Abstract P2-09-09: Initial safety and efficacy of a phase I/IIa trial of a modified whole tumor cell targeted immunotherapy in patients with advanced breast cancer

Background: SV-BR-1-GM is a GM-CSF transfected breast cancer cell line which expresses HLA class I & II antigens. In a previous clinical trial, a partial response of widely metastatic breast cancer was seen in a patient who matched SV-BR-1-GM at HLA-DRB3*02:02. Here we report the safety and efficacy analysis with immunologic correlates of response in the initial patients in a phase I/IIa trial of SV-BR-1-GM in patients with advanced breast cancer

Methods: This phase I/IIa trial enrolled patients with recurrent and/or metastatic breast cancer refractory to standard chemotherapy/targeted-therapy. Patients received low-dose cyclophosphamide 2-3d prior to intradermal injection of SV-BR-1-GM (20x106 cells divided into 4 sites) and interferon-α into the inoculation sites (10,000 IU/site) ˜2 & 4 days subsequently. Cycles were 2 weeks x3 then q mo x 3. Adverse events (AE) were evaluated after each inoculation and graded via CTCAE v4.03. Immunologic response was measured by delayed type hypersensitivity (DTH) after each inoculation. Disease response was evaluated radiographically q3 mo and as clinically indicated (clinical trial NCT03066947).

Results: To date, twenty-two patients have been enrolled and 17 have been inoculated for a total of 39 SV-BR-1-GM inoculations given. Per inoculation, the maximum related AE was grade 1 in 64%, grade 2 in 7.7%, and grade 3 in 7.7%. There were no related grade >3 or unexpected AE. Efficacy data is available on the first six (Table). Tumor regression was seen in 2 patients. 01-002 presented with liver, bone and 20 classic miliary lung metastases (up to 9mm). This subject previously received 7 chemotherapy regimens. She matched SV-BR-1-GM at Class I & II HLA loci. Imaging at 3 mo showed virtually complete regression of all 20 identifiable lesions in the lungs. This response was maintained at 6 mo but the subject was taken off protocol because of disease progression (liver and bone). 01-005, matching HLA-A*24:02, had notable regression of cutaneous lesions, but progressed in pleural and pericardial effusions, had irreversible cardiac arrest (unlikely related). DTH increased in 01-002 from 4mm (first dose) to 47mm (8th dose). Three of 3 patients evaluated developed antibodies responses (as measured by flow cytometry with SV-BR-1) including 01-002. Interleukin 8 also increased in 01-002.

Conclusions: SV-BR-1-GM in this regimen appears to be safe and well-tolerated. In this initial exploratory analysis, SV-BR-1-GM can produce regression of pre-treated metastatic breast cancer correlating with an immunologic response. HLA matching is being evaluated as a predictor of response.

PatientAgeMetastatic Sites# Prior RegimensHLA Matches# of CyclesTumor Regression?01-00146Pleura, Lymph Nodes7 chemo/bio, 5 hormonalDRB3*02:021No01-00273Lung, Liver, Bone6 chemo, 1 hormonalA*24:02, DRB3*02:028Lungs01-00554Lymph nodes, Pleura, Skin3 chemo/bioA*24:022Skin02-00170Lymph nodes1 chemo/bioNone1No02-00361Bone, Brain3 chemoNone6No02-00474Lymph nodes, Cutaneous3 chemo/bio, 1 hormonalDRB3*02:022Lost to Follow-up

Citation Format: Bhattacharya S, Holmes JP, Calfa C, Lukas J, Tan-Chiu E, Clifton GT, Peoples GE, Lacher M, Wiseman CL, Williams WV. Initial safety and efficacy of a phase I/IIa trial of a modified whole tumor cell targeted immunotherapy in patients with advanced 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 P2-09-09.

Tumor aggressiveness risk factors in the differentiated thyroid carcinoma

BACKGROUND

The differentiated thyroid carcinoma (DTC) is the most frequent malignancy in endocrinology (95%). Our aim was to retrospectively compare risk factors of tumor aggressiveness and history of thyroid disease in patients with conventional DTC and differentiated thyroid microcarcinoma (DTMC).

METHODS

Retrospective analysis of 167 patients after total thyroidectomy with a histologically confirmed DTC, of which 83 patients with conventional DTC (> 1 cm) and 84 with DTMC (≤ 1 cm). The analyzed factors were tumor size, its aggressiveness (i.e. multifocal or bilateral occurrence, angioinvasion, extracapsular growth, presence of cervical lymph node metastases, distant metastases, and early local relapse) and medical history of thyroid diseases.

RESULTS

In the DTMC group, there were 80/84 (95.2%) papillary carcinomas compared with 58/83 (69.9%) in the conventional DTC group (p=0.001). Patients with DTMC were significantly older than those with conventional DTC (p=0.006). In the conventional DTC group, there was a significantly higher occurrence of angioinvasion and extracapsular growth (p=0.001), cervical lymph node metastases (p=0.013), relapse (p=0.018), and distant metastases (p=0.007), compared with the DTMC group.

CONCLUSION

In patients with DTMC, there was a significantly lower presence of risk factors of tumor aggressiveness, compared with the conventional DTC group (Tab. 2, Ref. 17).

Correlation among the BRAF gene mutation status, clinicopathological features of primary tumour, and lymph node metastasizing of papillary thyroid carcinoma

BACKGROUND

Papillary thyroid carcinoma (PTC) is the most common malignant thyroid tumour. A common mutation of papillary thyroid carcinoma (PTC) is the somatic mutation of the BRAF (V600E) gene.

AIM

The aim was to 1) determine the association of lymph node metastases of PTC with the BRAF gene mutation of primary tumour; 2) evaluate association of the BRAF mutation in the -primary tumour with clinicopathological para-meters; 3) examine the extent of genetic heterogeneity by monitoring the BRAF mutation in multicentric tumours.

SUBJECTS AND METHODS

Retrospective analysis of the BRAF (V600E) mutation in PTC and PTC neck lymph node metastases in 156 patients operated from 2003 to 2012 in Prague and Zlín, the Czech Republic, using a qPCR assay. The results were correlated with clinicopathological factors.

