In vivo homing experiments and tissue distribution of phages SCID mice were injected subcutaneously (s.c.) in the dorsolateral flank with 1610 7 human NSCLC cells. The mice bearing size-matched lung cancer xenografts (approximately 500 mm 3 ) were injected i.v. with 10 9 pfu of the targeting or control phage. After perfusion, xenograft tumors and mouse organs were removed and homogenized. The phages bound to each tissue sample were recovered through the addition of ER2738 bacteria and titered on IPTG/X-Gal agar plates. In the peptide competitive inhibition experiments, the phages were injected along with 100 mg synthetic targeting peptide, control peptide or mutant peptide. The organs and tumor masses were fixed in Bouin's solution (Sigma, MO, USA). After fixation, the samples were embedded in paraffin blocks. The paraffin sections were deparaffinized, rehydrated, and subjected to immunostaining using the mouse M13 mAb as described above.