Responsiveness of Human Gastric Tumors Implanted in Nude Mice to Clinically Equivalent Doses of Various Antitumor Agents

To reproduce clinical effects of various antitumor agents in the human tumor/nude mouse model, we investigated the responsiveness of 11 lines of human gastric tumor xenografts to doses of the agents pharmacokinetically equivalent to the respective clinical doses, which we designated the "rational dose" (RD). We found that the response rates to mitomycin C, 3-[(4-amino-2-methyl-5-pyrimidinyl]methyl-1-[2-chloroethyl]-1-nitrosourea (ACNU), adriamycin, 5-fluorouracil were 18%, and that to vinblastine was 30%; on the other hand, those to vincristine, methotrexate, and cyclophosphamide were poor. In contrast, in our previous study using the maximum tolerated doses, response rates to mitomycin C, ACNU, and vinblastine were as high as 64–82%, and those to adriamycin and 5-fluorouracil were 18%. When these results were compared with the clinical response rates of gastric tumors, as a whole, the results with RD's exhibited much better coincidence with the clinical data in terms of relative therapeutic potency, indicating the validity of the use of clinically equivalent doses instead of maximum tolerated doses in the human tumor model.     

Responsiveness of subcutaneous human glioma xenografts to various antitumor agents

Responsiveness of seven human glioma xenografts to seven antitumor agents was investigated by an sc-iv system and the efficacies of these agents against human glioma were evaluated in terms of response rate. When their maximum tolerated doses were used, experimental response rates of nimustine (ACNU), vincristine (VCR), adriamycin (ADR) and vinblastine (VLB) were as high as 86-100%, while that of mitomycin (MMC) was 57%, and those of 5-fluorouracil (5-FU) and methotrexate (MTX) were 0%. On the other hand, when the doses pharmacokinetically equivalent to their clinical doses were employed, the response rate of ADR was the highest, followed by VCR and ACNU in this order. These results suggest that gliomas are significantly responsive to various antitumor agents in this sc-iv system.     

Evaluation of response rates to various antitumor agents of human gastric tumors implanted in nude mouse

To ascertain the clinical predictability and, in the long run, the usefulness of the human tumor/nude mouse model as a screening tool for antitumor agents, it seems particularly important to use as many tumor lines as possible and to evaluate the therapeutic effectiveness of antitumor agents in terms of the overall response rate of a range of tumors. In this study, using 11 strains of established human gastric tumor xenografts with various histological characteristics and proliferation behavior, the experimental response rates to 8 typical antitumor drugs (mitomycin C, cyclophosphamide, ACNU, cisplatin, adriamycin, vincristine, vinblastine and 5-fluorouracil) were determined and compared with the clinical values. The experimental response rates to adriamycin, vincristine and 5-fluorouracil were in good accordance with the clinical results. However, with the other drugs, significantly higher response rates were observed with the nude mouse model as compared to clinical therapy, indicating that this model tends to overestimate the responsiveness of human tumor to a number of antitumor agents. These results strongly suggest the importance of using appropriate dose levels in the nude mouse to reproduce clinically equivalent effects in this model.     

Responsiveness of human lung cancer/nude mouse to antitumor agents in a model using clinically equivalent doses

Summary The responses of 14 lines of human lung cancer xenografts in BALB/c-nu/nu mice to eight known antitumor agents were investigated. These xenografts consisted of four small-cell carcinomas (SCLC) and ten non-small-cell carcinomas (four large cell, three squamous cell, and three adenocarcinomas; NSCLC). The doses used in the experiments were the maximum tolerated dose (MTD) in nude mice and the rational dose (RD), the latter considered to be pharmacokinetically equivalent to the clinical dose. When given at MTDs, all drugs except 5-fluorouracil (5-FU) and methotrexate (MTX) were extremely effective against NSCLC as well as SCLC. The response rates of drug-sensitive SCLC to mitomycin C (MMC), ACNU, and vinblastine (VLB) were 100%, and those to Adriamycin (ADR) and vincristine (VCR) were 75%. In addition, the response rates of even drug-resistant NSCLC to MMC and VLB were 70% and 90%, respectively. In contrast, the response rates of NSCLC to RDs of the drugs were reduced to <40% and corresponded well to the respective clinical rates. In SCLC, a good correlation of experimental and clinical response rates was observed with four drugs [cyclophosphamide (CPM), ACNU, VLB, and 5-FU]. As a result, we emphasize that a more reasonable prediction of the clinical effectiveness of antitumor agents can be made by a protocol using clinically equivalent doses.Abbreviations SCLC small-cell lung cancer - NSCLC non-small-cell lung cancer - MTD maximum tolerated dose - RD rational dose - MMC mitomycin C - CPM cyclophosphamide - ACNU 1-(4-amino-2-methylpyrimidin-5-yl)-methyl-3-(2-chloroethyl)-3-nitrosourea hydrochloride - ADR Adriamycin - VCR vincristine - VLB vinblastine - 5-FU 5-fluorouracil - MTX methotrexate This study was supported in part by Grants-in-Aid for New Drug Development Research from the Ministry of Health and Welfare, Japan     

