Relationship between the parameters cellular differentiation, doubling time and platinum accumulation and cisplatin sensitivity in a panel of head and neck cancer cell lines

Modulation of PD‑L1 expression by standard therapy in head and neck cancer cell lines and exosomes

Although checkpoint inhibitors (CPI) have recently extended the treatment options and improved clinical response of advanced stage head and neck squamous cell carcinoma (HNSCC), treatment success remains unpredictable. Programmed cell death ligand‑1 (PD‑L1) is a key player in immunotherapy. Tumor cells, and exosomes derived therefrom, are carriers of PD‑L1 and efficiently suppress immune responses. The aim of the present study was to analyze the influence of established therapies on PD‑L1 expression of HNSCC cell lines and their exosomes. The HNSCC cell lines, UM‑SCC‑11B, UM‑SCC‑14C and UM‑SCC‑22C were treated with fractionated radiotherapy (RT; 5x2 Gy), cisplatin (CT) and cetuximab (Cetux) as monotherapy, or combined therapy, chemoradiotherapy (CRT; RT and CT) or radioimmunotherapy (RT and Cetux). The expression of PD‑L1 and phosphorylated (p)ERK1/2 as a mediator of radioresistance were assessed using western blotting, immunohistochemistry and an ex vivo vital tissue culture model. Additionally, exosomes were isolated from concentrated supernatants of the (un‑)treated HNSCC cell lines by size exclusion chromatography. Exosomal protein expression levels of PD‑L1 were detected using western blotting and semi‑quantitative levels were calculated. The functional impact of exosomes from the (un‑)treated HNSCC cell lines on the proliferation (MTS assay) and apoptosis (Caspase 3/7 assay) of the untreated HNSCC cell lines were measured and compared. The HNSCC cell lines UM‑SCC‑11B and UM‑SCC‑22B showed strong expression of pERK1/2 and PD‑L1, respectively. RT upregulated the PD‑L1 expression in UM‑SCC‑11B and UM‑SCC‑14C and in exosomes from all three cell lines. CT alone induced PD‑L1 expression in all cell lines. CRT induced the expression of PD‑L1 in all HNSCC cell lines and exosomes from UM‑SCC‑14C and UM‑SCC‑22B. The data indicated a potential co‑regulation of PD‑L1 and activated ERK1/2, most evident in UM‑SCC‑14C. Exosomes from irradiated UM‑SCC‑14C cells protected the unirradiated cells from apoptosis by Caspase 3/7 downregulation. The present study suggested a tumor cell‑mediated regulation of PD‑L1 upon platinum‑based CRT in HNSCC and in exosomes. A co‑regulation of PD‑L1 and MAPK signaling response was hypothesized.

Two anti-angiogenic TKI-PET tracers, [(11)C]axitinib and [(11)C]nintedanib: Radiosynthesis, in vivo metabolism and initial biodistribution studies in rodents

INTRODUCTION

Tyrosine kinase inhibitors (TKIs) are very attractive targeted drugs, although a large portion of patients remains unresponsive. PET imaging with EGFR targeting TKIs ([(11)C]erlotinib and [(18)F]afatinib) showed promise in identifying treatment sensitive tumors. The aim of this study was to synthesize two anti-angiogenic TKI tracers, [(11)C]axitinib and [(11)C]nintedanib, and to evaluate their potential for PET.

METHODS

Following successful tracer synthesis, biodistribution studies in VU-SCC-OE and FaDu xenograft bearing mice were performed. Furthermore, tracer stability studies in mice were performed employing (radio-)HPLC and LC-MS/MS techniques. For [(11)C]nintedanib an LC-MS/MS method was developed to detect the primary carboxylic acid metabolite, resulting from methylester cleavage, in plasma and tumors, because this metabolite is postulated to be important for nintedanib efficacy. LC-MS/MS was also explored to assess the metabolic fate of [(11)C]axitinib in vivo, since axitinib has an isomerizable double bond.

