Radiosensitization of vinorelbine and gemcitabine in NCI-H460 non–small-cell lung cancer cells

Rational design and structure-activity relationship studies reveal new esterified C20-diterpenoid alkaloid analogues active against MCF-7 human breast cancer cells

Although various diterpenoid alkaloids have been evaluated recently for antiproliferative activity against human tumor cell lines, little information is available regarding the antiproliferative effects of C20-diterpenoid alkaloids against MCF-7 cells. Six new diterpenoid alkaloid derivatives (13, 14, 22, 23, 25, 26) were prepared by C-11 and 15 esterification of kobusine (6). The natural parent alkaloid 6 and all synthesized derivatives (7 - 27, 12a, 15a, 15b, 18a, 18b) were evaluated for antiproliferative activity against MCF-7 cells. The structure-based design strategy resulted in an initial lead derivative, 11,15-dibenzoylkobusine (7; IC50 8.6 µM). Subsequent synthesized 11,15-diacylkobusine derivatives (9, 16, 20, 21, 23, 25, and 26) showed substantially increased suppressive effects against the MCF-7 cell line (IC50 2.3-4.4 µM). In contrast, parent alkaloid 6, two 11-acylkobusine derivatives (15a, 18a), and two 15-acylkobusine derivatives (15b, 18b) showed no effect. 11,15-Diacylation appears to be critical for producing antiproliferative activity in this alkaloid class and could introduce a new avenue in overcoming breast cancer cell proliferation using natural product derivatives. In a preliminary mechanism of action study, representative derivatives (5, 8, 9, and 17) decreased cyclin D1 mRNA expression.

Discovery of C20-Diterpenoid Alkaloid Kobusine Derivatives Exhibiting Sub-G1 Inducing Activity

Although many diterpenoid alkaloids have been evaluated recently for antiproliferative activity against human cancer cell lines, little data have been offered relating to the antiproliferative effects of hetisine-type C₂₀-diterpenoid alkaloids, such as kobusine (1), likewise as their derivatives. A total of 43 novel diterpenoid alkaloid derivatives (2-10, 2b, 3a, 3b, 6a-16a, 7b, 9b, 10b, 13, 15-26, 15b, 18a, 23a, 27a) were prepared by C-11 and -15 esterification of 1. Antiproliferative effects of the natural parent compound (1) and all synthesized kobusine derivatives against human cancer cell lines, including a triple-negative breast cancer (TNBC) cell line as well as a P-glycoprotein overexpressing multidrug-resistant subline, were assessed. The structure-based design strategy resulted in the lead derivative 11,15-dibenzoylkobusine (3; average IC₅₀ 7.3 μM). Several newly synthesized kobusine derivatives (particularly, 5-8, 10, 13, 15-26) exhibited substantial suppressive effects against all tested human cancer cell lines. In contrast, kobusine (1), 11,15-O-diacetylkobusine (2), 11-acylkobusine derivatives (3a, 6a, 9a, 11a, 12a, 15a, 27a), and 15-acylkobusine derivatives (2b, 3b, 7b, 9b, 10b, 15b) showed no effect. The most active kobusine derivatives primarily had two specific substitution patterns, C-11,15 and C-11. Notably, 11,15-diacylkobusine derivatives (3, 6-10, 13, 15, 16, 18, 23) were more potent compared with 11- and 15-acylkobusine derivatives (3a, 3b, 6a-10a, 7b, 9b, 10b, 13a, 15a, 15b, 16a, 18a, 23a). Derivatives 13 and 25 induced MDA-MB-231 cells to the sub-G1 phase within 12 h. 11,15-Diacylation of kobusine (1) appears to be crucial for inducing antiproliferative activity in this alkaloid class and could introduce a new avenue to overcome TNBC using natural product derivatives.

