5-Fluorouracil infusions and fractionated doses of radiation: studies with a murine squamous cell carcinoma

Phase II study of concurrent capecitabine and external beam radiotherapy for pain control of bone metastases of breast cancer origin

Background

Pain from bone metastases of breast cancer origin is treated with localized radiation. Modulating doses and schedules has shown little efficacy in improving results. Given the synergistic therapeutic effect reported for combined systemic chemotherapy with local radiation in anal, rectal, and head and neck malignancies, we sought to evaluate the tolerability and efficacy of combined capecitabine and radiation for palliation of pain due to bone metastases from breast cancer.

Methodology/Principal Findings

Twenty-nine women with painful bone metastases from breast cancer were treated with external beam radiation in 10 fractions of 3 Gy, 5 fractions a week for 2 consecutive weeks. Oral capecitabine 700 mg/m² twice daily was administered throughout radiation therapy. Rates of complete response, defined as a score of 0 on a 10-point pain scale and no increase in analgesic consumption, were 14% at 1 week, 38% at 2 weeks, 52% at 4 weeks, 52% at 8 weeks, and 48% at 12 weeks. Corresponding rates of partial response, defined as a reduction of at least 2 points in pain score without an increase in analgesics consumption, were 31%, 38%, 28%, 34% and 38%. The overall response rate (complete and partial) at 12 weeks was 86%. Side effects were of mild intensity (grade I or II) and included nausea (38% of patients), weakness (24%), diarrhea (24%), mucositis (10%), and hand and foot syndrome (7%).

Conclusions/Significance

External beam radiation with concurrent capecitabine is safe and tolerable for the treatment of pain from bone metastases of breast cancer origin. The overall and complete response rates in our study are unusually high compared to those reported for radiation alone. Further evaluation of this approach, in a randomized study, is warranted.

Trial Registration

ClinicalTrials.gov NCT01784393NCT01784393

Recent advances in the molecular imaging of programmed cell death: part I--pathophysiology and radiotracers

In humans, apoptosis (programmed cell death) is the most common form of cell death after necrosis. Apoptosis is a series of genetically preprogrammed biochemical and morphologic energy-requiring events that, after a specific external or internal stimulus, results in the physiologic disappearance of a cell via its self-disintegration and packaging of its contents into membrane vesicles called apoptotic bodies. Apoptotic bodies can readily be ingested, with their nutrients and even organelles recycled by neighboring cells or phagocytes without local inflammation. In contrast, necrosis is characterized by the primary loss of plasma membrane integrity and the uncontrolled release of a cell's contents, often causing local inflammation, tissue damage, and scarring. Alternate forms of cell death also exist, associated with specific molecular mechanisms involving enzymes, organelles, genes, external stimuli, or blockade of normal cell proliferation. In this review we will briefly outline the molecular mechanisms of apoptosis that can be imaged with radiotracers now under development.

Multimodality molecular imaging of apoptosis in oncology

OBJECTIVE

The purposes of this review are to describe the signaling pathways of and the cellular changes that occur with apoptosis and other forms of cell death, summarize tracers and modalities used for imaging of apoptosis, delineate the relation between apoptosis and inhibition of protein translation, and describe spectroscopic technologies that entail high-frequency ultrasound and infrared and midinfrared light in characterizing the intracellular events of apoptosis.

CONCLUSION

Apoptosis is a highly orchestrated set of biochemical and morphologic cellular events. These events present many potential targets for the imaging of apoptosis in vivo. Imaging of apoptosis can facilitate early assessment of anticancer treatment before tumor shrinkage, which may increase the effectiveness of delivery of chemotherapy and radiation therapy and speed drug development.

Acute and long-term toxicity following radiotherapy alone or in combination with chemotherapy for locally advanced cervical cancer

Randomised studies in locally advanced cervical cancer patients showed that cisplatin should be given concurrently with radiotherapy, because of a better long-term survival compared to radiotherapy alone. This increases the relevance of treatment related toxicity. This review summarises the acute and long-term toxicity of radiotherapy given with or without chemotherapy for cervical cancer. Acute toxicity (all grades) of radiotherapy is reported in 61% of the patients in the rectosigmoid, in 27% as urological, in 27% as skin and in 20% as gynaecological toxicity. Moderate and severe morbidity consists of 5% to 7% gastrointestinal and 1% to 4% genitourinary toxicity. Adding chemotherapy to radiotherapy increases acute haematological toxicity to 5% to 37% of the patients and nausea and vomiting in 12% to 14%. Late effects of radiotherapy include gastrointestinal, urological, female reproductive tract, skeletal and vascular toxicity, secondary malignancies and quality of life issues. For at least 20 years after treatment, new side effects may develop. Gastrointestinal toxicity usually occurs in the first 2 years after treatment in about 10% of the patients. The incidence of moderate and severe urological toxicity can increase up to 10% and rises over time. Gynaecological toxicity usually occurs shortly after treatment while skeletal and vascular toxicity can occur years to decades later. Thus far, no increase in late toxicity has been observed after the addition of cisplatin to radiotherapy. Finally, methods to prevent or decrease late toxicity and therapeutical options are discussed. However, most randomised studies still have a limited follow-up period.

