Isocyanide Substitution in Acridine Orange Shifts DNA Damage-Mediated Phototoxicity to Permeabilization of the Lysosomal Membrane in Cancer Cells

SIMPLE SUMMARY: Aside from tissue cell renewal, tumor cells are also produced every day. In ordinary conditions, immunologically controlled cell death mechanisms limit cancer development. There are several cell death processes used for how normal and tumor cells are eliminated at the end of their lifespan. In cancer therapy, cells dying via immunological death are more efficiently eradicated than cells dying by classical apoptosis. Photodynamic treatments with some photosensitizers target lysosomes. Lysosomal death diverts apoptosis to the immunologically more pertinent necrosis-like death pathways. Acridine orange (AO), a well-known photosensitizer, targets lysosomes as well. We have synthesized a new compound abbreviated as DM, a modified AO, and examined details of intracellular processes leading to photodynamic cell death. We have proven that DM targets lysosomes better than AO. Remarkably, with DM, we could visualize an abrupt nuclear DNA release from cells during the photodynamic process. Our work highlights which cellular events may enhance immunological cell death. ABSTRACT: In cancer therapy, immunogenic cell death eliminates tumor cells more efficiently than conventional apoptosis. During photodynamic therapy (PDT), some photosensitizer (PS) targeting lysosomes divert apoptosis to the immunologically more relevant necrosis-like cell death. Acridine orange (AO) is a PS targeting lysosome. We synthesized a new compound, 3-N,N-dimethylamino-6-isocyanoacridine (DM), a modified AO, aiming to target lysosomes better. To compare DM and AO, we studied optical properties, toxicity, cell internalization, and phototoxicity. In addition, light-mediated effects were monitored by the recently developed QUINESIn method on nuclei, and membrane stability, morphology, and function of lysosomes utilizing fluorescent probes by imaging cytometry in single cells. DM proved to be a better lysosomal marker at 405 nm excitation and lysed lysosomes more efficiently. AO injured DNA and histones more extensively than DM. Remarkably, DM’s optical properties helped visualize shockwaves of nuclear DNA released from cells during the PDT. The asymmetric polar modification of the AO leads to a new compound, DM, which has increased efficacy in targeting and disrupting lysosomes. Suitable AO modification may boost adaptive immune response making PDT more efficient.