Flavopiridol increases therapeutic ratio of radiotherapy by preferentially enhancing tumor radioresponse

PURPOSE: Recently we reported that inhibition of cyclin-dependent kinases (cdks) by flavopiridol enhanced the radiation response of murine ovarian carcinoma cells in culture. The purpose of this investigation was to extend these studies to in vivo tumor models and test whether flavopiridol increases the therapeutic ratio of radiotherapy. METHODS AND MATERIALS: Three transplantable syngeneic mouse tumors were used: mammary carcinoma (MCa-29), ovarian carcinoma (OCa-I), and a lymphoma (Ly-TH). Tumor treatment endpoints included growth delay, cure, and spontaneous lung metastases (OCa-I tumor). The normal tissue endpoint was survival of jejunal crypt cells quantified microscopically. A range of flavopiridol doses from 0.625 to 5.0 mg/kg were given systemically once or twice daily over 5, 10, or 20 days. Combined therapy flavopiridol treatments were initiated either several days before or shortly after the start of single dose or daily fractionated radiotherapy. RESULTS: The major findings of this study are that all three tumors treated with flavopiridol alone responded by tumor growth delay. Two of the tumors (MCa-29 and Ly-TH) responded in a schedule-dependent manner with larger radiation enhancement factors when flavopiridol treatment was started a few hours after irradiation (radioenhancement factors [EF] Ly-TH = 2.04, EF MCa-29 = 1.50 for single dose irradiation). When combined with fractionated irradiation (2.6 Gy daily for 10 or 20 days), flavopiridol enhanced the response of the MCa-29 tumor by a factor of 1.25-1.46. A fractional radiation dose of 6 Gy in combination with flavopiridol produced a 62.5% cure rate compared with 25% tumor cure for radiation alone. A novel finding of this study was the demonstration of antimetastatic activity of flavopiridol in addition to its effect on the local primary tumor. Both the incidence and absolute number of lung metastasis were reduced when flavopiridol followed surgical removal of the large (10 mm) primary leg tumor. The normal jejunum treated with flavopiridol and radiation responded in a schedule independent manner and the degree of radioenhancement (EF, 1.05-1.06) was much less than for any of the tumors studied. CONCLUSIONS: Therapeutic gain was achieved when flavopiridol treatment was initiated either before or after the start of radiotherapy. Flavopiridol shows promising clinical potential administered alone or in combination with other cytotoxic agents, including both chemotherapy and radiotherapy.     

Docetaxel/radiation combinations: rationale and preclinical findings

Concurrent chemoradiotherapy, administration of chemotherapeutic agents during the course of radiation therapy, has increasingly been used for treatment of advanced locoregional cancer. Improvements in radiation therapy are achieved through independent cytotoxic action of drugs and their ability to sensitize tumor cells to radiation. Laboratory investigations showed that docetaxel is potent in both of these actions. The drug increased the radiosensitivity of in vitro cultured cells and the in vivo tumor radioresponse. In contrast to exerting a strong enhancement of tumor radioresponse, the ability of docetaxel to modify normal tissue radiation damage was much lower. Thus, docetaxel can significantly increase therapeutic gain when combined with radiation therapy. The initial rationale for using docetaxel and other taxanes as radiation enhancers was the ability of these agents to arrest cells in the radiosensitive G2/M phases of the cell cycle. Additional mechanisms were subsequently detected, including the ability of docetaxel to eliminate radioresistant S-phase cells, cause tumor reoxygenation, stimulate antitumor immune resistance mechanisms, and possibly inhibit tumor angiogenesis. Because combined chemoradiotherapy treatments are limited by normal tissue toxicity, additional treatment strategies are needed to improve the antitumor efficacy and to minimize normal tissue toxicity. In this regard, many research avenues are being explored, particularly the possibility of combining chemoradiotherapy with molecular targeting. This overview addresses the rationale for major findings on the interaction of docetaxel and radiation in preclinical models and discusses how these findings may impact practical use of chemoradiotherapy.     

