Paclitaxel is only a weak radiosensitizer of human cervical carcinoma cell lines

Paclitaxel-Based Chemotherapy Targeting Cancer Stem Cells from Mono- to Combination Therapy

Paclitaxel (PTX) is a chemotherapeutical agent commonly used to treat several kinds of cancer. PTX is known as a microtubule-targeting agent with a primary molecular mechanism that disrupts the dynamics of microtubules and induces mitotic arrest and cell death. Simultaneously, other mechanisms have been evaluated in many studies. Since the anticancer activity of PTX was discovered, it has been used to treat many cancer patients and has become one of the most extensively used anticancer drugs. Regrettably, the resistance of cancer to PTX is considered an extensive obstacle in clinical applications and is one of the major causes of death correlated with treatment failure. Therefore, the combination of PTX with other drugs could lead to efficient therapeutic strategies. Here, we summarize the mechanisms of PTX, and the current studies focusing on PTX and review promising combinations.

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.

Paclitaxel Through the Ages of Anticancer Therapy: Exploring Its Role in Chemoresistance and Radiation Therapy

Paclitaxel (Taxol^®) is a member of the taxane class of anticancer drugs and one of the most common chemotherapeutic agents used against many forms of cancer. Paclitaxel is a microtubule-stabilizer that selectively arrests cells in the G2/M phase of the cell cycle, and found to induce cytotoxicity in a time and concentration-dependent manner. Paclitaxel has been embedded in novel drug formulations, including albumin and polymeric micelle nanoparticles, and applied to many anticancer treatment regimens due to its mechanism of action and radiation sensitizing effects. Though paclitaxel is a major anticancer drug which has been used for many years in clinical treatments, its therapeutic efficacy can be limited by common encumbrances faced by anticancer drugs. These encumbrances include toxicities, de novo refraction, and acquired multidrug resistance (MDR). This article will give a current and comprehensive review of paclitaxel, beginning with its unique history and pharmacology, explore its mechanisms of drug resistance and influence in combination with radiation therapy, while highlighting current treatment regimens, formulations, and new discoveries.

Pharmacotherapy options for locally advanced and advanced cervical cancer

Cervical cancer continues to be a significant health burden worldwide. Globally, the majority of cancers are locally advanced at diagnosis; hence, radiation remains the most frequently used therapeutic modality. Currently, the value of adding cisplatin or cisplatin-based chemotherapy to radiation for the treatment of locally advanced cervical cancer is strongly supported by randomized studies and meta-analyses. Nevertheless, despite these significant achievements, therapeutic results are far from optimal; thus, novel therapies need to be investigated. A recent, randomized, phase III trial has shown for the first time that combination chemotherapy with cisplatin and gemcitabine concurrently with radiation improves parameters of survival over cisplatin alone and establishes a new standard for the management of locally advanced cervical cancer. On the other hand, advanced disease, presenting either as an International Federation of Gynecology and Obstetrics (FIGO) stage IVB or as persistent or recurrent to primary therapy without local curative options, remains a devastating group of diseases with no options other than palliative chemotherapy. Recent results from the GOG (Gynecologic and Oncologic Group)-204 study demonstrate that cisplatin-doublets with paclitaxel, vinorelbine, gemcitabine or topotecan only produce small improvements in survival, although with different toxicity patterns; hence, patient-related factors are important when choosing any one of these regimens. The role of targeted therapies both in locally advanced and advanced disease is promising, but still at an investigational stage.

Radiosensitizers in cervical cancer. Cisplatin and beyond

Cervical cancer continues to be a significant health burden worldwide. Globally, the majority of cancers are locally advanced at diagnosis; hence, radiation remains the most frequently used therapeutical modality. Currently, the value of adding cisplatin or cisplatin-based chemotherapy to radiation for treatment of locally advanced cervical cancer is strongly supported by randomized studies and meta-analyses. Nevertheless, despite these significant achievements, therapeutic results are far from optimal; thus, novel therapies need to be assayed. A strategy currently being investigated is the use of newer radiosensitizers alone or in combination with platinum compounds. In the present work, we present preclinical information on known and newer cytotoxic agents as radiosensitizers on cervical cancer models, as well as the clinical information emanating from early phase trials that incorporate them to the cervical cancer management. In addition, we present the perspectives on the combined approach of radiation therapy and molecular target-based drugs with proven radiosensitizing capacity.

G2/M cell cycle checkpoint is functional in cervical cancer patients after initiation of external beam radiotherapy

PURPOSE

To investigate changes in cancer of the uterine cervix during radiotherapy (RT) with respect to G2/M transition in relation to tumor cell apoptosis and changes in the tumor vasculature in cervical carcinoma.

METHODS AND MATERIALS

A total of 40 consecutive patients with Stage IIA-IIIB cervical cancer underwent RT without any chemotherapy. Tumor biopsy was obtained before RT and after five fractions of 1.8 Gy. The tumor samples were stained for cyclin B1, cdc2, and Ki-67, the apoptotic index, using terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling staining. The tumor vasculature density was assessed. In 38 cases, the tissue samples were informative.

