FIGURE 3:

PET imaging of [⁸⁹Zr]Zr-Transferrin uptake in doxycycline-inducible KRAS-mutant murine xenografts, with corresponding biodistribution at 48 h, in vitro protein analysis of MYC and TfR levels, and tumor growth measurement and imaging timeline. Tumors were inoculated with mice on doxycycline water, and measured and randomized 1 week after inoculation (shown as day 0 in far right panel). A cohort of animals were removed from doxycycline water at day 0 (n = 5 /group). Tumors were followed for each group until endpoint (day 11 across each cohort). Arrows indicate the times of injection of [⁸⁹Zr]Zr-Tf for each group (dox-on* and dox-off). The nomenclature 4292*, 9805*, and 4668* denote tumors and cells that are doxycycline dependent (KRAS mutant). 4292, 9805, and 4668 (without the asterisk) denote tumors and cells that have been withdrawn from doxycycline and are therefore KRAS independent, which were imaged one week later. (A) Coronal slices of iKras*p53* 4292 tumors and (B) corresponding biodistribution at 48 h. Tumors had significantly more tumor uptake of [⁸⁹Zr]Zr-Tf in doxycycline-withdrawn mice (*P < 0.05). (C) Protein levels of MYC and TfR in doxycycline-on (4292*) and doxycycline-off cells (4292), showing a significant increase in protein levels in KRAS-WT cells (*P < 0.01–0.001). (D) Timeline of inoculation, imaging, and rebound of tumor size (4292) after doxycycline withdrawal. (E) Coronal slices or iKras*p53* 9805 tumors and (F) and corresponding biodistribution at 48 h. (G) Protein levels of MYC and TfR in doxycycline-on (9805*) and doxycycline-off cells (9805), showing a significant increase in protein levels in KRAS-WT cells (P < 0.001). (H) Timeline of inoculation, imaging, and rebound of tumor size (9805) after doxycycline withdrawal. (I) Coronal slices or iKras*p53* 4668 tumors and (J) and corresponding biodistribution at 48 h. Tumors had significantly more tumor uptake of [⁸⁹Zr]Zr-Tf in doxycycline-withdrawn mice (*P < 0.05). (K) Protein levels of MYC and TfR in doxycycline-on (4668*) and doxycycline-off cells (4668), showing a significant increase in protein levels in KRAS-WT cells (P < 0.01). (L) Timeline of inoculation, imaging, and rebound of tumor size (4668) after doxycycline withdrawal. *P < 0.05, **P < 0.01, ***P < 0.001.