Acquired resistance to sunitinib in human renal cell carcinoma cells is mediated by constitutive activation of signal transduction pathways associated with tumour cell proliferation

Authors


Correspondence: Hideaki Miyake, Division of Urology, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan.

e-mail: hideakimiyake@hotmail.com

Abstract

What's known on the subject? and What does the study add?

  • Although there have been a few studies investigating the molecular mechanism mediating the acquisition of resistance to molecular-targeted agents, including sunitinib, by renal cell carcinoma (RCC) cells, this mechanism remains largely unclear.
  • The maintenance of protein kinase activation during sunitinib treatment may be involved in the acquisition of a phenotype resistant to sunitinib in RCC, and additional treatment with agents targeting activated protein kinases could be a promising approach for overcoming resistance to sunitinib in RCC.

Objective

  • To characterise the mechanism involved in the acquired resistance to sunitinib, a potential inhibitor of multiple receptor tyrosine kinases (RTKs), in renal cell carcinoma (RCC).

Materials and Methods

  • A parental human RCC cell line, ACHN (ACHN/P), was continuously exposed to increasing doses of sunitinib, and a cell line resistant to sunitinib (ACHN/R), showing an ≈5-fold higher IC50 (concentration that reduces the effect by 50%) than that of ACHN/P, was developed.

Results

  • ACHN/R appeared to acquire significant cross resistance to sorafenib; however, there were no significant differences in sensitivities to the Mammalian target of rapamycin inhibitors, temsirolimus and everolimus, between ACHN/P and ACHN/R.
  • After sunitinib treatment, the expression levels of phosphorylated Akt and p44/42 mitogen-activated protein kinase in ACHN/P, but not those in ACHN/R, were significantly inhibited.
  • RTK assay showed that treatment of ACHN/P with sunitinib resulted in the marked downregulation of several phosphorylated RTKs compared with that of ACHN/R.
  • Additional treatment with a specific inhibitor of Akt significantly increased the sensitivity of ACHN/R to sunitinib, but not that of ACHN/P.
  • There were no significant differences between in vivo growth patterns of ACHN/P and ACHN/R in mice before and after the administration of sunitinib; however, the proportion of cells positive for TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling) staining in ACHN/P tumour was significantly greater than that in ACHN/R tumour in mice treated with sunitinib.

Conclusion

  • The maintenance of protein kinase activation during sunitinib treatment may be involved in the acquisition of resistant phenotype to sunitinib in RCC cells.

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