The HL-60 cell line, derived from a patient with acute promyelocytic leukemia, proliferates continuously in suspension culture and consists predominantly (greater than 90%) of promyelocytes. These cells can be induced to differentiate to morphologically and functionally mature granulocytes by incubation with a wide variety of compounds, including butyrate and hypoxanthine and polar planar compounds such as dimethyl sulfoxide and hexamethylene bisacetamide. We have now found that retinoic acid (all-trans-retinoic acid) induces differentiation (as measured morphologically and by the ability to reduce nitroblue tetrazolium) of HL-60 at concentrations as low as 1 nM. Maximal differentiation (approximately 90%) occurs at 1 micro M, a concentration 1/500th to 1/160,000th the concentrations of butyrate (0.5 mM) and dimethyl sulfoxide (160 mM) that promote a similar increase in differentiation. Continuous exposure to retinoic acid is necessary for optimal differentiation, with the percentage of mature cells in the culture directly related to the length of time of exposure to retinoic acid. Retinoic acid and 13-cis-retinoic acid are equally effective in inducing differentiation of HL-60. Retinol (vitamin A), retinal, and retinyl acetate are approximately 1/1000th less potent. This study suggests that retinoids could provide a therapeutic tool in the treatment of acute myeloid leukemia, a disease that has been looked upon as primarily involving a block in myeloid differentiation, and indicates that retinoids, in addition to their well-characterized involvement in epithelial cell differentiation, may also be involved in the differentiation of certain hematopoietic cells.

https://www.pnas.org/content/pnas/77/5/2936.full.pdf

Induction of differentiation of the human promyelocytic leukemia cell line (HL-60) by retinoic acid.

Effects of vitamin A and its analogs (retinoids) on normal and neoplastic cells

It has been known for more than 50 years that retinoids, the family of molecules comprising both the natural and synthetic analogues of retinol, are potent agents for control of both cellular differentiation and cellular proliferation (70). In their original clas sic paper describing the cellular effects of vitamin A deficiency in the rat, Wolbach and Howe clearly noted that there were distinct effects on both differentiation and proliferation of epithelial cells. During vitamin A deficiency, it was found that proper differentia tion of stem cells into mature epithelial cells failed to occur and that abnormal cellular differentiation, characterized in particular by excessive accumulation of keratin, was a frequent event. Furthermore, it was noted that there was excessive cellular proliferation in many of the deficient epithelia. Although the conclusion that an adequate level of retinoid was necessary for control of normal cellular differentiation and proliferation was clearly stated in the original paper by Wolbach and Howe, a satisfactory explanation of the molecular mechanisms underlying these effects on both differentiation and proliferation still eludes us more than 50 years later. It was inevitable that the basic role of retinoids in control of cell differentiation and proliferation would eventually find practical application in the cancer field, and there have been great ad vances in this area, particularly for prevention of cancer. Many studies have shown that retinoids can suppress the process of carcinogenesis in vivo in experimental animals (for reviews, see Refs. 7, 33, 51, 54, 56, and 57), and these results are now the basis of current attempts to use retinoids for cancer prevention in humans. Furthermore, there is now an extensive literature on the ability of retinoids to suppress the development of the malignant phenotype in vitro (for reviews, see Refs. 6, 8, 30, and 31 ), and these studies corroborate the use of retinoids for cancer prevention. Finally, most recently, it has been shown that reti noids can exert effects on certain fully transformed, invasive, neoplastic cells, leading in certain instances to a suppression of proliferation (30) and in other instances to terminal differentiation of these cells, resulting in a more benign, nonneoplastic pheno type (10,11,60,62). Even though there are many types of tumor cells for which this is not the case (33, 52) (indeed, at present there are only a limited number of instances in which such profound effects of retinoids on differentiation and proliferation of invasive tumor cells have been shown), this finding neverthe less has highly significant implications for the problem of cancer treatment. It emphasizes that in many respects cancer is fun damentally a disease of abnormal cell differentiation (36,44), and it raises the possibility that even invasive disease may eventually be controlled by agents which control cell differentiation rather than kill cells. Since carcinogenesis is essentially a disorder of cell differentiation, the overall scientific problem of the role of retinoids in either differentiation or carcinogenesis is essentially

https://cancerres.aacrjournals.org/content/canres/43/7/3034.full.pdf

Role of retinoids in differentiation and carcinogenesis.

✓ The natural history of primary intracranial germ-cell tumors (GCT's) is defined from 389 previously published cases, of which 65% were germinomas, 18% teratomas, 5% embryonal carcinomas, 7% endodermal sinus tumors, and 5% choriocarcinomas. Intracranial GCT's display specificity in site of origin. Ninety-five percent arise along the midline from the suprasellar cistern (37%) to the pineal gland (48%), and an additional 6% involve both sites. The majority of germinomas (57%) arise in the suprasellar cistern, while most nongerminomatous GCT's (68%) preferentially involve the pineal gland (p < 0.0001). The age distribution of afflicted patients is unimodal, centering with an abrupt surge in frequency in the early pubertal years; 68% of patients are diagnosed between 10 and 21 years of age. Nongerminomatous GCT's demonstrate an earlier age of onset than do germinomas (p < 0.0001). Prolonged symptomatic intervals prior to diagnosis are common in germinomas (p = 0.0007), in suprasellar GCT's (p = 0.001), and a...