Pharmacokinetic approach to rational therapeutic doses for human tumor-bearing nude mice

To improve clinical predictability from therapeutic results of various antitumor agents in human tumor/nude mouse models it seems to be important to use a dose pharmacokinetically equivalent to the clinical dose. Thus, we attempted to find the dose of a given drug that can reproduce in the nude mouse a plasma level similar to that seen in human patients treated with an effective dose of the drug based on comparative pharmacokinetic studies between man and nude mouse. As a result, those of 3 alkylating agents, mitomycin C, 3-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-1-(2-chloroethyl)-1-nitrosourea (ACNU) and cyclophosphamide, and those of 2 antimitotic agents, vincristine and vinblastine, were estimated to be one-fourth or one-fifth of their maximum tolerated doses (MTD's). On the other hand, in the case of adriamycin, its MTD was approximately equivalent to its clinical dose pharmacokinetically. In contrast, clinically equivalent doses of 2 antimetabolites tested, 5-fluorouracil and methotrexate, were significantly greater than their MTD's; i.e., their plasma levels did not reach the effective clinical ones even when their MTD's were administered to the nude mice. These results suggest that the antitumor effects of most antitumor agents are over- or underestimated in this model when MTD's are used as a therapeutic dose, and indicate that the use of clinically equivalent doses determined pharmacokinetically is desirable.     

Pharmacokinetic Approach to Rational Therapeutic Doses for Human Tumor-bearing Nude Mice

To improve clinical predictability from therapeutic results of various antitnmor agents in human tumor/nude mouse models it seems to be important to use a dose pharmacokinetically equivalent to the clinical dose. Thus, we attempted to find the dose of a given drug that can reproduce in the nude mouse a plasma level similar to that seen in human patients treated with an effective dose of the drug based on comparative pharmacokinetic studies between man and nude mouse. As a result, those of 3 alkylating agents, mitomycin C, 3-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-l-(2-chloroethyl)-l-nitrosourea (ACNU) and cyclophosphamide, and those of 2 antimitotic agents, vincristine and vinblastine, were estimated to be one-fourth or one-fifth of their maximum tolerated doses (MTD's). On the other hand, in the case of adriamycin, its MTD was approxmately equivalent to its clinical dose pharmacokinetically. In contrast, clinically equivalent doses of 2 antimetabolites tested, 5-fluorouracil and methotrexate, were significantly greater than their MTD's; i.e., their plasma levels did not reach the effective clinical ones even when their MTD's were administered to the nude mice. These results suggest that the antitumor effects of mostv antitumor agents are over- or underestimated in this model when MTD's are used as a therapeutic dose, and indicate that the use of clinically equivalent doses determined pharmacokinetically isdesirable.     

Evaluation of antitumor activity in a human breast tumor/nude mouse model with a special emphasis on treatment dose

Eight lines of human breast tumors implanted in nude mice were treated with various antitumor agents at two different doses, maximum tolerated doses (MTD) and rational doses (RD) that were pharmacokinetically equivalent to the clinical doses; the response rates to both doses were compared. With MTD, the response rates to mitomycin C and vinblastine were 100%, and those to other agents including cyclophosphamide, nimustine (a water-soluble nitrosourea), vincristine, Adriamycin (doxorubicin; Adria Laboratories, Columbus, OH), 5-fluorouracil (5-FU), and methotrexate were 30%-50%, indicating high responsiveness to the former two agents. In contrast, when the RD were used, the response rates to the majority of these agents were 25%-40%, and those to vincristine and nimustine were 13% and 0%, respectively. These results agree with the reported clinical results compared with those with MTD, suggesting the importance of the use of clinically equivalent doses in the evaluation of antitumor efficacy in a human tumor/nude mouse system.     

