Xenograft model systems for human melanoma

The Melding of Drug Screening Platforms for Melanoma

The global incidence of cancer is rising rapidly and continues to be one of the leading causes of death in the world. Melanoma deserves special attention since it represents one of the fastest growing types of cancer, with advanced metastatic forms presenting high mortality rates due to the development of drug resistance. The aim of this review is to evaluate how the screening of drugs and compounds for melanoma has been performed over the last seven decades. Thus, we performed literature searches to identify melanoma drug screening methods commonly used by research groups during this timeframe. In vitro and in vivo tests are essential for the development of new drugs; however, incorporation of in silico analyses increases the possibility of finding more suitable candidates for subsequent tests. In silico techniques, such as molecular docking, represent an important and necessary first step in the screening process. However, these techniques have not been widely used by research groups to date. Our research has shown that the vast majority of research groups still perform in vitro and in vivo tests, with emphasis on the use of in vitro enzymatic tests on melanoma cell lines such as SKMEL and in vivo tests using the B16 mouse model. We believe that the union of these three approaches (in silico, in vitro, and in vivo) is essential for improving the discovery and development of new molecules with potential antimelanoma action. This workflow would provide greater confidence and safety for preclinical trials, which will translate to more successful clinical trials and improve the translatability of new melanoma treatments into clinical practice while minimizing the unnecessary use of laboratory animals under the principles of the 3R's.

A structural perspective on the interactions of TRAF6 and Basigin during the onset of melanoma: A molecular dynamics simulation study

Metastatic melanoma is the most fatal type of skin cancer. The roles of matrix metalloproteinases (MMPs) have well been established in the onset of melanoma. Basigin (BSG) belongs to the immunoglobulin superfamily and is critical for induction of extracellular MMPs during the onset of various cancers including melanoma. Tumor necrosis factor receptor-associated factor 6 (TRAF6) is an E3-ligase that interacts with BSG and mediates its membrane localization, which leads to MMP expression in melanoma cells. This makes TRAF6 a potential therapeutic target in melanoma. We here conducted protein-protein interaction studies on TRAF6 and BSG to get molecular level insights of the reactions. The structure of human BSG was constructed by protein threading. Molecular-docking method was applied to develop the TRAF6-BSG complex. The refined docked complex was further optimized by molecular dynamics simulations. Results from binding free energy, surface properties, and electrostatic interaction analysis indicate that Lys340 and Glu417 of TRAF6 play as the anchor residues in the protein interaction interface. The current study will be helpful in designing specific modulators of TRAF6 to control melanoma metastasis.

Therapeutic implications of melanoma heterogeneity

Over the last decade, the treatment of metastatic melanoma has been revolutionized by the translation of molecular insights into therapeutic benefit for patients. These include advances in immunotherapeutic and small-molecule approaches aimed at destroying cells with immunogenic antigens or gene mutations. Despite these advances, the limited durability of clinical response and eventual disease progression underscores a need for better understanding of mechanisms underlying tumor development. Current targeted therapies are developed partly based on the rationale that tumors are primarily clonal with respect to mutant oncogene or cell surface antigen target. However, with the advancement of cell isolation and transplantation approaches coupled with deep sequencing and mutation detection techniques, it has become increasingly clear that tumors are polyclonal. As a result, sensitive malignant cells are eradicated by treatment while the remaining tumor cell populations are conferred varying degrees of resistance and survival advantages by harbouring or acquiring certain epigenetic and genetic abnormalities. Tumor heterogeneity thus represents a major obstacle to the successful application of current therapies. Gaining insights into the cellular and molecular aspects of tumor diversity will not only facilitate the development and selection of therapeutic targets but also promote the evolution of precision medicine. In this viewpoint, we will discuss the implications of tumor heterogeneity for the treatment of metastatic melanoma and propose approaches to accelerate the translation of scientific discovery into improved clinical outcomes.

Animal models of melanoma: a somatic cell gene delivery mouse model allows rapid evaluation of genes implicated in human melanoma

The increasing incidence and mortality associated with advanced stages of melanoma are cause for concern. Few treatment options are available for advanced melanoma and the 5-year survival rate is less than 15%. Targeted therapies may revolutionize melanoma treatment by providing less toxic and more effective strategies. However, maximizing effectiveness requires further understanding of the molecular alterations that drive tumor formation, progression, and maintenance, as well as elucidating the mechanisms of resistance. Several different genetic alterations identified in human melanoma have been recapitulated in mice. This review outlines recent progress made in the development of mouse models of melanoma and summarizes what these findings reveal about the human disease. We begin with a discussion of traditional models and conclude with the recently developed RCAS/TVA somatic cell gene delivery mouse model of melanoma.

Human cervical carcinoma xenograft models for studies of the physiological microenvironment of tumors

OBJECTIVE

To establish and characterize experimental tumor models of advanced squamous cell carcinoma of the uterine cervix.

METHODS

Permanent cell lines (CK-160 and TS-415) were established from pelvic lymph node metastases of two cervical carcinoma patients. Xenografted tumors were initiated by inoculating 5 x 10(5) cells into the gastrocnemius muscle of BALB/c nu/nu mice. The tumors were characterized with respect to histological appearance, fraction of necrotic tissue (NF), pimonidazole hypoxic fraction (HF(Pim)), interstitial fluid pressure (IFP), extracellular pH (pH(e)), metastatic propensity, and radiation sensitivity.

