Reversible PEGylation: A Novel Technology To Release Native Interferon α2 over a Prolonged Time Period

Many peptide and protein drugs have a short circulatory half-life in vivo. The covalent attachment of polyethylene glycol (PEG) chains (PEGylation) can overcome this deficiency, but pegylated peptides and proteins are often inactive. In this study, we present a novel PEG-IFNalpha2 conjugate, PEG(40)-FMS-IFNalpha2, capable of regenerating native interferon alpha2 (IFNalpha2) at a slow rate under physiological conditions. A 2-sulfo-9-fluorenylmethoxycarbonyl (FMS) containing bifunctional reagent, MAL-FMS-NHS, has been synthesized, enabling the linkage of a 40 kDa PEG-SH to IFNalpha2 through a slowly hydrolyzable bond. By use of a BIAcore binding assay, the in vitro rate of regeneration of native interferon was estimated to have a half-life of 65 h. Following subcutaneous administration to rats and monitoring circulating antiviral activity, active IFNalpha2 levels peaked at 50 h, with substantial levels still being detected 200 h after administration. This value contrasts with a half-life of about 1 h measured for unmodified interferon. The concentration of active IFNalpha2 scaled linearly with the quantity injected. Comparing subcutaneous to intravenous administration of PEG(40)-FMS-IFNalpha2, we found that the long circulatory lifetime of IFNalpha2 was affected both by the slow rate of absorption of the PEGylated protein from the subcutaneous volume and by the slow rate of discharge from the PEG in circulation. A numerical simulation of the results was in good agreement with the results observed in vivo. The pharmacokinetic profile of this novel IFNalpha2 conjugate combines a prolonged maintenance in vivo with the regeneration of active-native IFNalpha2, ensuring ready access to peripheral tissues and thus an overall advantage over currently used formulations.

Optimizing the Binding Affinity of a Carrier Protein

Prolonging the circulatory half-life of low mass protein drugs can be achieved either by administration of a pro-drug or through co-injection with a carrier protein that will slowly release the active protein. The rate of release is concentration and affinity dependent. The optimal relationship between these two in prolonging the half-life of a pro-drug is the focus of this work. Interferon (IFN) beta is one of the most widely used protein drugs in the clinic. Here, we show that the circulatory half-life of IFNbeta can be significantly extended by co-administration with the extracellular domain of the IFN receptor ifnar2 (ifnar2-EC). To investigate the concentration/affinity relation, a range of tighter binding ifnar2-EC mutants was designed that bind IFNbeta, but not IFNalpha2, up to 50-fold tighter compared with the wild-type ifnar2-EC. This increased affinity is related to a slower dissociation rate, whereas the association of IFNbeta with ifnar2-EC is already near optimum. Using the wild-type and mutant receptors, we investigated their potential in occluding IFNbeta from circulation in a tissue culture assay, as well as in rats. To determine the potential of ifnar2-EC as a carrier protein, we co-administered a mixture of IFNbeta and ifnar2-EC to rats both intravenously and subcutaneously, and followed the blood plasma concentrations of IFNbeta over time. The tighter binding ifnar2-EC mutant had a clear advantage in prolonging the half-life of IFNbeta in circulation, even when lower protein concentrations were administered. A numerical simulation of the in vivo data demonstrates that the optimal binding affinity of a carrier protein is around the concentration needed to obtain optimal activity of the ligand.

Ligand effects on the binding of cis- and trans-[PtCl(2)Am(1)Am(2)] to proteins

As part of a systematic study of the basic principles that govern the formation and reactivity of Pt-protein adducts, we report the effect of substituting the amine ligand of cis- and trans-[PtCl(2)(NH(3))(2)] complexes with bulkier planar aromatic or nonplanar cyclic amine ligands on the binding properties of the complexes to ubiquitin and to horse heart myoglobin. The ligand replacement had a different effect on the cis or trans isomers investigated. In the cis-Pt complexes, replacing one or both amine ligands by piperidine or 4-picoline dramatically decreased the binding of the complexes to the proteins studied, whereas in the substituted trans-Pt complexes replacement of the amine by a piperidine or 4-picoline increased the binding rate. This behavior may have to do with the different preferred binding sites of the cis- and trans-Pt complexes. The bulkier cis- or trans-Pt complexes investigated also did not display a preference for Met1 of ubiquitin, possibly owing to steric constraints imposed by the substituted ligands. The introduction of a charged piperazine ligand significantly decreased the rate of binding to the protein, possibly owing to electrostatic interactions or hydrogen-bond formations with the surface of the protein. The binding of the complexes to ubiquitin and myoglobin does not disrupt the folding of the proteins as judged by electrospray ionization mass spectrometry.

