MUC1-C oncoprotein as a target in breast cancer: activation of signaling pathways and therapeutic approaches.

Mucin 1 (MUC1) is a heterodimeric protein formed by two subunits that is aberrantly overexpressed in human breast cancer and other cancers. Historically, much of the early work on MUC1 focused on the shed mucin subunit. However, more recent studies have been directed at the transmembrane MUC1-C-terminal subunit (MUC1-C) that functions as an oncoprotein. MUC1-C interacts with EGFR (epidermal growth factor receptor), ErbB2 and other receptor tyrosine kinases at the cell membrane and contributes to activation of the PI3KAKT and mitogen-activated protein kinase kinase (MEK)extracellular signal-regulated kinase (ERK) pathways. MUC1-C also localizes to the nucleus where it activates the Wnt/ß-catenin, signal transducer and activator of transcription (STAT) and NF (nuclear factor)-κB RelA pathways. These findings and the demonstration that MUC1-C is a druggable target have provided the experimental basis for designing agents that block MUC1-C function. Notably, inhibitors of the MUC1-C subunit have been developed that directly block its oncogenic function and induce death of breast cancer cells in vitro and in xenograft models. On the basis of these findings, a first-in-class MUC1-C inhibitor has entered phase I evaluation as a potential agent for the treatment of patients with breast cancers who express this oncoprotein.

Translational strategies exploiting TNF-alpha that sensitize tumors to radiation therapy.

TNFerade is a radioinducible adenoviral vector expressing tumor necrosis factor-alpha (TNF-alpha) (Ad.Egr-TNF) currently in a phase III trial for inoperable pancreatic cancer. We studied B16-F1 melanoma tumors in TNF receptor wild-type (C57BL/6) and deficient (TNFR1,2-/- and TNFR1-/-) mice. Ad.Egr-TNF+IR inhibited tumor growth compared with IR in C57BL/6 but not in receptor-deficient mice. Tumors resistant to TNF-alpha were also sensitive to Ad.Egr-TNF+IR in C57BL/6 mice. Ad.Egr-TNF+IR produced an increase in tumor-associated endothelial cell apoptosis not observed in receptor-deficient animals. Also, B16-F1 tumors in mice with germline deletions of TNFR1,2, TNFR1 or TNF-alpha, or in mice receiving anti-TNF-alpha exhibited radiosensitivity. These results show that tumor-associated endothelium is the principal target for Ad.Egr-TNF radiosensitization and implicate TNF-alpha signaling in tumor radiosensitivity.

Ionizing radiation: a genetic switch for cancer therapy.

Gene therapy of cancer represents a promising but challenging area of therapeutic research. The discovery of radiation-inducible genes led to the concept and development of radiation-targeted gene therapy. In this approach, promoters of radiation-inducible genes are used to drive transcription of transgenes in the response to radiation. Constructs in which the radiation-inducible promoter elements activate a transgene encoding a cytotoxic protein are delivered to tumors by adenoviral vectors. The tumoricidal effects are then localized temporally and spatially by X-rays. We review the conceptual development of TNFerade, an adenoviral vector containing radiation-inducible elements of the early growth response-1 promoter upstream of a cDNA encoding human tumor necrosis factor-alpha. We also summarize the preclinical work and clinical trials utilizing this vector as a treatment for diverse solid tumors.

Selective gene expression using a DF3/MUC1 promoter in a human esophageal adenocarcinoma model.

The efficacy of replication-deficient adenoviral vectors in gene therapy is confined to the number of tumor cells the vector infects. To focus and enhance the therapeutic efficacy, we employed a conditionally replication-competent adenoviral vector with a tissue-specific promoter, DF3/MUC1, in a human esophageal adenocarcinoma model. Our results demonstrate that Ad.DF3.E1A.CMV.TNF (Ad.DF3.TNF) specifically replicates in Bic-1 (DF3-producing cells) and mediates an enhanced biologic effect due to increased TNF-alpha in the same DF3-producing cells. We also show that the increased TNF-alpha interacts with ionizing radiation to produce greater tumor regression and a greater delay in tumor regrowth in Bic-1 (DF3-producing cells) compared to Seg-1 (DF3 non-producers). Tumor cell targeting using conditionally replication-competent adenoviral vectors with tumor-specific promoters to drive viral replication and deliver TNF-alpha provides a novel approach to enhancing tumor radiosensitivity.

