Factors influencing the inhibition of repair of irradiation-induced DNA damage by 2′-deoxycoformycin and deoxyadenosine

Summary Permeabilized L5178Y cells were used to investigate the mechanism underlying inhibition of the repair of irradiation-induced DNA strand breaks by 2-deoxyeoformycin combined with deoxyadenosine. Permeabilized cells repaired DNA strand breaks as effectively as did intact cells, and at deoxyadenosine concentrations that produced similar levels of deoxyadenosine triphosphate (dATP), repair of DNA strand breaks was inhibited by 2-deoxycoformycin plus deoxyadenosine to a comparable extent in both types of cells. Accompanying the increase in intracellular dATP produced by 2-deoxycoformycin combined with deoxyadenosine was a fall in levels of deoxythymidine triphosphate (dTTP), deoxyguanosine triphosphate (dGTP), and deoxycytidine triphosphate (dCTP). The addition of dTTP, dGTP, and dCTP reversed the inhibition of DNA repair by 2-deoxycoformycin plus deoxyadenosine, although the level of dATP was not affected. Reducing the phosphorylation of deoxy-adenosine to dATP by the addition of adenosine prevented the decrease in levels of dTTP, dGTP, and dCTP and the inhibition of DNA repair by 2-deoxycoformycin and deoxyadenosine. In contrast, increasing the intracellular levels of dATP by the addition of 2-deoxycoformycin together with dATP, deoxyadenosine diphosphate (dADP), or deoxyadenosine monophosphate (dAMP) had no effect on the levels of the other deoxynucleotide triphosphates and did not inhibit DNA repair. Moreover, DNA repair was not inhibited by the breakdown products of deoxyadenosine, adenine, or deoxyribose. These results suggest that inhibition of the repair of irradiation-induced DNA strand breaks by 2-deoxycoformycin combined with deoxyadenosine requires the phosphorylation of deoxyadenosine and involves alterations in the levels of deoxynucleotide triphosphates.This study was supported by grants from the Medical Research Council of Canada, Parke-Davis Canada, Inc., and the National Cancer Institute of Canada.     

Activities of adenosine deaminase and 5′-nucleotidase in cancerous and noncancerous human colorectal tissues

In order to characterize human colorectal cancer, much attention has been paid to enzyme studies. However, little is known about the correlation between the levels of key enzymes of purine nucleotide pathway and some clinical and biological indicators of tumor invasiveness and aggressiveness. Adenosine deaminase (ADA) and 5′-nucleotidase (5′-NT) were measured in cancerous and cancer-free adjacent large bowel tissues from 38 patients with colorectal carcinoma. We have analyzed the relationship between the enzyme levels and some clinical and pathological parameters. The enzymes' activities were markedly higher in primary tumors than in corresponding normal mucosae. The ADA level in tumor tissue was significantly correlated with lymph node metastasis, histologic type, tumor location, and patient's age, whereas the 5′-NT level showed a significant correlation with tumor grade and tumor location. ADA activity in tumor tissues was significantly higher in patients whose clinical course remained stable than in those with recurrent diseases. The purine metabolism and salvage pathway activity of purine nucleotides are accelerated in the cancerous human colorectal tissue. Although our findings suggest that these enzymes' activities are most likely retated to the same histomorphological architecture of the tumor, the authors believe that long-term follow-up studies are needed to evaluate the prognostic value of purine enzymes for colorectal cancer.     

