Biomedical subjects

Patricia A Brafford

Publications and source records attributed to Patricia A Brafford.

3 recordsLinked to original sources

PubMed2006

Defining the conditions for the generation of melanocytes from human embryonic stem cells.

Because of their undifferentiated nature, human embryonic stem cells (hESCs) are an ideal model system for studying both normal human development and the processes that underlie disease. In the current study, we describe an efficient method for differentiating hESCs into a melanocyte population within 4-6 weeks using three growth factors: Wnt3a, endothelin-3, and stem cell factor. The hESC-derived melanocytes expressed melanocyte markers (such as microphthalmia-associated transcription factor and tyrosinase), developed melanosomes, and produced melanin. They retained the melanocyte phenotype during long-term cell culture (>90 days) and, when incorporated into human reconstructed skin, homed to the appropriate location along the basement membrane in the same manner as epidermis-derived melanocytes. They maintained a stable phenotype even after grafting of the reconstructs to immunodeficient mice. Over time in culture, the hESC-derived melanocytes lost expression of telomerase and underwent senescence. In summary, we have shown for the first time the differentiation of hESCs into melanocytes. This method provides a novel in vitro system for studying the development biology of human melanocytes.

Animals↗

PubMed2006

Multiple signaling pathways must be targeted to overcome drug resistance in cell lines derived from melanoma metastases.

Although >66% of melanomas harbor activating mutations in BRAF and exhibit constitutive activity in the mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK)/extracellular signal-regulated kinase signaling pathway, it is unclear how effective MEK inhibition will be as a sole therapeutic strategy for melanoma. We investigated the anticancer activity of MEK inhibition in a panel of cell lines derived from radial growth phase (WM35) and vertical growth phase (WM793) of primary melanomas and metastatic melanomas (1205Lu, 451Lu, WM164, and C8161) in a three-dimensional spheroid model and found that the metastatic lines were completely resistant to MEK inhibition (U0126 and PD98059) but the earlier stage cell lines were not. Similarly, these same metastatic melanoma lines were also resistant to inhibitors of the phosphatidylinositol 3-kinase/Akt pathway (LY294002 and wortmannin). Under adherent culture conditions, the MEK inhibitors blocked growth through the induction of cell cycle arrest and up-regulation of p27, but this was readily reversible following inhibitor washout. However, when the phosphatidylinositol 3-kinase and MEK inhibitors were combined, the growth and invasion of the metastatic melanoma three-dimensional spheroids were blocked. Taken together, these results suggest that the most aggressive melanomas are resistant to strategies targeting one signaling pathway and that multiple signaling pathways may need to be targeted for maximal therapeutic efficacy. It is further suggested that BRAF mutational status is not predictive of response to MEK inhibition under three-dimensional culture conditions.

Butadienes↗

PubMed2005

Selective evolutionary pressure from the tissue microenvironment drives tumor progression.

Cells grow within defined environmental niches and are subject to microenvironmental control. Outside of their niche, the environment is hostile, the normal cells lack appropriate survival signals which leads to anoikis. During tumor development and progression, malignant cells must escape the local tissue control and resist anoikis. The inherent genetic instability of tumor cells makes their phenotype very plastic, which changes under continuous environmental selection pressure. In this way the microenvironment drives the somatic evolution of the tumor. In the current review, we assess how this environmental selection pressure fits into the classical scheme of tumor progression.

Animals↗