A stochastic carcinogenesis model incorporating multiple types of genomic instability fitted to colon cancer data

A generalization of the two-mutation stochastic carcinogenesis model of Moolgavkar, Venzon and Knudson and certain models constructed by Little [Little, M.P. (1995). Are two mutations sufficient to cause cancer? Some generalizations of the two-mutation model of carcinogenesis of Moolgavkar, Venzon, and Knudson, and of the multistage model of Armitage and Doll. Biometrics 51, 1278-1291] and Little and Wright [Little, M.P., Wright, E.G. (2003). A stochastic carcinogenesis model incorporating genomic instability fitted to colon cancer data. Math. Biosci. 183, 111-134] is developed; the model incorporates multiple types of progressive genomic instability and an arbitrary number of mutational stages. The model is fitted to US Caucasian colon cancer incidence data. On the basis of the comparison of fits to the population-based data, there is little evidence to support the hypothesis that the model with more than one type of genomic instability fits better than models with a single type of genomic instability. Given the good fit of the model to this large dataset, it is unlikely that further information on presence of genomic instability or of types of genomic instability can be extracted from age-incidence data by extensions of this model.     

A stochastic carcinogenesis model incorporating genomic instability fitted to colon cancer data

A generalization of the two-mutation stochastic carcinogenesis model of Moolgavkar, Venzon and Knudson and certain models constructed by Little is developed; the model incorporates progressive genomic instability and an arbitrary number of mutational stages. This model is shown to have the property that, at least in the case when the parameters of the model are eventually constant, the excess relative and absolute cancer rates following changes in any of the parameters will eventually tend to zero. It is also shown that when the parameters governing the processes of cell division, death, or additional mutation (whether of the normal sort or that resulting in genomic destabilization) at the penultimate stage are subject to perturbations, there are relatively large fluctuations in the hazard function for the model, which start almost as soon as the parameters are changed. The model is fitted to US Caucasian colon cancer incidence data. A model with five stages and two levels of genomic destabilization fits the data well. Comparison with patterns of excess risk in the Japanese atomic bomb survivor colon cancer incidence data indicate that radiation might act on early mutation rates in the model; a major role for radiation in initiating genomic destabilization is less likely.     

A stochastic model for cancer risk

We propose a simple stochastic model based on the two successive mutations hypothesis to compute cancer risks. Assume that only stem cells are susceptible to the first mutation and that there are a total of D stem cell divisions over the lifetime of the tissue with a first mutation probability mu(1) per division. Our model predicts that cancer risk will be low if m = mu(1)D is low even in the case of very advantageous mutations. Moreover, if mu(1)D is low the mutation probability of the second mutation is practically irrelevant to the cancer risk. These results are in contrast with existing models but in agreement with a conjecture of Cairns. In the case where m is large our model predicts that the cancer risk depends crucially on whether the first mutation is advantageous or not. A disadvantageous or neutral mutation makes the risk of cancer drop dramatically.     

A new human colon carcinoma line

Supported by the “Tumorzentrum Heidelberg-Mannheim”.     

Analysis of diagnostic pathways for colon cancer

Colon cancer is a pathology that benefits largely from an early cure. There are screening guidelines well assessed and overall accepted in several world nations. The question is if they are actually applied in the healthcare practice. The difficulty in the analysis of the application of diagnostic pathways is in the necessity to do a sort of time travel in the past: to chose a group of patients that have the same diagnosis, say colon cancer, and to be able to trace the pathways that led to the diagnosis. By exploiting the ability of data mining techniques to extract sequences from large masses of raw data, it has been possible to reconstruct the actual diagnostic services accessed with larger frequency by the patients and even the sequence of accessed services. The results show that there is a large majority of patients that followed pathways differing from the standard guidelines. The study describes how the database was built, the techniques adopted to extract and group together the data and concludes with an analysis of the diagnostic pathways.     

Radioimmunodetection of human colon cancer in nude mice by a new monoclonal antibody A7 against human colorectal cancer

The in vivo localization of a monoclonal antibody A7 against a human colorectal cancer was studied in nude mice bearing human solid carcinomas, to evaluate potential applications of this antibody for radioimmunodetection of cancer. The tissue distribution of¹²⁵I-labeled A7 MoAb at 3 days after i.v. injection into mice bearing five different kinds of human solid tumors revealed a high uptake ratio by colon cancer, mammary cancer, and glioblastoma. In contrast, the uptake ratio by murine colorectal cancer (Colon-38) was extremely low. In immunoscintigraphic studies, HCT-15, one of the human colon cancer, was clearly visualized with ¹¹¹In-DTPA-A7 MoAb. Glioblastoma was also imaged with the same extent. These results suggest that A7 MoAb would be applicable to the in vivo radioimmunodetection of colon- and mammary-cancer, and of glioblastoma.     

