Sunday, November 13, 2016

Novel computational method for predicting polytherapy switching strategies to overcome tumor heterogeneity and evolution

Novel computational method for predicting polytherapy switching strategies to overcome tumor heterogeneity and evolution

 

Vanessa D JonssonColin M Blakely, Luping Lin, Saurabh Asthana, Victor Olivas, Matthew A Gubens, Nikolai Matni, Boris C Bastian, Barry S Taylor, John C Doyle, Trever G Bivona
 

Abstract

The success of targeted cancer therapy is limited by drug resistance that can result from tumor genetic heterogeneity. The current approach to address resistance typically involves initiating a new treatment after clinical/radiographic disease progression, ultimately resulting in futility in most patients. Towards a potential alternative solution, we developed a novel computational framework that uses human cancer profiling data to systematically identify dynamic, pre-emptive, and sometimes non-intuitive treatment strategies that can better control tumors in real-time. By studying lung adenocarcinoma clinical specimens and preclinical models, our computational analyses revealed that the best anti-cancer strategies addressed existing resistant subpopulations as they emerged dynamically during treatment. In some cases, the best computed treatment strategy used unconventional therapy switching while the bulk tumor was responding, a prediction we confirmed in vitro. The new framework presented here could guide the principled implementation of dynamic molecular monitoring and treatment strategies to improve cancer control.

 

Monday, October 24, 2016

Optimal structure of heterogeneous stem cell niche: The importance of cell migration in delaying tumorigenesis

Optimal structure of heterogeneous stem cell niche: The importance of cell migration in delaying tumorigenesis

Leili ShahriyariAli Mahdipour Shirayeh

Abstract

Studying the stem cell niche architecture is a crucial step for investigating the process of oncogenesis and obtaining an effective stem cell therapy for various cancers. Recently, it has been observed that there are two groups of stem cells in the stem cell niche collaborating with each other to maintain tissue homeostasis. One group comprises the border stem cells, which is responsible to control the number of non-stem cells as well as stem cells. The other group, central stem cells, regulates the stem cell niche. In the present study, we develop a bi-compartmental stochastic model for the stem cell niche to study the spread of mutants within the niche. The analytic calculations and numeric simulations, which are in perfect agreement, reveal that in order to delay the spread of mutants in the stem cell niche, a small but non-zero number of stem cell proliferations must occur in the central stem cell compartment. Moreover, the migration of border stem cells to the central stem cell compartment delays the spread of mutants. Furthermore, the fixation probability of mutants in the stem cell niche is independent of types of stem cell division as long as all stem cells do not divide fully asymmetrically. Additionally, the progeny of central stem cells have a much higher chance than the progeny of border stem cells to take over the entire niche.

Thursday, October 13, 2016

3D Hybrid Modelling of Vascular Network Formation


3D hybrid modeling of vascular network formation


Abstract
We develop an agent-based model of vasculogenesis, the de novo formation of blood vessels. Endothelial cells in the vessel network are viewed as linearly elastic spheres and are of two types: vessel elements are contained within the network; tip cells are located at endpoints. Tip cells move in response to forces due to interactions with neighbouring vessel elements, the local tissue environment, chemotaxis and a persistence force modeling their tendency to continue moving in the same direction. Vessel elements experience similar forces but not chemotaxis. An angular persistence force representing local tissue interactions stabilises buckling instabilities due to proliferation. Vessel elements proliferate, at rates that depend on their degree of stretch: elongated elements proliferate more rapidly than compressed elements. Following division, new cells are more likely to form new sprouts if the parent vessel is highly compressed and to be incorporated into the parent vessel if it is stretched. 
Model simulations reproduce key features of vasculogenesis. Parameter sensitivity analyses reveal significant changes in network size and morphology on varying the chemotactic sensitivity of tip cells, and the sensitivities of the proliferation rate and sprouting probability to mechanical stretch. Varying chemotactic sensitivity also affects network directionality. Branching and network density are influenced by the sprouting probability. Glyphs depicting multiple network properties show how network quantities change over time and as model parameters vary. We also show how glyphs constructed from in vivo data could be used to discriminate between normal and tumour vasculature and, ultimately, for model validation. We conclude that our biomechanical hybrid model generates vascular networks similar to those generated from in vitro and in vivo experiments.

Link:arXiv:1610.00661 [q-bio.QM]
 

Monday, September 19, 2016

Collateral sensitivity networks reveal evolutionary instability and novel treatment strategies in ALK mutated non-small cell lung cancer.

Collateral sensitivity networks reveal evolutionary instability and novel treatment strategies in ALK mutated non-small cell lung cancer.

