Reconstructing tumor history in breast cancer: signatures of mutational processes and response to neoadjuvant chemotherapy⋆

BACKGROUND

Different endogenous and exogenous mutational processes act over the evolutionary history of a malignant tumor, driven by abnormal DNA editing, mutagens or age-related DNA alterations, among others, to generate the specific mutational landscape of each individual tumor. The signatures of these mutational processes can be identified in large genomic datasets. We investigated the hypothesis that genomic patterns of mutational signatures are associated with the clinical behavior of breast cancer, in particular chemotherapy response and survival, with a particular focus on therapy-resistant disease.

PATIENTS AND METHODS

Whole exome sequencing was carried out in 405 pretherapeutic samples from the prospective neoadjuvant multicenter GeparSepto study. We analyzed 11 mutational signatures including biological processes such as APOBEC-mutagenesis, homologous recombination deficiency (HRD), mismatch repair deficiency and also age-related or tobacco-induced alterations.

RESULTS

Different subgroups of breast carcinomas were defined mainly by differences in HRD-related and APOBEC-related mutational signatures and significant differences between hormone-receptor (HR)-negative and HR-positive tumors as well as correlations with age, Ki-67 and immunological parameters were observed. We could identify mutational processes that were linked to increased pathological complete response rates to neoadjuvant chemotherapy with high significance. In univariate analyses for HR-positive tumors signatures, S3 (HRD, P < 0.001) and S13 (APOBEC, P = 0.001) as well as exonic mutation rate (P = 0.002) were significantly correlated with increased pathological complete response rates. The signatures S3 (HRD, P = 0.006) and S4 (tobacco, P = 0.011) were prognostic for reduced disease-free survival of patients with chemotherapy-resistant tumors.

CONCLUSION

The results of this investigation suggest that the clinical behavior of a tumor, in particular, response to neoadjuvant chemotherapy and disease-free survival of therapy-resistant tumors, could be predicted by the composition of mutational signatures as an indicator of the individual genomic history of a tumor. After additional validations, mutational signatures might be used to identify tumors with an increased response rate to neoadjuvant chemotherapy and to define therapy-resistant subgroups for future therapeutic interventions.

Abstract P2-09-04: Identification of a neoantigen targeted by tumor-infiltrating lymphocytes in a patient with Her2+ breast cancer

Background: Recent studies have demonstrated that the number of tumor infiltrating lymphocytes (TILs) positively correlates with outcome and response to chemotherapy in patients with HER2+ and Triple-Negative Breast Cancer (TNBC). Furthermore, first studies of immune-checkpoint inhibitors showed promising results in those patients. However, the targets of those TILs remain unknown. Neoantigens, which arise in the process of tumorigenesis, appear as potential targets. They can elicit high avidity, tumor-specific T-cell responses. Thus, it is the aim of our study to ascertainif these TILs are directed against tumor-specific mutations.

Methods: TILs from breast cancer biopsies taken at the time point of diagnosis were expanded by unspecific stimulation. Additionally, we used the Gentle Macs Dissociator in combination with flow cytometry to investigate the number of TILs in the tumor tissue. Furthermore, we performed whole-genome sequencing of tumor tissue and as reference autologous blood cells to determine tumor-specific mutations. Mutations leading to a non-synonymous amino acid change were analyzed for RNA expression of the encoding gene as well as to determine potential neoantigens. Neoantigens were evaluated for their potential binding to the patient's specific HLA molecules. Peptides for potential neoantigens were synthesized, loaded onto autologous antigen presenting cells (APCs) and cocultured with TILs. All IFNγ producing T-cells were clonally expanded and retested for peptide specificity to identify neoantigen specific T-cell clones.

Results: Our flow cytometric analysis of the tumor biopsy for more than 300 patients showed higher frequencies of TILs in TNBC as compared to other types of breast cancer or patients without malignancy. Screening for neoantigen specific T-cells in one patient led to identification of three peptide-specific CD4+ T-cell clones isolated from HER2+ breast cancer tissue taken at the time point of diagnosis. All T-cell clones specifically recognized the same tumor-specific mutation and not the wildtype counterpart. Furthermore, we demonstrated that these T-cell clones also recognized the endogenously expressed mutated antigen. This verified the ability of processing and presentation of the respective protein. Interestingly, we could also isolate a T-cell clone recognizing the same neoantigen in the resected tumor tissue after neoadjuvant therapy. Based on CDR3 sequencing we could prove that the four T-cell clones represented individual clones. This confirms the polyclonal nature of the immune response. Moreover, we showed that the same neoepitope was presented in two different HLA restriction molecules of the patient with three of the clones recognizing it in HLA-DPB1*0401 and one in HLA-DPB1*0201. These results further underline the immunogenicity of this neoantigen.

Conclusion: In conclusion, our data demonstrate tumor-specificity of TILs in a patient with HER2+ breast cancer. Furthermore, we show the feasibility to identify individual cancer specific T-cell targets in breast cancer patients. These results may contribute to the development of targeted patient-specific immunotherapies in the future.

Citation Format: Reimann H, Nguyen A, Hübner H, Erber R, Bausenwein J, Van der Meijden ED, Lux MP, Jud S, Griffioen M, Rauh C, Sanborn JZ, Benz SC, Rabizadeh S, Beckmann MW, Mackensen A, Rübner M, Fasching PA, Kremer AN. Identification of a neoantigen targeted by tumor-infiltrating lymphocytes in a patient with Her2+ breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-09-04.

Abstract P1-07-20: Developing prognostic indicators of poor outcomes in PRAEGNANT metastatic breast cancer cohort

Background: Despite novel, targeted therapies, metastatic breast cancer patients have an extremely unfavourable prognosis. Prognostic and predictive factors for patients with advanced breast cancer are not well understood. Molecular assessment of the patient and the tumor in the metastatic situation is not routinely performed despite advances in molecular precision medicine indicating great benefit to this patient group. Here we present early findings from the first 142 patients of a prospective molecular breast cancer registry with completed transcriptomic profiling.

Methods: The PRAEGNANT study proctocol (NCT02338767) is a molecular registry designed to provide an infrastructure for the real-time comprehensive analysis of tumor and patient molecular characteristics under study conditions. Formalin fixed paraffin embedded tumors have been used from this registry to identify molecular, transcriptomic predictors for overall survival (OS).

