Evaluating the Jaccard Similarity Index as a Persistence Measure of Multiple Anal Human Papillomavirus Among Nigerian Men Who Have Sex With Men.

BACKGROUND: Multiple anal human papillomavirus (HPVs) may increase the risk of anal cancer among men who have sex with men (MSM) living with human immunodeficiency virus (HIV). The Jaccard Similarity Index (JSI) was explored as a measure of multiple HPV persistence. METHODS: The TRUST/RV368 cohort enrolled MSM living with and without HIV in Abuja and Lagos, Nigeria. Participants with anal swabs at baseline, 3- and 12-month visits were tested for high- and low-risk HPVs using a next-generation sequencing assay. Persistence of the same HPV genotypes over time was calculated using the JSI and categorized into high, medium, and low similarity tertiles. Factors associated with higher versus lower similarity were estimated with multivariable ordinal logistic regression and reported as adjusted odds ratios (aORs) and 95% confidence intervals (CIs). RESULTS: Of the 225 participants, median age was 25 years (interquartile range, 22-29 years), 62% were living with HIV, median HPVs was 3 (interquartile range, 2-5), and HPV6 (28%), HPV16 (26%), HPV11 (23%), and HPV45 (20%) were most prevalent. Fifty-three percent of participants had highly similar HPVs at 3 months, and the similarity was associated with HIV (aOR, 3.11; 95% CI, 1.6-5.9) and recent receptive sex (aOR, 1.9; 95% CI, 1.0-3.5). By 12 months, 20% had highly similar HPVs, and it was associated with 12 years or longer since anal coital debut (aOR, 6.8; 95% CI, 3.1-5.2), self-reported genital warts (aOR, 3.1; 95% CI, 1.5-6.6), and 200 or less CD4 cells/mm3 (aOR, 13.3; 95% CI, 2.7-65.2) for those living with HIV. CONCLUSIONS: Studies evaluating the JSI as a predictor of high-grade intraepithelial lesions would further confirm its applicability as a quantitative measure of multiple HPV persistence.

Multiple HPV infections among men who have sex with men engaged in anal cancer screening in Abuja, Nigeria.

BACKGROUND: Anal precancers and cancers can be detected during screening with high-resolution anoscopy (HRA). The sensitivity of HRA depends on the burden and duration of human papillomavirus (HPV) among those screened as well as anoscopist proficiency, which is highly correlated with prior screening experience. Our objective was to compare the identification and type of HPV and the likelihood of HRA-detected precancer for men who have sex with men (MSM) undergoing their first HRA-screening in Nigeria. METHODS: MSM were recruited from an HIV test-and-treat cohort, TRUST/RV368, into a new anal cancer screening program. Anal swabs obtained during screening underwent Ion Torrent next-generation sequencing using barcoded HPV PCR broad-spectrum primers 5+/6+ to detect up to 161 HPVs. All high-risk (HR) HPVs and the most abundant low-risk (LR)-HPVs were evaluated as type-specific infections with some categorized as belonging to a multiple infection. HRA screening results included benign, low-grade squamous intraepithelial lesions (LSIL), or HSIL as detected by cytology or histology. Multivariable logistic regression was used to assess the association of HPV and other cofactors with any SIL. RESULTS: Among 342 MSM, 60% were HIV-infected, 89% were under 35 years of age, and 51% had 8 or more years since anal coital debut. Of those with SIL, 89% had LSIL and only 11% had HSIL. Prevalence of any HPV and high-risk (HR)-HPV was 92% and 74%, respectively. The most prevalent genotypes in rank order were HPV6 (31%), HPV16 (23%), HPV42 (20%), HPV11 (18%), HPV45 (18%), and HPV51 (17%). For multiple HR-HPVs, 31% had a single HR-HPV, 32% had 2-3, and 10% had 4 or more. Low-risk HPVs, type 6 and/or 11, were common (42%) and were significantly associated with SIL (adjusted odds ratio [aOR]:1.8, 95% confidence interval [CI]: 1.1-3.1) together with perianal warts (aOR:6.7, 95% CI: 3.3-13.5). In contrast, HR-HPV and multiple HR-HPVs were not significantly associated with SIL (all p > 0.05). CONCLUSIONS: Detection of HSIL was low. Although HR-HPV was abundant, HSIL development also depends on the duration of HR-HPV infections and the anoscopist's level of experience. As our cohort ages and the anoscopist becomes more skilled, detection of HSIL will likely improve.

