Establishment of tumor cell lines from a patient with head and neck cancer and their different sensitivities to anti-cancer agents

Pharmacological Activity of Cepharanthine

Cepharanthine, a natural bisbenzylisoquinoline (BBIQ) alkaloid isolated from the plant Stephania Cephalantha Hayata, is the only bisbenzylisoquinoline alkaloid approved for human use and has been used in the clinic for more than 70 years. Cepharanthine has a variety of medicinal properties, including signaling pathway inhibitory activities, immunomodulatory activities, and antiviral activities. Recently, cepharanthine has been confirmed to greatly inhibit SARS-CoV-2 infection. Therefore, we aimed to describe the pharmacological properties and mechanisms of cepharanthine, mainly including antitumor, anti-inflammatory, anti-pathogen activities, inhibition of bone resorption, treatment of alopecia, treatment of snake bite, and other activities. At the same time, we analyzed and summarized the potential antiviral mechanism of cepharanthine and concluded that one of the most important anti-viral mechanisms of cepharanthine may be the stability of plasma membrane fluidity. Additionally, we explained its safety and bioavailability, which provides evidence for cepharanthine as a potential drug for the treatment of a variety of diseases. Finally, we further discuss the potential new clinical applications of cepharanthine and provide direction for its future development.

Establishment and genetic characterization of six unique tumor cell lines as preclinical models for sinonasal squamous cell carcinoma

Sinonasal squamous cell carcinomas (SCC) are rare tumors, etiologically related to occupational exposure to wood and leather dust. In spite of surgical and radiotherapeutic advances, the 5 year survival is still 30–50%. Therefore, alternative treatment options are needed. We report the establishment and characterization of six unique human sinonasal SCC cell lines, named SCCNC1, 2, 4, 5, 6 and 7. In vitro growth and invasion characteristics were evaluated and genetic profiles were compared to those of the original primary tumors. The population doubling times ranged from 21 to 34 hours. Cell lines SCCNC2 and 7 were highly invasive in matrigel. Five cell lines carried a high number of copy number alterations, including amplifications and homozygous deletions, while one showed only three abnormalities. Sequence analysis revealed three cell lines with TP53 mutation and none with KRAS or BRAF. Overexpression of p53 was observed in five, and of EGFR in four cell lines. None of the cell lines showed strong immunopositivity of p16 or presence of human papilloma virus. In conclusion, we have created six new cell lines that are clinically and genetically representative of sinonasal SCC and that will be a useful tool for the preclinical testing of new therapeutic agents.

Ethical and technical considerations for the creation of cell lines in the head & neck and tissue harvesting for research and drug development (Part II): ethical aspects of obtaining tissue specimens

BACKGROUND

Although much has been published for the development of cell lines, these were lab based and developed for scientific technical staff.

OBJECTIVE OF REVIEW

We discuss the ethical implications of tissue retention and present a generic consent form (Part II). We also present a simple and successful protocol for the development of cell lines and tissue harvesting for the clinical scientist (Part I).

CONCLUSION

Consent is also more proximate and assurance can be given of appropriate usage. Ethical questions concerning tissue ownership are in many institutions raised during the current consenting procedure. We provide a robust ethical framework, based on the current legislation, which allows clinicians to be directly involved in cell and tissue harvesting.

Ethical and technical considerations for the creation of cell lines in the head & neck and tissue harvesting for research and drug development (Part I): techniques of tissue harvesting and propagation

Background

Although much has been published for the development of cell lines, these were lab based and developed for scientific technical staff.

Objective of review

We present a simple and successful protocol for the development of cell lines and tissue harvesting for the clinical scientist. We also discuss the ethical implications of tissue retention and present a generic consent form.

Conclusion

The advantages of hospital-based cell line creation are numerous. We can be more certain that cell lines are developed from the particular tissues of interest and accurate anatomical and appropriate clinico-pathological control tissues are also harvested. We can also be certain of less cell line cross contamination.

