Cyclin E–Associated Kinase Activity Predicts Response to Platinum-Based Chemotherapy

Abstract

Purpose: The role of cyclin E as a predictive marker of response to chemotherapy remains unknown. We have previously shown that deregulation of cyclin E in an ovarian tumor cell line model enhances cyclin E^associated kinase activity and sensitizes tumor cells to cisplatinum. We hypothesized that cyclin E deregulation would predict for responsiveness to platinum-based regimens in ovarian cancer patients. Experimental Design: Patients who met the following criteria were retrospectively identified from the institutional tumor bank records: (a) high-grade ovarian epithelial malignancy, (b) stage III/stage IV disease, (c) optimally debulked, (d) completed platinum-based therapy. Tumor samples were analyzed for cyclin E, p21, and p27 byWestern blot analysis and assessed for cyclin E^associated kinase activity. Results: Seventy-five patients, who met the study criteria, were identified. Cyclin E protein levels did not correlate with cyclin E^cdk2 kinase activity (Spearman's rho, 0.07; P = 0.58). Cyclin E^associated kinase activity was the only significant predictive marker for response to platinum-based therapy, with higher response rates seen in patients with higher levels of activity (P = 0.045). Cyclin E protein levels did not predict for platinum sensitivity (P = 0.20). In contrast, cyclin E protein levels, but not cyclin E^associated kinase activity, was a significant predictor for freedom from recurrence (P = 0.01and P = 0.25, respectively). Conclusions: Cyclin E overexpression and cyclin E^associated kinase activity have distinct roles in predicting for response to chemotherapy and outcome in ovarian cancer patients. These results suggest a compartmentalization of cyclin E functions in the oncogenic process.Overexpression of the cyclin E protein has been linked to shortening of the G 1 phase of the cell cycle (1), decreased requirement for growth factors (1), enhanced cell proliferation (2), induction of chromosomal instability (3, 4), and polyploidy (5). These processes contribute toward the oncogenic potential of cyclin E. Most importantly, cyclin E protein levels have been shown to correlate with a more aggressive tumor phenotype and adverse prognosis in a number of malignancies including breast, ovarian, gastric, non -small cell, and adrenocortical carcinomas, as well as non-Hodgkin's lymphoma (6-15).The major form of deregulation of cyclin E is at the level of protein. In examining cyclin E deregulation in breast cancer, we have previously published that irrespective of whether or not the gene is amplified (which occurs only in 10% of all breast cancer cases), the protein is independently deregulated. In fact, we have shown that in both normal and tumor cells, at the level of RNA, cyclin E is present as multiple splice variants; however, these splice variants do not give rise to protein products (16). Therefore, it seems that the primary process that contributes to deregulation of cyclin E is through posttranslational proteolytic cleavage of the full-length protein by elastase, which results in ge...

Small interference RNA-mediated suppression of overexpressed cyclin E protein restores G1/S regulation in NIH-OVCAR-3 ovarian cancer cells

“…These data indicated that cyclin E deregulation is an important event in ovarian tumorigenesis in vivo and are consistent with the high frequency of cyclin E overexpression reported in primary ovarian tumors (12)(13)(14)(15)(16)(17)(18)(19). Notably, whenever Western blot analysis has been used to assess cyclin E protein expression, a clear correlation has been found between the overexpression of cyclin EL1 and its LMW isoforms (15,16,18). To our knowledge, only three published studies in addition to our own have assessed cyclin E expression in ovarian tumors by Western blotting, which has the advantage over the more commonly used immunohistochemical approach in that it is able to distinguish the various isoforms of cyclin E. Thus, it is possible that the contribution of LMW isoform expression to ovarian cancer development (and potentially the development of other types of cancer) has, to-date, been underestimated.…”

“…These data indicated that cyclin E deregulation is an important event in ovarian tumorigenesis in vivo and are consistent with the high frequency of cyclin E overexpression reported in primary ovarian tumors (12)(13)(14)(15)(16)(17)(18)(19). Notably, whenever Western blot analysis has been used to assess cyclin E protein expression, a clear correlation has been found between the overexpression of cyclin EL1 and its LMW isoforms (15,16,18).…”

“…In the present study, however, we identified abnormally high levels of both the full-length and LMW isoforms of cyclin E protein in the p16-insensitive NIH-OVCAR-3 cells and in 70% of RB + /p16 + primary ovarian tumors, consistent with the high frequency of cyclin E overexpression in ovarian cancers reported by other groups (12)(13)(14)(15)(16)(17)(18)(19). The above expression data clearly support a role for the deregulation of cyclin E expression in ovarian tumorigenesis.…”

“…Using Western blot analysis, three studies have reported overexpression of the LMW isoforms of cyclin E in 68, 84 and 88% of primary ovarian cancers, respectively. In each study, the presence of the LMW isoforms were associated both with an advanced stage and grade of tumor and poor patient prognosis (15,16,18).…”

“…Overexpression of cyclin E has been detected at frequencies from 45 to 88% of primary ovarian cancers and is associated with tumors of a more advanced stage and grade (12)(13)(14)(15)(16)(17)(18)(19). Indeed, Sui et al (12) reported a correlation between increasing levels of cyclin E protein and ovarian cancer progression with only 9.1% of benign tumors versus 70.2% of malignant tumors showing elevated levels of cyclin E protein.…”