Computerized video time lapse study of cell cycle delay and arrest, mitotic catastrophe, apoptosis and clonogenic survival in irradiated 14-3-3sigma and CDKN1A (p21) knockout cell lines

Death through a tragedy: mitotic catastrophe

Mitotic catastrophe (MC) has long been considered as a mode of cell death that results from premature or inappropriate entry of cells into mitosis and can be caused by chemical or physical stresses. Whereas it initially was depicted as the main form of cell death induced by ionizing radiation, it is today known to be triggered also by treatment with agents influencing the stability of microtubule, various anticancer drugs and mitotic failure caused by defective cell cycle checkpoints. Although various descriptions explaining MC exist, there is still no general accepted definition of this phenomenon. Here, we present evidences indicating that death-associated MC is not a separate mode of cell death, rather a process ('prestage') preceding cell death, which can occur through necrosis or apoptosis. The final outcome of MC depends on the molecular profile of the cell.

Influence of the TP53 codon 72 polymorphism on the cellular responses to X-irradiation in fibroblasts from nonagenarians

In mice, genetic modification of the gene encoding p53 affects both cancer incidence and longevity. In humans, we recently found that a TP53 codon 72 Arginine (Arg) to Proline (Pro) polymorphism affected both cancer incidence and longevity as well. The TP53 codon 72 polymorphism has previously been shown to influence the apoptotic potential of human cells in response to oxidative stress. Here, we studied the influence of this polymorphism on the cellular responses to X-irradiation of fibroblasts obtained from nonagenarians. We found that the average clonogenic survival after X-irradiation was similar for the three TP53 codon 72 genotype groups. As described before, X-irradiation did not induce an appreciable degree of apoptosis in human fibroblasts. However, percentages of senescence-associated (SA)-beta-galactosidase positive cells (p < 0.001), micronucleated cells (p < 0.001) and cells displaying abnormal nuclear morphologies (p < 0.001) significantly increased with the radiation dose. Compared to Arg/Arg fibroblasts, Pro/Pro fibroblasts exhibited higher irradiation dose-dependent increases in SA-beta-galactosidase positive cells (p(interaction) = 0.018), micronucleated cells (p(interaction) = 0.005) and cells displaying abnormal nuclear morphologies (p(interaction) = 0.029) at 3 days after irradiation. Possibly, these differences in cellular responses to stress between the TP53 codon 72 genotypes contribute to the differences in cancer incidence and longevity observed earlier for these genotypes.

DNA damage induces two distinct modes of cell death in ovarian carcinomas

Activation of p53 by cellular stress may lead to either cell cycle arrest or apoptotic cell death. Restrictions in a cell's ability to halt the cell cycle might, in turn, cause mitotic catastrophe, a delayed type of cell death with distinct morphological features. Here, we have investigated the contribution of p53 and caspase-2 to apoptotic cell death and mitotic catastrophe in cisplatin-treated ovarian carcinoma cell lines. We report that both functional p53 and caspase-2 were required for the apoptotic response, which was preceded by translocation of nuclear caspase-2 to the cytoplasm. In the absence of functional p53, cisplatin treatment resulted in caspase-2-independent mitotic catastrophe followed by necrosis. In these cells, apoptotic functions could be restored by transient expression of wt p53. Hence, p53 appeared to act as a switch between apoptosis and mitotic catastrophe followed by necrosis-like lysis in this experimental model. Further, we show that inhibition of Chk2, and/or 14-3-3sigma deficiency, sensitized cells to undergo mitotic catastrophe upon treatment with DNA-damaging agents. However, apoptotic cell death seemed to be the final outcome of this process. Thus, we hypothesize that the final mode of cell death triggered by DNA damage in ovarian carcinoma cells is determined by the profile of proteins involved in the regulation of the cell cycle, such as p53- and Chk2-related proteins.

