ABSTRACT
The mitotic inhibitor docetaxel (DTX) is often used to treat endocrine-refractory metastatic breast cancer, but initial responses are mitigated as patients eventually have disease progression. Using a cohort of ex vivo cultures of circulating tumor cells (CTCs) from patients with heavily pretreated breast cancer (n=18), we find two distinct patterns of DTX susceptibility, independent of clinical treatment history. In CTCs cultured from some patients, treatment with a single dose of DTX results in complete cell killing, associated with accumulation of non-viable polyploid (≥8N) cells arising from endomitosis. In others, a transient viable drug-tolerant persister (DTP) population emerges, ultimately enabling renewed proliferation of CTCs with preserved parental cell ploidy and DTX sensitivity. In these CTC cultures, efficient cell cycle exit generates a ≤4N drug-tolerant state dependent on CDKN1B (p27Kip1). Exposure to DTX triggers stabilization of CDKN1B through AKT-mediated phosphorylation at serine 10. Suppression of CDKN1B reduces the number of persister CTCs, increases ≥8N mitotic cells and abrogates regrowth after DTX exposure. Thus, CDKN1B-mediated suppression of endomitosis contributes to a reversible persister state following mitotic inhibitors in patient-derived treatment refractory breast cancer cells.
Summary in bullets
Transient DTX tolerant persister cells emerge in some patient-derived cultured CTCs.
DTX-tolerant persisters restrict endoreduplication and polyploidy through CDKN1 (p27kip1).
DTX exposure induces CDKN1B stabilization through AKT mediated phosphorylation at serine 10.
Suppression of polyploidy underlies a drug tolerant persister state specific to mitotic inhibitors.
Competing Interest Statement
Massachusetts General Hospital (MGH) has applied for patents regarding the CTC-iChip technology and CTC detection signatures. S.M., and D.A.H. are cofounders and have equity in Tell-Bio, which is not related to this work. The interests of these authors were reviewed and managed by MGH and Mass General Brigham (MGB) in accordance with their conflict of interest policies. D.T.T. has received consulting fees from ROME Therapeutics, Sonata Therapeutics, and Tekla Capital. D.T.T. is a founder and has equity in ROME Therapeutics, PanTher Therapeutics and TellBio, Inc., which is not related to this work. D.T.T. is on the advisory board for ImproveBio, Inc. D.T.T. has received honorariums from Moderna and Ikena Oncology that are not related to this work. D.T.T. receives research support from ACD-Biotechne, AVA LifeScience GmbH, Incyte Pharmaceuticals, and Sanofi, which was not used in this work. D.T.T. interests were reviewed and are managed by Massachusetts General Hospital and Mass General Brigham in accordance with their conflict of interest policies. M.S.F received funding from Calico Life Sciences, Bristol-Myers Squibb, Istari Oncology and served as a consultant for Galvanize Therapeutics. W.H. has no conflict of interests.
Footnotes
Declaration of interests: Massachusetts General Hospital (MGH) has applied for patents regarding the CTC-iChip technology and CTC detection signatures. S.M., and D.A.H. are cofounders and have equity in Tell-Bio, which is not related to this work. The interests of these authors were reviewed and managed by MGH and Mass General Brigham (MGB) in accordance with their conflict of interest policies. D.T.T. has received consulting fees from ROME Therapeutics, Sonata Therapeutics, and Tekla Capital. D.T.T. is a founder and has equity in ROME Therapeutics, PanTher Therapeutics and TellBio, Inc., which is not related to this work. D.T.T. is on the advisory board for ImproveBio, Inc. D.T.T. has received honorariums from Moderna and Ikena Oncology that are not related to this work. D.T.T. receives research support from ACD-Biotechne, AVA LifeScience GmbH, Incyte Pharmaceuticals, and Sanofi, which was not used in this work. D.T.T.’s interests were reviewed and are managed by Massachusetts General Hospital and Mass General Brigham in accordance with their conflict of interest policies. M.S.F received funding from Calico Life Sciences, Bristol-Myers Squibb, Istari Oncology and served as a consultant for Galvanize Therapeutics. W.H. has no conflict of interests.
Contributions: E.H., D.A.H., and S.M. conceived the project and provided project leadership. B.S.W., B.C. and R.M., performed bioinformatics analyses. D.W., D.C., H.C.R. and D.B.F. assisted with molecular biology and biochemistry. E.A. assisted with flow cytometry. A.B. and T.D.D. collected, annotated and processed clinical samples. A.S., M.S.F. and D.T.T. provided RNA-seq support. J.K., X.I.H.L and W.H. provided mass spectrometry support.