Loading...
(1/11316) Interleukin-6 dependent induction of the cyclin dependent kinase inhibitor p21WAF1/CIP1 is lost during progression of human malignant melanoma.

Human melanoma cell lines derived from early stage primary tumors are particularly sensitive to growth arrest induced by interleukin-6 (IL-6). This response is lost in cell lines derived from advanced lesions, a phenomenon which may contribute to tumor aggressiveness. We sought to determine whether resistance to growth inhibition by IL-6 can be explained by oncogenic alterations in cell cycle regulators or relevant components of intracellular signaling. Our results show that IL-6 treatment of early stage melanoma cell lines caused G1 arrest, which could not be explained by changes in levels of G1 cyclins (D1, E), cdks (cdk4, cdk2) or by loss of cyclin/cdk complex formation. Instead, IL-6 caused a marked induction of the cdk inhibitor p21WAF1/CIP1 in three different IL-6 sensitive cell lines, two of which also showed a marked accumulation of the cdk inhibitor p27Kip1. In contrast, IL-6 failed to induce p21WAF1/CIP1 transcript and did not increase p21WAF1/CIP1 or p27kip1 proteins in any of the resistant lines. In fact, of five IL-6 resistant cell lines, only two expressed detectable levels of p21WAF1/CIP1 mRNA and protein, while in three other lines, p21WAF1/CIP1 was undetectable. IL-6 dependent upregulation of p21WAF1/CIP1 was associated with binding of both STAT3 and STAT1 to the p21WAF1/CIP1 promoter. Surprisingly, however, IL-6 stimulated STAT binding to this promoter in both sensitive and resistant cell lines (with one exception), suggesting that gross deregulation of this event is not the unifying cause of the defect in p21WAF1/CIP1 induction in IL-6 resistant cells. In somatic cell hybrids of IL-6 sensitive and resistant cell lines, the resistant phenotype was dominant and IL-6 failed to induce p21WAF1/CIP1. Thus, our results suggest that in early stage human melanoma cells, IL-6 induced growth inhibition involves induction of p21WAF1/CIP1 which is lost in the course of tumor progression presumably as a result of a dominant oncogenic event.  (+info)

(2/11316) L-[1-11C]-tyrosine PET to evaluate response to hyperthermic isolated limb perfusion for locally advanced soft-tissue sarcoma and skin cancer.

PET with L-[1-11C]-tyrosine (TYR) was investigated in patients undergoing hyperthermic isolated limb perfusion (HILP) with recombinant tumor necrosis factor alpha (rTNF-alpha) and melphalan for locally advanced soft-tissue sarcoma and skin cancer of the lower limb. METHODS: Seventeen patients (5 women, 12 men; age range 24-75 y; mean age 52 y) were studied. TYR PET studies were performed before HILP and 2 and 8 wk afterwards. The protein synthesis rates (PSRs) in nanomoles per milliliter per minute were calculated. After final PET studies, tumors were resected and pathologically examined. Patients with pathologically complete responses (pCR) showed no viable tumors after treatment. Those with pathologically partial responses (pPR) showed various amounts of viable tumors in the resected tumor specimens. RESULTS: Six patients (35%) showed a pCR and 11 patients (65%) showed a pPR. All tumors were depicted as hot spots on PET studies before HILP. The PSR in the pCR group at 2 and 8 wk after perfusion had decreased significantly (P < 0.05) in comparison to the PSR before HILP. A significant difference was found in PSR between the pCR and pPR groups at 2 and at 8 wk (P < 0.05). Median PSR in nonviable tumor tissue was 0.62 and ranged from 0.22 to 0.91. With a threshold PSR of 0.91, sensitivity and specificity of TYR PET were 82% and 100%, respectively. The predictive value of a PSR > 0.91 for having viable tumor after HILP was 100%, whereas the predictive value of a PSR < or = 0.91 for having nonviable tumor tissue after HILP was 75%. The 2 patients in the pPR groups with a PSR < 0.91 showed microscopic islets of tumor cells surrounded by extensive necrosis on pathological examination. CONCLUSION: Based on the calculated PSR after HILP, TYR PET gave a good indication of the pathological outcome. Inflammatory tissue after treatment did not interfere with viable tumor on the images, suggesting that it may be worthwhile to pursue TYR PET in other therapy evaluation settings.  (+info)

(3/11316) Effect of tumor necrosis factor alpha on vascular resistance, nitric oxide production, and glucose and oxygen consumption in perfused tissue-isolated human melanoma xenografts.

