Cellular X-ray repair parameters of early passage squamous cell carcinoma lines derived from patients with known responses to radiotherapy

Diffuse reflectance spectroscopy for optical characterizations of orthotopic head and neck cancer models in vivo

We demonstrated an easy-to-build, portable diffuse reflectance spectroscopy device along with a Monte Carlo inverse model to quantify tissue absorption and scattering-based parameters of orthotopic head and neck cancer models in vivo. Both tissue-mimicking phantom studies and animal studies were conducted to verify the optical spectroscopy system and Monte Carlo inverse model for the accurate extraction of tissue optical properties. For the first time, we reported the tissue absorption and scattering coefficients of mouse normal tongue tissues and tongue tumor tissues. Our in vivo animal studies showed reduced total hemoglobin concentration, lower tissue vascular oxygen saturation, and increased tissue scattering in the orthotopic tongue tumors compared to the normal tongue tissues. Our data also showed that mice tongue tumors with different sizes may have significantly different tissue absorption and scattering-based parameters. Small tongue tumors (volume was ∼60 mm3) had increased absorption coefficients, decreased reduced-scattering coefficients, and increased total hemoglobin concentrations compared to tiny tongue tumors (volume was ∼18 mm3). These results demonstrated the potential of diffuse reflectance spectroscopy to noninvasively evaluate tumor biology using orthotopic tongue cancer models for future head and neck cancer research.

Ethanol induces replication fork stalling and membrane stress in immortalized laryngeal cells

Although ethanol is a class I carcinogen and is linked to more than 700,000 cancer incidences, a clear understanding of the molecular mechanisms underlying ethanol-related carcinogenesis is still lacking. Further understanding of ethanol-related cell damage can contribute to reducing or treating alcohol-related cancers. Here, we investigated the effects of both short- and long-term exposure of human laryngeal epithelial cells to different ethanol concentrations. RNA sequencing shows that ethanol altered gene expression patterns in a time- and concentration-dependent way, affecting genes involved in ribosome biogenesis, cytoskeleton remodeling, Wnt signaling, and transmembrane ion transport. Additionally, ethanol induced a slower cell proliferation, a delayed cell cycle progression, and replication fork stalling. In addition, ethanol exposure resulted in morphological changes, which could be associated with membrane stress. Taken together, our data yields a comprehensive view of molecular changes associated with ethanol stress in epithelial cells of the upper aerodigestive tract.

EGFR overexpression increases radiotherapy response in HPV-positive head and neck cancer through inhibition of DNA damage repair and HPV E6 downregulation

High-risk Human Papillomavirus (HPV) infections have recently emerged as an independent risk factor in head and neck squamous cell carcinoma (HNSCC). There has been a marked increase in the incidence of HPV-induced HNSCC subtype, which demonstrates different genetics with better treatment outcome. Despite the favourable prognosis of HPV-HNSCC, the treatment modality, consisting of high dose radiotherapy (RT) in combination with chemotherapy (CT), remains similar to HPV-negative tumours, associated with toxic side effects. Epidermal growth factor receptor (EGFR) is overexpressed in over 80% of HNSCC and correlates with RT resistance. EGFR inhibitor Cetuximab is the only FDA approved targeted therapy for both HNSCC subtypes, however the response varies between HNSCC subtypes. In HPV-negative HNSCC, Cetuximab sensitises HNSCC to RT improving survival rates. To reduce adverse cytotoxicity of CT, Cetuximab has been approved for treatment de-escalation of HPV-positive HNSCC. The results of several recent clinical trials have concluded differing outcome to HPV-negative HNSCC. Here we investigated the role of EGFR in HPV-positive HNSCC response to RT. Remarkably, in HPV-positive HNSCC cell lines and in vivo tumour models, EGFR activation was strongly indicative of increased RT response. In response to RT, EGFR activation induced impairment of DNA damage repair and increased RT response. Furthermore, EGFR was found to downregulate HPV oncoproteinE6 expression and induced p53 activity in response to RT. Collectively, our data uncovers a novel role for EGFR in virally induced HNSCC and highlights the importance of using EGFR-targeted therapies in the context of the genetic makeup of cancer.

