Transcriptional repression by HDAC3 mediates T cell exclusion from Kras mutant lung tumors.

Histone Deacetylase 3 (HDAC3) function in vivo is nuanced and directed in a tissue-specific fashion. The importance of HDAC3 in Kras mutant lung tumors has recently been identified, but HDAC3 function in this context remains to be fully elucidated. Here, we identified HDAC3 as a lung tumor cell-intrinsic transcriptional regulator of the tumor immune microenvironment. In Kras mutant lung cancer cells, we found that HDAC3 is a direct transcriptional repressor of a cassette of secreted chemokines, including Cxcl10. Genetic and pharmacological inhibition of HDAC3 robustly up-regulated this gene set in human and mouse Kras, LKB1 (KL) and Kras, p53 (KP) mutant lung cancer cells through an NF-κB/p65-dependent mechanism. Using genetically engineered mouse models, we found that HDAC3 inactivation in vivo induced expression of this gene set selectively in lung tumors and resulted in enhanced T cell recruitment at least in part via Cxcl10. Furthermore, we found that inhibition of HDAC3 in the presence of Kras pathway inhibitors dissociated Cxcl10 expression from that of immunosuppressive chemokines and that combination treatment of entinostat with trametinib enhanced T cell recruitment into lung tumors in vivo. Finally, we showed that T cells contribute to in vivo tumor growth control in the presence of entinostat and trametinib combination treatment. Together, our findings reveal that HDAC3 is a druggable endogenous repressor of T cell recruitment into Kras mutant lung tumors.

The effect of repeated hurricanes on the age of organic carbon in humid tropical forest soil.

Increasing hurricane frequency and intensity with climate change is likely to affect soil organic carbon (C) stocks in tropical forests. We examined the cycling of C between soil pools and with depth at the Luquillo Experimental Forest in Puerto Rico in soils over a 30-year period that spanned repeated hurricanes. We used a nonlinear matrix model of soil C pools and fluxes ("soilR") and constrained the parameters with soil and litter survey data. Soil chemistry and stable and radiocarbon isotopes were measured from three soil depths across a topographic gradient in 1988 and 2018. Our results suggest that pulses and subsequent reduction of inputs caused by severe hurricanes in 1989, 1998, and two in 2017 led to faster mean transit times of soil C in 0-10 cm and 35-60 cm depths relative to a modeled control soil with constant inputs over the 30-year period. Between 1988 and 2018, the occluded C stock increased and δ13C in all pools decreased, while changes in particulate and mineral-associated C were undetectable. The differences between 1988 and 2018 suggest that hurricane disturbance results in a dilution of the occluded light C pool with an influx of young, debris-deposited C, and possible microbial scavenging of old and young C in the particulate and mineral-associated pools. These effects led to a younger total soil C pool with faster mean transit times. Our results suggest that the increasing frequency of intense hurricanes will speed up rates of C cycling in tropical forests, making soil C more sensitive to future tropical forest stressors.

Mean overall survival gain with aflibercept plus FOLFIRI vs placebo plus FOLFIRI in patients with previously treated metastatic colorectal cancer.

BACKGROUND: Mean survival in cancer trials can be estimated with statistical techniques to extrapolate study survival curves. This methodology was applied to data from the VELOUR trial, where use of the novel biologic aflibercept (ziv-aflibercept in the United States) in combination with fluorouracil+leucovorin+irinotecan (FOLFIRI), had significantly increased median overall survival (OS) by 1.44 months, vs placebo plus FOLFIRI in patients with metastatic colorectal cancer (mCRC) resistant to, or that had progressed following, an oxaliplatin-containing regimen. METHODS: Parametric survival analyses were used to identify distributions with the best fit to the empirical VELOUR data. Mean OS for the two treatment groups (and pre-defined subgroups) was calculated from the fitted curves over a 15-year survival period. RESULTS: Overall, the log-logistic distribution was the best-fitting for both treatment arms and, with it, the estimated difference in mean OS over 15 years between aflibercept+FOLFIRI and placebo+FOLFIRI was 4.7 months. In addition, the survival advantage with aflibercept was at least 3 months for the ITT population, whichever distribution was used to extrapolate survival. CONCLUSION: Extrapolation of survival curves suggests the mean OS difference for aflibercept in the VELOUR trial is at least 3 months in the ITT population and selected subgroups.