Prospects for viral-based strategies enhancing the anti-tumor effects of ionizing radiation.

Ionizing radiation (IR) has been extensively used to treat a variety of solid tumors to improve local control and overall survival in patients. Gene therapy strategies represent one experimental direction to improve radiocurability. These gene therapy strategies include (1) replacement of mutated or deleted tumor-suppressor genes, (2) delivery of prodrugs, (3) transduction of genes under the control of radiation-inducible promoters, and (4) genetically engineered viruses that replicate preferentially in tumor cells after IR. Although any one of these viral-based gene therapy approaches is unlikely to succeed independently, experimental results suggest that clinically important antitumor can be achieved when these strategies are combined with IR. Several of these strategies are currently being or soon will be evaluated in clinical trials. This review focuses on molecular mechanisms and potential clinical application of these viral-based gene therapy strategies to improve the therapeutic index of IR.

Angiostatin effects on endothelial cells mediated by ceramide and RhoA.

Angiostatin is a cleavage product of plasminogen that has anti-angiogenic properties. We investigated whether the effects of angiostatin on endothelial cells are mediated by ceramide, a lipid implicated in endothelial cell signaling. Our results demonstrate that angiostatin produces a transient increase in ceramide that correlates with actin stress fiber reorganization, detachment and death. DNA array expression analysis performed on ceramide-treated human endothelial cells demonstrated induction of certain genes involved in cytoskeleton organization. Specifically, we report that treatment with angiostatin or ceramide results in the activation of RhoA, an important effector of cytoskeletal structure. We also show that treatment of endothelial cells with the antioxidant N-acetylcysteine abrogates morphological changes and cytotoxic effects of treatment with angiostatin or ceramide. These findings support a model in which angiostatin induces a transient rise in ceramide, RhoA activation and free radical production.

Phagocytosis of breast cancer cells mediated by anti-MUC-1 monoclonal antibody, DF3, and its bispecific antibody.

Human epithelial mucin, MUC-1, is commonly expressed in adenocarcinoma including 80% of breast cancers. erbB-2 is overexpressed in approximately 30% of breast cancers. Expression of MUC-1 and erbB-2 may be partially overlapping but discoordinate. Therefore, combined use of antibodies directed against these two antigens might increase the number of patients who benefit from immunotherapy. Monoclonal antibody (MAb) DF3 recognizes the MUC-1 tandem repeat. We investigated phagocytosis and cytolysis of cultured human breast cancer cells by monocyte-derived macrophages mediated by MAb DF3 and its bispecific antibody (BsAb) DF3xH22 with the second epitope directed against the Fc component of phagocytic cells. Purified monocytes from healthy donors were cultured with granulocyte macrophage colony-stimulating factor with or without IFN-gamma. antibody-dependent cellular phagocytosis (ADCP) and antibody-dependent cellular cytotoxicity (ADCC) assays were performed with these macrophages and MUC-1-expressing target cells (ZR75-1) in the presence of MAb DF3 and BsAb DF3xH22. ADCP was measured by two-color fluorescence flow cytometry using PKH2 (green fluorescent dye) and R-phytoerythrin (RPE) (red)-conjugated MAb against human CD14 and CD11b and was confirmed by confocal microscopy. ADCC was measured by (51)Cr release assay. Immunohistochemical staining studies of MUC-1 and erbB-2 were performed on 67 primary breast cancer tissues. Expression of MUC-1 and erbB-2 was partially overlapping but discoordinate in 67 consecutive breast cancers. Both MAb DF3 and BsAb DF3xH22 mediated ADCP. However, ADCP mediated by MAb DF3 was greater than that mediated by BsAb DF3xH22. ADCC as detected by (51)Cr release was not seen with either antibody. The addition of IFN-gamma to monocyte-derived macrophage cultures inhibited ADCP compared to granulocyte macrophage colony-stimulating factor alone. Given the partially overlapping but discoordinate expression of MUC-1 and erbB-2 in breast cancer, therapy directed toward both antigens should be considered. MAb DF3 and the BsAb DF3xH22, can effectively mediate phagocytosis of MUC-1-expressing target cells. Further investigations are needed to determine whether this antibody-induced phagocytosis results in long-term specific T-cell activation against MUC-1.