RESULTS

[(11)C]axitinib and [(11)C]nintedanib were successfully synthesized with 10.5±2.6% and 25.6±3.3% radiochemical yield (corrected for decay), respectively. Biodistribution studies only demonstrated tumor uptake of [(11)C]nintedanib in FaDu xenografts of 1.66±0.02% ID/g at 60min p.i. In vivo stability analysis of [(11)C]axitinib at 45min p.i. revealed the formation of predominantly non-polar metabolites (36.6±6.8% vs 47.1±8.4% of parent tracer and 16.3±2.1% of polar metabolites), while for [(11)C]nintedanib mostly polar metabolites were found (70.9±4.1 vs 26.7±3.9% of parent tracer and only 2.4±1.6 of a non-polar metabolites). No isomerization of [(11)C]axtinib was observed in vivo; however, a sulfoxide metabolite could be detected using LC-MS/MS. For [(11)C]nintedanib, LC-MS/MS revealed formation of the reported primary carboxylic acid metabolite when in vitro plasma incubations were performed, with large differences in plasmas from different species. In vivo metabolite analysis, however, did not demonstrate the presence of the carboxylic acid in plasma or tumor tissue.

CONCLUSIONS

Reliable syntheses of [(11)C]axitinib and [(11)C]nintedanib were successfully developed. Tumor uptake was observed for [(11)C]nintedanib, albeit modest. The metabolic profiles of the tracers suggest that rapid metabolism is partly responsible for the modest tumor targeting observed.

Facile labelling of an anti-epidermal growth factor receptor Nanobody with 68Ga via a novel bifunctional desferal chelate for immuno-PET

Purpose

The ∼15 kDa variable domains of camelid heavy-chain-only antibodies (called Nanobodies®) have the flexibility to be formatted as monovalent, monospecific, multivalent or multispecific single chain proteins with either fast or slow pharmacokinetics. We report the evaluation of the fast kinetic anti-epidermal growth factor receptor (EGFR) Nanobody 7D12, labelled with ⁶⁸Ga via the novel bifunctional chelate (BFC) p-isothiocyanatobenzyl-desferrioxamine (Df-Bz-NCS). Df-Bz-NCS has recently been introduced as the chelate of choice for ⁸⁹Zr immuno-positron emission tomography (PET).

Methods

Nanobody 7D12 was premodified with Df-Bz-NCS at pH 9. Radiolabelling with purified ⁶⁸Ga was performed at pH 5.0–6.5 for 5 min at room temperature. For in vitro stability measurements in storage buffer (0.25 M NaOAc with 5 mg ml⁻¹ gentisic acid, pH 5.5) at 4°C or in human serum at 37°C, a mixture of ⁶⁷Ga and ⁶⁸Ga was used. Biodistribution and immuno-PET studies of ⁶⁸Ga-Df-Bz-NCS-7D12 were performed in nude mice bearing A431 xenografts using ⁸⁹Zr-Df-Bz-NCS-7D12 as the reference conjugate.

Results

The Df-Bz-NCS chelate was conjugated to Nanobody 7D12 with a chelate to Nanobody molar substitution ratio of 0.2:1. The overall ⁶⁸Ga radiochemical yield was 55–70% (not corrected for decay); specific activity was 100–500 MBq/mg. Radiochemical purity of the conjugate was >96%, while the integrity and immunoreactivity were preserved. ^68/67Ga-Df-Bz-NCS-7D12 was stable in storage buffer as well as in human serum during a 5-h incubation period (<2% radioactivity loss). In biodistribution studies the ⁶⁸Ga-labelled Nanobody 7D12 showed high uptake in A431 tumours (ranging from 6.1 ± 1.3 to 7.2 ± 1.5%ID/g at 1–3 h after injection) and high tumour to blood ratios, which increased from 8.2 to 14.4 and 25.7 at 1, 2 and 3 h after injection, respectively. High uptake was also observed in the kidneys. Biodistribution was similar to that of the reference conjugate ⁸⁹Zr-Df-Bz-NCS-7D12. Tumours were clearly visualized in a PET imaging study.

