Molecular refrigerators : a new approach in anti-cancer therapy

Introduction The temperature difference between normal and cancer cells was proven to be one of the fundamental quantities in the cancer growth. The allosteric transition is a conformational change of a protein conditioned to bind at a specific site; in an enzyme, two different parts can oscillate around their equilibrium state; if the temperature increases, these parts increase their oscillating amplitudes, decreasing in their functionality. This paper discusses a new method for anti-cancer therapy. Hypothesis The entropy generation approach has been used in order to evaluate the stationary conditions of tumoural cells in relation to the transport processes. The tumoural systems can assume all the values of volume, temperature, chemical reaction rate and the time of chemical reaction inside its stationary range of variation; outside of this range, the cancer cannot develop and cell dies. Evaluation of Hypothesis The control over these physical– chemical processes can be obtained by using molecular refrigerators, which help control the temperature of the cells. The aim is to maintain the temperature of a normal cell and not to allow the cell to increase its temperature up to the cancer state. This brings about conformation changes in a protein by supplying free energy on one site of the molecule, required for driving the cooling process. This thermalisation is suggested as anti-cancer therapy. The temperature variation is evaluated by using the entropy generation approach. Conclusion The results obtained represent a new approach to the study of the cancer and for the development of new anticancer therapy based on molecular refrigeration. Introduction Cells interact with their environment using powerful biochemical processing systems. Understanding how cells interact with and respond to the changes in their environment is essential to develop new approaches in biotechnology and medicine1,2. Consequently, there exists a continuous growing interest in applications of process system engineering techniques to biomedical problems3. In particular, there is a great interest in the analysis of the protein in relation to biological events, such as ligand binding, enzymatic modification and protease cleavage4. The carcinogenesis has always been considered as the result of the development of abnormal cell morphology towards metastatic invasive phenotype by means of increase in their number and density. In the last decades, many other characteristics were discovered related to cancer or genes behaviour5,6: • There are precursors, often present in cancers, which allow us to point out the relationship between cancer cells and their stroma. • There will be blood vessel formation, even if avascular tumour growth conditions still exist. • There are cancer genes, which regulate mitosis and apoptosis. • These genes are also expressed in pre-neoplastic states. • There exist genes related to the growing ability of the cancer at its place along with their invasive behaviour with high density. • The cancer has high mitosis on apoptosis ratio. • A fundamental role of the interaction between the cancer and its environment has experimentally been pointed out7. As a consequence of these results, cancer can be described as a nonlinear dynamic system in non-equilibrium thermodynamic states, with following characteristics: complexity8, robustness9, adaptability10,11 and self-organisation5. Consequently, the study of its stationary states results fundamental step in order to control the cancer behaviour. So, the entropy generation approach12 can be used in order to introduce a non-equilibrium thermodynamic approach to the cancer analysis. The cells reach their optimality by means of a redistribution of the flow pattern through the metabolic network by using the pattern of catalytic and regulatory proteins; indeed, mutations and genetic rearrangements are fundamental for an organism to adapt to environmental conditions. This paper discusses molecular refrigerators as a new approach in anticancer therapy. Hypothesis In this paper, we suggest a molecular cooling approach to cancer therapy. The recently obtained thermodynamic results and molecular cooling will be summarized and suggested in relation to a possible new anticancer therapy, * Corresponding author Email: umberto.lucia@polito.it DipartimentoEnergia, Politecnico di Torino, CorsoDucadegli Abruzzi 24, 10129 Torino, Italy


Introduction
Cells interact with their environment using powerful biochemical processing systems.Understanding how cells interact with and respond to the changes in their environment is essential to develop new approaches in biotechnology and medicine 1,2 .Consequently, there exists a continuous growing interest in applications of process system engineering techniques to biomedical problems 3 .In particular, there is a great interest in the analysis of the protein in relation to biological events, such as ligand binding, enzymatic modification and protease cleavage 4 .
The carcinogenesis has always been considered as the result of the development of abnormal cell morphology towards metastatic invasive phenotype by means of increase in their number and density.In the last decades, many other characteristics were discovered related to cancer or genes behaviour 5,6 : • There are precursors, often present in cancers, which allow us to point out the relationship between cancer cells and their stroma.• There will be blood vessel formation, even if avascular tumour growth conditions still exist.• There are cancer genes, which regulate mitosis and apoptosis.
• These genes are also expressed in pre-neoplastic states.• There exist genes related to the growing ability of the cancer at its place along with their invasive behaviour with high density.
• The cancer has high mitosis on apoptosis ratio.• A fundamental role of the interaction between the cancer and its environment has experimentally been pointed out 7 .
As a consequence of these results, cancer can be described as a nonlinear dynamic system in non-equilibrium thermodynamic states, with following characteristics: complexity 8 , robustness 9 , adaptability 10,11 and self-organisation 5 .Consequently, the study of its stationary states results fundamental step in order to control the cancer behaviour.So, the entropy generation approach 12 can be used in order to introduce a non-equilibrium thermodynamic approach to the cancer analysis.
The cells reach their optimality by means of a redistribution of the flow pattern through the metabolic network by using the pattern of catalytic and regulatory proteins; indeed, mutations and genetic rearrangements are fundamental for an organism to adapt to environmental conditions.This paper discusses molecular refrigerators as a new approach in anticancer therapy.

