Carboxylesterase-2-Selective Two-Photon Ratiometric Probe Reveals Decreased Carboxylesterase‑2 Activity in Breast Cancer Cells

Human carboxylesterase-2 (CE2) is a carboxylesterase that catalyzes the hydrolysis of endogenous and exogenous substrates. Abnormal CE2 levels are associated with various cancers, and CE2 is a key mediator of anticancer prodrugs, including irinotecan. Here, we developed a two-photon ratiometric probe for detecting CE2 activity using succinate ester as a recognition site for CE2. The probe showed high selectivity to CE2, a clear emission color change, high photostability, and bright two-photon microscopy (TPM) imaging capability, allowing the quantitative detection of CE2 activity in live cells. Using TPM ratio analysis, we show for the first time that CE2 activity was much lower in breast cancer cells than in normal cells. In CE2 overexpression studies, cancer cells had a markedly enhanced sensitivity to the cytotoxic effect of irinotecan, corresponding well with the TPM ratio of the probe. These results may provide useful information for quantitatively measuring CE2 activity in situ and predicting the responsiveness to anticancer drugs

Carboxylate-Containing Two-Photon Probe for the Simultaneous Detection of Extra- and Intracellular pH Values in Colon Cancer Tissue

Acidified extracellular pH (pHe) is directly related to various disorders such as tumor invasion and the resistance to drugs. In this study, we developed two-photon-excitable emission ratiometric probes (<b>XBH1–3</b>) for the in situ measurement of pHe. These probes, based on benzimidazole and polar solubilizing groups, exhibited a strong two-photon-induced fluorescence and sensitive blue-to-green emission color changes with p<i>K</i>_a values of 5.1–5.7. <b>XBH1</b>, containing a carboxylic acid, stained the extracellular region in neutral media; it entered the cell under acidic media, thereby allowing a precise measurement of the extra- and intra-cellular pH values in the acidified tissue. <b>XBH2</b>, containing the sulfonate peripheral unit, facilitated the monitoring of the pHe value only. Ratiometric two-photon microscopy imaging revealed that <b>XBH1</b> can directly monitor the pH values both inside and outside the cells in colon cancer tissue; there is also the morphological aspect. This could be useful for cancer analyses and drug development