[Possible new indications for erythropoietin therapy]. / Mögliche neue Indikationen für die Therapie mit Erythropoietin.

The use of hematopoietic growth factors has increased rapidly during the last decade. Among the growth factors available, erythropoietin (EPO) was the first growth factor to be used clinically. To date, EPO has shown activity in the treatment of the tumor-associated anemia and for correction of tumor hypoxia, however, when compared with transfusion of erythrocytes EPO treatment did not significantly prolong survival in cancer patients in any published study so far. Recently, novel extramedullary EPO receptors have been identified leading to a better understanding of the molecular mechanisms of action of EPO. Results from these experiments and from several clinical studies suggest that EPO treatment may be beneficial for patients with (chronic) infections (HIV, inflammatory bowel disease, septic episodes) and for treatment of the fatigue syndrome following cancer chemotherapy. In addition, EPO may also improve stem cell engraftment following high-dose chemotherapy and can increase survival rates of patients with aplastic anemia and myelodysplastic syndrome. Currently, new EPO derivatives, synthetic fusion proteins and gene therapeutic studies are under clinical investigation suggesting that the EPO-induced effects may be increased significantly by these agents in the future.

Cyclooxygenase-2: a novel target for cancer chemotherapy?

Epidemiologic studies have documented a 40-50% reduction in incidence of colorectal cancer in individuals taking nonsteroidal antiinflammatory drugs (NSAIDs). Since NSAIDs are known to inhibit cyclooxygenases (COX-1, COX-2), the basic mechanism of their antitumor effects is conceivably the altered metabolism of arachidonic acid and, subsequently, prostaglandins (PGs). Although COX-2, the inducible isoform, is regularly expressed at low levels in colonic mucosa, its activity increases dramatically following mutation of the APC (adenomatous polyposis coli) gene suggesting that beta-catenin/T-cell factor mediated Wnt-signaling activity may regulate COX-2 gene expression. In addition, hypoxic conditions and sodium butyrate exposure may also contribute to COX-2 gene transcription in human cancers. The development of selective COX-2 inhibitors has made it possible to further evaluate the role of COX-2 activity in colorectal carcinogenesis. To date, at least five mechanisms by which COX-2 contributes to tumorigenesis and the malignant phenotype of tumor cells have been identified, including: (1) inhibition of apoptosis; (2) increased angiogenesis; (3) increased invasiveness; (4) modulation of inflammation/immuno-suppression; and (5) conversion of procarcinogens to carcinogens. A clear positive correlation between COX-2 expression and inhibition of apoptosis has been established, associated with increased PGE2 levels resulting in modulation of pro- and anti-apoptotic factors (e.g., bcl-2, MAKs/ras, caspase-3, Par-4). In terms of angiogenesis and invasiveness, COX-2 activity was found to increase the expression of growth factors (e.g., VDEG, PDGF, bFGF) and matrix metalloproteinases (MMPs). Since COX-2 inhibitors have been demonstrated to interfere with tumorigenesis and apoptosis, COX-2 and its gene product may be attractive targets for therapeutic and chemoprotective strategies in colorectal cancer patients. This may lead to new perspectives that by controlling the cancer phenotype, rather than attempting to eradicate all affected cells, may provide significant benefits to the cancer patient.

[Carboxypeptidase-G2-rescue in a woman with methotrexate-induced renal failure]. / Carboxypeptidase-G2-Rescue bei einer Patientin mit Methotrexat-induziertem Nierenversagen.

BACKGROUND: Methotrexate (MTX) is a very effective chemotherapeutic drug, widely used in various malignant diseases for systemic therapy. In some cases, MTX-induced renal failure occurs which may not be prevented by the standard agent folin acid as a specific antidot. This results in a MTX-accumulation in the body tissue with subsequent massive toxic side effects. CASE REPORT: We report on a 62-year-old woman with acute lymphoblastic leukemia (first diagnosis November 1997) receiving chemotherapy with 2,340 mg methotrexate over 24 hours. After an increase of the MTX-plasma-level 36 hours following MTX-application, increased serum creatinine levels (maximum 5.07 mg/dl) were found. The application of folinic acid was without any significant effect. Fifty-six hours following MTX, 50 U/kg carboxypeptidase-G2 was infused. The MTX-plasma-level decreased rapidly and a recovery of renal function was monitored. CONCLUSION: CPDG2 may be highly effective in patients after development of an MTX-induced renal failure and delayed MTX-excretion.

