Drug discovery strategies for the identification of novel regulators of uterine contractility

Arrest of mouse preterm labor until term delivery by combination therapy with atosiban and mundulone, a natural product with tocolytic efficacy

There is a lack of FDA-approved tocolytics for the management of preterm labor (PL). In prior drug discovery efforts, we identified mundulone and mundulone acetate (MA) as inhibitors of in vitro intracellular Ca2+-regulated myometrial contractility. In this study, we probed the tocolytic potential of these compounds using human myometrial samples and a mouse model of preterm birth. In a phenotypic assay, mundulone displayed greater efficacy, while MA showed greater potency and uterine-selectivity in the inhibition of intracellular-Ca2+ mobilization. Cell viability assays revealed that MA was significantly less cytotoxic. Organ bath and vessel myography studies showed that only mundulone exerted inhibition of myometrial contractions and that neither compounds affected vasoreactivity of ductus arteriosus. A high-throughput combination screen identified that mundulone exhibits synergism with two clinical-tocolytics (atosiban and nifedipine), and MA displayed synergistic efficacy with nifedipine. Of these combinations, mundulone+atosiban demonstrated a significant improvement in the in vitro therapeutic index compared to mundulone alone. The ex vivo and in vivo synergism of mundulone+atosiban was substantiated, yielding greater tocolytic efficacy and potency on myometrial tissue and reduced preterm birth rates in a mouse model of PL compared to each single agent. Treatment with mundulone after mifepristone administration dose-dependently delayed the timing of delivery. Importantly, mundulone+atosiban permitted long-term management of PL, allowing 71% dams to deliver viable pups at term (>day 19, 4-5 days post-mifepristone exposure) without visible maternal and fetal consequences. Collectively, these studies provide a strong foundation for the development of mundulone as a single or combination tocolytic for management of PL.

Arrest of mouse preterm labor until term delivery by combination therapy with atosiban and mundulone, a natural product with tocolytic efficacy

Currently, there is a lack of FDA-approved tocolytics for the management of preterm labor (PL). In prior drug discovery efforts, we identified mundulone and its analog mundulone acetate (MA) as inhibitors of in vitro intracellular Ca 2+ -regulated myometrial contractility. In this study, we probed the tocolytic and therapeutic potential of these small molecules using myometrial cells and tissues obtained from patients receiving cesarean deliveries, as well as a mouse model of PL resulting in preterm birth. In a phenotypic assay, mundulone displayed greater efficacy in the inhibition of intracellular-Ca 2+ from myometrial cells; however, MA showed greater potency and uterine-selectivity, based IC 50 and E max values between myometrial cells compared to aorta vascular smooth muscle cells, a major maternal off-target site of current tocolytics. Cell viability assays revealed that MA was significantly less cytotoxic. Organ bath and vessel myography studies showed that only mundulone exerted concentration-dependent inhibition of ex vivo myometrial contractions and that neither mundulone or MA affected vasoreactivity of ductus arteriosus, a major fetal off-target of current tocolytics. A high-throughput combination screen of in vitro intracellular Ca 2+ -mobilization identified that mundulone exhibits synergism with two clinical-tocolytics (atosiban and nifedipine), and MA displayed synergistic efficacy with nifedipine. Of these synergistic combinations, mundulone + atosiban demonstrated a favorable in vitro therapeutic index (TI)=10, a substantial improvement compared to TI=0.8 for mundulone alone. The ex vivo and in vivo synergism of mundulone and atosiban was substantiated, yielding greater tocolytic efficacy and potency on isolated mouse and human myometrial tissue and reduced preterm birth rates in a mouse model of PL compared to each single agent. Treatment with mundulone 5hrs after mifepristone administration (and PL induction) dose-dependently delayed the timing of delivery. Importantly, mundulone in combination with atosiban (FR 3.7:1, 6.5mg/kg + 1.75mg/kg) permitted long-term management of PL after induction with 30 μg mifepristone, allowing 71% dams to deliver viable pups at term (> day 19, 4-5 days post-mifepristone exposure) without any visible maternal and fetal consequences. Collectively, these studies provide a strong foundation for the future development of mundulone as a stand-alone single- and/or combination-tocolytic therapy for management of PL.

Title: β3 Adrenergic Receptor Signaling in the Human Myometrium

Preterm labor leading to preterm birth is the leading cause of infant morbidity and mortality. Although β2 adrenergic agonists fail to provide adequate tocolysis, the expression of the β3 adrenergic receptor in myometrium and its unique signaling suggest a role for β3 agonist in the management of preterm labor. Western blot analysis showed that the β3 adrenergic receptor expression increased in human pregnancy myometrium compared to nonpregnant tissues (p < 0.0001). There was no difference in β3 adrenergic receptor expression throughout pregnancy (p > 0.05). The addition of the β3 agonist mirabegron in the tissue bath relaxed oxytocin contracted myometrium with an EC₅₀ of 41.5 µM. Relaxation was partially blocked by the addition of the eNOS blocker Nω-nitro-L-arginine, or the large conductance potassium channel blocker paxilline. Combination of Nω-nitro-L-arginine and paxilline prevented mirabegron-mediated relaxation. Imaging revealed that the β3 adrenergic receptors are expressed by both myocyte and microvascular endothelial cells isolated from human myometrium. Nitric oxide production measured by 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate revealed that mirabegron stimulated nitric oxide production in myometrial endothelial cells. These data suggest that both endothelial and smooth muscle cells contribute to relaxation through disparate signaling pathways. Repurposing of approved medications tested in human myometrium as uterine tocolytics can advance prevention of preterm birth. These data argue that further examination of β3 adrenergic receptor signaling in myometrium may reveal mirabegron as a useful tocolytic in combination tocolysis regimens.

