What does physics have to do with cancer?

Physiological random processes in precision cancer therapy

Many different physiological processes affect the growth of malignant lesions and their response to therapy. Each of these processes is spatially and genetically heterogeneous; dynamically evolving in time; controlled by many other physiological processes, and intrinsically random and unpredictable. The objective of this paper is to show that all of these properties of cancer physiology can be treated in a unified, mathematically rigorous way via the theory of random processes. We treat each physiological process as a random function of position and time within a tumor, defining the joint statistics of such functions via the infinite-dimensional characteristic functional. The theory is illustrated by analyzing several models of drug delivery and response of a tumor to therapy. To apply the methodology to precision cancer therapy, we use maximum-likelihood estimation with Emission Computed Tomography (ECT) data to estimate unknown patient-specific physiological parameters, ultimately demonstrating how to predict the probability of tumor control for an individual patient undergoing a proposed therapeutic regimen.

Transport Barriers and Oncophysics in Cancer Treatment

Transport processes in cancer are the focus of transport oncophysics (TOP). In the TOP approach, the sequential negotiation of transport barriers is critical to both drug delivery and metastasis development. New and creative therapeutic opportunities are currently emerging, stimulated by the study of cancer hallmarks with the TOP approach.

Enhancing cancer immunotherapy through nanotechnology-mediated tumor infiltration and activation of immune cells

Cancer immunotherapy has become arguably the most promising advancement in cancer research and therapy in recent years. The efficacy of cancer immunotherapy is critically dependent on specific physiological and physical processes - collectively referred to as transport barriers - including the activation of T cells by antigen presenting cells, T cells migration to and penetration into the tumor microenvironment, and movement of nutrients and other immune cells through the tumor microenvironment. Nanotechnology-based approaches have great potential to help overcome these transport barriers. In this review, we discuss the ways that nanotechnology is being leveraged to improve the efficacy and potency of various cancer immunotherapies.

Model of vascular desmoplastic multispecies tumor growth

We present a three-dimensional nonlinear tumor growth model composed of heterogeneous cell types in a multicomponent-multispecies system, including viable, dead, healthy host, and extra-cellular matrix (ECM) tissue species. The model includes the capability for abnormal ECM dynamics noted in tumor development, as exemplified by pancreatic ductal adenocarcinoma, including dense desmoplasia typically characterized by a significant increase of interstitial connective tissue. An elastic energy is implemented to provide elasticity to the connective tissue. Cancer-associated fibroblasts (myofibroblasts) are modeled as key contributors to this ECM remodeling. The tumor growth is driven by growth factors released by these stromal cells as well as by oxygen and glucose provided by blood vasculature which along with lymphatics are stimulated to proliferate in and around the tumor based on pro-angiogenic factors released by hypoxic tissue regions. Cellular metabolic processes are simulated, including respiration and glycolysis with lactate fermentation. The bicarbonate buffering system is included for cellular pH regulation. This model system may be of use to simulate the complex interactions between tumor and stromal cells as well as the associated ECM and vascular remodeling that typically characterize malignant cancers notorious for poor therapeutic response.

Strategies for improving drug delivery: nanocarriers and microenvironmental priming

INTRODUCTION

The ultimate goal in the field of drug delivery is to exclusively direct therapeutic agents to pathological tissues in order to increase therapeutic efficacy and eliminate side effects. This goal is challenging due to multiple transport obstacles in the body. Strategies that improve drug transport exploit differences in the characteristics of normal and pathological tissues. Within the field of oncology, these concepts have laid the groundwork for a new discipline termed transport oncophysics. Areas covered: Efforts to improve drug biodistribution have mainly focused on nanocarriers that enable preferential accumulation of drugs in diseased tissues. A less common approach to enhance drug transport involves priming strategies that modulate the biological environment in ways that favor localized drug delivery. This review discusses a variety of priming and nanoparticle design strategies that have been used for drug delivery. Expert opinion: Combinations of priming agents and nanocarriers are likely to yield optimal drug distribution profiles. Although priming strategies have yet to be widely implemented, they represent promising solutions for overcoming biological transport barriers. In fact, such strategies are not restricted to priming the tumor microenvironment but can also be directed toward healthy tissue in order to reduce nanoparticle uptake.

The transformation of the nuclear nanoarchitecture in human field carcinogenesis

Morphological alterations of the nuclear texture are a hallmark of carcinogenesis. At later stages of disease, these changes are well characterized and detectable by light microscopy. Evidence suggests that similar albeit nanoscopic alterations develop at the predysplastic stages of carcinogenesis. Using the novel optical technique partial wave spectroscopic microscopy, we identified profound changes in the nanoscale chromatin topology in microscopically normal tissue as a common event in the field carcinogenesis of many cancers. In particular, higher-order chromatin structure at supranucleosomal length scales (20-200 nm) becomes exceedingly heterogeneous, a measure we quantify using the disorder strength (L_d ) of the spatial arrangement of chromatin density. Here, we review partial wave spectroscopic nanocytology clinical studies and the technology's promise as an early cancer screening technology.

Detecting Swelling States of Red Blood Cells by "Cell-Fluid Coupling Spectroscopy"

Red blood cells are "shaken" with a holographic optical tweezer array. The flow generated around cells due to the periodic optical forcing is measured with an optically trapped "detector" particle located in the cell vicinity. A signal-processing model that describes the cell's physical properties as an analog filter illustrates how cells can be distinguished from each other.

