Protein-ligand (un)binding kinetics as a new paradigm for drug discovery at the crossroad between experiments and modelling.

In the last three decades, protein and nucleic acid structure determination and comprehension of the mechanisms, leading to their physiological and pathological functions, have become a cornerstone of biomedical sciences. A deep understanding of the principles governing the fates of cells and tissue at the molecular level has been gained over the years, offering a solid basis for the rational design of drugs aimed at the pharmacological treatment of numerous diseases. Historically, affinity indicators (i.e. Kd and IC50/EC50) have been assumed to be valid indicators of the in vivo efficacy of a drug. However, recent studies pointed out that the kinetics of the drug-receptor binding process could be as important or even more important than affinity in determining the drug efficacy. This eventually led to a growing interest in the characterisation and prediction of the rate constants of protein-ligand association and dissociation. For instance, a drug with a longer residence time can kinetically select a given receptor over another, even if the affinity for both receptors is comparable, thus increasing its therapeutic index. Therefore, understanding the molecular features underlying binding and unbinding processes is of central interest towards the rational control of drug binding kinetics. In this review, we report the theoretical framework behind protein-ligand association and highlight the latest advances in the experimental and computational approaches exploited to investigate the binding kinetics.

Renal resistive index and low-grade inflammation in patients with essential hypertension.

In essential hypertension, increased renal resistive index (RRI) is associated to a reduction of renal function and microalbuminuria, and to renal tubulo-interstitial damage. A tubulo-interstitial inflammatory infiltration was found in experimental models of hypertension, and serum high-sensitive C-reactive protein (hsCRP) levels correlated with urinary markers of tubulo-interstitial damage in humans. We studied the relationship between RRI and serum hsCRP in hypertensives with preserved renal function, without microalbuminuria. We investigated hypertensive patients without diabetes, renal failure, microalbuminuria or major inflammatory disease. Serum levels of hsCRP were assayed. RRI was calculated by intrarenal Doppler ultrasound and considered pathologic when ≥0.70 or >95% of upper confidence limit expected for age decade. The renal volume-to-resistive index ratio (RV/RRI) was also calculated. We evaluated 85 patients (57±14 years, 61 males). Patients with pathologic RRI (n=21) were older and had significantly higher hsCRP levels (4.70±2.30 vs 2.93±2.09 mg l(-1), P<0.01) compared with patients with normal RRI, as well as patients with decreased RV/RRI (n=43). HsCRP was directly related with RRI (r=0.41, P<0.001) and inversely with RV/RRI (r=-0.35, P<0.001). HsCRP proved to be a significant predictor of both pathologic RRI and decreased RV/RRI, even after adjustment. In essential hypertension low-grade inflammation is associated with tubulo-interstitial damage evaluated by Doppler ultrasonography.