Modulation of p53 expression by human recombinant interferon-alpha2a correlates with abrogation of cisplatin resistance in a human melanoma cell line.

G3361/CP cells, a cisplatin (CDDP)-resistant subclone of the human melanoma cell line G3361, overexpress wild-type p53 protein and demonstrate an increase in the percentage of cells in G0--G1 arrest compared to parental cells. Exposing G3361/CP cells to human recombinant IFN-alpha2a reduces the high basal levels of p53, releases G3361/CP cells from G0-G1 into S phase, and abrogates CDDP resistance. These findings suggest that recombinant IFN-alpha2a disrupts p53-mediated cell cycle regulation to restore CDDP sensitivity in G3361/CP cells.

Antitumor activity of basic fibroblast growth factor-saporin mitotoxin in vitro and in vivo.

Many cancer cell lines express basic fibroblast growth factor (FGF) receptors, making them potential targets for the delivery of FGF-based cytotoxic compounds. To this end, we have investigated the antitumor activity of a novel mitotoxin, Fibroblast Growth Factor-saporin (FGF-SAP), a conjugate of FGF and the ribosome-inactivating protein, saporin. In vitro, FGF-SAP is cytotoxic for human melanoma, teratocarcinoma, and neuroblastoma cells expressing FGF-receptors. Mice treated with FGF-SAP i.v., on a variety of schedules, showed dramatic tumor growth inhibition with minimal toxicity. Thus, FGF-SAP appears to be a well-tolerated and potent antitumor agent. The potential of FGF-targeted cytotoxicity is discussed.

Autocrine down-regulation of basic fibroblast growth factor receptors causes mitotoxin resistance in a human melanoma cell line.

The ability of melanoma to develop resistance to mitotoxins, growth-factor-directed anti-neoplastic agents that offer potential for the treatment of this highly refractory disease, may limit therapeutic efficacy. To address this problem, we developed a subcloned human melanoma cell line that is resistant to the mitotoxin composed of basic fibroblast growth factor conjugated to the ribosome-inactivating protein saporin. Resistance was caused by autocrine FGF ligands, which down-regulate bFGF receptors and reduce bFGF-saporin binding. Inhibiting the autocrine loop with suramin or with neutralizing antibodies to FGF up-regulated receptors and decreased resistance in vitro. Furthermore, suramin restored sensitivity in resistant tumor xenografts. These results suggest the potential of therapeutic modalities combining agents that neutralize growth factors with receptor-directed mitotoxins for targeting malignant melanoma either to prevent emergence of resistance or to circumvent resistance once it occurs.

Human recombinant interferon alpha-2a plus 3'-azido-3'-deoxythymidine. Synergistic growth inhibition with evidence of impaired DNA repair in human colon adenocarcinoma cells.

We reported that 3'-azidothymidine-3'-deoxythymidine (AZT) plus 5-fluorouracil or methotrexate produces additive cytotoxicity in HCT-8 cells: a reflection of increased AZT metabolism when de novo thymidylate (dTMP) synthesis was inhibited. We now report that AZT plus human recombinant interferon alpha-2a (rIFN-alpha 2a) produces synergistic growth inhibition in these cells. Evaluation of the effect of rIFN-alpha 2a on dTMP metabolism revealed that exposure to rIFN-alpha 2a (+/-AZT) did not affect dTMP synthase activity significantly but increased thymidine (dThd) kinase activity significantly. Consequently, AZT nucleotide production and incorporation into DNA were increased by coexposure to rIFN-alpha 2a. This alone, however, cannot explain the observed synergism. Therefore, the effect of these agents on DNA excision/repair processes was assessed. Isotope clearance studies demonstrated that rIFN-alpha 2a did not alter the rate of [3H]AZT excision from DNA. In contrast, filter-elution studies revealed that rIFN-alpha 2a (+/-AZT) produced more DNA damage and delayed repair compared with the effects produced by AZT alone. Since DNA polymerases alpha and beta are directly involved in gap-filling repair synthesis, experiments next assessed the effect of rIFN-alpha 2a and/or 3'- azido-3'-deoxythymidine-5'-triphosphate (AZTTP) on their activities. Polymerase alpha was inhibited slightly by AZTTP but not by rIFN-alpha 2a. Polymerase beta activity, however, was inhibited dramatically by rIFN-alpha 2a + AZTTP. Finally, western analysis revealed that a 24-hr exposure to 5000 IU/mL rIFN-alpha 2a (+/-20 microM AZT) significantly reduced wild-type p53 expression compared with AZT-exposed cells. We conclude that rIFN-alpha 2a enhances AZT-induced tumor cell growth inhibition by (i) increasing AZT metabolism, and (ii) inhibiting DNA repair and p53-mediated cell cycle control processes.

