Establishment of patient-derived xenografts (PDXs) from metastatic nasopharyngeal carcinoma

Abstract

Establishment of growth of nasopharyngeal carcinoma (NPC) in vitro as cell line and in vivo as patient-derived xenograft (PDX) is known to be difficult. In this study, nineteen biopsies from primary NPC tissues were grafted at subrenal capsule in NOD/SCID mice to establish PDX all failed to grow. In contrast, two out of two cases of NPC metastasized to vertebral column were successfully established as PDXs. The two newly established PDXs from metastatic NPC were named as Xeno111 and Xeno113 respectively. The much improved success rate of PDX establishment from metastatic NPC may suggest unique intrinsic properties of metastatic NPC compared to primary NPC. Nonetheless, the sample size is too small for this observation to be conclusive. The newly established NPC PDXs were further characterized and compared with the other four NPC PDX models recently established from our laboratory. They included two PDXs from primary NPC (Xeno32 and Xeno76) and two PDXs from recurrent NPC (Xeno23 and Xeno47). The growth rates of different PDXs in immunodeficient mice were variable but consistent within individual PDX. However, there was no obvious correlation between the growth rates of PDXs with the origins of NPC (primary, recurrent and metastatic). The EBV episomes in all the NPC PDXs were examined and shown to be stably maintained. It is well established that EBV episomes in NPC cell lines were rapidly lost upon propagation in vitro. This may suggest an essential role of EBV infection for NPC to grow in vivo. The heavy infiltration of inflammatory stromal cells in NPC grown in patient and propagated as PDX may play essential role in the maintenance of EBV in infected NPC cells. Activation of NF-B and STAT3 was observed in all the NPC PDXs established as illustrated by the nuclear localization of NF-B transcription units and phosphorylated STAT3. The Bcl-3/p50/p50 is the predominant activation pathway of NF-B in NPC PDXs which is different from the canonical (involving p65/p50) and non-canonical (involving RelB/p52) signaling pathways of NF-B. The significance of this atypical activation of NF-B in NPC is unclear. Nonetheless, a subpopulation of NPC cells in PDXs also exhibited canonical pathway of NF-B activation (as shown by nuclear translocation of p65/p50). PDXs from metastatic NPC showed the highest percentage of cells with nuclear translocated p65. Three authenticated EBV+ve NPC cell lines (C666-1, C17 and NPC43) were also examined for their signaling properties. Again, activation of atypical activation of NF-B involving nuclear translocation of Bcl-3/p50/p50 was also observed to be the predominant pathway of NF-B activation in all these three EBV+ve NPC cell lines grown in vitro and in vivo as xenografts. Interestingly, all the NPC PDXs and xenografts from the three established EBV+ve NPC cell lines also showed activation of STAT3 as indicated by the phosphorylation and nuclear translocation of Ser727 site of STAT3. The functional interaction of NF-B, STAT3 and Bcl-3 in growth properties of NPC and their role in regulating EBV infection in NPC remains to be investigated.