Improving cellular uptake and bioavailability of periplocymarin-linoleic acid prodrug by combining PEGylated liposome.

Periplocymarin (PPM), a cardiac glycoside isolated from Cortex periplocae, has a strong anti-tumor effect against various cancer cells. However, cardiotoxicity and rapid metabolism hinder its clinical applications. In this study, small molecule prodrug was integrated into PEGylated liposome to improve the efficiency of periplocymarin in vivo. The periplocymarin-linoleic acid (PL) prodrug was constructed by conjugating the linoleic acid with PPM via esterification, which was further facilitated to form PEGylated liposome (PL-Lip) through film dispersion. Compared with PL self-assembling nano-prodrug (PL-SNP), PL-Lip showed better colloid stability, sustained drug release kinetics, and enhanced cellular uptake by tumor cells. Notably, PL-Lip performed better than PPM and PL-SNP in terms of tumor distribution and pharmacokinetics, which include bioavailability and half-life. Altogether, the prodrug PEGylated liposome represents a good strategy and method for long-circulating and tumor-targeting delivery of periplocymarin with enhanced clinical application prospect.

Design and Synthesis of Polymer Prodrugs for Improving Water-Solubility, Pharmacokinetic Behavior and Antitumor Efficacy of TXA9.

PURPOSE: TXA9, a novel cardiac glycoside, has a potent anti-proliferative effect against A549 human lung cancer cells, however, possesses a poor water-solubility and a rapid metabolic rate in vivo which limited the further development of TXA9. To overcome the shortcomings of TXA9, four polymer prodrugs of TXA9 were designed and synthesized. METHODS: Poly (ethylene glycol) monomethyl ether (mPEG) and α-tocopherol polyethylene glycol succinate (TPGS) were applied to modify TXA9 via carbonate ester and glycine linkers respectively to obtain four polymer prodrugs. The water-solubility and stability of prodrugs were studied in vitro while their pharmacokinetic behaviors and antitumor activity were investigated in vivo. RESULTS: The water-solubility of TXA9 was obviously increased and prodrugs with glycine linkers showed a better stability in rat plasma. Their pharmacokinetic investigation found that the t1/2 and AUC0-∞ of TPGS-Gly-TXA9 was increased by 80- and 9.6-fold compared with that of TXA9, which was more superior than the other three prodrugs. More importantly, the tumor inhibition rate of TPGS-Gly-TXA9 (43.81%) on A549 xenograft nude mice was significantly increased compared with that of TXA9 (25.26%). CONCLUSION: The above results suggested that TPGS-Gly-TXA9 possessed better antitumor efficiency than TXA9 and could be further investigated as an anti-cancer agent.

GSH responsive nanomedicines self-assembled from small molecule prodrug alleviate the toxicity of cardiac glycosides as potent cancer drugs.

Cardiac glycosides (CGs) have been used to treat cancer for hundreds of years. However, the narrow therapeutic window and system toxicity have hindered their wide clinical applications. Herein, the small molecule prodrug strategy and nanotechnology were integrated into one drug delivery system with enhanced therapeutic effect. Using periplocymarin (PPM) as a target agent, we designed a novel redox-responsive prodrug conjugated with linoleic acid (PPM-ss-LA), which was capable of self-assembling independent of exogenous excipients. This prodrug could co-assemble with DSPE2k to form PEGylated prodrug nanoparticles (PPM-ss-LA/DSPE2k-NPs) with enhanced colloidal stability and blood circulation. Compared with free PPM, PPM-ss-LA/DSPE2k-NPs retained high anti-proliferative activity and showed increased cell uptake and therapeutic efficacy. Furthermore, the PPM-ss-LA/DSPE2k-NPs acquired a greatly enhancement of 50% lethal dose (LD50) in mice and reduced system toxicity compared with the free drug. Overall, the on-demand release of nanoprodrug delivery system could improve the therapeutic window and anticancer efficacy of CGs.

A review of cardiac glycosides: Structure, toxicokinetics, clinical signs, diagnosis and antineoplastic potential.