Hypothesis
In this paper, we suggest a molecular cooling approach to cancer therapy.The recently obtained thermodynamic results and molecular cooling will be summarized and suggested in relation to a possible new anticancer therapy, Licensee OA Publishing London 2013.Creative Commons Attribution License (CC-BY) For citation purposes: Lucia U. Molecular refrigerators: a new approach in anti-cancer therapy.OA Medical Hypothesis 2013 Jun 01;1(1):9.
Competing interests: none declared.Conflict of interests: none declared.
All authors contributed to conception and design, manuscript preparation, read and approved the final manuscript.All authors abide by the Association for Medical Ethics (AME) ethical rules of disclosure.
velocity, ρ i is the concentration of the i-th species and os and is means outside and inside the cell, respectively, τ 3 is the lifetime of this process, η is the average viscosity coefficient, ẋ B denotes the centre of mass velocity of all components in the cell, d e cytoplasm layer and r the mean cell radius, τ 4 is the lifetime of this process, N i is the number per unit time and volume of the i-th chemical reaction and A is the affinity, evaluated as the variation of the standard Gibbs free energy.
From this result it follows that if we can decrease the value of the temperature difference between the normal and the cancer cells, mathematically represented by the term DT, we can control the cancer growth.Of course, this approach can be improved, but it can be considered as a first step in the cooling approach by molecular motors.

Consequences of Hypothesis
Many chemical processes in cells use large molecules 23 (proteins, enzymes, etc.).A chemical or physical process which occurs at one border of a protein can lead to a change in the configuration at another site of the same protein, with a consequent interaction among atoms in the molecule 23 .This effect is the well-known allosteric transition, a conformational change of a protein conditioned to bind at a specific site, and it is very interesting in the regulation of enzyme activity, in motor proteins, in ion transport through membranes, etc. 11 .As a consequence of the interaction, the atoms have a transition between two thermodynamic stationary states and the protein reverts to the rest conformation, while the atoms revert to the rest model and the protein starts again, the protein needs to be supplied with free energy 11 to complete the cycle.
The control of these physicalchemical processes allows us to use molecules as molecular refrigerators in order to control the temperature • is on autopoietic pathways, because there exist continuous cycles for generation and autocatalytic feedbacks; • has exergy enhancement or maintenance, because it exports entropy products which exceed or equal the entropy production of the ingested free energy source and decreases its internal entropy; and • presents material conservation and maintains its physical components, because it maintains its structural basis for storing the acquired organisational exergy.
Cells are chemical engines in which specific ordered chemical reactions occur.By using the entropy generation extrema theorem 8 , the maximum volume reached by the cancer systems is obtained as 16,17 : Where V c is the maximum volume of the cancer and V i is the initial volume, T i the initial temperature and DT the temperature difference between a normal and a cancer cell [20][21][22] where τ 1 is the lifetime of this process, ẋ th is the molecular thermal velocity and u the cell volumetric internal energy, L typical length of a cell, which can be evaluated as its mean equivalent diameter, τ 2 is the lifetime of this process, μ i chemical potential of the i-th species, d m is the volume and depth of the membrane, where the chemical potential gradient, ∑ i ρ i (μ i,os -μ i,is )/d m , especially occurs in cytoplasm, ẋ th is the thermal

