Molecular chaperones, including the heat-shock proteins (Hsps), are a ubiquitous feature of cells in which these proteins cope with stress-induced denaturation of other proteins. Hsps have received the most attention in model organisms undergoing experimental stress in the laboratory, and the function of Hsps at the molecular and cellular level is becoming well understood in this context. A complementary focus is now emerging on the Hsps of both model and nonmodel organisms undergoing stress in nature, on the roles of Hsps in the stress physiology of whole multicellular eukaryotes and the tissues and organs they comprise, and on the ecological and evolutionary correlates of variation in Hsps and the genes that encode them. This focus discloses that (a) expression of Hsps can occur in nature, (b) all species have hsp genes but they vary in the patterns of their expression, (c) Hsp expression can be correlated with resistance to stress, and (d) species' thresholds for Hsp expression are correlated with levels of stress that they naturally undergo. These conclusions are now well established and may require little additional confirmation; many significant questions remain unanswered concerning both the mechanisms of Hsp-mediated stress tolerance at the organismal level and the evolutionary mechanisms that have diversified the hsp genes.

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Heat-shock proteins, molecular chaperones, and the stress response: evolutionary and ecological physiology

With the rapid development of clinical hyperthermia for the treatment of cancer either alone or in conjunction with other modalities, a means of measuring a thermal dose in terms which are clinically relevant to the biological effect is needed. A comparison of published data empirically suggests a basic relationship that may be used to calculate a "thermal dose." From a knowledge of the temperature during treatment as a function of time combined with a mathematical description of the time-temperature relationship, an estimate of the actual treatment calculated as an exposure time at some reference temperature can be determined. This could be of great benefit in providing a real-time accumulated dose during actual patient treatment. For the purpose of this study, a reference temperature of 43 degrees C has been arbitrarily chosen to convert all thermal exposures to "equivalent-minutes" at this temperature. This dose calculation can be compared to an integrated calculation of the "degree-minutes" to determine its prognostic ability. The time-temperature relationship upon which this equivalent dose calculation is based does not predict, nor does it require, that different tissues have the same sensitivity to heat. A computer program written in FORTRAN is included for performing calculations of both equivalent-minutes (t43) and degree-minutes (tdm43). Means are provided to alter the reference temperature, the Arrhenius "break" temperature and the time-temperature relationship both above and below the "break" temperature. In addition, the effect of factors such as step-down heating, thermotolerance, and physiological conditions on thermal dose calculations are discussed. The equations and methods described in this report are not intended to represent the only approach for thermal dose estimation; instead, they are intended to provide a simple but effective means for such calculations for clinical use and to stimulate efforts to evaluate data in terms of therapeutically useful thermal units.

Thermal dose determination in cancer therapy

In oncology, the term 'hyperthermia' refers to the treatment of malignant diseases by administering heat in various ways. Hyperthermia is usually applied as an adjunct to an already established treatment modality (especially radiotherapy and chemotherapy), where tumor temperatures in the range of 40-43 degrees C are aspired. In several clinical phase-III trials, an improvement of both local control and survival rates have been demonstrated by adding local/regional hyperthermia to radiotherapy in patients with locally advanced or recurrent superficial and pelvic tumors. In addition, interstitial hyperthermia, hyperthermic chemoperfusion, and whole-body hyperthermia (WBH) are under clinical investigation, and some positive comparative trials have already been completed. In parallel to clinical research, several aspects of heat action have been examined in numerous pre-clinical studies since the 1970s. However, an unequivocal identification of the mechanisms leading to favorable clinical results of hyperthermia have not yet been identified for various reasons. This manuscript deals with discussions concerning the direct cytotoxic effect of heat, heat-induced alterations of the tumor microenvironment, synergism of heat in conjunction with radiation and drugs, as well as, the presumed cellular effects of hyperthermia including the expression of heat-shock proteins (HSP), induction and regulation of apoptosis, signal transduction, and modulation of drug resistance by hyperthermia.

The cellular and molecular basis of hyperthermia.

The current status of the use of nanoparticles for photothermal treatments is reviewed in detail. The different families of heating nanoparticles are described paying special attention to the physical mechanisms at the root of the light-to-heat conversion processes. The heating efficiencies and spectral working ranges are listed and compared. The most important results obtained in both in vivo and in vitro nanoparticle assisted photothermal treatments are summarized. The advantages and disadvantages of the different heating nanoparticles are discussed.

Nanoparticles for photothermal therapies.

https://www.cell.com/cell/pdf/S0092-8674(05)00869-X.pdf

Cell-Surface Calreticulin Initiates Clearance of Viable or Apoptotic Cells through trans-Activation of LRP on the Phagocyte

A rational approach to the design of clinical protocols combining fractionated hyperthermia plus X-Irradiation or hyperthermia plus chemotherapy requires an understanding of the biology of fractionated heat alone. Mammalian cells growing in vitro can dramatically increase their tolerance to thermal damage ( i.e. , reduce the cellular inactivation rate) after prior heat conditioning. Although the mechanism(s) for this cellular thermotolerance is still unknown, it is apparent that the thermal history, the heat fractionation interval, and the recovery conditions all modify significantly the degree of thermotolerance subsequently exhibited. At the tissue level, the role of cellular thermotolerance is further complicated by host physiological mechanisms. Few data are available on heat fractionation in vivo , and the relative importance of physiological versus cellular effects remains to be defined.

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Heat Fractionation and Thermotolerance: A Review

The temperature compatible with biphasic hyperthermia-survival curves in Chinese hamster ovary cells was increased from 42.5 to 44°C by acute heat conditioning (10 min, 45°C). An Arrhenius analysis...

