Abstract 655: BR101801: A first-in-class triple-inhibitor of PI3K gamma/delta and DNA-PK targeting non-Hodgkin's lymphoma
Authors: Lee Bo Ram , Wang Seungho , Son Mi kwon , Jeon Byeongwook , Kim Soo Jung , Yang Eunhui , Park Min , Lee Joo Han , Myung Jayhyuk 
Published: September 2020

Introduction: The phosphoinositide 3-kinases (PI3Ks) are expressed in mammalian cells and are known to play an important role in cell survival and proliferation. Inhibition of PI3Kδ is one potential approach to reduce tumor survival and proliferation. However, some T-cell may activate PI3K-independent survival pathway in the tumor cells. Therefore, it is important to inhibit both PI3K-γ and -δ. In addition, the DNA-dependent protein kinase (DNA-PK) plays an instrumental role in the overall survival and proliferation of cells. So, deregulated DNA-PK activity is associated with a number of cancers. In this study, we demonstrated that the biological properties of BR101801 which is a first-in-class triple inhibitor PI3K γ/δ and DNA-PK and its potential as a candidate to target both iNHL and aggressive NHL.

Methods: In vitro selectivity for PI3K isotypes in cell-free systems was determined using Homogenous Time Resolved Fluorescence (HTRF) analysis. Cell based selectivity was assessed by the ratio of phosphor-Akt/Akt or phosphor-DNA-PK/DNA-PK using distinct inducer and cell lines. DNA-PK phosphorylation was determined by western blotting. In vitro anticancer effects of BR101801 were confirmed in various cell lines, a total of 52 cell line panels. For in vitro PD markers (PARP, caspase, c-Myc proteins) study, SU-DHL-4, 6, 10 cell lines were treated with BR101801 (1uM) for 24h and analysis of cell lysates by immunoblotting. A tumor mouse xenograft model was established by subcutaneously implanting human derived B-cell lymphoma cell line, SU-DHL-10 (Bendamustine, Rituximab) or DOHH-2 (Venetoclax) into female SCID mice.

Results: In vitro selectivity and target potency of BR101801 on different PI3K subtypes including DNA-PK were studied in cell-free systems in which the biochemical IC50 values of BR101801 for PI3K-α, -β, -γ, -δ and DNA-PK were 106 nM, 171 nM, 15 nM, 2 nM and 6 nM, respectively. The cellular IC50 of BR101801 on PI3K-α, -β, -γ, -δ and DNA-PK were analyzed to be 98.9 nM, 22.0 nM, 5.5 nM, 3.8 nM and 77.3 nM. Additionally, level of c-Myc in NHL cell lines was downregulated by BR101801 in a concentration dependent manner. In vivo DOHH-2 xenograft model, tumor growth inhibition was observed to be 37.2 % and 94.0 % for BR101801 alone 50 mg/kg and combination with Venetoclax 100 mg/kg, respectively. And in SU-DHL-10 xenograft model, Bendamustine and Etoposide combination efficacy were also investigated.

Conclusions: BR101801 is a first-in-class triple inhibitor of PI3K γ/δ and DNA-PK, and has shown highly potent effects to block cellular proliferation of NHL cell lines including both the indolent and aggressive subtypes. Therefore, the strategy of triple targeting against PI3K γ/δ and DNA-PK suggests rationale for BR101801 as innovative therapeutics for NHL patients.

Citation Format: Bo Ram Lee, Seungho Wang, Mi kwon Son, Byeongwook Jeon, Soo Jung Kim, Eunhui Yang, Min Park, Joo Han Lee, Jayhyuk Myung. BR101801: A first-in-class triple-inhibitor of PI3K gamma/delta and DNA-PK targeting non-Hodgkin's lymphoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 655.