RESULTS

DNA was successfully extracted from 137 samples. The BRAF (V600E) mutation was detected in 78 cases (56.9%). The patients with BRAF p.Val600Glu mutation of primary tumour had only non-significantly higher risk of cervical lymph node metastases [OR=2.39 (95%) CI 1.00-5.75, p=0.052]. In the classic papillary variant, the BRAF (V600E) mutation was found significantly more often than in other PTC subtypes (p=0.022). We did not confirm any significant association between the BRAF (V600E) mutation and other clinicopathological findings.

CONCLUSION

Except for the higher prevalence in papillary variant of PTC, BRAF p.Val600Glu mutation was not associated with other prognostic clinicopathological factors of PTC. BRAF mutation cannot be regarded as a reliable marker of node metastases in patients with PTC.

Treatment difficulty with acute GVHD - frequent cause of mortality after allogeneic hematopoietic stem cell transplantation

OBJECTIVE

Acute graft-versus-host disease (aGvHD) remains a significant cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (HSCT).

METHODS

In this study, we have retrospectively evaluated the major risk factors for the development of aGvHD in 100 patients who underwent allogeneic transplantation at the University Hospital in Bratislava between January 2007 and December 2011.

RESULTS

29 patients acquired acute GvHD (Grade I - 12 patients, G II - 5 , G III - 3, G IV - 9). We proved a higher incidence of developing aGvHD in patients with unrelated donor type, TBI conditioning and cyclosporine (CsA) replacement with mycophenolate mofetil due to CsA nephrotoxicity, while other risk factors such as older patient age, the use of peripheral blood progenitor cells and donor/recipient sex mismatch were without statistical significance. The average time of onset of aGvHD has been 57 days (range 13-260) after HSCT. Corticosteroids were used as standard initial therapy with 52 % complete response (CR) rate, although the likelihood of response rapidly decreased with increasing severity of disease (G IV - 100 % refracterness). The response to primary therapy also correlated with overall survival. Patients with steroid-refractory aGvHD received a different second-line therapies (antithymocyte globulin, anti-TNFα antibody, anti CD52 antibody) with response rate 45 % (CR - 18 %, PR - 27 %).

CONCLUSION

Outcome for the patients with steroid-refractory aGvHD was poor, disease very often returned or progressed with one year mortality rate 81 % , that represents an important therapeutic problem (Tab. 2, Ref. 10).

Combined therapy with cyclodextrin/allopregnanolone and miglustat improves motor but not cognitive functions in Niemann-Pick Type C1 mice

Niemann-Pick Type C1 (NPC1) is an autosomal recessive disorder characterized by the accumulation of cholesterol and glycosphingolipids. Combination-treatment utilizing cyclodextrin, allopregnanolone and miglustat (CYCLO/ALLO/miglustat) can ameliorate NPC1 disease in a mutant mouse model. The present study was designed to add behavioral analysis in NPC1 mutant mice upon CYCLO/ALLO/miglustat therapy. NPC1 mutant (BALB/cJ NPC1NIH) and control mice were used. For the combination treatment mice were injected with CYCLO/ALLO weekly, starting at P7. The miglustat injection was performed daily from P10 till P23. Starting at P23, miglustat was added to the powdered chow. For the sham treatment of control and mutant mice the same schedule was used with 0.9% NaCl injection. Locomotor activity was assessed in open field, elevated plus maze and accelerod tests. For assessment of spatial learning and memory the Morris water maze test was conducted. Electron microscopy has been performed to support the behavioral data. The sham-treated mutant mice exhibited motor impairments in all performed tests. In the water maze the sham-treated mutants exhibited impairment in remembering the location of the hidden platform. CYCLO/ALLO/miglustat treatment positively influenced motor dysfunction: total distance and number of visits significantly increased, and accelerod performance improved. The spatial learning, however, did not benefit from therapy. At the morphological level, an excessive accumulation of electron-dense material was seen in the cerebellar Purkinje cells of mutant mice. A regression of these autophagosomal inclusions was seen upon therapy. CYCLO/ALLO/miglustat therapy ameliorates motor but not cognitive deficits in NPC1 mutant mice, suggesting unequal vulnerability of different brain areas to the treatment.

Nucleoporin NUP153 guards genome integrity by promoting nuclear import of 53BP1

53BP1 is a mediator of DNA damage response (DDR) and a tumor suppressor whose accumulation on damaged chromatin promotes DNA repair and enhances DDR signaling. Using foci formation of 53BP1 as a readout in two human cell lines, we performed an siRNA-based functional high-content microscopy screen for modulators of cellular response to ionizing radiation (IR). Here, we provide the complete results of this screen as an information resource, and validate and functionally characterize one of the identified 'hits': a nuclear pore component NUP153 as a novel factor specifically required for 53BP1 nuclear import. Using a range of cell and molecular biology approaches including live-cell imaging, we show that knockdown of NUP153 prevents 53BP1, but not several other DDR factors, from entering the nuclei in the newly forming daughter cells. This translates into decreased IR-induced 53BP1 focus formation, delayed DNA repair and impaired cell survival after IR. In addition, NUP153 depletion exacerbates DNA damage caused by replication stress. Finally, we show that the C-terminal part of NUP153 is required for effective 53BP1 nuclear import, and that 53BP1 is imported to the nucleus through the NUP153-importin-β interplay. Our data define the structure-function relationships within this emerging 53BP1-NUP153/importin-β pathway and implicate this mechanism in the maintenance of genome integrity.

p53-dependent G(1) arrest in 1st or 2nd cell cycle may protect human cancer cells from cell death after treatment with ionizing radiation and Chk1 inhibitors

OBJECTIVES

This study was performed to explore the strategy of combining Chk1 inhibitors with ionizing radiation (IR) to selectively target p53-deficient cancer cells.

MATERIALS AND METHODS

Survival and cell cycle progression were measured in response to IR and the Chk1 inhibitors, UCN-01 and CEP-3891, in colon carcinoma HCT116 p53+/+ and p53-/- cells, and in osteosarcoma U2OS-VP16 cells with conditional expression of dominant-negative p53 (p53DD).

RESULTS

Clonogenic survival was selectively reduced in HCT116 p53-/- compared to p53+/+ cells after treatment with UCN-01 and IR, and HCT116 p53+/+ cells also displayed strong p53-dependent G(1) arrest in the 1st cell cycle after IR. In contrast, clonogenic survival was affected similarly in U2OS-VP16 cells with and without expression of p53DD. However, death of U2OS-VP16 cells was p53 dependent as assessed by cell viability assay at 72 h, and this was associated with p53-dependent G(1) arrest in the 2nd cell cycle after treatment. Notably, HCT116 cells were overall more resistant than U2OS cells to cytotoxic effects of Chk1 inhibitors.

