Glucocorticoid agonistic and antagonistic effects of mifepristone and onapristone on thymocyte subset composition and CD26/dipeptidyl peptidase IV activity in infant male rats

Onapristone Extended Release: Safety Evaluation from Phase I-II Studies with an Emphasis on Hepatotoxicity

Introduction

Antiprogestins have demonstrated promising activity against breast and gynecological cancers, but liver-related safety concerns limited the advancement of this therapeutic class. Onapristone is a full progesterone receptor antagonist originally developed as an oral contraceptive and later evaluated in phase II studies for metastatic breast cancer. Because of liver enzyme elevations identified during clinical studies, further development was halted. Evaluation of antiprogestin pharmacology and pharmacokinetic data suggested that liver enzyme elevations might be related to off-target or metabolic effects associated with clinical drug exposure.

Objective

We explored whether the use of a pharmaceutic strategy targeting efficacious systemic dose concentrations, but with diminished peak serum concentrations and/or total drug exposure would mitigate hepatotoxicity. Twice-daily dosing of an extended-release formulation of onapristone was developed and clinically evaluated in light of renewed interest in antiprogestin therapy for treating progesterone receptor-positive breast and gynecologic cancers. The hepatotoxic potential of extended-release onapristone was assessed from two phase I–II studies involving patients with breast, ovarian, endometrial, and prostate cancer.

Results

Among the 88 patients in two phase I–II studies in progesterone receptor-positive malignancies treated with extended-release onapristone, elevated alanine aminotransferase/aspartate aminotransferase levels were found in 20% of patients with liver metastases compared with 6.3% without metastases. Of five patients with grade 3 or higher alanine aminotransferase elevations with or without bilirubin elevations (four with breast cancer and one with endometrial cancer), four were assessed as unrelated to extended-release onapristone by the safety data review committee. Furthermore, while the fifth patient’s liver enzyme elevations were considered possibly drug related by the study investigator, they were adjudicated as unlikely to be related (< 25% likelihood) by a subsequent independent hepatologist.

Conclusions

These results suggest that the extended-release formulation by reducing drug exposure may be associated with a reduced risk of hepatotoxicity, and supports the continued clinical evaluation of extended-release onapristone for treating progesterone receptor-positive cancers.

Glucocorticoid exposure causes disrupted glucoregulation, cardiac inflammation and elevated dipeptidyl peptidase-4 activity independent of glycogen synthase kinase-3 in female rats

Objective: We tested the hypothesis that glucocorticoid (GC) exposure in female rats would lead to glucose dysregulation and elevated cardiac inflammatory biomarkers, which are dipeptidyl peptidase-4 (DPP-4)- and glycogen synthase kinase-3 (GSK-3)-dependent. Methods: Female Wistar rats received vehicle (control; n = 6) or GC (dexamethasone; n = 6; 0.2 mg/kg; p.o.) for six days. Insulin resistance was determined by HOMA-IR. DPP-4 activity was determined by fluorescence method, whereas vascular cell adhesion molecule-1 (VCAM-1), uric acid, malondialdehyde (MDA), lactate dehydrogenase (LDH) and nitric oxide (NO) from plasma and cardiac homogenate were estimated as cardiac pro-inflammatory biomarkers. Results: Results showed that GC exposure resulted in glucose dysregulation and increased plasma and cardiac pro-inflammatory markers which are associated with elevated DPP-4 activity but reduced GSK-3. Conclusions: The present results demonstrate that GC exposure would cause glucose dysregulation, increased DPP-4 activity and cardiac inflammation that is independent of GSK-3.