Known clinical correlates for OS (e.g. hormone-receptor status, age at diagnosis, and BMI) were analyzed by Cox proportional hazard ratios, and compared to transcriptomic markers of outcomes. Transcriptomes for all patient tumors were sequenced on the Illumina sequencing platform, and analyzed by RSEM to estimate transcripts per million (TPM) values for each gene isoform. Log-TPM values were used in established (PAM50) and novel (hierarchical clustering) expression-based subtyping of tumor samples. Expression-based subtypes were demonstrated to be strong prognostic indicators by Cox analysis. A Lasso regression machine learning algorithm was used to develop an expression-based predictive model of OS.

Results: Hormone receptor positivity (HR=0.7, p&lt;0.006) and TNBC status (HR=1.4, p&lt;0.01) were significantly associated with outcomes. PAM50 subtypes were also strong indicators of outcomes (e.g. Basal disease compared to Luminal-A subtype has HR=1.4, p&lt;0.017). A novel expression-based high-risk cluster in this cohort was more indicative of poor prognosis than clinical variates or Basal-type, with a HR=2.7 (p&lt;0.009) when compared to Luminal-A subtype. An expression-based survival prediction model achieved a concordance-index of 0.65 in an unseen validation cohort. Patients predicted as having the shortest survival times were in the high-risk cluster.

Conclusions: Here we demonstrate using molecular profiling to develop prognostic signatures that out-perform standard clinical correlates of poor outcomes, even in a small subset of the total cohort. As the PRAEGNANT cohort expands these prognostic tools will continue to improve and supplement physician knowledge to improve patient outcomes.

Citation Format: Szeto C, Benz S, Nguyen A, Rübner M, Wallwiener D, Tesch H, Hadji P, Fehm TN, Janni W, Overkamp F, Lueftner D, Lux MP, Wallwiener M, Beckmann MW, Huebner H, Ettl J, Hartkopf AD, Mueller V, Taran FA, Belleville E, Schneeweiss A, Soon-Shiong P, Rabizadeh S, Fasching PA. Developing prognostic indicators of poor outcomes in PRAEGNANT metastatic breast cancer cohort [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-07-20.

Abstract P2-02-16: Use of cell-free circulating RNA and expression of PD-L1 and HER2 in plasma to monitor and predict clinical response in metastatic breast cancer patients

Background: In addition to traditional radiology tests, cell-free circulating tumor RNA (cfRNA) extracted from plasma of cancer patients (pts) provides a means of evaluating tumor response, but based on molecular changes in the tumor. Measuring dynamic changes in gene expression and levels of total cfRNA (per ml of plasma) in metastatic patients has shown great potential for evaluating disease status and predicting outcome to anti-tumoral therapy in advance of imaging. Though checkpoint inhibitors have not been assessed widely in breast cancer, TNBC has shown mild responses to pembrozilumab and atezolizumab, with significantly better responses in pts with detectable PD-L1 expression.

Methods: Blood was drawn from pts at approximately 6-week intervals under various therapies and CT scans were performed at approximately 3-month intervals. CfRNA was extracted from the resulting plasma and reverse transcribed with random hexamers to cDNA. Levels of cfRNA were quantitated by RT-qPCR and correlated with pt response (PR/SD/PD), as determined by CT scans. Levels of gene expression in cfRNA (including PD-L1 and HER2) were monitored in pts across blood draws.

Results: A total of 28 breast cancer pts were enrolled in a 1-year clinical study. Of pts, 39% (11/28) were Caucasian and 36% (10/28) Hispanic. 19 pts completed the first two cycles of therapy: 2 pts had PR and showed no change (NC) or decrease (DEC) in levels of cfRNA, 11 pts achieved SD with 8 showing DEC or NC in cfRNA levels, and 6 pts had PD and all underwent increases (INC) in cfRNA levels (median increase: 788 ng/mL plasma) which correlated with progressive disease status. Of pts with SD/PR, 4 showed either an emergence or significant increase in PD-L1 expression across blood draws (3.7-98 ct); of PD pts, 1 showed a significant emergence of PD-L1 expression (12.5 ct) across blood draws. 3/5 of these PD-L1 expressing pts were being treated with an everolimus combination; the emergence or increase of PD-L1 in response to this therapy suggests use of checkpoint inhibitors as an option for these pts. In response to therapy, 3 of 5 pts had PD-L1 cfRNA levels above levels predictive of response to nivolumab in lung cancer pts. In the only pt with hyperexpressed HER2, the disappearance of HER2 cfRNA matched positive response (PR) to treatment with trastuzumab. PD-L1 decreased concomitantly for this pt.

Conclusion: We found a strong correlation between clinical responses and changes in plasma levels of ctRNA in breast cancer (84%). Most of these were documented several weeks before imaging was done. Levels of PD-L1 and HER2 expression in plasma can also be used to monitor pt response to specific therapies. The emergence of PD-L1 expression in response to various therapies in breast cancer may confer sensitivity to checkpoint inhibitor therapy.

Citation Format: Castrellon AB, Velez M, Raez LE, Danenberg K, Rabizadeh S, Usher J, Jaimes Y, Hunis B, Bittencourt AC, Milillo A, Blaya M, Habaue C, Danenberg PV. Use of cell-free circulating RNA and expression of PD-L1 and HER2 in plasma to monitor and predict clinical response in metastatic breast cancer patients [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-02-16.

Abstract P2-04-10: High-affinity activated natural killer (haNK) cells augment trastuzumab efficacy in a mouse model of HER2-positive human metastatic breast cancer

Background. The ability of NK cells to kill cancer cells makes them an attractive choice for clinical immunotherapy. Early phase clinical trials in patients (pts) with advanced cancers have demonstrated the safety of activated NK (aNK [NK-92]) cells, an investigational cell line that was established from the peripheral blood mononuclear cells of a pt with non-Hodgkin lymphoma. NK cells can participate in antibody-dependent cellular cytotoxicity (ADCC) mediated by recognition of the Fc fragment of the target-bound antibody (IgG1) via the CD16 Fc receptor. Among pts with HER2-positive breast cancer treated with trastuzumab (IgG1) the high-affinity CD16 V/V genotype was significantly correlated with better clinical outcomes (Musolino. JCO. 2008;26:1789-96). To enhance the killing activity of aNK cells, we modified aNK cells to stably express high-affinity CD16 and evaluated the resulting haNK cells in combination with trastuzumab in a mouse xenograft model of HER2-positive human breast cancer.

