Intracranial growth of pulmonary small cell carcinoma cells in nude athymic mice

Pulmonary small cell carcinoma of the lung cells were inoculated intracranially and subdermally in nude athymic mice (Balb/c strain). There was a 100% intracranial tumor incidence in response to 1/10th the cell dose required to produce subdermal tumors in immunosuppressed nude mice. Tumors did not grow in the brains of Balb/c normal (haired) mice.     

Chemo-adoptive immunotherapy of nude mice implanted with human colorectal carcinoma and melanoma cell lines

Summary The antitumor effects of chemotherapy, recombinant human interleukin-2 (IL-2), recombinant human interferon A/D (IFN), allogeneic human lymphokine-activated killer (LAK) cells, and antitumor monoclonal antibody (mAb), administered alone and in various combinations, were tested in athymic nude mice carrying human tumor xenografts. Treatment began 6–18 days after i.v. or i.p. inoculation of colorectal carcinoma or melanoma cell lines, when macroscopic growths were evident. Chemotherapy consisted of two or three courses of 5-fluorouracil (5-FU) or dacarbazine. IL-2 and/or IFN were administered three to five times weekly for 1–3 weeks, usually starting 2–5 days after chemotherapy. Human LAK cells were infused once or twice weekly for 2 or 3 weeks concurrently with IL-2. In some experiments, murine anticolorectal carcinoma mAb (SF25) was administered. In both tumor systems, chemotherapy alone or immunotherapy alone (IL-2, IL-2 + LAK cells, IFN, IL-2 + IFN ± LAK cells) had little or no therapeutic effects. Additive effects were obtained by combining chemotherapy with IL-2 and LAK cells or with IL-2 and IFN. In the majority of the experiments, the most effective combination was chemotherapy + IL-2 + IFN + LAK cells. Treatment with mAb was beneficial in the colorectal carcinoma system when combined with 5-FU + IL-2 or 5-FU + IL-2 + IFN. Homing experiments with radiolabeled human and mouse LAK cells injected i.v. showed increased early accumulation in the liver and lungs, whereas freshly explanted mouse splenocytes localized mostly in the spleen and liver. The tissue distribution pattern of human LAK cells was similar in normal and tumor-bearing mice (with lung metastases). These findings suggest that combination of chemotherapy with cytokines and LAK cells can be partially effective for advanced solid human tumors even in the absence of the host's T-cell immune response. Preliminary experiments showed that tumor-specific, anti-melanoma T-cell clones were effective in local (s.c.) tumor growth inhibition (Winn assay) following coinjection with the autologous tumor cells.     

Increasing ceramides sensitizes genistein-induced melanoma cell apoptosis and growth inhibition

The aim of the current study is to investigate the effect of ceramides on genistein-induced anti-melanoma effects in vitro. We found that exogenously added cell-permeable short-chain ceramides (C6) dramatically enhanced genistein-induced growth inhibition and apoptosis in cultured melanoma cells. Genistein treatment only induced a moderate intracellular ceramides accumulation in B16 melanoma cells. Two different agents including 1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), a ceramide glucosylation inhibitor, and the sphingosine kinase-1 (SphK1) inhibitor II (SKI-II), a sphingosine (ceramides precursor) phosphorylation inhibitor, both facilitated genistein-induced ceramides accumulation and melanoma cell apoptosis. Co-administration of ceramide (C6) and genistein induced a significant Akt inhibition and c-jun-NH(2)-kinase (JNK) activation, caspase-3 cleavage and cytochrome c release. Caspase-3 inhibitor z-DVED-fmk, JNK inhibitor SP 600125, or to restore Akt activation by introducing a constitutively active form of Akt (CA-Akt) diminished ceramide (C6) and genistein co-administration-induced in vitro anti-melanoma effect. Our study suggests that increasing cellular level of ceramides may sensitize genistein-induced anti-melanoma effects.     

Cellular tumorigenicity in nude mice: correlation with cell growth in semi-solid medium

Cultured cells derived from either normal or malignant tissues of several species have been tested by injection into the immune-deficient nude mouse in order to determine the cellular properties which are associated with tumorigenicity in vivo. Results show that one in vitro property consistently correlated with neoplastic growth in nude mice is the ability of the cell to form spherical colonies in a semi-solid growth medium such as methyl cellulose suspension. Cellular tumorigenicity is not determined solely by the malignancy of the tissue of origin, since cells derived from nonmalignant tissues become tumorigenic when they are no longer anchorage dependent for growth. In addition, acquisition of infinite growth potential in heteropioid cell lines is not in itself sufficient to confer tumorigenic capacity on the cells. These results suggest that the degree of cell growth in methyl cellulose is a useful parameter in vitro for predicting tumorigenicity in the animal, and also demonstrate the potential usefulness of the nude mouse for analysis of cellular malignancy irrespective of the tissue or species of origin.     

