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Biomedical subjects

M Beckett

Publications and source records attributed to M Beckett.

18 recordsLinked to original sources
PubMed1997

p53 expression induces apoptosis in hippocampal pyramidal neuron cultures.

The tumor suppressor gene p53 has been implicated in the induction of apoptosis in dividing cells. We now show that overexpression of p53 using an adenoviral vector in cultured rat hippocampal pyramidal neurons causes widespread neuronal death with features typical of apoptosis. p53 overexpression did not induce p21, bax, or mdm2 in neurons. X-irradiation of hippocampal neurons induced p53 immunoreactivity and cell death associated with features typical of apoptosis. Overexpression of a constitutively active nonphosphorylatable form of the retinoblastoma gene product blocked x-irradiation-induced neuronal death. However, overexpression of the cyclin-dependent kinase inhibitor p21 did not. Treatment of neurons with transforming growth factor-beta1 protected them from x-irradiation. These results are consistent with a role for p53 in nerve cell death that is distinct from its actions relating to cell cycle arrest.

Animals↗
PubMed1995

Conservative surgery and adjuvant radiation therapy in the management of adult soft tissue sarcoma of the extremities: clinical and radiobiological results.

PURPOSE: The outcome of adult patients with soft tissue sarcoma of the extremities treated with conservative surgery and adjuvant irradiation was evaluated to (a) determine the appropriate treatment volume and radiation dosage in the postoperative setting, and (b) correlate in vitro radiobiological parameters obtained prior to therapy with clinical outcome. METHODS AND MATERIALS: Sixty-four consecutive adult patients with soft tissue sarcoma of the extremities (40 lower, 24 upper) who underwent conservative surgery and adjuvant irradiation 7 preoperative, 50 postoperative, 7 perioperative) between 1978 and 1991 were reviewed. The initial radiation field margin surrounding the tumor bed/scar was retrospectively analyzed in all postoperative patients. Initial field margins were < 5 cm in 12 patients, 5-9.9 cm in 32 and > or = 10 cm in 6. Patients with negative pathological margins were initially treated with traditional postoperative doses (64-66 Gy); however, in later years the postoperative dose was reduced to 60 Gy. Thirteen cell lines were established prior to definite therapy, and radiobiological parameters (multitarget and linear-quadratic) were obtained and correlated with outcome. RESULTS: Postoperative patients treated with an initial field margin of < 5 cm had a 5-year local control of 30.4% vs. 93.2% in patients treated with an initial margin of > or = 5 cm (p = 0.0003). Five-year local control rates were similar in patients treated with initial field margins of 5-9.9 cm (91.6%) compared with those treated with > or = 10 cm margins (100%) (p = 0.49). While postoperative patients receiving < 60 Gy had a worse local control than those receiving > or = 60 Gy (p = 0.08), no difference was seen in local control between patients receiving less than traditional postoperative doses (60-63.9 Gy) (74.4% vs. those receiving 64-66 Gy (87.0%) (p = 0.5). The local control of patients treated in the later years of the study, with strict attention to surgical and radiotherapeutic technique, was 87.6%. Severe late sequelae were more frequent in patients treated with doses > or = 63 Gy compared to patients treated with lower doses (23.1% vs. 0%) (p < 0.05). Mean values for Do, alpha, beta, D, n and SF2 obtained from the 13 cell lines were 115.7, 0.66, 0.029, 2.15, 0.262, respectively. Four of the 13 cell lines established prior to therapy ultimately failed locally. The radiobiological parameters of these cell lines were similar to the other nine cell lines in terms of radiosensitivity. CONCLUSIONS: Our data confirm the importance of maintaining an initial field margin of at least 5 cm around the tumor bed/scar in the postoperative setting. No benefit was seen with the use of margins > or = 10 cm. In addition, patients undergoing wide local excision with negative margins can be treated with lower than traditional postoperative doses (60 Gy) without compromising local control and with fewer chronic sequelae. Finally, it does not appear that inherent tumor cell sensitivity is a major determinant of local failure following radiation therapy and conservative surgery in soft tissue sarcoma.

