Efficacy of immune checkpoint inhibitors for the treatment of advanced melanoma in patients with concomitant chronic lymphocytic leukemia

BACKGROUND

Immune checkpoint inhibitors (ICIs) have revolutionized the management of advanced melanoma (AM). However, data on ICI effectiveness have largely been restricted to clinical trials, thereby excluding patients with co-existing malignancies. Chronic lymphocytic leukemia (CLL) is the most prevalent adult leukemia and is associated with increased risk of melanoma. CLL alters systemic immunity and can induce T-cell exhaustion, which may limit the efficacy of ICIs in patients with CLL. We, therefore, sought to examine the efficacy of ICI in patients with these co-occurring diagnoses.

PATIENTS AND METHODS

In this international multicenter study, a retrospective review of clinical databases identified patients with concomitant diagnoses of CLL and AM treated with ICI (US-MD Anderson Cancer Center, N = 24; US-Mayo Clinic, N = 15; AUS, N = 19). Objective response rates (ORRs), assessed by RECIST v1.1, and survival outcomes [overall survival (OS) and progression-free survival (PFS)] among patients with CLL and AM were assessed. Clinical factors associated with improved ORR and survival were explored. Additionally, ORR and survival outcomes were compared between the Australian CLL/AM cohort and a control cohort of 148 Australian patients with AM alone.

RESULTS

Between 1997 and 2020, 58 patients with concomitant CLL and AM were treated with ICI. ORRs were comparable between AUS-CLL/AM and AM control cohorts (53% versus 48%, P = 0.81). PFS and OS from ICI initiation were also comparable between cohorts. Among CLL/AM patients, a majority were untreated for their CLL (64%) at the time of ICI. Patients with prior history of chemoimmunotherapy treatment for CLL (19%) had significantly reduced ORRs, PFS, and OS.

CONCLUSIONS

Our case series of patients with concomitant CLL and melanoma demonstrate frequent, durable clinical responses to ICI. However, those with prior chemoimmunotherapy treatment for CLL had significantly worse outcomes. We found that CLL disease course is largely unchanged by treatment with ICI.

Comparison of paediatric infectious disease deaths in public sector health facilities using different data sources in the Western Cape, South Africa (2007-2021)

BACKGROUND

Routinely collected population-wide health data are often used to understand mortality trends including child mortality, as these data are often available more readily or quickly and for lower geographic levels than population-wide mortality data. However, understanding the completeness and accuracy of routine health data sources is essential for their appropriate interpretation and use. This study aims to assess the accuracy of diagnostic coding for public sector in-facility childhood (age < 5 years) infectious disease deaths (lower respiratory tract infections [LRTI], diarrhoea, meningitis, and tuberculous meningitis [TBM]) in routine hospital information systems (RHIS) through comparison with causes of death identified in a child death audit system (Child Healthcare Problem Identification Programme [Child PIP]) and the vital registration system (Death Notification [DN] Surveillance) in the Western Cape, South Africa and to calculate admission mortality rates (number of deaths in admitted patients per 1000 live births) using the best available data from all sources.

METHODS

The three data sources: RHIS, Child PIP, and DN Surveillance are integrated and linked by the Western Cape Provincial Health Data Centre using a unique patient identifier. We calculated the deduplicated total number of infectious disease deaths and estimated admission mortality rates using all three data sources. We determined the completeness of Child PIP and DN Surveillance in identifying deaths recorded in RHIS and the level of agreement for causes of death between data sources.

RESULTS

Completeness of recorded in-facility infectious disease deaths in Child PIP (23/05/2007-08/02/2021) and DN Surveillance (2010-2013) was 70% and 69% respectively. The greatest agreement in infectious causes of death were for diarrhoea and LRTI: 92% and 84% respectively between RHIS and Child PIP, and 98% and 83% respectively between RHIS and DN Surveillance. In-facility infectious disease admission mortality rates decreased significantly for the province: 1.60 (95% CI: 1.37-1.85) to 0.73 (95% CI: 0.56-0.93) deaths per 1000 live births from 2007 to 2020.

CONCLUSION

RHIS had accurate causes of death amongst children dying from infectious diseases, particularly for diarrhoea and LRTI, with declining in-facility admission mortality rates over time. We recommend integrating data sources to ensure the most accurate assessment of child deaths.

Histopathological features of complete pathological response predict recurrence-free survival following neoadjuvant targeted therapy for metastatic melanoma

BACKGROUND

Recent clinical trials demonstrated the safety and efficacy of neoadjuvant dabrafenib and trametinib (DT) among patients with surgically resectable clinical stage III BRAFV600E/K mutant melanoma. Although patients achieving a complete pathological response (pCR) exhibited superior recurrence-free survival (RFS) versus those who did not, 30% of pCR patients relapsed. We sought to identify whether histopathological features of the pathological response further delineated risk of relapse.

METHODS

Surgical resection specimens from DT-treated patients in two phase 2 clinical trials were reviewed. Histopathological features, including relative amounts of viable tumour, necrosis, melanosis, and fibrosis (hyalinized or immature/proliferative) were assessed for associations with patient outcomes.

RESULTS

Fifty-nine patients underwent surgical resection following neoadjuvant DT. Patients achieving pCR (49%) had longer RFS compared with patients who did not (P = 0.005). Patients whose treated tumour showed any hyalinized fibrosis had longer RFS versus those without (P = 0.014), whereas necrosis (P = 0.012) and/or immature/proliferative fibrosis (P = 0.026) correlated with shorter RFS. Multivariable analyses showed absence of pCR or presence of immature fibrosis independently predicted shorter RFS. Among pCR patients, mature/hyalinized-type fibrosis correlated with improved RFS (P = 0.035).

CONCLUSIONS

The extent and composition of the pathological response following neoadjuvant DT in BRAFV600E/K mutant melanoma correlates with RFS, including pCR patients. These findings support the need for detailed histological analysis of specimens collected after neoadjuvant therapy.

Pathological assessment of resection specimens after neoadjuvant therapy for metastatic melanoma

Background

Clinical trials have recently evaluated safety and efficacy of neoadjuvant therapy among patients with surgically resectable regional melanoma metastases. To capture informative prognostic data connected to pathological response in such trials, it is critical to standardize pathologic assessment and reporting of tumor response after this treatment.

Methods

The International Neoadjuvant Melanoma Consortium meetings in 2016 and 2017 assembled pathologists from academic centers to develop consensus guidelines for pathologic examination and reporting of surgical specimens from AJCC (8th edition) stage IIIB/C/D or oligometastatic stage IV melanoma patients treated with neoadjuvant-targeted or immune therapy. Patterns of pathologic response are provided context to inform these guidelines.

Results

Based on our collective experience and guided by efforts in well-established neoadjuvant settings like breast cancer, procedures directing handling of pre- and post-neoadjuvant therapy-treated melanoma specimens are provided to facilitate comparison of findings across different trials and centers. Definitions of pathologic response are provided together with guidelines for reporting and quantifying the extent of pathologic response. Finally, the spectrum of histopathologic responses observed following neoadjuvant-targeted and immune-checkpoint therapy is described and illustrated.

