Vera Balz

T cells specific for HPV16 E7 epitopes in patients with squamous cell carcinoma of the oropharynx

Squamous cell carcinomas of the oropharynx (SCCO) are often infected with oncogenic human papilloma virus (HPV) subtype 16. To determine the frequency of T cells specific for human leukocyte antigen (HLA)‐A2.1 restricted HPV16 E7 protein‐derived epitopes, tetramer analysis was performed using peripheral blood lymphocytes of 20 HLA‐A2.1+ patients and 20 HLA‐A2.1+ healthy individuals. Tetramers specific for 3 HPV16 peptides (E711–20, E782–90 and E786–93), an influenza matrix peptide (a model recall antigen) or an HIV reverse transcriptase peptide (a model novel antigen) were used in multicolor flow analysis. The HPV‐specific T‐cell frequencies were correlated with the HPV16 E7 and p16 status in tumor sections. In vitro stimulation (IVS) with autologous dendritic cells (DC) pulsed with HPV16 E7 epitopes was performed to demonstrate proliferation and antitumor activity of the HPV‐responsive T cells. Frequencies of CD8+ T cells specific for HPV16 E7 peptides were not significantly different in patients with SCCO relative to normal donors. However, patients with tumors expressing HPV16 E7 (60%) and p16 (50%) had an increased frequency (p < 0.05) of T cells specific for the E711–20 epitope compared to those with tumors negative for both markers. HPV16 E711–20 and HPV16 E786–93 specific T cells were expandable upon IVS with cognate peptide‐pulsed DC and were reactive against peptide‐pulsed targets or, in case of the E711–20 epitope‐specific T cells, against HPV16 E7 expressing CaSki cell line. Thus, in patients with HPV16+ SCCO, precursor T cells specific for E711–20 epitope are present (1/3,947) in the circulation, are responsive to stimulation with the cognate viral peptide and recognize in vitro HPV16 E7+ tumor cells. Further studies have to elucidate why those T cells are unable to eliminate the tumor in vivo and this might also allow for finding potential strategies that will increase the chances of developing a future HPV‐based vaccine in patients with SCCO.

Alterations in the p53 pathway and their association with radio- and chemosensitivity in head and neck squamous cell carcinoma

Chemotherapy and/or radiotherapy are established measures in treatment protocols of head and neck squamous cell carcinoma (HNSCC). However, we still lack reliable predictive markers for the response to radio- and chemotherapy. The p53 pathway is involved in stress response and thus might influence chemo-/radiosensitivity. Using 29 HNSCC cell lines previously characterized for p53 mutations, we simultaneously analyzed several key players in the p53 pathway by RT-PCR, transcript sequencing and immunohistochemistry, and investigated their association with chemosensitivity and radiosensitivity. Cell lines with p53 mutations were slightly more sensitive to cisplatin than those with wild-type p53. The type of mutation did not influence radio- or chemosensitivity. p14(ARF), an activator of p53, was lost or mutated in all cell lines. Three cell lines showed overexpression of HDM-2, a major negative regulator of p53; however, HDM-2 levels did not correlate with radio- or chemosensitivity. HPV-16 oncoproteins were detected in one highly chemoresistant cell line. Our findings suggest that molecular events resulting in the inactivation of the p53 pathway occur in all HNSCC cell lines. However, single alterations in the p53 pathway are not reliable predictors for the response to radio- or chemotherapy in HNSCC.

A novel mechanism for anti-EGFR antibody action involves chemokine-mediated leukocyte infiltration

Overexpression of the epidermal growth factor receptor (EGFR) is a hallmark of squamous cell carcinoma of the head and neck (SCCHN). Monoclonal antibodies (mAbs) against EGFR are currently used for therapy of recurrent or metastatic disease; however, their mode of action is not completely understood. To investigate the immunological effects of anti‐EGFR mAb, we generated a three‐dimensional spheroid model of EGFR‐expressing SCCHN and used this model to study the effect of anti‐EGFR mAb on leukocyte migration toward tumors. Pretreatment with the blocking anti‐EGFR mAb EMD 72000, its F(ab′)2 fragments or an EGFR tyrosine kinase inhibitor led to substantially increased leukocyte infiltration into EGFR overexpressing tumor spheroids, but not into those with low EGFR expression. Nonblocking anti‐EGFR mAb or fibroblast‐specific mAb did not affect leukocyte infiltration, suggesting that the observed increase in leukocyte infiltration depends on interference with EGFR activation. Using a human cytokine macroarray, we demonstrated that the blockade of EGFR by anti‐EGFR mAb in EGFR‐overexpressing SCCHN cells leads to differential expression of several cytokines and chemokines, including the chemokine MCP‐1/CCL‐2. The significant upregulation of MCP‐1/CCL2 on exposure to anti‐EGFR mAb was confirmed by quantitative PCR and enzyme‐linked immunospot analyses. Moreover, blocking anti‐MCP‐1 antibody inhibited leukocyte migration toward tumor cells induced by anti‐EGFR mAb, pointing to an important role of MCP‐1/CCL2 in anti‐EGFR mAb‐induced leukocyte migration. Our findings demonstrate that anti‐EGFR mAb induces leukocyte infiltration to tumor spheroids by upregulating chemokine expression. This novel mechanism for anti‐EGFR mAb action may contribute to the antitumor effects of anti‐EGFR mAb in vivo.

