Systematic review and meta-analysis of immune checkpoint inhibitors as single agent or in combination with chemotherapy in early-stage non-small cell lung cancer: Impact of clinicopathological factors and indirect comparison between treatment strategies

BACKGROUND

In non-small cell lung cancer (NSCLC), the immune checkpoint inhibitors (ICI) revolution is rapidly moving from metastatic to early-stage, however, the impact of clinicopathological variables and optimal treatment sequencing remain unclear.

METHODS

Randomized controlled trials (RCTs) in patients with early-stage NSCLC treated with ICI as single agent or in combination with platinum-based chemotherapy (PCT) were included. Primary outcomes were pathological complete response (pCR), event free survival (EFS) (neoadjuvant/perioperative), and disease-free survival (DFS) (adjuvant). Secondary outcomes were major pathological response (MPR), overall survival (OS), toxicity, surgical outcomes (neoadjuvant/perioperative); OS and toxicity (adjuvant). An additional secondary endpoint was to compare EFS and OS between neoadjuvant and perioperative strategies.

RESULTS

8 RCTs (2 neoadjuvant, 4 perioperative, 2 adjuvant) (4661 participants) were included. Neoadjuvant/perioperative ICI+PCT significantly improved pCR, EFS, OS, MPR and R0 resection compared to PCT. Adjuvant ICI significantly improved DFS compared to placebo. There was a significant subgroup interaction by PD-L1 status (χ2 = 10.72, P = 0.005), pCR (χ2 = 17.80, P < 0.0001), and stage (χ2 = 4.46, P = 0.003) for EFS. No difference according to PD-L1 status was found for pCR, with 14% of patients having PD-L1 negative tumors still experiencing a pCR. No interaction by PD-L1 status was found for DFS upon adjuvant ICI. Indirect comparison showed no difference in EFS and OS between neoadjuvant and perioperative ICI+PCT.

CONCLUSIONS

PD-L1 status, pCR and stage impact on survival upon neoadjuvant/perioperative ICI. The restriction of neoadjuvant/perioperative ICI to PD-L1 + patients could preclude pCR and long-term benefit in the PD-L1- subgroup. Neoadjuvant and perioperative could be equivalent strategies.

Comutations and KRASG12C Inhibitor Efficacy in Advanced NSCLC

Molecular modifiers of KRASG12C inhibitor (KRASG12Ci) efficacy in advanced KRASG12C-mutant NSCLC are poorly defined. In a large unbiased clinicogenomic analysis of 424 patients with non-small cell lung cancer (NSCLC), we identified and validated coalterations in KEAP1, SMARCA4, and CDKN2A as major independent determinants of inferior clinical outcomes with KRASG12Ci monotherapy. Collectively, comutations in these three tumor suppressor genes segregated patients into distinct prognostic subgroups and captured ∼50% of those with early disease progression (progression-free survival ≤3 months) with KRASG12Ci. Pathway-level integration of less prevalent coalterations in functionally related genes nominated PI3K/AKT/MTOR pathway and additional baseline RAS gene alterations, including amplifications, as candidate drivers of inferior outcomes with KRASG12Ci, and revealed a possible association between defective DNA damage response/repair and improved KRASG12Ci efficacy. Our findings propose a framework for patient stratification and clinical outcome prediction in KRASG12C-mutant NSCLC that can inform rational selection and appropriate tailoring of emerging combination therapies.

SIGNIFICANCE

In this work, we identify co-occurring genomic alterations in KEAP1, SMARCA4, and CDKN2A as independent determinants of poor clinical outcomes with KRASG12Ci monotherapy in advanced NSCLC, and we propose a framework for patient stratification and treatment personalization based on the comutational status of individual tumors. See related commentary by Heng et al., p. 1513. This article is highlighted in the In This Issue feature, p. 1501.

Abstract 3431: Molecular determinants of KRAS p.G12C inhibitor efficacy in advanced NSCLC

Background: Irreversible allosteric KRAS p.G12C inhibitors (KG12Ci) such as sotorasib and adagrasib have revolutionized the therapeutic landscape of advanced KG12C-mutant NSCLC, however individual responses are heterogeneous and curtailed by innate and adaptive/acquired resistance. Molecular determinants of KG12Ci efficacy in NSCLC are poorly defined. We dissected the impact of major KG12C co-mutations and explored the effects of less prevalent co-alterations on the clinical activity of KG12Ci in the largest treated cohort to date of patients (pts) with advanced NSCLC. Key findings were validated in preclinical KG12C NSCLC models.

Methods: Baseline clinico-genomic features and clinical outcome data from pts with stage IV KG12C NSCLC (ECOG PS 0-2) treated with single-agent KG12Ci were collected retrospectively from 20 centers in the US and Europe. The Kaplan-Meier method was used to estimate PFS and OS and differences were assessed with the log-rank test. Hazard ratios (HR) and their 95% CI were estimated using a Cox proportional hazards model stratified for clinical co-variates. The impact of selected co-alterations on sotorasib efficacy was assessed in syngeneic (C57BL/6) KG12C NSCLC models.

Results: 411 eligible pts were included in the study. Median age was 68 years, 77% of pts had received both platinum-based chemotherapy and PD-(L)1 inhibitors and 35% had brain metastases. 83% of pts received sotorasib. ORR with KG12Ci was 32.4% (95% CI, 27.9-37.1), PFS was 5.1m (95% CI, 4.5-5.6) and OS was 10.2m (95% CI, 8.4-12.1). Co-alterations in KEAP1, SMARCA4 and CDKN2A/B were each associated with significantly shorter PFS (KEAP1: 2.8m vs 5.5m, HR 2.50, P&lt;0.001; SMARCA4: 1.7m vs 5.5m, HR 2.64, P=0.001; CDKN2A/B: 2.3m vs 5.3m, HR 2.57, P&lt;0.001) and OS with KG12Ci even after adjustment for clinical covariates. STK11 co-mutations without concurrent KEAP1 alterations did not impact clinical outcomes with KG12Ci. In an exploratory analysis, co-mutations in DNA damage repair (DDR) genes and genes encoding components of the ATRX/DAXX/EZH2 pathway were associated with improved KG12Ci efficacy, whereas PI3K/AKT/MTOR/PTEN alterations and missense ROS1/ALK/BRAF/NTRK1-3 mutations resulted in inferior outcomes. The impact of SMARCA4 and DDR gene inactivation was validated in isogenic syngeneic KG12CNSCLC models; additional co-alterations are under evaluation. Integration of KEAP1/SMARCA4/CDKN2A/B co-mutations identified a subgroup (KSCMUT, 37.6% of all pts) with significantly shorter PFS (2.7m vs 6.2m, P&lt;0.001) and OS (6.3m vs 14.6m, P&lt;0.001) that accounted for 57.3% of pts with primary refractory (PFS≤3m) disease.

