Circulating cell-free DNA: a novel biomarker for response to therapy in ovarian carcinoma

INTRODUCTION: Cell-free DNA (CFDNA) is a reflection of both normal and tumor-derived DNA released into the circulation through cellular necrosis and apoptosis. We sought to determine whether tumor-specific plasma DNA could be used as a biomarker for tumor burden and response to therapy in an orthotopic ovarian cancer model. METHODS: Female nude mice injected intraperitoneally with HeyA8 ovarian cancer cells were treated with either docetaxel alone or in combination with anti-angiogenic agents (AEE788-dual VEGFR and EGFR antagonist or EA5-monoclonal antibody against ephrin A2). Following DNA extraction from plasma, quantification of tumor-specific DNA was performed by real-time PCR using human specific beta-actin primers. The number of genome equivalents (GE/ml) were determined from a standard curve. Apoptosis was assessed by TUNEL staining of treated tumors. RESULTS: The levels of tumor-specific DNA in plasma increased progressively with increasing tumor burden (R2=0.8, p<0.01). Additionally, tumor-specific plasma DNA levels varied following treatment with chemotherapy. In mice with established tumors (19 days following tumor injection), tumor-specific plasma DNA levels increased by 63% at 24 hours following a single dose of docetaxel (15 mg/kg), and then declined to 20% below baseline at 72 hours and were 83% lower than baseline 10 days following therapy. In addition, docetaxel treatment resulted in a significant increase in the apoptotic index at 24 hours (p<0.01). Moreover, in two separate therapy experiments using a combination of cytotoxic chemotherapy with anti-angiogenic agents, tumor-specific plasma DNA levels were significantly higher in mice treated with vehicle compared to the treatment groups. The correlation between tumor weight and tumor-specific DNA in these experiments was 0.71-0.76 (p<0.01). CONCLUSIONS: Our results indicate that tumor-specific CFDNA levels correlate with increasing tumor burden and decline following therapy. Thus, tumor-specific DNA may be a useful surrogate biomarker of therapeutic response and should be evaluated in future clinical trials.     

Chemiluminescence and hematoporphyrin derivative: a novel therapy for mammary adenocarcinomas in mice

A Chemiluminescent System (CLS), using a Peroxyoxalate chemiluminescent solution (PCs), together with Hematoporphyrin derivative (HpD) Photofrin II., were utilized in the treatment of transplanted mammary adenocarcinomas in C3H/HeJ female mice. Tumor bearing animals aged 2-4 months were divided into five groups; Group I was the control. Groups 2 and 4 compared the effectiveness of both reagents HpD and PCs which were administered by intratumor injections fractionated over a 96 hour period. Groups 3 and 5 compared the effectiveness of PCs alone. Tests of the PCs were conducted with and without the presence of luminescence. Fifty-three percent of the animals in Group 4 and 47% of the animals in Group 2 remained tumor free 120 days after the completion of treatment. Thirty percent of the animals in Groups 2 and 4 survived one year without tumor recurrence. The results of this study suggest that a chemical light system can be a viable alternative in Photodynamic Therapy (PDT) to laser light for the activation of HpD and treatment of cancer.     

Radiation dosimetry for radionuclide therapy in a nonmyeloablative strategy

Radionuclide therapy extends the usefulness of radiation from localized disease of multifocal disease by combining radionuclides with disease-seeking drugs, such as antibodies or custom-designed synthetic agents. Like conventional radiotherapy, the effectiveness of targeted radionuclides is ultimately limited by the amount of undesired radiation given to a critical, dose-limiting normal tissue, most often the bone marrow. Because radionuclide therapy relies on biological delivery of radiation, its optimization and characterization are necessarily different than for conventional radiation therapy. However, the principals of radiobiology and of absorbed radiation dose remain important for predicting radiation effects. Fortunately, most radionuclides emit gamma rays that allow the measurement of isotope concentrations in both tumor and normal tissues in the body. By administering a small "test dose" of the intended therapeutic drug, the clinician can predict the radiation dose distribution in the patient. This can serve as a basis to predict therapy effectiveness, optimize drug selection, and select the appropriate drug dose, in order to provide the safest, most effective treatment for each patient. Although treatment planning for individual patients based upon tracer radiation dosimetry is an attractive concept and opportunity, practical considerations may dictate simpler solutions under some circumstances. There is agreement that radiation dosimetry (radiation absorbed dose distribution, cGy) should be utilized to establish the safety of a specific radionuclide drug during drug development, but it is less generally accepted that absorbed radiation dose should be used to determine the dose of radionuclide (radioactivity, GBq) to be administered to a specific patient (i.e., radiation dose-based therapy). However, radiation dosimetry can always be utilized as a tool for developing drugs, assessing clinical results, and establishing the safety of a specific radionuclide drug. Bone marrow dosimetry continues to be a "work in progress." Blood-derived and/or body-derived marrow dosimetry may be acceptable under specific conditions but clearly do not account for marrow and skeletal targeting of radionuclide. Marrow dosimetry can be expected to improve significantly but no method for marrow dosimetry seems likely to account for decreased bone marrow reserve.     

