INDUCED POLYPLOIDY AND SORTING OF DAMAGED DNA BY MICRONUCLEATION IN RADIORESISTANT RAT LIVER EPITHELIAL STEM-LIKE CELLS EXPOSED TO X-RAYS

OBJECTIVE

Rat liver stem-like epithelial cells (WB-F344) that under certain conditions may differentiate into hepa- tocyte and biliary lineages were subjected to acute X-irradiation with the aim to examine cell cycle peculiarities dur- ing the course of survival.

MATERIALS AND METHODS

Suspensions of WB-F344 cells that grew as a monolayer and reached sub-confluence were irradiated with 1, 5, and 10 Gy of X-rays (2 Gy/min). As an intact control, sham-irradiated cells were used. After irra- diation, cells were plated into 25-cm2 tissue culture flasks to culture them for over several days without reaching contact inhibition. On days 1, 2, 3, and 5 post-irradiation, cells were harvested and examined for nuclear morpholo- gy and DNA ploidy by stoichiometric toluidine blue reaction and image cytometry. On days 7 and 9 post-irradiation, only heavily irradiated (10 Gy) cells were examined. Also, 10 Gy-irradiated cells were chosen for immunofluorescence staining to monitor persistence of DNA lesions (γ-H2AX), cell proliferation (Ki-67), and self-renewal factors charac- teristic for stem cells (OCT4 and NANOG).

RESULTS

Radioresistance of WB-F344 cells was evidenced by the findings that they do not undergo rapid and mas- sive cell death that in fact was weakly manifested as apoptotic even in heavily irradiated cells. Instead, there was cell cycle progression delay accompanied by polyploidization (via Ki-67-positive mitotic slippage or via impaired cytokinesis) and micronucleation in a dose-dependent manner, although micronucleation to some extent went ahead of polyploidization. Polyploid cells amenable for recovering from DNA damage can mitotically depolyploidize. Many micronuclei contained γ-H2AX clusters, suggesting isolation of severely damaged DNA fragments. Both factors, OCT4 and NANOG, were expressed in the intact control, but became enhanced after irradiation.

CONCLUSIONS

Although the fact of micronucleation is indicative of genotoxic effect, WB-F344 cells can probably escape cell death via sorting of damaged DNA by micronuclei. Induction of polyploidy in these cells can be adaptive to promote cell survival and tissue regeneration with possible involvement of self-renewal mechanism.

PROBING BREAST CANCER THERAPEUTIC RESPONSES BY DNA CONTENT PROFILING

Background. Discrepancies in the interpretation of breast cancer therapeutic responses still exist mainly because of lack of standardized assessment criteria and methods. Objective. DNA content profiling of cells in the affected (cancerous) tissue before and after neoadjuvant chemotherapy (NAC) was applied to facilitate interpretation of therapeutic responses. Methods. Both diagnostic biopsy and operation materials representing the tissue of primary tumors surgically removed after NAC were subjected to DNA image cytometry. Polyploidy and aneuploidy in DNA histograms were evaluated with a prognostic Auer typing. Stemline DNA index (DI) values and percentages of cells that polyploidize (>4.5C) were also determined. Immunofluorescence staining was applied to evaluate proliferation (Ki-67), invasiveness (CD44), and self-renewal factors characteristic for stem cells (SOX2 and NANOG). Results. DNA content profiles of 12 breast cancer cases, of which 7 were triple-negative, revealed the features of tumor non-responsiveness to NAC in 7 cases, of which 5 were triple-negative. Among non-responsive cases there were 3 cases that showed enhanced polyploidization, suggesting the negative NAC effect. Near-triploid (DI=1.26-1.74) triple-negative cases were determined as most resistant to NAC. Cycling near-triploid cells may contribute to the excessive numbers of >4.5C cells. Polyploid cells were positive for Ki-67, CD44, SOX2, and NANOG. Conclusions. DNA content profiling data provide additional helpful information for interpreting therapeutic responses in NAC-treated breast cancers. Polyploid tumor cells possessing stem cell features can be induced by NAC. Because NAC effects in some cases may be unfavorable, the use of the further treatment strategy should be carefully considered.

Abstract P3-03-17: Can polyploid tumor cells possessing stem cell features be induced in resistant breast carcinomas?

