Anticancer activity of RecQL1 helicase siRNA in mouse xenograft models

Abstract

Small interfering RNAs (siRNAs) are expected to have a medical application in human therapy as drugs with a high specificity for their molecular target mRNAs. RecQL1 DNA helicase in the human RecQ helicase family participates in DNA repair and recombination pathways in the cell cycle of replication. Silencing the RecQL1 expression by RecQL1-siRNA induces mitotic death in vitro specifically in growing cancer cells. By contrast, the same RecQL1 silencing does not affect the growth of normal cells, emphasizing that RecQL1 helicase is an ideal molecular target for cancer therapy. In this study, we show that local and systemic administration of RecQL1-siRNA mixed with polyethyleneimine polymer or cationic liposomes prevented cancer cell proliferation in vivo in mouse models of cancer without noticeable adverse effects. The results indicate that RecQL1-siRNA in a complex with a cationic polymer is a very promising anticancer drug candidate, and that in particular, RecQL1-siRNA formulated with a cationic liposome has an enormous potential to be used by intravenous injection for therapy specific for liver cancers, including metastasized cancers from the colon and pancreas. (Cancer Sci 2008; 99: 1227-1236) H uman RecQL1 DNA helicase (RecQL1), a member of the RecQ helicase family, participates in the maintenance of genomic integrity and is highly up-regulated in rapidly growing cells, including various cancers and transformed cells.(1-5)RecQL1 unwinds specific DNA in vitro ATP-dependently and can increase base matching ATP-independently. (6,7) It is assumed to participate in the mismatch repair pathway in vivo because it binds to the incision activity of human EXO1 and the mismatch repair recognition complex MSH2/6.(8) Also, RecQL1 acts as an enzyme that resolves Holliday junctions during cell proliferation. (9) Consequently, down-regulation of RecQL1 expression in HeLa cells by RNA interference (RNAi) increases sister chromatid exchanges resulting from unprocessed Holliday junction structures, (10) . Although RecQL1-deficient mice show no apparent phenotypic differences when compared with wild-type mice, embryonic fibroblasts from RecQL1-deficient mice are sensitive to ionizing radiation (11) (and our unpublished data Sakamoto et al. 1999). All these findings collectively showed that RecQL1 suppresses chromosomal instability by participating in DNA repair associated with cell proliferation, but its function seems to be nonessential and complemented by other cellular repair system(s).Silencing RecQL1 in cancer cells by RNAi with siRNA induces mitotic catastrophe and death in a wide range of cancer cells that have defects in the cell cycle checkpoint system.(12) By contrast, the same silencing does not cause mitotic death in growing normal cells that have a competent checkpoint system, even though their cell cycles slowed down. To test the efficacy of RecQL1-siRNA in vivo, we previously studied the multicellular cancer spheroids system, a three dimensional (3-D) model that uses human hepatocarcinoma HuH-7 cell lines to m...

RECQ1 is required for cellular resistance to replication stress and catalyzes strand exchange on stalled replication fork structures

“…Chronic or persistent activation of DNA damage signaling (in specific phospho-ATM) has an important role in elimination of tumor cells that undergo excessive DNA replication stress. 54 Consistently, it was reported that RECQ1 silencing has anticancer effects, and that RECQ1 is considered a new suitable target for cancer therapy 34,43,55 (Fig. 8).…”

The Human RecQ Helicases, BLM and RECQ1, Display Distinct DNA Substrate Specificities

“…A recently published study indicates that endogenous DNA damage that remains unrepaired in cancer cells due to RECQ1 silencing induces cancer cell-specific mitotic catastrophe. Those authors suggest that RECQ1 might play an important role in the regulation of mitotic cell death in cancer and that this helicase might be a suitable target for the development of new chemotherapeutic agents (63). Although much progress has been made and it is now clear that RecQ enzymes do not simply play redundant roles in cells, the challenge of understanding the unique cellular function of RECQ1 in HR or in other DNA metabolic processes is still open.…”

Structure of the human RECQ1 helicase reveals a putative strand-separation pin

“…However, the knockout mice seemed healthy and fertile (12). Two recent reports show that RECQ1 depletion using inhibitory RNA has anticancer effects in cells (14) and xenografts (15); this indicates that RECQ1 may be an important target for cancer therapy.…”