In vivo induction of neoplastic growth in nude mouse connective tissue adjacent to xenografted human tumors

Horizontal Transfer of Malignant Traits and the Involvement of Extracellular Vesicles in Metastasis

Metastases are responsible for the vast majority of cancer deaths, yet most therapeutic efforts have focused on targeting and interrupting tumor growth rather than impairing the metastatic process. Traditionally, cancer metastasis is attributed to the dissemination of neoplastic cells from the primary tumor to distant organs through blood and lymphatic circulation. A thorough understanding of the metastatic process is essential to develop new therapeutic strategies that improve cancer survival. Since Paget's original description of the "Seed and Soil" hypothesis over a hundred years ago, alternative theories and new players have been proposed. In particular, the role of extracellular vesicles (EVs) released by cancer cells and their uptake by neighboring cells or at distinct anatomical sites has been explored. Here, we will outline and discuss these alternative theories and emphasize the horizontal transfer of EV-associated biomolecules as a possibly major event leading to cell transformation and the induction of metastases. We will also highlight the recently discovered intracellular pathway used by EVs to deliver their cargoes into the nucleus of recipient cells, which is a potential target for novel anti-metastatic strategies.

In-vivo fusion of human cancer and hamster stromal cells permanently transduces and transcribes human DNA

After demonstrating, with karyotyping, polymerase chain reaction (PCR) and fluorescence in-situ hybridization, the retention of certain human chromosomes and genes following the spontaneous fusion of human tumor and hamster cells in-vivo, it was postulated that cell fusion causes the horizontal transmission of malignancy and donor genes. Here, we analyzed gene expression profiles of 3 different hybrid tumors first generated in the hamster cheek pouch after human tumor grafting, and then propagated in hamsters and in cell cultures for years: two Hodgkin lymphomas (GW-532, GW-584) and a glioblastoma multiforme (GB-749). Based on the criteria of MAS 5.0 detection P-values ≤0.065 and at least a 2-fold greater signal expression value than a hamster melanoma control, we identified 3,759 probe sets (ranging from 1,040 to 1,303 in each transplant) from formalin-fixed, paraffin-embedded sections of the 3 hybrid tumors, which unambiguously mapped to 3,107 unique Entrez Gene IDs, representative of all human chromosomes; however, by karyology, one of the hybrid tumors (GB-749) had a total of 15 human chromosomes in its cells. Among the genes mapped, 39 probe sets, representing 33 unique Entrez Gene IDs, complied with the detection criteria in all hybrid tumor samples. Five of these 33 genes encode transcription factors that are known to regulate cell growth and differentiation; five encode cell adhesion- and transmigration-associated proteins that participate in oncogenesis and/or metastasis and invasion; and additional genes encode proteins involved in signaling pathways, regulation of apoptosis, DNA repair, and multidrug resistance. These findings were corroborated by PCR and reverse transcription PCR, showing the presence of human alphoid (α)-satellite DNA and the F11R transcripts in additional tumor transplant generations. We posit that in-vivo fusion discloses genes implicated in tumor progression, and gene families coding for the organoid phenotype. Thus, cancer cells can transduce adjacent stromal cells, with the resulting progeny having permanently transcribed genes with malignant and other gene functions of the donor DNA. Using heterospecific in-vivo cell fusion, genes encoding oncogenic and organogenic traits may be identified.

Real-time PCR-based assay to quantify the relative amount of human and mouse tissue present in tumor xenografts

Background

Xenograft samples used to test anti-cancer drug efficacies and toxicities in vivo contain an unknown mix of mouse and human cells. Evaluation of drug activity can be confounded by samples containing large amounts of contaminating mouse tissue. We have developed a real-time quantitative polymerase chain reaction (qPCR) assay using TaqMan technology to quantify the amount of mouse tissue that is incorporated into human xenograft samples.

Results

The forward and reverse primers bind to the same DNA sequence in the human and the mouse genome. Using a set of specially designed fluorescent probes provides species specificity. The linearity and sensitivity of the assay is evaluated using serial dilutions of single species and heterogeneous DNA mixtures. We examined many xenograft samples at various in vivo passages, finding a wide variety of human:mouse DNA ratios. This variation may be influenced by tumor type, number of serial passages in vivo, and even which part of the tumor was collected and used in the assay.

Conclusions

This novel assay provides an accurate quantitative assessment of human and mouse content in xenograft tumors. This assay can be performed on aberrantly behaving human xenografts, samples used in bioinformatics studies, and periodically for tumor tissue frequently grown by serial passage in vivo.

