THE NOVEL BISPECIFIC CD47‐CD19 ANTIBODY TG‐1801 POTENTIATES THE ACTIVITY OF UBLITUXIMAB‐UMBRALISIB (U2) DRUG COMBINATION IN PRECLINICAL MODELS OF B‐NHL (2019)

Umbralisib is an orally available PI3Kδ inhibitor that has demonstrated activity in preclinical models and primary B-cell non-Hodgkin lymphoma (B-NHL) cells, and in patients with B-cell malignancies. The doublet of umbralisib used in combination with the glycoengineered anti-CD20 mAb ublituximab (“U2” regimen), provides a non-chemotherapy backbone regimen on which novel multidrug combinations are being explored. TG-1801 is a novel, bispecific antibody currently in Phase 1 that selectively targets CD47 on CD19+ B-cells, sparing red blood cells or platelets, and blocking the CD47-SIRPα macrophage checkpoint on mature B cells. Here we show that activity of the U2 combination in B-NHL cell lines co-cultured with bone marrow-derived stromal cells, M2-polarized primary macrophages, and primary circulating PBMCs, is mainly associated with a decrease of anti-inflammatory cytokines genes (IL-6, IL-10, IL-1RA). In addition, upregulation of pro-inflammatory IL-2, accompanied by a 2-fold increase of M2-dependent antibody-dependent cell phagocytosis (ADCP), is also observed. Notably, when U2 is combined with TG-1801, this 2-fold increase in ADCP is doubled up to 4-fold increase. Moreover, the activated antibody-dependent cell death (ADCC) observed with TG-1801 alone (4.1-fold above control) becomes increased (7.2-fold above control) when combined with ublituximab, whereas umbralisib alone does not affect ADCC. RNA-seq analysis further reveals that U2 treatment is mainly associated with modulation of redox processes in B-NHL co-cultures (NES = -0.57, p = 0.016). Although TG-1801 single agent does not significantly affect B cell transcriptome, combination with U2 provokes the down-regulation of genes associated with cell architecture homeostasis, including cellular membranes (NES = -0.57, p = 0.006), cytoskeleton (NES = -0.51, p = 0.046), and cell proliferation (NES = -0.44, p = 0.018). In vivo, treatment with ublituximab alone (5mg/kg, qw) displays a tumor growth inhibition (TGI) of 88%, with 3/8 mice harboring a barely palpable tumor, while treatment with umbralisib alone (150mg/kg, bid) shows a TGI of 50%, with 2/8 mice lacking detectable tumors. TG-1801 (5mg/kg, qw) exhibits a 76% TGI with 1/8 tumor free-mouse. Most importantly, the combination of TG-1801 with umbralisib alone, ublituximab alone, and U2 achieves TGI of 85%, 93% and 93% respectively, and 35 days after the last dose 3/8 mice remain tumor-free in the triple combo groups, versus only 1/8 mouse in the TG-1801 group. Interestingly, this superior anti-tumor effect of the TG-1801-based combinations is associated with a higher infiltration of mouse macrophages within the tumors, as assessed by F4/80 IHC labeling. In conclusion, the results presented herein set the preclinical rationale for a combination strategy of the novel CD47-CD19 antibody TG-1801 with other B-cell targeted drugs, particularly umbralisib and ublituximab, in B-NHL. Keywords: antibody-dependent cytotoxicity (ADC); non-Hodgkin lymphoma (NHL); PI3K/AKT/mTOR. Disclosures: Normant, E: Employment Leadership Position: TG Therapeutics; Stock Ownership: TG Therapeutics. Miskin, H: Employment Leadership Position: TG Therapeutics; Stock Ownership: TG Therapeutics. Sportelli, P: Employment Leadership Position: TG Therapeutics; Stock Ownership: TG Therapeutics. Weiss, M: Employment Leadership Position: TG Therapeutics; Stock Ownership: TG Therapeutics. Bosch, F: Consultant Advisory Role: Roche; Honoraria: Roche; Research Funding: TG Therapeutics. Roue, G: Research Funding: TG Therapeutics.