Multicentric neoadjuvant phase II study of panitumumab combined with an anthracycline/taxane-based chemotherapy in operable triple-negative breast cancer: identification of biologically defined signatures predicting treatment impact

BACKGROUND

Triple-negative breast cancer (TNBC) is a heterogeneous group of tumors for some of which the epithelial growth factor receptor (EGFR) pathway may play an important role. We investigated the efficacy and toxicity of an anti-EGFR antibody (panitumumab) combined with a standard neoadjuvant anthracycline-taxane-based chemotherapy in patients with operable, stage II-III, TNBC.

PATIENTS AND METHODS

Treatment in this multicentric neoadjuvant pilot study consisted of panitumumab (9 mg/kg) for eight cycles q.3 weeks combined with four cycles of 5-fluorouracil, epidoxorubicin and cyclophosphamide (FEC100: 500/100/500 mg/m(2)) q.3 weeks, followed by four cycles of docetaxel (T: 100 mg/m(2)) q.3 weeks. Following therapy, all patients underwent surgical resection. Pathologic complete response (pCR) in assessable patients was the main end point while clinical response, toxicity and ancillary studies were secondary end points. Paraffin-embedded and frozen tumor samples were systematically collected with the aim to identify predictive biomarkers of efficacy and resistance in order to select biologically defined subpopulations for potential further clinical development of the anti-EGFR antibody.

RESULTS

Sixty patients were included with 47 assessable for pathologic response. The pCR rates were 46.8% [95% confidence interval (CI): 32.5% to 61.1%] and 55.3% [95% CI: 41.1% to 69.5%] according, respectively, to Chevallier and Sataloff classifications. The complete clinical response (cCR) rate was 37.5%. Conservative surgery was carried out in 87% of cases. Toxicity was manageable. The association of high EGFR and low cytokeratin 8/18 expression in tumor cells on one hand and high density of CD8+ tumor-infiltrating lymphocytes on the other hand were significantly predictive of pCR.

CONCLUSIONS

Panitumumab in combination with FEC100 followed by docetaxel appears efficacious, with acceptable toxicity, as neoadjuvant therapy of operable TNBC. Several biomarkers could help define large subsets of patients with a high probability of pCR, suggesting a potential interest to further develop this combination in biologically defined subgroups of patients with TNBC.

CLINICAL TRIAL NUMBER

NCT00933517.

Abstract P1-08-34: Is it possible to predict the efficacy of a combination of cetuximab plus docetaxel in patients with operable, triple negative breast cancer (TNBC)? Final biomarker results from a phase II neoadjuvant trial

Background: TNBC is a heterogenous group of tumors for some of which the Epithelial Growth Factor Receptor pathway (EGFR) may play an important role. We evaluated the efficacy and toxicity of an anti-EGFR antibody (cetuximab) combined with docetaxel, which were given to the TNBC patients (pts) in the neoadjuvant setting. A biomarker analysis accompanied this trial, aiming to identify predictors of response.

Methods: 35 patients with stage II-IIIA TN breast disease were prospectively included in this multicentre pilot study. Systemic therapy (ST) consisted of 6 cycles of docetaxel (100 mg/m2) each 3 weeks, in combination with weekly cetuximab (first dose 400mg/m2 then 250 mg/m2/week) for 6 cycles. All patients underwent surgery at completion of ST.

Patient characteristics : mean age 48 [28-67]; TNM: T1: 3%, T2: 73%, T3: 24%; N0: 61%, N1-N2: 39%; mean tumor size 40 mm [15-100]; SBR: grade III: 73%, grade II: 27%. The median number of cycles was for docetaxel 6 [1-6] and for cetuximab 15 [1-18]. Pathological complete response (pCR) rate was 24% according to the Chevallier and Sataloff classifications; 28% if we consider breast pCR only. Overall clinical response rate was 57% (22% CR). Conservative surgery was performed in 75% of cases. The main side effect was skin toxicity: grade II: 39%, grade III: 36%, grade IV: 3%. Other side effects were: neutropenia grade IV: 12.7%, febrile neutropenia: 1.3%, hand-foot syndrome grade III: 3%, grade II: 3%, ungueal toxicity grade III: 3%, grade II: 33%.

Paraffin-embedded and frozen samples were systematically collected before and after ST for biomarker studies. Germinal BRCA1 mutations and EGFR, KRAS, BRAF and PI3KCA somatic mutations were analyzed by NGS. EGFR, MET, cytokeratins 5/6 and 8/18, PTEN, P-cadherin, ALDH1, Ki67, p53 and the number of FOXP3+ or CD8+ tumor-infiltrating lymphocytes (TIL) were evaluated by immunohistochemistry.

