Design and Synthesis of Functionally Active 5-Amino-6-Aryl Pyrrolopyrimidine Inhibitors of Hematopoietic Progenitor Kinase 1

Immune activating agents represent a valuable class of therapeutics for the treatment of cancer. An area of active research is expanding the types of these therapeutics that are available to patients via targeting new biological mechanisms. Hematopoietic progenitor kinase 1 (HPK1) is a negative regulator of immune signaling and a target of high interest for the treatment of cancer. Herein, we present the discovery and optimization of novel amino-6-aryl pyrrolopyrimidine inhibitors of HPK1 starting from hits identified via virtual screening. Key components of this discovery effort were structure-based drug design aided by analyses of normalized B-factors and optimization of lipophilic efficiency.

Standards of Care for the Health of Transgender and Gender Diverse People, Version 8

Background: Transgender healthcare is a rapidly evolving interdisciplinary field. In the last decade, there has been an unprecedented increase in the number and visibility of transgender and gender diverse (TGD) people seeking support and gender-affirming medical treatment in parallel with a significant rise in the scientific literature in this area. The World Professional Association for Transgender Health (WPATH) is an international, multidisciplinary, professional association whose mission is to promote evidence-based care, education, research, public policy, and respect in transgender health. One of the main functions of WPATH is to promote the highest standards of health care for TGD people through the Standards of Care (SOC). The SOC was initially developed in 1979 and the last version (SOC-7) was published in 2012. In view of the increasing scientific evidence, WPATH commissioned a new version of the Standards of Care, the SOC-8. Aim: The overall goal of SOC-8 is to provide health care professionals (HCPs) with clinical guidance to assist TGD people in accessing safe and effective pathways to achieving lasting personal comfort with their gendered selves with the aim of optimizing their overall physical health, psychological well-being, and self-fulfillment. Methods: The SOC-8 is based on the best available science and expert professional consensus in transgender health. International professionals and stakeholders were selected to serve on the SOC-8 committee. Recommendation statements were developed based on data derived from independent systematic literature reviews, where available, background reviews and expert opinions. Grading of recommendations was based on the available evidence supporting interventions, a discussion of risks and harms, as well as the feasibility and acceptability within different contexts and country settings. Results: A total of 18 chapters were developed as part of the SOC-8. They contain recommendations for health care professionals who provide care and treatment for TGD people. Each of the recommendations is followed by explanatory text with relevant references. General areas related to transgender health are covered in the chapters Terminology, Global Applicability, Population Estimates, and Education. The chapters developed for the diverse population of TGD people include Assessment of Adults, Adolescents, Children, Nonbinary, Eunuchs, and Intersex Individuals, and people living in Institutional Environments. Finally, the chapters related to gender-affirming treatment are Hormone Therapy, Surgery and Postoperative Care, Voice and Communication, Primary Care, Reproductive Health, Sexual Health, and Mental Health. Conclusions: The SOC-8 guidelines are intended to be flexible to meet the diverse health care needs of TGD people globally. While adaptable, they offer standards for promoting optimal health care and guidance for the treatment of people experiencing gender incongruence. As in all previous versions of the SOC, the criteria set forth in this document for gender-affirming medical interventions are clinical guidelines; individual health care professionals and programs may modify these in consultation with the TGD person.

LTK fusions: A new target emerges in non-small cell lung cancer

Identification of targetable fusions as oncogenic drivers in non-small cell lung cancer has transformed its diagnostic and therapeutic paradigm. In a recent article in Nature, Izumi et al. report the discovery of CLIP1-LTK fusion as a novel oncogenic driver in lung cancer, targetable using the ALK tyrosine kinase inhibitor lorlatinib.

Quantitative evaluation of coronary artery occlusion by 3D coronary volume reconstruction in a large animal model of acute myocardial infarction

Background

Large animal models of acute myocardial infarction (MI) offer an important platform to test novel therapies. Consistency of infarct size between animals is critical to ensure an accurate assessment of therapies against control. However, anatomical variation challenges the ability to achieve a consistent infarct size and care must be taken to respect the principles of the 3Rs through minimisation of interventional fatalities.

Purpose

To standardise the approach of a closed chest model of balloon occlusion-facilitated MI. Novel 3-dimensional quantitative coronary angiography (3DQCA) software has been used retrospectively to identify a correlation between coronary volume occlusion and the extension of the myocardial scar.

Methods

Twenty-four Yorkshire pigs (mean weight 63.1±3 kg) underwent a closed chest MI model via percutaneous occlusion of the mid portion of the left anterior descending artery (LAD) for 60 minutes. The evaluation of the myocardial damage was obtained via cardiac magnetic resonance imaging (CMR) between 24 and 48 hours after the MI model (Acute) and at 4–5 weeks after MI (Chronic). Troponin I was also measured at multiple timepoints. 3DQCA reconstruction (QAngio XA 3D, Medis medical imaging systems NL) was generated from 2 angiographic projections with segmental analysis of all 3 major epicardial vessels including lumen volume, reference diameters, and segment length. The occlusive volume and vessel length was identified through co-registration of balloon position.

Results

At the short term timepoint, a significant correlation was found between the LAD volume occluded and the scar size as percentage of the LV mass (Spearman correlation 0.72, p value <0.01, Fig. 1). Using Youden index analysis we identified a cut-off point of 32.8% of the LAD volume to determine a scar volume >20% (Fig. 2). At chronic phase the correlation between these two variables was not significant, although there was a trend towards significance (p value = 0.06, Cor = 0.54). No significant correlation was found with serum Troponin I.

Conclusions

There is a significant correlation between the LAD volume occluded and the overall scar size in the acute phase and at least 32.8% of the LAD volume should be occluded to determine a scar volume >20% of the entire LV. This indicates that a prospective measure of occluded LAD volume might minimise the intra-experimental variability in studies aiming to reduce infarct size and acute myocardial injury.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): This research work was supported by grants awarded to Professor Ascione: the British Heart Foundation (BHF) (BHF IG/14/2/30991, BHF RM/13/2/30158), and the Medical Research Council (MRC) (MRC MR/L012723/1).

Diagnostic and prognostic role of peak troponin T in patients with acute coronary syndromes and non-obstructive coronary arteries

Background

Up to 10% of patients who present with an acute coronary syndrome have a myocardial infarction with non-obstructive coronary arteries (MINOCA). Troponin T predicts infarct size and outcomes in patients with ST-elevation myocardial infarction. The value of peak troponin T in patients with a working diagnosis of MINOCA is not well understood.

