Novel Pi3kδ Inhibitor Roginolisib Synergizes with the Bcl-2 Inhibitor Venetoclax in Hematological Malignancies

Abstract

Roginolisib (IOA-244) is a first in class allosteric modulator and non-ATP competitive, selective PI3Kδ inhibitor currently in a Phase 1 clinical study in lymphoma and solid tumors. Initial structural and biochemical studies identified unique chemical structure, excellent selectivity, and excellent PK properties for roginolisib as compared to earlier PI3Kδ inhibitors, while the clinical trial has demonstrated a favorable safety profile. Consistent with prior PI3Kδ inhibitors, roginolisib inhibits the in vitro growth of lymphoma cells. In contrast to other PI3Kδ inhibitors, roginolisib activity is correlated with the expression levels of PIK3CD, suggesting specific and on target cancer cell-intrinsic effects (PMID: 37066023). To identify rational combination strategies, initial pharmacological screening of 474 compounds in combination with roginolisib was carried out using a MTT assay in the lymphoma cell lines HH (cutaneous T cell lymphoma, CTCL) and SP-53 (mantle cell lymphoma, MCL). Initial screening identified that roginolisib synergized with the bcl-2 inhibitor venetoclax in the HH cell line with a combination index value (CI) of 0.003 by the Chou-Talalay method. To further validate this finding, the combination of roginolisib with venetoclax or with another bcl-2 inhibitor S55746 was tested in a broad range of lymphoma cell lines including GRANTA519, JVM2, SP49 (MCL); FARAGE, TMD8 (diffuse large B cell lymphoma); MEC1 (chronic lymphocytic leukemia); MJ (cutaneous T cell lymphoma); and YT (NK lymphoma). The combination showed synergism in all the cell lines (CI 0.81 - 0.05) except SP49 (CI- 1.3). Similarly, the combination of roginolisib with S55746 showed synergism in most of the cell lines (CI- 0.46 - 0.089), additive effect in SP49 (CI- 1) and antagonistic effect in GRANTA519 (CI- 1.3) and FARAGE (CI- 2.17). To assess the tumor-intrinsic effect of roginolisib in patient derived CLL cells, PBMCs isolated from CLL patients responding to prior BTK inhibitor (i) (n=4) or progressed on BTKi (n=6) were tested to check the effect of roginolisib on BCR signalling. Cells were treated with increasing doses of roginolisib from 0.625 μM to 5 μM in the presence of anti-IgM. Other BCRi such as idelalisib, duvelisib and acalabrutinib were used at 5 μM concentrations as positive controls. Roginolisib showed a dose dependent suppression of the activity of BCR downstream kinases such as AKT and ERK. The suppression of phosphorylation of AKT and ERK were comparable with other BCRi tested. Additionally, the apoptosis analysis by annexin/7AAD showed comparable activity of roginolisib with idelalisib, duvelisib or acalabrutinib at 5 μM concentration. To investigate the possible synergy of roginolisib with venetoclax in CLL patient samples who are BTKi responders (n=6) or BTKi progressors (n=8), apoptosis analysis was carried out in patient PBMCs. Viability of CLL cells following 48h of ex vivo treatment with increasing concentrations of roginolisib (0.625 to 5 μM) and venetoclax (1 to 8 nM) alone or in combination was tested. Both the BTKi responders and progressors showed strong synergy with the combination, with slightly better cell killing activity in BTKi progressors ( p=0.007) than responders ( p=0.019). To understand the mechanism by which roginolisib increases the sensitivity to venetoclax, changes in the expression levels of various Bcl-2 family proteins that have been implicated in venetoclax resistance such as Mcl-1, Bcl-xL, Bcl-2, A1 and BIM were measured by immunoblotting. Changes in expression were evaluated in PBMCs from both the BTKi responders (n=8) and progressors (n=7) after 24h treatment with 0.625 and 5 μM concentrations of roginolisib. A significant dose dependent downregulation of Mcl-1 was observed compared to DMSO treated cells in both BTKi responders ( p=0.0033) and progressors ( p= 0.0025). In addition, a significant increase in proapoptotic BIM EL was also observed at both the 0.625 μM ( p=0.0054) and 5 μM ( p=0.0194) concentrations compared to DMSO. In summary, the novel PI3Kδ selective inhibitor roginolisib shows tumor cell killing on various hematologic malignancies including CLL cells from patients with disease progression on BTK inhibitors. In addition, roginolisib synergized with venetoclax in lymphoma cell lines and CLL patient samples. Our data support extending this combination strategy to clinical trials in hematological malignancies.