Multidrug resistance gene 1 expression in salivary gland adenocarcinomas and oral squamous-cell carcinomas

In combined chemotherapy for head-and-neck cancer (HNC), salivary gland-cell adenocarcinoma (SGA) shows insufficient clinical outcome, and it has been suggested that the sensitivity and/or the mechanism of resistance to anti-cancer drugs are different between SGA and oral squamous-cell carcinoma (SCC). The aim of our study was to clarify whether P-glycoprotein (P-gp) expression is associated with multidrug resistance (MDR) in HNC and the difference in the process of its development between SGA and SCC. In immunohistochemical analysis, P-gp expression was found in the ductal cells of salivary glands but not in oral mucosal epithelium. In cancer tissues, a few SCC cells in 12 of 37 and most cells in all SGAs expressed P-gp. The intensive P-gp expression was significantly found in SGA compared with SCC. In an in vivo chemotherapeutic model using tumor-bearing nude mice, P-gp expression in counterparts was observed in only a few cells of the HSY line, while no P-gp expression was observed in Hepd cells. However, P-gp expression was developed in both HSY and Hepd cell lines after vincristine (VCR) treatment. RT-PCR showed that the mean ratios of mdr1 mRNA expression levels in HSY clones were 3.7-fold higher than those in Hepd clones after VCR treatment, while each cell line exhibited both induction and activated production of P-gp. These results suggest that P-gp-related MDR in SGA is an inherent phenotype caused by both high levels of P-gp induction and activated P-gp production during VCR treatment, while that in SCC is an acquired phenotype chiefly caused by induction of P-gp.

Multidrug resistance increment in a human colon carcinoma cell line by colchicine

The most important mechanism in drug resistance is the multidrug resistance (MDR) phenomenon. It is possible to select MDR cells by in vitro exposure to cytotoxic agents. The resistance is due to the hyperexpression of the P-glycoprotein (P-Gp) that take drugs out from the cells. In this study, a colchicine resistant subline (HCA-2/1cch) was selected from a human colon adenocarcinoma after a short period of drug exposure, as an in vitro model of drug resistance selection. These cells showed cross-resistance to other drugs, which were not present in the medium during selection. The relative resistance was 3.32 for colchicine, 3.15 for vinblastine, 2.62 for vincristine and 5.22 for mitomycin C. P-glycoprotein levels were assayed by flow cytometry. It was found that a significant increase of 2.35 and 1.59 had occurred in the peak and mean channel of fluorescence, respectively, indicating an increment of P-glycoprotein expression in relation to the parental line. Moreover, verapamil (10 microg/ml) produced a partial reversion of multidrug resistance. The sensitisation rates were 7.41 for colchicine, 1.25 for vinblastine, 2.36 for vincristine and 1.17 for mitomycin C. The data obtained suggest that colchicine exposure period (10 weeks) and dose (0.5 microg/ml) assayed were sufficient to produce an increment in multidrug resistance. This resistance could be due to higher level of P-Gp expression.

Global problem of drug-induced hearing loss

Clinically used drugs and chemical agents may potentially cause adverse effects to the human auditory and vestibular systems. Many of them, such as aminoglycosides and cisplatin, can play a critical role in the treatment of serious or life-threatening diseases; others, like loop diuretics or salycilates, offer such important therapeutical effects compared to the ototoxic side effects that the ototoxicity risk can be considered to be of minor importance. The problem of ototoxic side effects is more acute in developing countries, where highly effective and low-cost drugs are more easily prescribed without adequate monitoring. Medical awareness of doses, forms of administration, populations at risk, and possible synergism is necessary in order to develop appropriate care in the prescription of drugs with ototoxic side effects. Relatively recent issues such as risk-benefit analysis, patient-informed consent, and quality-of-life considerations, particularly when life expectancy can be low, are also to be considered. At present, a uniform method of monitoring for all potentially ototoxic therapeutics does not seem reasonable or practical. It is recommended, however, that individual auditory function be noted for a particular drug being employed. Protocols and exams should be easy, quick, sensitive, reliable, and as objective as possible. Benefits of audiological monitoring include the opportunity to change the patient's treatment course, improvement of patient and family awareness of the impact of hearing impairment, and timely prescription of amplification devices. Finally, particular attention should be paid to high-risk populations such as neonatal intensive care unit patients.

