Growth delay in small EMT6 spheroids induced by cytotoxic drugs and its modification by misonidazole pretreatment under hypoxic conditions

Construction of Tissue-Level Cancer-Vascular Model with High-Precision Position Control via In Situ 3D Cell Printing

During tumor progression, the size and location of the tumor are important factors closely associated with the metastatic potential of the cancer as they largely govern tumor hypoxia and angiogenesis. However, despite the achievements of previous studies, these critical factors are poorly studied, mainly due to the lack of a flexible technique that can readily control 3D tumor mimicking constructs and their spatial relations with vasculature. Here, a novel tissue-level platform consisting of a metastatic cancer unit (MCU) and a perfusable vascular endothelium system (VES) is presented using in situ 3D cell printing. Size-tunable and position-controllable 3D cancer spheroids (500-1000 µm) are directly printed within the established bath bioink with a self-driven perfusable vascular channel. The cancer-vascular interactions are generated through controlling the distance between MCU and VES to investigate metastasis-associated changes at adjacent and distal regions. The result shows that MCU in 600 µm diameter includes hypoxia, invasion, and angiogenetic signaling. The further observations demonstrate that the proximity of MCU to VES augments the epithelial-mesenchymal transition (EMT) in MCU and vascular dysfunction/inflammation in VES, corroborating the positional significance in tumor metastasis. The platform with the precise-positioning control enables the recapitulation of patient's detailed metastatic progression, opening the chance for precision cancer medicine.

Enhanced tumour uptake and in vitro radiotoxicity of no-carrier-added [131I]meta-iodobenzylguanidine: implications for the targeted radiotherapy of neuroblastoma

In vitro and in vivo neuroblastoma models were used to determine whether improvements in tumour targeting in vivo and therapeutic efficacy in vitro could result from the use of no-carrier-added (n.c.a.) [131I]MIBG. Results were compared with use of the conventional therapy MIBG preparation (ex. [131I]MIBG) of lower specific activity which is produced by iodide exchange reaction. The efficacy of n.c.a. [131I]MIBG was compared with that of [131I]MIBG over a range of specific activities by the assessment of neuroblastoma spheroid growth delay. Whereas n.c.a. [131I]MIBG at a radioactivity concentration of 2 MBq/ml prevented the regrowth of 84% of spheroids, toxicity was significantly reduced by the addition of non-radiolabelled MIBG to the incubation medium. The time-dependent biodistribution of n.c.a. [131I]MIBG in nude mice bearing human neuroblastoma xenografts was compared with that of the conventional therapy radiopharmaceutical. The n.c.a. agent gave improved tumour uptake but also significantly greater accumulation in normal tissues known to accumulate MIBG such as heart, adrenal and skin. However, uptake and retention in the blood was unaltered. For all tissues examined, the 3-day calculations were undertaken to predict organ to tumour dose ratios which would result in human neuroblastoma patients with each of the [131I]MIBG preparations. These results suggest that significant therapeutic gain may be achieved by the use of n.c.a. [131I]MIBG as a treatment agent in neuroblastoma. neuroblastoma.

131I-meta-iodobenzylguanidine therapy in neuroblastoma spheroids of different sizes

Mathematical models have predicted that targeted radiotherapy of neuroblastoma with metaiodobenzylguanidine (mIBG) is less likely to cure small rather than large micrometastases if 131I is the conjugated radionuclide. This study uses multicellular tumour spheroids as an in vitro model to test the hypothesis that smaller tumours of sub-millimetre dimensions are relatively resistant to 131I-mIBG. Spheroids of the human neuroblastoma cell line SK-N-BE(2c), either 250 microns or 400 microns diameter, were incubated with 131I-mIBG at concentrations of up to 6.0 MBq ml-1. Using both regrowth delay and spheroid 'cure' as endpoints, the greater vulnerability of larger spheroids was confirmed. From this in vitro result we conclude that when used in vivo 131I-mIBG may spare smaller micrometastases. Therefore, either a radionuclide such as 211At which emits a shorter path length radiation should be conjugated to mIBG, or targeted radiotherapy should be combined with a treatment such as total body irradiation, the efficacy of which is not reduced in smaller tumours.