Lack of correlation between mitotic arrest or apoptosis and antitumor effect of docetaxel

Purpose: To determine, as we did for paclitaxel, whether mitotic arrest and apoptosis induced in murine tumors in vivo by docetaxel correlate with the drug's antitumor effect and whether the antitumor efficacy of docetaxel depends on p53 mutational status of tumors. Methods: C3Hf/Kam mice were implanted with one of the following 15 syngeneic tumors: seven adenocarcinomas (MCa-4, MCa-29, MCa-35, MCa-K, OCa-I, ACa-SG, and HCa-I), two squamous cell carcinomas (SCC-IV and SCC-VII), five sarcomas (FSa, FSa-II, Sa-NH, NFSa, and Sa-4020) and one lymphoma (Ly-TH). When the tumors had grown to 8 mm in diameter, the mice were treated with 31.3 mg/kg docetaxel i.v. Tumor growth delay was the endpoint of docetaxel's antitumor effect. In separate groups of mice, mitotic arrest and apoptosis were determined micromorphometrically 1 to 72 h after docetaxel treatment. Tumors were assayed for their p53 status by sequence analysis of RNA prepared from freshly excised tumors. Results: Docetaxel caused statistically significant growth delay in six of seven adenocarcinomas, three of five sarcomas, and the lymphoma, but not in either of the squamous cell carcinomas. The drug induced mitotic arrest in all tumor types, but to various degrees ranging from 6.4 +/− 0.4% to 25.1 +/− 0.1%. In contrast, docetaxel induced appreciable apoptosis in only 5 of 15 tumors, with 10.3 +/− 1.6% being the highest apoptotic value. Neither mitotic arrest nor apoptosis were significantly correlated with tumor growth delay. However, tumors that responded to docetaxel by significant tumor growth delay histologically displayed massive cell destruction by cell lysis, and four of these tumors also showed marked infiltration with mononuclear lymphoid cells. Of the 15 tumors only 3 had mutant p53. Conclusions: Docetaxel exhibited a strong antitumor effect in two-thirds of murine tumors, and on a milligram per kilogram basis was more effective than paclitaxel against the same tumors. The drug was a potent inducer of mitotic arrest but a weak inducer of apoptosis, neither of which correlated with its antitumor effect. Tumor cell lysis appeared to be a major mode of tumor cell destruction and can be regarded as the main mechanism underlying antitumor efficacy of docetaxel. In contrast, paclitaxel's antitumor efficacy is related to its ability to induce apoptosis. At the molecular level, there was no dependency of antitumor efficacy of docetaxel on p53 mutational status of tumors. Received: 3 March 1998 / Accepted: 14 May 1998     

NOTCH3 promotes docetaxel resistance of prostate cancer cells through regulating TUBB3 and MAPK signaling pathway

Docetaxel is the preferred chemotherapeutic agent in patients with castrate-resistant prostate cancer (CRPC). However, patients eventually develop docetaxel resistance and in the absence of effective treatment options. Consequently, it is essential to investigate the mechanisms generating docetaxel resistance and develop novel alternative therapeutic targets. RNA sequencing was undertaken on docetaxel-sensitive and docetaxel-resistant prostate cancer (PCa) cells. Subsequently, chemoresistance, cancer stemness, and lipid metabolism were investigated. To obtain insight into the precise activities and action mechanisms of NOTCH3 in docetaxel-resistant PCa, immunoprecipitation, mass spectrometry, ChIP, luciferase reporter assay, cell metabolism, and animal experiments were performed. Through RNA sequencing analysis, we found that NOTCH3 expression was markedly higher in docetaxel-resistant cells relative to parental cells, and that this trend was continued in docetaxel-resistant PCa tissues. Experiments in vitro and in vivo revealed that NOTCH3 enhanced stemness, lipid metabolism, and docetaxel resistance in PCa. Mechanistically, NOTCH3 is bound to TUBB3 and activates the MAPK signaling pathway. Moreover, NOTCH3 was directly regulated by MEF2A in docetaxel-resistant cells. Notably, targeting NOTCH3 and the MEF2A/TUBB3 signaling axis was related to docetaxel chemoresistance in PCa. Overall, these results demonstrated that NOTCH3 fostered stemness, lipid metabolism, and docetaxel resistance in PCa via the TUBB3 and MAPK signaling pathways. Therefore, NOTCH3 may be employed as a prognostic biomarker in PCa patients. NOTCH3 could be a therapeutic target for PCa patients, particularly those who have developed docetaxel resistance.     

Maximizing therapeutic gain with gemcitabine and fractionated radiation

Purpose/Objective: The nucleoside analogue gemcitabine inhibits cellular repair and repopulation, induces apoptosis, causes tumor growth delay, and enhances radiation-induced growth delay. After single doses of drug and radiation, maximum enhancement of tumor response was obtained when gemcitabine preceded radiation by at least 24 h. Conversely, the cellular radioresponse of the normal gastrointestinal epithelium was slightly protected when gemcitabine and radiation were separated by 24 h. This differential response created a time frame within which therapeutic gain could be maximized. In our present investigation, we sought to define the most therapeutically beneficial scheme of gemcitabine administration when combined with fractionated radiotherapy.

