Biomedical subjects
Publications and source records attributed to J R Bertino.
A surprising finding in the report by Rahman et al. in this issue of Cancer Cell is that forced overexpression of human thymidylate synthase transforms immortalized murine cells into a malignant phenotype. We discuss the possibility that elevated levels of thymidylate synthase noted in some human malignancies may contribute to tumor progression and may also reflect increased levels of its transcriptional activator E2F-1.
BACKGROUND: The NHL-15 protocol is a novel, dose-intense, dose-dense, sequential chemotherapy program developed to improve outcome in advanced, aggressive non-Hodgkin's lymphomas. PATIENTS AND METHODS: The phase II NHL-15 protocol comprised: (i) induction [doxorubicin 60 mg/m(2) i.v. on weeks 1, 3, 5 and 7 plus vincristine 1.4 mg/m(2) i.v. (no cap) on weeks 1, 2, 3, 5 and 7]; and (ii) consolidation (cyclophosphamide 3000 mg/m(2) i.v. on weeks 9, 11 and 13 plus granulocyte colony-stimulating factor 5 microg/kg subcutaneous on days 3-10 following each cyclophosphamide dose). Patients with aggressive non-Hodgkin's lymphomas (working formulation: intermediate grade or immunoblastic), bulky stage I and stages II-IV, were eligible. RESULTS: There are 165 eligible patients with a 6.9-year median follow-up (range 0.5-141 months) and a median age of 48 years. For the entire group, 72.1% achieved complete remission, and at 5 years disease-free survival was 57.8% and overall survival (OS) was 62.2%. Ideal dose delivery was >90%. Acute and late toxicities of treatment were manageable and acceptable. Toxic death on treatment was 2.4%. When the diffuse large cell lymphoma histologies were grouped according to the International Prognostic Index (IPI), complete remission and OS in the low-intermediate (LI), and high-intermediate (HI) risk groups were improved by 5%-15% compared with historical CHOP (cyclophosphamide, doxorubicin, vincristine and prednisone). This improvement was also noted for LI and HI risk groups in the age-adjusted (aa)IPI analysis for patients < or =60 years of age. CONCLUSIONS: The NHL-15 program can be administered safely and effectively to achieve high rates of durable remission when used for the treatment of advanced stage, aggressive, non-Hodgkin's lymphomas. The 5%-15% improvement in 5-year OS compared with historical CHOP, according to the IPI/aaIPI model (in LI and HI risk groups), is encouraging. Further evaluation and prospective testing of the NHL-15 protocol appears to be warranted.
A recombinant fusion protein of colon carcinoma binding A33 single chain antibody with cytosine deaminase displayed specific antigen binding and enzyme activity in surface plasmon resonance and is catalytic activity assay. In vitro, it selectively increased the toxicity of 5-FC to A33 antigen-positive cells by 300-fold, demonstrating the potency of this ADEPT strategy.
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Intracellular metabolism of methotrexate (MTX) to MTX-polyglutamates (MTXPG) is one determinant of cytotoxicity. Steady-state accumulation of MTXPG seems to depend on the activity of two enzymes: folylpolyglutamate synthetase (FPGS), which adds glutamate residues, and gamma-glutamyl hydrolase (GGH), which removes them. Overexpression of GGH would be expected to decrease intracellular MTXPG, thereby increasing efflux of MTX and decreasing cytotoxicity. Increased expression of GGH has been shown to be associated with resistance to MTX in human sarcoma cell lines and a rat hepatoma cell line. To clarify the specific role of GGH in determining MTX sensitivity, we investigated the phenotype produced by forced GGH overexpression in two cell types. Furthermore, because MTX and folic acid share metabolic pathways, we measured the effects of GGH overexpression on folic acid metabolism. The full-length cDNA for GGH, subcloned into a constitutive expression vector, was transfected into a human fibrosarcoma (HT-1080) and a human breast carcinoma (MCF-7) cell line. Compared with the clones containing an empty vector, the GGH-overexpressing cells express 15- to 30-fold more GGH mRNA, more GGH protein, and 15- to 90-fold more GGH enzyme activity. GGH overexpression altered MTX accumulation and metabolism to long-chain polyglutamates. In contrast to expectations, however, GGH overexpression did not confer resistance to short MTX exposures in either cell line. Changes in MTX metabolism were found to be balanced by alterations in accumulation and metabolism of folic acid. The ratio of MTX:folate accumulation may be a better predictor of MTX cytotoxicity than the accumulation of either alone. We conclude that, at least for these two cell lines, GGH overexpression alone is insufficient to produce clinical resistance to MTX.
