Abstract A13: Establishment and characterization of a panel of melanoma patient-derived xenograft (PDX) models.
Authors: Gamez Lizette , Wick Michael J. , Vaught Teresa L. , Farley Monica , Tolcher Anthony W. , Rasco Drew , Patnaik Amita , Miller Alex , Drengler Ron , Papadopoulos Kyriakos P. 
Published: August 2014

Background: A majority of metastatic melanomas are driven by BRAF and NRAS mutations in the MAP/ERK kinase pathway. Recently approved therapies targeting B-Raf and Erk kinases have improved patient outcome; however, anticancer effects of these agents are transient, indicating additional pathways and mutations may play a role in disease progression. To better understand these mechanisms we have established a panel of melanoma patient-derived xenograft (PDX) models and characterized them by mutation, receptor and ligand density and drug sensitivity.

Methods: PDX melanoma models were established in athymic nude mice from primary or metastatic patient tissue and once established were confirmed by histologic comparative analysis and linked with patient treatment and outcome data. For each model, DNA was extracted and subjected to exon sequencing of 207 known oncogenes; growth factor receptor and ligand densities were interrogated using immunohistochemistry and quantitative RNA in situ hybridization. Drug sensitivity studies were performed evaluating sensitivity of models towards chemotherapy and targeted agents including oral vemurafenib and trametinib. Vemurafenib was administered twice daily at 50 mg/kg and trametinib once daily at 1-3 mg/kg for at least twenty-eight days; oral temozolomide was tested at 100 mg/kg on a qdx5 schedule. Study endpoints included tumor volume and time from treatment initiation; with tumor growth inhibition, delay and regression reported at study completion.

Results: BRAF mutations were identified in approximately 50% of melanoma models and 8% reported NRAS mutation; all identified mutations were concordant with clinical results reported from patients linked to the models. EGFR expression was reported in 13% of models (1+ to 3+) and HER3 expression (1+ to 3+) found in 55% of models with associated heregulin expression; HER2 was not found expressed in any evaluated melanoma model. Temozolomide tested at its maximum tolerated dose was ineffective in most models while vemurafenib was active in all evaluated B-RafV600E models and inactive in models with wildtype or alternate mutations. Trametinib was active in most B-RafV600E models and in some N-Ras-mutated models. Interestingly the ST054 model harboring B-RafL584 and N-RasQ61L mutations was sensitive to trametinib but not vemurafenib.

Conclusion: We have established a panel of melanoma PDX models and characterized mutation status, receptor and ligand density and drug sensitivity. We found HER 3 expressed in a majority of models and benchmarked vemurafenib and trametinib activity in these models. This panel can be utilized as a valuable screening tool in early and late-stage oncology drug development.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A13.

Citation Format: Lizette Gamez, Michael J. Wick, Teresa L. Vaught, Monica Farley, Anthony W. Tolcher, Drew Rasco, Amita Patnaik, Alex Miller, Ron Drengler, Kyriakos P. Papadopoulos. Establishment and characterization of a panel of melanoma patient-derived xenograft (PDX) models. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A13.