Update: the case for patient-specific dosimetry in radionuclide therapy

In this review of the literature and general practice in the use of radiopharmaceuticals for therapy, an argument is provided to demonstrate that the use of patient-individualized radiation dose assessment should become routine in these forms of therapy, as they are in other uses of radiation in therapy. Individual objections to patient-specific dosimetry will be raised and addressed, using findings presented in the literature. Such approaches are superior to the use of a fixed activity or activity per unit body weight approach in nuclear medicine therapy, which is current practice. It will be demonstrated that standardized and automated methods, with adjustment for patient-specific physical and biokinetic data, are of similar cost and difficulty to those used in other therapeutic modalities. Most importantly, the data show that careful use of patient-individualized dose calculations will produce calculated radiation dose estimates that correlate well with observed effects and that use of a dosimetry-based approach will result in better patient outcomes, improving the quality of medical care for patients and reducing costs for the institutions involved. The conclusion of this analysis is that the time has come for this reasonable paradigm to become routine practice.     

An enzyme-linked immunosorbent assay for hypoxia marker binding in tumours.

An enzyme-linked immunosorbent assay (ELISA) has been developed for measuring the in vivo binding of a hexafluorinated 2-nitroimidazole (CCI-103F) in tumour tissue biopsies. The binding of CCI-103F is believed to reflect the presence of hypoxia in tumours. The ELISA provides a sensitive and convenient method of measuring CCI-103F binding which does not require the injection of radioactive reagents. The ELISA is based on reagents prepared from synthetic antigens formed by the reductive activation and binding of CCI-103F to proteins in novel test tube experiments. Calibration of the ELISA involved comparing the ELISA with the radioactivity contained either in protein-CCI-103F adducts formed in vitro with tritiated CCI-103F or in tissues isolated from a tumour-bearing dog which had been injected with tritium-labelled CCI-103F. The two approaches to calibration are compared. The scope and limitation of the ELISA for measuring the binding of CCI-103F is discussed and an example of the application of the ELISA to measuring changes in tumour hypoxia in canine patients undergoing fractionated radiation therapy is presented.     

In vitro pharmacodynamic assay for cancer drug development: application to crisnatol, a new DNA intercalator

A microtiter pharmacodynamic assay is described that evaluates antitumor activity in vitro within a matrix of extracellular drug concentrations (C) and exposure times (T). The results were analyzed according to the pharmacodynamic principle: Cn x T = k, where n is the concentration coefficient and k is the drug exposure constant. This assay was used to characterize the antitumor activity of crisnatol (BW A770U), a member of the new arylmethylaminopropanediol class of DNA intercalators, in MCF-7 human breast cancer cells. The assay showed that drug action was a function of k, the extracellular drug exposure. Crisnatol had no effect at k less than 30 (n less than or equal to 1); was growth inhibitory at k = 30-1000 (n = 1), cytostatic at 1500, and cytotoxic at k greater than 2000 microMn-h (n = 2). These effects were directly related to increasing cellular retention of crisnatol. The threshold for growth inhibition was 0.02 fmol/cell, while cytoreduction required over 1 fmol/cell. The assay also yielded concentration-time curves of the form C = (k/T)1/n at specific surviving fractions, which were useful in selecting exposure conditions for further studies and emphasized the impact of exposure time on crisnatol activity. The hyperbolic nature of these curves suggested a unique parameter for comparing antitumor agents: the minimum C x T. This parameter represents the minimum exposure conditions required for a specified level of antitumor activity and accounts for differences in concentration coefficients among agents. The pharmacodynamic assay for crisnatol illustrates the importance of both concentration and exposure time in drug action and suggests a pharmacodynamic basis for comparing antitumor agents that conform to the Cn x T = k principle. Such agents include doxorubicin, 5-fluorouracil, cisplatin, etoposide, and tamoxifen. Analysis of these agents in the MCF-7 model shows that the minimum C x T parameter gives a relative cytotoxicity profile distinct from that found with the standard IC90 end point. This disparity was also seen in another, less differentiated breast cancer cell line (MDA-MB-231), and in normal human skin fibroblasts. Regardless of the end point, the in vitro cytotoxicity of crisnatol compares favorably with that of some clinically useful antitumor agents.     