Adolescent↗
PubMed1993

p53 mutation does not correlate with radiosensitivity in 24 head and neck cancer cell lines.

The molecular basis of tumor response to therapeutic radiation is poorly understood. Recent evidence suggests the p53 tumor suppressor gene may be involved in production of the G1 arrest seen following DNA damage by X-irradiation. It has further been proposed that tumor cells lacking the p53 checkpoint function are likely to be more sensitive to cell killing by X-irradiation because these cells enter S phase despite unrepaired DNA damage. We tested the hypothesis that tumor cells with p53 mutations are more radiosensitive by correlating the in vitro surviving fraction at 2 Gy with the mutational status of 24 head and neck squamous cell cancer cell lines. p53 mutations were present in 15 of 24 (63%) of tumors; all were homozygous changes occurring within exons 5-9. The surviving fraction at 2 Gy for the group with mutations was 0.568 compared to 0.507 for tumors without mutations (P = 0.28, Mann-Whitney test). Furthermore, no association between radiosensitivity and mutational type, codon location, or predicted amino acid alteration was noted. Our data do not support the hypothesis that p53 gene alteration predisposes tumor cells to increased cell killing via radiation.

Carcinoma, Squamous Cell↗
PubMed1992

Phosphorous metabolite and cell cycle kinetic response of two human squamous cell carcinomas to radiation.

Phosphorous metabolism and cell cycle phase kinetics in response to radiation of two perfused human squamous cell carcinoma cell lines, SQ20B (radioresistant) and SQ38 (relatively radiosensitive), embedded in both basement membrane (Matrigel) and agarose gel threads were studied. The findings for these human cancer cells in response to 2- and 50-Gy irradiation are as follows. (a) Well perfused pure cancer cells (both SQ20B and SQ38) in both proliferative (cells embedded in Matrigel) and static (cells embedded in agarose threads) states did not show significant alteration in either phosphorous bioenergetics or membrane metabolites at 24 and 48 h after irradiation, although a large fraction of the population was clonogenically impaired. Previously reported, sensitively detected, metabolite alterations in response to radiation in rodent and human tumors in situ were not seen in these homogeneous cancer cell populations. (b) The radiosensitive squamous cell carcinoma cell lines SQ38 exhibited G1 block (from 54.38 +/- 1.40% in control to 73.93 +/- 1.01% after irradiation; mean +/ SD) in response to low-dose 2-Gy irradiation and G2 block (from 12.98 +/- 2.15% in control to 25.6 +/- 3.15% after irradiation) in response to high-dose 50-Gy irradiation, while the radioresistant cell line SQ20B showed only conventional G2 block in response to both doses. The differential cell cycle phase response may indicate the difference in radioresistance. (c) The membrane metabolites (including phosphomonoesters and phosphodiesters) and phosphocreatine gradually increased from the early passages to late passages, suggesting that cell proliferation rates were increasing as the cells adapted to tissue culture. The results suggest that the radiation-induced metabolite changes observed in solid tumors in situ may not be a direct response to interim changes within the cancer cells but, rather, a consequence of radiation damage either to the vasculature or to other host-mediated factors.

Animals↗
PubMed1992

Occurrence of p53 gene deletions and human papilloma virus infection in human head and neck cancer.

