Synergistic activation of innate and adaptive immune mechanisms in the treatment of gonadotropin-sensitive tumors

Progesterone limits the tumor-promoting effects of the beta-subunit of human chorionic gonadotropin via non-nuclear receptors

The post-menopausal state in women is associated with increased cancer incidence, the reasons for which remain obscure. Curiously, increased circulating levels of beta-hCG (human chorionic gonadotropin) (a hormonal subunit linked with tumors of several lineages) are also often observed post-menopause. This study describes a previously unidentified interplay between beta-hCG and progesterone in tumorigenesis. Progesterone mediated apoptosis in beta-hCG responsive tumor cells via non-nuclear receptors. The transgenic expression of beta-hCG, particularly in the absence of the ovaries (a mimic of the post-menopausal state) constituted a potent pro-tumorigenic signal. Significantly, the administration of progesterone had significant anti-tumor effects. RNA-seq profiling identified molecular signatures associated with these processes. TCGA analysis revealed correlates between the expression of several newly identified genes and poor prognosis in post-menopausal patients of lung adenocarcinoma, colon adenocarcinoma, and glioblastoma. Specifically in these women, the detection of intra-tumoral/extra-tumoral beta-hCG may serve as a useful prognostic indicator, and treatment with progesterone on its detection may prove beneficial.

Unconventional Actions of Glycoprotein Hormone Subunits: A Comprehensive Review

The glycoprotein hormones (GPH) are heterodimers composed of a common α subunit and a specific β subunit. They act by activating specific leucine-rich repeat G protein-coupled receptors. However, individual subunits have been shown to elicit responses in cells devoid of the receptor for the dimeric hormones. The α subunit is involved in prolactin production from different tissues. The human chorionic gonadotropin β subunit (βhCG) plays determinant roles in placentation and in cancer development and metastasis. A truncated form of the thyrotropin (TSH) β subunit is also reported to have biological effects. The GPH α- and β subunits are derived from precursor genes (gpa and gpb, respectively), which are expressed in most invertebrate species and are still represented in vertebrates as GPH subunit paralogs (gpa2 and gpb5, respectively). No specific receptor has been found for the vertebrate GPA2 and GPB5 even if their heterodimeric form is able to activate the TSH receptor in mammals. Interestingly, GPA and GPB are phylogenetically and structurally related to cysteine-knot growth factors (CKGF) and particularly to a group of antagonists that act independently on any receptor. This review article summarizes the observed actions of individual GPH subunits and presents the current hypotheses of how these actions might be induced. New approaches are also proposed in light of the evolutionary relatedness with antagonists of the CKGF family of proteins.

The transgenic expression of the β-subunit of human chorionic gonadotropin influences the growth of implanted tumor cells

The beta subunit of human chorionic gonadotropin (βhCG) is secreted by various tumors, and its presence associated with poor prognosis. Though exogenous hCG elicits the synthesis of molecules associated with angiogenesis, invasion, immune suppression and chemoresistance from responsive tumor cells in vitro, the influence of cell-extrinsic βhCG on tumorigenesis in vivo has not been adequately explored. Female C57BL/6^-/- × FVB^βhCG/- F1 transgenic mice demonstrated ovarian hyperplasia and pituitary adenomas; transcripts of hCG-driven, tumor-associated molecules were heightened in the pituitary. Upon the implantation of Lewis Lung Carcinoma cells (murine lung tumor cells derived from C57BL/6 mice) in transgenic mice, tumor incidence and volume were enhanced, and increased transcription and expression of hCG-driven, tumor-associated molecules was observed in excised tumors. While treatment of these mice with Cabergoline (a potent dopamine receptor agonist) had no significant effects, ovariectomy resulted in a reduction in the lag phase, accompanied by an increase in tumor incidence and volume upon Lewis Lung Carcinoma cell implantation. In tumors derived from Lewis Lung Carcinoma cell-implanted ovariectomized, transgenic mice, the transcription and expression of hCG-driven, tumor-associated molecules remained elevated and enhanced animal mortality was observed. Cell-extrinsic βhCG can therefore induce pro-tumorigenic effects in vivo (even on tumor lineages not part of the reproductive axis), with ovarian products mediating an ameliorating influence.

Gonadotropin and tumorigenesis: Direct and indirect effects on inflammatory and immunosuppressive mediators and invasion

Human chorionic gonadotropin (hCG), a hormone essential for pregnancy, is also ectopically expressed by a variety of cancers and is associated with poor prognosis; molecular mechanisms which may contribute to tumor progression remain ill-defined. Exogenous hCG enhanced the viability of human colorectal and lung cancer cells and promoted the growth of syngeneic tumors in mice. It induced the synthesis of VEGF, IL-8, matrix metalloprotease (MMP)-2 and MMP-9, and increased invasiveness in an MMP-dependent manner. While inducing the secretion of the tumor-associated extra-cellular matrix proteoglycan versican from tumor cells, hCG consequently caused the TLR-2-mediated generation of the inflammatory, tumor-associated cytokines TNF-α and IL-6 from peripheral blood adherent cells. The molecule up-modulated the Treg-associated transcription factor FOXP3 in tumor cells and increased the secretion of TGFβ and IL-10, thereby inhibiting T cell proliferation and inducing the differentiation FOXP3^- CD4⁺ CD25^- cells into functional FOXP3⁺ CD4⁺ CD25⁺ suppressor cells. Co-culture of hCG-treated tumor cells with mature bone-marrow derived dendritic cells induced the generation of active indoleamine deoxygenase. While anti-hCG antibodies restricted the growth of implanted tumor cells in nude mice, immunization of immune competent mice with a βhCG-TT conjugate supplemented with Mycobacterium indicus pranii provided synergistic survival benefit in animals implanted with syngeneic, hCG-responsive tumor cells. These studies elucidate the pathways by which hCG can promote tumorigenesis, providing further rationale for anti-hCG vaccination in the treatment of gonadotropin-sensitive tumors. © 2016 Wiley Periodicals, Inc.