Evaluation of Hypothesis
The author has referenced some of his own studies in this hypothesis.These referenced studies have been conducted in accordance with the Declaration of Helsinki (1964) and the protocols of these studies have been approved by the relevant ethics committees related to the institution in which they were performed.All human subjects, in these referenced studies, gave informed consent to participate in these studies.
The recently obtained results in the thermodynamic approach to cancer can be summarized as follows [13][14][15][16][17] : • There is a possibility to convert an exergy source to entropy, where exergy is the energy that the system can really use 18 .• The biochemical reactions produce or consume external metabolites, accumulated inside the system, and they connect internal metabolites in constant concentrations in the cells at their steady states.So, living systems must exchange exergy and matter through their boundary.Consequently, cancer is also an open system which is in a state far from thermodynamic equilibrium [14][15][16][17] .• The cancer is a system which can be analysed by using a set of subsystems 17 .• The life of such systems is an organisational process, result of system cooperation between components, with an interconnection between sub-systems and system, such that for survival the system must export equal or more entropy products than its sub-system produces, towards maximum conversion of available energy (called exergy) sources to entropy products.
Consequently, from a thermodynamic point of view, a cell system [13][14][15][16][17] : • is open, because it exchanges energy and mass flows through its boundaries; • is far from equilibrium, because it is a source of high exergy values and basic materials; in accordance with the data used in reference 29 .Now, considering that DT is the temperature difference between a normal and a cancer cell, for example DT ~ 0.15 ÷ 0.40°C, it follows that the cancer cell will reach its final temperature 30 : 1. T 2 ~ 310.25 ÷ 310.55 K =37.10 ÷ 37.40°C for glucose reaction (5) 2. T 2 ~ 310.24 ÷ 310.49K = 37.09 ÷ 37.39°C for the palmitic acid reaction (6)   So, the frequency ratio useful to cool the cancer cell results as ν 0 / ν 1 ~ 0.99872 ÷ 0.99952 for both the reactions.
Consequently, the inside temperature control could represent a new approach to anti-cancer therapy.In particular, molecular refrigerators could be useful anti-cancer devices.Molecular refrigerators can be obtained by using many different techniques: • Catalysis as proposed by Briegel and Popescu 26,27 • Electric field interaction as proposed by Liu and Chen 31 • Electromagnetic or ultrasound waves as proposed by Luo [20][21][22] • Molecular machines 32 which behave as molecular refrigerators to be designed • Local inflow of nanoparticles of ferrofluids in interaction with magnetic field as a new approach to be developed

Conclusion
The results obtained represent a new approach to the study of the cancer and to the development of new anticancer therapy based on molecular refrigeration.

Discussion
The entropy generation approach has been used in order to evaluate the stationary states for the cancer system in relation to its volume and temperature.Following the entropy generation extrema theorem 19 , the cancer can assume all the values inside a range which represents its conditions of stability.Outside of this range, the cancer cannot develop and the cell dies.This analysis points out that the geometrical characteristics (chemical reaction rate and the time of chemical reaction) are fundamental in the growth of cancer.So, there exists a maximum value of volumetric growing after which the tumour invades other parts of the body.Cancer temperature results from the fundamental quantity in the analysis of the cancer growth related to the exergy flows.Indeed, the cellular metabolism can be studied by the analysis of the reactions of oxidation of the energy substrates 28 considering the oxidation of carbohydrates, lipids and protein, represented by the reactions of oxidation 28,29 Now, considering a normal cell and for example, the cell environmental temperature, T 0 = 309.60K = 36.45°C(mean temperature inside the body as environmental temperature) and the cell mean temperature T 1 = 309.95K = 36.8°C(mean temperature of a cell inside the human body), have been evaluated 30,31 with a final temperature inside the cell: 1. T 2 = 310.10K = 36.95°Cfor glucose reaction (5) 2. T 2 = 310.09K = 36.94°Cfor the palmitic acid reaction (6)   of the cells.It must be underlined that this temperature is the difference between the temperature of a cancer and normal cell.The aim is to maintain the temperature of a normal cell and not to allow the cell to increase its temperature up to the cancer state.Indeed, the interaction between two open systems can result time-dependent and externaldriven 24,25 .The useful effect results in conformational changes in a protein 25,26 by supplying free energy on one site of the molecule required for driving the cooling process 26 .The chemical reaction in one site of the protein drives the cooling effect to another site of the protein.
In an enzyme, two different parts can oscillate around their equilibrium state.If the temperature increases, these parts increase their oscillating amplitudes, with many possible vibration modes with a consequent decrease in the functionality of the enzyme.The thermalisation of the oscillator is a process which has a characteristic time-dependent on the interaction strength between the system and the environment 27 and the cooling can occur only if the thermalisation time τ therm is less than the oscillation time τ osc : τ therm << τ osc .It has been evaluated 27 that after a cooling cycle, the temperature of the interaction site of the enzyme can be reduced up to: with ν 0 the oscillation frequency of the initial configuration (before cooling) and ν 1 the oscillation frequency of the final configuration (after cooling).
In order to use this approach as an anti-cancer therapy, it is required that this temperature variation is the same as in the relation (1), so the frequency ratio between the initial and final configuration is suggested to follow this theoretical relation: :