RNA disruption is associated with response to multiple classes of chemotherapy drugs in tumor cell lines

Narendrula, Rashmi; Mispel-Beyer, Kyle; Guo, Baoqing; Parissenti, Amadeo M.; Pritzker, Laura B.; Pritzker, Ken; Masilamani, Twinkle; Wang, Xiaohui; Lannér, Carita

Although apoptosis-inducing agents have been shown to induce rRNA degradation in mammalian cells, other cytotoxic agents, such as chemotherapy drugs, have not yet been investigated in this respect. Recently, imageguided tumor core biopsies were taken from patients with locally advanced or inflammatory breast cancer enrolled in the CAN-NCIC-MA.22 clinical trial [18] . Samples were taken prior to, during, and post-treatment with an epirubicin/docetaxel combination chemotherapy. Tumor levels of several biomarkers, including RNA, were then assessed for their relationship to treatment response [18] . Interestingly, a significant association was observed between mid-treatment RNA degradation [19] and the absence of tumor cells in the breast and axilla after treatment (pathologic complete response). The RNA degradation bands were generally of high molecular weight, considerably greater than that observed during autolytic degradation of RNA in tissue samples [19] . These high molecular weight bands were observed following 8-18 weeks of chemotherapy treatment [18] . We refer to this ability of chemotherapy agents to induce long-lived rRNA fragments typically not seen after extensive autolytic degradation as "RNA disruption". Since the RIN algorithm specifically quantifies the formation of low molecular weight autolytic RNA degradation products [19] and since abnormal RNA banding patterns during RNA disruption results in the assignment of "n/a" values for RIN by the Agilent Bioanalyzer, we recently developed the RNA disruption assay (RDA), which quantifies RNA disruption in tumors and tumor cells as an RNA disruption index (RDI), and is a ratio of abnormal to normal rRNAs [20] . Chemotherapy treatment in the above clinical trial was also found to be associated with reduced tumor RNA content in patients, which may be attributed to both the observed RNA degradation and a suppression of RNA synthesis in tumor cells [20] . Moreover, the above study demonstrated that high tumor RNA disruption mid-treatment was associated with markedly enhanced disease-free survival post-chemotherapy. Our observations of reduced RNA content in patient tumors upon chemotherapy treatment were also consistent with previously published studies indicating that numerous cytotoxic chemotherapeutic drugs can strongly interfere with ribosome biogenesis [21, 22] .