Genotyping of high-risk anal human papillomavirus (HPV): ion torrent-next generation sequencing vs. linear array.

BACKGROUND: Our next generation sequencing (NGS)-based human papillomavirus (HPV) genotyping assay showed a high degree of concordance with the Roche Linear Array (LA) with as little as 1.25 ng formalin-fixed paraffin-embedded-derived genomic DNA in head and neck and cervical cancer samples. This sensitive genotyping assay uses barcoded HPV PCR broad-spectrum general primers 5+/6+ (BSGP)5+/6+ applicable to population studies, but it's diagnostic performance has not been tested in cases with multiple concurrent HPV infections. METHODS: We conducted a cross-sectional study to compare the positive and negative predictive value (PPV and NPV), sensitivity and specificity of the NGS assay to detect HPV genotype infections as compared to the LA. DNA was previously extracted from ten anal swab samples from men who have sex with men in Nigeria enrolled on the TRUST/RV368 cohort study. Two-sample tests of proportions were used to examine differences in the diagnostic performance of the NGS assay to detect high vs. low-risk HPV type-specific infections. RESULTS: In total there were 94 type-specific infections detected in 10 samples with a median of 9.5, range (9 to 10) per sample. Using the LA as the gold standard, 84.4% (95% CI: 75.2-91.2) of the same anal type-specific infections detected on the NGS assay had been detected by LA. The PPV and sensitivity differed significantly for high risk (PPV: 90%, 95% CI: 79.5-96.2; sensitivity: 93.1%, 95% CI: 83.3-98.1) as compared to low risk HPV (PPV: 73%, 95% CI: 54.1-87.7; sensitivity: 61.1, 95% CI: 43.5-76.9) (all p < 0.05). The NPV for all types was 92.5% (95% CI: 88.4-95.4). The NPV and specificity were similar for high and low risk HPVs (all p > 0.05). The NGS assay detected 10 HPV genotypes that were not among the 37 genotypes found on LA (30, 32, 43, 44, 74, 86, 87, 90, 91, 114). CONCLUSIONS: The NGS assay accurately detects multiple HPV infections in individual clinical specimens with limited sample volume and has extended coverage compared to LA.

Paucity of HPV-Related Head and Neck Cancers (HNC) in Nigeria.

INTRODUCTION: The burden of HPV-related Head and Neck Cancers (HNC) has been rising in the U.S. and other developed countries but this trend has not been reported in Africa. Objective of study was to evaluate the prevalence of HPV infection in HNC cancer cases seen between 1990 and 2011 at the tertiary health care institutions in Nigeria. METHODS: We retrieved 149 head and neck cancer formalin fixed, paraffin embedded tumor specimens diagnosed between 1990 and 2011 from four teaching hospitals in Nigeria. One hundred and twenty-three blocks (83%) contained appropriate HNC for analysis while DNA extraction was successful in 60% (90/149). PCR amplification was successful in 33% (49/149) and Linear Array genotyping for HPV was successful in 11% (17/149) of these cases. These were in tumors from the larynx (6), cervical lymph nodes (3), nasal cavity (2), parotid (1), palate (1), maxillary sinus (1) and mandible (1). Two cases were non-specific and none were from the oropharynx. Histologically, 41% (7/17) of the successfully genotyped blocks were squamous cell carcinomas (larynx 6, maxillary sinus 1). RESULTS AND CONCLUSION: We were unable to detect HPV in any of the HNC samples in our study. Our result may suggest that there is a low prevalence of HPV-related HNC among the adult population in Nigeria. Our results provide a benchmark to compare future incidence of HPV -related HNC in this community in future. We had significant analytical challenges from possible poor tissue processing and urge that future studies should prospectively collect samples and ensure high quality sample processing.