Anin vitro model to optimize dose scheduling of multimodal radioimmunotherapy and chemotherapy: Effects of p53 expression

Several reports have appeared on the use of combined radioimmunotherapy (RAIT) and chemotherapy. The choice of drug to use with RAIT and how to space the two treatments has not been completely addressed. Because every patient's cancer presents with a specific molecular phenotype, we hypothesized that it may be necessary to tailor therapy based on specific gene expression. We addressed how the form of expression of a single gene, the p53 tumor suppressor, would impact the choice of agents, as well as sequence and spacing of agents. p53 regulates cell cycle arrest to allow for DNA repair after therapy-induced small DNA damage or induction of apoptosis if damage is great and has been shown to affect chemo- and radiosensitivity of cancer cells. We established 3 stable p53 transfectants of the SKOV-3 p53null parental line (p53(wt), p53(143mut) or p53(273mut)). p53 expression was confirmed using flow cytometry, using the DO1 pan-p53 Ab and the PAb240 anti-p53mut Ab. The colorimetric MTT assay was then used to measure dose-dependent growth inhibition from single modality chemotherapy (doxorubicin, carboplatin, paclitaxel or topotecan) or radioimmunotherapy (90Y-RS-7 IgG anti-EGP1). The % survival vs. log [drug] were plotted to obtain the IC50. We then used a matrix design in which we varied the sequence of the first and second modality of treatment and the spacing between the 2 treatments to determine the most synergistic and antagonistic combinations for the parental SKOV-3 and each of the 3 transfectants. The IC50 for each therapeutic agent varied as a function of the form of p53 expressed. For example, of the 4 lines, the p53wt transfectant was the most resistant to topotecan and the 143mut was the most resistant to carboplatin. The 273mut was quite sensitive to both doxorubicin and paclitaxel, whereas the p53null and wt were not. For multimodal treatments, most combinations of RAIT and chemotherapy resulted in a 30-40% growth inhibition (GI) and were either additive or moderately antagonistic. The 3 best (>60% GI) and 3 worst (<25% GI) combinations were identified and were unique to the parental p53null and to the 3 transfectants. Certain combinations showed clear synergy and others were antagonistic, with the first treatment modality blocking the growth inhibitory effects of the second treatment modality. The form of p53 expressed affects chemosensitivity and radiosensitivity and will influence optimal multimodal therapy with RAIT and chemotherapy and the dose-schedule (sequential with RAIT first or with drug first) when more than 1 agent is used.

A multicentre phase II trial of primary chemotherapy with cisplatin and protracted venous infusion 5-fluorouracil followed by chemoradiation in patients with carcinoma of the oesophagus

BACKGROUND

We undertook a multicentre phase II trial to evaluate the safety and efficacy of primary chemotherapy followed by chemoradiation for localised adenocarcinoma or squamous carcinoma of the oesophagus.

PATIENTS AND METHODS

Chemotherapy comprised five 3-weekly cycles of cisplatin and protracted continuous infusion 5-fluorouracil, with conformally planned radiotherapy commencing at the start of the fifth cycle.

RESULTS

The planned treatment programme was completed by 39 of 72 patients (54%), and a further 13% completed chemotherapy and proceeded to surgical oesophagectomy. Response rates to chemotherapy and to the entire treatment programme were 47% [95% confidence interval (CI) 34% to 60%] and 56% (CI 43% to 68%). The dysphagia score improved in 54% of patients. The median survival duration was 14.6 months with 1- and 2-year survival rates of 58.7% and 44.1%, respectively. Grade III/IV chemotherapy-related toxicity occurred in 38% of patients, and there were no treatment-related deaths.

CONCLUSIONS

This is a feasible and active treatment regimen providing palliative benefits for patients with poor-prognosis localised oesophageal cancer.