Wortmannin, a phosphoinositide 3-kinase inhibitor, selectively enhances cytotoxicity of receptor-directed-toxin chimeras in vitro and in vivo.

BACKGROUND: Generalized resistance of some neoplastic cell lines to treatment with ligand-toxin chimeras has been attributed to an increased rate of lysosomal uptake and degradation following endocytosis of the chimera-receptor complex. Because phosphoinositide 3-kinase (Pl 3-kinase) activity is known to play a role in intracellular trafficking, particularly from endosomes to lysosomes, we hypothesized that co-exposing cells to the Pl 3-kinase inhibitor, wortmannin, might enhance cytotoxicity of ligand-toxin chimeras. METHODS: In vitro, cytotoxicity of five receptor directed-toxin chimeras (bFGF-SAP, bFGF-PE, aFGF-PE, HBEGF-SAP, bFGF-gelonin) and an immunotoxin (11A8-SAP) was examined in the presence or absence of this Pl 3-kinase inhibitor against a panel of human neoplastic cell lines: SK-MEL-5 (melanoma), PA-1 (ovarian teratocarcinoma), DU145 (prostatic carcinoma) and MCF-7 (breast carcinoma). In vivo, antitumor activity of a treatment regimen combining wortmannin (1 or 2 mg/kg i.p.) and bFGF-SAP (10 micrograms/kg i.v.) once a week for 4 weeks was evaluated compared to administration of each agent alone in C3H/HeN mice implanted with the FSallC murine fibrosarcoma. RESULTS: At concentrations greater than the reported Ki for Pl 3-kinase inhibition (1-10 microM), wortmannin enhanced cytotoxicity when combined with saporin or gelonin chimeras, but produced subadditive cytotoxicity when combined with Pseudomonas exotoxin chimeras. When low nanomolar concentrations selective for Pl 3-kinase inhibition (5-100 nM) were examined for effects on one receptor directed-toxin chimera, wortmannin dramatically enhanced bFGF-SAP cytotoxicity in three of the four cell lines. A different Pl 3-kinase inhibitor, LY294002 (Ki approximately 1 microM), however, failed to potentiate bFGF-SAP. When administered to mice, wortmannin combined with bFGF-SAP resulted in a significant decrease in tumor volumes compared to vehicle-treated controls that was not observed in mice treated with either agent alone. CONCLUSIONS: Taken together, these results suggest that although wortmannin increases the cytotoxic efficacy of some receptor-directed chimeras, potentiation may occur through an alternative pathway not involving Pl 3-kinase inhibition.

Mutagenicity of three agricultural soils.

A chemical and biological testing protocol was employed to evaluate the mutagenic potential of the organic compounds extracted from three agricultural soils. The analytical procedures used included bioassays with Salmonella typhimurium and Aspergillus nidulans for the detection of point mutations and a gas chromatography/mass spectrometry/computer system to identify major organic constituents. The extracts of all three soils exhibited mutagenic response in the bioassays. At a dose level of 1000 micrograms per plate, the organic extract of the Bastrop clay induced 434 net revertants; while at the same dose level the Norwood sandy clay and the Sassafrass sandy loam induced 35 and 178 net revertants, respectively, in the Salmonella assay with metabolic activation. In the Aspergillus assay, the extract of the Norwood and Bastrop soils induced a positive response without metabolic activation; this effect was reduced or eliminated in the presence of metabolic activation. Chemical analysis identified a variety of initiators, promotors, inhibitors, and cocarcinogens; however, there were no mutagenic compounds identified in any of the soil extracts. The results of this combined testing protocol indicate that the agricultural soils tested had an inherent level of mutagenic activity, which was not detected by GC/MS analysis alone, and this activity may be related to the past history of agricultural practices, including biocide applications, fertilization, and cultivation.