Phase I and pharmacokinetic study of LU79553, a DNA intercalating bisnaphthalimide, in patients with solid malignancies.

PURPOSE: To determine the maximum-tolerated dose and characterize the pharmacokinetic behavior of LU79553, a novel bisnaphthalimide antineoplastic agent, when administered as a daily intravenous infusion for 5 days every 3 weeks. PATIENTS AND METHODS: Patients with advanced solid malignancies received escalating doses of LU79553. Plasma sampling and urine collections were performed on both days 1 and 5 of the first course. RESULTS: Thirty patients received 105 courses of LU79553 at doses ranging from 2 to 24 mg/m(2)/d. Proximal myopathy, erectile dysfunction, and myelosuppression precluded the administration of multiple courses at doses above 18 mg/m(2)/d. These toxicities were intolerable in two of six patients after receiving three courses at the 24-mg/m(2)/d dose level. At the 18-mg/m(2)/d dose, one of six patients developed febrile neutropenia and grade 2 proximal myopathy after three courses of LU79553. The results of electrophysiologic, histopathologic, and ultrastructural studies supported a drug-induced primary myopathic process. A patient with a platinum- and taxane-resistant papillary serous carcinoma of the peritoneum experienced a partial response lasting 22 months. Pharmacokinetics were dose-independent, optimally described by a three-compartment model, and there was modest drug accumulation over the 5 days of treatment. CONCLUSION: Although no dose-limiting events were noted in the first two courses of LU79553, cumulative muscular toxicity precluded repetitive treatment with LU79553 at doses above 18 mg/m(2)/d, which is the recommended dose for subsequent disease-directed evaluations. The preliminary antitumor activity noted is encouraging, but the qualitative and cumulative nature of the principal toxicities, as well as the relatively small number of patients treated repetitively, mandate that rigorous and long-term toxicologic monitoring be performed in subsequent evaluations of this unique agent.

Phase I clinical trial of 7-cyanoquinocarcinol (DX-52-1) in adult patients with refractory solid malignancies.

PURPOSE: A phase I study of the antitumor antibiotic 7-cyanoquinocarcinol, DX-52-1, was conducted in patients with refractory solid malignancies. This study sought to determine the maximum tolerated dose and principal toxicities of this agent and to characterize its pharmacokinetic behavior. METHODS: Patients were required to have adequate bone marrow, renal and hepatic function. DX-52-1 was administered by i.v. continuous infusion over a 6-h period each week for four consecutive weeks followed by a 2-week rest period, which constituted one cycle of treatment. RESULTS: Initial dose levels were 3, 6, and 10 mg/m2. An intermediate dose level of 8 mg/m2 was added after acceptable toxicity was observed at the 6 mg/m2 dose level, but dose-limiting toxicities, including life-threatening ones, were seen at the 10 mg/m2 dose level in all three patients. The maximum tolerated dose (MTD) was subsequently determined to be 6 mg/m2. Because a clear pattern of toxicities was not initially evident, a larger than usual number of additional patients (16) were enrolled at the MTD to better distinguish toxicities due to the study drug from those secondary to the patients' underlying malignancies. Even at the MTD, the drug was poorly tolerated, with gastrointestinal toxicities (abdominal pain, nausea, vomiting and increased liver function tests) predominating and dose-limiting. Pharmacokinetic studies revealed that the mean maximum plasma concentration of DX-52-1 in patients evaluated at the MTD (138.8 +/- 59.3 ng/ml, n = 19) was considerably lower than the concentrations required for cytostatic or cytotoxic activity against sensitive human tumor cell lines in vitro. Further, the weekly dose intensity of the most efficacious treatment schedule identified during in vivo antitumor efficacy studies was 60 times greater than the 6 mg/m2 weekly dose tolerated by cancer patients. None of the 33 patients participating in this study, including the 22 patients evaluated at the MTD, had any response to treatment. CONCLUSION: Given the poor tolerability, the inability to achieve drug levels necessary to inhibit in vitro or in vivo tumor growth, and the lack of any responses in our study, DX-52-1, as given by this schedule, does not appear to warrant further investigation in phase II studies.

