N-Alkylaminoferrocene-Based Prodrugs Targeting Mitochondria of Cancer Cells

Abstract

Intracellular concentration of reactive oxygen species (e.g., H2O2) in cancer cells is elevated over 10-fold as compared to normal cells. This feature has been used by us and several other research groups to design cancer specific prodrugs, for example, N-alkylaminoferrocene (NAAF)-based prodrugs. Further improvement of the efficacy of these prodrugs can be achieved by their targeting to intracellular organelles containing elevated reactive oxygen species (ROS) amounts. For example, we have previously demonstrated that lysosome-targeted NAAF-prodrugs exhibit higher anticancer activity in cell cultures, in primary cells and in vivo (Angew. Chem. Int. Ed. 2017, 56, 15545). Mitochondrion is an organelle, where electrons can leak from the respiratory chain. These electrons can combine with O2, generating O2−• that is followed by dismutation with the formation of H2O2. Thus, ROS can be generated in excess in mitochondria and targeting of ROS-sensitive prodrugs to these organelles could be a sensible possibility for enhancing their efficacy. We have previously reported on NAAF-prodrugs, which after their activation in cells, are accumulated in mitochondria (Angew. Chem. Int. Ed. 2018, 57, 11943). Now we prepared two hybrid NAAF-prodrugs directly accumulated in mitochondria and activated in these organelles. We studied their anticancer activity and mode of action. Based on these data, we concluded that ROS produced by mitochondria is not available in sufficient quantities for activation of the ROS-responsive prodrugs. The reason for this can be efficient scavenging of ROS by antioxidants. Our data are important for the understanding of the mechanism of action of ROS-activatable prodrugs and will facilitate their further development.

Chimeric Drug Design with a Noncharged Carrier for Mitochondrial Delivery

“…In our hypothesis, a neutral carrier diffuses into the cytoplasm and enters the mitochondrial membrane, becoming trapped in the mitochondrial matrix by an oxidation reaction ( Scheme 1 ). During the progress of our research, a similar mechanism to this proposal was reported by Reshetnikov and colleagues [ 17 ] based on the oxidation of ferrocene to ferrocenium cations, and by Abelha et al [ 34 ], who employed oxidation of the TPP moiety. Another potential candidate for oxidation-driven mitochondrial accumulation is pyridine, a very stable aromatic substrate with a basic pair that can be oxidized to yield well-known pyridine oxides [ 35 , 36 ].…”

“…Mitochondrial visualization using fluorescent probes has been extensively studied and has yielded high- and super-resolution images of this organelle [ 10 , 11 , 12 ]. Moreover, fluorescent sensors that target mitochondria have been used to determine real-time chemical and physiological information [ 13 , 14 , 15 , 16 ], and specific drug delivery to this organelle has been accomplished to enhance drug activity [ 17 , 18 , 19 ]. The working mechanism of existing carriers is based on two different properties of the mitochondrial membrane: the negative membrane potential and selective use of the mitochondrial protein import machinery [ 20 ].…”

Chimeric Drug Design with a Noncharged Carrier for Mitochondrial Delivery

“…In our hypothesis, a neutral carrier diffuses into the cytoplasm and enters the mitochondrial membrane, becoming trapped in the mitochondrial matrix by an oxidation reaction (Scheme 1). During the progress of our research programme, a similar mechanism to such proposal was reported by Reshetnikov and colleagues [16], based on the oxidation of ferrocene to ferrocenium cations, and by Abelha et al [26], who employed the oxidation of the TPP moiety. Other potential candidate for oxidation-driven mitochondrial accumulation would be pyridine, a very stable aromatic substrate presenting a basic pair that can be oxidized to yield well-known pyridine oxides [27,28].…”

“…Mitochondria visualization using fluorescent probes has been extensively studied and yielded high-and super-resolution images of this organelle [9][10][11]. Moreover, fluorescent sensors that target mitochondria have been used to extract real-time chemical and physiological information [12][13][14][15], and specific drug delivery to this organelle has been developed to enhance the drug activity [16,17].…”

Aminoferrocene‐Based Anticancer Prodrugs Labelled with Cyanine Dyes for in vivo Imaging

“…The dye of the latter type can be detected directly in live animals using commercially available small animal fluorescence imaging systems, e. g. IVIS® Spectrum In Vivo Imaging System (Perkin Elmer, Germany). Previously, we have prepared NAAF prodrugs labelled with different fluorescent dyes including coumarins, [3a,c] fluorescein [3b] and N,N,N’,N’‐tetramethylrhodamine (TMR) [8] . However, none of these conjugates was compatible with in vivo fluorescence imaging due to the unfavorable photophysical properties of the corresponding dyes with excitation and emission wavelengths of <550 nm.…”