Methods. haNK cells were generated by transfection of aNK cells with a bicistronic plasmid coding for CD16 (158V) and an intracellular form of IL-2, which enables haNK cells to grow in the absence of exogenous IL-2. Female, 7 to 8-week-old NOD-scid IL2Rgammanull (NSG) mice were inoculated subcutaneously in the left and right flank area with 0.1mL of 1x108/mL MDA-MB-453 human breast cancer cells in 50% Matrigel. When tumors reached ≥100mm3, mice were randomly assigned to 10 groups of 4 mice per group and dosed (IV) with PBS, 1 or 3mg/kg IgG1 isotype control, 1 or 3mg/kg trastuzumab (determined from a dose range finding study), 1x107 non-irradiated haNK cells, or non-irradiated haNK cells in combination with IgG1 or trastuzumab. The dosing schedules were: PBS/haNK cells twice weekly for 4 weeks; IgG1/trastuzumab once weekly for 4 weeks. For the combination treatments, mice received antibodies at least 3h prior to the injection of haNK cells. Tumor growth and animal weights were measured twice weekly.

Results: Results obtained after 4 weeks of treatment are shown in the table. haNK alone and both doses of trastuzumab alone significantly inhibited the growth of human MDA-MB-453 breast tumors. The combination of haNK plus 1mg/kg trastuzumab was synergistic with a T/C value of -60.1%.

Conclusions: The combination of haNK cells and trastuzumab was synergistic at 1mg/kg trastuzumab resulting in tumor regressions and significantly better efficacy vs each agent alone. Trastuzumab monotherapy at 3mg/kg was very effective and likely masked any synergistic effect of haNK. This study illustrates the potential for combining haNK cells with trastuzumab in a clinical trial of pts with HER2-positive metastatic breast cancer.

ResultsGroupTreatmentT/C (%)BWC (%)APBS--0.6BIgG1 (1mg/kg)40.8-4.7CTrastuzumab (1mg/kg)-34.5-2.8DhaNK (1x107)-20.3-15.9EIgG1 (1mg/kg) + haNK (1x107)-10.7-16.0FTrastuzumab (1mg/kg) + haNK (1x107)-60.1-16.6GIgG1 (3mg/kg)39.1-0.4HTrastuzumab (3mg/kg)-95.2-1.8IIgG1 (3mg/kg)+ haNK (1x107)-26.4-16.7JTrastuzumab (3mg/kg) + haNK (1x107)-93.8-18.3%T/C, percent treated/control; BWC, body weight change.

Citation Format: Rabizadeh S, Zhou L, Toneguzzo F, Boissel L, Soon-Shiong P, Niazi K, Klingemann H. High-affinity activated natural killer (haNK) cells augment trastuzumab efficacy in a mouse model of HER2-positive human metastatic breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-04-10.

Abstract P2-04-26: Identifying patient-specific neoepitopes for cell-based and vaccine immunotherapy across breast cancer classifications reveals rarely shared recurrent neoepitopes

Introduction: Targeted therapies for breast cancers such as trastuzumab and everolimus have durable clinical benefits for patients that express the relevant biomarkers (HER2 and mTOR respectively). Triple negative breast cancer patients lack these biomarkers and are left with few options. Recent advances in immunotherapy agents against PD-1/CTLA4 for patients with melanoma have yielded amazing clinical benefits for a subset of patients and may have similar results in breast cancer patients, but again the vast majority of patients still undergo disease progression. We analyzed whole genome sequencing (WGS) and RNA sequencing data from The Cancer Genome Atlas (TCGA) to identify neoepitopes among breast cancer patients that could be used to develop next-generation, patient-specific cancer immunotherapies. Neoepitopes are tumor specific markers that arise from mutations acquired from cancer and may represent a path to targeted therapies even in triple negative breast cancers.

Results: We analyzed 99 breast cancer patients from TCGA, containing a mixture of PR+/HER2+/ER+ and TNBC classifications. These breast cancer patient samples were selected by the availability of whole genome sequencing (WGS) data, RNA-sequencing data as well as clinical outcome data. We identified an average of 680 potential neoepitopes per patient based solely on WGS data. To further refine and select high quality neoepitopes we restricted these neoepitopes based on gene expression yielding an average of 304 expressed neoepitopes per patient. We predicted each patient's HLA typing using only omics data, which we then used to predict HLA-expressed neoepitope binding analysis resulting in an average of 11 high-quality tumor specific neoepitopes per patient. We identified few recurrent neoepitopes that were bound and expressed, indicating the need for a personalized medicine approach.

Conclusions: Within the TCGA dataset, the majority of neoepitopes among patients with breast cancer were unique to each patient. Rarely within subsets of breast cancers such as HER2+, we identify neoepitopes that are shared between patients. For breast cancer patients who do not respond to targeted therapies, high-throughput identification of neoepitopes could serve as the basis for the development of next-generation, patient-specific immunotherapies.

Citation Format: Nguyen A, Sanborn JZ, Vaske CJ, Rabizadeh S, Niazi K, Soon-Shiong P, Benz SC. Identifying patient-specific neoepitopes for cell-based and vaccine immunotherapy across breast cancer classifications reveals rarely shared recurrent neoepitopes [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-04-26.

Abstract P6-05-08: Integrating whole exome sequencing data with RNAseq and quantitative proteomics to better inform clinical treatment decisions in patients with metastatic triple negative breast cancer

Background: The use of next-generation sequencing has significantly advanced personalized medicine for patients (pts) with breast cancer. Despite this technological advancement, there remains the challenge of understanding how and if tumor heterogeneity can confound molecular analysis and treatment decisions. It has been shown that the expression of ER, PR, and HER2 can vary widely within different areas of the same tumor and between matched primary and metastatic lesions. The "Intensive Trial of OMics in Cancer"-001 (ITOMIC-001; NCT01957514) enrolls pts with metastatic TNBC who are platinum-naive and scheduled to receive cisplatin. Multiple biopsies of up to 7 metastatic sites are performed prior to cisplatin and repeated upon completion of cisplatin and following subsequent therapies. A subset of specimens is chosen for DNA sequencing, RNA sequencing, and quantitative proteomics. We explored the discordance of genomic and proteomic alterations for intrapatient and temporal heterogeneity in pts with TNBC, and the potential benefit of panomic analysis to better inform treatment decisions.

Methods: Between 7 and 107 tumor samples/biopsy specimens were obtained from each pt from 1-23 different time points. Blood samples were collected for matched tumor-normal genomic analysis. DNA sequencing data were processed using Contraster; RNASeq data confirmed the presence of gene mutations and was used to identify mutational and transcript abundance. PARADIGM was used to determine associations between gene mutations and signaling pathways. Selected reaction monitoring-mass spectrometry (SRM-MS) was used for proteomics analysis.