Purpose

The aim of this study is to investigate the diagnostic and prognostic role of troponin in patients with MINOCA.

Methods

Consecutive patients with a working diagnosis of MINOCA from a single tertiary centre who underwent comprehensive cardiovascular magnetic resonance (CMR) imaging with late gadolinium enhancement (LGE) were followed prospectively. Peak troponin T was identified during the index admission and divided into deciles and quartiles for analysis. The primary endpoint was all-cause mortality.

Results

Among 796 patients undergoing CMR, 719 met the study criteria and had underwent a diagnostic quality scan. The peak Troponin T threshold for optimal diagnostic sensitivity and specificity was 211 ng/L. Peak troponin T ≥211 ng/L and time to CMR of ≤14 days has a sensitivity of 94%, specificity of 35%, PPV 57% and NPV 94% for the CMR making a diagnosis. Each increase in troponin decile increases the mean diagnostic yield of the CMR by 3.65% (p<0.001, 95% CI 3.38 – 3.91; R2 0.84; Figure 1).

If the troponin is in the lowest decile and the CMR is performed at ≤14 days, the diagnostic yield is still 72%. There is no overall difference in median troponin in patients who died and those who survived (229 ng/l v. 424 ng/l; p=0.157), however mortality is significantly lower in the highest two troponin quartiles (6.9% versus 11.9%; p=0.009; Figure 2).

Conclusion

Peak troponin T is readily available during the index admission in patients presenting with MINOCA and provides useful diagnostic and prognostic information for the attending cardiologist.

Funding Acknowledgement

Type of funding sources: None. Figure 1. CMR diagnosis by troponin decileFigure 2. Mortality by troponin quartile

Sex and age differences in patients with acute coronary syndrome and non-obstructive coronary arteries: presentation and outcome

Aims

A substantial number of patients present with acute coronary syndrome (ACS) and non-obstructive coronary arteries. Sex and age differences in these patients are not well understood. This study aims to evaluate the impact of sex and age on clinical presentation and outcome in patients with ACS and non-obstructive coronary arteries, with either an ischaemic or non-ischaemic cause.

Methods and results

Consecutive patients with an ACS and non-obstructive coronary arteries (n=719) from a single tertiary centre underwent comprehensive cardiovascular magnetic resonance (CMR) imaging with late gadolinium enhancement (LGE). The primary endpoint was all-cause mortality. CMR was performed at a median time of 30 days after presentation and identified a diagnosis in 74% of patients. Patients with an ischaemic or non-ischaemic aetiology (n=529) on CMR were followed prospectively. All-cause mortality was 11% over a median follow up of 4.9 years, with no significant difference between sexes (11% versus 11% p=0.732). Women were more likely to have an ischaemic aetiology on CMR (40% v 31%, p=0.037). Age group (HR 1.48, p=0.002), log peak troponin (HR 0.78, p=0.033) and LVEF (HR 0.98, p=0.032) were independent predictors of mortality. Men aged >60 years with a non-ischaemic aetiology on their CMR were at higher risk of death than women >60 years (p=0.003).

Conclusions

There is no difference in all-cause mortality between sexes in patients presenting with ACS and non-obstructive coronary arteries but increasing age is an important predictor of mortality in both sexes.

Funding Acknowledgement

Type of funding sources: None. Sex differences in CMR diagnosisSex, age and mortality

Impaired transcriptional compensation for oxidative damage in a porcine model of ischaemic cardiomyopathy

Background

The prognosis of heart failure remains poor. Energetic imbalances related to mitochondrial dysfunction, impaired oxidative phosphorylation and oxidative damage have been implicated in the pathogenesis or worsening of heart failure (1,2). Improved understanding of the metabolic alterations in heart failure may provide new biomarkers or therapeutic targets.

Purpose

We explored mutation rate, mitochondrial copy number and regional mitochondrial gene transcription in a porcine model of ischaemic cardiomyopathy. Specifically, we investigated the Dloop region – a promotor for mitochondrial DNA- in which mutations have been implicated in many cancers. We hypothesised that there may be differences in mutation rate and oxidative damage within the mitochondrial genome.

Methods

15 female Yorkshire pigs were studied. 7 animals underwent percutaneous balloon catheter myocardial infarction followed by termination at 4 weeks. A group of 8 healthy animals served as controls. Reverse transcription quantitative PCR (RT-qPCR) assays were performed to determine the gene expression levels of mitochondrial DNA codified genes (ND1, ND2, ND4, ATP6 and ND6). Quantitative PCR (qPCR) methodology was modified to obtain the relative mitochondrial copy number, mutation rate, and oxidative damage according to established methods (3–5).

Results

Significant mitochondrial transcriptional activity of the genes studied was seen in both groups (see Table 1 and 2). When examining the ND2-ND6 region (excluding the Dloop) in control animals, we note an inverse correlation with increased oxidative damage corresponding to a significantly lower mutation rate (p=0.017). There was no correlation between the mutation rate and oxidative damage in the ND6-ND2- including Dloop- region. However, when examining the Dloop specifically, there was a marked inverse correlation between oxidative damage and mutation rate (p=0.007). This suggests that in controls, there is regional variation in the susceptibility to damage within the mitochondrial genome which may trigger repair mechanisms. Indeed, the relative mitochondrial copy number was inversely associated to the mutation rate (p=0.08) in controls.

In contrast, in the chronic animals, we noted no correlation with the level of oxidative damage in the ND2-ND6, D-loop, or ND6–2 regions compared to mutation rate (p=0.52, p=0.53 and p=0.17 respectively). This indicates that there is a loss in the ability to instigate repair mechanisms in the setting of ischaemic cardiomyopathy.

Conclusions

This study demonstrates that in control animals, there appears to be regional variation in the ability to mitigate against mutations in response to oxidative damage within the mitochondrial genome. In contrast, this protection and/or the effectiveness of repair mechanisms appear to be impaired in the setting of ischaemic cardiomyopathy. This may be a driver, and in turn a therapeutic target, for adverse remodelling in this setting.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): This research work was supported by grants awarded to Professor Ascione: the British Heart Foundation (BHF) (BHF IG/14/2/30991, BHF RM/13/2/30158), and the Medical Research Council (MRC) (MRC MR/L012723/1).