Targeting human prostatic carcinoma through basic fibroblast growth factor receptors in an animal model: characterizing and circumventing mechanisms of tumor resistance.

BACKGROUND: Basic fibroblast growth factor receptors on DU145 human prostatic carcinoma xenografts serve as targets for the delivery of a growth factor-toxin chimera, basic fibroblast growth factor-saporin (bFGF-SAP), which produces significant antitumor activity in a nude mouse model. However, DU145 tumors often become resistant to prolonged treatment. METHODS: Nude mice bearing DU145 xenografts were intravenously administered bFGF-SAP (0.05 microg/kg weekly for 4 weeks), and a panel of eight tumors was isolated from the treated animals and established in monolayer culture. RESULTS: In cell-survival assays, sensitivity of the treated tumor-derived cell lines to bFGF-SAP (IC50 = 12-100 nM) varied widely from cells derived from a vehicle-treated control tumor (IC50 = 10 nM). A significant inverse correlation was observed between increased IC50 values in vitro and increased tumor growth delay in vivo. Pretreatment of tumor cells with suramin or neutralizing antibodies to bFGF or keratinocyte growth factor (KGF) circumvented resistance in one of the tumor lines, confirming autocrine-mediated resistance. In another tumor subline, a 3-fold decrease in bFGF high-affinity receptor sites, which concurred with a 4-fold decrease in ability to internalize the bFGF ligand, was consistent with a decrease in total cellular expression of the FGF2 receptor (Bek). Resistance was circumvented by alternatively targeting FGF1 receptor (Flg) on these cells with a saporin immunotoxin. CONCLUSIONS: These studies identify alterations in the ligand-targeted receptor as a frequent contributor to resistance arising in DU145 tumors to in vivo treatment with a bFGF receptor-directed-toxin chimera, and provide the basis for designing methods to circumvent resistance for the purpose of enhancing efficacy of receptor-directed therapies in the treatment of prostate cancer.

The mitotoxin, basic fibroblast growth factor-saporin, effectively targets human prostatic carcinoma in an animal model.

PURPOSE: The antitumor activity of the mitotoxin basic fibroblast growth factor-saporin (bFGF-SAP) against human prostatic carcinoma DU 145 was examined in athymic nude mice. Therapeutic efficacy was evaluated on the basis of dose, route of administration and treatment schedule. MATERIALS AND METHODS: Chemical conjugate or recombinant bFGF-SAP (0.02 to 50 micrograms/kg.) was administered by intravenous tail injection, intraperitoneal injection, or local or distal subcutaneous injection beginning 5 days (or 60 to 121 days for large tumor studies) after subcutaneous implantation of DU 145 cells. Tumor growth was monitored as long as 140 days by external caliper measurements. RESULTS: Recombinant bFGF-SAP, though less cytotoxic than its chemical conjugate form, effectively targeted DU 145 tumors growing as xenografts in nude mice in a dose-dependent manner. Antitumor response to treatment by intravenous, intraperitoneal, or distal subcutaneous injection suggested similar bioavailability of the mitotoxin administered by each route; local subcutaneous injection to the tumor site resulted in statistically better antitumor response. Schedules that included at least 1 bFGF-SAP treatment beyond day 23 increased long-term antitumor efficacy independent of total dose. Moreover, recombinant bFGF-SAP induced dramatic reduction of large, established tumors. CONCLUSIONS: These studies suggest a therapeutic potential for bFGF receptor-directed toxins in targeting prostate cancer; further, these data suggest that treatment of established tumors (> 3 weeks) results in qualitatively and quantitatively improved tumor responses.