Cancer stem cells are believed to be responsible for radio- and chemoresistance of malignant tumors. In vitro studies demonstrate that ionizing radiation is capable of reprogramming cancer cells from non-stem state into stem state [1, 2]. Moreover, the embryonic stemness cassette was found to be expressed in tumor cells (including breast cancer cells) after they were polyploidized as a result of genotoxic stress [2, 3], thus prompting us to suppose that the polyploid cells and their descendants released by depolyploidization can possess stem cell characteristics. The aim of the current work is to test whether polyploid cells having stem cell features can be also induced in vivo, namely in locally advanced breast carcinomas as a result of neoadjuvant chemotherapy (NAC), assuming that this process is not autonomous, but rather stipulated by the tumor microenvironment.

The study population consisted of 30 breast cancer patients of age ranged from 31 to 75 y. o. diagnosed in the Latvian Oncology Center of the Riga East University Hospital between 2013 and 2015. The tissue specimens were collected after the patients' informed consent was obtained in accordance with the Ethics regulations. The clinico-pathologic information about these patients, including Ki-67 index and the status of ER, PR and HER2 receptors, was obtained from the aforementioned clinics. The majority of patients (n = 28) had locally advanced breast cancer, predominantly Stage III disease. Both diagnostic biopsy and operation material, such as primary tumors surgically removed after NAC using standard doses of paclitaxel and doxorubicin, were subjected to DNA content analysis with image cytometry. Ploidy-related parameters, such as DNA index and the percentage of cells exceeding 4.5c (presumably proliferating and polyploid cells), were determined. Immunofluorescence staining was applied to evaluate expression of such markers/factors as proliferation (Ki-67), stemness (SOX2 and NANOG) and invasiveness (CD44).

At the time of diagnosis, 14 patients had primary tumors possessing near-triploid clones, and these cases in comparison with 16 other cases comprised of near-euploid clones had 4.5-fold increase of percentages of cells exceeding the ploidy of 4.5c (p < 0.05) and 1.3-fold increase of percentages of cells positive for Ki-67 (p > 0.05). Of 10 cases diagnosed as “triple-negative”, 6 were near-triploid. Among those cases that showed the resistance to NAC (grades 1 and 2 by Miller-Payne histopathologic scoring), 67% were near-triploid. Polyploidization, which in some resistant cases is gained by NAC, was likely to be attributed to near-triploid clones. Notably, polyploid cells were positive for Ki-67, SOX2, NANOG, and CD44. Thus, these non-quiescent polyploid cells can possess the invasiveness and self-renewal features that were also seen in descendants after depolyploidization. Perhaps, reversible polyploidy plays a definite role in gaining the resistance of tumor cells to chemo- and radiotherapy in vivo.

1. Ghisolfi L. et al. PLoS ONE 2012; 7: e43628.

2. Lagadec C. et al. Stem Cells 2012; 30: 833-44.

3. Salmina K. et al. Exp Cell Res 2010; 316: 2099-112.

Citation Format: Gerashchenko BI, Salmina K, Eglitis J, Erenpreisa J. Can polyploid tumor cells possessing stem cell features be induced in resistant breast carcinomas? [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P3-03-17.

Disentangling the aneuploidy and senescence paradoxes: a study of triploid breast cancers non-responsive to neoadjuvant therapy

Aneuploid cells should have a reduced proliferation rate due to difficulty in proceeding through mitosis. However, contrary to this, high aneuploidy is associated with aggressive tumour growth and poor survival prognosis, in particular in triploid breast cancer. A further paradox revolves around the observation that, while cell senescence should inhibit proliferation, the senescence marker p16INK4a correlates with poor treatment outcome in patients with a very aggressive triple-negative breast carcinoma (TNBC). In this study, we aim to pour light on the possible relationship of these conundrums with polyploidy of tumour cells. We performed detailed analysis of DNA histogram profiles in diagnostic core biopsies of 30 cases of operable breast cancer and found that near triploidy in TNBC and other forms correlated with weak or no response to neoadjuvant chemotherapy (NAC) as scored by Miller-Payne index. Polyploid cells in operation samples from tumours that were non-responsive to NAC treatment were Ki67 and CD44 positive. In addition, polyploid cells were positive for markers of embryonic stemness (OCT4, SOX2, NANOG) and senescence (p16INK4a). The relationship patterns between p16INK4a and NANOG were heterogeneous, with predominantly mutually exclusive expression but also synergistic and intermediate variants in the same samples. We conclude that the aneuploidy and senescence paradoxes can be explained by the mutual platform of polyploidy, conferring genomic and epigenetic instability as a survival advantage. Such cells are able to bypass aneuploidy restrictions of conventional mitosis and overcome the barrier of senescence by a shift to self-renewal, resulting in progression of cancer.