Conclusions: Co-mutations in KEAP1, SMARCA4 and CDKN2A/2B define subgroups of KG12C NSCLC pts with markedly distinct outcomes with KG12Ci monotherapy. Tailoring of KG12C inhibitor-anchored therapeutic strategies and patient stratification should take into account the co-mutation status of individual tumors.

Citation Format: Marcelo V. Negrao, Haniel A. Araujo, Giuseppe Lamberti, Alissa J. Cooper, Teng Zhou, Neal Akhave, Lukas Delasos, J Kevin Hicks, Mihaela Aldea, Gabriele Minuti, Jacobi Hines, Jacqueline V. Aredo, Michael J. Dennis, Turja Chakrabarti, Susan Scott, Paolo Bironzo, Matthias Scheffler, Petros Christopoulos, So Yeon Kim, Sarah Goldberg, Ying Ni, Blerina Resuli, Lorenza Landi, Shu-Chi Tseng, Mizuki Nishino, Dwight Owen, Collin Blakely, Giannis Mountzios, Catherine A. Shu, Christine Bestvina, Marina Garassino, Kristen Marrone, Jhanelle Gray, Sandip Pravin Patel, Amy L. Cummings, Heather A. Wakelee, Jurgen Wolf, Giorgio V. Scagliotti, Federico Cappuzzo, Fabrice Barlesi, Pradnya Patil, Don L. Gibbons, Funda Meric-Bernstam, J Jack Lee, John V. Heymach, David S. Hong, Rebecca S. Heist, Mark M. Awad, Ferdinandos Skoulidis. Molecular determinants of KRAS p.G12C inhibitor efficacy in advanced NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3431.

806 The Efficacy of Prostatic Arterial Embolisation as Indicated by Clinical Outcomes

Aim

PAE (prostatic arterial embolisation) is a non-surgical, minimally invasive procedure used to treat symptoms of benign prostatic hyperplasia (BPH). It is used to treat patients with moderate to severe lower urinary tract symptoms including those requiring long term urinary catheter placement and intermittent self-catheterisation. The incidence of urinary tract infection is greater in this group at baseline and the risk of infection as a complication of PAE is recognised in the literature. This study aimed to compare the clinical outcomes of PAE to those of TURP (transurethral resection of the prostate), the reference standard for BPH treatment.

Method

All patients who underwent PAE between 2019 to 2021 at a single centre were included in this retrospective study. Clinical outcomes of patients were also recorded including international prostate symptom score (IPSS) and urodynamic results. These were compared to TURP results provided in the UK ROPE study.

Results

82% of patients experienced an improved IPSS after PAE, with a median reduction of 15 points, compared with a median reduction of 17 points with TURP. PAE caused a greater reduction in median prostate volume but proved to be less effective in improving urodynamic test results when compared to TURP.

Conclusion

While still clinically effective, PAE is less effective for treatment of lower urinary tract symptoms from BPH when compared to TURP.

141 New Guidelines to Reduce Unnecessary Blood Tests, Delayed Discharge and Costs Following Robot Assisted Radical Prostatectomy

Objectives

Routine postoperative blood tests (POBT) following robot assisted radical prostatectomy (RARP) are used to evaluate the impact of surgery on pre-existing co-morbidities and to detect early complications. This practice dates back to an era of open surgery, when blood loss and complication rates were higher. We propose new guidelines to improve the specificity of POBT.

Method

The cases of 1040 consecutive patients who underwent a primary or salvage RARP at two large tertiary urology centres in the United Kingdom were retrospectively reviewed to form new guidelines. The new guidelines were prospectively validated in a sample of 300 patients.

Results

Derivation Dataset: 3% and 5% had intra- and post-operative Clavien-Dindo complications, respectively. 15% had clinical concerns postoperatively. 0.9% required perioperative transfusion. 78% had routine blood tests without clinical concerns, none of whom developed a complication. 98% of complications were suspected by clinical judgement. 6% of patients had a discharge delay of ≥ 1 day due to delayed or incomplete blood tests. Validation Dataset: No significant difference existed in complication, clinical concern or transfusion rates between the derivation and validation datasets. Number of POBT requested reduced by 73% (p &lt; 0.001). The new guidelines improved POBT sensitivity for complications from 98% to 100% and specificity from 0% to 74%. Discharge delays reduced from 6% to 0% (p = 0.008). Cost savings were £178 per patient.

Conclusions

Postoperative complications and transfusion following RARP are rare. Routine POBT without clinical indication are unnecessary and inefficient. A guideline-based approach to POBT can reduce costs and optimise discharge without compromising patient safety or care.

O50 New guidelines to reduce unnecessary blood tests, delayed discharge and costs following robot assisted radical prostatectomy

Introduction

Routine postoperative blood tests (POBT) are used to evaluate the impact of surgery on pre-existing co-morbidities and to detect early complications. This practice dates back to an era of open surgery, when blood loss and complication rates were higher. We propose new guidelines to improve the specificity of POBT.

Method

The cases of 1040 consecutive patients who underwent a primary or salvage RARP at two large tertiary urology centres in the United Kingdom were retrospectively reviewed, and new guidelines were designed. The guidelines were prospectively validated in a cohort of 300 patients.

Result

Derivation Dataset 3% and 5% had intra- and post-operative Clavien-Dindo complications, respectively. 15% had clinical concerns postoperatively. 0.9% required perioperative transfusion. 78% had routine blood tests without clinical concerns, none of whom developed a complication. 98% of complications were suspected by clinical judgement. 6% of patients had a discharge delay of ≥ 1 days due to delayed or incomplete blood tests.

Validation Dataset No significant difference existed in complication, clinical concern or transfusion rates between the derivation and validation datasets. New guidelines improved sensitivity for complications from 98% to 100% and specificity from 0% to 74%. The number of blood tests requested reduced by 73% (P &lt; 0.001). Discharge delays reduced from 6% to 0% (P = 0.008). Cost savings were £178 per patient.

Conclusion

Postoperative complications and transfusion following RARP are rare. Routine POBT without clinical indication are unnecessary and inefficient. A guideline-based approach to POBT can reduce costs and optimise discharge without compromising patient safety or care.

