In vivo photoacoustic potassium imaging of the tumor microenvironment

The accumulation of potassium (K⁺) in the tumor microenvironment (TME) has been recently shown to inhibit immune cell efficacy, and thus immunotherapy. Despite the abundance of K⁺ in the body, few ways exist to measure it in vivo. To address this technology gap, we combine an optical K⁺ nanosensor with photoacoustic (PA) imaging. Using multi-wavelength deconvolution, we are able to quantitatively evaluate the TME K⁺ concentration in vivo, and its distribution. Significantly elevated K⁺ levels were found in the TME, with an average concentration of approximately 29 mM, compared to 19 mM found in muscle. These PA measurements were confirmed by extraction of the tumor interstitial fluid and subsequent measurement via inductively coupled plasma mass spectrometry.