Methods and Materials: C3Hf/Kam mice were given identical drug and radiation schedules of administration, and both normal tissue (jejunal mucosa) and tumor (Sa-NH) responses were measured. Irradiation was given once per day for 5 days in normal tissue and tumor growth delay studies and twice per day for the tumor cure endpoint. A total dose of 25 mg/kg gemcitabine was given i.p. in 1 of 3 schedules: a single dose of 25 mg/kg 24 h before the start of fractionated irradiation, 12.5 mg/kg 24 h before the first and third radiation doses, or 24 h before each of 5 radiation doses. Groups of mice bearing 7- or 8-mm diameter tumors were treated with gemcitabine alone or in combination with fractionated irradiation under ambient or hypoxic conditions. The survival response of the jejunal mucosa was quantified by the microcolony assay and histologically by quantifying apoptosis, mitosis, S-phase fraction, and crypt cellularity.

Results: For tumor growth delay, dose-modifying factors (DMFs) were similar (1.34–1.46) for all 3 schedules of drug administration. In contrast, the response of the jejunum was strongly dependent on the schedule of gemcitabine administration. A single dose of gemcitabine before the start of fractionated radiotherapy resulted in slight radioprotection (DMF 0.96). Two doses and 5 daily doses of gemcitabine enhanced radiation response by factors of 1.09 and 1.23, respectively. Major factors affecting the response of the jejunal mucosa were apoptotic death of S-phase cells exposed to gemcitabine and cell cycle synchrony of surviving cells. Tumor reoxygenation was found to be a major mechanism for tumor radioenhancement, in addition to those reported earlier.

Conclusion: All 3 schedules of drug administration produced therapeutic gain; however, when gemcitabine was given more than once in a 5-fraction radiation treatment schedule, normal tissue toxicity increased. The highest therapeutic gain (1.4) was achieved by giving a single dose of gemcitabine (25 mg/kg) 24 h before the start of fractionated radiotherapy.     

前列腺癌PC-3多西紫杉醇耐药细胞株的蛋白组学分析

  目的  比较前列腺癌PC-3细胞株对多西紫杉醇(docetaxel)耐药前后的蛋白质差异性表达, 了解前列腺癌PC-3细胞株耐药性产生机制。  方法  利用逐渐加量的方式培养前列腺癌PC-3多西紫杉醇耐药细胞株, 利用双向荧光差异凝胶电泳(DIGE)定量筛选PC-3细胞敏感株与耐药株的差异蛋白, 并用基质辅助激光解吸电离飞行时间质谱技术(MALDI-TOF/TOF-MS)对差异位点蛋白进行成分鉴定。  结果  利用DIGE结合MALDI-TOF/TOF-MS质谱技术分析, PC-3细胞耐药株较敏感株成功分离出49种差异表达蛋白质, 29种表达上调, 20种表达下调。其中ATP synthase、Galectin-1等参与肿瘤血管的生成, Calreticulin、CathepsinD、Coflin-1蛋白参与肿瘤的转移; 78 kDa glucose-regulated protein(GRP78)、Microtubule-associated protein-6等参与肿瘤的耐药性调节。  结论  人前列腺癌PC-3细胞株多西紫杉醇耐药前后存在蛋白质的差异性表达, 为进一步发现前列腺癌转移及耐药性的分子机制以及晚期激素非依赖性前列腺癌的靶向药物治疗提供实验依据。      

Combination of radiation and celebrex (celecoxib) reduce mammary and lung tumor growth

