Characterization of injectable hydrogels based on poly(N-isopropylacrylamide)-g-chondroitin sulfate with adhesive properties for nucleus pulposus tissue engineering.

The goal of this work is to develop an injectable nucleus pulposus (NP) tissue engineering scaffold with the ability to form an adhesive interface with surrounding disc tissue. A family of in situ forming hydrogels based on poly(N-isopropylacrylamide)-graft-chondroitin sulfate (PNIPAAm-g-CS) were evaluated for their mechanical properties, bioadhesive strength, and cytocompatibility. It was shown experimentally and computationally with the Neo-hookean hyperelastic model that increasing the crosslink density and decreasing the CS concentration increased mechanical properties at 37 °C, generating several hydrogel formulations with unconfined compressive modulus values similar to what has been reported for the native NP. The adhesive tensile strength of PNIPAAm increased significantly with CS incorporation (p < 0.05), ranging from 0.4 to 1 kPa. Live/Dead and XTT assay results indicate that the copolymer is not cytotoxic to human embryonic kidney (HEK) 293 cells. Taken together, these data indicate the potential of PNIPAAm-g-CS to function as a scaffold for NP regeneration.

Non-natural peptide triazole antagonists of HIV-1 envelope gp120.

We investigated the derivation of non-natural peptide triazole dual receptor site antagonists of HIV-1 Env gp120 to establish a pathway for developing peptidomimetic antiviral agents. Previously we found that the peptide triazole HNG-156 [R-I-N-N-I-X-W-S-E-A-M-M-CONH(2), in which X=ferrocenyltriazole-Pro (FtP)] has nanomolar binding affinity to gp120, inhibits gp120 binding to CD4 and the co-receptor surrogate mAb 17b, and has potent antiviral activity in cell infection assays. Furthermore, truncated variants of HNG-156, typified by UM-24 (Cit-N-N-I-X-W-S-CONH(2)) and containing the critical central stereospecific (L)X-(L)W cluster, retain the functional characteristics of the parent peptide triazole. In the current work, we examined the possibility of replacing natural with unnatural residue components in UM-24 to the greatest extent possible. The analogue with the critical "hot spot" residue Trp 6 replaced with L-3-benzothienylalanine (Bta) (KR-41), as well as a completely non-natural analogue containing D-amino acid substitutions outside the central cluster (KR-42, (D)Cit-(D)N-(D)N-(D)I-X-Bta-(D)S-CONH(2)), retained the dual receptor site antagonism/antiviral activity signature. The results define differential functional roles of subdomains within the peptide triazole and provide a structural basis for the design of metabolically stable peptidomimetic inhibitors of HIV-1 Env gp120.