Cisplatin resistance and oncogenes--a review.

Cisplatin is among the most widely used broadly active cytotoxic anticancer drugs; however, its clinical efficacy is often limited by primary or the development of secondary resistance. Several mechanisms have been implicated in cisplatin resistance, including reduced drug uptake, increased cellular thiol/folate levels and increased DNA repair. More recently, additional pathways have been characterized indicating that altered expression of oncogenes that subsequently limit the formation of cisplatin-DNA adducts and activate anti-apoptotic pathways may also contribute to the resistance phenotype. Several lines of evidence suggest that expression of ras oncogenes can confer resistance to cisplatin by reducing drug uptake and increasing DNA repair; however, this is not a uniform finding. Tumor cells, in contrast to normal cells, respond to cisplatin exposure with transient gene expression to protect or repair their chromosomes. The c-fos/AP-1 complex, a master switch for turning on other genes in response to DNA-damaging agents, has been shown to play a major role in cisplatin resistance. In addition, AP-2 transcription factors, modulated by protein kinase A, are also implicated in cisplatin resistance by regulating genes encoding for DNA polymerase beta and metallothionines. Furthermore, considerable evidence indicates that mutated p53 plays a significant role in the development of cisplatin resistance since several genes implicated in drug resistance and apoptosis (e.g. mismatch repair, bcl-2, high mobility group proteins, DNA polymerases alpha and beta, PCNA, and insulin-like growth factor) are known to be regulated by the p53 oncoprotein. Improved understanding of molecular factors for the development of cisplatin resistance may allow the prediction of clinical response to cisplatin-based treatment. Furthermore, the identification of oncogenes involved in cisplatin resistance has already led to in vitro approaches which successfully inactivated these genes using ribozymes or antisense oligodeoxynucleotides, thus restoring cisplatin sensitivity. It is conceivable that these strategies, once transferred to a clinical setting, may have the potential to enhance the efficacy of cisplatin against a great variety of malignancies and thus more fully exploit the antineoplastic and curative potential of this drug.

[Hemorrhagic diathesis as initial symptom of stomach carcinoma]. / Hämorrhagische Diathese als Erstsymptom eines Magenkarzinoms.

BACKGROUND: Microangiopathic hemolytic anemia (MAHA) and disseminated intravasal coagulation (DIC) as initial paraneoplastic symptoms of a solid tumor present a rare clinical situation. CASE REPORT: In 1998 a female patient was admitted due to multiple thrombosis, thrombocytopenia and fever. The initial diagnostic procedures revealed peri-aortic lymphomas and a tumor bulk (7 x 8 cm) in the upper abdomen. Gastroscopy revealed a 2 cm ulcer at the back side of the gastric corpus. Histologically, a signet-ring cell carcinoma was diagnosed. Final diagnosis stated a multilocular metastasising gastric cancer with infiltration of bone, peritoneum and dura and signet-cell infiltration of the bone marrow. Hematologic investigation in view of multiple paraneoplastic thrombosis revealed a microangiopathic hemolytic anemia associated with disseminated intravasal coagulation. Parallel to initial symptomatic therapy of coagulopathy, systemic cytostatic therapy with CDDP and VP-16 was initiated. In addition, radiotherapy of the brain was performed. After histologic confirmation of the diagnosis, weekly therapy with 5-FU (2600 mg/m2) and folinic acid (500 mg/m2) according to the Ardalan protocol was performed. After first signs of moderate response, oxaliplatin (60 mg/m2, day 1) was added. Although the chemotherapy dose had to be reduced due to prolonged neutropenia, the disturbances of hemostasis resolved completely resulting in reduced substitution rates with fresh frozen plasma (FFP) and platelets. Unfortunately, the patient died at home due to pulmonary embolism. CONCLUSION: Tumor-associated hemostaseologic alteration requires immediate substitution of FFP and platelets. However, it should be followed by specific therapy of malignancy, since tumor-induced metabolites (e.g. mucin) maintain the alteration of hemostasis. Chemotherapy may therefore be the best strategy to prevent complications such as MAHA and DIC.