Bioactivity inspired C19-diterpenoid alkaloids for overcoming multidrug-resistant cancer

The pharmacological activities of C₁₉-diterpenoid alkaloids are related to their basic skeletons (e.g., aconitine-type or lycoctonine-type). Also, few studies have been reported on the chemosensitizing effects of diterpenoid alkaloids. Consequently, this study was aimed at determining the chemosensitizing effects of synthetic derivatives of lycoctonine-type C₁₉-diterpenoid alkaloids on a P-glycoprotein (P-gp)-overexpressing multidrug-resistant (MDR) cancer cell line KB-VIN. The acyl-derivatives of delpheline and delcosine showed moderate cytotoxicity against chemosensitive cancer cell lines. Among non-cytotoxic synthetic analogs (1-14), several derivatives effectively and significantly sensitized MDR cells by interfering with the drug transport function of P-gp to three anticancer drugs, vincristine, paclitaxel, and doxorubicin. The chemosensitizing effect of derivatives 2, 4, and 6 on KB-VIN cells against vincristine were more potent than 5 μM verapamil, and derivatives 4 and 13 were more effective than 5 μM verapamil for paclitaxel. Among them, 2 in particular increased the sensitivity of KB-VIN cells to vincristine by 253-fold.

Structure-activity relationships and evaluation of esterified diterpenoid alkaloid derivatives as antiproliferative agents

Diterpenoid alkaloids with remarkable chemical properties and biological activities are frequently found in plants of the genera Aconitum, Delphinium, and Garrya. However, little information has been reported on the antiproliferative effects of the diterpenoid alkaloid constituents of Aconitum and Delphinium plants. C-1 and 14 esterifications of delcosine (1) were carried out to provide 39 new diterpenoid alkaloid derivatives (3-14, 16-29, 3a-7a, 9a, 13a, 13b, 14a, 14b, 16a, 17a, 24a, 35a). Selected compounds (3-14, 16-29, 3a-7a, 9a, 13a, 13b, 14a, 14b, 16a, 17a, 24a, 35a) were evaluated for antiproliferative activity against three to five human tumor cell lines including triple-negative breast cancer (TNBC) and P-glycoprotein (P-gp) overexpressing multidrug-resistant (MDR) subline. Several newly synthesized delcosine derivatives (6, 7, 13, 13a, 13b) showed substantial suppressive effects against all human tumor cell lines tested. In contrast, the natural alkaloids (1, 31, 33) showed no effect. Most of the active compounds were delcosine derivatives with two specific substitution patterns-C-1 and C-1,14. In particular, 1-acyldelcosine derivative (5-7) displayed more potency than 1,14-diacyldelcosine derivatives (5a-7a). These acylated alkaloid derivatives caused accumulation of TNBC cells at sub-G1 within 24 h. 1-Acylation of 1 appears to be critical for producing antiproliferative activity in this alkaloid class and a means to provide promising new leads for further development into antitumor agents.

Two decades of advances in diterpenoid alkaloids with cytotoxicity activities

The important pharmacological activities and structural complexity of diterpenoid alkaloids have long stimulated strong scientific interest; some of these naturally abundant compounds have been reported to be highly promising for treating cancer. From 2008 to 2018, the cytotoxicity activities of more than 250 diterpenoid alkaloids were tested against several cancer cell lines. This review focuses on the progress of diterpenoid alkaloids with different structures derived from Ranunculaceae plants and some of their derivatives with potential anticancer activities. Then, we discuss the application prospects and development of active diterpenoid alkaloids.

Radiosensitivity of human ovarian cancer cells is enhanced by pseudolaric acid B due to the inhibition of the Ras/Raf/ERK signaling pathway

Ovarian cancer has the highest mortality rate among gynecological cancers; the most effective therapy for this cancer is a combination of radiation treatment and chemotherapy. However, radiation resistance is the leading factor associated with treatment failure. The present study aimed to investigate pseudolaric acid B (PAB) as a potential radiosensitizer for the treatment of ovarian cancer. The present study performed MTT and clonogenic assays, and demonstrated that PAB could induce a radiosensitizing effect on SKOV-3 cells. An Annexin V/propidium iodide staining assay revealed that PAB exerted a radiosensitizing effect by inducing SKOV-3 cell apoptosis. In addition, western blot analysis demonstrated that the activity of the Ras/RAF proto-oncogene serine/threonine-protein kinase/extracellular signal-regulated kinase signaling pathway was reduced by combination therapy with PAB and irradiation. In conclusion, the present study establishes PAB as a radiosensitizer, and provides a rational basis for the use of PAB and irradiation as a combination therapy to treat ovarian cancer.