Molecular targeting of gene therapy and radiotherapy.

The full promise of gene therapy has been limited by the lack of specificity of vectors for tumor tissue as well as the lack of antitumor efficacy of transgenes encoded by gene delivery systems. In this paper we review our studies investigating two modifications of gene therapy combined with radiotherapy. The first investigations described include studies of radiation inducible gene therapy. In this paradigm, radio-inducible DNA sequences from the CarG elements of the Egr-1 promoter are cloned upstream of a cDNA encoding TNFalpha. The therapeutic gene (TNFalpha) is induced by radiation within the tumor microenvironment. In the second paradigm, genetically engineered herpes simplex virus (HSV-1) is induced by ionizing radiation to proliferate within the tumor volume. These modifications of radiotherapy and gene therapy may enhance the efficacy of both treatments.

Antitumor interaction of short-course endostatin and ionizing radiation.

PURPOSE: The purpose of this study was to evaluate whether endostatin, an antiangiogenic cleavage fragment of collagen XVIII, enhances the antitumor effects of ionizing radiation (IR). Endostatin was injected to coincide with fractionated radiotherapy. METHODS: Xenografts of radioresistant SQ-20B tumor cells were established in athymic nude mice. Lewis lung carcinoma cells were injected into C57BI/6 mice. Mice bearing SQ-20B xenografts were injected intraperitoneally with 2.5 mg/kg/day of murine recombinant endostatin 5 times per week for 2 weeks 3 hours before IR treatment (50 Gy total dose). Mice bearing Lewis lung carcinoma tumors were injected intraperitoneally with endostatin (2.5 mg/kg/day) four times; the first injection was given 24 hours before the first IR dose (15 Gy) and then 3 hours before IR (15 Gy/day) for 3 consecutive days. Microvascular density was assessed on tumor tissue sections by use of CD31 immunohistochemistry and light microscopy. Endothelial cell survival analyses were employed to evaluate endostatin effects on human aortic endothelial cells and human umbilical vein endothelial cells. Endothelial cell apoptosis was examined by use of FACS analysis and DAPI microscopy. RESULTS: In SQ-20B xenografts, combined treatment with endostatin and IR produced tumor growth inhibition that was most pronounced at the nadir of regression (day 21). By day 35, tumors receiving combined treatment with endostatin and IR were 47% smaller than tumors treated with endostatin alone. Interactive cytotoxic treatment effects between endostatin and IR were also demonstrated in mice bearing Lewis lung carcinoma tumors. Significant tumor growth inhibition was observed in the endostatin/IR group at days 11 and 13 compared with IR alone. Histologic analyses demonstrated a reduction in microvascular density after combined treatment with endostatin and IR compared with endostatin treatment alone. Survival analyses confirmed interactive cytotoxicity between endostatin and IR in both human aortic endothelial cells and human umbilical vein endothelial cells but not in SQ-20B tumor cells. Combined treatment with endostatin and IR produced an increase in cow pulmonary artery endothelial apoptosis compared with either treatment alone. DISCUSSION: The tumor regression observed after combined treatment with endostatin and IR suggests additive antitumor effects in both human and murine tumors. Importantly, the concentrations of endostatin employed produced little tumor regression when endostatin was employed as a single agent. The results from the clonogenic and apoptosis assays support the hypothesis that the endothelial compartment is the target for the endostatin/IR interaction.