In vitro measurement of chemosensitivity of human small cell lung and gastric cancer cell lines toward cell cycle phase-nonspecific agents under the clinically equivalent area under the curve.

BACKGROUND. Based on the previous finding that cell killing effects of cell cycle phase-nonspecific agents depend on the concentration-time product (C x T) or the area under the curve (AUC), the authors investigated in vitro cytotoxic effects of nimustine hydrochloride (ACNU) and mitomycin C (MMC) under an experimental condition in which the assay AUC was equivalent to their clinically achievable AUC. METHODS. The cytotoxic effects of these agents on human cancer cell lines, consisting of 9 small cell lung carcinomas (SCLC) and 10 gastric cancers, were measured by a tetrazolium-based colorimetric assay (MTT assay). RESULTS. These cell lines individually responded to ACNU and MMC in this assay condition. When the authors considered 60% or greater cell kill to be effective, the in vitro response rates of SCLC to ACNU and MMC were 22% (two of nine carcinomas) and 67% (six of nine carcinomas), respectively. The response rates of gastric cancer to ACNU and MMC were 10% (1 of 10 carcinomas) and 40% (4 of 10 carcinomas), respectively. Except for the response of SCLC to ACNU, these in vitro response rates corresponded well to the clinical rates (SCLC to ACNU and MMC, 47% [14 of 30 carcinomas] and 50% [17 of 34 carcinomas], respectively; gastric cancer to ACNU and MMC, 11% [4 of 37 carcinomas] and 30% [63 of 211 carcinomas], respectively). CONCLUSIONS. These results suggest that the introduction of the clinically equivalent AUC to the in vitro chemosensitivity test for cell cycle phase-nonspecific agents may improve its clinical predictability.     

Xenografts in pharmacologically immunosuppressed mice as a model to test the chemotherapeutic sensitivity of human tumors

A human tumor xenograft model using pharmacologically immunosuppressed mice was assessed for its suitability to test preclinically the sensitivity of colorectal carcinomas, bone sarcomas and melanomas against anticancer agents. Besides ionizing radiation, 14 cytotoxic drugs including 5-fluorouracil (5-FU), dimethylmyleran (DMM), cytosine arabinoside, cyclophosphamide, melphalan, BCNU, mitomycin C, adriamycin, bleomycin, etoposide, vinblastine, cisplatin, procarbazine and DTIC were assayed. Ionizing radiation, 5-FU and DMM were also applied at lethal doses followed by bone-marrow rescue heavy therapy. Four colon carcinomas responded poorly to most of the agents but one tumor displayed marked sensitivity to BCNU. Lethal doses of radiation, 5-FU and DMM could also show considerable activity. High sensitivity was shown by a Ewing sarcoma to DMM and cyclophosphamide and by an osteosarcoma to the latter drug. No strong effects were seen against melanomas. Lethal doses of DMM induced the best regression of one colon carcinoma. In general, the superiority of heavy therapy for solid human tumors compared to maximally tolerated doses was demonstrated. Individual carcinomas of the same type displayed different drug sensitivity.     

Potentiation of the cytotoxic effects of various anticancer drugs by interferon on human neoplastic cells (HeLa) in culture

Potentiation of the cytotoxic effects of various anticancer agents by interferon on human malignant cells was examined in culture. The human neoplastic cells used were HeLa cells derived from uterine cervical cancer. The interferon was produced in human diploid fibroblasts treated with Poly I:C. Anticancer drugs examined were as follows; antibiotics (aclacinomycin, actinomycin D, adriamycin, cycloheximide, mitomycin C, peplomycin, puromycin), antimetabolites (cytosine arabinoside, 5-fluorouracil, 6-mercaptopurine, methotrexate), alkylating agents (ACNU, melphalan), and others (cisplatin, hydroxyurea, vincristine). The cytotoxic effects were determined by colony formation. Our results demonstrated that interferon potentiated significantly the cytotoxic effects of peplomycin, aclacinomycin, cisplatin, 5-fluorouracil, and adriamycin on HeLa cells. The present results indicate that a combined administration of interferon and these drugs may be effective in the treatment of human cancers.     