Conclusion

Via a rapid procedure under mild conditions a ⁶⁸Ga-Nanobody was obtained that exhibited high tumour uptake and tumour to normal tissue ratios in nude mice bearing A431 xenografts. Fast kinetic ⁶⁸Ga-Nanobody conjugates can be promising tools for tumour detection and imaging of target expression.

p-Isothiocyanatobenzyl-desferrioxamine: a new bifunctional chelate for facile radiolabeling of monoclonal antibodies with zirconium-89 for immuno-PET imaging

Purpose

Immuno-PET is an emerging imaging tool for the selection of high potential antibodies (mAbs) for imaging and therapy. The positron emitter zirconium-89 (⁸⁹Zr) has attractive characteristics for immuno-PET with intact mAbs. Previously, we have described a multi-step procedure for stable coupling of ⁸⁹Zr to mAbs via the bifunctional chelate (BFC) tetrafluorophenol-N-succinyldesferal (TFP-N-sucDf). To enable widespread use of ⁸⁹Zr-immuno-PET, we now introduce the novel BFC p-isothiocyanatobenzyl-desferrioxamine B (Df-Bz-NCS) and compare its performance in ⁸⁹Zr-immuno-PET with the reference BFC TFP-N-sucDf.

Methods

Three mAbs were premodified with Df-Bz-NCS and labeled with ⁸⁹Zr at different pHs to assess the reaction kinetics and robustness of the radiolabeling. Stability of both ⁸⁹Zr-Df-Bz-NCS- and ⁸⁹Zr-N-sucDf-conjugates was evaluated in different buffers and human serum. Comparative biodistribution and PET studies in tumor-bearing mice were undertaken.

Results

The selected conjugation conditions resulted in a chelate:mAb substitution ratio of about 1.5:1. Under optimal radiolabeling conditions (pH between 6.8–7.2), the radiochemical yield was >85% after 60 min incubation at room temperature, resulting in radioimmunoconjugates with preserved integrity and immunoreactivity. The new radioimmunoconjugate was very stable in serum for up to 7 days at 37°C, with <5% ⁸⁹Zr release, and was equally stable compared to the reference conjugate when stored in the appropriate buffer at 4°C. In biodistribution and imaging experiments, the novel and the reference radioimmunoconjugates showed high and similar accumulation in tumors in nude mice.

Conclusions

The novel Df-Bz-NCS BFC allows efficient and easy preparation of optimally performing ⁸⁹Zr-labeled mAbs, facilitating further exploration of ⁸⁹Zr-immuno-PET as an imaging tool.

APM2 is a novel mediator of cisplatin resistance in a variety of cancer cell types regardless of p53 or MMR status

Cisplatin is one of the most widely used chemotherapeutics in the world today. Unfortunately, chemoresistance often develops hindering the effectiveness of the drug. Mismatch-repair (MMR) and p53 have previously been shown to be important determinants of cisplatin resistance and can contribute to cisplatin resistance clinically. Here, we have used cDNA microarray to identify several genes as up or downregulated in a previously described, cisplatin resistant, clone of the HCT116 cell line (HCT116-K). On follow-up, one gene, APM2, was found to promote cisplatin resistance when overexpressed in sensitive HCT116 clones. Furthermore, silencing APM2 in a panel of cell lines encompassing all combinations of p53 status and MMR proficiency (HCT116-K, HCT116, SW620, MCF7, PC-3 and OV2008) resulted in sensitization regardless of these 2 factors. In addition, silencing APM2 stably using shRNA also resulted in the sensitization of cells to cisplatin. More importantly, cisplatin inhibited the growth of APM2 silenced tumor xenografts (HCT116-K or OV2008 cells) significantly better than it inhibited the growth of xenografts carrying nontargeting control shRNAs. These findings represent a novel strategy that could be exploited to overcome cisplatin resistance in patients regardless of p53 status or ability to perform MMR.