Combining suramin and a chimeric toxin directed to basic fibroblast growth factor receptors increases therapeutic efficacy against human melanoma in an animal model.

BACKGROUND: Suramin, which binds to and blocks autocrine and paracrine growth factors required for the proliferation of neoplastic cells, is a clinically effective antitumor agent against some human tumors; however, efficacy often is limited by toxicity. In this study, suramin treatment was combined with a fibroblast growth factor (FGF) receptor-directed toxin chimera, basic FGF-saporin (bFGF-SAP), based on the authors' previous observations that autocrine-mediated resistance to bFGF-SAP in melanoma in vitro is abrogated by suramin treatment. METHODS: Severe-combined immunodeficient-Beige mice bearing SK-Mel-5 human melanoma xenografts received weekly treatments of suramin (200 or 75 mg/kg intraperitoneally) beginning on Day 5 after tumor implantation followed 18 hours later by a treatment with bFGF-SAP (0.5-5 microg/kg intravenously) for 4 weeks. The optimal interlude between the administration of suramin and bFGF-SAP was determined by tumor excision assays. The efficacy of combination therapy as a function of alternative dosing regimens was determined by tumor growth inhibition (TGI) studies. RESULTS: Fifty days after implantation, a 79-82% TGI was observed in animals receiving the suramin (200 mg/kg) plus bFGF-SAP combination regimens compared with median tumor volumes from vehicle-treated controls (3070+/-440 mm(3)). TGI observed for combination therapies varied significantly (P<0.05-0.001) from TGI observed in treatment groups receiving suramin alone (57%) or bFGF-SAP alone (34-38%). Combining bFGF-SAP (5 microg/kg) with a low, therapeutically ineffective dose of suramin (75 mg/kg) produced a 68% rate of TGI compared with controls, thus lowering the therapeutic effective dose of suramin and eliminating the suramin-related lethal toxicity (12% mortality rate) observed in animals treated with high dose suramin. CONCLUSIONS: The results of the current study suggest that combining suramin with receptor-directed therapies offers a more effective regimen for the treatment of malignant melanoma.

Saporin toxins directed to basic fibroblast growth factor receptors effectively target human ovarian teratocarcinoma in an animal model.

BACKGROUND: The antitumor activity of the chemical conjugate and recombinant forms of the mitotoxin basic fibroblast growth factor (bFGF) saporin (SAP) and the bFGF receptor-directed immunotoxin 11A8-SAP against human ovarian teratocarcinoma PA-1 was examined in athymic nude mice. Alternative administration schedules to prolong therapeutic efficacy were explored. METHODS: Intravenous dosing (0.01-125 micrograms/kg) of chemical conjugate and recombinant bFGF-SAP or 11A8-SAP beginning 5 days after subcutaneous implantation of PA-1 cells was administered by i) weekly injection for 4 weeks, ii) continuous infusion for one week, or iii) daily injection five times a week for 4 weeks. RESULTS: Weekly injections (31.25 micrograms/kg) of chemical conjugate bFGF-SAP or 11A8-SAP, the latter of which is 25% the molarity of the former, resulted in mean tumor volumes that were, respectively, 35% or 52% of controls (day 30) and 52% or 76% of controls (day 60). Chemical conjugate or recombinant bFGF-SAP administered weekly resulted in mean tumor volumes that were, respectively, 51% or 77% (0.5 microgram/kg) and 42% or 31% (50 micrograms/kg) of controls (day 30). A mean tumor volume of 35% of controls (day 30) and of 49% of controls (day 60) were observed in animals treated by constant infusion of chemical conjugate bFGF-SAP (125 micrograms/kg, total dose). Alternatively, tumors of animals receiving daily injections (125 micrograms/kg, total dose) exhibited a mean volume of 21% of controls (day 30) and prolonged growth inhibition as demonstrated by a mean tumor volume of 22% of controls (day 60). CONCLUSIONS: These studies suggest a therapeutic potential for bFGF-receptor-directed saporin toxins in the treatment of ovarian teratocarcinoma and the importance of frequency of administration in achieving optimal tumor responses.