Anti-cachectic effect of ghrelin in nude mice bearing human melanoma cells

Ghrelin is a novel brain-gut peptide that stimulates food intake and body weight gain. We studied the anabolic effect of ghrelin in a cancer cachexia mouse model. SEKI, a human melanoma cell line, was inoculated into nude mice to examine the effects of ghrelin on food intake and body weight. The intraperitoneal administration of ghrelin twice a day (6 nmol/mice/day) for 6 days suppressed weight loss in SEKI-inoculated mice and increased the rate of weight gain in vehicle-treated nude mice. Ghrelin administration also increased food intake in both SEKI- and vehicle-treated mice. Both the weight of white adipose tissue and the plasma leptin concentration were reduced in tumor-inoculated mice compared with vehicle-treated mice; these factors increased following ghrelin administration. The levels of both ghrelin peptide and mRNA in the stomach were upregulated in tumor-inoculated mice. The anabolic effect of ghrelin efficiently reverses the cachexia in mice bearing SEKI human melanoma. Ghrelin therefore may have a therapeutic ability to ameliorate cancer cachexia.     

Tissue distribution and cancer growth inhibition of magnetic lipoplex-delivered type 1 insulin-like growth factor receptor shRNA in nude mice

The targeted delivery of therapeutic genes into specific tissues, as well as the determination of the biological fate and potential toxicity of nanoparticles, remains a highly relevant challenge for gene-based therapies. Type 1 insulin-like growth factor receptor (IGF-1R), an important oncogene, is frequently over-expressed in lung cancer and mediates cancer cell proliferation as well as tumor growth. In our previous studies, we have successfully applied gene delivery mediated by commercially available nanoparticles (CombiMAG) under a magnetic field, which suppresses IGF-1R expression in a non-small cell lung cancer cell line (A549) in vitro. In the present study, we aimed to investigate the biological distribution and target tumor suppression of magnetofection, as well as its potential toxicity via CombiMAG-carrying plasmids expressing green fluorescent protein (GFP) and short hairpin RNAs (shRNAs) targeting IGF-1R (pGFPshIGF-1Rs) in tumor-bearing mice. The peak expression in various organs appeared 48 h after transfection. Transgene expression via magnetofection was 3-fold improvement than via lipofection. On the 30th day after injection, the tumor size and weight of the CombiMAG-treated group (789.32 ± 39.43 mm(3), 105.5 ± 6.1 mg) were significantly decreased compared with those of the lipofection group (893.83 ± 31.23 mm(3), 164.5 ± 9.1 mg; P< 0.05), and the suppression rate was ～36%. After a 30-day observation, the injection of CombiMAG did not cause any apparent toxicity. Therefore, IGF-1R shRNA nanoparticles can be valuable and safe delivery agents for RNA interference therapy to tumors in vivo.     

Clonal variants of a melanoma cell line sensitive to growth inhibition by dexamethasone

We have isolated and characterized two clones of the RPMI 3460 Syrian hamster melanoma cell line which exhibit different responses to the synthetic glucocorticoid dexamethasone. In the presence of 10 nM dexamethasone, one clone (clone 6) exhibits the growth inhibition, morphological alterations, and reduction in final cell density observed in the parental RPMI 3460 cell line. In contrast, the other clone (clone 5), although exhibiting a reduction in final cell density, fails to exhibit the growth inhibition and morphological alterations. Thus, the effect of dexamethasone on growth and morphology can be expressed separately from the effect of dexamethasone on final cell density in these cells. This observation suggests that the two sets of responses can be controlled separately and that glucocorticoids may exert their influence through different or divergent biological pathways.In vitro receptor assays suggest that the different phenotypes of clone 5 compared with clone 6 cells cannot be explained by an absence of or reduction in cytosolic glucocorticoid receptor, in clone 5 cells. Additional receptor characterization suggests that the different responses to dexamethasone of clone 5 and clone 6 cells do not reflect changes in the ability of receptor to exist in a stably activated form. Differences in the accumulation or depletion of extracellular components in the growth medium also do not seem to be responsible for the altered phenotype of clone 5 vis-à-vis clone 6 cells.     

