Abstract 2437: Genotypic determinants of metastatic fitness: A delicate balance between passenger and driver mutations
Authors: Scott Jacob G. , McFarland Christopher M. , Wojtkowiak Jonathon W. , Basanta David , Anderson Alexander R. A. , Gillies Robert J. , Morse David L. , Leonid Mirny A. 
Published: June 2012

Background: The transformation of cancer from localized to metastatic is a highly lethal and poorly understood process. Evolutionary dynamics drive the primary tumor population, but also are important in the selection of successful metastases. A gene-centric mathematical model derived from population genetics was developed by which stochastically accrued mutations could either strongly benefit (driver mutation) or weakly detriment (passenger) a cancer cell's reproductive fitness. We modeled cells starting at the initial site of tumorigenesis and followed them to the site of metastasis and observed metastatic deposits in silico. We found that, on average, greater mutational load correlates with lesser metastatic fitness and endeavored to test this hypothesis experimentally.

Materials/Methods:

Experiment: MDA-mb-231 cells were stably transfected with luciferase by established methods. This cell line was then split and grown under two conditions for 3 months, one at a pH of 7.4 and one at a pH of 6.7.

In vitro migration was assayed using a modified Boyden chamber in the Excelligence cell analysis system. Upper chambers contained pH 7.4 serum free media containing MDA-MB 231 parental cells (pH 7.4) and low pH adapted MDA-mb-231 cells.

In vivo metastatic fitness was determined by injecting the two cell lines into the tail vein of SCID mice (n=19). The animals were imaged weekly to collect optical bioluminescence using an IVIS Small Animal Imaging System. Experimental metastasis to the lung was quantified using the Living Image Software.

Results: In vitro experiments show a lower migration index as measured by the Excelligence system (pH 7.4: mean cell index 0.5075, 95% CI 0.3591-0.6608, pH 6.7: mean cell index 0.2091, 95% CI 0.1479-0.2702, p&lt;0.05). In vivo metastatic fitness was significantly lower as measured by the bioluminescence assay (pH 7.4: 5.26 ± 1.37 x105 photons/sec, pH 6.7: 1.53 ± 0.211 x105 photons/sec, p&lt;0.05).

Conclusions: Acidic conditions have been shown by a number of groups to be mutagenic and clastogenic, resulting in significant genomic instability. It is therefore assumed that the cells grown under the acidic conditions over long time periods will accrue significantly greater amounts of mutations than those grown in physiologic pH. These putatively more mutated cells showed significantly less metastatic fitness as measured by both in vitro migration and in vivo metastasis assays, validating the hypothesis generated by the mathematical model. Future work will be focused on validating the levels of mutation by SNP chip array as well as further experiments using alternative methods of mutagenesis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2437. doi:10.1158/1538-7445.AM2011-2437