Patterns of Recurrence Following Radiation and ADT for Pathologic Lymph Node Positive Prostate Cancer: A Multi-Institutional Study

PURPOSE/OBJECTIVE(S)

Retrospective studies have suggested that post-operative radiation therapy (RT) can reduce the risk of cause-specific mortality in men with pathologic nodal involvement (pN1) after radical prostatectomy (RP). We evaluated prognostic factors and patterns of recurrence in patients who received post-operative RT +/- androgen deprivation therapy (ADT) for pN1 disease in a multicentric cohort of 4 academic centers.

MATERIALS/METHODS

Data from patients with pN1 prostate cancer after RP who subsequently received RT with short term (< = 6 mo) or long term (>6 mo) ADT were obtained from 4 academic institutions. Patterns of recurrence, biochemical progression free survival (bPFS) and distant metastasis free survival (DMFS) were evaluated.

RESULTS

A total of 270 patients with a median follow-up of 48 months were included. Gleason grade group (GG) 2 was present in 20 patients (7.5%), GG 3 in 81 (30%), GG4 in 36 (13.5%), GG5 in 130 (49%) patients. 256 (95%) patients had extracapsular extension, 70% had seminal vesicle invasion, 59% had positive surgical margins, and 66% had a detectable post-operative PSA. The number of positive nodes at surgery were 1 in 59%, 2 in 19% and >2 in 22% of patients. Of the 83 patients that had pre-RT imaging, 46 (55%) had a PET scan (PSMA, or fluciclovine); 25 (30%) of those had lymph nodes detected on imaging prior to RT. Median time from RP to RT was 6 mo (IQR 4.5-9.1 mo). 96% received radiation to both the prostate bed (median dose 68.4Gy) and pelvic lymph nodes (median dose 46Gy). ADT was prescribed short-term (20%) or long-term (68%), while 26 (10%) received no ADT, and 7 (3%) had an unknown duration. Biochemical failure (bF) was observed in 29% of men, with 5% having pelvic nodal failure and 11.5% having distant metastases (majority in bones, followed by paraaortic nodes) at last follow up. Of 59 patients who had normal baseline testosterone levels, 37% recovered their testosterone by last follow-up. The 4-year bRFS was 72% for all patients and was 83% for those with a pre-RT PSA of <0.1 ng/mL, 76% for PSA 0.1-<0.5 ng/mL, 60% for PSA 0.5-2 ng/mL, and 35% for PSA >2 ng/mL. On multivariable analysis, maximum pre-RT PSA ≥0.5 (0.5 to 2.0 vs <0.1 HR = 3.19; >2.0 vs <0.1 HR = 9.00), use of LTADT (HR = 0.47), and percent pN1 (HR = 1.03) were significantly associated with bF. Pre-RT PSA >2 (HR = 4.10), use of LT ADT (HR = 0.33) and percent pN1 (HR = 1.03) were also significantly associated with DM.

CONCLUSION

In pN1 patients, pelvic RT and ADT at low PSA levels is associated with improved oncologic outcomes compared to treatment at higher levels, suggesting that PSA may have prognostic value for pN1 prostate cancer.

Structural implications of placing cationic residues at either the NH2- or COOH-terminus in a pore-forming synthetic peptide

Restoration of chloride conductance via introduction of an anion-selective pore, formed by a channel-forming peptide, has been hypothesized as a novel treatment modality for patients with cystic fibrosis. Delivery of these peptides from an aqueous environment in the absence of organic solvents is paramount. M2GlyR peptides, designed based on the glycine receptor, insert into lipid bilayers and polarized epithelial cells and assemble spontaneously into chloride-conducting pores. Addition of 4 lysine residues to either terminus increases the solubility of M2GlyR peptides. Both orientations of the helix within the membrane form an anion-selective pore, however, differences in solubility, associations and channel-forming activity are observed. To determine how the positioning of the lysine residues affects these properties, structural characteristics of the lysyl-modified peptides were explored utilizing chemical cross-linking, NMR and molecular modeling. Initial model structures of the a-helical peptides predict that lysine residues at the COOH-terminus form a capping structure by folding back to form hydrogen bonds with backbone carbonyl groups and hydroxyl side chains of residues in the helical segment of the peptide. In contrast, lysine residues at the NH2-terminus form fewer H-bonds and extend away from the helical backbone. Results from NMR and chemical cross-linking support the model structures. The C-cap formed by H-bonding of lysine residues is likely to account for the different biophysical properties observed between NH2- and COOH-terminal-modified M2GlyR peptides.