Distinct metabolic transcriptional patterns and Warburg effect in porcine model of ischaemic cardiomyopathy

Background

Despite improvements in therapy for heart failure, the prognosis remains poor. Energetic imbalances related to mitochondrial dysfunction, impaired oxidative phosphorylation and oxidative damage have been implicated in the pathogenesis or worsening of heart failure. Improved understanding of the metabolic alterations of the heart may provide new biomarkers or therapeutic targets.

Purpose

It has been speculated that aerobic glycolysis, known as the Warburg effect, may be advantageous for cell survival whereby there is the opportunity for simultaneous energy production and production of intermediary metabolites crucial for anabolic pathways that sustain cell division and maintenance, and protein synthesis (1,2). In this study, we studied a preclinical model of ischaemic cardiomyopathy to investigate transcriptional patterns in two defined areas; peri-infarct and remote locations. Specifically, we investigated if aerobic glycolysis may be present in this setting.

Methods

18 female Yorkshire pigs were studied. 10 animals underwent balloon catheter myocardial infarction followed by termination at 4 weeks. A group of 8 healthy animals served as controls. All animals underwent cardiac MRI prior to termination confirming ventricular impairment and remodelling in the chronic animals (see Table 1). Gene expression profiles of glucose mobilisation and glucose metabolic markers (GLUT1, GLUT4, ANK2, GAPDH and LDHA), oxidative phosphorylation and mitochondrial function (ND1, TFAM, and PGC1-alpha), key markers of insulin resistance (AKT1, AS160) and a hypoxia marker (HIF1-alpha) were measured.

Results

Our results indicate the presence of two distinct metabolic profiles at the gene expression level, differing from control tissue but more interestingly with striking differences regionally. In the remote region compared to controls, we demonstrate a picture suggestive of increased glycolysis with significant transcriptional upregulation of GLUT1 and GLUT4 glucose transporters (p=0.01 and p=0.02 respectively), alongside a significant reduction in PGC1-alpha (p=0.04) with maintained transcriptional levels of LDHA and HIF1-alpha. Combined, these results are suggestive of reduced oxidative phosphorylation alongside compensated, or early stage, aerobic glycolytic metabolism in this region. In contrast, in peri-infarct tissue versus controls, we demonstrate a reduction in glycolysis (GLUT1 p=0.09, GLUT4 p=0.01 with a dramatic increase in GLUT1/GLUT4 ratio of 6.7 times) and reduced markers of mitochondrial function indicative of insulin-resistance with evidence of a fetal-pattern metabolic profile (see Table 2 for detailed results).

Conclusions

This study demonstrates distinct transcriptional profiles within hearts with ischaemic cardiomyopathy and for the first time suggests that the Warburg effect may be present in remote myocardium in this setting supporting the need for further work in this area.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): This research work was supported by grants awarded to Professor Ascione: the British Heart Foundation (BHF) (BHF IG/14/2/30991, BHF RM/13/2/30158), and the Medical Research Council (MRC) (MRC MR/L012723/1). Table 1. CMR parameters for animals studiedTable 2. Transcriptional signals

The role of peak troponin in patients with a working diagnosis of myocardial infarction with non-obstructive coronary arteries (MINOCA)

Funding Acknowledgements

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Rosetrees Trust James Tudor Foundation

Background

6-10% of patients who present with an acute coronary syndrome have a myocardial infarction with non-obstructive coronary arteries (MINOCA). Troponin T predicts infarct size and outcomes in patients with ST-elevation myocardial infarction. The value of peak troponin T in patients with a working diagnosis of MINOCA is not well understood.

Purpose

The aim of this study is to investigate the diagnostic and prognostic role of troponin in patients with MINOCA. 

Methods

Consecutive patients with a working diagnosis of MINOCA (n = 719) from a single tertiary centre who underwent comprehensive cardiovascular magnetic resonance (CMR) imaging with late gadolinium enhancement (LGE) were followed prospectively. The primary endpoint was all-cause mortality.

Results

Peak troponin T ≥211 ng/L and time to CMR of ≤17 days have a positive predictive value of 94% for being able to make a diagnosis on CMR. If the scan was performed in ≤17 days the diagnostic yield was still 75% even in the lowest troponin decile, but this was 59% if performed after 17 days. Each increase in troponin decile increases the mean diagnostic yield of the CMR by 3.7% (p < 0.001, 95% CI 3.4 – 3.9; R2 0.84; Figure 1). There is no overall difference in median troponin in patients who died and those who survived (229 ng/l v. 424 ng/l; p = 0.157), however mortality is significantly lower in the highest two troponin quartiles (11.9% versus 6.9%; p = 0.009, figure 2). 

Conclusions

Peak troponin T and time to CMR can be used by cardiologists to determine the likelihood of making a diagnosis using CMR. A higher troponin quartile is associated with lower mortality.

Sex and age differences in patients with a working diagnosis of myocardial infarction with non-obstructive coronary arteries (MINOCA): presentation and outcome

Funding Acknowledgements

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Rosetrees Trust James Tudor Foundation

Background Myocardial infarction with non-obstructive coronary arteries (MINOCA) is an increasingly recognised working diagnosis. Sex and age differences in MINOCA are not well understood.

Purpose  This study aims to evaluate the impact of sex and age in patients with MINOCA due to ischaemic and non-ischaemic causes on clinical presentation and outcome.

Methods and Results Consecutive patients with a working diagnosis of MINOCA (n = 719) from a single tertiary centre who underwent comprehensive cardiovascular magnetic resonance (CMR) imaging with late gadolinium enhancement (LGE) were followed prospectively. The primary endpoint was all-cause mortality.  CMR was performed at a median time of 30 days after presentation and identified a diagnosis in 74% of patients. Men were more likely to have a non-ischaemic cause on CMR (55% v. 41%, p < 0.001) and less likely to have a normal/non-specific scan (21% v. 32%, p = 0.001, figure 1).  All-cause mortality was 9.5% over a median follow up of 4.9 years, with no significant difference between sexes (8.7% versus 10.1% p = 0.456).  Age group (HR 1.61, p < 0.001) and LVEF (HR 0.98, p = 0.020) were independent predictors of mortality. Men aged >60 years with a non-ischaemic aetiology on their CMR were at higher risk of death than women with non-ischaemic causes >60 years (p = 0.003, figure 2).

Conclusions There is no difference in all-cause mortality between sexes in MINOCA but increasing age is the most important predictor of mortality in both sexes.