Oxidation of Ethidium using TAML Activators: A Model for High School Research Performed in Partnership with University Scientists.

A chemical research program at a public high school has been developed. The full-year Advanced Chemical Research class (ACR) in the high school enrolls 20 to 30 seniors each year, engaging them in long-term experimental projects. Through partnerships involving university scientists, ACR high school students have had the opportunity to explore a number of highly sophisticated original research projects. As an example of the quality of experimental work made possible through these high school-university partnerships, this article describes the development of a novel method for the oxidation of ethidium bromide, a mutagen commonly used in molecular biology. Data collected from ACR alumni show that the ACR program is instrumental in encouraging students to pursue careers in scientific fields and in creating life-long problem-solvers.

Activity of antifolates against Pneumocystis carinii dihydrofolate reductase and identification of a potent new agent.

The therapy of Pneumocystis carinii (PC) pneumonia is often unsuccessful, particularly in patients with acquired immune deficiency syndrome (AIDS). Because of difficulties in growing the organism in vitro or obtaining purified organisms, current treatment choices have been made with little information on the metabolic effects of therapeutic agents on PC. This report quantitates the effects of the commonly used antifolates as well as the classic antineoplastic antifolate methotrexate and a lipid-soluble analogue, trimetrexate, on the target enzyme, dihydrofolate reductase (DHFR), in the PC organisms. Trimethoprim and pyrimethamine were found to be weak inhibitors (ID50 = 39,600 and 2,800 nM, respectively), while methotrexate and trimetrexate were potent reductase inhibitors (ID50 = 1.4 and 26.1 nM, respectively). transport studies with radiolabeled compounds showed that compounds with the classic folate structure (methotrexate and leucovorin) were not taken up by the intact PC organisms. In contrast, trimetrexate exhibited rapid uptake. These results suggest a major therapeutic advantage may be gained by combining a potent, readily transported PC DHFR inhibitor such as trimetrexate with the reduced folate leucovorin to achieve a highly potent antiprotozoan effect while preventing toxicity to mammalian cells.

The CEAP-L classification for lymphedemas of the limbs: the Italian experience.

AIM: A method to classificate lymphedema has been needed to gather all the important information on the clinical evolution of the disease using a common language and an easy clinical applicability. METHODS: The proposal for a new classification of the limb lymphedema was inspired by the C.E.A.P. classification for chronic venous insufficiency of the lower limb. The classification adopts the acronym C.E.A.P. by adding the letter L to underline the aspect ''lymphedema'' and is based on clinical data such as extension of lymphedema, presence of lymphangitis, leg ulcers and loss of functionality of the limb and instrumental criteria that permit to confirm and precise diagnosis. The Clinical classification is based on the most objective sign in these patients, the edema which is subdivided into 5 classes depending on the clinical manifestations. The etiological aspect considers 2 types of alterations of the lymphatic system: congenital and acquired. The anatomic is aimed to locate the anatomical structures involved. Pathophysiological conditions are gathered into 5 groups: agenesia or hypoplasia, hyperplasia, reflux, overload, obstruction. RESULTS: The classification has already been appraised after 4 years of activity at the unit of Vascular and Endovascular Surgery of Ferrara, at the S. Giovanni Battista Hospital in Rome, at the Umberto I Ancona Hospital and at the S. Giovanni-Addolorata Hospital in Rome. CONCLUSIONS: The proposal for a new classification of lymphedema C.E.A.P. L was developed in order to categorize patients with definite and objective marks, creating clinical reports with a common vocabulary, clear to all clinicians, permitting to stage the disease, evaluate treatment and finally obtain epidemiological and statistical data.

Transgenic expression of human thymidylate synthase accelerates the development of hyperplasia and tumors in the endocrine pancreas.