Inhibition of cytidine deaminase by zebularine enhances the antineoplastic action of 5-aza-2′-deoxycytidine

Cytidine (CR) deaminase is a key enzyme in the catabolism of cytosine nucleoside analogues, since their deamination results in a loss of their pharmacological activity. In this report we have investigated the importance of CR deaminase with respect to the antineoplastic action of inhibitors of DNA methylation, 5-aza-2′-deoxycytidine (5-AZA-CdR) and zebularine. Zebularine has a dual mechanism of action, since it can also inhibit CR deaminase. The objective of our study was to investigate the importance of zebularine as an inhibitor of CR deaminase with respect to the antineoplastic action of 5-AZA-CdR. Using an in vitro clonogenic assay, we investigated the antineoplastic action of 5-AZA-CdR and zebularine, alone and in combination on wild type 3T3 murine fibroblasts and corresponding V5 cells transduced with CR deaminase gene to express a very high level of CR deaminase activity. The V5 cells were much less sensitive to 5-AZA-CdR than the wild type 3T3 cells. The addition of zebularine significantly enhanced the antineoplastic action of 5-AZA-CdR on V5 cells, but not 3T3 cells. Enzymatic analysis on CR deaminase purified from the V5 cells showed that zebularine is a competitive inhibitor of the deamination of 5-AZA-CdR. These in vitro observations are in accord with our in vivo study in mice with L1210 leukemia, which showed that zebularine increased the antileukemic activity of 5-AZA-CdR. Pharmacokinetic analysis also showed that zebularine increased the plasma level of 5-AZA-CdR during an i.v. infusion in mice. Our results indicate that the major mechanism by which zebularine enhances the antineoplastic action of 5-AZA-CdR is by inhibition of CR deaminase. These findings provide a rationale to investigate 5-AZA-CdR in combination with zebularine in patients with advanced leukemia.     

Activities of adenosine deaminase, 5′-nucleotidase,guanase, and cytidine deaminase enzymes in cancerous and non-cancerous human breast tissues

We measured activities of some DNA turnover enzymes in 9 breast tissues with stage II cancer, 6 breast tissues with stage IIIa cancer, and 9 non-cancerous adjacent breast tissues from the same patients with stage II cancer. We found higher Adenosine Deaminase (ADA) and 5-Nucleotidase (5NT) and lower Guanase (GUA) activities in the cancerous tissues compared with the non-cancerous ones. No meaningful differences were however found between Cytidine Deaminase (CD) activities. Regarding the correlation analysis, positive correlations were established between ADA and 5NT activities of the cancerous tissues (r = 0.45 for the tissues with stage II and r = 0.60 for the tissues with stage IIIa cancer). No meaningful correlations were however found between other enzyme activities. Relating to activity ratios, no meaningful differences were found between ADA/5NT values in the tissues. GUA/CD ratios were however lower and the other ratios higher in the cancerous tissues.Results indicated that ADA and 5NT activities increased and GUA activity decreased in the cancerous breast tissues but CD activities did not change in the tissues affected. It has been suggested that increased ADA and 5NT together with decreased GUA activities might be a physiologic attempt of the cancer cells to provide more substrates needed by cancer cells to accelerate the salvage pathway activity. Furthermore, high ADA activity might also play part in the detoxication process of high amounts of toxic adenosine and deoxyadenosine substrates produced from accelerated purine metabolism in the cancerous tissues.     

The role of DNA synthesis inhibition in the cytotoxicity of 2′,2′-difluoro-2′-deoxycytidine

