Evaluation of sample preparation methods for MALDI-TOF MS identification of highly dangerous bacteria

AIMS

To propose a universal workflow of sample preparation method for the identification of highly pathogenic bacteria by MALDI-TOF MS.

METHODS AND RESULTS

Fifteen bacterial species, including highly virulent Gram-positive (Bacillus anthracis and Clostridium botulinum) and Gram-negative bacteria (Brucella melitensis, Burkholderia mallei, Francisella tularensis, Shigella dysenteriae, Vibrio cholerae, Yersinia pestis and Legionella pneumophila), were employed in the comparative study of four sample preparation methods compatible with MALDI-TOF MS. The yield of bacterial proteins was determined by spectrophotometry, and the quality of the mass spectra, recorded in linear mode in the range of 2000-20,000 Da, was evaluated with respect to the information content (number of signals) and quality (S/N ratio).

CONCLUSIONS

Based on the values of protein concentration and spectral quality, the method using combination of ethanol treatment followed by extraction with formic acid and acetonitrile was the most efficient sample preparation method for the identification of highly pathogenic bacteria using MALDI-TOF MS.

SIGNIFICANCE AND IMPACT OF THE STUDY

The method using ethanol/formic acid generally shows the highest extraction efficacy and the spectral quality with no detrimental effect caused by storage. Thus, this can be considered as a universal sample preparation method for the identification of highly virulent micro-organisms by MALDI-TOF mass spectrometry.

Axillary Dissection in the Case of Positive Sentinel Lymph Nodes: Results of the Innsbruck Consensus Conference

The prognosis of breast cancer is most heavily influenced by the status of the axillary nodes. Until a few years ago, this knowledge was gained through radical axillary lymph node clearance. In the meantime, sentinel lymph node clearance has become an established part of the surgical treatment of breast cancer. With the development of this procedure, the morbidity caused by axillary dissection has been reduced significantly. Although comprehensive prospective, randomised data regarding the safe use of the sentinel concept are only now available, the focus currently, however, is on the question of whether in the case of positive sentinel lymph nodes, an axillary dissection can be done away with altogether without having any negative impact on the risk of loco-regional recurrence or on progression-free survival and overall survival. The results of the American ACOSOG-Z001 study have changed the fundamental perspective of this. In this study on the advantages of axillary dissection following the confirmation of tumour tissue in the sentinel lymph nodes, there were no statistically significant advantages from axillary dissection for women with a favourable overall risk profile who had received radiotherapy and systemic therapy. If this concept takes hold, the surgical treatment of node-positive breast cancer, at least in the axilla, would be reduced to a minimum, and the focus of treatment would in future lie more on the systemic treatment of this condition. As part of an interdisciplinary consensus meeting, a standardised approach for Austria with regard to this question was decided upon.

Association of a common genetic variant of the IGF1 gene with clinical outcome in patients with HER2-positive breast cancer

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Background: Insulin-like growth factor 1 (IGF1) stimulates mitosis and inhibits apoptosis. Circulating IGF1 levels may be linked with an increased risk of colorectal and breast cancer. Further, IGF1 single nucleotide polymorphisms (SNPs), especially variant rs2946834, recently have been associated with a poor clinical outcome in patients with colorectal cancer. However, the influence of IGF1 SNPs on the prognosis of patients with breast cancer is unknown. Therefore, we aimed at investigating the influence of IGF1 tagging polymorphisms associated with IGF1 levels on event-free survival in patients with HER2-positive breast cancer.

Methods: The present study included 161 consecutive white patients with HER2-positive breast cancer treated between 2000 and 2010 at the Department of Gynecology and Obstetrics, Medical University of Innsbruck, Austria. Event-free survival was calculated as the time from cancer diagnosis to either relapse or death from any cause. Genomic DNA was extracted from archived formalin-fixed paraffin embedded tumor tissue samples; five IGF1 tagging polymorphisms (rs2946834, rs6220, rs1520220, rs5742694, and rs5742678) were genotyped by SNaPshot assays.

