plx-4720 and Lung-Neoplasms

Human anaplastic thyroid cancer (ATC) is a lethal disease with an advanced clinical presentation and median survival of 3 months. The BRAF(V600E) oncoprotein is a potent transforming factor that causes human thyroid cancer cell progression in vitro and in vivo; therefore, we sought to target this oncoprotein in a late intervention model of ATC in vivo. We used the human ATC cell line 8505c, which harbors the BRAF(V600E) and TP53(R248G) mutations. Immunocompromised mice were randomized to receive the selective anti-BRAF(V600E) inhibitor, PLX4720, or vehicle by oral gavage 28 d after tumor implantation, 1 wk before all animals typically die due to widespread metastatic lung disease and neck compressive symptoms in this model. Mice were euthanized weekly to evaluate tumor volume and metastases. Control mice showed progressive tumor growth and lung metastases by 35 d after tumor implantation. At that time, all control mice had large tumors, were cachectic, and were euthanized due to their tumor-related weight loss. PLX4720-treated mice, however, showed a significant decrease in tumor volume and lung metastases in addition to a reversal of tumor-related weight loss. Mouse survival was extended to 49 d in PLX4720-treated animals. PLX4720 treatment inhibited cell cycle progression from 28 d to 49 d in vivo. PLX4720 induces striking tumor regression and reversal of cachexia in an in vivo model of advanced thyroid cancer that harbors the BRAF(V600E) mutation.

Topics: Animals; Antineoplastic Agents; Cell Cycle; Cell Line; Disease Models, Animal; Female; Humans; Indoles; Lung Neoplasms; Mice; Mice, SCID; Neoplasm Invasiveness; Proto-Oncogene Proteins B-raf; Random Allocation; Sulfonamides; Thyroid Carcinoma, Anaplastic; Thyroid Neoplasms; Weight Loss

Although B-Raf(V600E) is the most common somatic mutation in papillary thyroid carcinoma (PTC), how it induces tumor aggressiveness is not fully understood. Using gene set enrichment analysis and in vitro and in vivo functional studies, we identified and validated a B-Raf(V600E) gene set signature associated with tumor progression in PTCs. An independent cohort of B-Raf(V600E)-positive PTCs showed significantly higher expression levels of many extracellular matrix genes compared with controls. We performed extensive in vitro and in vivo validations on thrombospondin-1 (TSP-1), because it has been previously shown to be important in the regulation of tumor angiogenesis and metastasis and is present in abundance in tumor stroma. Knockdown of B-Raf(V600E) resulted in TSP-1 down-regulation and a reduction of adhesion and migration/invasion of human thyroid cancer cells. Knockdown of TSP-1 resulted in a similar phenotype. B-Raf(V600E) cells in which either B-Raf(V600E) or TSP-1 were knocked down were implanted orthotopically into the thyroids of immunocompromised mice, resulting in significant reduction in tumor size and fewer pulmonary metastases from the primary carcinoma as compared with the control cells. Treatment of orthotopic thyroid tumors, initiated 1 week after tumor cell implantation with PLX4720, an orally available selective inhibitor of B-Raf(V600E), caused a significant tumor growth delay and decreased distant metastases, without evidence of toxicity. In conclusion, B-Raf(V600E) plays an important role in PTC progression through genes (i.e., TSP-1) important in tumor invasion and metastasis. Testing of a patient's thyroid cancer for B-Raf(V600E) will yield important information about potential tumor aggressiveness and also allow for future use of targeted therapies with selective B-Raf(V600E) inhibitors, such as PLX4720.

Topics: Animals; Antineoplastic Agents; Cell Line, Tumor; Disease Progression; Female; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Humans; Indoles; Lung Neoplasms; Mice; Mice, SCID; Mutation; Protein Kinase Inhibitors; Proto-Oncogene Proteins B-raf; RNA Interference; Signal Transduction; Sulfonamides; Thrombospondin 1; Thyroid Neoplasms