An in vitro Study on the Contractility of Epileptic Myometrium and Effects of Antiepileptic Agents on Oxytocin-Induced Contractions of Myometrium Isolated from Absence Epileptic WAG/Rij Rats

BACKGROUND/AIMS

The aim of this study was to determine whether spontaneous and stimulated contractile activity of myometrium in epileptic rats is different from healthy ones, and whether antiepileptic drugs (AEDs) have any direct influence on myometrial contractility.

METHODS

Myometrial strips from nonpregnant and pregnant adult epileptic WAG/Rij and Wistar rats were suspended in organ bath containing physiological salt solution (37°C and pH 7.4, aerated with 95% oxygen-5% CO2), and isometric contractions were recorded. Effects of cumulative concentrations of selected AEDs including phenytoin, levetiracetam, and valproic acid alone and in combination on oxytocin-induced contractions was examined. Contractile parameters assessed included the area under curve, amplitude, and frequency of contractions, evaluated by 10-min periods. Data were analyzed using one-way analysis of variance and Tukey HSD test.

RESULTS

Spontaneous myometrial contractility and responses to oxytocin showed species difference. Compared with that of control Wistar rats, spontaneous contractions of myometrium from nonpregnant epileptic WAG/Rij rats were significantly higher while being significantly lower in pregnant preparations. Upon stimulation with oxytocin, WAG/Rij myometrium showed significantly lower contractile response compared with preparations from healthy control Wistars (p &lt; 0.01). Phenytoin and valproate caused concentration-dependent significant attenuation (p &lt; 0.05) of spontaneous and oxytocin-induced contractions of myometrium from WAG/Rij and Wistar rats, both nonpregnant and pregnant.

CONCLUSION

Myometrial smooth muscle from epileptic rats showed different spontaneous and oxytocin-induced contractility, and AEDs showed contractile modulatory actions, phenytoin being the most and levetiracetam the least effective. Although in vitro, our findings may be of clinical implications with regard to obstetric complications in epileptics and use of AEDs during pregnancy, and warrants further investigations.

Investigation of Effects of Gadolinium-Based Contrast Agents on Uterine Contractility Using Isolated Rat Myometrium

BACKGROUND

Despite concerns about safety, gadolinium-based contrast agents (GBCAs) are still used for abdominal and pelvic imaging during pregnancy. Researchers have mainly focused on teratogenicity, while very little is known about their possible direct effects on uterine contractility, yet free gadolinium potentially impacts contractility through interaction with calcium channels.

PURPOSE

To investigate possible effects of selected GBCAs (namely gadoteridol, gadoversetamide, gadobutrol, gadoterate meglumine, and gadoxetic acid) on the contractility of rat myometrium.

STUDY TYPE

In vitro organ bath study.

ANIMAL MODEL

Myometria were isolated from adult (10-12 weeks old) Sprague Dawley rats, both pregnant (N = 8) and nonpregnant (N = 36).

FIELD STRENGTH/SEQUENCE

NA.

ASSESSMENT

Myometrial strips were suspended in tissue bath containing physiological saline and isometric contractions were recorded. GBCAs were added to the tissue bath cumulatively, and their effects on contractility parameters (quantified by amplitude, frequency, and area under contractility curve [AUC]) were evaluated by 10-minute intervals.

STATISTICAL TESTS

Normality data, checked by Shapiro-Wilk test, were transformed by arcsine when needed. One- or two-way analysis of variance was performed, where appropriate, followed by Student-Newman-Keuls test. A P value of <0.05 was considered statistically significant.

RESULTS

All of the assayed GBCAs elicited some alterations in the myometrial contractility in a concentration-dependent manner. Gadoterate meglumine, gadoxetic acid, and gadoversetamide caused a concentration-dependent significant attenuation in AUC (oxytocin-induced, from 100% during control period to 45.1 ± 9.0% (nonpregnant) and 59.9 ± 8.5% (pregnant), for 90 μM gadoterate meglumine; respectively), and frequency of the spontaneous and oxytocin-induced contractions. Gadobutrol and gadoteridol at highest dose significantly attenuated mean AUC and frequency of oxytocin-induced contractions of nonpregnant myometrium.

DATA CONCLUSION

Results from this in vitro study indicate that GBCAs elicit modulation of myometrial contractions at clinically relevant concentrations. These effects may account, at least partially, for the known potential side effects (rare cases of miscarriages and elective abortion) of these agents.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 5.

Effects of Solvents, Emulsions, Cosolvents, and Complexions on Ex Vivo Mouse Myometrial Contractility

A great need exists to develop tocolytic and uterotonic drugs that combat poor, labor-related maternal and fetal outcomes. A widely utilized method to assess novel compounds for their tocolytic and uterotonic efficacy is the isometric organ bath contractility assay. Unfortunately, water-insoluble compounds can be difficult to test using the physiological, buffer-based, organ bath assay. Common methods for overcoming solubility issues include solvent variation, cosolvency, surfactant or complexion use, and emulsification. However, these options for drug delivery or formulation can impact tissue function. Therefore, the goal of this study was to evaluate the ability of common solvents, surfactants, cosolvents, and emulsions to adequately solubilize compounds in the organ bath assay without affecting mouse myometrial contractility. We found that acetone, acetonitrile, and ethanol had the least effect, while dimethylacetamide, ethyl acetate, and isopropanol displayed the greatest inhibition of myometrial contractility based on area under the contractile curve analyses. The minimum concentration of surfactants, cosolvents, and human serum albumin required to solubilize nifedipine, a current tocolytic drug, resulted in extensive bubbling in the organ bath assay, precluding their use. Finally, we report that an oil-in-water base emulsion containing no drug has no statistical effect beyond the control (water), while the drug emulsion yielded the same potency and efficacy as the freely solubilized drug.