Review Article
Transgenic mice expressing inhibin α-subunit promoter (inhα)/Simian Virus 40 T-antigen (Tag) transgene as a model for the therapy of granulosa cell-derived ovarian cancer

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Abstract

Granulosa cell tumors are rare, 3–7.6% of primary ovarian tumors, although with poor prognosis as the tumor-related mortality rate is 37.3%, with 80% of deaths occurring on recurrence. We have created a transgenic (TG) murine model for gonadal somatic cell tumors by expressing the powerful viral oncogene, Simian Virus 40 T-antigen (Tag), under the regulation of murine inhibin α-subunit 6 kb promoter (inhα/Tag). Gonadotropin dependent ovarian granulosa cell tumors were formed in females by the age of 5–6 months, with a 100% penetrance. We have successfully used the inhα/Tag model to test different treatment strategies for ovarian tumors. With a gene therapy trial in inhα/Tag mice crossbred with inhα/HSV-TK (herpes simplex virus thymidine kinase) mice (double TG), we proved the principle that targeted expression of HSV-TK gene in gonadal somatic cell tumors enabled tumor ablation by anti-herpes treatment. When we aimed at targeted destruction of luteinizing hormone/chorionic gonadotropin receptor (LHCGR) expressing inhα/Tag tumor cells in vivo by a lytic peptide Hecate-CGβ conjugate, we could successfully kill the tumor cells, sparing the normal cells. We recently found high zona pellucida glycoprotein 3 (ZP3) expression in inhα/Tag granulosa cell tumors, as well as in human granulosa cell tumors. We tested the concept of treating the ovarian tumors of inhα/Tag mice by vaccination against the ectopically expressed ZP3. Immunotherapy with recombinant human (rh) ZP3 was highly successful with no objective side effects in inhα/Tag females, suggesting rhZP3 immunization as a novel strategy for the immunotherapy of ovarian granulosa cell tumors.

Introduction

Ovarian cancer is the third most common type of gynecological malignancy (after cervical and endometrial cancer), although with the highest mortality rate in the female reproductive system [1]. Ovarian tumors originate from three cell types. Germ cell tumors of the ovary are uncommon (∼3%), but aggressive tumors are mostly seen among young women or adolescent girls, frequently unilateral, and are generally curable if diagnosed and treated early [2]. Ovarian sex cord-stromal tumors are a heterogeneous group of benign or malignant tumors derived from stromal components that comprise of the granulosa cells, theca cells and fibrocytes [3]. This group accounts for ∼7% of ovarian cancers, which occur in women of all ages, has a prognosis and tumor-related mortality rate of 37.3%, where ∼80% of deaths occur on recurrence [4]. Surface epithelium-derived tumors are the largest group (∼90%) of ovarian tumors, with 50% of all cases occurring in women older than 65 years [5]. For surface epithelial and stromal tumors, the most common sites of metastasis are the pleural cavity (33%), liver (26%), and lungs (3%) [6], [7], [8].

Section snippets

Granulosa cell tumor

Based on clinical behavior and histopathological findings granulosa cell tumors (GCT) can be divided into two subtypes: adult (AGCT; 95%) and juvenile (JGCT; 5%) [9]. Primary treatment for patients with stage I of GCTs is surgery. Postoperative treatment options such as chemotherapy, radiotherapy or hormonal treatment are often considered to be reasonable choice for patients with advanced disease by surgical staging, and for patients with recurrent tumor [9], [10], [11].

Many genetic and

Inhibin α-SV40 Tag transgenic mice

We have created transgenic mice carrying the SV40 large T-antigen under the inhibin α promoter (Inhα/Tag) [30], [31] for tissue-selective gonadal somatic cell tumors (GCT in females and Leydig cell tumors in males) (Fig. 1). These mice develop gonadal tumors, with 100% penetrance by the age of 5–7 months (Fig. 1) [30], [31]. Another important feature of the Inhα/Tag mice is that when prepubertally gonadectomized they develop adrenocortical tumors with 100% incidence [32], [33] (Fig. 1). Leydig

Gene therapy

Gene therapy is an experimental technique involving the introduction of foreign nucleic acid (DNA or RNA) into somatic or germ cells to treat or prevent a disease [40]. DNA delivery to the cells can be accomplished using recombinant viruses (viral vectors) or injection of purified fragment of DNA (non-viral methods/liposomes) [41]. Mechanism of gene therapy action involves: replacing a mutated gene with a healthy copy, inactivation of mutated gene or introduction a new gene into the abnormal

Targeted treatment with Hecate-CGβ conjugate

One of the developed anti-cancer approaches uses the fact that tumor cells are preferentially permeabilized by natural lytic peptides, or their synthetic analogs, due to negative charge on their outer plasma membrane [48]. The specificity and therapeutic potential of the lytic peptide can be increased by its fusion with specific ligand of the membrane receptor expressed on tumor cells. An example of fused polypeptide is Hecate-CGβ conjugate consisting of a 15-amino acid fragment of human

A novel target-defined GCT-associated antigen ZP3 mediated immunotherapy

Recently, abundant ectopic expression of ZP3 has been found in GCT of the inhα/Tag mice, as well as in human GCT and in cell lines established from these murine and human GCT tumors (KK-1, KGN) [35]. ZP3, like other zona pellucida glycoproteins (ZP1, -2 and -4), is synthesized exclusively by oocytes and it forms a glycoprotein coat surrounding the plasma membrane of the oocyte [55], [56], [57]. Due to its specific localization and key role in sperm binding and induction of acrosome reaction,

Conflict of interest statement

None of the authors have any conflict of interest to declare.

Acknowledgements

This work was supported partially by grants from the Finnish Cultural Foundation Varsinais-Suomi Regional Fund [personal grants to M.C. and N.R.] and grant 2012/05/B/NZ5/01867 from Polish National Science Centre.

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