- Title
- Preventing preterm birth: next generation tocolytic strategies for inhibiting pregnant human myometrial contractility
- Creator
- Hossain, Md Reduanul
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2023
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Background: Preterm birth is the most common cause of neonatal morbidity and mortality. Preterm birth affects millions of babies worldwide annually and is the subject of intense study in its pathophysiology and therapy. Tocolytic agents are contraction-blocking drugs used to prevent preterm birth and prolong pregnancy. Tocolysis allows the fetus to stay in the uterus for further maturation, permits antenatal corticosteroid treatment to accelerate fetal lung maturity, and allows time for the in-utero transfer of the baby to a tertiary care facility. However, tocolytic therapy is associated with both maternal and fetal side-effects, which hampers its usefulness. Hence, there is a pressing need to develop safer, more effective tocolytic therapies. Combination therapy has the potential to improve preterm birth outcomes. The underlying rationale is anchored in the benefits of drug synergism, whereby the effect of two drugs combined is greater than the sum of the individual drugs. Achieving synergism reduces the quantities of drugs required to achieve the desired therapeutic effect. In the context of preterm birth, combinational tocolysis thus has the potential to reduce maternal and/or fetal side-effects. Hypotheses: In light of the potential for a combinational approach to improve tocolysis in women experiencing preterm labour, this thesis hypothesised that: 1. Combinational tocolysis represents a more effective therapeutic strategy (enhanced efficacy) for inhibiting pregnant human myometrial contractility at reduced tocolytic quantities than single-drug therapy. 2. Combinational tocolysis that targets distinctly different components of the contraction signalling pathway will result in tocolytic synergism, whereas agents whose effects overlap will result in only an additive effect. Objectives: To assess and compare the contraction-blocking potency of some clinically deployed (previously tested) and novel classes of tocolytics in terms of inhibiting spontaneous pregnant human myometrial contractions ex vivo, and to quantitatively determine whether dual or triple combinations of these tocolytics result in synergism. Study Design: In conducting the study, myometrial specimens were obtained from term not-in-labour women undergoing elective caesarean section, dissected into strips, and suspended in organ baths connected to force transducers. The undertaken studies are divided into three parts: In the first part, the contraction-blocking potency of seven tocolytics (2-aminoethoxydiphenyl borate, glycyl-H-1152, HC067047, aminophylline, rolipram, nifedipine, and indomethacin) was determined. In conducting the study, spontaneously contracting strips were treated with cumulative concentrations of the contraction-blocking agents. Comprehensive dose–response curves were generated. The concentration of each agent required to inhibit spontaneous ex vivo human myometrial contractility by 50% (IC50) was determined as a 50% reduction in total area under the curve (AUC) relative to the contraction baseline. The IC25 concentration was then calculated for each tocolytic. In the second part, the contraction-blocking potency of eight dual tocolytic combinations was examined to quantitatively assess for tocolytic synergisms. In conducting the study, spontaneously contracting myometrial strips were exposed to IC25 or IC50 doses of dual combinations of different tocolytics. AUC for the baseline contractility (100%) (pre-treatment) and following combination treatment (post-treatment) was measured for 1 h. Effects of treatments were normalised against the baseline, and data were expressed as a percentage (%) of baseline contractility. The expected percentage of inhibition was calculated for each combination based on the individual tocolytic effects using the Bliss Independence Model and compared with experimentally observed inhibition. The combinational effect was considered synergistic if the experimentally observed inhibition scores were significantly greater than the sum of the effects of individual agents (theoretically expected inhibition). In the third part, synergistic dual combinations were combined to assess the contraction-blocking potency of three triple tocolytic combinations. A quantitative assessment was conducted to determine whether the triple combinations yielded tocolytic synergisms exceeding that of the dual combinations. In performing the study, spontaneously contracting strips were exposed to IC25 doses of triple combinations of different tocolytics. Then the percentage of contraction-inhibition was calculated for each triple combination based on the individual tocolytic effects using the Bliss Independence Model and compared with experimentally observed inhibition. The combinational effect was considered synergistic if the experimentally observed inhibition scores were significantly greater than the sum of the effects of individual agents (theoretically expected inhibition). Results: The IC50 concentrations were 53 µM for 2-APB, 18.5 µM for Glycyl-H-1152, 52 µM for HC-067047, 320 µM for aminophylline, 4 µM for rolipram, 10 nM for nifedipine, and 60 µM for indomethacin. Moreover, the IC25 concentrations were 27 µM for 2-APB, 4.6 µM for Glycyl-H-1152, 175 µM for aminophylline, 515 nM for rolipram, 3.4 nM for nifedipine, and 28 µM for indomethacin. Of all the drugs examined, the overall order of contraction-blocking potency in decreasing order was nifedipine > rolipram > glycyl-H-1152 > HC-067047 > 2-aminoethoxydiphenyl borate > indomethacin > aminophylline. Of the eight dual tocolytic combinations examined, six combinations were quantitatively demonstrated to inhibit myometrial contractility to significantly more than expected (sum of the individual drugs), indicating tocolytic synergism. The remaining two combinations were quantitatively demonstrated to produce only an additive effect. In the triple combination study, the tocolytic efficiency of three different low-dose triple combinations was assessed to measure their ability to inhibit spontaneous pregnant human myometrial contractions ex vivo. All three triple combinations were quantitatively demonstrated to result in tocolytic synergism. Moreover, all three triple combinations nearly completely abolished ex vivo contractions despite each constituent tocolytic being administered at just IC25 concentration. Conclusion: This thesis reports a comprehensive assessment of the tocolytic potency of some clinically established and novel tocolytics. These data were then used as a foundation on which to conduct a robust assessment of combinational tocolysis, with quantitative analyses used to confirm the emergence or absence of tocolytic synergism. Identification of emergent dual combination synergisms enabled synergistic combinations to be combined and led to the identification of three novel triple tocolytic combinations that not only yielded even more effective tocolytic synergism but almost completely abolished ex vivo contractility despite the constituent tocolytics being administered at just IC25 concentrations. The data, therefore, support the first hypothesis that combinational tocolysis is a strategy for achieving tocolysis at reduced drug concentrations when compared to single drug-therapy, which may improve both maternal and fetal safety. Moreover, analysis of the data also supports the second hypothesis that combinations of tocolytics that target distinctly different components of the contraction signalling pathway may be anticipated to yield tocolytic synergism, whereas agents whose effects overlap may be expected to yield an additive effect. Lastly, the identified synergistic tocolytic combinations may be excellent candidates for encapsulation into nanoparticle-based drug delivery systems as novel strategies for reducing the off-target side-effects of potent but non-specific tocolytics.
- Subject
- preterm birth; tocolytic drug combination; bliss Independence Model; quantitative drug combination analysis; synergistic tocolytic drug combination; human myometrial contraction ex vivo; dual and triple tocolytic drug combination
- Identifier
- http://hdl.handle.net/1959.13/1473342
- Identifier
- uon:48995
- Rights
- Copyright 2023 Md Reduanul Hossain
- Language
- eng
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