38P Hormonal modulation of photodynamic therapy efficacy in breast cancer 3D spheroid culture model

Background: Most preclinical cancer treatment studies focus on the investigation on monolayer cancer cells. However, there are significant differences in cell characteristics between monolayer cells and solid tumors, thus limiting the potential efficacy of in vitro Photodynamic Therapy (PDT) studies. Hence, PDT studies on 3D spheroids might provide insights in hormonal microenvironment. This study aims to elucidate the efficacy of hexyl-aminolaevulinic acid (H-ALA) mediated PDT on 3D spheroids in hormonal simulated microenvironment.

Methods: MCF7 3D spheroids were cultured by liquid overlay agarose-based technique in the hormonal conditions with estrogen (E2), progesterone (P), and estrogen with progesterone (E2+P). The protoporphyrin IX (PpIX) generated from H-ALA and reactive oxygen species (ROS) were measured and quantified by confocal microscopy and flow cytometry respectively. The hormonal modulated phototoxicity of H-ALAPDT and estrogen receptor alpha (ERa) expression was determined by MTT assay and flow cytometry respectively.

Results: Compared to H-ALA only, the PpIX generated distributed on the rim of spheroids at short (4h) incubation and, further more diffused into core regions at prolonged (8h) incubation with E2+P. At 50mM and 4J/cm2 , the phototoxicity of HALA-PDT increased 10% with E2+P. No significant difference of ERa expression with or without hormones, whereas the 1.5- to 2-fold increase of ROS levels at LD50 in all hormonal conditions suggesting the hormonal modulated phototoxicity of H-ALA-PDT might trigger hypoxia but not ERa expression.

Conclusions: This study evidenced that H-ALA-PDT efficacy on MCF7 3D spheroids was enhanced in the hormonal simulated microenvironment. The biomechanism of hormones on PDT efficacy are deserved to be delineated.