Biomedical subjects

A W Konings

Publications and source records attributed to A W Konings.

At least 19 recordsLinked to original sources

PubMed2001

Early to late sparing of radiation damage to the parotid gland by adrenergic and muscarinic receptor agonists.

Damage to salivary glands after radiotherapeutic treatment of head and neck tumours can severely impair the quality of life of the patients. In the current study we have investigated the early-to-late pathogenesis of the parotid gland after radiation. Also the ability to ameliorate the damage using pretreatment with adrenergic or muscarinic receptor agonists is studied. Rats were locally irradiated with or without i.p. pretreatment with phenylephrine (alpha-adrenoceptor agonist, 5 mg kg(-1)), isoproterenol (beta-adrenoceptor agonist, 5 mg kg(-1)), pilocarpine (4 mg kg(-1)), methacholine (3.75 mg kg(-1)) (muscarinic receptor agonists) or methacholine plus phenylephrine. Parotid salivary flow rate, amylase secretion, the number of cells and gland histology were monitored sequentially up to 240 days postirradiation. The effects were described in 4 distinct phases. The first phase (0-10 days) was characterised by a rapid decline in flow rate without changes in amylase secretion or acinar cell number. The second phase (10-60 days) consists of a decrease in amylase secretion and is paralleled by acinar cell loss. Flow rate, amylase secretion and acinar cell numbers do not change in the third phase (60-120 days). The fourth phase (120-240 days) is determined by a further deterioration of gland function but an increase in acinar cell number, albeit with poor tissue morphology. All drug pretreatments used could reduce radiation effects in phase I and II. The protective effects were lost during phase IV, with the exception of methacholine plus phenylephrine pretreatment. The latter combination of drugs ameliorated radiation-damage throughout the entire follow-up time. The data show that combined pre-irradiation stimulation of muscarinic acetylcholine receptors with methacholine plus alpha-adrenoceptors with phenylephrine can reduce both early and late damage, possibly involving the PLC/PIP2 second messenger pathways. This opens perspectives for the development of clinical applicable methods for long-term sparing of parotid glands subjected to radiotherapy of head and neck cancer patients.

Adrenergic alpha-Agonists↗

PubMed2001

Techniques for precision irradiation of the lateral half of the rat cervical spinal cord using 150 MeV protons [corrected].

Techniques for high precision irradiation experiments with protons, to investigate the volume dependence of the tolerance dose of the rat cervical spinal cord are described. In the present study, 50% of the lateral cross section of the spinal cord was irradiated. The diameter of the cross section of this part of the rat spinal cord is at maximum 3.5 mm. Therefore, a dedicated procedure was developed to comply with the needs for a very high positioning accuracy and high spatial resolution dosimetry. By using 150 MeV protons a steep dose gradient (20-80% = 1 mm) in the centre of the spinal cord was achieved. This yields a good dose contrast between the left and right halves of the cord. A home-made digital x-ray imager with a pixel resolution of 0.18 mm/pixel was used for position verification of the spinal cord. A positioning accuracy of 0.09 mm was obtained by using information of multiple pixels. The average position stability during the irradiation was found to be 0.08 mm (1 SD) without significant systematic deviations. Profiles of the dose distribution were measured with a 2D dosimetry system consisting of a scintillating screen and a CCD camera. Dose volume histograms of the whole spinal cord as well as separately of the white and grey matters were calculated using MRI imaging of the cross section of the rat cervical spinal cord. From the irradiation of 20 animals a dose-response curve has been established. MRI showed radiation-induced damage at the high dose side of the spinal cord. Analysis of the preliminary dose-response data shows a significant dose-volume effect. With the described procedure and equipment it is possible to perform high precision irradiations on selected parts of the spinal cord.

Animals↗

PubMed2000

Radiation induced cell loss in rat submandibular gland and its relation to gland function.

