Experimental and Computational Study of the Gas-Phase Acidities of Acidic Di- and Tripeptides.

Gas-phase acidities (GA or Δ Gacid) of acidic di- and tripeptides are determined for the first time. The peptides studied are composed of inert alanine (A) residues and one X residue of either aspartic acid (D) or glutamic acid (E): AX, XA, AAX, AXA, and XAA. Experimental GAs were measured by the thermokinetic method of deprotonation ion/molecule reactions in a Fourier transform ion cyclotron resonance mass spectrometer. Calculated GAs were obtained by composite correlated molecular orbital theory at the G3(MP2) level for deprotonation of carboxylic acid groups both at the C-terminus and at the side chain. Excellent agreement was found between experimental and calculated GA values. There is a slight preference for peptides with D being more acidic than analogous peptides with E, which agrees with the GAs of the corresponding amino acids. Experiments showed that peptides are more acidic (lower numerical GA values) when the acidic residue is located at the C-terminus (i.e., AX or AAX). The lowest energy form of deprotonated AAE has a unique structure where the longer side chain of E allows the two carboxylates, which are in close proximity, to share the proton. The tripeptides are less acidic (higher GA value) by 3-7 kcal/mol when the acidic residue is in the center. The tripeptides are more acidic (by 2-10 kcal/mol) than dipeptides containing the same acidic residue at the same location.

International Multicenter Validation of an Intermediate Risk Subclassification of Prostate Cancer Managed with Radical Treatment without Hormone Therapy.

PURPOSE: The NCCN Guidelines® recently endorsed a subclassification of intermediate risk prostate cancer into favorable and unfavorable subgroups. However, this subclassification was developed in a treatment heterogeneous cohort. Thus, to our knowledge the natural history of androgen deprivation treatment naïve favorable and unfavorable intermediate risk prostate cancer cases remains unknown. MATERIALS AND METHODS: Groups at 3 academic centers pooled data on patients with intermediate risk prostate cancer treated with radical monotherapy (dose escalated external beam radiotherapy, brachytherapy or radical prostatectomy) without combined androgen deprivation treatment. We used the cumulative incidence with competing risk analysis to estimate biochemical recurrence, distant metastasis and prostate cancer specific mortality. RESULTS: A total of 2,550 men at intermediate risk were included in study, of whom 1,063 and 1,487 were at favorable and unfavorable risk, respectively. Of the men 1,149 underwent radical prostatectomy, 1,143 underwent dose escalated external beam radiotherapy and 258 underwent brachytherapy. Median followup after the different treatments ranged from 60.4 to 107.4 months. The 10-year cumulative incidence of distant metastasis in the favorable vs unfavorable risk groups was 0.2% (95% CI 0.2-0.2) vs 11.6% (95% CI 7.7-15.5) for radical prostatectomy (p <0.001), 2.8% (95% CI 0.8-4.8) vs 13.5% (95% CI 9.6-17.4) for dose escalated external beam radiotherapy (p <0.001) and 3.5% (95% CI 0-7.4) vs 10.2% (95% CI 4.3-16.1) for brachytherapy (p = 0.063). The 10-year rate of prostate cancer specific mortality in the favorable vs unfavorable risk groups was 0% (95% CI 0-0) vs 3.7% (95% CI 1.7-5.7) for radical prostatectomy (p = 0.016), 0.5% (95% CI 0.5-0.5) vs 5.6% (95% CI 3.6-7.6) for dose escalated external beam radiotherapy (p = 0.015) and 0% (95% CI 0-0) vs 2.5% (95% CI 0.5-4.5) for brachytherapy (p = 0.028). CONCLUSIONS: This multicenter international effort independently validates the prognostic value of the intermediate risk prostate cancer subclassification in androgen deprivation treatment naïve cases across all radical treatment modalities. It is unlikely that treatment intensification would meaningfully improve oncologic outcomes in men at favorable intermediate risk.