The selective cyclooxygenase (COX)-2 inhibitor, celecoxib, alone and in combination with radiation was investigated in vitro and in vivo. Murine mammary tumor line (MCa-35) and human lung carcinoma line (A549) have high and low basal levels of COX-2 protein, respectively. Treatment of both tumor cells with celecoxib alone resulted in a dose- and time-dependent reduction of cell number (clonogenic cell death) and tumor cell growth rate in vitro; however, inhibition of tumor cell growth by celecoxib was not correlated with the reduction of COX-2 protein in tumor cells. Although both tumor cell types had similar DNA damage after celecoxib treatment, significant induction of tumor cell apoptosis was only observed in MCa-35. Celecoxib-mediated radiation sensitization also occurred in MCa-35 cells determined by clonogenic assay, in part due to a G2/M arrest at 8 to 24 hours after treatment. The tumor growth inhibitory effects of celecoxib were also studied in vivo. It was found that celecoxib inhibited both tumor growth after intragastric administration of celecoxib (5 daily doses of 50 mg/kg). Combined with a single 30-Gy dose of radiation, celecoxib resulted in additive effects on A549 tumors. Celecoxib-treated A549 tumors had marginal reduction of total and perfused blood vessels compared with untreated controls. Reduction of tumor angiogenic cytokine and growth factor mRNA was associated with decreased perfused vessels. Finally, reduction of vascular endothelial growth factor protein after celecoxib was also observed in both tumor lines by Western blot. Our results indicate that the selective inhibition of COX-2 combined with radiation has potential application in radiotherapy, and celecoxib-mediated antitumor effects may act through different mechanisms including direct inhibition of tumor cell proliferation, alteration of tumor cell cycle, and antiangiogenesis.     

Sensitizers and radiation dose fractionation: results and interpretations

Misonidazole is generally regarded as having been a clinical failure as a radiation sensitizer. It is hoped that the newer sensitizers SR-2508 and Ro 03-8799 will give better results because single dose studies with animal tumors have indicated that these two drugs give higher enhancement ratios than misonidazole at clinically tolerated doses. Other factors may also have influenced the clinical efficacy of misonidazole, however, particularly reoxygenation during the course of the fractionated treatments. In this paper reoxygenation in animal tumors and experimental studies in which fractionated radiation doses have been combined with sensitizers are reviewed. It is concluded that, even for dose fractions of 2 Gy, reoxygenation may not completely eliminate the influence of hypoxic cells on tumor response, when large total doses are given. Problems associated with tumor heterogeneity are also discussed to highlight the desirability of selecting the most suitable patients for clinical studies. Poorly reoxygenating tumors, rapidly growing tumors and tumors in patients in whom oxygen delivery to tissue is compromised are those whose control is most likely to be improved by combining radiation sensitizers with conventional treatment. However effective sensitizers should also allow fractionation schedules to be modified, to achieve a therapeutic gain, by taking advantage of differences in repair or repopulation between the tumor and critical normal tissue, without having to consider possible detrimental effects on reoxygenation.     

miRNA-34a is associated with docetaxel resistance in human breast cancer cells

Docetaxel is a chemotherapy drug to treat breast cancer, however as with many chemotherapeutic drugs resistance to docetaxel occurs in 50% of patients, and the underlying molecular mechanisms of drug resistance are not fully understood. Gene regulation through microRNAs (miRNA) has been shown to play an important role in cancer drug resistance. By directly targeting mRNA, miRNAs are able to inhibit genes that are necessary for signalling pathways or drug induced apoptosis rendering cells drug resistant. This study investigated the role of differential miRNA expression in two in vitro breast cancer cell line models (MCF-7, MDA-MB-231) of acquired docetaxel resistance. MiRNA microarray analysis identified 299 and 226 miRNAs altered in MCF-7 and MDA-MB-231 docetaxel-resistant cells, respectively. Docetaxel resistance was associated with increased expression of miR-34a and miR-141 and decreased expression of miR-7, miR-16, miR-30a, miR-125a-5p, miR-126. Computational target prediction revealed eight candidate genes targeted by these miRNAs. Quantitative PCR and western analysis confirmed decreased expression of two genes, BCL-2 and CCND1, in docetaxel-resistant cells, which are both targeted by miR-34a. Modulation of miR-34a expression was correlated with BCL-2 and cyclin D1 protein expression changes and a direct interaction of miR-34a with BCL-2 was shown by luciferase assay. Inhibition of miR-34a enhanced response to docetaxel in MCF-7 docetaxel-resistant cells, whereas overexpression of miR-34a conferred resistance in MCF-7 docetaxel-sensitive cells. This study is the first to show differences in miRNA expression, in particular, increased expression of miR-34a in an acquired model of docetaxel resistance in breast cancer. This serves as a mechanism of acquired docetaxel resistance in these cells, possibly through direct interactions with BCL-2 and CCND1, therefore presenting a potential therapeutic target for the treatment of docetaxel-resistant breast cancer.     

Inverse relationship between epidermal growth factor receptor expression and radiocurability of murine carcinomas.

