Radiosensitivity, repair capacity, and stem cell fraction in human soft tissue tumors: an in vitro study using multicellular spheroids and the colony assay

Pre-clinical phaeochromocytoma and paraganglioma models: Cell lines, animal models, and a human primary culture model

While the establishment of human phaeochromocytoma and paraganglioma (PPGL) cell lines has proven to be particularly difficult over several decades of research, there are other reliable pre-clinical PPGL models currently available. This review provides a summary of these models, together with our recently established personalised drug screening platform using patient-derived PPGL primary cultures. Such currently available PPGL models include murine and rat PPGL cell lines, of which only one cell line (PC12) is publicly accessible through a cell repository, and PPGL animal models, of which the patient-derived xenograft models are promising but complex to establish. We have developed next-generation implementation of human PPGL primary cultures, enabling reliable and personalised drug screening and an individualised analysis of tumour drug responsivity based on the tumour's unique genetic, biochemical, immunohistochemical and clinical profile. Overall, reliable PPGL models, including patient-derived primary culture models, are essential to advance pre-clinical research in the field of PPGLs.

Comparative In Silico Analysis of Ultra-Hypofractionated Intensity-Modulated Photon Radiotherapy (IMRT) Versus Intensity-Modulated Proton Therapy (IMPT) in the Pre-Operative Treatment of Retroperitoneal Sarcoma

BACKGROUND

While pre-operative radiation did not improve abdominal recurrence-free survival for retroperitoneal sarcoma (RPS) in the randomized STRASS trial, it did reduce rates of local recurrence. However, the risk of toxicity was substantial and the time to surgery was prolonged. A combination of hypofractionation and proton therapy may reduce delays from the initiation of radiation to surgery and limit the dose to surrounding organs at risk (OARs). We conducted a dosimetric comparison of the pre-operative ultra-hypofractionated intensity-modulated photon (IMRT) and proton radiotherapy (IMPT).

METHODS

Pre-operative IMRT and IMPT plans were generated on 10 RPS patients. The prescription was 25 Gy radiobiological equivalents (GyEs) (radiobiological effective dose of 1.1) to the clinical target volume and 30 GyEs to the margin at risk, all in five fractions. Comparisons were made using student T-tests.

RESULTS

The following endpoints were significantly lower with IMPT than with IMRT: mean doses to liver, bone, and all genitourinary and gastrointestinal OARs; bowel, kidney, and bone V5-V20; stomach V15; liver V5; maximum doses to stomach, spinal canal, and body; and whole-body integral dose.

CONCLUSIONS

IMPT maintained target coverage while significantly reducing the dose to adjacent OARs and integral dose compared to IMRT. A prospective trial treating RPS with pre-operative ultra-hypofractionated IMPT at our institution is currently being pursued.

Preclinical Models of Neuroendocrine Neoplasia

Neuroendocrine neoplasia (NENs) are a complex and heterogeneous group of cancers that can arise from neuroendocrine tissues throughout the body and differentiate them from other tumors. Their low incidence and high diversity make many of them orphan conditions characterized by a low incidence and few dedicated clinical trials. Study of the molecular and genetic nature of these diseases is limited in comparison to more common cancers and more dependent on preclinical models, including both in vitro models (such as cell lines and 3D models) and in vivo models (such as patient derived xenografts (PDXs) and genetically-engineered mouse models (GEMMs)). While preclinical models do not fully recapitulate the nature of these cancers in patients, they are useful tools in investigation of the basic biology and early-stage investigation for evaluation of treatments for these cancers. We review available preclinical models for each type of NEN and discuss their history as well as their current use and translation.

Long-term in vitro 2D-culture of SDHB and SDHD-related human paragangliomas and pheochromocytomas

The neuroendocrine tumours paraganglioma and pheochromocytoma (PPGLs) are commonly associated with succinate dehydrogenase (SDH) gene variants, but no human SDH-related PPGL-derived cell line has been developed to date. The aim of this study was to systematically explore practical issues related to the classical 2D-culture of SDH-related human paragangliomas and pheochromocytomas, with the ultimate goal of identifying a viable tumour-derived cell line. PPGL tumour tissue/cells (chromaffin cells) were cultured in a variety of media formulations and supplements. Tumour explants and dissociated primary tumour cells were cultured and stained with a range of antibodies to identify markers suitable for use in human PPGL culture. We cultured 62 PPGLs, including tumours with confirmed SDHB, SDHC and SDHD variants, as well as several metastatic tumours. Testing a wide range of basic cell culture media and supplements, we noted a marked decline in chromaffin cell numbers over a 4–8 week period but the persistence of small numbers of synaptophysin/tyrosine hydroxylase-positive chromaffin cells for up to 99 weeks. In cell culture, immunohistochemical staining for chromogranin A and neuron-specific enolase was generally negative in chromaffin cells, while staining for synaptophysin and tyrosine hydroxylase was generally positive. GFAP showed the most consistent staining of type II sustentacular cells. Of the media tested, low serum or serum-free media best sustained relative chromaffin cell numbers, while lactate enhanced the survival of synaptophysin-positive cells. Synaptophysin-positive PPGL tumour cells persist in culture for long periods but show little evidence of proliferation. Synaptophysin was the most consistent cell marker for chromaffin cells and GFAP the best marker for sustentacular cells in human PPGL cultures.