Impaired melanoma growth in VASP deficient mice

Progression of tumors depends on interactions of cancer cells with the host environment. Expression of the cytoskeleton protein VASP is upregulated in various cancer entities. We analyzed the role of VASP for melanoma growth in murine allograft models. Growth of VASP expressing melanomas was retarded in VASP^?/? versus wild-type animals. Over time tumor size was <50% in VASP^?/? versus wild-type animals and independent of expression levels of Ena/VASP protein family members. Histological analyses showed smaller cells with impaired nutrition status and less vascularization in melanomas derived from VASP^?/? versus counterparts from wild-type mice. Cumulatively, the data reveal a critical role of VASP in non-tumor cells in the tumor environment for melanoma growth in vivo.     

Genistein enhances the cisplatin-induced inhibition of cell growth and apoptosis in human malignant melanoma cells

Genistein, a naturally occurring isoflavone found chiefly in soybeans, has been reported to be a potent antitumor agent. Genistein is presumed to exert multiple effects related to the inhibition of cancer growth. Metastatic melanoma is a chemotherapy-refractory neoplasm. The present study was designed to explore the possible activity of genistein to inhibit the aberrant proliferation and to induce apoptosis of human malignant melanoma cells in cooperation with cisplatin treatment. Five human melanoma cell lines were utilized for these experiments. Genistein at physiologic concentrations (20 microM) did not induce apoptosis by itself but did enhance cisplatin-induced apoptosis in all five human melanoma cell lines tested. The enhanced susceptibility among the cell lines was diverse. Changes in the expression of two anti-apoptotic proteins, bcl-2 and bcl-xL, and one pro-apoptotic protein, apoptotic protease activating factor-1 (Apaf-1), were examined. Genistein alone or cisplatin alone generally did not alter bcl-2 expression or bcl-xL expression, but slightly increased Apaf-1 in some cell lines. The combined treatment with genistein and cisplatin significantly reduced bcl-2 and bcl-xL protein and increased Apaf-1 protein expression. These data suggest that genistein therapy may enhance the chemosensitivity of melanoma patients.     

3,5-二氯苯基双胍抑制黑色素瘤肺转移的裸鼠体内药效学研究

目的 确认整合素αvβ3新型抑制剂3,5-二氯苯基双胍对人黑色素瘤肺转移的抑制作用.方法 应用前期建立的人黑色素瘤裸鼠肺转移模型,观察3,5-二氯苯基双胍的治疗效果.裸鼠尾静脉接种黑色素瘤细胞(第1天)后,于第5、9、13、17和21天给予该药物治疗.50 d实验结束,处死裸鼠并取完整的肺组织,Bouin氏液固定24 h后根据肺表面癌结节的大小和数量给予评分,以此评价肺转移的程度.结果 3,5-二氯苯基双胍6、12 mg/kg和24 mg/kg治疗组的转移分数分别为(55.25±13.60)、(35.13±17.36)和(12.83±11.44),与溶剂对照组(转移分数是82.50±17.72)相比具有明显差异(P＜0.05).阳性对照组的转移分数为(11.50±10.44)(P＜0.05 vs 溶剂对照组),阴性对照组和PBS对照组的转移分数分别为(88.50±17.21)、和(88.87±11.29) (P ＞0.05 vs溶剂对照组).结论 3,5-二氯苯基双胍在裸鼠体内能够明显抑制黑色素瘤肺转移,并呈现一定的剂量依赖性.     

Quantitative evaluation of anticancer agents against human melanoma cells implanted in nude mice

BRO human melanoma cells, which are exceptionally tumorigenic and lethal for nude mice, were inoculated intraperitoneally or intracerebrally in varying numbers. An inverse linear correlation was observed between the logarithm of the number of cells inoculated and host survival. In mice bearing 10(7) cells intraperitoneally, 2.4-2.8 log10 units of cell kill were obtained after a single intraperitoneal injection of vincristine, and some mice inoculated with 10(5) cells were cured by this treatment. Fewer cells were killed by L-phenylalanine mustard. Vincristine did not prolong survival of nude mice with intracerebral BRO tumors. Cell kill after administration of anticancer agents can be quantitated for BRO cells inoculated intraperitoneally or intracerebrally.     