Conclusions

Standardizing pathologic evaluation of resected melanoma metastases following neoadjuvant-targeted or immune-checkpoint therapy allows more robust stratification of patient outcomes. This includes recognizing the spectrum of histopathologic response patterns to neoadjuvant therapy and a standard approach to grading pathologic responses. Such an approach will facilitate comparison of results across clinical trials and inform ongoing correlative studies into the mechanisms of response and resistance to agents applied in the neoadjuvant setting.

Using longitudinal targeted maximum likelihood estimation in complex settings with dynamic interventions

Longitudinal targeted maximum likelihood estimation (LTMLE) has very rarely been used to estimate dynamic treatment effects in the context of time-dependent confounding affected by prior treatment when faced with long follow-up times, multiple time-varying confounders, and complex associational relationships simultaneously. Reasons for this include the potential computational burden, technical challenges, restricted modeling options for long follow-up times, and limited practical guidance in the literature. However, LTMLE has desirable asymptotic properties, ie, it is doubly robust, and can yield valid inference when used in conjunction with machine learning. It also has the advantage of easy-to-calculate analytic standard errors in contrast to the g-formula, which requires bootstrapping. We use a topical and sophisticated question from HIV treatment research to show that LTMLE can be used successfully in complex realistic settings, and we compare results to competing estimators. Our example illustrates the following practical challenges common to many epidemiological studies: (1) long follow-up time (30 months); (2) gradually declining sample size; (3) limited support for some intervention rules of interest; (4) a high-dimensional set of potential adjustment variables, increasing both the need and the challenge of integrating appropriate machine learning methods; and (5) consideration of collider bias. Our analyses, as well as simulations, shed new light on the application of LTMLE in complex and realistic settings: We show that (1) LTMLE can yield stable and good estimates, even when confronted with small samples and limited modeling options; (2) machine learning utilized with a small set of simple learners (if more complex ones cannot be fitted) can outperform a single, complex model, which is tailored to incorporate prior clinical knowledge; and (3) performance can vary considerably depending on interventions and their support in the data, and therefore critical quality checks should accompany every LTMLE analysis. We provide guidance for the practical application of LTMLE.

Dabrafenib plus trametinib versus dabrafenib monotherapy in patients with metastatic BRAF V600E/K-mutant melanoma: long-term survival and safety analysis of a phase 3 study

Background

Previous analysis of COMBI-d (NCT01584648) demonstrated improved progression-free survival (PFS) and overall survival (OS) with combination dabrafenib and trametinib versus dabrafenib monotherapy in BRAF V600E/K-mutant metastatic melanoma. This study was continued to assess 3-year landmark efficacy and safety after ≥36-month follow-up for all living patients.

Patients and methods

This double-blind, phase 3 study enrolled previously untreated patients with BRAF V600E/K-mutant unresectable stage IIIC or stage IV melanoma. Patients were randomized to receive dabrafenib (150 mg twice daily) plus trametinib (2 mg once daily) or dabrafenib plus placebo. The primary endpoint was PFS; secondary endpoints were OS, overall response, duration of response, safety, and pharmacokinetics.

Results

Between 4 May and 30 November 2012, a total of 423 of 947 screened patients were randomly assigned to receive dabrafenib plus trametinib (n = 211) or dabrafenib monotherapy (n = 212). At data cut-off (15 February 2016), outcomes remained superior with the combination: 3-year PFS was 22% with dabrafenib plus trametinib versus 12% with monotherapy, and 3-year OS was 44% versus 32%, respectively. Twenty-five patients receiving monotherapy crossed over to combination therapy, with continued follow-up under the monotherapy arm (per intent-to-treat principle). Of combination-arm patients alive at 3 years, 58% remained on dabrafenib plus trametinib. Three-year OS with the combination reached 62% in the most favourable subgroup (normal lactate dehydrogenase and <3 organ sites with metastasis) versus only 25% in the unfavourable subgroup (elevated lactate dehydrogenase). The dabrafenib plus trametinib safety profile was consistent with previous clinical trial observations, and no new safety signals were detected with long-term use.

Conclusions

These data demonstrate that durable (≥3 years) survival is achievable with dabrafenib plus trametinib in patients with BRAF V600-mutant metastatic melanoma and support long-term first-line use of the combination in this setting.

Gut microbiome modulates response to anti-PD-1 immunotherapy in melanoma patients

Preclinical mouse models suggest that the gut microbiome modulates tumor response to checkpoint blockade immunotherapy; however, this has not been well-characterized in human cancer patients. Here we examined the oral and gut microbiome of melanoma patients undergoing anti-programmed cell death 1 protein (PD-1) immunotherapy (n = 112). Significant differences were observed in the diversity and composition of the patient gut microbiome of responders versus nonresponders. Analysis of patient fecal microbiome samples (n = 43, 30 responders, 13 nonresponders) showed significantly higher alpha diversity (P < 0.01) and relative abundance of bacteria of the Ruminococcaceae family (P < 0.01) in responding patients. Metagenomic studies revealed functional differences in gut bacteria in responders, including enrichment of anabolic pathways. Immune profiling suggested enhanced systemic and antitumor immunity in responding patients with a favorable gut microbiome as well as in germ-free mice receiving fecal transplants from responding patients. Together, these data have important implications for the treatment of melanoma patients with immune checkpoint inhibitors.

Anti-PD-1 therapy in patients with advanced melanoma and preexisting autoimmune disorders or major toxicity with ipilimumab

Background

Anti-PD-1 antibodies (anti-PD-1) have clinical activity in a number of malignancies. All clinical trials have excluded patients with significant preexisting autoimmune disorders (ADs) and only one has included patients with immune-related adverse events (irAEs) with ipilimumab. We sought to explore the safety and efficacy of anti-PD-1 in such patients.

Patients and methods

Patients with advanced melanoma and preexisting ADs and/or major immune-related adverse events (irAEs) with ipilimumab (requiring systemic immunosuppression) that were treated with anti-PD-1 between 1 July 2012 and 30 September 2015 were retrospectively identified.

Results

One hundred and nineteen patients from 13 academic tertiary referral centers were treated with anti-PD-1. In patients with preexisting AD (N = 52), the response rate was 33%. 20 (38%) patients had a flare of AD requiring immunosuppression, including 7/13 with rheumatoid arthritis, 3/3 with polymyalgia rheumatica, 2/2 with Sjogren's syndrome, 2/2 with immune thrombocytopaenic purpura and 3/8 with psoriasis. No patients with gastrointestinal (N = 6) or neurological disorders (N = 5) flared. Only 2 (4%) patients discontinued treatment due to flare, but 15 (29%) developed other irAEs and 4 (8%) discontinued treatment. In patients with prior ipilimumab irAEs requiring immunosuppression (N = 67) the response rate was 40%. Two (3%) patients had a recurrence of the same ipilimumab irAEs, but 23 (34%) developed new irAEs (14, 21% grade 3-4) and 8 (12%) discontinued treatment. There were no treatment-related deaths.

Conclusions

In melanoma patients with preexisting ADs or major irAEs with ipilimumab, anti-PD-1 induced relatively frequent immune toxicities, but these were often mild, easily managed and did not necessitate discontinuation of therapy, and a significant proportion of patients achieved clinical responses. The results support that anti-PD-1 can be administered safely and can achieve clinical benefit in patients with preexisting ADs or prior major irAEs with ipilimumab.