Cell cycle checkpoint models for cellular pharmacology of paclitaxel and platinum drugs

A pharmacokinetic-pharmacodynamic mathematical model is developed for cellular pharmacology of chemotherapeutic drugs for which the decisive step towards cell death occurs at a point in the cell cycle, presumably corresponding to a cell cycle checkpoint. For each cell, the model assumes a threshold level of some intracellular species at that checkpoint, beyond which the cell dies. The threshold level is assumed to have a log-normal distribution in the cell population. The kinetics of formation of the lethal intracellular species depends on the drug, and on the cellular pharmacokinetics and binding kinetics of the cell. Specific models are developed for paclitaxel and for platinum drugs (cisplatin, oxaliplatin and carboplatin). In the case of paclitaxel, two separate mechanisms of cell death necessitate a model that accounts for two checkpoints, with different intracellular species. The model was tested on a number of in vitro cytotoxicity data sets for these drugs, and found overall to give significantly better fits than previously proposed cellular pharmacodynamic models. It provides an explanation for the asymptotic convergence of dose-response curves as exposure time becomes long.

Monitoring response to radiotherapy in human squamous cell cancer bearing nude mice: comparison of 2'-deoxy-2'-[18F]fluoro-D-glucose (FDG) and 3'-[18F]fluoro-3'-deoxythymidine (FLT)

Objective

The uptake of 3′-[¹⁸F]fluoro-3′-deoxythymidine (FLT), a proliferation marker, was measured before and during fractionated radiotherapy to evaluate the potential of FLT-positron emission tomography (PET) imaging as an indicator of tumor response compared to 2′-deoxy-2′-[¹⁸F]fluoro-d-glucose (FDG).

Materials and Methods

Nude mice bearing established human head and neck xenografts (HNX-OE; nu/nu mice) were locally irradiated (three fractions/week; 22 Gy) using a 150-kV_p unit. Multiple FDG- and FLT-PET scans were acquired during treatment. Tumor volume was determined regularly, and tissue was analyzed for biomarkers involved in tracer uptake.

Results

Both groups revealed a significant decline in tumor volume (P < 0.01) compared to untreated tumors. For FDG as well as for FLT, a significant decline in retention was observed at day 4. For FLT, most significant decline in retention was observed at day 12; whereas, for FDG, this was already noted at day 4. Maximum decline in tumor-to-nontumor ratios (T/NT) for FDG and FLT was 42 ± 18% and 49 ± 16% (mean ± SD), respectively. FLT uptake was higher then that of FDG. For FLT, statistical significant correlations were found for both tumor volume at baseline and at day 29 with T/NT and ΔT/NT. All tumors demonstrated expression of glucose transporter-1, thymidine kinase-1, and hexokinase II. No differences were found for amount of tumor cells and necrosis at the end of treatment.

Conclusion

This new experimental in vivo model supports the promise of using FLT-PET, as with FDG-PET, to monitor response to external radiotherapy. This warrants further clinical studies to compare these two tracers especially in cancers treated with radiotherapy.

Cytotoxic effects of the oncolytic herpes simplex virus HSV1716 alone and in combination with cisplatin in head and neck squamous cell carcinoma

CONCLUSIONS

HSV1716 alone and combined with cisplatin was efficacious in destroying head and neck squamous cell carcinoma (HNSCC) cells. Combination treatment with HSV1716 and cisplatin gave additive efficacy. These results indicate that HSV1716 in combination with cisplatin could be of therapeutic value in HNSCC and warrants further investigation.