Andrew DhawanDaniel NicholFumi KinoseMohamed E. AbazeedAndriy MarusykEric B.HauraJacob G. Scott

Abstract

Drug resistance remains an elusive problem in cancer therapy, particularly with novel targeted therapy approaches. Much work is currently focused upon the development of an increasing arsenal of targeted therapies, towards oncogenic driver genes such as ALK-EML4, to overcome the inevitable resistance that develops as therapies are continued over time. The current clinical paradigm after failure of first line ALK TKI is to administer another drug in the same class. As to which drug however, the answer is uncertain, as clinical evidence is lacking. To address this shortcoming, we evolved resistance in an ALK rearranged non-small cell lung cancer line (H3122) to a panel of 4 ALK tyrosine kinase inhibitors used in clinic, and performed a collateral sensitivity analysis to each of the other drugs. We found that all of the ALK inhibitor resistant cell lines displayed a significant cross-resistance to all other ALK inhibitors. To test for the stability of the resistance phenotypes, we evaluated the ALK-inhibitor sensitivities after drug holidays of varying length (1, 3, 7, 14, and 21 days). We found the resistance patterns to be stochastic and dynamic, with few conserved patterns. This unpredictability led us to an expanded search for treatment options for resistant cells. In this expansion, we tested a panel of 6 more anti-cancer agents for collateral sensitivity among the resistant cells, uncovering a multitude of possibilities for further treatment, including cross-sensitivity to several standard cytotoxic therapies as well as the HSP-90 inhibitors. Taken together, these results imply that resistance to targeted therapy in non-small cell lung cancer is truly a moving target; but also one where there are many opportunities to re-establish sensitivities where there was once resistance.

Thursday, September 15, 2016

Reconstructing phylogenies of metastatic cancers

Reconstructing phylogenies of metastatic cancers

Johannes G ReiterAlvin P Makohon-Moore, Jeffrey M Gerold, Ivana Bozic, Krishnendu Chatterjee, Christine A Iacobuzio-Donahue, Bert Vogelstein, Martin A Nowak

Abstract

Reconstructing the evolutionary history of metastases is critical for understanding their basic biological principles and has profound clinical implications. Genome-wide sequencing data has enabled modern phylogenomic methods to accurately dissect subclones and their phylogenies from noisy and impure bulk tumor samples at unprecedented depth. However, existing methods are not designed to infer metastatic seeding patterns. We have developed a tool, called Treeomics, that utilizes Bayesian inference and Integer Linear Programming to reconstruct the phylogeny of metastases. Treeomics allowed us to infer comprehensive seeding patterns for pancreatic, ovarian, and prostate cancers. Moreover, Treeomics correctly disambiguated true seeding patterns from sequencing artifacts; 7% of variants were misclassified by conventional statistical methods. These artifacts can skew phylogenies by creating illusory tumor heterogeneity among distinct samples. Last, we performed in silico benchmarking on simulated tumor phylogenies across a wide range of sample purities (30-90%) and sequencing depths (50-800x) to demonstrate the high accuracy of Treeomics compared to existing methods.

Thursday, August 25, 2016

Ordinary Differential Equations in Cancer Biology

Ordinary Differential Equations in Cancer Biology

Margaret P Chapman, Claire J. Tomlin

Abstract


Ordinary differential equations (ODEs) provide a classical framework to model the dynamics of biological systems, given temporal experimental data. Qualitative analysis of the ODE model can lead to further biological insight and deeper understanding compared to traditional experiments alone. Simulation of the model under various perturbations can generate novel hypotheses and motivate the design of new experiments. This short paper will provide an overview of the ODE modeling framework, and present examples of how ODEs can be used to address problems in cancer biology.

Monday, August 8, 2016

Cancer treatment scheduling and dynamic heterogeneity in social dilemmas of tumour acidity and vasculature

Cancer treatment scheduling and dynamic heterogeneity in social dilemmas of tumour acidity and vasculature

Artem Kaznatcheev, Robert Vander Velde, Jacob G Scott, David Basanta
 

Abstract

Background: Tumours are diverse ecosystems with persistent heterogeneity in various cancer hallmarks like self-sufficiency of growth factor production for angiogenesis and reprogramming of energy-metabolism for aerobic glycolysis. This heterogeneity has consequences for diagnosis, treatment, and disease progression. Methods: We introduce the double goods game to study the dynamics of these traits using evolutionary game theory. We model glycolytic acid production as a public good for all tumour cells and oxygen from vascularization via VEGF production as a club good benefiting non-glycolytic tumour cells. This results in three viable phenotypic strategies: glycolytic, angiogenic, and aerobic non-angiogenic. Results: We classify the dynamics into three qualitatively distinct regimes: (1) fully glycolytic, (2) fully angiogenic, or (3) polyclonal in all three cell types. The third regime allows for dynamic heterogeneity even with linear goods, something that was not possible in prior public good models that considered glycolysis or growth-factor production in isolation. Conclusion: The cyclic dynamics of the polyclonal regime stress the importance of timing for anti-glycolysis treatments like lonidamine. The existence of qualitatively different dynamic regimes highlights the order effects of treatments. In particular, we consider the potential of vascular renormalization as a neoadjuvant therapy before follow up with interventions like buffer therapy.