Involvement of autophagy in recombinant human arginase-induced cell apoptosis and growth inhibition of malignant melanoma cells

Recombinant human arginase (rhArg) has been developed for arginine derivation therapy of cancer and is currently in clinical trials for a variety of malignant solid tumors. In this study, we reported for the first time that rhArg could induce obvious autophagy in human melanoma cells; inhibition of autophagy by chloroquine (CQ) significantly increased rhArg-induced cell apoptosis and growth inhibition of A375 cells. A significant increase in mitochondrial membrane potential loss and elevated intracellular reactive oxygen species (ROS) levels were detected in A375 cells after rhArg treatment when compared with control. Membrane transition inhibitor cyclosporine A blocked autophagy and accelerated cell death induced by rhArg, indicating that rhArg induced autophagy via mitochondria pathway. Furthermore, antioxidant N-acetyl-l-cysteine suppressed rhArg-induced autophagy and rescued cells from cell growth inhibition, suggesting that ROS played an important role in rhArg-induced A375 cell growth inhibition and autophagy. Akt/mTOR signaling pathway was involved in autophagy induced by rhArg in a time-dependent manner. Moreover, rhArg could induce ERK1/2 activation in a dose- and time-dependent manner and rhArg-induced autophagy was attenuated when p-ERK1/2 was inhibited by MEK 1/2 inhibitor, U0126. Taken together, this study provides new insight into the molecular mechanism of autophagy involved in rhArg-induced cell apoptosis and growth inhibition, which facilitates the development of rhArg in combination with CQ as a potential therapy for malignant melanoma.     

Selective growth inhibition of a human malignant melanoma cell line by sesame oil in vitro.

Ayurveda, an ancient and comprehensive system of natural medicine, recommends regular topical application to the skin of sesame oil, above all other oils, as a health-promoting procedure. We examined the effect of sesame oil and several other vegetable oils and their major component fatty acids on the proliferation rate of human normal and malignant melanocytes growing at similar rates in serum-free media. We found that sesame and safflower oils, both of which contain large amounts of linoleate in triglyceride form, selectively inhibited malignant melanoma growth over normal melanocytes whereas coconut, olive and mineral oils, which contain little or no linoleate as triglyceride, did not. These oils were tested at a range of 10-300 micrograms/ml. We found that of the fatty acids tested, only linoleic acid was selectively inhibitory while palmitic and oleic were not. These fatty acids were tested in the range of 3-100 micrograms/ml. These results suggest that certain vegetable oils rich in linoleic acid, such as the sesame oil, recommended for topical use by Ayurveda, may contain selective antineoplastic properties which are similar to those demonstrated for essential polyunsaturated fatty acids and their metabolites. This suggests that whole vegetable oils may have potential clinical usefulness.     

Linker-based GnRH-PE chimeric proteins inhibit cancer growth in nude mice

Since the number of cancer-related deaths has not decreased in recent years, major efforts are being made to find new drugs for cancer treatment. In this report we introduce the gonadotropin releasing hormone-Pseudomonas exotoxin (GnRH-PE) based chimeric proteins L-GnRH-PE66 and L-GnRH-PE40. These proteins are composed of a GnRH moiety attached to modified forms ofPseudomonas exotoxin via a polylinker (gly₄ser)₂. The chimeric proteins L-GnRH-PE66 and L-GnRH-PE40 have the ability to target and kill adenocarcinoma cell linesin vitro, whereas non-adenocarcinoma cell lines are not affected. We demonstrate that L-GnRH-PE66 and L-GnRH-PE40 efficiently inhibit cancer growth. Nude mice were injected subcutaneously with the SW-48 adenocarcinoma cell line to produce xenograft tumours. When the tumours were established and visible, the animals were injected with chimeric proteins for 10 days. At the end of this period, a reduction of up to 3-fold in tumor size was obtained in the treated mice, as compared with the control group, which received equivalent amounts of GnRH; the difference was even greater 13 days after termination of treatment. Thus, the chimeric proteins L-GnRH-PE66 and L-GnRH-PE40 are promising candidates for treatment of a variety of adenocarcinomas and their use in humans should be considered.     