Incidental germline variants in 1000 advanced cancers on a prospective somatic genomic profiling protocol

BACKGROUND

Next-generation sequencing in cancer research may reveal germline variants of clinical significance. We report patient preferences for return of results and the prevalence of incidental pathogenic germline variants (PGVs).

PATIENTS AND METHODS

Targeted exome sequencing of 202 genes was carried out in 1000 advanced cancers using tumor and normal DNA in a research laboratory. Pathogenic variants in 18 genes, recommended for return by The American College of Medical Genetics and Genomics, as well as PALB2, were considered actionable. Patient preferences of return of incidental germline results were collected. Return of results was initiated with genetic counseling and repeat CLIA testing.

RESULTS

Of the 1000 patients who underwent sequencing, 43 had likely PGVs: APC (1), BRCA1 (11), BRCA2 (10), TP53 (10), MSH2 (1), MSH6 (4), PALB2 (2), PTEN (2), TSC2 (1), and RB1 (1). Twenty (47%) of 43 variants were previously known based on clinical genetic testing. Of the 1167 patients who consented for a germline testing protocol, 1157 (99%) desired to be informed of incidental results. Twenty-three previously unrecognized mutations identified in the research environment were confirmed with an orthogonal CLIA platform. All patients approached decided to proceed with formal genetic counseling; in all cases where formal genetic testing was carried out, the germline variant of concern validated with clinical genetic testing.

CONCLUSIONS

In this series, 2.3% patients had previously unrecognized pathogenic germline mutations in 19 cancer-related genes. Thus, genomic sequencing must be accompanied by a plan for return of germline results, in partnership with genetic counseling.

Spinal and basilar extraparenchymal neurocysticercosis

The case of a 40 year old male with spinal and basilar neurocysticercosis is presented. After presentation with myelopathy many years later, the original diagnosis of aqueduct stenosis is under question. The case and disease process are discussed.

A phase I multi-institutional study of systemic sorafenib in conjunction with regional melphalan for in-transit melanoma of the extremity

BACKGROUND

Isolated limb infusion with melphalan (ILI-M) corrected for ideal body weight (IBW) is a well-tolerated treatment for patients with in-transit extremity melanoma with an approximate 29 % complete response (CR) rate. Sorafenib, a multi-kinase inhibitor, has been shown to augment tumor response to chemotherapy in preclinical studies.

METHODS

A multi-institutional, dose-escalation, phase I study was performed to evaluate the safety and antitumor activity of sorafenib in combination with ILI-M. Patients with AJCC stage IIIB/IIIC/IV melanoma were treated with sorafenib starting at 400 mg daily for 7 days before and 7 days after ILI-M corrected for IBW. Toxicity, drug pharmacokinetics, and tumor protein expression changes were measured and correlated with clinical response at 3 months.

RESULTS

A total of 20 patients were enrolled at two institutions. The maximum tolerated dose (MTD) of sorafenib in combination with ILI-M was 400 mg. Four dose-limiting toxicities occurred, including soft tissue ulcerations and compartment syndrome. There were three CRs (15 %) and four partial responses (20 %). Of patients with the Braf mutation, 83 % (n = 6) progressed compared with only 33 % without (n = 12). Short-term sorafenib treatment did alter protein expression as measured with reverse phase protein array (RPPA) analysis, but did not inhibit protein expression in the MAP kinase pathway. Sorafenib did not alter melphalan pharmacokinetics.

CONCLUSION

This trial defined the MTD of systemically administered sorafenib in combination with ILI-M. Although some responses were seen, the addition of sorafenib to ILI-M did not appear to augment the effects of melphalan but did increase regional toxicity.

Role and therapeutic potential of PI3K-mTOR signaling in de novo resistance to BRAF inhibition

BRAF inhibition is highly active in BRAF-mutant melanoma, but the degree and duration of responses is quite variable. Improved understanding of the mechanisms of de novo resistance may lead to rational therapeutic strategies with improved efficacy. Proteomic analysis of BRAF-mutant, PTEN-wild-type human melanoma cell lines treated with PLX4720 demonstrated that sensitive and de novo resistant lines exhibit similar RAS-RAF-MEK-ERK pathway inhibition, but the resistant cells exhibited durable activation of S6 and P70S6K. Treatment with the mTOR inhibitor rapamycin blocked activation of P70S6K and S6, but it also increased activation of AKT and failed to induce cell death. Combined treatment with rapamycin and PX-866, a PI3K inhibitor, blocked the activation of S6 and AKT and resulted in marked cell death when combined with PLX4720. The results support the rationale for combined targeting of BRAF and the PI3K-AKT pathways and illustrate how target selection will be critical to such strategies.

Quantitative assessment of AKT activation in melanoma

9022

Background: Activating mutations of BRAF are highly prevalent in melanoma. However, multiple lines of evidence suggest that other pathways must also contribute to this disease. Activation of the PI3K-AKT pathway has been implicated in melanoma by mutations of NRAS and PTEN. Little direct information is known about the activation of the PI3K-AKT signaling pathway in melanoma, particularly in metastases. Methods: Proteins isolated from 99 frozen melanoma tumors were measured by reverse phase protein arrays (RRPA). A total of 53 proteins were assessed using validated antibodies. Activating mutations were assessed by mass spectroscopy-based genotyping. Activation of AKT (phospho-AKT) was compared to mutations and anatomic sites. Results: Samples from 75 regional metastases (LN or in-transit) and 24 distant metastases were analyzed. Technical replicates (same lysate) and biological replicates (same tumor, different lysates) demonstrated average Pearson correlation coefficients (r) of > 0.90, supporting the high technical quality of the analysis. A positive correlation was observed between levels of p-AKT and known AKT substrates p-GSK3 and p-TSC2 (p< 0.001 for both), and a negative correlation with PTEN (p < 0.01), supporting the maintenance of phosphorylation events during sample processing. Relative differences in p-AKT by RPPA were also confirmed by immunohistochemistry of representative tumors. Tumors with BRAF mutations had higher levels of p-AKT than tumors with NRAS mutations (p = 0.03). Indeed, tumors with NRAS mutations had p-AKT levels similar to tumors wild-type for BRAF and NRAS (p =0.73). Detailed analysis demonstrated that all tumors with elevated p-AKT had low PTEN expression. Similar results were seen in human melanoma cell lines. Analysis of distant metastases demonstrated that brain metastases had higher levels of p-AKT, p-GSK3, and p-TSC2, and lower levels of PTEN, compared to metastases to the lung or liver. Conclusions: AKT activation in melanoma correlates with PTEN expression, and does not correlate with NRAS mutation. Activation of the PI3K-AKT pathway may contribute to the aggressiveness of brain metastases. These findings have clinical implications for targeting this pathway, and demonstrate the feasibility and potential of RPPA analysis of signaling pathways in melanoma.

No significant financial relationships to disclose.

