Combination of cisplatin and radiation in cell culture: effect of duration of exposure to drug and timing of irradiation

Combining Cisplatin with Different Radiation Qualities-Interpretation of Cytotoxic Effects In Vitro by Isobolographic Analysis

BACKGROUND

The combination of platinum-containing cytostatic drugs with different radiation qualities has been studied for years. Despite their massive side effects, these drugs still belong to the therapeutic portfolio in cancer treatment. To overcome the disadvantages of cisplatin, our study investigated the cytotoxic effects of combining radionuclides with cisplatin.

METHODS

FaDu cells were treated with cisplatin (concentration ≈ 2 µM) and additionally irradiated after two hours with the alpha-emitter 223Ra, the beta-emitter 188Re as well as external X-rays using dose ranges of 2-6 Gy. Cell survival was followed by colony formation assays and plotted against cisplatin concentration and radiation dose. The results were interpreted by isobolograms.

RESULTS

Isobolographic analyses revealed a supra-additive cytotoxic effect for the combination of cisplatin and 223Ra. A sub-additive effect was observed for the combination of cisplatin and 188Re, whereas a protective effect was found for the combination with X-rays.

CONCLUSIONS

The combination of cisplatin and 223Ra may have the potential to create a successfully working therapy scheme for various therapy approaches, whereas the combination with 188Re as well as single-dose X-ray treatment did not lead to a detectable radiosensitizing effect. Thus, the combination with alpha-emitters might be advantageous and, therefore, should be followed in future studies when combined with cytostatic drugs.

Timing of chemotherapy and radiation delivery for patients receiving chemoradiation for head and neck cancer: When does "concurrent" mean concurrent?

PURPOSE

To analyze practice patterns focusing on variations in the timing of chemotherapy relative to radiation in patients treated with concurrent chemoradiation for head and neck cancer.

METHODS AND MATERIALS

The medical records of 302 consecutive adult patients treated with concurrent chemoradiation for head and neck cancer between April 2014 and February 2022 were reviewed. After excluding 38 patients who received non-platinum-based regimens, induction chemotherapy, and/or had non-squamous cell histology, a total of 264 patients formed the primary population. To study the variability in which concurrent chemoradiation was delivered, descriptive statistics were used to determine the percentage of patients who deviated from starting chemotherapy and radiation on the same day. The chi-square statistic was used to compare differences in proportion among various subsets. A Cox proportional hazards model was then used to perform a multi-variate analysis to identify factors which independently influenced the likelihood for non-adeherence.

RESULTS

Among the 264 patients, a total of 187 patients (70.8%) had chemotherapy and radiation started on the same day with 171 of these (91.4%) receiving chemotherapy prior to radiation delivery. On multivariate analysis, both non-Caucasian ethnicity (OR: 1.13, 95% C.I. 1.01-1.20) and being non-English speaking (OR: 1.39; 95% C.I. 1.18--1.51) was significantly associated with greater likelihood of the receipt of radiation and chemotherapy on different days.

CONCLUSION

Significant variation exists in the timing of chemotherapy relative to radiation for concurrent chemoradiation in the clinical setting. The potential repercussions on outcome warrante further invesigtation and are discussed.

Impact of fractionated cisplatin and radiation treatment on cell growth and accumulation of DNA damage in two normal cell types differing in origin

Evidence on the impact of chemotherapy on radiotherapy-induced second malignant neoplasms is controversial. We estimated how cisplatin modulates the in vitro response of two normal cell types to fractionated radiation. AHH-1 lymphoblasts and VH10 fibroblasts were irradiated at 1 Gy/fraction 5 and 3 times per week during 12 and 19 days, respectively, and simultaneously treated with 0.1, 0.2, 0.4, 0.8, 1.7 and 3.3 µM of cisplatin twice a week. Cell growth during treatment was monitored. Cell growth/cell death and endpoints related to accumulation of DNA damage and, thus, carcinogenesis, were studied up to 21 days post treatment in cells exposed to radiation and the lowest cisplatin doses. Radiation alone significantly reduced cell growth. The impact of cisplatin alone below 3.3 µM was minimal. Except the lowest dose of cisplatin in VH10 cells, cisplatin reduced the inhibitory effect of radiation on cell growth. Delayed cell death was highest in the combination groups while the accumulation of DNA damage did not reveal a clear pattern. In conclusion, fractionated, concomitant exposure to radiation and cisplatin reduces the inhibitory effect of radiation on cell proliferation of normal cells and does not potentiate delayed effects resulting from accumulation of DNA damage.

