Overcoming chemoresistance to b-raf inhibitor in melanoma via targeted inhibition of phosphoenolpyruvate carboxykinase1 using 3-mercaptopropionic acid.

The resistance of melanoma to BRAF inhibitors remains a tough clinical challenge. In order to explore the underlying mechanism of drug resistance in melanoma, we established the resistant cell line to vemurafenib, and assessed the changes of drug-resistant cells on proliferation, apoptosis, oxidative stress and tumor stemness. Our results suggest that phosphoenolpyruvate carboxykinase1 (PCK1) is activated and inhibits the oxidative stress caused by vemurafenib in drug-resistant cells. Long term treatment of vemurafenib increases the expression of PCK1 which reduces the production of reactive oxygen species (ROS) by activating PI3K/Akt pathway. After the inhibition of PCK1 by 3-mercaptopropionic acid (3-MPA), the therapeutic sensitivity of vemurafenib is restored. In conclusion, this study disclosed that drug-resistant cells appeared to regulate their own proliferation, oxidative stress and tumor dryness by activating Akt/PCK1/ROS pathway, and shed new insights into acquiring drug resistance in melanoma.

PPAR-α targeting in kidney fibrosis: is BAY PP1 just another renoprotector?

Interstitial fibrosis plays a major role in the progression of renal diseases. Peroxisome proliferator-activated receptor-α (PPAR-α) ligands are increasingly explored for their potential to reverse or halt tubulointerstitial fibrosis. This Commentary discusses new findings by Boor et al., who show that BAY PP1, a novel PPAR-α agonist, ameliorates renal fibrosis and dysfunction.

The peroxisome proliferator-activated receptor-α agonist, BAY PP1, attenuates renal fibrosis in rats.

Recent studies have shown renoprotective effects of the peroxisome proliferator-activated receptor-α (PPAR-α), but its role in kidney fibrosis is unknown. In order to gain insight into this, we examined the effect of a novel PPAR-α agonist, BAY PP1, in two rat models of renal fibrosis: unilateral ureteral obstruction and the 5/6 nephrectomy. In healthy animals, PPAR-α was expressed in tubular but not in interstitial cells. Upon induction of fibrosis, PPAR-α was significantly downregulated, and treatment with BAY PP1 significantly restored its expression. During ureteral obstruction, treatment with BAY PP1 significantly reduced tubulointerstitial fibrosis, proliferation of interstitial fibroblasts, and TGF-ß(1) expression. Treatment with a less potent PPAR-α agonist, fenofibrate, had no effects. Treatment with BAY PP1, initiated in established disease in the 5/6 nephrectomy, halted the decline of renal function and significantly ameliorated renal fibrosis. In vitro, BAY PP1 had no direct effect on renal fibroblasts but reduced collagen, fibronectin, and TGF-ß(1) expression in tubular cells. Conditioned media of BAY PP1-treated tubular cells reduced fibroblast proliferation. Thus, renal fibrosis is characterized by a reduction of PPAR-α expression, and treatment with BAY PP1 restores PPAR-α expression and ameliorates renal fibrosis by modulating the cross-talk between tubular cells and fibroblasts. Hence, potent PPAR-α agonists might be useful in the treatment of renal fibrosis.

Carboxypeptidase U (TAFIa): a metallocarboxypeptidase with a distinct role in haemostasis and a possible risk factor for thrombotic disease.

Since the discovery of Carboxypeptidase U (CPU) in 1988, considerable information has been gathered about its biochemistry and function in physiological and pathophysiological circumstances. A variety of tools such as assays to measure proCPU and CPU, antibodies raised against (pro)CPU, selective CPU inhibitors and knock-out mice have been developed and are currently being used to explore the role of this metallocarboxypeptidase in different in vivo and in vitro settings. The knowledge that proCPU can be activated by thrombin and plasmin, enzymes with a key function in coagulation and fibrinolysis, and the ability of CPU to remove C-terminal lysine residues has led to the hypothesis that the proCPU/CPU pathway plays a role in the balance between coagulation and fibrinolysis. The maintenance of the equilibrium between coagulation and fibrinolysis is crucial for normal haemostasis and disturbance of this delicate balance can lead either to bleeding tendency or thrombosis. This review provides an update on several aspects of CPU known at the moment, including an extensive overview on the clinical studies performed up till now.

Inhibition of carboxypeptidase U (TAFIa) activity improves rt-PA induced thrombolysis in a dog model of coronary artery thrombosis.