Enriched environment regulates thymocyte development and alleviates experimental autoimmune encephalomyelitis in mice

Environmental and social factors have profound impacts on immune homeostasis. Our work on environmental enrichment (EE) has revealed a novel anti-obesity and anticancer phenotype associated with enhanced activity of CD8+ cytotoxic T lymphocytes in secondary lymphoid tissues. Here we investigated how an EE modulated thymus and thymocyte development. EE decreased thymus mass and cellularity, decreased the double positive thymocyte population, increased the proportion of CD8+ T cells, reduced the CD4:CD8 ratio, and downregulated CD69 expression in T cells. In a model of multiple sclerosis: experimental autoimmune encephalomyelitis (EAE), EE alleviated symptoms, inhibited spinal cord inflammation through regulation of type 1 T-helper cells mediated by glucocorticoid receptor signaling, and prevented EAE-induced thymic disturbance. Our mechanistic studies demonstrated that hypothalamic BDNF activated a hypothalamic-pituitary-adrenal axis mediating the EE's thymic effects. Our results indicate that a lifestyle intervention links the nervous, endocrine, and adaptive immune system, allowing the body to adapt to internal and external environments.

Gestational glucocorticoid exposure disrupts glucose homeostasis that is accompanied by increased endoglin and DPP-4 activity instead of GSK-3 in rats

Gestational glucocorticoid (GC) treatment has been associated with cardiometabolic disorder (CMD) in offspring's in later life. Elevated dipeptidyl peptidase-4 (DPP-4) activity, endoglin and glycogen synthase kinase-3 (GSK-3) has also been implicated in the development of insulin resistance (IR) and/or vascular inflammation. We aimed to investigate the impact of GC exposure on glucose metabolism and the circulating levels of inflammatory biomarkers, DPP-4 activity and GSK-3 in pregnant rats. Pregnant Wistar rats received either vehicle or dexamethasone (DEX; 0.2 mg/kg; po) between gestational days 14 and 19. Gestational GC exposure resulted in impaired glucose homeostasis that is accompanied with elevated circulating levels of inflammatory biomarkers (endoglin, uric acid, and platelet/lymphocyte ratio), oxidative stress (malondialdehyde), blood viscosity, reduced NO level and increased DPP-4 activity. However, these effects were associated with atherogenic dyslipidemia and reduced GSK-3.We conclude that plasma endoglin, a marker of vascular inflammation, and plasma DPP-4 activity are increased in pregnant rats treated with GC during late gestation. Therefore, glucose deregulation associated with gestational GC exposure is through endoglin-/DPP-4-dependent but GSK-3-independent pathway.

Lack of in vitro effect of aglepristone on IFN-γ and IL-4 production by resting and mitogen-activated T cells of luteal bitches

Background

Aglepristone (RU534) is an antiprogestin used for pregnancy termination, parturition induction and conservative pyometra treatment in bitches. Its molecular structure is similar to mifepristone, an antiprogestin used in human medicine. Mifepristone has been shown to suppress proliferation and cytokine production by T cells, whereas the effect of aglepristone on T cell function remains elusive. The purpose of this project was to investigate the in vitro influence of RU534 on IFN-γ and IL-4 synthesis by peripheral blood T cells isolated from healthy bitches (N = 16) in luteal phase. The peripheral blood mononuclear cells (PBMCs) were incubated with three different dosages of aglepristone, or dimethyl sulfoxide (DMSO), with or without mitogen. The production of cytokines by resting or mitogen-activated T cells was determined by intercellular staining and flow cytometry analysis or ELISA assay, respectively.

Results

Our results showed no statistically significant differences in the percentage of IFN-γ and IL-4-synthesizing CD4⁺ or CD8⁺ resting T cells between untreated and aglepristone-treated cells at 24 and 48 hours post treatment. Moreover, mitogen-activated PBMCs treated with RU534 displayed similar concentration of IFN-γ and IL-4 in culture supernatants to those observed in mitogen-activated DMSO-treated PBMCs. Presented results indicate that administration of aglepristone for 48 hours has no influence on IFN-γ and IL-4 synthesis by resting and mitogen-activated T cells isolated from diestral bitches.

Conclusions

We conclude that antiprogestins may differentially affect T cell function depending on the animal species in which they are applied.