CONCLUSION

Our results suggest that p53-dependent G(1) arrest in both 1st and 2nd cell cycles may protect human cancer cells from cell death after treatment with IR and Chk1 inhibitors. However, a challenge for future clinical use will be that different cancers display different intrinsic sensitivity to such inhibitors.

Replication stress and oxidative damage contribute to aberrant constitutive activation of DNA damage signalling in human gliomas

Malignant gliomas, the deadliest of brain neoplasms, show rampant genetic instability and resistance to genotoxic therapies, implicating potentially aberrant DNA damage response (DDR) in glioma pathogenesis and treatment failure. Here, we report on gross, aberrant constitutive activation of DNA damage signalling in low- and high-grade human gliomas, and analyze the sources of such endogenous genotoxic stress. Based on analyses of human glioblastoma multiforme (GBM) cell lines, normal astrocytes and clinical specimens from grade II astrocytomas (n=41) and grade IV GBM (n=60), we conclude that the DDR machinery is constitutively activated in gliomas, as documented by phosphorylated histone H2AX (gammaH2AX), activation of the ATM-Chk2-p53 pathway, 53BP1 foci and other markers. Oxidative DNA damage (8-oxoguanine) was high in some GBM cell lines and many GBM tumors, while it was low in normal brain and grade II astrocytomas, despite the degree of DDR activation was higher in grade II tumors. Markers indicative of ongoing DNA replication stress (Chk1 activation, Rad17 phosphorylation, replication protein A foci and single-stranded DNA) were present in GBM cells under high- or low-oxygen culture conditions and in clinical specimens of both low- and high-grade tumors. The observed global checkpoint signaling, in contrast to only focal areas of overabundant p53 (indicative of p53 mutation) in grade II astrocytomas, are consistent with DDR activation being an early event in gliomagenesis, initially limiting cell proliferation (low Ki-67 index) and selecting for mutations of p53 and likely other genes that allow escape (higher Ki-67 index) from the checkpoint and facilitate tumor progression. Overall, these results support the potential role of the DDR machinery as a barrier to gliomagenesis and indicate that replication stress, rather than oxidative stress, fuels the DNA damage signalling in early stages of astrocytoma development.

DNA damage signalling guards against activated oncogenes and tumour progression

DNA damage response (DDR), the guardian of genomic integrity, emerges as an oncogene-inducible biological barrier against progression of cancer beyond its early stages. Recent evidence from both cell culture and animal models as well as analyses of clinical specimens show that activation of numerous oncogenes and loss of some tumour suppressors result in DNA replication stress and DNA damage that alarm the cellular DDR machinery, a multifaceted response orchestrated by the ATR-Chk1 and ATM-Chk2 kinase signalling pathways. Such activation of the DDR network leads to cellular senescence or death of oncogene-transformed cells, resulting in delay or prevention of tumorigenesis. At the same time, the ongoing chronic DDR activation creates selective pressure that eventually favours outgrowth of malignant clones with genetic or epigenetic defects in the genome maintenance machinery, such as aberrations in the ATM-Chk2-p53 cascade and other DDR components. Furthermore, the executive DDR machinery is shared by at least two anticancer barriers, as both the oncogene-induced DNA replication stress and telomere shortening impact the cell fate decisions through convergence on DNA damage signalling. In this study, we highlight recent advances in this rapidly evolving area of cancer research, with particular emphasis on mechanistic insights, emerging issues of special conceptual significance and discussion of major remaining challenges and implications of the concept of DDR as a tumorigenesis barrier for experimental and clinical oncology.

The DNA damage signalling kinase ATM is aberrantly reduced or lost in BRCA1/BRCA2-deficient and ER/PR/ERBB2-triple-negative breast cancer

The ataxia-telangiectasia-mutated (ATM) kinase is a key transducer of DNA damage signals within the genome maintenance machinery and a tumour suppressor whose germline mutations predispose to familial breast cancer. ATM signalling is constitutively activated in early stages of diverse types of human malignancies and cell culture models in response to oncogene-induced DNA damage providing a barrier against tumour progression. As BRCA1 and BRCA2 are also components of the genome maintenance network and their mutations predispose to breast cancer, we have examined the ATM expression in human breast carcinomas of BRCA1/2 mutation carriers, sporadic cases and familial non-BRCA1/2 patients. Our results show that ATM protein expression is aberrantly reduced more frequently among BRCA1 (33%; P=0.0003) and BRCA2 (30%; P=0.0009) tumours than in non-BRCA1/2 tumours (10.7%). Furthermore, the non-BRCA1/2 tumours with reduced ATM expression were more often estrogen receptor (ER) negative (P=0.0002), progesterone receptor (PR) negative (P=0.004) and were of higher grade (P=0.0004). In our series of 1013 non-BRCA1/2 cases, ATM was more commonly deficient (20%; P=0.0006) and p53 was overabundant (47%; P<0.0000000001) among the difficult-to-treat ER/PR/ERBB2-triple-negative subset of tumours compared with cases that expressed at least one of these receptors (10 and 16% of aberrant ATM and p53, respectively). We propose a model of 'conditional haploinsufficiency' for BRCA1/2 under conditions of enhanced DNA damage in precancerous lesions resulting in more robust activation and hence increased selection for inactivation or loss of ATM in tumours of BRCA1/2 mutation carriers, with implications for genomic instability and curability of diverse subsets of human breast cancer.

DNA damage response in human testes and testicular germ cell tumours: biology and implications for therapy

DNA damage response (DDR) is emerging as a physiological anti-cancer barrier in early stages of cancer development, as shown for several types of solid cancers derived from somatic cells. Here we discuss our recently published and unpublished results on the exceptional paucity of such constitutive activation of the DDR machinery in human testicular germ cell tumours (TGCTs), including their common pre-invasive stage of carcinoma in situ (CIS). Our conclusions are supported by immunohistochemical analyses of multiple markers of activated DNA damage signalling, such as the phosphorylated ATM and Chk2 checkpoint kinases and phosphorylated histone H2AX. We propose that the unique lack of DDR activation in TGCTs reflects the biology of their cell of origin, the gonocyte. Furthermore, we propose that the lack of DDR activation avoids the pressure to select for mutations in DDR genes such as p53 or ATM, and the resulting intact DDR machinery may have implications for the exceptional curability of TGCTs by DNA damaging therapies.