Take-home Message

Routine postoperative blood tests following robot assisted radical prostatectomy are often unnecessary. A guideline-based approach can reduce costs and optimise patient care.

Steroid-refractory dermatologic and pulmonary toxicity in a patient on rituximab treated with pembrolizumab for progressive urothelial carcinoma: a case report

BACKGROUND

Increasingly widespread use of programmed cell death protein 1 (PD-1) immune checkpoint inhibitors (ICIs) for treatment of a variety of progressive malignancies continues to reveal a range of immune-related adverse events (irAEs), necessitating immunosuppressive therapy for management. While a single course of systemic corticosteroids may be sufficient for many irAEs, no clear standard-of-care guidelines exist for steroid-refractory cases. We present an unusual case of a patient who developed several steroid-refractory novel irAEs on pembrolizumab despite ongoing B cell-directed immunosuppressive therapy with rituximab, who ultimately noted resolution of symptoms with tacrolimus, a T-cell-directed immunosuppressant.

CASE PRESENTATION

This 72-year-old Caucasian man with Waldenstrom's macroglobulinemia and myelin-associated glycoprotein (MAG) immunoglobulin M (IgM) antibody-associated neuropathy was being treated with maintenance rituximab and intravenous immunoglobulin when he was started on pembrolizumab (2.26 mg/kg) for metastatic urothelial cancer 31 months after surgery and adjuvant chemotherapy. After his third dose of pembrolizumab, he developed a painful blistering papular rash of the distal extremities. He received two more doses of pembrolizumab before he also developed diarrhea, and it was held; he was initiated on 1 mg/kg prednisone for presumed ICI-induced dermatitis and colitis. Skin biopsy 10 weeks after cessation of pembrolizumab and taper of steroids to 20  mg daily revealed a unique bullous erythema multiforme. He was then admitted with dyspnea and imaging concerning for necrotizing pneumonia, but did not respond to antibiotic therapy. Bronchoscopy and biopsy revealed acute fibrinous organizing pneumonia. His symptoms failed to fully respond to multiple courses of high-dose systemic corticosteroids and a trial of azathioprine, but pneumonia, diarrhea, and skin rash all improved markedly with tacrolimus. The patient has since completed his therapy for tacrolimus, continues off of ICI, and has not experienced a recurrence of any irAEs, though has more recently experienced progression of his cancer.

CONCLUSION

Despite immunosuppression with rituximab and intravenous immunoglobulin, two immunomodulators targeting B cells, ICI cessation, and systemic corticosteroid therapy, our patient developed two high-grade unusual irAEs, bullous erythema multiforme and acute fibrinous organizing pneumonia. Our patient's improvement with tacrolimus can offer critical insight into the pathophysiology of steroid-refractory irAEs.

Biodiversity enhances the multitrophic control of arthropod herbivory

Arthropod herbivores cause substantial economic costs that drive an increasing need to develop environmentally sustainable approaches to herbivore control. Increasing plant diversity is expected to limit herbivory by altering plant-herbivore and predator-herbivore interactions, but the simultaneous influence of these interactions on herbivore impacts remains unexplored. We compiled 487 arthropod food webs in two long-running grassland biodiversity experiments in Europe and North America to investigate whether and how increasing plant diversity can reduce the impacts of herbivores on plants. We show that plants lose just under half as much energy to arthropod herbivores when in high-diversity mixtures versus monocultures and reveal that plant diversity decreases effects of herbivores on plants by simultaneously benefiting predators and reducing average herbivore food quality. These findings demonstrate that conserving plant diversity is crucial for maintaining interactions in food webs that provide natural control of herbivore pests.

Product dose considerations for real-world hand sanitiser efficacy

BACKGROUND

Alcohol based hand rubs (ABHR) are extremely effective at reducing microbial contamination and have an essential role in best practice hand hygiene described by the World Health Organization.

METHODS

We determined ABHR drying time when performing hand hygiene in a laboratory setting. Which was followed by identifying the amount of ABHR needed for complete hand coverage. When the aforementioned was analyzed real-time data were gathered to examine the amount used for hand hygiene in a hospital setting. In parallel hands of healthcare workers (HCWs) were monitored for drying time and perception on ABHR use.

RESULTS

In 86% (24,446,397/28,280,383) of the events a single dose of ABHR was used on clinical wards. Twenty-four HCWs expected hand hygiene to take 7.5 seconds (median; range 3-30 seconds). Forty-three HCWs show that 1.5 mL ABHR dose achieves the desired drying time according to World Health Organization guidelines (av. median 26 seconds), but is consistently perceived to have a longer drying time than expected (av. median 18 seconds). In-vivo results (n = 10) indicate that 2.25 mL ABHR is required for adequate coverage (82%-90%) of both sides of the hand.

CONCLUSIONS

Results indicate that set standards for the use of ABHR do not match "in-vivo" behaviour of HCWs. Perceived drying times are shorter than actual drying time. The needed drying time to reach acceptable antimicrobial efficacy of ABHRs should be revisited.

Discrete-choice experiment to analyse preferences for centralizing specialist cancer surgery services

Background

Centralizing specialist cancer surgery services aims to reduce variations in quality of care and improve patient outcomes, but increases travel demands on patients and families. This study aimed to evaluate preferences of patients, health professionals and members of the public for the characteristics associated with centralization.

Methods

A discrete‐choice experiment was conducted, using paper and electronic surveys. Participants comprised: former and current patients (at any stage of treatment) with prostate, bladder, kidney or oesophagogastric cancer who previously participated in the National Cancer Patient Experience Survey; health professionals with experience of cancer care (11 types including surgeons, nurses and oncologists); and members of the public. Choice scenarios were based on the following attributes: travel time to hospital, risk of serious complications, risk of death, annual number of operations at the centre, access to a specialist multidisciplinary team (MDT) and specialist surgeon cover after surgery.

Results

Responses were obtained from 444 individuals (206 patients, 111 health professionals and 127 members of the public). The response rate was 52·8 per cent for the patient sample; it was unknown for the other groups as the survey was distributed via multiple overlapping methods. Preferences were particularly influenced by risk of complications, risk of death and access to a specialist MDT. Participants were willing to travel, on average, 75 min longer in order to reduce their risk of complications by 1 per cent, and over 5 h longer to reduce risk of death by 1 per cent. Findings were similar across groups.