We examined the effects of flavopiridol (FP), a cyclin-dependent kinase inhibitor, on doxorubicin (DOX)-induced cell killing in an osteosarcoma cell line (SaOs-2) that lacks functional retinoblastoma protein (pRb). The IC50 value for DOX was 7-fold lower when combined with a low dose (100 nM) FP in pRb-deficient SaOs-2 cells than in the absence of FP. In contrast, the IC50 value for DOX was not decreased in the presence of 100 nM FP in pRb-restored SaOs-2 cells. Consistent with this, FP enhanced DOX-induced activation of caspase-3, which correlates with apoptosis, in pRb-deficient cells but not in pRb-restored cells. Additional studies showed that FP decreased DOX-induced cell accumulation in S phase in retinoblastoma-restored cells but not in pRb-deficient cells. An increased expression of p21 and inhibition of cyclin-dependent kinase 2 kinase activity by FP was also observed in pRb-deficient cells but not in retinoblastoma-restored SaOs-2 cells. We conclude that pRb plays a key role in determining whether FP selectively sensitizes DOX-induced cell killing in human sarcoma cells. Because lack of functional pRb is a common abnormality in human cancers, the combination of FP with DOX in tumors lacking pRb would be worthy of further investigation.
IgG polyclonal antiserum was generated in New Zealand White rabbits immunized with a 16-mer peptide consisting of a specific amino acid sequence at residues corresponding to the sixth to seventh predicted transmembrane domain of the human reduced folate carrier (RFC). Using Western immunoblotting to examine the cytosolic and membrane fractions of the human CCRF-CEM T-cell lymphoblastic leukemia cell line, polyclonal antihuman RFC antiserum recognized two bands in the cytosolic fraction (approximately 60 kDa and approximately 70 kDa) on 10% polyacrylamide gels. In the membrane fraction, an approximately 60-kDa protein was identified. Comparative studies of a panel of human tumor cell lines including the HT1080 fibrosarcoma, 8805 malignant fibrous histiocytoma, and the MCF breast cancer cell lines revealed similar findings. Likewise, a recombinant approximately 60-kDa membrane protein was identified after expression of baculovirus-infected Sf9 insect cells containing cDNA of the human RFC. In the CEM-7A cell line, a variant of the CCRF-CEM cell line that overexpresses the RFC, 21-fold overexpression of the approximately 60-kDa membrane protein (RFC) was shown by Western analysis. To characterize further the cellular distribution of the human RFC, immunohistochemical analyses were performed in CCRF-CEM T-cell lymphoblastic leukemia cells. Predominantly membrane localization of the antibody reacting sites was detected; however, a cytoplasmic component was noted as well. By confocal microscopy and by immunogold electron microscopy, the cytoplasmic expression was found to be largely of mitochondrial origin. These findings were corroborated by Western immunoblotting of mitochondrial membrane isolates from the CCRF-CEM cell line, which demonstrate an approximately 60-kDa protein. The localization of the human RFC to the mitochondrial membrane is a novel finding, and it suggests a role for the mitochondrial membrane in the transport of folates.
Salvage of patients with relapsed and refractory Hodgkin disease (HD) with high-dose chemoradiotherapy (HDT) and autologous stem cell transplantation (ASCT) results in event-free survival (EFS) rates from 30% to 50%. Unfortunately, the reduction in toxicity associated with modern supportive care has improved EFS by only 5% to 10% and has not reduced the relapse rate. Results of a comprehensive 2-step protocol encompassing dose-dense and dose-intense second-line chemotherapy, followed by HDT and ASCT, are reported. Sixty-five consecutive patients, 22 with primary refractory HD and 43 with relapsed HD, were treated with 2 biweekly cycles of ifosfamide, carboplatin, and etoposide (ICE). Peripheral blood progenitor cells from responding patients were collected, and the patients were given accelerated fractionation involved field radiotherapy (IFRT) followed by cyclophosphamide-etoposide and either intensive accelerated fractionation total lymphoid irradiation or carmustine and ASCT. The EFS rate at a median follow-up of 43 months, as analyzed by intent to treat, was 58%. The response rate to ICE was 88%, and the EFS rate for patients who underwent transplantation was 68%. Cox regression analysis identified 3 factors before the initiation of ICE that predicted for outcome: B symptoms, extranodal disease, and complete remission duration of less than 1 year. EFS rates were 83% for patients with 0 to 1 adverse factors, 27% for patients with 2 factors, and 10% for patients with 3 factors (P <.001). These results compare favorably with other series and document the feasibility and efficacy of giving uniform dose-dense and dose-intense cytoreductive chemotherapy and integrating accelerated fractionation radiotherapy into an ASCT treatment program. This prognostic model provides a basis for risk-adapted HDT.
