Fibroblasts from Li-Fraumeni patients are resistant to low dose-rate irradiation

TP53 oncomorphic mutations predict resistance to platinum‑ and taxane‑based standard chemotherapy in patients diagnosed with advanced serous ovarian carcinoma

Individual mutations in the tumor suppressor TP53 alter p53 protein function. Some mutations create a non-functional protein, whereas others confer oncogenic activity, which we term ‘oncomorphic’. Since mutations in TP53 occur in nearly all ovarian tumors, the objective of this study was to determine the relationship of oncomorphic TP53 mutations with patient outcomes in advanced serous ovarian cancer patients. Clinical and molecular data from 264 high-grade serous ovarian cancer patients uniformly treated with standard platinum- and taxane-based adjuvant chemotherapy were downloaded from The Cancer Genome Atlas (TCGA) portal. Additionally, patient samples were obtained from the University of Iowa and individual mutations were analyzed in ovarian cancer cell lines. Mutations in the TP53 were annotated and categorized as oncomorphic, loss of function (LOF), or unclassified. Associations between mutation types, chemoresistance, recurrence, and progression-free survival (PFS) were calculated. Oncomorphic TP53 mutations were present in 21.3% of ovarian cancers in the TCGA dataset. Patients with oncomorphic TP53 mutations demonstrated significantly worse PFS, a 60% higher risk of recurrence (HR=1.60, 95% confidence intervals 1.09, 2.33, p=0.015), and higher rates of platinum resistance (χ² test p=0.0024) when compared with single nucleotide mutations not categorized as oncomorphic. Furthermore, tumors containing oncomorphic TP53 mutations displayed unique protein expression profiles, and some mutations conferred increased clonogenic capacity in ovarian cancer cell models. Our study reveals that oncomorphic TP53 mutations are associated with worse patient outcome. These data suggest that future studies should take into consideration the functional consequences of TP53 mutations when determining treatment options.

Oncomorphic TP53 Mutations in Gynecologic Cancers Lose the Normal Protein:Protein Interactions with the microRNA Microprocessing Complex

Mutations in the tumor suppressor TP53 occur in almost all advanced ovarian cancers and in many advanced serous endometrial cancers. Mutations in TP53 can alter the function of the p53 protein, and some mutations result in a mutated protein with oncogenic activity. Previously referred to as gain of function (GOF) p53 proteins, we now term these “oncomorphic” mutations to better describe their function as oncogenes. We reviewed the data from The Cancer Genome Atlas (TCGA) and demonstrate that of the patients diagnosed with endometrial cancer that harbor TP53 mutations, approximately 30% of these mutations are oncomorphic. In ovarian cancer, approximately 20% are oncomorphic. The wild type (WT) p53 protein transactivates genes and micro- RNAs (miRNAs) necessary in the response to cellular stress, which turn off growth and induce apoptosis. In addition to direct transcriptional activation, WT p53 also acts through protein:protein interactions with Drosha and the miRNA processing complex to mediate rapid, enhanced processing of a subset of anti-growth miRNAs. We validated the interaction of WT p53 with the Drosha complex in the cell line UCI-107. We observed that miRNAs that inhibit the expression of oncogenes were induced. Specifically, some miRNAs were induced very rapidly over minutes, consistent with enhanced processing, while others required hours, consistent with transcriptional activation. In contrast, the most common oncomorphic TP53 mutations failed to interact with the Drosha complex and lost the ability to rapidly induce the miRNAs which inhibit oncogene expression. These studies highlight one mechanism underlying the oncomorphic properties of specific TP53 mutations: loss of the enhanced processing of anti-proliferative miRNAs.

Biochemical and imaging surveillance in germline TP53 mutation carriers with Li-Fraumeni syndrome: a prospective observational study

BACKGROUND

Individuals with Li-Fraumeni syndrome have a high lifetime risk of developing cancer. We assessed the feasibility and potential clinical effect of a comprehensive surveillance protocol in asymptomatic TP53 mutation carriers in families with this syndrome.

METHODS

We implemented a clinical surveillance protocol, using frequent biochemical and imaging studies, for asymptomatic TP53 mutation carriers on Jan 1, 2004, and did a prospective observational study of members of eight families with Li-Fraumeni syndrome who either chose to undergo surveillance or chose not to undergo surveillance. The primary outcome measure was detection of new cancers. The secondary outcome measure was overall survival.