Influence of dose per fraction and overall treatment time on the response of pulmonary micrometastases of the R1H-tumour to fractionated irradiation

BACKGROUND AND PURPOSE

Macroscopic subcutaneously growing R1H-tumours have been shown to respond almost independently of the dose per fraction when treated under ambient conditions. In addition decelerated repopulation during fractionated irradiation has been shown for this experimental tumour. The aim of the present study was to investigate whether this is also the case for pulmonary micrometastases which are assumed to be fully oxygenated or whether differences in the oxygenation status of the tumour possibly alters its response to fractionation. The influence of the dose per fraction and overall treatment time on the response of micrometastases to fractionated irradiation was studied.

MATERIALS AND METHODS

Pulmonary metastases were induced by i.v. injection of viable tumour cells. Treatment was started 14 days later, when metastases reached an average size of four cells. Total doses of 16 to 28 Gy were administered within an overall treatment time of 11 or 25 days, using doses per fraction of 1, 2, or 4 Gy. Tumour response was quantified by metastatic control (MCD(37%)).

RESULTS

Fractionation had a significant influence on local control (P=0.009). After application of 1, 2, or 4 Gy and an overall treatment time of 11 days the MCD(37%) was 25.4 (95% C.I.: 21.5-32.0) Gy, 20.7 (17. 0-24.0) Gy, and 18.5 (14.9-21.6) Gy, respectively. When overall treatment time was prolonged to 25 days the MCD(37%) increased to 25. 5 (21.3-33.5) Gy when fractions of 2 Gy where applied, but this difference was not significant (P=0.13). The doubling time of 12.8 days determined for the metastatic clonogenic tumour cells during fractionated irradiation was significantly longer than the 4.1 days observed for untreated metastases (P=0.006).

CONCLUSIONS

The results show a strong influence of fractionation on treatment outcome and a decelerated repopulation during fractionated irradiation treatment for well oxygenated pulmonary metastases of the R1H-tumour.

Radiation enhancement by biochemical modulation and 5-fluorouracil

PURPOSE

To evaluate the effects of biochemical modulation by N-(phosphonacetyl)-L-aspartate (PALA), 6-methylmercaptopurine riboside (MMPR), and 6-aminonicotinamide (6AN), (PALA + MMPR + 6AN is referred to as PMA) on tumor radiosensitivity, and evaluate the efficacy of the addition of 5-FU to the PMA + XRT regimen for enhancement of tumor response to radiation without exceeding normal tissue tolerance.

METHODS AND MATERIALS

A first generation transplant of the CD8F1 spontaneous murine tumor was studied. 31P nuclear magnetic resonance spectroscopy was used to determine the interval between chemotherapy and radiation based on energy depletion. PMA was administered three times with fractionated XRT (15 Gy x 3 = 45 Gy) on days 1, 10, or 11, and 21. The addition of 5-fluorouracil (5-FU) at maximum tolerated doses was evaluated and intergroup comparisons were made for tumor growth delay, local control, and disproportionate normal tissue damage.

RESULTS

The combination of 5-FU + XRT induced a tumor doubling time of 75.4 days (67.4-84.4) (p < 0.0001 compared to XRT), validating that in this tumor model, pretreatment with bolus i.p. 5-FU enhanced XRT. In comparison, mice treated with PMA + XRT had a tumor doubling time (TDT) > 123.2 days (109.4-138.7), (p < 0.0001 compared to 5-FU + XRT). The addition of 5-FU to PMA + XRT induced a doubling time of > 170.8 days (150.7-193.7) (p = 0.0002 compared to PMA + XRT). The doubling time for the PMA + XRT cohort and the PMA + 5-FU + XRT cohorts are underestimates since some of the tumor bearing mice continue to have a complete regression (CR). The CR rate (measured on day 250) for the PMA + 5-FU + XRT cohort was 31.7% compared to 0% for 5-FU + XRT and 10% for PMA + XRT (p < 0.05). Mortality and local effects induced by radiation in the PMA + XRT group were comparable to the toxicity for the PMA + 5-FU + XRT group indicating that the addition of 5-FU at 75 mg/kg to PMA + XRT was tolerated and induced both greater CR and tumor doubling times than XRT alone, 5-FU (150 mg/kg) + XRT, or PMA + XRT.

CONCLUSIONS

PMA is superior to 5-FU as a radiosensitizer in the schedule studied. The combination of PMA + 5-FU further enhanced XRT without exceeding normal tissue tolerance.

Hyperfractionation: where do we stand?

