Importance of orthotopic implantation for human tumor as model systems: Relevance to metastasis and invasion
Transplantation of human tumors into immunodeficient athymic nude mice has become an important experimental approach to study the biology and the treatment of human cancer. Most human tumor xenograft experiments have employed subcutaneous injection procedures, but the main limit of this technique is the lack of metastasis from the subcutaneous site. The possibility of producing experimental metastasis by intravenous injection of cells in the animals has been known for a long time, and it has been recently reported that tumorigenic properties and metastatic ability of human cancer can be altered by transplantation of the tumor into its organ or tissue of origin in the recipient animals (orthotopic transplantation). In this paper we review (1) the principal techniques of orthotopic injection of most solid tumors, (2) the most recent techniques to achieve experimental metastases, and (3) the methods for preparing tumor cell suspensions from human surgical specimens suitable for transplantation into animals. These animal models should be used for a more appropriate evaluation of new antitumor treatments including the ones targeted to inhibit metastatic spread.
Available from: Terence Tang
- "Unfortunately, such models do not accurately reflect certain aspects of the respective clinical disease because the tumors are grown and treated in an ectopic and thus possibly inappropriate microenvironment. Indeed, previous studies involving comparisons between orthotopic and ectopic subcutaneous tumors have shown differences in invasiveness, angiogenesis, ability to metastasize, and response to therapy  . Advanced orthotopic HCC models, Figure 5. (continued). "
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ABSTRACT: Hepatocellular carcinoma (HCC) is an intrinsically chemotherapy refractory malignancy. Development of effective therapeutic regimens would be facilitated by improved preclinical HCC models. Currently, most models consist of subcutaneous human tumor transplants in immunodeficient mice; however, these do not reproduce the extensive liver disease associated with HCC or metastasize. To address this deficiency, we developed an orthotopic model. Human HCC cells were transfected with the gene encoding secretable beta-subunit human choriogonadotropin (beta-hCG), which was used as a surrogate marker of tumor burden. The HCC cells were implanted into the left liver lobe of severe combined immunodeficient (SCID) mice, after which the efficacy of different therapies was evaluated on established, but liver-confined human Hep3B cell line HCC. Treatments included sorafenib or metronomic chemotherapy using cyclophosphamide (CTX), UFT, an oral 5-fluorouracil prodrug, or doxorubicin either alone or in various combinations, with or without an antiangiogenic agent, DC101, an anti-vascular endothelial growth factor receptor-2 antibody. Sorafenib inhibited tumor growth in a dose-dependent manner but caused severe weight loss in SCID mice, thus necessitating use of DC101 in subsequent experiments. Although less toxicity was observed using either single or doublet metronomic chemotherapy without any added antiangiogenic agent, none, provided survival benefit. In contrast, significantly improved overall survival was observed using various combinations of metronomic chemotherapy regimens such as UFT + CTX with DC101. In conclusion, using this model of liver-confined but advanced HCC suggests that the efficacy of a targeted antiangiogenic drug or metronomic chemotherapy can be mutually enhanced by concurrent combination treatment.
Available from: David Edward Leahy
- "These mice are born without thymus gland and therefore can not generate mature T lymphocytes and are unable to mount most types of immune responses. Their immuno deficient status allows a variety of human tumours to be grafted without rejection which serve to investigate tumour growth inhibition of potential anti-tumour agents . Parallel to in vivo screening for identifying pharmacological active and potent antitumour compounds, in vivo studies are performed to evaluate the safety and pharmacokinetic properties of drug candidates . "
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ABSTRACT: CD-1 mice are commonly used in oncology metabolism and toxicity to support drug discovery and development and to examine drug metabolism and toxicity properties of new chemical entities. On the other hand, athymic nude mice are the preferred animals to investigate tumor growth inhibition. Therefore, a frequently asked question is: are the metabolic and pharmacokinetic characteristics of xenobiotics in these two mouse strains comparable or not? To address this issue, we characterized drug metabolism and efflux transporter properties in both strains and in different organs. The metabolic stability of a set of 20 compounds and metabolite formation of cytochrome P450 (CYP) marker substrates (testosterone, ethoxyresorufin and pentoxyresorufin) were measured in liver microsomes. Drug conjugation was studied by following the disappearance of 7-hydroxycoumarin and the formation of its glucuronide and sulfate conjugates in freshly prepared liver slices. In addition, mRNA expression levels of the main cyp genes and drug efflux transporters were investigated by real-time RT-PCR in the liver, kidney, intestine and adrenal glands. No significant differences in enzymatic activities and metabolite formation were observed between the two strains. Also mRNA expression profiles of cyp and drug transporter genes were similar between CD-1 and nude mice.
Available from: Richard P Hill
- "This outcome may also be partially due to the low spontaneous metastatic efficiency of the B16F1 cell line. It is well known that growth site of the primary tumour can have a significant impact on the (metastatic) outcome of any given experiments and the predominant view supports an orthotopic rather than nonorthotopic site for maximal spontaneous metastatic effect (Manzotti et al, 1993; Blouw et al, 2003). It is possible that in our case, intradermally injected tumours might have given more metastases, however, such tumours tend to ulcerate at small sizes and we felt that they would be unsuitable for a study involving multiple needle insertions (personal observation, R Kuba). "
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ABSTRACT: In addition to hypoxia, acidic extracellular pH (pH(e)) is recognised as one of the microenvironmental characteristics of solid tumours. A number of studies have examined ways to increase tumour acidity in order to improve tumour-specific targeting of certain drugs and the effectiveness of hyperthermia. However, previous data have shown that exposure of murine tumour cells to acid conditions in culture can enhance their metastatic potential when injected subsequently into mice, raising the concern that deliberate tumour acidification might increase the probability of metastasis. In this study, we examined the effects of in vivo tumour acidification and hypoxia on the spontaneous metastatic potential of the murine KHT-C fibrosarcoma and B16F1 melanoma cell lines. A tumour-specific increase in extracellular acidity, demonstrated by measurements with pH electrodes, was achieved by daily intraperitoneal injections of meta-iodo-benzylguanidine (MIBG) and/or glucose. This method of tumour acidification during tumour growth did not significantly enhance the spontaneous metastatic potential of the two murine cell lines.
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