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Background: Prostate cancer continues to show challenges in disease management and ultimately leads to advanced disease with poor survival. These unmet needs, despite recent advances, are leading researchers to identify novel targets to develop next-generation therapeutics. Considerable evidence from the published reports and TCGA database analysis indicates that CRM1, which functions as a nuclear export protein, amplifies prostate cancer, resulting in dysregulated nuclear export machinery. This dysregulation is also seen to correlate with mislocalization of p53, FOXO-1, and 3a, cyclinD1, p16, p21, and p27 in prostate cancer. Besides these mislocalized proteins, key DNA repair pathway members such as BRCA1 and Rad51 exhibit a nuclear export signal (NES) and are putative CRM1 cargoes. Nuclear-cytoplasmic shuttling of these repair proteins may play an essential role in repairing damaged DNA. We hypothesize that inhibition of CRM1 would result in defective DNA repair through disruption of nuclear-cytoplasmic shuttling of important repair protein cargoes. Methods: PCa cells (both AR-positive and negative lines) were treated with Selinexor to estimate the subtoxic doses. Cell lysates and total mRNA were collected to evaluate the relative levels of BRCA-1, RAD51, p53, ATM, ATR transcripts, and proteins. Activation of the DNA damage pathway was measured through a phosphorylated form of these proteins, and functional assessment of homologous recombination(HR) was measured through an HR sensor plasmid construct. Results: Treatment of PCa cells with Selinexor affected expression, localization, and kinetics of DNA repair leading to unrepaired DNA and induced apoptosis. Citation Format: Rajendra Kumar, Janet Mendonca, Kavya Boyapati, Yuhan Yang, Deven Topiwala, Suthicha Kanacharoen, Keerti Soundappan, Lillian Wilson, Eleni Panagopoulos, Michael Carducci, Sushant K. Kachhap. Exploring the role of CRM1 in DNA repair pathway in prostate cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1505.

Complementary and alternative medicines are explored for their role in improving the quality of life of patients with cancer. Many anti-cancer drugs have been derived from natural sources. Mistletoe extract, composed of lectins, viscotoxins, flavonoids, and other biologically active substances, has two mechanisms of action: tumor cytotoxicity and immunomodulation. The cytotoxic effects of mistletoe extract are a result of protein synthesis interference, cell cycle inhibition, and apoptosis induction. Further, mistletoe extract has been shown to have anti-angiogenic properties. In Europe, Helixor M, mistletoe extract from Viscum album mali, is used as an anthroposophic medicine in the treatment of malignant and non-malignant tumors, malignant disorders with accompanying impairment of the hematopoietic organs, stimulation of bone marrow activity, reducing the risk of tumor recurrence, and diagnosed pre-cancerous disorders. However, only limited evaluation of mistletoe extract has been conducted in the United States. We studied the effects of Helixor M in prostate cancer. To evaluate its effect on cell proliferation and survival, we treated androgen receptor (AR) positive (LNCaP, LAPC4 and VCaP) and AR negative (PC3 and DU-145) cell lines with Helixor M. Our data indicates that LNCaP and LAPC4 cells were most sensitive to Helixor M while PC3, DU-145, and VCaP cells were relatively resistant to treatment. While AR protein levels and NF-kappaB subunits remained unaffected by treatment, there was an induction of apoptosis along with a concomitant decrease in LC3B, an autophagy marker, in all the sensitive prostate cancer cell lines. In search of pathways that may synergize with growth inhibition by Helixor M, we utilized CRISPR knockouts of TBK1, a kinase involved in autophagy induction, in LNCaP cells and tested whether TBK1 knockouts are synthetically lethal with Helixor M. Helixor M induced increased apoptosis in TBK1 knockouts as compared to parental LNCaP cells, indicating that TBK1 loss might be synthetically lethal with Helixor M. Citation Format: Kavya Boyapati, Rajendra Kumar, Lillian Wilson, Yuhan Yang, Deven Topiwala, Keerti Soundappan, Eleni Panagopoulos, Ivelisse Page, Jennifer Durham, Michael Carducci, Channing Paller, Sushant Kachhap. Effect of mistletoe extract on growth and proliferation of prostate cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB102.