The 4q12 Amplicon in Malignant Peripheral Nerve Sheath Tumors: Consequences on Gene Expression and Implications for Sunitinib Treatment

Abstract

BackgroundMalignant peripheral nerve sheath tumors (MPNST) are highly aggressive tumors which originate from Schwann cells and develop in about 10% of neurofibromatosis type 1 (NF1) patients. The five year survival rate is poor and more effective therapies are needed. Sunitinib is a drug targeting receptor tyrosine kinases (RTK) like PDGFRα, c-Kit and VEGFR-2. These genes are structurally related and cluster on chromosomal segment 4q12.Methodology/Principal FindingsHere we characterize this region by multiplex ligation-dependent probe amplification (MLPA) in MPNST. Our probe set encompasses the 3 adjacent RTK genes (PDGFRA, KIT, KDR) and 6 flanking genes. We found amplification of several genes within this region in a subset of MPNST and MPNST cell lines. Transcript and protein expression of PDGFRA matched well with its increased copy number suggesting a central role of PDGFRA within the amplicon. Studying the effect of sunitinib on 5 MPNST cell lines revealed that cell line S462 harboring the 4q12 amplicon was extremely sensitive to the drug with an IC50 below 1.0µM. Moreover, sunitinib induced apoptosis and prevented PDGF-AA induced signaling via PDGFRα as determined by western blotting. Co-expression of VEGF and its receptor VEGFR-2 (KDR) was present in MPNST cell lines suggesting an autocrine loop. We show that VEGF triggered signal transduction via the MAPK pathway, which could be blocked by sunitinib.Conclusions/SignificanceSince multiple receptors targeted by sunitinib are expressed or over-expressed by MPNST cells sunitinib appears as an attractive drug for treatment of MPNST patients. Presence of the 4q12 amplicon and subsequent over-expression of PDGFRA might serve as predictive markers for efficacy of sunitinib.

Increased gene copy number of KIT and VEGFR2 at 4q12 in primary breast cancer is related to an aggressive phenotype and impaired prognosis

“…FISH positivity for KIT and VEGFR2 was strongly correlated (v 2 test, P < 0.001), suggesting possible co-amplification, which has also been observed in other tumor types (Puputti et al, 2008;Blom et al, 2010). There was no correlation between FISH positivity for VEGFR2 or KIT and protein expression, a finding previously reported in other tumor forms (Tabone et al, 2005, Blom et al, 2010Zietsch et al, 2010).…”

Sustained Inhibition of Receptor Tyrosine Kinases and Macrophage Depletion by PLX3397 and Rapamycin as a Potential New Approach for the Treatment of MPNSTs

“…More recent evidence (9, 11, 37) has shown that several genes are amplified in a subset of MPNST cell lines along the 4q12 amplicon, some of which include genes for receptor tyrosine kinases such as PDGFR, VEGFR and c-Kit. Attempts have been made to identify “druggable” tyrosine kinases in MPNSTs (7, 38) and treatments have been targeted at down-regulating pathways that include Src, PDGFR, IGF-1R, c-Kit as well as c-Met and EGFR (9, 10, 20, 21, 39, 40).…”

“…MPNSTs have been shown to have gene amplification for receptor tyrosine kinases such as PDGFR as well as c-Kit (9, 11). The role of c-Kit oncogenic mutations in gastro-intestinal stromal tumors (GIST) is well established (12, 13).…”

Radiation-induced intradural malignant peripheral nerve sheath tumor of the cauda equina with diffuse leptomeningeal metastasis

“…13 The expanding scientific literature suggests that MPNST can be treated more effectively with the addition of agents that target and inhibit specific pathways and/or cellular processes: PI3K/mTOR pathway with XL765, 12 autophagy with chloroquine, 12 and plateletderived growth factor receptor with sunitinib. 35 The reported 5-year survival rate for patients diagnosed with MPNST is poor, ranging from 16% to 52%. 10,18,34 Among reported cases of spinal intradural MPNST, the calculated 1-year, 3-year, and 5-year survival rates are 81%, 50%, and 25%, respectively.…”