Auger electrons for cancer therapy - a review

Background

Auger electrons (AEs) are very low energy electrons that are emitted by radionuclides that decay by electron capture (e.g. ¹¹¹In, ⁶⁷Ga, ^99mTc, ^195mPt, ¹²⁵I and ¹²³I). This energy is deposited over nanometre-micrometre distances, resulting in high linear energy transfer (LET) that is potent for causing lethal damage in cancer cells. Thus, AE-emitting radiotherapeutic agents have great potential for treatment of cancer. In this review, we describe the radiobiological properties of AEs, their radiation dosimetry, radiolabelling methods, and preclinical and clinical studies that have been performed to investigate AEs for cancer treatment.

Results

AEs are most lethal to cancer cells when emitted near the cell nucleus and especially when incorporated into DNA (e.g. ¹²⁵I-IUdR). AEs cause DNA damage both directly and indirectly via water radiolysis. AEs can also kill targeted cancer cells by damaging the cell membrane, and kill non-targeted cells through a cross-dose or bystander effect. The radiation dosimetry of AEs considers both organ doses and cellular doses. The Medical Internal Radiation Dose (MIRD) schema may be applied. Radiolabelling methods for complexing AE-emitters to biomolecules (antibodies and peptides) and nanoparticles include radioiodination (¹²⁵I and ¹²³I) or radiometal chelation (¹¹¹In, ⁶⁷Ga, ^99mTc). Cancer cells exposed in vitro to AE-emitting radiotherapeutic agents exhibit decreased clonogenic survival correlated at least in part with unrepaired DNA double-strand breaks (DSBs) detected by immunofluorescence for γH2AX, and chromosomal aberrations. Preclinical studies of AE-emitting radiotherapeutic agents have shown strong tumour growth inhibition in vivo in tumour xenograft mouse models. Minimal normal tissue toxicity was found due to the restricted toxicity of AEs mostly on tumour cells targeted by the radiotherapeutic agents. Clinical studies of AEs for cancer treatment have been limited but some encouraging results were obtained in early studies using ¹¹¹In-DTPA-octreotide and ¹²⁵I-IUdR, in which tumour remissions were achieved in several patients at administered amounts that caused low normal tissue toxicity, as well as promising improvements in the survival of glioblastoma patients with ¹²⁵I-mAb 425, with minimal normal tissue toxicity.

Conclusions

Proof-of-principle for AE radiotherapy of cancer has been shown preclinically, and clinically in a limited number of studies. The recent introduction of many biologically-targeted therapies for cancer creates new opportunities to design novel AE-emitting agents for cancer treatment. Pierre Auger did not conceive of the application of AEs for targeted cancer treatment, but this is a tremendously exciting future that we and many other scientists in this field envision.

Effects of Gemcitabine in Normaland Transformed Human Lung Cell Cultures: Cytotoxicity and Increase in Radiation Sensitivity

Aims and Background

Several anticancer drugs increase cell sensitivity to irradiation. Gemcitabine (2′, 2′ difluorodeoxycytidine) decreases the cellular dNTP pools and thus significantly increases the sensitivity to the DNA damaging effects of low-dose radiation. In this study we have investigated whether gemcitabine may play a role as radiosensitizer also in lung adenocarcinoma treatment.

Methods & Study Design

We studied this nucleoside analogue in normal and transformed human cell lines (fetal lung and lung adenocarcinoma). After drug treatment, cell lines were irradiated with different doses. Cell damage following drug treatment and/or irradiation was assessed by measuring intracellular ATP level and by the colony forming assay.

Results

The two cell lines significantly differed in their sensitivity to the toxic effects of the drug; the normal cell line was much more resistant than its transformed counterpart. This difference was observed in both assays, although it was more evident in the colony forming assay. A low radiation dose (50-100 cGy) did not cause any significant damage to transformed cells; normal cells were more resistant and doses up to 500 cGy caused little damage. However, when transformed cells were pretreated for three hours with gemcitabine, even a nontoxic concentration of the drug (1-10 nM) caused a marked sensitization of the cells to irradiation (50-100 cGy). The radiosensitizing effect of gemcitabine could be observed also in normal cells, although these cells were more resistant to the damaging effects of both anticancer treatments.

Conclusions

This study demonstrates that gemcitabine, a chemotherapeutic agent already used in the clinic, could be proposed as a radiosensitizer for radiation therapy of lung adenocarcinoma, having a clearly potentiating effect on low-dose radiation.