Results: Almost all pts had loss of TP53 (common in TNBC), and 5 pts had germline BRCA1/2 events, some exhibiting a signature of mutations corresponding to a mismatch repair defect in ≥1 pt. FGFR1/2/3 mutations/amplifications occurred in 5 pts. Three of 12 pts (25%) achieved partial responses after receiving treatments (post cisplatin) based on the molecular profile of their tumor: 1 pt with two FGFR2 activating mutations treated with ponatinib, 1 with a germline BRCA2 mutation treated with veliparib, and 1 with highly expressed Gpnmb treated with an antibody drug conjugate against Gpnmb. Tumor samples showed increased mutational and rearrangement burdens over time but shared mutational characteristics that were unique to each pt. Through the shared alterations across time points for 3 pts, it was possible to reconstruct the clonal history and heterogeneity of the tumors as various therapeutic approaches were attempted.

Conclusions: Here we show in TNBC, intrapatient and temporal heterogeneity that may lead to a lack of response to identified targeted therapies. Tumor samples taken over time from the same pt become enriched for more complex genomic structures post therapy but share mutational characteristics, indicating the presence of recurrent tumor populations. This study enabled us to reconstruct the clonal history and heterogeneity of tumors across space (metastatic vs primary at t=0) and time, illustrating the need for comprehensive molecular analysis and combination/multi-targeted therapeutics for optimal treatment in TNBC.

Citation Format: Soon-Shiong P, Rabizadeh S, Benz S, Cecchi F, Hembrough T, Mahen E, Burton K, Song C, Senecal F, Schmechel S, Pritchard C, Dorschner M, Blau S, Blau A. Integrating whole exome sequencing data with RNAseq and quantitative proteomics to better inform clinical treatment decisions in patients with metastatic triple negative breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-05-08.

Abstract P6-04-14: Integrating whole genome sequencing data with RNAseq, pathway analysis, and quantitative proteomics to determine prognosis after standard adjuvant treatment with trastuzumab and chemotherapy in primary breast cancer patients

Background: Despite improvements in the treatment of HER2+ breast cancer (BC), almost all patients (pts) progress in the metastatic setting. Three examples of resistance mechanisms are: PI3K mutations, lack of ADCC, or low expression of HER2. We recently showed that among 237 pts who had HER2 amplifications, 49% had normal or low levels of HER2 RNA. In addition, quantification of HER2 protein by selected reaction monitoring mass spectrometry (SRM-MS) accurately predicted HER2 expression status compared with IHC (3+)/ISH (≥2.0). Here we report a comprehensive panomic approach that integrates whole genome sequencing (WGS), RNASeq, quantitative proteomics, and pathway analysis to determine associations between tumor molecular profiles and prognosis among HER2+ pts.

Methods: Matched tumor-normal samples (FFPE tumors and blood) were obtained from 58 pts with HER2+ BC who had received standard adjuvant chemotherapy and trastuzumab. Pts were divided into 2 groups: those who had no recurrence after 5 years and those who had developed metastases. The HER2 status of each pt was previously determined using IHC/FISH. Samples underwent WGS and RNASeq according to NantOmics CLIA-approved assay specifications. WGS data were processed using Contraster; RNASeq data confirmed the presence of gene mutations and was used to identify mutational and transcript abundance. PARADIGM was used to reveal associations between gene mutations and pathway levels. SRM-MS was used for proteomics analysis of a panel of 53 proteins. Tumor areas from FFPE tissue sections were analyzed after laser microdissection. Absolute protein quantitation was accomplished through simultaneous detection of endogenous target and synthetic labeled heavy peptide identical to analytical targets. Genetic alterations in germline and tumor DNA were compared in pts with vs without recurrence.

Results: There was no statistically significant difference in the mean concentration of HER2 in the tumors of pts with vs without recurrence: 2.34 fmol/µL vs 2.56 fmol/µL. Other analyzed proteins did not appear to be associated with recurrence; however, expected correlations between pt and tumor characteristics and protein expression were found. With regard to clinically relevant mutations, we found one germline BRCA2 mutation in a pt with no family history of this mutation. The most commonly found somatic mutations were in TP53 (11 pts), AMBRA1 (11 pts), MORC4 (10 pts), SETD2 (8 pts), CDC27 (6 pts), BCLAF1 (5 pts), ZNF479 (4 pts) , PIK3CA (3 pts), PIK3R1 (3 pts), RUNX1 (3 pts), and GATA3 (3 pts).

Conclusion: Whereas HER2 expression status was predictive of OS and PFS in pts treated with trastuzumab (Nuciforo et al. Mol Onc. 2015), in this small exploratory study of HER2+ BC pts, HER2 expression status was not predictive of recurrence. To better understand the molecular mechanisms driving recurrence beyond HER2 status alone, genomic sequencing may define a signature of recurrence after anti-HER2 therapy.

Citation Format: Benz SC, Rabizadeh S, Cecchi F, Beckman MW, Brucker SY, Hartmann A, Golovato J, Hembrough T, Janni W, Rack B, Sanborn JZ, Schneeweiss A, Vaske CJ, Soon-Shiong P, Fasching PA. Integrating whole genome sequencing data with RNAseq, pathway analysis, and quantitative proteomics to determine prognosis after standard adjuvant treatment with trastuzumab and chemotherapy in primary breast cancer patients. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-04-14.

Abstract P2-11-12: Novel protocol combining metronomic nant-paclitaxel with HER2-targeted natural killer cells (innate immunotherapy) for HER2-positive metastatic breast cancer

Background. Natural killer (NK) cells are an important effector cell type for adoptive cancer immunotherapy. Phase 1 clinical trials in patients with advanced cancers demonstrated the safety of unmodified, activated NK-92 cells (aNK), with no evidence of cytokine storm from 18 infusions delivered over 6 months; clinical responses were observed in a subset of patients. Like T cells, NK cells can be engineered to express chimeric antigen receptors (CARs) to enhance their antitumor activity. A stable clonal HER2-specific NK-92 cell line (HER2.taNK) mediated selective and sequential killing of HER2-expressing MDA-MB-453 cells in vitro (Schönfeld. MolTher. 2015;23:330-338). In addition, HER2.taNK cells were enriched in MDA-MB-453/EGFP xenografts and reduced the number of pulmonary metastasis in a renal cell carcinoma model, suggesting that HER2.taNK cells are a promising clinical candidate for use in adoptive cancer immunotherapy. Metronomic (low-dose, continuous) chemotherapy can be more effective than high-dose therapy in patients with advanced breast cancer (Montagna. Canc. Treat. Rev. 2014;40:922-950). Here we evaluate HER2.taNK cells in combination with metronomic nant-paclitaxel (lyophilized polymeric micellar formulation of paclitaxel) in a mouse model of HER2-positive breast cancer to determine the feasibility of a human clinical trial of HER2.taNK in combination with metronomic nant-paclitaxel.