HCG induced hyperthyreosis in germ cell cancer.

Human germ cell tumors have the unique capacity for totipotential differentiation. AFP (the product of normal yolk sac) and HCG (produced by trophoblastic tissues) are frequently produced by germ cell tumors. The a-subunit of the glycoprotein HCG is identical to that of several pituitary glycoprotein hormones (e.g. TSH, LH, FSH), whereas the b-subunit of HCG, TSH, LH and FSH is homologous but distinct in the terminal amino acid sequence suggesting that HCG is part of a superfamily of gestational hormones. However, the role of TSH within this hormone superfamily is still not yet established. A 24-year old patient was admitted to our clinic because of a widespread recurrence of a germ cell tumor (stage IIIC, Lugano classification). The routine hematologic and blood chemical tests were normal, yet, an elevated HCG was found. In addition, increased levels of the thyroid hormones FT3 and FT4 were seen, although, this was not associated with clinical symptoms of a hyperthyreosis. There was no history of hyperthyreosis and thyroidal autoantibody screening revealed normal titers. An ultrasound examination of the thyroid gland showed no abnormalities and no iodine exposure had occurred during the last months. To mobilize peripheral stem cells (PBSC) he was initially treated with paclitaxel (175 mg/m2) and ifosfamide (8.000 mg/m2)) followed by apheresis of PBSC. The patient was then entered in our phase-II-study for relapsing germ cell carcinomas using a high-dose chemotherapy regime (paclitaxel 175 mg/m2, ifosfamide 9.000 mg/m2, carboplatin 900 mg/m2, etoposide 900 mg/m2) with subsequent retransfusion of collected stem cells. Due to cranial metastases an cranial irradiation was also performed. After three courses of this protocol an excellent partial remission of the tumor lesions was achieved and the HCG value dramatically decreased. Due to elevated thyroidal hormones, the patient was initially treated with thiamazole (20 mg) resulting in decrease of the thyroidal hormones. Thus, the thiamazole dose was reduced to 5 mg and then omitted. The decrease of the thyroidal hormones FT3 and FT4 strongly correlated with the reduction of HCG values (r2 0.91 and 0.77, p < 0.0008). To date there is only slight evidence that enhanced HCG levels may cause, at least in part, a hyperthyreosis (e.g. gestational hyperthyreosis), however, the underlying biochemical mechanism still remains unclear. In this case report we have demonstrated a clear positive correlation between HCG levels and thyroidal hormones in a patient with germ cell tumor suggesting a direct stimulation of hormone producing thyroidal cells by HCG, however, this was not associated with clinical symptoms of hyperthyreosis. Currently, several in vitro studies are underway in our laboratory to further elucidate the biochemical mechanisms of HCG induced hyperthyreosis.

Human hematopoietic growth factors: old lessons and new perspectives.