Results: The biomarker analysis was interpretable on the samples from 21 pts (3 pCR and 18 non-pCR).

We applied the ROC curve to identify the best cut-off value for Ki67, EGFR, MET, cytokeratin 5/6 and 8/18, p53, ALDH1, PTEN, P-cadherin and the FOXP3+ or CD8+ TIL counts. None of these biomarkers was predictive of pCR except for the CD8+/FOXP3+ TIL count ratio. pCR rate was higher in the pts with the ratio equal or higher than 2.75 than in the others (43% versus 0%, p = 0.047).

BRCA1 mutations were detected in 16% of pts. PI3K and EGFR somatic mutations were observed in 1 and 3 patients, respectively. The presence of the mutations was not predictive of pCR.

Conclusion: Similarly to the previously reported trial by our group (SABCS 2012, abstract 1081), the immune component of the tumor microenvironment plays a very important role in the TNBC response to cytotoxic therapy.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-08-34.

Abstract P3-14-19: Panitumumab in combination with FEC 100 (5-fluorouracil, epirubicin, cyclophosphamide) followed by docetaxel for operable, triple negative breast cancer (TNBC): Patient outcome

Background: Panitumumab is an antibody targeting the epidermal growth factor receptor (EGFR) for which an important role has been suggested in TNBC. Consequently, we evaluated a combination of the standard chemotherapy (FEC 100 followed by docetaxel) with panitumumab as neoadjuvant therapy of operable TNBC. Complete pathologic response (pCR) was the primary endpoint, with clinical response, toxicity, and outcome as secondary endpoints. An investigation of biomarkers possibly predictive of pCR accompanied this trial. Here we focus on tumor recurrence, after a median follow up of 33 months [25-40] as on April, 1, 2013.

Methods: Sixty patients (pts) with stage II-IIIA TNBC were prospectively included. Systemic neoadjuvant treatment (ST) consisted of the anti-EGFR antibody panitumumab combined with FEC 100, followed by 4 cycles of docetaxel. All pts underwent surgery after ST completion. Patient characteristics: median tumor size: 40 mm [20-120]; SBR grade III: 71.7%; pCR rate: 55.3% and 46.8% (the Sataloff and the Chevallier classifications, respectively). Paraffin-embedded and frozen tumor samples were collected before and after ST for biomarker analysis. EGFR, IGF-1R, MET, cytokeratins 5/6 and 8/18, PTEN, P-cadherin, ALDH1, Ki-67, p53, tumoral FOXP3 expression and the number of FOXP3+ or CD8+ tumor-infiltrating lymphocytes (TIL) were evaluated by immunohistochemistry.

Results :.We have observed 9 recurrences: 1 local and 8 distant recidives, including 1 both local and distant.

The distant recidives (metastases) were as follows: brain (4 pts); brain and lungs (1 pt); lungs only (1 pt), pleura (1 pt); liver (1 pt). 6 out of the 8 metastatic pts died and all were non-pCR post-ST. The 2 alive pts had brain metastases, but reached a pCR after the ST.

Among the 9 relapsed pts 6 were 55 years old or less at the diagnosis. Seven out of those 9 pts had tumors with the clinical size equal or higher than 4 cm.

As previously reported (SABCS 2012, abstract 1081), the pCR-predictive biomarkers in this study were high CD8+ TIL count (p = 3.4.10−6) and high ratio between the CD8+ and FOXP3+ TIL counts (CD8+/FOXP3+ > 1.23, p = 8.5.10−5). With this in mind, we have evaluated whether those parameters, assessed before or after the ST, could predict the recurrences. No difference was found in the preoperative CD8+ and the FOXP3+ TIL counts, as well as in the CD8+/FOXP3+ ratio, between the patiens who have recurred and the others.

Conclusion : As it has been reported in previous studies, in our cohort of TNBC pts, the relapses occurred early after the administration of the last systemic treatment. The patients who relapsed died rapidly and most of them have not reached pCR after the ST. In addition, half of the metastatic pts got brain deposits. This implies that research on the resistance factors in TNBC should focus on those important for seeding of the “sanctuaries”, like brain. This research is ongoing in our group.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P3-14-19.

[Analysis of gene expression data regulated by clock-genes: methodological approach and optimization]

BACKGROUND

In microarray data, wide-scale correlations are numerous and increase the number of genes correlated to a test condition (phenotype, mutation status, etc.) either positively or negatively. Several methods have been developed to limit the effect of such correlations on the false discovery rate, but these may reject too many genes that have a mild or indirect impact on the studied condition. We propose here a simple methodology to correct this spurious effect without eliminating weak but true correlations.