DNA microfiltration assay: a simple technique for detecting DNA damage in mammalian cells

A simple method for detection of DNA single-strand breaks (DNA-SSB)in cultured cells is described, based on filtration of alkaline-lysedcells through microfilters. After exposure to potentially DNAdamaging agents, the cells are transferred to 0.8 µm celluloseacetate filters mounted in microfihter devices where they arewashed, lysed and centrifuged to separate undamaged DNA fromdamaged DNA. When human bronchiolar cells (l4Br) were exposedto different DNA damaging agents, hydrogen peroxide, N-methyl-N-nitroN-nitrosoguanidine or 4-nitroquinoline-1-oxide, there was goodcorrelation between the extent of DNA damage assessed by thisfiltration techniqe and by DNA precipitation assay. DNA-SSBwere also detected by the filtration technique after exposureof bronchiolar cells to phorbol ester-stimulated human neutrophils.The filtration assay is easy to perform, the sample handlingcapacity is very high, and no expensive or complicated laboratoryequipment is required. It may therefore be an alternative, ora complement, to other methods for detection of DNA-SSB.     

Use of a tetrazolium based colorimetric assay in assessing photoradiation therapy in vitro

The suitability of a colorimetric [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)] assay to the determination of cell viability following photoradiation therapy (PRT) of human breast and melanoma cell lines has been examined. Results have been shown to correlate with those obtained using a clonogenic assay system. Using the MTT assay system it was shown that differences occur in the susceptibility of both lines to PDT. In addition it has been demonstrated that both lines differ with respect to their ability to develop photosensitivity in the presence of hematoporphyrin derivative (HpD). In the absence of serum this difference is not as obvious. This MTT assay provides a valid, simple and semi-automatable system for assessment of PRT in vitro.     

Evaluation of arylmethylaminopropanediols by a novel in vitro pharmacodynamic assay: correlation with antitumor activity in vivo

The pharmacodynamics of a new series of antitumor DNA intercalators, known as arylmethylaminopropanediols (AMAPs), has been evaluated in vitro against adherent (MCF-7 human breast cancer) and nonadherent (P388 murine leukemia) cell lines. Previous work had shown that the in vitro antitumor activity of the model AMAP crisnatol was a function of exposure (Cn x T), rather than concentration alone. A unique exposure parameter, the minimum C x T, was proposed as an end point for antitumor activity in cell culture. Comparison of crisnatol to several established agents by the minimum C x T versus the standard concentration producing 10% survival indicated that these end points were not equivalent. The current work examined the validity of the pharmacodynamic approach using AMAP isomers from three different ring systems that were known to exhibit a spectrum of activity against the P388 tumor in vivo. The results indicated that antiproliferative, but not cytotoxic, activity of AMAPs in the pharmacodynamic assay correlated with their differential activity in vivo, expressed as percentage of increase in life span. In contrast, the concentration producing 10% survival either at 1 h or after continuous exposure did not show a similar correlation. The pharmacodynamic assay also revealed that certain AMAPs, while equipotent by concentration alone, required significantly less time and therefore less overall exposure for efficacy. Finally, the activity of AMAP isomers in P388 cells differed from that in MCF-7 cells, which may indicate AMAP selectivity for certain tumor types. Since AMAP action was a function of exposure, drug effects on cellular targets could likewise depend on exposure rather than concentration. These findings emphasize the importance of relating drug mechanisms to the pharmacodynamics of anticancer agents.     

