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Biomedical subjects

F L Meyskens

Publications and source records attributed to F L Meyskens.

At least 127 records · Page 7Linked to original sources
PubMed1987

Effect of tumor colony definition on ionizing radiation survival curves of melanoma-colony forming cells.

Definition of survival and measurement of colony size in soft agar assays is important in establishing in vitro radiation survival curves. Conventionally, survival is assessed according to colony-forming ability. The distinction between small colonies that are abortive and those that are viable often involves a difficult and arbitrary choice for the investigator. We have examined the effect of different minimum colony sizes (greater than or equal to 25, greater than or equal to 50, greater than or equal to 75, and greater than or equal to 100 cells) on ionizing radiation survival curves for cells from established murine (CCL 53.1) and human (M1RW5) melanoma cell lines as well as from short-term human melanoma cell strains (C8146A, C8146C, C8161, C83-2C, C82-7A1, and C8442) and patient biopsy (83-4). Single cell suspensions were plated in the upper layer of the agar bilayer and cells were irradiated by single dose X rays. Giant cells did not form in colonies containing 50 or more cells. D0 values were highest (D0 values, from 390 to 100 cGy) for cells forming smaller colonies (greater than or equal to 25 cells, greater than or equal to 4-5 doublings) and lowest (D0 values, from 190 to 50 cGy) for cells forming larger colonies (greater than or equal to 100 cells, greater than or equal to 6-7 doublings). Therefore, apparent radiosensitivity was dependent on colony size selected for analysis. Precise measurement of colony size was important in establishing radiation survival curves because errors in determining the colony size will alter apparent radiosensitivity of cells. These results should help define the biological meaning of tumor colony growth in semisolid medium, and alter the interpretation of survival curves which measure sensitivity to agents using this assay.

Agar↗
PubMed1987

Median effect and long term recovery analysis of biological modifier interactions with difluoromethylornithine on the proliferation of human melanoma cells.

The ability of difluoromethylornithine (DFMO), a specific polyamine synthesis inhibitor, to interact with various biological modifiers to inhibit the colony-forming growth of human melanoma cells was determined by using the median effect principle to computer model the strength of two agent interactions. Either alpha- or gamma-IFN (interferon) in combination with DFMO resulted in a synergistic inhibition on human melanoma colony formation. For human melanoma cells which were not resistant to 13-cis RA (retinoic acid), an additive suppression on colony formation was obtained with the retinoid-DFMO combination. Dexamethasone (DEX) interacted with DFMO to yield a synergistic reduction in melanoma colony number on glucocorticoid sensitive cells and no growth enhancement with DFMO on glucocorticoid resistant melanoma lines. Human melanoma cells displayed differential long-term growth sensitivity to DFMO treatment. C8146C human melanoma cells were terminally growth-inhibited by a 96 h exposure to DFMO, in a manner which was concentration and time dependent. The proliferation of C82-7A melanoma cells was inhibited by 95% in presence of DFMO, but upon removal of DFMO the cells regained their ability to proliferate and form colonies. The simultaneous addition of DEX plus alpha-IFN plus 13-cis-RA with DFMO caused most of the human melanoma cells in these lines to become permanently growth arrested. Pre-treatment with DEX plus alpha-IFN plus 13-cis RA, but without DFMO, did not have any long term effect on the ability of melanoma cells to recover and proliferate in soft agar.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Division↗
PubMed1987

Treatment of advanced squamous cell carcinoma of the skin with isotretinoin.

STUDY OBJECTIVE: To determine the efficacy of oral isotretinoin in refractory advanced squamous cell carcinoma of the skin. DESIGN: Case series trial. SETTING: Tertiary care center at a university hospital. PATIENTS: A consecutive collection of four patients with advanced squamous cell carcinoma of the skin who failed to respond to standard surgical or radiation therapy. INTERVENTIONS: Isotretinoin in gelatin capsules was given at a total daily dose of 1 mg/kg body weight in two divided doses for at least 4 weeks. MEASUREMENTS AND MAIN RESULTS: Bidimensional tumor measurements at monthly intervals showed striking responses to isotretinoin in all four patients. Response durations ranged from 2 to more than 23 months. The drug produced reversible moderate mucocutaneous side effects and asymptomatic laboratory abnormalities. CONCLUSIONS: Impressive responses to isotretinoin occurred in our four patients and in six of ten other reported patients. Retinoic acid's mechanisms of action in cutaneous squamous cell carcinoma is not precisely known, but may involve the modulation of epidermal growth factor receptors and certain protein kinases. These in-vitro findings and the clinical data suggest that retinoids may be an effective and well-tolerated therapy for refractory advanced squamous cell carcinoma of the skin. The absence of any other effective systemic therapy indicates the need for continuing trials with retinoids in this disease.