RESULTS

This methodology was applied to a microarray dataset designed to distinguish heterozygous BRCA1 mutation carriers from non-carriers. As our samples were collected at different times in the morning, we evaluated the effect of correlations due to circadian rhythm. The circadian system is a well-known correlation network, regulated by a small number of period genes whose expression varies throughout the day in predictable ways. The downstream effects of this variation on the expression of other genes, however, are incompletely characterized. We used two different strategies to correct this correlation bias, by either dividing or multiplying the expression of correlated genes by the expression of the considered period gene according to the sign of the correlation between the period gene and correlated gene (respectively positive or negative).

CONCLUSIONS

We observed a linear relationship between the number of false-positive/negative genes and the strength of the correlation of the candidate gene to the test condition. BRCA1 was highly correlated to the period gene Per1; our correction methodology enabled us to recover genes coding for BRCA1-interacting proteins which were not selected in the initial direct analysis. This methodology may be valuable for other studies and can be applied very easily in case of well-known correlation networks.

Abstract P3-06-20: Is it possible to predict the efficacy of a combination of Panitumumab plus FEC 100 followed by docetaxel (T) for patients with triple negative breast cancer (TNBC)? Final biomarker results from a phase II neoadjuvant trial

Background: TNBC is an heterogeneous group of tumors for some of which the Epithelial Growth Factor Receptor pathway (EGFR) may play an important role. We evaluated the efficacy and toxicity of an anti-EGFR antibody (panitumumab) combined with a standard neoadjuvant chemotherapy in order to identify predictive biomarkers of efficacy and target biologically defined subpopulations for potential further development.

Methods: Sixty patients with stage II-IIIA disease were prospectively included in this multicentre neoadjuvant study. Systemic therapy (ST) consisted of panitumumab (9 mg/kg q.3 weeks x8) combined with FEC 100 (500/100/500 mg/m2q.3 weeks x4) followed by 4 cycles of T (100 mg/m2 q.3weeks x4). All patients underwent surgery at completion of ST.

Paraffin-embedded and frozen samples were systematically collected before and after ST for biologic studies.

Patients characteristics are as follows: mean age 50 [27–72]; median tumor size: 40 mm [20–120]; invasive ductal carcinoma: 96.7%; Scarff-Bloom-Richardson Grade III: 71.7%, grade II: 28.3%.

Complete pathological response (pCR) rate was 52.3% [95% IC: 37.3–67.5] (Sataloff's classification) and 46.7% [95% IC: 31.6–61.4](Chevallier's classification). Conservative surgery was performed in 88% of cases.

Skin toxicity was the main side-effect: Cutaneous toxicity grade IV: 5%, grade III: 30%, grade II: 20%. Neutropenia grade IV: 27%; febrile neutropenia: 5%. Infection: 0%. Hand-foot syndrome grade III: 3.3%. Ungueal toxicity grade III: 1.6%, grade II: 20%.

Results: We performed a ROC curve to identify the best cut-off value for KI-67, EGFR, cytokeratin 5–6 and p53 in order to predict a pCR.

Tumors with more than 40% of positive cells for KI-67 and tumors with a score for EGFR greater than 70 tend to be associated with pCR according to Chevallier's classification (p = 0.06). No predictive value was identified for Cytokeratin 5–6 and p53 (p = 0.61 and p = 0.27, respectively).

Immunohistochemistry results show that two thirds of tumors have more than 40% of positive cells for KI-67 and that two thirds of tumors present a score for EGFR greater than 70.

About half of the tumors express cytokeratin 5–6 and p53 (cut off: 1%).

Chi-squared tests were performed to assess relations between cutaneous toxicities and pCR.

The cutaneous toxicities were not predictive of pCR (p = 0.94) and no correlations were found with KI-67, EGFR, Cytokeratin 5–6 and p53.

In terms of BRCA1 and BRCA2 status, 35 tumors were analysed so far: BRCA1: 6 mutations (17%); BRCA2 (30 patients): 1 mutation (3.3%).

Conclusions: These results suggest the possibility to identify a subpopulation with high probability of pCR (KI-67 > 40%, EGFR score > 70).

Further biological studies are ongoing and will be presented at the meeting, including EGFR polymorphisms, C-met, ALDH1, pCadherine and PTEN.

This will help us further define subpopulations of TNBC patients, potential targets for antiEGFR development.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P3-06-20.

Report of a family segregating mutations in both the APC and MSH2 genes: juvenile onset of colorectal cancer in a double heterozygote

BACKGROUND AND AIMS

Mutations in DNA mismatch repair genes are associated with high risk of digestive malignancies [hereditary non-polyposis colorectal cancer (HNPCC); Lynch syndrome]; mutations of APC and MYH are associated with classic and attenuated familial adenomatous polyposis (FAP). Although the early onset of tumors in both syndromes is characteristic of their genetic origin, pediatric malignancies remain rare. Certain reports have found familial colorectal cancer (CRC) occurring in very young patients associated with mutations in more than one gene.