Purpose Cytotoxicity from the anticancer drug 2,2-difluoro-2-deoxycytidine (dFdCyd) has been correlated with its incorporation into DNA. However, cytotoxicity may also result from inhibition of DNA synthesis, due to either (1) dFdCyd diphosphate-mediated inhibition of ribonucleotide reductase, or (2) direct inhibition of DNA polymerases by the 5-triphosphate of dFdCyd (dFdCTP). To elucidate the role of DNA synthesis inhibition in the cytotoxicity of dFdCyd, we compared dFdCyd to hydroxyurea (HU), a ribonucleotide reductase inhibitor, and aphidicolin, an inhibitor of DNA polymerases, in the U251 and D54 human glioblastoma cell lines.Methods Sensitivity to dFdCyd, HU, and aphidicolin were determined using a colony formation assay. The effects of these drugs on DNA synthesis were measured by dual parameter flow cytometry, while the effects on nucleotide pool levels were analyzed by high-performance liquid chromatography.Results HU and aphidicolin elicited substantially less cytotoxicity than the multi-log killing with dFdCyd. When used at equitoxic concentrations (24-h IC₅₀ values), dFdCyd and HU decreased purine dNTP pools primarily, but dFdCyd was less effective than HU. dFdCyd had decreased dATP by about 80% after 4–12 h, and required 8–24 h to decrease DNA synthesis by 50%. In contrast, HU rapidly depleted dATP by >98% within 2 h, which resulted in >90% inhibition of DNA synthesis. Aphidicolin at a concentration similar to its K_i values for DNA polymerases (1 M) decreased DNA synthesis by >70% within 2 h. However, this decreased cell survival by only 10% (U251 cells) and 40% (D54 cells).Conclusions These results demonstrate that HU and aphidicolin produced a more rapid and profound inhibition of DNA synthesis than dFdCyd, but resulted in significantly less cytotoxicity. This suggests that inhibition of DNA synthesis accounted for less than one log of the multi-log cytotoxicity observed with dFdCyd, whereas incorporation of dFdCTP into DNA is a more lethal event.     

Synergistic effect of 3′-deoxyadenosine N 1-oxide and adenosine deaminase inhibitors on growth of Ehrlich ascites tumor cells in vivo

Summary The simultaneous administration of 3-deoxyadenosine N ^l-oxide (3-dANO) and the adenosine deaminase inhibitors erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA) or 2-deoxycoformycin (2-dCF) to mice bearing Ehrlich ascites tumor cells resistant to 3-dANO resulted in 80%–90% inhibition of tumor growth in vivo. 3-dANO and 2-dCF increased the survival time of tumor-bearing mice by a factor of 2. In vitro studies showed that the 3-dANO resistant Ehrlich cells initiate the metabolism of 3-dANO by a reduction to 3-deoxyadenosine, which is converted primarily to 3-deoxyinosine by adenosine deaminase and, to a small extent, phosphorylated to the cell toxic agent 3-dATP. By the addition of EHNA or 2-dCF it was possible to block the formation of 3-deoxyinosine, resulting in a profound stimulation in the accumulation of 3-dAtP. The development of resistance to 3-dANO was studied in cell cultures and found to be accompanied by changes in the enzyme activities of the reductase, the adenosine kinase, and the adenosine deaminase.Abbreviations 3-dANO 3-deoxyadenosine N ^l-oxide - 3-dA 3-deoxyadenosine - 3-dI 3-deoxyinosine - 3-dATP 3-deoxyadenosine triphosphate - EHNA erythro-9-(2-hydroxy-3-nonyl) adenine - 2-dCF 2-deoxycoformycin This work was supported by the Danish Medical Research Council, Gerda and Åge Haensch Foundation, Dirktør Åge Henriksens Foundation, P. Carl Petersens Foundation and the Danish Cancer Society     

Cell cycle effects and cellular pharmacology of 5-AZA-2′-deoxycytidine

Summary The cytotoxic action of 5-aza-2-deoxycytidine (5-AZA-CdR) in synchronized cells and logarithmic- and plateau-phase cultures of EMT₆ murine tumor cells was investigated. 5-AZA-CdR produced a greater cell kill of S phase cells than of cells in G₁ phase. Cells in the logarithmic phase of growth were more sensitive to the cytotoxic effects of 5-AZA-CdR than cells in the plateau phase of growth. These results indicate that 5-AZA-CdR produces a preferential kill of cells in the S phase of the cell cycle. 5-AZA-CdR did not block the cell cycle progression of cells into S phase. The survival curve of EMT₆ cells exposed to 5-AZA-CdR suggests that the cytotoxic action of this analogue is not self-limiting. The mutagenic activity of 5-AZA-CdR was investigated using induction of 6-thioguanine resistance in Chinese hamster ovary cells. 5-AZA-CdR was not a detectable mutagen in this assay system.     

