BODIPY-Tagged Platinum(II) Curcumin Complexes for Endoplasmic Reticulum-Targeted Red Light PDT

[Pt­(RB)­(Cur)]­NO₃ (RBC), [Pt­(IRB)­(Cur)]­NO₃ (IRBC), and [Pt­(L)­(Cur)]­NO₃ (PBC), where HCur is curcumin, L is 1-benzyl-2-(2-pyridyl)­benzimidazole, and RB and IRB are red-light-active non-iodo and diiodo-BODIPY tagged to L, respectively, were synthesized and characterized, and their anticancer activities were studied (BODIPY, boron-dipyrromethene). RBC and IRBC displayed BODIPY-centered absorption bands within 615–635 nm along with the respective curcumin bands at 445 and 492 nm in 10% dimethyl sulfoxide (DMSO)–Dulbecco’s phosphate-buffered saline (DPBS). Emission bands were observed at 723 and 845 nm for RBC and IRBC, respectively, in 10% DMSO–DPBS. RBC (Φ_Δ, 0.27) and IRBC (Φ_Δ, 0.40) generated singlet oxygen in red light (λ = 642 nm) as evidenced from 1,3-diphenylisobenzofuran (DPBF) titrations. The formation of ¹O₂ from BODIPY and HO^• from the curcumin was evidenced from the mechanistic pUC19 DNA photocleavage studies. The BODIPY complexes showed photocytotoxicity in A549, HeLa, and MDA-MB-231 cells while being less toxic in the dark [IC₅₀: 1.3–6.9 μM, red light; 7.2–12.8 μM, 400–700 nm visible light]. The emissive RBC displayed localization in the endoplasmic reticulum (ER). Apoptotic cell death was evidenced from the Annexin-V/fluorescein isothiocyanate (FITC)/propidium iodide (PI) assay and green fluorescence in red light in the Fluo-4 AM assay due to ER stress, and mitochondrial dysfunction was evidenced from the 5,5,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimidazolylcarbocyanine iodide (JC-1) assay in A549 cells.