Radiation Therapy in Adult Soft Tissue Sarcoma-Current Knowledge and Future Directions: A Review and Expert Opinion

Simple Summary

Radiation therapy (RT) is an integral part of the treatment of adult soft-tissue sarcomas (STS). Although mainly used as perioperative therapy to increase local control in resectable STS with high risk features, it also plays an increasing role in the treatment of non-resectable primary tumors, oligometastatic situations, or for palliation. This review summarizes the current evidence for RT in adult STS including typical indications, outcomes, side effects, dose and fractionation regimens, and target volume definitions based on tumor localization and risk factors. It covers the different overall treatment approaches including RT either as part of a multimodal treatment strategy or as a sole treatment and is accompanied by a summary on ongoing clinical research pointing at future directions of RT in STS.

Abstract

Radiation therapy (RT) is an integral part of the treatment of adult soft-tissue sarcomas (STS). Although mainly used as perioperative therapy to increase local control in resectable STS with high risk features, it also plays an increasing role in the treatment of non-resectable primary tumors, oligometastatic situations, or for palliation. Modern radiation techniques, like intensity-modulated, image-guided, or stereotactic body RT, as well as special applications like intraoperative RT, brachytherapy, or particle therapy, have widened the therapeutic window allowing either dose escalation with improved efficacy or reduction of side effects with improved functional outcome. This review summarizes the current evidence for RT in adult STS including typical indications, outcomes, side effects, dose and fractionation regimens, and target volume definitions based on tumor localization and risk factors. It covers the different overall treatment approaches including RT either as part of a multimodal treatment strategy or as a sole treatment, namely its use as an adjunct to surgery in resectable STS (perioperative RT), as a primary treatment in non-resectable tumors (definitive RT), as a local treatment modality in oligometastatic disease or as palliative therapy. Due to the known differences in clinical course, general treatment options and, consequently, outcome depending on lesion localization, the main part of perioperative RT is divided into three sections according to body site (extremity/trunk wall, retroperitoneal, and head and neck STS) including the discussion of special applications of radiation techniques specifically amenable to this region. The review of the current evidence is accompanied by a summary on ongoing clinical research pointing at future directions of RT in STS.

Low dose ionizing radiation‐induced activation of connexin 43 expression

PURPOSE

Connexin 43 has been implicated in the cellular response to ionizing radiation by enabling cell-to-cell communication. It is established here that the expression of connexin 43 is affected by ionizing radiation and the mechanism involved is investigated.

MATERIALS AND METHODS

The human connexin 43 promoter was cloned into a Luciferase reporter plasmid and activation by ionizing radiation was measured in normal human fibroblasts as well as HeLa cells. The regions responsible for the radiation inducibility were defined using deletion and point mutations of the construct. The results were confirmed by Northern and Western blotting.

RESULTS

Ionizing radiation activates the human connexin 43 promoter in a time- and dose-dependent manner with a maximal induction (4.2-fold +/-0.58) after 6 h and a dose of 0.5 Gy. Higher doses up to 5 Gy led to a less marked increase (2-fold) over the same period. This promoter activation was associated with comparable increases in both connexin 43 mRNA and protein levels. The low dose radiation response of the promoter is mainly dependent on consensus binding sites for nuclear factor of activated T-cells (NFAT) and activator protein (AP1) in a region -2537 and -2110 bp from the transcriptional start site as determined by mutation analysis.

CONCLUSIONS

Low doses of ionizing radiation induce the transcriptional upregulation of connexin 43 expression employing NFAT and AP1 sites.

[Late outcome of 89 patients with soft-tissue sarcomas treated by surgery and three different radiotherapy schedules]

PURPOSE

To evaluate the outcome of patients treated for soft tissue sarcoma using three different post-operative radiotherapy schedules.