The genetic transfer of drug resistance to hematopoietic cells is an attractive approach to overcoming myelosuppression caused by high-dose chemotherapy. Because cyclophosphamide (CTX) and methotrexate (MTX) are commonly used non-cross-resistant drugs, generation of dual drug resistance in hematopoietic cells that allows dose intensification may increase anti-tumor effects and circumvent the emergence of drug-resistant tumors. We constructed a retroviral vector containing both a human cytosolic ALDH-1 cDNA and a human doubly mutated DHFR cDNA (Phe22/Ser31; termed F/S in the description of constructs) to generate increased resistance to both CTX and MTX. Infection of NIH3T3 cells resulted in increased resistance to both 4-hydroperoxycyclophosphamide (4HC) (1.9 +/- 0.1-fold) and MTX (73 +/- 2.8-fold). Transduced human CD34(+) enriched hematopoietic progenitor cells were also resistant to both 4HC and MTX by CFU-GM readout. Lethally irradiated mice transplanted with SFG-ALDH-IRES-F/S or mock-transduced bone marrow cells were treated with high-dose pulse CTX or high-dose CTX/MTX. Animals receiving marrow not transduced with ALDH-1 or mutated DHFR cDNA died from CTX or CTX/MTX toxicity, whereas mice transduced with ALDH-1 and mutated DHFR cDNA-containing marrow were able to tolerate the same doses of CTX or CTX/MTX treatment posttransplant. These data taken together indicate that ALDH-1 overexpression and mutant DHFR increased both 4HC and MTX resistance in vitro and in the in vivo mouse model. This construct may be useful for protecting patients from high-dose CTX- and MTX-induced myelosuppression.
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Severe 5-fluorouracil (5-FU) toxicity has been reported among patients lacking dihydropyrimidine dehydrogenase (DPD) enzymatic activity. DPD is the principal enzyme involved in the degradation of 5-FU to 5'-6'-dihydrofluorouracil, which is further metabolized to fluoro-beta-alanine. We demonstrate here that overexpression of human DPD confers resistance to 5-FU in NIH3T3 cells, mouse bone marrow cells, and in human CD34+-enriched hematopoietic progenitor cells. An SFG-based dicistronic retroviral vector containing human DPD cDNA, an internal ribosomal entry site (IRES), and the neomycin phosphotransferase (Neo) gene was constructed (SFG-DPD-IRES-Neo). Transduced NIH3T3 cells demonstrated a 2-fold (ED50) increase in resistance to a 4-hour exposure of 5-FU in comparison to nontransduced cells. Expression of DPD was confirmed by Northern and Western blot analyses, and DPD enzyme activity was detectable only in transduced cells. Infection of mouse bone marrow cells with this retroviral construct resulted in an increased number of 5-FU-resistant CFU-GM colonies, compared to mock-transduced bone marrow in both 4-hour and 12- to 14-day exposures. Infection of human CD34+-enriched cells with this construct and incubation with 5-FU (10(-6) M) for 14 days also resulted in an increased number of 5-FU-resistant colonies. Retroviral transduction of human hematopoietic progenitor cells with a cDNA-expressing human DPD conferred resistance to 5-FU in NIH3T3 cells, mouse bone marrow cells, and human CD34+-enriched cells. These results encourage the use of this gene as a method to protect patients from 5-FU myelotoxicity.
Four new cell lines were established from the primary tumors of patients with untreated colorectal adenocarcinoma. Drug sensitivity and characterization of these cell lines was performed. Three of the four cell lines formed colonies in soft agar and all were tumorigenic in nude mice. The cell lines were morphologically similar but had differences in growth characteristics. Two of the cell lines, C18 (CCCL-4) and C29 (CCCL-6), had a longer doubling time compared with C85 (CCCL-1) and C86 (CCCL-2). The C18 and C29 cell lines had chromosome 17 abnormalities and evidence by immunohistochemistry of a mutant p53 and had decreased levels of thymidylate synthase and dihydrofolate reductase proteins, associated with decreased thymidylate synthase catalytic activity in C18 and no detectable activity in C29. Raltitrexed and GW1843U89 showed potent cytotoxic activity and all four cell lines displayed similar cytotoxicity to these folate thymidylate synthase inhibitors. The C18 and C29 cell lines were in general resistant to the other agents tested (methotrexate, 5-fluorouracil, nolatrexed) when compared with the C85 and C86 cell lines. These new cell lines may be useful for the study of colorectal adenocarcinoma and for evaluating new drugs or treatment schedules.
