Abstract
2012 Background: XL765 is a potent pan PI3K inhibitor with activity against mTOR and XL147 is a potent pan-PI3K inhibitor. Inhibition of the PI3K/mTOR pathway may be beneficial in the treatment of GBM. Methods: Patients with GBM who were candidates for a surgical resection were eligible for this exploratory study. Cohorts of 6-10 patients were treated with one of three regimens: Cohort 1: XL765 50mg twice daily (BID), Cohort 2: XL147 200mg once daily (QD), Cohort 3: XL765 90mg QD for >10 days prior to undergoing tumor resection. Tumor tissue was obtained at ~12, 24 and 3 hours after the last dose, respectively. Frozen tumor tissue and blood were analyzed for drug concentration (PK) and pathway modulation was analyzed in post-dose frozen tumor tissue and compared to reference tumor samples from GBM patients not treated with XL765 or XL147. Pharmacodynamic impact (PD) on the pathway, apoptosis and proliferation was examined by immunohistochemistry (IHC) in an FFPE tumor sample from each patient and compared to an archived tumor sample from an earlier surgery. Results: Enrollment is complete with 21 patients enrolled; 6, 6 and 7 were evaluable for the PK/PD analysis in cohorts 1, 2 and 3, respectively. The toxicity profiles for both drugs were consistent with previous studies. PK analyses revealed a mean tumor to plasma ratio of 0.38 and 0.40 in cohorts 1 and 3 and 0.27 in cohort 2. PD analysis by IHC revealed reduction compared to archived tumor in pS6K1 in 4/6 and 7/7 patients in cohorts 1 and 3 and 6/6 patients in cohort 2. Reduction in Ki67 was observed in 6/6 and 5/7 patients in cohorts 1 and 3 and 4/6 patients in cohort 2. Conclusions: XL765 when given on a QD or BID schedule to patients with glioma yields moderately higher distribution of XL765 into CNS tumor compared to XL147 based on tumor to plasma ratios. Decreases in pS6K1, consistent with pathway inhibition, and decreases in Ki67, consistent with inhibition of proliferation, were observed following treatment with both XL147 and XL765. Clinical trial information: NCT01240460.
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