Selective activity of dasatinib for the most common KIT mutation in melanoma (L576P)

9019

Background: Point mutations in the KIT receptor tyrosine kinase gene have recently been identified in melanomas from mucosal, acral lentiginous (AL), and chronically sun-damaged (CSD) sites. An improved understanding of the molecular characteristics of melanoma-prevalent KIT mutations may lead to more effective therapeutic approaches. Methods: Human melanoma cell lines were screened by mass-spectroscopy based genotyping for KIT mutations, and a cell line with an endogenous L576P KIT mutation was identified. The cell line was treated in vitro with a panel of small molecule KIT inhibitors and the effects on cell viability were quantified. Molecular modeling of the interaction of the inhibitors with the KIT L576P mutant protein was determined to estimate binding affinity. PET/CT studies were performed on patients with mucosal melanoma harboring the L576P mutation pre- and post-dasatinib treatment. Results: We have identified the first human melanoma cell line with an endogenous L576P mutation, the most common KIT mutation in melanoma. In vitro testing demonstrated that this cell line is resistant to imatinib, nilotinib and sorafenib (0 - 1 uM), KIT inhibitors shown to be effective in non-melanoma cells with other KIT mutations. However, the mutant cell line was inhibited by dasatinib at concentrations as low as 10 nM, and was significantly more sensitive than melanoma cell lines with wild-type KIT (p = 0.02). No difference in sensitivity to Src inhibitors was observed, supporting that this sensitivity was due to KIT inhibition. Molecular modeling demonstrated that the L576P mutation induces structural changes in KIT that reduce the affinity for imatinib but not for dasatinib. Two metastatic melanoma patients with the L576P KIT mutation were treated with dasatinib, including one patient previously treated with imatinib. Both patients had marked reduction and elimination of tumor FDG- avidity by PET imaging after dasatinib treatment. Conclusions: This data supports that dasatinib has a selective inhibitory effect against the most common KITmutation in melanoma and has implications for the development of AL, CSD, and mucosal melanoma treatment.

[Table: see text]

Phase I/II study of the combination of sorafenib and temsirolimus in patients with metastatic melanoma

9026

Background: Inhibition of Signal transduction pathways at multiple levels may be a more effective therapeutic cancer strategy for advanced cancer patients. Sorafenib, a multikinase inhibitor and temsirolimus, an inhibitor of critical survival pathways, are targeted compounds with single agent anti-tumor activity in several solid tumors. Inhibition of mutant B-Raf and the AKT signaling pathway has been effective in vitro with melanoma cell lines. Therefore, we designed a phase I/II study of the combination of sorafenib and temsirolimus to inhibit multiple pathways for greater clinical efficacy.Methods: Patients (pts) with stage IV or unresectable or recurrent stage III melanoma and ECOG performance status of 0 to 1 were eligible. Pts with treated brain metastases were eligible if they had not progressed for 3 months. Sorafenib was given orally twice daily and temsirolimus was given intravenously once a week, both starting on day 1, with a 4-week cycle. Responses were assessed every 2 cycles per RECIST. Results: To date, 22 pts have been enrolled and treated. Median age was 56.5, and 17 were male. Median ECOG PS was 1. The MTD doses were sorafenib 400 mg in AM / 200 mg in PM daily and temsirolimus 25 mg IV weekly. The dose-limiting toxicity (DLT) included thrombocytopenia, hand-foot syndrome (HFS), serum transaminase elevation and hypertriglyceridemia. Other common adverse events were dry skin, fatigue, taste alteration, anorexia, flatulence, diarrhea, skin rash, insomnia, neuropathy, myalgia, and headaches, anemia, hypercholesterolemia, hyperglycemia and hypophosphatemia. There were 9 pts with stable disease among 21 evaluable pts for response. Conclusions: Sorafenib and temsirolimus can be administered concomitantly although with significant toxicity at higher dose levels. Currently, pts are enrolled in a dose expansion cohort. Pharmacokinetic data will be presented. Supported in part by NCI grant UO1 CA062461 and N01 CM17003.

[Table: see text]

No significant financial relationships to disclose.

The collaborative care practice model in the long-term care of individuals with bipolar disorder: a case study

Effective therapies for the long-term care of individuals with bipolar disorder feature medication management and an interactional component between patients and care providers. In this paper, we discuss the effectiveness of applying a collaborative practice model to the long-term care of individuals with bipolar disorder who receive outpatient treatment. The model emphasizes that patients are co-managers of their illness and successful outcomes are enhanced within a supportive social environment. Key elements include joint patient-provider treatment planning and decision making. Several controlled trials have demonstrated that when the model is adopted, significant improvements in clinical and functional outcomes can be achieved. The paper concludes with a case study, which illustrates that the model can be successfully implemented in a clinical setting. Given that the clinical and research evidence demonstrates the effectiveness of the model, we suggest that advanced practice psychiatric nurses apply key elements of the collaborative practice model in their work with clients with bipolar disorder.

Comparison of cervical disk implants and cervical disk fusion treatments in human cadaveric models

Articulating cervical disk implants have been proposed as an alternative to disk fusion in the treatment of cervical disk disease. To examine the mechanical effect of articulating cervical disk implants (ACDI) versus simulated cervical disk fusion, a mechanical test device was constructed and cadaveric tests were carried out. While results show little effect on the pressures above and below the treatment level, the percent hysteretic behavior of the specimens trended to be higher for the ACDI, indicating that these implants retain more of the natural energy absorption capability of the cervical spine.

Natural history of metastatic melanoma patients with CNS metastases

8054

Background: Melanoma has a high rate of CNS metastasis (mets). The objective of this study was to evaluate the characteristics and outcomes of melanoma patients (pts) who develop CNS mets. Methods: 333 pts with a diagnosis of CNS mets were identified from databases of 743 chemotherapy naïve metastatic melanoma (MM) pts enrolled on clinical trials between 1986 and 2004. Their clinical and pathological characteristics were reviewed. Results: The site of primary melanoma was head or neck (60/333; 18%), trunk/abdomen (144/333; 43%), limbs (66/333; 20%), ocular (2/333; 1%), or unknown (61/333; 18%). Median Breslow thickness (BT) = 2.2 mm; BT < 1 mm = 39/217 (18%); and BT < 2 mm = 95/217 (44%). Median Clark level (CL)= IV; CL I = 0/180 (0%); CL II = 14/180 (8%); CL III = 70/180 (39%); and CL IV = 96/180 (53%) . The median interval from diagnosis of primary melanoma to CNS mets = 29.6 (range 0.3–393) months (mos). Median survival (MS) from CNS diagnosis = 4.6 (range 0–120) mos. MS was highest for pts with brain mets (n=307; 4.8 mos) compared to pts with brain mets plus leptomeningeal disease (LMD) (14; 2.0 mos) or pts with LMD alone (11; 1.2 mos) (p=.0048 for pts with LMD vs. without). MS varied for pts with 1 (6.6 mos), 2 (4.2 mos), 3 (5.9 mos) or >3 (3.5 mos) brain lesions at diagnosis of CNS mets. Among pts diagnosed with CNS mets at or prior to systemic therapy, MS was longer for pts with CNS mets only (n=20; 14.3 mos) compared to pts with CNS mets concurrent with extracranial mets (63; 7 mos) (p=.003). Patients who developed CNS mets after starting chemotherapy for extracranial mets (n=250; 3.7 mos) had a shorter MS than those diagnosed at or before systemic therapy (83; 7.9 mos, p<.001). Among pts diagnosed after starting systemic therapy, CNS mets were detected ≤ 12 months from the start of chemotherapy in 30% of pts (MS = 3 mos), 12–24 mos in 37% of pts (MS = 4.6 mos), and > 36 mos in 32% of pts (MS = 11.1 mos, p=.044 vs. other groups). Conclusions: This study represents one of the largest cohorts of pts with melanoma CNS mets. The presence of LMD, or development of CNS mets after starting systemic therapy, is associated with a worse prognosis. Among pts diagnosed with CNS mets at or before starting systemic therapy, the presence of concurrent non-CNS mets also portends for a worse outcome. Supported in part by Carol Courtney Memorial fund and Chiron Corporation.