Enhanced prostaglandin synthesis as a mechanism for inhibition of melanoma cell growth by ascorbic acid

Both ascorbic acid and the 1-series prostaglandins have been reported to be important regulators of cell growth and since ascorbic acid also increases the synthesis of the 1-series prostaglandins, it is possible that the effects of ascorbic acid on cell growth might be mediated by changes in 1-series prostaglandin synthesis induced by ascorbic acid. This study attempted to examine this possible relationship. The effects of ascorbic acid, prostaglandin E1 and the essential fatty acid precursors of the prostaglandins, linoleic acid and gamma-linolenic acid on the in vitro growth of transformed BL6 murine melanoma cells and untransformed monkey kidney (LLCMK) cells was determined. The effects of ascorbic acid addition on the growth inhibitory effect of the essential fatty acids and on the activity of delta-6-desaturase, a key enzyme in 1-series prostaglandin synthesis were also examined. Addition of ascorbic acid, prostaglandin E1 and both essential fatty acids was found to reduce BL6 growth while PGE1 and to a lesser extent the essential fatty acids reduced LLCMK cell growth. The growth inhibitory effect of the essential fatty acids was enhanced by ascorbic acid which was also found to stimulate delta-6-desaturase activity in BL6 cells. The growth inhibitory effect of ascorbic acid on BL6 cells may thus be mediated by changes in prostaglandin synthesis through an association with the metabolism of the essential fatty acid precursors of the prostaglandins.     

Specificity of growth inhibition of melanoma by 4-hydroxyanisole

An experimental study using human melanoma (NEL-MI), rat hepatoma (Fu5-5), and human kidney (293-31) cell lines was undertaken in order to evaluate the antitumor activity of 4-hydroxyanisole (4-OHA) in vitro. Prior reports have indicated highly specific antitumor activity of 4-OHA against melanoma cells in vitro. This specific antitumor activity has been proposed to be due to the oxidation of 4-OHA by tyrosinase to cytotoxic oxidation products. Dose-dependent cytotoxicity was observed when cells were cultured for 72 h in the presence of 4-OHA. At 100 microM, 4-OHA produced growth inhibition of 62%, 32%, and 55% in melanoma, hepatoma, and kidney cell lines, respectively. No effect was seen at 10 microM 4-OHA. 1,000 microM 4-OHA produced 100% kill. Tyrosinase activity was detected only in melanoma cells. The effect of 100 microM 4-OHA on the incorporation of 3H DNA precursors in melanoma, hepatoma, and kidney cells was also studied. Thymidine incorporation was inhibited in all three cell lines at the lowest cell density tested, with the greatest inhibition seen on melanoma cells. As cell density increased, the effect of 4-OHA on thymidine incorporation decreased. With respect to RNA synthesis, 4-OHA significantly reduced the incorporation of uridine in all three cell lines, with the greatest effect in melanoma cells. Cell density also affected the inhibition of uridine incorporation, but to a lesser extent than that observed on thymidine incorporation. The effect of 4-OHA on leucine incorporation was modest and uninfluenced by cell density. Thus, cytotoxicity of 4-OHA may involve two different mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)     

siRNA blocking the RAS signalling pathway and inhibits the growth of oesophageal squamous cell carcinoma in nude mice

The aim of this study was to study RAS‐siRNA blocking RAS pathway and suppressing cell growth in human oesophageal squamous cell carcinoma in nude mice. The methods in this study was to construct RAS‐siRNA expression vector, establish 40 oesophageal squamous cell carcinoma xenograft animal models and divided them into five groups: control group, siRNA control group, RAS‐siRNA group, paclitaxel group and RAS‐siRNA and paclitaxel group. We observed tumour growth in nude mice, studied histology by HE staining, tumour growth inhibition by TUNEL assay and detected the RAS, MAPK and cyclin D1 protein expression by immunohistochemistry and western blot. We have obtained the following results: (i) successfully established animal models; (ii) nude mice in each group after treatment inhibited tumour volume was significantly reduced compared with the control group (p < 0.05); (iii) compared with the control group, the number of apoptotic cells were significantly increased in the siRNA control group and the RAS‐siRNA group, and the number of apoptosis cells in the paclitaxel and RAS‐siRNA group is significantly most than the paclitaxel group and RAS‐siRNA group (p < 0.05); and (iv) after treatment, RAS, MAPK and cyclin D1 expression in five groups was decreasing gradually. After adding paclitaxel, the protein expression in the paclitaxel and RAS‐siRNA group was significantly lower than that of paclitaxel group, negative control and paclitaxel group (p < 0.05). We therefore conclude that RAS‐siRNA can block the RAS signal transduction pathway, reduce the activity of tumour cells, arrest tumour cell cycle, promote apoptosis, inhibit cell proliferation and increase tumour cell sensitivity to chemotherapeutic drugs. Copyright © 2014 John Wiley & Sons, Ltd.     

