Abstract 1069: MiR-21 may serve as a predictive biomarker of response in the assessment of efficacy of HSP-90 inhibition in gastrointestinal (GI) cancers
Authors: Lampis Andrea , Cascione Luciano , Burke Rosemary , Clarke Paul , Simbolo Michele , Scarpa Aldo , Bosma Else , Yu Sijia , Cole Rebecca , Stubbs Mark , Sharp Swee , Van Montfort Rob , Hahne Jens C. , Fassan Matteo , Workman Paul , Valeri Nicola , Braconi Chiara 
Published: July 2016

Abstract
Background and Aims: MicroRNAs mediate drug resistance and are often deregulated in cancer with miR-21 upregulation being shared across different gastrointestinal (GI) cancers. In this study we aim to identify small drugs for which miR-21 may be considered a biomarker of sensitivity.
Methods: High throughput screening technologies (HST) was applied in RKO colorectal cancer (CRC) cells engineered to knock out miR-21 locus (miR-21KO) and parental isogenic wild type (WT) cells, as well as 6 Biliary Tract Cancer (BTC) cell lines that were NGSed for a panel of 64 genes. Library included 484 small molecules that were screened at 3 doses against each cell line in triplicate. Transient miR-21 inhibition was achieved by reverse transfection. Stable doxycycline-activated miR-21 expressing clones of BTC and CRC cells were generated with doxycycline-inducible TRIPZ lentiviral vectors.
Results: Twenty four drugs reduced cell viability compared to DMSO at a greater extent in miR-21KO RKO in comparison to WT cells. Enrichment in HSP-90 inhibitors (including 17-DMAG, 17-AAG and AUY-922) was noticed, suggesting that miR-21 may be involved in resistance to HSP-90 inhibition. HST in BTC cells showed enrichment of HSP-90 inhibitors independently on mutational status. However IC50 to AUY-922 was correlated to baseline miR-21 expression in BTC cells. Transient inhibition of miR-21 enhanced sensitivity to AUY-922 in BTC cells. AUY-922 IC50 was 35nM for WT and 17nM for miR-21KO RKO cells. Knock-out of miR-21 in DLD-1 cells did not change sensitivity to AUY-922 in line with the lower baseline levels of miR-21 in DLD-1 wild type cells. However, the reduced levels of baseline miR-21 made them more sensitive to AUY-922 than RKO. Doxycycline-activated overexpression of miR-21 in miR-21KO DLD-1 cells conferred resistance to AUY-922. When co-cultured with non-infected miR-21KO DLD-1 cells, miR-21 overexpressing miR-21KO DLD-1 cells were able to drive cell growth in presence of AUY-922. To similar extent CCLP with enforced expression of miR-21 were more resistant compared to control cells; inactivation of the induction of miR-21 overexpression recovered sensitivity to the drug. HSP Array blot of AUY-922-treated cells with induced expression of miR-21 showed reduction of the co-chaperone HSP-40 protein expression compared to control cells.
Conclusions: Our data suggest the development of studies looking at the biomarker potential of miR-21 to guide treatment with HSP-90 inhibitors in GI cancers, as well as pursuing the combination with miR-21 inhibitors that may enhance the effect of the drug and avoid toxicity by enabling dose reduction.
Citation Format: Andrea Lampis, Luciano Cascione, Rosemary Burke, Paul Clarke, Michele Simbolo, Aldo Scarpa, Else Bosma, Sijia Yu, Rebecca Cole, Mark Stubbs, Swee Sharp, Rob Van Montfort, Jens C. Hahne, Matteo Fassan, Paul Workman, Nicola Valeri, Chiara Braconi. MiR-21 may serve as a predictive biomarker of response in the assessment of efficacy of HSP-90 inhibition in gastrointestinal (GI) cancers. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1069.