No significant financial relationships to disclose.

Pharmacologic analysis of non-synonymous coding h5-HT2A SNPs reveals alterations in atypical antipsychotic and agonist efficacies

The 5-HT(2A)-serotonin receptor is a major molecular target for most atypical antipsychotic drugs as well as most hallucinogens, which can exacerbate psychotic symptoms. In this study, we examined whether random sequence variations in the gene (single nucleotide polymorphisms, SNPs) encoding the 5-HT(2A)-serotonin receptor could explain inter-individual variability in atypical antipsychotic and agonist drug response. We examined the in vitro pharmacology of four non-synonymous SNPs, which give rise to T25N, I197V, A447V, and H452Y variant 5-HT(2A)-serotonin receptors. Our data indicate that these non-synonymous SNPs exert statistically significant, although modest, effects on the affinity and functional effects of several currently approved atypical antipsychotics (aripiprazole, clozapine, olanzapine, quetiapine, risperidone, and ziprasidone). Also, the 5-HT(2A) receptor SNPs slightly altered the potency and relative efficacy of a small number of selected agonists (2,5-dimethoxy-4-iodoamphetamine, tryptamine, 5-hydroxytryptamine, m-chlorophenylpiperazine, and 5-methoxy-N, N-dimethyltryptamine). In all, our results show that the in vitro pharmacological effects of the SNPs are drug specific.

Management of traumatic cerebrospinal fluid fistula

Cerebrospinal fluid fistulae present a common management problem for the surgeon managing craniofacial trauma. Controversies exist concerning various aspects of treatment. These controversial management issues include cerebrospinal fluid drainage, antibiotic prophylaxis, timing of surgical intervention, and techniques of repair. Although most cerebrospinal fluid fistulae cease spontaneously, some fistulae persist, resulting in the potential for life-threatening complications. A review of these issues is presented, together with a suggested management protocol.

Suppression of matrix metalloproteinase-2 gene expression and invasion in human glioma cells by MMAC/PTEN

Human gliomas are highly invasive, and remain to be a major obstacle for any effective therapeutic remedy. Among many other factors, gliomas express elevated levels of matrix metalloproteinases (MMPs), which have been implicated to play an important role in tumor invasion as well as neovascularization. The tumor suppressor gene mutated in multiple advanced cancers/phosphatase and tensin homologue (MMAC/PTEN) has been shown to inhibit cell migration, spreading, and focal adhesion. In this study, we determined whether MMAC/PTEN inhibits tumor invasion by modulating MMP-2 activity. Our results showed that reintroduction of the MMAC/PTEN gene into human glioma U251 and U87 cells modified their phenotype and growth characteristics. The ability of MMAC/PTEN to induce anoikis in U251 cells was accompanied by a significant inhibition of in vitro invasion (70%). Expression of MMAC/PTEN in U251 and U87 cells inhibited MMP-2 enzymatic activity as determined by zymography. Furthermore, MMAC/PTEN expression strongly decreased MMP-2 mRNA levels, which correlated well with the inhibition of invasion capacity in these cells. Concomitant with MMP-2 expression and activity, MMP-2 promoter activity was also reduced in MMAC/PTEN expressing cells. Our observations suggest that MMAC/PTEN inhibits tumor cell invasion in part by regulating MMP-2 gene transcription and thereby its enzymatic activity. Further characterization of this regulation will facilitate the development of MMAC/PTEN based gene therapy for gliomas.

Differential effects of phosphatidylinositol-3/Akt-kinase inhibition on apoptotic sensitization to cytokines in LNCaP and PCc-3 prostate cancer cells

Alterations in phosphatidylinositol 3'-kinase (PI3'-kinase) and Akt activation frequently occur in prostate cancer and may disrupt apoptotic induction by such cytokines as tumor necrosis factor (TNF) and TNF-related apoptosis-inducing ligand (TRAIL). To examine the role of PI3' phosphorylation in the cellular response to cytokines, two prostate cancer cell lines with constitutively activated PI3'-kinase cascades (LNCaP and PC-3) were examined for direct sensitivity to cytokines. TNF or TRAIL alone failed to activate apoptosis in either LNCaP or PC-3 cells, and drug-mediated inhibition of the PI3k/Akt cascade caused only minimal activation of apoptosis in either cell line. Suppression of PI3'-kinase/Akt signaling markedly enhanced the apoptotic activity of both TNF and TRAIL in LNCaP cells but not in PC-3 cells. Adenovirus-mediated PTEN/MMAC1 expression in LNCaP cells reduced Akt activation, activated apoptosis, and sensitized cells to TNF but not to TRAIL. Together, these results suggest that PI3'-kinase signaling inhibits both TNF-mediated and TRAIL-mediated apoptosis but may represent one of several apoptotic resistance mechanisms that inhibit cytokine-mediated killing of prostate cancer cells.

MMAC1/PTEN inhibits cell growth and induces chemosensitivity to doxorubicin in human bladder cancer cells

The development and progression of bladder cancer is associated with multiple alterations in the genome, including loss of chromosome 10. Recently, MMAC1/PTEN, a phosphatidylinositol phosphatase, has been mapped to chromosome 10q23. We previously demonstrated that MMAC1/PTEN has tumor suppressive properties in glioblastoma and prostate cancer. To investigate the efficacy of gene therapy with MMAC1/PTEN, we examined whether the exogenous introduction of MMAC1/PTEN via an adenoviral vector (Ad-MMAC) can inhibit tumor growth and reverse drug resistance to doxorubicin in human bladder cancer cells. Human bladder cancer cell lines UM-UC-3 and T24 were infected with Ad-MMAC to induce exogenous expression of MMAC1/PTEN. The cells were then analysed for cell growth and expression of phosphorylated protein kinase B (Akt/PKB) and MMAC1/PTEN. UM-UC-6dox, a doxorubicin resistant subline, was infected with Ad-MMAC to evaluate its role in reversing drug resistance to doxorubicin. We found that MMAC1/PTEN suppressed tumor growth in UM-UC-3 and T24 cells with arrest in the G1 phase of the cell cycle. We also showed that gene therapy with MMAC1/PTEN abrogated phosphorylated Akt/PKB expression in UM-UC-3, T24 and UMUC-6dox cells, and restored doxorubicin sensitivity in UM-UC-6dox. These data demonstrate that MMAC1/PTEN can induce growth suppression and increase sensitivity to doxorubicin in bladder cancer cells and suggest that the MMAC1/PTEN gene and its pathways can be therapeutic targets for bladder cancer.

