Development of targeted formulations for the delivery of a cytochrome c-based drug for application in cancer therapy

Abstract

The progression of a cell toward apoptosis, upon cellular stress, is accompanied by a set of characteristic events which includes permeabilization of the mitochondrial outer membrane and release of cytochrome c into the cytosol. The latter event, which is an apoptosis trigger one, is often inhibited in cancer cells, allowing them to proliferate in an uncontrolled fashion. Inducing the apoptotic pathway by delivery of exogenous cytochrome c into the cytosol of cancer cells to initiate apoptosis appears to be a smart method to overcome the resistance of certain cancer cells against this programmed cell death. Once triggered by the release of mitochondrial Cytc into the cytosol, apoptosis is believed by some researchers to be an irreversible commitment to cell death. However, other research groups reported that apoptotic cells can recover from death even after caspase activation, a process called anastasis. Even though the scientific community is divided on that matter, no recovery of cells in apoptotic process triggered by microinjection or transport of exogenous Cytc into their cytoplasm has been investigated and reported. Despite the rich literature on the ability of exogenous cytochrome c to initiate apoptosis and cause death in cancer cells, no formulation of cytochrome c has yet started clinical trials to be, further, developed, so potentials of cytochrome c can be exploited. The absence of reliable interest to develop cytochrome c as an anticancer seems to be due to a lack of satisfactory requirements of the available formulations of cytochrome c as it is a cell membrane-impermeable protein, that necessitates the development of formulations systems capable of delivering it into target cancer cells for apoptosis activation. For instance, two formulations of Cytc with novel features that enhance and maintain the protein functionality, are investigated and compared. The first formulation is a tuned set of ordered mesoporous silica nanoparticles modified with folate which showed considerable statistical improvement in cytotoxicity toward MDA-MB-231 cells, compared to the ones that are folate-free in all the tested concentrations. This result is further associated with the targeted capacity of the formulation. The second formulation which is a 1:1 recombinant hybrid of cytochrome c and chlorotoxin displays impressive cytotoxicity toward glioma cells at 50 and 25 μM of the hybrid. The results of the studied formulations establish appropriate methodologies for not only developing novel Cytc formulations but also for in vivo testing of these systems, which could eventually lead to Cytc's approval as an anticancer drug.