Abstract 527: A new generation of PARP interfering drug candidates for cancer treatment
Authors: Jdey Wael , Zandanel Christelle , Trochon-Joseph Véronique , Doizelet Chloé , Hayes Vincent , Lienafa Marie-Christine , Tripelon Richard , Bono Françoise 
Published: July 2021

Purpose: Therapeutic strategies targeting DNA repair defects have been widely explored, but often restricted to a specific population of patients and tackled with resistance issues. We pioneered a new approach of anti-cancer treatment to tackle emergence of resistance: the decoy agonist mechanism of action. Drugs based on this mechanism hijack and hyperactivate therapeutic targets leading to an impairment of the repair signaling. This breakthrough decoy agonist action has already shown, using our lead compound AsiDNA™, target engagement, excellent safety profile in humans, and importantly lack of acquired resistance. Here, we describe mechanistically the immunomodulatory properties and metabolic effects of a new generation product OX401, generated using the proprietary PlatON™ platform of oligonucleotides designed to trap PARP proteins.

Experimental design: OX401-induced PARP activation, NAD+ consumption and cell cytotoxicity were monitored using tumor and non-tumor cells. DNA repair abrogation was monitored by analyzing repair protein recruitment to damage sites. Accumulation of cytoplasmic DNA fragments was monitored after DNA staining and microscopy analysis. OX401 effect on the innate immune response was assessed by following STING pathway activation and T-cell mediated anti-tumor cytotoxicity. OX413, a “super” OX401 was designed to be more stable and less prone to intracellular enzymatic degradation. In a cell-derived xenograft model of mouse breast cancer, OX413-induced PARP activation and percentages of tumor-infiltrating leucocytes (CD45+: CD3+, CD8+, NK, DCs) were analyzed ex-vivo by flow cytometry.

Results: Using different tumor models, we showed that OX401 binds and hyper-activates PARP1 with a high affinity and in a dose-dependent manner. As a consequence, OX401 impaired DNA repair due to PARP sequestration leading to an accumulation of cytoplasmic chromatin fragments (CCFs). In line with this, we demonstrated that OX401 displayed cell-autonomous immunomodulatory properties. Mechanistically, the generated CCFs triggered an innate immunity activation through cGAS/STING pathway, downstream CCL5 secretion and potentiation of the anti-tumor T-cell dependent immune response. Through PARP hyper-activation, OX401 also induced a rapid NAD+ consumption (below the viability threshold). This metabolic exhaustion caused selective tumor cell death while sparing healthy cells. These effects were enhanced using the optimized OX413 molecule, and at doses approximately 10 to 100-fold lower compared to OX401. In-vivo, OX413 triggered PARP1 target engagement and STING pathway activation, correlated to an increased innate and adaptive immune cells infiltration.

Conclusions: Our results provide a preclinical rationale for using OX413 as an immunomodulatory and “metabolic exhauster” agent, especially in appropriately molecularly selected patients with tumors showing metabolic deficiencies.

Citation Format: Wael Jdey, Christelle Zandanel, Véronique Trochon-Joseph, Chloé Doizelet, Vincent Hayes, Marie-Christine Lienafa, Richard Tripelon, Françoise Bono. A new generation of PARP interfering drug candidates for cancer treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 527.