Abstract 2929: Exploratory evolved strategies that limit cancer growth for possible new therapeutic strategies
Authors: Abrahams Dominique , Hashim Arig Ibrahim , Luddy Kim , Gillies Robert , Gatenby Robert , Brown Joel 
Published: July 2017

Strong selection can promote mammalian evolution of a remarkably diverse phenotypic range over a short period of time. With appropriate selection forces, we tested the hypothesis that laboratory animals can evolve phenotypes that are resistant to the growth of implanted tumors. We propose that strong selection can produce evolution of different strategies to generate resistance to the growth of inoculated tumors,1. Changes in the supportive cell layer that decrease limited growth of cancer cell populations. 2. Increase of immunologic response to tumor antigens.

Hence, we examined the evolution of resistance in immuno-competent and immuno-deficient mice. Fixed number of cells from luciferase tagged LL/2 (Lewis lung carcinoma) cancer cells were implanted in groups of 10 male C57BL/6 and SCID mice. All tumor cells were obtained from frozen samples of a single large tumor population to eliminate any contribution from tumor cell evolution. Tumor growth in each animal was measured by calipers and luciferase imaging. The two animals that exhibited the slowest tumor growth in each cohort were bred with females from the same litter. Over 12 generations, the selection pressures resulted in emergence of SCID mice in which tumors grew at approximately 1/10th the rate compared their initial generation. The immunocompetent C57BL/6 mice evolved significant changes in immune-mediated parental tumor cell killing but this has yet resulted in significantly delayed tumor growth because the LL/2 cells rapidly evolve resistance strategies. Injection of the same tumor cells into unevolved wild type strains of both SCID and C57BL/6 mice produced rapid tumor growth identical to that seen in the first generation.

Using immunohistochemistry we observed decrease in blood supply among generations, proliferation, and apoptosis while no differences were observed in Glut-1 and CA-9 expression. To investigate this observation, first we examined changes in the molecular characteristics of the tumor cells during in-vivo growth by microarray on tumor cells isolated from “final” adapted cell population(s) in the animals that have been selected to decrease tumor growth compared to the wild type as well as normal cells in parallel. Our results showed that there are 158 genes different between tumors growing in the evolved and selected mice, among them are genes involved in extracellular matrix organization, hence we used second-harmonic generation (SHG) microscopy to image and quantify collagen,

our results showed significant increase in collagen at the edge as well as the core of the tumor of the evolved mice compared to wild type mice.

In conclusion our evolutionary study has reduced tumor growth in SCID mice but has had limited success in the C57BL/6. The SCID mice adaptation to tumor was likely through alteration in function of the supportive cell layer (Collagen), thus generating biomechanical forces and protective cellular events during tumor progression at early stages.

Citation Format: Dominique Abrahams, Arig Ibrahim Hashim, Kim Luddy, Robert Gillies, Robert Gatenby, Joel Brown. Exploratory evolved strategies that limit cancer growth for possible new therapeutic strategies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2929. doi:10.1158/1538-7445.AM2017-2929