A Novel Peptide for Simultaneously Enhanced Treatment of Head and Neck Cancer and Mitigation of Oral Mucositis

We have characterized a novel 21 amino acid-peptide derived from Antrum Mucosal Protein (AMP)-18 that mediates growth promotion of cultured normal epithelial cells and mitigates radiation-induced oral mucositis in animal models, while suppressing in vitro function of cancer cells. The objective of this study was to evaluate these dual potential therapeutic effects of AMP peptide in a clinically relevant animal model of head and neck cancer (HNC) by simultaneously assessing its effect on tumor growth and radiation-induced oral mucositis in an orthotopic model of HNC. Bioluminescent SCC-25 HNC cells were injected into the anterior tongue and tumors that formed were then subjected to focal radiation treatment. Tumor size was assessed using an in vivo imaging system, and the extent of oral mucositis was compared between animals treated with AMP peptide or vehicle (controls). Synergism between AMP peptide and radiation therapy was suggested by the finding that tumors in the AMP peptide/radiation therapy cohort demonstrated inhibited growth vs. radiation therapy-only treated tumors, while AMP peptide-treatment delayed the onset and reduced the severity of radiation therapy-induced oral mucositis. A differential effect on apoptosis appears to be one mechanism by which AMP-18 can stimulate growth and repair of injured mucosal epithelial cells while inhibiting proliferation of HNC cells. RNA microarray analysis identified pathways that are differentially targeted by AMP-18 in HNC vs. nontransformed cells. These observations confirm the notion that normal cells and tumor cells may respond differently to common biological stimuli, and that leveraging this finding in the case of AMP-18 may provide a clinically relevant opportunity.

Optical metabolic imaging of treatment response in human head and neck squamous cell carcinoma

Optical metabolic imaging measures fluorescence intensity and lifetimes from metabolic cofactors nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD). These molecular level measurements provide unique biomarkers for early cellular responses to cancer treatments. Head and neck squamous cell carcinoma (HNSCC) is an attractive target for optical imaging because of easy access to the site using fiber optic probes. Two HNSCC cell lines, SCC25 and SCC61, were treated with Cetuximab (anti-EGFR antibody), BGT226 (PI3K/mTOR inhibitor), or cisplatin (chemotherapy) for 24 hours. Results show increased redox ratio, NADH α1 (contribution from free NADH), and FAD α1 (contribution from protein-bound FAD) for malignant cells compared with the nonmalignant cell line OKF6 (p<0.05). In SCC25 and SCC61 cells, the redox ratio is unaffected by cetuximab treatment and decreases with BGT226 and cisplatin treatment (p<0.05), and these results agree with standard measurements of proliferation rates after treatment. For SCC25, NADH α1 is reduced with BGT226 and cisplatin treatment. For SCC61, NADH α1 is reduced with cetuximab, BGT226, and cisplatin treatment. Trends in NADH α1 are statistically similar to changes in standard measurements of glycolytic rates after treatment. FAD α1 is reduced with cisplatin treatment (p<0.05). These shifts in optical endpoints reflect early metabolic changes induced by drug treatment. Overall, these results indicate that optical metabolic imaging has potential to detect early response to cancer treatment in HNSCC, enabling optimal treatment regimens and improved patient outcomes.

A keratinocyte hypermotility/growth-arrest response involving laminin 5 and p16INK4A activated in wound healing and senescence

