“Two hits - one stone”; increased efficacy of cisplatin-based therapies by targeting PCNA’s role in both DNA repair and cellular signaling

// Caroline Krogh Søgaard 1, 3, * , Augun Blindheim 1, 2, * , Lisa M. Røst 4 , Voin Petrović 1 , Anala Nepal 1 , Siri Bachke 1 , Nina-Beate Liabakk 1 , Odrun A. Gederaas 1 , Trond Viset 5 , Carl-Jørgen Arum 1, 2 , Per Bruheim 4 and Marit Otterlei 1, 3, 6 1 Department of Clinical and Molecular Medicine, Norwegian University of Science and Technology (NTNU), Trondheim, Norway 2 Department of Urology and Surgery, St. Olavs Hospital, Trondheim University Hospital, Trondheim, Norway 3 Clinic of Surgery, St. Olavs Hospital, Trondheim University Hospital, Trondheim, Norway 4 Department of Biotechnology and Food Science, NTNU, Trondheim, Norway 5 Department of Pathology, St. Olavs Hospital, Trondheim University Hospital, Trondheim, Norway 6 APIM Therapeutics A/S, Trondheim, Norway * These authors have contributed equally to this work Correspondence to: Marit Otterlei, email: marit.otterlei@ntnu.no Keywords: muscle-invasive bladder cancer; APIM-peptide; cellular signaling; DNA repair; cisplatin resistance Received: June 06, 2018     Accepted: July 31, 2018     Published: August 21, 2018 ABSTRACT Low response rate and rapid development of resistance against commonly used chemotherapeutic regimes demand new multi-targeting anti-cancer strategies. In this study, we target the stress-related roles of the scaffold protein PCNA with a cell-penetrating peptide containing the PCNA-interacting motif APIM. The APIM-peptide increased the efficacy of cisplatin-based therapies in a muscle-invasive bladder cancer (MIBC) solid tumor model in rat and in bladder cancer (BC) cell lines. By combining multiple omics-levels, from gene expression to proteome/kinome and metabolome, we revealed a unique downregulation of the EGFR/ERBB2 and PI3K/Akt/mTOR pathways in the APIM-peptide-cisplatin combination treated cells. Additionally, the combination treatment reduced the expression of anti-apoptotic proteins and proteins involved in development of resistance to cisplatin. Concurrently, we observed increased levels of DNA breaks in combination treated cells, suggesting that the APIM-peptide impaired PCNA - DNA repair protein interactions and reduced the efficacy of repair. This was also seen in cisplatin-resistant cells, which notably was re-sensitized to cisplatin by the APIM-peptide. Our data indicate that the increased efficacy of cisplatin treatment is mediated both via downregulation of known oncogenic signaling pathways and inhibition of DNA repair/translesion synthesis (TLS), thus the APIM-peptide hits both nuclear and cytosolic functions of PCNA. The novel multi-targeting strategy of the APIM-peptide could potentially improve the efficacy of chemotherapeutic regiments for treatment of MIBC, and likely other solid tumors.