Analysis of cell differentiation by division tracking cytometry

We propose a quantitative method to characterize growth and differentiation dynamics of multipotent cells from time series carboxyfluorescein diacetate, succinimidyl ester (CFDA-SE) division tracking data. The dynamics of cell proliferation and differentiation was measured by combining (CFDA-SE) division tracking with phenotypic analysis. We define division tracking population statistics such as precursor cell frequency, generation time and renewal rate that characterize growth of various phenotypes in a heterogeneous culture system. This method is illustrated by study of the divisional recruitment of cord blood CD34(+) cells by hematopoietic growth factors. The technical issue of assigning the correct generation number to cells was addressed by employing high-resolution division tracking methodology and daily histogram analysis. We also quantified division-tracking artifacts such as CFDA-SE degeneration and cellular auto-fluorescence. Mitotic activation of cord blood CD34(+) cells by cytokines commenced after 2 days of cytokine stimulation. Mean generation number increased linearly thereafter, and it was conclusively shown that CD34(+) cells cycle slower than CD34(-) cells. Generation times for CD34(+) and CD34(-) cells were 24.7 +/- 0.8 h and 15.1 +/- 0.9 h (+/-SD, n = 5), respectively. The 20-fold increase in CD34(+) cell numbers at Day 6 could be attributed to a high CD34(+) cell renewal rate (91% +/- 2% per division). Although cultures were initiated with highly purified CD34(+) cells (approximately 96%), CD34(-) numbers had expanded rapidly by Day 6. This rapid expansion could be explained by their short generation time as well as a small fraction of CD34(+) cells (approximately 5%) that differentiated into CD34(-) cells. Multitype division tracking provides a detailed analysis of multipotent cell differentiation dynamics.

Cancer: a matter of life cycle?

In the last decade, the concept of "cancer stem cells" has emerged, recognised by the fact that only a small fraction of tumour cells appears to retain the stem cell properties of self-renewal and unlimited proliferation. At the same time, it is well known that cancer is an age-related disease developing at the limit of proliferating cell senescence. The apparent need to link senescence and the capacity for self-renewal has lead some authors to suggest that cancers develop from amongst senescing stem cells. However, an alternative solution has recently been proffered by Sundaram M, Guernsey DL, Rajaraman MM, Rajaraman R [Neosis: a novel type of cell division in cancer. Cancer Biol Ther 2004;3:207-18], who suggest that stemness may be a transient, cyclic property afforded by de-polyploidisation of senescing cells which have undergone polyploidisation. In this mini-review, we attempt to reconcile both of these views by the idea that cycling polyploidy intermitting senescence and rejuvenation may be features of a life cycle analogous to the life cycles of certain unicellular organisms. Furthermore, we suggest that mitotic catastrophe may represent a mechanism through which the cell can switch from the usual mitotic cell-cycle to this evolutionarily conserved life cycle. Intriguingly, some most recent data suggest that cell senescence may be reversible and that stem cells are tolerant to polyploidy caused by genotoxic stress.

Radiobiology of systemic radiation therapy

Although systemic radionuclide therapy (SRT) is effective as a palliative therapy in patients with metastatic cancer, there has been limited success in expanding patterns of utilization and in bringing novel systemic radiotherapeutic agents to routine clinical use. Although there are many factors that contribute to this situation, we hypothesize that a better understanding of the radiobiology and mechanism of action of SRT will facilitate the development of future compounds and the future designs of prospective clinical trials. If these trials can be rationalized to the biological basis of the therapy, it is likely that the long-term outcome would be enhanced therapeutic efficacy. In this review, we provide perspectives of the current state of low-dose-rate (LDR) radiation research and offer linkages where appropriate with current clinical knowledge. These include the recently described phenomena of low-dose hyper-radiosensitivity-increased radioresistance (LDH-IRR), adaptive responses, and biological bystander effects. Each of these areas require a major reconsideration of existing models for radiation action and an understanding of how this knowledge will integrate into the evolution of clinical SRT practice. Validation of a role in vivo for both LDH-IRR and biological bystander effects in SRT would greatly impact the way we would assess therapeutic response to SRT, the design of clinical trials of novel SRT radiopharmaceuticals, and risk estimates for both therapeutic and diagnostic radiopharmaceuticals. We believe that the current state of research in LDR effects offers a major opportunity to the nuclear medicine community to address the basic science of clinical SRT practice, to use this new knowledge to expand the use and roles of SRT, and to facilitate the introduction of new therapeutic radiopharmaceuticals.

Lack of p53 function promotes radiation-induced mitotic catastrophe in mouse embryonic fibroblast cells

BACKGROUND

We have demonstrated that in some human cancer cells both chronic mild heat and ionizing radiation exposures induce a transient block in S and G2 phases of the cell cycle. During this delay, cyclin B1 protein accumulates to supranormal levels, cyclin B1-dependent kinase is activated, and abrogation of the G2/M checkpoint control occurs resulting in mitotic catastrophe (MC).