Keratinocytes become migratory to heal wounds, during early neoplastic invasion, and when undergoing telomere-unrelated senescence in culture. All three settings are associated with expression of the cell cycle inhibitor p16INK4A (p16) and of the basement membrane protein laminin 5 (LN5). We have investigated cause-and-effect relationships among laminin 5, p16, hypermotility, and growth arrest. Plating primary human keratinocytes on the gamma2 precursor form of laminin 5 (LN5') immediately induced directional hypermotility at approximately 125 microm/hour, followed by p16 expression and growth arrest. Cells deficient in p16 and either p14ARF or p53 became hypermotile in response to LN5' but did not arrest growth. Plating on LN5' triggered smad nuclear translocation, and all LN5' effects were blocked by a transforming growth factor (TGF) beta receptor I (TGFbetaRI) kinase inhibitor. In contrast, plating cells on collagen I triggered a TGFbetaRI kinase-independent hypermotility unaccompanied by smad translocation or growth arrest. Plating on control surfaces with TGFbeta induced hypermotility after a 1-day lag time and growth arrest by a p16-independent mechanism. Keratinocytes serially cultured with TGFbetaRI kinase inhibitor exhibited an extended lifespan, and immortalization was facilitated following transduction to express the catalytic subunit of telomerase (TERT). These results reveal fundamental features of a keratinocyte hyper-motility/growth-arrest response that is activated in wound healing, tumor suppression, and during serial culture.

Cyclopamine increases the cytotoxic effects of paclitaxel and radiation but not cisplatin and gemcitabine in Hedgehog expressing pancreatic cancer cells

INTRODUCTION

The hedgehog signaling pathway (Hh) is frequently over expressed in pancreatic adenocarcinomas. We studied the potential cytotoxic interactions between cyclopamine, a Hh pathway inhibitor and paclitaxel, cisplatin, gemcitabine and ionizing radiation (IR).

METHODS

In vitro clonogenic survival analysis was performed with cyclopamine alone or cyclopamine in combination with paclitaxel, gemcitabine, cisplatin and IR in Hh expressing human pancreatic tumor cells and Hh non-expressing colon cancer cells. Relative cytotoxicity was assessed in combination treatment compared with exposure to single agents. Assays of apoptosis (annexin V) were performed in the presence of cyclopamine, chemotherapeutic agents, and IR.

RESULTS

We report that cyclopamine increased the cytotoxic effects of paclitaxel and IR in Hh expressing pancreatic carcinoma cells. These effects were not observed in Hh non-expressing cells. Cyclopamine did not significantly increase killing by cisplatin or gemcitabine in Hh expressing pancreatic cancer cells.

CONCLUSIONS

These data suggest strategies to combine Hh inhibitors with radiotherapy and chemotherapeutic agents, specifically paclitaxel and related compounds in the treatment of pancreatic cancer.

Effect of photodynamic therapy in combination with ionizing radiation on human squamous cell carcinoma cell lines of the head and neck

Photodynamic therapy (PDT) is a promising treatment modality for head and neck, and other tumours, using drugs activated by light. A second generation drug, 5-aminolaevulinic acid (5-ALA), is a precursor of the active photosensitizer protoporphyrin IX (PpIX) and has fewer side-effects and much more transient phototoxicity than previous photosensitizers. We have investigated the effect of 5-ALA mediated PDT in combination with gamma-irradiation on the colony forming ability of several human head and neck tumour cell lines. The effect of treatments on the DNA cell cycle kinetics was also investigated. Our results indicate that the combination of 5-ALA mediated PDT and gamma-irradiation results in a level of cytotoxicity which is additive and not synergistic. 5-ALA mediated PDT had no discernible effect on DNA cell cycle distributions. gamma-irradiation-induced cell cycle arrest in G2 did not enhance the phototoxicity of 5-ALA.

Evaluation of radiation-induced DNA damage and DNA repair in human lung cancer cell lines with different radiosensitivity using alkaline and neutral single cell gel electrophoresis

Using the comet assay, radiation-induced DNA strand breaks were evaluated in human lung cancer cell lines with different radiosensitivity (U-1285, U-1906E, U-1752 and U-1810). Single strand breaks were more sensitive indicators of the radiation-induced damage than double strand breaks. However, there was no consistent pattern in the way the various cell lines responded to 1-5 Gy of gamma-irradiation and all cell lines showed a remarkably efficient DNA repair after 1 h. In a separate study of the repair kinetics of DNA double strand breaks, the radioresistant cell line U-1810 showed a more efficient initial strand rejoining than the radiosensitive cell line U-1285 after irradiation at 2 Gy. The latter finding suggests that the detection of early DNA repair may be useful when monitoring the intrinsic radiosensitivity of human lung cancer cells.