Hyperfractionation is generally expected to allow an escalation of total dose, thereby increasing tumour control rate, without increasing the risk of late complications. The purpose of this review is to assess the empirical evidence for this therapeutic gain from hyperfractionated radiotherapy. Although extensive clinical data have been accumulated until now, especially on treatment of head and neck cancer, the line of evidence is not consistent. The present analysis indicates that the dose per fraction generally used in standard radiotherapy is already a good choice.

Combined effect of clinically relevant doses of emitefur, a new 5-fluorouracil derivative, and radiation in murine tumours

We investigated the combined effect of radiation and clinically relevant doses of emitefur (BOF-A2), a newly developed anti-cancer agent consisting of a masked form of 5-fluorouracil (5-FU) and a potent inhibitor of 5-FU degradation, in two types of murine tumours. In preliminary pharmacokinetic studies, the area under the curve for 5-FU in plasma, after administration of 12.5 mg kg-1 and 25 mg kg-1 emitefur in mice, appeared to be similar to that obtained on the first day and that on the seventh day, respectively, after starting administration of 400-600 mg day-1 in humans. These doses (12.5 and 25 mg kg-1) of emitefur were evaluated either alone or in combination with single (15 Gy), five-fraction (4 Gy each) or ten-fraction (2.8 Gy each) irradiation using a tumour growth delay assay for SCCVII tumours and in combination with four-fraction (5 Gy each) irradiation using an in vivo-in vitro assay for EMT6 tumours. The anti-tumour and radiation-enhancing effects of 12.5 mg kg-1 emitefur were not significant in any except the ten-fraction experiment. On the other hand, multiple doses of 25 mg kg-1 emitefur given either alone or in combination with radiation produced marked effects. The mean tumour growth delay time (the time to double in volume for treated tumours minus that for untreated tumours) was 8.1 days for five administrations of 25 mg kg-1 emitefur. 10.4 days for five fractions of 4 Gy and 22.1 days for five treatments with the combination of the two. Thus, the increase in growth delay afforded by this combination was at least additive. The effect of four fractions of 5 Gy with 25 mg kg-1 emitefur in EMT6 tumours was lower than that of four fractions of 7.5 Gy, but the effect of five fractions of 4 Gy with this dose of emitefur in SCCVII tumours was similar to the effect of five fractions of 6 Gy, and the effect of ten fractions of 2.8 Gy with 25 mg kg-1 emitefur was much higher than that of ten fractions of 4.2 Gy. In conclusion, emitefur given either alone or in combination with radiation appears to have a significant anti-tumour effect even at clinically relevant dose levels, although a threshold dose exists between 12.5 and 25 mg kg-1. Further clinical studies of this compound are warranted.

Tumor retention of 5-fluorouracil following irradiation observed using 19F nuclear magnetic resonance spectroscopy

PURPOSE

The combination of 5-fluorouracil (5FU) and radiation results in improved tumor control in a variety of gastrointestinal cancers. We propose the enhancement is related to radiation potentiating the antitumor effects of 5FU. To better understand the mechanism of the 5FU-radiation interaction, 19F nuclear magnetic resonance (NMR) spectroscopy experiments were performed to observed the tumor clearance and metabolism of 5FU.

METHODS AND MATERIALS

Experiments were performed on 10 3-6-week-old female (Nu/Nu) athymic nude mice. Flank tumors measuring approximately 1.0 cm in diameter 3 weeks following a subcutaneous injection of 1 x 10(6) human colon adenocarcinoma (HT-29) cells were studied. In our first group, all animals received an intravenous bolus injection of 5FU (100 mg/kg) immediately before spectroscopic analysis. Animals in the second group were first treated with a single tumor radiation dose of 10 Gy just before the 5FU injection and subsequent spectroscopy. Spectroscopic analysis was performed with a 2.0-T NMR spectroscopy system.

RESULTS

The tumor retention of 5FU was prolonged in animals receiving radiation before the drug infusion. The tumor clearance rate of the 5FU for nonirradiated animals was 0.0178 +/- 0.0082/min vs. 0.0055 +/- 0.0027/min for irradiated animals, reflecting a threefold reduction in drug clearance in the irradiated tumors. The difference was significant at p < 0.005.

CONCLUSION

Our preliminary experiments suggest the enhanced cytotoxicity seen with concurrent 5FU and radiation is related to prolonged tumor retention of 5FU induced by radiation. This is consistent with the hypothesis that radiation is potentiating the cytotoxic effects of 5FU.

Combined modality treatment of the rhabdomyosarcoma R1H of the rat: tumor and normal tissue response after cisplatin and conventional or accelerated irradiation treatment

PURPOSE

To test the importance of the sequence of cisplatin and irradiation, either conventional or accelerated fractionated.

