The effects of anticancer treatments on cell heterogeneity and their proliferative potential play an important role in tumor persistence and metastasis. However, little is known about de-polyploidization, cell fate, and physiologic stemness of the resulting cell populations. Here, we describe a distinctive cell type termed "pregnant" P1 cells found within chemotherapy-refractory ovarian tumors, which generate and gestate daughter generation Gn cells intracytoplasmically. Release of Gn cells occurred by ejection through crevices in the P1 cell membrane by body contractions or using a funiculus-like structure. These events characterized a not yet described mechanism of cell segregation. Maternal P1 cells were principally capable of surviving parturition events and continued to breed and nurture Gn progenies. In addition, P1 cells were competent to horizontally transmit offspring Gn cells into other specific proximal cells, injecting them to receptor R1 cells via cell–cell tunneling. This process represents a new mechanism used by tumor cells to invade surrounding tissues and ensure life cycles. In contrast to the pregnant P1 cells with low expression of stem cell markers despite their physiologic stemness, the first offspring generations of daughter G1 cells expressed high levels of ovarian cancer stem cell markers. Furthermore, both P1 and Gn cells overexpressed multiple human endogenous retroviral envelope proteins. Moreover, programmed death-ligand 1 and the immunosuppressive domain of the retroviral envelope proteins were also overexpressed in P1 cells, suggesting effective protection against the host immune system. Together, our data suggest that P1 oncogenerative cancer cells exhibit a not yet described cell biological mechanism of persistence and transmission of malignant cells in patients with advanced cancers. Significance: P1 oncogenerative cell entities express low levels of CSC markers, which are characteristic of their histological origin. Cancer Res; 78(9); 2318–31. ©2018 AACR.

Endoretroviruses account for circa 8 % of all transposable elements found in the genome of humans and other animals. They represent a genetic footprint of ancestral germ-cell infections of exoviruses that is transmittable to the progeny by Mendelian segregation. Traces of human endogenous retroviruses are physiologically expressed in ovarial, testicular and placental tissues as well as in stem cells. In addition, a number of these fossil viral elements have also been related to carcinogenesis. However, a relation between endoretroviruses expression and chemoresistance has not been reported yet. Twenty colorectal carcinoma patient samples were scrutinized for HERV-WE1 and HERV-FRD1 endoretroviruses using immunohistochemical approaches. In order to search for differential expression of these elements in chemotherapy refractory cells, a resistant HCT8 colon carcinoma subline was developed by serial etoposide exposure. Endoretroviral elements were detected by immunocytochemical staining, qPCR and ELISA. IC50-values of antiviral and cytostatic drugs in HCT8 cells were determined by MTT proliferation assay. The antivirals-cytostatics interaction was evaluated by the isobologram method. In this work, we show for the first time that HERV-WE1, HERV-FRD1, HERV-31, and HERV-V1 are a) simultaneously expressed in treatment-naïve colon carcinoma cells and b) upregulated after cytostatic exposure, suggesting that these retroviral elements are intimately related to chemotherapy resistance. We found a number of antiviral drugs to have cytotoxic activity and the ability to force the downregulation of HERV proteins in vitro. We also demonstrate that the use of different antiviral compounds alone or in combination with anticancer agents results in a synergistic antiproliferative effect and downregulation of different endoretroviral elements in highly chemotherapy-resistant colorectal tumor cells. Enhanced HERV-expression is associated with chemoresistance in colon carcinomas which can be overcome by antiviral drugs alone or in combination with anticancer drugs. Therefore, the introduction of antiviral compounds to the current chemotherapy regimens potentially improves patient outcomes.

Background/Aim: Pressurized intraperitoneal aerosol chemotherapy (PIPAC) is a novel clinical approach to the treatment of peritoneal carcinomatosis. A well-established, not anatomic ex vivo PIPAC model was used to investigate the influence of changes in internal pressure, distance of the Micropump^© (MIP) to the distributing surface and the drug concentration on the penetration depth of doxorubicin in the target tissue. Materials and Methods: Doxorubicin was aerosolized in an ex vivo PIPAC model using a hermetic container system mimicking the abdominal cavity. Fresh post-mortem swine peritoneum was cut into proportional samples. Tissue specimens were spatially placed at 4 different spots within the box: P₁, on the distributing surface of the box, directly opposite to MIP; P₂, on the side wall of the box; P₃, on the ceiling of the box; P₄, on the distributing surface with a partial cover. Impact of changes in the following parameters were analyzed and compared with clinically established values (CEVs) at our center: pressure (CEV=12 mmHg), distance of the MIP from the distributing surface (CEV=8 cm) and doxorubicin concentration (CEV=3 mg/50 ml). In-tissue doxorubicin penetration depth was measured using fluorescence microscopy on frozen thin sections. Results: Tissue positioning in the box had a significant impact on drug penetration after PIPAC with CEV. Under CEV conditions, the highest drug penetration depth was observed in the tissue placed on the distributing surface directly opposite to the MIP (P₁: 351 μm, P₂: 77 μm, P₃: 66 μm, P₄: 34 μm). A closer positioning of the MIP lead to a significantly higher mean depth penetration of doxorubicin in the P1 in contrast to other samples in which a reduced drug penetration was observed (1 cm vs. 8 cm distance from MIP to the distributing surface, P₁ at 1 cm: 469 μm vs. P₁ at 8 cm: 351 μm, p<0.0001; P₂ at 1 cm: 25 μm vs. P₂ at 8 cm: 77 μm, p<0.0001; P₃ at 1 cm: 21 μm vs. P₃ at 8 cm: 66 μm, p<0.001; P₄ at 1 cm: 13 μm vs. P₄ at 8 cm: 39 μm, p=0.021). Higher doxorubicin concentrations led to a highly significant increase of drug penetration in P1 (1 cm vs. 8 cm, p<0.0001), but only a little significant increase in other samples. An increase of internal pressure did not show a significant increase in penetration depth of doxorubicin. Conclusion: Our ex vivo data suggest that a higher pressure does not increase the penetration deepness of doxorubicin. Higher drug dosage and a closer positioning of the MIP toward the target lead to a higher penetration of doxorubicin within the samples. A more homogeneous penetration within all targets cannot be achieved by changing drug concentration, position of the nozzle or pressure increase.