Post-nano strategies for drug delivery: Multistage porous silicon microvectors

Nanodelivery systems usually improve the biodistribution of drugs, leading to reduced side effects and enhanced therapeutic efficacy. However, only a small portion of the injected nanoparticle dose accumulates in pathological tissue. Challenges in drug delivery arise due to a multitude of transport obstacles in the body, including the endothelium, the extracellular matrix, and the cell membrane. In general, nanoparticles are designed to overcome only a few biological barriers, making them inadequate for localized drug delivery. Accordingly, a multifunctional and multicomponent systems are required to effectively address a wide variety of transport obstacles. A suitable approach to obtain high levels of multifunctionality is to bring together the nanoscale with the microscale, resulting in post-nano strategies for drug delivery. This review discusses several such post-nano approaches, with an emphasis on the multistage vector (MSV) platform. The MSV consists of three components on different spatial scales, each intended to address biological barriers that exist in a specific compartment in the body. The first stage vector is a microparticle that is designed to navigate in the vascular compartment. The second stage vector consists of nanoparticles that are released from the microparticle into the tissue interstitium, where they address biological barriers in extracellular and intracellular compartments. The final component of the system is a small molecule therapeutic agent. A new generation of microparticle-based strategies with expanded applications has recently been developed, including injectable nanoparticle generators and silicon particles for immunotherapy. Notably, the advantage of incorporating microstructures in drug delivery vehicles is apparent from the observation that superior functionality only appears on the microscale, highlighting the inherent functional limitations of nanostructures.

Bridging the gap between clinicians and systems biologists: from network biology to translational biomedical research

With the wealth of data accumulated from completely sequenced genomes and other high-throughput experiments, global studies of biological systems, by simultaneously investigating multiple biological entities (e.g. genes, transcripts, proteins), has become a routine. Network representation is frequently used to capture the presence of these molecules as well as their relationship. Network biology has been widely used in molecular biology and genetics, where several network properties have been shown to be functionally important. Here, we discuss how such methodology can be useful to translational biomedical research, where scientists traditionally focus on one or a small set of genes, diseases, and drug candidates at any one time. We first give an overview of network representation frequently used in biology: what nodes and edges represent, and review its application in preclinical research to date. Using cancer as an example, we review how network biology can facilitate system-wide approaches to identify targeted small molecule inhibitors. These types of inhibitors have the potential to be more specific, resulting in high efficacy treatments with less side effects, compared to the conventional treatments such as chemotherapy. Global analysis may provide better insight into the overall picture of human diseases, as well as identify previously overlooked problems, leading to rapid advances in medicine. From the clinicians’ point of view, it is necessary to bridge the gap between theoretical network biology and practical biomedical research, in order to improve the diagnosis, prevention, and treatment of the world’s major diseases.

The rich phase structure of a mutator model

We propose a modification of the Crow-Kimura and Eigen models of biological molecular evolution to include a mutator gene that causes both an increase in the mutation rate and a change in the fitness landscape. This mutator effect relates to a wide range of biomedical problems. There are three possible phases: mutator phase, mixed phase and non-selective phase. We calculate the phase structure, the mean fitness and the fraction of the mutator allele in the population, which can be applied to describe cancer development and RNA viruses. We find that depending on the genome length, either the normal or the mutator allele dominates in the mixed phase. We analytically solve the model for a general fitness function. We conclude that the random fitness landscape is an appropriate choice for describing the observed mutator phenomenon in the case of a small fraction of mutators. It is shown that the increase in the mutation rates in the regular and the mutator parts of the genome should be set independently; only some combinations of these increases can push the complex biomedical system to the non-selective phase, potentially related to the eradication of tumors.

Biomimetic carriers mimicking leukocyte plasma membrane to increase tumor vasculature permeability

Recent advances in the field of nanomedicine have demonstrated that biomimicry can further improve targeting properties of current nanotechnologies while simultaneously enable carriers with a biological identity to better interact with the biological environment. Immune cells for example employ membrane proteins to target inflamed vasculature, locally increase vascular permeability, and extravasate across inflamed endothelium. Inspired by the physiology of immune cells, we recently developed a procedure to transfer leukocyte membranes onto nanoporous silicon particles (NPS), yielding Leukolike Vectors (LLV). LLV are composed of a surface coating containing multiple receptors that are critical in the cross-talk with the endothelium, mediating cellular accumulation in the tumor microenvironment while decreasing vascular barrier function. We previously demonstrated that lymphocyte function-associated antigen (LFA-1) transferred onto LLV was able to trigger the clustering of intercellular adhesion molecule 1 (ICAM-1) on endothelial cells. Herein, we provide a more comprehensive analysis of the working mechanism of LLV in vitro in activating this pathway and in vivo in enhancing vascular permeability. Our results suggest the biological activity of the leukocyte membrane can be retained upon transplant onto NPS and is critical in providing the particles with complex biological functions towards tumor vasculature.

Intravital Microscopy Imaging Approaches for Image-Guided Drug Delivery Systems

Rapid technical advances in the field of non-linear microscopy have made intravital microscopy a vital pre-clinical tool for research and development of imaging-guided drug delivery systems. The ability to dynamically monitor the fate of macromolecules in live animals provides invaluable information regarding properties of drug carriers (size, charge, and surface coating), physiological, and pathological processes that exist between point-of-injection and the projected of site of delivery, all of which influence delivery and effectiveness of drug delivery systems. In this Review, we highlight how integrating intravital microscopy imaging with experimental designs (in vitro analyses and mathematical modeling) can provide unique information critical in the design of novel disease-relevant drug delivery platforms with improved diagnostic and therapeutic indexes. The Review will provide the reader an overview of the various applications for which intravital microscopy has been used to monitor the delivery of diagnostic and therapeutic agents and discuss some of their potential clinical applications.