METHODS AND MATERIALS

Between 1990 and 2003, 89 patients (median age 50.8 years) presenting with soft tissue sarcoma (located to the limbs for 66 of them) underwent post-conservative-surgery radiotherapy. Pathology was liposarcoma in 35 cases and 54 others tumors. Tumors grades (FNCLCC classification) were 1, 2, 3 or unknown in 29, 32, 19 and 9 cases, respectively. Surgery was considered as complete in 68 patients. Irradiation was normofractionated (NF) in 62 cases, hyperfractionated (BF) in 19 cases and hypofractionated (HF) in 8 cases. For all the patients, median delivered dose was 61 Gy [34-76 Gy].

RESULTS

Median follow-up of alive patients was 73,8 months [3-184]. Five-year local control (LC) and overall survival (OS) rates were 85.5 and 71.2% respectively. According to multifactorial analysis, favourable prognostic factors were for local control, complete surgery (P=0.0075) and for overall survival, complete surgery (P=0.0267), grade 1 tumor (P=0.012) and absence of distant recurrence (P=0.0488). There was no statistical evidence of difference for the five-year LC and OS rates between the patients who received NF, BF or HF. There were few complications and there were comparable in the three groups.

CONCLUSIONS

This retrospective serie showed similar results for all the schedules. There is no evidence to recommend bifractionation. Hypofractionation should be used only in selected patients with poor performans status.

Neural stem cell-preserving external-beam radiotherapy of central nervous system malignancies

PURPOSE

Recent discoveries have implicated neural stem cells (NSC) as the source of plasticity and repair in the mature mammalian brain. Treatment-induced NSC dysfunction may lead to observed toxicity. This study evaluates the feasibility of NSC-preserving external beam radiotherapy.

METHODS AND MATERIALS

A single computed tomography (CT) dataset depicting a right periventricular lesion was used in this study as this location reflects the most problematic geometric arrangement with respect to NSC preservation. Conventional and NSC preserving radiotherapy (RT) plans were generated for the same lesion using two clinical scenarios: cerebral metastatic disease and primary high-grade glioma. Disease-specific target volumes were used. Metastatic disease was conventionally treated with whole-brain radiotherapy (WBRT) to 3,750 cGy (15 fractions) followed by a single stereotactic radiosurgery (SRS) boost of 1,800 cGy to gross disease only. High-grade glioma was treated with conventional opposed lateral and anterior superior oblique beams to 4,600 cGy (23 fractions) followed by a 1,400 cGy (7 fractions) boost. NSC preservation was achieved in both scenarios with inverse-planned intensity modulated radiotherapy (IMRT).

RESULTS

Cumulative dose reductions of 65% (metastatic disease) and 25% (high-grade glioma) to the total volume of the intracranial NSC compartments were achieved with NSC-preserving IMRT plans. The reduction of entry and exit dose to NSC niches located contralateral to the target contributed most to NSC preservation.

CONCLUSIONS

Neural stem cells preservation with current external beam radiotherapy techniques is achievable in context of both metastatic brain disease and high-grade glioma, even when the target is located adjacent to a stem cell compartment. Further investigation with clinical trials is warranted to evaluate whether NSC preservation will result in reduced toxicity.

A Caenorhabditis elegans tissue model of radiation-induced reproductive cell death

We have developed a tissue model of radiation-induced reproductive cell death in the nematode Caenorhabditis elegans. Reproductive cell death is the primary mode of death in tissue multipotential precursor cells, or "clonogens," the targets of cytotoxic therapy, whose elimination results in normal tissue damage as well as solid-tumor eradication. Through extensive morphologic and genetic analysis, we have confirmed that cell death in this model represents reproductive cell death in isolation from apoptotic cell death, affording the opportunity to define the genetic pathways required for protection from reproductive cell death. We have additionally found that the DNA damage response pathway is necessary for protection from reproductive cell death, supporting the long-held tenet that DNA damage is the cause of reproductive cell death and further validating this model. This genetic tissue model provides a valuable tool for oncology-based research and affords a platform to broaden our insight into responses to cytotoxic therapy in tissues.