A phase I clinical and pharmacokinetic study of the dolastatin analogue cemadotin administered as a 5-day continuous intravenous infusion.

PURPOSE: The dolastatins are a class of naturally occurring cytotoxic peptides which function by inhibiting microtubule assembly and tubulin polymerization. Cemadotin is a synthetic analogue of dolastatin 15 with potent antiproliferative and preclinical antitumor activity. This report describes a phase I study to evaluate the administration of cemadotin to adult cancer patients by a 5-day continuous intravenous (CIV) infusion. METHODS: All patients had histologically confirmed refractory solid tumors. The dose was escalated from an initial level of 2.5 mg/m2 (0.5 mg/m2 daily) according to a modified Fibonacci algorithm. A minimum of three patients was evaluated at each dose level until the maximum tolerated dose (MTD) was established. Treatment was repeated every 21 days until patients were removed from the study due to toxicity or disease progression. Drug-related toxicities were evaluated and graded by the U.S. National Cancer Institute's Common Toxicity Criteria. A radioimmunoassay (RIA) that detected both the parent drug and its metabolites with an intact N-terminal region of the molecule was used for pharmacokinetic studies. RESULTS: Twenty heavily pretreated patients received a total of 40 courses of cemadotin over five dose levels ranging from 2.5 to 17.5 mg/m2. Reversible dose-related neutropenia was the principal dose-limiting toxicity and 12.5 mg/m2 was established as the MTD. Nonhematologic toxicities attributed to the drug were moderate, and there was no evidence of the cardiovascular toxicity noted in the prior phase I studies of cemadotin given IV as a 5-min injection or 24-h infusion. There were no objective antitumor responses. Time courses of the cemadotin RIA equivalent concentration in whole blood were defined in 14 patients during the first cycle of therapy. The RIA-detectable species exhibited apparent first-order pharmacokinetics across the entire range of doses. The mean +/- SD of the observed steady-state blood concentration at the 12.5 mg/m2 MTD was 282 +/- 7 nM (n = 3). Blood levels decayed monoexponentially following the end of the infusion, with a mean half-life of 13.2 +/- 4.3 h (n = 14) in all patients. Mean values (n = 14) of the total blood clearance and apparent volume of distribution at steady state were 0.52 +/- 0.09 lh/m2 and 9.9 +/- 3.3 l/m2, respectively. CONCLUSIONS: The cardiotoxic effects of cemadotin were completely avoided by administering it as a 120-h CIV infusion. Thus. cardiovascular toxicity appears to be associated with the magnitude of the peak blood levels of the parent drug or its metabolites, whereas myelotoxicity is related to the duration of time that blood levels exceed a threshold concentration. Nevertheless, the data acquired during the extensive clinical experience with cemadotin requires careful examination to assess whether advancing this compound into disease-oriented efficacy studies is merited.

Selectivity of a replication-competent adenovirus for human breast carcinoma cells expressing the MUC1 antigen.

The DF3/MUC1 gene is aberrantly overexpressed in human breast and other carcinomas. Previous studies have demonstrated that the DF3/MUC1 promoter/enhancer confers selective expression of diverse transgenes in MUC1-positive breast cancer cells. In this study, we show that an adenoviral vector (Ad.DF3-E1) in which the DF3/MUC1 promoter drives expression of E1A selectively replicates in MUC1-positive breast cancer cells. We also show that Ad.DF3-E1 infection of human breast tumor xenografts in nude mice is associated with inhibition of tumor growth. In contrast to a replication-incompetent adenoviral vector that infects along the injection track, Ad.DF3-E1 infection was detectable throughout the tumor xenografts. To generate an Ad.DF3-E1 vector with the capacity for incorporating therapeutic products, we inserted the cytomegalovirus (CMV) promoter upstream of the TNF cDNA. Infection with Ad.DF3-E1/CMV-TNF was associated with selective replication and production of TNF in cells that express MUC1. Moreover, treatment of MUC1-positive, but not MUC1-negative, xenografts with a single injection of Ad.DF3-E1/CMV-TNF was effective in inducing stable tumor regression. These findings demonstrate that the DF3/MUC1 promoter confers competence for selective replication of Ad.DF3-E1 in MUC1-positive breast tumor cells, and that the antitumor activity of this vector is potentiated by integration of the TNF cDNA.