Results: Mean follow up period was 4.3 (± 2.5) years. Kaplan-Meier analysis showed a poorer clinical outcome for carriers of the rare allele of SNP rs2946834 (log-rank test, p = 0.029). Concordantly, in univariate Cox regression analyses the rare allele of SNP rs2946834 was significantly associated with a decreased event-free survival (HR = 2.87 [1.07 –7.70]; p = 0.036). Multivariate analysis adjusted for age and tumor stage confirmed this result (HR = 2.86 [1.06 –7.71]; p = 0.038). Thus, our results are in concordance with a recent report that the same SNP is associated with poorer clinical outcome in colorectal cancer patients. Other investigated genetic variants of the IGF1 gene were not significantly associated with event-free survival (all p-values > 0.05).

Conclusions: For the first time, our study investigates the influence of IGF1 tagging polymorphisms on the clinical outcome of HER2-positive breast cancer patients suggesting SNP rs2946834 as a predictor for reduced event-free survival.

Abstract P4-02-04: Impact of CYP2D6 Genotype and Side-Effects on Adherence Rates to Tamoxifen in Premenopausal Breast Cancer Patients

Background: Only few studies have investigated the issue of breast cancer patients’ adherence to tamoxifen therapy and factors influencing adherence behavior. Especially in the context of different CYP2D6 genotypes adherence to tamoxifen has not been extensively studied yet. Variations in the CYP2D6 genotype, as well as patients taking inhibitors of CYP2D6 (e.g. antidepressants) contribute to different side effects and adherence rates to adjuvant tamoxifen.

Materials and Methods: 106 premenopausal breast cancer patients who met inclusion criteria were consecutively included in the study at the outpatient unit of the Department of Gynecology, Innsbruck Medical University. Within their routine after care appointment patients completed a comprehensive PRO assessment including the FACT-B/ES, the HADS and a self-report questionnaire on adherence behavior (SMAQ). The multi-method approach comprised the Simplified Medication Adherence Questionnaire, a semi-structured interview, physicians’ ratings and blood levels for tamoxifen metabolites. Additionally, the CYP2D6 genotype was determined in all patients participating in this part of the study.

Results: 19% patients were poor metabolizer (PM), 51% intermediate metabolizer (IM), 29% extensive metabolizer (EM) and 7% ultra-rapid metabolizer (UM). Significant group differences with regard to tamoxifen and endoxifen serum concentrations were found between the metabolization groups (p=0.044). UMs had the lowest tamoxifen and highest endoxifen concentrations. Only 3.2% of the patients analyzed had no measurable tamoxifen concentrations in their serum. All non-compilant patients were from the extensive metabolizer group. However, during follow-up 25% (2/6) of patients with UM genotype, 13% (4/30) with EM genotype, 1% (1/50) with IM genotype and 0% (0/19) with the PM genotype discontinued their tamoxifen therapy due to therapy related side effects. In addition anti-depressants were more frequently prescribed in the extensive metabolizer group leading to lower levels of the active metabolite endoxifen. Conclusion: A trend towards higher hot flashes was observed in the EM and UM group. We did not find significant differences in QOL between

CYP2D6 metabolizing groups. Trend level significance was found for global QOL (on a descriptive level) physical well-being and emotional well-being. Non-adherence to tamoxifen therapy is more frequent in patients with CYP2D6 EM and UM genotype. These preliminary data may explain part of the current controversy over CYP2D6 genotype predicting response to tamoxifen and suggest that patients most likely to benefit from tamoxifen are paradoxically most likely to stop their tamoxifen therapy prematurely.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P4-02-04.

Abstract P5-11-09: A Validated Analytical Method for Monitoring the Plasma Levels of Tamoxifen, Anastrozole and Letrozole in Patients Undergoing Endocrine Therapy

Background: Clinical data have repeatedly shown that tamoxifen as well as anastrazole and letrozole significantly increase the overall survival among breast cancer patients. However, in several cases the use of these drugs is limited by side effects, whose appearance are described to impair the adherence of a patient to endocrine treatment. Frequently, adherence is rated based on patient self-reports. One competent approach to obtain impartial information about patient adherence and its clinical relevance is based on the determination of plasma drug concentrations. The individual steady state plasma level represents an objective measure that may serve as an important comparator to check the patient-reported adherence status in clinical studies. In addition, it may also reveal useful information for the treating physician regarding concentration dependent side effects or therapeutic failure. We have developed and validated a liquid chromatography-tandem mass spectrometry (LC/MS/MS) method for the simultaneous analysis of tamoxifen, anastrazole and letrozole in human plasma. The method was applied in the PRO-BETh study to monitor 320 breast cancer patients undergoing endocrine therapy.