METHODS AND MATERIALS

30 fractions of 2 Gy were given in 6 or 3 weeks preceded or followed by (time interval between cisplatin and radiotherapy: 3 days) a single IP dose of 5 mg/kg cisplatin in the rhabdomyosarcoma R1H of the rat. Survival curves were generated, and comparisons were made by the log-rank test.

RESULTS

After 60 Gy in 6 weeks, no local tumor controls were observed. If cisplatin was injected 3 days before start of 60 Gy/6 weeks, 11 +/- 10% (mean +/- SE) of the tumors were controlled. Cisplatin after radiotherapy resulted in 50 +/- 14% local controls. The difference was significant (p = 0.01) for cisplatin after radiotherapy in comparison to radiotherapy alone where no local controls were observed. After accelerated fractionation, 57 +/- 19% of the animals were cured with or without cisplatin before radiotherapy. If the drug was injected after end of 60 Gy/3 weeks, 86 +/- 13% survived recurrence free. The difference to accelerated radiotherapy alone was not significant. Accelerated radiotherapy produced significantly higher control rates than conventional radiotherapy (p < 0.001).

CONCLUSIONS

Accelerated radiotherapy resulted in higher local tumor control rates as compared to conventional fractionated irradiation. Cisplatin combined with radiotherapy showed significantly better results if given after but not before irradiation, either conventional or accelerated fractionated.

The role of cell cycle redistribution in radiosensitization: implications regarding the mechanism of fluorodeoxyuridine radiosensitization

PURPOSE

Radiosensitization has previously been demonstrated in a human colon cancer cell line (HT-29) following a 2 h exposure to low, clinically relevant concentrations (0.05-0.5 microM) of fluorodeoxyuridine (FdUrd) (15). The sensitizer enhancement ratio value (measured at 10% survival) plateaued at approximately 1.7 between 16 and 32 h following removal of drug. Parallel studies investigating the effect of FdUrd on the distribution of cells throughout the cell cycle found that the percentage of cells in early S-phase increased to approximately 70% during the same period that maximal radiosensitization was noted. As a follow-up to these findings, experiments have been designed to investigate the contribution of this early S-phase delay to radiosensitization.

METHODS AND MATERIALS

Synchronized populations of HT-29 cells have been obtained with three separate techniques. Two involve the induction of a reversible metaphase arrest (with high pressure N2O or colcemid) followed by a shakeoff of mitotic cells. The third uses a plant amino acid, mimosine, to induce a reversible block at the G1/S boundary. Flow cytometry was used to analyze the degree of synchrony based on bromodeoxyuridine (BrdUrd) uptake and propidium iodide (PI) staining. Radiation survival curves were obtained on these synchronized populations to investigate changes in radiosensitivity through the cell cycle. Additionally, levels of thymidylate synthase (TS), the primary target of FdUrd cytotoxicity, were measured in each phase of the cell cycle using the TS 106 monoclonal antibody against human TS.

RESULTS

Synchronization with mitotic shakeoff produced relatively pure populations of cells in G1; however, the degree of synchrony in early S-phase was limited both by cells remaining in G1 and by cells progressing into late S-phase. These techniques failed to reveal increased radiosensitivity in early S-phase at 10% survival. An 18 h exposure to mimosine resulted in populations that more closely resembled the early S-phase enrichment following FdUrd exposure and revealed increased radiosensitivity during early S-phase. TS levels were noted to be only 1.3 times higher in S phase than in G0/G1.

CONCLUSION

Radiation survival data from cells synchronized with mitotic shakeoff techniques suggest that early S-phase delay is unlikely to be the primary mechanism of FdUrd radiosensitization. In contrast, the increased sensitivity seen in early S-phase with mimosine synchronized cells is similar to that seen with FdUrd. Although confounding biochemical pertubations cannot be ruled out, these data continue to suggest an association between early S-phase enrichment and radiosensitization. The significance of TS inhibition as a mechanism of FdUrd radiosensitization remains unclear.

