CTGF is a therapeutic target for metastatic melanoma [electronic resource]

While only representing 4% of all skin cancers, melanoma accounts for over 70% of skin cancer deaths. Once metastasized, melanoma patient prognosis is poor with a median survival of 6 -15 months and a five-year survival rate of less than 5%. Clinically, low oxygen, or hypoxia, signaling has been associated with poor outcome in many solid tumors, including melanoma, and is a key factor regulating melanoma metastasis. Using microarray technology to identify mechanisms by which hypoxia promotes metastasis and potential therapeutic targets, we identified connective tissue growth factor (CTGF) as a gene differentially expressed in hypoxia (2% O2)-treated metastatic melanoma cells compared to normal oxygen conditions, or normoxia (21% O2). CTGF is a secreted, matricellular, and multimodular protein that interacts with many binding partners in the extracellular matrix (ECM) to modulate various cellular functions such as ECM production, cell adhesion, migration, proliferation, and survival. CTGF has been implicated in various pathological conditions and its involvement in the tumor progression of various human cancers has been demonstrated. Clinically, we observe that CTGF expression correlates with melanoma tumor progression. On this finding, we hypothesize that CTGF, as a modulator of multiple cellular functions, may represent a potential target for therapy for melanoma. Herein we identify CTGF as a hypoxia-inducible target gene through HIF-dependent mechanisms. Next, we elucidate the biological role and therapeutic potential of targeting CTGF in metastatic melanoma. In vitro, we observe that genetic inhibition of CTGF reduces the metastatic potential of metastatic melanoma cells by inhibiting migration, invasion, and anchorage-independent growth. In vivo, we use genetic or therapeutic inhibition (FG-3019, a human monoclonal antibody to CTGF, FibroGen) of CTGF in orthotopic melanoma mouse models and metastasis tail vein mouse models in order to determine the therapeutic potential of targeting CTGF. We observe that CTGF inhibition significantly reduces primary tumor growth and metastasis, suggesting that CTGF plays an important role in the aggressive phenotype of metastatic melanoma. To further explore the therapeutic potential of targeting CTGF in melanoma, we determine if CTGF can be targeted as a therapy in BRAF-inhibitor resistance melanoma. Several of the recent FDA-approved therapies for metastatic melanoma, including Vemurafenib (PLX4032), are small molecule inhibitors against the mutant form of BRAF, BRAFV600E, which is mutated in 50% of melanomas. Despite recent advances with these novel therapies, clinical benefit is short-lived, and many patients develop resistance within 5-7 months. Strikingly, we find that CTGF expression is significantly upregulated at the RNA and protein level in PLX4032-resistant cells compared to their PLX4032-sensitive matched cells. Functionally, inhibition of CTGF is sufficient to significantly decrease the enhanced metastatic behavior of the PLX-resistant cell lines. Importantly, in vivo, we observe that genetic inactivation of CTGF reduces the growth of PLX402-resistant melanoma primary tumors. In summary, this thesis has unveiled a novel therapy for metastatic melanoma. Our results are the first pre-clinical validation of CTGF as a therapeutic target for metastatic melanoma. This is also the first implication of CTGF as a target for therapy for patients who are unresponsive to BRAF inhibitor therapies. Our work is important because new melanoma therapies with long-term clinical benefits are needed. Future studies to elucidate the precise molecular mechanism through which CTGF promotes the aggressive phenotype of melanoma are currently ongoing. Additionally, the therapeutic efficacy of CTGF in combination with current melanoma therapeutics and in other genetic and drug resistant subtypes of melanoma is also being explored.

Advisor: Giaccia Amato J.
Cochran Jennifer R. advisor. Thesis advisor
Koong Albert
Lipsick Joseph Steven