PURPOSE: To understand early and late radiation-induced loss of function of the submandibular gland, changes in cell number were documented and correlated with data on gland function. Modulation of the radiation effect by sialogogues was used to investigate possible mechanisms of action. MATERIALS AND METHODS: Rats were irradiated with a single dose of 15 Gy of X-rays after pre-treatment with either saline, the muscarinic receptor agonists methacholine or pilocarpine, the adrenergic receptor agonist phenylephrine or methacholine plus phenylephrine. Before and 1-240 days after irradiation, submandibular saliva flow rate was measured. At the same time points and from comparable animals submandibular glands were carefully extirpated, weighed and prepared for light microscopic examination. RESULTS: Soon after irradiation (<30 days) no significant loss of cells was observed, whereas the gland function was severely compromised. Sialogogue pre-treatment attenuated the radiation-induced loss of gland function. At later intervals a considerable loss of acinar cells and to a lesser extent loss of granular convoluted tubule cells were observed. Gland function subsequently declined slowly. Pre-treatment with sialogogues gave transient protection against cell loss and loss of gland function. CONCLUSIONS: The lack of cell loss observed soon after irradiation indicates that the observed reduction in gland function was caused by a compromised functioning of the acini. The later loss of cells is probably due to death of cells that normally proliferate, leading to a further reduced secretory capacity. Protection of gland morphology and function by sialogogues at later times must therefore involve resistance of progenitor cells to radiation-induced cell death.

Adrenergic alpha-Agonists↗

PubMed2000

Cycloheximide- and puromycin-induced heat resistance: different effects on cytoplasmic and nuclear luciferases.

Inhibition of translation can result in cytoprotection against heat shock. The mechanism of this protection has remained elusive so far. Here, the thermoprotective effects of the translation inhibitor cycloheximide (CHX) and puromycin were investigated, using as reporter firefly luciferase localized either in the nucleus or in the cytoplasm. A short preincubation of O23 cells with either translation inhibitor was found to attenuate the heat inactivation of a luciferase directed into the cytoplasm, whereas the heat sensitivity of a nuclear-targeted luciferase remained unaffected. After a long-term CHX pretreatment, both luciferases were more heat resistant. Both the cytoplasmic and the nuclear luciferase are protected against heat-induced inactivation in thermotolerant cells and in cells overexpressing heat shock protein (Hsp)70. CHX incubations further attenuated cytoplasmic luciferase inactivation in thermotolerant and in Hsp70 overexpressing cells, even when Hsp70-mediated protection was saturated. It is concluded that protection by translation inhibition is unlikely due to an increase in the pool of free Hsps normally engaged in translation and released from the nascent polypeptide chains on the ribosomes. Rather, a decrease in nascent chains and thermolabile polypeptides may account for the heat resistance promoted by inhibitors of translation.

Animals↗

PubMed2000

Early radiation effects on muscarinic receptor-induced secretory responsiveness of the parotid gland in the freely moving rat.

Although the salivary glands have a low rate of cell turnover, they are relatively radiosensitive. To study the possible mechanism behind this inherent radiosensitivity, a rat model was developed in which saliva can be collected after local irradiation of the parotid gland without the use of anesthetics or stressful handling. Saliva secretion was induced by the partial muscarinic receptor agonist pilocarpine (0.03-3 mg/kg) with or without pretreatment with the beta-adrenoceptor antagonist propranolol (2.5 mg/kg), or the full muscarinic receptor agonist methacholine (0.16-16 mg/min), and measured during 5 min per drug dose before and 1, 3, 6 and 10 days after irradiation. The maximal secretory response induced by pilocarpine plus propranolol was increased compared to that with pilocarpine alone but did not reach the level of methacholine-induced secretion, which was about five times higher. One day after irradiation a decrease in maximal pilocarpine-induced secretion was observed (-22%) using the same dose of pilocarpine that induces 50% of the maximal response (ED(50)), in both the absence and presence of propranolol, indicating that the receptor-drug interaction was not affected by the radiation at this time. The secretory response to methacholine 1 day after irradiation, however, was normal. At day 3 after irradiation, the maximal methacholine-induced secretion was also affected, whereas pilocarpine (+/-propranolol)-induced maximal secretion decreased further. At day 6 after irradiation, maximal secretory responses had declined to approximately 50% regardless of the agonist used, whereas ED(50) values were still unaffected. No net acinar cell loss was observed within the first 10 days after irradiation, and this therefore could not account for the loss in function. The results indicate that radiation does not affect cell number or receptor-drug interaction, but rather signal transduction, which eventually leads to the impaired response. We hypothesize that the early radiation effect, within 3 days, may be membrane damage affecting the receptor-G-protein signaltransfer. Later critical damage, however, is probably of a different nature and may be located in the second-messenger signal transduction pathway downstream from the G protein, not necessarily involving cellular membranes.

Adrenergic beta-Antagonists↗

PubMed1999

Preservation of the rat parotid gland function after radiation by prophylactic pilocarpine treatment: radiation dose dependency and compensatory mechanisms.

