Abstract Cell surface mono-ADP ribosyltransferases (ARTs) transfer the ADP-ribose moiety from NAD to amino acid residues on target proteins and post-translationally regulate their function. Most mammalian ARTs are extracellular with glycosylphosphatidylinositol (GPI) anchors. ARTs can target cell surface proteins on bystander cells or soluble proteins in the tumor microenvironment, particularly P2RX7 on T cells1. We hypothesized that an evolutionarily conserved parallel protective role may be provided by ART1 expression in lung cancer cells, particularly during times of cellular stress2. A mouse KP1 lung tumor cell line with ART1 expression was established from KRASG12D/P53-/- mice and transduced with shRNA targeting ART1 (KP1-sh) or an empty vector (KP1-ev). For in vitro studies, KP1 WT cells were treated with an ER stress inducer thapsigargin, with radiation, or with chemotherapy. Using human materials, we evaluated ART1 expression in NSCLC tumors by whole tumor RT-PCR/RNAseq, immunofluorescence (IF), and immunohistochemistry (IHC). For evaluation of tumor growth in immune competent models, KP1 cells were injected into syngeneic C57BL/6 mice into the flank or intravenously to generate orthotopic lung tumors. Following in vitro treatment with thapsigargin, expression of ART1 increased 11.8-fold in KP1 WT cells (24 hrs). Similarly, following radiation (8Gy x 3,) ART1 expression increased 1.93-fold by RT-PCR and surface protein expression increased by 1.87 fold (p<0.0005) by IF in KP1 cells. Similar increases were seen following cisplatin (10uM, 24 hrs) treatment (1.87-fold). Radiation (2.26-fold) and cisplatin (25uM, 3.30-fold) also induced ART1 expression in human A549 cells (24 hrs). In a human tissue microarray of patients who received neoadjuvant chemotherapy or radiation therapy (n=200), all tumors expressed ART1 and 38% of strongly expressed ART1. We also compared pre-treatment biopsy and post-treatment surgical resection tumor samples (n=21) in an ongoing clinical trial (NCT02904954) of neoadjuvant durvalumab +/- stereotactic radiation (8Gy x 3). ART1 was expressed at low levels by RNAseq, but trended upward (4-fold) after treatment, particularly in those patients who received radiation therapy (6-fold). Expression trended higher in nonresponders. Of these tumors without major pathologic response (n=13), 44% had moderate-strong ART1 expression by IHC. In murine flank tumor models, KP1-ev cells grew significantly faster than KP1-sh cells (688 mm3 vs. 331mm3 at 4 weeks, p=0.004). Similarly, following tail vein injection, mice injected with KP1-ev cells had heavier tumor burdens by micro-CT scan and significantly greater total lung weights (p=0.036) at sacrifice than did mice injected with KP1-sh cells. In conclusion, ART1 is broadly expressed in human lung tumors and is upregulated by cellular stress invoked by common treatments such as radiation and chemotherapy. Knockdown of ART1 abrogates tumor growth and may be a potential therapeutic target for combination therapy in lung cancer patients. 1. PMID: 7930612 2. PMID: 25292337 Citation Format: Sumit Mukherjee, Erik Wennerberg, Clarey Hung, Najla Saadallah, Shashi Kariyawasam, Christopher Agrusa, Amanda Valeta, Nasser Altorki, Timothy McGraw, Sandra Demaria, Brendon Stiles. Art1, an extracellular mono-ADP-ribosyltransferase, is upregulated in response to cellular stress and promotes lung cancer growth [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 1820.