Citation: Rajtak, A.; Czerwonka, A.; Pitter, M.; Kotarski, J.; Okla, K. Clinical Relevance of Mortalin in Ovarian Cancer Patients. Cells 2023, 12, 701. https://doi.org/10.3390/ cells12050701 Academic Editors: Anahid Jewett and Kawaljit Kaur Received: 30 January 2023 Accepted: 20 February 2023 Published: 23 February 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). cells Article Clinical Relevance of Mortalin in Ovarian Cancer Patients Alicja Rajtak 1 , Arkadiusz Czerwonka 2 , Michael Pitter 3 , Jan Kotarski 1 and Karolina Okla 1,3, * 1 The First Department of Oncologic Gynecology and Gynecology, Medical University of Lublin, 20-081 Lublin, Poland 2 Department of Biochemistry and Molecular Biology, Medical University of Lublin, 20-081 Lublin, Poland 3 Department of Surgery, University of Michigan, Ann Arbor, MI 48109-2200, USA * Correspondence: karolinaokla@umlub.pl Abstract: Background: Ovarian cancer (OC) is the most lethal malignancy of the female reproductive tract. Consequently, a better understanding of the malignant features in OC is pertinent. Mortalin (mtHsp70/GRP75/PBP74/HSPA9/HSPA9B) promotes cancer development, progression, metastasis, and recurrence. Yet, there is no parallel evaluation and clinical relevance of mortalin in the peripheral and local tumor ecosystem in OC patients. Methods: A cohort of 92 pretreatment women was recruited, including 50 OC patients, 14 patients with benign ovarian tumors, and 28 healthy women. Blood plasma and ascites fluid-soluble mortalin concentrations were measured by ELISA. Mortalin protein levels in tissues and OC cells were analyzed using proteomic datasets. The gene expression profile of mortalin in ovarian tissues was evaluated through the analysis of RNAseq data. Kaplan– Meier analysis was used to demonstrate the prognostic relevance of mortalin. Results: First, we found upregulation of local mortalin in two different ecosystems, i.e., ascites and tumor tissues in human OC compared to control groups. Second, abundance expression of local tumor mortalin is associated with cancer-driven signaling pathways and worse clinical outcome. Third, high mortalin level in tumor tissues, but not in the blood plasma or ascites fluid, predicts worse patient prognosis. Conclusions: Our findings demonstrate a previously unknown mortalin profile in peripheral and local tumor ecosystem and its clinical relevance in OC. These novel findings may serve clinicians and investigators in the development of biomarker-based targeted therapeutics and immunotherapies. Keywords: mortalin/mtHsp70/GRP75/PBP74/HSPA9/HSPA9B; ovarian cancer; biomarker; metastasis; recurrence; OXPHOS; EMT; stemness; RNAseq 1. Introduction Ovarian cancer (OC) is the most lethal of all gynecological malignancies [1]. Specif- ically, 75% of patients are diagnosed at advanced stages, and 75% of these patients die within 5 years. The majority of these mortalities are due to recurrence of disease, resistance to current therapies, significant heterogeneity of tumors, and immune suppression in tumor microenvironments (TMEs) [2–5]. Additionally, early-stage OC is usually asymptomatic; therefore, it is mainly diagnosed at an advanced stage, during spread of disease across the peritoneal cavity, usually accompanied by malignant ascites [6]. While in the initial phase of the disease, OC patients usually respond well to cytoreductive debulking surgery and chemotherapy, bur most women develop recurrence of a chemotherapy-resistant form of the disease within 12 to 18 months [7,8]. In recent years, immunotherapy has revolution- ized cancer treatment; however, the results of immunotherapy are unsatisfactory in OC [9]. Although OC is an immunogenic tumor that can be recognized by the host immune system, spontaneous antitumor immune response has only been demonstrated in about 50% of patients, mainly due to tumor-favorable immunosuppressive TMEs [10]. The previous results of our and other research groups described the establishment of the immunosup- pressive milieu in OC, including the presence of monocytic myeloid-derived suppressor cells (M-MDSCs) and others [4,11,12]. This provides a very rich “soil” in TMEs for immune Cells 2023, 12, 701. https://doi.org/10.3390/cells12050701 https://www.mdpi.com/journal/cells