Next-Generation Sequencing-Based HPV Genotyping Assay Validated in Formalin-Fixed, Paraffin-Embedded Oropharyngeal and Cervical Cancer Specimens.

Available clinical human papilloma virus (HPV) diagnostics for head and neck cancer have limited sensitivity and/or fail to define the HPV genotype. Common HPV genotyping assays are costly and labor intensive. We sought to develop a next-generation sequencing (NGS)-based HPV genotyping assay that was sensitive enough to work on formalin-fixed paraffin-embedded (FFPE) samples. We developed an ion torrent NGS HPV genotyping assay using barcoded HPV PCR broad-spectrum general primers 5(+)/6(+) (BSGP)5(+)/6(+). To validate genotype specificity and use in archived clinical FFPE tumor samples, we compared NGS HPV genotyping at 2 sequencing centers with typing by Roche Linear Array assay in 42 oropharyngeal and cervical cancer specimens representing 10 HPV genotypes, as well as HPV-negative cases. To demonstrate the detection of a broad range of HPV genotypes, we genotyped a cohort of 266 cervical cancers. A comparison of NGS genotyping of FFPE cancer specimens with genotyping by Linear Array showed concordant results in 34/37 samples (92%) at sequencing site 1 and 39/42 samples (93%) at sequencing site 2. Concordance between sites was 92%. Designed for use with 10 ng genomic DNA, the assay detected HPV using as little as 1.25 ng FFPE-derived genomic DNA. In 266 cervical cancer specimens, the NGS assay identified 20 different HPV genotypes, including all 13 carcinogenic genotypes. This novel NGS assay provides a sensitive and specific high-throughput method to detect and genotype HPV in a range of clinical specimens derived from FFPE with low per-sample cost.

Oropharyngeal cancer as a driver of racial outcome disparities in squamous cell carcinoma of the head and neck: 10-year experience at the University of Maryland Greenebaum Cancer Center.

BACKGROUND: Racial outcome disparities have been observed in head and neck squamous cell carcinoma (HNSCC) with diminished survival for black patients compared with white patients. METHODS: We retrospectively analyzed 1318 patients with primary HNSCC treated at the University of Maryland Greenebaum Cancer Center (UMGCC) from 2000 to 2010. RESULTS: Of all the patients, 65.9% were white, 30.7% were black, and 3.3% were of other races. Black patients were less likely to present with oral cavity cancer, and more likely to present with laryngeal or hypopharyngeal cancers. White patients were more likely to have early stage disease, especially in the oral cavity. Black race was independently associated with worse overall survival (OS) in the entire cohort. Black patients had a significantly worse OS among oral cavity and oropharyngeal cancers, with the largest disparity in oropharyngeal cancer. However, in multivariate analysis, race was only still significant in oropharyngeal cancer. CONCLUSION: We observed differences by race in distribution of disease site, stage, and OS. Survival disparity in the entire cohort was driven mostly by differences among oropharyngeal cancer.

Correlation of p16 expression and HPV type with survival in oropharyngeal squamous cell cancer.