Misonidazole chemosensitization of EMT6 spheroids to melphalan

Nitroaromatic radiosensitizers are effective chemosensitizers in vitro and in vivo. We have used EMT6 tumour cells grown as multicellular spheroids to try and further understand the role that hypoxia plays in this process. Our results show that the cell killing produced in whole spheroids following a 1-h exposure to melphalan (L-PAM) was enhanced by a 3-h pre-exposure to 5 mM misonidazole (MISO), an enhancement ratio of 1.3-1.7 being obtained. Sequentially disaggregating spheroids we also found that both L-PAM toxicity and MISO chemosensitization were relatively constant as a function of depth within the spheroid. The binding of 14C-MISO to spheroid cells, measured by scintillation counting of disaggregated cells and by autoradiography analysis of sectioned spheroids, demonstrated that binding increased with depth. However, cells in the outer layers of the spheroid bound more 14C-MISO than expected with fully aerobic cells, while in the innermost viable cells the binding was less than that measured in cells which were fully radiobiologically hypoxic. This suggests that the majority of viable spheroid cells were at oxygen tensions intermediate between those found in either fully aerobic or radiobiologically hypoxic cells, yet their levels of oxygenation were sufficiently low for MISO chemosensitization to occur.

Antitumour activity and pharmacokinetics of niosome encapsulated adriamycin in monolayer, spheroid and xenograft

Niosomes are multilamellar vesicles formed from nonionic surfactants of the alkyl or dialkyl polyglycerol ether class and cholesterol. Adriamycin has been trapped within vesicles prepared from a monoalkyl triglycerol ether and its activity compared with adriamycin solution in human lung tumour cells grown in monolayer and spheroid culture and in tumour xenografted nude mice. The activity of the encapsulated adriamycin in vitro is maintained with similar clonogenic survival curves following treatment of monolayers and identical growth delays following spheroid exposure. The pharmacokinetics of adriamycin are altered in vivo in human lung tumour-bearing nude mice, when it is administered in niosomal form. There is prolonged release of drug from the plasma compartment with significantly lower peak levels; lower peak cardiac adriamycin concentrations with a shorter tissue half-life and decreased cardiac AUC and a greater degree of hepatic metabolism to inactive 7-deoxyaglycones. The tumour peak drug level and AUC was similar irrespective of the mode of administration of adriamycin. The growth delay (i.e. the time taken for the tumour volume to double) was significantly longer for adriamycin (15 days) and niosomal adriamycin (11 days) than for control (5.8 days). It is possible that the therapeutic ratio of adriamycin could be enhanced by administration in niosomal form.

Cytotoxic drug penetration studies in multicellular tumour spheroids

1. The three-dimensional structure of human lung tumour spheroids conferred a degree of resistance to the anthracyclines adriamycin, 4'-deoxydoxorubicin, daunomycin and daunomycin-low density lipoprotein complex in comparison with cells grown as a monolayer, as assessed by delayed growth and clonogenic cell survival. 2. 4'-Deoxydoxorubicin induced a longer growth delay and greater clonogenic cell kill than adriamycin in spheroids, although it was no more cytotoxic in monolayer. 3. Fluorescent microscopy demonstrated that the more lipophilic analogues partitioned into the spheroid more rapidly and to a greater degree than adriamycin. 4. The spheroid model demonstrated that penetration is an important aspect of resistance to anthracycline drugs, and this approach may represent a better in vitro system for testing lipophilic analogues of cytotoxic drugs.