Intracranial germ-cell tumors: natural history and pathogenesis.

Publisher Summary This chapter discusses the cellular biology and biochemistry of the retinoids In isolated 9-day-old rat embryos, retinoic acid prevents the formation of the pharyngeal arches, which are derived from cephalic mesenchyme; these structures later form the maxilla and the mandible Another mesenchymal derivative, whose formation is markedly suppressed by retinoic acid in rat embryos, is the yolk sac circulation Retinoids can exert a powerful influence on cell differentiation in many different types of epithelia The effects of retinoids on differentiation of epithelia in organ culture result from a combination of complex cellular responses and interactions of different cell types in the explant One of the most illuminating examples of the ability of retinoids to promote differentiation is the effect of retinoids on mouse embryonal carcinoma cells These undifferentiated stem cells of teratocarcinomas are multipotential, that is, they can differentiate into a multiplicity of somatic cell types Another example of the ability of retinoic acid to promote terminal differentiation of neoplastic cells to nonneoplastic cell types is the effect of retinoic acid on human promyelocytic leukemia cells

Cellular Biology and Biochemistry of the Retinoids

Sixty-one patients with midline pineal tumors and 16 patients with suprasellar germinomas were treated with surgical decompression and relatively high-dose radiotherapy of the primary site Results were excellent, and there were no long-term complications Ten per cent of midline pineal tumors and 37% of suprasellar germinomas metastasized to the cerebral or spinal subarachnoid space within 6 months to 5 years Irradiation of the entire neural axis is recommended for locally extensive tumors, simultaneous pineal and hypothalamic lesions, and all biopsy-proved germinomas The five-year survival rate was 79% for midline pineal tumors and 77% for suprasellar germinomas

Midline pineal tumors and suprasellar germinomas: highly curable by irradiation.

The ability of vitamin A and its analogues (retinoids) to prevent chemically-induced tumours has been studied in various experimental systems1. We have investigated here the possibility that retinoids might also inhibit radiation-induced oncogenic transformation using a cell line of C3H mouse embryo fibroblasts grown in culture. We report a marked reduction in the transformation frequency by using one such compound, Ro-11-1430, the synthesis and structure of which has been described by Bollag2.

A vitamin A analogue inhibits radiation-induced oncogenic transformation

Exposure of hamster cells to 42.5 degrees C for long periods leads to the development of thermal tolerance; the slope of the survival curve become shallower after about 3.5 to 4 hours. If two 4-hour exposures at 42.5 degrees C are separated by various periods of time, thermal tolerance is eliminated by 20 hours. Prolonged exposure at 42.5 degrees C offers considerable protection from subsequent treatments to acute hyperthermia at 45 degrees C indicate or in conditioned medium or balanced salt solution failed to reveal any evidence of repair of potentially lethal damage.

Thermal tolerance and repair of thermal damage by cultured cells.

Hyperthermia combined with 60Co gamma irradiation was studied using V79 hamster cells cultured in vitro. Modest hyperthermia (41 degrees C for 6 hrs.) enhanced the cell killing produced by acute exposure to radiation. The same treatment enhanced the effect of low dose-rate irradiation (200 rads/hr.) even more. The sequence in which modest hyperthermia was combined with low dose-rate irradiation was important. Maximal enhancement was observed when hyperthermia was followed by irradiations. The probable explanation is that, by damaging the repair system, prior heat renders the cells unable to repair sublethal damage during subsequent low dose-rate irradiation.

Hyperthermia and low dose-rate irradiation.

Modification of sister chromatid exchanges and radiation-induced transformation in mouse C3H/10T1/2 and Syrian hamster embryo cells by the tumor promoter 12- O -tetradecanoylphorbol-13-acetate and two retinoids, the trimethylmethoxy-phenyl analog of N -ethyl retinamide and β-all- trans -retinoic acid, has been studied. 12- O -tetradecanoylphorbol-13-acetate alone enhances, and retinoids alone reduce radiation-induced transformation. When both compounds were present, the retinoids not only reduced the oncogenic effects of radiation but completely eliminated the promoting effects of 12- O -tetrade-canoylphorbol-13-acetate. These results were not paralleled by changes in sister chromatid exchange frequencies, indicating that, while sister chromatid exchanges may be useful as indicators of primary carcinogen mutagens, they may have little utility when secondary agents alter the response of cells to a primary initiator.

Modification of Sister Chromatid Exchanges and Radiation-induced Transformation in Rodent Cells by the Tumor Promoter 12-O-Tetradecanoylphorbol-13-acetate and Two Retinoids

Leon Harisiadis

Papers

Midline pineal tumors and suprasellar germinomas: highly curable by irradiation.

A vitamin A analogue inhibits radiation-induced oncogenic transformation

Thermal tolerance and repair of thermal damage by cultured cells.

Hyperthermia and low dose-rate irradiation.

Modification of Sister Chromatid Exchanges and Radiation-induced Transformation in Rodent Cells by the Tumor Promoter 12-O-Tetradecanoylphorbol-13-acetate and Two Retinoids