The study investigated whether a relationship exists between the extent of epidermal growth factor receptor (EGFR) expression and in vivo radiocurability of murine tumors. EGFR expression was determined in nine carcinomas (four mammary carcinomas, designated MCa-4, MCa-29, MCa-35, and MCa-K; two squamous cell carcinomas, designated SCC-IV and SCC-VII; an ovarian adenocarcinoma, OCa-I; a hepatocarcinoma, HCa-I; and an adenosquamous carcinoma, ACa-SG) syngeneic to C3Hf/Kam mice using Western blot analysis. These tumors greatly differed in their radioresponse, assessed by TCD50 assay, and in their susceptibility to radiation-induced apoptosis. Likewise, the expression of EGFR greatly varied, by as much as 21-fold, and the magnitude of the EGFR expression positively correlated with increased tumor radioresistance. The levels of EGFR inversely correlated with radiation-induced apoptosis, suggesting that the lack of sensitivity to apoptosis induction was a major mechanism responsible for radioresistance of tumors with high EGFR. This correlation was highly significant only for wild-type p53 carcinomas. Radiation activated EGFR autophosphorylation and increased the activity of protein tyrosine kinase, but only in tumors with high EGFR expression. Thus, EGFR expression was a major determinant of tumor radioresponse in vivo. The pretreatment assessment of EGFR expression could predict radiotherapy outcome and may assist in selecting an effective treatment modality.     

Pathophysiological effects of vascular endothelial growth factor receptor-2-blocking antibody plus fractionated radiotherapy on murine mammary tumors

Although clinical trials of antiangiogenic strategies have been disappointing when administered as single agents, such approaches can play an important role in cancer treatment when combined with conventional therapies. Previous studies have shown that DC101, an antiangiogenic monoclonal antibody against vascular endothelial growth factor receptor-2, can produce significant growth inhibition in spontaneous and transplanted tumors but can also induce substantial hypoxia. Because DC101 appears to potentiate radiotherapy in some tumors, the present studies were undertaken to characterize pathophysiological changes following combined therapy and to determine whether radioresponse is enhanced despite the induction of hypoxia. MCa-4 and MCa-35 mammary carcinomas were treated with: (a) DC101; (b) 5 x 6 Gy radiation fractions; or (c) the combination. Image analysis of frozen tumor sections was used to quantitate: (a) hypoxia; (b) spacing of total and perfused blood vessels; and (c) endothelial and tumor cell apoptosis. For MCa-4, combination treatment schedules produced significant and prolonged delays in tumor growth, whereas single-modality treatments had minor effects. For MCa-35, radiation or the combination led to equivalent growth inhibition. In all tumors, hypoxia increased markedly after either radiation or DC101 alone. Although combination therapy produced no immediate pathophysiological changes, hypoxia ultimately increased after cessation of therapy. Preferential increases in endothelial apoptosis following combination treatment suggest that in addition to blocking tumor angiogenesis, DC101 enhances radiotherapy by specifically sensitizing endothelial cells, leading to degeneration of newly formed blood vessels.     

C225 antiepidermal growth factor receptor antibody enhances the efficacy of docetaxel chemoradiotherapy

PURPOSE: C225 anti-EGFR (epidermal growth factor receptor) antibody has been shown to enhance tumor response to radiation and a number of chemotherapeutic agents. Because of increased use of concurrent chemoradiotherapy in cancer treatment, it is important to determine whether C225 enhances also the antitumor efficacy of radiation when combined with chemotherapy. This study assessed the effect of C225 on tumor response when combined with docetaxel plus single or fractionated radiation. METHODS AND MATERIALS: MDA468 human adenocarcinoma and A431 human epidermoid carcinoma cells growing as xenografts in the right hind leg of nude mice were used. Mice bearing 8-mm tumors were treated with C225 antibody at a dose of 1 mg given i.p. once, twice, or three times 3 days apart, 10 or 30 mg/kg docetaxel given i.v., and/or local tumor irradiation of 8 or 10 Gy single dose or fractionated irradiation consisting of 2 Gy daily for 5 days. When all three agents were combined, C225 was given 6 h before or 18 h after docetaxel, and radiation was given 24 h after docetaxel. The treatment end point was tumor growth delay. RESULTS: C225 enhanced the antitumor efficacy of docetaxel, local tumor irradiation, and docetaxel combined with radiation. The response of both MDA468 and A431 carcinomas was enhanced. The enhancement factors ranged from 1.19 to 8.52, the degree of the enhancement depending on experimental conditions such as administration of multiple vs. single dose C225 or single or fractionated irradiation. C225 given twice or 3 times was more effective than when administered as a single dose. The effect of C225 was more pronounced when combined with single than fractionated irradiation with or without docetaxel. The triple-agent therapy was more effective than a single agent or double combination therapies, expressed by both increased tumor growth delay and the rate of tumor cure. CONCLUSIONS: Our results show that C225 anti-EGFR antibody is a potent enhancer of tumor response to docetaxel or radiation as single agents, and to docetaxel when combined with radiation. Thus, these findings provide strong preclinical evidence in support of combination of anti-EGFR blockade with chemoradiotherapy.     

