Nonsteroidal anti-inflammatory drugs as a targeted therapy for bone marrow failure in Ghosal hematodiaphyseal dysplasia.

Advances in genomic diagnostics hold promise for improved care of rare hematologic diseases. Here, we describe a novel targeted therapeutic approach for Ghosal hematodiaphyseal dysplasia, an autosomal recessive disease characterized by severe normocytic anemia and bone abnormalities due to loss-of-function mutations in thromboxane A synthase 1 (TBXAS1). TBXAS1 metabolizes prostaglandin H2 (PGH2), a cyclooxygenase (COX) product of arachidonic acid, into thromboxane A2. Loss-of-function mutations in TBXAS result in an increase in PGH2 availability for other PG synthases. The current treatment for Ghosal hematodiaphyseal dysplasia syndrome consists of corticosteroids. We hypothesize that nonsteroidal anti-inflammatory drugs (NSAIDs), which inhibit COX-1 and COX-2, could ameliorate the effects of TBXAS1 loss and improve hematologic function by reducing prostaglandin formation. We treated 2 patients with Ghosal hematodiaphyseal dysplasia syndrome, an adult and a child, with standard doses of NSAIDs (aspirin or ibuprofen). Both patients had rapid improvements concerning hematologic parameters and inflammatory markers without adverse events. Mass spectrometry analysis demonstrated that urinary PG metabolites were increased along with proinflammatory lipoxygenase (LOX) products 5-hydroxyeicosatetraenoic acid and leukotriene E4. Our data show that NSAIDs at standard doses surprisingly reduced both COX and LOX products, leading to the resolution of cytopenia, and should be considered for first-line treatment for Ghosal hematodiaphyseal dysplasia syndrome.

Phase I Trial of Regorafenib, Hydroxychloroquine, and Entinostat in Metastatic Colorectal Cancer.

BACKGROUND: The antiangiogenic tyrosine kinase inhibitor regorafenib provides a survival benefit in patients with previously treated metastatic colorectal cancer (CRC). Antiangiogenic therapy causes hypoxic stress within tumor cells, which activates autophagy as a survival mechanism. The histone deacetylase inhibitor (HDAC) entinostat increases dependence on autophagy through epigenetic mechanisms. Hydroxychloroquine (HCQ) blocks autophagy by blunting lysosomal acidification. We hypothesized that HCQ and entinostat would be tolerable with regorafenib and potentiate the antitumor response. METHODS: This was a 3+3 phase I trial of HCQ and entinostat with regorafenib in patients with metastatic CRC. The primary objective was safety, and the secondary objective was clinical efficacy. RESULTS: Twenty patients received study therapy. Six evaluable patients were enrolled at each of the three planned dose levels, one patient at an intermediate dose level, and one additional patient withdrew consent after 4 days to receive treatment closer to home. One dose-limiting toxicity was noted in the study at dose level 2 (grade 3 fatigue). Seven patients discontinued therapy due to related toxicities; rapid weight loss was near universal, with a median weight loss of 4.4 kg (range 1.5-12.2 kg) in the first 2 weeks of treatment. No objective responses were observed. CONCLUSION: The combination of regorafenib, HCQ, and entinostat was poorly tolerated without evident activity in metastatic CRC. CLINICALTRIALS.GOV IDENTIFIER: NCT03215264.

Rates of appropriate laxative prophylaxis for opioid-induced constipation in veterans with lung cancer: a retrospective cohort study.

PURPOSE: Opioid-induced constipation (OIC) is the most common side effect in patient-prescribed opioids for cancer pain treatment. Current guidelines recommend routine prescription of a laxative for preventing OIC in all patients prescribed an opioid unless a contraindication exists. We determined patterns of prescription of laxative agents in patients with lung cancer initiating opioids. METHODS: We performed a retrospective cohort study evaluating the prescription of laxatives for OIC to adult patients with incident lung cancer seen in the Veteran's Affairs (VA) system, between January 1, 2003, and December 31, 2016. Exposure to laxative agents was categorized as follows: none, docusate monotherapy, docusate plus another laxative, and other laxatives only. Prevalence of OIC prophylaxis was analyzed using descriptive statistics. Linear regression was performed to identify time trends in the prescription of OIC prophylaxis. RESULTS: Overall, 130,990 individuals were included in the analysis. Of these, 87% of patients received inadequate prophylaxis (75% no prophylaxis and 12% docusate alone), while 5% received OIC prophylaxis with the unnecessary addition of docusate to another laxative. Through the study period, laxative prescription significantly decreased, while all other categories of OIC prophylaxis were unchanged. We noted an inverse relationship with OIC prophylaxis and likelihood of a diagnosis of constipation at 3 and 6 months. CONCLUSIONS: In this study of veterans with lung cancer, almost 90% received inadequate or inappropriate OIC prophylaxis. Efforts to educate physicians and patients to promote appropriate OIC prophylaxis in combination with systems-level changes are warranted.