Arrhenius analysis of heat survival curves from normal and thermotolerant CHO cells.

The inhibition and resumption of biosynthetic activity in asynchronous Chinese hamster ovary cells following 45° hyperthermia were documented in an attempt to correlate changes in macromolecular synthesis either with the recovery of sublethal heat damage or with the development of thermotolerance.

Growth curves after a heat shock of either 10 or 17.5 min at 45° indicated that cell division was inhibited for 10 or 17 hr, respectively; following recovery, the doubling time was increased from 13 to 37 or 46 hr, respectively. In the cells heated 10 min at 45°, the doubling time shortened to 16.5 hr by 45 hr posthyperthermia; whereas in the cells heated 17.5 min, the doubling time remained at 46 hr.

Nucleic acid synthesis (pulsed [3H]thymidine or [3H]uridine incorporation) was immediately reduced by 90% and resumed after 4 to 6 hr, independently of the hyperthermia exposure time. The rate of DNA synthesis recovered to 20 to 40% of control by 10 hr posthyperthermia, whereas the labeling index remained near control levels until about 12 hr posthyperthermia when it decreased to approximately 20% (25 to 30 hr). In the cells heated 10 min at 45°, the labeling index returned to 45% as the doubling time shortened from 37 to 16.5 hr; whereas after 17.5 min at 45°, the labeling index remained depressed at approximately 22% corresponding to the doubling time of 46 hr.

After the onset of recovery, the rate of RNA synthesis increased so that it exceeded 150% of control by 50 hr posthyperthermia. Hyperthermia inhibited protein synthesis (pulsed incorporation of 14C-labeled amino acids), but recovery occurred over the period 4 to 8 hr after 10 min at 45° or 4 to 26 hr after 17.5 min at 45° to approximately 90% of control in both cases. Precursor incorporation was linear over the period of the pulse label, and cellular permeability to the precursors was not significantly altered by hyperthermia.

The recovery of protein synthesis over the period of 4 to 8 hr after 10 min at 45° correlated in time with the onset of thermotolerance which also began at 4 hr and was completed by 8 hr after heating. In general, however, hyperthermia-induced perturbation of biosynthetic activity did not exhibit a strong dependence on hyperthermia exposure and did not correlate with recovery from sublethal damage.

Effects of Hyperthermia (45°) on Macromolecular Synthesis in Chinese Hamster Ovary Cells

Thermotolerance induced in Chinese hamster ovary (CHO) cells by a 45° heat treatment and developed at 37° resulted in an increased D 0 but a reduced extrapolation number, n , of a subsequent 45° heat survival curve. The time course and magnitude of thermotolerance development were dependent upon the conditioning hyperthermia treatment. Within 2 hr after a 10-min exposure to 45°, the n of the subsequent 45° hyperthermia survival curve increased approximately 5-fold with little change in the D 0 . Thereafter, n returned to control values, whereas the D 0 increased by a factor of 5 by 8 hr and then only slowly disappeared at a rate of 0.1 min at 45° per hr of incubation at 37°. A conditioning dose of 5 min at 45° increased the D 0 of the subsequent 45° heat survival curve by a factor of 3.3 within 2 hr, but then the D 0 returned to control values at the same rate as after a conditioning treatment of 10 min at 45°. CHO cells incubated at 40° grew normally without any evidence of cell killing for more than 2 generations, and incubation at 40° for 0 to 7 hr prior to acute heating at 45° did not induce thermotolerance in terms of an increased D 0 . However, the D q of the 45° heat survival curve was increased approximately 3-fold by 40° preincubation for 7 hr. Increasing the incubation temperature from 37 to 39–41° between 45° heat treatments did not alter the thermotolerant D 0 of the subsequent 45° heat survival curve but did reduce n to 1.0. In addition, the survival curves following 45° conditioning and incubation at 39, 40, or 41° were displaced downward by factors of 5.3, 47, and 360, respectively. The enhanced cell killing resulting from post-45° hyperthermia incubation at 39–41° may be due to the conversion of sublethal damage to lethal damage independently of the induction of thermotolerance.

Induction of thermotolerance in Chinese hamster ovary cells by high (45 degrees) or low (40 degrees) hyperthermia.

The protein content of chromatin isolated from mammalian cells that are heated at temperatures between 40 and 48°C, is increased relative to that from control cells The kinetics of this increase in chromatin protein content was defined by heating HeLa cells at temperatures between 40 and 48°C for periods of up to 60 min At temperatures above 43°C, these kinetics show a rapid initial rate of increase which decays to a slower limiting rate The initial rate of increase in chromatin protein content obeys the Arrhenius law with an activation enthalpy of 868 ± 14 kcal/mole Hyperthermia-cell-survival curves, determined between 44 to 48°C, show an activation enthalpy of 1538 ± 25 kcal/mole for cell killing At 48°C, the activation entropies are 2082 cal/mole K for the protein increase and 4196 cal/mole K for cell killing Although the activation enthalpy and entropy for the increased protein content of chromatin are about half those for cell killing, the Gibbs free energy of activation is similar for bo

Kurt J. Henle

Papers

Heat Fractionation and Thermotolerance: A Review

Arrhenius analysis of heat survival curves from normal and thermotolerant CHO cells.

Effects of Hyperthermia (45°) on Macromolecular Synthesis in Chinese Hamster Ovary Cells

Induction of thermotolerance in Chinese hamster ovary cells by high (45 degrees) or low (40 degrees) hyperthermia.

The Kinetics of Increase in Chromatin Protein Content in Heated Cells: A Possible Role in Cell Killing