Erythropoietin (EPO), granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage stimulating factor (GM-CSF) are currently licensed for use in cancer patients and play a significant role in the management of anemia and neutropenia following myeloblative chemotherapy. EPO was the first recombinant hematopoietic growth factor to be used clinically after a number of clinical trials which demonstrated its effectiveness in treating mild to moderate cancer-associated anemia with or without concomitant chemotherapy (particulary cisplatin). An extensive research has been made for the improvement of the quality of life with EPO therapy, however, when formally assessed, variable effects of this important treatment have been observed. Recently, EPO has been shown to significantly accelerate hematopoietic reconstitution after peripheral blood stem cell transplantation (PBSCT) resulting in reduced infection rates. Both, G-CSF and GM-CSF have been shown, in numerous trials, to shorten the period of chemotherapy-induced neutropenia, with reduction in attendant morbidity and to mobilize PBSC. In addition, administration of both cytokines after PBSCT significantly reduced the use of antibiotics and duration of hospitalization suggesting an economic benefit. The narrower therapeutic window of GM-CSF at higher doses accounts for the fact that it is used much less frequently than G-CSF. To date, none of the growth factors used clinically has been shown to stimulate thrombopoiesis. Although thrombopoietin (TPO) has been found to induce megakaryocyte differentiation in vitro, it is unlikely to enter routine clinical use for treatment of post-chemotherapy thrombocytopenia, since results of clinical trials are not very encouraging, mainly because TPO is difficult to schedule and platelet aggregation may occur. Recently, innovative chimeric growth factor receptor agonists have been synthesized. Synthokine (SC-55494) (a high-affinity human IL-3 receptor ligand analog), myelopoietin (MPO) (activates human IL-3 and G-CSF receptors) and promegapoietin (PMP) (stimulates the human IL-3 and c-mpl receptors) were found to be multilineage hematopoietic growth factors and are currently undergoing clinical trials. Preliminary results suggest that these compounds may have a major impact on the management of myeloablative chemotherapy because of their ability to enhance platelet recovery in addition to their neutrophil restorative activity.

Where do we stand with 5-fluorouracil?

For nearly four decades, 5-fluorouracil (5-FU) has been the mainstay of treatment for colorectal cancer. Due to the lack of other agents with significant activity, tremendous efforts have been undertaken to increase the efficacy of 5-FU by investigating alternative schedules of delivery and biomodulation. However, bolus 5-FU in combination with folinic acid (FA), either as the Mayo Clinic or Roswell Park protocol, still represents the standard treatment for adjuvant and first-line palliative chemotherapy of colorectal cancer. In a recent meta-analysis, infusional protocols of 5-FU demonstrated increased response rates (14% to 22%) and a marginal, but significant survival benefit of 3 weeks (11.3 to 12.1 months). In view of the much higher costs and complicated management of infusional 5-FU regimens, this marginal survival benefit does not yet allow protracted 5-FU application to be defined as standard therapy. However, protracted 5-FU infusion in combination with radiation can be considered standard therapy as adjuvant treatment of rectal cancer, since it has demonstrated a significant increase in survival. In the future, oral 5-FU prodrugs may be substituted for infusional 5-FU. Furthermore, current data indicate that 5-FU will also be an essential component of combination chemotherapy protocols with the new active agents oxaliplatin, irinotecan, and raltitrexed. Preclinical studies show synergistic antitumor activity of 5-FU with these agents, which corresponds well with clinical response rates of 50% in untreated and 15% to 25% in 5-FU-refractory patients. Moreover, 5-FU-based pro-drug-active drug systems serve as excellent models for tumor-targeted gene therapy.

Treatment of malignant pericardial effusion with 32P-colloid.

Malignant pericardial effusion is usually treated only when signs of cardiac tamponade develop. Several methods of treatment have been reported with an overall response rate of approximately 75%. Since our initial study using intrapericardial 32P-colloid instillation as a treatment modality for pericardial effusion demonstrated a significant higher response rate, this study was conducted to further evaluate the efficacy of intrapericardial 32P-colloid in terms of response rates and duration of remissions. Intrapericardial instillation of 185-370 MBq (5-10 mCi) 32P-colloid in 36 patients with malignant pericardial effusion resulted in a complete remission rate of 94.5% (34 patients) whereas two patients did not respond to treatment due to a foudroyant formation of pericardial fluid. The median duration time was 8 months. No side-effects were observed. These results suggest that intrapericardial instillation of 32P-colloid is a simple, reliable and safe treatment strategy for patients with malignant pericardial effusions. Therefore, since further evidence is provided that 32P-colloid is significantly more effective than external radiation or non-radioactive sclerosing agents, this treatment modality should be considered for the management of malignant pericardial effusion.

The role of insulin-like growth factor I and its receptor in cell growth, transformation, apoptosis, and chemoresistance in solid tumors.