Ex vivo drug response profiling detects recurrent sensitivity patterns in drug-resistant acute lymphoblastic leukemia.

Drug sensitivity and resistance testing on diagnostic leukemia samples should provide important functional information to guide actionable target and biomarker discovery. We provide proof of concept data by profiling 60 drugs on 68 acute lymphoblastic leukemia (ALL) samples mostly from resistant disease in cocultures of bone marrow stromal cells. Patient-derived xenografts retained the original pattern of mutations found in the matched patient material. Stromal coculture did not prevent leukemia cell cycle activity, but a specific sensitivity profile to cell cycle-related drugs identified samples with higher cell proliferation both in vitro and in vivo as leukemia xenografts. In patients with refractory relapses, individual patterns of marked drug resistance and exceptional responses to new agents of immediate clinical relevance were detected. The BCL2-inhibitor venetoclax was highly active below 10 nM in B-cell precursor ALL (BCP-ALL) subsets, including MLL-AF4 and TCF3-HLF ALL, and in some T-cell ALLs (T-ALLs), predicting in vivo activity as a single agent and in combination with dexamethasone and vincristine. Unexpected sensitivity to dasatinib with half maximal inhibitory concentration values below 20 nM was detected in 2 independent T-ALL cohorts, which correlated with similar cytotoxic activity of the SRC inhibitor KX2-391 and inhibition of SRC phosphorylation. A patient with refractory T-ALL was treated with dasatinib on the basis of drug profiling information and achieved a 5-month remission. Thus, drug profiling captures disease-relevant features and unexpected sensitivity to relevant drugs, which warrants further exploration of this functional assay in the context of clinical trials to develop drug repurposing strategies for patients with urgent medical needs.

Dissemination of Information on Neutropenic Diet by Top US Cancer Centers: In-line with the Evidence?

Aim: The neutropenic diet is commonly prescribed to cancer patients with neutropenia with the goal of reducing infections. However, multiple randomized trials have proved no benefit with neutropenic diets compared to less restricted diets with regards to reducing infectious risk. We aimed to ascertain if top cancer centers recommended for or against the use of neutropenic diets on their official websites. Methods: We reviewed the websites of the top 20 hospitals in the 2017 US News Best Hospitals for Cancer©, and ascertained recommendations for neutropenic diet (for, against, equivocal, or not addressed). Results: Seven websites (35%) made recommendations for, four (20%) against, and nine (45%) did not address the neutropenic diet. Only five (25%) backed any of their recommendations with evidence (four against, one for), including two (10%) links to abstracts (both against), whereas seven mentioned the FDA safe food handling guidelines (non-exclusive). Type of recommendation made (for or against) did not depend on US News rank (top vs bottom 10; p = 1.00.). Conclusion: The neutropenic diet continues to be recommended on many (35%) websites of top US cancer centers, despite strong evidence against its use. The website content of major US cancer centers should be updated to better guide patients regarding neutropenic diets.

Therapeutic effect of Northern Labrador tea extracts for acute myeloid leukemia.

Acute myeloid leukemia (AML) is an aggressive hematological malignancy that is one of the more common pediatric malignancies in addition to occurring with high incidence in the aging population. Unfortunately, these patient groups are quite sensitive to toxicity from chemotherapy. Northern Labrador tea, or Rhododendron tomentosum Harmaja (a.k.a. Ledum palustre subsp. decumbens) or "tundra tea," is a noteworthy medicinal plant used by indigenous peoples in Alaska, Canada, and Greenland to treat a diversity of ailments. However, laboratory investigations of Northern Labrador tea, and other Labrador tea family members, as botanical sources for anticancer compounds have been limited. Utilizing an AML cell line in both in vitro and in vivo studies, as well as in vitro studies using primary human AML patient samples, this study demonstrated for the first time that Northern Labrador tea extracts can exert anti-AML activity and that this may be attributed to ursolic acid as a constituent component. Therefore, this medicinal herb holds the potential to serve as a source for further drug discovery efforts to isolate novel anti-AML compounds.

