DNA-based aptamer fails as a simultaneous cancer targeting agent and drug delivery vehicle for a phenanthroline-based platinum(II) complex

Abstract

The sgc8c aptamer is a 41-base DNA oligonucleotide that binds to leukaemia cells with high affinity and specificity. In this work we examined the utility of this aptamer as both a delivery vehicle and an active targeting agent for an inert platinum complex [(1,10-phenathroline)(ethylenediamine)platinum(II)] 2+ . The aptamer forms a stem-and-loop confirmation as determined by circular dichroism. This conformation is adopted in both water and phosphate buffered saline solutions. The metal complex binds to the aptamer through intercalation into the aptamer's double helical stem with a binding constant of approximately 4.3 × 10 4 M -1 . Binding of the metal complex to the aptamer had a significant effect on the aptamer's global conformation, and increased its melting temperature by 28 o C possibly through lengthening and stiffening of the aptamer stem. The effect of the aptamer on the metal complex's cytotoxicity and cellular uptake was determined using in vitro assays with the target leukaemia cell line CCRF-CEM and the off-target ovarian cancer cell lines A2780 and A2780cp70. The aptamer has little inherent cytotoxicity and when used to deliver the metal complex results in a significant decrease in the metal complex's cytotoxicity and uptake. The reason(s) for the poor uptake and activity may be due to the change in aptamer conformation which affects its ability to recognise leukaemia cells.

The state-of-play and future of platinum drugs

“…This aptamer forms a loop and stem structure into which the platin complex, PHENEN, was intercalated for simultaneous targeting and drug delivery. Unfortunately, intercalation of the platin into the aptamer locked the stem and loop conformation and resulted in a decrease in both the in vitro cytotoxicity and uptake of the platin compared with its free form (McGinely et al 2013).…”

DNA Aptamer Based Nanodrugs: Molecular Engineering for Efficiency

“…Despite the effectiveness of intercalation, several concerns need to be addressed, including the instability of the aptamer-drug conjugates due to the reversibility of the interaction, the limited numbers of drugs that are feasible for intercalation, the disruption of aptamer structure and function upon intercalation, [21] and the limited drug payload capacity.…”

Oligonucleotide Aptamers: New Tools for Targeted Cancer Therapy

“…67 On the other side of the spectrum, covalent conjugation is the most commonly used method of aptamer-drug conjugation, especially for agents that cannot intercalate into the nucleic acid structure or whose intercalation would disrupt aptamer structure. 68 Evidence suggests that these covalently conjugated aptamer-drug compounds are significantly more stable than the corresponding noncovalently conjugated intercalations. 69 …”