Material and methods: Blood plasma samples were collected from 320 patients undergoing endocrine breast cancer therapy and stored at -20° C. To prepare a sample for LC/MS/MS analysis, 1 ml plasma was treated with a solid phase extraction procedure using a cation mixed-mode polymeric sorbent phase (Strata-X-C cartridges, Phenomenex, CA). Chromatographic separation was accomplished on a reversed-phase column (200 mm x 0.5 mm, Eurosphere-C18, 5 μm, Knauer, Berlin) by using a gradient of acetone in an aqueous hexafluorobutyric acid solution. Mass spectrometric detection was performed on a quadrupole-quadrupole-linear ion trap instrument (Q Trap 3200, Applied Biosystems, Foster City, CA). Results: We have developed a fully validated method for the simultaneous quantitative analysis of tamoxifen, anastrozole and letrozole in human plasma. Validation was accomplished for a concentration range of 25-500 ng/ml for tamoxifen, 10-200 ng/ml for endoxifen, 5-200 ng/ml for anastrozol and 10-300 ng/ml for letrozole. The applicability of the method was demonstrated in the context of the PRO-BETh study, by analyzing plasma samples of 320 patients undergoing endocrine breast cancer therapy. The observed plasma levels showed a high inter-patient variability with measured values between 26-307 ng/ml (mean 125 ng/ml) regarding tamoxifen, 17-301 ng/ml (mean 107 ng/ml) regarding letrozole and 6-102 ng/ml (mean 37 ng/ml) regarding anastrozole. Eight samples did not contain a quantifiable amount of drug, indicating longer abstinence of the corresponding patients regarding endocrine therapy. Conclusions: The developed method represents a reliable and convenient tool for the quantitative analysis of tamoxifen, anastrozol and letrozole in human plasma. The method is dedicated to drug monitoring which is an important part of adherence rating. As exemplified in the context of the PRO-BETh study, the measured steady state plasma levels represent objective measures that serve as important comparators to check the patient-reported adherence status.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P5-11-09.

Abstract P5-11-10: Gonadotropins Plasma Levels Are Significantly Influenced by Body Mass Index in Postmenopausal Breast Cancer Patients Undergoing Endocrine Therapy with Aromatase Inhibitors: Is This a Surrogate Marker for Serum Estrogen Bioactivity?

Background: Estrogens play a crucial role in breast carcinogenesis and progression. The third-generation aromatase inhibitors (AIs) have therefore become the first choice endocrine drugs for post-menopausal women with breast cancer, since they present greater efficacy when compared with tamoxifen. However, mode of action, side effects and tolerability are distinct compared to tamoxifen. In this study, we evaluated clinical side-effects, levels of gonadotropin, prolactin, progesterone and estradiol in postmenopausal women undergoing endocrine treatment with aromatase inhibitors.

Materials and Methods: 128 postmenopausal patients undergoing endocrine therapy with aromatase inhibitors were included in the study. They completed the assessment at their regular 3-month check up. For the assessment of side-effects and symptom burden we used the FACT-B/+ES and the HADS. Blood samples were collected within the routine blood collection and measurement of follicle stimulation hormone (FSH), luteinizing hormone (LH), progesterone, estradiol and prolactin plasma levels were performed by Immunoassay. Data were analyzed using Spearman rank correlation.

Results: We found a significant negative correlation of LH and FSH with body mass index (BMI) of postmenopausal breast cancer patients (LH r=- 0.281, p=0.014; FSH r=-0.250, p=0.029) receiving aromatase inhibitors. Analyses revealed a significant positive correlation for LH and FSH levels with subjectively experienced weight gain (LH r=0.499, p=0.008; FSH r=0.550, p=0.003), dyspareunia and vaginal dryness. Moreover, patients with a BMI ≥25 had significantly more gynaecological symptoms (dyspareunia p=0.008 and vaginal dryness p=0.026) than patients witha lower BMI. Progesterone was significantly associated with subjective weight gain (r=0.248, p=0.014). Prolactin significantly correlated with loss of sex drive (r=0.256, p=0.050), mood swings (r=0.239, p=0.050) and irritability (r=0.244, p=0.046).