Cisplatin radiosensitizes radioresistant human mesenchymal stem cells

Cisplatin-based chemo-radiotherapy is widely used to treat cancers with often severe therapy-associated late toxicities. While mesenchymal stem cells (MSCs) were shown to aid regeneration of cisplatin- or radiation-induced tissue lesions, the effect of the combined treatment on the stem cells remains unknown. Here we demonstrate that cisplatin treatment radiosensitized human bone marrow-derived MSCs in a dose-dependent manner and increased levels of radiation-induced apoptosis. However, the defining stem cell properties of MSCs remained largely intact after cisplatin-based chemo-radiation, and stem cell motility, adhesion, surface marker expression and the characteristic differentiation potential were not significantly influenced. The increased cisplatin-mediated radiosensitivity was associated with a cell cycle shift of MSCs towards the radiosensitive G2/M phase and increased residual DNA double-strand breaks. These data demonstrate for the first time a dose-dependent radiosensitization effect of MSCs by cisplatin. Clinically, the observed increase in radiation sensitivity and subsequent loss of regenerative MSCs may contribute to the often severe late toxicities observed after cisplatin-based chemo-radiotherapy in cancer patients.

Cisplatin Concentrations in Long and Short Duration Infusion: Implications for the Optimal Time of Radiation Delivery

INTRODUCTION

Cisplatin has radiosensitizing properties and the best sensitization to radiotherapy occurs with a higher plasma concentration of cisplatin. To our knowledge the optimal time sequence between chemotherapy and administration of radiation therapy, to obtain maximum effect from concurrent chemoradiation is unclear.

AIM

The aim of this study was to measure the two cisplatin infusion regimens in order to determine the total and free cisplatin post infusion concentration changes over time. These changes may have clinical implications on the optimum time of administration of post infusion radiation therapy.

MATERIALS AND METHODS

Two cohorts of patients were recruited and both, total and free plasma concentration of cisplatin following long and short durations of intravenous infusion was determined. Blood samples were collected at 0.5, 1, 1.5, 2, 3 and 5 hours from the start of the infusion in the 1hour infusion group and at 2, 3, 3.5, 4, 6 and 24 hours from the start of the infusion, in the 3 hour infusion group. Total and free cisplatin concentrations were measured using a validated HPLC-UV method.

RESULTS

The highest concentration of total and free cisplatin was achieved at the end of the infusion in both regimens. Total cisplatin concentration declined 30 minutes after the end of infusion in both the groups. After 1hour of discontinuing cisplatin, the free cisplatin concentration also declined significantly.

CONCLUSION

We conclude that radiation should be administered within 30 minutes of completion of the infusion irrespective of the duration of infusion.

Conventional radiotherapy with concurrent weekly Cisplatin in locally advanced head and neck cancers of squamous cell origin - a single institution experience

BACKGROUND

Platinum based concurrent chemo-radiation is the de-facto standard of care in the non-surgical management of locally-advanced head and neck cancer of squamous origin. Three-weekly single agent cisplatin at 100 mg/m2 concurrent with radical radiotherapy has demonstrated consistent improvement in loco-regional control and survival. This improvement is however at the cost of considerable hematologic toxicity and poor overall compliance. The routine use of this regime is improbable in developing countries with limited resources. We therefore aimed to determine the safety and efficacy of an alternative regime of weekly cisplatin and concurrent radiotherapy in such patients.

MATERIALS AND METHODS

January-05 and April-12, 188 patients of locally-advanced head and neck cancer of squamous origin were treated with concurrent weekly-cisplatin at 35 mg/m2 and conventional radiotherapy 60-66Gy/30-33 fractions/5 days per week.

RESULTS

Overall, 95% patients received planned doses of RT while 74% completed within the stipulated overall treatment time of <50 days. Eighty-two percent received at-least 5 weekly cycles. Grade-III/IV mucositis was seen in 58%/9% respectively, which resulted in mean weight loss of 9.2% from a pre-treatment mean of 54.5 kg. Grade-III hematologic toxicity-0.5%; grade II nephrotoxicity-2.5% and grade III emesis-3% were also seen. Grade-III/IV subcutaneous toxicity-10%/1% and grade-III/IV xerostomia-10%/0% were observed. Complete responses at the primary site, regional nodes and overall disease were seen in 86%, 89% and 83% patients respectively. The median and 5-years disease-free survival were 26 months and 39.4% respectively, while the median and overall survival were 27 months and 41.8% respectively.

