Optimizing Sequential Targeted Therapies in Advanced Renal Cell Carcinoma Using Patient-Derived Orthotopic Xenograft Mouse Avatars

Background/Objectives: Advanced renal cell carcinoma (aRCC) remains incurable, with no established optimal sequence of targeted therapies due to interpatient heterogeneity and acquired resistance. We developed a luciferase-enabled patient-derived orthotopic xenograft (PDOX) avatar platform to evaluate sequential targeted therapies in individualized aRCC models that recapitulate tumor architecture, proliferation, angiogenesis, metastasis, and PD-L1 expression. Methods: Tumor specimens from two renal cell carcinoma (RCC) patients were expanded subcutaneously in NOD/SCID mice, transduced with luciferase/red fluorescent protein (Luc/RFP), and orthotopically implanted into mouse kidneys (KiCa-Pt58: sarcomatoid RCC, pT3aN1M1, Fuhrman grade 4; KiCa-Pt118: clear cell RCC with sarcomatoid component, pT3aNxM0, Fuhrman grade 4, respectively). Tumor growth and metastasis were monitored weekly by bioluminescence imaging (BLI). Mice were randomized into vehicle control or four sequential treatment groups (Everolimus→Sunitinib [E→S], Sunitinib→Everolimus [S→E], Pazopanib→Sunitinib [P→S], Pazopanib→Everolimus [P→E]). Drugs were administered orally three times weekly until resistance (>200% BLI increase), with one switch. At necropsy, tumor burden, ex vivo BLI metastasis, weights, H&E histology, and immunohistochemistry (Ki67, CD44, CD31, PD-L1) were assessed. Results: Two independent experiments were performed. In dosing optimization, PDOX tumors recapitulated parental histology and proliferative indices, mirroring patient trajectories. KiCa-Pt58 (metastatic sarcomatoid RCC; deceased 1-month post-nephrectomy) showed aggressive features: rapid engraftment at low doses, early growth (week 2), and lung metastases in 78% of mice (sacrifice day 34), reflecting a fulminant course. KiCa-Pt118 (non-metastatic; patient recurrence-free >8 years post nephrectomy) exhibited indolent behavior: delayed engraftment requiring higher doses plus lymph node stromal (HK) support, slower growth (week 4), no metastases, and later sacrifice (day 78), consistent with remission. In sequential therapy evaluation, for KiCa-Pt58, P→E yielded greatest reductions in tumor weight (p < 0.01), lung metastases (p < 0.01), Ki67+ proliferation, CD31+ angiogenesis, and PD-L1 expression versus control; E→S and S→E were also effective. For KiCa-Pt118, S→E and P→E reduced tumor burden (p < 0.01) and Ki67+ proliferation; S→E lowered CD31 and PD-L1. Conclusions: This RCC PDOX platform faithfully preserves patient-specific biology—including metastatic propensity, engraftment efficiency, growth kinetics, and stromal dependency—while enabling real-time evaluation of sequential targeted therapies. Given the limited number of models tested, these findings provide proof-of-concept for individualized treatment exploration in advanced RCC and support future investigation of rational combinations with immune checkpoint blockade in humanized or immunocompetent systems.