Correlation of epidermal growth factor receptor and radiosensitivity in human maxillary carcinoma cell lines

To determine the relationship between epidermal growth factor receptor (EGFR) and radiosensitivity, we immunostained cells from three maxillary carcinoma cell lines with an anti-EGFR antibody. The intensity of staining reactivity, determined by means of an image analysis system, was expressed as grey value (0-black to 255-white). The mean grey values for cell lines IMC-2, IMC-3, and IMC-4 were 181, 210, and 222, respectively, and differed significantly (p < 0.001). This indicates that IMC-2 had the highest number of EGFR, followed by IMC-3 and IMC-4. The cells were then irradiated at 1, 2, 4, or 6 Gy, and cell survival was assessed by means of a standard colony-forming assay. IMC-2 had the highest survival rates at 1, 2 and 4 Gy, followed by IMC-3 and IMC-4. Therefore, the survival rates for IMC-2, IMC-3, and IMC-4 after irradiation increased in proportion to the amount of EGFR in each cell line. These results support the findings of previous clinical studies which showed that increased expression of EGFR was associated with higher recurrence rates of glottic and maxillary sinus carcinoma in patients treated with radiation therapy. The amount of EGFR in cells may therefore be associated with their radiosensitivity.

Drug resistance in human neuroblastoma cell lines correlates with clinical therapy

To determine if neuroblastoma acquires a sustained drug-resistant phenotype from patient exposure to therapy, we studied neuroblastoma cell lines established at different points of therapy: at diagnosis prior to therapy, at progressive disease after induction therapy and at relapse after intensive chemoradiotherapy and bone marrow transplantation (post-BMT). Melphalan, cisplatin, carboplatin, doxorubicin, and etoposide cytotoxicities were determined by DIMSCAN assay. Drug resistance progressively increased with therapy and 3/5 post-BMT lines showed high resistance to most drugs. IC 90s 37, 78, 719 and 256 times higher than clinically achievable drug levels were obtained in post-BMT cell lines for melphalan, cisplatin, doxorubicin and etoposide, respectively. Resistance correlated with the therapies patients received: considerable etoposide and doxorubicin resistance (> 1000-fold resistance) was seen in cell lines obtained from patients treated with these drugs. These cell lines indicate that neuroblastoma acquires resistance to cytotoxic drugs that is probably due to stable genetic alterations occurring during therapy.

In vitro effects of hyperthermia combined with cisplatin or peplomycin on the human maxillary carcinoma cell line IMC-2

We examined the interactive effects of hyperthermia combined with cisplatin (CDDP) (0.5 micrograms/ml) or peplomycin (PEP) (1.0 microgram/ml) on surviving fractions of human maxillary carcinoma IMC-2 cells. Either CDDP or PEP enhanced the 44 degree C thermosensitivity of thermotolerant cells after heating at 42 degrees C for 2 hours. The development of thermotolerance at 42 degrees C with either of the two drugs for 2 hours was not inhibited by CDDP, but it was partially inhibited by PEP. Moreover, for PEP throughout the entire period of 42-44 degrees C step-up heating, the 44 degree C thermosensitivity of thermotolerant cells after heating at 42 degrees C with PEP for 2 hours was enhanced similarly to that at 44 degrees C with PEP. Heating at 42 degrees C combined with either of the two drugs showed a marked interactive effect.