Thymidylate synthase (TS) is an essential enzyme for DNA synthesis and repair and elevated levels of TS have been identified as an important prognostic biomarker for colorectal cancer and several other common human malignancies. In addition, TS gene expression has been linked with cell-cycle regulation and cell proliferation through the ability of retinoblastoma protein to repress the transcriptional activation of E2F target genes such as TS. Therefore, overproduction of TS could participate in the progression to a neoplastic phenotype. Consistent with this model, a recent study has suggested that ectopic TS expression can induce a transformed phenotype in mammalian cells. To investigate the role of deregulated TS activity in tumor development, we generated transgenic mice that express high levels of catalytically active human TS (hTS) exclusively in the pancreas and low levels of hTS in multiple other tissues. Analyses of pancreatic tissue in TS transgenic mice revealed abnormalities within the endocrine pancreas, ranging from pancreatic islet hyperplasia to the detection of islet cell tumors. Overexpression of hTS in murine islets provides a new model to study genetic alterations associated with the progression from normal cells to hyperplasia to islet cell tumors, and suggests that this mouse model may be useful for regulating TS activity in vivo for development of cancer prevention and new therapies.

Effect of methotrexate on intracellular folate pools in purified myeloid precursor cells from normal human bone marrow.

We investigated the effects of the antifolate methotrexate on intracellular folate pools of human myeloid precursor cells (MPCs). Immature MPCs, representing 3.2% of the original marrow population, were selected from normal human bone marrow by immune rosetting. The intracellular folate pools were labeled by incubation with 5 X 10(-8) M [3H]5-formyl-FH4 and were quantitated by high performance liquid chromatography. The predominant folates were 5-methyl-tetrahydrofolate (5-methyl-FH4) (36%), 10-formyl-FH4 (41.4%), 5-formyl-FH4 (12.3%), and FH4 (10.3%). A 12-h exposure to 1 microM methotrexate (MTX) resulted in a 34% reduction in the intracellular concentration of 10-formyl-FH4, a 61% decrease in 5-formyl-FH4, and a 62% decrease in 5-methyl-FH4, as well as the appearance and progressive expansion of the FH2 and 10-formyl-FH2 pools. These changes were maximal after 4 h of incubation with MTX. Paralleling the changes in folates, particularly the increase in FH2, were a 64% reduction in myeloid colony formation and a 77% depression of de novo purine synthesis after 4 h of MTX. We conclude that MTX does not produce quantitative depletion of 10-formyl-FH4 and that its antipurine effect may be mediated by direct inhibition of de novo purine synthesis by FH2 and, at later time points, by MTX polyglutamates.

Interaction of sulfonamide and sulfone compounds with Toxoplasma gondii dihydropteroate synthase.

Toxoplasma gondii is a common protozoan disease that often causes life-threatening disease, particularly among patients with the acquired immunodeficiency syndrome. This study demonstrates that the dihydropteroate synthase in T. gondii is kinetically distinct from the enzyme characterized from other sources and can be highly purified with a high yield using sequential dye-affinity chromatography. Conditions have been identified that allow for stabilization of the purified enzyme, and its physical characteristics have been elucidated. The molecular weight of the native protein was 125,000 and the protein appeared to contain both dihydropteroate synthase and 6-hydroxymethyl-dihydropterin pyrophosphokinase activities. The sulfonamide class of compounds vary in inhibitory potency by more than three orders of magnitude. Sulfathiazole, sulfamethoxazole, and sulfamethazine, with 50% inhibitory concentrations (IC50's) of 1.7, 2.7, and 5.7 microM, respectively, represent the most potent of this class of inhibitors. Several sulfone analogues, including dapsone, were identified as highly potent inhibitors with IC50's less than 1 microM. The results of these cell-free experiments were corroborated by investigating the metabolic inhibition produced by the various inhibitors in intact organisms. The qualitative and quantitative relations among the inhibitors were preserved in both the cell-free and intact cell assay systems. These studies suggest that the sulfones may be important therapeutic agents for the treatment of toxoplasmosis.

Potent in vitro and in vivo antitoxoplasma activity of the lipid-soluble antifolate trimetrexate.

Trimetrexate, a highly lipid-soluble quinazoline antifolate now undergoing trials as an anticancer agent, was found to be a potent inhibitor of the dihydrofolate reductase (DHFR) isolated from Toxoplasma gondii. The concentration required for 50% inhibition of protozoal DHFR was 1.4 nM. As an inhibitor of this enzyme, trimetrexate was almost 600-fold (amount of antifolate required to inhibit catalytic reaction by 50%) and 750-fold (inhibition constant) more potent than pyrimethamine, the DHFR inhibitor currently used to treat toxoplasma infection. When the protozoan was incubated with 1 microM trimetrexate, the drug rapidly reached high intracellular concentrations. Since toxoplasma organisms lack a transmembrane transport system for physiologic folates, host toxicity can be prevented by co-administration of the reduced folate, leucovorin, without reversing the antiprotozoal effect. The effectiveness of trimetrexate against toxoplasma was demonstrated both in vitro and vivo. Proliferation of toxoplasma in murine macrophages in vitro was completely inhibited by exposure of these cells to 10(-7) M trimetrexate for 18 h. When used alone, trimetrexate was able to extend the survival of T. gondii-infected mice.

