Abstract B11: Adaptive therapy modifies tumor vascularity
Authors: Enriquez-Navas Pedro M. , Wojtkowiak Jonathan , Ruiz Epi , Hassan Sabrina , Gillies Robert J. , Gatenby Robert A. 
Published: December 2015

Introduction: Disseminated cancers are typically treated with the highest possible dose of drug (i.e. maximum tolerated dose) to achieve the goal of killing as many tumor cells as possible. However, these therapies eventually fail due to emergence of resistant clones. We have predicted, using mathematical models of Darwinian dynamics, that treatment regimens that adapt the dosing to the tumor spatial variability and tumor microenvironment, can retard the emergence of chemoresistance. Here we present an evolutionary-guided treatment strategy (Adaptive Therapy, AT) designed to maintain stable chemosensitive populations while limiting the proliferation of chemoresistant clones by exploiting the fitness cost of the resistant phenotype. We also evaluated how this novel treatment strategy modifies tumor vascularity.

Methods: Four cohorts (composed by 12, 11, 13, and 10 mice, respectively) of nude mice were injected with 10x106 MDA-MB-231 (triple-negative breast cancer) cells in the mammary fat pad. Control animals didn't receive any treatment. Mice under standard therapy received 20mg/kg of Tamoxifen twice per week for a total of 5 times. We defined two different Tamoxifen AT algorithms (Table 1), under which AT mice were treated. Table 1.Adaptive Therapy treatment algorithmsAT-1Initial Dose = 20 mg/kg (highest dose)&gt; If VT(n)≤ .8*VT(n-1) -&gt;Dose decreased by 50%&gt; If VT(n)≥ 1.2*VT(n-1) -&gt;Dose increased by 50%&gt; If the tumor volume is within 20% range, we will apply same dose as previous dose.Lower Limit: 150mm3 and skip the doseAT-2Starting dose = 15 mg/kg&gt; If VT(n)≥ 1.25*VT(n-2) -&gt;Dose = 15 mg/kg&gt; If VT(n) &lt; 1.25*VT(n-2) -&gt;Skip Dose

When the tumors achieve the volume of, approximately 300 mm3, MRI T2 and Diffusion Weighted acquisitions were performed on a horizontal Agilent ASR 310 7T scanner, with 205/120/HDS gradients and 310 mm bore to determine volume and cellularity, respectively. Thereafter, dynamic contrast enhanced (DCE-) MRI was preformed following bolus of 0.1mmol/kg Magnevist to assess distribution of blood flow. Images were processed with different in-house developed MATLAB scripts to obtain reliable information from these images. At the end of the monitoring time, tumors were collected and processed for H&E and CD31 immunohistochemistry staining to study the viable and necrotic tissue, and vessel presence, respectively. The slides were examined using the Aperio ScanScope XT microscope. Using different selected slides, an algorithm was built in order to analyze all tissue samples (software Spectrum Version 10.2.5.2352, Aperio Technologies with a pixel-wise resolution.

Results and Discussion: Tumor growth was monitored during the treatment period using the MRI techniques previously described. The AT treatment algorithm has been modified to fine tune the dose and scheduling based on tumor volume. Among these three protocols (2 AT and one ST), AT-1 resulted in the most significant cancer control. AT-1 protocol was able to maintain tumors at a small size for &gt;120 days. Also, AT-1 has demonstrated to decrease the percent tumor necrosis (data not shown), and increase vascular density. New experiments and data analysis are currently undergoing in order to get more information and a deeper insight on how the AT can benefit the in-vivo cancer treatment.

Conclusion: In summary, initial results demonstrate that AT, guided by MRI measurement of tumor volume, can maintain a stable small tumor burden with prolonged progression free survival compared to standard high dose therapy. Also, AT is able to maintain the lower necrotic volume and the higher vessel density, which, in addition with the tumor volume, was correlated with tumor stabilization.

Citation Format: Pedro M. Enriquez-Navas, Jonathan Wojtkowiak, Epi Ruiz, Sabrina Hassan, Robert J. Gillies, Robert A. Gatenby. Adaptive therapy modifies tumor vascularity. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Angiogenesis and Vascular Normalization: Bench to Bedside to Biomarkers; Mar 5-8, 2015; Orlando, FL. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl):Abstract nr B11.