OBJECTIVES

HSV1716 is a replication competent herpes simplex virus which selectively replicates and lyses actively dividing cells but not normal or terminally differentiated cells. The objective of this study was to determine the efficacy of HSV1716 alone and in combination with cisplatin in HNSCC.

MATERIALS AND METHODS

Three HNSCC cell lines were studied; UM-SCC 14C, UM-SCC 22A and UM-SCC 22B. The permissivity of HSV1716 in these cell lines was determined using multicycle growth experiments. In vitro, cytotoxicity of HSV1716 and cisplatin was determined using an MTS proliferation assay. Isobologram analysis was used to determine the interaction between HSV1716 and cisplatin combination treatment.

RESULTS

The three HNSCC cell lines studied were permissive for HSV1716 replication. Cytotoxicity increased in a dose-dependent fashion in all three cell lines. Cisplatin was non-toxic to the virus. Isobologram analysis showed additive cytotoxicity when HSV1716 was combined with cisplatin in all three cell lines.

Tumor and normal tissue pharmacokinetics of perifosine, an oral anti-cancer alkylphospholipid

Clinical use of anti-cancer alkylphospholipids is limited by gastrointestinal toxicity. However, new interest has emerged since it was shown that these drugs enhance the cytotoxic effect of conventional chemotherapy and radiotherapy in preclinical models. The aim of this study was to characterize the pharmacokinetic profile of perifosine, an oral analog of alkylphosphocholine (APC), and to compare in vitro drug uptake with in vivo drug accumulation in three human-derived squamous cell carcinomas (A431, HNXOE and KB). In vitro, KB cells showed a remarkably high uptake and sensitivity for perifosine compared with A431 and HNXOE cells. In vivo, perifosine reached a clinically relevant plasma concentration in mice after a single oral dose of 40 mg/kg. Perifosine was not metabolized and displayed slow elimination, with a terminal half-life of 137 (+/- 20) hours and an apparent volume of distribution of 11.3 l/kg. Comparable tumor accumulation was observed for A431 and HNXOE tumors, whereas perifosine uptake by KB xenografts was substantially higher. Tissue distribution occurred throughout the whole body reaching high perifosine levels in the gastro-intestinal tract, while heart and brain tissue contained relatively low levels. Based on its stability and relatively high tumor uptake in vivo, perifosine is an attractive candidate for further evaluation, e.g. as radiosensitizer.

Tumour resistance to cisplatin: a modelling approach

Although chemotherapy has revolutionized the treatment of haematological tumours, in many common solid tumours the success has been limited. Some of the reasons for the limitations are: the timing of drug delivery, resistance to the drug, repopulation between cycles of chemotherapy and the lack of complete understanding of the pharmacokinetics and pharmacodynamics of a specific agent. Cisplatin is among the most effective cytotoxic agents used in head and neck cancer treatments. When modelling cisplatin as a single agent, the properties of cisplatin only have to be taken into account, reducing the number of assumptions that are considered in the generalized chemotherapy models. The aim of the present paper is to model the biological effect of cisplatin and to simulate the consequence of cisplatin resistance on tumour control. The 'treated' tumour is a squamous cell carcinoma of the head and neck, previously grown by computer-based Monte Carlo techniques. The model maintained the biological constitution of a tumour through the generation of stem cells, proliferating cells and non-proliferating cells. Cell kinetic parameters (mean cell cycle time, cell loss factor, thymidine labelling index) were also consistent with the literature. A sensitivity study on the contribution of various mechanisms leading to drug resistance is undertaken. To quantify the extent of drug resistance, the cisplatin resistance factor (CRF) is defined as the ratio between the number of surviving cells of the resistant population and the number of surviving cells of the sensitive population, determined after the same treatment time. It is shown that there is a supra-linear dependence of CRF on the percentage of cisplatin-DNA adducts formed, and a sigmoid-like dependence between CRF and the percentage of cells killed in resistant tumours. Drug resistance is shown to be a cumulative process which eventually can overcome tumour regression leading to treatment failure.

