Evaluation of the structure-activity relationship of rifabutin and analogs: a drug-membrane study.

This work focuses on the influence of rifabutin and two novel analogs, namely, N'-acetyl-rifabutin and N'-butanoyl-rifabutin, on the biophysical properties of lipid membranes. Monolayers and multilamellar vesicles composed of egg L-α-phosphatidylcholine:cholesterol in a molar ratio of 4:1 are chosen to mimic biological membranes. Several accurate biophysical techniques are used to establish a putative relationship between the chemical structure of the antimycobacterial compounds and their activity on the membranes. A combination of in situ experimental techniques, such as Langmuir isotherms, Brewster angle microscopy, polarization-modulated infrared reflection-absorption spectroscopy, and small-angle X-ray scattering, is used to assess the drug-membrane interaction. A relationship between the effect of a drug on the organization of the membranes and their chemical structure is found and may be useful in the development of new drugs with higher efficacy and fewer toxic effects.

Effects of a novel antimycobacterial compound on the biophysical properties of a pulmonary surfactant model membrane.

In this work, the interactions of a novel rifabutin's analogue (N'-acetyl-rifabutin, RFB2) with two-dimensional (Langmuir monolayers) and three-dimensional (large unilamellar and multilamellar vesicles) membrane models of the pulmonary surfactant (PS) were evaluated. The main purpose of this study is to obtain detailed information at the molecular level between the interactions of RFB2 with the phospholipids of the PS, under physiological conditions. Therefore, the effects of RFB2 in the monolayer phase behaviour at the air-water interface and in the lipid bilayer of membrane models composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) have been systematically compared. In this context, several biophysical techniques were carried out to establish the interactions of RFB2 with the two-dimensional membrane models of the PS: Langmuir isotherms, Brewster angle microscopy (BAM), and polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS); and with three-dimensional membrane models of the PS: derivate spectrophotometry partition coefficient (Kp), dynamic light scattering (DLS), small and wide angle X-ray scattering (SAXS and WAXS). The results gathered by the different biophysical techniques and the PS membrane model used provide detailed information about the strong interactions of RFB2 with the polar head groups of the PS phospholipids and permit to establish the impact of the RFB2-PS membrane interactions, justifying an often unexplored biophysical approach to the drug's pharmacokinetics and toxicological effect.

Drug-membrane interaction studies applied to N'-acetyl-rifabutin.

This work aims the systematic study of the biophysical interactions of a novel antimycobacterial compound (N'-acetyl-rifabutin, RFB2) with membrane models of different lipid composition and surface charge. Membrane mimetic models were used to evaluate the RFB2's membrane partition, its preferential location across the membrane, and the effect of RFB2 on the biophysical properties of the membrane, which ultimately might be related with the antimycobacterial compound bioavailability and the membrane toxicity. According to the aforementioned, liposomes of dimyristoyl-sn-glycero-phosphocholine (DMPC) and 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) were, respectively, used as mimetic models of human and bacterial cell membranes. The antimycobacterial compound lipophilicity was evaluated by spectroscopic methods, which enabled the determination of the partition coefficient (Kp). To study the RFB2 membrane's location, fluorescence quenching studies and lifetime measurements were executed in liposomes labeled with fluorescent probes. In order to evaluate the changes induced by RFB2 on the membrane biophysical properties, dynamic light scattering (DLS) and steady-state anisotropy were performed. The overall results reveal a strong interaction between RFB2 and the membrane models and allowed the evaluation of its lipophilicity, which is a key molecular descriptor in the characterization of novel potential drugs. Moreover, the higher partition of RFB2 and the more pronounced changes in the biophysical parameters of the negatively charged membrane model suggest that RFB2 has more affinity to the bacterial membrane. For the above-mentioned reasons, this work supports that RFB2 has a potential value as a drug in pharmaceutical formulations used to treat mycobacterial infections.

Differential interactions of rifabutin with human and bacterial membranes: implication for its therapeutic and toxic effects.

This work focuses on the interaction of rifabutin (RFB), a naphthalenic ansamycin, with membrane models. Since the therapeutic and toxic effects of this class of drugs are strongly influenced by their lipid affinity, we concerned specifically on the ability of this antibiotic to affect the membrane biophysical properties. The extent of the interaction between RFB and membrane phospholipids was quantified by the partition coefficient (K(p)), using membrane model systems that mimic the human (liposomes of 1,2-dimyristoyl-sn-glycero-phosphocholine, DMPC) and the bacterial (liposomes of 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol, DMPG) plasma membranes. To predict the drug location in the membranes, fluorescence quenching and lifetime measurements were carried out using the above-mentioned membrane models labeled with fluorescent probes. Steady-state anisotropy measurements were also performed to evaluate the effect of RFB on the microviscosity of the membranes. Overall, the results support that RFB has higher affinity for the bacterial membrane mediated by electrostatic interactions with the phospholipid head groups.