Therapeutic Targeting of TFE3/IRS-1/PI3K/mTOR Axis in Translocation Renal Cell Carcinoma.

Abstract

Translocation renal cell carcinoma (tRCC) represents a rare subtype of kidney cancer associated with various <i>TFE3, TFEB</i>, or <i>MITF</i> gene fusions that are not responsive to standard treatments for RCC. Therefore, the identification of new therapeutic targets represents an unmet need for this disease. We have established and characterized a tRCC patient-derived xenograft, RP-R07, as a novel preclinical model for drug development by using next-generation sequencing and bioinformatics analysis. We then assessed the therapeutic potential of inhibiting the identified pathway using <i>in vitro</i> and <i>in vivo</i> models. The presence of a <i>SFPQ-TFE3</i> fusion [t(X;1) (p11.2; p34)] with chromosomal break-points was identified by RNA-seq and validated by RT-PCR. TFE3 chromatin immunoprecipitation followed by deep sequencing analysis indicated a strong enrichment for the PI3K/AKT/mTOR pathway. Consistently, miRNA microarray analysis also identified PI3K/AKT/mTOR as a highly enriched pathway in RP-R07. Upregulation of PI3/AKT/mTOR pathway in additional TFE3-tRCC models was confirmed by significantly higher expression of phospho-S6 (<i>P</i> < 0.0001) and phospho-4EBP1 (<i>P</i> < 0.0001) in established tRCC cell lines compared with clear cell RCC cells. Simultaneous vertical targeting of both PI3K/AKT and mTOR axis provided a greater antiproliferative effect both <i>in vitro</i> (<i>P</i> < 0.0001) and <i>in vivo</i> (<i>P</i> < 0.01) compared with single-node inhibition. Knockdown of <i>TFE3</i> in RP-R07 resulted in decreased expression of IRS-1 and inhibited cell proliferation. These results identify TFE3/IRS-1/PI3K/AKT/mTOR as a potential dysregulated pathway in TFE3-tRCC, and suggest a therapeutic potential of vertical inhibition of this axis by using a dual PI3K/mTOR inhibitor for patients with TFE3-tRCC.