PEGylation

FIGURE 3.29 Commercial strained cyclooctynes (dibenzylcyclooctyne (DBCO)-NHS, difluorinated cyclooctyne (DIFO) acid, bicyclenonyne (BCN) carbonate) for introduction into (bio)macromolecules. 

In the first generation of PEGylated drugs, the attachment of PEG was usually achieved with a functional group that is reactive toward the hydroxyl end groups of PEG, which were typically anhydrides, acid chlorides, chlorofor-mates, or carbonates [38]. In the second generation, more efficient groups like aldehydes, esters, and amides are reacted with the biomolecule to achieve 

FIGURE 3.30 Blood level of native versus PEGylated protein. 

FIGURE 3.31 Molecular structure of pure interferon a-2a (left) and a schematic representation of its PEGylated analog [35, 36]. Source Klaus et al. [37]. Reproduced with permission from Elsevier. 

Multiple-protein functionalization has some drawbacks such as blocking of active sites and incomplete coupling reactions that lead to complex mixtures. 

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Liposomal encapsulation of DOX or DNR Preferred anthracycline delivery to the tumor Breast cancer, ovarian cancer, AIDS-related Kaposi s sarcoma, multiple myeloma (pegylated liposomal DOX). Breast cancer (uncoated liposomal DOX). AIDS-related Kaposi s sarcoma, acute mye-loblastic leukemia, multiple myeloma, non-Hodgkin s lymphomas (uncoated liposomal DNR)... 

DOX, as EPI seems to form fewer amounts of ROS and secondary alcohol metabolite, (ii) encapsulation of anthracyclines in uncoated or pegylated liposomes that ensure a good drug delivery to the tumor but not to the heart, (iii) conjugation of anthracyclines with chemical moieties that are selectively recognized by the tumor cells, (iv) coadministration of dexrazoxane, an iron chelator that diminishes the disturbances of iron metabolism and free radical formation in the heart, and (v) administration of anthracyclines by slow infusion rather than 5-10 min bolus (Table 1). Pharmacological interventions with antioxidants have also been considered, but the available clinical studies do not attest to an efficacy of this strategy. 

Polyethylene glycol (PEG) consists of repeating units of ethylene glycol forming linear or branched polymers with different molecular masses. Pegylation is the process by which PEG chains are covalently attached to lEN molecules. Pegylation confers a number of properties on lEN-a molecules, such as sustained blood levels that enhance antiviral effectiveness and reduce adverse reactions, as well as a longer half-life and improved patient compliance (Kozlowski et al. 2001). 

Two forms of pegylated IFN-a have been approved by the Food and Drug Administration (FDA) and by the European Medicines Agency (EMEA) for the... 

Table 3 Pharmacological parameters of pegylated IFN-a molecules approved for the treatment of chronic hepatitis C...

Other IFNs that can be used in the treatment of viral infections include IFN-P, IFN-m, a molecule that is more potent than its nonglycosylated form, which itself has activity comparable to that of IFN-a (Buckwold et al. 2007), and that will be delivered continuously by an implantable device, IFN-y and 1FN-A,1, a pegylated form of which will soon be available. 

Redwood City, California, and Roche) and two clones have been selected for their improved in vitro activity relative to human IFN-a. One of them has been pegylated but its development has been halted because of strong immune reaction. 

Pegylated IFN-a-ribavirin combination therapy can be improved by increasing the dose of pegylated IFN-a and/or ribavirin in selected patients and by tailoring the length of treatment to the virological response. 

HCV infection is rarefy diagnosed in the acute phase, as most acutely infected individuals are asymptomatic. Between 50% and 90% of patients develop chronic infection, however, and this warrants early therapy. After occupational exposure with a known date, treatment should not be started before the acute episode characterized by alanine aminotransferase elevation, but it should always be started within 24 weeks after the onset of symptoms. The optimal treatment schedule for acute hepatitis C is controversial. Pegylated IFN-a monotherapy at the standard dose for 24 weeks yielded SVR rates close to 100% in symptomatic patients referred to tertiary care centers (De Rosa et al. 2006 Jaeckel et al. 2001 Santantonio et al. 2005 Wiegand et al. 2006). Shorter therapy may be envisaged (Calleri et al. 2007). Combination with ribavirin is recommended if a first course of pegylated IFN-a monotherapy fails to eradicate the infection. Viral elimination appears to be independent of the HCV genotype and the HCV RNA level (Calleri et al. 2007 De Rosa et al. 2006 Jaeckel et al. 2001). 

Villa et al. 1996). Recent reports from Japan suggest that daily IFN-p administration is highly effective in patients with low or moderate HCV RNA levels (Horiike and Onji 2003 Shiratori et al. 2000). Twice-daily administration of IFN-P as induction therapy has also been reported to be effective (Kim et al. 2005 Naka-jima et al. 2003). It is unlikely, however, that IFN-p will be used in routine clinical practice unless it is pegylated or otherwise modified, and until specific clinical trials are done. 

IFN-)il exhibits dose- and time-dependent inhibition of HCV rephcation in various models, independently of type I and IIIFN receptors and induced pathways (Marcello et al. 2006). A pegylated form of IFN-A, will soon enter clinical evaluation. 

The results of IFN-a-based therapy can theoretically be improved by using better-tolerated drugs that mimic the action of ribavirin and/or by using HCV inhibitors that, when combined, substantially reduce HCV replication. Since the mechanism of action of ribavirin is still unknown, no credible alternative approach is currently available. In contrast, many specific inhibitors of the HCV replication cycle are in preclinical development and several have reached chnical development (Pawlotsky et al. 2007). A number of them are being tested in combination with pegylated IFN-a, with or without ribavirin. 

In nonresponders to IFN-a-ribavirin, the antiviral effect of boceprevir appeared to be strictly additive to that of pegylated IFN-a2b (Sarrazin et al. 2007). In an ongoing phase II chnical trial, higher doses of boceprevir are being administered to treatment-naive patients, in combination with pegylated IFN-a and ribavirin. 

IFN-a was first nsed empirically in chronic hepatitis B in 1986 (Peters et al. 1986). The effect of hnman recombinant IFN-a on lymphocyte proliferation and differentiation was stndied in 18 patients with chronic hepatitis B. Inhibition of immnnoglob-nlin synthesis was observed, and the anthors postnlated that the immnnomodnlatory effect of IFN-a could be important in the therapentic response of chronic hepatitis B (Peters et al. 1986). The first study to evaluate the antiviral efficacy of IFN-a involved nine patients, who received different doses administered three times a week for two weeks. Two of them entered snstained remission, with nndetectable HBV DNA, loss of HBeAg, and ALT normalization (Dooley et al. 1986). Two forms of IFN-a have been used in the treatment of chronic hepatitis B, namely standard and pegylated IFN-a. 

In a clinical phase II trial, the efficacy of varions doses of pegylated IFN-a2a (90-270 pg weekly) administered for 24 weeks was studied in treatment-naive patients, by comparison with standard IFN-a2a at a dose of 4.5 MU three times a week... 

In two published cohort studies, pegylated IFN-a was effective in approximately one-third of HBeAg-positive patients in whom standard IFN-a or lamivudine had failed (Flink et al. 2006a Leemans et al. 2006). 

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