分割放射治疗中剂量、时间因素的生物学基础

经过100年来临床实践证实,分割放射治疗(ＦｒａｃｔｉｏｎａｔｅｄＲａｄｉｏｔｈｅｒａｐｙ)是行之有效的基本放射治疗原则。影响正常组织和肿瘤组织辐射生物效应的因素很多,但主要决定于细胞损伤后的修复,增殖,细胞周期的重新分布及肿瘤内乏氧细胞的氧化等因素的相互作用。根     

Radiation enhancement by 9-aminocamptothecin: the effect of fractionation and timing of administration.

PURPOSE: The camptothecins (CPTs) are potent radiation sensitizers in vivo but the optimal schedule of administration is unknown. In this article, the effects of irradiation combined with 9-aminocamptothecin (9AC) on a mouse mammary cancer and the gastrointestinal tract were compared for single and fractionated treatment. We also examined the circadian dependency for cytotoxicity, radiation sensitization, and acute toxicity after single doses of 9AC given at six different times over 24 h. MATERIALS AND METHODS: 9AC was administered intramuscularly to C3Hf/Kam mice with and without an 8 mm mouse mammary carcinoma (MCa-4). Acute toxicity was assessed by examination of body weight loss, peripheral blood counts, clinical assessment of diarrhea, and survival. Radiation sensitization was assessed using the tumor regrowth delay model. RESULTS: Regrowth delay of MCa-4 tumor after a single treatment of 15 Gy is comparable to 28 Gy given in 14 fractions (absolute regrowth delays of 7.1 days and 6.6 days, respectively). With 9AC alone, comparable tumor regrowth was obtained with a total dose of 4 mg/kg given intramuscularly repeated twice weekly (1 mg/kg doses X 4), or as a single injection of 4 mg/kg (2.9 days and 3.8 days, respectively). 9-AC and irradiation together in single doses of 15 Gy and 4 mg/kg resulted in little radiation sensitization compared to the repeated 9AC schedule combined with fractionated irradiation [Dose Modifying Factors (DMF) of 1.12 vs. 2.8, respectively]. Acute normal tissue toxicity after single or fractionated 9AC treatment was assessed at six times over a 24-h period (6 A.M., 10 A.M., 2 P.M., 6 P.M., 10 P.M., and 2 A.M.) and was highest at 2 A.M. after either single or multiple doses. A single dose of 9AC administered with single fraction irradiation could be escalated by 33% when given at the best-tolerated time. CONCLUSION: The frequency and timing of CPT administration with irradiation are important factors to be considered in the design of clinical protocols. CPTs are S-phase inhibitors that are better tolerated by the mouse when given during the rest phase when intestinal mucosal proliferation is relatively low. A modest increase in CPT dosage was possible by choosing the best tolerated time to administer the radiation sensitizer. This concept could potentially be evaluated in clinical trials with this class of agents.     

Schedule-dependent therapeutic gain from the combination of fractionated irradiation and cis-diamminedichloroplatinum (II) in C3H/Km mouse model systems

The interaction of cis-diamminedichloroplatinum(II) (c-DDP) with daily fractionated radiotherapy was studied in the SCCVII tumor, the duodenum, and the lungs of C3H/Km mice. The experimental end points were the time required for treated tumors to reach 3 times their treatment size, the survival of stem cells in the duodenal crypts, and the breathing rate measured early (19-23 weeks) and late (41-46 weeks) after treatment. In the 8 treatment schedules that were evaluated, radiation was delivered in 5 daily doses of 2-7 Gy, for total doses of 10-35 Gy; and c-DDP was administered either daily (2.4 or 1.6 mg/kg/day) or as a single bolus (8 or 12 mg/kg). Schedule 2, in which 2.4 mg/kg c-DDP was administered immediately before X-ray on 5 consecutive days produced the highest degree of enhancement of radiation effect (expressed as dose-effect factor); and the next greatest enhancement was produced by 12 mg/kg c-DDP administered 24 h before the start of fractionated daily radiotherapy. Those schedules also caused some enhancement in the normal tissues, but the dose-effect factors for those tissues were lower than for the tumor, which was reflected in the finding of maximal therapeutic gain factors for those same schedules. There was little or no enhancement nor were the therapeutic gain factors significantly greater than 1.00 when the 2 modalities were administered more than 24 h apart. Thus, for both normal tissue toxicity and antitumor effect there is striking schedule dependence with respect to both sequence and timing of these 2 modalities. This is of major relevance in clinical treatment planning.     

