title: Combinatorial treatments that overcome PDGFRβ-driven resistance of melanoma cells to V600EB-RAF inhibition.
abstract: (V600E)B-RAF mutation is found in 50% to 60% of melanomas, and the novel agents PLX4032/vemurafenib and GSK2118436 that inhibit the (V600E)B-RAF kinase achieve a remarkable clinical response rate. However, as might be expected, acquired clinical resistance to these agents arises in most melanoma patients. PLX4032/vemurafenib resistance that arises in vivo in tumor matched short-term cultures or in vitro in melanoma cell lines is not caused by acquisition of secondary mutations in (V600E)B-RAF but rather is caused by upregulating platelet-derived growth factor receptor β (PDGFRβ) or N-RAS which results in resistance or sensitivity to mitogen-activated protein (MAP)/extracellular signal-regulated (ERK; MEK) kinase inhibitors, respectively. In this study, we define a targeted combinatorial strategy to overcome PLX4032/vemurafenib resistance in melanoma cell lines or short-term culture where the resistance is driven by PDGFRβ upregulation, achieving synergistic growth inhibition and cytotoxicity. PDGFRβ-upregulated, PLX4032-resistant (PPRM) cell lines show dual phospho (p)-ERK and p-AKT upregulation, and their growth inhibitory responses to specific small molecule inhibitors correlated with p-ERK, p-AKT, and p-p70S6K levels. Coordinate inhibition of (V600E)B-RAF inhibition and the RTK-PI3K-AKT-mTORC axis led to functionally significant rebound signaling, illustrating a robust and dynamic network connectivity. Combined B-RAF, phosphoinositide 3-kinase (PI3K), and mTORC1/2 inhibition suppressed both immediate early and delayed compensatory signaling, resulting in a highly synergistic growth inhibitory response but less efficient cytotoxic response. In contrast, the combination of MEK1/2, PI3K, and mTORC1/2 inhibitors consistently triggered apoptosis in a highly efficient manner. Together, our findings offer a rational strategy to guide clinical testing in preidentified subsets of patients who relapse during treatment with (V600E)B-RAF inhibitors.
authors.affiliation: Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA, USA.
authors.forename: Hubing
authors.initials: H
authors.lastname: Shi
authors.forename: Xiangju
authors.initials: X
authors.lastname: Kong
authors.forename: Antoni
authors.initials: A
authors.lastname: Ribas
authors.forename: Roger S
authors.initials: RS
authors.lastname: Lo
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000187:drug effects* / Q000502:physiology; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology*; D007211:Indoles / Q000494:pharmacology*; D020930:MAP Kinase Kinase Kinases / Q000037:antagonists & inhibitors; D000076222:Mechanistic Target of Rapamycin Complex 1; D008545:Melanoma / Q000188:drug therapy / Q000473:pathology*; D009025:Morpholines / Q000494:pharmacology*; D046912:Multiprotein Complexes; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017354:Point Mutation; D011506:Proteins / Q000037:antagonists & inhibitors / Q000502:physiology; D048493:Proto-Oncogene Proteins B-raf / Q000037:antagonists & inhibitors* / Q000235:genetics; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000502:physiology; D011804:Quinolines / Q000494:pharmacology*; D020797:Receptor, Platelet-Derived Growth Factor beta / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D018874:Spheroids, Cellular / Q000187:drug effects; D013449:Sulfonamides / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000502:physiology; D000077484:Vemurafenib
chemical_list: D000970:Antineoplastic Agents; D007093:Imidazoles; D007211:Indoles; D020930:MAP Kinase Kinase Kinases; D000076222:Mechanistic Target of Rapamycin Complex 1; D009025:Morpholines; D046912:Multiprotein Complexes; D009363:Neoplasm Proteins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011506:Proteins; D048493:Proto-Oncogene Proteins B-raf; D051057:Proto-Oncogene Proteins c-akt; D011804:Quinolines; D020797:Receptor, Platelet-Derived Growth Factor beta; D011993:Recombinant Fusion Proteins; D013449:Sulfonamides; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors; D000077484:Vemurafenib; C493245:CRTC2 protein, human; C546624:(5-(2,4-bis((3S)-3-methylmorpholin-4-yl)pyrido(2,3-d)pyrimidin-7-yl)-2-methoxyphenyl)methanol; C494918:AKT1 protein, human; C482119:BRAF protein, human; C531198:dactolisib