DSE‐FRET: A new anticancer drug screening assay for DNA binding proteins

Nuclear factor-κB (NF-κB) is a key regulator of cancer progression and the inflammatory effects of disease. To identify inhibitors of DNA binding to NF-κB, we developed a new homogeneous method for detection of sequence-specific DNA-binding proteins. This method, which we refer to as DSE-FRET, is based on two phenomena: protein-dependent blocking of spontaneous DNA strand exchange (DSE) between partially double-stranded DNA probes, and fluorescence resonance energy transfer (FRET). If a probe labeled with a fluorophore and quencher is mixed with a non-labeled probe in the absence of a target protein, strand exchange occurs between the probes and results in fluorescence elevation. In contrast, blocking of strand exchange by a target protein results in lower fluorescence intensity. Recombinant human NF-κB (p50) suppressed the fluorescence elevation of a specific probe in a concentration-dependent manner, but had no effect on a non-specific probe. Competitors bearing a NF-κB binding site restored fluorescence, and the degree of restoration was inversely correlated with the number of nucleotide substitutions within the NF-κB binding site of the competitor. Evaluation of two NF-κB inhibitors, Evans Blue and dehydroxymethylepoxyquinomicin ([−]-DHMEQ), was carried out using p50 and p52 (another form of NF-κB), and IC₅₀ values were obtained. The DSE-FRET technique also detected the differential effect of (−)-DHMEQ on p50 and p52 inhibition. These data indicate that DSE-FRET can be used for high throughput screening of anticancer drugs targeted to DNA-binding proteins.     

自杀基因靶向核素治疗肿瘤研究进展

肿瘤的基因治疗是近年来的研究热点。而基因治疗与放射性核素结合产生的基因靶向性放射性核素治疗，是在自杀基因疗法等基础上建立起来的一种新的肿瘤基因治疗方法。它形成了自杀基因和放射性核素对肿瘤的双重杀伤作用，为肿瘤的基因治疗开拓了新的研究方向。     

Evaluation of a novel in vitro assay for assessing drug penetration into avascular regions of tumours.

The poor blood supply to solid tumours introduces many factors that affect the outcome of chemotherapy, one of which is the problem of drug delivery to poorly vascularized regions of tumours. Whereas poor drug penetration has been recognized as a contributing factor to the poor response of many solid tumours, the question of drug penetration through multicell layers has not been thoroughly addressed, largely because of restrictions imposed upon these studies by the requirement for either radiolabelled or naturally fluorescent compounds. The aim of this study is to describe modifications made to a recently published assay that broadens the scope for assessing drug penetration during the early stages of drug development and to characterize the ability of various drugs to penetrate multicell layers. DLD-1 human colon carcinoma cells were cultured on Transwell-COL plastic inserts placed into 24-well culture plates so that a top and bottom chamber were established, the two chambers being separated by a microporous membrane. Drugs were added to the top chamber at doses equivalent to peak plasma concentrations in vivo and the rate of appearance of drugs in the bottom chamber determined by high-performance liquid chromatography (HPLC). Both 3-amino-1,2,4-benzotriazine 1,4-dioxide (tirapazamine) and 7-[4''-(2-nitroimidazol-1-yl)-butyl]-theophylline (NITP) rapidly penetrated DLD-1 multicell layers (50.9 +/- 12.1 microm thick) with t(1/2) values of 1.36 and 2.38 h respectively, whereas the rate of penetration of 5-aziridino-3-hydroxymethyl-1-methyl-2-[1H-indole-4,7-dione] prop-beta-en-alpha-ol (EO9) and doxorubicin through multicell layers was significantly slower (t(1/2) = 4.62 and 13.1 h respectively). Inclusion of dicoumarol increases the rate of EO9 penetration, whereas reducing the oxygen tension to 5% causes a reduction in tirapazamine penetration through multicell layers, suggesting that the extent of drug metabolism is one factor that determines the rate at which drugs penetrate multicell layers. The fact that EO9 does not readily penetrate a multicell layer, in conjunction with its rapid elimination in vivo (t(1/2) < 10 min), suggests that EO9 is unlikely to penetrate more than a few microm from a blood vessel within its pharmacokinetic lifespan. These results suggest that the failure of EO9 in the clinic is due to a combination of poor drug penetration and rapid elimination in vivo.     

Serum cell-free DNA in renal cell carcinoma: a diagnostic and prognostic marker

BACKGROUND:

Currently, there are no established diagnostic and prognostic serum markers for renal cell carcinoma (RCC). The objective of this study was to evaluate the putative significance of serum cell‐free DNA.