The use of porous scaffold as a tumor model

Background. Human cancer is a three-dimensional (3D) structure consisting of neighboring cells, extracellular matrix, and blood vessels. It is therefore critical to mimic the cancer cells and their surrounding environment during in vitro study. Our aim was to establish a 3D cancer model using a synthetic composite scaffold. Methods. High-density low-volume seeding was used to promote attachment of a non-small-cell lung cancer cell line (NCI-H460) to scaffolds. Growth patterns in 3D culture were compared with those of monolayers. Immunohistochemistry was conducted to compare the expression of Ki67, CD44, and carbonic anhydrase IX. Results. NCI-H460 readily attached to the scaffold without surface pretreatment at a rate of 35% from a load of 1.5 × 10⁶ cells. Most cells grew vertically to form clumps along the surface of the scaffold, and cell morphology resembled tissue origin; 2D cultures exhibited characteristics of adherent epithelial cancer cell lines. Expression patterns of Ki67, CD44, and CA IX varied markedly between 3D and monolayer cultures. Conclusions. The behavior of cancer cells in our 3D model is similar to tumor growth in vivo. This model will provide the basis for future study using 3D cancer culture.

Can drugs enhance hypofractionated radiotherapy? A novel method of modeling radiosensitization using in vitro data

PURPOSE

Hypofractionated radiotherapy (hRT) is being explored for a number of malignancies. The potential benefit of giving concurrent chemotherapy with hRT is not known. We sought to predict the effects of combined modality treatments by using mathematical models derived from laboratory data.

METHODS AND MATERIALS

Data from 26 published clonogenic survival assays for cancer cell lines with and without the use of radiosensitizing chemotherapy were collected. The first three data points of the RT arm of each assay were used to derive parameters for the linear quadratic (LQ) model, the multitarget (MT) model, and the generalized linear quadratic (gLQ) model. For each assay and model, the difference between the predicted and observed surviving fractions at the highest tested RT dose was calculated. The gLQ model was fitted to all the data from each RT cell survival assay, and the biologically equivalent doses in 2-Gy fractions (EQD2s) of clinically relevant hRT regimens were calculated. The increase in cell kill conferred by the addition of chemotherapy was used to estimate the EQD2 of hRT along with a radiosensitizing agent. For comparison, this was repeated using conventionally fractionated RT regimens.

RESULTS

At a mean RT dose of 8.0 Gy, the average errors for the LQ, MT, and gLQ models were 1.63, 0.83, and 0.56 log units, respectively, favoring the gLQ model (p < 0.05). Radiosensitizing chemotherapy increased the EQD2 of hRT schedules by an average of 28% to 82%, depending on disease site. This increase was similar to the gains predicted for the addition of chemotherapy to conventionally fractionated RT.

CONCLUSIONS

Based on published in vitro assays, the gLQ equation is superior to the LQ and MT models in predicting cell kill at high doses of RT. Modeling exercises demonstrate that significant increases in biologically equivalent dose may be achieved with the addition of radiosensitizing agents to hRT. Clinical study of this approach is warranted.

Radiosensitization of oropharyngeal squamous cell carcinoma cells by human papillomavirus 16 oncoprotein E6∗I

PURPOSE

Patients with oropharyngeal squamous cell carcinoma (OSCC) whose disease is associated with high-risk human papillomavirus (HPV) infection have a significantly better outcome than those with HPV-negative disease, but the reasons for the better outcome are not known. We postulated that they might relate to an ability of HPV proteins to confer a better response to radiotherapy, a commonly used treatment for OSCC.

METHODS AND MATERIALS

We stably expressed the specific splicing-derived isoforms, E6∗I and E6∗II, or the entire E6 open reading frame (E6total), which gives rise to both full length and E6∗I isoforms, in OSCC cell lines. Radiation resistance was measured in clonogenicity assays, p53 activity was measured using transfected reporter genes, and flow cytometry was used to analyze cell cycle and apoptosis.