Cirurgia conservadora, radioterapia externa e reforço de dose com braquiterapia de alta taxa de dose: uma nova perspectiva no tratamento de sarcomas de partes moles do adulto

OBJETIVO: Avaliar a influência no controle local de pacientes adultos e portadores de sarcoma de partes moles em extremidades e submetidos a cirurgia conservadora do membro, com braquiterapia de alta taxa de dose (BATD) como reforço para a radioterapia externa (RT). MATERIAL E MÉTODOS: Foram avaliados 16 pacientes tratados, de 1993 até 1999. A RT foi utilizada com finalidade pré ou pós-operatória (30--55 Gy) e BATD com dose de 18--36 Gy (fx 3--6 Gy BID). Com base no modelo linear quadrático calculou-se a dose efetiva biológica ("biological effective dose" - BED) para o tumor e comparou-se seu valor a dados da literatura internacional, que utiliza tratamentos com RT e braquiterapia de baixa taxa de dose (BBTD). RESULTADOS: Os valores médios e medianos da BED para os sarcomas de partes moles foram de 78,5 Gy7 e 80 Gy7. A análise univariada mostrou que a BED para o tumor, quando utilizada BATD, era semelhante ao valor de 83 Gy7 quando utilizada BBTD (p = 0,008). As taxas de controle local, sobrevida livre de doença e sobrevida global atuarial em cinco anos foram de 83,2%, 75% e 93,7%, respectivamente. CONCLUSÕES: A BATD, quando utilizada como método complementar no reforço de dose da RT no tratamento conservador dos sarcomas de partes moles, apresenta taxas de controle local equiparáveis às da literatura internacional; no entanto, estudos com número maior de pacientes e período maior de seguimento são ainda necessários para determinar o verdadeiro potencial da BATD em substituir a BBTD.

Postoperative radiotherapy in the management of adult soft tissue sarcoma of the extremities: results with two different total dose, fractionation, and overall treatment time schedules

PURPOSE

This retrospective study was performed to evaluate two postoperative radiotherapy schedules in terms of dose, fractionation, and overall treatment time in soft tissue sarcoma (STS) of the extremities.

METHODS AND MATERIALS

Between January 1984 and December 1993, 62 patients with newly diagnosed localized STS of the extremities were treated with maximal conservative surgery and postoperative radiotherapy (RT). Forty-five patients received 50 Gy with conventional fractionation plus a boost dose (5 to 20 Gy). Seventeen patients had hyperfractionated accelerated radiotherapy (HFART) up to a dose of 45 Gy in 3 weeks.

RESULTS

With a median follow-up of 72 months, the 5-year local failure rate was 25%, the 5-year disease-free and overall survival rates were respectively 42% and 62%. The 3-year local relapse, disease-free, and overall survival rates were respectively 16%, 44%, and 70% in the conventional radiotherapy group, and 36%, 47%, and 82% in the HFART group (NS). No factor significantly influenced local control with a trend, however, in favor of conventional RT (p = 0.10).

CONCLUSION

HFART at the dose of 45 Gy does not seem to be superior to the standard RT schedule, neither in terms of local control, survival, nor in terms of long-term side effects. However this dose could be considered too low as well as the power of comparison between the two groups to draw definitive conclusions.

Targeted radiotherapy of multicell neuroblastoma spheroids with high specific activity [125I]meta-iodobenzylguanidine

PURPOSE

Iodine-125 induces cell death by a mechanism similar to that of high linear energy transfer (high-LET) radiation. This study investigates the cytotoxicity of high-specific-activity [125I]meta-iodobenzylguanidine (125I-mIBG) in human SK-N-MC neuroblastoma cells grown as three-dimensional multicellular spheroids.

MATERIALS AND METHODS

Spheroids were incubated with high-specific-activity 125I-mIBG (6 mCi/microg, 1000 times that of the conventional specific activity used for autoradiography). Cytotoxicity was assessed by fluorescence viability markers and confocal microscopy for intact spheroids, fluorescence-activated cell sorting and clonogenic assay, and clonogenic assays for dispersed whole spheroids. Distribution of radioactive mIBG was determined by quantitative light-microscope autoradiography of spheroid cryostat sections. Dose estimation was based on temporal knowledge of the retained radioactivity inside spheroids, and of the radiolabel's emission characteristics. Findings were compared with those of spheroids treated under the same conditions with 131I-mIBG, cold mIBG, and free iodine-125.

RESULTS

125I-mIBG exerted significant cell killing. Complete spheroids were eradicated when they were treated with 500 microCi of 125I-mIBG, while those treated with 500 microCi or 1000 microCi of 131I-mIBG were not. The observed difference in cytotoxicity between treatments with 125I- and 131I-mIBG could not be accounted for by the absorbed dose of spheroid alone. The peripheral, proliferating cell layer of the spheroids remained viable at the moderate radioactivity of 100 microCi for both isotopes. Cytotoxicity induced by 125I-mIBG was quantitatively comparable by the peripheral rim thickness to that of 131I-mIBG at the dose of 100 microCi. The peripheral rim thickness decreased most significantly in the first 17 hours after initial treatment. There was no statistical decrease in the rim thickness identified afterwards for the second, third, and fourth days of incubation.