Renal handling of 2′-deoxyadenosine and adenosine in humans and mice

Summary In a child lacking adenosine deaminase and in patients treated with deoxycoformycin (a potent inhibitor of the enzyme), apparent renal secretion of 2-deoxyadenosine (dAdo) and reabsorption of adenosine (Ado) were observed. The renal clearance of dAdo in humans was approximately five-fold that of creatinine, whereas the renal clearance of Ado was only one-fifth that of creatinine. In mice treated with deoxycoformycin, a similar paradigm was observed. Specifically, plasma levels of Ado and dAdo were elevated to detectable levels and apparent renal secretion and reabsorption of these purine nucleosides became manifest. Thus, the mouse may serve as a suitable model to study the renal handling of these two compounds. The active renal secretion of dAdo may occur because the compound has not been appreciably synthesized by mouse kidney in situ, and ion-trapping of dAdo in acid urine could not explain the net secretion. The differential transport of these similar purine nucleosides suggests a very selective transport system in mammalian kidney. Although carrier-mediated, facilitated diffusion of purine nucleosides across cell membranes is a well-known phenomenon, the present data indicate the existence of (an) active transport sysem(s) for the transepithelial secretion of dAdo, and possibly for the reabsorption of Ado.The abbreviations used in this paper are ADA adenosine aminohydrolase EC 3.5.4.4 - Ado adenosine - dAdo 2-deoxyadenosine - DCF 2-deoxycoformycin - HPLC high-performance liquid chromatography - PBS 0.14 M NaCl plus 0.01 M phosphate buffer, pH 7.4 - PNPase purine nucleoside: orthophosphate ribosyltransferase EC 2.4.2.1 - SCID: ADA^- severe combined immunodeficiency disease associated with ADA deficiency     

Potent inhibitors for the deamination of cytosine arabinoside and 5-aza-2′-deoxycytidine by human cytidine deaminase

Summary Deamination of the nucleoside analogues ARA-C and 5-AZA-CdR by CR deaminase results in a loss of antileukemic activity. To prevent the inactivation of these analogues, inhibitors of CR deaminase may prove to be useful agents. In the present study we investigated the effects of the deaminase inhibitors Zebularine, 5-F-Zebularine, and diazepinone riboside on the deamination of CR, ARA-C, and 5-AZA-CdR using highly purified human CR deaminase (EC 3.5.4.5). These inhibitors produced a competitive type of inhibition with each substrate, the potency of which followed the patterns diazepinone riboside>5-F-Zebularine and THU>Zebularine. 5-AZA-CdR was more sensitive than ARA-C to the inhibition produced by these deaminase inhibitors. The inhibition constants for diazepinone riboside lay in the range of 5–15nm, suggesting that this inhibitor could be an excellent candidate for use in combination chemotherapy with either ARA-C or 5-AZA-CdR in patients with leukemia.Abbreviations CdR deoxycytidine - CR cytidine - ARA-C cytosine arabinoside - ARA-U uridine arabinoside - 5-AZA-CdR 5-aza-2-deoxycytidine - 5-AZA-UdR 5-aza-2-deoxyuridine - THU tetrahydrouridine This work was supported by CAFIR (Université de Montréal) and Centre de Recherche HSJ. J. L. is supported by a studentship from HSJ and MRC     

The role of deoxycytidine-metabolizing enzymes in the cytotoxicity induced by 3′-amino-2′,3′-dideoxycytidine and cytosine arabinoside