Spectrum of Mechanisms of Resistance to Crizotinib and Lorlatinib in ROS1 Fusion-Positive Lung Cancer

PURPOSE

Current standard initial therapy for advanced, ROS proto-oncogene 1, receptor tyrosine kinase fusion (ROS1)-positive (ROS1⁺) non-small cell lung cancer (NSCLC) is crizotinib or entrectinib. Lorlatinib, a next-generation anaplastic lymphoma kinase/ROS1 inhibitor, recently demonstrated efficacy in ROS1⁺ NSCLC, including in crizotinib-pretreated patients. However, mechanisms of lorlatinib resistance in ROS1⁺ disease remain poorly understood. Here, we assessed mechanisms of resistance to crizotinib and lorlatinib.

EXPERIMENTAL DESIGN

Biopsies from patients with ROS1 ⁺ NSCLC progressing on crizotinib or lorlatinib were profiled by genetic sequencing.

RESULTS

From 55 patients, 47 post-crizotinib and 32 post-lorlatinib biopsies were assessed. Among 42 post-crizotinib and 28 post-lorlatinib biopsies analyzed at distinct timepoints, ROS1 mutations were identified in 38% and 46%, respectively. ROS1 G2032R was the most commonly occurring mutation in approximately one third of cases. Additional ROS1 mutations included D2033N (2.4%) and S1986F (2.4%) post-crizotinib and L2086F (3.6%), G2032R/L2086F (3.6%), G2032R/S1986F/L2086F (3.6%), and S1986F/L2000V (3.6%) post-lorlatinib. Structural modeling predicted ROS1^L2086F causes steric interference to lorlatinib, crizotinib, and entrectinib, while it may accommodate cabozantinib. In Ba/F3 models, ROS1^L2086F, ROS1^{G2032R/L2086F}, and ROS1^{S1986F/G2032R/L2086F} were refractory to lorlatinib but sensitive to cabozantinib. A patient with disease progression on crizotinib and lorlatinib and ROS1 L2086F received cabozantinib for nearly 11 months with disease control. Among lorlatinib-resistant biopsies, we also identified MET amplification (4%), KRAS G12C (4%), KRAS amplification (4%), NRAS mutation (4%), and MAP2K1 mutation (4%).

CONCLUSIONS

ROS1 mutations mediate resistance to crizotinib and lorlatinib in more than one third of cases, underscoring the importance of developing next-generation ROS1 inhibitors with potency against these mutations, including G2032R and L2086F. Continued efforts are needed to elucidate ROS1-independent resistance mechanisms.

Multiple conformational states of the HPK1 kinase domain in complex with sunitinib reveal the structural changes accompanying HPK1 trans-regulation

Hematopoietic progenitor kinase 1 (HPK1 or MAP4K1) is a Ser/Thr kinase that operates via the c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) signaling pathways to dampen the T-cell response and antitumor immunity. Accordingly, selective HPK1 inhibition is considered a means to enhance antitumor immunity. Sunitinib, a multi-receptor tyrosine kinase (RTK) inhibitor approved for the management of gastrointestinal stromal tumors (GISTs), renal cell carcinoma (RCC), and pancreatic cancer, has been reported to inhibit HPK1 in vitro In this report, we describe the crystal structures of the native HPK1 kinase domain in both nonphosphorylated and doubly phosphorylated states, in addition to a double phosphomimetic mutant (T165E,S171E), each complexed with sunitinib at 2.17-3.00-Å resolutions. The native nonphosphorylated cocrystal structure revealed an inactive dimer in which the activation loop of each monomer partially occupies the ATP- and substrate-binding sites of the partner monomer. In contrast, the structure of the protein with a doubly phosphorylated activation loop exhibited an active kinase conformation with a greatly reduced monomer-monomer interface. Conversely, the phosphomimetic mutant cocrystal structure disclosed an alternative arrangement in which the activation loops are in an extended domain-swapped configuration. These structural results indicate that HPK1 is a highly dynamic kinase that undergoes trans-regulation via dimer formation and extensive intramolecular and intermolecular remodeling of the activation segment.

Reviving B-Factors: Activating ALK Mutations Increase Protein Dynamics of the Unphosphorylated Kinase

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase that can become oncogenic by activating mutations or overexpression. Full kinetic characterization of both phosphorylated and nonphosphorylated wildtype and mutant ALK kinase domain was done. Our structure-based drug design programs directed at ALK allowed us to interrogate whether X-ray crystallography data could be used to support the hypothesis that activation of ALK by mutation occurs due to increased protein dynamics. Crystallographic B-factors were converted to normalized B-factors, which allowed analysis of wildtype ALK, ALK-C1156Y, and ALK-L1196M. This data suggests that mobility of the P-loop, αC-helix, and activation loop (A-loop) may be important in catalytic activity increases, with or without phosphorylation. Both molecular dynamics simulations and hydrogen-deuterium exchange experimental data corroborated the normalized B-factors data.

Reviving B-Factors: Retrospective Normalized B-Factor Analysis of c-ros Oncogene 1 Receptor Tyrosine Kinase and Anaplastic Lymphoma Kinase L1196M with Crizotinib and Lorlatinib

Structure-based drug design (SBDD) is commonly leveraged in rational drug design. Usually, ligand and binding site atomic coordinates from crystallographic data are exploited to optimize potency and selectivity. In addition to traditional, static views of proteins and ligands, we propose using normalized B-factors to study protein dynamics as a part of the drug optimization process. A retrospective case study of crizotinib and lorlatinib bound to both c-ros oncogene 1 kinase (ROS1) and anaplastic lymphoma kinase (ALK) L1196M related normalized B-factors to differences in binding affinity. This analysis showed that ligand binding can have protein-stabilizing effects that start near the ligand but propagate through nearby residues and structural waters to more distal motifs. The potential opportunities for analyzing normalized B-factors in SBDD are also discussed.