Angiostatin induces mitotic cell death of proliferating endothelial cells.

Angiostatin is an inhibitor of tumor angiogenesis that induces regression of experimental tumors and enhances the antitumor effects of radiation therapy. We report that the cytotoxic effects of angiostatin are restricted to the proliferating endothelial cell population. In addition, angiostatin and ionizing radiation (IR) interact by inducing death of dividing endothelial cells. We also show that angiostatin and IR interact to inhibit endothelial cell migration. These findings demonstrate that angiostatin targets the proliferating tumor vasculature and provide a mechanistic basis for the cytotoxic interaction of angiostatin and IR.

A phase I trial of a recombinant vaccinia virus expressing prostate-specific antigen in advanced prostate cancer.

A recombinant vaccinia virus encoding human prostate-specific antigen (rV-PSA) was administered as three consecutive monthly doses to 33 men with rising PSA levels after radical prostatectomy, radiation therapy, both, or metastatic disease at presentation. Dose levels were 2.65 x 10(6), 2.65 x 10(7), and 2.65 x 10(8) plaque forming units. Ten patients who received the highest dose also received 250 microg/m2 granulocyte-macrophage colony-stimulating factor (GM-CSF) as an immunostimulatory adjunct. No patient experienced any virus-related effects beyond grade I cutaneous toxicity. Pustule formation and/or erythema occurred after the first dose in all 27 men who received > or =2.65 x 10(7) plaque forming units. GM-CSF administration was associated with fevers and myalgias of grade 2 or lower in 9 of 10 patients. PSA levels in 14 of 33 men treated with rV-PSA with or without GM-CSF were stable for at least 6 months after primary immunization. Nine patients remained stable for 11-25 months; six of these remain progression free with stable PSA levels. Immunological studies demonstrated a specific T-cell response to PSA-3, a 9-mer peptide derived from PSA. rV-PSA is safe and can elicit clinical and immune responses, and certain patients remain without evidence of clinical progression for up to 21 months or longer.

Anti-angiogenic cues from vascular basement membrane collagen.

Vascular basement membrane is an important structural component of blood vessels and has been shown to interact with and modulate vascular endothelial behavior during angiogenesis. During the inductive phase of tumor angiogenesis, this membrane undergoes many degradative and structural changes and reorganizes to a native state around newly formed capillaries in the resolution phase. Such matrix changes are potentially associated with molecular modifications that include expression of matrix gene products coupled with conformational changes, which expose cryptic protein modules for interaction with the vascular endothelium. We speculate that these interactions provide important endogenous angiogenic and anti-angiogenic cues. In this report, we identify an important antiangiogenic vascular basement membrane-associated protein, the 26-kDa NC1 domain of the alpha1 chain of type IV collagen, termed arresten. Arresten was isolated from human placenta and produced as a recombinant molecule in Escherichia coli and 293 embryonic kidney cells. We demonstrate that arresten functions as an anti-angiogenic molecule by inhibiting endothelial cell proliferation, migration, tube formation, and Matrigel neovascularization. Arresten inhibits the growth of two human xenograft tumors in nude mice and the development of tumor metastases. Additionally, we show that the anti-angiogenic activity of arresten is potentially mediated via mechanisms involving cell surface proteoglycans and the alpha1beta1 integrin on endothelial cells. Collectively, our results suggest that arresten is a potent inhibitor of angiogenesis with a potential for therapeutic use.

Down-regulation of ceramide production abrogates ionizing radiation-induced cytochrome c release and apoptosis.