Reliable detection of p53 aberrations in squamous cell carcinomas of the head and neck requires transcript analysis of the entire coding region.

Aberrations of the p53 tumor suppressor gene are common events in squamous cell carcinomas of the head and neck (SCCHN). However, reported frequencies range considerably, and the predictive value of aberrant p53 is continuing to be an issue of controversy. These inconsistencies are possibly caused by methodical limitations.

Homozygous deletions of CDKN2A caused by alternative mechanisms in various human cancer cell lines

The CDKN2A tumor‐suppressor locus on chromosome band 9p21, which encodes p16INK4A, a negative regulator of cyclin‐dependent kinases, and p14ARF1, an activator of TP53, is inactivated in many human cancers by point mutation, promoter hypermethylation, and, often, deletion. Homozygous deletions are unusually prevalent at this locus in very different human cancers. In the present study, we compared deletions in squamous cell carcinoma of the head and neck (SCCHN) cell lines to those in T‐cell acute lymphatic leukemia (T‐ALL), glioma, and bladder carcinoma (TCC) cell lines. Of 14 SCCHN lines, 10 showed homozygous deletions of CDKN2A, one displayed promoter hypermethylation with gene silencing, and one had a frameshift deletion in exon 2. Many deletion ends were in or proximal to the repetitive sequence clusters flanking the locus. Breakpoint junctions displayed variable microhomologies or insertions characteristic of DNA repair by nonhomologous end‐joining. In general, deletions were much smaller in SCCHN than in TCC and glioma. In T‐ALL, breakpoints were near consensus sites for recombination mediated by RAG (recombination activating genes) enzymes, and the structure of the junctions was consistent with this mechanism. We suggest that different mechanisms of CDKN2A deletion prevail in different human cancers. Aberrant RAG‐mediated recombination may be responsible in T‐ALL, and exuberant DNA repair by nonhomologous end‐joining is the likely prevailing mechanism in SCCHN, but a distinct mechanism in TCC and glioma remains to be elucidated.

Comprehensive analysis of the p53 status in mucosal and cutaneous melanomas

The abrogation of the function of the “gatekeeper of the genome”, p53, is the most prevalent molecular alteration in solid human tumors. Regarding melanomas the involvement of p53 alterations is discussed controversially to date. In order to evaluate the status of p53 in detail, primary tumors and metastases of 63 sporadic cutaneous (CM) and mucosal (MuM) melanomas were examined by immunohistochemistry and sequence analysis of the entire coding region of the p53 transcript, i.e., exons 2 to 11. In addition, loss of heterozygosity (LOH) and loss of allele‐specific transcription (LOT) were determined. Accumulation of the p53 protein occurred in most of the CM and MuM specimens (71% and 58%, respectively). In contrast, protein stabilizing p53 mutations were observed in 14% of the CM and no mutation was found in MuM specimens. Two of the aberrations located outside the core domain. LOH was detected in 22% CM and 58% MuM, and LOT in 25% of the CM specimens. The genotype distribution at the polymorphic p53 codon 72 in melanoma patients differed significantly from control subjects. The calculation of odds ratios (OR) and 95% confidence intervals (CI) indicated an increased risk for developing cutaneous melanomas in individuals carrying the Pro‐coding allele. Altogether, aberrant p53 expression appears to be a common event in both CM and MuM.

Antitumor activity of protein kinase C inhibitors and cisplatin in human head and neck squamous cell carcinoma lines

Protein kinase C (PKC) plays a pivotal role in signal transduction involved in the control of cell proliferation, differentiation and apoptosis. Interference with such signaling pathways may result in altered tumor cell response to antineoplastic drugs. We investigated the effects of two selective PKC inhibitors as single agents and in combination with cisplatin in cell lines derived from squamous cell carcinomas of the head and neck (SCCHN). Safingol (Saf) is directed against the regulatory domain, whereas chelerythrine (Che) interacts with the catalytic domain of PKC. In six SCCHN cell lines (UM-SCC 11B, 14A, 14C and 22B, 8029NA, and a 5-fold cisplatin-resistant subline 8029DDP). PKC activities ranged between 1 and 158 IU/1×107 cells, and they were inversely proportional to the amount of cellular epidermal growth factor receptor. Using the colorimetric MTT assay, PKC inhibitors Saf and Che showed comparable dose-dependent growth inhibition. The 50% inhibitory concentrations (IC50) were between 3.8–8.6 μ M for Saf and 8.5–13.6 μ M for Che with no relationship to PKC activity or cisplatin sensitivity of the respective cell lines. Combinations of cisplatin (IC50 = 0.4–5.8 μ g/ml) and either PKC inhibitor (5 μ M Saf, 10 μ M Che) led to a significant decrease of cisplatin IC50 values in most cell lines. However, comparison with theoretical additive dose–response curves showed additive rather than synergistic effects for both PKC inhibitors.