Methods. HER2.taNK cells were generated as described previously (Schönfeld. MolTher. 2015;23:330-338). MDA-MB-453 cells were implanted into the mammary fat pads of female nude mice. When tumors reached 100 mm3, mice were divided into 6 groups of 5 mice and dosed (IV) with saline (10 mL/kg, qd x 15), nant-paclitaxel (2.5-4 mg/kg q2d x 15), γ-irradiated (5 Gy) HER2.taNK cells (1 x 107 cells, days 1, 3, 5, and 8), or nant-paclitaxel + γ-irradiated (5 Gy) HER2.taNK cells–γ-irradiation is a potential safety measure for clinical application and prevents HER2.taNK cell replication while preserving antitumor activity. Tumor size and animal weights were measured every other day post-implantation.

Results: Results obtained 20 days post-treatment are shown in the table. Nant-paclitaxel alone and HER2.taNK alone significantly inhibited tumor growth. The combination of nant-paclitaxel + HER2.taNK led to significant tumor regressions (p&lt;0.05).

Treatment Dose T/C (%) P-ValueSalinenant-paclitaxel5 mg/kg-26.7 P &lt; 0.05 (vs saline) HER2.taNK1 x 107 cells-22.2 P &lt; 0.05 (vs saline)nant-paclitaxel +5 mg/kg +-60.0P &lt; 0.05 (vs nant-paclitaxel)HER2.taNK1 x 107 cellsP &lt; 0.05 (vs HER2.taNK)

Conclusions: Single agent nant-paclitaxel and HER2.taNK were similarly effective at inhibiting tumor growth in this mouse model of HER2+ breast cancer. The combination of nant-paclitaxel + HER2.taNK appeared to be synergistic resulting in tumor regressions and significantly better efficacy vs each agent alone. This study illustrates the potential for combining metronomic low-dose chemotherapy with NK-based immunotherapy in a clinical trial of patients with metastatic breast cancer.

Citation Format: Rabizadeh S, Simon B, Klingemann H, Sims D, Weiss R, Soon-Shiong P. Novel protocol combining metronomic nant-paclitaxel with HER2-targeted natural killer cells (innate immunotherapy) for HER2-positive metastatic breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-11-12.

Receptors that mediate cellular dependence

Cells depend for their survival on stimulation by trophic factors and other prosurvival signals, the withdrawal of which induces apoptosis, both via the loss of antiapoptotic signaling and the activation of proapoptotic signaling via specific receptors. These receptors, dubbed dependence receptors, activate apoptotic pathways following the withdrawal of trophic factors and other supportive stimuli. Such receptors may feature in developmental cell death, carcinogenesis (including metastasis), neurodegeneration, and possibly subapoptotic events such as neurite retraction and somal atrophy. Mechanistic studies of dependence receptors suggest that these receptors form ligand-dependent complexes that include specific caspases. Complex formation in the absence of ligand leads to caspase activation by a mechanism that is typically dependent on caspase cleavage of the receptor itself, releasing proapoptotic peptides. Cellular dependence receptors, considered in the aggregate, may thus form a system of molecular integration, analogous to the electrical integration system provided by dendritic arbors in the nervous system.

A monoclonal antibody that induces neuronal apoptosis binds a metastasis marker

The cell surface molecules controlling apoptosis in cortical neurons are largely unknown. A monoclonal antibody was derived that induces cultured neocortical neurons to undergo apoptosis. A Fab fragment of the antibody, however, lacked the ability to induce cell death. The antigen was purified, and characterized by compositional analysis, fast atom bombardment (FAB) mass spectrometry, sequential exoglycosidase treatments, methylation analysis, and (1)H-nuclear magnetic resonance spectroscopy, proving to be isoglobotetraosylceramide (IsoGb4). IsoGb4 has been shown previously to be a metastasis marker, antibodies against which block metastases in a mammary adenocarcinoma model (S. A. Carlsen et al., Cancer Res., 53: 2906-2911, 1993). Addition of the purified antigen to cells lacking this glycolipid demonstrated that it is capable of functioning as a portable apoptosis-transducing molecule. Intracellular ceramide levels were increased after the treatment with the apoptosis-inducing antibody, but the membrane sphingomyelin level remained unchanged. Fumonisin B1 inhibited both the ceramide increase and the apoptosis induced via IsoGb4, which indicated that the ceramide synthase pathway is likely to be involved in apoptosis induction by IsoGb4.

Neurotrophin dependence domain: a domain required for the mediation of apoptosis by the p75 neurotrophin receptor

The mechanisms underlying neurotrophin dependence, and cellular dependent states in general, are unknown. We show that a 29 amino acid region in the intracellular domain of the common neurotrophin receptor, p75NTR, is required for the mediation of apoptosis by p75NTR. Furthermore, contrary to results obtained with Fas, monomeric p75NTR is required for apoptosis induction, whereas multimerization inhibits the pro-apoptotic effect. Within the 29-residue domain required for apoptosis induction by p75NTR, a 14-residue region is sufficient as a peptide inducer of apoptosis. This 14-residue peptide requires the positively charged carboxyterminal residues for its effect on cell death, and these same residues are required by the full-length p75NTR. These studies define a novel type of domain that mediates neurotrophin dependence, and suggest that other cellular dependent states may be mediated by proteins displaying similar domains.

Dimerization-dependent block of the proapoptotic effect of p75(NTR)

The biochemical mechanism by which neurons become dependent on neurotrophins for survival is unknown. We found previously that the common neurotrophin receptor, p75(NTR), is a mediator of neurotrophin dependence and that this effect requires a novel type of domain dubbed a neurotrophin dependence domain. We report here that, in contrast to other proapoptotic receptors such as Fas, apoptosis induction by p75(NTR) requires monomerization, with dimerization inhibiting the effect. Blocking the proapoptotic effect of the monomer by dimerization requires a distinct domain that lies at the carboxyterminus of p75(NTR). These results define a novel type of domain required for inhibiting apoptosis induction by p75(NTR).

A second cytotoxic proteolytic peptide derived from amyloid beta-protein precursor

The amyloid beta-protein precursor gives rise to the amyloid beta-protein, the principal constituent of senile plaques and a cytotoxic fragment involved in the pathogenesis of Alzheimer disease. Here we show that amyloid beta-protein precursor was proteolytically cleaved by caspases in the C terminus to generate a second unrelated peptide, called C31. The resultant C31 peptide was a potent inducer of apoptosis. Both caspase-cleaved amyloid beta-protein precursor and activated caspase-9 were present in brains of Alzheimer disease patients but not in control brains. These findings indicate the possibility that caspase cleavage of amyloid beta-protein precursor with the generation of C31 may be involved in the neuronal death associated with Alzheimer disease.