RESULTS

Cyclin B1 was positive in all biopsies before and after initiation of RT, and staining for cdc2 was positive in 35 (92%) of 38 biopsies before and 33 (87%) of 38 after 1 week of RT. Nuclear staining for cyclin B1 was observed in 92% of patients, staining an average of 15% of cells before RT. After initiating RT, 73% of patients showed positive staining on about 5% of tumor cells (p < 0.01). Nuclear staining for cdc2 was detected in 89% of patients, staining an average of 21% of cells before RT. After initiating RT, 79% of patients showed positive staining on 9% of cells (p < 0.01). The apoptotic index of the tumor cells increased after initiating RT, and a slight decrease in the vascular density after 1 week of RT was noted (p = 0.08). Changes in G2/M were associated with the clinical response, but changes in apoptosis or tumor vasculature were not.

CONCLUSION

RT leads to significant changes in the cell cycle in cervical cancer indicating intact G2/M checkpoint function. Targeting G2/M with compounds interfering with G2/M transition may further enhance the effect of RT in cervical cancer patients.

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

Concurrent paclitaxel and radiation has given promising results in the treatment of a variety of solid tumors. We wanted to test the efficacy of this combination for vulvar carcinoma, which currently has a poor outcome in advanced stages. The radiation sensitivity, sublethal damage repair (SLDR) capacity and effect of paclitaxel during fractionated radiation were assessed in our study on 7 vulvar inherently radioresistant squamous cell carcinoma (SCC) cell lines. The 96-well plate clonogenic assay was used. Survival data were fitted to the linear quadratic model. The area under the curve (AUC), equivalent to mean inactivation dose (D), was obtained with numerical integration. AUC ratios between single-dose radiation and fractionated radiation with or without paclitaxel were used to determine the SLDR of the cell lines and the effect of paclitaxel on it. Seven currently tested vulvar SCC cell lines were found to have a limited capacity of repairing sublethal damage (SLD). Only 3 of them presented SLDR of significance. The effect of concurrent radiation and paclitaxel was clearly additive when the radiation dose was fractionated in most of the cell lines. In addition, 2 of the cell lines having SLDR exhibited a trend toward losing the repair capacity when paclitaxel was present during the irradiation. In addition, the survival curve of the UM-SCV-1A cell line gave the impression of a true paclitaxel effect on SLDR. Paclitaxel used concurrently with fractionated radiation showed effectiveness on vulvar carcinoma. The effect was at least additive and could even be expected to abrogate the SLDR during split-dose radiation.

Paclitaxel is preferentially cytotoxic to human cervical tumor cells with low Raf-1 kinase activity: implications for paclitaxel-based chemoradiation regimens

BACKGROUND AND PURPOSE

Low Raf- kinase activity has been reported to be associated with radioresistance in epithelial tumor cell lines and with paclitaxel sensitivity in cervical tumor cells. Paclitaxel might thus be effective in eliminating radioresistant clones from cervical tumors, even in the absence of synergistic interaction between these therapeutic modalities. We thus established the relationship between Raf-1 kinase activity and radiosensitivity in human cervical tumor cells and determined if paclitaxel is preferentially cytotoxic to radio-resistant tumor clones.

MATERIALS AND METHODS

We established and contrasted the radiation and paclitaxel sensitivity of 12 human cervical tumor clones that exhibited a wide range of Raf-1 kinase activity.

RESULTS

Raf-1 kinase activity was inversely correlated (P = 0.001) with SF2 values in the 12 cervical tumor clones studied. Paclitaxel was preferentially cytotoxic to radioresistant tumor clones, with the level of paclitaxel-induced cytotoxicity being significantly (P = 0.0016) influenced by Raf-1 kinase activity levels.

CONCLUSIONS

Our in vitro data indicate that there are marked, but completely opposite, Raf-1 kinase dependencies of radiation and paclitaxel cytotoxicity in cervical tumor cells. The use of combined paclitaxel and radiotherapy treatment may thus lead to higher local control rates for squamous cell carcinoma of the cervix. Circumstantially, our data suggest that the greatest therapeutic gains might accrue if paclitaxel was administered when there is the greatest proportion of tumor clones with low Raf-1 kinase activity. It may thus be desirable to use paclitaxel towards the end of radiotherapy treatment or post-radiotherapy as consolidation therapy.