FINDINGS

As of Nov 1, 2010, 33 TP53 mutation carriers were identified, 18 of whom underwent surveillance. The surveillance protocol detected ten asymptomatic tumours in seven patients, including small, high-grade tumours and low-grade or premalignant tumours. All seven mutation carriers were alive after a median follow-up of 24 months (IQR 22-65 months). 12 high-grade, high-stage tumours developed in 10 individuals in the non-surveillance group, two of whom (20%) were alive at the end of follow-up (p=0·0417 for comparison with survival in the surveillance group). 3-year overall survival was 100% in the surveillance group and 21% (95% CI 4-48%) in the non-surveillance group (p=0·0155).

INTERPRETATION

Our findings show the feasibility of a clinical surveillance protocol for the detection of asymptomatic neoplasms in individuals with germline TP53 mutations. This strategy offers a management option for affected individuals, and its benefits lend support to the use of early genetic testing of at-risk individuals and families.

FUNDING

Canadian Cancer Society Research Institute, Canadian Institutes of Health Research, SickKids Foundation, and Soccer for Hope.

Evaluation of the molecular mechanisms involved in the gain of function of a Li-Fraumeni TP53 mutation

The TP53 tumor suppressor gene is the most frequent target for genetic alterations in human cancer. TP53 gene alterations may result in the gain of oncogenic functions such as neoangiogenesis and resistance to therapy. The TP53 germ line mutation c.659A>C (p.Y220S) was identified in stored DNA from related patients with Li-Fraumeni syndrome (LFS) who died after developing clinically aggressive tumors. All of the patients were treated with protocols that included doxorubicin hydrochloride (DX) as a pivotal drug. To define the in vitro mutational phenotype of this germ line mutation, we used murine fibroblasts explanted from wild-type (wt) and p53 knockout (KO) mice from the same littermate. p53Y220S and p53R175H fibroblasts, obtained from p53KO fibroblasts transfected with expression vectors encoding the human Y220S and R175H p53 mutants, respectively, exhibited resistance to DX treatment. Moreover, p53Y220S fibroblasts exhibited angiogenetic properties, and after DX treatment, p53Y220S failed to translocate into the nucleus and showed an increase in its cytosolic levels. DX treatment does not influence p53 distribution within the nuclear and cytosolic compartments in p53R175H fibroblasts. Peroxiredoxin II (Prx II), a protein that is involved in eliminating reactive oxygen species (ROS), showed increased expression intensity in p53Y220S fibroblasts after DX treatment, as observed by two-dimensional electrophoresis analysis. Moreover, Thioredoxin (Trx), a protein that cooperates with Prx II, is overexpressed in p53Y220S mutants under basal conditions. These data suggest a relationship between the presence of the p53Y220S mutation and enhanced levels of Prx II and Trx in mutant fibroblasts. Since one of the mechanisms of the DX antitumor effect has been ascribed to production of ROS, future studies will evaluate the involvement of PrxII and Trx in the chemoresistance of p53Y220S fibroblasts to DX.

Malignant transformation and new primary tumours after therapeutic radiation for benign disease: substantial risks in certain tumour prone syndromes

In recent years the use of radiation treatment for benign tumours has increased with the advent of stereotactic delivery and, in particular, single high dose gamma knife therapy. This has been particularly true for benign CNS (central nervous system) tumours such as vestibular schwannoma, meningioma, pituitary adenoma, and haemangioblastoma. While short term follow up in patients with isolated tumours suggests this treatment is safe, there are particular concerns regarding its use in childhood and in tumour predisposing syndromes. We have reviewed the use of radiation treatment in these contexts with particular regard to malignant transformation and new tumour induction. This review indicates that much more caution is warranted regarding the use of radiation treatment for benign tumours in childhood and in tumour prone conditions such as the neurofibromatoses.