OBJECTIVES: Examine the effect of concordance between p16 overexpression and HR (high risk) HPV DNA status on overall survival in a large series of oropharyngeal squamous cell carcinoma (OPSCC) cases. MATERIALS AND METHODS: A total of 185 patients with primary OPSCC had genomic DNA tested by PCR for the HPV16 E6 and E7 oncogenes. 184 of 185 patients had p16 IHC performed. Linear array HPV genotyping was performed in all 21 HPV16/p16 discordant cases (HPV16+/p16- or HPV16-/p16+) as well as in 43 control cases. RESULTS: 73 of 185 patients were positive for HR HPV (39%). Six of 73 HPV infections were due to HR HPV types other than HPV16: types 31 (1), 33 (2), 51 (1), 58 (1), and 59 (1); all 6 cases were p16 positive. p16 IHC was concordant with HR HPV testing in 169 of 184 cases (92%), and had a sensitivity and specificity of 92% and 92%. HR HPV+/p16+ and discordant HR HPV/p16 patients had significantly improved overall survival compared to HR HPV-/p16- patients. CONCLUSION: p16 IHC is a reliable surrogate marker for HR HPV testing in OPSCC. Prognostically favorable HR HPV genotypes other than HPV16 are reflected in p16 positivity.

A phase I dose escalation trial of MAGE-A3- and HPV16-specific peptide immunomodulatory vaccines in patients with recurrent/metastatic (RM) squamous cell carcinoma of the head and neck (SCCHN).

BACKGROUND: We conducted a phase I dose escalation study to evaluate the safety and immunologic response to peptide immunomodulatory vaccines GL-0810 (HPV16) and GL-0817 (MAGE-A3) in HPV16 and MAGE-A3-positive RM-SCCHN patients, respectively. METHODS: Three dose levels (500, 1,000, and 1,500 µg) of GL-0810 or GL-0817 with adjuvants Montanide (1.2 ml) and GM-CSF (100 µg/m2) were administered subcutaneously q2 weeks for a total of four vaccinations in HPV16 and MAGE-A3-positive RM-SCCHN patients, respectively. RESULTS: Nine and seven patients were enrolled in the HPV16 and MAGE-A3 cohorts, respectively. No dose-limiting toxicities were observed, and toxicity was predominantly local and grade 1 (erythema, pain, and itching at the injection site). In those patients who received all four vaccinations, 80 % (4/5) of the HPV16 cohort and 67 % (4/6) of the MAGE-A3 cohort developed antigen-specific T cell and antibody responses to the vaccine. Significant concordance between T cell and antibody responses was observed for both groups. No clear dose-response correlation was seen. All patients progressed by RECIST at first repeat imaging, except for one patient in the MAGE-A3 500 µg cohort who had stable disease for 10.5 months. The median PFS and OS for the MAGE-A3 cohorts were 79 and 183 days, respectively, and for the HPV16 cohort 80 and 196 days, respectively. CONCLUSIONS: GL-0810 and GL-0817 were well tolerated in patients with RM-SCCHN with T cell and antibody responses observed in the majority of patients who received all four vaccinations.

Emergence of HPV16-positive oropharyngeal cancer in Black patients over time: University of Maryland 1992-2007.

While we previously reported a striking racial difference in the prevalence of human papilloma virus (HPV)-positive squamous cell carcinoma of the oropharynx (OPSCC), less is known about differences in outcomes and trends over time in OPSCC by HPV status and race. We conducted a retrospective analysis of 467 patients with OPSCC treated at the University of Maryland Greenebaum Cancer Center (Baltimore, MD) between 1992 and 2007, of which 200 had tissue available for HPV16 testing. HPV16-positive patients were significantly more likely to be white, with 45.5% of whites and 15.5% of blacks testing positive for HPV16. There was a significant increase in HPV16-positive OPSCC for all patients over time from 15.6% in 1992 to 1995 to 43.3% in 2004 to 2007 (P = 0.01). From 1992 to 1995, 33% of white patients were HPV16-positive, with no black patients positive. From 2004 to 2007, 17.7% of black patients and 54% of white patients were HPV16-positive. White and black patients with HPV16-positive tumors had an identical and favorable overall survival (OS; median, 8.1 and 8.1 years, respectively). However, among HPV16-negative patients, whites had an improved OS compared with blacks (median, 2.3 vs. 0.9 years, respectively; P = 0.02), including when analyzed in a multivariable Cox regression model. From 1992 to 2007, the percentage of HPV16-positive OPSCC increased for white patients and was seen for the first time in black patients. While survival for HPV-positive black and white patients was similar and favorable, outcomes for HPV-negative patients were poor, with blacks having worse survival even after controlling for baseline characteristics.