The PTEN/MMAC1/TEP tumor suppressor gene decreases cell growth and induces apoptosis and anoikis in breast cancer cells

The PTEN/MMAC1/TEP (PTEN) tumor suppressor gene at 10q23.3 is mutated in multiple types of sporadic tumors including breast cancers and also in the germline of patients with the Cowden's breast cancer predisposition syndrome. The PTEN gene encodes a multifunctional phosphatase capable of dephosphorylating the same sites in membrane phosphatidylinositols phosphorylated by phosphatidylinositol 3'-kinase (PI3K). We demonstrate herein that loss of PTEN function in breast cancer cells results in an increase in basal levels of phosphorylation of multiple components of the P13K signaling cascade as well as an increase in duration of ligand-induced signaling through the P13K cascade. These alterations are reversed by wild-type but not phosphatase inactive PTEN. In the presence of high concentrations of serum, enforced expression of PTEN induces a predominant G1 arrest consistent with the capacity of PTEN to evoke increases in the expression of the p27Kip1 cyclin dependent kinase inhibitor. In the presence of low concentrations of serum, enforced PTEN expression results in a marked increase in cellular apoptosis, a finding which is consistent with the capacity of PTEN to alter the phosphorylation, and presumably function, of the AKT, BAD, p70S6 kinase and GSK3 alpha apoptosis regulators. Under anchorage-independent conditions, PTEN also induces anoikis, a form of apoptosis that occurs when cells are dissociated from the extracellular matrix, which is enhanced in conjunction with low serum culture conditions. Together, these data suggest that PTEN effects on the PI3K signaling cascade are influenced by the cell stimulatory context, and that depending on the exposure to growth factors and other exogenous stimuli such as integrin ligation, PTEN can induce cell cycle arrest, apoptosis or anoikis in breast cancer cells.

Regulation of Akt/PKB activity, cellular growth, and apoptosis in prostate carcinoma cells by MMAC/PTEN

Understanding the functional roles of the molecular alterations that are involved in the oncogenesis of prostate cancer, the second most frequent cause of cancer-related deaths among men in the United States is the focus of numerous investigations. To examine the possible significance of alterations associated with the tumor suppressor gene, MMAC/PTEN, in prostate carcinoma, the biological and biochemical effects of MMAC/PTEN expression were examined in LNCaP cells, which are devoid of a functional gene product. Acute expression of MMAC/PTEN via an adenoviral construct resulted in a dose-dependent and specific inhibition of Akt/PKB activation, consistent with the phosphatidylinositol phosphatase activity of MMAC/PTEN. MMAC/PTEN expression induced apoptosis in LNCaP cells, although to a lesser extent than that observed with p53 via an adenoviral construct. However, MMAC/PTEN expression produced a growth inhibition that was significantly greater than that achieved with p53. Overexpression of Bcl-2 in LNCaP cells blocked MMAC/PTEN- and p53-induced apoptosis but not the growth-suppressive effects of MMAC/ PTEN, suggesting that the growth regulatory effects of MMAC/PTEN involve multiple pathways. These studies further implicate the loss of MMAC/PTEN as a significant event in prostate cancer and suggest that reintroduction of MMAC/PTEN into deficient prostate cancer cells may have therapeutic implications.

Adenoviral transgene expression of MMAC/PTEN in human glioma cells inhibits Akt activation and induces anoikis

The MMAC/PTEN tumor suppressor gene encodes for a phosphatase that recently has been shown to have phosphotidylinositol phosphatase activity, implicating its possible involvement in phosphatidylinositol 3'-kinase-mediated signaling. To investigate possible alterations in growth factor-mediated signal transduction, an adenovirus containing MMAC/PTEN, Ad-MMAC, previously shown to inhibit growth and tumorigenicity in glioma cells, was used to acutely express the transgene. Human glioma cells infected with Ad-MMAC but not with control adenoviruses exhibited an inhibition of phosphorylation of both activating residues of Akt, Ser-473, and Thr-308, along with Akt's serine/threonine kinase activity, without significantly altering Akt expression. The effects of functional MMAC/PTEN expression were relatively specific, because members of several other growth factor-mediated signaling pathways showed no altered responses. The presence of MMAC/PTEN also inhibited phosphorylation of BAD, although no evidence of apoptosis in the in situ treated cells was observed. However, U251 glioma cells infected with Ad-MMAC were induced to undergo anoikis at a significantly higher rate than U251 cels treated with control viruses or mock infected with media. These results demonstrate that the acute administration of MMAC/PTEN results in the inhibition of Akt-mediated signaling, growth inhibition, and anoikis, implying that loss of MMAC/PTEN increases cellular proliferation and significantly augments a cell's survival potential during cellular processes that are associated with malignancy.

The efficacy of treatment for malignant epidural spinal cord compression

The aims of this study were to document the efficacy of treatment and to identify factors that were predictive of the outcome in malignant epidural spinal; cord compression. The medical records of patients treated at the Prince Henry and Prince of Wales Hospitals in the period 1980-1989 with a diagnosis of malignant epidural spinal cord compression were reviewed. A total of 94 patients were eligible for the study and were treated by radiotherapy alone (37), surgery alone (19) and surgery followed by radiotherapy (38). Efficacy was determined by measuring complete resolution of symptoms and signs at 1 month after presentation, and also by using an overall functional improvement score (FIS). Complete resolution of individual pre-treatment symptoms that were measured 1 month after treatment occurred as follows: pain (30/88), sensory disturbance (12/61), weakness (8/17), bladder dysfunction (10/42), and bowel dysfunction (10/36). Complete resolution of motor deficit occurred in 7/82 and of sensory deficit in 9/73. The ability to walk was regained in 19/51 previously non-ambulatory patients, and bladder function improved sufficiently to remove an indwelling catheter in 9/32 previously catheterized patients. As judged by FIS, 67 patients improved, 15 patients remained stable and 12 patients deteriorated. Of the treatments given, a combination of surgery followed by radiotherapy was associated with the greatest functional improvement (P = 0.001). The coexistence of 'liver failure' was the only patient-related factor identified which was associated with outcome (P = 0.041). The treatment of malignant spinal cord compression appears to be worthwhile; however, the outcome of treatment is not easy to predict from pretreatment factors. A 'functional improvement score' may be useful in assessing treatment efficacy.