Sequential ALK Inhibitors Can Select for Lorlatinib-Resistant Compound ALK Mutations in ALK-Positive Lung Cancer

The cornerstone of treatment for advanced ALK-positive lung cancer is sequential therapy with increasingly potent and selective ALK inhibitors. The third-generation ALK inhibitor lorlatinib has demonstrated clinical activity in patients who failed previous ALK inhibitors. To define the spectrum of ALK mutations that confer lorlatinib resistance, we performed accelerated mutagenesis screening of Ba/F3 cells expressing EML4-ALK. Under comparable conditions, N-ethyl-N-nitrosourea (ENU) mutagenesis generated numerous crizotinib-resistant but no lorlatinib-resistant clones harboring single ALK mutations. In similar screens with EML4-ALK containing single ALK resistance mutations, numerous lorlatinib-resistant clones emerged harboring compound ALK mutations. To determine the clinical relevance of these mutations, we analyzed repeat biopsies from lorlatinib-resistant patients. Seven of 20 samples (35%) harbored compound ALK mutations, including two identified in the ENU screen. Whole-exome sequencing in three cases confirmed the stepwise accumulation of ALK mutations during sequential treatment. These results suggest that sequential ALK inhibitors can foster the emergence of compound ALK mutations, identification of which is critical to informing drug design and developing effective therapeutic strategies.Significance: Treatment with sequential first-, second-, and third-generation ALK inhibitors can select for compound ALK mutations that confer high-level resistance to ALK-targeted therapies. A more efficacious long-term strategy may be up-front treatment with a third-generation ALK inhibitor to prevent the emergence of on-target resistance. Cancer Discov; 8(6); 714-29. ©2018 AACR.This article is highlighted in the In This Issue feature, p. 663.

The Axl kinase domain in complex with a macrocyclic inhibitor offers first structural insights into an active TAM receptor kinase

The receptor tyrosine kinase family consisting of Tyro3, Axl, and Mer (TAM) is one of the most recently identified receptor tyrosine kinase families. TAM receptors are up-regulated postnatally and maintained at high levels in adults. They all play an important role in immunity, but Axl has also been implicated in cancer and therefore is a target in the discovery and development of novel therapeutics. However, of the three members of the TAM family, the Axl kinase domain is the only one that has so far eluded structure determination. To this end, using differential scanning fluorimetry and hydrogen-deuterium exchange mass spectrometry, we show here that a lower stability and greater dynamic nature of the Axl kinase domain may account for its poor crystallizability. We present the first structural characterization of the Axl kinase domain in complex with a small-molecule macrocyclic inhibitor. The Axl crystal structure revealed two distinct conformational states of the enzyme, providing a first glimpse of what an active TAM receptor kinase may look like and suggesting a potential role for the juxtamembrane region in enzyme activity. We noted that the ATP/inhibitor-binding sites of the TAM members closely resemble each other, posing a challenge for the design of a selective inhibitor. We propose that the differences in the conformational dynamics among the TAM family members could potentially be exploited to achieve inhibitor selectivity for targeted receptors.

The ALK inhibitor PF-06463922 is effective as a single agent in neuroblastoma driven by expression of ALK and MYCN

The first-in-class inhibitor of ALK, c-MET and ROS1, crizotinib (Xalkori), has shown remarkable clinical efficacy in treatment of ALK-positive non-small cell lung cancer. However, in neuroblastoma, activating mutations in the ALK kinase domain are typically refractory to crizotinib treatment, highlighting the need for more potent inhibitors. The next-generation ALK inhibitor PF-06463922 is predicted to exhibit increased affinity for ALK mutants prevalent in neuroblastoma. We examined PF-06463922 activity in ALK-driven neuroblastoma models in vitro and in vivo In vitro kinase assays and cell-based experiments examining ALK mutations of increasing potency show that PF-06463922 is an effective inhibitor of ALK with greater activity towards ALK neuroblastoma mutants. In contrast to crizotinib, single agent administration of PF-06463922 caused dramatic tumor inhibition in both subcutaneous and orthotopic xenografts as well as a mouse model of high-risk neuroblastoma driven by Th-ALK(F1174L)/MYCN Taken together, our results suggest PF-06463922 is a potent inhibitor of crizotinib-resistant ALK mutations, and highlights an important new treatment option for neuroblastoma patients.

CNS Anticancer Drug Discovery and Development Conference White Paper

Following the first CNS Anticancer Drug Discovery and Development Conference, the speakers from the first 4 sessions and organizers of the conference created this White Paper hoping to stimulate more and better CNS anticancer drug discovery and development. The first part of the White Paper reviews, comments, and, in some cases, expands on the 4 session areas critical to new drug development: pharmacological challenges, recent drug approaches, drug targets and discovery, and clinical paths. Following this concise review of the science and clinical aspects of new CNS anticancer drug discovery and development, we discuss, under the rubric "Accelerating Drug Discovery and Development for Brain Tumors," further reasons why the pharmaceutical industry and academia have failed to develop new anticancer drugs for CNS malignancies and what it will take to change the current status quo and develop the drugs so desperately needed by our patients with malignant CNS tumors. While this White Paper is not a formal roadmap to that end, it should be an educational guide to clinicians and scientists to help move a stagnant field forward.

Resensitization to Crizotinib by the Lorlatinib ALK Resistance Mutation L1198F

In a patient who had metastatic anaplastic lymphoma kinase (ALK)-rearranged lung cancer, resistance to crizotinib developed because of a mutation in the ALK kinase domain. This mutation is predicted to result in a substitution of cysteine by tyrosine at amino acid residue 1156 (C1156Y). Her tumor did not respond to a second-generation ALK inhibitor, but it did respond to lorlatinib (PF-06463922), a third-generation inhibitor. When her tumor relapsed, sequencing of the resistant tumor revealed an ALK L1198F mutation in addition to the C1156Y mutation. The L1198F substitution confers resistance to lorlatinib through steric interference with drug binding. However, L1198F paradoxically enhances binding to crizotinib, negating the effect of C1156Y and resensitizing resistant cancers to crizotinib. The patient received crizotinib again, and her cancer-related symptoms and liver failure resolved. (Funded by Pfizer and others; ClinicalTrials.gov number, NCT01970865.).

Abstract 130: PF-06463922, a novel next generation ALK/ROS1 inhibitor, overcomes resistance to 1st and 2nd generation ALK inhibitors in pre-clinical models

Overcoming resistance to targeted kinase inhibitors is a major clinical challenge in oncology.