Conclusion

Respondents' preferences in this selected sample were consistent with centralization.

Most favour it

Dose considerations for alcohol-based hand rubs

BACKGROUND

Manufacturers' recommended dosages for alcohol-based hand rubs are typically determined by measuring product efficacy using a model protocol such as EN 1500; however, anecdotal reports and informal observation suggests that in many cases users self-titrate to much lower doses in real-world application.

AIM

To examine the interdependence of alcohol-based hand-rub volume on in-vivo efficacy using the EN 1500 standard test method, on drying time on users' hands, and on their perceptions of acceptability.

METHODS

Three formulations were studied using EN 1500 and a modification of this method. The modification used volumes ranging from 0.5 to 3.0 mL and 30 s application. Drying times were recorded and user acceptability was established using a three-point scale (too long, OK, or too short). Dying times were analysed in relation to hand surface area.

FINDINGS

The drying time for all three products increased as a function of volume. The drying time displayed a positive association with volume and a negative association with hand surface area. The optimum volume for user acceptability was between 1.5 and 2 mL, yielding a drying time of between 20 and 30 s.

CONCLUSION

Whereas EN 1500 is appropriate for establishing the efficacy of a hygienic hand-rub formulation compared to a benchmark, it does not reflect actual in-use conditions or the likely clinical effectiveness of the product. In particular, it fails to address the need to optimize the volume of application and user acceptability of the product.

The three moments of skin cream application: an evidence-based proposal for use of skin creams in the prevention of irritant contact dermatitis in the workplace

Contact dermatitis is one of the most common occupational diseases, with serious impact on quality of life, lost days at work and a condition that may be chronically relapsing. Regular prophylactic skin cream application is widely acknowledged to be an effective prevention strategy against occupational contact dermatitis; however, compliance rates remain low. To present a simple programme for skin cream application in the workplace with focus on implementation to drive down the rate of occupational irritant contact dermatitis, an expert panel of eight international dermatologists combined personal experience with extensive literature review. The recommendations are based on clinical experience as supported by evidence-based data from interventional studies. The authors identified three moments for skin cream application in the work place: (i) before starting a work period; (ii) after washing hands; and (iii) after work. Affecting behaviour change requires systematic communications, monitoring and reporting, which is proposed through Kotter's principles of organizational change management. Measurement tools are provided in the appendix. Interventional data based on application of this proposal is required to demonstrate its effectiveness.

Hemodynamics in the cephalic arch of a brachiocephalic fistula

The care and outcome of patients with end stage renal disease (ESRD) on chronic hemodialysis is directly dependent on their hemodialysis access. A brachiocephalic fistula (BCF) is commonly placed in the elderly and in patients with a failed lower-arm, or radiocephalic, fistula. However, there are numerous complications such that the BCF has an average patency of only 3.6 years. A leading cause of BCF dysfunction and failure is stenosis in the arch of the cephalic vein near its junction with the axillary vein, which is called cephalic arch stenosis (CAS). Using a combined clinical and computational investigation, we seek to improve our understanding of the cause of CAS, and to develop a means of predicting CAS risk in patients with a planned BCF access. This paper details the methodology used to determine the hemodynamic consequences of the post-fistula environment and illustrates detailed results for a representative sample of patient-specific anatomies, including a single, bifurcated, and trifurcated arch. It is found that the high flows present due to fistula creation lead to secondary flows in the arch owing to its curvature with corresponding low wall shear stresses. The abnormally low wall shear stress locations correlate with the development of stenosis in the singular case that is tracked in time for a period of one year.

Interaction of somatostatin receptors with G proteins and cellular effector systems

Somatostatin induces its multiple biological actions by interacting with a family of receptors, referred to as sstr1-sstr5. To determine the molecular mechanisms of action of somatostatin, we have investigated the interaction of the different cloned receptors with G proteins and cellular effector systems. sstr2, sstr3 and sstr5 associate with pertussis toxin-sensitive G proteins and are able to mediate the inhibition of adenylyl cyclase activity by somatostatin. Two forms of sstr2, sstr2A and sstr2B, are generated by alternative splicing and differ in their C-terminal amino acid sequence. sstr2B couples to adenylyl cyclase whereas sstr2A does not. To investigate the basis for the differential coupling to adenylyl cyclase, we truncated sstr2B to the point of amino acid sequence divergence from sstr2A. The truncated sstr2B mediated the inhibition of cAMP formation by somatostatin, indicating that the C-terminus is not needed for coupling sstr2 to adenylyl cyclase. It is likely that the C-terminus of sstr2A hinders coupling to adenylyl cyclase. sstr2A associates with Gi alpha 3 and G(o) alpha but does not effectively interact with Gi alpha 1, a G protein that is necessary for coupling somatostatin receptors to adenylyl cyclase. The differential association of the splice variants with Gi alpha 1 may explain their contrasting effects on adenylyl cyclase activity. sstr3 also couples to adenylyl cyclase. Gi alpha 1 links sstr3 to adenylyl cyclase and mutagenesis studies have shown that the C-terminus of Gi alpha 1 is necessary for this coupling. The C-terminus of the Gi alpha proteins differ by only a few amino acid residues and only Gi alpha 1 couples sstr3 to adenylyl cyclase.(ABSTRACT TRUNCATED AT 250 WORDS)

Lifeguard--a personal physiological monitor for extreme environments

Monitoring vital signs in applications that require the subject to be mobile requires small, lightweight, and robust sensors and electronics. A body-worn system should be unobtrusive, noninvasive, and easy-to-use. It must be able to log vital signs data for several hours as well as transmit it on demand in real-time using secure wireless technologies. The NASA Ames Research Center (Astrobionics) and Stanford University (National Center for Space Biological Technologies) are currently developing a wearable physiological monitoring system for astronauts, called LifeGuard, that meets all of the above requirements and is also applicable to clinical, home-health monitoring, first responder and military applications.

Long-Term Outcomes in Patients with Prostate Cancer Managed with Intermittent Androgen Suppression

OBJECTIVES

To assess the long-term outcomes of patients with prostate cancer managed with intermittent androgen suppression (IAS) following their enrollment in an open, non-randomised feasibility study initiated 10 years ago.

PATIENTS AND METHODS

Patients with prostate cancer who developed marked side effects following androgen deprivation were considered for entry into the study. All patients were required to have been managed with androgen deprivation for a minimum of 9 months and to have achieved PSA remissions to levels <4 ng/ml or falls to greater than 90% of pre-treatment levels. Patients remained off treatment until PSA values rose to >20 ng/ml or individuals became symptomatic--at which stage a 9-month cycle of androgen suppression was repeated. Such on-off cycling continued until hormone-resistant disease developed and patients proceeded (off trial) to second-line therapies.