DNA damage response mediators MDC1 and 53BP1: constitutive activation and aberrant loss in breast and lung cancer, but not in testicular germ cell tumours

MDC1 and 53BP1 are critical components of the DNA damage response (DDR) machinery that protects genome integrity and guards against cancer, yet the tissue expression patterns and involvement of these two DDR adaptors/mediators in human tumours remain largely unknown. Here we optimized immunohistochemical analyses of human 53BP1 and MDC1 proteins in situ and identified their virtually ubiquitous expression, both in proliferating and quiescent, differentiated tissues. Focus formation by 53BP1 and/or MDC1 in human spermatogenesis and subsets of breast and lung carcinomas indicated physiological and 'pathological' activation of the DDR, respectively. Furthermore, aberrant reduction or lack of either protein in significant proportions of carcinomas supported the candidacy of 53BP1 and MDC1 for tumour suppressors. Contrary to carcinomas, almost no activation or loss of MDC1 or 53BP1 were found among testicular germ-cell tumours (TGCTs), a tumour type with unique biology and exceptionally low incidence of p53 mutations. Such concomitant presence (in carcinomas) or absence (in TGCTs) of DDR activation and DDR aberrations supports the roles of MDC1 and 53BP1 within the ATM/ATR-regulated checkpoint network which, when activated, provides an early anti-cancer barrier the pressure of which selects for DDR defects such as p53 mutations or loss of 53BP1/MDC1 during cancer progression.

‘Blind’ antibiotic treatment targeting Chlamydia is not effective in patients with MALT lymphoma of the ocular adnexa

BACKGROUND

Recent results have implicated Chlamydia, especially Chlamydia psittaci, in the development of ocular adnexal lymphoma in the large majority of patients. We present our experience with ex-juvantibus antibiotic treatment in patients diagnosed with MALT lymphoma of the ocular adnexa.

PATIENTS AND METHODS

A retrospective analysis identified a total of 11 patients (six female, five male) with MALT-lymphoma of the ocular adnexa who were given doxycyclin 200 mg p.o. daily over 3 weeks. Patients were tested also for autoimmune conditions, Helicobacter status and hepatitis along with assessment of MALT-lymphoma specific genetic changes.

RESULTS

After a median follow-up of 9 months, none of the patients responded to 'blind' antibiotic treatment with doxycyclin. Only one patient with bilateral conjunctival lymphoma related a short lasting subjective improvement, but was referred to alternative therapy due to progression and worsening symptoms after 6 months.

CONCLUSIONS

In this uncontrolled series, no effect of 'blind' antibiotic treatment with doxycyclin could be found in our patients with MALT lymphoma of the ocular adnexa. These results are in contrast to other series and suggest a potential geographic difference in the role of Chlamydia in ocular adnexal lymphoma. Thus, antibiotic therapy without prior testing for Chlamydia should be discouraged.

Fine-needle aspiration biopsy in the diagnostic of the tumors and non-neoplastic lesions of salivary glands

OBJECTIVES

Fine-needle aspiration biopsy (FNAB) has not been part of the basic algorithm of preoperative evaluation of tumors of the major salivary glands in the Czech Republic. Most opponents of salivary gland FNAB consider it unnecessary. This paper documents the utility of the punction aspiration biopsy in the diagnosis of these lesions.

METHODS

Between January 1998, and December 2003, 136 patients with clinically significant masses of the salivary glands were evaluated using FNAB. The parotid gland was involved in 68 patients, the submandibular gland in 58 patients and the region of the sublingual gland in 10 cases. In the retrospective analysis, the preoperative cytological findings were correlated with the postoperative histopathological evaluation.

RESULTS

Histopathological evaluation revealed 107 benign lesions (79%), of which 68 were non-neoplastic, and 39 were benign neoplasms, and 19 malignant tumors (21%). The cytological specimens were found to be non-diagnostic in 15 (11%) cases, true-positive in 68 (50%), true-negative in 40 (29.4%), false-positive in 1 (0.73%) and false-negative in 12 (8.8%) cases in detecting tumors. The sensitivity, specificity and diagnostic accurary aspiration cytology were 85.0%, 97.5% and 89.2%, respectively. We recorded complications in only one case (0.7%), a subcutaneous haematoma.

CONCLUSION

Our results document the utility of the FNAB in the diagnosis of salivary gland masses. FNAB does not substitute other diagnostic methods or as an adjunct to sound clinical judgement. Together with the clinical and ultrasonographical evaluations it should belong to the basic algorithm of diagnosis in salivary gland lesions (Tab. 3, Ref. 18).

Variable frequencies of MALT lymphoma-associated genetic aberrations in MALT lymphomas of different sites

Although several recurrent genetic aberrations are known to occur in MALT lymphoma, no comprehensive study on the most prevalent MALT lymphoma-associated genetic aberrations is available. We therefore screened 252 primary MALT lymphomas for translocations t(11;18)(q21;q21), t(14;18)(q32;q21), and t(1;14)(p22;q32), and trisomies 3 and 18. The above-listed translocations occurred mutually exclusively and were detected overall in 13.5, 10.8, and 1.6% of the cases; trisomy 3 and/or 18 occurred in 42.1%. The frequency at which the translocations occurred varied markedly with the primary site of disease. The t(11;18)(q21;q21) was mainly detected in pulmonary and gastric tumors, whereas the t(14;18)(q32;q21) was most commonly found in lesions of the ocular adnexa/orbit, skin, and salivary glands. Trisomies 3 and 18 each occurred most frequently in intestinal and salivary gland MALT lymphomas. Our results demonstrate that the three translocations and trisomies 3 and 18 occur at markedly variable frequencies in MALT lymphoma of different sites.