RESULTS

Using syngenic mouse embryonic fibroblasts (MEF) with wild-type or mutant p53, we now show that, while both cell lines exhibit delays in S/G2 phase post-irradiation, the mutant p53 cells show elevated levels of cyclin B1 followed by MC, while the wild-type p53 cells present both a lower accumulation of cyclin B1 and a lower frequency of MC.

CONCLUSION

These results are in line with studies reporting the role of p53 as a post-transcriptional regulator of cyclin B1 protein and confirm that dysregulation of cyclin B1 promote radiation-induced MC. These findings might be exploited to design strategies to augment the yield of MC in tumor cells that are resistant to radiation-induced apoptosis.

Induction of p21CIP/WAF-1 and G2 arrest by ionizing irradiation impedes caspase-3-mediated apoptosis in human carcinoma cells

There is an ongoing controversy regarding the relevance of apoptosis induction by ionizing irradiation as compared with other end points including transient or permanent cell cycle arrest of damaged cells. Here, we show that such permanent cell cycle arrest and apoptosis represent two sides of the same coin. MCF-7 cells fail to express procaspase-3, which results in resistance to apoptosis induced by anticancer drugs. Conversely, restoration of procaspase-3 sensitizes MCF-7 cells to chemotherapeutics including epirubicine, etoposide and taxol. In contrast, irradiation does not trigger apoptotic cell death but results in prolonged arrest in the G2 phase of the cell division cycle regardless of procaspase-3 expression. This suggested that the propensity of MCF-7 cells to arrest at the G2 checkpoint results in resistance to apoptosis upon gamma-irradiation. This G2 arrest was associated with upregulation of p21CIP/WAF-1. Inhibition of DNA-damage-induced stress kinases and p21CIP/WAF-1 expression by caffeine abrogated G2 arrest and induced apoptosis of the irradiated cells in a caspase-3-dependent manner. Inhibition of cell cycle progression by adenoviral expression of the cyclin dependent kinase inhibitor p21CIP/WAF-1 prevented apoptosis upon caffeine treatment indicating that cell cycle progression, that is, G2-release, is required for induction of apoptosis. Likewise, cells homozygously deleted for p21CIP/WAF-1 (HCT116 p21-/-) display enhanced irradiation-induced apoptosis via a caspase-3-dependent mechanism. These data indicate that the disruption of G2 checkpoint control overcomes cell cycle arrest and resistance to gamma-irradiation-induced cell death. Thus, DNA damage may trigger a permanent G2 arrest as an initial inactivation step of tumor cells where the phenomenon of apoptosis is hidden unless cell cycle arrest is overcome. The efficient induction of apoptosis upon G2 release thereby depends on the propensity to activate the key executioner caspase-3. This finding is of crucial importance for the understanding of molecular steps underlying the efficacy of ionizing radiation to delete tumor cells.

Counting heads in the war against cancer: defining the role of annexin A5 imaging in cancer treatment and surveillance

The unveiling of the heterogeneous nature of cell death modes has compromised the long-lived consensus that cancer treatment typically kills cancer cells through apoptosis. Moreover, it implies that measures of apoptosis may be misleading indicators of treatment efficacy. Simultaneously, it has become clear that phosphatidylserine exposition, traditionally considered a hallmark of apoptosis, is also associated with most other cell death programs, rendering phosphatidylserine an attractive target for overall cell death imaging. Annexin A5 binds with strong affinity to phosphatidylserine and hence offers an interesting opportunity for visualization of aggregate cell death, thus providing a fit benchmark for in vivo monitoring of anticancer treatment. This might be of significant value for pharmacologic therapy development as well as clinical monitoring of treatment success.

Mcl-1, vascular endothelial growth factor-R2, and 14-3-3sigma expression might predict primary response against radiotherapy and chemotherapy in patients with locally advanced squamous cell carcinomas of the head and neck

PURPOSE

This study was done to explore whether the expression of a selected set of proteins could predict primary response to radiotherapy or concomitant radiotherapy and chemotherapy in patients with advanced head and neck cancer.

EXPERIMENTAL DESIGN

Forty-three pretreatment tumor biopsies were taken during diagnostic panendoscopy and examined for Mcl-1, vascular endothelial growth factor (VEGF)-R2, CD9, and 14-3-3sigma expression by immunohistochemistry. Forty-three patients underwent primary radiotherapy, of which, 29 patients received concomitant chemotherapy (low dose daily cisplatin, mitomycin C bolus). The primary end-point was locoregional tumor control 6 months after completion of radiotherapy. Mcl-1, VEGF-R2, CD9, and 14-3-3sigma expression were correlated with patients' primary response to radiotherapy and chemotherapy and with established clinicopathologic variables.