Residential agricultural pesticide exposures and risks of selected birth defects among offspring in the San Joaquin Valley of California.

BACKGROUND: We examined associations of birth defects with residential proximity to commercial agricultural pesticide applications in California. Subjects included 367 cases representing five types of birth defects and 785 nonmalformed controls born 1997 to 2006. METHODS: Associations with any versus no exposure to physicochemical groups of pesticides and specific chemicals were assessed using logistic regression adjusted for covariates. Overall, 46% of cases and 38% of controls were classified as exposed to pesticides within a 500 m radius of mother's address during a 3-month periconceptional window. RESULTS: We estimated odds ratios (ORs) for 85 groups and 95 chemicals with five or more exposed cases and control mothers. Ninety-five percent confidence intervals (CI) excluded 1.0 for 11 ORs for groups and 22 ORs for chemicals, ranging from 1.9 to 3.1 for groups and 1.8 to 4.9 for chemicals except for two that were <1 (noted below). CONCLUSION: For groups, these ORs were for anotia/microtia (n = 95 cases) and dichlorophenoxy acids/esters and neonicotinoids; anorectal atresia/stenosis (n = 77) and alcohol/ethers and organophosphates (these ORs were < 1.0); transverse limb deficiencies (n = 59) and dichlorophenoxy acids/esters, petroleum derivatives, and triazines; and craniosynostosis (n = 79) and alcohol/ethers, avermectins, neonicotinoids, and organophosphates. For chemicals, ORs were: anotia/microtia and five pesticides from the groups dichlorophenoxy acids/esters, copper-containing compounds, neonicotinoids, organophosphates, and triazines; transverse limb deficiency and six pesticides - oxyfluorfen and pesticides from the groups copper-containing compounds, 2,6-dinitroanilines, neonicotinoids, petroleum derivatives and polyalkyloxy compounds; craniosynostosis and 10 pesticides - oxyfluorfen and pesticides from the groups alcohol/ethers, avermectins, n-methyl-carbamates, neonicotinoids, ogranophosphates (two chemicals), polyalkyloxy compounds (two chemicals), and pyrethroids; and congenital diaphragmatic hernia (n = 62) and a copper-containing compound.

Metabolic changes during ovarian cancer progression as targets for sphingosine treatment.

Tumor cells often exhibit an altered metabolic phenotype. However, it is unclear as to when this switch takes place in ovarian cancer, and the potential for these changes to serve as therapeutic targets in clinical prevention and intervention trials. We used our recently developed and characterized mouse ovarian surface epithelial (MOSE) cancer progression model to study metabolic changes in distinct disease stages. As ovarian cancer progresses, complete oxidation of glucose and fatty acids were significantly decreased, concurrent with increases in lactate excretion and (3)H-deoxyglucose uptake by the late-stage cancer cells, shifting the cells towards a more glycolytic phenotype. These changes were accompanied by decreases in TCA flux but an increase in citrate synthase activity, providing substrates for de novo fatty acid and cholesterol synthesis. Also, uncoupled maximal respiration rates in mitochondria decreased as cancer progressed. Treatment of the MOSE cells with 1.5 µM sphingosine, a bioactive sphingolipid metabolite, decreased citrate synthase activity, increased TCA flux, decreased cholesterol synthesis and glycolysis. Together, our data confirm metabolic changes during ovarian cancer progression, indicate a stage specificity of these changes, and suggest that multiple events in cellular metabolism are targeted by exogenous sphingosine which may be critical for future prevention trials.

Targeted therapies in advanced biliary malignancies: a clinical review.

INTRODUCTION: Despite several therapeutic advancements, the proportion of patients with advanced biliary tract cancers (BTC) surviving 5 years from diagnosis remains dismal. The increasing recognition of targetable genetic alterations in BTCs has ushered in a new era in the treatment of these patients. Newer therapeutic agents targeting mutations such as isocitrate dehydrogenase (IDH), fibroblastic growth factor receptor (FGFR), human epidermal growth factor receptor (HER), and so on have established a new standard of care for treatment upon progression on frontline therapy in patients with disease harboring these mutations. AREAS COVERED: The current review aims to concisely summarize progress with various targeted therapy options for BTC. We also briefly discuss future directions in clinical and translational research for the adoption of a personalized approach for the treatment of unresectable or advanced BTC. EXPERT OPINION: Several new agents continue to emerge as feasible treatment options for patients with advanced BTC harboring targetable mutations. There is a growing need to identify mechanisms to conquer primary and acquired resistance to these agents. The identification of potential biomarkers that predict response to targeted therapy may be helpful in adopting a more tailored approach. All patients receiving treatment for advanced BTC should undergo tissue genomic profiling at diagnosis.