Aged↗
PubMed1987

Isotretinoin and cutaneous helper T-cell lymphoma (mycosis fungoides).

Retinoids, including isotretinoin, have demonstrated antiproliferative and antineoplastic activity in laboratory and clinical trials. In a phase II trial, 25 patients with extensive mycosis fungoides were evaluated for response to isotretinoin. There was a 44% (11 patients) objective clinical response rate with three clinical complete responses without concomitant evidence of pathologic clearing of the disease. An additional 24% (six patients) showed a minor degree of clinical improvement. The median time to response was two months (range, 0.5 to eight months) and the median response duration was eight months or longer (range, one to 25 months). Chronic toxic reactions consisted primarily of drying of the skin and mucous membranes and resulted in dose reduction in the majority of patients. It is concluded that isotretinoin produces significant clinical benefit to some patients with mycosis fungoides.

Adult↗
PubMed1987

Retinoids as preventive and therapeutic anticancer agents (Part I).

Retinoids, the synthetic and natural analogs of vitamin A, frequently block the phenotypic expression of cancer in vitro; they also inhibit growth and induce differentiation in many animal and human malignant cell types. Only recently has it become possible to propose a unifying mechanism of retinoid action, which involves the protein kinase-C cascade system. This system may mediate retinoids' many diverse actions, including their effects on enzyme synthesis, membrane properties, growth factors, binding proteins, genomic and postgenomic expression, the extracellular matrix, and immunologic responses. Ongoing in vitro studies of retinoid structure-activity relationships, effects on oncogene expression, reversal of drug-resistance, and, especially, the protein kinase-C cascade system should help clarify the precise mechanism of their anticancer action. Many in vitro and in vivo assay systems are available for testing the 2000 + synthetic retinoids. These assays indicate specific drug sensitivities, which may help focus future clinical trials. In human cancer prevention, retinoids have been most effective for skin diseases, including actinic keratosis, keratoacanthoma, and basal cell carcinoma; however, nondermatologic premalignancies, such as oral leukoplakia, bronchial metaplasia, laryngeal papillomatosis, cervical dysplasia, myelodysplastic syndromes, and the urinary bladder, also respond to retinoid therapy. Significant therapeutic advances are also occurring with this class of drugs in refractory malignancies, including advanced cutaneous squamous and basal cell cancer, mycosis fungoides, and acute promyelocytic leukemia. Newer third-generation retinoids, such as the highly potent retinoidal benzoic acid derivatives, are demonstrating therapeutic indexes far higher than earlier-generation retinoids. Current in vitro testing is also demonstrating that retinoids have synergistic activity in combination with other agents (eg, biologic modifiers, hormones, and DNA synthesis inhibitors) and treatment modalities (eg, irradiation). Notwithstanding the progress already made with retinoids in human cancer, many in vitro questions remain, and clinical work is just beginning.

Animals↗
PubMed1986

Biological characterization of an acid-sensitive growth factor from human platelets: role in the proliferation of human melanoma and bovine endothelial cells.

An acid-sensitive growth factor for human melanoma has been partially purified from human platelets. TSK gel filtration HPLC provides a molecular weight estimation of 60,000 daltons. This factor is not only mitogenic for human melanoma, but also stimulates 3H-thymidine uptake and increases the number of bovine aortic endothelial cells, while fibroblasts are nonresponsive. Radioiodination of active HPLC fraction has been accomplished. The human melanoma cell line, M1RW5 demonstrates specific, time-dependent binding of the labeled protein. These studies suggest that the growth of human melanoma may in part be regulated by a newly described growth factor present in human platelets.

Animals↗
PubMed1986

Difluoromethylornithine enhances inhibition of melanoma cell growth in soft agar by dexamethasone, clone A interferon and retinoic acid.

Five human melanoma cell lines (C8146C, C8161, C82-7A, C83-2CY and MIRW5) were shown to contain a significant number of melanoma colony-forming units resistant to single-agent treatment by dexamethasone, alpha-interferon and trans-retinoic acid. These biological modifiers were combined with difluoromethylornithine into a low-dose combination using concentrations below pharmacologically achievable levels. The suppression of melanoma colony formation induced by this combination was consistent and significantly higher than that seen with any single agent, colony formation being reduced by an average of 90%. Leaving either DEX or DFMO out of the 4-agent combination resulted in a significant decrease in the observed inhibition. This was also verified by the addition of putrescine which inhibited only the DFMO activity. Median effect analysis of the DFMO + IFN inhibition of C8161 cells demonstrated that the 2 agents interacted synergistically over the entire dose-response curve. Of the high-dose combination-treated melanoma colony-forming units, 97% did not form small growth units; most remained as arrested single cells, but the cells and small growth units could still metabolize tetrazolium stain after the experiment, suggesting that the high-dose combination arrested the growth of the melanoma colony-forming units via a non-cytotoxic mechanism.

