CIC-Mutation As a Potential Molecular Mechanism of Acquired Resistance to Combined BRAF/MEK Inhibition in CNS Multiple Myeloma

Abstract

Central nervous system (CNS) involvement is an extremely rare extramedullary multiple myeloma (MM) manifestation, diagnosed in less than 1% of patients. It is considered an ultimate high-risk feature, associated with unfavorable cytogenetics, and, even with intense treatment applied, survival is short, reaching less than 12 months in most cases. In June 2017 an 81 years old male with a κ light chain MM was referred to our institution for an isolated CNS MM relapse. His cerebrospinal fluid (CSF) demonstrated a high load of clonal plasma cells, however, the patient's bone marrow infiltration was very little with a percentage of plasma cells less than 5%. Imaging, including gold standard MRI and experimental 11C-methionine PET scan, was performed, and high metabolic activity was detected supra- and infratentorially as well as in the right femur and the clivus. Following CD138+ cell purification we analyzed the specimen with M3P (v3.0) a disease specific in-house customized, next generation targeted sequencing panel for MM (Ion torrent platform). This includes most commonly mutated MM genes, actionable drug targets and drug resistance associated genes. The average sequencing depth increased 700X and spatial MM heterogeneity was detected, as the CFS cells harbored a clonal BRAFV600E mutation, absent in the bone marrow. Initial intrathecal and systemic chemotherapy with Cytarabine and Thiotepa was intolerable, thus the patient underwent a combined target inhibition with Dabrafenib/Trametinib, well known specific BRAF and a MEK 1/2 inhibitors. The patient displayed a rapid complete response (Figure. 1A), however, disease relapse occurred after three months of therapy. We obtained a sequential CFS sample and Whole Exome Sequencing (Illumina platform) was applied to pre and post therapy CFS sampling. Exome sequencing of the two time points performed an average sequencing depth of 115X; a total number of 97 non-silent coding variants (missense, nonsense, indels, splice) with an allele frequency higher than 5% were detected. In detail, 19 point mutations were acquired at relapse, including a subclonal missense mutation in CIC (p.A984P, VRF 17%), recently identified as a candidate gene contributing to MEK/BRAF resistance development. Next, we established a CIC knock-down model electroporating a specific anti-CIC siRNA into U266 MM cell line. We cultured the silenced and not-silenced cells with Trametinib and Dabrafenib, either as single agents, or in combination. As expected, we observed resistance induction to the combination of the two drugs (Row Factor 85.94%; P<0.0001, Two-way ANOVA) suggesting a critical role for this patient derived mutation for his MEK/BRAF resistance development (Figure 1C, D). In order to better clarify the landscape pathway related to CIC we analyzed expression data from 647 patients enrolled in the MMRF CoMMpass trial. Remarkably, we found a significant down-regulation of ERF and ETV6 (t-test -9.95, -9.93, P <0.001, respectively), two well characterized tumor suppressor genes correlated with the re-activation of the RAS downstream pathway (Figure 1B). This is the first report giving evidence for a potential role of point mutations in CIC as a resistance mechanism to targeted MEK/BRAF inhibition in BRAF mutated MM. The performed pathway analysis significantly extends the insights of the resistance mechanisms highlighted. Our results foster a statistically powered study to corroborate the clinical relevance. Figure 1. Figure 1. Disclosures No relevant conflicts of interest to declare.

Multiple myeloma presenting as an intramedullary spinal cord tumor: a case report and review of the literature

“…More recently, selinexor was approved for patients with advanced MM, and this agent seems to cross the BBB. Combination BRAF and mitogen-activated protein kinase kinase 1/2 inhibitors dabrafenib/trametinib have also been employed to good response; however, recent evidence suggests potential mechanisms of drug resistance [ 33 ]. Given the reported radiosensitivity of plasma cell dyscrasias, concurrent radiotherapy may be considered [ 4 , 34 , 35 ].…”

New Insights into Diffuse Large B-Cell Lymphoma Pathobiology

“…Remarkably, CNS spreading represents a paradigmatic extranodal localization with peculiar pathobiology involving adhesion molecule deregulated expression [ 129 ] and hyperactivation of the angiogenesis fueling pathway [ 130 ] along with a truncal genomic signature [ 131 ], which can contribute to drug sensitivity and resistance [ 132 , 133 , 134 ], as in other malignancies [ 135 , 136 , 137 ]. Therefore, given that the aberrant expression of adhesion molecules on bone marrow endothelial cells of patients with lymphoid and myeloid neoplasia was also discovered to predict poor clinical outcome [ 138 , 139 , 140 , 141 ], it is tempting to speculate a vicious cycle in DLBCL by paralleling the neoplastic cell behavior [ 128 ], whereby the described molecular signature [ 36 , 142 ] has more interactions among themselves than what would be expected for a random set of gene-encoding proteins drawn from the genome [ 143 ].…”

New insights in Diffuse Large B Cell Lymphoma Pathobiology

“…Remarkably, CNS spreading represents a paradigmatic extranodal localization with peculiar pathobiology involving adhesion-molecule deregulated expression [129], hyperactivation of angiogenesis fueling pathway [130] along with truncal genomic signature [131] that can contribute to drug sensitivity and resistance [132][133][134], as in other malignancies [135][136][137]. Therefore, given that the aberrant expression of adhesion molecules also on bone marrow endothelial cells of patients with lymphoid and myeloid neoplasia has been discovered to predict poor clinical outcome [138][139][140][141], it is tempting to speculate a vicious cycle in DLBCL by paralleling the neoplastic cells behavior [128] and that the described molecular signature [36,142] have more interactions among themselves than what would be expected for a random set of gene encoding proteins drawn from the genome [143].…”