We investigate the elasticity of two types of single-stranded synthetic DNA homopolydeoxynucletides, poly(dA) and poly(dT), by AFM-based single-molecule force spectroscopy. We find that poly(dT) exhibits the expected entropic elasticity behavior, while poly(dA) unexpectedly displays two overstretching transitions in the force-extension relationship. We suggest that these transitions, which occur at approximately 23 pN and approximately 113 pN, directly capture, for the first time, the mechanical signature of base-stacking interactions among adenines in DNA, in the absence of base pairing.
Key Points Radiation is appropriate primary therapy in approximately 25% of cases. Radiation provides long-term remissions in more than 50% of patients.
448 Background: POEMS syndrome is a rare form of plasma cell dyscrasia that presents with polyneuropathy and various other systemic findings. Patients with 1–3 lesions and bone marrows without clonal plasma cells have been given targeted radiation as the initial and potentially definitive therapy. Outcomes of patients treated thus have not been systematically studied. Patients and Methods: One hundred and forty-six patients with POEMS syndrome were seen at the Mayo Clinic in Rochester, MN between January 1999 and September 2011. Charts of patients with research authorization were reviewed with IRB approval. Patients who had been given targeted radiation as their initial primary therapy were eligible for this study. Thirty-eight patients satisfied criteria and comprise the study population. Three patients had either short or poorly documented follow-up and were excluded from the response and time to next treatment analyses. Patients were categorized by systems that were involved at diagnosis, time of radiation, response after radiation, and the need for further therapy. Statistical analyses were performed using JMP statistical software (SAS, Carey, NC). Results: The median age was 50, with 76% of the population being male. Median time from diagnosis to radiation was 0.7 months, ranging from 0 to 9.4 months. 20, 14, 11 and 2 patients had immunosuppressive therapy with corticosteroids, IVIG, plasmapheresis, or rituximab, respectively, directed at a prior presumptive, but incorrect, diagnosis of CIDP. Five patients had one cycle or less of alkylator, lenalidomide, or bortezomib, prior to receiving what was hoped to be definitive radiation therapy. The median number of bone lesions was 1, range 1–6. In total 55 lesions of the possible 64 were irradiated being mostly found in the pelvic bones including the sacrum, ileum, ischium, and pubis. The median dose of radiation given was 45 Gy range 35 Gy to 54 Gy. Forty-nine percent had clinical improvement, 26% had a mixed clinical picture, 3% merely stabilized, and 23% had a clinical worsening. 29% had a complete hematologic response, 9% had a very good partial hematologic response, 9% had a partial hematologic response, 26% had no hematologic response, and the remaining were either non- or oligo-secretory or undocumented. 11% had a complete FDG-PET response, 11% had a partial FDG-PET response, 11% had no FDG-PET response, and the remaining had no documented FDG-PETs to analyze. 11% had a complete VEGF response, 3% had partial VEGF response, 14% had no VEGF response, and the rest were either not documented or unevaluable. The median follow up of living patients is 30 months, and the 4-year OS is 95%. Forty-eight percent of patients went on to receive additional therapy after their radiation (Figure). The median time to next therapy (TTNT) for these patients was 7.6 months (range 2.2 –73 months). Subsequent therapies included high dose chemotherapy with autologous hematopoietic stem cell transplant (n=10), low dose alkylator (n=2), thalidomide/lenalidomide (n=3), and more radiation (n=3). None of the baseline characteristics predicted for whether a patient would receive (or require) subsequent therapy, including the number of bone lesions at baseline. Conclusion: The results show that radiation is sufficient to produce clinical improvements and hematologic and radiographic responses approximately 50% of patients, even those with as many as 3 lesions. Disclosures: No relevant conflicts of interest to declare.
We report the results of direct measurements by atomic force microscopy of solvent-driven structural transitions within polyadenylic acid (poly(A)). Both atomic force microscopy imaging and pulling measurements reveal complex strand arrangements within poly(A) induced by acidic pH conditions, with a clear fraction of double-stranded molecules that increases as pH decreases. Among these complex structures, force spectroscopy identified molecules that, upon stretching, displayed two distinct plateau features in the force-extension curves. These plateaus exhibit transition forces similar to those previously observed in native double-stranded DNA (dsDNA). However, the width of the first plateau in the force-extension curves of poly(A) varies significantly, and on average is shorter than the canonical 70% of initial length corresponding to the B-S transition of dsDNA. Also, similar to findings in dsDNA, stretching and relaxing elasticity profiles of dspoly(A) at forces below the mechanical melting transition overlap but reveal hysteresis when the molecules are stretched above the mechanical melting transition. These results strongly suggest that under acidic pH conditions, poly(A) can form duplexes that are mechanically stable. We hypothesize that under acidic conditions, similar structures may be formed by the cellular poly(A) tails on mRNA.
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