Little is known regarding the molecular genetic events in head and neck carcinoma. Epidemiological evidence suggests that both alcohol and tobacco use are related to the development of these neoplasms, and viral infections have also been postulated to play a role in some tumors. Loss of p53 tumor suppressor gene function has been found in many malignancies and can occur through either gene mutation or by interaction with the E6 protein of oncogenic human papilloma viruses (HPV). Because the mucosal surfaces of the head and neck are exposed to mutagens and HPVs, we studied DNA derived from 30 stage I-IV squamous cell carcinomas of the head and neck (9 primary tumors and 21 early passage cell lines) for p53 gene mutations as well as for the presence of oncogenic HPV DNA. Exons 2 through 11 of the p53 gene were examined using single strand conformation polymorphism analysis followed by direct genomic sequencing of all variants. HPV detection was done using polymerase chain reaction amplification with HPV E6 region type specific primers as well as L1 region degenerate ("consensus") primers; HPV type was determined by restriction fragment length polymorphism analysis of the amplified fragment as well as by Southern blotting of genomic DNA. Sixteen of 30 tumors (53%) had p53 mutations and oncogenic HPV DNA was detected in 3 of 30 (10%) tumors, none of which had p53 mutations. The p53 mutational spectrum observed was characterized by equal frequencies of transversions (6 of 16), transitions (5 of 16), and deletions (5 of 16). This distribution of mutations differs from the spectrum of p53 mutation reported in esophageal (P = 0.05) and lung (P = 0.02) cancers, two other tobacco associated neoplasms. A previously undescribed clustering of 3 mutations at codon 205 was also observed. A trend toward a shorter time to tumor recurrence after treatment was noted for those patients with tumors exhibiting p53 gene mutations, and no relationship between p53 mutations and tumor stage or node status was noted. Alteration in p53 gene function appears common in head and neck cancer, and the mutational spectrum observed may reflect the role of different mutagens or mutagenic processes than those responsible for the p53 mutations in lung and esophageal neoplasms.

Alcohol Drinking↗
PubMed1992

Chromosome 3p deletions in head and neck carcinomas: statistical ascertainment of allelic loss.

Loss of function of tumor suppressor genes is important in the origin and progression of common adult tumors. Loss of heterozygosity indicating allelic loss has been used to detect chromosomal regions that harbor these genes. Using over 20 restriction fragment length polymorphism markers spaced throughout the entire length of chromosome 3p, we have generated 3p allelotypes for 18-26 head and neck squamous cell carcinoma cell lines. We then estimated the average heterozygosity over 19 loci for a random sample drawn from natural populations to be 7.80 and that for the tumor lines to be 1.65, indicating a gross reduction of heterozygosity, presumably due to allelic loss. Further comparison of per locus heterozygosity in normal and tumor DNAs showed which loci contributed to the general loss of heterozygosity. We showed that the commonly deleted region of 3p probably lies telomeric to D3S3 (3p14) and centromeric to RAF1 (3p25). This large region includes several putative tumor suppressor genes involved in multiple common tumor types of lung, breast, kidney, ovary, and cervix. The data demonstrate that chromosome 3p allelic loss is a common event in head and neck cancers and suggest that chromosome 3p tumor suppressor genes contribute to the pathogenesis of these tumors.

Alleles↗
PubMed1992

The interaction of 5-fluorouracil, hydroxyurea, and radiation in two human head and neck cancer cell lines.

We have investigated the effects of 5-fluorouracil (5-FU) and hydroxyurea (HU) with radiation on two human head and neck squamous carcinoma cell lines. SQ-20B has a D0 of 239 cGy and an S phase fraction of 37%, while SQ-38 has a D0 of 146 cGy and an S phase fraction of 31%. For SQ-20B the surviving fraction at 100 cGy was significantly reduced (p < 0.05) when cells were exposed to HU or to 5-FU or both chemotherapy agents together with radiation. No significant effect was seen for SQ-38 with either chemotherapy agent alone or in combination with radiation as compared with radiation alone. Therefore, additive cytotoxicity between 5-FU and HU and radiotherapy was observed only in a head and neck cancer cell line with a higher D0 and a higher S phase fraction.

Cell Survival↗
PubMed1991

Mechanisms of X-ray-mediated protooncogene c-jun expression in radiation-induced human sarcoma cell lines.

c-jun is a protooncogene associated with neoplastic transformation and is transcriptionally induced by ionizing radiation. To examine the possible mechanisms of radiation-induced c-jun transcription, we analyzed RNA from human tumor cell lines RIT-3 and STSAR-5 following x-irradiation in the presence of protein kinase inhibitors, or the absence of serum and calcium. Protooncogene c-jun expression increased several fold following irradiation of these radiation-induced human sarcoma cell lines. The expression of c-jun was not altered following irradiation in conditioned medium containing serum as compared to that of cells in serum free medium. Depletion of PKC by prolonged TPA treatment resulted in inhibition of c-jun expression. In addition, nonspecific protein kinase inhibitors, staurosporin and H7 attenuated c-jun expression, whereas the analogue of ATP (sangivamycin) did not. Furthermore, the selective inhibitor of cAMP dependent protein kinase HA 1004 did not alter radiation-mediated c-jun induction. These data indicate that ionizing radiation exposure results in c-jun induction which is dependent upon the activation of PKC. Protein kinase C activation and the subsequent expression of the protooncogene c-jun by ionizing radiation may further define the molecular mechanisms of radiation-induced neoplastic transformation.