RESULTS

E6∗I and E6total sensitized the OSCC cells to irradiation, E6∗I giving the greatest degree of radiosensitization (approximately eightfold lower surviving cell fraction at 10 Gy), whereas E6∗II had no effect. In contrast to radiosensitivity, E6∗I was a weaker inhibitor than E6total of tumor suppressor p53 transactivator activity in the same cells. Flow cytometric analyses showed that irradiated E6∗I expressing cells had a much higher G2M:G1 ratio than control cells, indicating that, after G2, cells were diverted from the cell cycle to programmed cell death.

CONCLUSION

This study supports a role for E6∗I in the enhanced responsiveness of HPV-positive oropharyngeal carcinomas to p53-independent radiation-induced death.

Dose escalation of gemcitabine concomitant with radiation and cisplatin for nonsmall cell lung cancer: a phase 1-2 study

BACKGROUND

The current study was conducted to evaluate the maximum tolerable dose of weekly gemcitabine administered simultaneously with radiation and cisplatin in patients with locally advanced nonsmall cell lung cancer (NSCLC).

METHODS

Patients with stage IIIA/B NSCLC received concurrently 63 grays radiation and 20 mg/m² cisplatin Day 1 to 3 in Weeks 1 and 5, plus weekly gemcitabine at escalating doses (150-700 mg/m²) on Fridays after radiation to avoid radiosensitization. The authors assessed dose-limiting toxicities according to Common Toxicity Criteria. The primary endpoint was maximum tolerated dose (MTD) of gemcitabine. Tumor resectability, survival, and disease-free survival (DFS) were also determined.

RESULTS

Forty-two patients were accrued, of whom 95% received radiation and 66% cisplatin as above. Weekly doses of gemcitabine were escalated to 700 mg/m². Grade 3 dysphagia and 1 case of fatal, probably treatment-related pulmonary deterioration established the MTD of gemcitabine at 550 mg/m² weekly. Twenty-five patients underwent surgery, and histopathological complete regression was documented in 26% of these patients. Overall, median actuarial survival and DFS were 23.8 and 12.4 months, respectively.

CONCLUSIONS

Gemcitabine at doses up to 550 mg/m² weekly can be given simultaneously with radiation and cisplatin to patients with locally advanced NSCLC. Radical resection thereafter is feasible. The impact of this aggressive therapy should be evaluated further.

Structure-activity relationships and the cytotoxic effects of novel diterpenoid alkaloid derivatives against A549 human lung carcinoma cells

The cytotoxicity of three alkaloids from the roots of Aconitum yesoense var. macroyesoense as well as 36 semi-synthetic C(20)-diterpenoid atisine-type alkaloid derivatives against A549 human lung carcinoma cells was examined. Ten acylated alkaloid derivatives, pseudokobusine 11-veratroate (9), 11-anisoate (12), 6,11-dianisoate (14), 11-p-nitrobenzoate (18), 11,15-di-p-nitrobenzoate (22), 11-cinnamate (25) and 11-m-trifluoromethylbenzoate (27), and kobusine 11-p-trifluoromethylbenzoate (35), 11-m-trifluoromethylbenzoate (36) and 11,15-di-p-nitrobenzoate (39), exhibited cytotoxic activity, and 11,15-dianisoylpseudokobusine (16) was found to be the most potent cytotoxic agent. Their IC(50) values against A549 cells ranged from 1.72 to 5.44 μM. In the occurrence of cytotoxic effects of atisine-type alkaloids, replacement by an acyl group at both C-11 and C-15 resulted in the enhancement of activity of the parent alkaloids compared to that from having hydroxy groups at this position, and the presence of a hydroxy group at the C-6 position was required for the cytotoxic effects. These acylated alkaloid derivatives inhibit cell growth through G1 arrest.

The role of apoptotic cell death in the radiosensitising effect of gemcitabine

Background:

The aim of this study was to evaluate the radiosensitising effect of gemcitabine, in terms of cell-cycle progression, induction of apoptosis, and to investigate the molecular events regulating apoptosis.