Disruption of Myc-tubulin interaction by hyperphosphorylation of c-Myc during mitosis or by constitutive hyperphosphorylation of mutant c-Myc in Burkitt's lymphoma.

Somatic mutations at Thr-58 of c-Myc have been detected in Burkitt's lymphoma (BL) tumors and have been shown to affect the transforming potential of the Myc oncoprotein. In addition, the N-terminal domain of c-Myc has been shown to interact with microtubules in vivo, and the binding of c-Myc to alpha-tubulin was localized to amino acids 48 to 135 within the c-Myc protein. We demonstrate that c-Myc proteins harboring a naturally occurring mutation at Thr-58 from BL cell lines have increased stability and are constitutively hyperphosphorylated, which disrupts the in vivo interaction of c-Myc with alpha-tubulin. In addition, we show that wild-type c-Myc-alpha-tubulin interactions are also disrupted during a transient mitosis-specific hyperphosphorylation of c-Myc, which resembles the constitutive hyperphosphorylation pattern of Thr-58 in BL cells.

Thymidylate synthase binds to c-myc RNA in human colon cancer cells and in vitro.

Using an immunoprecipitation-reverse transcription-PCR technique, we characterized a thymidylate synthase (TS) ribonucleoprotein complex in cultured human colon cancer cells that consists of TS protein and the mRNA of the nuclear oncogene c-myc. TS protein is complexed in intact cells with the C-terminal coding region of c-myc mRNA that includes nucleotide positions 1625 to 1790. RNA electrophoretic gel mobility shift assays confirm a specific interaction between TS protein and c-myc mRNA and provide additional evidence that the C-terminal coding region represents an important cis-acting regulatory element. Further evidence demonstrates that the in vitro translational efficiency of c-myc mRNA is inhibited as a result of its direct interaction with TS protein. In addition, the presence of exogenous c-myc mRNA specifically relieves the inhibitory effects of TS protein on TS mRNA translation.

Identification of a thymidylate synthase ribonucleoprotein complex in human colon cancer cells.

Translation of thymidylate synthase (TS) mRNA is controlled by its own protein product, TS, in an autoregulatory manner. Direct binding of TS protein to two different cis-acting elements on the TS mRNA is associated with this translational regulation. In this study, an immunoprecipitation-reverse transcription-PCR technique was used to identify a TS ribonucleoprotein (RNP) complex in cultured human colon cancer cells. Using antibodies specific for TS protein, we show that TS is complexed in vivo with its own TS RNA. Furthermore, evidence demonstrating a direct interaction between the mRNA of the nuclear oncogene c-myc and TS protein is presented.

Thymidylate synthase protein and p53 mRNA form an in vivo ribonucleoprotein complex.

A thymidylate synthase (TS)-ribonucleoprotein (RNP) complex composed of TS protein and the mRNA of the tumor suppressor gene p53 was isolated from cultured human colon cancer cells. RNA gel shift assays confirmed a specific interaction between TS protein and the protein-coding region of p53 mRNA, and in vitro translation studies demonstrated that this interaction resulted in the specific repression of p53 mRNA translation. To demonstrate the potential biological role of the TS protein-p53 mRNA interaction, Western immunoblot analysis revealed nearly undetectable levels of p53 protein in TS-overexpressing human colon cancer H630-R10 and rat hepatoma H35(F/F) cell lines compared to the levels in their respective parent H630 and H35 cell lines. Polysome analysis revealed that the p53 mRNA was associated with higher-molecular-weight polysomes in H35 cells compared to H35(F/F) cells. While the level of p53 mRNA expression was identical in parent and TS-overexpressing cell lines, the level of p53 RNA bound to TS in the form of RNP complexes was significantly higher in TS-overexpressing cells. The effect of TS on p53 expression was also investigated with human colon cancer RKO cells by use of a tetracycline-inducible system. Treatment of RKO cells with a tetracycline derivative, doxycycline, resulted in 15-fold-induced expression of TS protein and nearly complete suppression of p53 protein expression. However, p53 mRNA levels were identical in transfected RKO cells in the absence and presence of doxycycline. Taken together, these findings suggest that TS regulates the expression of p53 at the translational level. This study identifies a novel pathway for regulating p53 gene expression and expands current understanding of the potential role of TS as a regulator of cellular gene expression.

