Thermal enhancement of DNA damage by an alkylating agent in human cells

Influence of hyperthermia on efficacy and uptake of carbon nanohorn-cisplatin conjugates

Single-walled carbon nanohorns (SWNHs) have significant potential for use in photothermal therapies due to their capability to absorb near infrared light and deposit heat. Additionally, their extensive relative surface area and volume makes them ideal drug delivery vehicles. Novel multimodal treatments are envisioned in which laser excitation can be utilized in combination with chemotherapeutic-SWNH conjugates to thermally enhance the therapeutic efficacy of the transported drug. Although mild hyperthermia (41-43 °C) has been shown to increase cellular uptake of drugs such as cisplatin (CDDP) leading to thermal enhancement, studies on the effects of hyperthermia on cisplatin loaded nanoparticles are currently limited. After using a carbodiimide chemical reaction to attach CDDP to the exterior surface of SWNHs and nitric acid to incorporate CDDP in the interior volume, we determined the effects of mild hyperthermia on the efficacy of the CDDP-SWNH conjugates. Rat bladder transitional carcinoma cells were exposed to free CDDP or one of two CDDP-SWNH conjugates in vitro at 37 °C and 42 °C with the half maximal inhibitory concentration (IC50) for each treatment. The in vitro results demonstrate that unlike free CDDP, CDDP-SWNH conjugates do not exhibit thermal enhancement at 42 °C. An increase in viability of 16% and 7% was measured when cells were exposed at 42 deg compared to 37 deg for the surface attached and volume loaded CDDP-SWNH conjugates, respectively. Flow cytometry and confocal microscopy showed a decreased uptake of CDDP-SWNH conjugates at 42 °C compared to 37 °C, revealing the importance of nanoparticle uptake on the CDDP-SWNH conjugate's efficacy, particularly when hyperthermia is used as an adjuvant, and demonstrates the effect of particle size on uptake during mild hyperthermia. The uptake and drug release studies elucidated the difference in viability seen in the drug efficacy studies at different temperatures. We speculate that the disparity in thermal enhancement efficacy observed for free drug compared to the drug SWNH conjugates is due to their intrinsic size differences and, therefore, their mode of cellular uptake: diffusion or endocytosis. These experiments indicate the importance of tuning properties of nanoparticle-drug conjugates to maximize cellular uptake to ensure thermal enhancement in nanoparticle mediated photothermal-chemotherapy treatments.

Spatially controlled photothermal heating of bladder tissue through single-walled carbon nanohorns delivered with a fiberoptic microneedle device

Laser-based photothermal therapies for urothelial cell carcinoma (UCC) are limited to thermal ablation of superficial tumors, as treatment of invasive lesions is hampered by shallow light penetration in bladder tissue at commonly used therapeutic wavelengths. This study evaluates the utilization of sharp, silica, fiberoptic microneedle devices (FMDs) to deliver single-walled carbon nanohorns (SWNHs) serving as exogenous chromophores in conjunction with a 1,064-nm laser to amplify thermal treatment doses in a spatially controlled manner. Experiments were conducted to determine the lateral and depth dispersal of SWNHs in aqueous solution (0.05 mg/mL) infused through FMDs into the wall of healthy, inflated, ex vivo porcine bladders. SWNH-perfused bladder regions were irradiated with a free-space, CW, 1,064-nm laser in order to determine the SWNH efficacy as exogenous chromophores within the organ. SWNHs infused at a rate of 50 μL/min resulted in an average lateral expansion rate of 0.36 ± 0.08 cm(2)/min. Infused SWNHs dispersal depth was limited to the urothelium and muscular propria for 50 μL/min infusions of 10 min or less, but dispersed through the entire thickness after a 15-min infusion period. Irradiation of SWNH-perfused bladder tissue with 1,064 nm laser light at 0.95 W/cm(2) over 40 s exhibited a maximum increase of approximately 19 °C compared with an increase of approximately 3 °C in a non-perfused control. The results indicate that these silica FMDs can successfully penetrate into the bladder wall to rapidly distribute SWNHs with some degree of lateral and depth control and that SWNHs may be a viable exogenous chromophore for photothermal amplification of laser-based UCC treatments.