Cardiac glycosides (CGs) are secondary compounds found in plants and amphibians and are widely distributed in nature with potential cardiovascular action. Their mechanism is based on the blockage of the heart's sodium potassium ATPase, with a positive inotropic effect. Some of the most well-known CGs are digoxin, ouabain, oleandrin, and bufalin. They have similar chemical structures: a lactone ring, steroid ring, and sugar moiety. Digoxin, ouabain, and oleandrin are classified as cardenolides, consisting of a lactone ring with five carbons, while bufalin is classified as bufodienolides, with a six-carbon ring. Small structural differences determine variations in the toxicokinetics and toxicodynamics of such substances. Most case reports of poisoning caused by CGs are associated with cardiovascular toxicity, causing a variety of arrhythmias and lesions in the heart tissue. Experimental studies also describe important similarities among different CGs, especially regarding species sensitivity. Recent studies furthermore focus on their antineoplastic potential, with controversial results. Data from research studies and case reports were reviewed to identify the main characteristics of the CGs, including toxicokinetics, toxicodynamics, clinical signs, electrocardiographic, pathological findings, antineoplastic potential and the main techniques used for diagnostic purposes.

Revisiting the binding kinetics and inhibitory potency of cardiac glycosides on Na+,K+-ATPase (α1ß1): Methodological considerations.

INTRODUCTION: Ouabain and digoxin are classical inhibitors of the Na+,K+-ATPase. In addition to their conventional uses as therapeutic agents or experimental tools there is renewed interest due to evidence suggesting they could be endogenous hormones. Somewhat surprisingly, different publications show large discrepancies in potency for inhibiting Na+,K+-ATPase activity (IC50), particularly for the slow binding inhibitors, ouabain and digoxin. METHODS: Using purified pig kidney Na+,K+-ATPase (α1ß1FXYD2) and purified detergent-soluble recombinant human Na+,K+-ATPase (α1ß1FXYD1) we have re-evaluated binding and inhibition kinetics and effects of K+ concentration for ouabain, digoxin, ouabagenin and digoxigenin. RESULTS: We demonstrate unequivocally that for slow binding inhibitors, ouabain and digoxin, long incubation times (≥60 min at 37 °C) are required to avoid under-estimation of potency and correctly determine inhibition (IC50 around 100-200 nM at 5 mM K+) contrary to what occurs when pre-incubation of the drugs without ATP is followed by a short incubation time. By contrast, for the rapidly bound inhibitors, ouabagenin and digoxigenin, short incubation times suffice (<10 min). The strong reduction of inhibitory potency observed at high un-physiological K+ concentrations (≥5 mM) also explained the low potency reported by some authors. DISCUSSION: The data resolve discrepancies in the literature attributable to sub-optimal assay conditions. Similar IC50 values are obtained for pig kidney and recombinant human Na+,K+-ATPase, showing that inhibitory potencies are not determined by the species difference (pig versus human) or environment (membrane-bound versus detergent-soluble) of the Na+,K+-ATPase. The present methodological considerations are especially relevant for drug development of slow binding inhibitors.

Tissue distribution study of periplocin and its two metabolites in rats by a validated LC-MS/MS method.

Periplocin is a cardiac glycoside and has been used widely in the clinic for its cardiotonic, anti-inflammatory and anti-tumor effects. Although it is taken frequently by oral administration in the clinic, there have been no reports demonstrating that periplocin could be detected in vivo after an oral administration, so there is an urgen need to determine the characteristics of periplocin in vivo after oral administration. In this study, a sensitive and reliable liquid chromatography-tandem mass spectrometry method was developed and validated to identify and quantify periplocin and its two metabolites in rat tissue after a single dosage of perplocin at 50 mg/kg. The results demonstrated that periplocin and its two metabolites were detected in all of the selected tissues; periplocin could reach peak concentration quickly after administration, while periplocymarin and periplogenin reached maximum concentration > 4.83 h after administration. The tissue distribution of analytes tended to be mostly in the liver, and higher analyte concentrations were found in the heart, liver, spleen, lung and kidney, but a small amount of chemical constituents was distributed into the brain. The consequences obtained using this method might provide a meaningful insight for clinical investigations and applications.

Octreotide-periplocymarin conjugate prodrug for improving targetability and anti-tumor efficiency: synthesis, in vitro and in vivo evaluation.