 

 

Thursday, June 16, 2016

The Evolutionary Trade-off between Stem Cell Niche Size, Aging, and Tumorigenesis

The Evolutionary Trade-off between Stem Cell Niche Size, Aging, and Tumorigenesis

Vincent L. Cannataro, Scott A. McKinley, Colette M. St. Mary

Abstract

Many epithelial tissues within large multicellular organisms are continually replenished by small independent populations of stem cells. These stem cells divide within their niches and differentiate into the constituent cell types of the tissue, and are largely responsible for maintaining tissue homeostasis. Mutations can accumulate in stem cell niches and change the rate of stem cell division and differentiation, contributing to both aging and tumorigenesis. Here, we create a mathematical model of the intestinal stem cell niche, crypt system, and epithelium. We calculate the expected effect of fixed mutations in stem cell niches and their expected effect on tissue homeostasis throughout the intestinal epithelium over the lifetime of an organism. We find that, due to the small population size of stem cell niches, fixed mutations are expected to accumulate via genetic drift and decrease stem cell fitness, leading to niche and tissue attrition, and contributing to organismal aging. We also explore mutation accumulation at various stem cell niche sizes, and demonstrate that an evolutionary trade-off exists between niche size, tissue aging, and the risk of tumorigenesis; where niches exist at a size that minimizes the probability of tumorigenesis, at the expense of accumulating deleterious mutations due to genetic drift. Finally, we show that the probability of tumorigenesis and the extent of aging trade-off differently depending on whether mutational effects confer a selective advantage, or not, in the stem cell niche.

Thursday, June 9, 2016

Evolutionary dynamics of CRISPR gene drives

Evolutionary dynamics of CRISPR gene drives

Charleston Noble, Jason Olejarz, Kevin Esvelt, George Church, Martin Nowak

Abstract

The alteration of wild populations has been discussed as a solution to a number of humanity's most pressing ecological and public health concerns. Enabled by the recent revolution in genome editing, CRISPR gene drives, selfish genetic elements which can spread through populations even if they confer no advantage to their host organism, are rapidly emerging as the most promising approach. But before real-world applications are considered, it is imperative to develop a clear understanding of the outcomes of drive release in nature. Toward this aim, we mathematically study the evolutionary dynamics of CRISPR gene drives. We demonstrate that the emergence of drive-resistant alleles presents a major challenge to previously reported constructs, and we show that an alternative design which selects against resistant alleles greatly improves evolutionary stability. We discuss all results in the context of CRISPR technology and provide insights which inform the engineering of practical gene drive systems.

 

 

Tuesday, June 7, 2016

tHapMix: simulating tumour samples through haplotype mixtures

tHapMix: simulating tumour samples through haplotype mixtures

Sergii Ivakhno, Camilla Colombo, Stephen Tanner, Philip Tedder, Stefano Berri, Anthony J. Cox
 

Abstract

Motivation: Large-scale rearrangements and copy number changes combined with different modes of clonal evolution create extensive somatic genome diversity, making it difficult to develop versatile and scalable variant calling tools and create well-calibrated benchmarks. Results: We developed a new simulation framework tHapMix that enables the creation of tumour sam-ples with different ploidy, purity and polyclonality features. It easily scales to simulation of hundreds of somatic genomes, while re-use of real read data preserves noise and biases present in sequencing platforms. We further demonstrate tHapMix utility by creating a simulated set of 140 somatic genomes and showing how it can be used in training and testing of somatic copy number variant calling tools. Availability and implementation: tHapMix is distributed under an open source license and can be downloaded from https://github.com/Illumina/tHapMix .

 

 

Friday, May 27, 2016

Non-linear tumor-immune interactions arising from spatial metabolic heterogeneity

Non-linear tumor-immune interactions arising from spatial metabolic heterogeneity

Mark Robertson-TessiRobert J GilliesRobert A GatenbyAlexander RA Anderson

Abstract

A hybrid multiscale mathematical model of tumor growth is used to investigate how tumoral and microenvironmental heterogeneity affect the response of the immune system. The model includes vascular dynamics and evolution of metabolic tumor phenotypes. Cytotoxic T cells are simulated, and their effect on tumor growth is shown to be dependent on the structure of the microenvironment and the distribution of tumor phenotypes. Importantly, no single immune strategy is best at all stages of tumor growth.

http://biorxiv.org/content/early/2016/05/04/038273