Synergistic effects of tamoxifen and cepharanthine for circumventing the multidrug resistance

We examined the synergistic effects of tamoxifen (TAM) and cepharanthine (CEP) for doxorubicin (DOX) sensitivity using MTT assay. The augmentation of DOX sensitivity by TAM and CEP was significantly correlated with the P-glycoprotein expression. The cytotoxic effect of DOX with TAM and CEP was significantly higher than that of DOX alone, or DOX with TAM, and this synergistic effect was dominant in cell lines with high expression of P-glycoprotein. It was also examined that the intracellular concentration of DOX was increased in combined exposure of TAM and CEP, compared with the exposure of TAM, because TAM and CEP promoted the influx and inhibited the efflux of DOX. Thus, TAM and CEP might be able to circumvent DOX-resistance for treatment in cancer patients.

Cell, tissue and organ culture as in vitro models to study the biology of squamous cell carcinomas of the head and neck

In vitro models are currently being used to study head and neck squamous cell carcinoma (HNSCC). Several hundred HNSCC cell lines have been established by various investigators and used to study a broad spectrum of questions related to head and neck cancer. The head and neck model with respect to multistage carcinogenesis is now complete. Several techniques exist for the culture of normal epithelial cells from the upper aerodigestive tract (UADT). The biology of these UADT cells (oral cavity, oropharynx, hypopharynx and larynx) is being studied. Successful culture of premalignant lesions (dysplastic mucosa, leukoplakia, erythroplakia) has resulted in establishment of a limited number of premalignant cell lines and cell cultures. HPV infection of normal oral epithelial cells for immortalization (approximately premalignant cells) coupled with transformation with carcinogens (malignant cells) has established an experimental model for progression. Two in vivo models for oral carcinogenesis, the 7,12 dimethylbenz(a)anthracene-induced hamster cheek pouch model and the 4-nitroquinoline-N-oxide rat oral model, have been established in culture. Thus, multistage carcinogenesis models have been established from both human tissues and animal models and include cultures of normal, premalignant and malignant cells. Culture techniques for growing dissociated primary tumor cells for short term experimental analysis are being used. The culture of normal or tumor tissue as organ/explant cultures allows for the maintenance of normal cell-cell and cell-matrix interaction, but limits experimentation since these cultures cannot be propagated. Several three dimensional model systems are being used to obtain this histological complexity but allow for experimentation. The ability to culture normal, premalignant and malignant cells coupled with the use of a variety of culture techniques, should allow for the continued growth and experimentation in head and neck cancer research.

Induction of bleomycin resistance in a human oral squamous carcinoma cell line and characterisation of bleomycin-resistant and -sensitive clones

We examined the change of sensitivity to antitumour agents by repeated treatment with bleomycin (BLM) using two oral squamous carcinoma cell lines, SCCTF and SCCKN. SCCTF exhibited minimal sensitivity to BLM and strong heterogeneity in BLM sensitivity, whereas SCCKN was highly sensitive to BLM and showed weak heterogeneity. When SCCTF was treated continuously with low-dose BLM (0.1 microgram/ml) but not intermittently with high-dose BLM (1 microgram/ml), the BLM sensitivity was rapidly decreased to acquire drug resistance. On the other hand, SCCKN was completely killed by the same treatments. To investigate the mechanism of induction of resistance in SCCTF, BLM-sensitive and -resistant clones, TF-S and TF-R, were isolated and analysed. Consequently, TF-R showed decreased cellular accumulation and retention of BLM, increased BLM hydrolase activity and elevated DNA repair activity concomitant with increased poly(ADP-ribose) polymerase activity as compared with TF-S. Therefore, it was suggested that antitumour drug-resistant clones were selectively grown from heterogeneous tumour cell population.

Additive effects of cepharanthin in CDDP/hyperthermia combination therapy against transplantable human esophageal cancer in nude mice

PURPOSE

Additive effects of cepharanthin in CDDP/hyperthermia combination therapy were evaluated.

