Combination of Loncastuximab Tesirine and Polatuzumab Vedotin Shows Increased Anti-Tumor Activity in Pre-Clinical Models of Non-Hodgkin Lymphoma

Abstract Loncastuximab tesirine-lpyl (formerly ADCT-402) is an antibody-drug conjugate (ADC) comprising a humanised anti-CD19 monoclonal antibody conjugated to the pyrrolobenzodiazepine (PBD) dimer-based payload tesirine. Once bound to CD19 on the cell membrane, loncastuximab tesirine is rapidly internalised and the released PBD dimer warhead causes interstrand DNA crosslinks which ultimately trigger cell death. Pre-clinically, loncastuximab tesirine has shown potent and specific anti-tumor activity in lymphoma models both as single agent and in combination with other approved drugs, like venetoclax, idelalisib and bendamustine (Zammarchi, Corbett et al. 2018, Tarantelli, Spriano et al. 2019). Loncastuximab tesirine has been recently approved by the United States Food and Drug Administration (FDA) for the treatment of relapsed or refractory (r/r) diffuse large B-cell lymphoma (DLBCL) and it is currently being tested in multiple clinical trials, either as monotherapy or in combination with other anti-lymphoma drugs. Polatuzumab vedotin is an ADC composed of a humanized anti-CD79b monoclonal antibody conjugated to monomethyl auristatin E (vcMMAE) and it is approved by the FDA for treatment of r/r DLBCL when used in combination with bendamustine and rituximab. Here, we investigated the in vitro and in vivo anti-tumor activity of loncastuximab tesirine combined with polatuzumab vedotin in pre-clinical models of non-Hodgkin lymphoma (NHL). In vitro, the combination of loncastuximab tesirine and polatuzumab vedotin was tested in three human-derived, CD19 and CD79b-positive NHL cell lines (WSU-DLCL2, TMD8 and Ramos) and it resulted in synergistic (TMD8 and Ramos) and additive (WSU-DLCL2) activity, as assessed by the Chou-Talalay method. Quantification of cell viability (propidium iodide [PI]-negative and Annexin V-negative) and early/late apoptosis (Annexin V-positive and PI-negative/ Annexin V-positive and-PI positive) on TMD8 and Ramos cells treated with loncastuximab tesirine, polatuzumab vedotin or the combination of the two agents showed a significant reduction of viable cells accompanied by an increase in apoptotic cells in the combination setting compared to the single agents. In vivo, loncastuximab tesirine was tested either alone (0.25 or 0.5 mg/kg, single dose) or in combination with polatuzumab vedotin (1 mg/kg, single dose) in the WSU-DLCL2 xenograft model. At the highest dose of loncastuximab tesirine, combination with polatuzumab vedotin resulted in improved anti-tumor activity and superior response rate compared to the 2 agents in monotherapy. All treatment regimens were well tolerated by the mice, as assessed by body weight measurements and frequent observation for signs of treatment-related side effects. In conclusion, the combination of loncastuximab tesirine and polatuzumab vedotin resulted in improved anti-tumor activity both in vitro and in vivo in lymphoma preclinical models and it was well tolerated. Altogether, these novel pre-clinical data warrant translation of the combination of loncastuximab tesirine and polatuzumab vedotin into the clinic for the treatment of NHL. Disclosures Sachini: ADC Therapeutics: Current Employment, Current equity holder in publicly-traded company. Jabeen: ADC Therapeutics: Current Employment, Current equity holder in publicly-traded company. van Berkel: ADC Therapeutics: Current Employment, Current equity holder in publicly-traded company, Patents & Royalties. Zammarchi: ADC Therapeutics: Current Employment, Current equity holder in publicly-traded company, Patents & Royalties.