High dose external beam radiation therapy with or without concomitant chemotherapy for esophageal carcinoma

Esophageal cancer patients treated with radiotherapy (RTx) are most often those with malignancies too extensive for surgery or those who deemed medically unsuitable for an aggressive surgical approach. Summarizing RTx series, the 2-year survival rate is in the range of 10% and at 5 years about 5%. Although not randomly compared, these results are not significantly worse than those achieved with surgery in more advanced tumors. In stage I/II tumors, more recent trials reported of 5-year survival rates varying between 12% and 20%. These data indicate that irradiation may be administered with curative intention but usually only for patients who are also candidates for primary surgery. On the other hand, modern RTx (doses > 60 Gy) +/- endoluminal after-loading may provide good palliation (relief of dysphagia) for patients with good prognostic factors such as weight loss of less than 10% body weight, good performance status, younger age, and location of the tumor. In the perioperative setting, RTx reduced the frequency of the local recurrences but did not increase the overall resection and R0 resection rates and did not improve survival due to more patients relapsing at distant sites. Combined chemoradiotherapy has shown to be superior to RTx alone with respect to local control, disease free survival and overall survival and in a marked reduction of distant failures. These data support the use of chemoradiotherapy as standard treatment of locally advanced and nonresectable esophageal cancer. They also provide a basis for randomized trials comparing chemoradiotherapy alone versus preoperative treatment modalities.

Combination therapy with radiation, mitomycin C, and 5-fluorouracil in EMT6 tumors

PURPOSE

The primary purpose of these studies was to assess whether concomitant treatment with 5-fluorouracil increased the cytotoxicity of radiation, mitomycin C, or the combination of these two agents to cells in solid tumors.

METHODS AND MATERIALS

All studies were performed using EMT6 mouse mammary tumor cells. In vitro studies used exponentially-growing monolayers. In vivo studies used solid EMT6 tumors growing in BALB/c Rw mice. The effects of treatment on tumors or cultures were assessed using clonogenic assays which considered both the colony forming abilities of the intact cells and the numbers of cells in the cultures or tumors.

RESULTS

EMT6 cells in vitro were killed effectively by 5-fluorouracil. The cytotoxicity increased as the drug concentration increased from 1 microM to 1 mM or as the treatment time increased from 1 to 48 hr. However, 5-fluorouracil was only marginally active against solid EMT6 tumors: treatment with doses of up to 400 micrograms/gm killed less than 50% of the tumor cells, regardless of whether the drug was given as an injection or an infusion over 48 hr and regardless of the time between injection of the drug and assay of cell survival. Treatment with 5-fluorouracil produced only a statistically insignificant increase in the effect of 15 Gy of x-rays, whether the drug was given by injection or infusion over 48 hr. Both injection of 200 micrograms/g 5 FU and infusion of 100 micrograms/g 5-fluorouracil decreased the cytotoxicity of 6 micrograms/g of MC to cells in solid tumors. Injection of 200 micrograms/g of 5-fluorouracil decreased the cytotoxic effects of a regimen combining 6 micrograms/g MC plus 15 Gy of x-rays.

CONCLUSION

In this solid tumor system, a regimen combining single doses of mitomycin C and x-rays was more effective in killing the tumor cells than was the same regimen combined with 5-fluorouracil.

The clinical rationale for S-phase radiosensitization in human tumors

Nonhypoxic cell radiosensitizers, principally the halogenated pyrimidines and hydroxyurea, have been studied in the laboratory and clinical setting for more than 30 years. Early clinical experience in the 1960s and 1970s with the thymidine analogs 5-bromodeoxyuridine (BUdR) and 5-iododeoxyuridine (IUdR) was disappointing because normal tissue toxicity eliminated any potential for therapeutic gain. Inadequate delivery systems for intravenous and intraarterial infusions also contributed to the decline of this strategy. More recently, laboratory investigations have revealed further information regarding the mechanism of IUdR/BUdR radiosensitization. This knowledge provided a rationale for the sequence and timing of drug and radiation exposure, which could be both effective and tolerable. Advancing technology also provided safer infusion devices, and a resurgence in clinical trials combining IUdR or BUdR and radiation resulted. Current laboratory studies are now providing data on tumor cell kinetics, which is being applied to ongoing clinical trials. Fluoropyrimidines, principally 5-fluorouracil (5-FU), were also used in early clinical trials and unlike IUdR/BUdR were found to have significant activity as single agents against a variety of tumor types. The clinical integration of 5-FU and radiation occurred more slowly, but recent trials have demonstrated a therapeutic gain. Improved rates of local control and survival with combined 5-FU and radiation versus radiation alone have now been demonstrated in patients with rectal, esophageal, and anal carcinomas. However, the mechanism of interaction between the fluoropyrimidines and radiation remains uncertain and continues to be investigated with the hope of improved clinical outcome. As the cellular pathways influenced by the halogenated pyrimidines have been defined, the potential for biochemical modulation of these agents has been recognized. Leucovorin, the most commonly applied modulator, has been shown to enhance the activity of 5-FU in patients with metastatic colorectal carcinoma. These studies serve as an example for current trials that use biochemical modulators of IUdR, BUdR, and 5-FU as radiosensitizers. Hydroxyurea, currently used in the treatment of chronic leukemia, has also been considered a radiosensitizer. As with IUdR/BUdR, the clinical trials have often been inconclusive and interest in this radiosensitizer has waned. A poor understanding of the mechanism of action and tumor cell/normal tissue kinetics may be responsible for the lack of overall success with this strategy. Current investigations of cell kinetics in humans and potential mechanisms of hydroxyurea action could provide information critical to future trials of hydroxyurea radiosensitization.

