Effect of Prolactin receptor antagonist in treatment of ovarian cancer

Understanding of hormone actions and hormone sensitivity has lead to successful cancer treatments, where breast and prostate cancer are routinely treated with agents interfering with hormones. Other types of cancers respond to treatments targeting growth factors e.g. EGF and PDGF and both of these factors exert actions on cells that change regulatory cell signals. The cancer to be investigated in this study (ovarian cancer) is not regarded to be hormone responsive tumor in a classical sense but may use local production of PRL to create signals leading to tumor survival (eg. growth factors). The recent finding of local PRL production in tumors motivates the present investigation as do our preliminary finding that CMV can activate local PRL production. A viral participation in tumorigenesis has been demonstrated in some cases but how latent viral infections, like CMV, affects the host genome and tumor growth has not been well investigated. The project will be carried out as a collaboration with in-house experts on the subject (Drs Norstedt , Al-Bahri and Al-Zadjali) and experts in other countries including the US and Sweden. Together we believe that we have a unique opportunity to advance this research field using different methodologies including IHC , cell based assays and in vivo studies.

Understanding of hormone actions and hormone sensitivity has lead to successful cancer treatments, where breast and prostate cancer are routinely treated with agents interfering with hormones. Other types of cancers respond to treatments targeting growth factors e.g. EGF and PDGF and both of these factors exert actions on cells that change regulatory cell signals. The cancer to be investigated in this study (ovarian cancer) is not regarded to be hormone responsive tumor in a classical sense but may use local production of PRL to create signals leading to tumor survival (eg. growth factors). The recent finding of local PRL production in tumors motivates the present investigation as do our preliminary finding that CMV can activate local PRL production. A viral participation in tumorigenesis has been demonstrated in some cases but how latent viral infections, like CMV, affects the host genome and tumor growth has not been well investigated. The project will be carried out as a collaboration with in-house experts on the subject (Drs Norstedt , Al-Bahri and Al-Zadjali) and experts in other countries including the US and Sweden. Together we believe that we have a unique opportunity to advance this research field using different methodologies including IHC , cell based assays and in vivo studies.

CONTROL OF PROLACTIN SENSITIVITY Several hormone systems are characterized by changes in target tissue sensitivity. Key factors in hormone sensitivity include the number of cell-surface receptors, and the duration of receptor-activated intracellular signals. Many studies have addressed agents that control receptor number, and it is also recognized that tight control of receptor number is required to regulate the duration of hormone-activated signals. In this work, particular focus will be given to two different proteins, SOCS2 and TSC2 that uniquely impinge on JAK-STAT and mTOR pathways activation in response to PRL. PRLR antagonist development There are several compounds that target the PRL system, with the exception of a PRLR antagonist (PRLRA). The development of a PRLRA (not yet in clinical use) is described below. The different utilities of such an antagonist can be considered since PRL production is not solely restricted to the pituitary gland, but also occurs in extra-pituitary tissues, e.g. the mammary gland, prostate and lymphocytes. Locally-produced PRL can take part in proliferation and in tumor development [17?21]. One may note that dopamine receptor agonists are clinically used as anti-PRL drugs. These drugs reduce production of PRL from the pituitary, but cannot target extra-pituitary PRL production. PRL interacts through two binding sites (BS1 and BS2) with receptor dimer molecules and forms the PRL-PRLR homodimer [22,23]. In hPRL, 13 residues are involved in the process of receptor binding. PRLRA were designed to impair BS2 [24]. By substituting glycine at position 129 in the conserved helix 3 for arginine, first generation antagonists were created and named G129R-hPRL [25]. A successful strategy to generate antagonists with significantly improved affinity to block the receptor has identified a series of single mutation sites, which enhanced BS1 affinity. By combining the single mutations, researchers succeeded in generating an antagonist with significantly improved affinity to block the receptor. We have used this antagonist, PRL-S33A, Q73L, G129R, K190R in our previous studies [26,27] and planning to use it in forthcoming studies. PRL role in cancer There are many different causes of cancer including infection, chemical exposure, genetic mutations and local cytokine production. The hallmarks of cancer are self-sufficient growth signals, unlimited proliferation, permanent angiogenesis, and failure of apoptotic mechanisms and insensitivity to anti-growth signals. Many human cancers develop as a result of exposure to viral infection. A new line of research in the last years suggest that human cytomegalovirus (CMV) infection can also contribute to several human malignancies including breast, colon, prostate, rhabdomyosarcoma, hepatocellular cancer, salivary gland tumors, neuroblastoma, and brain tumors [28]. A supportive study by Shanmughapriya et al [29], showed that CMV DNA was present in 50% of fresh ovarian carcinoma tissue samples (39 samples). It was suggested that human CMV is able to create a more malignant phenotype of tumor cells by the action of its regulatory proteins and non-coding RNA, which will affect their proliferation, invasion of other tissues, survival and other cellular properties [30]. Our preliminary studies showed that an experimental CMV infection of ovarian cancer cell line activates Prl and Prl signals. This might open a new therapeutic angel of combining anti viral treatment and PRLRA along with anti cancer agents. Ovarian cancer Ovarian cancer is the second most frequent gynecologic malignancy and carries a higher mortality rate than all other female genital cancers combined. There are many types of ovarian tumors including benign, borderline, and malignant types. About two-thirds occur in women of reproductive age. Approximately 80% of ovarian tumors are benign and 90% of malignant tumors are diagnosed after the age of 40 years [31]. Based on the ovarian cell type of origin, ovarian epithelial tumors considered the most common type (approximately 60%). As it is difficult to detect ovarian cancer early in its evolution when it is still curable, over three-fourths of patients already have extra-ovarian tumor spread to the pelvis or abdomen at the time of diagnosis. Survival for patients with malignant ovarian tumors is generally poor. The most important prognostic index is the surgical stage of the tumor [32]. With regard to PRL, elevated levels of serum PRL in ovarian cancers have been reported indicating a potential role for prolactin in ovarian carcinogenesis. Furthermore, serum PRL levels are significantly elevated in women with a strong family history of ovarian cancer [33]. Another study suggested that prolactin might be associated with increased risk of ovarian cancer, particularly in overweight/obese women. Prolactin receptor expression and circulating prolactin levels have been shown to be higher among women with ovarian cancer vs. benign-condition or healthy controls [33,34]. However, the relationship between circulating prolactin levels and risk of ovarian cancer and the molecular pathways involved in this is still unknown (our study aim).