In vivo imaging of hypoxia generation stimulated by testosterone using a micelle-based near-infrared fluorescent probe

Abstract

Hypoxia generation is caused by insufficient oxygen (O2) in aggressively proliferating cancer cells or tumors, which can lead to resistance to chemotherapy and radiotherapy. However, current hypoxic probes have been evaluated only in artificially induced hypoxic phenomena while ignoring latent stimuli. Testosterone, as a major stimulus of androgen, can cause hypoxia and hypoxia-inducible factor-1α generation during prostate cancer cell (LNCaP) proliferation or prostate cancer growth. Therefore, the improvement of hypoxia probes in the context of testosterone stimulation is critical. In response to this need, we have designed a micelle-based near-infrared fluorescent probe for imaging hypoxia stimulated by testosterone. In this study, we synthesized an amphiphilic copolymer, PEG−b−poly(MPC), in which fluorescent squarylium (SQ) dye and black hole quencher 2 (BHQ2) were enwrapped to form a PMPC@BHQ2/SQ probe. In this design, the fluorescence of the SQ dye is quenched by the BHQ2. In the context of hypoxia in this study, the BHQ2 was destroyed with the reduction of azo-reductase and the fluorescence of the SQ dye was recovered. This process is oxygen level-dependent, and the sensitivity of the probe is sufficient to distinguish different levels of hypoxia (<1% O2). We demonstrated the feasibility of the developed PMPC@BHQ2/SQ probe for investigating testosterone-induced hypoxia in both cells and in vivo. As far as we know, this paradigm is the first design of a rational strategy for the fluorescent imaging of hypoxia generation stimulated by testosterone. This work will contribute to hypoxia-related biomedical research.