TH9402

TH9402 is a **photosensitizer** of the rhodamine family, specifically 4,5-dibromorhodamine methyl ester. It mediates **photodynamic therapy (PDT)**, where, after activation by green light (around 515 nm), it generates reactive oxygen species that induce targeted cytotoxicity. Its primary use has been in **ex vivo cell purging**, such as eliminating malignant cells from autologous stem cell transplants intended for hematologic malignancies (e.g., multiple myeloma, breast cancer), while largely sparing normal hematopoietic progenitor cells[1][5][6]. The key mechanism involves uptake by cells, followed by light activation that leads to apoptosis/necrosis, with evidence of selective depletion of alloreactive T cells and preservation of regulatory T cells. This selectivity has been leveraged experimentally for immunomodulation in contexts like chronic graft-versus-host disease (GVHD), with ongoing clinical and preclinical studies relating to ex vivo photodepletion to reduce transplant-related complications[1][2][4]. TH9402 acts through both Type I and Type II photodynamic mechanisms upon activation: (1) electron transfer leading to DNA photo-oxidation, and (2) triplet–triplet energy transfer generating singlet oxygen and other reactive oxygen species[3].

Other names

4,5-dibromorhodamine methyl ester