Paclitaxel combined with fractionated radiation in vitro: a study with vulvar squamous cell carcinoma cell lines

Additive Damage Models for Cellular Pharmacodynamics of Radiation-Chemotherapy Combinations

Many cancer patients receive combination treatments with radiation and chemotherapy. Available mathematical models for cellular pharmacodynamics have limited ability to represent observed in vitro responses to radiochemotherapy. Here, a family of additive damage models is proposed to describe cell kill resulting from radiochemotherapy with fixed schedule and variable doses. The pathways by which the agents produce cellular damage are assumed to converge in a single cell death process, so that survival depends on total damage, which can be represented as a sum of contributions from the various damage pathways. Heterogeneity in response across the cell population is ascribed to variations in the damage threshold for cell kill. The family of proposed models includes effects of one or two pathways of damage for each agent, saturation in drug responses, and cooperative or antagonistic interactions between agents. Models from this family with 4-7 unknown parameters are tested for their ability to fit 218 in vitro literature data sets for a range of drugs and cell lines. Overall, the additive damage models are found to outperform models based on the existing concept of independent cell kill, according to the corrected Akaike Information Criterion. The results are used to assess the importance of the various effects included in the models. These additive damage models have potential applications to the optimization of treatment and to the analysis and interpretation of in vitro screening data for new drug-radiation combinations.

MPT0B098, a novel microtubule inhibitor that destabilizes the hypoxia-inducible factor-1α mRNA through decreasing nuclear-cytoplasmic translocation of RNA-binding protein HuR

Microtubule inhibitors have been shown to inhibit hypoxia-inducible factor-1α (HIF-1α) expression through inhibition translation or enhancing protein degradation. Little is known of the effect of microtubule inhibitors on the stability of HIF-1α mRNA. We recently discovered a novel indoline-sulfonamide compound, 7-aryl-indoline-1-benzene-sulfonamide (MPT0B098), as a potent microtubule inhibitor through binding to the colchicine-binding site of tubulin. MPT0B098 is active against the growth of various human cancer cells, including chemoresistant cells with IC50 values ranging from 70 to 150 nmol/L. However, normal cells, such as human umbilical vein endothelial cells (HUVEC), exhibit less susceptibility to the inhibitory effect of MPT0B098 with IC50 of 510 nmol/L. Similar to typical microtubule inhibitors, MPT0B098 arrests cells in the G2-M phase and subsequently induces cell apoptosis. In addition, MPT0B098 effectively suppresses VEGF-induced cell migration and capillary-like tube formation of HUVECs. Distinguished from other microtubule inhibitors, MPT0B098 not only inhibited the expression levels of HIF-1α protein but also destabilized HIF-1α mRNA. The mechanism of causing unstable of HIF-1α mRNA by MPT0B098 is through decreasing RNA-binding protein, HuR, translocation from the nucleus to the cytoplasm. Notably, MPT0B098 effectively suppresses tumor growth and microvessel density of tumor specimens in vivo. Taken together, our results provide a novel mechanism of inhibiting HIF-1α of a microtubule inhibitor MPT0B098. MPT0B098 is a promising anticancer drug candidate with potential for the treatment of human malignancies.

G2 checkpoint abrogator abates the antagonistic interaction between antimicrotubule drugs and radiation therapy

BACKGROUND AND PURPOSE

We previously demonstrated that radiation may arrest tumor cells at G2 phase, which in turn prevents the cytotoxicity of antimicrotubule drugs and results in antagonistic interaction between these two modalities. Herein we tested whether G2 abrogators would attenuate the above antagonistic interaction and improve the therapeutic efficacy of combination therapy between radiation and antimicrotubule drugs.

MATERIALS AND METHODS

Breast cancer BCap37 and epidermoid carcinoma KB cell lines were administered with radiation, UCN-01 (a model drug of G2 abrogator), paclitaxel or vincristine, alone or in combinations. The antitumor activities of single and combined treatments were analyzed by a series of cytotoxic, apoptotic, cell cycle, morphological and biochemical assays.

RESULTS

UCN-01 significantly enhanced the cytotoxicity of radiation, antimitotic drugs, and their combined treatments in vitro. Further investigations demonstrated that UCN-01 attenuated radiation-induced G2 arrest, and subsequently repressed the inhibitory effect of radiation on drug-induced mitotic arrest and apoptosis.