Pharmacological induction of vascular extracellular superoxide dismutase expression in vivo

Pentaerythritol tetranitrate (PETN) treatment reduces progression of atherosclerosis and endothelial dysfunction and decreases oxidation of low‐density lipoprotein (LDL) in rabbits. These effects are associated with decreased vascular superoxide production, but the underlying molecular mechanisms remain unknown. Previous studies demonstrated that endogenous nitric oxide could regulate the expression of extracellular superoxide dismutase (ecSOD) in conductance vessels in vivo. We investigated the effect of PETN and overexpression of endothelial nitric oxide synthase (eNOS++) on the expression and activity of ecSOD. C57BL/6 mice were randomized to receive placebo or increasing doses of PETN for 4 weeks and eNOS++ mice with a several fold higher endothelial‐specific eNOS expression were generated. The expression of ecSOD was determined in the lung and aortic tissue by real‐time PCR and Western blot. The ecSOD activity was measured using inhibition of cytochrome C reduction. There was no effect of PETN treatment or eNOS overexpression on ecSOD mRNA in the lung tissue, whereas ecSOD protein expression increased from 2.5‐fold to 3.6‐fold (P < 0.05) by 6 mg PETN/kg body weight (BW)/day and 60 mg PETN/kg BW/day, respectively. A similar increase was found in aortic homogenates. eNOS++ lung cytosols showed an increase of ecSOD protein level of 142 ± 10.5% as compared with transgene‐negative littermates (P < 0.05), which was abolished by Nω‐nitro‐L‐arginine treatment. In each animal group, the increase of ecSOD expression was paralleled by an increase of ecSOD activity. Increased expression and activity of microvascular ecSOD are likely induced by increased bioavailability of vascular nitric oxide. Up‐regulation of vascular ecSOD may contribute to the reported antioxidative and anti‐atherosclerotic effects of PETN.

Immunological characterization of missense mutations occurring within cytotoxic T cell‐defined p53 epitopes in HLA‐A*0201+ squamous cell carcinomas of the head and neck

Previous analyses of p53 in 40 HLA‐A*0201(HLA‐A2)+ squamous cell carcinomas of the head and neck (SCCHN) indicated that 6/13 p53 missense mutations that were detected, S149C, T150R, V157F, Y220C, Y220H and E271K, occurred within HLA‐A2‐restricted cytotoxic T lymphocyte (CTL)‐defined p53 epitopes. Of the 6, the p53 S149C, Y220C and Y220H peptides were immunogenic. Anti‐p53 mutant S149C and Y220H effector cells cross‐reacted against the parental wild type sequence (wt) p53 peptides, whereas anti‐p53 Y220C effector cells were specific for the mutant peptide, p53 Y220C cDNA‐transfected HLA‐A2+ SaOS cells, and an HLA‐A2+ SCCHN cell line naturally expressing the mutation. These results indicate that the p53 Y220C mutation can be processed and presented for CD8+ T cell recognition. Furthermore, using an autologous PBMC/tumor system, anti‐p53 Y220C peptide‐effector cells recognizing the autologous tumor could also be generated. Our analysis of p53 in 10 additional HLA‐A2+ SCCHN tumors detected the p53 Y220C in 2/10 tumors raising the overall frequency of the p53 Y220C mutation to 6/50 (12%) HLA‐A2+ SCCHN tumors. In contrast, independent of their HLA class I genotypes, the p53 Y220C mutation frequency for all human tumors analyzed to date is ∼1.5%. This unexpectedly high frequency of the p53 Y220C mutation in HLA‐A2+ SCCHN suggests that vaccines targeting this mutation would not only be expected to induce robust anti‐tumor immune responses in HLA‐A2+ subjects, but also be more widely applicable than previously envisioned for any given p53 missense mutation.

Analysis of BRCA1, TP53, and TSG101 germline mutations in German breast and/or ovarian cancer families

About 5%-10% of breast cancers are considered to be hereditary and associated with germline mutations of specific genes. As yet, the most frequently affected genes identified are BRCA1 and BRCA2, but also other genes such as TP53 are supposed to influence the predisposition toward breast cancer. In the present study, we analyzed patients of 19 German families with early onset breast cancer and/or a family history of breast and/or ovarian cancer for the presence of mutations in BRCA1 and TP53. In addition, we screened for germline mutations in the putative tumor suppressor gene TSG101. For this purpose we used direct sequence analysis of the entire coding regions for all three genes and, in the case of BRCA1, single-strand conformation polymorphism analysis and protein transcription-translation assays. We identified eight previously described polymorphisms and several aberrations in BRCA1: 1 unclassified missense mutation, 3 small protein truncating mutations, 1 novel pseudoexon, and 5 splicing variants. No mutation was detected in TP53. Analysis of TSG101 transcripts revealed an aberrant transcript in two breast cancer patients belonging to the same family, suggesting TSG101 as a predisposing gene in hereditary breast cancer.