Cytotoxic effect of 1,3 bis (2-chloroethyl)-N-nitrosourea at elevated temperatures: Arrhenius plot analysis and tumour response

The effect of hyperthermia on the cytotoxicity of 1,3-bis-(2-chloroethyl)-N-nitrosourea (BCNU) was investigated in vitro and in vivo. Tumour cells were early-generation isotransplants of a spontaneous C3Hf/Sed mouse fibrosarcoma, FSa-II. For in vitro studies, single cell suspensions containing 1.0 x 10(6) cells/ml were treated in a water bath where a desired temperature was maintained by a constant-temperature circulator. Cell survival was determined by lung colony assay immediately thereafter. For in vivo studies the tumour cell suspensions were transplanted into the dorsal site of the C3Hf/Sed mouse foot. Tumours were treated by immersing animal feet into a constant-temperature water bath when tumours reached an average diameter of 4 mm (35 mm3). The tumour growth (TG) time or the time for one-half of the treated tumours to reach 1000 mm3 from initial treatment day was used as an endpoint. BCNU dose-cell survival curve at 37 degrees C was exponential with a D0 of 1.1 microgram/ml. Dose-cell survival curves at 37-43 degrees C were determined as a function of treatment time at pH 6.7 and 7.4. BCNU of 1 microgram/ml was added immediately before treatment. The slope of the survival curve became steeper with increasing temperature, indicating that the cytotoxic effect of BCNU was enhanced by hyperthermia. The Arrhenius plot analysis showed that activation energies at pH 6.7 and 7.4 were 53 and 51 kcal/M, respectively (no significant difference). Of interest in this analysis was that the Arrhenius plot did not show a breaking point which has been observed for other agents. Further investigation demonstrated that the decomposition of BCNU, which has been reported to be essential for production of reactive intermediates, occurred in aqueous medium at elevated temperatures. The magnitude of this decomposition depended on treatment temperature. As a result, preheated BCNU became less cytotoxic with an increase in preheating temperatures. The activation energy for this decomposition was about one-half of the activation energy for BCNU cytotoxicity. Studies in vivo indicated that the effect of BCNU was enhanced with increasing temperatures, and the enhancement was greatest when BCNU was administered i.p. immediately before hyperthermia. A glucose dose of 5 g/kg administered i.p. 60 min before hyperthermia further enhanced the antitumour effect of BCNU.

Whole-body hyperthermia. Rationale and potential use for cancer treatment

Whole-body hyperthermia is the controlled elevation of systemic temperature for therapeutic purposes. Historically, this treatment has been used for symptomatic control of many diseases. Recently, the potential therapeutic benefit of whole-body hyperthermia in the management of neoplastic disease has been investigated vigorously. The rationale for improved tumor control is based on heat-induced enhancement of the antineoplastic effects of radiation and chemotherapy. Although the complex biologic interaction of heat and radiation has been studied for many years, chemotherapy combined with hyperthermia has been studied less thoroughly. Despite a lack of adequate long-term laboratory and clinical investigation, use of whole-body hyperthermia with chemotherapy and radiotherapy is a logical and potentially powerful therapeutic strategy for neoplasia. Relevant issues regarding the application of whole-body hyperthermia with more traditional modes of therapy are being studied in preliminary clinical trials involving dogs and humans. Identification of optimal timing and sequencing of adjunctive therapy, proper cytotoxic drug application, methods to further minimize toxicity, and heat-sensitive tumor types will lead to expanded clinical use of whole-body hyperthermia. The historical development, clinical rationale, and application of whole-body hyperthermia for the control of disseminated or refractory neoplasia in humans and dogs is reviewed.

Interstitial hyperthermia and iridium brachytherapy in treatment of malignant glioma. A phase I clinical trial

An oncolytic effect of hyperthermia in the 42 degrees to 43 degrees C range has been previously demonstrated in cell culture and animal models. To apply this modality clinically, an interstitial microwave antenna array system has been developed for the delivery of controlled hyperthermia to an intracranial tumor volume, and a Phase I clinical trial involving six patients with malignant gliomas was undertaken. The protocol to study technical feasibility and patient tolerance combined interstitial iridium-192 irradiation and interstitial hyperthermia with 60-minute hyperthermia sessions immediately before and after brachytherapy. After-loading catheters suitable for both treatment modalities were implanted using a computerized tomography-assisted technique. Thermometry data confirmed the ability of a microwave antenna system to achieve reliable temperature distributions, and reasonable patient tolerance was documented.