Effect of Actin Organization on the Stiffness of Living Breast Cancer Cells Revealed by Peak-Force Modulation Atomic Force Microscopy

We study the correlation between cytoskeleton organization and stiffness of three epithelial breast cancer cells lines with different degrees of malignancy: MCF-10A (healthy), MCF-7 (tumorigenic/noninvasive), and MDA-MB-231 (tumorigenic/invasive). Peak-force modulation atomic force microscopy is used for high-resolution topography and stiffness imaging of actin filaments within living cells. In healthy cells, local stiffness is maximum where filamentous actin is organized as well-aligned stress fibers, resulting in apparent Young's modulus values up to 1 order of magnitude larger than those in regions where these structures are not observed, but these organized actin fibers are barely observed in tumorigenic cells. We further investigate cytoskeleton conformation in the three cell lines by immunofluorescence confocal microscopy. The combination of both techniques determines that actin stress fibers are present at apical regions of healthy cells, while in tumorigenic cells they appear only at basal regions, where they cannot contribute to stiffness as probed by atomic force microscopy. These results substantiate that actin stress fibers provide a dominant contribution to stiffness in healthy cells, while the elasticity of tumorigenic cells appears not predominantly determined by these structures. We also discuss the effects of the high-frequency indentations inherent to peak-force atomic force microscopy for the identification of mechanical cancer biomarkers. Whereas conventional low loading rate indentations (1 Hz) result in slightly differentiated average stiffness for each cell line, in high-frequency measurements (250 Hz) healthy cells are clearly discernible from both tumorigenic cells with an enhanced stiffness ratio; however, the two cancerous cell lines produced indistinguishable results.

An injectable nanoparticle generator enhances delivery of cancer therapeutics

The efficacy of cancer drugs is often limited because only a small fraction of the administered dose accumulates in tumors. Here we report an injectable nanoparticle generator (iNPG) that overcomes multiple biological barriers to cancer drug delivery. The iNPG is a discoidal micrometer-sized particle that can be loaded with chemotherapeutics. We conjugate doxorubicin to poly(L-glutamic acid) by means of a pH-sensitive cleavable linker, and load the polymeric drug (pDox) into iNPG to assemble iNPG-pDox. Once released from iNPG, pDox spontaneously forms nanometer-sized particles in aqueous solution. Intravenously injected iNPG-pDox accumulates at tumors due to natural tropism and enhanced vascular dynamics and releases pDox nanoparticles that are internalized by tumor cells. Intracellularly, pDox nanoparticles are transported to the perinuclear region and cleaved into Dox, thereby avoiding excretion by drug efflux pumps. Compared to its individual components or current therapeutic formulations, iNPG-pDox shows enhanced efficacy in MDA-MB-231 and 4T1 mouse models of metastatic breast cancer, including functional cures in 40-50% of treated mice.

Predicting the growth of glioblastoma multiforme spheroids using a multiphase porous media model

Tumor spheroids constitute an effective in vitro tool to investigate the avascular stage of tumor growth. These three-dimensional cell aggregates reproduce the nutrient and proliferation gradients found in the early stages of cancer and can be grown with a strict control of their environmental conditions. In the last years, new experimental techniques have been developed to determine the effect of mechanical stress on the growth of tumor spheroids. These studies report a reduction in cell proliferation as a function of increasingly applied stress on the surface of the spheroids. This work presents a specialization for tumor spheroid growth of a previous more general multiphase model. The equations of the model are derived in the framework of porous media theory, and constitutive relations for the mass transfer terms and the stress are formulated on the basis of experimental observations. A set of experiments is performed, investigating the growth of U-87MG spheroids both freely growing in the culture medium and subjected to an external mechanical pressure induced by a Dextran solution. The growth curves of the model are compared to the experimental data, with good agreement for both the experimental settings. A new mathematical law regulating the inhibitory effect of mechanical compression on cancer cell proliferation is presented at the end of the paper. This new law is validated against experimental data and provides better results compared to other expressions in the literature.

Redirecting Transport of Nanoparticle Albumin-Bound Paclitaxel to Macrophages Enhances Therapeutic Efficacy against Liver Metastases

Current treatments for liver metastases arising from primary breast and lung cancers are minimally effective. One reason for this unfavorable outcome is that liver metastases are poorly vascularized, limiting the ability to deliver therapeutics from the systemic circulation to lesions. Seeking to enhance transport of agents into the tumor microenvironment, we designed a system in which nanoparticle albumin-bound paclitaxel (nAb-PTX) is loaded into a nanoporous solid multistage nanovector (MSV) to enable the passage of the drug through the tumor vessel wall and enhance its interaction with liver macrophages. MSV enablement increased nAb-PTX efficacy and survival in mouse models of breast and lung liver metastasis. MSV-nAb-PTX also augmented the accumulation of paclitaxel and MSV in the liver, specifically in macrophages, whereas paclitaxel levels in the blood were unchanged after administering MSV-nAb-PTX or nAb-PTX. In vitro studies demonstrated that macrophages treated with MSV-nAb-PTX remained viable and were able to internalize, retain, and release significantly higher quantities of paclitaxel compared with treatment with nAb-PTX. The cytotoxic potency of the released paclitaxel was also confirmed in tumor cells cultured with the supernatants of macrophage treated with MSV-nAB-PTX. Collectively, our findings showed how redirecting nAb-PTX to liver macrophages within the tumor microenvironment can elicit a greater therapeutic response in patients with metastatic liver cancer, without increasing systemic side effects.

The Tumor Microenvironment as a Barrier to Cancer Nanotherapy

Although extensive research effort and resources have been dedicated to the development of nanotherapeutics to treat cancer, few formulations have reached clinical application. A major reason is that the large number of parameters available to tune nanotherapy characteristics coupled with the variability in tumor tissue precludes evaluation of complex interactions through experimentation alone. In order to optimize the nanotechnology design and gain further insight into these phenomena, mathematical modeling and computational simulation have been applied to complement empirical work. In this chapter, we discuss modeling work related to nanotherapy and the tumor microenvironment. We first summarize the biology underlying the dysregulated tumor microenvironment, followed by a description of major nano-scale parameters. We then present an overview of the mathematical modeling of cancer nanotherapy, including evaluation of nanotherapy in multi-dimensional tumor tissue, coupling of nanotherapy with vascular flow, modeling of nanotherapy in combination with in vivo imaging, modeling of nanoparticle transport based on in vitro data, modeling of vasculature-bound nanoparticles, evaluation of nanotherapy using pharmacokinetic modeling, and modeling of nano-based hyperthermia. We conclude that an even tighter interdisciplinary effort between biological, material, and physical scientists is needed in order to eventually overcome the tumor microenvironment barrier to successful nanotherapy.