Classification and Regression Trees to Predict for Survival for Patients With Hepatocellular Carcinoma Treated With Atezolizumab and Bevacizumab.

PURPOSE: Systemic therapy with atezolizumab and bevacizumab can extend life for patients with advanced hepatocellular carcinoma (HCC). However, there is substantial variability in response to therapy and overall survival. Although current prognostic models have been validated in HCC, they primarily consider covariates that may be reflective of the severity of the underlying liver disease of patients with HCC. We developed and internally validated a classification and regression tree (CART) to identify patient characteristics associated with risks of early mortality, at or before 6 months from treatment initiation. METHODS: This retrospective cohort study used the nationwide Flatiron Health electronic health record-derived deidentified database and included patients with a diagnosis of HCC after January 1, 2020, who received initial systemic therapy with atezolizumab and bevacizumab. CART was developed from available baseline clinical and demographic information to predict mortality within 6 months from treatment initiation. Model characteristics were compared to the albumin-bilirubin (ALBI) model and was further validated against a contemporary validation cohort of patients after a data update. RESULTS: A total of 293 patients were analyzed. The CART identified seven cohorts of patients from baseline demographic and laboratory characteristics. The model had an area under the receiver operating curve (AUROC) of 0.739 (95% CI, 0.683 to 0.794) for predicting 6-month mortality. This model was internally valid and performed more favorably than the ALBI model, which had an AUROC of 0.608 (95% CI, 0.557 to 0.660). The model applied to the contemporary validation cohort (n = 111) had an AUROC of 0.666 (95% CI, 0.506 to 0.826). CONCLUSION: Using CART, we identified unique cohorts of patients with HCC treated with atezolizumab and bevacizumab with distinct risks of early mortality. This approach outperformed the ALBI model and used clinical and laboratory characteristics that are readily available to oncologists caring for these patients.

Clinical, pathological, and adjuvant chemotherapy use differences among microsatellite unstable and microsatellite stable colon cancers.

Background: Colon cancers are categorized into mismatch repair deficient/microsatellite unstable (MSI-H) and mismatch repair proficient/microsatellite stable (MSS) cancers. This study aims to compare the disease characteristics and trends in the utilization of cancer therapies across different age groups and stages in these two groups. Methods: MSI-H and MSS colon adenocarcinomas from 2010 to 2016 were identified using the National Cancer Database. We compared patient and disease characteristics between the two groups and evaluated the use of adjuvant chemotherapy across age groups and cancer stages. Within MSI-H and MSS groups, we conducted a landmark analysis after propensity score matching for adjuvant chemotherapy versus no chemotherapy to determine its effect on survival. Results: Of the 542,368 patients that met inclusion criteria, 120,751 (22%) had mismatch repair results available-out of these 96,928 (80%) had MSS colon cancers while 23,823 (19.7%) had MSI-H cancers. MSI-H disease had a bimodal age distribution (<40 years = 22%; ≥75 years = 26%) and was frequent among females (22%) and non-Hispanic Whites (20%). Among those < 65 years, 15% of low-risk stage 2 MSI-H patients and 40% of high-risk stage 2 MSI-H patients received adjuvant chemotherapy. More than two-thirds of stage 3 patients <65 years received adjuvant chemotherapy in both groups. After conducting propensity-score matching for age, gender, and co-morbidities, we found that adjuvant chemotherapy use had a trend towards lower overall survival (OS) in low-risk stage 2 MSI-H (HR = 1.8 [95% CI, 0.8-4.02]) and high-risk stage 2 MSI-H (HR = 1.42 [95% CI, 0.96-2.12]) groups. Adjuvant chemotherapy significantly improved OS in stage 3 colon cancer patients irrespective of microsatellite status or risk category of disease. Conclusions: MSI-H colon cancer had bimodal age distribution. Among stage 2 MSI-H patients <65 years, a notable proportion received adjuvant chemotherapy. Among MSI-H stage 2 patients, adjuvant chemotherapy use was associated with lower survival while it significantly improved survival for stage 3 patients, irrespective of MSI status.

Oral Carbon Monoxide Enhances Autophagy Modulation in Prostate, Pancreatic, and Lung Cancers.