PURPOSE: To study the ability of a prophylactic pilocarpine administration to preserve the rat parotid gland function after unilateral irradiation with graded doses of X-rays. METHODS: The right parotid gland of male albino Wistar rats was irradiated with single doses of X-rays (10-30 Gy, at 1.5 Gy min(-1)). Pilocarpine (4 mg/kg) was administered intraperitoneally, 1 hour prior to irradiation. Saliva samples of both left and right parotid gland were collected by means of miniaturized Lashley cups 4 days before and 3, 7, 10, and 30 days after irradiation. The parotid salivary flow rate (microl/min) was used as a parameter for the assessment of parotid gland function. RESULTS: Our data confirm that a single prophylactic treatment of pilocarpine can attenuate radiation-induced loss of gland function. Surprisingly, the effect of pilocarpine was not restricted to the irradiated gland only. Pilocarpine also enhanced the flow rate in the contralateral, nonirradiated gland. The latter effect was found for all doses above 10 Gy and became apparent around 7 days after the radiation treatment. The effectiveness of pilocarpine to attenuate function loss in the irradiated gland decreased with increasing dose and was lost after single doses of 30 Gy. CONCLUSIONS: Our data provide direct evidence that increasing the compensatory potential of the nondamaged gland, at least in part, underlies the "radioprotective effect" of pilocarpine in case of unilateral radiation. The ability of pilocarpine to ameliorate the early radiation-induced impairment of the parotid gland function in the irradiated gland may therefore be dependent on the remaining number of functional cells, and thus on the volume of the gland that lies within the radiation portal.

Animals↗

PubMed1999

Altered association of transcriptionally active DNA with the nuclear-matrix after heat shock.

PURPOSE: Exposure of human cells to heat leads to denaturation and aggregation of proteins. Within the nucleus, it has been suggested that protein aggregation is linked to the selective inhibition by hyperthermia of nucleotide excision repair in transcriptionally active genes. In this study it was investigated in detail whether and how the inhibition of repair of transcriptionally active genes might be related to alterations in their association with the nuclear-matrix. MATERIAL AND METHODS: Different protocols for nuclear-matrix isolation (high salt and lithium 3',5'-diiodosalycilate [LIS] extraction of nuclei) were used to compare DNA loop organization and positioning of transcriptionally active genes in both heated and non-heated cells. RESULTS: DNaseI digestion of total genomic DNA in Cu2+ -stabilized LIS-extracted nuclei revealed that heat shock perturbed the formation of nuclear-matrix attachment sites. Specific labelling of active genes indicated that the number of nuclear-matrix attachment sites in transcriptionally active DNA was increased due to the heat shock. At the level of individual genes, heat treatment led to stabilization of the 5' matrix attachment site (MAR) in the transcriptionally active adenosine deaminase (ADA) housekeeping gene. Moreover, heat shock resulted in the formation of an additional MAR at the 3' end of the ADA gene. The inactive 754 locus was unassociated, irrespective of a heat shock. CONCLUSIONS: The reported changes in chromatin structure might underlie the selective inhibition of repair in transcriptionally active genes and consequently may be mechanistically linked to the sensitization of heated cells to ionizing radiation.

Adenosine Deaminase↗

PubMed1999

Role of DNA-PK subunits in radiosensitization by hyperthermia.

Thermal radiosensitization is thought to result from inhibition of repair of radiation-induced DNA damage, DNA double-strand breaks in particular. Since the DNA-dependent protein kinase (DNA-PK) complex plays a major role in the nonhomologous end-joining of DSBs, it has been suggested that inactivation of this complex as a whole or of its individual subunits by heat might be involved in radiosensitization by heat. To test this hypothesis further, the ability of heat to enhance the radiosensitivity of cells proficient or deficient in either Ku80 or the DNA-PK catalytic subunit (DNA-PKcs) was investigated. In cells of two Ku80-deficient and two DNA-PKcs-deficient and double-strand break-deficient cell lines, the extent of radiosensitization by heat was not reduced compared to that in both their isogenic gene-complemented counterparts as well as to that in their parental cells. Thus radiosensitization by hyperthermia can be obtained irrespective of the Ku80 or DNA-PKcs status in cells. Therefore, Ku80 or DNA-PKcs and hence nonhomologous DSB end-joining do not play a crucial role in the enhancement of cellular radiosensitivity by hyperthermia.