The validity of classification for the clinical presentation of intracranial dural arteriovenous fistulas

A number of classification schemes for intracranial dural arteriovenous fistulas (AVFs) have been published that claim to predict which lesions will present in a benign or aggressive fashion based on radiological anatomy. We have tested the validity of two proposed classification schemes for the first time in a large single-institution study. A series of 102 intracranial dural AVFs in 98 patients assessed at a single institution was analyzed. All patients were classified according to two grading scales: the more descriptive schema of Cognard, et al. (Cognard) and that recently proposed by Borden, et al. (Borden). According to the Borden classification, 55 patients were Type I, 18 Type II, and 29 Type III. Using the Cognard classification, 40 patients were Type I, 15 Type IIA, eight Type IIB, 10 Type IIA+B, 13 Type III, 12 Type IV, and four Type V. Intracranial hemorrhage (ICH) or nonhemorrhagic neurological deficit was considered an aggressive presenting clinical feature. A total of 16 (16%) of 102 intracranial dural AVFs presented with hemorrhage. Eleven of these hemorrhages (69%) occurred in either anterior cranial fossa or tentorial lesions. When analyzed according to the Borden classification, none (0%) of 55 Type I intracranial dural AVFs, two (11%) of 18 Type II, and 14 (48%) of 29 Type III intracranial dural AVFs presented with hemorrhage (p < 0.0001). After exclusion of visual or cranial nerve deficits that were clearly related to cavernous sinus intracranial dural AVFs, nonhemorrhagic neurological deficits were a feature of presentation in one (2%) of 55 Type I, five (28%) of 18 Type II, and nine (31%) of 29 Type III patients (p < 0.0001). When combined, an aggressive clinical presentation (ICH or nonhemorrhagic neurological deficit) was seen most commonly in intracranial dural AVFs located in the tentorium (11 (79%) of 14) and the anterior cranial fossa (three (75%) of four), but this simply reflected the number of higher grade lesions in these locations. Aggressive clinical presentation strongly correlated with Borden types: one (2%) of 55 Type I, seven (39%) of 18 Type II, and 23 (79%) of 29 Type III patients (p < 0.0001). A similar correlation with aggressive presentation was seen with the Cognard classification: none (0%) of 40 Type I, one (7%) of 15 Type IIA, three (38%) of eight Type IIB, four (40%) of 10 Type IIA+B, nine (69%) of 13 Type III, 10 (83%) of 12 Type IV, and four (100%) of four Type V (p < 0.0001). No location is immune from harboring lesions capable of an aggressive presentation. Location itself only raises the index of suspicion for dangerous venous anatomy in some intracranial dural AVFs. The configuration of venous anatomy as reflected by both the Cognard and Borden classifications strongly predicts intracranial dural AVFs that will present with ICH or nonhemorrhagic neurological deficit.

Cost effectiveness of clozapine in neuroleptic-resistant schizophrenia

OBJECTIVE

The goal of this study was to determine whether clozapine is a cost-effective treatment for treatment-resistant schizophrenia.

METHOD

Data were collected on 96 treatment-resistant patients with schizophrenia for 2 years before they entered a clozapine treatment study and for at least 2 years after they entered the study. Information about the cost of inpatient and outpatient treatment, housing costs, other costs, and family burden through direct interview or questionnaire of these patients and their families were available for 47 of the 96 patients. Data on lost income and Social Security disability insurance were also obtained. Outcome measures included psychopathology, quality of life, global functioning, work function, and rehospitalization.

RESULTS

The cost of treatment was significantly decreased in the patients who continued clozapine treatment for at least 2 years. This was primarily due to a dramatic decrease in the frequency and cost of rehospitalization. Costs were nonsignificantly lower in patients who dropped out of treatment. The estimated total 2-year cost for the 59 patients who continued clozapine treatment, the 34 patients who dropped out, and the three who interrupted treatment decreased from $7,390,206 to $5,719,463, a savings of $8,702/year per patient. There was a decrease in total costs of $22,936/year for the 37 patients who continued clozapine treatment for whom cost data were available. There were no significant changes in lost income or Social Security disability insurance payments in either group. Clozapine produced a marked improvement in Brief Psychiatric Rating Scale total scores as well as positive negative symptom scores, Global Assessment Scale scores, Quality of Life Scale scores, work functioning, capacity for independent living, and rehospitalization rates.

CONCLUSIONS

Clozapine is a cost-effective treatment for treatment-resistant schizophrenic patients. Cost savings result almost exclusively from the reduced cost of hospitalization.

Hemispherectomy: a further modification using omentum vascularized free flaps

This report describes the authors' technique designed to further prevent the late complications of hemispherectomy. A vascularized omental free flap is used to fill the extradural dead space left following the procedure advocated by Adams. This procedure may provide further stability to the residual brain and reduce infective complications.

3-D spatial chaos in the elastica and the spinning top: Kirchhoff analogy

The existence of spatially chaotic deformations in an elastica and the analogous motions of a free spinning rigid body, an extension of the problem originally examined by Kirchhoff are investigated. It is shown that a spatially periodic variation in cross sectional area of the elastica results in spatially complex deformation patterns. The governing equations for the elastica were numerically integrated and Poincare maps were created for a number of different initial conditions. In addition, three dimensional computer images of the twisted elastica were generated to illustrate periodic, quasiperiodic, and stochastic deformation patterns in space. These pictures clearly show the existence of spatially chaotic deformations with stunning complexity. This finding is relevant to a wide variety of fields in which coiled structures are important, from the modeling of DNA chains to video and audio tape dynamics to the design of deployable space structures.

Acyl chain conformational ordering in 1,2 dipalmitoylphosphatidylethanolamine. Integration of FT-IR and 2H NMR results

The extent of trans-gauche isomerization at the 4 and 4' positions of the acyl chains of fully hydrated 4,4,4',4'-d4 1,2-dipalmitoylphosphatidylethanolamine (4-d4 DPPE) bilayers was quantitatively evaluated from the infrared (IR) intensity of the CD2 rocking modes. About 20% gauche conformers were observed at 72 degrees C (above Tm), while at 23 degrees C, well below Tm, about 4% were noted. The order parameter SC-D was determined from 2H nuclear magnetic resonance (NMR) quadrupolar splittings. SC-D is the product of a segmental order parameter (S gamma), which depends on conformational order, and a chain order parameter (S alpha) which depends on slower motions such as chain wobble. The IR-determined percentage of gauche forms was converted into a segmental order parameter and factored out of the measured value for SC-D to yield an estimate of S alpha = 0.59 for L alpha phase DPPE. A comparison with S alpha for 1,2-dipalmitoylphosphatidylcholine (DPPC) suggests that increased wobble is responsible for enhanced motional averaging of the quadrupolar splittings in the latter at a similar reduced temperature. The extent of conformational disordering [at the 4(4') position] is essentially unchanged between the two molecules. The current study demonstrates the advantage of integrating quantitative IR with 2H NMR data, for elucidation of the contributions of the individual motions that average the NMR quadrupolar splittings.

Akathisia: clinical phenomenology and relationship to tardive dyskinesia

Akathisia and tardive dyskinesia (TD) are disorders of movement that are often associated with administration of antipsychotic medication. We surveyed 196 outpatients in a schizophrenia clinic, all receiving antipsychotic medication, for the presence of these disorders. Clinical global ratings of akathisia were reliable. Akathisia was found in 36% of patients, and TD in 23.5%. Akathisia was disproportionately common in patients receiving high-potency neuroleptics. The data affirmed recent revisions in the dose-equivalence formulas used with fluphenazine decanoate. Akathisia and TD did not seem to be interrelated. Because akathisia is common and often limits medication dose and contributes to noncompliance, psychiatrists must take this into account when prescribing antipsychotic medication.