The copper transport protein Atox1 promotes neuronal survival

Atox1, a copper transport protein, was recently identified as a copper-dependent suppressor of oxidative damage in yeast lacking superoxide dismutase. We have previously reported that Atox1 in the rat brain is primarily expressed in neurons, with the highest levels in distinct neuronal subtypes that are characterized by their high levels of metal, like copper, iron, and zinc. In this report, we have transfected the Atox1 gene into several neuronal cell lines to increase the endogenous level of Atox1 expression and have demonstrated that, under conditions of serum starvation and oxidative injury, the transfected neurons are significantly protected against this stress. This level of protection is comparable with the level of protection seen with copper/zinc superoxide dismutase and the anti-apoptotic gene bcl-2 that had been similarly transfected. Furthermore, neuronal cell lines transfected with a mutant Atox1 gene, where the copper binding domain has been modified to prevent metal binding, do not afford protection against serum starvation resulting in apoptosis. Therefore, Atox1 is a component of the cellular pathways used for protection against oxidative stress.

Neurotrophin dependence mediated by p75NTR: contrast between rescue by BDNF and NGF

During development, neurons pass through a critical phase in which survival is dependent on neurotrophin support. In order to dissect the potential role of p75NTR, the common neurotrophin receptor, in neurotrophin dependence, we expressed wild-type and mutant p75NTR in cells that do not express endogenous p75NTR or Trk family members (NIH3T3). Expression of wild-type p75NTR created a state of neurotrophin dependence: cells could be rescued by nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), or neurotrophin-3 (NT-3), but not by a mutant NGF that binds well to Trk A but poorly to p75NTR. Similarly, expression of p75NTR in human prostate cancer cells in culture rendered a metastatic tumor cell line (PC-3) sensitive to the availability of neurotrophins for survival. Moreover, expression of mutant p75NTR's in another neurotrophin-insensitive cell line (HEK293T) showed that a domain within the intracellular domain governs alternate responses to neurotrophins: the carboxy terminus of the intracellular domain of p75NTR including the sixth alpha helix domain is necessary for rescue by BDNF, but not NGF. These results, when considered with previous studies of the timing of p75NTR expression, support the hypothesis that p75NTR is a mediator of neurotrophin dependence during the critical phase of developmental cell death and during the progression of carcinogenesis in prostate cancer.

Functional interaction of Fas-associated phosphatase-1 (FAP-1) with p75(NTR) and their effect on NF-kappaB activation

The common neurotrophin receptor p75(NTR), a member of the tumor necrosis factor (TNF) receptor superfamily, plays an important role in several cellular signaling cascades, including that leading to apoptosis. FAP-1 (Fas-associated phosphatase-1), which binds to the cytoplasmic tail of Fas, was originally identified as a negative regulator of Fas-mediated apoptosis. Here we have shown by co-immunoprecipitation that FAP-1 also binds to the p75(NTR) cytoplasmic domain in vivo through the interaction between the third PDZ domain of FAP-1 and C-terminal Ser-Pro-Val residues of p75(NTR). Furthermore, cells expressing a FAP-1/green fluorescent protein showed intracellular co-localization of FAP-1 and p75(NTR) at the plasma membrane. To elucidate the functional role of this physical interaction, we examined TRAF6 (TNF receptor-associated factor 6)-mediated NF-kappaB activation and tamoxifen-induced apoptosis in 293T cells expressing p75(NTR). The results revealed that TRAF6-mediated NF-kappaB activation was suppressed by p75(NTR) and that the p75(NTR)-mediated NF-kappaB suppression was reduced by FAP-1 expression. Interestingly, a mutant of the p75(NTR) intracellular domain with a single substitution of a Met for Val in its C-terminus, which cannot interact with FAP-1, displayed enhanced pro-apoptotic activity in 293T transfected cells. Thus, similar to Fas, FAP-1 may be involved in suppressing p75(NTR)-mediated pro-apoptotic signaling through its interaction with three C-terminal amino acids (tSPV). Thus, FAP-1 may regulate p75(NTR)-mediated signal transduction by physiological interaction through its third PDZ domain.

TRAF family proteins interact with the common neurotrophin receptor and modulate apoptosis induction

The common neurotrophin receptor, p75(NTR), has been shown to signal in the absence of Trk tyrosine kinase receptors, including induction of neural apoptosis and activation of NF-kappaB. However, the mechanisms by which p75(NTR) initiates these intracellular signal transduction pathways are unknown. Here we report interactions between p75(NTR) and the six members of TRAF (tumor necrosis factor receptor-associated factors) family proteins. The binding of different TRAF proteins to p75(NTR) was mapped to distinct regions in p75(NTR). Furthermore, TRAF4 interacted with dimeric p75(NTR), whereas TRAF2 interacted preferentially with monomeric p75(NTR). TRAF2-p75(NTR), TRAF4-p75(NTR), and TRAF6-p75(NTR) interactions modulated p75(NTR)-induced cell death and NF-kappaB activation with contrasting effects. Coexpression of TRAF2 with p75(NTR) enhanced cell death, whereas coexpression of TRAF6 was cytoprotective. Furthermore, overexpression of TRAF4 abrogated the ability of dimerization to prevent the induction of apoptosis normally mediated by monomeric p75(NTR). TRAF4 also inhibited the NF-kappaB response, whereas TRAF2 and TRAF6 enhanced p75(NTR)-induced NF-kappaB activation. These results demonstrate that TRAF family proteins interact with p75(NTR) and differentially modulate its NF-kappaB activation and cell death induction.

Kennedy's disease: caspase cleavage of the androgen receptor is a crucial event in cytotoxicity

X-linked spinal and bulbar muscular atrophy (SBMA), Kennedy's disease, is a degenerative disease of the motor neurons that is associated with an increase in the number of CAG repeats encoding a polyglutamine stretch within the androgen receptor (AR). Recent work has demonstrated that the gene products associated with open reading frame triplet repeat expansions may be substrates for the cysteine protease cell death executioners, the caspases. However, the role that caspase cleavage plays in the cytotoxicity associated with expression of the disease-associated alleles is unknown. Here, we report the first conclusive evidence that caspase cleavage is a critical step in cytotoxicity; the expression of the AR with an expanded polyglutamine stretch enhances its ability to induce apoptosis when compared with the normal AR. The AR is cleaved by a caspase-3 subfamily protease at Asp146, and this cleavage is increased during apoptosis. Cleavage of the AR at Asp146 is critical for the induction of apoptosis by AR, as mutation of the cleavage site blocks the ability of the AR to induce cell death. Further, mutation of the caspase cleavage site at Asp146 blocks the ability of the SBMA AR to form perinuclear aggregates. These studies define a fundamental role for caspase cleavage in the induction of neural cell death by proteins displaying expanded polyglutamine tracts, and therefore suggest a strategy that may be useful to treat neurodegenerative diseases associated with polyglutamine repeat expansions.