Characterization of the human Ly-6 antigens, the newly annotated member Ly-6K included, as molecular markers for head-and-neck squamous cell carcinoma

The E48 antigen is a successfully explored molecular marker for the diagnosis and therapy of HNSCC. The applicability of E48 as an HNSCC-associated antigen, however, is restricted due to its heterogeneous expression in 30% of tumors; and identification of additional target antigens is therefore desired. E48 belongs to the Ly-6 antigen family, comprising a group of highly homologous, low m.w., GPI-anchored surface proteins, of which some show tissue-restricted expression patterns. To identify novel human HNSCC-associated Ly-6 members with squamous cell-associated expression patterns, we performed comprehensive gene-screening consisting of BLAST searches within GenBank databases, followed by expression analysis. Using this approach, the Ly-6K gene could be annotated as a novel member of the human Ly-6 family. Expression of the human Ly-6 genes E48, Ly-6K, PSCA, GML, RIG-E, G6C and Ly-6H was prescreened by qualitative RT-PCR and subsequently analyzed by quantitative RT-PCR in normal keratinocytes, HNSCC cell lines, normal mucosa, HNSCC tumors as well as normal peripheral blood and bone marrow cells. PSCA was highly expressed in normal mucosa, but 100-fold decreased expression was seen in HNSCC. For Ly-6H, GML and G6C, no or very low expression was observed in keratinocytes and HNSCC. Expression of RIG-E was high in normal and malignant squamous cells and in peripheral blood and bone marrow cells, thus limiting its applicability as an HNSCC-associated marker. In contrast, besides the E48 gene, the Ly-6K gene also appeared to be selectively expressed in HNSCC and normal squamous cells. Moreover, expression of Ly-6K was shown in HNSCC cell lines, in which no E48 expression could be detected. These data justify further evaluation of Ly-6K as potential target antigen for the diagnosis and therapy of HNSCC.

Expression of retinoic acid receptor gamma correlates with retinoic acid sensitivity and metabolism in head and neck squamous cell carcinoma cell lines

Retinoids, analogues of vitamin A, can reverse premalignant lesions and prevent second primary tumors in patients with head and neck squamous cell carcinoma (HNSCC). The effects of retinoids are mediated by retinoic acid receptors (RARs) and retinoid X receptors (RXRs), which act as ligand-activated transcription factors. The regulation of cell growth, differentiation and retinoid metabolism in normal, premalignant and malignant cells by retinoids is thought to be a result of their effects on gene expression. We investigated mRNA expression of RARs (alpha, beta, and gamma) and RXR-beta by means of RNase protection and related this to retinoic acid (RA)-induced growth inhibition and RA turnover in four HNSCC cell lines (UM-SCC-14C, UM-SCC-22A, UM-SCC-35 and VU-SCC-OE). An RA-resistant subline of UM-SCC-35 was generated by exposure to increasing concentrations of RA for 8 months (designated UM-SCC-35R). RA turnover was determined on the basis of decreasing RA levels in the cells and culture medium after exposure to 1 microM RA. We found that RAR-gamma mRNA expression was strongly correlated with RA-induced growth inhibition (p = 0.016, R = 0.92) and RA turnover (p = 0.041, R = 0.86). RAR-beta transcript levels were reduced in three of five cell lines compared with normal mucosa, and these did not correlate with RA-induced growth inhibition and RA turnover. Expression of RAR-alpha and RXR-beta was not substantially altered in any of the cell lines. These findings suggest that in HNSCC cell lines RAR-gamma is the most important retinoid receptor for regulation of RA turnover rate and RA-induced growth inhibition.