Summary The cellular metabolism of 3-amino-2,3-dideoxycytidine (3-NH₂-dCyd), a cytotoxic agent previously reported to be a poor substrate for purified Cyd/dCyd deaminase (dCydD), was compared with that of cytosine arabinoside (ara-C) in cells that displayed dCydD activity (HeLa) and in cells that did not (L1210). Growth inhibition induced by 3-NH₂-dCyd was dependent on the levels of anabolic enzymes, particularly dCyd kinase (dCydK), whereas cytotoxicity induced by ara-C was dependent on the expression of both anabolic and catabolic enzyme activities. Competition kinetics using purified enzyme revealed that the binding affinity of ara-C to dCydK was 5-fold that of the amino analog. However, this binding advantage is apparently offset in cells that contain high levels of dCydD, since the K_i values for this enzyme were 0.2 and 23mm for ara-C and 3-NH₂-dCyd, respectively. This was reflected in the decrease in analog sensitivity observed between the two cell lines, whereby the concentrations of ara-C and 3-NH₂-dCyd required to inhibit growth by 50% were 200 and 7 times higher, respectively, in the dCydD-containing HeLa cells as compared with the dCydD-deficient L1210 cells. The metabolic stability and cytotoxicity of 3-NH₂-dCyd was independent of cell number. An unexpected finding was the extent to which the effectiveness of ara-C could be mitigated by the number of dCydD-containing cells. A completely cytotoxic concentration of ara-C was rendered nontoxic by a 10-fold increase in cell number. This observation was supported by an increase in I--d-arabinofuranosyluracil (ara-U) formation, a decrease in ara-C 5-triphosphate (ara-CTP) accumulation, and a rise in cell viability with increasing cell number. These findings indicate that unlike ara-C, the effectiveness of 3-NH₂-dCyd is independent of the level of deaminase, which suggests its possible utility in situations in which high levels of deaminase are manifest.Supported by grant CH-452 from the American Cancer Society     

Potentiation of the antitumor activity of 5-trifluoromethyl-2′-deoxyuridine by the use of depot forms of the parent compound

Summary 5-Trifluoromethyl-2-deoxyuridine (CF₃dUrd), an antitumor agent, is known to be short-lived in human plasma. Since its rapid elimination from the blood-stream seems to have descouraged the clinical evaluation of this drug, we explored the potential use of masked derivatives of CF₃dUrd as depot forms of the parent compound. First, we observed that the toxicity of CF₃dUrd against HeLA cells in culture was 10⁴ times greater for a 24-h treatment as compared with a 1-h treatment at identical concentrations of the drug, which suggests the importance of using a prolonged treatment period. In fact, the divided dosing of CF₃dUrd to L1210-bearing mice was markedly more effective than its single administration. 5-O-Hexanoyl-,N ³-p-butylbenzoyl-, 5-O-benzyloxymethyl-, and 3-O-benzyl-CF₃dUrd were found to be effective in maitaining the CF₃dUrd concentration in plasma. The oral doses of these agents required to achieve 50% growth inhibition (ED₅₀) in mice bearing sarcoma 180 tumors were 19, 34, 10, and 13 mg kg^–1 day^–1, respectively, whereas that of CF₃dUrd was 63 mg kg^–1 day^–1. The ED₅₀ values for these compounds were inversely correlated with the residence time of CF₃dUrd in plasma. The therapeutic indices of these compounds, calculated as the dose producing a 50% inhibition of body-weight gain (IB₅₀) divided by the ED₅₀ value (1.89, 1,21, 1.40, and 2.15, respectively), were significantly higher than that of CF₃dUrd (0.78). Consequently, these depot forms of CF₃dUrd, particularly 3-O-benzyl-CF₃dUrd, are expected to be more useful than the parent compound as antitumor agents.Abbreviations CF₃dUrd 5-trifluoromethyl-2-deoxyuridine - CF₃dUMP 5-trifluoromethyl-2-deoxyuridine-5-monophospate - S180 sarcoma 180 - L1210 L1210 leukemia - k_el elimination rate constant - T1/2 half-life time - AUC area under the curve - ILS increase in life span - TS thymidylade synthase - FdUMP 5-fluoro-2-deoxyuridine-5 monophosphate - FUra 5-fluorouracil     

The clinical significance evaluation of serum β2-microglobulin for thyroid cancer patients

Objective

The aim of this study was to investigate the clinical value and relevance on the serum β₂-microglobulin (β₂-MG) of patients with thyroid cancer.

