Citation: Jannoo, R.; Xia, Z.; Row, P.E.; Kanamarlapudi, V. Targeting of the Interleukin-13 Receptor (IL-13R)α2 Expressing Prostate Cancer by a Novel Hybrid Lytic Peptide. Biomolecules 2023, 13, 356. https://doi.org/10.3390/ biom13020356 Academic Editor: Mikhail Soloviev Received: 20 December 2022 Revised: 31 January 2023 Accepted: 9 February 2023 Published: 12 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/). biomolecules Article Targeting of the Interleukin-13 Receptor (IL-13R)α2 Expressing Prostate Cancer by a Novel Hybrid Lytic Peptide Riaz Jannoo 1 , Zhidao Xia 2 , Paula E. Row 2 and Venkateswarlu Kanamarlapudi 2, * 1 UCL ECMC GCLP Facility, UCL Cancer Institute, University College London, London WC1E 6DD, UK 2 Institute of Life Science, School of Medicine, Swansea University, Singleton Park, Swansea SA2 8PP, UK * Correspondence: k.venkateswarlu@swansea.ac.uk; Tel.: +44-1792-295012 Abstract: The IL-13Rα2 cell surface receptor is highly expressed in tumours such as prostate cancer. In this report, we evaluated the hypothesis that prostate cancer cells with enhanced IL-13Rα2 expression are a suitable target for the hybrid lytic peptide (Pep-1-Phor21) peptide, which is generated by fusing the IL-13Rα2 specific ligand (Pep-1) and a cell membrane disrupting lytic peptide (Phor21). The expression of IL-13Rα2 mRNA and protein in prostate cancer tissues and cell lines was assessed via real-time PCR (RT-PCR) and immunoblotting. The effect of Pep-1-Phor21 on the viability of prostate cancer cells grown in monolayers (2D) and microtissue spheroids (3D) was assessed via CellTox green cytotoxic assay. IL-13Rα2 expression and Pep-1-Phor21-mediated killing were also determined in the cells treated with epigenetic regulators (Trichostatin A (TSA) and 5-aza-2 deoxycytidine (5-Aza-dC)). The hybrid lytic peptide cytotoxic activity correlated with the expression of IL-13Rα2 in prostate cancer cell lines cultured as monolayers (2D) or 3D spheroids. In addition, TSA or 5-Aza-dC treatment of prostate cancer cells, particularly those with low expression of IL-13Rα2, enhanced the cells’ sensitivity to the lytic peptide by increasing IL-13Rα2 expression. These results demonstrate that the Pep-1-Phor21 hybrid lytic peptide has potent and selective anticancer properties against IL-13Rα2-expressing prostate cancer cells. Keywords: prostate cancer; IL-13Rα2; hybrid lytic peptide; Pep-1; Phor21; therapeutic peptide; 3D spheroids; epigenetics 1. Introduction Prostate cancer is the second most diagnosed cancer type and the fifth leading cause of cancer death in men worldwide [1]. Like most solid tumours, prostate cancer is a highly lethal tumour that can metastasise to distant organs such as the bone, liver, lungs and brain if not detected early [1]. Patients diagnosed with prostate cancer at its early stages have a 5-year survival rate of 100% [1]. However, the 5-year survival rate drops significantly to 31% in patients diagnosed with advanced stages of the disease [1]. Current treatments (such as chemotherapy) cannot cure but only prolong patients’ lives. Chemotherapeutic treatment is usually given when cancer becomes metastatic [2]. Although chemotherapeutic drugs are effective, they destroy both rapidly dividing cancerous and non-cancerous cells, and hence their use can cause serious side effects by destroying healthy tissue and organs. Moreover, these drugs are unable to target dormant cancer cells and slow-growing tumours [3]. The effectiveness of these chemotherapeutic drugs is further reduced once the cancer cells overexpress drug efflux pumps such as P-glycoprotein, developing resistance to the treatment [4,5]. Although hormonal therapy has been shown to reduce tumour size in most men with advanced prostate cancer, with few side effects, its use can cause the disease to re- emerge and differentiate into a more aggressive form, making the treatment ineffective [4,6]. These studies clearly illustrate the need for the development of novel effective treatments for metastatic prostate cancer, with fewer or no side effects. The cytokine Interleukin (IL)-13 plays an important role in allergy and atopic dis- eases [7]. It has two receptors, a low-affinity IL-13Rα1 and a high-affinity IL-13Rα2[8–10]. Biomolecules 2023, 13, 356. https://doi.org/10.3390/biom13020356 https://www.mdpi.com/journal/biomolecules