Characterization of a cis-acting regulatory element in the protein coding region of thymidylate synthase mRNA.

Thymidylate synthase (TS) functions as an RNA-binding protein by interacting with two different sequences on its own mRNA. One site is located in the 5'-upstream region of human TS mRNA while the second site is located within the protein coding region corresponding to nt 434-634. In this paper, a 70 nt RNA sequence, corresponding to nt 480-550, was identified that binds TS protein with an affinity similar to that of full-length TS mRNA and TS434-634 RNA. In vitro translation studies confirmed that this sequence is critical for the translational autoregulatory effects of TS. To document in vivo biological significance, TS sequences contained within this region were cloned onto the 5'-end of a luciferase reporter plasmid and transient transfection experiments were performed using H630 human colon cancer cells. In cells transfected with p644/TS434-634 or p644/TS480-550, luciferase activity was decreased 2.5-fold when compared to cells transfected with p644 plasmid alone. Luciferase mRNA levels were identical for each of these conditions as determined by RNase protection and RT-PCR analysis. Immunoprecipitation of TS ribonucleoprotein complexes revealed a direct interaction between TS protein and TS480-550 RNA in transfected H630 cells. Treatment with 5-fluorouridine resulted in a nearly 2-fold increase in luciferase activity only in cells transfected with p644/TS434-634 and p644/TS480-550. This study identifies a 70 nt TS response element in the protein coding region of TS mRNA with in vitro and in vivo translational regulatory activity.

Toxicity of levamisole and 5-fluorouracil in human colon carcinoma cells.

The combination of 5-fluorouracil (5-FU) with the immunomodulator levamisole (Lev) has been clinically tested in patients with metastatic colorectal carcinoma and as adjuvant therapy following primary tumor surgery. In some studies in advanced disease, the addition of Lev to 5-FU improved the median duration of response; in the adjuvant setting, the combination was associated with improvement in the disease-free survival. We studied whether Lev was directly toxic to three human colorectal carcinoma cell lines (HCT 116, SNU-C4, and NCI-H630). We also evaluated the toxicity of Lev in combination with 5-FU in these three cell lines. Lev inhibited the growth of all three colorectal cell lines, but only at concentrations two logs above that achieved with a standard 150-mg oral dose of Lev. In cell growth studies, 500 and 1,000 microM Lev increased the toxicity of 5-FU in HCT 116 cells in an additive fashion. In clonogenic assays, continuous exposure to 10 or 100 microM Lev was minimally toxic and did not enhance the lethality associated with a 24-hour exposure to 5-FU in any of the cell lines. Lev alone at 1,000 microM decreased colony formation by 45% in HCT 116 cells. A combination of 1,000 microM Lev with 10 microM 5-FU resulted in a decrease in HCT 116 colony formation from 54% to 6% of control levels. Continuous exposure of NCI-H630 cells to 500 microM Lev decreased colony formation to 76.5% of control levels; when Lev was combined with 50 microM 5-FU, colony formation was decreased from 59.5% to 27.5% of control levels. We conclude that at concentrations achievable with conventional doses of Lev, there was no evidence of direct toxicity in these colorectal cell lines. Furthermore, an additive interaction with 5-FU was evident only at suprapharmacologic doses of Lev.

Decreased catabolism of fluorouracil in peripheral blood mononuclear cells during combination therapy with fluorouracil, leucovorin, and interferon alpha-2a.