CONCLUSIONS

This is the first report demonstrating that G2 checkpoint abrogation represses the inhibitory effect of radiation on antimicrotubule drugs, which may be implicated in cancer combination therapy. Considering that G2 abrogators are under extensive evaluation for cancer treatment, our findings provide valuable information for this class of promising compounds.

Survivin counteracts the therapeutic effect of microtubule de-stabilizers by stabilizing tubulin polymers

Background

Survivin is a dual function protein. It inhibits the apoptosis of cells by inhibiting caspases, and also promotes cell growth by stabilizing microtubules during mitosis. Over-expression of survivin has been demonstrated to induce drug-resistance to various chemo-therapeutic agents such as cisplatin (DNA damaging agent) and paclitaxel (microtubule stabilizer) in cancers. However, survivin-induced resistance to microtubule de-stabilizers such as Vinca alkaloids and Combretastatin A-4 (CA-4)-related compounds were seldom demonstrated in the past. Furthermore, the question remains as to whether survivin plays a dominant role in processing cytokinesis or inhibiting caspases activity in cells treated with anti-mitotic compounds. The purpose of this study is to evaluate the effect of survivin on the resistance and susceptibility of human cancer cells to microtubule de-stabilizer-induced cell death.

Results

BPR0L075 is a CA-4 analog that induces microtubule de-polymerization and subsequent caspase-dependent apoptosis. To study the relationship between the expression of survivin and the resistance to microtubule de-stabilizers, a KB-derived BPR0L075-resistant cancer cell line, KB-L30, was generated for this study. Here, we found that survivin was over-expressed in the KB-L30 cells. Down-regulation of survivin by siRNA induced hyper-sensitivity to BPR0L075 in KB cells and partially re-stored sensitivity to BPR0L075 in KB-L30 cells. Western blot analysis revealed that down-regulation of survivin induced microtubule de-stabilization in both KB and KB-L30 cells. However, the same treatment did not enhance the down-stream caspase-3/-7 activities in BPR0L075-treated KB cells. Translocation of a caspase-independent apoptosis-related molecule, apoptosis-inducing factor (AIF), from cytoplasm to the nucleus was observed in survivin-targeted KB cells under BPR0L075 treatment.

Conclusion

In this study, survivin plays an important role in the stability of microtubules, but not with caspases inhibition. Over-expression of survivin counteracts the therapeutic effect of microtubule de-stabilizer BPR0L075 probably by stabilizing tubulin polymers, instead of the inhibition of caspase activity in cancer cells. Besides microtubule-related caspase-dependent cell death, caspase-independent mitotic cell death could be initiated in survivin/BPR0L075 combination treatments. We suggest that combining microtubule de-stabilizers with a survivin inhibitor may attribute to a better clinical outcome than the use of anti-mitotic monotherapy in clinical situations.

Radiation-induced effects on telomerase in gynecological cancer cell lines with different radiosensitivity and repair capacity

PURPOSE

Telomerase activation in response to irradiation might enhance the radioresistance of cells. Thus, we have investigated radiation-induced effects on telomerase in six gynecological cancer cell lines, with different intrinsic radiosensitivity and capacity for sublethal damage repair (SLDR).

MATERIALS AND METHODS

Three endometrial adenocarcinoma (UM-EC-1, UT-EC-2B and UT-EC-3) and three vulvar squamous cell carcinoma (A431, UM-SCV-2 and UM-SCV-7) cell lines were irradiated with doses of 5, 10 and 25 Gy and the effects on telomerase were evaluated at 0.5, 6, 24 and 48 h post-irradiation. Telomerase activity was quantitatively measured by SYBR Green real-time telomeric repeat amplification protocol.

RESULTS

The most radioresistant cell line A431 had the strongest stimulatory effects (approximately 2.0 - 2.5-fold) on telomerase activity 24 and 48 h post-irradiation with the highest radiation doses. In contrast to that, telomerase activities in the highly radiosensitive cell line UT-EC-2B remained below the basal level throughout the 48-h period of post-irradiation with the highest doses, and even a decline to approximately 50% of the basal level was found 24 h after exposure. In other cell lines being either moderately or highly radiation resistant, telomerase activity levels in response to irradiation remained mainly at the basal level or gradually increased.

CONCLUSIONS

The present findings indicate that there might be a connection between the radiation-induced telomerase response and radiosensitivity. However, no correlation was found between the radiation-induced effects on telomerase and the sublethal damage repair capacity of the cells.