For 1st and 2nd generation ALK inhibitors acquired resistance due to ALK kinase domain mutations and/or pharmacological drug resistance are major causes for disease relapse. Here, we report the preclinical evaluation of PF-06463922, a potent and brain penetrant ALK/ROS1 inhibitor with sub to low nanomolar cell potency against ALK fusions and all known clinically-acquired resistant mutations. PF-06463922 exhibited marked cytoreductive activity in tumor xenografts driven by various ALK mutants. Furthermore, PF-06463922 led to significant regression of EML4-ALK driven lung cancer brain metastasis and prolonged mouse survival. Compared to other clinically available ALK inhibitors, PF-06463922 is unique in its superior potency against a broad spectrum of acquired ALK mutations, including the highly resistant G1202R mutant and its robust antitumor activity in the brain. Furthermore, PF-06463922 demonstrated remarkable selectivity and safety margins in a variety of preclinical studies. These results suggest that PF-06463922 may be highly effective for the treatment of patients with ALK-driven lung cancers, including those who relapsed on clinically available ALK inhibitors due to ALK secondary mutations and/or brain metastases.

Citation Format: Luc Friboulet, Helen Zou, David P. Kodack, Lars D. Engstrom, Qiuhua Li, Melissa West, Ruth W. Tang, Hui Wang, Konstantinos Tsaparikos, Jinwei Wang, Sergei Timofeevski, Dac M. Dinh, Hieu Lam, Justine L. Lam, Shinji Yamazaki, Wenyue Hu, Bhushankumar Patel, Divya Bezwada, Sidra Mahmood, Eugene Lifshits, Timothy Affolter, Patrick B. Lappin, Hovhannes Gukasyan, Nathan Lee, Shibing Deng, Rakesh K. Jain, Ted W. Johnson, Alice T. Shaw, Valeria R. Fantin, Tod Smeal. PF-06463922, a novel next generation ALK/ROS1 inhibitor, overcomes resistance to 1st and 2nd generation ALK inhibitors in pre-clinical models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 130. doi:10.1158/1538-7445.AM2015-130

PF-06463922, an ALK/ROS1 Inhibitor, Overcomes Resistance to First and Second Generation ALK Inhibitors in Preclinical Models

We report the preclinical evaluation of PF-06463922, a potent and brain-penetrant ALK/ROS1 inhibitor. Compared with other clinically available ALK inhibitors, PF-06463922 displayed superior potency against all known clinically acquired ALK mutations, including the highly resistant G1202R mutant. Furthermore, PF-06463922 treatment led to regression of EML4-ALK-driven brain metastases, leading to prolonged mouse survival, in a superior manner. Finally, PF-06463922 demonstrated high selectivity and safety margins in a variety of preclinical studies. These results suggest that PF-06463922 will be highly effective for the treatment of patients with ALK-driven lung cancers, including those who relapsed on clinically available ALK inhibitors because of secondary ALK kinase domain mutations and/or brain metastases.

Abstract PR10: Is CNS availability for oncology a no-brainer? Discovery of PF-06463922, a novel small molecule inhibitor of ALK/ROS1 with preclinical brain availability and broad spectrum potency against ALK-resistant mutations

Oncogenic fusions of anaplastic lymphoma kinase (ALK) define a subset of human lung adenocarcinoma. The 1st generation ALK inhibitor crizotinib demonstrated impressive clinical benefit in ALK-fusion positive lung cancers and was approved by the FDA for the treatment of ALK-fusion positive NSCLC in 2011. However, as seen with most kinase inhibitors, patients treated with crizotinib eventually develop resistance to therapy. Acquired ALK kinase domain mutations and disease progression in the central nervous system (CNS) are reported as main contributors to patient relapse after ALK inhibitor therapy. Preclinically, crizotinib lacks significant brain penetration and does not potently inhibit activity of ALK kinase domain mutants, so a drug discovery program was initiated aimed to develop a second generation ALK inhibitor that is more potent than existing ALK inhibitors, capable of inhibiting the resistant ALK mutants and penetrating the blood-brain-barrier. These objectives present a considerable challenge in kinase inhibitor chemical space. Here we report that PF-06463922, a novel small molecule ATP-competitive inhibitor of ALK/ROS1, showed exquisite potencies against non-mutant ALK (Ki <0.2 nM; cell IC50 ∼2 nM) and ROS1 kinase (Ki <0.005 nM; cell IC50 ∼0.2 nM), and demonstrated low nanomolar inhibitory activity against a panel of ALK kinase domain mutants representing all of the patient crizotinib resistant mutations reported to date. The more commonly reported L1196M gatekeeper mutant shows significant sensitivity to PF-06463922 (Ki 0.7 nM; cell IC50 16 nM). PF-06463922 is also very selective, and showed >100 fold kinase selectivity against 95% of the kinases tested in a 207 recombinant kinase panel. Specific design considerations were developed leading to novel ATP-competitive kinase inhibitors with desired low efflux in cell lines over-expressing p-glycoprotein and breast cancer resistance protein, providing excellent blood-brain-barrier and cell penetration properties. Efforts to optimize ligand efficiency and lipophilic efficiency leveraging structure based drug design techniques led to ligands with overlapping broad spectrum potency and low efflux. Single and repeat dose preclinical rat in vivo studies of PF-06463922 demonstrated excellent oral bioavailability and CNS availability with free brain exposure approximately 30% of free plasma levels. In addition, CNS-directed safety studies showed no adverse events at predicted efficacious concentrations. It is anticipated that PF-06463922 with its potent activities on non-mutant ALK, ALK kinase domain mutations and CNS metastases would provide great promise for patients with ALK and ROS1 positive cancers.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):PR10.

Citation Format: Ted W. Johnson, Simon Bailey, Benjamin J. Burke, Michael R. Collins, J. Jean Cui, Judy Deal, Ya-Li Deng, Martin P. Edwards, Mingying He, Jacqui Hoffman, Robert L. Hoffman, Qinhua Huang, Robert S. Kania, Phuong Le, Michele McTigue, Cynthia L. Palmer, Paul F. Richardson, Neal W. Sach, Graham L. Smith, Lars Engstrom, Wenyue Hu, Hieu Lam, Justine L. Lam, Tod Smeal, Helen Y. Zou. Is CNS availability for oncology a no-brainer? Discovery of PF-06463922, a novel small molecule inhibitor of ALK/ROS1 with preclinical brain availability and broad spectrum potency against ALK-resistant mutations. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr PR10.