Cardiac glycosides could increase intracellular Ca2+ ion by inhibiting the Na+/K+ATPase to induce apoptosis in many tumor cells. However, narrow therapeutic index, poor tumor selectivity and severe cardiovascular toxicity hinder their applications in cancer treatment. To improve the safety profile and tumor targetablility of cardiac glycosides, we designed octreotide conjugated periplocymarin, a cardiac glycoside isolated from Cortex periplocae. The conjugate showed higher cytotoxicity on MCF-7 cells and HepG2 tumor cells (SSTRs overexpression) but much less toxicity in L-02 normal cells. Tissue distribution studies of the conjugate using H22 tumor model in mice showed higher accumulation in tumor and lower distribution in heart and liver than periplocymarin. Furthermore, in vivo anticancer effects of the conjugate on mice bearing H22 cancer xenografts confirmed enhanced anti-tumor efficacy and decreased systemic toxicity. Altogether, octreotide-conjugated periplocymarin demonstrated tumor selectivity and may be useful as a targeting agent to improve the safety profile of cardiac glycosides for cancer therapy.

Periplocymarin is a potential natural compound for drug development: highly permeable with absence of P-glycoprotein efflux and cytochrome P450 inhibitions.

Periplocymarin, a cardiac glycoside isolated from Periploca sepium (P. sepium) and Periploca graeca (P. graeca), is a potential anti-cancer compound. The aim of the study was to investigate the potential for periplocymarin to interact with P-glycoprotein (P-gp) and to inhibit cytochrome P450s known to be expressed in the human small intestine. The in vitro and in situ permeability of periplocymarin were studied using Madin-Darby canine kidney (MDCK-II-WT) cells transfected with or without the human multidrug resistance (MDR1) gene and the single-pass perfused rat intestinal model. The cell system exhibited high functional activity and a net efflux ratio (NER) of 4.32 after transport of Rhodamine 123 (R123) (the P-gp substrate). Periplocymarin is highly permeable (Papp > 10 × 10(-6) cm/s; Peff(rat) > 5.09 × 10(-5) cm/s) and independent of P-gp influences. The NER at 100 µm periplocymarin (0.8) was unchanged in the presence of cyclosporine A (a non-specific P-gp inhibitor) (0.82). In the single-pass intestinal model, the Peff (rat) of 5 µg/ml periplocymarin (5.490 × 10(-5) cm/s) did not change in the presence of cyclosporine A (5.394 × 10(-5) cm/s). In the R123-inhibition assay, periplocymarin did not competitively inhibit P-gp. The inhibitory potential of periplocymarin on cytochrome P450 (CYP450s) was also studied. Periplocymarin (5, 50 µm) did not inhibit CYP1A2, CYP2C9, CYP2C19, CYP2D6 or CYP3A4. Thus, periplocymarin is unlikely to encounter drug-drug interactions with P-gp and CYP450s. Periplocymarin could be taken forward for further studies in drug development to test bioavailability, Phase II enzyme interactions and additional transporter interactions.

Treatment characteristics in elderly.

The pharmacodynamics and pharmacokinetics of medications, their therapeutic and toxic effects are age dependant. In the treatment of old people polypharmacy is widely used. The most common results of polypharmacy are increased adverse drug reactions, drug-drug interactions. In this study the use of different medications at the Departments of General Medicine and Cardiology (Tbilisi Republic Hospital) was analyzed. The case histories (1995, 2000 and 2005) of 1708 patients were studied. It was found that in 2005 the number of 60 years and older patients has doubled comparably with 1995, but the number of 24-44 years old patients remained almost the same. The complication rate was higher in elderly as compared with younger patients. It was found that in treatment of elderly population hypotensive drugs, diuretics and cardiac glycosides are used excessively. In the case of excess use of antihypertension medications there is a big risk of developing arterial hypotension. In old people it may lead to orthostatic hypotension, in youth - to dizziness. The frequent use of diuretics in old people may be accompanied with dehydration and risk of developing thromb formation. Hyponatraemia, hypokalaemia, hypomagnesemia lead to heart rhythm disturbances and risk of glycoside intoxication. In old people the therapeutical doses of diuretics depend not only on their biological activity, but also on the ability of their absorption from the gastrointestinal tract, on the organism's resistance and in the case of repeated intake on their cumulation quality and extraction.

