Luminescent iridium(III)-pyridyl based complexes: tumor inhibitory studies in 4T1 mammary carcinoma mice model

Abstract

Aim: The iridium(III) [Ir(III)] complexes exhibit anticancer properties, and along with their photoluminescence properties, they can be employed as diagnostic agents. Hence, we have tried to evaluate both properties. For this, the complexes of Ir(III) with pyridyl-based heterocyclic ligands, viz., [(TPQ)₃Ir] (1), [(TPQ)₂Ir(4-EO₂-pic)] (2), and [(ppy)₂Ir(dfpmpy)] (3) were prepared and evaluated for their cytotoxicity and emissive properties.

Methods: These complexes were authenticated by NMR (¹H and¹³C{¹H}) spectroscopy and high-resolution mass spectrometry (HRMS). Their photophysical properties were evaluated by UV-Vis spectroscopy and photoluminescence studies. Among them, [(TPQ)₃Ir] (1) and [(TPQ)₂Ir(4-EO₂-pic)] (2) complexes have exhibited red emission centred at ~600–625 nm range, which is appropriate for bio-imaging. The cellular internalization of [(TPQ)₂Ir(4-EO₂-pic)] (2) complex was investigated by confocal microscopy and flow cytometry at time intervals of 3 h and 6 h after its treatment with cancer cells. These Ir(III) complexes (1–3) were evaluated for their cytotoxicity against 4T1 mammary carcinoma cells by MTT assay. The moderately potent [(TPQ)₂Ir(4-EO₂-pic)] (2) complex was evaluated in vivo against 4T1 mammary carcinoma induced in BALB/c mice.

Results: Among these Ir(III) complexes (1–3), the [(TPQ)₂Ir(4-EO₂-pic)] (2) complex has exhibited moderate cytotoxicity (IC₅₀ ~60 µM) as observed from their evaluations against triple-negative breast cancer (TNBC), a 4T1 mammary carcinoma cell line in vitro by MTT assay. Hence, its in vivo anticancer potency was evaluated by its treatment against 4T1 mammary carcinoma induced in BALB/c mice. This study exhibited tumor-inhibitory activity.

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