40例晚期胃癌联合化疗疗效分析

本文对40例晚期胃癌应用3个化疗方案的疗效进行了评价。FMV、FMA和FM-UFT方案的有效率分别为50％、40％和50％,3个方案的疗效之间无差异,中数生存期为5个月。根治术后复发病人有效率(67％)较未手术者有效率(40％)明显为高(P<0.05)。副作用主要为恶心、呕吐、白细胞和血小板下降。但无因副作用而终止治疗者。     

Chemotherapy of advanced gastric carcinoma

The results of current chemotherapeutic treatment for advanced gastric carcinoma are reviewed. Recent results of phase-II trials suggest that besides 5-fluorouracil, the nitrosoureas, adriamycin and mitomycin C, cis-platinum is also an effective drug in advanced gastric carcinoma. The favorable results obtained with the FAM-regimen in the late seventies, which were believed to be a significant step towards an improved treatment of gastric carcinoma, could not be confirmed, and several tested FAM-modifications were not able to improve treatment results. However, some recent investigations of cis-platinum within combination chemotherapy, i.e. with 5-fluorouracil and adriamycin (FAP), showed response rates beyond 30% and possibly a prolongation of median survival. These favorable data, which suggest an encouraging progress within the treatment of advanced gastric carcinoma, have to be confirmed in further controlled clinical trials.     

Manganese superoxide dismutase expression correlates with chemosensitivity in human gastric cancer cell lines.

PURPOSE: The purpose is to investigate the potential correlation between antioxidant enzyme (AOE) levels and resistance to anticancer drugs in human gastric carcinoma cell lines. EXPERIMENTAL DESIGN: Protein contents of AOEs such as manganese superoxide dismutase (MnSOD), copper/zinc superoxide dismutase, catalase, glutathione S-transferase-pi, p-glycoprotein, and multidrug resistance-associated protein were observed by Western blot analysis, and MnSOD activity was measured in six Korean gastric cancer cell lines. The direct correlation between AOEs and the chemosensitivity to doxorubicin (DOX), mitomycin C, 5-fluorouracil, and vinblastine was analyzed by cytotoxicity test. MnSOD was overexpressed by transient transfection of human MnSOD cDNA. RESULTS: Expressions of AOEs in gastric cancer cell lines were variable. MnSOD expression was related with the resistance to DOX and mitomycin C but not with that to 5-fluorouracil and vinblastine. In comparison, expressions of other AOEs, p-glycoprotein and multidrug resistance-associated protein, were not correlated with tumor sensitivity to any of the drugs used. Cell lines with a high MnSOD protein content showed higher MnSOD activity than those with a low MnSOD protein content. In addition, MnSOD overexpression increased the resistance of gastric carcinoma cells to DOX. CONCLUSIONS: MnSOD is an important factor of drug response to reactive oxygen species-generating anticancer drugs in the gastric cancer cells. Thus, measurement of MnSOD levels in clinical samples may provide an indication of subsequent treatment response of gastric cancer patients.     

In vivo inhibitory effect of anticancer agents on human pancreatic cancer xenografts transplanted in nude mice

Pancreatic cancer is one of the neoplasms resistant to chemotherapy. In the present study human pancreatic cancer xenografts (3 adenocarcinomas and 1 cystoadenocarcinoma) were subcutaneously transplanted in nude mice and after the tumors grew to 100-300 mm3, the mice were intraperitoneally administered with mitomycin C (MMC), adriamycin (ADR), 5-fluorouracil (5-FU), carboquone (CQ), cisplatinum (CDDP), nimustine chloride (ACNU) or DWA2114R at 1/3 LD50 on days 0.4, and 8. The tumor sizes on day 12 were compared with those on day 0. MMC and CQ significantly inhibited the tumor growth of 3 lines, and ACNU, CDDP and ADR inhibited the growth of 1 line. Further, 5-FU, futrafur, carmofur, UFT and L-phenylalanine mustard (L-PAM) were orally administered to mice into which 1 adenocarcinoma line had been transplanted. While none of fluoropyrimidines inhibited tumor growth, L-PAM at 4 mg/kg significantly inhibited growth, although it was accompanied by severe body weight loss. In the present study several agents significantly inhibited tumor growth, but none of them could induce the regression of the tumor when used singly. These results suggest that CQ, ACNU, CDDP and L-PAM may be applied to the chemotherapy of pancreatic cancer. However, the effect of a single agent is restricted and the development of new combination treatments is urgently required.     