Simulation of the Protein-Shedding Kinetics of a Fully Vascularized Tumor

Circulating biomarkers are of significant interest for cancer detection and treatment personalization. However, the biophysical processes that determine how proteins are shed from cancer cells or their microenvironment, diffuse through tissue, enter blood vasculature, and persist in circulation remain poorly understood. Since approaches primarily focused on experimental evaluation are incapable of measuring the shedding and persistence for every possible marker candidate, we propose an interdisciplinary computational/experimental approach that includes computational modeling of tumor tissue heterogeneity. The model implements protein production, transport, and shedding based on tumor vascularization, cell proliferation, hypoxia, and necrosis, thus quantitatively relating the tumor and circulating proteomes. The results highlight the dynamics of shedding as a function of protein diffusivity and production. Linking the simulated tumor parameters to clinical tumor and vascularization measurements could potentially enable this approach to reveal the tumor-specific conditions based on the protein detected in circulation and thus help to more accurately manage cancer diagnosis and treatment.

Multistage vector (MSV) therapeutics

One of the greatest challenges in the field of medicine is obtaining controlled distribution of systemically administered therapeutic agents within the body. Indeed, biological barriers such as physical compartmentalization, pressure gradients, and excretion pathways adversely affect localized delivery of drugs to pathological tissue. The diverse nature of these barriers requires the use of multifunctional drug delivery vehicles that can overcome a wide range of sequential obstacles. In this review, we explore the role of multifunctionality in nanomedicine by primarily focusing on multistage vectors (MSVs). The MSV is an example of a promising therapeutic platform that incorporates several components, including a microparticle, nanoparticles, and small molecules. In particular, these components are activated in a sequential manner in order to successively address transport barriers.

The mathematics of cancer: integrating quantitative models

Mathematical modelling approaches have become increasingly abundant in cancer research. The complexity of cancer is well suited to quantitative approaches as it provides challenges and opportunities for new developments. In turn, mathematical modelling contributes to cancer research by helping to elucidate mechanisms and by providing quantitative predictions that can be validated. The recent expansion of quantitative models addresses many questions regarding tumour initiation, progression and metastases as well as intra-tumour heterogeneity, treatment responses and resistance. Mathematical models can complement experimental and clinical studies, but also challenge current paradigms, redefine our understanding of mechanisms driving tumorigenesis and shape future research in cancer biology.

Engineering cancer microenvironments for in vitro 3-D tumor models

The natural microenvironment of tumors is composed of extracellular matrix (ECM), blood vasculature, and supporting stromal cells. The physical characteristics of ECM as well as the cellular components play a vital role in controlling cancer cell proliferation, apoptosis, metabolism, and differentiation. To mimic the tumor microenvironment outside the human body for drug testing, two-dimensional (2-D) and murine tumor models are routinely used. Although these conventional approaches are employed in preclinical studies, they still present challenges. For example, murine tumor models are expensive and difficult to adopt for routine drug screening. On the other hand, 2-D in vitro models are simple to perform, but they do not recapitulate natural tumor microenvironment, because they do not capture important three-dimensional (3-D) cell-cell, cell-matrix signaling pathways, and multi-cellular heterogeneous components of the tumor microenvironment such as stromal and immune cells. The three-dimensional (3-D) in vitro tumor models aim to closely mimic cancer microenvironments and have emerged as an alternative to routinely used methods for drug screening. Herein, we review recent advances in 3-D tumor model generation and highlight directions for future applications in drug testing.

Evaluation of uptake and distribution of gold nanoparticles in solid tumors

Although nanotherapeutics offer a targeted and potentially less toxic alternative to systemic chemotherapy in cancer treatment, nanotherapeutic transport is typically hindered by abnormal characteristics of tumor tissue. Once nanoparticles targeted to tumor cells arrive in the circulation of tumor vasculature, they must extravasate from irregular vessels and diffuse through the tissue to ideally reach all malignant cells in cytotoxic concentrations. The enhanced permeability and retention effect can be leveraged to promote extravasation of appropriately sized particles from tumor vasculature; however, therapeutic success remains elusive partly due to inadequate intra-tumoral transport promoting heterogeneous nanoparticle uptake and distribution. Irregular tumor vasculature not only hinders particle transport but also sustains hypoxic tissue kregions with quiescent cells, which may be unaffected by cycle-dependent chemotherapeutics released from nanoparticles and thus regrow tumor tissue following nanotherapy. Furthermore, a large proportion of systemically injected nanoparticles may become sequestered by the reticuloendothelial system, resulting in overall diminished efficacy. We review recent work evaluating the uptake and distribution of gold nanoparticles in pre-clinical tumor models, with the goal to help improve nanotherapy outcomes. We also examine the potential role of novel layered gold nanoparticles designed to address some of these critical issues, assessing their uptake and transport in cancerous tissue.

Design Principles for Nanoparticles Enveloped by a Polymer-Tethered Lipid Membrane

We propose the design for a nanoparticle carrier that combines three existing motifs into a single construct: a liposome is stabilized by anchoring it to an enclosed solid core via extended polymeric tethers that are chemically grafted to the core and physisorb into the surrounding lipid membrane. Such a design would exhibit several enticing properties, among them: (i) the anchoring stabilizes the liposome against a variety of external stresses, while preserving an aqueous compartment between core and membrane; (ii) the interplay of design parameters such as polymer length or grafting density enforces strong constraints on nanoparticle size and hence ensures a high degree of uniformity; and (iii) the physical and chemical characteristics of the individual constituents equip the construct with numerous functionalities that can be exploited in many ways. However, navigating the large parameter space requires a sound prior understanding for how various design features work together, and how this impacts potential pathways for synthesizing and assembling these nanoparticles. In this paper, we examine these connections in detail, using both soft matter theory and computer simulations at all levels of resolution. We thereby derive strong constraints on the experimentally relevant parameter space, and also propose potential equilibrium and nonequilibrium pathways for nanoparticle assembly.