Determination of radiosensitivity in established and primary squamous cell carcinoma cultures using the micronucleus assay

In this study, the cytokinesis-block micronucleus assay (CBMN) was used to measure radiosensitivity in three established cell lines (SCC-61, V175 and V134) and 10 primary cell cultures of squamous cell carcinoma (SCC) of the head and neck. Assessment involved optimisation of the assay to determine cytochalasin-B (CB) concentration and sampling time postirradiation. A much closer correlation between dose-response data measured in the clonogenic and micronucleus assays was found when the micronucleus assay was performed under standardised conditions for each cell line (2 micrograms/ml CB: 48 h postirradiation) instead of predetermined optimised assay conditions. This indicates that, for these SCC cell lines, the CBMN assay may be able to predict in vitro radiosensitivity. To be of clinical use in predicting radiosensitivity, the CBMN assay also needs to be evaluated with primary cell cultures. In this study, no relationship between micronucleus frequency at 2 or 6 Gy and patient clinical outcome 12 months following surgery and radiotherapy was seen. Similarly, no association between patient outcome and tumour stage, nodal stage and histology was observed. These CBMN assay data from the primary cell cultures are presently inconclusive as a measure of patient tumour radiosensitivity.

Modulation of clonogenicity, growth, and radiosensitivity of three human epidermoid tumor cell lines by a fibroblastic environment

PURPOSE

To develop a model vitro system to examine the influence of fibroblasts on the growth and survival of human tumor cells after exposure to ionizing radiation.

METHODS AND MATERIALS

The cell system of three epidermoid carcinoma cell lines derived from head and neck tumors having differing growth potentials and intrinsic radiosensitivities, as well as a low passage skin fibroblast strain from a normal human donor. The tumor cells were seeded for five days prior to exposure to radiation: (a) in the presence of different numbers of fibroblasts, (b) in conditioned medium from stationary fibroblast cultures, and (c) on an extracted fibroblastic matrix.

RESULTS

When grown with fibroblasts, all three tumor cell lines showed increased clonogenicity and increased radioresistance. The radioprotective effect was maximal at a density of approximately 10(5) fibroblasts/100 mm Petri dish, and was greatest in the intrinsically radiosensitive tumor cell line. On the other hand, the effects of incubation with conditioned medium or on a fibroblastic matrix varied among the tumor cell lines. Thus, the protective effect afforded by coculture with fibroblasts must involve several cellular factors related to the fibroblast itself.

CONCLUSIONS

These observations emphasize the importance of cultural conditions on the apparent radiosensitivity of human tumor cell lines, and suggest that the fibroblastic connective tissue enveloping the malignant cells should be considered when the aim is to establish a radiopredictive assay from surgical tumor fragments.

A review of human cell radiosensitivity in vitro

The survival curves of 694 human cell lines irradiated in exponentially growing phase in vitro were collected from the literature. Among them, 271 were derived from tumors, 423 were nontransformed fibroblasts and other normal cell strains from healthy people or people with some genetic disorders. Seventy-six different cell types are identified, and a specific radiosensitivity could be associated with each, using D and surviving fraction at 2 Gy. Technical factors such as culture medium, feeder cells, and scoring method were found to affect intrinsic radiosensitivity. In particular, the cell type is not a discriminating factor when cells are studied in agar. Results obtained with cells irradiated in agar must be used cautiously, depending on how the cells were prepared for the experiments. The use of feeder cells narrows the range of radiosensitivity of human cells. For cells irradiated as monolayer, it was possible to build a scale of radiosensitivity according to cell type, ranging, in terms of D from 0.6 Gy for the most sensitive cell lines to more than 4 Gy for the most resistant. Considering that, in most cases, we could estimate the variation of radiosensitivity within each cell type, our classification among cell types can be used by researchers to place their results in the context of the literature.