CONCLUSIONS

Weekly-cisplatin at 35 mg /m2 when delivered concurrently with conventional radical RT (at-least 66y/33 fractions) in locally-advanced head and neck cancer is well tolerated with minimal hematologic and neprologic toxicity and can be routinely delivered on an out-patient basis. It is an effective alternative to the standard 3-weekly cisplatin especially in the context of developing countries.

Complex cisplatin-double strand break (DSB) lesions directly impair cellular non-homologous end-joining (NHEJ) independent of downstream damage response (DDR) pathways

The treatment for advanced stage non-small cell lung cancer (NSCLC) often includes platinum-based chemotherapy and IR. Cisplatin and IR combination therapy display schedule and dose-dependent synergy, the mechanism of which is not completely understood. In a series of in vitro and cell culture assays in a NSCLC model, we investigated both the downstream and direct treatment and damage effects of cisplatin on NHEJ catalyzed repair of a DNA DSB. The results demonstrate that extracts prepared from cisplatin-treated cells are fully capable of NHEJ catalyzed repair of a DSB using a non-cisplatin-damaged DNA substrate in vitro. Similarly, using two different host cell reactivation assays, treatment of cells prior to transfection of a linear, undamaged reporter plasmid revealed no reduction in NHEJ compared with untreated cells. In contrast, transfection of a linear GFP-reporter plasmid containing site-specific, cisplatin lesions 6-bp from the termini revealed a significant impairment in DSB repair of the cisplatin-damaged DNA substrates in the absence of cellular treatment with cisplatin. Together, these data demonstrate that impaired NHEJ in combined cisplatin-IR treated cells is likely the result of a direct effect of cisplatin-DNA lesions near a DSB and that the indirect cellular effects of cisplatin treatment are not significant contributors to the synergistic cytotoxicity observed with combination cisplatin-IR treatment.

γ-Secretase inhibitor enhances antitumour effect of radiation in Notch-expressing lung cancer

Background:

Notch receptor has an important role in both development and cancer. We previously reported that inhibition of the Notch3 by γ-secretase inhibitor (GSI) induces apoptosis and suppresses tumour proliferation in non-small-cell lung cancer. Although radiation is reported to induce Notch activation, little is known about the relationship between radiation and Notch pathway.

Methods:

We examined the effect of combining GSI and radiation at different dosing in three Notch expressing lung cancer cell lines. The cytotoxic effect of GSI and radiation was evaluated using MTT assay and clonogenic assay in vitro and xenograft models. Expressions of Notch pathway, mitogen-activated protein kinase (MAPK) pathway and Bcl-2 family proteins were investigated using western blot analysis.

Results:

We discovered that the antitumour effect of combining GSI and radiation was dependent on treatment schedule. γ-Secretase inhibitor administration after radiation had the greatest growth inhibition of lung cancer in vitro and in vivo. We showed that the combination induced apoptosis of lung cancer cell lines through the regulation of MAPK and Bcl-2 family proteins. Furthermore, activation of Notch after radiation was ameliorated by GSI administration, suggesting that treatment with GSI prevents Notch-induced radiation resistance.

Conclusion:

Notch has an important role in lung cancer. Treatment with GSI after radiation can significantly enhance radiation-mediated tumour cytotoxicity.

Targeting ErbB-1 and ErbB-4 in irradiated head and neck cancer: results of in vitro and in vivo studies

BACKGROUND

ErbB oncogenes have a major role in cancer. The role of ErbB-4 in cancer cell biology and the effect of anti-ErbB-1 and anti-ErbB-4 monoclonal antibodies were evaluated in this study.

METHODS

ErbB-4 expression and binding was evaluated by Western blot, enzyme-linked immunosorbent assay (ELISA), fluorescent microscopy, and flow cytometry. Cell survival was measured by XTT assay. Tumor progression was followed up in nude mice model.

RESULTS

High ErbB-1 levels in head and neck cancer cell lines were determined, whereas ErbB-4 expression varied. Specific antibody binding to the cells was demonstrated. High ErbB-4 expressing squamous cell carcinoma 1 (SCC-1) cells proliferated faster and generated faster growing tumors in mice. Cetuximab and mAb-3 reduced cell survival proportional to ErbB-1 and ErbB-4 expression. Combination of antibodies with irradiation was most effective in reducing cell survival and tumor growth.

CONCLUSION

ErbB-4 plays a role in head and neck cancer cell biology. Anti-ErbB-4 targeted therapy can serve as a new strategy against head and neck cancer when combined with established treatments.

