Abstract P5-04-08: Timing provides context for the paradoxical effects of AMPK activation in ER+ breast cancer: Suppressing growing tumors, but promoting dormant tumor cell survival and recurrence

Precision oncology requires delivering the right drug to the right patient at the right time, but “time” is rarely studied preclinically before a drug enters a particular clinical setting. Despite showing efficacy against recurrent/metastatic solid tumors, drugs sometimes fail to prevent tumor recurrence when given (neo)adjuvantly. The biology and microenvironments of overt tumors likely differ substantially from dormant cancer cells. The development of preclinical models to investigate clinically dormant disease will increase understanding of residual tumor cell biology and enable the development of therapeutics for rational adjuvant trials. Despite treatment with adjuvant anti-estrogen therapies, ˜30% of patients with ER+ breast cancer (BC) experience recurrence. In contrast to other BC subtypes, ER+ relapses occur late, often appearing years to decades after initial diagnosis and treatment. This delay suggests that ER+ BC cells can undergo extended periods of clinical dormancy. We developed novel, clinically relevant xenograft models of dormancy in ER+ BC. Low systemic levels of estrogens in mice can be further suppressed by ovariectomy, mimicking the effects of aromatase inhibitor (AI)-induced estrogen deprivation (ED) therapy. In ovariectomized mice, luciferase-labeled MCF-7, HCC-1428, HCC-1500, and MDA-MB-415 cells, as well as the HCI-017 PDX model, formed palpable orthotopic tumors upon 17b-estradiol supplementation. ED induced rapid tumor regression and decreased bioluminescent signal. However, a small proportion of ER+ BC cells survived ED for >1 year in a clinically dormant, growth-suppressed state. This residual cell population stabilized after ˜90 days of ED, as evidenced by stabilization of bioluminescent signal. Transcriptional and immunohistochemical analyses revealed significant upregulation of AMP-activated protein kinase (AMPK)-alpha-2 levels and activity in clinically dormant tumor cells compared to estrogen-driven or acutely ED xenografts. Dormant tumor cells were dependent upon AMPK activity for survival, as short-term pharmacologic inhibition of AMPK reduced residual bioluminescent signal. Metformin is an AMPK-activating drug approved for the treatment of diabetes. Metformin is currently being tested as an anti-cancer agent in many clinical trials at various points in the disease progression of diverse cancer types. In our models of clinically dormant ER+ BC, AMPK activation via metformin slowed ED-induced tumor regression, promoted residual tumor cell survival, and caused earlier tumor regrowth. In vitro studies indicated that metformin promotes cell survival during ED by enhancing fatty acid β-oxidation. Conversely, metformin treatment slowed estrogen-driven tumor growth, in agreement with prior observations that metformin slows growth of various tumor subtypes. These findings suggest that AMPK activation may be efficacious against growing tumors, but deleterious when used in combination with drugs that suppress tumor growth and induce regression. More broadly, this work highlights the issue that the time in a disease course needs to be considered when testing potential anti-cancer agents such as AMPK modulators. Citation Format: Miller TW, Hampsch RA, McCleery CF, Wells JD, Fields JL, Dillon LM, Shee K. Timing provides context for the paradoxical effects of AMPK activation in ER+ breast cancer: Suppressing growing tumors, but promoting dormant tumor cell survival and recurrence [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-04-08.