Methods:

Tumour cells were treated with gemcitabine, radiation, or the combination. 0–72 h after treatment, cells were collected for cell-cycle analysis and apoptosis determination. Caspase 8 and 9, Bid and tBid expression were determined by western blot. The mitochondrial membrane potential was determined using flow cytometry. An RT²Profiler PCR Array for human apoptotic genes was performed after the combination or TRAIL treatment.

Results:

Gemcitabine and radiation resulted in an early S-phase block immediately after treatment, after which the cells moved synchronously through the cell cycle. When cell-cycle distribution returned to pre-treatment levels, an increased induction of apoptosis was observed with activation of caspase 8 and 9 and a reduction of the mitochondrial membrane potential. Gene expression after treatment with radiosensitising conditions was comparable with expression after the TRAIL treatment.

Conclusion:

A role for the cell-cycle perturbations and the induction of apoptosis could be attributed to the radiosensitising effect of gemcitabine. Apoptosis induction was comparable with the apoptotic pathway observed after the TRAIL treatment, that is the involvement of the extrinsic apoptosis pathway.

Myelopathy After Radiation Therapy and Chemotherapy with Capecitabine and Gemcitabine

This article describes a woman with metastatic upper gastrointestinal cancer who developed thoracic myelopathy unexpectedly after standard dosage and fractionation radiotherapy. She also was receiving capecitabine and gemcitabine concomitantly. There are few reported cases of chemotherapy potentiation of spinal cord radiation toxicity. These agents are known radiosensitizers, making it likely that they contributed to this adverse outcome. As these agents are increasingly incorporated into clinical trials of combined therapy, caution will be necessary in both trial design and clinical management.

Further mechanistic unravelling of the influence of the cell cycle effects on the radiosensitising mechanism of vinflunine, in vitro

PURPOSE

Vinflunine is an innovative microtubule inhibitor belonging to the vinca alkaloid class that possesses radiosensitising properties, which could lead to promising activity in chemoradiation studies in the clinic.

METHOD

In the current study, different incubation times with vinflunine, immediately before radiation and different time intervals between vinflunine treatment and radiation were investigated, in vitro, using four different human tumour cell lines differing in cell type and p53 status. Results were correlated with the cell cycle distribution at the moment of radiation, in order to elucidate the role of cell cycle perturbations caused by vinflunine on its radiosensitising effect.

RESULTS

Radiosensitisation was observed in all cell lines, and maximal radiosensitisation was both cell line- and schedule-dependent. The cell cycle distributions were cell line-dependent also, and when correlated with the observed radiosensitising effects could explain many (but not all) of the radiosensitising properties of vinflunine.

CONCLUSION

The cell cycle perturbations caused by vinflunine may definitely have an impact on its radiosensitising potential, but other factors must play a role because of some unaccountable differences between cell cycle distribution and the radiosensitising potential.

Characterization of an NBS1 C-terminal peptide that can inhibit ataxia telangiectasia mutated (ATM)-mediated DNA damage responses and enhance radiosensitivity

ATM and NBS1, mutation of which lead to the human autosomal recessive diseases ataxia telangiectasia and Nijmegen breakage syndrome (NBS), respectively, are essential elements in the cellular response to DNA damage induced by ionizing radiation (IR). ATM is a member of the phosphatidylinositol 3-kinase family and is activated by IR in an NBS1-dependent manner. The extreme C terminus of NBS1 contains an evolutionarily conserved sequence motif that is critical for binding to and activation of ATM after IR. ATM phosphorylates a series of targets to initiate cell cycle arrest and promote cell survival in response to DNA damage. Therefore, targeting the NBS1-ATM interaction may lead to a novel approach for specific ATM inhibition and radiosensitization. We developed small peptides containing the conserved C-terminal sequence of NBS1 to investigate whether these peptides can interfere with the DNA damage pathway. We found that wild-type NBS1 inhibitory peptides (wtNIP) can abrogate NBS1-ATM association in the presence or absence of IR. We also found that cells exposed to wtNIP displayed a significant reduction in radiation-induced gamma-H2AX and NBS1 focus formation compared with cells treated with control peptides, demonstrating that wtNIP possesses a strong inhibitory effect on ATM. The inhibitory effect of wtNIP also leads to a significant decrease in clonogenic survival in response to IR. Furthermore, wtNIP does not radiosensitize cells with defective ATM, suggesting a specific inhibition of ATM. Together, these data provide a proof of principle for the use of NBS1 C-terminal small peptides as specific ATM inhibitors and radiosensitizers.

