Effect of doxorubicin and/or natural killer cells on RNA disruption in K562 chronic myeloid leukemia cells

Abstract

It has recently been observed that a variety of mechanistically distinct chemotherapy agents and cellular stressors induce ribosomal RNA (rRNA) degradation in tumour cells, a phenomenon termed RNA disruption. The RNA disruption assay (RDA) has been developed to quantify RNA disruption in a manner that can predict pathologic complete response and improved disease-free survival early in treatment. Immune checkpoint inhibitor (ICI) drugs are novel anti-cancer agents that can result in significant improvement in patient survival, but not all patients respond to these drugs. Thus, the RDA may be able to identify early in treatment ICI non-responders in order to avoid the continued costs and harmful side effects of this class of drugs and to consider alternate treatments. Since ICI drugs function by enhancing the efficacy of endogenous immune cells, this study assessed the ability of the RDA to quantify and monitor immune cell-mediated destruction of tumour cells in the absence or presence of the cytotoxic chemotherapy drug doxorubicin (DOX). This involved using the RDA to determine the RNA disruption index (RDI) for a particular sample via capillary gel electrophoresis and a proprietary algorithm. Loss of membrane integrity was also used to measure the cytotoxicity of immune cells towards tumour cells. In the K562 chronic myeloid leukemia cell line, RNA disruption was induced by a variety of chemotherapy agents, including DOX. Freshly isolated primary human natural killer (NK) cells also induced RNA disruption and loss of membrane integrity in K562 cells in a cell number-dependent manner. Pre-activation of NK cells with IL-2 augmented K562 cell RNA disruption and loss of membrane integrity in a dose-dependent manner. Preliminary studies suggested that pre-treatment with DOX may also augment NK cell-mediated RNA disruption in K562 cells. NK cell-mediated RNA disruption and loss of membrane integrity appear to correlate in a strong, positive manner in K562 cells. The pattern of rRNA degradation fragments induced by NK cells was very similar to that induced by chemotherapy agents. Taken together, these findings suggest that the RDA may have clinical utility in monitoring immune cell-mediated destruction of tumour cells induced by ICI therapies (prior to or after chemotherapy).