RESULTS

75 patients were recruited to the study following an initial referral with treatment-related side effects specifically associated with androgen deprivation. 86% of these remain alive at a median of 134 months (11 years) since initial histological diagnosis. Survival times and times to hormone resistance (from first cycle hormone deprivation) have also been calculated. Overall there is a median survival time of 95 months (8 years) from initial (first-cycle) androgen deprivation in those presenting with localised or locally advanced disease and a median survival time of 87 months (7 years) for those presenting with metastatic disease. There exists a median of 83 months to hormone resistance in the localised and locally advanced group and a median of 50 months in those presenting with metastatic disease. We have calculated a 100% 5-year actuarial survival rate for those presenting with localised or locally advanced disease (from time of first cycle hormone ablation) and a 70% 5-year actuarial survival rate for those presenting with metastatic.

CONCLUSIONS

Long-term outcome figures and actuarial survival rates presented here provide further support for a pulsed or intermittent approach to androgen ablation in patients with prostate cancer. In addition, they serve as valuable extended outcome data for patients managed in this way. Likewise, data presented here suggests that apparent survival advantages appear related, at least in part, to a delay in the onset of androgen resistance and that such a management approach is both safe and effective in those presenting with both metastatic disease as well as those with more localised pathology.

Formative research activities to provide Web-based nutrition education to adults in the Upper Rio Grande Valley

The Internet is a promising new tool for disseminating cancer prevention information. Barriers to full implementation include disparities in access and skill and availability of information relevant at the local level. A nutrition education Web site to promote fruit and vegetable intake is being produced for a tri-ethnic adult population in Colorado and New Mexico. Development is guided by findings from formative research including focus groups with local residents, a survey on computer and Internet use with 200 adults in 1998, an assessment of public access computer sites, and in-depth discussion with local community computer skills trainers.

Chimeric AT1/AT2 receptors reveal functional similarities despite key amino acid dissimilarities in the domains mediating agonist-dependent activation

Chimeric AT1/AT2 angiotensin II (AngII) receptors in which the sixth and/or seventh transmembrane-spanning domains of the AT2 receptor were substituted into the AT1 receptor were used to investigate the activation mechanisms of the two receptor subtypes. Numerous reports have identified amino acid residues in the sixth and seventh transmembrane-spanning domains of the AT1 receptor involved in the intrareceptor activation mechanism following agonist binding. Many of these residues are not conserved in the AT2 receptor; the corresponding AT2 receptor residues are, in fact, disruptive of AngII-dependent activation when substituted into the AT1 receptor. Surprisingly, the chimeric AT1/AT2 receptors--which also lack these crucial AT1 residues--exhibited AngII-induced activation of phosphoinositide hydrolysis with efficacies and potencies similar to the wild-type AT1 receptor. Consistent with earlier reports, a AT1[Y292F] point mutant demonstrated greatly decreased agonist-induced activation of phosphoinositide hydrolysis. However, a AT1[Y292F/N295S] double-point mutant allowed for normal agonist-induced activation with a pharmacodynamic profile indistinguishable from the wild-type receptor. Despite amino acid dissimilarities, the same corresponding domains and even the same residue loci in both of the AngII receptor subtypes are equally able to mediate agonist-induced receptor activation. This suggests that these corresponding domains in the AT1 and the AT2 receptors are crucial to the activation mechanism, demonstrating greater structural flexibility than previously believed regarding AT1 receptor activation and supporting the possibility of a common activation mechanism for the two receptor subtypes.

Overexpression of manganese superoxide dismutase suppresses tumor formation by modulation of activator protein-1 signaling in a multistage skin carcinogenesis model

Manganese superoxide dismutase (MnSOD) is a nuclear encoded primary antioxidant enzyme localized in mitochondria. Because expression of MnSOD plays a major role in maintaining cellular redox status and reactive oxygen species are known to play a role in signal transduction and carcinogenesis, we investigated the role of MnSOD in the development of cancer using a two-stage [7,12-dimethylbenz(a)-anthracene plus 12-O-tetradecanoylphorbol-13-acetate (TPA)] skin carcinogenesis model. Female transgenic mice expressing the human MnSOD gene in the skin and their nontransgenic counterparts were used in this study. Pathological examination demonstrated significant reduction of papilloma formation in transgenic mice. Quantitative analysis of 4-hydroxy-2-nonenal-modified proteins showed greater accumulation of oxidative damage products in nontransgenic compared with transgenic mice, and this oxidative damage was demonstrated to be present in both mitochondria and nucleus. TPA increased activator protein-1 (AP-1) binding activity within 6 h in nontransgenic mice, but increased AP-1 binding activity was delayed in the transgenic mice. Electrophoretic mobility shift assay, transcription of the target genes, and Western analysis studies indicated that the increased AP-1 binding activity was attributable to induction of the Jun but not the Fos protein families. Overexpression of MnSOD selectively inhibited the TPA-induced activation of protein kinase Cepsilon and prevented subsequent activation of c-Jun NH(2)-terminal kinase in response to TPA. Overall, these results indicate that MnSOD regulates both cellular redox status and selectively modulates PKCepsilon signaling, thereby delaying AP-1 activation and inhibiting tumor promotion, resulting in reduction of tumors in MnSOD transgenic mice.

Identification of angiotensin II type 2 (AT2) receptor domains mediating high-affinity CGP 42112A binding and receptor activation

Chimeric angiotensin II (AngII) receptors constructed of portions of the AT2 receptor substituted into the AT1 receptor revealed the AT2 third extracellular loop and seventh transmembrane-spanning domain as major determinants for the ability to bind and activate in response to the AT2 receptor-selective agonist CGP 42112A. Radioligand binding experiments showed that chimeric AngII receptors possessing the AT2 third extracellular loop and seventh transmembrane-spanning domain bound CGP 42112A with high affinity approaching that of the wild-type AT2 receptor. The presence of the AT2 third extracellular loop appeared sufficient for high-affinity CGP 42112A binding, which was further enhanced by the additional presence of the AT2 seventh transmembrane-spanning domain. Experiments with PD 123319, losartan, and [Sar1,Ile8]-AngII showed that increases in binding affinity associated with these domains were specific for CGP 42112A. Use of phosphoinositide hydrolysis as a functional index to measure activation of these chimeric AngII receptors further demonstrated that the AT2 seventh transmembrane-spanning domain was especially critical for CGP 42112A to act as an agonist. The absence of the AT2 seventh transmembrane-spanning domain prohibited CGP 42112A-induced activation of these receptors, even in the presence of high concentrations of CGP 42112A sufficient to saturate the binding sites. This study is the first to identify binding determinants of the AT2 receptor that are selective for CGP 42112A, and indicates that these determinants are at least partially distinct from those for the AT2-selective antagonist PD 123319. These differences may be a factor in the pharmacodynamic difference between these two ligands.

