Two vinyl sulfone functionalized crosslinkers were developed for the purpose of preparing degradable poly(ethylene glycol) (PEG) hydrogels (EMXL and GABA-EMXL hydrogels). the degradation of both hydrogels in mouse plasma was 12-times slower than in PBS. The slower degradation rate in plasma as compared to buffer is consistent with the presence of γ-glutamyltransferase γ-glutamylcyclotransferase and/or glutaminyl cyclase (QC) which have been shown to suppress pyroglutamic acid formation. The current studies suggest that EMXL and GABA-EMXL hydrogels may have biomedical applications where 1 to 2 2 week degradation timeframes are optimal. 1 Introduction Hydrogels have been used in various SGI-1776 biomaterial and biotechnology applications such as tissue engineering [1] artificial organs [2] and drug delivery [3-6] as well as for drug carriers especially for proteins [7]. Biodegradation is considered a critical requirement for most hydrogel applications since surgical removal from the body is painful at best. Degradation occurs by means of labile bonds that are introduced into the hydrogel matrix. A variety of linkages including esters [8] polyesters [9] polyanhydrides [10] imine (Schiff bases) [11] acetal [12] ketal [13] and enzymaticaly labile peptides [14] have been incorporated into degradable polymeric hydrogels. The hydrogels based on ester and anhydride bonds were designed to be cleaved by simple hydrolysis initiated under acidic or basic pH conditions [15 16 For example Harris and Zhao prepared a linear amine reactive PEG crosslinker containing two built-in ester bonds. This crosslinker was reacted with branched PEG amines to form degradable hydrogels [17]. There have been many other similar attempts at making degradable hydrogels based on ester mechanisms. Unfortunately these hydrogels form carboxylic acid degradation products that raise the local acidity of the surrounding tissue resulting in to scaffold degradation by autocatalysis and the elicitation of a pronounced inflammatory response [18 19 Acid-sensitive degradable linkers such as acetals cyclic acetals ketals and Schiff-base linkages have also been used to prepare degradable hydrogels [12 13 20 21 These linkers degrade via hydrolysis to produce hydroxyl and carbonyl terminals [20] in a pH dependent manner [22]. Enzymatically cleavable polymeric linkers have been copolymerized with PEG to LRRC63 form degradable gels [23]. Similar linkers have been used for covalently linking drug conjugates to the hydrogel matrix SGI-1776 [24]. SGI-1776 The rate of degradation of these hydrogels was found to be dependent on both the length of the polymer or copolymer and the concentration of enzyme. Recently degradable hydrogels based on self-immolative bifunctional hyaluronan-bisphosphonate conjugates were used for localized delivery and cell specific targeting [25]. This hydrogel degradation process occurs a two-step mechanism. Hydrogel degradation begins with the cleavage of a disulfide bond in the conjugate followed by spontaneous elimination resulting in the formation of ethylene episulfide carbon dioxide and free hydrazide. The conjugate used for this mechanism requires a multistep synthesis and it forms toxic degradation products like hydrazide [26 27 In the current report a new class of biodegradable hydrogels based on a unique self-elimination cleavage mechanism has SGI-1776 been developed in order to achieve precise control of hydrogel degradation. This self-cleaving mechanism is based on a chemical reaction in which an N-terminal residue of a glutamine in the peptide participates in the displacement of its γ-amino group by its α-amino group. Upon degradation of these hydrogels PEG-based degradation products are released that are expected to be nontoxic. 2 Materials and Methods 2.1 Reagents Polyoxyethylene bis (amine) (MW 3350 Da DAP) dithiothreitol (DTT) and 2SO2-CH) 6.6 (2H t 2 vinyl-CH2) 6.4 (2H t 2 vinyl-CH) 4.4 (1H m Cys-α) 4.2 (1H m Cys-α) 4 (4H m 2 3.78 (8H m 4 3.6 (brm PEG-CH2O-CH2) 3.4 (brm PEG-CH2) 3.1 (4H s CH2 and Glu-α) 2.8 (4H t 2 1.85 (4H m 2 1.8 (4H brm 2 2.1 brm Cys-β) 1.7 (8H m 4 and 1.1 (8H m 4 MALDI-TOF-MS. (m/z): Calculated: 4374 observed: 4206. the Michael addition reaction between copolymer (SH groups) and crosslinker.