Novel biomarker panel predicts prognosis in human papillomavirus-negative oropharyngeal cancer: an analysis of the TAX 324 trial.

BACKGROUND: New treatment strategies for locally advanced head and neck squamous cell carcinoma combine induction chemotherapy and chemoradiation. Identifying the predictors of outcome in sequentially treated patients is critical for focusing therapeutic research. In this analysis, the authors evaluated human papillomavirus type 16 (HPV-16) status and the expression levels of a defined set of biomarkers to identify predictors of response to this treatment modality. METHODS: In total, 114 patients with oropharyngeal cancer (OPC) who were treated on the TAX 324 trial (cisplatin and fluorouracil with or without docetaxel in patients with locally advanced head and neck squamous cell carcinoma) had pretreatment biopsy specimens that were evaluable for HPV-16 DNA and immunohistochemical expression of the following biomarkers: beta-tubulin II (ßT-II), glutathione S-transferase (GST-π), p53, and B-cell lymphoma 2 (Bcl-2). Patients were categorized into risk groups based on their HPV status and biomarker expression levels. RESULTS: Patients with high-risk OPC were defined by HPV-negative status and either elevated expression of ßT-II or levels of at least 2 of the other 3 adverse markers (elevated GST-π, elevated p53, or low Bcl-2). All other HPV-negative patients were categorized as moderate risk. In total, 55 patients were HPV-positive, and 59 patients were HPV-negative, with 34 were categorized as high risk and 25 categorized as moderate risk. The median survival for HPV-positive patients was not reached. The median survival was 44.2 months for moderate-risk patients (95% confidence interval, 20.9 months to not reached) and 12.1 months for high-risk patients (95% confidence interval, 7.5-19.7 months). The 24-month survival rate was 89% for HPV-positive patients, 67% for moderate-risk patients, and 29% for high-risk patients (P < .0001). CONCLUSIONS: The molecular data set in this study readily differentiated between 2 distinct groups of patients with locally advanced, HPV-negative OPC. This risk-stratification strategy may serve as a guide for treatment selection.

Racial survival disparity in head and neck cancer results from low prevalence of human papillomavirus infection in black oropharyngeal cancer patients.

The burden of squamous cell carcinoma of the head and neck (SCCHN) is greater for blacks than for whites, especially in oropharyngeal cases. We previously showed retrospectively that disease-free survival was significantly greater in white than in black SCCHN patients treated with chemoradiation, the greatest difference occurring in the oropharyngeal subgroup. Oropharyngeal cancer is increasing in incidence and in its association with human papillomavirus (HPV) infection; HPV-positive oropharyngeal cancer patients have significantly better outcomes (versus HPV-negative). These collective data led to the present analyses of overall survival (OS) in our retrospective cohort and of OS and HPV status (tested prospectively in pretreatment biopsy specimens) in the phase 3, multicenter TAX 324 trial of induction chemotherapy followed by concurrent chemoradiation in SCCHN patients. Median OS in the retrospective cohort of 106 white and 95 black SCCHN patients was 52.1 months (white) versus only 23.7 months (black; P = 0.009), due entirely to OS in the subgroup of patients with oropharyngeal cancer--69.4 months (whites) versus 25.2 months (blacks; P = 0.0006); no significant difference by race occurred in survival of non-oropharyngeal SCCHN (P = 0.58). In TAX 324, 196 white patients and 28 black patients could be assessed for HPV status. Median OS was significantly worse for black patients (20.9 months) than for white patients (70.6 months; P = 0.03) and dramatically improved in HPV-positive (not reached) versus HPV-negative (26.6 months, 5.1 hazard ratio) oropharyngeal patients (P < 0.0001), 49% of whom were HPV-16 positive. Overall, HPV positivity was 34% in white versus 4% in black patients (P = 0.0004). Survival was similar for black and white HPV-negative patients (P = 0.56). This is the first prospective assessment of confirmed HPV status in black versus white SCCHN patients. Worse OS for black SCCHN patients was driven by oropharyngeal cancer outcomes, and that for black oropharyngeal cancer patients by a lower prevalence of HPV infection. These findings have important implications for the etiology, prevention, prognosis, and treatment of SCCHN.

