{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,17]],"date-time":"2026-03-17T07:55:48Z","timestamp":1773734148970,"version":"3.50.1"},"reference-count":43,"publisher":"MDPI AG","issue":"6","license":[{"start":{"date-parts":[[2026,3,14]],"date-time":"2026-03-14T00:00:00Z","timestamp":1773446400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100000024","name":"Canadian Institutes of Health Research","doi-asserted-by":"crossref","id":[{"id":"10.13039\/501100000024","id-type":"DOI","asserted-by":"crossref"}]},{"DOI":"10.13039\/501100001804","name":"Canada Research Chairs program","doi-asserted-by":"crossref","award":["#233198"],"award-info":[{"award-number":["#233198"]}],"id":[{"id":"10.13039\/501100001804","id-type":"DOI","asserted-by":"crossref"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>CRISPR screens are a powerful functional genomics approach for identifying genes that confer sensitivity and resistance to anti-cancer therapies. CFI-402257 (luvixasertib, 2257) is a small molecule inhibitor of threonine tyrosine kinase (TTK), a promising therapeutic target in genomically unstable cancers due to its critical role in establishing the spindle assembly checkpoint (SAC) during mitosis. To inform its ongoing development and evaluation in clinical trials, we sought to use CRISPR activation (i.e., gain of function) screens to identify cellular mechanisms of resistance to 2257 in models of triple-negative breast cancer (TNBC). In vitro screens conducted in two TNBC cell lines nominated ABCG2 as the top resistance-conferring gene in both models. Validation studies assessing clonogenic survival and apoptosis confirmed that ABCG2 overexpression enhanced TNBC resistance to 2257 in vitro, while knockdown enhanced sensitivity. These findings suggest that 2257 is a substrate of ABCG2\u2019s drug efflux activity. However, overexpression of ABCG2 failed to confer resistance to 2257 in TNBC xenografts grown in mice and treated with a moderately active dose and schedule. Our results highlight the potential impact of drug transporters in in vitro CRISPR screens and the importance of confirming the relevance of drug response mechanisms identified in cultured cells using in vivo models that recapitulate drug pharmacokinetics and pharmacodynamics.<\/jats:p>","DOI":"10.3390\/ijms27062665","type":"journal-article","created":{"date-parts":[[2026,3,16]],"date-time":"2026-03-16T10:10:43Z","timestamp":1773655843000},"page":"2665","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Genome-Wide CRISPR Screens Identify ABCG2-Mediated Drug Resistance to the Threonine Tyrosine Kinase (TTK) Inhibitor CFI-402257 in Breast Cancer"],"prefix":"10.3390","volume":"27","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-9262-7238","authenticated-orcid":false,"given":"Kelsie L.","family":"Thu","sequence":"first","affiliation":[{"name":"Keenan Research Centre for Biomedical Science, St. Michael\u2019s Hospital, Unity Health Toronto, Toronto, ON M5B 1X3, Canada"},{"name":"Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON M5S 3K3, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Soode","family":"Jafari","sequence":"additional","affiliation":[{"name":"Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2C4, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jennifer","family":"Silvester","sequence":"additional","affiliation":[{"name":"Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2C4, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jennifer","family":"Cruickshank","sequence":"additional","affiliation":[{"name":"Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2C4, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Isabel","family":"Soria-Bretones","sequence":"additional","affiliation":[{"name":"Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2C4, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kelsey","family":"Hodgson","sequence":"additional","affiliation":[{"name":"Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2C4, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Chantal","family":"Tobin","sequence":"additional","affiliation":[{"name":"Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2C4, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jillian","family":"Haight","sequence":"additional","affiliation":[{"name":"Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2C4, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0009-0009-7423-6028","authenticated-orcid":false,"given":"Asa P. Y.","family":"Lau","sequence":"additional","affiliation":[{"name":"Keenan Research Centre for Biomedical Science, St. Michael\u2019s Hospital, Unity Health Toronto, Toronto, ON M5B 1X3, Canada"},{"name":"Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON M5S 3K3, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Tessa","family":"Bray","sequence":"additional","affiliation":[{"name":"Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2C4, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Drew","family":"Wakeham","sequence":"additional","affiliation":[{"name":"Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2C4, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Mark R.","family":"Bray","sequence":"additional","affiliation":[{"name":"Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2C4, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6766-861X","authenticated-orcid":false,"given":"Tak W.","family":"Mak","sequence":"additional","affiliation":[{"name":"Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2C4, Canada"},{"name":"Department of Immunology, University of Toronto, Toronto, ON M5S 3K3, Canada"},{"name":"Department of Medical Biophysics, University of Toronto, Toronto, ON M5G 2C4, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1080-0998","authenticated-orcid":false,"given":"David W.","family":"Cescon","sequence":"additional","affiliation":[{"name":"Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2C4, Canada"},{"name":"Institute of Medical Science, University of Toronto, Toronto, ON M5S 3K3, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,3,14]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"543","DOI":"10.1038\/s41580-023-00593-z","article-title":"Principles and Dynamics of Spindle Assembly Checkpoint Signalling","volume":"24","author":"McAinsh","year":"2023","journal-title":"Nat. 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