In situ hybridization of Calu-6 tumors using PDGFRα and PDGFRβ probes. In situ hybridization of Calu-6 tumors using PDGFRα and PDGFRβ probes. Paraffin sections of Ad-LacZ-treated Calu-6 tumors were hybridized with [33P]-labeled riboprobes specific for human and murine PDGFA and PDGFB and murine PDGFRα and PDGFRβ as indicated. In all cases, control sense probe signal was found to be negligible. Only representative results are included. A, abundant expression human PDGFA is evident throughout the tumor mass, particularly around necrotic areas (arrowheads), whereas the sense control produces no signal. The human PDGFB signal is generally weak in the viable tumor with increased intensity around necrotic regions (arrowheads). B, murine PDGFA signal is weak and scattered throughout the tumor mass, whereas PDGFB signal occurs in discrete clusters consistent with vasculature (arrows). C, murine PDGFRα signal exhibits a stromal pattern with increased intensity at the tumor periphery (arrowheads) and in a region of infiltrating stromal cells (arrows). In contrast, PDGFRβ displays a more focal pattern of expression associated with discrete stromal cell clusters. D, a probe generated from exon 3 of the murine VEGF gene produces a modest signal in both the tumor (arrowheads) and stromal (arrows) compartments, whereas the control sense probe produced no signal. Parallel images were taken with dark-field or bright-field illumination. Bar, 200, 100, 50, or 25 μm, depending on magnification. Max L. Tejada et al. Clin Cancer Res 2006;12:2676-2688 ©2006 by American Association for Cancer Research