Concurrent cetuximab, cisplatin, and radiation for squamous cell carcinoma of the head and neck in vitro

BACKGROUND AND PURPOSE

For locoregionally advanced HNSCC, chemoradiotherapy with cisplatin or another platinum compound is considered as one of the standard treatment regimes. Cisplatin has improved the loco-regional control, but also increased especially the acute side effects. Cetuximab blocks ligand binding and receptor activation by binding to the extracellular domain of the EGFR. The blockade of EGFR signaling in combination with cytotoxic drugs or with radiotherapy could be a novel effective management with a relatively favourable toxicity for HNSCC. In the present study we have examined in vitro a potentially novel effective management for HNSCC, cetuximab combined with cisplatin and radiotherapy.

MATERIALS AND METHODS

Seven head and neck SCC cell lines were studied. Cetuximab concentrations of 0.22-8.20 nM and cisplatin concentrations of 0.038-0.220 microg/ml were used. In order to test the concurrent use of cetuximab, cisplatin and radiation, the cells were treated with the desired drug concentrations immediately after irradiation, plated into 96-well culture plates, and incubated for 4 weeks. The number of positive wells was counted. The PE was calculated and fraction survival data were fitted to the LQ model. AUC value was obtained with numerical integration. The types of interaction were analyzed.

RESULTS

Cetuximab and cisplatin constantly induced an additive or supra-additive effect when combined with irradiation in the seven HNSCC cell lines tested.

CONCLUSIONS

We evaluated concurrent cetuximab, cisplatin, and radiation for HNSCC cell lines. Preliminary efficacy results are encouraging, and further development of this targeted combined modality paradigm is warranted.

Concurrent use of vinorelbine and gefitinib induces supra-additive effect in head and neck squamous cell carcinoma cell lines

PURPOSE

Squamous cell carcinoma of the head and neck (HNSCC) remains a clinical challenge because of the high rate of locoregional disease recurrence. Standard treatment includes surgery, radiation, chemoradiation or a combination of these approaches. New therapies are needed to achieve improved survival, quality of life and organ function in these patients. A novel molecular targeted therapy incorporated into our current treatment strategies may have a significant role in the treatment of HNSCC. The aim of this study was to evaluate the sensitivity of HNSCC cell lines to vinorelbine combined with gefitinib in vitro.

METHODS

Six recently established cell lines were used: UT-SCC-9, -11, -19A, -29 and -34 (laryngeal SCC) and UT-SCC-33 (oral cavity SCC). Chemosensitivity was tested using the 96-well plate clonogenic assay. The vinorelbine concentrations used varied between 0.4 and 1.0 nM and the gefitinib concentrations varied between 0.05 and 1.6 muM. Survival data were fitted to the LQ model, and the area under the curve (AUC) value was obtained with numerical integration. The type of interaction was determined by comparing the AUC ratio of the two drugs to the survival fraction (SF) of gefitinib alone.

RESULTS

In the current study the combination of vinorelbine and gefitinib had a clear supra-additive or additive cytotoxic effect on the HNSCC cell lines.

CONCLUSIONS

This finding is encouraging as a proof of the possible benefit of combing an EGFR targeting compound with a cell cycle specific drug and warrants further studies of available combinations in vitro.

Old and new perspectives in the management of high-risk, locally advanced or recurrent, and metastatic vulvar cancer

During the last decades there has been a continuing evolution in the surgical approach of squamous cell carcinoma of the vulva that has been traditionally treated with radical vulvectomy and bilateral inguinal-femoral lymphadenectomy. Patients with T1 tumour are usually treated with radical local excision, if the lesion is unifocal and the remainder of the vulva is normal. Patients with T1a disease have no risk of groin metastases and do not need lymphadenectomy, whereas those with T1b disease need ipsilateral inguinal-femoral lymphadenectomy if the lesion is lateral, and bilateral lymphadenectomy if the lesion is midline. Modifications of the surgical technique of deep femoral lymphadenectomy and the mapping of sentinel node can offer new interesting therapeutic perspectives. Postoperative adjuvant pelvic and groin irradiation is warranted for patients with two or more or macroscopically involved groin nodes. Locally advanced squamous cell carcinoma of the vulva has been long surgically treated with en-block radical vulvectomy and bilateral inguinal-femoral lymphadenectomy plus partial resection of urethra, vagina or anum, or by exenteration, with severe postsurgical complications, poor quality of life, and unsatisfactory survival rates. 5-Fluorouracil [5-FU] or 5-FU- and cisplatin-based chemotherapy concurrent with irradiation followed by tailored surgery represents an attractive therapeutic option for advanced disease, planned to avoid such ultra-radical surgical procedures and, hopefully, to improve patient outcome. Chemotherapy has also been used in neoadjuvant setting, with contrasting and generally unsatisfactory results, and in palliative treatment of patients with distant metastases. Surgery is the primary treatment also for vulvar malignancies other than squamous cell carcinoma, whereas the clinical usefulness of adjuvant irradiation or chemotherapy is still to be defined. Primary chemoradiation can be also used for advanced carcinoma of the Bartholin gland or for advanced adenocarcinoma associated with extramammary Paget's disease. The drugs used for chemotherapy of metastatic melanomas or sarcomas of the vulva are the same employed for the melanomas or sarcomas developed in other sites.

