Chronic sulforaphane administration inhibits resistance to the mTOR-inhibitor everolimus in bladder cancer cells

  • Progressive bladder cancer growth is associated with abnormal activation of the mammalian target of the rapamycin (mTOR) pathway, but treatment with an mTOR inhibitor has not been as effective as expected. Rather, resistance develops under chronic drug use, prompting many patients to lower their relapse risk by turning to natural, plant-derived products. The present study was designed to evaluate whether the natural compound, sulforaphane (SFN), combined with the mTOR inhibitor everolimus, could block the growth and proliferation of bladder cancer cells in the short- and long-term. The bladder cancer cell lines RT112, UMUC3, and TCCSUP were exposed short- (24 h) or long-term (8 weeks) to everolimus (0.5 nM) or SFN (2.5 µM) alone or in combination. Cell growth, proliferation, apoptosis, cell cycle progression, and cell cycle regulating proteins were evaluated. siRNA blockade was used to investigate the functional impact of the proteins. Short-term application of SFN and/or everolimus resulted in significant tumor growth suppression, with additive inhibition on clonogenic tumor growth. Long-term everolimus treatment resulted in resistance development characterized by continued growth, and was associated with elevated Akt-mTOR signaling and cyclin-dependent kinase (CDK)1 phosphorylation and down-regulation of p19 and p27. In contrast, SFN alone or SFN+everolimus reduced cell growth and proliferation. Akt and Rictor signaling remained low, and p19 and p27 expressions were high under combined drug treatment. Long-term exposure to SFN+everolimus also induced acetylation of the H3 and H4 histones. Phosphorylation of CDK1 was diminished, whereby down-regulation of CDK1 and its binding partner, Cyclin B, inhibited tumor growth. In conclusion, the addition of SFN to the long-term everolimus application inhibits resistance development in bladder cancer cells in vitro. Therefore, sulforaphane may hold potential for treating bladder carcinoma in patients with resistance to an mTOR inhibitor.

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Author:Saira JustinORCiDGND, Jochen RutzGND, Sebastian MaxeinerGND, Felix ChunORCiDGND, Eva JüngelORCiDGND, Roman A. BlahetaORCiD
Parent Title (English):International journal of molecular sciences
Place of publication:Basel
Document Type:Article
Date of Publication (online):2020/06/04
Date of first Publication:2020/06/04
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2020/08/14
Tag:bladder cancer; drug resistance; everolimus; growth; mTOR; proliferation; sulforaphane
Issue:11, art. 4026
Page Number:17
First Page:1
Last Page:17
© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (
Dewey Decimal Classification:6 Technik, Medizin, angewandte Wissenschaften / 61 Medizin und Gesundheit / 610 Medizin und Gesundheit
Licence (German):License LogoCreative Commons - Namensnennung 4.0