Complementary cytotoxicity of GD2-targeted photoimmunotherapy and 5-aminolevulinic acid photodynamic therapy in neuroblastoma and osteosarcoma

Phototherapy, a method that employs light to kill cancer cells, operates through two distinct mechanisms. The first is photoimmunotherapy (PIT), which necessitates near-infrared light to activate a photoabsorber, targeting the tumor cells through antigen specificity. The second mechanism is photodynamic therapy (PDT), which generates reactive oxygen species by activating intracellular protoporphyrin IX, produced from 5-aminolevulinic acid uptake and metabolism, when exposed to red light.

While PIT may exhibit limited efficacy in antigen-low cells, PDT generally lacks the same level of tumor selectivity. The researchers sought to combine these therapies to enhance their overall effect and ascertain if simultaneous treatment could diminish the necessary light dose. They conjugated dinutuximab, a molecule targeting the GD2 antigen, with IRDye 700DX to confirm the plasma-membrane localization of the conjugate via confocal and widefield microscopy.

Both PIT and PDT monotherapies were subjected to evaluations across various agent and light doses in neuroblastoma (NB) and osteosarcoma (OS) cell lines. Combination matrices were assessed using interaction, highest-single-agent, and Bliss analyses. Both monotherapies revealed significant light-dose-dependent effects in NB and OS.

PIT showed no observable cytotoxicity in antigen-blunted control cells, while PDT retained its effectiveness, thereby confirming the antigen-dependence of PIT and the antigen-independence of PDT. The interaction between the two therapies was notable in SK-N-BE(2) but not in LM7. However, certain combinations yielded a greater killing effect than the more potent matched monotherapy in both SK-N-BE(2) and LM7 (Padj).