Thymus atrophy during Trypanosoma cruzi infection is caused by an immuno-endocrine imbalance

C57BL/6 mice infected with Trypanosoma cruzi, the causal agent of Chagas' disease, develop severe thymocyte depletion paralleled by an inflammatory syndrome mediated by tumor necrosis factor-alpha (TNF-alpha). The exacerbated inflammatory reaction induces the activation of hypothalamus-pituitary-adrenal (HPA) axis with the consequent release of corticosterone (CT) into the circulation as a protective response. Thymocyte apoptosis has been related to a rise in TNF-alpha and CT levels, and both mediators are increased in T. cruzi-infected C57BL/6 mice. The depletion of immature CD4(+)CD8(+) thymocytes by apoptosis following infection with the parasite was still present in mice defective in both types of TNF-receptors (double knockout). However, thymic atrophy was prevented by adrenalectomy combined with RU486 administration, demonstrating that this is a CT-driven phenomenon. Our results put emphasis on the importance of an appropriated immuno-endocrine balance during T. cruzi infection and show that functional deviations in the immuno-endocrine equilibrium have profound effects on the thymus and disease outcome.

Low glucocorticoid receptor (GR), high Dig2 and low Bcl-2 expression in double positive thymocytes of BALB/c mice indicates their endogenous glucocorticoid hormone exposure

Several studies have shown that of the four major thymocyte subsets, the CD4/CD8 double positive (DP) thymocytes are the most sensitive to in vivo glucocorticoid hormone (GC)-induced apoptosis. Our aim was to analyse fine molecular differences among thymocyte subgroups that could underlie this phenomenon. Therefore, we characterised the glucocorticoid hormone receptor (GR) expression of thymocyte subgroups both at the mRNA and protein levels by real-time PCR and flow cytometry, and correlated these features to their apoptotic sensitivity. We also investigated the time-dependent effects of the GC agonist dexamethasone (DX) with or without GC antagonist (RU486) treatments on GR mRNA/protein expression. We also analysed the expression of two apoptosis-related gene products: dexamethasone-induced gene 2 (Dig2) mRNA and Bcl-2 protein. We found that DN thymocytes had the highest GR expression, followed by CD8 single positive (SP), CD4 SP and DP thymocytes in 4-week-old BALB/c mice, both at the mRNA and protein levels, respectively. In DP cells, the Dig2 expression was significantly higher, while the Bcl-2 expression was significantly lower than in DN, CD4 SP and CD8 SP thymocytes. Single high dose DX treatment caused time-dependent depletion of DP thymocytes due to their higher apoptosis rate, which could not be abolished with RU486 pretreatment. After a single high dose DX treatment, there was a transient, significant increase of the GR mRNA and protein level of unsorted thymocytes after 8 and 16 h, followed by a significant decrease at 24 h, respectively. The time-dependent GR expression changes after DX administration could not be inhibited by the GC antagonist RU486. Twenty-four hours after exposure to high dose DX the DN, CD4 SP and CD8 SP cells showed a significant decrease of GR mRNA and protein expression, whereas the DP thymocytes, showed no significant alteration of GR mRNA or protein expression. The kinetical analysis of GR expression and apoptotic marker changes upon single high dose GC analogue administration revealed a two-phase process in thymocytes: early events, within 4-8 h, include GR upregulation and early apoptosis induction, while the late events appear most prominently at 16-20 h, when the GR is already downregulated and apoptotic cell ratio reaches its peak, with marked DP cell depletion. The low GR, high Dig2 and low Bcl-2 expression, coupled with the absence of homologous downregulation of GR after exogenous GC analogue treatment, could contribute to the high GC sensitivity of DP thymocytes. The downregulated GR and Bcl-2 together with the upregulated Dig2 level in DP cells indicates the significance of intrathymic GC effects at this differentiation stage. Since GR expression changes and apoptotic events could not be completely inhibited by GC antagonist, we propose the involvement of non-genomic GR mechanisms in these processes.