Insulin-like growth factor I (IGF-I) exerts pleiotropic effects on mammalian cells via stimulation of its receptor (IGF-IR), a receptor tyrosine kinase. In vivo, IGF-I acts both as a local tissue growth factor and as a circulating hormone. In oncological research, IGF-I has received increased attention as the activated IGF-I/IGF-IR system displays mitogeneic, transforming, and anti-apoptotic properties in various cell types by stimulating distinct intracellular signaling pathways. Recent data suggest that the anti-apoptotic effect of IGF-I may mediate decreased sensitivity to chemotherapeutic drugs in vitro and in vivo. Thus, targeting the IGF-I/IGF-IR system could serve as an approach to overcome clinical drug resistance in certain tumors.

An early phase II study of intratumoral P-32 chromic phosphate injection therapy for patients with refractory solid tumors and solitary metastases.

BACKGROUND: In this early Phase II study, the authors investigated the efficacy of intratumoral injection of P-32 chromic phosphate in 17 patients with refractory solid tumors or solitary metastases in terms of response rates and overall survival. METHODS: Seventeen patients (median age, 60 years) with either cytostatic drug-resistant tumors or tumors known to be primarily chemotherapy-resistant were entered into the study. After sonographic determination of the tumor volume, P-32 chromic phosphate (74-555 MBq) was injected into the central part of the tumor under sonographic guidance. Follow-up investigations included serial scintigraphy, sonographic examinations, and hematologic studies. RESULTS: Injection of P-32 chromic phosphate into refractory tumors resulted in remarkable regression. The median survival of all patients was 13 months (range, 8-25 months). The response rate was 71% (12 patients). A complete remission was seen in 7 patients (41%), and the rate of partial remissions was 29% (5 patients). However, 5 patients (30%) did not respond to the treatment. In one patient thrombocytopenia was observed, but no other side effects were apparent. Important pathologic and anatomic changes within the tumor tissue were demonstrated in solitary liver metastases of gastrointestinal malignancies excised in second-look operations. In all cases examined, formation of a cyst within the area of central activity, surrounded by a centrifugal necrotic ring and a marginal fibrotic structure, was found. CONCLUSIONS: Lack of persistent systemic or local side effects, as well as noteworthy efficacy, are properties of this optimal regional treatment modality with P-32 chromic phosphate. This modality deserves consideration for further clinical trials.

[Diagnostic and therapeutic management of the superior vena cava syndrome]. / Diagnostisches und therapeutisches Management der oberen Einflussstauung.

BACKGROUND: Superior vena cava syndrome (SVCS) is the clinical expression of obstruction of blood flow through the superior caval vein. In more than 80% of patients this complication is due to a malignant tumor, and in 60% of cases the first symptom of this tumor. DIAGNOSIS AND TREATMENT: If the clinical course of SVCS represents an absolute emergency, irradiation may have to be started immediately, even before the histologic diagnosis is established. Alternatively, expandable metallic stents have been used with considerable success for treatment of vena caval obstruction since patients respond immediately after stent implantation. For diagnosis, a chest X-ray and a CT scan should be performed. Chemotherapy is the treatment of choice for high-grade lymphomas, germ cell tumors and small-cell lung cancer since this modality is more effective than radiotherapy (response rate: 80%). For less chemotherapy responsive tumors radiotherapy is the primary treatment. Successful experience with thrombolytic agents is limited to treatment of catheter-induced SVCS, in contrast, only 20% of patients respond to thrombolytic therapy in the absence of a central catheter. Surgical resection of SVCS associated tumors has not improved survival rates and should be avoided.

Preferential repair of the N-ras gene in K 562 cells after exposure to cisplatin.