RESULTS

Thirty complete and 13 partial responses were observed in our patient group. High expression levels of Mcl-1 (P=0.021), VEGF-R2 (P=0.032), and 14-3-3sigma (P=0.013), but not of CD9, in tumor biopsies was correlated with complete response. Overexpression of at least two of the three aforementioned proteins in pretreatment biopsies predicted-with a likelihood of 80%-whether a patient would achieve complete response to radiotherapy and chemotherapy. However, if only one of these proteins is overexpressed, there is a likelihood of 84.6% that this patient would not completely respond to therapy.

CONCLUSION

Determining the expression levels of Mcl-1, VEGF-R2, and 14-3-3sigma may be helpful in predicting the early clinical response in head and neck tumor patients receiving primary radiotherapy and chemotherapy and may further allow a pretherapeutic selection of patients.

Cdc2 and Cdk2 play critical roles in low dose doxorubicin-induced cell death through mitotic catastrophe but not in high dose doxorubicin-induced apoptosis

In Huh-7 hepatoma cells, low dose (LD) doxorubicin treatment induces cell death through mitotic catastrophe accompanying the formation of large cells with multiple micronuclei, whereas high dose (HD) doxorubicin induces apoptosis. In this study, we investigated the role of Cdc2 and Cdk2 kinase in the regulation of the two modes of cell death induced by doxorubicin. During HD doxorubicin-induced apoptosis, the histone H1-associated activities of Cdc2 and Cdk2 both progressively declined in parallel with reductions in cyclin A and cyclin B protein levels. In contrast, during LD doxorubicin-induced cell death through mitotic catastrophe, the Cdc2 and Cdk2 kinases were transiently activated 1 day post-treatment, with similar changes seen in the protein levels of cyclin A, cyclin B, and Cdc2. Treatment with roscovitine, a specific inhibitor of Cdc2 and Cdk2, significantly blocked LD doxorubicin-induced mitotic catastrophe and cell death, but did not affect HD doxorubicin-induced apoptosis in Huh-7, SNU-398, and SNU-449 hepatoma cell lines. Our results demonstrate that differential regulation of Cdc2 and Cdk2 activity by different doses of doxorubicin may contribute to the induction of two distinct modes of cell death in hepatoma cells, either apoptosis or cell death through mitotic catastrophe.

Two distinct modes of cell death induced by doxorubicin: apoptosis and cell death through mitotic catastrophe accompanied by senescence-like phenotype

Chronic exposure of many human hepatoma cell lines to a low dose (LD) of doxorubicin induced a senescence-like phenotype (SLP) accompanied by enlargement of cells and increased senescence-associated beta-galactosidase activity. LD doxorubicin-induced SLP was preceded by multinucleation and downregulation of multiple proteins with mitotic checkpoint function, including CENP-A, Mad2, BubR1, and Chk1. LD doxorubicin-treated cells eventually underwent cell death through mitotic catastrophe. When we investigated whether LD doxorubicin-induced cell death shares biochemical characteristics with high dose (HD) doxorubicin-induced apoptosis in Huh-7 cells, we observed that externalization of phosphatidyl serine and release of mitochondrial cytochrome c into the cytosol was associated with both types of cell death. However, propidium iodide exclusion assays showed that membrane integrity was lost in the initial phase of LD doxorubicin-induced cell death through mitotic catastrophe, whereas it was lost during the late phase of HD doxorubicin-induced apoptosis. Furthermore, HD doxorubicin-induced apoptosis but not LD doxorubicin-induced mitotic catastrophe led to transient activation of NF-kappaB and strong, sustained activations of p38, c-Jun N-terminal kinase, and caspases. Collectively, these results indicate that different doses of doxorubicin activate different regulatory mechanisms to induce either apoptosis or cell death through mitotic catastrophe.

The role of apoptosis in cancer development and treatment response

The inactivation of programmed cell death, or apoptosis, is central to the development of cancer. This disabling of apoptotic responses might be a major contributor both to treatment resistance and to the observation that, in many tumours, apoptosis is not the main mechanism for the death of cancer cells in response to common treatment regimens. Importantly, this suggests that other modes of cell death are involved in the response to therapy.