Methods

One thousand and two normal cases, 95 thyroid cancer patients and 243 nodular goiter patients were selected to measure serum β₂-MG levels using double-antibody sandwich enzyme-linked immunosorbent assay (ELISA).

Results

The positive rate of 7.78% in normal population (78/1002) and 31.57% in thyroid cancer patients (30/95). There were significant differences between the normal population and thyroid cancer patients (χ ² = 55.352; P = 0.000). The positive rate of 7.81% in nodular goiter patients (19/243) and there were no significant differences between the normal population and nodular goiter patients (χ ² = 0.0004; P = 0.986), but significant differences between nodular goiter patients and thyroid cancer patients (χ ² = 31.106; P = 0.000). Meanwhile, the significant difference of the positive rate existed in between the various pathological types of thyroid cancer (χ ² = 10.015; P = 0.007), anaplastic thyroid cancer patients with the highest positive rate and The significant difference was found between the positive lymph node metastasis groups and negative lymph node metastasis groups (χ ² = 4.441; P = 0.035), the presence of distant metastasis group and absence of distant metastasis group (χ ² = 9.795; P = 0.002).

Conclusion

Serum β₂-MG levels and prognosis of thyroid cancer patients was negatively correlated. It showed important clinical value to detect the level of β₂-MG in the early diagnosis, prognosis and the clinical observation for thyroid cancer patients.     

Radiosensitizing potential of gemcitabine (2′,2′-difluoro-2′-deoxycytidine) within the cell cycle in vitro

Purpose: Gemcitabine (2′,2′-difluorodeoxycytidine; dFdCyd) is a new deoxycitidine analog which exhibits substantial activity against solid tumors and radiosensitizing properties in vitro. To examine cell cycle–specific effects of a combined treatment with gemcitabine and radiation, the in vitro clonogenic survival of two different cell lines was measured for cells from log-phase culture, G1 and S-phase cells.Methods and Materials: Chinese hamster (V79) and human colon carcinoma (Widr) cells were exposed to different radiation doses and for different points of time relative to gemcitabine treatment (2 h). Experiments were also carried out with different cell-cycle populations obtained after mitotic selection (V79) or after serum stimulation of plateau-phase cells (Widr). The resulting survival curves were analyzed according to the LQ model, and mean inactivation doses (MID) and the cell cycle–specific enhancement ratios (ER) were calculated from the survival curve parameters.Results: Effectiveness of combined treatment of log-phase cells was greatest when cells were irradiated at the end of the gemcitabine exposure [ER: 1.28 (V79), 1.24 (Widr)]. For later times after the removal of the drug, radiosensitization declined, approaching independent toxicity. From the time course of interactive-type damage decay half-life values of 75 min (V79) and 92 min (Widr) were derived. Gemcitabine did not radiosensitize G1 Widr cells or V79 cells from the G1/S border, but substantial radiosensitization was observed for the S-phase cell preparations [ER: 1.45 (V79-lateS), 1.57 (Widr)].Conclusions: Treatment of cells with gemcitabine immediately before irradiation eliminates, or at least greatly reduces, the variation in radiosensitivity during the cell cycle that is manifested by radioresistance during S phase. This reversal of S-phase radioresistance could imply that gemcitabine interferes with the potentially lethal damage repair/fixation pathway. Other approaches have been taken to overcome S-phase radioresistance, such as hyperthermia or densely ionizing radiation, and combined treatments with dFdCyd could prove of value to complement such efforts.     