Radiation therapy for colorectal cancer

The role of radiation therapy in the management of colorectal cancer has become more clearly defined as the number of clinical studies has grown. It is now evident that radiation is capable of sterilizing subclinical deposits of cancer at doses tolerable by adjacent normal tissues, and to a lesser extent, these doses can control more bulky cancers. The integration of radiation and chemotherapy has already led to some improvement in survival rates in the adjuvant treatment of rectal cancer. The further development of such combinations seems likely to improve tumor control and survival rates in many stages of cancer. In the next decade, it is also likely that there will be refinement of the use of radiation through better understanding of the biology of colorectal cancer, perhaps supplemented by the development of predictive assays that can guide both the selection of patients for treatment and the choice of the most effective radiation schedule.

Combined modality treatment of the rhabdomyosarcoma R1H of the rat: influence of sequence of cisplatin and fractionated irradiation

The effect of irradiation with 30 fractions of 2 Gy in 6 weeks combined with a single dose of 5mg/kg cisplatin was studied in the rhabdomyosarcoma R1H of the rat and tumor response and normal tissue toxicity were assessed for various combinations of radiotherapy and chemotherapy. Cisplatin was given 3 days before, during (after the 5th and after the 10th fraction), or 3 and 17 days after radiotherapy. Five of the 12 tumors treated with cisplatin injected 3 days after radiotherapy were locally controlled (42%; 95% confidence intervals: 14-70%) as compared to 0/10 for radiotherapy alone (0%; 0-21%; p < 0.02). A similar trend was found for cisplatin injected 17 days after irradiation (2/6 local controls; 33%; 0-71%). With cisplatin given 3 days before radiotherapy 1/13 local controls were observed (8%; 0-22%; p < 0.05 when tested vs. cisplatin 3 days after radiotherapy). Tumor cure was dependent upon tumor size at time of cisplatin administration with 7/9 small tumors (< 2 mm3) cured versus only 2/35 cures of larger tumors (> 2 mm3). By contrast, net growth delay and skin damage were the same for combined modality treatment and for irradiation alone. General toxicity as assessed by body weight change was significantly higher for animals treated with cisplatin before or after radiotherapy, whereas cisplatin during radiotherapy showed equal effects as compared to radiotherapy alone. Although for the rhabdomyosarcoma R1H of the rat the combined modality treatment was shown to be more effective than radiotherapy alone when cisplatin was applied after radiotherapy, general toxicity was also higher for this mode of treatment.

Adjuvant radiation therapy for colorectal cancer

BACKGROUND

Despite apparently complete resection of cancers of the rectum or colon, many patients have recurrences in the area from which their primary cancer was excised and in more distant organs. Radiation therapy has been used either alone or in combination with chemotherapy as an adjuvant to surgery to reduce the risk of recurrence.

METHODS

The literature describing the results of adjuvant radiation treatment for colorectal cancer was reviewed.

RESULTS

In randomized studies in patients with moderately advanced rectal cancers (T2-4 N0, M0 or N1-3, M0) adjuvant radiation therapy has often reduced the risk of pelvic recurrence, but has had little effect on survival rates or the risk of extrapelvic metastases. Recent reports show that combined radiation and chemotherapy can improve both disease-free survival and survival rates. Such treatment has caused only moderate toxicity in most studies. Nonrandomized studies in patients in whom small superficial rectal cancers are treated by local excision suggest that adjuvant radiation therapy reduces the risk of pelvic recurrence after this limited surgery and allows anorectal function to be preserved. Strategies similar to those developed for the treatment of rectal cancer are being studied in patients with colon cancer.

CONCLUSIONS

In moderately advanced rectal cancers, the combination of chemotherapy and radiation is more effective than radiation alone in reducing local recurrence and increasing survival rates. Additional trials are needed to improve results and to refine drug and radiation schedules. Radiation alone may be sufficient as an adjuvant treatment when combined with local excision of small rectal cancers. The role of radiation in the adjuvant treatment of colon cancer is investigational. There is a need to more accurately delineate the patients with colorectal cancer most likely to benefit from adjuvant therapy.

