Repurposed Trifluoperazine (TFP) May Be Effective PAH Therapy
In rat models of PAH, trifluoperazine was found to provide therapeutic benefits — without causing detectable side effects.
The study, “Preclinical Investigation of Trifluoperazine as a Novel Therapeutic Agent for the Treatment of Pulmonary Arterial Hypertension,” was published in the International Journal of Molecular Sciences.
One of the key features of PAH is the thickening of blood vessels in the lungs, which may restrict blood flow and ultimately lead to an increase in lung blood pressure. Despite advances in the treatment of PAH, there remains a need to develop better therapies that can target the narrowing of blood vessels.
TFP is a medication typically prescribed for treating certain mental disorders, specifically schizophrenia. Moreover, in preclinical models, it showed effectiveness in reducing tumor cell proliferation and in promoting tumor cell death. Given such results, it’s now being considered by scientists as a suitable therapy for cancer.
In PAH, blood vessel thickening is caused in part by the proliferation of pulmonary artery smooth muscle cells, known as PASMCs. Thus, scientists in Canada hypothesized that trifluoperazine also could work to prevent PASMC proliferation and to treat PAH.
To test their hypothesis, the researchers first assessed the effect of TFP on PAH-PASMCs isolated from small lung arteries from 11 PAH patients. Seven control cell lines were obtained commercially or isolated from patients without PAH to serve as controls.
Both the treated and untreated cells were first stained with Ki67, a marker of proliferating cells. Cells exposed to TFP were then found to have lower Ki67 staining compared with untreated cells. This result was confirmed using another marker, called 5-ethynyl-2′-deoxyuridine or EdU, which is incorporated, or taken up, only by dividing cells. Likewise, PAH-PASMCs treated with TFP incorporated less EdU than control cells.
The team also observed that TFP could induce apoptosis, a form of programmed cell death.
“Our results indicate that TFP exerts anti-proliferative and anti-survival effects on PAH-PASMCs,” the researchers wrote.
In the next set of experiments, the team investigated the mechanisms underlining TFP’s effect on cell proliferation by focusing on FOXO3.
FOXO3 belongs to a family of transcription factors that control cell division and death in the nucleus of cells. In PAH-PASMCs, FOXO3 was found in the cytosol, which is outside the cell’s nucleus, or control center. Meanwhile, in cells treated with TFP, FOXO3 was located mostly in the nucleus — where it exerts its activity.
The PAH-PASMCs were then genetically manipulated to study the function of FOXO3 in more detail. These cells were forced into expressing an active form of FOXO3, which resulted in lower proliferating abilities, as observed by a decrease in the number of Ki67-positive PAH-PASMCs.
The team next tested the therapeutic potential of TFP on two rat models of PAH: the SuHx rat model and the MCT model. With SuHx, rats are injected with sugen and exposed to hypoxia, or low oxygen levels, to induce PAH. PAH is induced in the MCT model with the use of a toxic chemical called monocrotaline (MCT).
TFP significantly decreased the right ventricular systolic pressure (RVSP), the mean pulmonary artery pressure, and the total pulmonary resistance — as determined by the ratio of RVSP to cardiac output — in both rat models.
The medial wall thickness of distal pulmonary arteries also was notably reduced after TFP treatment in SuHx and MCT rats. The use of TPR also increased the stroke volume, or the amount of blood pumped by the left ventricle of the heart in one contraction. However, TPR did not affect right ventricle (RV) hypertrophy, which refers to the thickening of the walls of the RV in rat models.
“Although RV hypertrophy was unchanged after TFP treatment in animal models (possibly due to insufficient treatment duration), examination of RV function by right heart catheterization revealed no deleterious or even salutary effects,” the researchers wrote.
As expected, PASMC proliferation was reduced and apoptosis was increased in rats treated with trifluoperazine. Additionally, in PASMCs from TFP-treated rats, FOXO3 was primarily located in the nucleus.
“Altogether, these results indicate that TFP provides therapeutic benefits in two preclinical PAH animal models without causing detectable side effects,” the researchers wrote.
Overall, based on the results, the team concluded that repurposing TFP as a PAH therapy might lead to clinical benefits.
“Regardless of the exact mechanisms by which TFP exerts its anti-survival and anti-proliferative effects on PAH-PASMCs, the present study provides evidence that its administration improved established PAH in two preclinical models, which supports the view that seeking new uses for old drugs may represent a fruitful approach,” the researchers concluded.