Human pancreatic leiomyosarcoma (PZX-7) growing as a serially transplantable xenograft in immunosuppressed mice

BACKGROUND

Several human leiomyosarcoma xenografts have been established, but pancreatic smooth muscle sarcomas have never been serially transplanted and investigated.

METHOD

Immunosuppression of CBA/CA mice was achieved by thymectomy, whole-body irradiation, and bone marrow reconstruction. Tumor fragments were subcutaneously implanted from a Grade III pancreatic leiomyosarcoma and serially passaged for more than 24 mo. The xenografted tumors were characterized by morphological, morphometrical, biochemical, and flow cytometric methods.

RESULTS

The tumor has retained its characteristic morphology and no further differentiation occurred. The mitotic counts and the amount of the connective tissue all remained constant. The calculated volume doubling time was 11.3 d. Immunohistochemically, the tumor proved to be p53-negative, but the strong expression of the bcl-2 remained as a constant feature throughout successive transplantations. The DNA index and the proliferation indices did not change significantly with the time (mean DI: 1.65, range: 1.561-1.70; mean PI: 17.9%, range: 15.3-20.7%). Lactose dehydrogenase (LDH) isoenzyme electrophoresis evidenced a retained human pattern of the tumor even after 32 mo of transplantations.

CONCLUSION

The first human pancreatic leiomyosarcoma xenograft (PZX-7) growing in immuno-suppressed mice is described and characterized.

Monoclonal antibodies produced by in vitro immunization with sera of human-xenotransplant-bearing mice

In vitro immunization procedures, using sera of athymic mice bearing human WOC ovarian tumors or CM III mammary tumors as immunizing antigen, induced a highly efficient formation of mABs (44% of antibody-producing clones) reacting with human ovarian and/or mammary tumor cells. More than half of these mABs showed cross-reactivity with mouse cell lines. Immunogenicity of normal mouse components in the sera from tumor bearers can be excluded since control immunization with sera of normal athymic mice yielded no mABs reacting with mouse or human cell lines. Furthermore, immunization with sera from tumor bearers did not induce mABs only reacting with mouse cells since 20% of the antibody-producing clones showed an exclusive specificity for the human tumor cells. On the basis of these results we concluded that the human-mouse cross-reacting mABs were induced by circulating human TAA with epitopes shared by mouse cellular components.

Serial xenotransplantation of a human embryonal carcinoma in experimental urology

The rare incidence of testicular germ cell tumours makes it necessary for clinicians to look for a valid experimental model to investigate basic tumour properties and different therapeutic modalities preclinically in order to improve clinical cure rates. A human embryonal carcinoma with hCG-production was successfully established in nude mice for more than 40 passages. We were able to show striking maintenance of histological and ultrastructural features, tumour markers (Beta-hCG) and DNA indices of the original tumour during subsequent xenograft passages as well as stability of tumour growth. Dedifferentiation of the tumour with changing growth fractions or loss of hCG production was not evident.

Human tumour cell lines established in vitro from tumours after long-term passage as nude mouse xenografts. Comparative fingerprinting of their concanavalin-A acceptor glycoproteins

Two human colon cancer xenografts (EC and AC) were established in tissue culture only after long-term passage in nude mice. Earlier attempts to establish cell lines were unsuccessful. The epithelioid cells retain their tumourigenicity after in vitro growth, giving rise to tumours with a take rate of 60-80%. After reimplantation, the xenografts retain a similar morphology to that of the original human tumours. Both cell lines show human karyology. Comparative mapping of Concanavalin-A acceptor glycoproteins provides a fingerprint characteristic of each cell line. These glycoprotein patterns are similar to those shown by HT-29, an established colon cancer cell line.

Cell fusion responsible for horizontal oncogenesis by human tumors in nude mice

Human tumor xenotransplants derived from 4 different carcinomas were established in athymic mice and maintained by serial passage. In vivo human/mouse cell fusion and induction of neoplastic growth of adjacent mouse tissue was investigated in serial passages by isoenzyme analysis, by chromosome analysis and by cloning of induced tumorigenic mouse cells. In 2 xenotransplants human/murine hybrid isoenzyme complexes of pyruvate-glutamate transaminase, glucosephosphate isomerase and mitochondrial malate dehydrogenase were detected. Metaphases containing human and murine chromosomes were found in the first in vitro passage of excised xenotransplants. Cloning of induced mouse tumor cells yielded tumor cell lines tumorigenic in athymic as well as in immunocompetent mice.