Mode of interaction of 5-fluorouracil, radiation, and mitomycin C: in vitro studies

An examination of the effects of radiation combined with either 5-fluorouracil, Mitomycin C, or both drugs in vitro has been made using a mouse squamous tumor cell line SCC VIITo and cell viability as an endpoint. Depending on how the survival endpoint was calculated, the interaction of 5-fluorouracil, Mitomycin C, or 5-fluorouracil plus Mitomycin C with radiation was greater than additive (plating efficiency) or only additive (viable cells per flask). These results suggest that the cytostatic effect of these drugs may be an important aspect of their action clinically.

Anal cancer

Combined modality treatment with radiation, chemotherapy, and conservative surgery controls most epidermoid cancers of the anal canal and advanced squamous cell cancers of the perianal skin. Anorectal function is preserved in about 70% of patients or more. Five-year survival rates are similar to those previously obtained with radical surgery or radical radiation therapy. The cytotoxic drugs 5-Fluorouracil and Mitomycin C are frequently given concurrently with radiation, but other effective regimens have also been described. The mechanisms of interaction of radiation and cytotoxic drugs in the treatment of anal cancer are not known.

Radiation sensitivity of tumour cells stained in vitro or in vivo with the bisbenzimide fluorochrome Hoechst 33342

The DNA-binding bisbenzimide fluorochrome Hoechst 33342 is being used routinely in radiobiological studies to assess cell kinetic parameters and tumour blood flow. However, there are reports in the literature which indicate that exposure to this compound can affect the radiation sensitivity of tumour cell populations. In this investigation, it was found that staining murine tumour cells in vitro with H33342 at concentrations greater than 0.1 microM before irradiation resulted in radioprotection. The protection factor calculated for fibrosarcoma cells stained with 10 microM H33342 was 1.7. Varying the time between radiation treatment and exposure to the fluorochrome demonstrated that the effect rapidly changed to radiosensitization when staining was performed subsequent to irradiation. Cells in transplanted KHT tumours were stained in vivo by intravenous administration of H33342 to determine whether the radiation sensitivity of these populations might also be modified. Flow cytometric analysis of suspensions prepared from tumours stained in this manner revealed that recovered cells exhibited a greater than 100-fold range in fluorescence intensities. These suspensions were irradiated in vitro and the cells were then fractionated according to fluorochrome content using cell sorting. Little evidence for a radioprotective effect was observed when these subpopulations were assessed for survival, even when tumour-bearing mice were given doses of H33342 which approached the LD50. Further analysis demonstrated that insufficient amounts of the fluorochrome were taken up by cells during in vivo staining to attain levels required for radioprotection. However, our results indicate that the amount of H33342 accumulated by cells may affect the radiation sensitivity of populations exposed to high concentrations of this fluorochrome, such as those required to achieve stoichiometric binding to DNA.

Comparative antitumor activity of 5-fluorouracil and 5'-deoxy-5-fluorouridine in combination with radiation therapy in mice bearing colon 26 adenocarcinoma

The present study compared the antitumor activities of chemotherapy with 5-fluorouracil (5-FU) and with its prodrug 5'-deoxy-5-fluorouridine (5'-DFUR) in combination with radiotherapy on a solid colon 26 adenocarcinoma in the mouse. A single administration of 5'-DFUR immediately after local irradiation on day 10 after tumor inoculation produced more than additive antitumor effects, while only an additive effect was observed in the combined treatment with 5-FU and radiation. This over-additive effect of 5'-DFUR was more obvious in a fractionated-dose treatment schedule, where the same combined modality treatment was given three times on days 6, 10 and 14 after inoculation of the tumor cells. 5'-DFUR enhanced the radiation effects on the tumor in terms of the delay in tumor growth as well as the increase in the survival time. 5-FU produced only a marginal additive antitumor effect. Furthermore, radiation damage to normal tissues (skin damage by local irradiation and bone marrow and spleen damage by whole-body irradiation) was not enhanced by 5'-DFUR, though radiation damage to the thymus was additive. On the other hand, 5-FU produced toxic effects that were additive for all normal tissues tested. Thus, at doses that were the most effective against tumors, relative therapeutic gain factors (the ratio of the effect on tumors to that on the bone marrow) of 5'-DFUR and 5-FU were 1.24 and 0.49, respectively. These results suggest that 5'-DFUR will have a greater potential than 5-FU in combined modality treatment of cancer patients.