Modulation of autophagy, specifically its inhibition, stands to transform the capacity to effectively treat a broad range of cancers. However, the clinical efficacy of autophagy inhibitors has been inconsistent. To delineate clinical and epidemiological features associated with autophagy inhibition and a positive oncological clinical response, a retrospective analysis of patients is conducted treated with hydroxychloroquine, a known autophagy inhibitor. A direct correlation between smoking status and inhibition of autophagy with hydroxychloroquine is identified. Recognizing that smoking is associated with elevated circulating levels of carbon monoxide (CO), it is hypothesized that supplemental CO can amplify autophagy inhibition. A novel, gas-entrapping material containing CO in a pre-clinical model is applied and demonstrated that CO can dramatically increase the cytotoxicity of autophagy inhibitors and significantly inhibit the growth of tumors when used in combination. These data support the notion that safe, therapeutic levels of CO can markedly enhance the efficacy of autophagy inhibitors, opening a promising new frontier in the quest to improve cancer therapies.

Synthesis and study of cationic, two-coordinate triphenylphosphine-gold-π complexes.

Cationic, two-coordinate triphenylphosphine-gold(I)-π complexes of the form [(PPh3)Au(π ligand)]⁺SbF6⁻ (π ligand=4-methylstyrene, 1∙SbF6), 2-methyl-2-butene (3∙SbF6), 3-hexyne (6∙SbF6), 1,3-cyclohexadiene (7∙SbF6), 3-methyl-1,2-butadiene (8∙SbF6), and 1,7-diphenyl-3,4-heptadiene (10∙SbF6) were generated in situ from reaction of [(PPh3)AuCl], AgSbF6, and π ligand at -78 °C and were characterized by low-temperature, multinuclear NMR spectroscopy without isolation. The π ligands of these complexes were both weakly bound and kinetically labile and underwent facile intermolecular exchange with free ligand (ΔG(≠) ≈9 kcal mol(-1) in the case of 6∙SbF6) and competitive displacement by weak σ donors, such as trifluoromethane sulfonate. Triphenylphosphine-gold(I)-π complexes were thermally unstable and decomposed above -20 °C to form the bis(triphenylphosphine) gold cation [(PPh3)2Au]⁺SbF6⁻ (2∙SbF6).

Advancements in Systemic Therapy for Pancreatic Cancer.

Outcomes for patients with advanced pancreatic cancer have improved in the past 12 years, mainly because of progress made in systemic therapies. New treatment strategies for advanced pancreatic cancer include switch maintenance with cytotoxic therapies, induction maintenance, and the utilization of targeted agents for patients with actionable variants, as well as ongoing development of cytotoxic regimens, such as NALIRIFOX. The activity of immunotherapy has been disappointing to date, but novel combinations and identifying appropriate patient populations may further unlock its potential.

Outcomes of hepatocellular carcinoma by etiology with first-line atezolizumab and bevacizumab: a real-world analysis.

PURPOSE: Hepatocellular carcinoma (HCC) is a common and deadly form of liver cancer. Combination atezolizumab and bevacizumab has improved the outcomes for patients with advanced disease. We sought to determine the impact of etiology on outcomes of patients treated with atezolizumab and bevacizumab. METHODS: This study used a real-world database. The primary outcome was overall survival (OS) by etiology of HCC; the secondary outcome was real-world time to treatment discontinuation (rwTTD). Time-to-event analyses was performed by the Kaplan-Meier method; the log-rank test to assess for differences by etiology from date of first receipt of atezolizumab and bevacizumab. The Cox proportional hazards model was used to calculate hazard ratios. RESULTS: In total, 429 patients were included (n = 216 Viral-HCC; n = 68 Alcohol-HCC; n = 145, NASH-HCC). The median overall survival for the entire cohort was 9.4 months (95% CI 7.1-10.9). Compared with Viral-HCC, the hazard ratio (HR) of death was 1.11 (95% CI 0.74-1.68, p = 0.62) for Alcohol-HCC and was 1.34 (95% CI 0.96-1.86, p = 0.08) for NASH-HCC. The median rwTTD for the entire cohort was 5.7 months (95% CI 5.0-7.0 months). The HR of rwTTD was 1.24 (95% CI 0.86-1.77, p = 0.25) for Alcohol-HCC and was 1.31 (95% CI 0.98-1.75, p = 0.06) in reference to TTD with Viral-HCC. CONCLUSIONS: In this real-world cohort of patients with HCC receiving first-line atezolizumab and bevacizumab, we did not identify an association between etiology and OS or rwTTD. This suggests that the efficacy of atezolizumab and bevacizumab may be similar across HCC etiologies. Further prospective studies are needed to confirm these findings.