Cisplatin is one of the most active and widely used anticancer drugs; however, its clinical efficiacy is often limited by the development of resistance. Since several studies indicated that ras oncogenes may modulate the cellular response to cisplatin or radiation, we investigated the gene-specific repair of the N-ras gene in the human K 562 cell line after exposure to cisplatin using a novel nonradioactive polymerase chain reaction inhibition assay. This assay is based on the fact that DNA lesions can block the Taq polymerase and thereby result in a decreased amplification of a damaged segment compared to the amplification of the same segment in a non-damaged template. The overall genomic repair rate was measured by atomic absorption spectroscopy. Immediately after cisplatin exposure no amplification segment was observed. However, a complete restoration of the N-ras gene (2.4 kb) was seen after 8 h posttreatment incubation. In contrast, only 60% of the overall genome was repaired at this time. Our results clearly indicate that cisplatin-induced DNA lesions are more efficiently removed from transcribed regions within the DNA, suggesting that the efficiency of DNA repair in a given gene may be correlated to its transcriptional activity. Since ras oncogenes control several cellular signal transduction pathways, known to be involved in DNA damage response, preferential repair of the N-ras gene could therefore be an important step to prevent inactivation of cellular defense mechanisms after exposure to genotoxic agents.

[Unusual course of hemangiopericytoma]. / Ungewöhnlicher Verlauf eines Hämangioperizytoms.

BACKGROUND: Hemangiopericytomas, rare perivascular tumors, normally tend to be well circumscribed, however, since some have a malignant behavior they are recognized to be potentially malignant. CASE REPORT: In the case presented here, we report the medical history of a 46-year-old man with a hemangiopericytoma of the nose. In 1983, the tumor was surgically removed, and histological examination revealed no signs of malignancy. In 1987, a local recurrence was removed followed by X-irradiation. In March 1995, the patient presented with multiple hepatic and bone metastases. Chemotherapy with ifosfamide (5 g/m2, day 1) and epirubicin (50 mg/m2, day 1) was performed. After three courses of chemotherapy a tumor stabilization was achieved. In November 1995, however, a massive progression of the hepatic lesions was found. Therefore, six courses of a second-line chemotherapy with dacarbazine (200 mg/m2, day 1 to 5) and adriamycin (60 mg/m2, day 1) were applied. A partial remission was achieved lasting until November 1996. A couple of weeks later the patient died due to hepatic failure. CONCLUSION: Despite of unacceptably low survival rates in patients with advanced soft tissue sarcomas (especially after pretreatment with ionizing radiation) our report demonstrates that it is also possible to induce long lasting remissions without altered quality of life.

Somatostatin receptor scintigraphy in malignant lymphoma: first results and comparison with glucose metabolism measured by positron-emission tomography.

Somatostatin receptor scintigraphy with 111In-labeled octreotide was performed in 22 patients with suspected or known malignant lymphoma. The majority of extra-abdominal lesions (21/24 = 87.5%) were correctly localized, however, only one of nine intraabdominal lymphomas could be detected. No significant correlation was found between scintigraphic results and histological type of lymphoma. Metabolic imaging by positron-emission tomography with 18F-labeled deoxyglucose yielded a higher rate of detection of lymphoma manifestations (92% vs 64%) and better tumor contrast. Further prospective studies are needed to establish the clinical relevance of somatostatin receptor scintigraphy in malignant lymphoma.

Expression of resistance to etoposide and vincristine in vitro and in vivo after X-irradiation of ovarian tumor cells.

Two human ovarian carcinoma cell lines (JA-T/P and SK-OV-3/P) were exposed to 10 fractions of 5 Gy X-irradiation in vitro. Surviving populations generated sublines designated DXR-10 which expressed significant resistance to etoposide (VP-16) and vincristine (VCR), but not to adriamycin (ADR) or acute X-irradiation, as judged by clonogenic assays. JA-T/P and JA-T/DXR-10 tumor cells were xenografted into nude mice and treated with a single dose of VCR (1.8 mg/kg), VP-16 (24.5 mg/kg) or ADR (10.0 mg/kg) and 48 h later the surviving clonogenic cells in each tumor were quantitated. Significantly fewer colonies grew from the JA-T/P xenografts treated with either VCR or VP-16, as opposed to the JA-T/DXR-10 tumors, whilst comparable colony numbers were recorded after ADR treatment. These data suggest that the resistant phenotype following exposure to fractionated X-irradiation in vitro is also expressed in vivo.