CONCLUSION

The cytotoxic effect of high-specific-activity 125I-mIBG appears to be comparable to, if not more efficient than that of conventionally used 131I-mIBG at the same level of total radioactivity. 125I-mIBG may improve the therapeutic index over that of 131I-mIBG in the clinical management of metastatic neuroblastoma due to the short range of Auger electrons.

Multicellular spheroids: a three-dimensional in vitro culture system to study tumour biology

The growth of tumour cells as three-dimensional multicellular spheroids in vitro has led to important insights in tumour biology, since properties of the in vivo-tumour such as proliferation or nutrient gradients, can be studied under controlled conditions. While this review starts with an update of recent data on spheroid monocultures, especially concerning tumour microenvironment and therapeutic modalities, the main emphasis is put on the spectrum of heterologous cultures which have evolved in previous years. This type of culture includes tumour cell interaction with endothelial, fibroblast or immunocompetent cells. The relation of the spheroid culture model to other types of three-dimensional culture and our critical evaluation and presentation of the technical aspects of growing and analysing spheroids are included in the text. These topics are chosen to help the experimental pathologist design experiments with tumour spheroids and to stimulate discussion.

Improved models of tumour cure

The standard mechanistic model for the probability of tumour cure (the "Poisson model') is based on the assumption that the number of surviving clonogens at the end of treatment follows a Poisson distribution from tumour to tumour. This assumption is not correct, however, if proliferation of tumour clonogens occurs during treatment, as would be expected in general during a fractionated course of radiotherapy. In the present study, the possible magnitude of the error in the Poisson model was investigated for tumours treated with either conventional fractionation or split-course therapy. An example is presented in which the Poisson model has an absolute error of nearly 100%, predicting a cure rate of 0% when in fact the cure rate was close to 100%. The largest errors in the Poisson model found in this study were for very small tumours (approximately 100 clonogens), but for larger tumours (> or = 10(6) clonogens), the Poisson model may still be highly inaccurate, predicting a cure rate that differs from the actual cure rate by as much as 40%. Three new tumour-cure models are proposed (the GS, PS, and GS+ models), and their accuracy is also investigated. Two of these (the GS and PS models) are better than the Poisson model for the clinically relevant cases tested here. The third model, the GS+ model, consistently produced the most accurate estimate of the tumour cure rate, but has more limited use than the GS and PS models because it is more highly parametrized. It is demonstrated here that no tumour-cure model based on the effective clonogen doubling time will be perfectly accurate in all cases, since the cure rate depends on the details of the cell kinetics contributing to the effective doubling time.

Comparison between the in vitro intrinsic radiation sensitivity of human soft tissue sarcoma and breast cancer cell lines

The purpose of this study is to evaluate the radiation sensitivity of human soft tissue sarcoma cell lines in vitro and to compare with that of human breast carcinoma and glioblastoma cell lines. The intrinsic radiation sensitivity parameters of seven human soft tissue sarcomas and eight breast carcinoma cell lines were investigated in vitro by clonogenic assays for single-dose irradiation under aerobic conditions on cells in exponential phase of growth. The results for sarcoma cell lines showed that the mean surviving fraction at 2 Gy (SF2) was 0.39 (SD +/- 0.09) with a range of 0.24 to 0.53, and the average mean inactivation dose (MID) was 1.92 (SD +/- 0.35) range from 1.36 Gy to 2.49 Gy. These values were not different from that of breast cell lines examined concurrently and using the same experimental methods (mean SF2 0.38, SD +/- 0.09; MID 1.9 Gy, SD +/- 0.37). However radiobiological parameters of nine karyotyped human malignant glioma cell lines determined earlier in this laboratory were significantly higher (mean SF2 0.50 +/- 0.14; mean MID 2.61 +/- 0.60). In conclusion, the data presented here do not support the view that cells of sarcomas show unusual radiation resistance. To the extent that the in vitro determined cellular radiation sensitivity reflects the tumor response in vivo, the success rate for radiation applied against sarcoma and breast carcinoma of comparable size could be similar.

