Hydrogels that degrade under appropriate conditions of pH and temperature by virtue of crosslinking compounds that cleave through an elimination reaction are described. The hydrogels may be used for delivery of various agents, such as pharmaceuticals. This invention provides hydrogels that degrade to smaller, soluble components in a non-enzymatic process upon exposure to physiological conditions and to methods to prepare them. The hydrogels are prepared from crosslinking agents that undergo elimination reactions under physiological conditions, thus cleaving the crosslinking agent from the backbone of the hydrogel. The invention also relates to the crosslinking agents themselves and intermediates in forming the hydro gels of the invention. The biodegradable hydro gels prepared according to the methods of the invention may be of use in diverse fields, including biomedical engineering, absorbent materials, and as carriers for drug delivery.

The present invention provides diacylhydrazine ligands and chiral diacylhydrazine ligands for use with ecdysone receptor-based inducible gene expression systems. Thus, the present invention is useful for applications such as gene therapy, large scale production of proteins and antibodies, cell-based screening assays, functional genomics, proteomics, metabolomics, and regulation of traits in transgenic organisms, where control of gene expression levels is desirable. An advantage of the present invention is that it provides a means to regulate gene expression and to tailor expression levels to suit the user's requirements.

The present invention provides diacylhydrazine ligands and chiral diacylhydrazine ligands for use with ecdysone receptor-based inducible gene expression systems. Thus, the present invention is useful for applications such as gene therapy, large scale production of proteins and antibodies, cell-based screening assays, functional genomics, proteomics, metabolomics, and regulation of traits in transgenic organisms, where control of gene expression levels is desirable. An advantage of the present invention is that it provides a means to regulate gene expression and to tailor expression levels to suit the user's requirements.

Provided is a compound comprising the structure:
(SIG)-(SI-MOD).sub.m. In this compound, SIG is a signaling molecule, SI is a self-immolative structure bound to SIG such that SIG has a reduced signal relative to the signal of SIG without SI, MOD is a moiety bound to SI that is subject to modification by an activator, and m is an integer from 1 to about 10. With this compound, when MOD is modified by an activator, SI is destabilized and self-cleaved from SIG such that SIG generates an increased signal. Also provided is a method of determining whether a sample comprises an activator, using the above-described compound. Additionally provided is a method of determining whether a cell comprises a nitroreductase using the above-described compound where nitroreductase is the activator. Further provided is a method of determining whether a mammalian cell is hypoxic using the above-described compound where nitroreductase is the activator. A method of detecting a microorganism that comprises a nitroreductase, using the above-described compound where nitroreductase is the activator, is also provided. Also provided is a method of identifying nitroreductase in a sample, using the above-described compound where nitroreductase is the activator.

Hydrogels that degrade under appropriate conditions of pH and temperature by virtue of crosslinking compounds that cleave through an elimination reaction are described. The hydrogels may be used for delivery of various agents, such as pharmaceuticals.

Hydrogels that degrade under appropriate conditions of pH and temperature by virtue of crosslinking compounds that cleave through an elimination reaction are described. The hydrogels may be used for delivery of various agents, such as pharmaceuticals.

Provided is a compound comprising the structure:
(SIG)-(SI-MOD).sub.m. In this compound, SIG is a signaling molecule, SI is a self-immolative structure bound to SIG such that SIG has a reduced signal relative to the signal of SIG without SI, MOD is a moiety bound to SI that is subject to modification by an activator, and m is an integer from 1 to about 10. With this compound, when MOD is modified by an activator, SI is destabilized and self-cleaved from SIG such that SIG generates an increased signal. Also provided is a method of determining whether a sample comprises an activator, using the above-described compound. Additionally provided is a method of determining whether a cell comprises a nitroreductase using the above-described compound where nitroreductase is the activator. Further provided is a method of determining whether a mammalian cell is hypoxic using the above-described compound where nitroreductase is the activator. A method of detecting a microorganism that comprises a nitroreductase, using the above-described compound where nitroreductase is the activator, is also provided. Also provided is a method of identifying nitroreductase in a sample, using the above-described compound where nitroreductase is the activator.

Provided is a compound comprising the structure:
(SIG)-(SI-MOD).sub.m. In this compound, SIG is a signaling molecule, SI is a self-immolative structure bound to SIG such that SIG has a reduced signal relative to the signal of SIG without SI, MOD is a moiety bound to SI that is subject to modification by an activator, and m is an integer from 1 to about 10. With this compound, when MOD is modified by an activator, SI is destabilized and self-cleaved from SIG such that SIG generates an increased signal. Also provided is a method of determining whether a sample comprises an activator, using the above-described compound. Additionally provided is a method of determining whether a cell comprises a nitroreductase using the above-described compound where nitroreductase is the activator. Further provided is a method of determining whether a mammalian cell is hypoxic using the above-described compound where nitroreductase is the activator. A method of detecting a microorganism that comprises a nitroreductase, using the above-described compound where nitroreductase is the activator, is also provided. Also provided is a method of identifying nitroreductase in a sample, using the above-described compound where nitroreductase is the activator.