MATERIALS AND METHOD

A family corresponding to the Amsterdam criteria for HNPCC, including two cases of colorectal cancer before the age of 25 years, was analyzed for mutations in the MSH2 genes by sequencing. Because polyposis was observed in a patient who developed CRC at age 16, the APC gene was also sequenced.

RESULTS

A truncating mutation in the MSH2 gene, c.258_259delTG, was carried by patients developing cancer of the colon (two patients), uterus, kidney, bladder, and/or small intestine at ages 16, 24, 43, 44, 45, and 57, respectively. A patient with CRC at age 16 was found to carry the APC c.3183_3187del5 mutation as well as the MSH2 mutation, and it is inferred that her father, deceased of CRC at age 24, was also a double heterozygote.

INTERPRETATION

These results confirm that vigilance is required when interpreting molecular results for families with very young patients, as more than one gene may contribute to the genetic risk. Cancer screening measures must also be adapted to the earlier and more penetrant risk to double heterozygotes.

Complete mutation screening and haplotype characterization of BRCA1 gene in Tunisian patients with familial breast cancer

Breast cancer, the most commonly diagnosed cancer in women, is the second leading cause of cancer death in women worldwide. To investigate the contribution of BRCA1 gene mutations to familial breast cancer in Tunisia, 32 unrelated patients who had at least one first degree relative affected with breast and/or ovarian cancer were analysed. BRCA1 mutation analysis was performed by DNA sequencing of all BRCA1 exons. We identified four different BRCA1 frameshift mutations: c.4041delAG, c.2551delG and c.5266dupC already been described and one novel mutation, c.211dupA, observed in two unrelated families. C.5266dupC has previously been found among Jewish Ashkenazi and Eastern European populations. Our study describes it in Arabic/Berber population. Five out of thirty two familial cases had deleterious BRCA1 mutations. Fifteen additional cases carried unclassified variants (UV) or single nucleotide polymorphisms (SNPs). Our study is the first molecular investigation on the role of BRCA1 in hereditary breast cancer in North Tunisia.

Contribution of the BRCA1 and BRCA2 mutations to breast cancer in Tunisia

Hereditary breast cancer accounts for 3-8% of all breast cancers, with mutations in the BRCA1 and BRCA2 genes responsible for up to 30% of these. To investigate the prevalence of BRCA1 and BRCA2 gene mutations in breast cancer patients with affected relatives in Tunisia, we studied 36 patients who had at least one first degree relative with breast and/or ovarian cancer Thirty-four 34 patients were suggestive of the BRCA1 mutation and two were suggestive of the BRCA2 mutation, based on the presence of male breast cancer detected in their corresponding pedigrees. Four mutations in BRCA1 were detected, including a novel frame-shift mutation (c.211dupA) in two unrelated patients and three other frameshift mutations--c.4041delAG, c.2551delG and c.5266dupC. Our study is the first to describe the c.5266dupC mutation in a non-Jewish Ashkenazi population. Two frameshift mutations (c.1309del4 and c.5682insA) were observed in BRCA2. Nineteen percent (7/36) of the familial cases had deleterious mutations of the BRCA1 or BRCA2 genes. Almost all patients with deleterious mutations of BRCA1 reported a family history of breast and/or ovarian cancer in the index case or in their relatives. Our data are the first to contribute to information on the mutation spectrum of BRCA genes in Tunisia, and we give a recommendation for improving clinical genetic testing policy.

Immunolocalization of BRCA1 protein in tumor breast tissue: prescreening of BRCA1 mutation in Tunisian patients with hereditary breast cancer?

BRCA1 is a tumor suppressor gene which is inactivated by mutation in familial breast and ovarian cancers. Over 300 different disease causing germ-line mutations have been described; 60% are unique to an individual family. This diversity and the large size of the gene lead us to search for a prescreening method for BRCA1 mutations. Since BRCA1 is a nuclear protein in normal cells, but reported by some authors to be cytoplasmic in breast tumor cells of patients with BRCA1 mutation, we evaluated immunohistochemistry as a prescreening technique to identify BRCA1 mutations in patients with familial presentation of breast cancer. Using a monoclonal antibody against the carboxy-terminal region of BRCA1, we performed immunohistochemistry on 18 tumor samples from patients with hereditary breast cancer. Cytoplasmic staining of BRCA1 was observed in 10 cases. Of the 18 tumors, 12 (66%) showed either BRCA mutation or BRCA1 accumulation or both, indicating that BRCA1 function might be lost in breast tumor cells not only through mutation, but also via abnormal cytoplasmic location. The immunohistochemical test used in this study would not be efficient as a pre-screening method of deleterious mutations, but it appeared useful to investigate tumor physiology.