The effect of tumor necrosis factor alpha (TNF-alpha) on vascular resistance, nitric oxide production, and consumption of oxygen and glucose was examined in a perfused tissue-isolated tumor model in nude mice. One experimental group was perfused with heparinized Krebs-Henseleit buffer, a second one was perfused with TNF-alpha (500 microgram/kg) 5 h before perfusion. The vascular resistance increased significantly 5 h after TNF-alpha injection. The increase in vascular resistance did not seem to be mediated by a decrease in tumor nitric oxide production, as determined by perfusate nitrate/nitrite concentrations, but may be due to aggregation of leukocytes, platelets, and erythrocytes and/or endothelial consumption among the three experimental groups. The oxygen consumption was linearly dependent on the amount of available oxygen in the perfusate, whereas the glucose consumption was constant and independent of the glucose delivery rate. The present experiments provide new insights into physiological and metabolic mechanisms of action of TNF- alpha for optimization of future treatment schedules involving TNF-alpha.  (+info)

(4/11316) Frequent nuclear/cytoplasmic localization of beta-catenin without exon 3 mutations in malignant melanoma.

Beta-Catenin has a critical role in E-cadherin-mediated cell-cell adhesion, and it also functions as a downstream signaling molecule in the wnt pathway. Mutations in the putative glycogen synthase kinase 3beta phosphorylation sites near the beta-catenin amino terminus have been found in some cancers and cancer cell lines. The mutations render beta-catenin resistant to regulation by a complex containing the glycogen synthase kinase 3beta, adenomatous polyposis coli, and axin proteins. As a result, beta-catenin accumulates in the cytosol and nucleus and activates T-cell factor/ lymphoid enhancing factor transcription factors. Previously, 6 of 27 melanoma cell lines were found to have beta-catenin exon 3 mutations affecting the N-terminal phosphorylation sites (Rubinfeld B, Robbins P, Elgamil M, Albert I, Porfiri E, Polakis P: Stabilization of beta-catenin by genetic defects in melanoma cell lines. Science 1997, 275:1790-1792). To assess the role of beta-catenin defects in primary melanomas, we undertook immunohistochemical and DNA sequencing studies in 65 melanoma specimens. Nuclear and/or cytoplasmic localization of beta-catenin, a potential indicator of wnt pathway activation, was seen focally within roughly one third of the tumors, though a clonal somatic mutation in beta-catenin was found in only one case (codon 45 Ser-->Pro). Our findings demonstrate that beta-catenin mutations are rare in primary melanoma, in contrast to the situation in melanoma cell lines. Nonetheless, activation of beta-catenin, as indicated by its nuclear and/or cytoplasmic localization, appears to be frequent in melanoma, and in some cases, it may reflect focal and transient activation of the wnt pathway within the tumor.  (+info)

(5/11316) Identification of the human melanoma-associated chondroitin sulfate proteoglycan antigen epitope recognized by the antitumor monoclonal antibody 763.74 from a peptide phage library.

To identify the epitope of the melanoma-associated chondroitin sulfate proteoglycan (MCSP) recognized by the monoclonal antibody (mAb) 763.74, we first expressed random DNA fragments obtained from the complete coding sequence of the MCSP core glycoproteins in phages and selected without success for binders to the murine mAb 763.74. We then used a library of random heptapeptides displayed at the surface of the filamentous M13 phage as fusion protein to the NH2-terminal portion of the minor coat protein III. After three rounds of selection on the bound mAb, several phages displaying related binding peptides were identified, yielding the consensus sequence Val-His-Leu-Asn-Tyr-Glu-His. Competitive ELISA experiments showed that this peptide can be specifically prevented from binding to mAb 763.74 by an anti-idiotypic MK2-23 mouse:human chimeric mAb and by A375 melanoma cells expressing the antigen MCSP. We screened the amino acid sequence of the MCSP molecule for a region of homology to the consensus sequence and found that the amino acid sequence Val-His-Ile-Asn-Ala-His spanning positions 289 and 294 has high homology. Synthetic linear peptides corresponding to the consensus sequence as well as to the MCSP-derived epitope inhibit the binding of mAb 763.74 to the phages displaying the consensus amino acid sequence. Finally, the biotinylated consensus peptide absorbed to streptavidin-microtiter plates can be used for the detection of mAb 763.74 in human serum. These results show clearly that the MCSP epitope defined by mAb 763.74 has been identified.  (+info)

(6/11316) Interleukin-10-treated human dendritic cells induce a melanoma-antigen-specific anergy in CD8(+) T cells resulting in a failure to lyse tumor cells.