Deoxyglucose uptake by a head and neck squamous carcinoma: influence of changes in proliferative fraction

PURPOSE

Positron emission tomography, using the glucose analogue fluorodeoxy-D-glucose (FDG), is proving to be useful in the early response detection of head and neck tumors. Presently mechanisms underlying changes in FDG uptake after therapy are poorly understood. Response of tumors to therapy is often accompanied by a decrease in tumor cell proliferation. The purpose of this study was to assess whether or not changes in the uptake of deoxyglucose (DG) may reflect differences in proliferative fraction independent of other metabolic changes induced by using therapeutic agents.

METHODS AND MATERIALS

HN5 head and neck tumor cells were grown to different cell densities producing populations of cells with different proliferative indices without the need for exogenous agents to manipulate cell-cycle kinetics. (3)H-DG uptake, S-phase fraction (Spf), and lactate production were determined in each population of cells.

RESULTS

Large differences in Spf between populations of cells were associated with differences in DG incorporation. Lactate production was also found to correlate strongly with DG uptake.

CONCLUSION

Therapy-induced changes in FDG uptake by tumors may be partly due to changes in proliferation.

Effect of cisplatin exposure on platinum accumulation and growth inhibition in human neoplastic and normal squamous epithelial cells of the mucosa of the upper-aerodigestive tract

The aim of the present study was to investigate how normal head and neck epithelial cells (NHNEC) respond to cisplatin compared to their neoplastic counterparts with respect to intracellular platinum (Pt) levels and growth inhibition. A colorimetric assay was used to assess growth inhibition after exposure to cisplatin for 72 h. Growth inhibition did not differ between cultures of neoplastic (n = 5) and normal cells (n = 5). Intracellular Pt levels, determined with atomic absorption spectroscopy were about 30-fold higher in the normal epithelial cells. The main finding of this study is that normal epithelial cells from the head and neck region have a much higher tolerance for cisplatin than their neoplastic counterparts. Interestingly, this characteristic is without consequence for growth inhibition.

Regulation of CD95 (Apo-1/Fas) ligand and receptor expression in squamous-cell carcinoma by interferon-gamma and cisplatin

CD95 (Apo-1/Fas) ligand (CD95L) expression has been observed in various malignancies. In human primary cell lines from a squamous cell carcinoma (SCC) of the vulva, the effect of cisplatin (CDDP) and IFNgamma on the expression of CD95L and its 2 receptor isoforms, CD95 transmembrane (CD95tm) and CD95 soluble receptor, was studied at the mRNA and protein levels. Addition of CDDP and IFNgamma increased CD95L mRNA levels in the primary cell line 6-fold and 1.7-fold, respectively. In comparison, CD95tm mRNA levels were diminished by CDDP but increased 8-fold upon IFNgamma challenge. CD95L expressed by SCC cells was functionally relevant since these cells were able to induce CD95-specific apoptosis in autologous lymphocytes from the SCC-bearing patient. Thus, CD95L expression in SCC may contribute to tumor-associated immunosuppression, which may be modulated by CDDP and IFNgamma. In tumor samples of the primary SCC, CD95L expression was enhanced in the area of the border between invasive tumor tissue and surrounding stroma cells. The locally restricted over-expression of CD95L was congruent with the arrangement of apoptotic stroma cells in the direct vicinity of invading tumor tongues, suggesting a role as invasion factor for CD95L.

Pharmacodynamics of cisplatin in human head and neck cancer: correlation between platinum content, DNA adduct levels and drug sensitivity in vitro and in vivo

