Anticancer Section / Original Paper Chemotherapy 2019;64:138–145 Effects of Glutathione Transferase-Targeting Nitrobenzoxadiazole Compounds in Relation to PD-L1 Status in Human Melanoma Cells Francesca Sciarretta a Chiara Fulci a Camilla Palumbo b Dante Rotili c Lucio Tentori d Grazia Graziani d Anna Maria Caccuri a, e a Department of Experimental Medicine, University of Rome Tor Vergata, Rome, Italy; b Department of Clinical Sciences and Translational Medicine, University of Rome Tor Vergata, Rome, Italy; c Department of Drug Chemistry and Technologies, University of “Sapienza,” Rome, Italy; d Department of Systems Medicine, University of Rome Tor Vergata, Rome, Italy; e The NAST Centre for Nanoscience and Nanotechnology and Innovative Instrumentation, University of Rome Tor Vergata, Rome, Italy Received: July 25, 2019 Accepted: September 12, 2019 Published online: October 22, 2019 Anna Maria Caccuri Department of Experimental Medicine, University of Rome Tor Vergata via Montpellier 1 IT–00133 Rome (Italy) E-Mail caccuri @uniroma2.it © 2019 S. Karger AG, Basel E-Mail karger@karger.com www.karger.com/che DOI: 10.1159/000503339 Keywords PD-L1 · NBDHEX · Chloroquine · Vemurafenib · Melanoma · Autophagy Abstract Background: PD-L1 is a membrane protein with inhibitory effects on immune responses, whose expression has been correlated with high aggressiveness and the propensity of melanoma to metastasize. The nitrobenzoxadiazole (NBD) NBDHEX and its analog MC3181 are endowed with strong antitumor activity towards melanoma and a significant abil- ity to reduce its adhesion and invasiveness. Therefore, we investigated whether PD-L1 status could affect cell sensitiv- ity to the cytotoxic effects of NBDs. We then evaluated the effects of NBDHEX on PD-L1 expression and autophagy in melanoma cells. We used the BRAF-mutated A375 melano- ma cell line and an A375 variant population enriched for PD- L1+ cells as a model. The cytotoxic effects of NBDs were eval- uated in comparison to those of the BRAF inhibitor vemu- rafenib and the autophagy inhibitor chloroquine. Methods: The effect of NBDHEX on autophagy was determined by measuring LC3-II and p62 protein levels by Western blot. The cytotoxic activity of the compounds was evaluated by sul- forhodamine B assay. PD-L1 expression and plasma mem- brane localization were analyzed by FACS and Western blot analysis. Results: NBDHEX behaves as a late-autophagy in- hibitor in A375 melanoma cells, as previously found in other tumor cell lines. NBDHEX and MC3181 showed strong and comparable cytotoxic activity in both parental and PD-L1+ A375 cells, with IC 50 values in the sub-micromolar range. Conversely, cells sorted for high PD-L1 expression had lower sensitivity to both the BRAF inhibitor vemurafenib and the autophagy inhibitor chloroquine. NBDHEX treatment did not change the total expression and cell surface localization of PD-L1 in both parental and PD-L1+ A375 cells. Conclu- sions: Our data suggest that NBDs may represent a promis- ing treatment strategy for melanoma with elevated PD-L1 expression. © 2019 S. Karger AG, Basel