Enzyme Activation↗
PubMed1989

Effect of antisense c-raf-1 on tumorigenicity and radiation sensitivity of a human squamous carcinoma.

Antisense RNA-mediated inhibition of gene expression was used to investigate the biological function of the c-raf-1 gene in a radiation-resistant human squamous carcinoma cell line, SQ-20B. S1 nuclease protection assays revealed that transfection of full-length raf complementary DNA in the antisense orientation (AS) leads to a specific reduction (greater than tenfold) of steady-state levels of the endogenous c-raf-1 sense (S) transcript in SQ-20B cells. In nude mice, the malignant potential of SQ-20B cells transfected with raf (S) was significantly increased relative to that of SQ-20B cells transfected with raf (AS). SQ-20B cells containing transfected raf (S) maintained a radiation-resistant phenotype as compared to those cells harboring the AS version, which appeared to have enhanced radiation sensitivity. These data indicate that the reduced expression of endogenous c-raf-1 is sufficient to modulate the tumorigenicity and the radiation-resistant phenotype of SQ-20B cells, thus implicating c-raf-1 in a pathway important to the genesis of this type of cancer.

Animals↗
PubMed1988

Some retinoblastomas, osteosarcomas, and soft tissue sarcomas may share a common etiology.

DNA and RNA were extracted from primary human osteosarcomas and soft tissue sarcomas obtained from patients without retinoblastoma and were analyzed by hybridization with a cDNA probe for RB mRNA; absence or alterations of the RB gene are associated with development of retinoblastoma. Most of the osteosarcomas or soft tissue sarcomas examined by us did not express detectable levels of RB mRNA, whereas normal cells and epithelial tumor cells did. One osteosarcoma expressed a 2.4-kilobase transcript in addition to a normal 4.7-kilobase species. Our data suggest that transcriptional inactivation or post-transcriptional down-regulation of the RB gene may be important in the etiology of some osteosarcomas and soft tissue sarcomas as well as retinoblastomas.

Bone Neoplasms↗
PubMed1987

The maximum recovery potential of human tumor cells may predict clinical outcome in radiotherapy.

We studied inherent radiosensitivity/resistance (D0), ability to accumulate sublethal damage (n) and repair of potentially lethal damage (PLDR) in established human tumor cell lines as well as early passage human tumor cell lines derived from patients with known outcome following radiotherapy. Survival 24 hrs after treatment of human tumor cells with X rays in plateau phase cultures is a function of initial damage (D0, n), as well as recovery over 24 hrs (PLDR). A surviving fraction greater than .1 24 hrs following treatment with 7 Gy in plateau phase cultures is associated with tumor cell types (melanoma, osteosarcoma) with a high probability of radiotherapy failure or tumor cells derived from patients who actually failed radiotherapy. Therefore, total cellular recovery following radiation may be an important determinant or radiocurability. Accurate assays of radiotherapy outcome may need to account for all these radiobiological parameters.

Cell Line↗
PubMed1986

Radiation-resistant and repair-proficient human tumor cells may be associated with radiotherapy failure in head- and neck-cancer patients.

Inherent cellular radioresistance and repair of x-ray damage was studied in 19 early-passage squamous cell carcinoma lines derived from head- and neck-cancer patients with known clinical results following radiotherapy. Human tumor cells that were radioresistant and/or proficient in accumulation/repair of x-ray damage were cultured from patients unsuccessfully treated with radiotherapy. Thus, the presence of radiation-resistant and repair-proficient tumor cells was associated with clinical radiation failure, suggesting the possibility of a predictive assay based on in vitro radiobiological parameters.

Carcinoma, Squamous Cell↗