Interactions of cisplatin and transplatin with proteins. Comparison of binding kinetics, binding sites and reactivity of the Pt-protein adducts of cisplatin and transplatin towards biological nucleophiles

In this manuscript we report on the interactions of cis-DDP (cisplatin, cis-diamminedichloroplatinum(II)) and trans-DDP (transplatin, trans-diamminedichloroplatinum(II)) with two model proteins, ubiquitin (Ub) and horse heart myoglobin (Mb), and attempt to answer the question whether proteins that have methionine-Pt adducts can transfer the platinum to biological nucleophiles and particularly to DNA. Our study shows that cisplatin and transplatin form different adducts with ubiquitin: transplatin forms one major adduct, trans-[Pt(Ub)(NH(3))(2)Cl], while cisplatin forms four distinct adducts, [Pt(Ub)(NH(3))(2)Cl], [Pt(Ub)(NH(3))(2)(H(2)O)], [Pt(Ub)(NH(3))(2)], and [Pt(Ub)(NH(3))]. When binding ubiquitin, Met1 is the preferred binding site of cisplatin, but not of transplatin. Cisplatin binds faster than transplatin to both ubiquitin and horse heart myoglobin. Both cisplatin and transplatin adducts form stable ternary adducts when reacted with 5'-guanosine monophosphate (5'-GMP) or a tetranucleotide. No transfer of the Pt moiety from the proteins to the nucleotides was observed. Glutathione efficiently removes the platinum from preformed adducts of both cisplatin and transplatin with ubiquitin.

Characterization of sterically stabilized cisplatin liposomes by nuclear magnetic resonance

Extensive scientific efforts are directed towards finding new and improved platinum anticancer agents. A promising approach is the encapsulation of cisplatin in sterically stabilized, long circulating, PEGylated 100 nm liposomes. This liposomal cisplatin (STEALTH cisplatin, formerly known as SPI-77) shows excellent stability in plasma and has a longer circulation time, greater efficacy and lower toxicity than much free cisplatin. However, so far, the physicochemical characterization of STEALTH cisplatin has been limited to size distribution, drug-to-lipid ratio and stability. Information on the physical state of the drug in the liposome aqueous phases and the drug's interaction with the liposome membrane has been lacking. This study was aimed at filling this gap. We report a multinuclear NMR study in which several techniques have been used to assess the physical nature of cisplatin in liposomal formulations and if and to what extent the drug affects the liposome phospholipids. Since NMR detects only the soluble cisplatin in the liposomes and not the insoluble drug, combining NMR and atomic absorption data enables one to determine how much of the encapsulated drug is soluble in the intraliposomal aqueous phase. Our results indicate that almost all of the cisplatin remains intact during the loading process, and that the entire liposomal drug is present in a soluble form in the internal aqueous phase of the liposomes.

Effects of monofunctional platinum binding on the thermal stability and conformation of a self-complementary 22-mer

We investigated the effect of various monofunctional platinum complexes on the thermal stability and conformation of a self-complementary 22-mer duplex oligonucleotide by means of CD and UV melting profiles. We studied several families of triamine complexes of the general formula PtA2AmCl where A2=(NH3)2 and ethylenediamine and where Am=N1-4-methyl-pyridine, N7-guanosine, and 9-ethyl-guanine. Platination by the N1-4-methyl-pyridine and 9-ethyl-guanine complexes led to a decrease in the Tm of the oligonucleotide by 2-11.5 degrees C while platination with the N7-guanosine complexes led to a rise in the melting temperature of the oligonucleotides by 4.5 degrees C. A similar inverse correlation between the two groups of platinum compounds was found in the CD spectra. In all cases, the cis isomer had a more pronounced effect on both the melting curve and the CD spectrum. The cis isomer was found to have a more destabilizing effect than its trans counterpart. This indicates that the cis geometry in fact forces a greater structural constraint on the backbone of the double helix. We have also found that the sugar of the guanosine has a significant influence on both the Tm and CD spectra; the sugar moiety contributes to the stability of the double helix, probably through the formation of hydrogen bonds.

Monofunctional platinum amine complexes destabilize DNA significantly

Both cis-[Pt(NH3)2(4-Me-Py)Cl]+ and trans-[Pt(NH3)2(4-Me-Py)Cl]+ bind DNA covalently at the N7 site of guanine residues forming mono-dentate adducts. However, like cisplatin and transplatin, only the cis isomer has anti-cancer activity, whereas the trans-isomer does not. In order to understand the molecular basis of the different activities associated with cis-[Pt(NH3)2(4-Me-Py)Cl]+ and trans-[Pt(NH3)2(4-Me-Py)Cl]+, the interactions of these two platinum compounds with the DNA heptamer CCTG*TCC:GGACAGG duplex (G* is the platinated guanine) have been examined. The reaction rate of cis-[Pt(NH3)2(4-Me-Py)Cl]+ with the single-stranded CCTGTCC is significantly faster than that of the trans isomer. The solution structure of the platinum-DNA adducts has been studied by two-dimensional NMR spectroscopy. Both the cis-platinum adducts and the trans-platinum adducts destabilize the DNA duplex significantly. The melting temperature (Tm) of the platinated heptamer duplex is estimated to be 10 degrees C lower than for the unplatinated duplex by NMR. At 2 degrees C, the base pairs located on the 5' side of the oligonucleotide, beyond the platinum lesion site, are disrupted. Over time, the platinum-DNA complex decomposes and the cis-[Pt(NH3)2(4-Me-Py)] platinum complex is gradually detached from DNA. No interstrand crosslinking is observed. The biological implications of the structural studies are discussed.