Effect of Chinese herbal therapy on breast cancer adenocarcinoma cell lines

Despite the widespread use of medicinal herbs to prevent and treat many diseases, including cancer, there are insufficient scientific data on the safety and efficacy of the majority of herbal therapies. The aim of this study was to assess the effect of a unique Chinese herbal therapy (CHT) from controlled manufactured concentrated powders, on an in vitro model of breast cancer. Three breast adenocarcinoma cell lines (MDA-231, MDA-453, T47D) were exposed to CHT for 72 h. Cell viability was assessed by XTT (sodium 3'-[1-(phenylaminocarbonyl)-3, 4-tetra zolium]-bis(4-methoxy-6-nitro) benzene sulphonic acid hydrate) assay. Apoptosis and cell cycle stage were determined by fluorescence-activated cell sorting (FACS) analysis. CHT decreased cell survival in a dose-dependent manner in all tested cell lines. FACS analysis of treated and non-treated T47D cells demonstrated that the inhibitory effect of CHT was associated with an increase in apoptosis. A randomized clinical trial is currently underway to investigate CHT as supplementary therapy for breast cancer patients receiving chemotherapy.

Uptake of CDDP-containing polymeric micelles by cells using particle induced X-ray emission

Polymeric micelles loaded with cis-diamminedichloroplatinum(II), CDDP, (cisplatin micelles) enable higher accumulation in solid tumors and lower toxicities compared with CDDP alone. The combined use of cisplatin micelles with radiation is expected to enhance therapeutic effects and reduce side effects. The kinetics of cisplatin micelle uptake, however, have not been fully understood. Particle Induced X-Ray Emission has been employed in this study to measure the time transients of platinum in Chinese Hamster ovary cells. The results show that the platinum content of cells treated with cisplatin micelles increased more slowly than with CDDP alone, suggesting that cellular uptake could be controlled using micelles. The CDDP released from micelles was predominantly incorporated into the cells by diffusion. The uptake characteristics were further analyzed using micelles with different collapse rates. The results and techniques used in this study will be useful for designing an optimum treatment plan combining platinum-containing polymeric micelles and radiation in clinical applications.

Modulation of radiosensitivity in Chinese hamster lung fibroblasts by cisplatin

The effects of cisplatin exposure time, concentration, and irradiation sequence on the sensitivity of Chinese hamster lung fibroblasts (V79) to gamma-ray exposure were examined. Based on clonogenic cell survival, the cisplatin concentrations corresponding to 50% cell survival (EC(50)) for exposure times of 1 h to 7 days followed a 2-phase exponential decay and ranged from 28.26 +/- 3.32 to 1.53 +/- 0.24 micromol/L, respectively. When cells were treated at EC(50) for exposures of less than 4 h and irradiated immediately, cisplatin inhibited the effect of radiation. Exposures of 4-6 h did not affect radiosensitivity. For exposures of 8-12 h, radiosensitization was observed, which disappeared at 14 h and reappeared for much longer cisplatin treatments. At the lowest achievable EC(50) (1.53 micromol/L), radiosensitization was observed if irradiation was delayed for 1-8 h. This enhancement in radiosensitivity disappeared for irradiation delays of 10-12 h, but reappeared when irradiation was delayed for 14-18 h. These data demonstrate that the mode of interaction between cisplatin and gamma-irradiation depends on the concentration and exposure time of cisplatin, as well as on the timing of irradiation after cisplatin administration. Consideration of changes in cell cycle kinetics may contribute to the improvement of treatment outcomes in adjuvant chemoradiotherapy involving cisplatin.

Physicochemical and biological characterization of ceramide-containing liposomes: paving the way to ceramide therapeutic application

Ceramides mediate antiproliferative responses, and it has been proposed that increasing the level of ceramides in cancer cells may have a therapeutic antitumor effect. However, ceramides, because of their high "packing parameter" (PP), do not form lipid assemblies that can be dispersed in a form suitable for intravenous administration. We found that nanoliposomes containing short- or medium-chain ceramides are unstable because of their very high (>1.3) PP. To overcome this major obstacle, we included the lipopolymer 2kPEG-DSPE, which reduces the additive PP. The presence of PEG-DSPE allows the formation of highly stable (>1 year) ceramide (Cer)-containing nanoliposomes suitable for systemic administration. Using tumor cell lines, we found that the ceramide cytotoxicity was not impaired by their inclusion in nanoliposomes. The use of 14C-labeled ceramides shows that the C6Cer, but not C16Cer, was transferred from the nanoliposomes to the cells and metabolized efficiently. The difference between the two ceramides is related to the large difference between their critical aggregation concentration and was correlated with the much higher cytotoxity of liposomal C6Cer. The activity of 2kPEG-DSPE as a steric stabilizer (as previously shown for Doxil) was also confirmed for C6Cer-containing nanoliposomes. The 2kPEG-DSPE lipopolymer significantly reduced the desorption rate of the ceramide from the liposome bilayer, thereby allowing liposomes containing C6Cer to reach the tumor site and to demonstrate therapeutic efficacy.