The composition of the T cell receptor repertoire in nude mice

Previous results from several laboratories have demonstrated the presence of functional T lymphocytes in congenitally athymic (nude) mice. The present study represents an analysis of the T cell receptor repertoire exhibited by such cells. Clones of H-2Kb-specific cytotoxic T lymphocytes (CTL) were generated under primary limiting dilution conditions by using spleen cells from nude mice. These clones were analyzed on a panel of Kb mutant target cells to assess the receptor specificity of each clone. Unlike thymic bearing mice the CTL repertoires of which are exceedingly diverse, it was found that in most cases the vast majority of clones from each individual exhibited the same reactivity pattern. The particular pattern varied from individual to individual. Clones from three animals that exhibited this phenomenon were additionally analyzed by using a monoclonal antibody that can detect the utilization of the gene products of the V beta 8 family. In one animal all clones were V beta 8 positive, whereas in the others, all clones were negative. We conclude that the T cell receptor repertoire in nude mice is extremely limited and represents in vivo expansion of a relatively small number of functional precursors.     

Chemotactic factor and P15E-related chemotaxis inhibitor in human melanoma cell lines with different macrophage content and tumorigenicity in nude mice

The present study was designed to characterize the production of chemoattractants by human melanoma lines with high (M4Be, M3Da, NTerDa) or low tumorigenic (Doc8, M1Do) potential when heterotransplanted in nude mice. Supernatants from the Doc8 and M1Do cell lines were strongly chemotactic in vitro for mononuclear phagocytes. Chemotactic activity was destroyed by proteolytic enzymes, and upon gel filtration on Sephadex G75, it eluted in the cytochrome c region corresponding to an apparent m.w. of 12,000. Upon chromatofocusing, the Sephadex-separated tumor-derived chemotactic factor (TDCF) showed an isoelectric point of 5.5 to 6. Cell lines with high tumorigenic potential contained low or no detectable chemotactic activity. When culture supernatants of cell lines with modest (M3Da) or no (M4Be) chemotactic activity were exposed to immobilized monoclonal antibodies directed against the retroviral transmembrane protein P15E, appreciable chemotactic activity was detectable (M4Be) or preexisting levels increased (M3Da). The material eluted from Sepharose-bound anti-P15E antibodies inhibited the migration of monocytes in response to chemoattractants. These findings demonstrate the coexistence in some human melanoma cell line supernatants of factors (TDCF and P15E-related inhibitor) with opposite influence on monocyte chemotaxis. That tumor cell products play a pivotal role in regulating the extravasation of monocytes into neoplastic tissues is suggested by the close correlation observed between macrophage levels in melanomas grown in nude mice and levels of chemotactic activity detectable in culture supernatants.     

Evaluation of antibody inhibition assays of melanoma antigens in sera to monitor tumor growth in melanoma patients

Summary It was reported previously that melanoma leukocyte-dependent antibody (LDA) in the sera of melanoma patients was inhibited by small-molecular-weight (small-mol.-wt.) glycoproteins which were similar to cell surface antigens identified in cell membrane extracts of melanoma cells. The present study was to determine whether measurement of the levels of these factors in sera may be a useful monitor of tumor growth in melanoma patients. Small-mol.-wt. fractions were obtained by gel filtration or membrane chromatography of acidified sera and tested for their ability to inhibit LDA in ⁵¹Cr release cytotoxic assays. A panel of LDA was used, consisting of three antisera from melanoma patients, which appeared relatively specific for melanoma, and three non-melanoma antisera against carcinoembryonic antigen, ₂ microglobulin, and fetal antigens. The results showed that in patients with melanoma, approximately 70% had melanoma LDA-inhibitory activity detected in the small-mol.-wt. fractions of their sera when these were tested against the panel of melanoma LDA. The specificity of the inhibitory activity for melanoma LDA was shown by failure of the serum fractions to inhibit non-melanoma LDA and by absence of inhibitory activity in equivalent serum fractions from non-melanoma carcinoma patients for melanoma LDA. The levels of melanoma LDA-inhibitory activity in the serum fractions appeared to correlate with tumor growth, as shown by clearance of the inhibitory activity after surgical removal of melanoma and reappearance in the serum of patients who subsequently developed recurrent melanoma. The 30% false-negative rate indicated that the assays could not be used to reliably exclude melanoma, but the close correlation with tumor growth and the low number of false-positive results suggested that in 70% of patients detection of these small-mol.-wt. antigens would be of value to detect recurrence from melanoma and to monitor the effectiveness of therapy.