METHODS:

Preoperative serum samples from 200 consecutive patients with sporadic, solid renal tumors were analyzed (157 patients with RCC and 43 patients with benign renal tumors). Quantitative real‐time polymerase chain reaction was used to assess total cell‐free DNA (ring finger protein 185 [RNF185]) and CpG island methylation of Ras association domain family member 1A (RASSF1A) von Hippel‐Lindau (VHL), prostaglandin‐endoperoxidase synthase 2 (PTGS2), and P16 (cyclin‐dependent kinase inhibitor 2A). Associations with RCC, pathologic variables, and disease‐specific survival were evaluated.

RESULTS:

Total cell‐free DNA levels and CpG island methylation of RASSF1A and VHL were highly diagnostic for RCC with an area under the receiver operating characteristic curve of 0.755, 0.705, and 0.694, respectively. VHL methylation was detected more frequently in patients with clear cell RCC than in those with other subtypes (P = .007). Total cell‐free DNA levels were higher in patients with metastatic RCC (P < .001) and necrotic RCC (P = .003) and were associated with poorer disease‐specific survival (P < .001). In multivariate analysis, the tumor stage, size, grade, and necrosis (SSIGN) score (P < .001) and categorized total cell‐free DNA levels (P = .028) were retained as independent prognostic factors.

CONCLUSIONS:

The current results indicated that cell‐free DNA represents a novel serum‐based diagnostic and prognostic biomarker for RCC. Total serum cell‐free DNA levels and CpG island methylation of RASSF1A and VHL may be useful diagnostic biomarkers for RCC. VHL methylation of cell‐free DNA is suggestive of clear cell RCC. Total serum cell‐free DNA may be a useful prognostic biomarker that may assist in tailoring postoperative surveillance and therapy. External prospective validation of these data will be required. Cancer 2012;. © 2011 American Cancer Society.     

DA-125, a novel anthracycline derivative showing high-affinity DNA binding and topoisomerase II inhibitory activities, exerts cytotoxicity via c-Jun N-terminal kinase pathway

PURPOSE: DA-125 [(8S,10S)-8-(3-Aminopropanoyloxyacetyl)-10-[(2,6-dideoxy-2-fluoro-alpha-L-talopyranosyl) oxy]-7,8,9,10-tetrahydro-6,8,11-trihydroxy-1-methoxy-5,12-naphthacene-dione hydrochloride] is a novel anthracycline derivative with anticancer activity. In the present study, we compared the cytotoxicity of DA-125 with that of doxorubicin in H4IIE rat hepatoma cells and investigated the mechanistic basis. Because activation of MAP kinases, in particular c-Jun N-terminal kinase (JNK), is implicated in apoptotic cell death, the signaling pathways responsible for DA-125-induced apoptosis were studied. METHODS: Cytotoxicity and apoptosis were measured in H4IIE cells and cells were stably transfected with a dominant-negative mutant of JNK1 (JNK1-) by MTT and TUNEL assays. Inhibition of topoisomerase II activity was determined in vitro. Drug accumulation and DNA binding affinity were determined by fluorescence spectroscopy. RESULTS: The cytotoxicity of DA-125 was greater than that of doxorubicin (IC50 11.5 vs 70 microM). DA-125 induced apoptosis with 30-fold greater potency than doxorubicin. Inhibition of topoisomerase II by DA-125 was fourfold greater. The presence of excess beta-alanine, a DA-125 moiety, failed to alter cytotoxicity and accumulation of DA-125, indicating that the improved cytotoxicity of DA-125 did not result from the beta-alanine moiety. Greater cellular accumulation of DA-125 correlated with its high-affinity DNA binding. Although neither PD98059 nor SB203580 altered the degree of cytotoxicity induced by DA-125, JNK1 cells exhibited about a twofold greater viability than control cells. DA-125-induced apoptosis was also decreased in JNK1- -transfected cells. CONCLUSIONS: DA-125 potently inhibited topoisomerase II activity and induced apoptosis by a high rate of prooxidant production. DA-125 exhibited high-affinity DNA binding with improved cellular drug accumulation. Apoptosis induced by DA-125 involved the pathway of JNK1, but not ERK1/2 or p38 kinase.     

