In vitro binding and specificity of OTL78. In vitro binding and specificity of OTL78. A, Excitation (Ex) and emission (Em) spectra of OTL78. B, Dose-dependent binding of OTL78 to PSMA+ 22Rv1 cells and PSMA− PC3 cells in culture (n = 2). C, Binding and internalization of OTL78 to (i) 22Rv1, (ii) LNCaP, or (iii) PC3 (fluorescence image), and (iv) PC3 (DIC image) cells by epifluorescence (epi) microscopy. Note: OTL78 is highly concentrated in the acidic endosomes of 22Rv1 and LNCaP cells. DIC, deferential interference contrast images. Sumith A. Kularatne et al. Clin Cancer Res 2019;25:177-187 ©2019 by American Association for Cancer Research