The DCC gene product induces apoptosis by a mechanism requiring receptor proteolysis

The development of colonic carcinoma is associated with the mutation of a specific set of genes. One of these, DCC (deleted in colorectal cancer), is a candidate tumour-suppressor gene, and encodes a receptor for netrin-1, a molecule involved in axon guidance. Loss of DCC expression in tumours is not restricted to colon carcinoma, and, although there is no increase in the frequency of tumour formation in DCC hemizygous mice, reestablishment of DCC expression suppresses tumorigenicity. However, the mechanism of action of DCC is unknown. Here we show that DCC induces apoptosis in the absence of ligand binding, but blocks apoptosis when engaged by netrin-1. Furthermore, DCC is a caspase substrate, and mutation of the site at which caspase-3 cleaves DCC suppresses the pro-apoptotic effect of DCC completely. These results indicate that DCC may function as a tumour-suppressor protein by inducing apoptosis in settings in which ligand is unavailable (for example, during metastasis or tumour growth beyond local blood supply) through functional caspase cascades by a mechanism that requires cleavage of DCC at Asp 1,290.

p75NTR and the concept of cellular dependence: seeing how the other half die

Cells depend on specific stimuli, such as trophic factors, for survival and in the absence of such stimuli, undergo apoptosis. How do cells initiate apoptosis in response to the withdrawal of trophic factors or other dependent stimuli? Recent studies of apoptosis induction by neurotrophin withdrawal argue for a novel form of pro-apoptotic signal transduction - 'negative signal transduction' - in which the absence of ligand-receptor interaction induces cell death. We have found that the prototype for this form of signaling - the common neurotrophin receptor, p75NTR - creates a state of cellular dependence (or addiction) on neurotrophins, and that this effect requires an 'addiction/dependence domain' (ADD) in the intracytoplasmic region of p75NTR. We have recently found other receptors that include dependence domains, arguing that dependence receptors, and their associated dependence domains, may be involved in a rather general mechanism to create cellular states of dependence on trophic factors, cytokines, adhesion, electrical activity and other dependent stimuli.

Expression of CD40 induces neural apoptosis

The tumor necrosis factor receptor superfamily includes 12 members, some of which (e.g., tumor necrosis factor receptor I and FAS) induce cell death triggered by ligand binding. Another member of the superfamily, the neurotrophin receptor p75NTR, induces neural apoptosis, with apoptosis being inhibited by binding of ligand to the receptor. As such, it is a candidate for the mediation of neurotrophin dependence. Here, we show that CD40, a superfamily member that is closely related to p75NTR, also induces neural apoptosis, but apoptosis is inhibited by binding of the G28-5 monoclonal antibody to CD40. These results provide further support for a model in which some members of the tumor necrosis factor receptor superfamily induce apoptosis triggered by ligand binding, whereas other members may, at least under certain conditions, induce apoptosis in the absence of ligand binding, with apoptosis being inhibited by binding of ligand or monoclonal antibody.

A cytoplasmic peptide of the neurotrophin receptor p75NTR: induction of apoptosis and NMR determined helical conformation

The neurotrophin receptor (NTR) and tumor necrosis factor receptor family of receptors regulate apoptotic cell death during development and in adult tissues [Beutler and van Huffel, Science 264 (1994) 667-668]. We have examined a fragment of p75NTR from the carboxyl terminus of the receptor and a variant form of this peptide via NMR techniques and in vitro assays for apoptotic activity. The wild type peptide induces apoptosis and adopts a helical conformation oriented parallel to the surface of lipid micelles, whereas the variant form adopts a non-helical conformation in the presence of lipid and shows no activity. These experiments suggest a link between structure and function of the two peptides.

Establishment of a cell-free system of neuronal apoptosis: comparison of premitochondrial, mitochondrial, and postmitochondrial phases

Apoptosis is a fundamental process required for normal development of the nervous system and is triggered during neurodegenerative disease. To dissect the molecular events leading to neuronal cell death, we have developed a cell-free model of neuronal apoptosis. The model faithfully reproduces key elements of apoptosis, including chromatin condensation, DNA fragmentation, caspase activation/processing, and selective substrate cleavage. We report that cell-free apoptosis is activated in premitochondrial, mitochondrial, and postmitochondrial phases by tamoxifen, mastoparan, and cytochrome c, respectively, allowing a functional ordering of these proapoptotic modulators. Furthermore, this is the first report of mitochondrial-mediated activation of cell-free apoptosis in a cell extract. Although Bcl-2 blocks activation at the premitochondrial and mitochondrial levels, it does not affect the postmitochondrial level. The cell-free system described here provides a valuable tool to elucidate the molecular events leading to neuronal cell death.

p75NTR and apoptosis: Trk-dependent and Trk-independent effects

The ongoing dissection of the roles of p75NTR and TrkA, -B and -C in neurotrophin signaling has generated a number of apparent paradoxes. Limiting consideration to the role of p75NTR in cell death, a theory is proposed that is based on the following postulates: (1) that p75NTR displays a pro-apoptotic intrinsic (ligand-independent, Trk-independent) receptor effect (IRE), which is inhibited by ligand binding; (2) that p75NTR and TrkA exhibit mutual repression of signaling; and (3) that p75NTR and TrkA are required for the efficient generation of high-affinity NGF binding sites.

Cell death mechanisms in ALS

Mutations in copper-zinc superoxide dismutase (CuZnSOD) that are associated with familial ALS (FALS) are dominant, gain-of-function mutations, but the nature of the function gained has not been identified. In addition to catalyzing the dismutation of superoxide, copper-zinc superoxide dismutase also displays peroxidase activity. Whereas mutants A4V and G93A retained superoxide dismutase activity, they demonstrated a markedly enhanced copper-dependent peroxidase activity in comparison with that of the wild type enzyme as detected by the spin trap 5,5'-dimethyl-1-pyrroline N-oxide (DMPO) in electron paramagnetic resonance measurements. Two copper chelators, diethyldithiocarbamate and penicillamine, inhibited the mutants' peroxidase activity, but not that of the wild type enzyme, at stoichiometric concentrations; furthermore, these copper chelators enhanced neural survival in a cell-culture model of ALS but did not alter survival of cells expressing only wild type copper-zinc superoxide dismutase. These observations suggest that oxidative reactions catalyzed by mutant copper-zinc superoxide dismutases may initiate the neuropathologic changes of FALS.