Cytotoxicity of restriction enzyme-induced DNA strand breaks in radiosensitive and radioresistant human tumor cell lines

PURPOSE

To examine the role of sensitivity to specific types of DNA double strand breaks in human tumor cell response.

METHODS AND MATERIALS

The X ray-sensitive human squamous carcinoma cell line SCC-61 and the X ray-resistant line SQ-20B were exposed to the restriction enzymes HaeIII, HinfI, PvuII, BamHI by electroporation. Cytotoxicity of these restriction endonucleases was measured by a colony formation assay.

RESULTS

Cell killing by each enzyme occurred in a concentration-dependent manner. The radiosensitive cell line was more sensitive to all four restriction enzymes than the radioresistant line, paralleling the response to ionizing radiation. However, the magnitude of the difference was smaller than for radiation. The 5-base sticky ended cutter HinfI and 6-base blunt ended cutter PvuII were much more effective in killing cells from both lines than BamHI, a 6-base sticky ended cutter, whereas the 4-base blunt ended cutter HaeIII was intermediate in its effectiveness. Thus, enzyme sensitivity could not be related to the type of cutter or the distance between cutting sites.

Sublethal damage repair in squamous cell carcinoma cell lines

Squamous cell carcinoma (SCC) cell lines recently established from head and neck tumors were studied for their capability of repairing sublethal radiation induced damage (SLDR). Total doses of 1.25, 2.50, 5.00, and 7.50 Gy were used either as a single dose or split in two equal fractions with a 24 h interval. Cell survival was determined using a 96-well plate clonogenic assay based on limiting dilution. Survival data was fitted by linear quadratic model, and the area under the survival curve (AUC) was obtained with numerical integration. The amount of SLDR was expressed as AUC-ratio comparing survivals from split dose vs single dose experiments. SLDR capacity was observed to vary markedly between individual cell lines (AUC-ratios 1.0-1.5). The relatively radiation-sensitive cell lines had a tendency toward higher SLDR proficiency (correlation coefficient 0.85). The differences in repair capacity could not be explained by the differences in doubling times of the cell lines. The inverse relationship between SLDR capacity and inherent radiosensitivity could explain the poor radiocurability of the sensitive donor tumors. Two of the most resistant cell lines were found SLDR deficient. This is a novel finding, since SLDR has been previously reported in all studied cells.

A linear-quadratic model of cell survival considering both sublethal and potentially lethal radiation damage

We assessed the dose-dependence of repair of potentially lethal damage in Chinese hamster ovary cells x-irradiated in vitro. The recovery ratio (RR) by which survival (SF) of the irradiated cells was enhanced increased exponentially with a linear and a quadratic component, namely xi and psi: RR = e xi D + psi D2. Survival of irradiated cells can thus be expressed by a combined linear-quadratic model considering four variable, namely alpha and beta for the capacity of the cells to accumulate sublethal damage, and xi and psi for their capacity to repair potentially lethal damage: SF = e(xi - alpha)D + (psi - beta)D2.

In vitro radiation resistance among cell lines established from patients with squamous cell carcinoma of the head and neck

Twenty-five squamous cell carcinoma (SCC) cell lines from 20 patients with head and neck cancer were assessed for radiosensitivity in vitro using a 96-well plate assay. Four non-SCC lines were also tested. Radiation sensitivity of individual cell lines was compared using the area under the survival curve (AUC) as a measure of the mean inactivation dose. Tumor lines were tested with either a cobalt-60 (60Co) gamma-irradiator having a dose rate of 100 cGy/minute or with a 4-meV photon beam having a dose rate of 200 cGy/minute. The mean AUC of the 25 SCC cell lines was 188 +/- 7 (SEM) cGy (range, 100 to 250 cGy) whereas the four non-SCC lines had a mean AUC of 225 +/- 9 cGy. The SCC cell lines with mean inactivation dose values greater than 188 cGy were classified as relatively radioresistant whereas those with values less than 188 cGy were considered relatively radiosensitive. In seven cases SCC cell lines were derived from patients who had already received radiation therapy. In four of these cases the tumor cell lines were radioresistant (AUC, 210 to 250) but in the other three cases the tumor lines were radiosensitive (AUC, 160 to 180). Thus, failure of a tumor to respond to radiation did not always select for radioresistant cells. The mean of the AUC for cell lines from previously irradiated patients (197 +/- 11 cGy) did not differ significantly from that of the cell lines from patients who received no prior radiation therapy (182 +/- 9 cGy). However, among radiation-resistant lines those from the four previously irradiated patients were significantly more resistant (mean AUC = 235 +/- 9) than seven other radioresistant lines from nonirradiated patients (mean AUC, 208 +/- 4) (P = 0.0194). In four cases more than one cell line was derived from different tumor specimens in the same patient. In each of these cases the lines from the same patients were similar to one another in their degree of radioresistance. Based on these observations the authors conclude that the degree of in vitro radiation resistance is an inherent property of some squamous cell tumors.