Cisplatin preferentially binds mitochondrial DNA and voltage-dependent anion channel protein in the mitochondrial membrane of head and neck squamous cell carcinoma: possible role in apoptosis.

PURPOSE: Cisplatin adducts to nuclear DNA (nDNA) are felt to be the molecular lesions that trigger apoptosis, but the mechanism linking nDNA adduct formation and cell death is unclear. Some literature in the last decade has suggested a possible direct effect of cisplatin on mitochondria independent of nDNA interaction. In this study, we define separately the sequelae of cisplatin interactions with nDNA and with mitochondria in head and neck squamous cell carcinoma (HNSCC) cell lines. EXPERIMENTAL DESIGN: Cisplatin binding to mitochondrial DNA (mtDNA) and proteins was analyzed by atomic absorption spectroscopy and other methods. RESULTS: Following 1 hour of exposure to cisplatin, platinum adducts to mtDNA were 300- to 500-fold more abundant than adducts to nDNA; these differences were not due to differences in rates of adduct repair. Whereas HNSCC cell cytoplasts free of nDNA retained the same dose-dependent cisplatin sensitivity as parental cells, HNSCC rho(0) cells free of mtDNA were 4- to 5-fold more resistant to cisplatin than parental cells. Isolated mitochondria released cytochrome c within minutes of exposure to cisplatin, and ultrastructural analysis of intact HNSCC cells by electron microscopy showed marked mitochondrial disruption after 4 hours of cisplatin treatment, whereas the nucleus and other cellular structures remain intact. The very prompt release of cytochrome c from isolated mitochondria implies that apoptosis does not require alteration in mitochondrial gene transcription. Further, cisplatin binds preferentially to mitochondrial membrane proteins, particularly the voltage-dependent anion channel. CONCLUSIONS: Cisplatin binding to nDNA is not necessary for induction of apoptosis in HNSCC, which can result from direct action of cisplatin on mitochondria.

Estrogen receptor expression and sensitivity to paclitaxel in breast cancer.

A retrospective analysis of CALGB trial 9344 suggested paclitaxel administration following cyclophosphamide and doxorubicin adjuvant chemotherapy is most beneficial for patients with ERalpha negative (ERalpha-) breast cancer. Since the cytotoxic effects of paclitaxel are cell cycle dependent, we postulated that the relationship between ERalpha and the effectiveness of adjuvant paclitaxel reflects the observation that ERalpha positive (ERalpha+) breast cancers proliferate more slowly than ERalpha- breast cancers. Three in vitro models (MCF-7, T47D and ZR-75) were examined to compare growth rates and paclitaxel-induced apoptosis in ERalpha+ and ERalpha- clones of the same, originally ERalpha+ cell line. For the T47D and ZR-75 cell lines, loss of ERalpha was associated with a decrease in doubling time and an increase in paclitaxel sensitivity. However, when cell culture conditions were altered to achieve equivalent cell proliferation rates, no difference in paclitaxel sensitivity was observed. Similarly, an ERalpha- clone of MCF-7 cells that did not exhibit an enhanced growth rate compared to its ERalpha+ counterpart also did not show increased paclitaxel sensitivity. The combined apoptotic effects of tamoxifen and paclitaxel on MCF-7 cells were not synergistic or even clearly additive. In these in vitro models, the effectiveness of paclitaxel correlated more closely with growth rate than ERalpha expression. These data suggest that measurements of tumor proliferation may provide more accurate predictive markers for the benefits of adjuvant paclitaxel than ERalpha analysis.