Previous work has demonstrated that down-regulation of ceramide production after selection of cells with N-oleoylethanolamine (OE), an inhibitor of ceramidase, results in resistance to DNA damage-induced apoptosis. We report here that acute exposure of WEHI-231 cells (murine B-cell lymphoma) to OE activates neutral sphingomyelinase, induces ceramide production and increases intracellular reactive oxygen species. OE exposure also induces mitochondrial permeability, cytochrome c release, and apoptosis. Cells selected for resistance to OE exhibit little if any change in reactive oxygen species and cytochrome c release when exposed either to OE or to toxic doses of ceramide. Importantly, the OE resistant cells are also resistant to ionizing radiation-induced cytochrome c release and apoptosis. These findings demonstrate that down-regulation of neutral sphingomyelinase activity is associated with decreased DNA-damage-induced apoptosis. In addition, the data suggests that agents that modify extranuclear targets responsible for ceramide production select for cells resistant to ionizing radiation-induced apoptosis through alterations in mitochondrial function.

In vitro and in vivo activity of protein kinase C inhibitor chelerythrine chloride induces tumor cell toxicity and growth delay in vivo.

Although clonogenic or divisional death is the main mechanism by which DNA-damaging agents demonstrate antitumor activity, recent data indicate that strategies specifically designed to trigger apoptosis may also prove to be useful antitumor agents. Protein kinase C (PKC) isoenzymes are involved in the regulation of cell proliferation, differentiation, and survival. Whereas pharmacological inhibition of PKC activity triggers apoptosis in most mammalian cells, cell line and tissue differences in sensitivities to these inhibitors remain. Whereas PKC inhibitors have potential as antitumor agents, issue of kinase specificity and solubility have remained obstacles to their clinical use. In this report, we investigated the antitumor activity of the PKC inhibitor chelerythrine chloride (chelerythrine), a selective inhibitor of group A and B PKC isoforms. Chelerythrine exhibited cytotoxic activity against nine human tumor cell lines tested in vitro. On the basis of the finding that radioresistant and chemoresistant squamous cell carcinoma lines (HNSCC) undergo apoptosis rapidly after treatment with chelerythrine in vitro, we assessed the effects of this agent on p53-deficient SQ-20B HNSCC cells in vivo. The results demonstrate that chelerythrine treatment of nude mice bearing SQ-20B is associated with significant tumor growth delay. Significantly, treatment with chelerythrine resulted in minimal toxicity. These findings demonstrate a potential for chelerythrine as an antitumor drug against squamous cell carcinoma.

NM-3, an isocoumarin, increases the antitumor effects of radiotherapy without toxicity.

We examined the effects of a new antiangiogenic isocoumarin, NM-3, as a radiation modifier in vitro and in vivo. The present studies demonstrate that NM-3 is cytotoxic to human umbilical vein endothelial cells (HUVECs) but not to Lewis lung carcinoma (LLC) cells nor Seg-1, esophageal adenocarcinoma cells, in clonogenic survival assays. When HUVEC cultures are treated with NM-3 combined with ionizing radiation (IR), additive cytotoxicity is observed. In addition, the combination of NM-3 and IR inhibits HUVEC migration to a greater extent than either treatment alone. The effects of treatment with NM-3 and IR were also evaluated in tumor model systems. C57BL/6 female mice bearing LLC tumors were given injections for 4 consecutive days with NM-3 (25 mg/kg/day) and treated with IR (20 Gy) for 2 consecutive days. Combined treatment with NM-3 and IR significantly reduced mean tumor volume compared with either treatment alone. An increase in local tumor control was also observed in LLC tumors in mice receiving NM-3/IR therapy. When athymic nude mice bearing Seg-1 tumor xenografts were treated with NM-3 (100 mg/kg/day for 4 days) and 20 Gy (four 5 Gy fractions), significant tumor regression was observed after combined treatment (NM-3 and IR) compared with IR alone. Importantly, no increase in systemic or local tissue toxicity was observed after combined treatment (NM-3 and IR) when compared with IR alone. The bioavailability and nontoxic profile of NM-3 suggests that the efficacy of this agent should be tested in clinical radiotherapy.