Combining radiation with oxaliplatin: a review of experimental results

Oxaliplatin is integrated in treatment strategies against a variety of cancers including chemoradiation protocols against gastrointestinal, especially rectal cancers. Solid biological data with respect to radiosensitizing activity of oxaliplatin are still rare. This review is based on in vitro and experimental in vivo data concerning the combination of oxaliplatin and radiation published until July 2007. Taking either cell viability or clonogenic survival as an endpoint all reported on oxaliplatin-induced radiosensitization, and enhancement ratios ranged from 1.1 to 2.2. In vivo, enhanced tumor growth delay after combined oxaliplatin and radiation treatment was also reported. Therefore, oxaliplatin should be considered a potent radiosensitizer, although the mechanisms causing radiosensitizing properties of oxaliplatin have not been studied in detail. Herein, they are discussed with respect to apoptosis induction, p53-related signalling, cell cycle control, and DNA-repair.

Effect of treatment schedule on the interaction of Cisplatin and radiation in human lung cancer cells

This study was designed to determine the effects of the treatment schedule on the interaction between cisplatin and radiation. Cells of a human squamous cell lung cancer cell line were treated with cisplatin and radiation using three treatment protocols: 1-h exposure to cisplatin immediately followed by irradiation (A), 4-day continuous exposure to cisplatin immediately followed by irradiation (B), and 1-h exposure to cisplatin followed by irradiation after a 4-day interval (C). The interactions were assessed by isobologram, cell cycle distribution and apoptosis. The combination resulted in a additive effect in every protocol. Cell cycle accumulation at G(2)/M phase before irradiation was observed in Protocols B and C, whereas no cell cycle shift in the limited time course was noted in Protocol A. Although a 4-day continuous exposure to cisplatin and a 1-h exposure to cisplatin followed by a 4-day interval before irradiation caused significantly increased apoptosis, an additional increase in apoptosis after irradiation was not observed in Protocols B and C, whereas Protocol A showed an additional increase. Despite a cell cycle shift favoring radiation sensitivity, the drug-radiation interactions in Protocols B and C were additive, possibly because of negative effects including induction of a durable G(2)/M-phase arrest and suppression of apoptosis by cisplatin.

Controlling liposomal drug release with low frequency ultrasound: mechanism and feasibility

The ability of low-frequency ultrasound (LFUS) to release encapsulated drugs from sterically stabilized liposomes in a controlled manner was demonstrated. Three liposomal formulations having identical lipid bilayer compositions and a similar size ( approximately 100 nm) but differing in their encapsulated drugs and methods of drug loading have been tested. Two of the drugs, doxorubicin and methylpredinisolone hemisuccinate, were remote loaded by transmembrane gradients (ammonium sulfate and calcium acetate, respectively). The third drug, cisplatin, was loaded passively into the liposomes. For all three formulations, a short exposure to LFUS (<3 min) released nearly 80% of the drug. The magnitude of drug release was a function of LFUS amplitude and actual exposure time, irrespective of whether irradiation was pulsed or continuous. Furthermore, no change in liposome size distribution or in the chemical properties of the lipids or of the released drugs occurred due to exposure to LFUS. Based on our results, we propose that the mechanism of release is a transient introduction of porelike defects in the liposome membrane, which occurs only during exposure to LFUS, after which the membrane reseals. This explains the observed uptake of the membrane-impermeable fluorophore pyranine from the extraliposomal medium during exposure to LFUS. The implications of these findings for clinical applications of controlled drug release from liposomes are discussed.

