Mitochondria play essential roles in numerous cellular processes, including oxidative phosphorylation and apoptotic initiation. As a result, organellar dysfunction has been implicated in several pathologies such as cancer, diabetes and neurodegenerative diseases. The opportunity to deliver compounds to probe or treat these conditions would be highly beneficial but accessing this organelle is challenging. Prior work investigated the physicochemical properties required for mitochondrial targeting and yielded mitochondria-penetrating peptides (MPPs). MPPs possess hydrophobic and cationic character and exhibit efficient cellular uptake and mitochondrial localization.
In this proof-of-principle study, MPPs were harnessed to re-route an anti-leukemia agent, chlorambucil (Cbl), from the nucleus to mitochondria. This DNA alkylating agent was selected for its rapid kinetics and facile conjugation to an MPP. In addition, because mitochondria possess their own genome, the target of this drug would also be present in the organelle. Conjugation of an MPP to Cbl (mt-Cbl) confirmed that the drug was re-routed to the mitochondria and an increase in potency was observed in several cell lines and patient samples. This gain in activity was due to the increased accessibility of the mitochondrial genome, its lack of introns and its limited repair capacity. However, despite this enhanced toxicity, a therapeutic window continued to be maintained due to the elevated mitochondrial membrane potential in cancer cells.
The re-routing of Cbl also resulted in evasion of several drug resistance mechanisms. Damage directly within the organelle was sufficient to initiate apoptosis even in cell lines with disabled apoptotic triggering. In addition, mitochondrial sequestration protected mt-Cbl from drug inactivation mechanisms. Lastly, mt-Cbl inhibited Pgp efflux by unexpectedly interacting with the pumps and inhibiting activity for a short period of time.
The anti-cancer activity of mt-Cbl was also assessed in vivo in xenograft models of leukemia. The conjugate was stable in mouse plasma and displayed an improved pharmacokinetic profile. In addition, mt-Cbl successfully delayed tumor growth in two xenograft models and continued to alkylate mitochondrial DNA in vivo.
These studies demonstrate that MPPs can be harnessed to re-route drugs to this organelle. Mitochondrial re-targeting could be a novel method of re-purposing FDA-approved drugs to enhance activity and evade resistance.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/34000 |
| Date | 11 December 2012 |
| Creators | Fonseca, Sonali |
| Contributors | Kelley, Shana O. |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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