Theranostic Activity of a Fluorescent Heterobimetallic Ir^III-Pd^II Complex toward Cancer Cells

Advanced and inexpensive imaging techniques need to be developed urgently to mitigate the burden of cancer globally. Compared with traditional imaging techniques, fluorescence imaging offers an immensely sensitive and selective tool for cancer cell imaging with the advantage of high spatial and temporal resolution. Herein, we present a fluorescent heterobimetallic complex (HBMC) of Ir(III)/Pd(II), which selectively images the nucleus of cancer cells (HeLa) over normal cells (HaCaT) 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 and hence allows selective imaging of cancer cells over normal cells. The cell viability of HeLa cells showed an IC50 of 18 μM for HBMC. However, the homonuclear subunits of HBMC are ineffective in imaging cancer cells. The possible reason behind its selectivity toward cancer cells is its interaction with a protein with ∼44 kDa molecular weight, which was obtained from mass spectrometric analysis. A bioinformatics study predicted the protein with ∼44 kDa molecular weight as a serotonin receptor, 5-HT, overexpressed in HeLa cells. The most interesting fact is that HBMC has a dual effect in selective fluorescence imaging and a cytotoxic effect toward HeLa cells, establishing its remarkable theranostic properties toward cancer cells in contrast to normal cells. Interactions of DNA with HBMC establish a sequential binding pattern between them. Hence, our low-cost fluorosensor may have dual applicability in the early diagnosis of patients having cancer with a therapeutic approach.