Syndrome de Werner (progeria de l’adulte)

Werner's syndrome (adult onset progeria) is a rare form of autosomal recessive genodermatosis associated in almost 80% of cases with mutation of the WRN gene. This prototype of rapid ageing syndromes is characterized by short stature with skin and hair anomalies (early graying of the hair, alopecia, depilation, sclerosed skin), orthopedic complications (flat foot, hallux valgus and other joint deformations) as well as systemic signs (early cataract, premature and diffuse atherosclerosis, endocrinopathies) and high risk of certain types of cancer (sarcomas, myeloid blood dyscrasias). Death occurs around the age of 40 - 50 years mainly as a result of cardiovascular accident or development of a malignant tumour. Signs of early aging should evoke this basic diagnosis and arrangements should be made for appropriate follow-up with screening for and treatment of systemic complications.

[p53 activation by PI-3K family kinases after DNA double-strand breaks]

p53 plays a central role in the cellular response to DNA double-strand breaks (DSBs), and to DNA damage in general. The protein kinases ATM, ATR and DNA-PK detect DSBs and transmit this information to p53 by phosphorylation. This phosphorylation dissociates p53 from its negative regulator, mdm2. p53 then undergoes further modification and activates transcription of the genes responsible for cell cycle arrest. In certain circumstances, p53 also activates transcription of the genes responsible for apoptosis. The dysfunction of this cascade of events is oncogenic, with P53 itself being the most commonly mutated gene in malignant cells, although mutations in both the DNA damage sensors and cell cycle checkpoint and apoptosis effectors are frequent. A more complete understanding of p53 and the proteins it interacts with may allow the development of new cancer treatments.

Allelic imbalance at NBS1 is frequent in both proximal and distal colorectal carcinoma

Nijmegen breakage syndrome (NBS) is a hereditary disorder involving chromosomal instability, cancer risk and radiosensitivity. NBS carriers have an increased risk of cancer, though the significance of mutations in the NBS1 gene in sporadic cancer has not yet been investigated. Because the loss of NBS1 is associated with increased chromosomal re-arrangements, and tumors of the colon are particularly prone to chromosomal anomalies, we have begun to study the NBS1 locus in colorectal cancer (CRC). DNA was isolated from 99 microdissected colorectal tumors, and microsatellite markers flanking the NBS1 locus at 8q21.3 as well as elsewhere on 8q were analyzed. Normal lymphocyte DNA from each patient served to normalize the amplification of each allele, and a reduction of at least 35% in the intensity of one allele was taken as evidence of allelic imbalance (AI). In proximal and distal CRCs we found 25.9 and 36.2% with AI at 8q21.3, respectively. AI in proximal CRC tended not to extend to marker D8S555 at 8q24.1, whereas in distal CRC the region of AI frequently included all the informative markers. AI of 8q21.3 was not associated with any clinical variable. These results suggest that 8q21.3 contains a tumor suppressor gene involved in proximal CRC, possibly NBS1. The large regions of AI make it difficult to determine the importance of AI at the NBS1 locus in distal CRC.

High incidence of cancer in a family segregating a mutation of the ATM gene: possible role of ATM heterozygosity in cancer

ATM mutations predispose cells to malignancy by promoting chromosomal instability. We have identified a family with multiple cancers that segregates a mutant allele of ATM, IVS61+2insTA, which causes skipping of exon 61 in the mRNA, as well as a previously undescribed polymorphism, IVS61+104C(54):T(46). The mutation was inherited by two sisters, one who developed breast cancer at age 39 and the second at age 44, from their mother, who developed kidney cancer at age 67. Molecular studies were undertaken to determine the role of the ATM gene in the development of cancer in this family. Studies of irradiated lymphocytes from both sisters revealed elevated numbers of chromatid breaks, typical of A-T heterozygotes. Studies on lymphoblastoid cell lines established from these individuals revealed abnormal p53 induction and apoptosis after DNA damage. Loss of heterozygosity (LOH) in the ATM region of chromosome 11q23.1 showed that the normal ATM allele was lost in the breast tumor of the older sister. LOH was not seen at the BRCA1 or BRCA2 loci. BRCA2 is not likely to be a cancer-predisposing gene in this family because each sister inherited different chromosomes 13 from each parent. The sisters share their maternal BRCA1 allele, although no mutation in this gene was detected in the family. Our findings suggest that haploinsufficiency at ATM may promote tumorigenesis, even though LOH at the locus supports a more classic two-hit tumor suppressor gene model.

