Abstract 4518: The PI3K-δ inhibitor TGR-1202 induces cytotoxicity and inhibits phosphorylation of AKT in 17p deleted and non-17p deleted CLL cells in vitro

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Background: The PI3K pathway is a central pro-survival mechanism in chronic lymphocytic leukemia (CLL), with expression of the delta isoform of PI3K largely restricted to lymphocytes. Clinical evaluation of PI3K-δ inhibitors, such as idelalisib, in CLL patients has been promising. CLL patients with 17p deletion (17pdel) have displayed inferior responses to chemo-immunotherapy, and we hypothesized that inhibiting the PI3K/AKT pathway would be equally efficacious in patients with and without 17pdel. TGR-1202 is a novel PI3K-δ specific inhibitor with unique pharmacologic properties and demonstrated in-vitro activity. Herein, we evaluate the in vitro effect of TGR-1202 on CLL lymphocytes, specifically evaluating differences between 17pdel CLL and non-17pdel CLL samples. Methods: We collected blood from CLL patients seen at the Duke Center for CLL and enrolled in IRB approved protocols at the Duke University and Durham VA Medical Centers. CLL lymphocytes were isolated using negative selection yielding greater than 95% purity. Primary CLL cells were incubated with serial dilutions of TGR-1202 tested for apoptosis by activated caspase-3 and 7AAD staining measured by flow cytometry. Cytotoxicity was measured using the colorimetric MTS reagent. Phosphorylated AKT (S473) was measured by flow cytometry after incubation with TGR-1202 followed by incubation with anti-IgM or anti-IgD. AKT phosphorylation was quantified by median fluorescent intensity (MFI). Results: We have evaluated TGR-1202 in 15 CLL lymphocyte samples, 10 with normal non-17pdel cytogenetics, and 5 with 17pdel. TGR-1202 induced cytotoxicity and apoptosis in a dose-dependent manner in concentrations between 4 nM and 25 μM with no significant difference in results observed between normal CLL lymphocytes those that had 17pdel cytogenetics. The mean ED50 in 17pdel CLL cells was 326 nM, whereas the mean ED50 in non-17pdel CLL cells was 887 nM, although due to the small sample size, this difference was not statistically significant (p = 0.16, t-test). We also found that TGR-1202 significantly suppressed AKT phosphorylation in CLL lymphocytes. Conclusions: TGR-1202 is a potent PI3K-δ inhibitor that suppresses AKT phosphorylation and induces apoptosis-dependent cytotoxicity in primary CLL lymphocytes, both with favorable and adverse cytogenetics. We observed that higher concentrations of TGR-1202 were required to induce cytotoxicity in non-17pdel CLL lymphocytes on average, than in 17pdel CLL. Evaluation of additional CLL cell samples with 17pdel is ongoing to confirm initial findings. A Phase I trial with once-daily TGR-1202 is currently ongoing in patients with hematologic malignancies, including CLL. To date, TGR-1202 has been well tolerated, with no drug-related hepatic toxicities observed. Our initial observations suggest that clinical evaluation of TGR-1202 enriched in CLL patients with 17pdel may be warranted. Citation Format: Daphne R. Friedman, Tiffany Simms, Sallie D. Allgood, Danielle M. Brander, Peter Sportelli, Hari P. Miskin, Swaroop Vakkalanka, Srikant Viswanadha, J. Brice Weinberg, Mark C. Lanasa. The PI3K-δ inhibitor TGR-1202 induces cytotoxicity and inhibits phosphorylation of AKT in 17p deleted and non-17p deleted CLL cells in vitro. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4518. doi:10.1158/1538-7445.AM2014-4518