Characterization of human bladder cancer patient-derived xenograft in vivo and in organoids.

Abstract

479 Background: To establish and molecularly characterize a human bladder cancer patient-derived xenograft (PDX) in vivo and in an organoid system derived from the PDX for preclinical studies. Methods: Two-mm3 bits of urothelial carcinoma originated from muscle invasive disease excised in cystectomy were implanted subcutaneously into male severe combined immunodeficient mice to establish PDXs. Established PDXs (CoCaB 1) were passaged subcutaneously in SCID mice and histopathology of each passage was compared with the originating tumor. Tumor size was measured weekly by caliper to determine the growth rate of PDXs from early (P1/P2) through late passage (P8/P9). Representative early and late passages were collected for organoid establishment. For both early and late passages, proliferation was assessed by Ki67 in PDXs and organoids, and cell cycle analysis and MTS assay specifically in organoids. RNA sequencing was performed to compare the fidelity of PDX and organoids vs. primary tumor. Results: Histologically, 16 of the 16 (100%) PDXs generated from early through late passage (1-2 tumors per passage) were similar to the original high-grade urothelial carcinoma. In vivo, the latency of PDX establishment decreased upon passage (9 weeks to take in early P1/2 vs. 2 weeks to take in late P8/9) and the growth rate increased upon passage. Concordantly, Ki67 proliferation index increased from 40% in P1 to 95% in P8 and was positively correlated with increasing passage (Spearman R=0.804, p=0.001). Similarly, in organoids, late passage demonstrated a shorter growth doubling time, higher Ki67 proliferation index, and faster progression through cell cycle. Transcriptional analysis showed that the PDX contained 81-92% human transcripts, whereas organoids contained >99% human transcripts. Conclusions: Bladder cancer PDXs histologically represented the originating disease. PDX and organoid systems demonstrated concordant increase in proliferation upon serial passages, suggesting clonal selection may take place in this aggressive tumor type. Despite more mouse stromal content in PDX, PDX and organoid represent two independent model systems with highly similar biological responses that allow therapeutic studies.