Cell Line↗
PubMed1986

A phase I trial of topically applied trans-retinoic acid in cervical dysplasia-clinical efficacy.

Forty-two patients were entered into a phase I trial to evaluate the vitamin A derivative, trans-retinoic acid, in cervical intraepithelial neoplasia. Treatment consisted of four consecutive 24-h applications of retinoids via an inert collagen sponge in a cervical cap. Patients were followed for response at 3-month intervals using cytology, colposcopy, and selected biopsies. Thirty-six patients were evaluable (mild dysplasia, 13; moderate dysplasia, 17; severe dysplasia, 6) with follow-up from 5 to 18 months. Complete regression was seen in 2/14 (14%) patients treated with concentrations of 0.05%----0.1167% and in 10/22 (45%) patients treated with concentrations of 0.1583%----0.484% (p less than 0.05). One patient with negative biopsies at 12 months has subsequently recurred at 18 months.

Administration, Topical↗
PubMed1986

Cervical tissue uptake of all-trans-retinoic acid delivered via a collagen sponge-cervical cap delivery device in patients with cervical dysplasia.

The present study was undertaken to evaluate the systemic absorption and cervical tissue uptake of all-trans-retinoic acid (TRA), delivered via a collagen spongecervical cap delivery device in patients with intraepithelial cervical dysplasia. Ten patients with histologically proven mild or moderate cervical dysplasia were included in this pharmacologic study. The two TRA concentrations (0.05% and 0.372%) selected for study represent the starting and maximally tolerated doses used in phase I clinical trial. All-trans-retinoic-11-3H acid (3H-TRA, 500 mu Ci) was used to facilitate cervical tissue uptake studies. Cervical biopsies and post-treatment blood samples were obtained from each patient after TRA exposure. The uptake of TRA into cervical tissues four hours after drug administration was significantly increased at the maximally tolerated TRA dose. There was a rapid decrease in cervical tissue concentration of TRA at the 0.372% dose between 4 and 24 h after drug exposure, suggesting a relatively short elimination half-life of TRA in cervical tissues. HPLC analysis of post-treatment blood samples indicate that there was no systemic absorption of TRA after local cervical administration.

Administration, Topical↗
PubMed1986

A phase II study of alpha-difluoromethylornithine (DFMO) for the treatment of metastatic melanoma.

Difluoromethylornithine (DFMO) is an irreversible enzyme-activated inhibitor of ornithine decarboxylase, a key enzyme in polyamine synthesis. We have screened for potential anti-cancer activity of DFMO using a clonogenic assay, which suggested that melanoma might have sensitivity to this agent. Accordingly, we have performed a phase II trial of DFMO (2 g/m2 po q 8 h) in 24 patients, 21 of whom were evaluable for response. One patient achieved a complete response of a large subcutaneous mass for 11 months. Although stabilization is frequently difficult to measure, seven patients appeared to stabilize previously active disease, with a median duration of response of eight weeks. Toxicity was significant and DFMO was discontinued in five patients due to side effects - hearing loss alone in four and hearing loss associated with thrombocytopenia in the fifth patient. Hearing changes occurred in ten patients. Other side effects were mild. These data indicate that DFMO as a single agent may be an effective therapy for melanoma. A phase II trial of DFMO in previously untreated patients using a different schedule to decrease hearing loss is warranted. Additionally, several in vitro and animal models suggest that DFMO plus interferon are synergistic, and this combination might be used for a clinical trial as well.

Adult↗
PubMed1986

Long-term and residual melanotropin-stimulated tyrosinase activity in S91 melanoma cells is density dependent.

Cell density is a factor that affects the capacity of Cloudman S91 melanoma cells to respond to melanotropins in monolayer culture. Continuous exposure of melanoma cells to alpha-melanotropin or its potent analog [Nle4, D-Phe7]-alpha-MSH, resulted in maximal stimulation of tyrosinase after 2 d of treatment, but the magnitude of stimulation decreased thereafter despite the continued presence of the melanotropins. However, when melanoma cells continually exposed to melanotropins were subcultured to an initial low cell density and maintained in contact with alpha-MSH or [Nle4, D-Phe7]-alpha-MSH (long-term culture), tyrosinase activity was rapidly restored and greatly enhanced. Also, when cells were seeded at initial densities ranging from 0.2 to 3.2 X 10(6) cells/flask, and exposed for 24 h to 10(-7) M alpha-MSH, only the cultures seeded at low densities (0.2 and 0.4 X 10(6) cells/flask) exhibited maximal tyrosinase activity during the 24 h exposure to the melanotropins. Therefore, tyrosinase activity was primarily affected by cell density rather than by the duration of time the cells were in culture or by continuous exposure to melanotropin. Other flasks of various cell densities were treated with 10(-7) M alpha-MSH or [Nle4, D-Phe7]-alpha-MSH for 24 h, followed by removal of the melanotropins from the culture medium. The magnitude and duration of the residual stimulation of melanoma tyrosinase activity by melanotropins were also found to be dependent on the initial cell density. These results reveal that there is a limited range of optimal cell densities at which melanoma cells can respond to melanotropins and express increased tyrosinase activity.