The Clinical Implications of Reversions in Patients with Advanced Pancreatic Cancer and Pathogenic Variants in BRCA1, BRCA2, or PALB2 after Progression on Rucaparib.

PURPOSE: PARP inhibitors (PARPi) provide an effective maintenance option for patients with BRCA- or PALB2-mutated pancreatic cancer. However, mechanisms of PARPi resistance and optimal post-PARPi therapeutic strategies are poorly characterized. EXPERIMENTAL DESIGN: We collected paired cell-free DNA samples and post-PARPi clinical data on 42 patients with advanced, platinum-sensitive pancreatic cancer who were treated with maintenance rucaparib on NCT03140670, of whom 32 developed progressive disease. RESULTS: Peripherally detected, acquired BRCA or PALB2 reversion variants were uncommon (5/30; 16.6%) in patients who progressed on rucaparib. Reversions were significantly associated with rapid resistance to PARPi treatment (median PFS, 3.7 vs. 12.5 months; P = 0.001) and poor overall survival (median OS, 6.2 vs. 23.0 months; P < 0.0001). All patients with reversions received rechallenge with platinum-based chemotherapy following PARPi progression and experienced faster progression on this therapy than those without reversion variants (real-world time-to-treatment discontinuation, 2.4 vs. 5.8 months; P = 0.004). Of the patients who progressed on PARPi and received further chemotherapy, the OS from initiation of second-line therapy was significantly lower in those with reversion variants than in those without (5.5 vs. 12.0 months, P = 0.002). Finally, high levels of tumor shedding were independently associated with poor outcomes in patients who received rucaparib. CONCLUSIONS: Acquired reversion variants were uncommon but detrimental in a population of patients with advanced BRCA- or PALB2-related pancreatic ductal adenocarcinoma who received maintenance rucaparib. Reversion variants led to rapid progression on PARPi, rapid failure of subsequent platinum-based treatment, and poor OS of patients. The identification of such variants in the blood may have both predictive and prognostic value. See related commentary by Tsang and Gallinger, p. 5005.

Mechanistic analysis of gold(I)-catalyzed intramolecular allene hydroalkoxylation reveals an off-cycle bis(gold) vinyl species and reversible C-O bond formation.

Mechanistic investigation of gold(I)-catalyzed intramolecular allene hydroalkoxylation established a mechanism involving rapid and reversible C-O bond formation followed by turnover-limiting protodeauration from a mono(gold) vinyl complex. This on-cycle pathway competes with catalyst aggregation and formation of an off-cycle bis(gold) vinyl complex.

Structures and dynamic solution behavior of cationic, two-coordinate gold(I)-π-allene complexes.

A family of seven cationic gold complexes that contain both an alkyl substituted π-allene ligand and an electron-rich, sterically hindered supporting ligand was isolated in >90% yield and characterized by spectroscopy and, in three cases, by X-ray crystallography. Solution-phase and solid-state analysis of these complexes established preferential binding of gold to the less substituted C=C bond of the allene and to the allene π face trans to the substituent on the uncomplexed allenyl C=C bond. Kinetic analysis of intermolecular allene exchange established two-term rate laws of the form rate=k(1)[complex]+k(2)[complex][allene] consistent with allene-independent and allene-dependent exchange pathways with energy barriers of ΔG(≠)(1)=17.4-18.8 and ΔG(≠)(2)=15.2-17.6 kcal mol(-1), respectively. Variable temperature (VT) NMR analysis revealed fluxional behavior consistent with facile (ΔG(≠)=8.9-11.4 kcal mol(-1)) intramolecular exchange of the allene π faces through η(1)-allene transition states and/or intermediates that retain a staggered arrangement of the allene substituents. VT NMR/spin saturation transfer analysis of [{P(tBu)(2)o-binaphthyl}Au(η(2)-4,5-nonadiene)](+)SbF(6)(-) (5), which contains elements of chirality in both the phosphine and allene ligands, revealed no epimerization of the allene ligand below the threshold for intermolecular allene exchange (ΔG(≠)(298K)=17.4 kcal mol(-1)), which ruled out the participation of a η(1)-allylic cation species in the low-energy π-face exchange process for this complex.