超选择动脉插管灌注化疗与栓塞治疗中晚期胃癌

[目的]探讨超选择动脉插管灌注化疗与栓塞治疗中晚期胃癌的临床疗效。[方法]对36例不能手术切除及6例术后复发的中晚期胃癌患者行超选择性动脉插管灌注化疗与栓塞治疗。治疗方案为FAM(5-氟尿嘧啶、阿霉素或表阿霉素、丝裂霉素)或FPM(5-氟尿嘧啶、顺铂或卡铂、丝裂霉素),栓塞剂为超液化碘油。[结果]每例进行2～3次插管,共108人次。完全缓解3例,部分缓解35例,无变化4例,无PD病例,显效率90.5%。1、2、3年生存率分别为61.9%(26/42)、19.0%(8/42)、9.5%(4/42)。[结论]超选择动脉插管灌注化疗与栓塞治疗中晚期胃癌是一种安全有效的治疗方法,不仅能增加疗效,而且能改善生存质量,提高生存率。     

A current overview of chemotherapy in advanced gastric cancer

Four drugs including 5-fluorouracil (5-FU), adriamycin (ADM), mitomycin C (MMC) and cisplatin (CDDP) can produce response rates ranging from 15% to 20% when used as single agents for advanced gastric cancer. Various combinations employing these agents have been tested and FAM (5-FU, ADM, MMC) has been the most extensively studied, obtaining response rates ranging from 21% to 45% by the original regimen. More recently FAP (5-FU, ADM, CDDP) has been studied and response rates reported were ranged from 29% to 50%, and therefore it was judged that the efficacy is comparable to FAM. However, overall survival gain has been limited when used these combinations. Consequently a serious question has been raised whether past combinations are superior over single agent 5-FU. Prospective randomized trials compared 5-FU alone vs various combination failed to show advantage of combinations over 5-FU alone.     

In vitro chemosensitivity of various human tumors evaluated by the succinate dehydrogenase inhibition (SDI) test (2)

In vitro chemosensitivity was evaluated by succinate dehydrogenase inhibition (SDI) test in 94 human tumors including 59 gastric cancers, 27 colo-rectal cancers and 8 malignant lymphomas. Tumor fragments were exposed to 12 kinds of antitumor drugs at ten times peak plasma concentration. Evaluable rates were 86/94 (91%) for all cases, 56/59 (95%) for gastric cancers, 22/27 (81%) for colo-rectal cancers and 8/8 (100%) for malignant lymphomas. The mean of SD activity was decreased to 48% of that of control cells with aclacinomycin, 49% with carboquone, 53% with actinomycin D, 54% with mitomycin C and 54% with daunomycin for gastric cancers, 59% with adriamycin for colo-rectal cancers and 33% with cyclophosphamide (40487 S), and 33% with actinomycin D, 37% with vinblastine and 39% with adriamycin for malignant lymphomas. When the SD activity was reduced to below 50% by antitumor drugs, the chemosensitivity was defined as positive. The antitumor drugs which had a higher chemosensitive-positive rate were aclacinomycin, carboquone and mitomycin C for gastric cancers, adriamycin for colo-rectal cancers and 40487 S, daunomycin and vinblastine for malignant lymphomas. Our results suggest that the origin of a tumor is a critical factor in its chemosensitivity.     

Past and present achievements, and future direction of the Gastrointestinal Oncology Study Group (GIOSG), a Division of Japan Clinical Oncology Group (JCOG)