Animals↗

PubMed1998

Enhanced selectivity of hyperthermic purging of human progenitor cells using Goralatide, an inhibitor of cell cycle progression.

Recurrence of leukemia is a major problem after autologous stem cell transplantation. One potential means of reducing this risk is to purge the autologous transplant in vitro by hyperthermia. We have demonstrated that after a hyperthermic treatment of 120 min at 43 degrees C, the leukemic progenitor cells (CFU-AML) are decreased by 5-log but the normal hematopoietic committed progenitor cells (CFU-GM, BFU-E and CFU-E) are reduced by only 1-log. Moreover, the hyperthermic sensitivity coincides with the stem cell hierarchy, ie CFU-GM are less heat sensitive than BFU-E, while CFU-E are the most sensitive. The impact of pretreatment with the tetrapeptide AcSDKP (Goralatide) on the proliferative activity and heat sensitivity of the normal and leukemic progenitor cells was determined. An incubation of 21 h at 37 degrees C with 10(-9) M Goralatide reduces the number of normal hematopoietic progenitor cells in S-phase and concomitantly decreases their hyperthermic sensitivity. This effect implies that the proliferative activity is the major determinant for the detected differences in hyperthermic sensitivity of the subsets in the normal hematopoietic stem cell compartment. In contrast, the cell cycle progression of leukemic progenitor cells is not affected and hence these cells are not protected from hyperthermia-induced cell killing after preincubation with Goralatide. Thus, the treatment with Goralatide increases the therapeutic window of hyperthermia and increases the potential value of this physical purging technique.

Cell Cycle↗

PubMed1998

Artemisinin-derived sesquiterpene lactones as potential antitumour compounds: cytotoxic action against bone marrow and tumour cells.

We determined the in vitro cytotoxic activity of the sesquiterpene lactone endoperoxide artemisinin (1) and some chemically prepared derivatives, which have been found to display cytotoxicity to cloned murine Ehrlich ascites tumour (EAT) cells and human HeLa cells and against murine bone marrow using a clonogenic assay for committed progenitor cells of the granulocyte-monocyte lineage (CFU-GM assay). Comparing artemisinin (1) to deoxyartemisinin (2), the endoperoxide group appeared to play a role in cytotoxicity to CFU-GM cells. Dimers of dihydroartemisinin and dihydrodeoxyartemisinin revealed that the stereochemistry of the ether linkage of the dimers was a more important determinant for this cytotoxic activity. The nonsymmetrical dimer of dihydroartemisinin (3) and the corresponding endoperoxide-lacking dimer of dihydrodeoxyartemisinin (5) were equally cytotoxic to CFU-GM cells. Despite the differences between both systems, it may be stated that most compounds displayed higher cytotoxicity to CFU-GM cells than to EAT cells. Dimers of dihydroartemisinin (3, 4) were selected as potential antitumour compounds and subjected to the National Cancer Institute drug-screening programme consisting of about sixty human cancer cell lines derived from nine different tissues. Both compounds displayed the same specific cytotoxicity pattern. Throughout the screen dimer 3 was more active than 4.

Animals↗

PubMed1998

Radiation-induced apoptosis in relation to acute impairment of rat salivary gland function.

PURPOSE: To find an answer to the question: Are the acute radiation effects on salivary gland function, as seen in earlier studies, causally related to radiation-induced apoptosis? MATERIALS AND METHODS: Rat parotid and submandibular glands were X-irradiated with doses up to 25 Gy and morphological damage assayed up to 6 days after irradiation. Damage to the different cell types in the glands was assessed after H & E staining. Apoptotic appearance was judged by compacted chromatin and fragmentation of cells into lobulated masses. RESULTS: In about 3% of the cells aberrant nuclei were observed after doses as low as 2 Gy and around 7.5 and 24 h after irradiation. About half of these aberrant nuclei had an apoptotic appearance. After a dose of about 5 Gy no dose-response for apoptotic cells was found, as evidenced by a plateau in the dose-effect curve. At 6 days after 2 Gy, no signs of radiation-induced apoptosis was apparent and for most cell types a value close to zero was observed. CONCLUSIONS: Radiation studies on salivary function in the rat show the typical response with respect to dose (5-15 Gy) and time (1-3 days). This differs from reported findings with light microscopy. Therefore, the extent of apoptosis induced by radiation cannot explain the observed gland malfunction. Alternative mechanisms are proposed.

