Phototoxic aptamers selectively enter and kill epithelial cancer cells.

The majority of cancers arise from malignant epithelial cells. We report the design of synthetic oligonucleotides (aptamers) that are only internalized by epithelial cancer cells and can be precisely activated by light to kill such cells. Specifically, phototoxic DNA aptamers were selected to bind to unique short O-glycan-peptide signatures on the surface of breast, colon, lung, ovarian and pancreatic cancer cells. These surface antigens are not present on normal epithelial cells but are internalized and routed through endosomal and Golgi compartments by cancer cells, thus providing a focused mechanism for their intracellular delivery. When modified at their 5' end with the photodynamic therapy agent chlorin e(6) and delivered to epithelial cancer cells, these aptamers exhibited a remarkable enhancement (>500-fold increase) in toxicity upon light activation, compared to the drug alone and were not cytotoxic towards cell types lacking such O-glycan-peptide markers. Our findings suggest that these synthetic oligonucleotide aptamers can serve as delivery vehicles in precisely routing cytotoxic cargoes to and into epithelial cancer cells.

An evolved ribosome-inactivating protein targets and kills human melanoma cells in vitro and in vivo.

BACKGROUND: Few treatment options exist for patients with metastatic melanoma, resulting in poor prognosis. One standard treatment, dacarbazine (DTIC), shows low response rates ranging from 15 to 25 percent with an 8-month median survival time. The development of targeted therapeutics with novel mechanisms of action may improve patient outcome. Ribosome-inactivating proteins (RIPs) such as Shiga-like Toxin 1 (SLT-1) represent powerful scaffolds for developing selective anticancer agents. Here we report the discovery and properties of a single chain ribosome-inactivating protein (scRIP) derived from the cytotoxic A subunit of SLT-1 (SLT-1A), harboring the 7-amino acid peptide insertion IYSNKLM (termed SLT-1A IYSNKLM) allowing the toxin variant to selectively target and kill human melanoma cells. RESULTS: SLT-1A IYSNKLM was able to kill 7 of 8 human melanoma cell lines. This scRIP binds to 518-A2 human melanoma cells with a dissociation constant of 18 nM, resulting in the blockage of protein synthesis and apoptosis in such cells. Biodistribution and imaging studies of radiolabeled SLT-1A IYSNKLM administered intravenously into SCID mice bearing a human melanoma xenograft indicate that SLT-1AI YSNKLM readily accumulates at the tumor site as opposed to non-target tissues. Furthermore, the co-administration of SLT-1A IYSNKLM with DTIC resulted in tumor regression and greatly increased survival in this mouse xenograft model in comparison to DTIC or SLT-1A IYSNKLM treatment alone (115 day median survival versus 46 and 47 days respectively; P values < 0.001). SLT-1A IYSNKLM is stable in serum and its intravenous administration resulted in modest immune responses following repeated injections in CD1 mice. CONCLUSIONS: These results demonstrate that the evolution of a scRIP template can lead to the discovery of novel cancer cell-targeted compounds and in the case of SLT-1A IYSNKLM can specifically kill human melanoma cells in vitro and in vivo.

Chx10 is required to block photoreceptor differentiation but is dispensable for progenitor proliferation in the postnatal retina.

In the Chx10-null ocular retardation (or(J)) mouse, retinal progenitor cell (RPC) proliferation is impaired, and bipolar neurons, a late born cell type, fail to differentiate. It is unclear whether Chx10 is required to maintain proliferation throughout retinogenesis or whether the bipolar cell defect is an indirect effect of growth arrest. We show that Chx10 is dispensable for late-stage RPC proliferation but is essential to promote bipolar cell genesis in place of rods. Ectopic Chx10 expression drove bipolar instead of rod cell differentiation without affecting division. Converting Chx10 to an activator impaired bipolar cell differentiation, implying that repression is important for Chx10 activity. In the Chx10 null or(J) retina, only a small fraction of cells expressing mutated Chx10 mRNA were rods, but this fraction increased after p27(Kip1) inactivation, which partially rescues proliferation. Most significantly, acute Chx10 knockdown in the postnatal retina promoted rods in place of bipolar neurons without affecting division. Thus, Chx10 directly controls bipolar cell genesis by inhibiting rod differentiation independent of its temporally limited early effect on RPC proliferation.