Discovery of the Highly Potent PI3K/mTOR Dual Inhibitor PF-04979064 through Structure-Based Drug Design

PI3K, AKT, and mTOR are key kinases from PI3K signaling pathway being extensively pursued to treat a variety of cancers in oncology. To search for a structurally differentiated back-up candidate to PF-04691502, which is currently in phase I/II clinical trials for treating solid tumors, a lead optimization effort was carried out with a tricyclic imidazo[1,5]naphthyridine series. Integration of structure-based drug design and physical properties-based optimization yielded a potent and selective PI3K/mTOR dual kinase inhibitor PF-04979064. This manuscript discusses the lead optimization for the tricyclic series, which both improved the in vitro potency and addressed a number of ADMET issues including high metabolic clearance mediated by both P450 and aldehyde oxidase (AO), poor permeability, and poor solubility. An empirical scaling tool was developed to predict human clearance from in vitro human liver S9 assay data for tricyclic derivatives that were AO substrates.

Design and synthesis of novel N-hydroxy-dihydronaphthyridinones as potent and orally bioavailable HIV-1 integrase inhibitors

HIV-1 integrase (IN) is one of three enzymes encoded by the HIV genome and is essential for viral replication, and HIV-1 IN inhibitors have emerged as a new promising class of therapeutics. Recently, we reported the synthesis of orally bioavailable azaindole hydroxamic acids that were potent inhibitors of the HIV-1 IN enzyme. Here we disclose the design and synthesis of novel tricyclic N-hydroxy-dihydronaphthyridinones as potent, orally bioavailable HIV-1 integrase inhibitors displaying excellent ligand and lipophilic efficiencies.

Using the Golden Triangle to optimize clearance and oral absorption

The Golden Triangle is a visualization tool developed from in vitro permeability, in vitro clearance and computational data designed to aid medicinal chemists in achieving metabolically stable, permeable and potent drug candidates. Classifying compounds as permeable and stable and plotting molecular weight (MW) versus octanol:buffer (pH 7.4) distribution coefficients (logD) or estimated octanol:buffer (pH 7.4) distribution coefficients (elogD) reveals useful trends. Analysis of at least two orthogonal trends, such as permeability and clearance, can be extremely effective in balancing and optimizing multiple properties. In addition, molecular weight and logD impact potency-efficiency calculations, allowing potency, clearance and permeability to be optimized simultaneously.

Is peri-operative cortisol secretion related to post-operative cognitive dysfunction?

BACKGROUND

The pattern of cortisol secretion is influenced by surgery. As cortisol can adversely affect neuronal function, this may be an important factor in the development of post-operative cognitive dysfunction (POCD). We hypothesized that the incidence of POCD would be related to changes in cortisol level.

METHODS

We studied 187 patients aged over 60 years undergoing major non-cardiac surgery with general or regional anaesthesia. Saliva cortisol levels were measured pre-operatively and at 1 day, 7 days and 3 months post-operatively in the morning (08.00 h) and in the afternoon (16.00 h) using salivettes. Cognitive function was assessed pre-operatively, on day 7 and at 3 months using four neuropsychological tests. POCD was defined as a combined Z score of greater than 1.96.

RESULTS

After surgery, salivary cortisol concentrations increased significantly. POCD was detected in 18.8% of subjects at 1 week and in 15.2% after 3 months. The pre-operative ratios between the morning and afternoon cortisol concentrations (am/pm ratios) were 2.8 and 2.7 in patients with POCD at 1 week vs. those without POCD at 1 week, respectively. The am/pm ratios decreased significantly post-operatively to 1.9 and 1.6 at 1 week, respectively (P = 0.02 for both). In an analysis considering all am/pm ratios, it was found that the persistent flattening in am/pm ratio was significantly related to POCD at 1 week.

CONCLUSION

The pattern of diurnal variation in cortisol level was significantly related to POCD. Thus, circadian rhythm disturbance or metabolic endocrine stress could be an important mechanism in the development of cognitive dysfunction after major surgery.

Zoosporangial discharge in a Protoachlya hypogyna (Saprolegniaceae) isolate from southeastern North Carolina

Inadequate attention to zoosporangial discharge has led to confusion in watermold taxonomic literature. This problem is discussed in light of a specimen of Protoachlya hypogyna that manifests discharge characteristic of three watermold genera, and recommendations are made to reduce future inaccuracies.

Recruitment of a foreign quinone into the A1 site of photosystem I. In vivo replacement of plastoquinone-9 by media-supplemented naphthoquinones in phylloquinone biosynthetic pathway mutants of Synechocystis sp. PCC 6803

Interruption of the phylloquinone (PhQ) biosynthetic pathway by interposon mutagenesis of the menA and menB genes in Synechocystis sp. PCC 6803 results in plastoquinone-9 (PQ-9) occupying the A(1) site and functioning in electron transfer from A(0) to the FeS clusters in photosystem (PS) I (Johnson, T. W., Shen, G., Zybailov, B., Kolling, D., Reategui, R., Beauparlant, S., Vassiliev, I. R., Bryant, D. A., Jones, A. D., Golbeck, J. H., and Chitnis, P. R. (2000) J. Biol. Chem. 275, 8523-8530. We report here the isolation of menB26, a strain of the menB mutant that grows in high light by virtue of a higher PS I to PS II ratio. PhQ can be reincorporated into the A(1) site of the menB26 mutant strain by supplementing the growth medium with authentic PhQ. The reincorporation of PhQ also occurs in cells that have been treated with protein synthesis inhibitors, consistent with a displacement of PQ-9 from the A(1) site by mass action. The doubling time of the menB26 mutant cells, but not the menA mutant cells, approaches the wild type when the growth medium is supplemented with naphthoquinone (NQ) derivatives such as 2-CO(2)H-1,4-NQ and 2-CH(3)-1,4-NQ. Since PhQ replaces PQ-9 in the supplemented menB26 mutant cells, but not in the menA mutant cells, the phytyl tail accompanies the incorporation of these quinones into the A(1) site. Studies with menB26 mutant cells and perdeuterated 2-CH(3)-1,4-NQ shows that phytylation occurs at position 3 of the NQ ring because the deuterated 2-methyl group remains intact. Therefore, the specificity of the phytyltransferase enzyme is selective with respect to the group present at ring positions 2 and 3. Supplementing the growth medium of menB26 mutant cells with 1,4-NQ also leads to its incorporation into the A(1) site, but typically without either the phytyl tail or the methyl group. These findings open the possibility of biologically incorporating novel quinones into the A(1) site by supplementing the growth medium of menB26 mutant cells.