Participation of gap-junctional cell communication on the adaptive response in human cells induced by low dose of X-rays

To investigate the radioadaptive response of normal cells to low-dose radiation, we irradiated human embryonic (HE) cells and HeLa cells with low-dose X-rays and examined the changes in sensitivity to subsequent high-dose X-irradiation using the trypan blue dye-exclusion test. When HE cells were irradiated by 200 cGy, the growth ratio of the living cells 5 days after the irradiation decreased to 37% of that of the cells which received no X-irradiation. When the cells received a conditioning irradiation of 10-20 cGy 4 h before the irradiation of 200 cGy, the relative growth ratios increased significantly to 45-53%, and a peak was reached at a conditioning dose of 13 cGy to the cells. This conditioning effect was not observed in LeLa cells. When the HE cells were suspended in a Ca2+ ion-free medium or TPA added to the medium while receiving the conditioning irradiation of 13 cGy, the effect of the conditioning dose was not observed. This indicates that normal cells show an adaptive response to low-dose radiation and become more radioresistant. These results suggest that gap junctional intercellular communication may play a role in radioadaptive responses in human cells.

Radiation-induced apoptosis in human sarcoma and glioma cell lines

Six human soft-tissue sarcoma and 14 glioma cell lines, exhibiting considerable differences in radioresponsiveness and histological grade of differentiation of the parental tumour, were examined with respect to apoptosis development after irradiation with 60Co gamma-rays. After test doses of 6 and 25 Gy, significant changes characteristic of apoptosis occurring within 6 to 30 hr were exhibited by only 2 differentiated sarcoma cell lines, EL7 and ESS2. The characteristic internucleosomal fragmentation of DNA was detected as early as 6 hr after exposure of subconfluent monolayer cultures to 6 Gy. It was limited to cells that had detached from the culture plate, whereas adherent cells showed random degradation of DNA, namely after higher doses (25Gy) or longer incubation times (30 hr). As assessed by fluorescence microscopy of unfixed cultures stained with Hoechst 33342 and propidium iodide, the proportion of cells showing apoptotic bodies in non-irradiated controls was < 0.1% and 0.3% for EL7 and ESS2, respectively. The dose-response relationship for apoptosis was determined at 9 hr post-irradiation. After 2 Gy, the percentage of apoptotic cells was elevated to 3.4% in EL7 and 4.5% in ESS2 cultures. Saturation was obtained above 6 Gy, with 8.4% apoptosis in EL7 and 15% in ESS2 after 25 Gy. Taken together, rapid ionizing-radiation-induced apoptosis seems to be limited to a subgroup of sarcomas and is unlikely to occur in gliomas.

Heterogeneity in the fractionation sensitivities of human tumor cell lines: studies in a three-dimensional model system

PURPOSE

Current concepts to optimize the therapeutic gain of radiotherapy by hyperfractionation assume that human tumors are less sensitive to fractionation than late reacting normal tissues. The aim of this study was to investigate the extent of the intercell line heterogeneity of fractionation sensitivity of a wide variety of human tumor cell lines in a three-dimensional model system under fully oxic conditions using schedules with one to eight fractions. Biological characteristics of the tumors that correlate with fractionation sensitivity should be identified.

METHODS AND MATERIALS

A total of 21 cell lines from human tumors maintained as multicellular spheroids consisting of 1000-1500 cells were given fractionated irradiation within a total treatment time of maximally 50 h. Complete dose-spheroid control curves were determined for each fractionation scheme. The spheroid control data were adequately described by the linear quadratic model assuming Poisson statistics. In addition, the induction of a G2 block by a fractionated test dose of seven 3 Gy fractions given at 6-h intervals was determined in spheroid cells using flow cytometry of propidium bromide stained cell nuclei.

RESULTS

The fractionation sensitivities of human tumor cells in multicellular spheroids could be characterized by alpha/beta values, ranging from 2.8-37 Gy in dependence on the cell line. The log normally distributed alpha/beta values were positively correlated with the percentage increase in G2/M phase after the fractionated test dose compared to the controls (r = 0.72, p < 0.01), and were associated with the degree of tumor differentiation (p = 0.01, ANOVA F-test). No significant correlation between the log (alpha/beta) values and the surviving fractions at 2 Gy (SF2) or the total doses with 2 Gy per fraction necessary to control 50% of the spheroids (SCD50) was observed. Despite the intercell line variability of the alpha/beta values, the SCD50 values of the different cell lines, given with one and eight fractions or one fraction and 2 Gy per fraction, were closely associated (Spearman rank correlation coefficients: r = 0.89 or r = 0.90, p < 0.0001).