Physical map of the region surrounding the ataxia-telangiectasia gene on human chromosome 11q22-23

Ataxia telangiectasia (A-T) is an autosomal recessive disease affecting multiple systems, including the development of the cerebellum and thymus. This results in a progressive cerebellar ataxia with onset between 1-3 years, telangiectasia occurs within the subsequent 3-5 years. We localized the A-T gene by linkage analysis to chromosome 11q22-23, between the markers D11S384, and D11S535, and constructed a series of contigs using three BACs and twelve cosmids, spanning a region of approximately 400 kb. We developed a set of sequence-tagged site (STS) markers from the ends of the BACs and cosmids. The A-T gene was isolated from within this region. It is now possible to precisely orient specific BACs, cosmids, and STSs with respect to the exons of the A-T gene (ATM). We anticipate that this information will be useful for further studies of functional domains and regulatory elements within the ATM gene, as well as for other genes in this region. In addition, these clones can be used for FISH studies of deletions, translocations and for loss of heterozygosity in various tumors.

Human fibroblasts transfected with an ATM antisense vector respond abnormally to ionizing radiation

ATM, the gene mutated in ataxia-telangiectasia (A-T), mediates multiple cellular responses to DNA damage. A-T homozygotes have a high risk of cancer and exhibit spontaneous chromosomal instability, and cultured A-T cells react abnormally to ionizing radiation. We have developed an ATM antisense vector that confers an A-T phenotype on normal cells. An episomal antisense vector was created that contained a 1.3 kb segment of the ATM cDNA, and was transfected into normal human fibroblasts. Intracellular levels of ATM protein were typically reduced 10-fold in antisense-expressing (GM639-46alpha) clones. GM639-46alpha clones exhibited the low threshold for radiation-induced apoptosis, low clonogenic survival, and cell cycle defects normally seen in A-T cells. Transfection with the corresponding ATM sense strand vector had no effect on the behavior of normal cells, and neither vector affected the behavior of A-T cells. Our results demonstrate that interference with ATM gene expression recreates the A-T phenotype in normal cells, and provide functional evidence linking the ATM gene to cellular DNA damage responses. The ATM antisense vector should prove a useful tool for studying ATM function in a variety of normal, mutant, and malignant cell lines.

ATM heterozygote cells exhibit intermediate levels of apoptosis in response to streptonigrin and etoposide

Ataxia-telangiectasia (A-T) is a rare recessive disease characterised by cerebellar ataxia, immunodeficiency, sensitivity to ionising radiation and increased cancer risk. Heterozygotes have an increased risk of cancer and may comprise 1% of the population. In vitro, A-T heterozygote cell lines show radiosensitivity intermediate between normal and A-T homozygotes. Furthermore, in A-T homozygotes, hypersensitivity to chemical agents which cause DNA damage, similar to that produced by ionising radiation, has been observed. To investigate the chemosensitivity of A-T heterozygote cell lines, we used TUNEL to analyse the level of apoptosis after drug treatment with etoposide and streptonigrin. Our samples included four normal, eight A-T heterozygote and 10 A-T homozygote lymphoblastoid cell lines. All cell lines were exposed to drugs for 24 h, then cultivated in fresh media for 0 and 72 h. The levels of apoptosis increased significantly in all cell lines, with the greatest increase in homozygote cells and an intermediate increase in heterozygote cells (P values of < 0.01 for etoposide treatment and < 0.02 for streptonigrin treatment were obtained using the Kruskal-Wallis H-test). Our results indicate that A-T heterozygotes express intermediate sensitivity to etoposide and streptonigrin similar to that observed in response to ionising radiation.

Loss of heterozygosity at the ATM locus in colorectal carcinoma

Patients homozygous for mutation of the ATM gene exhibit constitutional genetic instability and have a high risk of cancer. A-T heterozygotes also have an increased tendency to develop adenocarcinomas. Colorectal cancer (CRC) is the second most common cancer in western populations, and tumors of the right colon are typically highly genetically unstable. The DNA mismatch repair genes mutated in most familial and some sporadic CRCs account for one route by which cells acquire additional oncogenic mutations during the progression of malignancy. Mismatch repair defects, however, do not seem to account for the majority of CRCs. Because of its role in maintaining genomic stability, and the high risk of cancer to homozygotes, ATM is a candidate gene for inactivation in the evolution of chromosomal instability in tumor cells. We have examined 114 CRC patients for loss of heterozygosity (LOH) using six microsatellite markers tightly linked to the ATM locus. Our data suggest that LOH of this region is not associated with cancer of the proximal colon. In the distal colon, LOH was found in 23-31% of cases, which is moderately elevated above the non-specific LOH reported in tumors of this tissue. No correlations were found with regard to clinicopathological variables aside from tumor location.