Dendritic cells (DC) are critically involved in the initiation of primary immune processes, including tumor rejection. In our study, we investigated the effect of interleukin-10 (IL-10)-treated human DC on the properties of CD8(+) T cells that are known to be essential for the destruction of tumor cells. We show that IL-10-pretreatment of DC not only reduces their allostimulatory capacity, but also induces a state of alloantigen-specific anergy in both primed and naive (CD45RA+) CD8(+) T cells. To investigate the influence of IL-10-treated DC on melanoma-associated antigen-specific T cells, we generated a tyrosinase-specific CD8(+) T-cell line by several rounds of stimulation with the specific antigen. After coculture with IL-10-treated DC, restimulation of the T-cell line with untreated, antigen-pulsed DC demonstrated peptide-specific anergy in the tyrosinase-specific T cells. Addition of IL-2 to the anergic T cells reversed the state of both alloantigen- or peptide-specific anergy. In contrast to optimally stimulated CD8(+) T cells, anergic tyrosinase-specific CD8(+) T cells, after coculture with peptide-pulsed IL-10-treated DC, failed to lyse an HLA-A2-positive and tyrosinase-expressing melanoma cell line. Thus, our data demonstrate that IL-10-treated DC induce an antigen-specific anergy in cytotoxic CD8(+) T cells, a process that might be a mechanism of tumors to inhibit immune surveillance by converting DC into tolerogenic antigen-presenting cells.  (+info)

(7/11316) Natural variation of the expression of HLA and endogenous antigen modulates CTL recognition in an in vitro melanoma model.

Increasing attention has been devoted to elucidating the mechanism of lost or decreased expression of MHC or melanoma-associated antigens (MAAs), which may lead to tumor escape from immune recognition. Loss of expression of HLA class I or MAA has, as an undisputed consequence, loss of recognition by HLA class I-restricted cytotoxic T cells (CTLs). However, the relevance of down-regulation remains in question in terms of frequency of occurrence. Moreover the functional significance of epitope down-regulation, defining the relationship between MHC/epitope density and CTL interactions, is a matter of controversy, particularly with regard to whether the noted variability of expression of MHC/epitope occurs within a range likely to affect target recognition by CTLs. In this study, bulk metastatic melanoma cell lines originated from 25 HLA-A*0201 patients were analyzed for expression of HLA-A2 and MAAs. HLA-A2 expression was heterogeneous and correlated with lysis by CTLs. Sensitivity to lysis was also independently affected by the amount of ligand available for binding at concentrations of 0.001 to 1 mM. Natural expression of MAA was variable, independent from the expression of HLA-A*0201, and a significant co-factor determining recognition of melanoma targets. Thus, the naturally occurring variation in the expression of MAA and/or HLA documented by our in vitro results modulates recognition of melanoma targets and may (i) partially explain CTL-target interactions in vitro and (ii) elucidate potential mechanisms for progressive escape of tumor cells from immune recognition in vivo.  (+info)

(8/11316) Biochemical identification of a mutated human melanoma antigen recognized by CD4(+) T cells.

CD4(+) T cells play a critical role in generating and maintaining immune responses against pathogens and alloantigens, and evidence suggests an important role for them in antitumor immunity as well. Although major histocompatibility complex class II-restricted human CD4(+) T cells with specific antitumor reactivities have been described, no standard method exists for cloning the recognized tumor-associated antigen (Ag). In this study, biochemical protein purification methods were used in conjunction with novel mass spectrometry sequencing techniques and molecular cloning to isolate a unique melanoma Ag recognized by a CD4(+) tumor-infiltrating lymphocyte (TIL) line. The HLA-DRbeta1*0101-restricted Ag was determined to be a mutated glycolytic enzyme, triosephosphate isomerase (TPI). A C to T mutation identified by cDNA sequencing caused a Thr to Ile conversion in TPI, which could be detected in a tryptic digest of tumor-derived TPI by mass spectrometry. The Thr to Ile conversion created a neoepitope whose T cell stimulatory activity was enhanced at least 5 logs compared with the wild-type peptide. Analysis of T cell recognition of serially truncated peptides suggested that the mutated amino acid residue was a T cell receptor contact. Defining human tumor Ag recognized by T helper cells may provide important clues to designing more effective immunotherapies for cancer.  (+info)