Nanomedicine delivery: does protein corona route to the target or off road?

Nanomedicine aims to find novel solutions for urgent biomedical needs. Despite this, one of the most challenging hurdles that nanomedicine faces is to successfully target therapeutic nanoparticles to cells of interest in vivo. As for any biomaterials, once in vivo, nanoparticles can interact with plasma biomolecules, forming new entities for which the name protein coronas (PCs) have been coined. The PC can influence the in vivo biological fate of a nanoparticle. Thus for guaranteeing the desired function of an engineered nanomaterial in vivo, it is crucial to dissect its PC in terms of formation and evolution within the body. In this contribution we will review the 'good' and 'bad' sides of the PC, starting from the scientific aspects to the technological applications.

Lamin A/C deficiency reduces circulating tumor cell resistance to fluid shear stress

Metastasis contributes to over 90% of cancer-related deaths and is initiated when cancer cells detach from the primary tumor, invade the basement membrane, and enter the circulation as circulating tumor cells (CTCs). While metastasis is viewed as an inefficient process with most CTCs dying within the bloodstream, it is evident that some CTCs are capable of resisting hemodynamic shear forces to form secondary tumors in distant tissues. We hypothesized that nuclear lamins A and C (A/C) act as key structural components within CTCs necessary to resist destruction from elevated shear forces of the bloodstream. Herein, we show that, compared with nonmalignant epithelial cells, tumor cells are resistant to elevated fluid shear forces in vitro that mimic those within the bloodstream, as evidenced by significant decreases in cellular apoptosis and necrosis. Knockdown of lamin A/C significantly reduced tumor cell resistance to fluid shear stress, with significantly increased cell death compared with parental tumor cell and nontargeting controls. Interestingly, lamin A/C knockdown increased shear stress-induced tumor cell apoptosis, but did not significantly affect cellular necrosis. These data demonstrate that lamin A/C is an important structural component that enables tumor cell resistance to fluid shear stress-mediated death in the bloodstream, and may thus facilitate survival and hematogenous metastasis of CTCs.

Radiofrequency treatment alters cancer cell phenotype

The importance of evaluating physical cues in cancer research is gradually being realized. Assessment of cancer cell physical appearance, or phenotype, may provide information on changes in cellular behavior, including migratory or communicative changes. These characteristics are intrinsically different between malignant and non-malignant cells and change in response to therapy or in the progression of the disease. Here, we report that pancreatic cancer cell phenotype was altered in response to a physical method for cancer therapy, a non-invasive radiofrequency (RF) treatment, which is currently being developed for human trials. We provide a battery of tests to explore these phenotype characteristics. Our data show that cell topography, morphology, motility, adhesion and division change as a result of the treatment. These may have consequences for tissue architecture, for diffusion of anti-cancer therapeutics and cancer cell susceptibility within the tumor. Clear phenotypical differences were observed between cancerous and normal cells in both their untreated states and in their response to RF therapy. We also report, for the first time, a transfer of microsized particles through tunneling nanotubes, which were produced by cancer cells in response to RF therapy. Additionally, we provide evidence that various sub-populations of cancer cells heterogeneously respond to RF treatment.

Capillary collagen as the physical transport barrier in drug delivery to tumor microenvironment

The capillary wall is among the most important barriers that controls mass exchange between tumor microenvironment and systemic circulation. There are numerous studies on endothelial cells role in this mass exchange, but the role of capillary collagen of Type-IV in transport of small molecules and nanotherapeutics is less known. Our recent study revealed that the capillary wall collagen modulates the drug transport across the wall, and that it can be taken as a biophysical marker for drug transport. In our in vivo investigations with the 3LL and 4T1 tumors we noticed the differences in the collagen content in capillary walls. The imaging analysis and transport computational model of the capillary microenvironment showed that the penetration of doxorubicin (DOX) and pegylated liposomal doxorubicin (PLD) is substantially reduced by larger collagen content in the capillaries of the 3LL tumors. The results pointed to the importance of transport oncophysics, which opens a new avenue with respect to classical biology in understanding and improving drug delivery by nanotherapeutics, and aims to better explain the therapeutic resistance.

Tracking miRNAs' footprints in tumor-microenvironment interactions: Insights and implications for targeted cancer therapy

In the past decades, cancer medicine studies have mainly focused on tumor cell biology as the main promoter of solid tumor progression. However, tumor biology does not explain the intertwinement and ambiguity of the tumors' territory. Recently, the approach of understanding cancer has shifted from investigating the biology of tumor cells to studying the microenvironment surrounding them. MicroRNAs (miRNAs), which play a role in exploiting indigenous stromal cells and are components that cooperate and produce a favorable microenvironment for progressive tumor formation, have been implicated in numerous processes essential for tumor initiation and growth. Understanding the mechanisms underlying interactions between tumor cells and their adjacent environment holds many promises for the future of cancer-targeted therapies. Herein, we provide a step-by-step account of miRNA involvement in tumor-microenvironment interactions as the micromediators of tumor cell and stroma communications. We also focus on the clinical challenges in using miRNAs tof overcome therapy resistance mechanisms and tumor heterogeneity bias in cancer therapy.

