorticoids but antagonizes with methotrexate in T-cell acute lymphoblastic leukemia.

The PI3K pathway is frequently hyperactivated in primary T-cell acute lymphoblastic leukemia (T-ALL) cells. Activation of the PI3K pathway has been suggested as one mechanism of glucocorticoid resistance in T-ALL, and patients harboring mutations in the PI3K negative regulator PTEN may be at increased risk of induction failure and relapse. By gene expression microarray analysis of T-ALL cells treated with the PI3K inhibitor AS605240, we identified Myc as a prominent downstream target of the PI3K pathway. A significant association was found between the AS605240 gene expression signature and that of glucocorticoid resistance and relapse in T-ALL. AS605240 showed anti-leukemic activity and strong synergism with glucocorticoids both in vitro and in a NOD/SCID xenograft model of T-ALL. In contrast, PI3K inhibition showed antagonism with methotrexate and daunorubicin, drugs that preferentially target dividing cells. This antagonistic interaction, however, could be circumvented by the use of correct drug scheduling schemes. Our data indicate the potential benefits and difficulties for the incorporation of PI3K inhibitors in T-ALL therapy.

In Vitro and In Vivo Analysis of RTK Inhibitor Efficacy and Identification of Its Novel Targets in Glioblastomas.

Treatment for glioblastoma consists of radiotherapy and temozolomide-based chemotherapy. However, virtually all patients recur, leading to a fatal outcome. Receptor tyrosine kinase (RTK)-targeted therapy has been the focus of attention in novel treatment options for these patients. Here, we compared the efficacy of imatinib, sunitinib, and cediranib in glioblastoma models. In the present work, the biologic effect of the drugs was screened by viability, cell cycle, apoptosis, migration, and invasion in vitro assays or in vivo by chick chorioallantoic membrane assay. Intracellular signaling was assessed by Western blot and the RTK targets were identified using phospho-RTK arrays. The amplified status of KIT, PDGFRA, and VEGFR2 genes was assessed by quantitative polymerase chain reaction. In a panel of 10 glioblastoma cell lines, we showed that cediranib was the most potent. In addition, cediranib and sunitinib synergistically sensitize the cells to temozolomide. Cediranib efficacy was shown to associate with higher cytostatic and unique cytotoxic effects in vitro and both antitumoral and antiangiogenic activity in vivo, which could associate with its great capacity to inhibit mitogen-activated protein kinase (MAPK) and AKT pathways. The molecular status of KIT, PDGFRA, and VEGFR2 did not predict glioblastoma cell responsiveness to any of the RTK inhibitors. Importantly, phospho-RTK arrays revealed novel targets for cediranib and sunitinib therapy. In conclusion, the novel targets found may be of value as future biomarkers for therapy response in glioblastoma and lead to the rational selection of patients for effective molecular targeted treatment.

Low doses of ionizing radiation promote tumor growth and metastasis by enhancing angiogenesis.

Radiotherapy is a widely used treatment option in cancer. However, recent evidence suggests that doses of ionizing radiation (IR) delivered inside the tumor target volume, during fractionated radiotherapy, can promote tumor invasion and metastasis. Furthermore, the tissues that surround the tumor area are also exposed to low doses of IR that are lower than those delivered inside the tumor mass, because external radiotherapy is delivered to the tumor through multiple radiation beams, in order to prevent damage of organs at risk. The biological effects of these low doses of IR on the healthy tissue surrounding the tumor area, and in particular on the vasculature remain largely to be determined. We found that doses of IR lower or equal to 0.8 Gy enhance endothelial cell migration without impinging on cell proliferation or survival. Moreover, we show that low-dose IR induces a rapid phosphorylation of several endothelial cell proteins, including the Vascular Endothelial Growth Factor (VEGF) Receptor-2 and induces VEGF production in hypoxia mimicking conditions. By activating the VEGF Receptor-2, low-dose IR enhances endothelial cell migration and prevents endothelial cell death promoted by an anti-angiogenic drug, bevacizumab. In addition, we observed that low-dose IR accelerates embryonic angiogenic sprouting during zebrafish development and promotes adult angiogenesis during zebrafish fin regeneration and in the murine Matrigel assay. Using murine experimental models of leukemia and orthotopic breast cancer, we show that low-dose IR promotes tumor growth and metastasis and that these effects were prevented by the administration of a VEGF receptor-tyrosine kinase inhibitor immediately before IR exposure. These findings demonstrate a new mechanism to the understanding of the potential pro-metastatic effect of IR and may provide a new rationale basis to the improvement of current radiotherapy protocols.