Seventh International Workshop on Ataxia-Telangiectasia

Ataxia-telangiectasia (A-T) is a rare hereditary syndrome involving cerebellar degeneration, immunodeficiency, cancer risk, and radiosensitivity. Since the cloning of the A-T gene, ATM, in 1995, research on this pleiotropic disease and its molecular basis has expanded tremendously. ATM is a large protein kinase that appears to be one of the primary sensors of DNA strand-break damage. The vast majority of mutations in ATM result in truncation and destabilization of the protein, but certain missense and splicing errors have been shown to result in a less severe phenotype. A-T heterozygotes have been shown to have a slightly increased risk of cancer, but their increased in vitro radiosensitivity does not seem to result in any in vivo sensitivity. ATM does seem to act as a classic tumor suppressor gene in T-prolymphocytic leukemia, and LOH at the ATM locus is a common event in some tumor types, suggesting a general role for ATM in cancer. Recent work has shown the interaction of ATM with proteins involved in cell cycle control, and the direct phosphorylation of some of these interactors by ATM. ATM knockout mice have been created by several groups, and recapitulate the immunodeficiency, radiosensitivity, cancer risk, and fertility defects of A-T, although the effect on the cerebellum is slight. These diverse topics, and their integration into a global understanding of A-T, were the basis of the 7th International A-T Workshop.

No evidence for constitutional ATM mutation in breast/gastric cancer families

Ataxia-Telangiectasia (A-T) is a rare autosomal recessive disease characterised by cutaneous telangiectasia, cerebellar ataxia, immunodeficiency, high sensitivity to ionising radiation, chromosomal instability and an increased risk of cancer. The gene mutated in A-T patients, ATM, is located on chromosome 11q22-23. ATM heterozygotes are thought to have a high tendency to develop malignancies, such as breast cancer. In order to determine the contribution of heterozygous ATM mutation to cancer, studies of cancer-affected patients have been undertaken in non site-specific cancer families and sporadic breast cancer cases. No evidence of an important role of ATM heterozygous mutations has been shown. In order to give another contribution to these results, we tried to define a specific family phenotype according to the most common cancers observed in ATM heterozygotes. Breast and gastric cancers appear to be the most frequent malignancies in A-T carriers and one ATM germ-line mutation has been described in a breast/gastric cancer family. Therefore we further investigated the role of ATM mutation in additional breast/gastric cancer families. In eighteen families associating these two malignancies, we used the protein transcription/translation test to detect ATM mutations in the index case from each family. We found one case of ATM mutation which did not cosegregate with the gastric cancer in the family.

CAND3: a ubiquitously expressed gene immediately adjacent and in opposite transcriptional orientation to the ATM gene at 11q23.1

Using a magnetic beads-mediated cDNA selection procedure and a fetal brain expression library, we identified a transcriptional unit within a cosmid positive for the marker D11S384. Pursuit of its full-length cDNA led to the cloning of the third candidate gene (CAND3) we studied in our quest for the ataxia-telangiectasia (A-T) gene, ATM. CAND3 spans approximately 140 kb of genomic DNA and is located immediately centrimeric to ATM, with 544 bp of DNA separating the two genes. CAND3 encodes two ubiquitously expressed transcripts of approximately 5.8 kb and approximately 4.6 kb that are divergently transcribed from a promoter region common to ATM. Nucleotide sequence was determined for one of its alternately spliced transcripts. The predicted protein has 1175 amino acids and is novel in sequence, with only weak homologies to transcriptional factors, nucleoporin protein, and protein kinases, including members of the phosphatidylinositol 3-kinase (PI-3 kinase) family. Although neither homology to ATM nor any mutation of CAND3 in A-T patients has been found, the head-to-head arrangement of CAND3 and ATM, with expression of both housekeeping genes from a common stretch of 544 bp intergenic DNA, suggests a bi-directional promoter possibly for co-regulation of biologically related functions. YACs, BACs, cosmids, and STSs are defined to aid in further study of this gene.

Sublocalization of an ataxia-telangiectasia gene distal to D11S384 by ancestral haplotyping in Costa Rican families

In an effort to localize a gene for ataxia-telangiectasia (A-T), we have genotyped 27 affected Costa Rican families, with 13 markers, in the chromosome 11q22-23 region. Significant linkage disequilibrium was detected for 9/13 markers between D11S1816 and D11S1391. Recombination events observed in these pedigrees places A-T between D11S1819 and D11S1960. One ancestral haplotype is common to 24/54 affected chromosomes and roughly two-thirds of the families. Inferred (ancestral) recombination events involving this common haplotype in earlier generations suggest that A-T is distal to D11S384 and proximal to D11S1960. Several other common haplotypes were identified, consistent with multiple mutations in a single gene. When considered together with all other evidence, this study further sublocalizes the major A-T locus to approximately 200 kb, between markers S384 and S535.