The effect on human neuroblastoma spheroids of fractionated radiation regimes calculated to be equivalent for damage to late responding normal tissues

Multicellular tumour spheroids (MTS) are a useful in vitro model of human cancer. An experiment was designed to assess the likely therapeutic advantage of hyperfractionation--a proposed strategy in radiotherapy. A cell line (NB1-G) derived from human neuroblastoma was grown as MTS. This MTS line is radiosensitive with low capacity for repair of sublethal radiation damage. These properties make NB1-G a suitable line to test the theoretical advantage of hyperfractionation. MTS were irradiated using alternative fractionated regimens, with fraction sizes varying from 0.5 to 4 Gy. In each experiment, the total dose was chosen to make the regimens theoretically isoeffective for damage to late-responding normal tissues (calculated using the linear-quadratic mathematical model with alpha/beta = 3 Gy). The radiation responses of MTS were evaluated using the end-points of regrowth delay and "proportion cured". Regimens using smaller doses per fraction were found to be markedly more effective in causing damage to neuroblastoma MTS, as assessed by either end-point. These experimental findings support the proposal that hyperfractionation should be a therapeutically advantageous strategy in the treatment of tumours whose radiobiological properties are similar to those of the MTS neuroblastoma line NB1-G.

Multicellular spheroids. A review on cellular aggregates in cancer research

Cellular aggregates have been used in developmental biology and in experimental cancer research for several decades. Spherical aggregates of malignant cells, i.e. multicellular tumor spheroids, may serve as in vitro models of tumor microregions and of an early, avascular stage of tumor growth. The similarities between the original tumor and the respective spheroids include volume growth kinetics, cellular heterogeneity, e.g. the induction of proliferation gradients and quiescence, as well as differentiation characteristics, such as the development of specific histological structures or the expression of antigens. Research using cell aggregates has been focussed on mechanisms involved in the control of proliferation, invasion and metastasis. Immunological studies with spheroids have resulted in the characterization of defense cells which are responsible for specific host-versus-tumor reactions. The vast majority of investigations on spheroids concerns the simulation of therapy with regard to various treatment modalities, combination treatments and systematic analyses of using various endpoints in predictive assays. Only a few pathophysiological studies on the interrelationship among tumor-specific micromilieu, cellular metabolism, proliferative status, and cellular viability have been undertaken with the spheroid model up to now. Since these studies are indicative of a large influence of the cellular microenvironment on basic biological properties of cancer cells, investigations of these epigenetic mechanisms should be intensified in future research on cell aggregates. Similarly, the molecular basis of the biological peculiarities found in malignant cells grown as three-dimensional aggregates has to be investigated more intensively.

Biological properties of a tumour cell line (NB1-G) derived from human neuroblastoma

The properties of a new tumour cell line (NB1-G) derived from human neuroblastoma by xenografting in nude rats followed by adaptation to tissue culture are described. Studies using a panel of monoclonal antibodies demonstrate the neuro-ectodermal nature of the cells and support the diagnosis of the primary tumour as neuroblastoma. Cytogenetic studies have revealed a human karyotype with several chromosomal abnormalities. Genetic analysis by in situ DNA hybridization has demonstrated the presence of multiple copies of the N-myc gene. Approximately 20-30 fold amplification of the gene is observed on Southern blot analysis. The cell line has been adapted to growth as multicellular tumour spheroids as well as monolayer culture. Radiobiological studies on spheroids show the cells to be radiosensitive with low capacity for sub-lethal damage accumulation and repair. The cell line should be useful for fundamental studies of human neuroblastoma as well as experimental therapy in vitro.

In vitro chemosensitivity testing using the multicellular tumor spheroid model

Using growth delay and clonogenic cell survival as end points, we have shown that the 3-dimensional structure of human lung tumour spheroids confers a degree of resistance to the anthracyclines doxorubicin and 4'-deoxydoxorubicin, relative to cells grown as monolayer. 4'-deoxydoxorubicin induces a longer growth delay and greater clonogenic cell kill than doxorubicin in spheroids, although it is no more cytotoxic in monolayer. Using fluorescent microscopy we have demonstrated, qualitatively, that lipophilic anthracycline analogues partition into the spheroid more rapidly and to a greater degree than doxorubicin. It is apparent that penetration is an important aspect of anthracycline drug resistance in spheroids, and the spheroid model may represent a better in vitro system for testing lipophilic analogues of cytotoxic drugs.