BACKGROUND AND OBJECTIVES: Methotrexate (MTX) is a key drug in the curative regimen of children with acute lymphocytic leukemia. This drug is widely used not only in the treatment of neoplastic diseases such as leukemia, lymphoma, choriocarcinoma, head and neck cancer and osteogenic sarcoma, but also for various autoimmune diseases, e.g., rheumatoid arthritis and psoriasis, and for the prevention of graft-versus-host disease after transplantation. The development of drug resistance is the limiting factor in the use of MTX. This review will outline the mechanisms of acquired and natural resistance to MTX that have been studied in patients affected by acute lymphocytic leukemia and acute myelocytic leukemia and the cell cycle genes involved in MTX resistance. This information may improve the use of MTX or could lead to the development of better drugs. Moreover a short description of newer antifolates with their mechanisms of action is presented. EVIDENCE AND INFORMATION SOURCES: The authors of this review have a long-standing interest in the mechanism of action of and resistance to MTX and other antifolates. Information from journal articles covered by the Science Citation Index and Medline has been reviewed together with work performed by the authors. PERSPECTIVES: Antifolates continue to be an extremely important class of drugs for the treatment of non-neoplastic as well as neoplastic diseases. New inhibitors that target dihydrofolate reductase as well as other folate-dependent enzymes are being evaluated in the clinic, and show promise.
BACKGROUND: The G52S mutation in the Arg50 loop of thymidylate synthase leads to decreased binding of FdUMP. It has been suggested that the mutation affects the Arg50 residue (within the Arg50 loop) responsible for binding the phosphate of FdUMP. The binding of the methylguanidinium moiety as a model for Arg50 to a methylphosphate entity as a model for FdUMP was investigated with theoretical calculations, as well as the structure of the Arg50-Thr51-Gly52 tripeptide in comparison with the Arg50-Thr51-Ser52 tripeptide. METHODS: Gaussian-98 and PC Spartan programs were used to perform Hartree-Fock and Post-Hartree-Fock quantum chemical calculations as well as MNDO (semi-empirical calculations). RESULTS: It was found that the strongest binding occurs between the negative methylphosphate ion and methylguanidine. The replacement of Gly52 by Ser52 leads to a significant displacement of Arg50, which may be responsible for the decreased binding to FdUMP. CONCLUSION: The arginine-phosphate binding appears to be geometry dependent. Thus, the displacement of the Arg50 residue, as observed in these calculated models, upon mutation of Gly52 to Ser may contribute to decreased binding of FdUMP to mTS (G52S).
The cytotoxic effects of ecteinascidin-743(ET-743), a novel marine natural product, were evaluated and compared with that of clinically used anticancer agents methotrexate, doxorubicin, etoposide, and paclitaxel in eight human soft tissue sarcoma (STS) cell lines. HT-1080, a fibrosarcoma cell line, and HS-42, a malignant mesodermal cell line, were the most sensitive of the cell lines to methotrexate, doxorubicin, etoposide, and paclitaxel. Other cell lines (IC50s) varied considerably and were more resistant to these agents. ET-743 was more potent than any of these agents, with IC50s in the pM range in all of the cell lines. Cytotoxicity of ET-743 was dose- and time-related (4-72 h exposure). Cytotoxic concentrations of ET-743 produced a S/G2 block in all of the cell lines tested. Three colon adenocarcinoma cell lines, HCT-8, HT-29, and HCT-116, and one breast cancer cell line, MCF-7, were 1-2 logs less sensitive to ET-743 than the STS cell lines. Cell lines were also characterized as to expression of oncogenes and tumor suppressor genes to attempt to correlate sensitivity of these cell lines to ET-743 and other chemotherapeutic agents. All of the cell lines except M8805, a malignant fibrous histiocytoma cell line, had mutations in p53 and/or overexpressed the MDM2 protein. Only HS-18, a liposarcoma cell line, lacked expression of the retinoblastoma protein. None of the cell lines had detectable expression of P-glycoprotein as measured by immunohistochemistry. ET-743 is an extremely potent cytotoxic agent against human STS cell lines and is being evaluated as an antitumor agent in this disease.
Ecteinascidin 743 (ET-743) is a potent antitumor agent from the Caribbean tunicate Ecteinascidin turbinata and is presently in clinical trials for human cancers. To better understand how ET-743 might be used clinically, the present study used SRB assays to examine the cytotoxicity resulting from combining ET-743 with three other antineoplastic agents: doxorubicin (DXR), trimetrexate, and paclitaxel in different administration schedules in two soft tissue sarcoma cell lines, HT-1080 and HS-18, in vitro. Concurrent exposure of ET-743 with DXR resulted in synergistic interactions in both cell lines. Addition of ET-743 for 24 h before DXR was the most effective cytotoxic regimen against both cell lines. Morphological study by fluorescence microscopy revealed that combination treatment of both cells with ET-743 and DXR induced apoptosis. Exposure to paclitaxel before ET-743 was also an effective regimen. These results encourage studies of the combination of ET-743 and DXR in the treatment of soft tissue sarcoma, because each of these agents have activity in this disease.
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