BACKGROUND: We previously reported that recombinant interferon alpha-2a (IFN alpha-2a) therapy was associated with a dose-dependent decrease in fluorouracil (5-FU) clearance. PURPOSE: In this study, we used peripheral blood mononuclear cells (PBMCs), which are responsive to IFNs, as surrogate tissue to determine whether the change in clearance might be explained by decrease in 5-FU catabolism during IFN alpha-2a therapy. METHODS: The study population consisted of 45 patients with adenocarcinoma arising in the gastrointestinal tract. Thirty-seven patients received therapy containing IFN alpha-2a at a median dose of 5 million U/m2 per day (range, 1.7-7.5 million U/m2 per day) starting on day 1 and continuing through either day 7 or day 14 in conjunction with intravenous high-dose leucovorin (LV) followed by bolus 5-FU on days 2-6. Eight patients received the same schedule of 5-FU and LV daily for 5 days without IFN alpha-2a but with granulocyte-macrophage colony-stimulating factor starting on day 6 and ending at least 3 days prior to the start of the next cycle. Peripheral blood was collected during 70 cycles on days 1, 2, and 4 prior to the daily treatment with IFN alpha-2a + 5-FU+LV and during 19 cycles on days 1 and 4 prior to the daily treatment with 5-FU+LV without IFN alpha-2a. In a given patient cycle, matched samples were drawn at approximately the same time of day. PBMCs were isolated, and the intact cells were exposed to 4 microM [3H]5-FU, and the formation of [3H]dihydrofluorouracil was determined by reverse-phase high-performance liquid chromatography. RESULTS: In 47 matched patient cycles from IFN alpha-2a + 5-FU+LV-treated patients in which samples were available on days 1, 2, and 4, 5-FU catabolism decreased by 20% (P2 = .03) and 41% (P2 = .0001) from the baseline catabolic rate (2.5 +/- 0.2 pmol/min per 10(6) cells [mean +/- SE]) on days 2 and 4, respectively. Using information from all paired samples, the mean change from baseline on day 2 was -0.4 +/- 0.2 pmol/min per 10(6) cells (n = 54; P2 = .05), and the change from baseline on day 4 was -1.3 +/- 0.3 pmol/min per 10(6) cells (n = 63; P2 = .0001). In contrast, changes in 5-FU catabolism were not evident in the PBMCs of the reference population receiving 5-FU+LV without IFN alpha-2a. CONCLUSIONS: The magnitude of the change in 5-FU catabolism is similar to the magnitude of the decrease in 5-FU clearance in our previous study. These observations suggest that changes in 5-FU catabolism during therapy with IFN alpha-2a, 5-FU, and LV may account for the decreased 5-FU clearance.

Thymidylate synthase expression and response to neoadjuvant chemotherapy in patients with advanced head and neck cancer.

BACKGROUND: Thymidylate synthase (TS), an essential enzyme in DNA synthesis, is a target for the fluoropyrimidines, an important group of antineoplastic agents used widely in the treatment of head and neck cancer. PURPOSE: We evaluated relationships between the level and/or pattern of tumor TS expression and response to fluorouracil (5-FU)-based neoadjuvant chemotherapy in patients with advanced head and neck cancer. METHODS: Tumor specimens from 86 patients were available for this retrospective analysis. The patients were enrolled in four consecutive phase II studies that tested combinations of 5-FU, leucovorin, and cisplatin with or without added methotrexate plus piritrexim or interferon alfa-2b (IFN alpha-2b). TS protein expression in the tumors was assessed by use of the TS 106 monoclonal antibody and standard immunohistochemical staining techniques. TS immunostaining was classified according to its level of intensity (TS 0-1 = low, TS 2 = intermediate, and TS 3 = high) and according to its extent (focal pattern = less than 25% of tumor cells positive; diffuse pattern = greater than or equal to 25% of tumor cells positive). Data from 79 patients were available for an analysis of tumor TS expression and patient/tumor characteristics; 70 patients were assessable for their response to neoadjuvant chemotherapy. RESULTS: There was a statistically significant association between the level of tumor TS expression and the degree of tumor differentiation; a higher proportion of patients whose tumors exhibited TS 0-1 immunostaining had undifferentiated or poorly differentiated tumors than patients whose tumors exhibited TS 2 or TS 3 immunostaining (P = .04, Jonckheere-Terpstra trend test). Among the 70 patients who were assessable for response to neoadjuvant chemotherapy, TS 3 tumor immunostaining was associated with a lower rate of complete response (i.e., complete disappearance of clinically detectable disease for a minimum of 4 weeks from time of initial determination) than was TS 2 or TS 0-1 immunostaining, but this association was not statistically significant (P = .09, exact trend test); among the 39 patients who were treated with regimens that included 5-FU, leucovorin, cisplatin, and IFN alpha-2b, this inverse association between TS immunostaining intensity and response was statistically significant (P = .02, exact trend test). Tumor TS immunostaining intensity and overall survival were not found to be associated. Patients with tumors exhibiting a focal pattern of TS immunostaining have experienced significantly longer survival than patients with tumors exhibiting a diffuse pattern; for the 53 patients with diffuse tumor TS immunostaining, the median survival was 24.7 months, whereas the median survival has not yet been reached for the 22 patients with focal tumor TS immunostaining (P = .04, two-tailed logrank test). However, the survival advantage for the focal versus diffuse TS immunostaining pattern was limited to patients whose tumors also exhibited a TS 3 level of immunostaining intensity. CONCLUSIONS AND IMPLICATIONS: Characterization of tumor TS expression may be of value in identifying patients with advanced head and neck cancer who would benefit from fluoropyrimidine-based neoadjuvant chemotherapy.

