Fig. 4: MYCN overexpression in human NCSC is capable of tumor initiation and progression in vivo

NCSC transduced with MYCN were subcutaneously injected into the right flanks of NOD-SCID mice and normal NCSC were injected into the contralateral flanks. Mice were fed water with doxycycline for in vivo gene induction and monitored for local tumor formation at injection sites. a Large, bulky and locally invasive tumor formation occurred at NCSC-MYCN injection sites within 120 days with average engraftment of 67% (10/15 mice developed primary tumors). No tumors formed at the normal NCSC injection sites. b In addition to primary tumors at the site of injections of NCSC-MYCN cells, necropsy revealed evidence of distant metastatic spread in 50% of xenografts. Solid tumors metastasized to the abdominal cavity, specifically to the peritoneal surfaces and mesenteric lymph nodes. c Primary tumor excised and examined by H&E staining. Tumors exhibited typical primitive neuroectodermal (PNET) features with poorly differentiated basophilic cells with angular nuclei, which palisaded around blood vessels forming pseudorosettes, histologically diagnostic of human NBL. d NCSC-MYCN primary tumors were fixed and assayed by immunohistochemistry for MYCN, TH, TRKB, and Chromogranin A expression. MYCN immunolabeling was observed as distinct nuclear staining in tumor cells. Areas with primitive neuroectodermal morphology were diffusely positive for MYCN. Tumors with PNET morphology also displayed distinct TH, TRKB, and Chromogranin A immunolabeling in the perinuclear and cytoplasmic regions. e Sections of lymph node metastasis showing focal cytoplasmic immunolabeling for TH