Cisplatin sensitizes cancer cells to ionizing radiation via inhibition of nonhomologous end joining

The combination of cisplatin and ionizing radiation (IR) treatment represents a common modality for treating a variety of cancers. These two agents provide considerable synergy during treatment, although the mechanism of this synergy remains largely undefined. We have investigated the mechanism of cisplatin sensitization to IR using a combination of in vitro and in vivo experiments. A clear synergistic interaction between cisplatin and IR is observed in cells proficient in nonhomologous end joining (NHEJ) catalyzed repair of DNA double-strand breaks (DSB). In contrast, no interaction between cisplatin and IR is observed in NHEJ-deficient cells. Reconstituted in vitro NHEJ assays revealed that a site-specific cisplatin-DNA lesion near the terminus results in complete abrogation of NHEJ catalyzed repair of the DSB. These data show that the cisplatin-IR synergistic interaction requires the DNA-dependent protein kinase-dependent NHEJ pathway for joining of DNA DSBs, and the presence of a cisplatin lesion on the DNA blocks this pathway. In the absence of a functional NHEJ pathway, although the cells are hypersensitive to IR, there is no synergistic interaction with cisplatin.

Effects of cisplatin and gamma-irradiation on cell survival, the induction of chromosomal aberrations and apoptosis in SW-1573 cells

PURPOSE

Cisplatin was found to radiosensitize SW-1573 cells by inhibition of PLDR. Therefore, it was investigated whether cisplatin combined with gamma-radiation leads to an increase in the number of chromosomal aberrations or apoptotic cells compared with radiation alone.

METHODS

Confluent cultures of the human lung carcinoma cell line SW-1573 were treated with 1 microM cisplatin for 1 h, 4 Gy gamma-radiation, or a combination of both. Cell survival was studied by the clonogenic assay. Aberrations were analysed by FISH in prematurely condensed chromosomes (PCC) and the induction of apoptosis by counting fragmented nuclei.

RESULTS

A radiosensitizing effect of cisplatin on cell survival was observed if time for PLDR was allowed. An increased number of chromosomal fragments were observed immediately after irradiation compared with 24 h after irradiation whereas color junctions are only formed 24 h after irradiation. No increase in chromosomal aberrations was found after combined treatment, but a significantly enhanced number of fragmented nuclei were observed when confluent cultures were replated after allowing PLDR.

CONCLUSION

The inhibition of PLDR by cisplatin in delayed plated SW-1573 cells did not increase chromosomal aberrations, but increased the induction of apoptosis.

Novel apoptosis-inducing trans-platinum piperidine derivatives: synthesis and biological characterization

The synthesis, chemical characterization, and interaction with cells of new sterically hindered trans- and cis-diaminedichloroplatinum(II) complexes are described. The amine ligands include monofunctional piperidine (pip) and piperazine (pz). The poor solubility of trans-diaminedichloroplatinum complexes was overcome by introducing the positively charged pz ligand, which allows retaining of the classic platinum coordination sphere. In vitro evaluation in OV-1063 and C-26 tumor cells revealed that replacing one NH3 of the inactive transplatin by an aromatic planar ligand (4-picoline, 4-pic) or by an aliphatic nonplanar heterocyclic ligand (pip) or replacing both NH3 groups with a 4-pic ligand and a pip or pz ligand significantly increases the cytotoxic activity of these complexes. The unsymmetric complexes trans-[PtCl2(4-pic)(pip)] and trans-[PtCl2(4-pic)(pz)]HCl were the most cytotoxic compounds against the cisplatin-sensitive tumor cell line C-26 (IC50 = 4.5 and 5.5 microM, respectively) and the cisplatin-sensitive tumor cell line OV-1063 (IC50 = 6.5 and 7.4 microM, respectively). In contrast, replacing one NH3 of the cis isomer by an aromatic planar ligand (4-pic) or by an aliphatic amine lowered their cytotoxiciy in comparison to cisplatin. Cell penetration and Pt-DNA adduct formation were also evaluated, and it was clearly shown that both trans-[PtCl2(4-pic)(pip)] and trans-[PtCl2(4-pic)(pz)]HCl penetrate efficiently the cellular membrane of the tumor cells and platinate the cellular DNA. When comparing cellular DNA platination, positively charged trans-[PtCl2(4-pic)(pz)]HCl was 7-fold higher than both cisplatin and its neutral analogue trans-[PtCl2(4-pic)(pip)]. Moreover, in contrast to cisplatin, in the cell lines used, cell death caused by both complexes appeared to be apoptotic according to several criteria including early phosphatidylserine exposure, activation of caspases, and characteristic morphological changes. Our results suggest that these novel mixed nonclassical trans-Pt(II) complexes are biologically and mechanistically distinct from known Pt complexes and deserve evaluation of their efficacy in tumor-bearing animals.