Enantiospecific synthesis of the proposed structure of the antitubercular marine diterpenoid pseudopteroxazole: revision of stereochemistry

An enantiospecific synthesis of structure 1, previously assigned to the antitubercular marine natural product pseudopteroxazole, has been accomplished as outlined in Scheme 1. Coupling of diene acid 3 and amino phenol 4 produced the amide 5, which was subjected to a novel oxidative intramolecular Diels-Alder reaction to generate the tricyclic lactam 6a stereoselectively. This product was transformed via intermediates 7-11 into the diene 13. Cationic cyclization of 13 afforded two diastereomeric tricyclic amphilectanes which were separated and transformed by parallel four-step sequences into 1 and 2, respectively. Neither 1 nor 2 were identical with pseudopteroxazole, indicating a need for revision of the structure, probably to 16.

A case of Susac syndrome

Susac syndrome is a readily recognized but often misdiagnosed disorder almost exclusively affecting women in the 20- to 40-year age range. Characterized by the clinical triad of encephalopathy, branch retinal artery occlusions, and sensorineural hearing loss, patients with Susac syndrome are often misdiagnosed with multiple sclerosis (MS). Unlike MS, however, the disease process extends over a 1- to 2-year period and then goes into remission. This presentation describes the progression of symptoms of a patient eventually diagnosed with Susac syndrome.

Personality, job level, job stressors, and their interaction as predictors of coping behavior

Hypotheses concerning the relationships among job stressors, job level, personality, and coping responses were investigated in a sample of 305 electrical contracting employees. Coping behaviors were measured with questionnaire items based on interviews conducted with a sample of the subjects. Neuroticism (N) and Extraversion (E) were the personality variables most strongly related to coping behavior. Overall, more coping variance was explained by personality than by job stressors; however, when the effects of job level and job stressors were combined, they explained more variance in complaining/quitting and seeking social support than did the personality variables. Both work situation and personality seem to be important variables in the choice of coping behaviors. There was no evidence of interactions among personality, stressors, and job level in explaining coping behavior.

Syntheses and stereochemical revision of pseudopterosin G-J aglycon and helioporin E

Revised structures are proposed for pseudopterosin G-J aglycon and helioporin E.

Recruitment of a foreign quinone into the A(1) site of photosystem I. II. Structural and functional characterization of phylloquinone biosynthetic pathway mutants by electron paramagnetic resonance and electron-nuclear double resonance spectroscopy

Electron paramagnetic resonance (EPR) and electron-nuclear double resonance studies of the photosystem (PS) I quinone acceptor, A(1), in phylloquinone biosynthetic pathway mutants are described. Room temperature continuous wave EPR measurements at X-band of whole cells of menA and menB interruption mutants show a transient reduction and oxidation of an organic radical with a g-value and anisotropy characteristic of a quinone. In PS I complexes, the continuous wave EPR spectrum of the photoaccumulated Q(-) radical, measured at Q-band, and the electron spin-polarized transient EPR spectra of the radical pair P700(+) Q(-), measured at X-, Q-, and W-bands, show three prominent features: (i) Q(-) has a larger g-anisotropy than native phylloquinone, (ii) Q(-) does not display the prominent methyl hyperfine couplings attributed to the 2-methyl group of phylloquinone, and (iii) the orientation of Q(-) in the A(1) site as derived from the spin polarization is that of native phylloquinone in the wild type. Electron spin echo modulation experiments on P700(+) Q(-) show that the dipolar coupling in the radical pair is the same as in native PS I, i.e. the distance between P700(+) and Q(-) (25.3 +/- 0.3 A) is the same as between P700(+) and A(1)(-) in the wild type. Pulsed electron-nuclear double resonance studies show two sets of resolved spectral features with nearly axially symmetric hyperfine couplings. They are tentatively assigned to the two methyl groups of the recruited plastoquinone-9, and their difference indicates a strong inequivalence among the two groups when in the A(1) site. These results show that Q (i) functions in accepting an electron from A(0)(-) and in passing the electron forward to the iron-sulfur clusters, (ii) occupies the A(1) site with an orientation similar to that of phylloquinone in the wild type, and (iii) has spectroscopic properties consistent with its identity as plastoquinone-9.

Recruitment of a foreign quinone into the A(1) site of photosystem I. I. Genetic and physiological characterization of phylloquinone biosynthetic pathway mutants in Synechocystis sp. pcc 6803

Genes encoding enzymes of the biosynthetic pathway leading to phylloquinone, the secondary electron acceptor of photosystem (PS) I, were identified in Synechocystis sp. PCC 6803 by comparison with genes encoding enzymes of the menaquinone biosynthetic pathway in Escherichia coli. Targeted inactivation of the menA and menB genes, which code for phytyl transferase and 1,4-dihydroxy-2-naphthoate synthase, respectively, prevented the synthesis of phylloquinone, thereby confirming the participation of these two gene products in the biosynthetic pathway. The menA and menB mutants grow photoautotrophically under low light conditions (20 microE m(-2) s(-1)), with doubling times twice that of the wild type, but they are unable to grow under high light conditions (120 microE m(-2) s(-1)). The menA and menB mutants grow photoheterotrophically on media supplemented with glucose under low light conditions, with doubling times similar to that of the wild type, but they are unable to grow under high light conditions unless atrazine is present to inhibit PS II activity. The level of active PS II per cell in the menA and menB mutant strains is identical to that of the wild type, but the level of active PS I is about 50-60% that of the wild type as assayed by low temperature fluorescence, P700 photoactivity, and electron transfer rates. PS I complexes isolated from the menA and menB mutant strains contain the full complement of polypeptides, show photoreduction of F(A) and F(B) at 15 K, and support 82-84% of the wild type rate of electron transfer from cytochrome c(6) to flavodoxin. HPLC analyses show high levels of plastoquinone-9 in PS I complexes from the menA and menB mutants but not from the wild type. We propose that in the absence of phylloquinone, PS I recruits plastoquinone-9 into the A(1) site, where it functions as an efficient cofactor in electron transfer from A(0) to the iron-sulfur clusters.

First total synthesis of xestobergsterol A and active structural analogues of the xestobergsterols

[formula: see text] A novel pentacyclic polyhydroxylated sterol, xestobergsterol A (1a), has been synthesized in 24 steps and in good overall yield from stigmasterol 17. The key steps of the synthesis are the Breslow remote functionalization of the polyoxygenated steroid derived from 25 and the base-catalyzed epimerization-aldol condensation of the dione derived from 27.