RESULTS

The xenografted tumors reflected the donor patients' tumors in histological appearance, metastatic propensity, and radiation sensitivity and showed significant intertumor heterogeneity in growth rate, NF, HF(Pim), IFP, and pH(e).

CONCLUSIONS

CK-160 and TS-415 xenografts possess properties making them relevant models for studies of the physiological microenvironment of cervical carcinoma and its influence on metastatic dissemination and response to treatment.

Acidic extracellular pH promotes experimental metastasis of human melanoma cells in athymic nude mice

Extracellular pH (pH(e)) is lower in many tumors than in the corresponding normal tissue. The significance of acidic pH(e) in the development of metastatic disease was investigated in the present work. Human melanoma cells (A-07, D-12, and T-22) were cultured in vitro at pH(e) 6.8 or 7.4 (control) before being inoculated into the tail vein of BALB/c nu/nu mice for formation of experimental pulmonary metastases. Cell invasiveness was studied in vitro by using Matrigel invasion chambers and angiogenesis was studied in vivo by using an intradermal assay. Protein secretion was measured by ELISA and immunocapture assays. Cells cultured at acidic pH(e) showed increased secretion of proteinases and proangiogenic factors, enhanced invasive and angiogenic potential, and enhanced potential to develop experimental metastases. Acidity-induced metastasis was inhibited by treatment with the general matrix metalloproteinase (MMP) inhibitor GM6001, the general cysteine proteinase inhibitor E-64, or blocking antibody against vascular endothelial growth factor-A (VEGF-A) or interleukin-8 (IL-8). Our study indicates that acidic pH(e) promotes experimental pulmonary metastasis in A-07, D-12, and T-22 human melanoma cells by a common mechanism involving acidity-induced up-regulation of the proteolytic enzymes MMP-2, MMP-9, cathepsin B, and cathepsin L and acidity-induced up-regulation of the proangiogenic factors VEGF-A and IL-8. One consequence of this observation is that treatment strategies involving deliberate tumor acidification to improve the efficacy of chemotherapy, photodynamic therapy, and hyperthermia should be avoided. Moreover, the possibility that the pH(e) of the primary tumor may be an important prognostic parameter for melanoma patients merits clinical investigation.

Transvascular and interstitial transport of a 19 kDa linear molecule in human melanoma xenografts measured by contrast-enhanced magnetic resonance imaging

Cancer therapy involving blood-borne macromolecular therapeutic agents often fails, owing to inadequate macromolecule uptake in malignant tissue. The transvascular and interstitial transport of a 19 kDa linear molecule (NC22181 or poly-[Gd-DTPA]-co-[1,6-diaminohexane]) was studied in the present work in an attempt to identify transport barriers limiting the delivery of macromolecules to tumors. Tumors of four human melanoma xenograft lines were included in the study. The uptake of NC22181 was measured by spoiled gradient recalled magnetic resonance imaging (MRI). The effective microvascular permeability constant and the interstitial influx constant of NC22181 were calculated from NC22181 uptake curves by using a three-compartment tissue model. The uptake of NC22181 was limited by the interstitial transport and not by the transvascular transport in all xenograft lines. If the melanoma xenografts used in this study are representative models of human cancer, our results suggest that strategies for increasing the delivery of macromolecular therapeutic agents to tumors should focus on improving the transport conditions in the interstitium, rather than enhancing the permeability of the microvascular wall.

Augmentation of human leukemic cell invasion by activation of a small GTP-binding protein Rho

OBJECTIVE

The functions of a small GTP-binding protein, Rho, in human leukemic cell invasion was investigated in vivo and in vitro.

MATERIALS AND METHODS

Human leukemic KM3 and Reh cells (derived from B-cell-type common acute lymphoid leukemias) were inoculated into severe combined immundeficiency (SCID) mice. Alteration of invasion in SCID mice inoculated with KM3 cells that were introduced with the expression vector for Rho Val14 (Rho V14), an activated mutant form of Rho, was observed.

RESULTS

SCID mice inoculated with KM3 and Reh cells developed paraplegia 21 days after inoculation. All died by day 26-27. The leukemic cells were localized to bone marrow and around the spinal cord, with no infiltration into peripheral blood, spleen, liver, thymus, or lymph nodes. SCID mice inoculated with Rho V14-transfected KM3 cells showed a 5-day reduction in the time to paraplegia and death compared with SCID mice inoculated with hygromycin-resistance gene-transfected KM3 (hyg(r)) cells. In addition, the mice inoculated with Rho V14 cells showed leukemic cell infiltration, not only into bone marrow and around the spinal cord but also into peripheral blood, liver, and spleen. There were no in vitro or in vivo differences in growth rates of Rho V14 and hyg(r) cells. However, the Rho V14 cells showed markedly increased cell adhesion compared to the hyg(r) cells.

CONCLUSION

Results suggest that Rho activation accelerates human leukemic cell invasion via augmentation of cell adhesion.