A novel human ex vivo model for the analysis of molecular events during lung cancer chemotherapy

Background

Non-small cell lung cancer (NSCLC) causes most of cancer related deaths in humans and is characterized by poor prognosis regarding efficiency of chemotherapeutical treatment and long-term survival of the patients. The purpose of the present study was the development of a human ex vivo tissue culture model and the analysis of the effects of conventional chemotherapy, which then can serve as a tool to test new chemotherapeutical regimens in NSCLC.

Methods

In a short-term tissue culture model designated STST (Short-Term Stimulation of Tissues) in combination with the novel *HOPE-fixation and paraffin embedding method we examined the responsiveness of 41 human NSCLC tissue specimens to the individual cytotoxic drugs carboplatin, vinorelbine or gemcitabine. Viability was analyzed by LIFE/DEAD assay, TUNEL-staining and colorimetric MTT assay. Expression of Ki-67 protein and of BrdU (bromodeoxyuridine) uptake as markers for proliferation and of cleaved (activated) effector caspase-3 as indicator of late phase apoptosis were assessed by immunohistochemistry. Transcription of caspase-3 was analyzed by RT-PCR. Flow cytometry was utilized to determine caspase-3 in human cancer cell lines.

Results

Viability, proliferation and apoptosis of the tissues were moderately affected by cultivation. In human breast cancer, small-cell lung cancer (SCLC) and human cell lines (CPC-N, HEK) proliferative capacity was clearly reduced by all 3 chemotherapeutic agents in a very similar manner. Cleavage of caspase-3 was induced in the chemo-sensitive types of cancer (breast cancer, SCLC). Drug-induced effects in human NSCLC tissues were less evident than in the chemo-sensitive tumors with more pronounced effects in adenocarcinomas as compared to squamous cell carcinomas.

Conclusion

Although there was high heterogeneity among the individual tumor tissue responses as expected, we clearly demonstrate specific multiple drug-induced effects simultaneously. Thus, STST provides a useful human model to study numerous aspects of mechanisms underlying tumor responsiveness towards improved anticancer treatment. The results presented here shall serve as a base for multiple functional tests of novel chemotherapeutic approaches to NSCLC in the future.

*Hepes – Glutamic acid buffer mediated Organic solvent Protection Effect

Exploitable mechanisms for combining drugs with radiation: concepts, achievements and future directions

Widening indications for combining radiation therapy with cytotoxic or molecular-targeted drugs have mainly been driven by pragmatic clinical trials. With a flurry of novel drugs in various stages of preclinical and clinical development there is a need to revise the framework that has traditionally been used for discussing possible drug-radiation interactions, especially because many of the new drugs are directed at a specific molecular target. Spatial cooperation, cytotoxic enhancement, biological cooperation, temporal modulation and normal tissue protection are proposed as five primary exploitable mechanisms for the rational combination of drugs with radiation for cancer therapy. These five mechanisms produce different clinical outcomes and, therefore, the optimum clinical end point for assessing therapeutic benefit will depend on the mechanism tested. The dependence of outcome on these mechanisms also affects the selection of preclinical models and the optimum scheduling of the two modalities, i.e. the timing and dosing of the drug relative to the radiation dose fractions. These considerations are discussed in some detail for each mechanism and illustrated with specific clinical examples. Multi-modality therapy for head and neck squamous-cell carcinoma is used to illustrate these concepts. Further clinical progress in this field will require hypothesis-driven trials to ensure efficient identification of treatments with the most favorable risk:benefit ratio.