Amylases↗

PubMed1998

DNA damage induction and tumour cell radiosensitivity: PFGE and halo measurements.

PURPOSE: To test whether induction of DNA damage is correlated with tumour-cell radiosensitivity. MATERIALS AND METHODS: Initial DNA damage caused by X-irradiation was measured in ten human tumour cell lines, which largely differed in radiosensitivity, using either the pulsed-field gel electrophoresis assay or the halo technique. RESULTS: None of the parameters of DNA damage correlated with any parameter of cellular radiosensitivity. This was not only true when the analysis was performed on all data but also when the analysis was performed after separating the cell lines into radioresistant and sensitive groups. Even when differences in chromosome number, ploidy and cell cycle distribution were taken into account, no significant correlations were obtained. CONCLUSIONS: Contrary to previous suggestions, differences in the number of double-strand breaks induced or chromatin-related 'presentation' of DNA lesions, measured by pulsed-field gel electrophoresis or halo respectively, are generally not the dominant factors determining tumour-cell radiosensitivity.

Cell Survival↗

PubMed1997

Hsp70 and Hsp40 chaperone activities in the cytoplasm and the nucleus of mammalian cells.

The existence and function of a Hsp40-Hsp70 chaperone machinery in mammalian cells in vivo was investigated. The rate of heat inactivation of firefly luciferase transiently expressed in hamster O23 fibroblasts was analyzed in cells co-transfected with the gene encoding the human Hsp40 (Ohtsuka, K. (1993) Biochem. Biophys. Res. Commun. 197, 235-240), the human inducible Hsp70 (Hunt, C., and Morimoto, R. I. (1985) Proc. Natl. Acad. Sci. U. S. A. 82, 6455-6459), or a combination of both. Whereas the expression of human Hsp70 alone in hamster cells was sufficient for the protection of firefly luciferase during heat shock, expression of the human Hsp40 alone was not. Rather, this led to a small but significant increase in the heat sensitivity of luciferase. The expression of the human Hsp40 only led to heat protection when the human Hsp70 was expressed as well. Under such conditions the rate of luciferase reactivation from the heat-inactivated state was increased, but the rate of inactivation during heat shock was not affected. Using constructs that direct firefly luciferase either to the cytoplasm or to the nucleus (Michels, A. A., Nguyen, V.-T., Konings, A. W. T., Kampinga, H. H., and Bensaude, O. (1995) Eur. J. Biochem. 234, 382-389), it was demonstrated that these chaperone functions are found in both compartments. Our data provide the first evidence on how the Hsp40/Hsp70 chaperone complex acts as heat protector in mammalian cells in vivo.

Animals↗

PubMed1997

Quantification of transforming growth factor-beta in biological material using cells transfected with a plasminogen activator inhibitor-1 promoter-luciferase construct.

Transforming growth factor-beta (TGF-beta), a multifunctional cytokine, can be quantified by a variety of bioassays or immunoassays. One of the disadvantages of these techniques is that they require sample purification to remove components that interfere with the TGF-beta signal. In the current study the feasibility of quantifying TGF-beta in complex biological fluids directly with a recently developed bioassay was examined. This assay is based on the ability of TGF-beta to induce plasminogen activator inhibitor-1 (PAI-1) expression. Mature TGF-beta binds to the receptors of mink lung epithelial cells transfected with a plasminogen activator inhibitor-1 promoter-luciferase construct (PAI/L), resulting in a dose-dependent increase of luciferase activity. Specificity for TGF-beta was proven by treatment of the samples with neutralizing antibodies. The sensitivity and the intraassay precision are comparable to the ELISA. It is demonstrated, however, that, unlike the ELISA, a purification step by, e.g., acid-ethanol extraction prior to the PAI/L assay, is not required. This not only simplifies the assay but also reduces the minimal sample volume and allows to discriminate between latent and mature TGF-beta. The present study furthermore provides insight in the critical steps for accurate TGF-beta determination, which include careful blood collection and sample handling (storage and preparation). With this protocol TGF-beta has been quantified in human plasma, rat plasma, rat saliva, tissue extracts from rat lung, and in culture medium of TGF-beta-producing cells.

Animals↗

PubMed1997

Plasma TGFbeta level in rats after hemithoracic irradiation.

Changes in TGF-beta plasma levels were observed 18 weeks after hemithoracic irradiation in rats. This coincides with an increase in the breathing frequency. being most pronounced between 22 and 28 weeks after irradiation. The correlation suggests a potential role of the circulating TGF-beta in the monitoring of localized radiation-induced lung injury.