Significance of scheduling on the cytotoxicity of radiation and cisplatin combination treatment in nasopharyngeal carcinoma cells

The use of cisplatin as a potential radiosensitizer in nasopharyngeal carcinoma (NPC) has produced encouraging results in clinical trials. In order to provide information on improving the design of clinical treatments, we investigated the effect of cisplatin dose, and the time interval and sequence between administration of cisplatin and radiation on cell survival of two NPC cell lines, CNE1 and SUNE1. When cisplatin was applied first, an exposure time of 24 h resulted in up to 2.6-fold increase in cell death and 7-fold increase in radiation effect (cell survival after cisplatin/cell survival after cisplatin plus radiation) in the cisplatin-radiation combination treatment compared to the cells treated with cisplatin for 4 h. When radiation was applied first, a shorter interval time of 4 h followed by cisplatin treatment resulted in up to 3-fold increase in cell death and a 3-fold enhanced radiation effect over longer time intervals of 24 h. By changing the order of radiation and cisplatin treatment alone, a 2-fold difference in radiation effect was observed. The differential cytotoxicity was partially explained by the alterations in cell cycle distribution. Our results indicate the importance of scheduling the radiation and cisplatin combination regimens on the survival of NPC cells.

Targeting DNA mismatch repair for radiosensitization

Postreplicational mismatch repair (MMR) proteins are capable of recognizing and processing not only single base-pair mismatches and insertion-deletion loops (IDLs) that occur during DNA replication, but also adducts in DNA resulting from treatment with cancer chemotherapy agents. These include widely varying types of DNA adducts resulting from methylating agents such as MNNG, MNU, temozolomide, and procarbazine; CpG crosslinks resulting from cisplatin and carboplatin; and S(6)-thioguanine and S(6)-methylthioguanine residues in DNA. Although MMR proteins can recognize both replicational errors and chemotherapy-induced adducts in DNA, the end results of this recognition are very different. Base-base mismatches and IDLs can be repaired by MMR, restoring genomic integrity, whereas MMR-mediated recognition and processing of chemotherapy-induced adducts in DNA results in apoptosis. After the loss of MMR, the inability of cells to recognize and correct single base-pair mismatches and insertion-deletion loops can lead to secondary mutations in proto-oncogenes and tumor-suppressor genes, thereby contributing to the development of cancer. In addition, the inability of MMR-deficient cells to recognize chemotherapy-induced adducts in DNA can result in a damage-tolerant phenotype that translates to clinically significant resistance by allowing for selection of MMR-deficient cancer cells. We have shown recently that these MMR-deficient, drug-resistant cells can be targeted for radiosensitization by the halogenated thymidine analogs iododeoxyuridine (IdUrd) and bromodeoxyuridine (BrdUrd). These thymidine (dThd) analogs become incorporated into DNA and form reactive uracil radicals after ionizing radiation (IR), increasing strand breaks. IdUrd and BrdUrd appear to be removed from DNA in MMR-proficient cells with limited toxicity or disruption of the cell cycle, while accumulating at much higher levels in MMR-deficient cells. As a result, it is possible to effectively increase the radiosensitization of MMR-deficient cells at levels of halogenated dThd analog that demonstrate limited toxicity to MMR-proficient cells. This indicates that a combined approach of IdUrd or BrdUrd with IR may be effective in killing MMR-deficient tumors in patients, which are resistant to many cancer chemotherapy agents commonly used in the clinic.

Correlation between cell survival, micronuclei-induction, and LDH activity in V79 cells treated with teniposide (VM-26) before exposure to different doses of gamma radiation

The influence of teniposide (VM-26) treatment was studied on the radiation-induced alterations in cell survival, micronuclei (MN) formation and lactate dehydrogenase (LDH) release in V79 cells. Treatment of V79 cells with 10 nM teniposide before exposure to different doses of gamma radiation resulted in a significant decline in the cell survival when compared with the PBS + irradiation group. The decline in cell survival was dose related. The cell proliferation indices also declined in a dose-dependent manner in both PBS + irradiation and VM-26 + irradiation groups. The decline was higher in the VM-26 + irradiation group in comparison with the PBS + irradiation group. In contrast, the frequency of micronuclei increased in a dose-related manner in both PBS + irradiation and VM-26 + irradiation groups. However, the frequency of micronuclei was significantly greater in the latter group when compared with the former group at all the post-irradiation time periods studied. The LDH contents increased in a dose-dependent manner in both PBS + irradiation and VM-26 + irradiation groups at all the post-irradiation time periods evaluated. This elevation in LDH contents was significantly greater in the VM-26 + irradiation group in comparison with the PBS + irradiation group.