食管癌放射治疗非常规分次方案的剂量—效应分析

目的：对近年国内报道的食管癌非常规分次方案剂量－效应分析，探索改善放射治疗疗效较合理的方法，方法：收集1989年以来食管癌非常规分次（ICF）照射和以常规剂量分次（CF）作为对照的前瞻性随机分组结果，比较肿瘤局部控制率或（及）生存率。依LQ模式计算各个方案对肿瘤组织的放射生物学效应剂量（BEDT）值，与各自的CF对照组进行剂量－效应比较。结果：超分割（HF）3个组中2个组疗效显著提高。其BEDT值降低17．2Gy；疗效无差异1个组BEDT值降低6．8Gy。加速超分割（AHF）2个组中1个组BEDT值降低17．2Gy，疗效无差异；1个组疗效显著提高不能用BEDT值降低11．3Gy来解释，后程加速超分割（LAHF）的7个组中，疗效显著提高的有6个组，其BEDT值比较不能用于预测LAHF对CF方案的疗效差别。后程加速分割（LAF）1个组BEDT值仅高出2．8Gy，但1、3年生存率提高非常显著。前程加速分割（EAF）1个组的已知疗效完全缓解率提高的相关因素是剂量高6．8Gy。结论（1）用ICF方案有可能在肿瘤局部控制率、生存率方面显著高于CF60－70Gy，6－7周方案者。（2）AHF、LAHF和LAF的疗效显著提高不能用该方案的BEDT值来解释和预测，疗效的显著改善不依赖于剂量的增加。（3）照射后使肿瘤细胞集群对放射杀灭再敏感化。（4）LAF能提高治疗获得（TG），是一些ICF方案治疗效应提高的放射生物学基础。     

Tumor and normal tissue tolerance for fractionated low-dose-rate radiotherapy

Radiobiological evidence suggests that an improved therapeutic ratio might be achieved through the use of smaller than conventional dose fractions. The ultimate in small dose fractions for external beam radiotherapy would be fractionated low-dose-rate (LDR) irradiation, and clinical trials of fractionated external beam LDR therapy are already in progress. Using the BA1112 rat sarcoma, we have determined the 50% tumor control dose for LDR and for conventional-dose-rate (CDR) fractionated radiotherapy. These tumor control doses were compared to normal tissue tolerance doses for hemi-body irradiation in similar CDR and LDR schedules. Animals were treated 3 times per week without anesthesia using 10-19 fractions. LDR radiotherapy was done with 60Co at dose rates of 0.028-0.033 Gy/min; CDR radiotherapy was done with 250 kVp X rays at dose rates of 0.54-2.1 Gy/min. The tumor control dose modification factor (DMF) for LDR compared to CDR irradiation was 1.3 (1.0-1.5). For LDR and CDR hemi-body irradiation, the dose modification factor for 7 day lethality (gastrointestinal damage) was 1.7 (1.5-1.9), for 100 day morbidity was 1.8 (1.6-2.2), and for radiation nephritis at 90 days was 1.9 (1.7-2.3). The therapeutic gain factor for fractionated low-dose-rate irradiation compared to conventional-dose-rate fractionated radiotherapy was therefore 1.8/1.3 = 1.4 (1.2-1.8). The study shows that there is an experimental as well as a theoretical basis for anticipating a therapeutic benefit from the use of external beam fractionated LDR radiotherapy, and implies that the recognized therapeutic efficacy of brachytherapy is not due solely to the high localized dose.     

