A Fluorescent Heterobimetallic IrIII-PdII Complex (HBMC) Selectively Images Cancer Cells

Abstract

Early detection and treatment of cancer cell is the only way to eradicate cancer in patients and this can be efficiently achieved via fluorescence imaging technique. Henceforth, we present a fluorescent heterobimetallic complex (HBMC) of Ir(III)/Pd(II) which selectively images the nucleus of the cancer cells over normal cells at a very low concentration (12 μM), established by confocal laser scanning microscopy. HBMC has a unique property by virtue of which it is selectively taken up by cancer cells (HeLa) and hence allows selective imaging of cancer cells over normal cells (HaCat). However, the subunits of HBMC, i.e., homonuclear Ir(III) and Pd(II) complexes are ineffective in imaging cancer cells. HBMC showed pH dependent uptake into HeLa cells followed by its subsequent localization in nucleus, supported by fluorescence microscopy. The possible reason behind its selectivity towards cancer cells is its interaction with a protein of ~44 KDa molecular weight as obtained from mass spectrometric analysis. Bioinformatics study predicted the protein of ~44 KDa molecular weight as serotonin receptor, 5-HT, overexpressed in HeLa cells. Moreover, HBMC is also found to interact with DNA with a sequential binding pattern and the interaction of DNA with HBMC has been established by fluorescence spectroscopy, isothermal calorimetric titration, and theoretical studies as well. Hence, our low-cost fluorosensor may have dual applicability in early diagnosis of patients having cancer and therapeutic approach as DNA binder.

Keywords: Heterobimetallic complex; Cancer cell-imaging; Confocal microscopy; Fluorescence spectroscopy; DNA binding