Streptokinase increases the sensitivity of colon cancer cells to chemotherapy by gemcitabine and cis-platine in vitro

The aim was to determine the effect of fybrinolytic therapy by streptokinase on chemotherapy and radiation response in human colon cancer cells. The cells were treated with different concentrations of gemcitabine, cis-platine and streptokinase, at a single use or in combinations. Radiation was tested at a dose 0.5, 5 and 15 Gy in three different schedules. The chemotherapy showed higher cytotoxic effect in combination with streptokinase. On the other hand, the combination of chemotherapy with streptokinase and radiotherapy provide no improvement in sensitivity of cancer cells to treatment. The data suggest that fybrinolytic therapy could influence the effect of chemotherapy.

In vitro studies on gemcitabine combinations with other antiblastics

The use of gemcitabine in combination with chemotherapeutic agents, including cisplatin, pemetrexed and taxanes, is characterized by the enhancement of their anticancer activity. The analysis of the underlying pharmacodynamics has revealed that modulation of nucleotide pools, drug metabolism, and cellular DNA repair capability are the most common factors to explain the additive to synergistic interaction between gemcitabine and anticancer agents in several human cancers in vitro and in vivo.

Iodide sensitizes genetically modified non-small cell lung cancer cells to ionizing radiation

While external ionizing radiation has been used for treating non-small cell lung cancer (NSCLC), improved efficacy of this modality would be an important advance. Ectopic expression of the sodium iodide symporter (NIS) and thyroperoxidase (TPO) genes in NSCLC cells facilitated concentration of iodide in NSCLC cells, which markedly induced apoptosis in vitro and in vivo. Pre-incubation of the NIS/TPO-modified NSCLC cells in iodide followed by ionizing radiation generates bystander tumoricidal effects and potently enhances tumor cell killing. This iodide-induced bystander effect is associated with enhanced gap junction intercellular communication (GJIC) activity and increased connexin-43 (Cx43) expression. Thus, iodide may serve as an enhancer to markedly improve the efficacy of radiation therapy in combined therapeutic modalities.

Combination of γ-radiation antagonizes the cytotoxic effects of vincristine and vinblastine on both mitotic arrest and apoptosis

PURPOSE

Combination therapy with different modalities is a common practice in the treatment of cancer. The promising clinical profile of vincristine and vinblastine has promoted considerable interest in combining these vinca alkaloids with radiation therapy to treat a variety of solid tumors. However, the therapeutic efficacy and the interaction between the vinca alkaloids with radiation is not entirely clear. In this study, we assessed the potential interactions in the combination of vincristine or vinblastine with gamma-radiation against human tumor cells in vitro.

METHODS AND MATERIALS

Vincristine or vinblastine and gamma-radiation were administrated at three different sequences designed as preradiated, coradiated, and postradiated combinations in human breast cancer cells and human epidermoid carcinoma cells. The cytotoxic interactions and mutual influences between these two modalities were analyzed by a series of assays including cytotoxic, morphologic, and biochemical examinations.

RESULTS

Our results showed that the combination of these two modalities did not produce any synergistic or additive effects. Instead, the clonogenic assays showed the survival rates of these combinations were increased up to 2.17-fold and 2.7-fold, respectively, of those treated with vincristine or vinblastine alone (p < 0.01). DNA fragmentation, TalphaT-mediated dUTP nick end labeling (TUNEL) assay, and flow cytometric assays also showed that the combination of gamma-radiation significantly interfered with the ability of these vinca alkaloids to induce apoptosis. Further analyses indicated that addition of gamma-radiation resulted in cell cycle arrest at the G(2) phase, which subsequently prevented the mitotic arrest induced by vincristine or vinblastine. In addition, biochemical examinations revealed that gamma-radiation regulated p34(cdc2)/cyclin B1 and survivin, and inhibited IkappaBalpha degradation and bcl-2 phosphorylation.

CONCLUSIONS

These results suggest that gamma-radiation might specifically block the cell cycle at the G(2) phase, which in turn interferes with the cytotoxic effects of vincristine or vinblastine on mitotic arrest and apoptosis. Thereby, it eventually results in an antagonistic interaction between these two modalities. This finding may be implicated in the clinical application of combination therapy of vinca alkaloids and radiation.