Identification and function of disulfide bridges in the extracellular domains of the angiotensin II type 2 receptor

The angiotensin II (AngII) receptor family is comprised of two subtypes, type 1 (AT(1)) and type 2 (AT(2)). Although sharing low homology (only 34%), mutagenesis has identified some key residues that are conserved between both subtypes, including four extracellular cysteines. Previous AT(1) mutagenesis demonstrated that the cysteines form two disulfide bonds, one linking the first and second extracellular loops and another connecting the amino terminus to the third extracellular loop. The importance of these AT(1) disulfides in ligand binding is supported by the effect of dithiothreitol (DTT). DTT breaks disulfide bonds, thereby strongly inhibiting ligand binding in AT(1) receptors. Despite retaining the same cysteines, AT(2) receptor ligand binding is paradoxically enhanced by DTT. Thus, we constructed a series of AT(2) cysteine mutations, either individually or paired, to establish the role of the cysteines and the source of DTT's effects. The AT(2) cysteine mutants surprisingly confirmed that the cysteines form disulfide bonds in the same manner as in the AT(1) subtype. However, breaking the AT(2) disulfide bridges yielded two responses. As in AT(1) receptors, mutations disrupting the disulfide bond between the first and second extracellular loops reduced AT(2) binding by 4-fold. In contrast, mutations breaking the disulfide bridge between the amino terminus and the third extracellular loop increased AT(2) binding, mimicking DTT's effect on this subtype. Further analysis of AT(1)/AT(2) chimeric exchange mutants of these domains suggested that the AT(2) amino terminus and third extracellular loop may possess latent binding epitopes that are only uncovered after DTT exposure.

Structure-function analysis of Yersinia pestis YopM's interaction with alpha-thrombin to rule on its significance in systemic plague and to model YopM's mechanism of binding host proteins

The plague virulence protein YopM of Yersinia pestis KIM5 belongs to the large family of leucine-rich repeat (LRR) proteins. The only activity demonstrated so far for YopM is thrombin-binding, which could be a function of the small amount of YopM that is released into surrounding tissues by the bacteria. This study combined deletional and mutational analysis, chemical crosslinking assays, and in vitro functional tests with molecular modelling to identify key features of YopM necessary for interacting with thrombin. Two Y. pestis strains expressing YopM variants that differed in thrombin binding were used to assess the importance of thrombin-binding for lethality of plague. Both strains suffered a similar decrease in virulence by three orders of magnitude, indicating that thrombin-binding per se was not the major deficiency for lethality in the systemic disease model employed. It remains possible that extracellular YopM could contribute to plague pathology and to early events in peripheral tissues. The structural studies provided a model for how YopM may interact with thrombin and an insight into how YopM's LRR structure may assemble distinct regions for binding different targets.

Novel nuclear signaling pathway mediates activation of fibroblast growth factor-2 gene by type 1 and type 2 angiotensin II receptors

In bovine adrenal medullary cells synergistically acting type 1 and type 2 angiotensin II (AII) receptors activate the fibroblast growth factor-2 (FGF-2) gene through a unique AII-responsive promoter element. Both the type 1 and type 2 AII receptors and the downstream cyclic adenosine 1',3'-monophosphate- and protein kinase C-dependent signaling pathways activate the FGF-2 promoter through a novel signal-transducing mechanism. This mechanism, which we have named integrative nuclear FGF receptor-1 signaling, involves the nuclear translocation of FGF receptor-1 and its subsequent transactivation of the AII-responsive element in the FGF-2 promoter.

Unenhanced helical computed tomography for the evaluation of suspected renal colic in the adolescent population: a pilot study

OBJECTIVES

Unenhanced helical computed tomography (UHCT) is rapidly becoming the preferred imaging modality for the evaluation of suspected renal colic in the adult population; however, a series addressing its use in the adolescent population has not been previously published. We assessed the utility of UHCT in the evaluation of suspected renal colic in this age group.

METHODS

Seventeen patients between the ages of 8 and 18 years (mean 14.7) presented to the emergency departments of four hospitals for evaluation of suspected renal colic. All patients were studied with UHCT immediately after initial evaluation. A single helical acquisition was performed from the midpoint of T-12 vertebra to a point below the bladder base, using a slice thickness of 5 mm. Films were reviewed by the institutional radiologist, and results were quantified.

RESULTS

Of the 17 patients who underwent evaluation, no abnormality was detected in 8 patients. A stone was localized in 7 patients who were then appropriately treated. One patient had no stone visualized, but secondary signs suggested a recently passed stone. The final patient had no stone; however, marked bilateral hydroureteronephrosis was noted that led to further evaluation. A single phlebolith was seen in only 1 patient, and no study was nondiagnostic.

CONCLUSIONS

UHCT is a safe, rapidly performed test for the evaluation of suspected renal colic in adolescents. It is highly sensitive and specific for renal and ureteral calculi and, more importantly, allows visualization of alternate pathology. In addition, secondary signs are seen that aid in determining obstruction and are helpful if no stone is visualized. Phleboliths, which can simulate a stone, are rarely seen in adolescence. We believe UHCT allows for rapid triage and localization of stones and should be recommended as the primary diagnostic modality for the evaluation of adolescents with suspected renal colic.

Fludarabine compared with chlorambucil as primary therapy for chronic lymphocytic leukemia

BACKGROUND

Fludarabine is an effective treatment for chronic lymphocytic leukemia that does not respond to initial treatment with chlorambucil. We compared the efficacy of fludarabine with that of chlorambucil in the primary treatment of chronic lymphocytic leukemia.