Conclusion: Our results reveal distinct endocrine changes among postmenopausal breast cancer patients undergoing endocrine treatment with AIs. These results confirm the central role of estrogens in the evolution of adverse events to aromatase inhibitors. The main observation in this study, however, was the correlation of BMI and levels of hormone influenced by estrogenic activity. LH and FSH which are under control of various estrogen metabolites, were significantly associated with the BMI and might therefore serve as surrogate marker of estrogenic activity in serum of breast cancer patients. Direct measurement of estradiol (E2) showed no correlation with BMI indicating the influence of various other estrogen metabolites on the secretion of gonadotropins. Analysis of serum estrogen receptor bioactivity in these patients is currently underway.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P5-11-10.

Abstract P4-02-17: Polymerase Chain Reaction-Liquid Chromatography-Mass Spectrometry — A Convenient and Cost-Effective Strategy for CYP2D6 Genotyping

Background: Genetic polymorphisms in the drug metabolizing enzyme Cyotchrome P450 2D6 (CYP2D6) gene can significantly influence a person's ability to mediate CYP2D6 dependent metabolism. For example, a notable influence of the CYP2D6 genotype has been described regarding the conversion of tamoxifen to its pharmacologically active metabolites. Thus, the genetic determination of the CYP2D6 metabolizer status has the potential to represent a valuable therapeutic supplement in breast cancer therapy. However, the clinical relevance of the CYP2D6 genotype regarding the treatment of breast cancer with tamoxifen still remains to be elucidated. Due to the high number of relevant polymorphisms to be screened, pharmacogenetic CYP2D6 testing is considered to be time-consuming and laborious and is therefore limited to a few clinical studies only. To enable a more widespread use, we present polymerase chain reaction (PCR) - ion-pair reversed-phase high-performance liquid chromatography — electrospray ionization time of flight mass spectrometry (ICEMS) as fast, convenient and cost-effective strategy for CYP2D6 genotyping.

Material and Methods: After DNA extraction from saliva swabs, the CYP2D6 gene was amplified by a long range PCR. Subsequently, polymorphism-specific short amplicons were generated in a multiplexed PCR. The amplicons were directly analysed by ICEMS. The information necessary to determine the allelic state of a PCR-amplified polymorphic locus were obtained from the measured molecular masses. Gene duplications or deletions were analysed by a long range PCR protocol and subsequent agarose gel detection.

Results: The developed CYP2D6 genotyping approach enables the reliable determination of the most frequent CYP2D6 alleles in Europe (*1, *2, *3, *4, *6, *7, *8, *9, *10, *11, *12, *17, *41) including whole gene duplications and deletions (*5). The assay involves the following steps: (1) collecting biological material in form of non-invasive saliva swabs; (2) DNA extraction; (3) long range PCR for a specific CYP2D6 amplification; (3) multiplexed PCR for the generation of polymorphism-specific short amplicons; (4) direct analysis of the reaction mixture with ICEMS; (4) determination of the allelic state with the measured molecular masses; (5) analysis of gene duplications or deletions by a long range PCR protocol and subsequent agarose gel detection. Genotyping of a single sample costs about 5-10 USD and can be accomplished within 2-3 days. Parallelization increases the sample throughput and reduces costs. For proof of principle, we have applied the developed method in the context of the PRO-BETh study to determine the CYP2D6 status of 106 breast cancer patients treated with tamoxifen. According to the classification of Gaedik A. et al [1], 19% of the typed breast cancer patients turned out to be “Poor Metabolizers", 51% were “Intermediate Metabolizers", 29% were “Extensive Metabolizers” and 7% turned out to be “Ultrarapid Metabolizers”.

Conclusion: PCR-ICEMS represents a cost-effective and convenient tool for pharmacogenetic testing, which enables the determination of the CYP2D6 status using DNA obtained from a non-invasive saliva swab as template.

[1] Gaedigk A. et al, J. Clin Pharmacol Ther. 2007 Jun;81(6):817-20.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P4-02-17.

Abstract P5-11-04: Phenotype-Genotype Correlations in Breast Cancer Patients Treated with Tamoxifen

Background: Personalized medicine strategies are especially relevant for drugs which show a high inter-individual variability regarding their pharmacokinetic and -dynamic properties. Considerable inter-patient variations have been described regarding the plasma concentrations of tamoxifen and its metabolites. Due to the observation that tamoxifen metabolites can show a high pharmacological activity, tamoxifen metabolism has received considerable attention. The metabolism of tamoxifen is complex resulting in a huge number of different products. Important metabolic transformation reactions include demethylation catalyzed by Cytochrome P450 3A4 and hydroxylation mainly catalyzed by Cytochrome P450 2D6 (CYP2D6). The impact of the CYP2D6 activity, which can be predicted from genetic information, on plasma levels and the related pharmacological effects has controversially been discussed. To get a better understanding of the inter-individual differences of the plasma levels of tamoxifen and some of its metabolites we have used liquid chromatography-tandem mass spectrometry (LC/MS/MS) to screen the plasma samples of 106 breast cancer patients. This method enabled the quantification of tamoxifen as well as a relative quantification of demethyltamoxifen and hydroxylated tamoxifen metabolites. To study the impact of enzyme activity on plasma levels, CYP2D6 genotypes were determined as well.