METHODS AND MATERIALS

Nude mice bearing a transplantable human esophageal cancer (ES0-2), classified histologically as a moderately differentiated squamous cell carcinoma, were treated with cepharanthin (20 mg/kg IP) in addition to cis-diamminedichloroplatinum(II) (CDDP; 4 mg/kg IP) and/or hyperthermia at 42 degrees C for 30 min, to determine the additive effects of cepharanthin. Furthermore, effects of cepharanthin on intratumoral concentration of CDDP were evaluated.

RESULTS

Cepharanthin itself did not have an anti-tumor effect. This agent did not enhance the anti-tumor effect of CDDP alone, but enhanced the anti-tumor effects of both 42 degrees C hyperthermia alone, and combination therapy with CDDP and 42 degrees C hyperthermia. The concentration of CDDP in the tumors treated by 42 degrees C hyperthermia was slightly higher than in nonheated tumors. Cepharanthin did not affect the intratumoral concentration of CDDP, irrespective of whether hyperthermia was applied.

CONCLUSION

Cepharanthin enhanced the effect of CDDP/hyperthermia combination therapy through thermoenhancing effect.

Different sensitivities of human esophageal cancer cells to multiple anti-cancer agents and related mechanisms

Mechanisms responsible for drug resistance in human esophageal cancer cell lines were investigated. Three cell lines established from human esophageal carcinoma (TE-1, SH-1, and TH) showed different sensitivities to vindesine, vincristine, cisplatin (CDDP), etoposide (VP-16), and pepleomycin. Both SH-1 and TH cell lines were twofold to sevenfold more resistant to pepleomycin, vindesine, and vincristine than TE-1 was. SH-1 showed twofold more resistance to CDDP than either TE-1 or TH did, and TH and TE-1 showed a 3-fold or 1.5-fold more resistance, respectively, to VP-16 than SH-1 did. The accumulation of tritiated vincristine in SH-1 and TH was approximately 50% that in TE-1. Two multidrug resistance reversal agents, cepharanthine and a synthetic dihydropyridine analogue (NK-252; Nikken Chemicals, Saitama, Japan), potentiated the cytocidal actions of vindesine against SH-1, TH, and TE-1 cells, with no apparent expression of P-glycoprotein in the three cell lines. The glutathione S-transferase pi gene was expressed in all three cell lines. DNA topoisomerase II levels were lowest in TE-1, followed by SH-1 and TH, although the accumulation of tritiated VP-16 was less in both TH and SH-1 than in TE-1. Differential sensitivities to anti-cancer drugs appear to be mediated through pleiotropic mechanisms.

Heterogeneity in epidermal growth factor responsiveness and tumor growth of human maxillary cancer cell lines

We have established three cell lines (IMC-2, IMC-3, and IMC-4) from a human maxillary tumor, which exhibited different sensitivities to epidermal growth factor (EGF). It was inhibitory to colony-forming abilities of IMC-3 and IMC-4 cells in culture, while it affected that of IMC-2 cells slightly if at all. The differential sensitivities to EGF among the three cell lines were reproducibly observed when several cell sublines were further established from tumors appearing in nude mice. Saturation-binding kinetics with 125I-EGF showed similar levels of EGF-binding activities among the three cell lines. However, IMC-2, IMC-3, and IMC-4 showed almost similar sensitivities to cisplatin. Autophosphorylation of EGF receptor in the presence of EGF proceeded at similar levels among the three cell lines. Tumor growth was followed in nude mice when IMC-2, IMC-3, and IMC-4 at 1 x 10(7) cells were inoculated. The IMC-2 tumors enlarged at much faster rates than the other two cell lines. The IMC-4 tumors showed very slow growth rates, and IMC-3 tumors enlarged at an intermediate rate. These data suggest that the maxillary tumor used comprised cell populations that differed in their growth behaviors in response to EGF.