Tracheostomy in critically ill patients

The authors made a retrospective analysis of results and complications of elective tracheostomies performed by percutaneous dilatational technique (PDT) as well as standard surgical procedure (ST) in critically ill patients in the ICU. The indication for tracheostomy was to facilitate long-term mechanical ventilation, to facilitate cleaning and management of the airway and to maintain upper airway patency. During a 5-year period there were 495 elective tracheostomies performed in the ICU setting, in 209 females and 286 males. From these, 408 were standard (82.4%) and 87 percutaneous dilatational tracheostomies (17.6%). Mean age of patients with tracheostomy was 63.3 years (range 17-93 years) and the mean duration of endotracheal intubation before tracheostomy was 7 days (range from 13 minutes to 21 days). During the monitored period 144 patients (29.0%) were decannulated, out of which 34 patients (23.6%) had PDT and 110 patients (76.4%) ST. A total of 265 patients (53.5%) with tracheostomy died and 86 patients (17.3%) had the tracheostomy cannule in place at the study conclusion. Perioperative complications totaled 14 (2.8%), the most serious being one cardiac arrest and death (0.4%) both in ST as well as in PDT groups. Early postoperative complications totaled 46 (9.2%). Late postoperative complications totaled 7 (1.4%). Percutaneous dilatational tracheostomy is an alternative method to standard surgical tracheostomy in critically ill patients in the ICUs. Standard surgical tracheostomy is an irreplaceable procedure in patients with complex anatomic condition or in high-risk patients. (Tab. 3, Ref. 11).

CHK2 kinase--a busy messenger

Checkpoint kinase 2 (Chk2) is emerging as a key mediator of diverse cellular responses to genotoxic stress, guarding the integrity of the genome throughout eukaryotic evolution. Recent studies show the fundamental role of Chk2 in the network of genome-surveillance pathways that coordinate cell-cycle progression with DNA repair and cell survival or death. Defects in Chk2 contribute to the development of both hereditary and sporadic human cancers, and earmark this kinase as a candidate tumour suppressor and an attractive target for drug discovery.

Mammalian G1- and S-phase checkpoints in response to DNA damage

The ability to preserve genomic integrity is a fundamental feature of life. Recent findings regarding the molecular basis of the cell-cycle checkpoint responses of mammalian cells to genotoxic stress have converged into a two-wave concept of the G1 checkpoint, and shed light on the so-far elusive intra-S-phase checkpoint. Rapidly operating cascades that target the Cdc25A phosphatase appear central in both the initiation wave of the G1 checkpoint (preceding the p53-mediated maintenance wave) and the transient intra-S-phase response. Multiple links between defects in the G1/S checkpoints, genomic instability and oncogenesis are emerging, as are new challenges and hopes raised by this knowledge.

Chk2 tumour suppressor protein in human spermatogenesis and testicular germ-cell tumours

Chk2 is a transducer of DNA damage signals and a tumour suppressor whose germ-line mutations predispose to diverse tumour types. Unlike its downstream targets such as the p53 tumour suppressor, the expression patterns of Chk2 in tissues and tumours remain unknown. As DNA breaks occur commonly during gametogenesis, and p53 is wild-type and overexpressed in testicular cancer, we examined abundance and localisation of the Chk2 protein during normal development of human testes, and at various stages of germ-cell tumour (GCT) pathogenesis. Our results show that Chk2 is abundant in foetal germ cells and adult spermatogonia, yet only weakly expressed or lacking during the meiotic and later stages of spermatogenesis. High levels of Chk2 are detected in the majority of GCTs including all pre-invasive carcinoma-in-situ lesions, contrary to variable expression and even lack of Chk2 in subsets of invasive GCTs and some teratoma structures, respectively. Together with our analyses of cell culture models, these results indicate that downmodulation or lack of Chk2 is not simply attributable to quiescence or differentiation, they suggest a role for Chk2 in mitotic rather than meiotic divisions, support the concept of foetal origin of GCTs, and have implications for protein-based screening for tumour-associated aberrations of Chk2.

Functional impact of concomitant versus alternative defects in the Chk2-p53 tumour suppressor pathway

Recent evidence identified a genetic and functional link between Chk2 kinase and p53 as a candidate genome integrity checkpoint and a tumour suppressor pathway. Here we report that in human cells, Chk2 and p53 form protein-protein complexes whose abundance increased upon DNA damage, and whose formation was abrogated through cancer associated mutations in the FHA domain of Chk2, or mutations in the tetramerization domain of p53. Whereas among Li-Fraumeni syndrome families mutations of Chk2 or p53 occur in a mutually exclusive manner, we document that the colon cancer cell line HCT-15 concomitantly lacks functions of both Chk2 and p53, the latter demonstrated by a non-invasive reporter assay monitoring p53-dependent transactivation in live cells. Despite the preserved ability of common cancer-derived mutant p53 proteins to bind and potentially 'titrate' activated Chk2, the integrity of the S phase checkpoint response to ionizing radiation remained largely intact and dependent on Chk2 in cells with wild-type, mutant, or no p53. These results provide new mechanistic insights into the Chk2-p53 interplay, suggest how mutations in Chk2 may abrogate its tumour suppressor function, and indicate that compared with individual defects in either Chk2 or p53, concomitant mutations in both of these cell cycle checkpoint regulators may provide some additional selective advantage to tumour cells.

Inhibitory effects of 1alpha,25-dihydroxyvitamin D(3) on the G(1)-S phase-controlling machinery

The nuclear hormone 1alpha,25-dihydroxyvitamin D(3) induces cell cycle arrest, differentiation, or apoptosis depending on target cell type and state. Although the antiproliferative effect of 1alpha,25-dihydroxyvitamin D(3) has been known for years, the molecular basis of the cell cycle blockade by 1alpha,25-dihydroxyvitamin D(3) remains largely unknown. Here we have investigated the mechanisms underlying the G(1) arrest induced upon 1alpha,25-dihydroxyvitamin D(3) treatment of the human breast cancer cell line MCF-7. Twenty-four-hour exposure of exponentially growing MCF-7 cells to 1alpha,25-dihydroxyvitamin D(3) impeded proliferation by preventing S phase entry, an effect that correlated with appearance of the growth-suppressing, hypophosphorylated form of the retinoblastoma protein (pRb), and modulation of cyclin-dependent kinase (cdk) activities of cdk-4, -6, and -2. Time course immunochemical and biochemical analyses of the cellular and molecular effects of 1alpha,25-dihydroxyvitamin D(3) treatment for up to 6 d revealed a dynamic chain of events, preventing activation of cyclin D1/cdk4, and loss of cyclin D3, which collectively lead to repression of the E2F transcription factors and thus negatively affected cyclin A protein expression. While the observed 10-fold inhibition of cyclin D1/cdk 4-associated kinase activity appeared independent of cdk inhibitors, the activity of cdk 2 decreased about 20-fold, reflecting joint effects of the lower abundance of its cyclin partners and a significant increase of the cdk inhibitor p21(CIP1/WAF1), which blocked the remaining cyclin A(E)/cdk 2 complexes. Together with a rapid down-modulation of the c-Myc oncoprotein in response to 1alpha,25-dihydroxyvitamin D(3), these results demonstrate that 1alpha,25-dihydroxyvitamin D(3) inhibits cell proliferation by targeting several key regulators governing the G(1)/S transition.