CONCLUSION

Human tumor cell lines showed a marked heterogeneity in the fractionation sensitivity when irradiated as multicellular spheroids and assayed in situ using the spheroid control end point. Therefore, the therapeutic gain of altered fractionation also depends on those biological characteristics of each individual tumor that affects its fractionation sensitivity. Parameters that correlate with fractionation sensitivity of the tumor lines in the spheroid system were identified as grade of tumor differentiation and percentage increase in G2/M cells at the end of an eight-fraction schedule.

Radiosensitivity of multicellular tumour spheroids obtained from human ovarian cancers

The radioresponsiveness of immunologically characterised (KL1, antivimentin and OC125) human ovarian carcinoma cells, obtained from effusions or solid tumours, was assayed in vitro using the multicellular tumour spheroids (MTS) three-dimensional model. Great interspecimen variabilities were observed in MTS doubling time (1.0-8.5 days), as well as in the doses inducing a 50% decrease in the MTS individual volume (ID50) (0.56-9.15 Gy), or in the overall population MTS number (SCD50) (1.9-15.7 Gy) and the residual/initial MTS individual volume ratio after 2 Gy irradiation (RSV2) (10-88%). The doubling time, DNA-ploidy and S-phase fraction did not correlate with the ID50. Significant correlations were found between the new parameters defined (RSV2 and ID50) and the SCD50, a well-accepted local control parameter. These parameters demonstrated their usefulness for studying the radiosensitivity of MTS prepared from human ovarian tumour biopsies.

Interaction between ionizing radiation, estrogens and antiestrogens in the modification of tumor microenvironment in estrogen dependent multicellular spheroids

MCF7 human breast cancer cells growing as multicellular spheroids were examined as a model of three-dimensional cellular organization. Estrogen-free medium inhibited spheroid formation. In medium containing estrogens, the antiestrogen hydroxytamoxifen decreased the spheroid growth rate. Analyses with the recursion formula after Gompertz fitting showed that the rate of exponential decrease in growth rate (alpha) was alpha 0.099 +/- 0.013 d-1, and the decrease in alpha' was 0.061 +/- 0.015 d-1 for 0.1 microM hydroxytamoxifen and control spheroids respectively. MCF7 cells which had been growth arrested in an estrogen-free medium showed a significant decrease in radiosensitivity (surviving fraction at 2 Gy, SF2 = 63%) when compared with 0.1 nM 17 beta-estradiol-treated cells (SF2 = 38%). No differences in radiosensitivity were seen in MCF7 spheroids in estrogen-supplemented medium (radiation dose necessary to control 50% of spheroids (SCD50) was 5.51 Gy; derived alpha, beta and SF2 were 0.301 +/- 0.110 Gy-1, 0.018 +/- 0.005 Gy-2, and 51% respectively) when compared with monolayer cultures in the same medium (alpha = 0.316 +/- 0.059 Gy-1, beta = 0.023 +/- 0.006 Gy-2 and SF2 = 50%). In the spheroid model, manipulating the cellular environment, i.e., with estrogen treatment, modulates sensitivity to ionizing radiation.

Local recurrences of soft tissue sarcomas in adults: a retrospective analysis of prognostic factors in 102 cases after surgery and radiation therapy

Between 1974 and 1990, 102 adult patients (age 18-86 years) with the diagnosis of a soft tissue sarcoma (STS) were treated with photons and/or electrons in combination with surgery. The total doses in the initial treatment volume (second order target volume) was 40-50 Gy. For the coning down volume (first order target volume) the median total dose was 59 Gy (range 45-72 Gy). A total of 18% (18/102) local failures was observed. In multivariate analysis, prognostic factors for the occurrence of a local failure were identified as follows: treatment of a primary or recurrent STS (P = 0.02), total dose (P = 0.025) and tumour grade (P = 0.05). Mode of surgery, tumour size (trunk versus extremity), pre- or postoperative radiotherapy, combined chemotherapy and tumour size (T1 versus T2) had no significant impact on the local relapse-free survival. These data give further evidence that combined surgery and radiotherapy is an effective modality in treatment of soft tissue sarcomas.

Radioresponsiveness of human glioma, sarcoma, and breast cancer spheroids depends on tumor differentiation

PURPOSE

Differences in the intrinsic radiosensitivity within and between different tumor classes have been noticed for human tumor cell lines using the clonogenic assay. By far, most of the cell lines studied up to now were derived from poorly differentiated tumors. In this study, the influence of tumor differentiation on the radiation doses necessary to control 50% of small oxic spheroids (SCD50) was determined. Evidence of a distinct dependence of radioresponsiveness on tumor progression provides a background for an investigation of the underlying mechanisms.