Variation in radiation sensitivity during the cell cycle of two human squamous cell carcinomas

Changes in the radiation age response are described in two cell lines derived from human squamous cell carcinomas. A radioresistant tumor cell line, JSQ-3, has a DO of 240 cGy and is polyploid with a DNA content of 2.68. A relatively radiosensitive tumor cell line, SCC-61, has a DO of 126 cGy and has a DNA index of 1.16. Tumor cells were separated and synchronized by centrifugal elutriation; flow cytometry was used to determine cell-cycle parameters and relative synchrony. The radioresistant cell line, JSQ-3B, was found to have twice the number of cells in S-phase than the more sensitive cell line (28% and 13% for JSQ-3B and SCC-61B, respectively). Both cell lines, despite differences in intrinsic radiosensitivity, were most resistant during S-phase (DOs of 258 and 157 cGy for JSQ-3B and SCC-61B, respectively) and were maximally sensitive during G1 (DOs of 193 and 95 cGy for JSQ-3B and SCC-61B, respectively). Clinical implications of our findings are discussed.

Platinum-dye complexes inhibit repair of potentially lethal damage following bleomycin treatment

Several new complexes of platinum with positively charged cellular dyes have been synthesised in an effort to find chemotherapeutic drugs with increased antitumour cytotoxicity. As part of this effort, the direct cytotoxicities of some of these complexes as well as their ability to inhibit bleomycin potentially lethal damage repair (PLDR) was studied in vitro in a squamous cancer cell line of human origin (SCC-25). All of the new agents were more cytotoxic against exponentially growing than against plateau phase cell cultures. Exposure of cells to non-lethal drug concentrations for between 1 and 6 h led to measurable inhibition of bleomycin PLDR in the case of each drug tested. In order of decreasing ability to inhibit bleomycin PLDR, Pt(fast black)2, Pt(thioflavin)2 and Pt(thionin)2 were more effective than CDDP, while Pt(methylene blue)2, Pt(Rh-123)2 and Pt(pyronin Y)2 were less effective. The most directly cytotoxic agents were Pt(thioflavin)2, Pt(pyronin Y)2 and Pt(Rh-123)2 which also proved to be the least selectively toxic drugs towards exponential versus plateau phase cells. These results indicate that several of the new platinum complexes may be effective cytotoxic agents as well as effective inhibitors of DNA repair process following exposure of cells to other DNA interactive modalities.

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.

