4-Amino-1, 8-naphthalimide-ferrocene conjugates as multi-targeted anticancer and fluorescent cellular imaging agents

In the quest for novel drug entities, the hybrid approach is a promising path to drug molecules that can effectively target cancer. The hybrid approach can also be used to optimize certain biological properties like affinity and selectivity, but also to gain novel biological activities distinct from individual components. In general, hybridization of ≥ 2 structurally or functionally distinct pharmacologic substances in a molecule forms the basis for innovative cancer interventions. For example, Ferroquine – is an antimalarial and anticancer drug, ferrocifen – is a hormone-dependent breast cancer drug, while the molecule class called naphthalimide – is an antiproliferative drug – that is effective against cancer lesions. Ferroquine is a conjugate of ferrocene, chloroquine, and a basic alkylamine. Ferroquine reduces the viability of cancerous cells and binds effectively with the biological receptors and enzymes. Ferrocifen works by binding with estrogen receptors and has negligible adverse effects on normal human cells. Naphthalimides are resistant to enzymes that transfer drugs out of neoplastic cells.

Based on the hybridization approach, researchers from the University of Malta: PhD student Alex Johnson, Associate Professor Joseph Buhagiar and Associate Professor David Magri examined eight ferrocene and 4-amino-1, 8-naphthalimide conjugates and tested them in two cancer cell lines. The authors hypothesized that the ferrocene group might promote the production of free radicals, which in turn would have a synergistic cytotoxic effect on the cancerous cells by damaging the DNA. They also mention that the naphthalimide group hinders the activity of topoisomerase enzymes. The activity of the drug conjugates were demonstrated against myelogenous leukemia and human breast cancer cells, using a colorimetric assay. Moreover, the research team also postulated that those compounds that are non-toxic could be used as fluorescence cellular imaging probes.

Out of the 8 ferrocene-naphthalimide compounds reported in their study, one molecule (compound 4, N-methylethylenediamine) was the most cytotoxic against myelogenous leukemia cells while another compound 6 (piperazine) was most potent against human breast cancer cells. The difference between the cytotoxic properties and growth inhibition values of the different compounds is perceived to be due to the higher basicity levels of secondary amine moieties and enhanced aqueous solubility. The authors also observed that different compounds demonstrated different trends in growth inhibition over 24-72 hours duration of observation. The original research article is now published in the peer-reviewed journal – RSC Medicinal Chemistry.

The authors observed that the 8 ferrocene-containing naphthalimide compounds did not achieve the optimal growth inhibition levels against the two cancer cell lines within 24 hours of administration of these compounds, except for compound 6 containing a piperazine moiety. The authors concluded that the greatest cytotoxic activity against myelogenous leukemia cell lines was demonstrated by compounds 4 and non-ferrocene compounds 9 and 10. For the breast cancer cell line, compound 6 attributes greater cytotoxic activity as compared to other compounds. The study was the first to demonstrate the application and efficacy of Pourbaix sensors as cellular imaging stains for acidity and oxidisability. Compounds 1, 2 and 5 , which were not cytotoxic to either the human breast cancer or myelogenous leukemia cell lines within a 24 hour incubation period, were proposed as useful cellular imaging applications.

The study addressed the unique tasks of hybrid molecule design, and described how to use the approach to enhance biological activity with respect to both activity and selectivity of the hybrid approach in two cancer cell lines. The researchers demonstrated that the hybrids can be more than the sum of their components, and really should be considered as new innovative pharmacological entities in their own respect. Moreover, the study carefully analysed the structure-activity of a drug combination of ferrocene and naphthalimide against human breast cancer and myelogenous leukemia cell lines. The growth inhibition properties of ferrocene and non-ferrocene compounds were variable, as were the trends in the activity of the same compound over different time durations. Further investigations into the study and utility of these compounds by Professor Magri and colleagues is underway.