DNA damage-activated kinase Chk2 is independent of proliferation or differentiation yet correlates with tissue biology

The Chk2 kinase is a tumor suppressor and key transducer of DNA-damage checkpoints. We show that the human Chk2 protein is relatively stable, nuclear, and responding to gamma-radiation throughout the cell cycle. Contrary to the retinoblastoma protein-regulated, labile Chk1 kinase restricted to S-G(2) phases, Chk2 remains activatable even in quiescent and differentiating cells. In human tissues, Chk2 is homogeneously expressed in renewing cell populations such as epidermis or intestine, heterogeneous in conditionally renewing tissues, and absent or cytoplasmic in static tissues such as muscle or brain. These data highlight striking differences between Chk2 and Chk1 and show unexpected correlation of Chk2 expression with tissue biology.

A conserved cyclin-binding domain determines functional interplay between anaphase-promoting complex-Cdh1 and cyclin A-Cdk2 during cell cycle progression

Periodic activity of the anaphase-promoting complex (APC) ubiquitin ligase determines progression through multiple cell cycle transitions by targeting cell cycle regulators for destruction. At the G(1)/S transition, phosphorylation-dependent dissociation of the Cdh1-activating subunit inhibits the APC, allowing stabilization of proteins required for subsequent cell cycle progression. Cyclin-dependent kinases (CDKs) that initiate and maintain Cdh1 phosphorylation have been identified. However, the issue of which cyclin-CDK complexes are involved has been a matter of debate, and the mechanism of how cyclin-CDKs interact with APC subunits remains unresolved. Here we substantiate the evidence that mammalian cyclin A-Cdk2 prevents unscheduled APC reactivation during S phase by demonstrating its periodic interaction with Cdh1 at the level of endogenous proteins. Moreover, we identified a conserved cyclin-binding motif within the Cdh1 WD-40 domain and show that its disruption abolished the Cdh1-cyclin A-Cdk2 interaction, eliminated Cdh1-associated histone H1 kinase activity, and impaired Cdh1 phosphorylation by cyclin A-Cdk2 in vitro and in vivo. Overexpression of cyclin binding-deficient Cdh1 stabilized the APC-Cdh1 interaction and induced prolonged cell cycle arrest at the G(1)/S transition. Conversely, cyclin binding-deficient Cdh1 lost its capability to support APC-dependent proteolysis of cyclin A but not that of other APC substrates such as cyclin B and securin Pds1. Collectively, these data provide a mechanistic explanation for the mutual functional interplay between cyclin A-Cdk2 and APC-Cdh1 and the first evidence that Cdh1 may activate the APC by binding specific substrates.

16S rDNA-based identification of bacteria from conjunctival swabs by PCR and DGGE fingerprinting

PURPOSE

Establishment of a new molecular biology technique for the identification of multiple bacteria from the ocular environment, which can be applied supplementarily to cultivation in cases of severe bacterial infections.

METHODS

From 60 human conjunctivae (29 with purulent and 31 with nonpurulent conjunctivitis), swabs were taken and DNA was extracted. Fragments of 200 bp, spanning the V3 region of the eubacterial 16S rDNA, were amplified by polymerase chain reaction (PCR) and separated by denaturing gradient gel electrophoresis (DGGE). For phylogenetic identification, DGGE bands were excised and directly sequenced, or 16S rDNA clone libraries were constructed and clones were screened by DGGE. Sequences were compared with sequences of known bacteria listed in the EMBL database. Furthermore, the results were compared with results obtained from conventional cultivation.

RESULTS

16S rDNA could be amplified from 25 of 29 investigated swabs taken from purulent conjunctivitis eyes and from 2 of 31 investigated swabs taken from nonpurulent conjunctivitis eyes. Sixteen samples showed monomicrobial and 11 samples showed polymicrobial infections. The following genera (n is number of samples) were detected: Staphylococcus (n = 8), Corynebacterium (n = 7), Propionibacterium (n = 7), Streptococcus (n = 6), Bacillus (n = 2), Acinetobacter (n = 3), Pseudomonas (n = 3), Proteus (n = 1), and Brevundimonas (n = 1). Four sequences could not be identified to the genus level. They had highest sequence similarities both to sequences of Pantoea and Enterobacter (n = 1), Kingella and Neisseria (n = 1), Serratia and Aranicola (n = 1), and Leuconostoc and Weissella (n = 2), respectively. Culture was only positive for coagulase-negative staphylococci (n = 9), Corynebacteria (n = 3), Staphylococcus aureus (n = 1), Streptococcus sp. (n = 1), Proteus sp. (n = 1), Klebsiella oxytoca (n = 1), and Pseudomonas aeruginosa (n = 1). In total, 45% of the 60 analyzed conjunctival swabs were PCR positive, whereas only 22% were culture positive. No sample positive by culture gave negative results by PCR.

CONCLUSIONS

16S rDNA sequence analyses and DGGE fingerprinting are appropriate methods for the detection and identification of monomicrobial as well as polymicrobial ocular infections of bacteria that might not be detected by conventional cultivation.

The ATM-Chk2-Cdc25A checkpoint pathway guards against radioresistant DNA synthesis

When exposed to ionizing radiation (IR), eukaryotic cells activate checkpoint pathways to delay the progression of the cell cycle. Defects in the IR-induced S-phase checkpoint cause 'radioresistant DNA synthesis', a phenomenon that has been identified in cancer-prone patients suffering from ataxia-telangiectasia, a disease caused by mutations in the ATM gene. The Cdc25A phosphatase activates the cyclin-dependent kinase 2 (Cdk2) needed for DNA synthesis, but becomes degraded in response to DNA damage or stalled replication. Here we report a functional link between ATM, the checkpoint signalling kinase Chk2/Cds1 (Chk2) and Cdc25A, and implicate this mechanism in controlling the S-phase checkpoint. We show that IR-induced destruction of Cdc25A requires both ATM and the Chk2-mediated phosphorylation of Cdc25A on serine 123. An IR-induced loss of Cdc25A protein prevents dephosphorylation of Cdk2 and leads to a transient blockade of DNA replication. We also show that tumour-associated Chk2 alleles cannot bind or phosphorylate Cdc25A, and that cells expressing these Chk2 alleles, elevated Cdc25A or a Cdk2 mutant unable to undergo inhibitory phosphorylation (Cdk2AF) fail to inhibit DNA synthesis when irradiated. These results support Chk2 as a candidate tumour suppressor, and identify the ATM-Chk2-Cdc25A-Cdk2 pathway as a genomic integrity checkpoint that prevents radioresistant DNA synthesis.