Potentially lethal damage repair in human cells

Potentially lethal damage repair (PLDR) in human cells was investigated by delayed plating experiments with three malignant tumor cell lines (breast, colon and neuroblastoma) and two normal diploid lines (lung fibroblasts) in exponential and plateau phases. All cell lines demonstrated PLDR which was considerably higher for all the cell lines in plateau phase compared to log phase. At survival levels of 0.01, the two fibroblast lines had recovery ratios of 3.8 and 4.0 for 6 h delayed plating in plateau phase. The malignant lines showed recovery ratios of 5.7 (neuroblastoma), 3.2 (breast carcinoma) and 2.4 (colon carcinoma). The data were fitted to the linear quadratic equation and in addition, a repair factor was developed to compare survival for immediate and delayed plating: S(D) = exp[-gamma (alpha D + beta D2)] where gamma = 1 for immediate plating. Previously published data on human tumor and normal lines were also fitted to this equation. In all instances the three parameter equation (alpha, beta, gamma) allowed a good fit of the survival data for immediate and delayed plating. By using the same alpha, beta for the zero hour and 6 h survival curves, the gamma factor allows a much more useful method of comparing PLDR among different cell lines. The gamma factor for the two lung fibroblast lines were 0.70 and 0.71 while skin fibroblasts also had a 0.71 factor. The six malignant lines ranged from 0.62 to 0.93 with all but the neuroblastoma line having a higher factor (and therefore decreased PLDR capacity) than the normal lines. No correlation between PLDR and in vitro radiosensitivity or clinical radiosensitivity of the tumor type was found.

Platinum complexes inhibit repair of potentially lethal damage following bleomycin treatment

The SCC-25 cell line is a well-established line derived from a human squamous carcinoma of the head and neck. The capacity of this cell line for recovery from potentially lethal damage following X-ray treatment has been documented. The survival curve of stationary phase SCC-25 cells exposed to various concentrations of bleomycin is biphasic with an initial sensitive phase and a less sensitive second phase as is common for many cell lines. Stationary phase SCC-25 cells were exposed to 100 mU ml-1 of bleomycin for 1 h. The drug was removed and the cells were allowed various periods to recover from potentially lethal damage. After 24 h, the SCC-25 cells showed a recovery ratio (R/R0) of 7.0 which corresponded to an immediate survival at a drug level of 27 mU ml-1, a dose 3.7-fold less than the exposure concentration of 100 mU ml-1. Over the course of the first 4 h following bleomycin exposure, 0.5 microM CDDP was a very effective inhibitor of potentially lethal damage repair, giving a R/R0 of 1.1 or nearly complete inhibition of recovery. Between 2 and 4 h the R/R0 was 1.6-1.8 with CDDP and 4.1-5.3 without CDDP indicating appreciable inhibition of recovery. Plant (10 microM) and Plato (10 microM) produced potentially lethal damage recovery inhibition patterns very similar to that of CDDP. After 1 h the recovery ratios in the presence of Plant and Plato were 1.1-1.3. Between 2 and 4 h, Plato and Plant gave recovery ratios of 1.8-2.3 and 1.6-1.9, respectively. NIPt and Pt(terpy) were examined at both 10 microM and 25 microM for their ability to inhibit potentially lethal damage recovery after bleomycin treatment. After 1 h, NIPt gave a recovery ratio of 1.3-1.4, and after 2-4 h the recovery ratio was 1.7-2.6. Pt(terpy) gave recovery ratios of 1.3-1.6 after 1 h and 1.5-1.8 after 24 h.

Radioresistant and repair proficient cells may determine radiocurability in human tumors

Radiosensitivity and repair of radiation damage was studied in 29 human tumor cell lines. Nine tumor lines appeared radioresistant (RAD+) and were associated with radioincurable tumors. When the ability to repair potentially lethal damage was studied in plateau phase cultures, some tumor cell lines derived from radioincurable tumors were more efficient in this process (PLDR+). The results suggest that the presence of radioresistant or repair proficient cells may be responsible for local failure following radiotherapy. Advancements in cell culture and molecular biology may lead to predictive assays useful to clinicians.

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.

Inherently radioresistant cells exist in some human tumors

We investigated the survival of 29 human tumor cell lines after treatment with ionizing radiation during exponential growth. The radiosensitivity of 20 tumor cell lines was within the range of normal fibroblasts. However, 9 cell lines derived from radio-incurable tumors appeared inherently radioresistant. When the ability to repair potentially lethal x-ray damage was studied in plateau phase cultures, some tumor cell lines derived from radio-incurable tumors were more efficient in this process. These results indicate that the presence of radioresistant and/or repair-proficient cells, which exist in some human tumors, may be responsible for failure to obtain local control following therapeutic x-ray treatment.