Piezo1 forms mechanosensitive ion channels in the human MCF-7 breast cancer cell line

Mechanical interaction between cells - specifically distortion of tensional homeostasis-emerged as an important aspect of breast cancer genesis and progression. We investigated the biophysical characteristics of mechanosensitive ion channels (MSCs) in the malignant MCF-7 breast cancer cell line. MSCs turned out to be the most abundant ion channel species and could be activated by negative pressure at the outer side of the cell membrane in a saturable manner. Assessing single channel conductance (GΛ) for different monovalent cations revealed an increase in the succession: Li(+) < Na(+) < K(+) ≈Rb(+) ≈ Cs(+). Divalent cations permeated also with the order: Ca(2+) < Ba(2+). Comparison of biophysical properties enabled us to identify MSCs in MCF-7 as ion channels formed by the Piezo1 protein. Using patch clamp technique no functional MSCs were observed in the benign MCF-10A mammary epithelial cell line. Blocking of MSCs by GsMTx-4 resulted in decreased motility of MCF-7, but not of MCF-10A cells, underscoring a possible role of Piezo1 in invasion and metastatic propagation. The role of Piezo1 in biology and progression of breast cancer is further substantiated by markedly reduced overall survival in patients with increased Piezo1 mRNA levels in the primary tumor.

Etiologic field effect: reappraisal of the field effect concept in cancer predisposition and progression

The term 'field effect' (also known as field defect, field cancerization, or field carcinogenesis) has been used to describe a field of cellular and molecular alteration, which predisposes to the development of neoplasms within that territory. We explore an expanded, integrative concept, 'etiologic field effect', which asserts that various etiologic factors (the exposome including dietary, lifestyle, environmental, microbial, hormonal, and genetic factors) and their interactions (the interactome) contribute to a tissue microenvironmental milieu that constitutes a 'field of susceptibility' to neoplasia initiation, evolution, and progression. Importantly, etiological fields predate the acquisition of molecular aberrations commonly considered to indicate presence of filed effect. Inspired by molecular pathological epidemiology (MPE) research, which examines the influence of etiologic factors on cellular and molecular alterations during disease course, an etiologically focused approach to field effect can: (1) broaden the horizons of our inquiry into cancer susceptibility and progression at molecular, cellular, and environmental levels, during all stages of tumor evolution; (2) embrace host-environment-tumor interactions (including gene-environment interactions) occurring in the tumor microenvironment; and, (3) help explain intriguing observations, such as shared molecular features between bilateral primary breast carcinomas, and between synchronous colorectal cancers, where similar molecular changes are absent from intervening normal colon. MPE research has identified a number of endogenous and environmental exposures which can influence not only molecular signatures in the genome, epigenome, transcriptome, proteome, metabolome and interactome, but also host immunity and tumor behavior. We anticipate that future technological advances will allow the development of in vivo biosensors capable of detecting and quantifying 'etiologic field effect' as abnormal network pathology patterns of cellular and microenvironmental responses to endogenous and exogenous exposures. Through an 'etiologic field effect' paradigm, and holistic systems pathology (systems biology) approaches to cancer biology, we can improve personalized prevention and treatment strategies for precision medicine.

Impact of dimensionality and network disruption on microrheology of cancer cells in 3D environments

Dimensionality is a fundamental component that can have profound implications on the characteristics of physical systems. In cell biology, however, the majority of studies on cell physical properties, from rheology to force generation to migration, have been performed on 2D substrates, and it is not clear how a more realistic 3D environment influences cell properties. Here, we develop an integrated approach and demonstrate the combination of mitochondria-tracking microrheology, microfluidics, and Brownian dynamics simulations to explore the impact of dimensionality on intracellular mechanics and on the effects of intracellular disruption. Additionally, we consider both passive thermal and active motor-driven processes within the cell and demonstrate through modeling how active internal fluctuations are modulated via dimensionality. Our results demonstrate that metastatic breast cancer cells (MDA-MB-231) exhibit more solid-like internal motions in 3D compared to 2D, and actin network disruption via Cytochalasin D has a more pronounced effect on internal cell fluctuations in 2D. Our computational results and modeling show that motor-induced active stress fluctuations are enhanced in 2D, leading to increased local intracellular particle fluctuations and apparent fluid-like behavior.

Biomechanical properties at the cellular and subcellular levels are important in providing proper biological functions, from cell migratory capabilities to intracellular transport. Deregulation in these properties can lead to disease states such as cancer metastasis. We develop and demonstrate an integrated experimental and computational approach to study intracellular mechanics. We demonstrate that a key environmental factor, dimensionality, plays a significant role in modulating intracellular mechanical behavior. This is important as typical cell biology and mechanics experiments are performed on 2D substrates, which do not capture the physiological features of 3D matrices and may not induce physiologically accurate cell properties. We further develop an effective temperature model to describe how dimensionality changes intracellular particle motion by altering the activity of molecular motors.

cgDNA: a software package for the prediction of sequence-dependent coarse-grain free energies of B-form DNA

cgDNA is a package for the prediction of sequence-dependent configuration-space free energies for B-form DNA at the coarse-grain level of rigid bases. For a fragment of any given length and sequence, cgDNA calculates the configuration of the associated free energy minimizer, i.e. the relative positions and orientations of each base, along with a stiffness matrix, which together govern differences in free energies. The model predicts non-local (i.e. beyond base-pair step) sequence dependence of the free energy minimizer. Configurations can be input or output in either the Curves+ definition of the usual helical DNA structural variables, or as a PDB file of coordinates of base atoms. We illustrate the cgDNA package by comparing predictions of free energy minimizers from (a) the cgDNA model, (b) time-averaged atomistic molecular dynamics (or MD) simulations, and (c) NMR or X-ray experimental observation, for (i) the Dickerson–Drew dodecamer and (ii) three oligomers containing A-tracts. The cgDNA predictions are rather close to those of the MD simulations, but many orders of magnitude faster to compute. Both the cgDNA and MD predictions are in reasonable agreement with the available experimental data. Our conclusion is that cgDNA can serve as a highly efficient tool for studying structural variations in B-form DNA over a wide range of sequences.