METHODS AND MATERIALS

Spheroids were aggregated from 1000-1500 cells in agarose coated 24 multi-well plates. Their diameters ranged from 156 to 405 microns, depending on the cell line. Spheroids were irradiated with graded 60Co single doses using spheroid control as end point and a minimum follow-up period of 3 months.

RESULTS

Cell lines from three low grade gliomas and 10 malignant gliomas were studied in the spheroid control assay. The group mean SCD50 values were 6.1 +/- 1.6 Gy and 13.1 +/- 3.3 Gy, respectively. Four cell lines from grade 2 soft tissue sarcomas had a mean SCD50 value of 6.2 +/- 0.5 Gy and one undifferentiated sarcoma line of 11.0 Gy. Three well-differentiated breast cancer lines expressed the cell adhesion molecule E-cadherin, had an epithelioid morphology in monolayer culture, were estrogen receptor positive or contact inhibited in multicellular spheroids. Two undifferentiated breast cancer lines had a fibroblastoid morphology and were marker negative. The mean SCD50 value of the former was 10.5 +/- 1.0 Gy while that of the undifferentiated lines was 14.8 +/- 2.8 Gy. Analysis of variance revealed a significant effect of the tumor type as well as the grade of dedifferentiation on the SCD50 after irradiation with one fraction or 2Gy/fraction. The surviving fractions at 2 Gy (SF2), obtained from the spheroid control rates after different fractionation schedules by approximation of the linear quadratic model assuming Poisson statistics were significantly dependent on tumor type (p = 0.001, ANOVA F-test) but not on tumor differentiation (p = 0.27). The alpha/beta ratios did not depend on tumor type (p = 0.08, ANOVA F-Test) but significantly increased with the grade of tumor cell dedifferentiation (p = 0.03).

CONCLUSION

The spheroid model is suitable for measuring the radioresponsiveness of differentiated cell lines with very low colony forming efficiencies. Tumor cell differentiation is an important factor for the radioresponsiveness and recovery capacity of human tumor cells.

Spheroid control of malignant glioma cell lines after fractionated irradiation: relation to the surviving fractions at 2 Gy and colony forming efficiencies in a soft agar clonogenic assay

Spheroid control doses (SCD50) were determined for ten human glioma lines after fractionated irradiation under oxic conditions. In addition, SF2 values and colony forming efficiencies (CFE) were measured in a soft agarose clonogenic assay. A significant relationship existed between the SCD50 values and the SF2-CFE data pairs (p = 0.01) but the SCD50 values were higher than expected from the SF2 and CFE values. This comparison shows the influence of environmental factors (different in both model systems) on reproductive tumour cell death after irradiation.

The TCD50 and regrowth delay assay in human tumor xenografts: differences and implications

The response to irradiation of five human xenograft cell lines--a malignant paraganglioma, a neurogenic sarcoma, a malignant histiocytoma, a primary lymphoma of the brain, and a squamous cell carcinoma--were tested in nude mice. All mice underwent 5 Gy whole body irradiation prior to xenotransplantation to minimize the residual immune response. The subcutaneous tumors were irradiated at a tumor volume of 120mm3 under acutely hypoxic conditions with single doses between 8 Gy and 80 Gy depending on the expected radiation sensitivity of the tumor line. Endpoints of the study were the tumor control dose 50% (TCD50) and the regrowth delay endpoints growth delay, specific growth delay, and the tumor bed effect corrected specific growth delay. Specific growth delay and corrected specific growth delay at 76% of the TCD50 was used in order to compare the data to previously published data from spheroids. The lowest TCD50 was found in the lymphoma with 24.9 Gy, whereas the TCD50 of the soft tissue sarcomas and the squamous cell carcinoma ranged from 57.8 Gy to 65.6 Gy. The isoeffective dose levels for the induction of 30 days growth delay, a specific growth delay of 3, and a corrected specific growth delay of 3 ranged from 15.5 Gy (ECL1) to 37.1 Gy (FADU), from 7.2 Gy (ENE2) to 45.6 Gy (EPG1) and from 9.2 Gy (ENE2) to 37.6 Gy (EPG1), respectively. The corrected specific growth delay at 76% of the TCD50 was correlated with the number of tumor rescue units per 100 cells in spheroids, which was available for three tumor lines, and with the tumor doubling time in xenografts (n = 5). The TCD50 values corresponded better to the clinical experience than the regrowth delay data. There was no correlation between TCD50 and any of the regrowth delay endpoints. This missing correlation was most likely a result of large differences in the number of tumor rescue units in human xenografts of the same size.