Development of self-eliminating linkers for drug conjugates

Abstract

Newly discovered compounds through bioprospecting are screened for cytotoxicity, and many of them are found to be highly toxic. Because they are often not specifically toxic only against cancer cells, they are not further studied. These new compounds could be of further interest by temporarily masking a functional group which regulate the anticancer activity of a cytotoxic compound. This means that the compound would be inactive until the effect is restored. A linker is used to chemically modify the functional group which facilitates the cytotoxic effect. In this project the linker connects the drug to a peptide, which would act as a homing beacon to a desired target site. To release the drug, the linker self-eliminates through mediation of glutathione (GSH).

Synthesis of linkers were performed by nucleophilic reaction. The linkers were conjugated with a peptide and two different drugs. The peptide conjugation was achieved by disulphide exchange reaction and the conjugation of drug was accomplished by nucleophilic reaction. The purity of the products were estimated with ultra-high performance liquid chromatography with a photodiode array detector (UPLC-PDA) and the mass was determined by mass spectrometry (MS). Kinetic analyses with GSH were performed on all three of the synthesised drug-linker-peptide conjugates.

The syntheses of self-eliminating linkers with conjugation to hydroxyl- and amine-containing drugs, and a peptide as homing beacon were successful. Kinetic analyses followed with UPLC-PDA and MS showed free drug from only two of the three drug-linker-peptide conjugates. The two drug-linker-peptide conjugates had very different estimation of drug release, where one showed 32% free drug after 20 h, and the other showed 5% free drug after 22.5 h.