Poly(L-glutamic acid)-paclitaxel conjugate is a potent enhancer of tumor radiocurability

PURPOSE: Conjugating drugs with polymeric carriers is one way to improve selective delivery to tumors. Poly (L-glutamic acid)-paclitaxel (PG-TXL) is one such conjugate. Compared with paclitaxel, its uptake, tumor retention, and antitumor efficacy are increased. Initial studies showed that PG-TXL given 24 h before or after radiotherapy enhanced tumor growth delay significantly more than paclitaxel. To determine if PG-TXL-induced enhancement is obtained in a more clinically relevant setting, we investigated PG-TXL effects on tumor cure. METHODS AND MATERIALS: Mice bearing 7-mm-diameter ovarian carcinomas were treated with PG-TXL at an equivalent paclitaxel dose of 80 mg/kg, single dose or 5 daily fractions of radiation or both PG-TXL and radiation. Treatment endpoint was TCD(50) (radiation dose yielding tumor control in 50% of mice). Acute radioresponse of jejunum, skin, and hair was determined for all treatments. RESULTS: PG-TXL dramatically improved tumor radioresponse, reducing TCD(50) of single-dose irradiation from 53.9 (52.2-55.5) Gy to 7.5 (4.5-10.7) Gy, an enhancement factor (EF) of 7.2. The drug improved the efficacy of fractionated irradiation even more, reducing the TCD(50) of 66.6 (62.8-90.4) Gy total fractionated dose to only 7.9 (4.3-11.5) Gy, for an EF of 8.4. PG-TXL did not affect normal tissue radioresponse resulting from either single or fractionated irradiation. CONCLUSION: PG-TXL dramatically potentiated tumor radiocurability after single-dose or fractionated irradiation without affecting acute normal tissue injury. To our knowledge, PG-TXL increased the therapeutic ratio of radiotherapy more than that previously reported for other taxanes, thus, PG-TXL has a high potential to improve clinical radiotherapy.     

Association of increased radiocurability of murine carcinomas with low constitutive expression of p21(WAF1/CIP1) protein

PURPOSE: The study investigated whether basal, constitutive levels of p21(WAF1/CIP1) protein in murine carcinomas are related to in vivo tumor radioresponse. The study is based on recent observations demonstrating that in vitro cancer cell lines are resistant to cytotoxic drugs when they express high basal levels of p21(WAF1/CIP1) protein, and that the loss of the p21 gene in the HCT116 human colorectal cancer cell line results in increased radioresponse of xenografts derived from that cell line. METHODS AND MATERIALS: Protein levels of p21(WAF1/CIP1), p53, bax, and bcl-2 were determined in 8 carcinomas (3 mammary carcinomas designated MCa-4, MCa-29, and MCa-35, 2 squamous cell carcinomas designated SCC-IV and SCC-VII, ovarian adenocarcinoma OCa-I, hepatocarcinoma HCa-I, and adenosquamous carcinoma ACa-SG) syngeneic to C3Hf/Kam mice using Western blot analysis. The tumors, growing in the right hind legs of mice, were 8 mm in diameter at the time of analysis. These tumors greatly differ in their radioresponse, assessed by TCD50 assay, and in their susceptibility to radiation-induced apoptosis. RESULTS: Protein levels of these oncogenes varied among tumors, with p21(WAF1/CIP1) showing the greatest variation: its mean densitometric value ranged from 1 to 19. Bcl-2 levels also showed broad variation in densitometric values, from 1 to 10. In comparison, bax and p53 (7 of 8 tumors contained wild-type p53) varied much less among different tumor types; their variation was within a 5-fold range, and the level of p53 was similar in 6 of 8 tumors. Tumor radioresponse correlated significantly (R = 0.77, p = 0.02) only with the magnitude of p21(WAF1/CIP1)expression: tumors with high levels of p21(WAF1/CIP1)were less radiocurable than those with lower levels. Tumor radiocurability showed a significant positive correlation (p = 0.02) with the extent of radiation-induced apoptosis, indicating that tumors that responded to radiation with higher percentages of apoptosis were more curable by radiation. Despite a strong trend to correlation, (p = 0.15), p21(WAF1/CIP1) expression did not correlate significantly with radiation-induced apoptosis, which suggested that p21(WAF1/CIP1) influenced tumor radioresponse by mechanisms beyond that of apoptosis induction. CONCLUSION: Our findings showed that murine tumors exhibit wide variation in constitutive levels of p21(WAF1/CIP1) which had a significant relationship with tumor radioresponse: tumors with high levels of p21(WAF1/CIP1) were less radiocurable than those with lower levels. These findings support the concept that p21(WAF1/CIP1) is a major determinant of tumor radioresponse in vivo, and may have important clinical implications. The pretreatment assessment of p21(WAF1/CIP1) protein could serve as a useful predictor of radiotherapy outcome and may assist in selecting an effective treatment modality.