Cell Cycle–Dependent Antagonistic Interactions between Paclitaxel and γ-Radiation in Combination Therapy

PURPOSE

The promising clinical activity of paclitaxel, a naturally occurring antimicrotubule agent, has promoted considerable interest in combining this drug with radiation therapy, but it remains unclear whether such a combination would increase the therapeutic efficacy. This study is to assess the potential interactions between paclitaxel and gamma-radiation against human tumor cells in vitro.

EXPERIMENTAL DESIGN

Paclitaxel and gamma-radiation were administered in three different sequences designated as pre-radiated, co-radiated, and post-radiated to BCap37 (human breast cancer cell line) and KB (human epidermoid carcinoma cell line) cells. The cytotoxic interactions between and mutual influences of these two agents on their antitumor activities were analyzed by a series of assays including cytotoxic, morphological, and biochemical examinations.

RESULTS

The combination of paclitaxel and gamma-radiation did not produce a synergistic or additive effect. Instead, the overall in vitro cytotoxicity of these combinations was much lower than that of paclitaxel treatment alone. DNA fragmentation and flow cytometric assays showed that the addition of gamma-radiation interfered with paclitaxel-induced apoptosis. Further analyses indicated that the addition of gamma-radiation resulted in a transient or prolonged cell cycle arrest at G(2) phase, which likely prevented the cytotoxic effects of paclitaxel on both mitotic arrest and apoptosis. In addition, biochemical examinations revealed that gamma-radiation inhibited paclitaxel-induced IkappaBalpha degradation and bcl-2 phosphorylation and increased the protein levels of cyclin B1 and inhibitory phosphorylation of p34(cdc2).

CONCLUSIONS

Our results suggest that gamma-radiation might specifically block the cell cycle at G(2) phase, which in turn prevents the cytotoxic effects of paclitaxel on both mitotic arrest and apoptosis. Therefore, it eventually results in a cell cycle-dependent antagonistic effect on the antitumor activity of paclitaxel. This finding may be relevant to the clinical application of combination therapy with paclitaxel and radiation.

Supra-additive effect with concurrent paclitaxel and cisplatin in vulvar squamous cell carcinoma in vitro

The effect of concurrent paclitaxel and cisplatin was tested in vitro in 5 vulvar squamous cell carcinoma (SCC) cell lines (UM-SCV-1A, -2, -4 and -7 and UT-SCV-3). Chemosensitivity was tested using the 96-well plate clonogenic assay. Paclitaxel concentrations used varied between 0.4 and 1.6 nM, and cisplatin concentrations varied between 0.1 and 0.9 microg/ml. These drug concentrations are clinically achievable. Survival data were fitted to the LQ model, and the area under the curve (AUC) value was obtained with numerical integration. The type of interaction was determined by comparing the AUC ratio of the 2 drugs with the survival fraction (SF) of paclitaxel alone. With all cell lines tested the growth-inhibitory effect of simultaneous paclitaxel and cisplatin was at least additive. The effect of the tested combination on the UM-SCV-1A and UT-SCV-3 cell lines was clearly supra-additive with all paclitaxel concentrations tested, and the UM-SCV-4 and UM-SCV-7 cell lines exhibited a supra-additive effect with increasing paclitaxel concentrations. The degree of supra-additivity was dose-dependent in the UM-SCV-7 cell line with increasing synergy at higher paclitaxel doses. In the current study the combination of paclitaxel and cisplatin had a clear additive or supra-additive cytotoxic effect on the vulvar SCC cell lines, and it has been successfully used in other gynecologic malignancies; therefore concurrent paclitaxel and cisplatin also deserves further testing in clinical settings in advanced-stage vulvar carcinoma, which has a poor prognosis.