Apoptosis induction in human lung and colon cancer cells via impeding VEGF signaling pathways

Molecular Biology Reports - There is ample evidence to suggest that vascular endothelial growth factor (VEGF) is a potent mitogen factor in vasculogenesis and angiogenesis and that blockade of...     

A state space model of local energy exchange and circulatory control

Based on the assumption that the maintenance of the energy content of the living tissue was the goal of the control, a generalized model of the regulation of local circulation was developed. The goodness of the model realised on a microcomputer was verified by the good fits of simulation with various physiological reactions obtained in animal experiments that were performed in cats anaesthetized with alpha-chloralose (50 mg/kg, i.v.). The reactions were elicited by tilting the animal (45 degrees head up) and by obstructing hindlimb blood flow by means of inflation of a pressure cuff. The appropriateness of energetic considerations of the hypothesis and the properness of the construction of the model was confirmed also by the similarity of the simulated static and dynamic pressure-flow and flow-temperature characteristics, respectively, with those obtained in animal experiments reported in the literature. The performance of the model suggests that the well-known regulatory phenomena of the local circulation are the results of a set point-free control system.     

A mathematical model of human atrioventricular nodal function incorporating concealed conduction

This work develops a mathematical model for the atrioventricular (AV) node in the human heart, based on recordings of electrical activity in the atria (the upper chambers of the heart) and the ventricles (the lower chambers of the heart). Intracardiac recordings of the atrial and ventricular activities were recorded from one patient with atrial flutter and one with atrial fibrillation. During these arrhythmias, not all beats in the atria are conducted to the ventricles. Some are blocked (concealed). However, the blocked beats can affect the properties of the AV node. The activation times of the atrial events were regarded as inputs to a mathematical model of conduction in the AV node, including a representation of AV nodal concealment. The model output was compared to the recorded ventricular response to search for and identify the best possible parameter combinations of the model. Good agreement between the distribution of interbeat intervals in the model and data for durations of 5 min was achieved. A model of AV nodal behavior during atrial flutter and atrial fibrillation could potentially help to understand the relative roles of atrial input activity and intrinsic AV nodal properties in determining the ventricular response.     

Abundance and state of phosphorylation of the retinoblastoma susceptibility gene product in human colon cancer

In an effort to understand the possible role of Rb in cellular growth control, we have investigated the abundance and the state of phosphorylation of Rb protein (pRb) in normal and colon tumor cell lines as well as in matched colon tumors, adenomas and adjoining normal colonic mucosa. Resting normal human fibroblast cell lines were found to have only unphosphorylated pRb and phosphorylation of pRb occurred when the cells entered G1-S phase. In general, the colon tumor tissues had atleast 1.5–2.0 fold increase in the abundance of pRb and 1.5–2.5 fold increase in the percentage of its phosphorylation as compared to the corresponding normal colonic mucosa. Whereas, the adenomas had similar pRb level and its phosphorylation status as observed in the normal colonic mucosa. The actively growing tumor cell lines had approximately two fold higher total pRb than normal cell lines. Although, the percentage of phosphorylated form in growing tumor cell lines as well as normal cell lines were almost equal, it was still considerably higher than normal colonic mucosa. Moreover, DNA binding assay revealed reduced binding affinity of pRb from colon tumor cell line SW480 as compared to the normal cell line W138. These results suggest that the abundance of pRb and its phosphorylation level may have a role in the cellular growth control in human colonic epithelium.     

Feasibility and limits of an orthotopic human colon cancer model in nude mice

We sought to develop an accurate colorectal cancer model in nude mice with stable local growth, tumor cell dissemination, and reproducible metastatic capacity. To this end, we orthotopically transplanted histologically intact human colorectal cancer tissue from 10 human patients into nude mice. After successful local tumor growth, tumor tissues were retransplanted as many as 9 times in serial passage. All specimens were transplanted using microsurgical techniques. Histologic, immunohistochemical, and polymerase chain reaction techniques were used to determine tumor growth rates and kinetics, development of regional lymph node and distant hepatic metastases, and the induction of minimal residual disease (MRD). Stable local tumor growth rates with variable growth kinetics were detected in 73.4% of all mice. The lymph node and hepatic metastasis rates were low, at 18.4% and 4.9%, respectively. MRD, as reflected by CK20 positivity of the bone marrow in animals with lymph node and hepatic metastases, was present in 22.2%. The orthotopic colorectal cancer model described here is feasible for the induction of reproducible local tumor growth but is limited by variable growth kinetics and the low rate of lymph node and hepatic metastases. Cytokeratin-positive cells indicative of MRD could be detected in the bone marrow of approximately 25% of the nude mice with metastases. The observed induction of MRD after orthotopic implantation of intact human colon cancer in animals with lymph node and hepatic metastases might be improved if established colon cancer cell lines were used.     

A new and versatile reagent for incorporating multiple primary aliphatic amines into synthetic oligonucleotides.