Alternative and aberrant messenger RNA splicing of the mdm2 oncogene in invasive breast cancer

mdm2 is part of a complex mechanism that regulates the expression of p53 as well as the function of Rb, p19ARF, and other genes. In humans, mdm2 dysregulation is associated with gene amplification. This study was undertaken to characterize altered mdm2 expression in a cohort of 38 invasive breast cancers and 9 normal breast specimens. Reverse-transcription PCR with primers spanning the entire open reading frame of the mdm2 gene in breast tissue RNA samples generated PCR products of full-length mdm2 (1526 bp) as well as smaller products (653, 281, 254, and 219 bp). Sequence analysis demonstrated that the 653-bp product was an alternatively spliced product (defined as splicing at the exon/intron boundary consensus sites), whereas the 281, 254, and 219 bp mdm2 products were aberrantly spliced products (splicing at sites not considered to be exon/intron boundary sites). Reverse-transcription-PCR with normal breast tissue RNA samples yielded only the 1526-bp product in five samples and the 1526-bp product and the 653-bp product in four samples. The 653-bp alternatively spliced product was expressed in 21% of breast cancers, and the smaller, aberrantly spliced mRNA products (281 bp, 254 bp, and/or 219 bp) were expressed in 16% of breast cancers. The protein products predicted by the alternatively spliced mRNAs and the aberrantly spliced mRNAs lacked either the entire binding domain for p53 or the majority of the binding domain for p53. Immunohistochemical analysis of HER2/neu (c-erbB2), estrogen receptor, progesterone receptor, epidermal growth factor receptor, and p53 protein was performed. p53 sequence alterations were identified by mismatch detection and confirmed by p53 oligonucleotide microarray technology. An association was demonstrated between the expression of aberrantly and/or alternatively spliced mdm2 mRNAs and a lack of progesterone receptor. An association was also demonstrated between mdm2 aberrantly and/or alternatively expression products and the presence of p53 tumor suppressor gene mutations. mdm2 is transcribed from two different promoters: one, p53-dependent, and the other, p53-independent. The 5' untranslated region of the transcripts was evaluated to determine the promoter usage in each breast cancer specimen. No correlation was observed between mdm2 splice products and promoter usage. The presence of aberrant expression products of mdm2 in breast cancer specimens was correlated with a shortened overall patient survival. These observations suggest that mdm2 expression is altered in invasive breast cancer and is associated with more aggressive disease.

Repression of p15INK4b expression by Myc through association with Miz-1

Deregulated expression of c-myc can induce cell proliferation in established cell lines and in primary mouse embryonic fibroblasts (MEFs), through a combination of both transcriptional activation and repression by Myc. Here we show that a Myc-associated transcription factor, Miz-1, arrests cells in G1 phase and inhibits cyclin D-associated kinase activity. Miz-1 upregulates expression of the cyclin-dependent kinases (CDK) inhibitor p15INK4b by binding to the initiator element of the p15INK4b promoter. Myc and Max form a complex with Miz-1 at the p15 initiator and inhibit transcriptional activation by Miz-1. Expression of Myc in primary cells inhibits the accumulation of p15INK4b that is associated with cellular senescence; conversely, deletion of c-myc in an established cell line activates p15INK4b expression. Alleles of c-myc that are unable to bind to Miz-1 fail to inhibit accumulation of p15INK4b messenger RNA in primary cells and are, as a consequence, deficient in immortalization.

Pathways governing G1/S transition and their response to DNA damage

The ability to self-replicate is a fundamental feature of life, reflected at the cellular level by a highly regulated process initiated in G1 phase via commitment to a round of DNA replication and cell division. Here we briefly highlight recent advances in understanding the molecular pathways which govern the decision of mammalian somatic cells to enter S phase, and the so-called cell cycle checkpoints which guard the G1/S transition and S phase progression against potentially deleterious effects of genotoxic stress. Particular emphasis is put on the emerging parallel yet cooperative pathways of retinoblastoma protein (pRB)-E2F and Myc, their convergence to control the activity of the cyclin-dependent kinase 2 (Cdk2) at the G1/S boundary, as well as the two waves of checkpoint responses at G1/S: the rapid pathway(s) leading to Cdc25A degradation, and the delayed p53-p21 cascade, both silencing the Cdk2 activity upon DNA damage.

Bacteriology and antibiotic therapy in congenital nasolacrimal duct obstruction

AIMS

To determine the current bacteriology of mucopurulent discharge in congenital nasolacrimal duct obstruction (CNDO), the in vitro response to different antibiotics and clinical effectiveness of the antibiotics used to relieve babies from mucopurulent discharge.

METHODS

A clinical study evaluated the effectiveness of local antibiotic agents clinically and in vitro. 50 samples were obtained from the lacrimal sac in 47 young children with CNDO. The patients' mean age was 21.45 +/- 17.09 months. The cultures were incubated and the infectious agents isolated. Sensitivity testing was performed in each case, testing 10 different local antibiotics. A control group of 10 babies expected for cataract surgery was constituted.

RESULTS

Cultures were positive for bacteria from 72.64% of the samples. 73 isolates were recovered from the 50 samples. The bacterial species most frequently cultured was Streptococcus pneumoniae, representing 35.4% of the isolates, followed by Haemophilus influencae (19.6%). The sensitivity testing revealed ofloxacin and tetracycline to be the most effective drugs as monotherapy. Clinically the combination of bacitracin and neomycin, primarily used in half of the patients as initial therapy, was successful in curing the dacryocystitis in 82.5% of all patients.

CONCLUSION

Chronic dacryocystitis due to CNDO is associated with an equal proportion of Gram positive and negative bacteria, which can be treated with a high effectiveness by a combination drug of bacitracin and neomycin.