Results of genotoxicity testing of mazindol (degonan), lithium carbonicum (contemnol) and dropropizine (ditustat) in Chinese hamster V79 and human EUE cells

We studied inhibition of DNA synthesis, alkaline elution of DNA, cytotoxicity and occurrence of induced 6-thioguanine resistant mutants in mammalian cells, treated with mazindol, lithium carbonicum, and dropropizine, respectively, in the presence and in the absence of microsomal fraction S9. Among the above-mentioned clinically used drugs only dropropizine showed neither mutagenic nor clastogenic effects. Lithium carbonicum manifested a weak and mazindol a medium genotoxic response which was in both cases reduced in the presence of microsomal fraction S9.

Integration of allogeneic lymphocyte immunotherapy with short-course chemotherapy and hypoenergic hyperthermia: a "triple-threat" treatment for disseminated cancer

A strategy for treatment of disseminated cancer is proposed which unites short-course chemotherapy, local hyperthermia, and allogeneic lymphocyte immunotherapy, designed and timed so as to optimize their synergistic interactions. Short-course chemotherapy potentiates allogeneic lymphocyte immunotherapy, and in turn is potentiated by subsequent courses of local hyperthermia. Response to hyperthermia can be enhanced by measures which selectively inhibit tumor blood flow, impair tumor energy metabolism, and produce tumor acidification; these include induction of prolonged hyperglycemia, and administration of selectively activated "hypoenergic" agents which inhibit or uncouple tumor respiration. It is anticipated that these methods will enable a significant advance in the control of metastasized solid tumors.

Effect of timing and sequence of hyperthermia and cyclophosphamide on a neurogenic rat tumor (BT4A) in vivo

The interaction of hyperthermia (HT) 1 hour at 44.0 degrees C and cyclophosphamide (CP) 200 mg/kg was studied in vivo in a solid transplantable neurogenic rat tumor (BT4A) in the foot of BD IX rats. HT was given by water bath heating. When both modalities were close in time (CP immediately before HT or 1 hour before HT), an enhanced effect with complete regression and cure of tumors was seen. This could not be obtained with either modality alone. Extending the interval between treatments within 24 hours, an effect equal to the sum of each modality was obtained when HT was given before CP, while HT after CP was less effective. Timing and sequence may be critical factors for the optimal combination of HT and cytotoxic drugs.

Thermal inhibition of repair of methylmethane sulfonate-damaged DNA in chick embryo fibroblasts

Chick embryo fibroblasts were treated with the monofunctional alkylating agent methylmethane sulfonate at various concentrations for 1 h at 42 degrees C, rinsed and then incubated post-treatment at various temperatures at which the kinetics of alkali-labile bond disappearance was followed. Growth experiments showed that these cells grew similarly at temperatures of either 37 degrees C or 42 degrees C. Repair as assessed by removal of alkali-labile bond was also similar for postincubation in the temperature range 37-42 degrees C for damage due to methylmethane sulfonate treatment at concentrations less than 1.5 mM. When the postincubation temperature was raised higher than 42.5-43 degrees C, this type of repair was stopped. The normal internal body temperature of adult chickens is about 41.6 degrees C. Hence the present finding indicates that chick cells are much more severely restricted in DNA repair at temperatures above normal than are mammalian cells, which can function in this respect for several deg. C above 37 degrees C.

DNA repair assays as tests for environmental mutagens. A report of the U.S. EPA Gene-Tox Program