Establishment of human squamous carcinoma cell lines highly and minimally sensitive to bleomycin and analysis of factors involved in the sensitivity

Human squamous carcinoma cell lines that were highly and minimally sensitive to bleomycin were established from clinical specimens and designated as SCCKN and SCCTF, respectively. Although these cell lines showed a similar growth doubling time in vitro, SCCTF was approximately ten times less sensitive to bleomycin than SCCKN. The bleomycin high and low sensitivities were stable even at the 70-cell passage level in vitro. In addition, nude mouse tumors produced by SCCTF were less sensitive to bleomycin that those produced by SCCKN, and the ratio of the mean tumor weight in bleomycin-treated mice to that in control mice was 89.2% in SCCTF and 18.8% in SCCKN. As compared with SCCKN, SCCTF also was less sensitive to peplomycin (5-fold), mitomycin C (2.3-fold), cis-diamine dichloroplatinum (2.5-fold), and vincristine (6.5-fold). Analyses of low bleomycin sensitivity showed that SCCTF had an approximately 20% decreased cellular accumulation and retention of bleomycin, 1.2-fold increase of bleomycin hydrolase activity, elevated DNA repair activity, and increased poly(adenosine diphosphate-ribose) polymerase activity as compared with SCCKN.

The response to epidermal growth factor of human maxillary tumor cells in terms of tumor growth, invasion and expression of proteinase inhibitors

Three cancer cell lines, IMC-2, IMC-3 and IMC-4, were established from a single tumor of a patient with maxillary cancer. We examined responses to epidermal growth factor (EGF) of these 3 cell lines with regard to cell growth and tumor invasion. The growth rate of IMC-2 in nude mice was markedly faster than that of the IMC-3 and IMC-4 cell lines. Assay for invasion through fibrin gels showed significantly enhanced invasive capacity of IMC-2 cells in response to EGF, but no change for IMC-3 and IMC-4 cells. We examined response to EGF of IMC-2 cells with regard to expression of a growth-related oncogene (c-fos), proteinases and their inhibitors. Expression of c-fos was transiently increased in IMC-2 cells at rates comparable to those seen in the 2 other lines in the presence of EGF. There was no apparent effect of EGF on the expression of urokinase-type plasminogen activator and 72-kDa type-IV collagenase in IMC-2 cells. In contrast, EGF specifically enhanced the expression of plasminogen activator inhibitor-I (PAI-I) and tissue inhibitor of metalloproteinases-I (TIMP-I) in IMC-2 cells. Our data suggest that proteinase inhibitors or other related factors may play an important role in tumor growth and invasion in response to EGF.

Appearance of drug-resistant tumor cells in a maxillary cancer patient undergoing chemotherapy and chemoradiotherapy

In this study, we examine drug resistance and sensitivity in tumor cell lines cultured from a patient undergoing prolonged chemotherapy. Four serially established primary tumor cell lines (KKM-A, -B, -C, and -D) were cultured from a case of maxillary sinus carcinoma: KKM-A from the nontreated primary tumor; KKM-B from the residual tumor after chemotherapy with cisplatin (CDDP) and 5-fluorouracil (5-FU); KKM-C from the local tumor that recurred following complete remission with chemoradiotherapy (combination of 5-FU, vitamin A, and radiation); and KKM-D from a metastatic lymph node tumor after further chemotherapy with CDDP and peplomycin. The sensitivity of the four cell lines to CDDP, 5-FU bleomycin (BLM), carboquone (CQ), and colchicine was assessed according to the reduction in colony formation. The KKM-A cell line was very sensitive to CDDP, BLM, CQ, and colchicine, whereas the posttreatment cell lines were resistant to these four drugs. The resistant cell lines were probably selected as a result of chemotherapy and radiotherapy. The nontreated KKM-A cell line was naturally somewhat resistant to 5-FU. The 5-FU-resistance of the KKM-B, -C, and -D cell lines was reduced in that order, corresponding to their relative degree of treatment. The KKM-D cell line from the metastatic lymph node showed a different sensitivity from the KKM-B and -C cell lines from the primary site, suggesting a heterogeneity in drug sensitivity between primary and metastatic tumor cells.