Nonperiodic activity of the human anaphase-promoting complex-Cdh1 ubiquitin ligase results in continuous DNA synthesis uncoupled from mitosis

Ubiquitin-proteasome-mediated destruction of rate-limiting proteins is required for timely progression through the main cell cycle transitions. The anaphase-promoting complex (APC), periodically activated by the Cdh1 subunit, represents one of the major cellular ubiquitin ligases which, in Saccharomyces cerevisiae and Drosophila spp., triggers exit from mitosis and during G(1) prevents unscheduled DNA replication. In this study we investigated the importance of periodic oscillation of the APC-Cdh1 activity for the cell cycle progression in human cells. We show that conditional interference with the APC-Cdh1 dissociation at the G(1)/S transition resulted in an inability to accumulate a surprisingly broad range of critical mitotic regulators including cyclin B1, cyclin A, Plk1, Pds1, mitosin (CENP-F), Aim1, and Cdc20. Unexpectedly, although constitutively assembled APC-Cdh1 also delayed G(1)/S transition and lowered the rate of DNA synthesis during S phase, some of the activities essential for DNA replication became markedly amplified, mainly due to a progressive increase of E2F-dependent cyclin E transcription and a rapid turnover of the p27(Kip1) cyclin-dependent kinase inhibitor. Consequently, failure to inactivate APC-Cdh1 beyond the G(1)/S transition not only inhibited productive cell division but also supported slow but uninterrupted DNA replication, precluding S-phase exit and causing massive overreplication of the genome. Our data suggest that timely oscillation of the APC-Cdh1 ubiquitin ligase activity represents an essential step in coordinating DNA replication with cell division and that failure of mechanisms regulating association of APC with the Cdh1 activating subunit can undermine genomic stability in mammalian cells.

Ubiquitin/proteasome-mediated degradation of p19INK4d determines its periodic expression during the cell cycle

Assembly and activity of the proto-oncogenic cyclin D/CDK4(6) complexes, the major driving force of G1 phase progression, is negatively regulated by a family of INK4 CDK inhibitors p16INK4a, p15INK4b, p18INK4c, and p19INK4d. Expression of the INK4 family members is controlled at the transcriptional level, through differential response to environmental and intracellular signals such as cytokines, oncogenic overload, or cellular senescence. Here we show that the periodic oscillation of the p19INK4d protein during the cell cycle is determined by the ubiquitin/proteasome-dependent mechanism, allowing the protein abundance to follow the changes in its mRNA expression. Within the INK4 family, this regulatory mode appears restricted to p19INK4d whose ubiquitination was dependent on the integrity of lysine 62, and binding to CDK4. These results highlight unexpected differences among the INK4 inhibitors, and suggest how p19INK4d may help regulate the rate of cyclin D/CDK4(6) complex formation, and thereby timely progression through the mammalian cell division cycle. Oncogene (2000) 19, 2870 - 2876

Rapid destruction of human Cdc25A in response to DNA damage

To protect genome integrity and ensure survival, eukaryotic cells exposed to genotoxic stress cease proliferating to provide time for DNA repair. Human cells responded to ultraviolet light or ionizing radiation by rapid, ubiquitin- and proteasome-dependent protein degradation of Cdc25A, a phosphatase that is required for progression from G1 to S phase of the cell cycle. This response involved activated Chk1 protein kinase but not the p53 pathway, and the persisting inhibitory tyrosine phosphorylation of Cdk2 blocked entry into S phase and DNA replication. Overexpression of Cdc25A bypassed this mechanism, leading to enhanced DNA damage and decreased cell survival. These results identify specific degradation of Cdc25A as part of the DNA damage checkpoint mechanism and suggest how Cdc25A overexpression in human cancers might contribute to tumorigenesis.

Cell cycle arrest by the PTEN tumor suppressor is target cell specific and may require protein phosphatase activity

PTEN, a tumor suppressor commonly targeted in human cancer, possesses phosphatase activities toward both protein and lipid substrates. While PTEN suppresses gliomas through cell cycle inhibition which requires its lipid phosphatase activity, PTEN's effects on other tumor types and the role of its protein phosphatase activity are controversial or unknown. Here we show that exogenous wild-type PTEN arrests some, but not all human breast cancer cell lines in G1, in a manner independent of endogenous PTEN. Unexpectedly, the G129E mutant of PTEN selectively deficient in the lipid phosphatase activity still blocked the cell cycle of MCF-7 cells, while the G129R and H123Y mutants lacking both phosphatase activities were ineffective. These results suggest that PTEN's protein phosphatase activity likely contributes to its tumor suppressor function in subsets of tumors and that elucidation of downstream targets which dictate cellular responses to PTEN may have important implications for future cancer treatment strategies.

Involvement of Myc activity in a G(1)/S-promoting mechanism parallel to the pRb/E2F pathway

The retinoblastoma protein (pRb)/E2F pathway regulates commitment of mammalian cells to replicate DNA. On the other hand, mitogen-stimulated cells deprived of E2F activity can still maintain physiologically relevant levels of cyclin E-dependent kinase activity and gradually enter S phase, suggesting the existence of a DNA synthesis-inducing mechanism parallel to the pRb/E2F axis. Here we show that regulatable ectopic expression of cyclin E or transcriptionally active Myc can rapidly induce DNA synthesis in U2OS-derived cell lines whose E2F activity is blocked by a constitutively active pRb (pRbDeltacdk) mutant. The effect of Myc is associated with Cdc25A phosphatase and cyclin E-CDK2 kinase activation and abolished by antagonizing Myc activity with the dominant-negative (dn) MadMyc chimera. Moreover, while abrogation of either endogenous E2F or Myc activity only delays and lowers DNA synthesis in synchronized U2OS cells or rat diploid fibroblasts, concomitant neutralization of both abolishes it. Whereas ectopic Myc and E2F1 rescue the G(1)/S delay caused by pRbDeltacdk (or dnDP1) and MadMyc, respectively, cyclin E or Cdc25A can restore DNA replication even in cells concomitantly exposed to pRbDeltacdk and MadMyc. However, coexpression of dnCDK2 neutralizes all of these rescuing effects. Finally, proper transcription of cyclin E and Cdc25A at the G(1)/S transition requires both Myc and E2F activities, and subthreshold levels of ectopic cyclin E and Cdc25A synergistically restore DNA synthesis in cells with silenced Myc and E2F activities. These results suggest that Myc controls a G(1)/S-promoting mechanism regulating cyclin E-CDK2 in parallel to the "classical" pRb/E2F pathway.