Antiproliferative effects of PCA-4230, a new antithrombotic drug, in vascular smooth muscle cells

Growth inhibitory activity of indapamide on vascular smooth muscle cells

Abnormal vascular smooth muscle cell proliferation has a fundamental role in the pathogenesis of vascular diseases. Indapamide is an oral diuretic antihypertensive drug effective for patients with mild or moderate essential hypertension. We now investigated the effects of indapamide on the growth of aortic vascular smooth muscle cells (A10 cell line). Indapamide inhibited cell proliferation as measured by the tetrazolium salt XTT (sodium 3'-[1-(phenylamino-carbonyl)-3,4-tetrazolium]-bis(4-methoxy-6-nitro)benzene sulfonic acid hydrate) test. The increase in cell number was significantly reduced in the presence of indapamide 10(-6) and 5 x 10(-4) M (P < 0.05 n = 3 and P < 0.01, n = 3, respectively). Serum-induced DNA synthesis, determined as the incorporation of 5-bromo-2'-deoxyuridine (BrdU), was concentration-dependently inhibited by indapamide. BrdU incorporation was 47.2+/-1.6% (10% foetal calf serum). Indapamide treatment markedly prevented BrdU incorporation (37.2+/-2.1%, 29.2+/-4.8%, 15.0+/-1.8%, 8.7+/-2.1%) indapamide 10(-6), 10(-5), 5 x 10(-5) and 5 x 10(-4) M, respectively. Cell-cycle progression was also evaluated. Flow cytometry analysis of DNA content in synchronised cells revealed blocking of the serum-inducible cell-cycle progression by indapamide. This inhibition was abolished when the drug was added 2 h after serum repletion, indicating that indapamide must act at the early events of a cell cycle to be fully effective against DNA synthesis. In addition, serum-induced intracellular Ca2+ movements and also p44/p42 mitogen-activated protein kinase (MAPK) phosphorylation were studied in the presence or absence of indapamide. Indapamide 10(-5) and 5 x 10(-5) M decreased significantly cytosolic free calcium, and the p44/p42 mitogen-activated protein kinase phosphorylation (5 x 10(-5) M) stimulated by 10% foetal calf serum. In accordance with this finding, indapamide (5 x 10(-4) M) caused a 95% to 99% decrease in the early elevation of c-fos expression as evaluated by northern blot analysis of mRNA induced after serum addition. In conclusion, our results indicate that indapamide reduces vascular smooth muscle cell proliferation by a mechanism which involves a decrease in the intracellular Ca2+ movements that might link with the mitogen-activated protein kinase (MAPK) pathway, altering cell-cycle progression.

TZDs inhibit vascular smooth muscle cell growth independently of the cyclin kinase inhibitors p21 and p27

The thiazolidenediones (TZDs) are commonly used to treat hyperglycemia in type 2 diabetes. Diabetes is associated with macrovascular disease, leading to accelerated atherosclerosis caused by aberrant vascular smooth muscle (VSM) cell proliferation. Although VSM cell proliferation is inhibited by the TZDs, the mechanism of this effect has not been established. Because of reports that the cyclin kinase inhibitors (CKIs) p21(Waf1/Cip1) and p27(Kip1) can exhibit both growth-inhibitory and growth-permissive effects in VSM cells, we asked whether alterations in these cell cycle regulatory proteins are the mechanism by which the TZDs inhibit VSM cell growth. We show that platelet-derived growth factor-BB increases p21 and p27 and that this increase is attenuated by TZDs. Surprisingly, when VSM cells were transfected with antisense oligodeoxynucleotides to p21 and p27, inhibition of DNA synthesis by TZDs occurred to the same degree as in control cells. Furthermore, the TZDs have inhibitory effects on cyclin D1 and cyclin E levels, suggesting another mechanism by which these drugs decrease VSM cell growth. These data suggest that the TZD-mediated reduction in CKI levels is not the sole mechanism for their antiproliferative effects. The observed decrease in levels of the G1 cyclins by the TZDs suggests a possible mechanism of VSM cell growth inhibition.

Inhibition of the cyclin D1/E2F pathway by PCA-4230, a potent repressor of cellular proliferation

1. Tight control of cellular growth is essential to ensure normal tissue patterning and prevent pathological responses. Excessive vascular smooth muscle cell (VSMC) proliferation is associated with the pathophysiology of atherosclerosis and restenosis post-angioplasty. Thus, drug targeting of pathological VSMC growth may be a suitable therapeutic intervention in vascular proliferative diseases. 2. In the present study, we investigated the mechanisms underlying VSMC growth arrest induced by the pharmacological agent PCA-4230. Addition of PCA-4230 to cultured VSMCs blocked the induction of cyclin D1 and cyclin A expression normally seen in serum-restimulated cells. Moreover, PCA-4230 inhibited cyclin-dependent kinase 2 (CDK2) activity and abrogated hyperphosphorylation of the retinoblastoma (Rb) gene product. Similarly, PCA-4230-dependent growth arrest of transformed cell lines correlated with reduced level of cyclin D1 protein and inhibition of CDK2 activity. Consistent with these findings, PCA-4230 repressed serum-inducible cyclin A promoter activity, and overexpression of either cyclin D1 or E2F1 efficiently circumvented this inhibitory effect. Importantly, adenovirus-mediated overexpression of E2F1 restored S-phase entry in PCA-4230-treated VSMCs, demonstrating that PCA-4230 represses cyclin A gene expression and VSMC growth via inhibition of the cyclin D1/E2F pathway. 3. Because of its ability to inhibit the growth of human VSMCs and transformed cell lines, future studies are warranted to assess whether PCA-4230 may be a suitable therapeutic intervention for the treatment of hyperproliferative disorders, including cardiovascular disease and cancer.