Mechanisms associated with the expression of cisplatin resistance in a human ovarian tumor cell line following exposure to fractionated X-irradiation in vitro.

Interactions between cisplatin (CDDP) and irradiation are of potential significance for the combined modality treatment of cancer. Previous data have indicated that following in vitro exposure to X-irradiation certain tumour cells expressed resistance to CDDP. To identify parameters associated with this CDDP resistance, the human ovarian carcinoma cell line SK-OV-3/P was pre-exposed to fractionated X-irradiation (total dose: 50 Gy) in vitro. The resultant subline (SK-OV-3/DKR-10) proved 2-fold resistant to CDDP, but not to acute X-irradiation. Consistent with unaltered dihydrofolate reductase and thymidylate synthase activities, SK-OV-3/DXR-10 cells were neither cross-resistant to methotrexate nor to 5-fluorouracil. Verapamil (6.6 microM) significantly (P less than 0.05) enhanced CDDP-induced cytotoxicity in the resistant DXR-10 subline, but not in the parental cells. Total glutathione levels were significantly (P less than 0.01) lower in the resistant subline and BSO pretreatment failed to influence cytotoxicity, whilst related enzyme activities were not consistently modified in the SK-OV-3/DXR-10 cells. Resistance in these cells was associated with significantly decreased cisplatin uptake (P less than 0.002). Immediately following drug exposure the total platination level of the DNA, quantitated immunochemically, was higher (P less than 0.05) in the resistant subline indicative of increased tolerance to DNA damage. After an 18 h post-treatment incubation the parental cell line appeared proficient in the removal of the intrastrand adduct Pt-AG, but deficient in removing the major adduct Pt-GG and the difunctional Pt-(GMP)2 lesion, whilst the DXR-10 resistant subline appeared proficient in removal of all four Pt-DNA adducts. DNA polymerases alpha and beta activities, however, were comparable in both cell lines. These data implicate both enhanced repair and increased tolerance of DNA damage as mechanisms of resistance to CDDP resulting from in vitro exposure of a human ovarian carcinoma cell line to fractionated X-irradiation.

Characterization of a cisplatin-resistant human ovarian carcinoma cell line expressing cross-resistance to 5-fluorouracil but collateral sensitivity to methotrexate.

In vitro exposure of the TR170 ovarian carcinoma cell line to six intermittent 24-h treatments with a 90% inhibitory concentration of cisplatin (CDDP) (0.15 micrograms/ml; 0.5 microM) resulted in a 2-fold stably resistant subline designated TR170/CP+ (B.T. Hill et al., Int. J. Cancer, 39: 219-225, 1987). Resistance to CDDP in these CP+ cells has now been associated with reduced uptake of 195mCDDP (2-fold; P less than 0.01) and decreased removal of specific Pt-DNA adducts, quantitated immunochemically, indicative of an apparent increased tolerance of CDDP-induced DNA damage. Specifically these resistant cells appeared deficient in removal of the major cis-Pt-(NH3)2d(pGpG) adduct and the difunctional cis-Pt(NH3)2d(GMP)2 lesion, showed less efficiency in removing cis-Pt(NH3)2d(pApG) adducts, but proved as proficient as the parental cell line in removing DNA-DNA interstrand cross-links. Activities of DNA polymerase-alpha and -beta were comparable in both lines, and no significant alterations in glutathione metabolism were identified. Response to acute X-irradiation was not modified in these TR170/CP+ cells, but they showed marked (10-fold) cross-resistance to 5-fluorouracil and, unusually, proved collaterally sensitive (12-fold) to methotrexate. Resistance to 5-fluorouracil was associated with significantly increased thymidylate synthase activity (P less than 0.01), but this was not reflected in altered gene expression, while increased sensitivity to methotrexate was accompanied by increased drug uptake but by unaltered activity and expression of dihydrofolate reductase. These results indicate that exposure to CDDP can result in numerous alterations, both intracellularly and at the cellular membrane, reflected in significant changes in the tumor cells' responses to the cytotoxic effects of a range of antitumor drugs. The clinical relevance of these observations remains to be established.