Career Development Program
Identification of Mechanisms Controlling the Upregulation of PDGFRB Transcription in B-RAF(V600E)-Inhibitor-Resistant Melanoma Cells
Principal Investigator: Yong Qin, Ph.D.
Somatic mutations of B-Raf kinases are present in about 60% melanomas. An activated single substitution V600E accounted for 80% of B-Raf mutations in malignant melanoma. The Phase I clinical trial of a specific BRAF (V600E) inhibitor, PLX4032, in metastatic melanoma patients with B-RAF(V600E) mutation demonstrated a pronounced 80% antitumor response rate. However, most of these responsive patients have developed recurrences that are resistant to PLX4032. This seriously obstructs the therapeutic strategy targeting BRAF (V600E) in metastatic melanoma. The upregulation of platelet-derived growth factor receptor B (PDGFRB) transcription had been shown to account for the acquired PLX4032 resistance in a subset of melanoma cells and some malignant melanoma patients in clinic. Therefore, I hypotheses that the dysfunction of PDGFRB transcription contributes to upregulating PDGFRB levels and possibly the other kinases, resulting in acquired resistance to B-RAF(V660E) inhibition. In this proposal, I aim identifying crucial transcription factors and related signaling pathways accounting for the aberrant expression of PDGFRB in melanoma cells, which are resistant to B-RAF(V600E)-kinase-inhibitors (PLX-4032 and PLX-4720). The proposed research will be addressed by a series of experiments 1) to investigate the roles of transcription factors, Ap-1, NFE2, NF-Y, and Sp1, and related signaling pathways in upregulating PDGFRB transcription in B-RAF(V600E)-inhibitor resistant melanoma cells; 2) to identify new and currently unknown regulators for PDGFRB transcription, by comparing the transcriptional profiles of B-RAF(V600E)-kinase-inhibitor-resistant and sensitive melanoma cells. The successful completion of the proposed research will provide valuable insight into the mechanism of B-RAF(V600E)-inhibitor resistance and help to develop more effective therapy to overcome the drug resistance in malignant melanoma.
Characterization of Synthetic Lethal Agents that Overcome AZD6244 Resistance in Human Melanoma Cells
Principal Investigator: Guo Chen, Ph.D.
There is strong evidence that the RAS-RAF-MEK-MAPK pathway is activated in the overwhelming majority of melanomas. This is supported primarily by the high prevalence of activating BRAF (~50%) and NRAS (~20%) mutations in cutaneous melanoma. We have also observed that melanomas without mutations in either gene (“Wild-type”) frequently have activation of the pathway, and are sensitive to MEK inhibitors. Recently, selective BRAF inhibitors have achieved unprecedented clinical response rates in metastatic melanoma patients with activating BRAF mutations. However, RAS-RAF-MEK-MAPK pathway inhibitors have failed to demonstrate clinical efficacy in melanoma patients without a BRAF mutation. Further, most BRAF-mutant melanoma patients who respond to selective BRAF inhibitors rapidly develop secondary resistance. Thus, there is a critical need to develop new, more effective approaches to inhibit the RAS-RAF-MEK-MAPK pathway. Previously, we have reported that combined inhibition of the RAS-RAF-MEK-MAPK and the PI3K-AKT pathway results in synergistic cell killing in BRAF-mutant melanoma cells with resistance to MEK inhibitors. In preliminary experiments, we have performed a high-throughput screen with clinically relevant small molecule inhibitors to identify agents that overcome the resistance to MEK inhibition in the highly-resistant, BRAF/NRAS-wild-type HS294T human melanoma cell line. This screen has identified 7 agents that achieved marked synthetic lethality with the MEK inhibitor AZD6244. These results suggest several candidate combinatorial approaches that could lead to novel clinical trials for patients with metastatic melanoma. This development will be facilitated by an improved understanding of the determinants of efficacy of these combinations, in order to identify both optimal patient populations and critical biomarkers that can be used in the design and execution of clinical trials. This information will provide critical preliminary data for subsequent independent funding applications, and potentially lead to new, personalized therapeutic approaches. Genetic Polymorphisms of IL-12p35 and IL-23p19 in Melanoma Progression
Principal Investigator: Shenying Fang, M.D., Ph.D.
As a part of the Melanoma SPORE, project 5 evaluated the relationship of genetic variations with plasma IL-12p40 levels and the association of IL-12p40 as a biomarker with melanoma outcome. IL-12p40 is a subunit of both IL-12 and IL-23, which are involved in suppressing and promoting tumor growth, respectively. To determine whether IL-23 has a dominant role over IL-12 or vice versa in melanoma progression and also determine the whole ensemble of genetic factors influencing these traits, we propose to evaluate whether IL-12p40+IL-12p35 and IL-12p40+IL-23p19 can predict melanoma outcomes, particularly among stage III/IV patients (Aim1). Then we will perform genome-wide association studies to identify genetic variants for IL-12p35 and IL-23p19 (Aim2). And, finally, we will evaluate association between risk of melanoma recurrence or death and the SNPs identified in Aim 2 and the SNPs that predict IL-12p40 levels (Aim3). Our results will help to elucidate the mechanism of melanoma progression, define high-risk groups for adjuvant therapy, and provide new clinical indicators for response to therapy over time.