Synthetic chloride channel restores glutathione secretion in cystic fibrosis airway epithelia

Cystic fibrosis (CF), an inherited disease characterized by defective epithelial Cl- transport, damages lungs via chronic inflammation and oxidative stress. Glutathione, a major antioxidant in the epithelial lung lining fluid, is decreased in the apical fluid of CF airway epithelia due to reduced glutathione efflux (Gao L, Kim KJ, Yankaskas JR, and Forman HJ. Am J Physiol Lung Cell Mol Physiol 277: L113-L118, 1999). The present study examined the question of whether restoration of chloride transport would also restore glutathione secretion. We found that a Cl- channel-forming peptide (N-K4-M2GlyR) and a K+ channel activator (chlorzoxazone) increased Cl- secretion, measured as bumetanide-sensitive short-circuit current, and glutathione efflux, measured by high-performance liquid chromatography, in a human CF airway epithelial cell line (CFT1). Addition of the peptide alone increased glutathione secretion (181 +/- 8% of the control value), whereas chlorzoxazone alone did not significantly affect glutathione efflux; however, chlorzoxazone potentiated the effect of the peptide on glutathione release (359 +/- 16% of the control value). These studies demonstrate that glutathione efflux is associated with apical chloride secretion, not with the CF transmembrane conductance regulator per se, and the defect of glutathione efflux in CF can be overcome pharmacologically.

NH(2)-terminal modification of a channel-forming peptide increases capacity for epithelial anion secretion

A synthetic, channel-forming peptide, derived from the alpha-subunit of the glycine receptor (M2GlyR), has been synthesized and modified by adding four lysine residues to the NH(2) terminus (N-K(4)-M2GlyR). In Ussing chamber experiments, apical N-K(4)-M2GlyR (250 microM) increased transepithelial short-circuit current (I(sc)) by 7.7 +/- 1.7 and 10.6 +/- 0.9 microA/cm(2) in Madin-Darby canine kidney and T84 cell monolayers, respectively; these values are significantly greater than those previously reported for the same peptide modified by adding the lysines at the COOH terminus (Wallace DP, Tomich JM, Iwamoto T, Henderson K, Grantham JJ, and Sullivan LP. Am J Physiol Cell Physiol 272: C1672-C1679, 1997). N-K(4)-M2GlyR caused a concentration-dependent increase in I(sc) (k([1/2]) = 190 microM) that was potentiated two- to threefold by 1-ethyl-2-benzimidazolinone. N-K(4)-M2GlyR-mediated increases in I(sc) were insensitive to changes in apical cation species. Pharmacological inhibitors of endogenous Cl(-) conductances [glibenclamide, diphenylamine-2-dicarboxylic acid, 5-nitro-2-(3-phenylpropylamino)benzoic acid, 4,4'-dinitrostilben-2,2'-disulfonic acid, indanyloxyacetic acid, and niflumic acid] had little effect on N-K(4)-M2GlyR-mediated I(sc). Whole cell membrane patch voltage-clamp studies revealed an N-K(4)-M2GlyR-induced anion conductance that exhibited modest outward rectification and modest time- and voltage-dependent activation. Planar lipid bilayer studies yielded results indicating that N-K(4)-M2GlyR forms a 50-pS anion conductance with a k([1/2]) for Cl(-) of 290 meq. These results indicate that N-K(4)-M2GlyR forms an anion-selective channel in epithelial monolayers and shows therapeutic potential for the treatment of hyposecretory disorders such as cystic fibrosis.