Red light active Pt(iv)–BODIPY prodrug as a mitochondria and endoplasmic reticulum targeted chemo-PDT agent

Abstract

A cisplatin-based platinum(IV) prodrug, [Pt(NH₃)₂Cl₂(OH)(L¹)], having L¹ as a red-light active boron-dipyrromethene (BODIPY) pendant, was synthesized and characterized and its application as a chemo-cum-photodynamic therapy agent was studied. Me-L¹ as the ligand precursor is structurally characterized. The complex displayed an intense absorption band near 650 nm (ε ∼ 8.8 × 10⁴ dm³ mol⁻¹ cm⁻¹) in 1 : 1 (v/v) DMSO/DPBS. It showed an emission band at 674 nm (λ_ex = 630 nm) with a fluorescence quantum yield (Φ_F) value of 0.37. In red light (600–720 nm), it generated singlet oxygen as evidenced from the 1,3-diphenylisobenzofuran (DPBF) titration experiment giving a singlet oxygen quantum yield (Φ_Δ) value of 0.28 in DMSO. The mechanistic pUC19 DNA photocleavage study and singlet oxygen sensor green (SOSG) assay ascertained its ability to generate singlet oxygen in both extracellular and intracellular media by a type-II photo-process. The complex exhibited high stability in the dark, but on red-light irradiation, it displayed rapid activation in the presence of a reducing environment. It displayed remarkable apoptotic photocytotoxicity with half-maximal inhibitory concentration (IC₅₀) ranging from 0.58 to 0.76 μM in human cervical cancer (HeLa) and breast cancer (MCF-7) cells with a respective photo-cytotoxicity index value of >172 and >131. The photodynamic activity was significantly less in non-cancerous human peripheral lung epithelial (HPL1D) cells. The emissive complex showed localization in the mitochondria and endoplasmic reticulum (ER) with a similar Pearson's correlation coefficient value, making it a dual organelle-targeted therapeutic agent. JC-1, fluo-4-AM and annexin V-FITC/propidium iodide assays in HeLa cells showed cellular apoptosis by arresting cells in the sub-G1 phase via mitochondrial dysfunction and ER stress.