Enhancement of fluorinated pyrimidine-induced cytotoxicity by leucovorin in human colorectal carcinoma cell lines.

Reduced folates have been shown to increase the cytotoxicity of 5-fluorouracil (5-FU) by stabilizing the 5-fluoro-2'-deoxyuridine-5'-monophosphate-thymidylate synthase complex, thus increasing the block in the DNA synthetic pathway. Using an in vitro colorimetric [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] cytotoxicity assay, we tested the effects of 5-FU and 5-fluoro-2'-deoxyuridine (FdUrd) with and without leucovorin (LV) on a panel of 11 human colorectal carcinoma cell lines. The effect of LV on 5-FU and FdUrd was quantitatively similar. A clinically achievable level of LV (20 microM) increased the cytotoxicity in all three replicate experiments in 10 of the 11 cell lines (P less than .05, binomial test). LV alone at a concentration of 20 microM had no effect on cell survival. In three cell lines, 50% inhibition of growth occurred at a clinically achievable area under the curve of 5-FU alone. With the addition of LV, one additional cell line showed 50% growth inhibition at a clinically achievable level of 5-FU. Hence large clinical trials may be necessary to detect a significant improvement in survival as a result of adding LV to the fluorinated pyrimidines.

Adjuvant 5-fluorouracil and leucovorin with or without interferon alfa-2a in colon carcinoma: National Surgical Adjuvant Breast and Bowel Project protocol C-05.

BACKGROUND: National Surgical Adjuvant Breast and Bowel Project (NSABP) protocol C-03 showed a benefit from leucovorin (LV)-modulated 5-fluorouracil (5-FU) adjuvant therapy (5-FU + LV) in patients with Dukes' stage B or C carcinoma of the colon. Preclinical and clinical phase I/II data suggested that interferon alfa-2a (IFN) enhanced the efficacy of 5-FU therapy. Accordingly, in NSABP protocol C-05, the addition of recombinant IFN to 5-FU + LV adjuvant therapy was evaluated. METHODS: Data are presented for 2176 patients with Dukes' stage B or C cancer entered onto protocol C-05 during the period from October 1991 through February 1994. Individuals with an Eastern Cooperative Oncology Group performance status of 0-2 (ranges from fully active to ambulatory and capable of self-care but unable to work), a life expectancy of at least 10 years, and curative resection were stratified by sex, disease stage, and number of involved lymph nodes and were randomly assigned to receive either 5-FU + LV or 5-FU + LV + IFN; the mean time on the study as of June 30, 1997, was 54 months. All statistical tests were two-sided. RESULTS: There was no statistically significant difference in either disease-free survival (5-FU + LV, 69%; 5-FU + LV + IFN, 70%) or overall survival (5-FU + LV, 80%; 5-FU + LV + IFN, 81%) at 4 years of follow-up. Toxic effects of grade 3 or higher were observed in 61.8% of subjects in the group treated with 5-FU + LV and in 72.1% of subjects in the group treated with 5-FU + LV + IFN; fewer patients in the latter group completed protocol-mandated 5-FU + LV therapy than in the former group (77.1% versus 88.5%). CONCLUSION: The addition of IFN to 5-FU + LV adjuvant therapy confers no statistically significant benefit, but it does increase toxicity.