Results of ulnar neuropathy at the elbow treated by decompression or anterior transposition

A retrospective study was conducted on 148 patients with ulnar neuropathy at the elbow, who underwent surgical treatment between 1981 and 1989. Of the 178 nerves operated on, 105 underwent subcutaneous anterior transposition, and 73 were decompressed without transposition. We compared the surgical results of these two groups, and factors influencing prognosis. Overall, 92% of patients improved postoperatively. Pre-operatively, electrophysiological assessment corresponded well to clinical findings, and to macroscopic findings at operation in 95% of cases. The severity of pre-operative clinical findings, advancing age, duration of symptoms and the presence of intraneural fibrosis did not predict an adverse outcome. A satisfactory outcome in 72% of those decompressed compared with 60% of those who were transposed was not statistically significant. However, there was a lower percentage of those with unsatisfactory results in the decompressed series. Thus, we advise that, except where there is persistent deformity or a mass lesion in the region of the ulnar groove, decompression is the operation of choice.

CD2 rocking modes as quantitative infrared probes of one-, two-, and three-bond conformational disorder in dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylcholine/cholesterol mixtures

The use of CD2 rocking modes in the IR spectrum as quantitative probes of phospholipid conformational disorder has recently been described for aqueous dispersions of 1,2-dipalmitoylphosphatidylcholine (DPPC) and DPPC/cholesterol mixtures [Mendelsohn et al. (1989) Biochemistry 28, 8934-8939; Davies et al. (1990) Biochemistry 29, 4368-4373]. Initial studies focused at the 4, 6, and 10 acyl chain positions of DPPC. In the current work, the method is extended to the 2, 3, 12, and 13 positions. Conformational disorder in the L alpha phase is approximately the same (about 20% gauche) at positions 4, 10, and 13, but an unexpected higher value is observed (about 30%) at the 6 position. Cholesterol (33 mol%) restricts gauche rotamer formation by factors ranging from 6 to 9 at positions 4 and 6, respectively, to 1.5-2 at positions 10, 12, and 13. Quantitative analysis for the DPPC/cholesterol "liquid-ordered" phase indicates the occurrence of 1.2 gauche bonds/chain, a marked reduction from the 3.6-4.2 gauche bonds/chain for DPPC alone. Proximity to the ester moiety at acyl chain position 3 perturbs the vibrational coupling patterns of the CD2 rocking modes and eliminates their sensitivity to conformational change. In addition, the feasibility of a method based on the conformation-dependent coupling between CD2 rocking frequencies of two successive CD2 groups for the quantitative detection of specific, position-dependent king (gtg') and isolated gauche (gtt) conformers is demonstrated. Finally, comparisons between IR measurements and explicit theoretical predictions of acyl chain conformational order are presented.

Effects of cholesterol on conformational disorder in dipalmitoylphosphatidylcholine bilayers. A quantitative IR study of the depth dependence

A method originally proposed by Snyder and Poore [(1973) Macromolecules 6, 708-715] as a specific probe of trans-gauche isomerization in hydrocarbon chains and recently applied [Mendelsohn et al. (1989) Biochemistry 28, 8934-8939] to the quantitative determination of phospholipid acyl chain conformational order is utilized to monitor the effects of cholesterol at various depths in dipalmitoylphosphatidylcholine (DPPC) bilayers. The method is based on the observation that the CD2 rocking modes from the acyl chains of specifically deuterated phospholipids occur at frequencies in the Fourier transform infrared spectrum which depend upon the local geometry (trans or gauche) of the C-C-C skeleton surrounding a central CD2 group. Three specifically deuterated derivatives of DPPC, namely, 4,4,4',4'-d4 DPPC (4-d4 DPPC), 6,6,6',6'-d4 DPPC (6-d4 DPPC), and 12,12,12',12'-d4 DPPC (12-d4 DPPC), have been synthesized, and the effects of cholesterol addition at 2:1 DPPC/cholesterol (mol:mol) on acyl chain order at various temperatures have been determined. At 48 degrees C, cholesterol inhibits gauche rotamer formation by factors of approximately 9 and approximately 6 at positions 6 and 4, respectively, of the acyl chains, thus demonstrating a strong ordering effect in regions of the bilayer where the sterol rings are presumed to insert parallel to the DPPC acyl chains. In contrast, the ability of the sterol to order the acyl chains is much reduced at the 12-position. The sterol demonstrates only a slight disordering of phospholipid gel phases. Finally, the contributions of different classes of gauche conformers to the spectra have been determined.(ABSTRACT TRUNCATED AT 250 WORDS)

A quantitative infrared determination of acyl chain conformation in gramicidin/dipalmitoylphosphatidylcholine mixtures

A quantitative infrared characterization of phospholipid acyl chain disordering in 6,6,6'6'-d4 dipalmitoylphosphatidylcholine/ Gramicidin D bilayers has been made. Three CD2 rocking modes, at 622 cm-1, 646-649 cm-1, and 651-653 cm-1, assigned to particular conformers, were used to determine disorder in the presence of peptide, as well as percentages of particular classes of conformer within the total gauche population. At 44C, the gauche percentages in 10:1 and 30:1 lipid/peptide mixtures were 15% and 17%, respectively. At 34C, the corresponding values were 9.8% and 2.6%. The percentage of (single gauche bend + kink) conformers, relative to multiple gauche forms, decreases dramatically from 78% in the 30:1 mixture to 15% in the 10:1 mixture at 44C. These data provide the first quantitative measure of the extent to which a membrane-spanning peptide disorders phospholipid gel phases and orders liquid crystal phases.

Quantitative determination of conformational disorder in the acyl chains of phospholipid bilayers by infrared spectroscopy

A method is proposed and demonstrated for the direct determination of conformational disorder (trans-gauche isomerization) as a function of acyl-chain position in phospholipid bilayer membranes. Three specifically deuterated derivatives of dipalmitoylphosphatidylcholine (DPPC), namely 4,4,4',4'-d4-DPPC (4-d4-DPPC), 6,6,6',6'-d4-DPPC (6-d4-DPPC), and 10,10,10',10'-d4-DPPC (10-d4-DPPC), have been synthesized. The CD2 rocking modes in the Fourier transform infrared (FT-IR) spectrum have been monitored as a function of temperature for each derivative. A method originally applied by Snyder and Poore [(1973) Macromolecules 6, 708-715] as a specific probe of hydrocarbon chain conformation in alkanes has been used to analyze the data. The rocking modes appear at 622 cm-1 for a CD2 segment surrounded by a trans C-C-C skeleton and between 645 and 655 cm-1 for segments surrounded by particular gauche conformers. The integrated band intensities of these modes have been used to monitor trans-gauche isomerization in the acyl chains at particular depths in the bilayer. At 48 degrees C, above the gel-liquid-crystal phase transition, the percentage of gauche rotamers present is 20.7 +/- 4.2, 32.3 +/- 2.3, and 19.7 +/- 0.8 for 4-d4-DPPC, 6-d4-DPPC, and 10-d4-DPPC, respectively. The gel phase of the latter two molecules is highly ordered. In contrast, a substantial population of gauche rotamers was observed for the 4-d4-DPPC. The conformational analysis yields a range of 3.6-4.2 gauche rotamers/acyl chain of DPPC above the phase transition. This range is in excellent accord with the dilatometric data of Nagle and Wilkinson [(1978) Biophys. J. 23, 159-175]. The significant advantages of the FT-IR approach are discussed.