Two metachronous tumors in the radiotherapy fields of a patient with Li-Fraumeni syndrome

A woman with a family history of brain tumors in her daughter and sister presented with a breast cancer. She subsequently developed two metachronous primary tumors: a small-cell lung cancer and a colon carcinoma. These tumors arose within the internal mammary radiotherapy field and within the field irradiated for ovariolysis. The p53 gene was analyzed in whole blood lymphocytes using a functional assay developed in yeast Saccharomyces cerevisiae, which tests the transcriptional competence of p53. DNA from the colon cancer cells was analyzed by polymerase chain reaction and sequencing. The patient had a germline-inactivating p53 mutation, confirming the diagnosis of Li-Fraumeni syndrome (LFS). The colon tumor and the lung tumor both conserved the mutant p53 allele but had lost the wild-type allele. This observation and the experimental data suggest an abnormal sensitivity of LFS patients to radiogenic carcinogenesis. The indications and extent of radiotherapy in patients with a clinical or molecular diagnosis of LFS should be discussed individually and should take into account the risk of secondary neoplasms arising in the radiation fields.

Genomic instability: potential contributions to tumour and normal tissue response, and second tumours, after radiotherapy

PURPOSE

Induced genomic instability generally refers to a type of damage which is transmissible down cell generations, and which results in a persistently enhanced frequency of de novo mutations, chromosomal abnormalities or lethality in a significant fraction of the descendant cell population. The potential contribution of induced genomic instability to tumour and normal tissue response, and second tumours, after radiotherapy, is explored.

RESULTS

The phenomenon of spontaneous genomic instability is well known in some rare genetic diseases (e.g. Gorlin's syndrome), and there is evidence in such cases that it can lead to a greater propensity for carcinogenesis (with shortened latency) which is enhanced after irradiation. It is unclear what role induced genomic instability plays in the response of normal individuals, but persistent chromosomal instability has been detected in vivo in lymphocytes and keratinocytes from irradiated normal individuals. Such induced genomic instability might play some role in tumour response in a subset of tumours with specific defects in damage response genes, but again its contribution to radiocurability in the majority of cancer patients is unclear. In normal tissues, genomic instability induced in wild-type cells leading to delayed cell death might contribute to more severe or prolonged early reactions as a consequence of increased cell loss, a longer time required for recovery, and greater residual injury. In tumours, induced genomic instability reflected in delayed reductions in clonogenic capacity might contribute to the radiosensitivity of primary tumours, and also to a lower incidence, longer latency and slower growth rate of recurrences and metastases.

CONCLUSIONS

The evidence which is reviewed shows that there is little information at present to support these propositions, but what exists is consistent with their expectations. Also, it is not yet clear to what extent mutations associated with genomic instability, particularly gene polymorphisms, or other low penetrant gene mutations, contribute to the recognized spectrum of normal tissue radiosensitivity amongst cancer patients, or in the general population. Tests for such genetic modifications may help in the search for more accurate prognostic markers of response, which hopefully could be used in addition to other strategies to further improve the outcome for cancer patients given radiotherapy.

Normal tissue radiobiology: from the laboratory to the clinic

This manuscript is in four parts, presenting the four talks given in a symposium on normal tissue radiobiology. The first part addresses the general concept of the role of parenchymal cell radiosensitivity vs. other factors, highlighting research over the last decade that has altered our understanding of factors underlying normal tissue response. The other three parts expand on specific themes raised in the first part dealing in particular with (1) modifications of fibroblast response to irradiation in relation to the induction of tissue fibrosis, (2) the use of the linear-quadratic equation to model the potential benefits of using different means (both physical and biologic) of modifying normal tissue response, and (3) the specific role of the growth factor TFG-beta1 in normal tissue response to irradiation. The symposium highlights the complexities of the radiobiology of late normal tissue responses, yet provides evidence and ideas about how the clinical problem of such responses may be modified or alleviated.

Inverse radiation dose-rate effects on somatic and germ-line mutations and DNA damage rates

The mutagenic effect of low linear energy transfer ionizing radiation is reduced for a given dose as the dose rate (DR) is reduced to a low level, a phenomenon known as the direct DR effect. Our reanalysis of published data shows that for both somatic and germ-line mutations there is an opposite, inverse DR effect, with reduction from low to very low DR, the overall dependence of induced mutations being parabolically related to DR, with a minimum in the range of 0.1 to 1.0 cGy/min (rule 1). This general pattern can be attributed to an optimal induction of error-free DNA repair in a DR region of minimal mutability (MMDR region). The diminished activation of repair at very low DRs may reflect a low ratio of induced ("signal") to spontaneous background DNA damage ("noise"). Because two common DNA lesions, 8-oxoguanine and thymine glycol, were already known to activate repair in irradiated mammalian cells, we estimated how their rates of production are altered upon radiation exposure in the MMDR region. For these and other abundant lesions (abasic sites and single-strand breaks), the DNA damage rate increment in the MMDR region is in the range of 10% to 100% (rule 2). These estimates suggest a genetically programmed optimatization of response to radiation in the MMDR region.