The protein kinase C inhibitor Gö6976 is a potent inhibitor of DNA damage-induced S and G2 cell cycle checkpoints

In response to DNA damage, cells arrest progression through the cell cycle at either G(1), S, or G(2). We have reported that UCN-01 (7-hydroxystaurosporine) abrogates DNA damage-induced S and G(2) arrest and enhances cytotoxicity selectively in p53 mutant cells, thus providing a potential, tumor-targeted therapy. Unfortunately, UCN-01 binds avidly to human plasma proteins, limiting bioavailability. Because UCN-01 also inhibits protein kinase C (PKC), we screened other PKC inhibitors, expecting them to be unable to abrogate arrest. However, G?6976 potently abrogated S and G(2) arrest and enhanced the cytotoxicity of the topoisomerase I inhibitor SN38 only in p53-defective cells. Importantly, G?6976 was nearly as potent at abrogating S and G(2) arrest in human serum, a property not possessed by UCN-01. Cell viability studies demonstrated that G?6976 was impressively nontoxic as a single agent. Analysis of proteins that regulate cell cycle arrest suggested that both drugs inhibit the checkpoint kinases Chk1 and/or Chk2. Additionally, G?6976 abrogated S and G(2) arrest at a concentration substantially lower than that required to inhibit PKC; UCN-01 did not demonstrate this selectivity for checkpoint inhibition. These properties make G?6976 a promising candidate for preclinical and clinical studies.     

The clinical application of fibroblast interferon—An overview

Preclinical as well as clinical studies with fibroblast interferon (IFN) are still lagging behind on those with leukocyte interferon. Its side-effects seem to be less pronounced than those of human IFN-α, yet it may be slightly pyrogenic after intravenous injection. Pyrogenicity of current impure preparations might for the larger part be due to impurities. Higher doses of HuIFN-β than of HuIFN-α are required to obtain measurable blood titers by intramuscular injections. Since there is concern about this being due to destruction of the interferon before it has reached its target organ(s), most current clinical studies use either local (e.g. intratumoral) treatment or intravenous infusions. A study of topical treatment for acute rhinovirus infection has indicated that there is very little if any chance for fibroblast interferon to be a clinically useful substance to prevent or cure common cold. In herpetic dendritic keratitis eye drops of fibroblast interferon may be useful as such or in combination with debridement. Topical treatment of warts (multiple intralesional injections) has been shown to yield a high success rate, especially in the case of verrucae vulgares, but less so in the case of verrucae planae juveniles. Studies on condyloma accuminatum are not so far advanced as to permit a documented conclusion. Topical (intralesional) treatment of neoplastic diseases has been investigated, especially in Japan, to demonstrate that fibroblast interferon does have an antineoplastic effectin vivo. While there seems to be little doubt that local delivery does indeed cause tumor nodules to regress, the question is whether this procedure can offer a true clinical benefit to the patient. Systemic (intravenous) administration for chronic hepatitis B has been investigated further: given alone or in combination with adenine-arabinoside, fibroblast interferon seems to be able to reduce the level of viral activity. Whether this will lead to a generally accepted treatment of chronic active hepatitis is difficult to say at this moment. In treating herpes zoster in cancer patients, results have been obtained which are comparable to those found for leukocyte interferon. The practical significance of this finding must be seen in the perspective of recent developments in the chemotherapy of herpes zoster. In breast cancer patients given intramuscular injections, metastases in the skin, but not in other organs, showed alterations suggestive of an effect on tumor progression. Yet there was no true clinical benefit for the patient. In other tumors, e.g. head and neck epithelioma, no effect was seen. Intravenous infusions have met with some success in nasopharyngeal carcinoma: temporary stabilization or regression occurred, but no definitive cures were noted. A large neuroblastoma trial yielded negative results. Disappointing results were also obtained in non-Hodgkin's lymphoma. In initial studies on myeloma and brain tumors ‘response rates’ of 25% were recorded; the significance of this in terms of clinical benefit to the patient is not clear yet.