Animals↗
PubMed1986

Role of topical tretinoin in melanoma and dysplastic nevi.

The retinoids have been investigated extensively as chemopreventive and therapeutic agents in a variety of neoplasms. They have been shown to inhibit the proliferation of transformed cell lines in vitro and transplanted tumors in vivo. In cultured murine melanoma cells, retinoids inhibit proliferation and induce differentiation. Human melanoma cell lines have shown a mixed response. The clinical experience with retinoids in melanoma has been limited. Previously we investigated the activity of topical B-all-trans-retinoic acid (Retin-A, vitamin A acid, retinoic acid, and tretinoin) against intracutaneous metastases from malignant melanoma. We saw complete remission of multiple lesions in one individual and regression of several lesions in a second patient. This experience led us to conduct the present pilot trial of topical tretinoin in dysplastic nevus syndrome. The latter is a precursor of malignant melanoma. We saw regression of some of the treated lesions to benign nevi showing minimal or no dysplasia. Thus topical tretinoin appears to possess some activity against melanoma and at least one of its precursor conditions. In view of these preliminary results, more extensive trials are warranted to better define the role of tretinoin in the chemoprevention of malignant melanoma in high-risk lesions.

Administration, Topical↗
PubMed1986

Clinical experience with topical tretinoin in the treatment of cervical dysplasia.

Dysplasia of the uterine cervix is a recognized preneoplastic condition. Because of the observed ability of retinoids to reverse other dysplastic conditions in vitro and in vivo, a number of clinical studies have been carried out of the effect of these agents on cervical dysplasia, with the object of developing a means of chemoprevention of cervical malignancies in women at risk. We have conducted phase I and II trials of topical tretinoin (retinoic acid and Retin-A) delivered by means of a cervical cap and inert collagen sponge system. The results of these studies warranted a phase III trial, which is now underway. The outcome of the latter investigation will have important implications, not only for the management of patients with cervical dysplasia but also for therapeutic approaches to other precancerous conditions.

Administration, Topical↗
PubMed1986

Sunshine and skin cancer: a school-based skin cancer prevention project.

Over 50 percent of the cancers diagnosed in the U.S. are skin cancers. The incidence in Arizona far exceeds the national average for all types of skin cancers, currently having the second highest incidence and prevalence in the world. Results from skin cancer prevention programs elsewhere have suggested that awareness, attitudes, and behavior could be changed by educational efforts with eventual decreases in measurable outcomes such as morbidity and mortality. Sensible sun habits develop early in life. Most health educators agree that the ideal place to begin to teach values regarding health choices is with school-aged children. We have evaluated a primary skin cancer prevention education program in a controlled situation. The target population was chosen in a formal school setting and represented pre-adolescents and early adolescents, who were just beginning to develop "sun-worshipping" tendencies as a part of their increasing preoccupation with appearance. Two unique comprehensive "Sunshine and Skin Cancer" curricula comprised of six units about the sun, its benefits and disadvantages, the skin, cancer and skin cancer, and sun damage prevention were developed. The curricula were very well received by the school system, teachers, children, and the community, and have received local, national, and international attention. This program was shown to significantly change the knowledge and the self-reported behavior (p less than .001) of the children with respect to skin cancer prevention. Steps are being taken to integrate this curriculum into all Arizona middle schools.

Adolescent↗
PubMed1986

Actions of melanotropins on mouse melanoma cell growth in vitro.

Melanotropins induce melanogenesis in mouse Cloudman S91 melanoma cells by stimulating the activity of tyrosinase. In monolayer culture, alpha-melanocyte-stimulating hormone and the superpotent analogue 4-norleucine, 7-D-phenylalanine-alpha-melanocyte, which had prolonged effects on tyrosinase activity, did not inhibit the proliferation of melanoma cells even at concentrations that elicited maximal tyrosinase stimulation. In soft agar the melanotropins stimulated the formation of melanized colonies and increased the cloning and proliferative potentials of melanoma cells. Both melanotropins increased the number of small (42-104 microns in diameter) colonies at initial plating densities ranging from 625 to 7,500 cells/dish. The number of larger (greater than 104 microns in diameter) colonies was also increased except at densities 5,000 cells or more/dish, wherein the proliferative capacity was inhibited; yet the cloning efficiency was still increased. Therefore, in bilayer soft agar cultures, melanotropins stimulate the growth of the clonogenic S91 melanoma cell population under conditions that allow for optimal expression of the cloning and proliferative potentials of these cells.

Animals↗