Silk–elastinlike protein polymer hydrogels: Influence of monomer sequence on physicochemical properties

Silk-elastin-like hydrogel improves the safety of adenovirus-mediated gene-directed enzyme-prodrug therapy

Recombinant silk-elastin-like protein polymers (SELPs) are well-known for their highly tunable properties on both the molecular and macroscopic hydrogel levels. One specific structure of these polymers, SELP-815K, has been investigated as an injectable controlled delivery system for the treatment of head and neck cancer via a gene-directed enzyme prodrug therapy (GDEPT) approach. Due to its pore size and gelation properties in vivo, SELP restricts the distribution and controls the release of therapeutic viruses for up to one month. It has been shown that SELP-mediated delivery significantly improves therapeutic outcome of the herpes simplex virus thymidine kinase (HSVtk)/ganciclovir (GCV) system in xenograft models of human head and neck cancer. However little is known about potential benefits of this approach with regard to toxicity in the presence of a fully intact immune system. The studies presented here were designed to assess the change in toxicity of the SELP-mediated viral delivery compared to free viral injection in a non-tumor-bearing immune competent mouse model. Toxicity was assessed at 1, 2, 4, and 12 weeks via body weight monitoring, complete blood count (CBC), and blood chemistry. It was found that in the acute and subacute phases (weeks 1-4) there is significant toxicity in groups combining the virus and the prodrug, and matrix-mediated gene delivery with SELP demonstrates a reduction in toxicity from the 2 week time point through the 4 week time point. At the end of the subchronic phase (12 weeks), signs of toxicity had subsided in both groups. Based on these results, recombinant SELPs offer a significant reduction in toxicity of virus-mediated GDEPT treatment compared to free virus injection in the acute and subacute phases.

Silk-elastinlike protein polymers improve the efficacy of adenovirus thymidine kinase enzyme prodrug therapy of head and neck tumors

BACKGROUND

Adenoviral-directed enzyme prodrug therapy is a promising approach for head and neck cancer gene therapy. The challenges faced by this approach, however, comprise transient gene expression and dissemination of viruses to distant organs.

METHODS

We used recombinant silk-elastinlike protein polymer (SELP) matrices for intratumoral delivery of adenoviruses containing both thymidine kinase-1 and luciferase genes in a nude mouse model of JHU-022 head and neck tumor. Hydrogels made from two SELP analogues (47K and 815K), with similar silk to elastinlike block ratios but different block lengths, were studied for intratumoral viral delivery. Tumor-bearing mice were followed up for tumor progression and luciferase gene expression concomitantly for 5 weeks. Polymer safety was evaluated through body weight change, blood count, and liver and kidney functions, in addition to gross and microscopic histological examination.

RESULTS

SELP-815K analogues efficiently controlled the duration and extent of transfection in tumors for up to 5 weeks with no detectable spread to the liver. An approximately five-fold greater reduction in tumor volume was obtained with matrix-mediated delivery compared to intra-tumoral injection of adenoviruses in saline. SELP matrix proved safe in all injected mice compared to the control group.

CONCLUSIONS

The SELP-controlled gene delivery approach could potentially improve the anticancer activity of virus-mediated gene therapy at the same time as limiting viral spread to normal organs.

A smart supramolecular hydrogel of N(alpha)-(4-n-alkyloxybenzoyl)-L-histidine exhibiting pH-modulated properties

Six L-histidine-based amphiphiles, N(alpha)-(4-n-alkyloxybenzoyl)-L-histidine of different hydrocarbon chain lengths, were designed, synthesized, and examined for their ability to gelate water. Four of members of this family of amphiphiles were observed to form thermoreversible hydrogels in a wide range of pH at room temperature. The structural variations were characterized by critical gelation concentration, gelation time, gel melting temperature (T(gs)), rheology, and electron microscopy. Among the amphiphiles, the n-octyl derivative showed better gelation ability in the studied pH range. The amphiphiles were found to have T(gs) higher than body temperature (37 degrees C) showing their stability. Also, relatively higher yield stress (>1000 Pa) values of the hydrogels show their higher strength. The effective gelator molecules self-assemble into fibrous structures. Scanning electron microscopic picture of the hydrogels revealed large ribbons with right-handed twist. Small-angle XRD and circular dichroism spectroscopy were also employed to characterize the hydrogels. It was observed that pi-pi stacking, hydrophobic interaction, amide hydrogen bonding, and solubility factor contribute to the stability and strength of the hydrogels.

Silk-elastinlike recombinant polymers for gene therapy of head and neck cancer: from molecular definition to controlled gene expression

Silk-elastinlike protein polymers (SELP's) are block copolymers of silk-like and elastin-like tandem repeats. With appropriate sequence and composition SELPs can be liquid at room temperature and form hydrogels at body temperature. The influence of polymer structure and concentration on biodegradation in vitro and controlled delivery of adenoviruses carrying reporter genes to head and neck tumors in vivo was evaluated using hydrogels made from three SELP analogs. SELP-815K, with eight silk and fifteen elastin units and a lysine (K) modified elastin, was compared to SELP-415K and SELP-47K. Hydrogels with higher silk content and concentration degraded at a slower rate compared to other analogs. Intratumoral injection of adenoviruses with SELPs enhanced gene expression in tumor tissue up to 10 fold compared to viral injection without polymer. Viruses delivered with SELP-815K at 4 wt.% polymer concentration showed the highest level of gene expression. Tumor to liver ratio of expression was up to 55 fold higher for SELP-mediated systems. This study demonstrates the influence of exquisite control over polymer structure using recombinant techniques on spatial and temporal control over adenoviral delivery and establishes the utility of SELP matrices as biodegradable systems for gene therapy of head and neck cancer.