The effect of adriamycin and 4'-deoxydoxorubicin on cell survival of human lung tumour cells grown in monolayer and as spheroids

Using growth delay and clonogenic cell survival as end points, we have shown that the 3-dimensional structure of human lung tumour spheroids confers a degree of resistance to the anthracyclines adriamycin and 4'-deoxydoxorubicin, relative to cells grown as monolayer. 4'-deoxydoxorubicin induces a longer growth delay and greater clonogenic cell kill than adriamycin in spheroids, although it is no more cytotoxic in monolayer (exponential and plateau phase). There is a log linear relationship between clonogenic cell survival and duration of adriamycin exposure in monolayers, and biphasic curve with a lesser degree of cell kill for disaggregated spheroid cells. Using fluorescent microscopy we have demonstrated, qualitatively, that the more lipophilic analogue partitions into the spheroid more rapidly and to a greater degree than adriamycin. It is possible that adriamycin penetration is a relatively important aspect of spheroid drug resistance, which may be related to intraspheroidal pH gradients, and that we have partially overcome this by using a lipophilic analogue.

Radiation studies on multicellular tumour spheroids derived from human neuroblastoma: absence of sparing effect of dose fractionation

In vitro experiments were carried out to compare the effects of single-dose and split-dose irradiation on a cell line (NB1-G) derived from human neuroblastoma and grown as multicellular tumour spheroids (MTS). The radiation response was evaluated in terms of regrowth delay; estimates of in situ cell survival were made by back-extrapolation of regrowth curves. These studies showed no significant difference in the effectiveness of single as compared to split dose irradiation i.e. no sparing effect of fractionation. If MTS constitute a realistic model for micrometastases in vivo, these results provide a radiobiological rationale for hyperfractionated treatment regimes in the adjuvant radiotherapy of neuroblastoma.

The effects of alpha and gamma interferons on human lung cancer cells grown in vitro or as xenografts in nude mice

We have compared the effects of alpha and recombinant gamma interferons (IFNs) on the growth of human lung cancer cell lines in vitro. There was a diversity of response amongst the lines studied, the most sensitive being COR-L23 (a large cell anaplastic carcinoma line) and POC (a small cell line). In these two lines, IFN-gamma was found to be more potent than IFN-alpha. During cell growth of line POC in the presence of IFN-gamma no significant shift in cell cycle distribution occurred. When lines COR-L23 and POC were grown as xenograft tumours in nude mice, daily injection of 4 X 10(5) units per mouse per day of IFN-gamma produced no discernible retardation of tumour growth.

Misonidazole protects mouse tumour and normal tissues from the toxicity of oral CCNU

Because the nitrosourea CCNU is given exclusively by the oral route in man, we have carried out studies in mice on the antitumour activity, acute toxicity and pharmacokinetics of oral CCNU, either alone or in combination with the chemosensitizer misonidazole. In both plasma and KHT tumour the peak concentration and "early" AUC for total nitrosoureas were about 1.4-1.5 fold greater for the oral compared to the i.p. route. These differences were reflected in the roughly twofold greater antitumour activity for the oral route. In contrast, acute toxicity tests showed that oral CCNU was 1.45 times less toxic to normal tissue, although the dose-limiting organ may be different for the two routes. Misonidazole reduced the antitumour activity of oral CCNU by dose modifying factors (DMF) of 0.58-0.71. Similarly, the acute toxicity was also diminished by a DMF of 0.74. Misonidazole has a complex effect on oral CCNU pharmacokinetics. The plasma and tumour total nitrosourea peak concentrations were reduced by 1.5 and 1.7 fold respectively. Misonidazole also reduced the "early" nitrosourea AUC, with the extent of the reduction depending on the minimum effective concentration (MEC) chosen. For example, the plasma nitrosourea AUC was reduced by factors of 1.05 and 9.6 for MEC values of 1 and 2 micrograms ml-1 respectively. We propose these pharmacokinetic changes to be the underlying mechanism for the reduction of oral CCNU cytotoxicity by misonidazole. Clinical trials of such combinations should be accompanied by detailed pharmacokinetic evaluation.