Total platinum contents and cisplatin-DNA adduct levels were determined in vivo in xenografted tumour tissues in mice and in vitro in cultured tumour cells of head and neck squamous cell carcinoma (HNSCC), and correlated with sensitivity to cisplatin. In vivo, a panel of five HNSCC tumour lines growing as xenografts in nude mice was used. In vitro, the panel consisted of five HNSCC cell lines, of which four had an in vivo equivalent. Sensitivity to cisplatin varied three- to sevenfold among cell lines and tumours respectively. However, the ranking of the sensitivities of the tumour lines (in vivo), also after reinjection of the cultured tumour cells, did not coincide with that of the corresponding cell lines, which showed that cell culture systems are not representative for the in vivo situation. Both in vitro and in vivo, however, significant correlations were found between total platinum levels, measured by atomic absorption spectrophotometry (AAS), and tumour response to cisplatin therapy at all time points tested. The levels of the two major cisplatin-DNA adduct types were determined by a recently developed and improved 32P post-labelling assay at various time points after cisplatin treatment. Evidence is presented that the platinum-AG adduct, in which platinum is bound to guanine and an adjacent adenine, may be the cytotoxic lesion because a significant correlation was found between the platinum-AG levels and the sensitivities in our panel of HNSCC, in vitro as well as in vivo. This correlation with the platinum-AG levels was established at 1 h (in vitro) and 3 h (in vivo) after the start of the cisplatin treatment, which emphasizes the importance of early sampling.

Role of glutathione, glutathione S-transferases and multidrug resistance-related proteins in cisplatin sensitivity of head and neck cancer cell lines

Resistance to chemotherapy is a major problem in the treatment of patients with head and neck squamous cell carcinoma (HNSCC). Important factors involved are drug detoxification by glutathione (GSH) and reduced drug accumulation due to active transport out of the cell by so-called 'multidrug resistance-related proteins'. We have studied a panel of eight HNSCC cell lines showing differences in sensitivity to the anti-cancer drug cisplatin. Our previous studies indicated that the IC50 values were inversely correlated with the intracellular accumulation of platinum (Pt). In the present study, cellular GSH levels were found not to be related to the IC50 values. The expression levels of the enzymes glutathione S-transferase (GST) alpha, mu, and pi, the multidrug resistance-related proteins P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP) and the lung resistance protein (LRP) were determined semiquantitatively by means of immunocytochemistry. The levels of the GSTs, P-gp and LRP were not found to be correlated with the IC50 values of the HNSCC cell lines. Surprisingly, however, an inverse correlation was found between MRP levels and IC50 values. The MRP expression levels were in agreement with the results of the MRP functional assay, based on the transport of calcein across the cell membrane as performed for two of the cell lines. Further studies should prove whether other pump mechanisms or DNA repair are involved in the cisplatin accumulation and the subsequent HNSCC cell growth inhibition.

The formation and repair of cisplatin-DNA adducts in wild-type and cisplatin-resistant L1210 cells: comparison of immunocytochemical determination with detection in isolated DNA

We have studied the formation and repair of cisplatin-DNA adducts in wild-type mouse leukemia L1210/0 cells and in the sublines L1210/2 and L1210/5, which differ in cisplatin sensitivity. In a colony-formation assay these sublines were 9- and 22-fold more resistant compared to L1210/0, respectively. Cisplatin-induced DNA modification was studied at the cellular level by immunocytochemistry with antiserum NKI-A59 raised against cisplatin-treated DNA. Levels of nuclear staining immediately after a 1-h treatment were similar to those seen after a 24-h post-incubation in drug-free medium. Clear differences in DNA platination were found between the cell lines: immediately after exposure, L1210/2 and L1210/5 showed only 32 and 14%, respectively, of the nuclear staining observed in L1210/0, and 48 and 13% after 24 h. In these experiments, adduct-specific nuclear staining was quantified as the area under the adduct versus concentration curves (AUC). The formation and repair in these cell lines of the bifunctional adducts cis-Pt(NH3)2d(pGpG) (Pt-GG), cis-Pt(NH3)2d(pApG) (Pt-AG) and cis-Pt(NH3)2(dGMP)2 (G-Pt-G) were studied with an enzyme-linked immunosorbent assay (ELISA). No relation between repair and resistance was observed. The results suggest that differences in induced DNA platination levels, rather than in repair, are responsible--at least in part--for the differences in cisplatin resistance. A mechanism such as an increased tolerance of the resistant cells to plantinum-DNA damage may also be involved.