Drug exsorption from blood into the gastrointestinal tract.

Drugs are exsorbed from the blood across the gastrointestinal membranes by passive or active processes. In the case of a passive transport mechanism, the exsorption of drugs depends on the concentration gradients between the serosal and mucosal sides. The extent of secretion (exsorption) is determined by numerous factors such as extent of binding to serum proteins, distribution volume, lipophilicity, pKa and molecular size of drugs, and the blood flow rate in the gut. Specific transport systems such as P-glycoprotein (P-gp), organic cation and organic anion transporters are found to be involved in active intestinal secretion of drugs. Intestinal secretory transport systems reduce the extent of drug absorption sometimes resulting in low oral bioavailability. It is, therefore, important to know whether poor drug absorption is due to the involvement of specialized secretory transport systems. Modulation of intestinal secretory transport can be a means to enhance absorption of drugs with low oral bioavailability if exsorption of drugs is based on active secretion pathways that are open for control from the "outside".

Cardiac glycosides. Drug interactions of clinical significance.

Several commonly coadministered drugs interfere significantly with the pharmacokinetics or pharmacodynamics of cardiac glycosides. Only a few of these interactions (e.g. amiodarone, propafenone, quinidine) take place consistently, and although their extent may vary in individual patients, digitalis dosage adjustments should be made to avoid underdigitalization or toxicity. In other instances the appearance of clinically significant interactions depends on individual pharmacokinetic/metabolic characteristics (e.g. erythromycin, tetracycline), and the result cannot be anticipated on clinical grounds. Some interactions are controversial, having not been confirmed by all studies; others have been shown only in healthy volunteers but lack the definition of their relevance in the context of disease states. In view of the possible impact on the individual patient, close clinical monitoring (which may be supplemented with evaluation of digitalis plasma concentration) is recommended when prescribing cardiac glycosides with other therapeutic agents for which the possibility of an interaction has been reported.

Receptor kinetics and concentration-effect relation of cardiac glycosides.

Therapeutic and toxic actions of cardiac glycosides are attributed to an inhibition of Na, K-ATPase. The therapeutically relevant range is between 25% and 50% inhibition. There is a good correlation between the average steady state serum concentration of glycosides and their therapeutic action. However, therapeutic and toxic effects set in with a latency and therefore do not follow the daily variations in glycoside concentration. Although the effect follows the average serum concentrations, only the minimal concentration is measured. In principle this is only adequate if the ratio of average/minimal concentration is constant. A model calculation showed that with a constant average steady state concentration an increase in the distribution volume or a decrease in total body clearance with corresponding reduction of the daily dose lead to an increase of the minimal concentrations of 5-7%. This means a corresponding underestimation of the average concentration from the minimum concentration. However, the deviations are too small to be of clinical relevance.

How fast do cardioactive steroids act independently of diffusion in guinea-pig myocardium?

1 The rate of onset of the inotropic effect of different cardioactive steroids (in order of increasing potency: dihydroouabain, digoxigenin, digoxin, ouabain, digitoxin) was studied in guinea-pig papillary muscles stimulated at 0.5 Hz. For an estimate of diffusion rate the time to defined levels of effect was evaluated in relation to the diameter of cylindrical muscles. 2 The dependence of onset rates on muscle diameter was more pronounced with a highly potent steroid, e.g., digitoxin, than with a less potent compound, e.g., dihydroouabain; that is, the apparent rate of diffusion was inversely correlated with the inotropic potency. Reduction of the ratio of receptor to steroid concentration with increase of ouabain or K+ concentration enhanced the apparent rate of diffusion. 3 Extrapolation to negligibly short diffusion distance indicated that the effects of the various steroids develop faster in the absence of diffusion. The effect of 50 mumol l-1 of dihydroouabain appeared more quickly than with ouabain in the perfused heart. The time courses of the inotropic effect in perfused hearts and in papillary muscles of diameters less than 0.75 mm were superimposable, indicating that the onset of the dihydroouabain effect was not controlled by diffusion. 4 After the interference of diffusion had been excluded, the rates of onset of action correlated inversely with the inotropic potencies of the steroids. The dissociation rate of the drug-receptor complex appeared to be related to the different receptor affinities.