Animals↗

PubMed1997

Structure-cytotoxicity relationships of some helenanolide-type sesquiterpene lactones.

This study deals with the cytotoxicity of helenanolide-type (10 alpha-methylpseudoguaianolide) sesquiterpene lactones. We determined the influence of substitution patterns on the toxicity of 21 helenanolides to a cloned Ehrlich ascites tumor cell line, EN2. Within a series of helenalin esters, the acetate (2) and isobutyrate (3) were more toxic than helenalin itself (1). Esters with larger acyl groups (tiglate 4 and isovalerate 5) exhibited a decreased toxicity compared with the parent alcohol (1). Similar relationships were observed between the 6,8-diastereomer of helenalin, mexicanin I (6) and its acetate (7) and isovalerate (8). In contrast, cytotoxicity within a series of 11 alpha, 13-dihydrohelenalin esters (9-12) was shown to be directly related to the size and lipophilicity of the ester side chain, dihydrohelenalin (9) being the least toxic compound in this group. Investigation of several 2,3-dihydrohelenalin derivatives (13-21) with 2 alpha-hydroxy-4-oxo- and 2 alpha,4 alpha-dihydroxy- or -O-acyl-substituted cyclopentane rings (arnifolins and chamissonolides, respectively), for which no pharmacological data have been reported so far, revealed further interesting influences of the substitution pattern on cytotoxicity. The results may be interpreted in terms of lipophilicity and steric effects on the accessibility of the reactive sites considered responsible for biological activity.

Animals↗

PubMed1997

Stereochemistry-dependent cytotoxicity of some artemisinin derivatives.

We determined the cytotoxicity of some artemisinin derivatives against EN2 tumor cells using the MTT assay. Artemisinin (1) was clearly more cytotoxic than deoxyartemisinin (2), which lacks the endoperoxide bridge. Ether-linked dimers of dihydroartemisinin with defined stereochemistry were found to differ in the extent of cytotoxic effect on EN2 cells. The nonsymmetrical dimer (3) was more cytotoxic than the symmetrical dimer (4). The nonsymmetrical dimer of dihydrodeoxyartemisinin (5) lacking the endoperoxide bridges was also effective in the MTT assay, although less cytotoxic than 3 and 4. Similarly, the symmetrical dimer (6) was less effective than 5. Epoxides of artemisitene also showed that stereochemistry was an important factor for cytotoxicity. The results suggested that the endoperoxide bridge was not crucial for cytotoxicity to the tumor cells, but contributed to the cytotoxic effect apparently exerted by the ether linkage of the dimers. Flow cytometry data indicated that the dimers 3 and 4 caused an accumulation of the cells in the G1-phase of the cell cycle. In contrast, artemisinin (1) caused a slight increase of S-phase cells.

Antineoplastic Agents, Phytogenic↗

PubMed1997

Mechanism of hyperthermic potentiation of cisplatin action in cisplatin-sensitive and -resistant tumour cells.

In this study, the mechanism(s) by which heat increases cis-diamminedichloroplatinum (cisplatin, cDDP) sensitivity in cDDP-sensitive and -resistant cell lines of murine as well as human origin were investigated. Heating cells at 43 degrees C during cDDP exposure was found to increase drug accumulation significantly in the cDDP-resistant cell lines but had little effect on drug accumulation in the cDDP-sensitive cell lines. DNA adduct formation, however, was significantly increased in all cell lines studied. Furthermore, ongoing formation of platinum (Pt)-DNA adducts after the end of cDDP treatment was enhanced and/or adduct removal was decreased in heated cells, resulting in relatively more DNA damage remaining at 24 h after the end of cDDP exposure. Correlation plots with survival revealed weak correlations with cellular Pt accumulation (r2 = 0.59) and initial Pt-DNA adduct formation (r2 = 0.64). Strong correlations, however, were found with Pt-DNA adducts at 6 h (r2 = 0.97) and 24 h (r2 = 0.89) after the incubation with the drug. In conclusion, the mechanism by which heat sensitizes cells for cDDP action seems to be the sum of multiple factors, which comprise heat effects on accumulation, adduct formation and adduct processing. This mechanism did not seem to differ between cDDP-sensitive and -resistant cells, emphasizing the potential of hyperthermia to reduce cDDP resistance.

Animals↗