Initially, Gastrointestinal Study Group in Japan Clinical Oncology Group (GIOSG/JCOG) focused on gastric cancer. In 1980s, fluoropyrimidine, cisplatin and mitomycin C were key drugs. A randomized Phase II trial (JCOG8501) comparing futrafur plus mitomycin C and uracil plus futrafur and mitomycin C showed a higher response rate of uracil plus futrafur and mitomycin C than futrafur plus mitomycin C. From the results of two Phase II trials of etoposide, adriamycin and cisplatin, and cisplatin plus 5-fluorouracil, uracil plus futrafur and mitomycin C and cisplatin plus 5-fluorouracil were adopted for the test arms of the Phase III trial (JCOG9205) comparing with continuous infusion of 5-fluorouracil as a control arm. Neither cisplatin plus 5-fluorouracil nor uracil plus futrafur and mitomycin C showed a survival benefit over continuous infusion of 5-fluorouracil. In late 1990s, new agents, irinotecan and S-1, were developed for gastric cancer in Japan. GIOSG conducted a Phase III trial (JCOG9912) investigating superiority of irinotecan plus cisplatin and non-inferiority of monotherapy with S-1 compared with continuous infusion of 5-fluorouracil, and S-1 succeeded in showing non-inferiority. Then, SPIRITS trial showed a survival benefit of S-1 plus cisplatin over S-1, resulting in the establishment of a standard care for advanced gastric cancer in Japan. GIOSG have merged with Gastric Cancer Study Group as the Stomach Cancer Study Group (SCSG) from 2011. Recent progress in the development of new drugs has been remarkable. From the point of the roles shared with many other study groups for clinical trials, including registration trials of new drugs conducted by pharmaceutical companies, SCSG should recognize its role and conduct clinical trials with high quality for establishing new standard treatment.     

Cell kinetics and chemosensitivity of human carcinomas serially transplanted into nude mice

Six human carcinoma xenografts serially transplanted into nude mice were used for the study of chemosensitivity and cell kinetics. Three gastric carcinomas (St-4, St-40 and H-111), two colon carcinomas (Co-3 and Co-4) and one breast carcinoma (MX-1) were inoculated into the subcutaneous tissue of BALB/cA nude mice. The maximum tolerable doses of mitomycin C (MMC), adriamycin (ADM), cyclophosphamide (CPA) and 5-fluorouracil (5-FU) were administered when the tumor weights reached 100-300 mg. The response rates of the tumor to these drugs were found to be 3/6 for MMC, 2/6 for 5-FU and 1/6 for ADM and CPA. Percent labeled mitosis curves obtained from 3H-thymidine pulse labeling were analyzed by the method of Quastler and Sherman. It was found that the antitumor effect of MMC was closely correlated with the growth fractions of the tumors (r = -0.98, P less than 0.001), and it appeared that the tumor cells were more sensitive to MMC in the resting stages during the proliferating phase than in the other cell cycle phases. Cell kinetics is considered to be an important factor in determining chemosensitivity, and the system of human tumor xenografts-nude mice seems to be a suitable experimental model for investigating the correlation between cell kinetics and chemosensitivity in vivo.     

In vitro pharmacological characterizations of the anti-angiogenic and anti-tumor cell migration properties mediated by microtubule-affecting drugs,with special emphasis on the organization of the actin cytoskeleton

The aim of the present work is to investigate whether microtubule-affecting drugs including vincristine, vinblastine, vindesine and vinorelbine are able to produce an anti-angiogenic effect at non-cytotoxic doses in the same way of taxol. The cytotoxic effects were determined by means of the colorimetric MTT assay, and the anti-angiogenic effects on HUVEC cells growing on Matrigel and forming capillary networks. Sixteen additional drugs (camptothecin, SN38, topothecan, adriamycin, daunomycin, etoposide, bleomycin, melphalan, mitomycin C, TNP-470, cisplatin, carboplatin, 5-fluorouracil, methotrexate, suramin and batimastat) were used as control in order to test the specificity of the microtubule-affecting drug effects. We also investigated by means of videomicroscopy whether microtubule-affecting drugs could produce anti-migratory effects at non-cytotoxic doses on tumor cells. Finally, we used computer-assisted fluorescence microscopy to characterize the influence of microtubule-affecting drugs on the polymerization/depolymerization dynamics of the actin cytoskeleton in tumor cells. Our results show that taxol, vincristine and vindesine behave similarly in their ability to reduce the capillary network formation by HUVEC cells cultured on Matrigel. These anti-angiogenic effects appear at non-cytotoxic concentrations. In contrast, vinblastine and vinorelbine produce apparent anti-angiogenic effects by direct cytotoxicity. Microtubule-affecting agents are also able to significantly reduce the level of migration of tumor cells at non-cytotoxic concentrations, some of these effects may occur via modifications to the actin cytoskeleton organization. Several types of microtubule-affecting agents could be used as anti-angiogenic agents by administering them at non-cytotoxic concentrations, and some microtubule-affecting agents abandoned in pharmacological assays could turn out to be potent anti-migratory drugs acting on tumor cells, though without being too cytotoxic.