A novel and versatile phosphoramidite, N-Fmoc-O1-DMT-O2-cyanoethoxydiisopropylamino-phosphinyl-3-am ino-1,2-propanediol (1, Fig. 1), has been synthesized and used to incorporate primary aliphatic amines into synthetic oligonucleotides. Its convenient preparation and use in solid phase oligonucleotide synthesis is described. Using phosphoramidite 1, an amino-modified oligonucleotide probe complementary to M13mp18 DNA was constructed with five primary amines attached to the 5'-terminus. The amino-modified oligonucleotide was subsequently labeled with biotin and employed in a dot-blot hybridization assay. As little as 0.5 ng of M13mp18 target DNA was colorimetrically detected.     

A stochastic model of neuronal growth cone guidance regulated by multiple sensors

Neuronal growth cones migrate directionally under the control of axon guidance molecules, thereby forming synapses in the developing brain. The signal transduction system by which a growth cone detects surrounding guidance molecules, analyzes the detected signals, and then determines the overall behavior remains undetermined. In this study, we describe a novel stochastic model of this behavior that utilizes multiple sensors on filopodia to respond to guidance molecules. Overall growth cone behavior is determined by using only the concentration gradients of guidance molecules in the immediate vicinity of each sensor. The detected signal at each sensor, which is treated as a vector quantity, is sent to the growth cone center and then integrated to determine axonal growth in the next step by means of a simple vector operation. We compared the results of computer simulations of axonal growth with observations of actual axonal growth from co-culture experiments using olfactory bulb and septum. The probabilistic distributions of axonal growth generated by the computer simulation were consistent with those obtained from the culture experiments, indicating that our model accurately simulates growth cone behavior. We believe that this model will be useful for elucidating the as yet unknown mechanisms responsible for axonal growth in vivo.     

A stochastic model of cancer initiation including a bystander effect

A stochastic model of cancer initiation is considered. The model is used to evaluate whether a bystander effect may be important in the pre-malignant and malignant stages of carcinogenesis, and furthermore, on the basis of epidemiological data, to estimate the mutation rates of genes involved in the development of oral leukoplakias. The bystander effect is defined here as the capability of oncogenic mutations to increase the mutation probability of neighbouring (bystander) cells, thus leading potentially to a cascade of neighbouring mutated and neoplastic cells as a pre-stage in the development to leukoplakias and cancer. We find that incidence data for oral cancer are indeed in accordance with a significant bystander effect, operating either alone or in combination with genomic instability in the early stages of carcinogenesis, i.e. the development of neoplasia. Simulations performed gave a picture of how mutations and neoplasia may spread in a tissue, to form characteristic leukoplakias with a core of neoplastic cells. The model also showed that the probability of finding at least one neoplastic cell in the tissue after a given number of years is more sensitive to changes in genomic instability within the cell itself than to changes in a bystander effect. Based on epidemiological data we also calculate the maximum number of oncogenic genes that may be involved in the bystander effect and development of genomic instability. Even if capable of explaining the initial development of oncogenic mutations towards neoplastic cells, the bystander model could not reproduce the observed incidence rates of leukoplakia without assuming a carcinogen mutation probability per cell per year of neoplastic cells practically equal to one. This means that the bystander effect, to be of substantial importance in the final development of neoplastic cells towards leukoplakias, requires a very significant increase in mutation probabilities for bystanders to neoplastic cells. Alternatively, additional mechanisms such as abnormal cell differentiation and uncontrolled proliferation and apoptotis in the neoplastic stage may be of major importance during the development to cancerization.     

A model for Ca waves in networks of glial cells incorporating both intercellular and extracellular communication pathways

Networks of glial cells, and in particular astrocytes, are capable of sustaining calcium (Ca²⁺) waves both in vivo and in vitro. Experimentally, it has been shown that there are two separate modes of communication: the first by the passage of an agent (inositol 1,4,5-triphosphate, IP₃) through gap junctions (GJs) joining cells; the second by the diffusion of an extracellular agent (adenosine triphosphate, ATP) that binds to receptors on the cells. In both cases, the outcome is the release of Ca²⁺ from internal stores in the glial cells. These two modes of communication are not mutually exclusive, but probably work in conjunction in many cases. We present a model of a two-dimensional network of glial cells that incorporates regenerative intercellular (GJ) and extracellular (ATP) pathways. In the extreme cases of only one type of pathway, the results are in agreement with previous models. Adding an extracellular pathway to the GJ model increased the extent and duration of the Ca²⁺ wave, but did not significantly change the speed of propagation. Conversely, adding GJs to the extracellular model did increase the wave speed. The model was modified to apply to the retina by extending it to include both astrocytes and Müller cells, with GJs the dominant coupling between astrocytes and ATP responsible for most of the remaining communication. It was found that both pathways are necessary to account for experimental results.