The scrapie prion protein (PrP Sc ) is the major, and possibly the only, component of the infectious prion; it is generated from the cellular isoform (PrP C ) by a conformational change. N-terminal truncation of PrP Sc by limited proteolysis produces a protein of Ϸ142 residues designated PrP 27-30, which retains infectivity. A recombinant protein (rPrP) corresponding to Syrian hamster PrP 27-30 was expressed in Escherichia coli and purified. After refolding rPrP into an ␣-helical form resembling PrP C , the structure was solved by multidimensional heteronuclear NMR, revealing many structural features of rPrP that were not found in two shorter PrP fragments studied previously. Extensive side-chain interactions for residues 113-125 characterize a hydrophobic cluster, which packs against an irregular ␤-sheet, whereas residues 90-112 exhibit little defined structure. Although identifiable secondary structure is largely lacking in the N terminus of rPrP, paradoxically this N terminus increases the amount of secondary structure in the remainder of rPrP. The surface of a long helix (residues 200-227) and a structured loop (residues 165-171) form a discontinuous epitope for binding of a protein that facilitates PrP Sc formation. Polymorphic residues within this epitope seem to modulate susceptibility of sheep and humans to prion disease. Conformational heterogeneity of rPrP at the N terminus may be key to the transformation of PrP C into PrP Sc , whereas the discontinuous epitope near the C terminus controls this transition.

The benefit of a hydrogel spacer in reducing the rectal dose, toxicity, and QOL declines after image guided intensity modulated radiation therapy for prostate cancer was maintained or increased with a longer follow-up period, providing stronger evidence for the benefit of hydrogel spacer use in prostate radiation therapy.

BACKGROUND: Extranodal natural killer/T-cell lymphoma (ENKTL), nasal-type, is a distinct entity of lymphoid tissue. ENKTL is sensitive to radiotherapy (RT), but the prognosis is poorer than for other types of early lymphoma. The treatment schedule is controversial. METHODS: A phase 2 study was conducted of ''sandwich'' protocols, with earlier RT after an initial 2 to 3 cycles of LVP (L-asparaginase, vincristine, and prednisone), followed by further ''consolidation'' cycles. Patients aged 18 years and older who had previously untreated ENKTL and localized lesions in the upper aerodigestive tract were enrolled. The primary endpoints were objective response rate and complete remission rate. The secondary endpoints were 2-year overall survival, 2-year progression-free survival, and toxicity. This study is registered with www.Chictr.org, number ChicTR-TNC-00000394, and is ongoing for long-term follow-up. RESULTS: Twenty-six patients completed total therapy, which resulted in 88.5% response that included 21 patients (80.8%) with complete response (CR) and 2 patients (7.7%) with partial response. Three (11.5%) of 26 patients progressed during therapy. With a median follow-up of 27 months (range, 4-35 months), the 2-year overall survival was 88.5%, and the 2-year progression-free survival was 80.6%. Patients with CR had better prognosis than patients without CR. Only 2 patients (7.7%) experienced grade 3 leukocytopenia. No grade 4 toxicity or treatment-related deaths were observed. CONCLUSIONS: The research showed that the ''sandwich'' protocol of LVP combined with RT was a safe and effective treatment for localized nasal natural killer/T-cell lymphoma, and the results warrant further investigation into this protocol. Cancer 2012;118:3294-

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