Expression of ret proto-oncogene in human neuroblastomas

We examined the expression of ret proto-oncogene (proto-ret) in surgically resected human neuroblastomas. Slot blot RNA hybridization revealed that all 29 neuroblastomas examined expressed the proto-ret, the relative intensity of the hybridization ranging from 1 to 48. No correlation was found between the level of expression of proto-ret and the clinical stage. The level of expression was also not correlated with N-myc amplification, the patient's age or the histological type of the tumor. Based on the previous finding that proto-ret expression is very rarely detected in tumor cell lines other than those of neuroblastoma, proto-ret expression was suggested to be a characteristic of neuroblastomas, and possibly to be involved in the genesis of neuroblastomas.

Potentiation of some anticancer agents by dipyridamole against drug-sensitive and drug-resistant cancer cell lines

In this study, we have used two different vincristine (VCR)-resistant variants, VJ-300 and HC-7-5/VCR. VJ-300 was isolated from a human cancer KB cell line and HC-7-5/VCR from a human cancer HC-7-5 cell line. VJ-300 and HC-7-5/VCR are both multidrug-resistant (MDR) variants, showing resistance to multiple anticancer drugs such as VCR, adriamycin, actinomycin D and daunomycin. Dipyridamole, a specific inhibitor of nucleoside transport, potentiated these anticancer drugs about 2- to 10-fold against KB and VJ-300. Dipyridamole almost completely reversed drug resistance to actinomycin D in VJ-300 cells with about a 70-fold higher resistance to actinomycin D. Dipyridamole inhibited the efflux of actinomycin D and VCR from VJ-300 cells. Dipyridamole enhanced the uptake of VCR but not that of actinomycin D in VJ-300 and KB. Dipyridamole at 10-100 microM inhibited photoaffinity labeling with [3H]azidopine of the cell-surface protein P-glycoprotein in VJ-300 cells. Dipyridamole potentiated 5-fluorouracil and hexylcarbamoyl-5-fluorouracil in cultured KB and VJ-300, but it annihilated the cytotoxic action of 5-fluorouridine. Potentiation of 5-fluorouracil by dipyridamole against HC-7-5 and HC-7-5/VCR was also observed, but appeared to be less than in VJ-300 and KB cells. Dipyridamole almost completely inhibited the cellular accumulation of 5-fluorouridine, but not that of 5-fluorouracil. Thus, dipyridamole appeared to potentiate anticancer agents through pleiotropic action sites, one of which is inhibition of enhanced efflux of MDR cell lines and the other of which is inhibition of nucleoside transport. Dipyridamole might be a useful and potent agent to potentiate anticancer agents and reverse drug-resistance.

Vincristine-resistant human cancer KB cell line and increased expression of multidrug-resistance gene

A multidrug-resistant clone of human cancer KB cells was isolated by stepwise selection on exposure to increasing doses of vincristine. The final clone, VJ-300, obtained after ethylmethane sulfonate mutagenesis showed 400-fold higher resistance to vincristine than did KB cells. Cellular accumulation of vincristine in VJ-300 was decreased to less than one-tenth of that in KB. The cells were also cross-resistant to daunomycin, adriamycin, actinomycin D, colchicine and VP-16. During continuous culturing in the absence of any drug for several months, a different colchicine-resistant and multidrug-resistant clone, KB-C1, reverted almost completely to drug sensitivity, whereas drug resistance in VJ-300 was stably maintained. Amplification of the multidrug-resistance-1 (mdr-1) gene was more than 20-fold in KB-C1, but less than 2-fold in VJ-300. mdr-1 mRNA was, however, expressed in VJ-300 at a rate comparable to KB-C1. Acquisition of high multidrug resistance in VJ-300 might be correlated with both activated transcription of mdr-1 gene and amplification.