Genetic haplotyping of ataxia-telangiectasia families localizes the major gene to an approximately 850 kb region on chromosome 11q23.1

The genotyping data given localize the major A-T gene to an approximately 850 kb region. They also localize the group A A-T gene (ATA) to a region that contains the approximately 850 kb region. They are compatible with linking A-TFresno to 11q22-23. NBS-V2 does not link to this region. Four non-linking families contain only single affecteds, suggesting that these may be spontaneous mutations rather than evidence for an A-T gene outside the 11q22-23 region. Finally, two other non-linking families contain recombinant haplotypes that are compatible with a second A-T gene at 11q22-23, slightly distal to the approximately 850 kb region. However, convincing evidence for a second gene is still lacking.

Genetic haplotyping of ataxia-telangiectasia families localizes the major gene to an approximately 850 kb region on chromosome 11q23.1

The genotyping data given localize the major A-T gene to an approximately 850 kb region. They also localize the group A A-T gene (ATA) to a region that contains the approximately 850 kb region. They are compatible with linking A-TFresno to 11q22-23. NBS-V2 does not link to this region. Four non-linking families contain only single affecteds, suggesting that these may be spontaneous mutations rather than evidence for an A-T gene outside the 11q22-23 region. Finally, two other non-linking families contain recombinant haplotypes that are compatible with a second A-T gene at 11q22-23, slightly distal to the approximately 850 kb region. However, convincing evidence for a second gene is still lacking.

A pulsed-field gel electrophoresis map in the ataxia-telangiectasia region of chromosome 11q22.3

Our interest in isolating the gene(s) for ataxia-telangiectasia has prompted us to construct a physical map of chromosome 11q22.3 using markers localized to this region by linkage analysis and/or hybrid cell panels. Twenty-two markers have been analyzed by pulsed-field gel electrophoresis. Nine of these markers form an approximately 2-Mb long-range contiguous map. An average distance of 200 kb between probes in this map should facilitate the isolation of new cDNAs, anonymous probes, and YACs in an orderly way.

Juvenile GM2 gangliosidosis caused by substitution of histidine for arginine at position 499 or 504 of the alpha-subunit of beta-hexosaminidase

Juvenile GM2 gangliosidosis is a rare neurodegenerative disorder closely related to Tay-Sachs disease but of later onset and more protracted course. The biochemical defect lies in the alpha-subunit of the lysosomal enzyme beta-hexosaminidase. Cultured fibroblasts derived from patient A synthesized an alpha-subunit which could acquire mannose 6-phosphate and be secreted, but which failed to associate with the beta-subunit to form the enzymatically active heterodimer. By contrast, fibroblasts from patient B synthesized an alpha-subunit that was retained in the endoplasmic reticulum. To identify the molecular basis of the disorder, RNA from fibroblasts of these two patients was reverse-transcribed, and the cDNA encoding the alpha-subunit of beta-hexosaminidase was amplified by the polymerase chain reaction (PCR) in four overlapping fragments. The PCR fragments were subcloned and shown by sequence analysis to contain a G to A transition corresponding to substitution of histidine for arginine at position 504 in the case of patient A and at position 499 in the case of patient B. The mutations were confirmed by hybridization of allele-specific oligonucleotides to PCR-amplified fragments of DNA corresponding to exon 13 of the alpha-subunit gene. The Arg504----His mutation was found on both alleles of patient A as well as of another unrelated patient; the homozygosity of this mutant allele is attributable to consanguinity in the two families. The Arg499----His mutation was found in patient B in compound heterozygosity with a common infantile Tay-Sachs allele. There is additional heterogeneity in juvenile GM2 gangliosidosis, as neither mutation was found in the DNA of a fourth patient. The Arg----His mutations at positions 499 and 504 are located at CpG dinucleotides, which are known to be mutagenic "hot spots."

Regulation of expression of an auxin-induced soybean sequence by cadmium

An auxin-regulated soybean sequence has been characterized and shown to be induced by the heavy metals cadmium, silver, and copper. Cadmium induces the accumulation of two size classes of mRNA: a 1-kilobase (kb) RNA class, which is the same size as the RNA class induced by auxin, silver, and copper, and a 1.4-kb RNA class. DNA sequence analysis of cDNA clones and a soybean genomic fragment has shown the presence of an intron in this gene. A restriction fragment probe isolated from the intron segment hybridizes specifically to the 1.4-kb mRNA. The transcription rate of this sequence is rapidly increased following exposure of soybean primary leaves to cadmium, as assayed by nuclear run-off transcription experiments. These results suggest that cadmium not only induces the transcription of a specific soybean sequence, but interferes with the processing of the precursor mRNA, resulting in the accumulation of the 1.4-kb mRNA precursor species.