The objective of this study was to test the hypothesis if thrombolysis induced by recombinant tissue-type plasminogen activator, (rt-PA) could be facilitated by inhibiting carboxypeptidase U (CPU, active Thrombin Activatable Fibrinolysis Inhibitor, TAFIa) activity. The efficacy of rt-PA alone, or in combination with the carboxypeptidase inhibitor MERGETPA, was compared in a dog model of coronary artery thrombosis. Twenty dogs were randomised in two groups, one received rt-PA, 1 mg kg(-1), as intravenous infusion over 20 min starting 30 min after thrombus formation, and the other group received rt-PA, 1 mg kg(-1), as group one with the addition of MERGEPTA 5 mg kg(-1) starting 25 min prior to coronary artery occlusion and followed by infusion of 5 mg kg(-1) h(-1) until the end of experiment. Efficacy was assessed by determination of time to lysis, duration of patency and blood flow during patency. Both groups had similar baseline characteristics with respect to haemodynamic parameters, i.e., heart rate, blood pressure and coronary artery blood flow. Coadministration of rt-PA and MERGETPA resulted in significant decrease in time to lysis (15+/-1.5 min vs. 20+/-1.7 min, p=0.03), increased patency time (87+/-16 min vs. 46+/-12 min, p=0.047) and increased coronary blood flow during patency (1131 mL h(-1) vs. 405 mL h(-1), p=0.015), compared to rt-PA alone. These results indicate that an inhibitor of CPU activity may have a beneficial effect in patients undergoing thrombolytic therapy by attaining shorter time to reperfusion and improved coronary patency.

Effects of the angiotensin converting enzyme inhibitors captopril, rentiapril, and alacepril in patients with essential and renovascular hypertension.

The effects of captopril, rentiapril, and alacepril were compared in five patients with renovascular hypertension (RVH) and five with essential hypertension (EH). The dose of each drug was equivalent to 50 mg of captopril. Rentiapril inhibited angiotensin converting enzyme activity more strongly and for longer periods than did the other two drugs. In the patients with RVH, blood pressure was significantly reduced more quickly and for longer periods by rentiapril than by captopril or alacepril; in the patients with EH, alacepril was the most potent antihypertensive agent. The results indicate that rentiapril is as effective as the other two drugs in patients with hypertension and that alacepril is more effective in patients with low-renin hypertension or renin-independent hypertension than captopril or rentiapril.

[Antihypertensive effects of SA446, hydralazine and the combination on renal hypertensive rats and spontaneously hypertensive rats by long-term treatment].

SA446 [(2R, 4R)-2-(o-hydroxyphenyl)-3-(3-mercaptopropionyl)-4- thiazolidinecarboxylic acid] (30 mg/kg/day), an orally active angiotensin-converting enzyme inhibitor, lowered significantly indirect systolic blood pressure (SBP) of 2-kidney, 1-clip renal hypertensive rats (RHR) by consecutive oral administration over a 14 week period. Daily oral dosing of hydralazine (2 mg/kg/day) for 14 weeks had little or no effect on SBP, but potentiated the antihypertensive effect of SA446. One to two weeks after discontinuation of the drugs, SBP in SA446 and the combination groups returned to the control level. Survival rates were 64%, 30% in the control and hydralazine group, respectively, but no death was observed in the SA446 group and the combination group throughout the administration period. Twenty-four hour urine volume and water intake tended to increase in the hydralazine group through the administration period, but increased apparently in the SA446 group and the combination group after discontinuation of the drugs. Daily oral dosing of SA446 (45 mg/kg/day) for over 16 weeks completely prevented the development of hypertension in spontaneously hypertensive rats (SHR). Daily oral dosing of hydralazine (2 mg/kg/day) similarly prevented the development. The combined effect with SA446 and hydralazine on the development was also observed. SBP in the SA446 group and the combination group increased gradually after discontinuation of the drugs, but were maintained at a low level as compared with the control group 3 weeks after discontinuation, while hydralazine gave a rapid return. No influences were observed in 24 hr-urine volume and water intake during and after the administration period in SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal kallikrein-kinin system and the depressor effect of angiotensin converting enzyme inhibitors MK 421, SA 446, and captopril in rats.

Responses in urinary kallikrein and kinin excretion and systolic blood pressure to MK 421, SA 446 or captopril were studied in normotensive rats fed on a regular or a low sodium diet to assess the role of renal kallikrein-kinin system in their hypotensive effect. MK 421, SA 446 or captopril were infused at a rate of 6 mg/kg/day by osmotic minipump implanted intraperitoneally for up to 6 days. The magnitude of fall in systolic blood pressure was greater on a low sodium diet when compared to on a regular diet, whereas the pattern of the fall was similar on both diets. The magnitude of falls in plasma angiotensin II and aldosterone concentration induced by MK 421, SA 446 and captopril was not significantly different between both regular and low sodium diets. Urinary kallikrein and kinin excretion and sodium excretion were increased during infusion of MK 421, SA 446 or captopril on a low sodium diet, however any significant changes were not found in each of them on a regular diet. The present results suggest that on a low sodium diet the augmented hypotensive response to angiotensin converting enzyme inhibitors in the rats might be due to the enhanced renal kallikrein-kinin system in addition to suppressed renin-angiotensin system.