The radiosensitivity of human fibroblast cell lines correlates with residual levels of DNA double-strand breaks

PURPOSE

To study the correlation of residual DNA double-strand breakage after irradiation and cellular radiosensitivity in cells showing marked differences in radiosensitivity.

MATERIALS AND METHODS

The levels of DNA double-strand breaks remaining at 4 h after irradiation were measured by graded-voltage gel electrophoresis in fibroblast cell strains derived from seven individuals either with normal radiosensitivity (n = 2), or with genetic abnormalities known to show increased (two ataxia telangiectasia, one scid) or possibly decreased (two Li-Fraumeni family members) sensitivity.

RESULTS

The slope of the dose-response curve for DNA breaks remaining unrepaired at 4 h showed a highly significant correlation with cellular radiosensitivity characterized by SF2, alpha, or D (r > or = 0.91, P < 0.001). Hence, this measure of genotoxic damage was predictive of radiation sensitivity for cells affected by a variety of mutations in different damage signalling/repair components.

DISCUSSION

This correlation confirms another published study and extends it to cell lines with other genetic defects. The technique may be useful in the development of rapid assays to predict the sensitivity of normal tissues in patients receiving radiotherapy.

Chromosome instability is a predominant trait of fibroblasts from Li-Fraumeni families

Previous work has indicated a role for p53 in cell cycle control, genomic stability and cellular responses to DNA-damaging agents. However, few data are available for human fibroblasts heterozygous for defined germline mutations in TP53. We report studies on 25 strains derived from 12 families with Li-Fraumeni syndrome (LFS) and 18 strains from normal volunteers. The families include three that are classical LFS families, but in whom no TP53 mutation has been found. In the families with mutations, increased longevity and resistance to low-dose-rate ionizing radiation showed a statistically significant association with the presence of TP53 mutations. However, not all heterozygotes had increased longevity or were radioresistant, and fibroblasts from cancer-affected members of LFS families without TP53 mutations showed no significant increase in either of these end points. In contrast, all mutation-carrying strains showed evidence of genomic instability, expressed as aneuploidy, and accumulated structural chromosome aberrations in up to 100% of cells, usually accompanied by loss of the wild-type TP53 allele, immediately before senescence. Levels of aneuploidy higher than in normal cells were also observed in fibroblasts from families without TP53 mutations, suggesting that chromosome instability is a major factor in determining the cancer proneness of these families.

Li-Fraumeni syndrome and the role of the p53 tumor suppressor gene in cancer susceptibility

Mutation of the tumor suppressor gene p53 is a molecular genetic event frequently observed in human cancer, and inactivating missense mutations usually are accompanied by the resultant overexpression of mutant p53 protein. In gynecologic cancers, p53 is also often altered; the frequency varies depending on types of cancers and where they develop. Further, human papillomavirus oncoproteins that inactivate p53 and Rb proteins play important roles in the development of several gynecologic cancers. Individuals who are heterozygous for germline mutations of the p53 gene are strongly predisposed to a variety of cancers. The identification of these individuals may have profound value in the future when therapies or chemopreventive agents specific for the p53 alteration are available. The role of p53 tumor suppressor gene in gynecologic cancers and heritable cancer susceptibility syndromes including Li-Fraumeni and Lynch II syndromes is an active and important area of study.

[Evaluation of cancer risk through genetic analysis?]

BACKGROUND

The recent literature of familial cancer, specifically related to germline mutations of RB1, p53, NF1, ATM, BRCA1, Mismatch repair genes and APC is reviewed.

RESULTS AND CONCLUSIONS

Germline mutations do not relate to an increased tumor risk of any single tissue, but instead to spectra of neoplastic diseases. The genetic background plays a major role in modifying the cancer risk. Therefore, mass screening for mutations of single genes seems to be without practical value. Only in combination with an adequate and informative family history can molecular genetic analysis significantly support the care for the individual. Comparison of the data of patients inheriting germline mutations and the experience from the corresponding "knockout" mouse demonstrate that only the p53 and APC knockout mice are useful models of human disease.