Effect of misonidazole pretreatment on nitrogen mustard-induced DNA cross-linking in mouse tissues in vivo

In the present study we have used the alkaline elution technique to study the effect of misonidazole (MISO) on the initial amount of DNA cross-linking in various normal and neoplastic tissues of C3H mice treated with nitrogen mustard (HN2) in vivo. Tissue samples for analysis of the cross-links were prepared 1 h after injection with HN2 to minimize the effect of subsequent repair processes on the yield of lesions. For mice receiving HN2 alone, the greatest level of cross-linking was found in spleen and jejunum, with the liver showing the lowest level. In animals that had been pretreated with MISO (1 mg g-1, i.p.) for 0.5 h prior to injection with HN2, the amount of cross-linking in the spleen and jejunum was not affected by MISO; however, in all other tissues that were examined, cross-linking was enhanced by MISO to a varying extent depending on the specific tissue. The greatest enhancement was observed in the liver (X 6) and kidney (X 3.1), both of these tissues showing a greater enhancement than either of the two fibrosarcomas. The potentiation of HN2 cross-linking in a particular tissue correlated well with two cellular processes that are known to be nitroreduction-dependent in vitro, namely, the degree of MISO-induced GSH depletion and the binding of MISO to cellular macromolecules. Thus, the potentiation of cross-linking in normal tissues such as liver and kidney, and by inference in tumours, may be intimately related to the generation and/or accumulation of nitro-reduced MISO metabolites in those tissues.

Modification of chemotherapy by nitroimidazoles

The potentiation of chemotherapeutic agents by radiation sensitizers has been extensively studied for several years. There is little doubt that the effectiveness of certain anti-cancer drugs, primarily alkylating agents, can readily be enhanced both in vitro and in vivo through the addition of a sensitizer. While enhanced effects have been observed in certain critical normal tissues, in general most animal model studies have demonstrated a therapeutic gain at large sensitizer doses. This approach to combination therapies therefore appears promising. Yet many questions concerning the interaction between chemotherapeutic agents and radiosensitizers, particularly in the area of mechanisms of action, still remain. This overview attempts to focus on some of these questions. Four aspects of modification of chemotherapy by nitroimidazoles are reviewed and discussed. These address the importance in chemopotentiation of i) hypoxia, ii) alterations in DNA damage and/or repair, iii) depletion of intracellular sulfhydryls and iv) modification of drug pharmacokinetics. It is concluded that: i) even though chemopotentiation can occur at intermediate oxygen levels, hypoxia ultimately plays a pivotal role, ii) no single unifying mechanism for chemopotentiation exists; alterations in drug pharmacokinetics, cellular SH levels and DNA damage/repair all are involved, the relative importance of each factor is dependent on the particular drug-sensitizer combination, iii) it is important to continue the evaluation of chemopotentiation under conditions mimicking clinically achievable sensitizer pharmacokinetics and iv) further investigations into more effective utilization of chemopotentiation are warranted.

An investigation of the possibility of chemosensitization by clinically achievable concentrations of misonidazole

Experiments have been carried out both in vitro and in vivo to examine the possibility of chemosensitization by misonidazole (MISO) at concentrations which are achievable in the clinic. Using multicellular tumour spheroids in vitro we found that a 16 h pre-incubation with 100 micrograms ml-1 MISO under hypoxic conditions led to a considerable enhancement of sensitivity to melphalan (MEL) but not to CCNU. Pre-incubation for 16 h under hypoxia alone also produced a degree of sensitization to MEL, but there was no effect of oxic pre-incubation with MISO. In vivo experiments using the KHT or RIF-1 tumours in C3H mice were designed so that repeated administration of MISO maintained blood concentrations of around 100 micrograms ml-1 for either 7 h or 16 h. For the 7 h regime, cytotoxic drugs were administered at the 4 h point. In most experiments the tumour response to MEL, cyclosphosphamide (CTX), chlorambucil or CCNU was no greater in mice receiving multiple MISO than in mice receiving multiple injections of a balanced salt solution. In the occasional experiment where there was an apparent increase in response, the effect was only small (dose modifying factor less than 1.5). For the 16 h regime the effect was studied of administering CTX (100 mg kg-1) at various times during the regime. There was a clear trend towards increased CTX response in mice receiving multiple MISO compared with controls. There was, however, no clear tendency for the effect to increase with length of MISO pre-exposure.