Material and methods: For metabolic profiling 1 ml plasma was treated with a solid phase extraction procedure. Chromatographic separation was accomplished on a reversed-phase column. Analytes were detected by mass spectrometry. For genotyping, the CYP2D6 gene was amplified by a long range PCR followed by a multiplexed PCR to generate specific short amplicons. The amplicons were directly analysed by LC/MS. The information necessary to determine the allelic state were obtained from the measured molecular masses.

Results: We determined the CYP2D6 genotype of 106 breast cancer patients treated with tamoxifen. We found 19% “Poor Metabolizers", 51% “Intermediate Metabolizers", 29% “Extensive Metabolizers” and 7% “Ultrarapid Metabolizers”. The observed plasma concentrations of tamoxifen and its metabolites showed a high inter-patient variability For instance, plasma concentrations between 26-307 ng/ml (mean 125 ng/ml) were observed for tamoxifen. We did not find a significant impact of the CYP2D6 status on tamoxifen plasma levels. However, the demethyltamoxifen/tamoxifen as well as the hydroxytamoxifen/tamoxifen ratios appear to be influenced by the CYP2D6 status: the higher the metabolic activity, the higher the hydroxytamoxifen content and the lower the demethyltamoxifen content.

Conclusions: We have developed analytical tools, which allow the determination of the content of tamoxifen and its major metabolites in human plasma and the genotyping of the CYP2D6 gene. Phenotypic and genotypic data of 106 patients were acquired. Correlation of the data revealed that the genotype had no significant impact on tamoxifen plasma levels. Nevertheless, patients with a predicted higher CYP2D6 activity showed lower demethyltamoxifen/tamoxifen ratios as well as higher hydroxytamoxifen/tamoxifen ratios.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P5-11-04.

Abstract PD08-02: The Impact of Patient Reported Outcomes (PRO) on the Evaluation of Therapy Related Side-Effects and the Improvement of Adherence to Endocrine Treatment in Breast Cancer Patients

Background: Long term treatment regimen with significant side effects may diminish a patient's quality of life (QOL) and consequently undermine adherence. Endocrine treatment for breast cancer causes various side effects, which can lead to early discontinuation of this effective therapy. Current knowledge on patients’ quality of life (QOL) impairments caused by endocrine therapy originates from clinicians’ impressions and expert ratings. This runs the risk of underestimating the effects of endocrine therapy on patients’ quality of life. Patient reported outcome (PRO) may provide higher accuracy and may therefore essentially contribute to medication evaluation and clinical decision making. In this study, we report on the patient reported outcome (PRO) related to endocrine therapy in early breast cancer.

Methods: Pre-and postmenopausal breast cancer outpatients treated with aromatase inhibitors (AIS) or tamoxifen were approached at their routine control appointment with the treating physician. We conducted a comprehensive PRO assessment comprising the following scales: FACT-B/+ES and HADS (high scores indicate high symptoms). In a short, semi-structured interview data on patients’ general medication intake behavior were collected focusing on the intake of complementary and alternative medicine (CAM)

Results: We analyzed PRO data of 240 patients undergoing endocrine treatment. 66.6% received AI therapy, 71.9% were postmenopausal. We found high levels of symptom burden in this study group: 55.9% had moderate to severe bone pain, 47.8% menopausal symptoms and 49.1% loss of sex drive. Postmenopausal women in the AI group had significantly more symptoms on the endocrine subscale (mean 24.25 vs. 16.42, p=0.045), significantly more anxiety (mean 8.8 vs. 5.11, p=0.036) and depression (mean 8.75 vs. 3.86, p=0.011). In the tamoxifen group premenopausal patients scored significantly higher on all scales. Moreover, patients who used complementary substances had a significant lower physical well-being (22.70 vs. 24.39, p=0.007) and more endocrine symptoms (22.63 vs. 16.30, p=0.004).