Altered reactivity of superoxide dismutase in familial amyotrophic lateral sclerosis

A subset of individuals with familial amyotrophic lateral sclerosis (FALS) possesses dominantly inherited mutations in the gene that encodes copper-zinc superoxide dismutase (CuZnSOD). A4V and G93A, two of the mutant enzymes associated with FALS, were shown to catalyze the oxidation of a model substrate (spin trap 5,5'-dimethyl-1-pyrroline N-oxide) by hydrogen peroxide at a higher rate than that seen with the wild-type enzyme. Catalysis of this reaction by A4V and G93A was more sensitive to inhibition by the copper chelators diethyldithiocarbamate and penicillamine than was catalysis by wild-type CuZnSOD. The same two chelators reversed the apoptosis-inducing effect of mutant enzymes expressed in a neural cell line. These results suggest that oxidative reactions catalyzed by mutant CuZnSOD enzymes initiate the neuropathologic changes in FALS.

Mutations associated with amyotrophic lateral sclerosis convert superoxide dismutase from an antiapoptotic gene to a proapoptotic gene: studies in yeast and neural cells

Familial amyotrophic lateral sclerosis (FALS) is associated with mutations in SOD1, the gene encoding copper/zinc superoxide dismutase (CuZnSOD). However, the mechanism by which these mutations lead to amyotrophic lateral sclerosis is unknown. We report that FALS mutant SODs expressed in yeast lacking CuZnSOD are enzymatically active and restore the yeast to the wild-type phenotype. In mammalian neural cells, the overexpression of wild-type SOD1 inhibits apoptosis induced by serum and growth factor withdrawal or calcium ionophore. In contrast, FALS-associated SOD1 mutants promote, rather than inhibit, neural apoptosis, in a dominant fashion, despite the fact that these mutants retain enzymatic SOD activity both in yeast and in mammalian neural cells. The results dissociate the SOD activity of FALS-associated mutants from the induction of neural cell death, suggesting that FALS associated with mutations in SOD1 may not be simply the result of a decrease in the enzymatic function of CuZnSOD. Furthermore, the results provide an in vitro model that may help to define the mechanism by which FALS-associated SOD1 mutations lead to neural cell death.

Expression of the low-affinity nerve growth factor receptor enhances beta-amyloid peptide toxicity

The low-affinity nerve growth factor receptor (NGFR) p75NGFR induces apoptosis in the absence of nerve growth factor (NGF) binding but enhances neural survival when bound by NGF. Basal forebrain cholinergic neurons express the highest levels of p75NGFR in the adult human brain and are preferentially involved in Alzheimer disease, raising the question of whether there may be a functional relationship between the expression of p75NGFR and basal forebrain cholinergic neuronal degeneration in Alzheimer disease. The expression of p75NGFR by wild-type and mutant PC12 cells potentiated cell death induced by beta-amyloid peptide. NGF binding to p75NGFR inhibited the toxicity of beta-amyloid peptide, whereas NGF binding to TrkA, the high-affinity NGFR, enhanced it. These results suggest a possible link between beta-amyloid peptide toxicity and preferential degeneration of cells expressing p75NGFR.

Neural-targeted gene therapy for rodent and primate hemiparkinsonism

Expression of the rate-limiting enzyme for catecholamine biosynthesis, tyrosine hydroxylase (TH), via retroviral and plasmid expression vectors improved the efficacy of conditionally immortalized nigral neural cells in ameliorating rodent and nonhuman primate models of Parkinson's disease through neural transplantation. No improvement in rotational behavior occurred when sham transplants or nondopaminergic transplants were performed. Transplantation of the temperature-sensitive immortalized parental nigral neural line with a TH expression vector resulted in improvement for at least 2 months. Improvement was accompanied by HPLC evidence of increased L-DOPA production and immunocytochemical evidence of TH in the transfected cells increased over that of the parental line. No tumor formation was detected. These results suggest that: (1) temperature-sensitive immortalized neural cells may be genetically engineered successfully to improve their efficacy for the treatment of parkinsonism; and (2) a change in L-DOPA production, as opposed to growth factor production or other factors, is likely to account for the observed improvement, since the parental and derived lines differ by a single gene.

Is p75NGFR involved in developmental neural cell death?

The tumor necrosis factor receptor superfamily includes twelve members, at least two of which--tumor necrosis factor receptor I and FAS/Apo-1--induce cell death following ligand binding. This review summarizes data suggesting that two other members of the family--p75NGFR and CD40--achieve a similar effect in the inverse fashion; they induce apoptosis constitutively when unbound by their respective ligands, with the induction of apoptosis being inhibited by the binding of their respective ligands. The potential roles that such receptors may play in development and pathological processes are discussed.

Expression of the baculovirus p35 gene inhibits mammalian neural cell death

Expression of the apoptosis suppressor gene p35, derived from the baculovirus Autographa californica nuclear polyhedrosis virus, markedly inhibited the cell death of stably transfected mammalian neural cells whether the cell death was induced by glucose withdrawal, calcium ionophore, or serum withdrawal. The p35 protein, which is required to block virus-induced apoptosis of cultured insect cells, is only the second gene product shown to block mammalian neural cell death, with Bcl-2 being the first. Because there is no apparent homology between p35 and Bcl-2, the existence of a cellular death program that may be modulated at multiple points is suggested. Furthermore, these findings demonstrate that the putative cellular death program is conserved across species and cell types.

Induction of apoptosis by the low-affinity NGF receptor

Nerve growth factor (NGF) binding to cellular receptors is required for the survival of some neural cells. In contrast to TrkA, the high-affinity NGF receptor that transduces NGF signals for survival and differentiation, the function of the low-affinity NGF receptor, p75NGFR, remains uncertain. Expression of p75NGFR induced neural cell death constitutively when p75NGFR was unbound; binding by NGF or monoclonal antibody, however, inhibited cell death induced by p75NGFR. Thus, expression of p75NGFR may explain the dependence of some neural cells on NGF for survival. These findings also suggest that p75NGFR has some functional similarities to other members of a superfamily of receptors that include tumor necrosis factor receptors, Fas (Apo-1), and CD40.