Inhibition Of IGF1R by IGF-1R/IR Inhibitor OSI906 as a Targeted Therapy for Glioblastoma: In Vitro & in Vivo Studies

Abstract

Background: CNS tumors are the most frequent solid tumors in children. In paediatric gliomas, IGF-1R nuclear localization was significantly associated with both high grade tumours and increased risk of death and contributed to the aggressive phenotype of glioblastoma by increasing motility and metabolism of tumor cells rather than increasing its proliferation. For children chemotherapy after surgical resection is the mainstay of therapy. However, the best regimen needs to be determined.Aim: To characterize the response of glioblastoma cells to treatment with OSI906 (IGF1R/IR dual inhibitor) alone or in combination with Temozolomide used as a current adjuvant chemotherapy for paediatric patients.Methods: stably transfected U87Mg glioblastoma cells with 5 times basal expression of wild type mature GFP-IGF1R fusion protein (wt-IGF1R, WtU87) or GFP-IGF1R fusion protein mutated in Lys1025-1100-1120 to avoid IGF-1R nuclear translocation (m-IGF1R, MutU87) were used for in vitro and in vivo assays. Proliferation assays were carried out for 3 days using complete media (10%FBS), or in the presence of IGF-1R/IR inhibitor OSI906 (0.5uM), Temozolomide (TMZ, 40 or 100uM) or the combination of both treatments. Male nude mice were injected for in vivo experiments (1,5e6cells/flank/mice). OSI906 (50mg/kg) and TMZ (400mg/kg) were given by gavage once daily or as a single dose respectively. Treatments were started when tumors reached 150 mm3.Results: After 24 h of culture, MutU87 cells showed decreased proliferation when treated with TMZ40 and OSI906; OSI906 had an additive effect when combined with TMZ40 compared to control condition. However, cells resumed proliferation after 3 days in culture. On the contrary, treatment with TMZ100 had a strong inhibitory effect, that was not increased by the combination with OSI906. WtU87 treated with TMZ40 or 100 also resumed proliferation after 24 h treatment, although the total number of cells was decreased compared to control. OSI906 was able to abolish proliferation of WtU87 cells when used alone or in combination with TMZ 40 or 100, having the latter the strongest effect. In vivo studies showed similar trends.Conclusion: The capacity of the IGF1R to translocate to the nucleus, renders glioblastoma cells sensitive to the IGF-1R targeted therapy alone or in combination with TMZ, in vitro and in vivo. These results suggest that the use of IGF1R inhibitors in pediatric patients showing nuclear localization for this receptor, could be useful to reduce TMZ doses and or avoid radiotherapy in children.