Abstract 2572: Metronomic scheduling: a promising strategy to manage intratumor heterogeneity and control treatment resistance
Authors: Carre Manon , Bondarenko Maryna , Montero Marie-Pierre , Chapuisat Guillemette , Benabdallah Assia , Le Grand Marion , Braguer Diane , Andre Nicolas , Pasquier Eddy 
Published: August 2015

Abstract
To date, the emergence of drug resistance is never dealt with until it occurs. Yet, studies have shown that treatment-sensitive and -resistant malignant cell subpopulations coexist within the same tumor. Being able to decipher their complex relationship and characterize the impact of intratumor heterogeneity on treatment efficacy is essential to understand tumor biology and define adaptive therapeutic strategies to overcome resistance. We developed 2D and 3D spheroid co-culture models to analyze the expansion of A549 (DsRed expressing) and A549-EpoB40 (GFP expressing) cells over time (for up to one month), which are drug-sensitive and -resistant lung carcinoma cells, respectively. The fluorescent signals were recorded daily to quantify and localize each tumor subpopulation. We showed that the sensitive cells constitute the predominant subpopulation in the absence of any chemotherapeutic treatment, since they have an unexpected suppressive effect on the growth of resistant cells (-79% at day 14, p&lt;0.001). Using cell-free conditioned medium and Transwell systems, we demonstrated that this inhibition was independent from cell-to-cell interactions. We then showed that a conventional treatment schedule that eradicates the sensitive cells (cytotoxic dose, once a week) irremediably resulted in the selection of the resistant subpopulation in the different co-culture models. Conversely, a metronomic treatment schedule (ten times lower doses of drugs, five times a week) was an effective strategy to suppress the growth of sensitive cells (100-fold decrease vs untreated control at day 14, p&lt;0.001) while maintaining intra-tumor heterogeneity and thus preventing the selection of resistant cells (-85% vs conventional schedule, p&lt;0.001). Similar trends were observed with HT29 colon cancer cells sensitive or resistant to oxaliplatin. Our results thus support the fact that daily low doses of drugs would lead to better results than high cytotoxic doses in the long term, to overcome problems of drug resistant cell selection that underlies many cases of cancer recurrence. Mathematical modeling of cell expansion and response to treatment is in progress to further define situations of tumor heterogeneity where resistant cells could be controlled by metronomic-based treatment schedules, to achieve a stable or reduced global tumor population. Mathematical models that support adaptive therapeutic approaches, by changing the drug doses and schedule over time, will also likely help us to optimize the global efficacy of chemotherapeutic agents and targeted therapies in heterogeneous cancer populations. Leading-edge technologies such as 3D imaging and high sensitivity genomics will be required, in the near future, to further unravel the complex interactions among cancer cell subpopulations and increase knowledge of the influence of intra-tumor heterogeneity on treatment response.
Citation Format: Manon Carre, Maryna Bondarenko, Marie-Pierre Montero, Guillemette Chapuisat, Assia Benabdallah, Marion Le Grand, Diane Braguer, Nicolas Andre, Eddy Pasquier. Metronomic scheduling: a promising strategy to manage intratumor heterogeneity and control treatment resistance. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2572. doi:10.1158/1538-7445.AM2015-2572