The proteasome: a novel target for anticancer therapy

The proteasome is an ubiquituous enzyme complex that plays a critical role in the degradation of many proteins involved in cell cycle regulation, apoptosis and angiogenesis. Since these pathways are fundamental for cell survival and proliferation, particularly in cancer cells, the inhibition of proteasome is an attractive potential anticancer therapy. Bortezomib (Velcade, formerly PS-341) is an extremely potent and selective proteasome inhibitor that shows strong activity inin vitro andin vivo laboratory studies against many solid and hematologic tumor types. Moreover, bortezomib, mainly by inhibition of the NF-κB pathway, has a chemosensitizing effect when administered together with other antitumoral drugs. Clinical phase I trials, showed good tolerance of bortezomib at doses that achieved a desired degree of proteasome inhibition. Phase II studies showed high response rates in refractory multiple myeloma patients, which led to the accelerated approval of bortezomib by the Food and Drug Administration (FDA) and the European Medicines Agency (EMEA) for this indication. A phase III trial comparing bortezomib to dexamethasone in refractory/relapsed multiple myeloma patients had to be halted due to a survival advantage in the bortezomib arm. Additional studies are focusing in the potential benefit of bortezomib in newly diagnosed multiple myeloma patients. In other solid and hematological malignancies, phase II studies with bortezomib alone or in combination are ongoing with encouraging results, particularly in lung cancer and lymphoma. Supported by an unrestricted educational grant from Pfizer. This work was supported in part by Spanish Science and Technology Ministry (MCYT) SAF 2003/08181.     

Antitumor effects of a novel phenoxazine derivative on human leukemia cell lines in vitro and in vivo.

2-Amino-4,4alpha-dihydro-4alpha,7-dimethyl-3H-phenoxazine-3-one (Phx) was synthesized by reacting 2-amino-5-methylphenol with bovine hemolysates. Because Phx is a phenoxazine derivative like actinomycin D, we examined its effects on the proliferation of the human leukemia cell lines K562, HL-60, and HAL-01. Phx inhibited proliferation and induced apoptosis in all of the leukemia cell lines we tested, in a dose-dependent manner. We further investigated the antitumor effect of this compound on HAL-01-bearing nude mice. Treatment with Phx markedly reduced the tumor growth rate in the experimental group, as compared with the control group. Moreover, Phx was found to have few adverse effects on weight loss and WBC count. In addition, we examined the effects of Phx on human normal hematopoietic progenitor cells by a clonogenic assay, and we observed less suppression of normal progenitor cells than of leukemic progenitors. These results suggest that Phx may be used to treat patients affected by different types of leukemia.     

A comparison of high- versus low-linear energy transfer somatostatin receptor targeted radionuclide therapy in vitro

INTRODUCTION: The somatostatin analog [DOTA(0)-Tyr(3)]-octreotide (DOTATOC) has been widely used to target somatostatin receptor expressing tumors for therapy using radionuclides such as (90)Y or (177)Lu. AIM: This aim of this study was to compare the effects of DOTATOC labeled to high linear energy transfer (LET) alpha-emitter (213)Bi and low-LET beta-emitter (177)Lu in vitro. MATERIALS AND METHODS: Somatostatin receptor (sstr)-positive cell line Capan-2 and sstr-negative control cell line A549 were used for the experiments. The effects of two exposure times using different radiation doses of high-LET alpha-emitter (213)Bi and low-LET beta-emitter (177)Lu were investigated using cell survival assay. The apoptotic effects were investigated using Cell Death Detection ELISA(PLUS)10x. The cumulated activity and the mean absorbed dose per unit cumulated activity were calculated using MIRD cellular Svalues. RESULTS: (213)Bi-DOTATOC had an approximately four times greater induction of apoptosis than (177)Lu-DOTATOC and a 100 times greater induction of apoptosis than nonradiolabeled DOTATOC. Nonspecific radiolabeled tetra-azacyclododecanetetra-acetic acid (DOTA) had a less pronounced effect on the cell survival and apoptosis, as compared to the sstr-specific radiolabeled DOTATOC. CONCLUSION: (213)Bi-DOTATOC is significantly more potent than (177)Lu-DOTATOC in vitro because of its high-LET alpha-emission.(213)Bi-DOTATOC shows enhanced effects on mitotic and apoptotic cell deaths.