IL-6 mediates platinum-induced enrichment of ovarian cancer stem cells.

In high-grade serous ovarian cancer (OC), chemotherapy eliminates the majority of tumor cells, leaving behind residual tumors enriched in OC stem cells (OCSC). OCSC, defined as aldehyde dehydrogenase-positive (ALDH+), persist and contribute to tumor relapse. Inflammatory cytokine IL-6 is elevated in residual tumors after platinum treatment, and we hypothesized that IL-6 plays a critical role in platinum-induced OCSC enrichment. We demonstrate that IL-6 regulates stemness features of OCSC driven by ALDH1A1 expression and activity. We show that platinum induces IL-6 secretion by cancer-associated fibroblasts in the tumor microenvironment, promoting OCSC enrichment in residual tumors after chemotherapy. By activating STAT3 and upregulating ALDH1A1 expression, IL-6 treatment converted non-OCSC to OCSC. Having previously shown altered DNA methylation in OCSC, we show here that IL-6 induces DNA methyltransferase 1 (DNMT1) expression and the hypomethylating agent (HMA) guadecitabine induced differentiation of OCSC and reduced - but did not completely eradicate - OCSC. IL-6 neutralizing antibody (IL-6-Nab) combined with HMA fully eradicated OCSC, and the combination blocked IL-6/IL6-R/pSTAT3-mediated ALDH1A1 expression and eliminated OCSC in residual tumors that persisted in vivo after chemotherapy. We conclude that IL-6 signaling blockade combined with an HMA can eliminate OCSC after platinum treatment, supporting this strategy to prevent tumor recurrence after standard chemotherapy.

Expression of NF-kappaB and ERK following heavy ion irradiation.

Heavy ion irradiation of cells is known to increase cytotoxic, mutagenic, and carcinogenic effects. The increased biological effectiveness of these ions is as yet unexplained, except for the fact that, unlike gamma-radiation, they result in clustered damage. It is likely that the increased biological effectiveness is a consequence of altered signaling pattern, which in turn may be due to the difference in the nature of damage produced. Gamma irradiation has been known to activate both pro- and anti-apoptotic signaling pathways. Nuclear factor-kappaB (NF-kappaB) and extracellular signal regulated kinase (ERK) contribute to the survival of the irradiated cell. Moreover, NF-kappaB acts as a redox sensor. In the present study, we examined NF-kappaB and ERK as antiapoptotic factors that could lead to the inhibition of apoptosis and, consequently, to increased mutagenicity. Both these signaling factors show a fluctuation in their levels with time.

Fractionated and acute irradiation induced signaling in a murine tumor.

The effect of fractionated doses of Co(60) gamma-irradiation (2 Gy per fraction over 5 days), as is delivered in cancer radiotherapy, was compared with acute doses of 10 and 2 Gy, in a serially transplanted mouse fibrosarcoma grown in Swiss mice. The aspects that were studied included the three major mitogen-activated protein (MAP) kinases, namely p44 MAP kinase, p38 MAP kinase, and stress-activated protein (SAP) kinase, which are known to be involved in determining the cell fate following exposure to ionizing radiation. The response of dual specificity phosphatase PAC1 which is involved in the dephosphorylation of MAP kinases was also looked at. There were significant differences in the response to different dose regimens for all the factors studied. Fractionated irradiation elicited an adaptive response with a sustained activation over 7 days of prosurvival p44 MAP kinase which was balanced by the increased activation of proapoptotic p54 SAP kinase up to 1 day post-irradiation, whereas, phosphorylated p38 MAP kinase showed a decrease at most time points. PAC1 was induced following fractionated irradiation and may be acting as a feed back regulator of p44 MAP kinase. The activation of SAP kinase after fractionated irradiation may be a stress response, whereas, constitutively activated p44 MAP kinase may play an important role in the induction of radioresistance during fractionated radiotherapy of cancer and may serve as a promising target for specific inhibitors to enhance the efficacy of radiotherapy.

Radiation-induced bystander effect: activation of signaling molecules in K562 erythroleukemia cells.

Gap junction independent signaling mechanism was investigated using K562 human erythroleukemia cells. They were exposed to 2, 5, or 10 Gy of (60)Co gamma irradiation, the medium isolated 20 min post-irradiation and added to fresh cells. Evidence of radiation-induced bystander effect was observed wherein there was activation of p21, nuclear factor-kappaB (NF-kappaB), Bax, Bcl-2 and cleavage of poly(ADP-ribose) polymerase in bystander cells. The study implicates the involvement of signaling molecules released into the medium and factors like stable free radicals that are generated in the surrounding medium. The response elicited appears to be primarily via NF-kappaB and p21 activation.

MAP kinases: differential activation following in vivo and ex vivo irradiation.

Mitogen activated protein kinases (MAPK) play a critical role in controlling cell survival and repopulation following exposure to ionising radiation. Most investigations on these pathways have been done using cultured cells or by ex vivo treatments. The present study was carried out to determine whether the response of MAPKs in mouse lymphocytes differs following in vivo and ex vivo irradiation with 60Co gamma-rays. We observed that ex vivo treatment resulted in a very significant decrease in the activated p44/42 and p38 MAPK as compared to in vivo. However, stress activated protein kinase (SAPK) response showed no significant difference between in vivo and ex vivo treatments. These observations point towards the differences in response elicited when the treatment is given in vivo as compared to in vitro. Therefore the findings reported from in vitro or ex vivo treatments should be treated with caution especially if it has to be clinically applied.

Alteration in the expression of signaling parameters following carbon ion irradiation.

Ionizing radiation induces DNA damage, which generates a complex array of genotoxic responses. These responses depend on the type of DNA damage, which in turn can lead to unique cellular responses. High LET radiation results in clustered damages. This evokes specific signaling responses, which can be cytotoxic or cytoprotective in nature. In the present study the effect of carbon ion irradiation on p 44/42 MAPK and NF-kappaB, which are essentially survival factors, have been studied. Moreover, the effect of inhibition of DNA-PK, which is an important component of DNA repair mechanism, with wortmanin on these signaling factors has been studied. The expression of p 44/42 MAPK was different at 0.1 Gy and 1 Gy and wortmanin was found to inhibit its expression. NF-kappaB expression was higher at 1 Gy than at 0.1 Gy and its expression is unaffected by inhibition of DNA-PK. The notable findings of this study are that the responses to high and low dose of high LET radiation are essentially different and the 6 h time point post irradiation is crucial in deciding the response and needs further investigation.