Paclitaxel. An update of its use in the treatment of metastatic breast cancer and ovarian and other gynaecological cancers

The antitumour agent paclitaxel has proved to be effective for the treatment of patients with metastatic breast or ovarian cancer, and limited data also indicate its clinical potential in patients with cervical or endometrial cancer. The regimen of paclitaxel administration has varied in clinical trials, the most common including a dosage of between 135 and 250 mg/m2 administered over an infusion period of 3 or 24 hours once every 3 weeks. Promising results have been achieved in phase I/II trials of a weekly regimen of paclitaxel (60 to 175 mg/m2). The objective response rate in patients with metastatic breast cancer (either pretreated or chemotherapy-naive) is generally between 20 and 35% with paclitaxel monotherapy, which compares well with that of other current treatment options including the anthracycline doxorubicin. Combination therapy with paclitaxel plus doxorubicin appears superior to treatment with either agent alone in terms of objective response rate and median duration of response. However, whether combination therapy also provides a survival advantage remains unclear; recent results of a phase III study indicate that it does not. Paclitaxel is also a useful second-line option in some patients with anthracycline-resistant disease. Combination therapy with paclitaxel and cisplatin has proved highly effective as first-line therapy for patients with advanced ovarian cancer, showing superior efficacy to cyclophosphamide/cisplatin in terms of progression-free survival time and median duration of survival. Combination therapy with paclitaxel and carboplatin has also shown promising results. Paclitaxel monotherapy is a useful second-line option for patients with platinum-refractory metastatic ovarian cancer (objective response rates have ranged from 15 to 48%). The major dose-limiting adverse events associated with paclitaxel include myelotoxicity and peripheral neuropathy. Paclitaxel has acceptable tolerability in most patients, although adverse events are common.

CONCLUSION

Paclitaxel generally appears to be as effective as other antineoplastic agents used in the treatment of metastatic breast cancer, including doxorubicin. Importantly, it is a useful second-line option for some patients with anthracycline-resistant disease. Combination therapy with both paclitaxel and doxorubicin is a highly effective first-line option for metastatic breast cancer; however, recent results indicate no survival advantage versus monotherapy. Paclitaxel is a valuable agent for second-line treatment of patients with platinum-refractory metastatic ovarian cancer and, when combined with cisplatin or carboplatin, is recommended as first-line therapy for this disease.

Phase I trial of taxol as a radiation sensitizer with cisplatin in advanced cervical cancer

OBJECTIVE

The aim of this study was to determine tolerable doses and potential toxicities of taxol, administered weekly, with concomitant cisplatin and radiation therapy in advanced cervical cancer.

METHODS

Patients with cervical cancer, either with evidence of distant metastatic disease at presentation or otherwise at high risk for recurrent disease, were eligible for this phase I study. Taxol was administered weekly as a 3-hr intravenous infusion in addition to the prescribed radiation therapy. The starting dose was 10 mg/m2/week and escalated at 10 mg/m2/week increments if tolerated by successive cohorts of three new patients. Cisplatin was given every 3 weeks at 50 mg/m2. Chemotherapy was continued until radiation was completed. For each patient quality of life was assessed weekly during therapy.

RESULTS

Sixteen patients, undergoing a total of 102 cycles, have been enrolled. Dose escalation of taxol from 10 mg/m2/week to 50 mg/m2/week was well tolerated, with no significant change in quality of life during therapy. Two radiation fractions (0.5%) were delayed due to toxicity from this chemotherapy regimen. Of 102 cycles, 6 resulted in grade 2 and 1 in grade 3 neutropenia, and no patient developed >grade 2 anemia or thrombocytopenia. Three patients developed GI-related toxicities and 1 patient presented with urosepsis during treatment. There was a 93% response rate to this regimen, with 10 patients (63%) presently having no evidence of disease.

CONCLUSIONS

This study has demonstrated that up to 50 mg/m2/week of taxol is well tolerated in patients undergoing radiation therapy for advanced cervical cancer. A phase II trial will assist in determining the efficacy of taxol as a radiation sensitizer in these patients.

The role of apoptosis in gynaecological malignancies

Apoptosis is a process of single-cell deletion requiring active participation of the cell in its own demise. First described in 1972, it is now known to play a major role in embryogenesis, tissue homeostasis and neoplasia. Apoptosis can be initiated when DNA damage occurs causing the cell to pause in its reproductive cycle. If the DNA damage is beyond repair, the cell proceeds to apoptotic cell death. When the genetic mechanism(s) involved in the pathway of apoptosis is altered, the cell does not die. Further mutations occur by proliferation and such multiple mutational events can lead to a malignant phenotype and cancer growth. The tumour suppressor gene p53 causes a DNA-damaged cell to rest and attempt repair. If damage is irreparable, p53 levels will continue to increase, initiating apoptosis. Mutation of p53, found in approximately 50% of cancers, can stop the apoptotic process. Increased bcl-2 expression, an apoptosis inhibitor, also plays a role in cellular transformation and cancer growth. Its altered expression occurs in the presence of oncogene expression. This paper reviews the role of apoptosis in malignant transformation, cancer growth, and response to therapy for gynaecological cancers. For cervical cancer and its precursors, data on apoptotic index, bcl-2 and Bax expression are presented and discussed in relationship to human papillomavirus expression. In ovarian epithelial malignancies, the role that apoptosis plays in chemotherapeutic responses is reviewed. The data for endometrial cancer are currently limited to apoptotic index.