MECHINISTIC CHARATERIZATION OF NOVEL DRUG COMBINATIONS FOR PREVENTION OF PRETERM BIRTH

Preterm birth (PTB) is the leading cause of death for children under the age of 5. Pre-maturely delivered infants suffer from various medical complications, including neurological disorders and respiratory disorders. Therefore, it is important to develop effective preventions for PTB. Although multiple studies have shown the close relationship between PTB and infection, the inflammation tends to be subclinical until delivery, which makes diagnosis and prevention of PTB challenging. In this situation, understanding the mechanisms of pathological physiology involved in PTB is critical for developing PTB therapeutics. It has been demonstrated that intrauterine injection of an endotoxin (lipopolysaccharide, LPS) in mice can mimic the inflammation induced by infection, establishing a model for PTB study. The most common treatment approaches for PTB prevention use progestins, such as progesterone, which is a key hormone in gestation and parturition. We previously found that progesterone was not able to delay labor in LPS-induced PTB, while the combination of progesterone with trichostatin A (TSA), a histone deacetylase inhibitor (HDACi) that selectively inhibits histone deacetylase families of enzymes, could effectively prevent PTB. This study is aimed to investigate the underlying cellular mechanisms through in vitro approaches. We focused on two proposed mechanisms in PTB: functional progesterone withdrawal and inflammation. We measured gene and protein expression levels for markers that have been reported to participate in initiating labor in healthy pregnancy in human myometrial cells. Our immunoblotting results showed the combination of progesterone and TSA was capable of decreasing the ratio of progesterone receptor A (PR-A) to progesterone receptor B (PR-B), leading to a PR-B dominant state, which is essential for maintaining myometrium quiescence. Our gene expression data, however, did not reflect a reduction in inflammation-associated and contractile-associated gene expression. In contrast, the combination upregulated expression of these genes after treating the cells with drugs for 24 h. In addition, we also conducted a collagen gel contraction assay to observe the cellular contraction under different conditions, and contraction was significantly suppressed by the combination of progesterone and TSA, without causing cellular toxicity. We further investigated whether such inhibition was a TSA-specific mechanism, so we used another HDACi, vorinostat, to repeat the contraction assay. Similarly, we observed reduced contraction when the cells were treated with the combination of progesterone and vorinostat. Together, our results demonstrated the possibility of using progesterone and HDACi as an alternative therapy for prevention of inflammation-induced PTB