Gonadotropin-mediated chemoresistance: Delineation of molecular pathways and targets

Background

Human chorionic gonadotropin (hCG) has essential roles in pregnancy. Reports linking hCG in non-trophoblastic tumors with poor patient prognosis has spurred interest in patho-physiological roles the hormone might play.

Methods

The ability of hCG to prevent tumor cell death and sustain viability in the presence of chemotherapeutic drugs was assessed and potential synergies with TLR ligands explored. hCG-induced up-modulation of genes involved in chemoresistance was documented and targets validated by siRNA knock-down. Whether hCG could drive collaboration between tumor cells and macrophages in the production of IL-6 and consequent chemoresistance was assessed. The effects of concurrent anti-hCG immunization and chemotherapy on the growth of syngeneic murine tumors were evaluated.

Results

hCG maintained basal levels of cytokine secretion by tumor cells exposed to chemotherapeutic drugs, and enhanced viability and proliferation; pre-treatment with hCG also decreased apoptosis, as assessed by Annexin-V binding and the cleavage of caspase 3. While co-incubation with hCG along with several TLR ligands mediated heightened chemo-resistance, TLR-2/6 and TLR-9 ligands increased the phosphorylation of JNK, and TLR-2 and TLR-8 ligands the phosphorylation of ERK in presence of hCG and curcumin, providing evidence of tri-molecular synergy. The hormone increased the transcription and/or expression of molecular intermediates (SURVIVIN, HIF-1α, PARP-1, Bcl-2, c-FLIP, KLK-10, XIAP, c-IAP-1) associated with chemo-resistance and increased levels of stress modulators (PON2, HO-1, HSP27 and NRF-2). siRNAs to SURVIVIN, NRF-2, HO-1 and HIF-1α attenuated hCG-mediated chemo-resistance. hCG-conditioned tumor cell supernatants induced heightened secretion of IL-6 and TNF-α from peripheral blood adherent cells and secreted IL-6 imparted chemo-resistance to naïve tumor cells. Co-administration of curcumin along with an anti-hCG vaccine (hCGβ conjugated to Tetanus Toxoid (TT)) to mice carrying syngeneic tumors resulted in significantly enhanced benefits on animal survival; synergy was demonstrated between anti-hCG antibodies and curcumin in the reduction of tumor cell viability.

Conclusions

The data suggest that hCG, via direct as well as collaborative effects with TLR ligands and accessory cell-secreted cytokines, mediates chemo-resistance in gonadotropin-sensitive tumors and outlines the potential benefits of combination therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1938-x) contains supplementary material, which is available to authorized users.

TGF-β-induced hCG-β regulates redox homeostasis in glioma cells

Transforming growth factor (TGF-β) is associated with the progression of glioblastoma multiforme (GBM)-the most malignant of brain tumors. Since there is a structural homology between TGF-β and human chorionic gonadotropin (hCG) and as both TGF-β and hCG-β are known regulators of oxidative stress and survival responses in a variety of tumors, the role of TGF-β in the regulation of hCG-β and its consequences on redox modulation of glioblastoma cells was investigated. A heightened hCG-β level was observed in GBM tumors. TGF-β treatment increased hCG-β expression in glioma cell lines, and this heightened hCG-β was found to regulate redox homeostasis in TGF-β-treated glioma cells, as siRNA-mediated knockdown of hCG-β (i) elevated reactive oxygen species (ROS) generation, (ii) decreased thioredoxin Trx1 expression and thioredoxin reductase (TrxR) activity, and (iii) abrogated expression of TP53-induced glycolysis and apoptosis regulator (TIGAR). Silencing of hCG-β abrogated Smad2/3 levels, suggesting the existence of TGF-β-hCG-β cross-talk in glioma cells. siRNA-mediated inhibition of elevated TIGAR levels in TGF-β-treated glioma cells was accompanied by an increase in ROS levels. As a farnesyltransferase inhibitor, Manumycin is known to induce glioma cell apoptosis in a ROS-dependent manner, and we investigated whether Manumycin could induce apoptosis in TGF-β-treated cells with elevated hCG-β exhibiting ROS-scavenging property. Manumycin-induced apoptosis in TGF-β-treated cells was accompanied by elevated ROS levels and decreased expression of hCG-β, Trx1, Smad2/3, and TIGAR. These findings indicate the existence of a previously unknown TGF-β-hCG-β link that regulates redox homeostasis in glioma cells.