Polycystin-1 and polycystin-2 are involved in the acquisition of aggressive phenotypes in colorectal cancer

The polycystins PC1 and PC2 are emerging as major players in mechanotransduction, a process that influences all steps of the invasion/metastasis cascade. We hypothesized that PC1 and PC2 facilitate cancer aggressiveness. Immunoblotting, RT-PCR, semi-quantitative and quantitative real-time PCR and FACS analyses were employed to investigate the effect of polycystin overexpression in colorectal cancer (CRC) cells. The impact of PC1 inhibition on cancer-cell proliferation was evaluated through an MTT assay. In vitro data were analyzed by Student's t-test. HT29 human xenografts were treated with anti-PC1 (extracellular domain) inhibitory antibody and analyzed via immunohistochemistry to determine the in vivo role of PC1 in CRC. Clinical significance was assessed by examining PC1 and PC2 protein expression in CRC patients (immunohistochemistry). In vivo and clinical data were analyzed by non-parametric tests, Kaplan-Meier curves, log-rank test and Cox model. All statistical tests were two-sided. PC1 overexpression promotes epithelial-to-mesenchymal transition (EMT) in HCT116 cells, while PC2 overexpression results in upregulation of the mTOR pathway in SW480 cells. PC1 inhibition causes reduced cell proliferation in CRC cells inducing tumor necrosis and suppressing EMT in HT29 tumor xenografts. In clinical study, PC1 and PC2 overexpression associates with adverse pathological parameters, including invasiveness and mucinous carcinomas. Moreover, PC1 overexpression appears as an independent prognostic factor of reduced recurrence-free survival (HR = 1.016, p = 0.03) and lowers overall survival probability, while aberrant PC2 expression predicts poor overall survival (p = 0.0468). These results support, for the first time, a direct link between mechanosensing polycystins (PC1 and PC2) and CRC progression.

Capillary-wall collagen as a biophysical marker of nanotherapeutic permeability into the tumor microenvironment

The capillary wall is the chief barrier to tissue entry of therapeutic nanoparticles, thereby dictating their efficacy. Collagen fibers are an important component of capillary walls, affecting leakiness in healthy or tumor vasculature. Using a computational model along with in vivo systems, we compared how collagen structure affects the diffusion flux of a 1-nm chemotherapeutic molecule [doxorubicin (DOX)] and an 80-nm chemotherapy-loaded pegylated liposome (DOX-PLD) in tumor vasculature. We found a direct correlation between the collagen content around a tumor vessel to the permeability of that vessel permeability to DOX-PLD, indicating that collagen content may offer a biophysical marker of extravasation potential of liposomal drug formulations. Our results also suggested that while pharmacokinetics determined the delivery of DOX and DOX-PLD to the same tumor phenotype, collagen content determined the extravasation of DOX-PLD to different tumor phenotypes. Transport physics may provide a deeper view into how nanotherapeutics cross biological barriers, possibly helping explain the balance between biological and physical aspects of drug delivery.

USNCTAM perspectives on mechanics in medicine

Over decades, the theoretical and applied mechanics community has developed sophisticated approaches for analysing the behaviour of complex engineering systems. Most of these approaches have targeted systems in the transportation, materials, defence and energy industries. Applying and further developing engineering approaches for understanding, predicting and modulating the response of complicated biomedical processes not only holds great promise in meeting societal needs, but also poses serious challenges. This report, prepared for the US National Committee on Theoretical and Applied Mechanics, aims to identify the most pressing challenges in biological sciences and medicine that can be tackled within the broad field of mechanics. This echoes and complements a number of national and international initiatives aiming at fostering interdisciplinary biomedical research. This report also comments on cultural/educational challenges. Specifically, this report focuses on three major thrusts in which we believe mechanics has and will continue to have a substantial impact. (i) Rationally engineering injectable nano/microdevices for imaging and therapy of disease. Within this context, we discuss nanoparticle carrier design, vascular transport and adhesion, endocytosis and tumour growth in response to therapy, as well as uncertainty quantification techniques to better connect models and experiments. (ii) Design of biomedical devices, including point-of-care diagnostic systems, model organ and multi-organ microdevices, and pulsatile ventricular assistant devices. (iii) Mechanics of cellular processes, including mechanosensing and mechanotransduction, improved characterization of cellular constitutive behaviour, and microfluidic systems for single-cell studies.

Postulates on electromagnetic activity in biological systems and cancer

A framework of postulates is formulated to define the existence, nature, and function of a coherent state far from thermodynamic equilibrium in biological systems as an essential condition for the existence of life. This state is excited and sustained by energy supply. Mitochondria producing small packets of energy in the form of adenosine and guanosine triphosphate and strong static electric field around them form boundary elements between biochemical-genetic and physical processes. The transformation mechanism of chemical energy into useful work for biological needs and the excitation of the coherent state far from thermodynamic equilibrium are fundamental problems. The exceptional electrical polarity of biological objects and long-range interactions suggest a basic role of the endogenous electromagnetic field generated by living cells. The formulated postulates encompass generation, properties and function of the electromagnetic field connected with biological activity and its pathological deviations. Excited longitudinal polar oscillations in microtubules in eukaryotic cells generate the endogenous electromagnetic field. The metabolic activity of mitochondria connected with water ordering forms conditions for excitation. The electrodynamic field plays an important role in the establishment of coherence, directional transport, organization of morphological structures, interactions, information transfer, and brain activity. An overview of experimental results and physical models supporting the postulates is included. The existence of the endogenous biological electromagnetic field, its generation by microtubules and supporting effects produced by mitochondria have a reasonable experimental foundation. Cancer transformation is a pathological reduction of the coherent energy state far from thermodynamic equilibrium. Malignancy, i.e. local invasion and metastasis, is a direct consequence of mitochondrial dysfunction, disturbed microtubule polar oscillations and the generated electromagnetic field.