METHODS

Between 1990 and 1994, we randomly assigned 509 previously untreated patients with chronic lymphocytic leukemia to one of the following treatments: fludarabine (25 mg per square meter of body-surface area, administered intravenously daily for 5 days every 28 days), chlorambucil (40 mg per square meter, given orally every 28 days), or fludarabine (20 mg per square meter per day for 5 days every 28 days) plus chlorambucil (20 mg per square meter every 28 days). Patients with an additional response at each monthly evaluation continued to receive the assigned treatment for a maximum of 12 cycles.

RESULTS

Assignment of patients to the fludarabine-plus-chlorambucil group was stopped when a planned interim analysis revealed excessive toxicity and a response rate that was not better than the rate with fludarabine alone. Among the other two groups, the response rate was significantly higher for fludarabine alone than for chlorambucil alone. Among 170 patients treated with fludarabine, 20 percent had a complete remission, and 43 percent had a partial remission. The corresponding values for 181 patients treated with chlorambucil were 4 percent and 33 percent (P< 0.001 for both comparisons). The median duration of remission and the median progression-free survival in the fludarabine group were 25 months and 20 months, respectively, whereas both values were 14 months in the chlorambucil group (P<0.001 for both comparisons). The median overall survival among patients treated with fludarabine was 66 months, which was not significantly different from the overall survival in the other two groups (56 months with chlorambucil and 55 months with combined treatment). Severe infections and neutropenia were more frequent with fludarabine than with chlorambucil (P=0.08), although, overall, toxic effects were tolerable with the two single-drug regimens.

CONCLUSIONS

When used as the initial treatment for chronic lymphocytic leukemia, fludarabine yields higher response rates and a longer duration of remission and progression-free survival than chlorambucil.

Communication problems of hearing-impaired patients

AIM

The main objective of this national survey was to check the findings of an earlier pilot survey. This had found that patients who had a hearing-impairment and were in hospital were often seriously disadvantaged by their disability.

METHOD

The survey was conducted by questionnaire and the sampling frame confined to hearing-impaired patients who had been in hospital during the previous three years. A total of 359 completed and valid questionnaires were returned.

RESULTS

The responses confirmed the finding of the pilot survey. They indicated that there were serious shortcomings in the ability of many hospital staff to cope with the problems of hearing-impaired patients.

CONCLUSION

Common causes of the problems were identified. The major factor was inadequate training of both nurses and doctors in deaf awareness and the associated communication skills. Other significant factors included patients concealing their disability, pressure of work and poor communication between staff. Appropriate training at all staff levels should eliminate a high proportion of these problems.

The angiotensin AT(1) receptor antagonist irbesartan has near-peptide affinity and potently blocks receptor signaling

The angiotensin II type 1 (AT(1)) receptor plays a pivotal role in the regulation of blood pressure and electrolyte balance, and is involved in the control of specific ingestive behaviours. Irbesartan (SR 47436/BMS 186295) is a recently developed angiotensin AT(1) receptor antagonist, chemically described as 2-butyl-3-([2'-¿1H-tetrazol-5-yl¿biphenyl-4-yl]methyl)-1, 3-diazaspiro (4,4)non-1-en-4-one. Irbesartan displays higher affinity for its target receptor than other similar antagonists. In radioligand binding assays performed on membranes from WB-Fischer 344 (WB) rat liver epithelial cells, irbesartan was able to displace [125I]angiotensin II with a K(i) of 4.05 nM as compared to losartan (DuP 753) and tasosartan (WAY 126756), which had K(i) values of 25.2 nM and 46.6 nM, respectively. Similarly, in functional assays, irbesartan exhibited the highest functional potency to block angiotensin II-induced inositol trisphosphate (IP(3)) turnover. The improved affinity of irbesartan for the angiotensin AT(1) receptor does not coincide with a concomitant increase in affinity for the angiotensin AT(2) receptor, as irbesartan and losartan exhibited the same low potency to displace [125I]angiotensin II in radioligand binding assays performed on membranes from PC-12w cells. In binding assays performed on peripheral tissues in rat, irbesartan bound to the angiotensin AT(1) receptor expressed in liver, adrenal, kidney and pituitary with an overall affinity closely approaching that of the high affinity peptidic antagonist [Sar(1), Ile(8)]angiotensin II. Due to the higher affinity of irbesartan over other similar antagonists for the angiotensin AT(1) receptor in many tissues and its greater potency to block receptor activation, irbesartan may be quite useful in the study of the angiotensin AT(1) receptor and its role in controlling ingestive behaviours and, furthermore, shows great potential to improve the treatment of hypertension and other cardiovascular disease states.

Fat collection related to the intrahepatic inferior vena cava on CT

OBJECTIVE

The purpose of our study is to describe the CT findings of fat collections related to the intrahepatic inferior vena cava and to review the literature about this benign incidental finding.

CONCLUSION

Focal collections of fat related to the inferior vena cava are benign incidental findings located exclusively at the level of the liver. The fat collections are always adjacent to the medial wall of the inferior vena cava; appear to be extraluminal in origin and may, in fact, be entirely extraluminal; and are uncommon findings that are usually of no clinical significance.

Lipomas of the pancreas

OBJECTIVE

The purpose of this study was to describe the CT findings of pancreatic lipomas in four patients.

CONCLUSION

In all four cases, the lipoma was revealed incidentally on CT scans obtained for other reasons. CT scans were diagnostic, showing well-circumscribed masses within the pancreas composed almost entirely of fat, with a few scattered vessels or septa or both, which ranged in size from 1.4 x 2.0 cm to 4.5 x 5.3 cm in the axial plane. Pancreatic lipomas are rare, usually incidental tumors and, as with lipomas found elsewhere in the body, conservative management is often indicated.

Expression of apoptosis-regulating proteins in chronic lymphocytic leukemia: correlations with In vitro and In vivo chemoresponses