Conclusion:The results of our study show a significantly higher assessment of physical side-effects and psychosocial burden on part of the patients than implied by clinicians’ reports and expert ratings. PRO data may therefore provide a more accurate measure for symptom burden and contribute to individualized clinical decision making. It is an important tool to detect and effectively treat therapy related side effect to ultimately preserve adherence to endocrine treatment. According to our findings, it appears mandatory to incorporate PRO data in individualized clinical decision making to arrive at a more accurate assessment of symptom burden.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr PD08-02.

Regulation of the EGFR-E2F3a axis by the interferon regulatory factor (IRFs) and by promoter methylation of miR-34a in ovarian cancer

e16522

Background: Although, EGFR targeting has reached “bedside” in various tumor entities, including ovarian cancer, the essential role of E2F3a in EGFR mediated proliferation remained uncovered. Recently, we outlined the clinical relevance of E2F3a in ovarian cancer. Now we were able to elucidate the pathway between EGFR activation and E2F3a induction. Methods: Promoter mapping of E2F family members was assessed using the JASPER software. E2F3a protein was assessed by immunoblot analyses in siRNA based IRF-1, IRF-2 knockdown HOC-7 cells. Cell growth was determined by MTT assays after siRNA based knockdown of E2F3a. Expression of E2F3a regulating miR-34a, miR-210 and miR-20a were assessed by RT-PCR in 130 ovarian cancer patients and methylation status of the E2F3a promoter and of miRNA promoters were estimated using Methyllight. 6p22 amplification status of patients was determined by FISH analyses. Results: Promoter mapping of E2F family members revealed that IRF-1 and IRF-2 are potential intermediate components of the herein described EGFR-E2F3a axis. As evidenced by knock-down of IRF-1, IRF-2 or both, the ratio between the two mutually antagonistic IRF-1 and IRF-2 was found to be substantial for EGF induced E2F3a up-regulation. E2F3a knock-down yielded a complete abolishment of EGF induced cancer cell proliferation. Although, activated EGFR status showed a highly significant correlation with E2F3a expression, a subgroup of patients presented high E2F3a mRNA levels without EGFR activation. Within this subgroup promoter methylation of miRNA-34a, that regulates E2F3a, was revealed to represent an alternative mechanism of E2F3a regulation in ovarian cancer, whereas promoter methylation of E2F3a itself was not relevant in E2F3a control. Unlike in prostate or bladder cancer 6p22 amplification was not found to be relevant for E2F3a up-regulation in ovarian cancer. Conclusions: Our present data point to the substantial role of the ratio between IRF-1 and IRF-2 in EGFR mediated E2F3a induction. Furthermore, in vivo regulation of E2F3a involves methylation and thereby silencing of miR-34a. Targeting of the herein described molecular pathway, downstream EGFR, could represent an appealing therapeutic approach in ovarian cancer.

No significant financial relationships to disclose.

Tailoring an antibacterial peptide of human lysosomal cathepsin G to enhance its broad-spectrum action against antibiotic-resistant bacterial pathogens

Neutrophils contain several cationic antimicrobial proteins or peptides (CAPs) that exert antibiotic-like action against bacteria. These host-derived antibiotics kill susceptible bacteria by oxygen-independent mechanisms. Considerable interest in their activity has been generated in recent years due not only to their likely important role in innate host defense against infection, but also their possible use as therapeutic agents in treating infections caused by antibiotic-resistant pathogens. We have studied the antibacterial properties of human lysosomal cathepsin G (cat G). This highly cationic serine protease contains at least three antibacterial regions that by themselves can exert antibacterial action against Gram-negative bacteria, such as Pseudomonas aeruginosa. Only one of these peptides, defined by residues 117-136 of full-length cat G, has bactericidal action against Gram-positive pathogens, such as Staphylococcus aureus. Due to the broad-spectrum antibacterial action of this peptide, we have sought to define the amino acids within its primary sequence required for this activity and have developed variants with improved activity. This review emphasizes the importance of both cationicity and hydrophobicity as necessary characteristics for the antibacterial action of CAPs. It also proposes the strategy that naturally occurring large human CAPs can be dissected to smaller CAPs and then modified to enhance their activity in vitro. This approach could prove beneficial to those interested in developing antimicrobial peptides as therapeutic agents.