Tumor and the microenvironment: a chance to reframe the paradigm of carcinogenesis?

The somatic mutation theory of carcinogenesis has eventually accumulated an impressive body of shortfalls and paradoxes, as admittedly claimed by its own supporters given that the cell-based approach can hardly explain the emergence of tissue-based processes, like cancer. However, experimental data and alternatives theories developed during the last decades may actually provide a new framework on which cancer research should be reframed. Such issue may be fulfilled embracing new theoretical perspectives, taking the cells-microenvironment interplay as the privileged level of observation and assuming radically different premises as well as new methodological frameworks. Within that perspective, the tumor microenvironment cannot be merely considered akin to new “factor” to be added to an already long list of “signaling factors”; microenvironment represents the physical-biochemical support of the morphogenetic field which drives epithelial cells towards differentiation and phenotype transformation, according to rules understandable only by means of a systems biology approach. That endeavour entails three fundamental aspects: general biological premises, the level of observation (i.e., the systems to which we are looking for), and the principles of biological organization that would help in integrating and understanding experimental data.

Transport properties of pancreatic cancer describe gemcitabine delivery and response

BACKGROUND

The therapeutic resistance of pancreatic ductal adenocarcinoma (PDAC) is partly ascribed to ineffective delivery of chemotherapy to cancer cells. We hypothesized that physical properties at vascular, extracellular, and cellular scales influence delivery of and response to gemcitabine-based therapy.

METHODS

We developed a method to measure mass transport properties during routine contrast-enhanced CT scans of individual human PDAC tumors. Additionally, we evaluated gemcitabine infusion during PDAC resection in 12 patients, measuring gemcitabine incorporation into tumor DNA and correlating its uptake with human equilibrative nucleoside transporter (hENT1) levels, stromal reaction, and CT-derived mass transport properties. We also studied associations between CT-derived transport properties and clinical outcomes in patients who received preoperative gemcitabine-based chemoradiotherapy for resectable PDAC.

RESULTS

Transport modeling of 176 CT scans illustrated striking differences in transport properties between normal pancreas and tumor, with a wide array of enhancement profiles. Reflecting the interpatient differences in contrast enhancement, resected tumors exhibited dramatic differences in gemcitabine DNA incorporation, despite similar intravascular pharmacokinetics. Gemcitabine incorporation into tumor DNA was inversely related to CT-derived transport parameters and PDAC stromal score, after accounting for hENT1 levels. Moreover, stromal score directly correlated with CT-derived parameters. Among 110 patients who received preoperative gemcitabine-based chemoradiotherapy, CT-derived parameters correlated with pathological response and survival.

CONCLUSION

Gemcitabine incorporation into tumor DNA is highly variable and correlates with multiscale transport properties that can be derived from routine CT scans. Furthermore, pretherapy CT-derived properties correlate with clinically relevant endpoints.

TRIAL REGISTRATION

Clinicaltrials.gov NCT01276613.

FUNDING

Lustgarten Foundation (989161), Department of Defense (W81XWH-09-1-0212), NIH (U54CA151668, KCA088084).

Alterations in mechanical properties are associated with prostate cancer progression

Cancer progression and metastasis have been shown to be accompanied by alterations in the mechanical properties of tissues, but the relationship between the mechanical properties and malignant behavior in prostate cancer (Pca) is less clear. The aims of this study were to detect the mechanical properties of benign prostatic hyperplasia (BPH) and Pca tissues on both the macro- and micro-scales, to explore the relationships between mechanical properties and malignant behavior and, finally, to identify the important molecules in the mechanotransduction signaling pathway. We demonstrated that the strain index of Pca tissue was significantly higher than that of BPH tissue on the macro-scale but the Young's modulus of the Pca tissues, especially in advanced Pca, was lower than that of BPH tissues on the micro-scale. These two seemingly contradictory results can be explained by the excessive proliferation of tumor cells (Ki-67) and the degradation of scaffold proteins (collagens). These data indicate that alterations of the macro- and micro-mechanical properties of Pca tissues with malignant behavior are contradictory. The mechanical properties of tissues might be useful as a new risk factor for malignancy and metastasis in Pca. Furthermore, collagens, matrix metalloproteinase, fibronectin, and integrins might be the important molecules in the mechanotransduction signaling pathway.

Integrating physical sciences perspectives in cancer research

Cancer research integrated a physical sciences perspective through team science, which fostered communication, trust, joint publication, and open access to data.

Systematic, spatial imaging of large multimolecular assemblies and the emerging principles of supramolecular order in biological systems

Understanding biological systems at the level of their relational (emergent) molecular properties in functional protein networks relies on imaging methods, able to spatially resolve a tissue or a cell as a giant, non-random, topologically defined collection of interacting supermolecules executing myriads of subcellular mechanisms. Here, the development and findings of parameter-unlimited functional super-resolution microscopy are described-a technology based on the fluorescence imaging cycler (IC) principle capable of co-mapping thousands of distinct biomolecular assemblies at high spatial resolution and differentiation (<40 nm distances). It is shown that the subcellular and transcellular features of such supermolecules can be described at the compositional and constitutional levels; that the spatial connection, relational stoichiometry, and topology of supermolecules generate hitherto unrecognized functional self-segmentation of biological tissues; that hierarchical features, common to thousands of simultaneously imaged supermolecules, can be identified; and how the resulting supramolecular order relates to spatial coding of cellular functionalities in biological systems. A large body of observations with IC molecular systems microscopy collected over 20 years have disclosed principles governed by a law of supramolecular segregation of cellular functionalities. This pervades phenomena, such as exceptional orderliness, functional selectivity, combinatorial and spatial periodicity, and hierarchical organization of large molecular systems, across all species investigated so far. This insight is based on the high degree of specificity, selectivity, and sensitivity of molecular recognition processes for fluorescence imaging beyond the spectral resolution limit, using probe libraries controlled by ICs.