Glutathione S-transferase pi amplification is associated with cisplatin resistance in head and neck squamous cell carcinoma cell lines and primary tumors.

PURPOSE: The purpose is to evaluate the association of glutathione S-transferase pi (GST-pi) amplification and cisplatin resistance in head and neck cancer. EXPERIMENTAL DESIGN: An analysis of chromosomal abnormalities in 10 head and neck cancer cell lines by comparative genomic hybridization was performed. GST-pi amplification and expression were evaluated in head and neck cell lines and paraffin-embedded tissue by fluorescence in situ hybridization (FISH) and immunohistochemistry. RESULTS: Changes in the DNA copy number were seen in all 10 cell lines by comparative genomic hybridization. The most frequent chromosomal alterations were: gain at 3q; loss at 3p; gain at 8q; loss of 18q; gain at 20q; loss at 8p; and gain of 11q11-q13. Using FISH, 9 of 10 cell lines showed increased GST-pi copy number. GST-pi amplification was detected in 7 of 10 cell lines. Five were relatively cisplatin resistant, and 2 were relatively cisplatin sensitive (mean IC(50), 11.2 and 2.75 microM). Two relatively cisplatin-sensitive cell lines showed GST-pi gain and another relatively cisplatin-sensitive cell line had predominantly two copies of the gene. In 10 tumor specimens, 4 had two copies of GST-pi. All 4 had a complete response to neoadjuvant chemotherapy, 3 of whom are alive >50 months from treatment compared with 2 patients showing GST-pi amplification. Neither responded to chemotherapy, and both died of disease <9 months from diagnosis. CONCLUSIONS: Using FISH, GST-pi amplification is a common event in head and neck squamous cell carcinoma and may be associated with cisplatin resistance and poor clinical outcomes in head and neck cancer patients treated with cisplatin-based therapy.

Inhibition of glutathione synthesis reverses Bcl-2-mediated cisplatin resistance.

Cisplatin is a potent cytotoxic agent that functions as a bivalent electrophile, forming both interstrand and intrastrand DNA cross-links. Cisplatin-mediated DNA damage results in cell cycle arrest and initiation of apoptotic cell death. Increased cellular glutathione concentrations have been closely correlated with cisplatin resistance but do not reduce the extent of cisplatin-DNA adduct formation. One hypothesis to explain the ability of glutathione to inhibit cisplatin cytotoxicity is that glutathione, through its antioxidant function, plays a role in apoptotic regulatory pathways. We tested this hypothesis using MCF-7 breast cancer cells transfected with the apoptotic inhibitor Bcl-2. Bcl-2 overexpression in MCF-7 cells was associated with a nearly 3-fold increase in cellular glutathione levels and with increased resistance to cell death after cisplatin exposure. Treatment of MCF-7 lines with buthionine sulfoximine, an inhibitor of glutathione synthesis, normalized glutathione levels in Bcl-2 and control transfectants and completely abrogated Bcl-2-mediated cisplatin resistance without affecting Bcl-2 expression. Bcl-2 overexpression and up-regulation of glutathione were not associated with a change in either cisplatin-DNA adduct formation or repair over time. These results suggest that Bcl-2-mediated cisplatin resistance in MCF-7 cells is dependent on up-regulation of glutathione production, which contributes to cell survival by mechanisms independent of cisplatin inactivation or inhibition of DNA adduct formation. A similar dependence on glutathione for Bcl-2-mediated inhibition of cisplatin toxicity was confirmed in a second cell line, the lymphocytic precursor FL5.12. Taken together, these data suggest that apoptotic signaling after genotoxic exposure can be inhibited by the antioxidant activity of glutathione. Inhibition of glutathione synthesis or modulation of glutathione stores in tumors that overexpress Bcl-2 may comprise a novel anticancer strategy.