A literature review was undertaken to determine the usefulness of DNA repair assays, other than unscheduled DNA synthesis, as screening techniques for mutagenic carcinogens. 92 reports were found to contain useful data for 49 chemicals using 6 techniques, namely, (1) cesium chloride equilibrium density gradients to study repair replication, (2) benzoylated naphthoylated diethylaminoethyl cellulose columns to study repair replication, (3) 313-nm irradiation of DNA containing bromodeoxyuridine to study repair replication, (4) alkaline elution to study repair of single-strand breaks and crosslinks, (5) alkaline sucrose gradients to study repair of single-strand breaks, and (6) direct assays for removal of adducts from DNA. Almost all of the 49 chemicals studied were known mutagens or carcinogens and/or known inducers of DNA repair, 9 compounds failed to elicit DNA repair by at least 1 assay technique, and at least 3 of these were not tested by the most appropriate and sensitive method. Nevertheless, although valid for studying repair phenomena in eukaryotic cells, these assays are not considered useful for screening. They are time-consuming, expensive, and/or require highly specialized skills. Despite the high frequency of positive reports, it is obvious from the literature that repair assays will fail to detect, or will detect with low efficiency, those agents whose main action is either intercalation or induction of strand breaks. For these and other reasons, DNA repair as a basis for screening for mutagenic carcinogens is not considered to be a useful concept.

Synergistic denaturant therapy--a general strategy for treatment of solid malignancies

"Synergistic denaturant therapy" is defined as the acute disruption of tumor cell structure by concurrent application of "denaturant" modalities such as hyperthermia, tumor-specific acidification, hypoenergia, ischemia, sulphydryl blockade, free-radical generation, detergents, and chemical denaturants (e.g. DMSO). Possible techniques for effective and tumor-specific clinical application of these modalities are discussed, and experimental investigations of their use in cancer therapy, alone or in synergistic combinations, are cited. Various of these modalities may also be used to potentiate the efficacy and specificity of traditional anti-mitotic therapies. Numerous therapeutic advantages are offered by a "synergistic denaturant" approach.

The response of mouse skin to combined hyperthermia and X-rays

The effects of combined hyperthermia and X-irradiation were studied in the skin of the mouse ear. Ears were heated for 1 hour by immersion in a waterbath at temperatures ranging from 37 degrees C--43 degrees C. These heat treatments had little visible effect alone, but when combined with X-rays, enhanced the radiation response. Enhancement depended on the degree of heating. When heat was given immediately after X-rays, the radiation dose to cause a given skin reaction had to be reduced by about 10 per cent for 37 degrees C and about 40 per cent of 43 degrees C. The timing and sequence of the two treatments were important. Heat after X-rays was less effective than heat before X-rays. When heat followed X-rays, the enhancing effect was lost completely if the interval exceeded 4 hours. When heat preceded X-rays, the effect was lost more slowly, depending on temperature. The implications of this for the treatment of cancer by combined therapy are discussed.

Repair processes and the response of dividing and non-dividing cells to methyl methanesulphonate and dimethyl sulphate

A method for producing a viable non-dividing population of Chinese hamster V79 cells in suspension is described and the characteristics of the population outlined. The stationary population is more sensitive to methylating agents than a similar but exponentially growing population, the increased sensitivity arising from the loss of the shoulder from the survival curve. The extent of reaction of the agent with cellular macromolecules is similar in both cases. The repair capabilities of the two populations was examined. Non-semiconservative DNA repair synthesis occurs whether the cells are in a growth or no-growth condition when insulted. Repair of single-strand breaks, which arise following methylation, also proceeds up to the size of the replicon. The relationship of this stationary population to other no-growth conditions and its utility as a model for carcinogenesis studies is discussed.

Temperature-sensitive DNA repair of ultraviolet damage in human cell lines

Following exposure to ultraviolet irradiation (UV), two of three human fibroblast strains and one of three melanoma cell lines showed lower rates of thymine dimer excision during 24 h at 40 degrees C than at 36 degrees C. All lines had lower rates at 32 degrees C. Autoradiographic studies of three fibroblast strains and four melanoma lines incubated for four hours after irradiation revealed decreased unscheduled DNA synthesis at 42 degrees C compared with 36 degrees C. The rate of semiconservative DNA synthesis was decreased at the upper temperature in both series of experiments. All eight cell lines tested showed decreased repair at 42 degrees C, as judged by slower sedimentation and increased heterogeneity of parental DNA in alkaline sucrose gradients. Experiments using the DNA synthesis inhibitor Actinomycin D suggested that these effects were due to temperature-sensitive repair synthesis. In the two lines studied, preincubation of cells at 42 degrees C apparently increased the extent of UV damage. Although by no means conclusive, these results are consistent with the possibility that temperature-sensitive DNA repair is a contributory factor in some cases of solar carcinogenesis.