B-cell chronic lymphocytic leukemia (B-CLL) represents a neoplastic disorder caused primarily by defective programmed cell death (PCD), as opposed to increased cell proliferation. Defects in the PCD pathway also contribute to chemoresistance. The expression of several apoptosis-regulating proteins, including the Bcl-2 family proteins Bcl-2, Bcl-XL, Mcl-1, Bax, Bak, and BAD; the Bcl-2-binding protein BAG-1; and the cell death protease Caspase-3 (CPP32), was evaluated by immunoblotting using 58 peripheral blood B-CLL specimens from previously untreated patients. Expression of Bcl-2, Mcl-1, BAG-1, Bax, Bak, and Caspase-3 was commonly found in circulating B-CLL cells, whereas the Bcl-XL and BAD proteins were not present. Higher levels of the anti-apoptotic protein Mcl-1 were strongly correlated with failure to achieve complete remission (CR) after single-agent therapy (fludarabine or chlorambucil) (P = .001), but the presence of only seven CRs among the 42 patients for whom follow-up data were available necessitates cautious interpretation of these observations. Higher levels of the anti-apoptotic protein BAG-1 were also marginally associated with failure to achieve CR (P = .04). Apoptosis-regulating proteins were not associated with patient age, sex, Rai stage, platelet count, hemoglobin (Hb) concentration, or lymph node involvement, although higher levels of Bcl-2 and a high Bcl-2:Bax ratio were correlated with high numbers (>10(5)/microL) of white blood cells (WBC) (P = .01; .007) and higher levels of Bak were weakly associated with loss of allelic heterozygosity at 13q14 (P = .04). On the basis of measurements of apoptosis induction by fludarabine using cultured B-CLL specimens, in vitro chemosensitivity data failed to correlate with in vivo clinical response rates (n = 42) and expression of the various apoptosis-regulating proteins. Although larger prospective studies are required before firm conclusions can be reached, these studies show the expression in B-CLLs of multiple apoptosis-regulating proteins and suggest that the relative levels of some of these, such as Mcl-1, may provide information about in vivo responses to chemotherapy. In vitro chemosensitivity data, however, do not appear to be particularly useful in predicting responses in B-CLL.

Measurement of self-esteem in repeat assault victims

Background characterization of assault-related injuries have demonstrated that lifestyle, substance abuse, education, employment, mental illness, and high-risk behavior contribute to low self-esteem in repeat assault victims. Recurrent-assault patients have never been studied with respect to self-esteem. This study evaluated self-esteem and assault-related injury in 28 consecutive male assault patients (11 first-assault and 17 recurrent-assault patients) and 19 controls with no previous assault history. Study participants were administered the Walmyr Assessment Scales Index of Self-Esteem (WASISE) as part of a three-item survey to determine the relationship between self-esteem and assault-related injury. No demographic differences were found between the groups. The mean (+/- standard error) WASISE score for recurrent-assault patients (34.9 +/- 3.4) was significantly higher than mean scores for no-assault and first-time assault-injured patients (14.7 +/- 1.4 and 15.0 +/- 2.3, respectively). The recurrent-assault patients had a lower mean education level than both no-assault and first-time assault-injured patients (2.1 +/- 0.26 and 1.9 +/- 0.57, respectively). Eighteen (2%) first-time assault-injured and 11 (7%) recurrent-assault patients were employed. These data suggest that self-esteem, education, and employment history need to be considered when evaluating and developing interventions for repeat-assault patients.

Preclinical and phase I clinical studies with the nonclassical antifolate thymidylate synthase inhibitor nolatrexed dihydrochloride given by prolonged administration in patients with solid tumors

PURPOSE

A phase I, multicenter trial of the thymidylate synthase (TS) inhibitor THYMITAQ (nolatrexed dihydrochloride; Agouron Pharmaceuticals, Inc, San Diego, CA) given by 5-day continuous infusion was performed to establish the maximum-tolerated dose (MTD) and to investigate pharmacokinetics, pharmacodynamics, and antitumor effects.

METHODS

In vitro and in vivo preclinical studies demonstrated increased activity with prolonged nolatrexed exposure. In 32 patients, nolatrexed was given as a 5-day infusion at 96 to 1,040 mg/m2/d for 5 days. Pharmacokinetics were determined from high-performance liquid chromatography (HPLC) analyses of plasma and urine. In addition to studying toxicity, plasma deoxyuridine (UdR) elevations were measured as a marker of TS inhibition.

RESULTS

The MTD was 904 mg/m2/d for 5 days and the recommended phase II dose is 800 mg/m2/d for 5 days. The dose-limiting toxicity was neutropenia with clinically significant thrombocytopenia and mucositis. These antiproliferative toxicities of nolatrexed were predictable and reversible. A partial response that lasted 3 months occurred in a patient with metastatic colorectal cancer. Pharmacokinetics were nonlinear, with the median plasma clearance (CI) decreasing from 151 mL/min/m2 (range, 124 to 211) at 96 mg/m2/d for 5 days to 49 mL/min/m2 (range, 30 to 84) at 768 mg/ m2/d for 5 days. The half-life (t1/2) was 173 minutes (range, 43 to 784) and 18% (range, 9% to 35%) of the dose was excreted unchanged in the urine. Plasma UdR increased, but returned to pretreatment levels after the end of infusion. Hematologic toxicity was significantly related to nolatrexed plasma concentrations and dose.

CONCLUSION

Nolatrexed can be safely administered to patients at a dose of 800 mg/m2/d over 5 days by continuous intravenous infusion and this schedule is associated with antitumor effects. The phase II evaluation of nolatrexed is ongoing.

Skin irritation potential of mixed surfactant systems

Virtually all current detergent formulations contain mixtures of surfactants. Our experience and test data on these formulations, which is in agreement with that of many others, has shown that in use the formulations exhibit lower acute irritation potential than predicted by simple summation of the irritation potential of the individual actives. Using the criteria of the Dangerous Preparations Directive (EC Directive 88/379/EEC), many of these formulations classify as irritant in the neat state, with consequent labelling requirements. Such classification is based on addition of irritant components giving a total concentration which exceeds a nominal threshold. In this study, mixtures of surfactants were tested by application to a panel of 31 human volunteers for up to 4 hr, using the technique established for the assessment of acute skin irritation potential. The positive control, sodium dodecyl sulfate (SDS) at 20% concentration, gave an 84% positive response. Dimethyl dodecyl amido betaine (DDAB) at the same concentration gave a 94% response. However, a combination of 20% of each of these surfactants in the same panellists gave a response of only 44%--a significant reduction in the irritation potential. A further test conducted with a mixture of 10% SDS and 10% DDAB in a second panel gave a 31% positive response compared with a 94% positive response to the 20% SDS control in that panel. These results clearly demonstrate that the acute irritation potential of mixed surfactants cannot be predicted by simple summation of the irritation potential of the component substances. Initial results of the mechanistic investigation indicate that the reduced irritation induced by the mixed surfactant systems correlates with a reduced critical micelle concentration (CMC). However, the reduced CMC itself seems not to be responsible for the lowered irritation, since these experiments were conducted at concentrations well above the CMC. It is proposed that the critical event leading to skin irritation is binding to skin protein and that in mixed surfactant systems, the individual surfactants exhibit less affinity for this protein.