Inhibition by cysteamine of hepatocarcinogenesis induced by N-nitrosomorpholine in Sprague-Dawley rats

A Review on the Antimutagenic and Anticancer Effects of Cysteamine

Cancer is one of the leading causes of death worldwide. First-line treatments usually include surgery, radiotherapy, and/or systemic therapy. These methods can be associated with serious adverse events and can be toxic to healthy cells. Despite the new advances in cancer therapies, there is still a continuous need for safe and effective therapeutic agents. Cysteamine is an aminothiol endogenously synthetized by human cells during the degradation of coenzyme-A. It has been safely used in humans for the treatment of several pathologies including cystinosis and neurodegenerative diseases. Cysteamine has been shown to be a potent antimutagenic, anticarcinogenic, and antimelanoma in various in vitro and in vivo studies, but a review on these aspects of cysteamine's use in medicine is lacking in the current literature. The efficacy of cysteamine has been shown in vitro and in vivo for the treatment of different types of cancer, such as gastrointestinal cancer, pancreatic cancer, sarcomas, hepatocellular carcinoma, and melanoma, leading to the significant reduction of lesions and/or the increase of survival time. Although the mechanisms of action are not fully understood, possible explanations are (i) free radical scavenging, (ii) alteration of the tumor cell proliferation by affecting nucleic acid and protein synthesis or inhibition of DNA synthesis, and (iii) hormone regulation. In conclusion, regarding the high safety profile of cysteamine and the current literature data presented in this article, cysteamine might be considered as an interesting molecule for the prevention and the treatment of cancer. Further clinical studies should be performed to support these data in humans.

Comparison of the efficacy of cysteamine 5% cream and hydroquinone 4%/ascorbic acid 3% combination cream in the treatment of epidermal melasma

BACKGROUND

Few safe and effective treatments are available for melasma. Cysteamine, a non-melanocytotoxic molecule is a safer alternative to hydroquinone and usable for the long-term use.

AIM

To evaluate the effect of cysteamine 5% cream in the treatment of melasma METHODS: Sixty-five of 80 patients completed this single-blind, randomized, controlled trial. The patients received cysteamine 5% or hydroquinone 4%/ascorbic acid 3% (HC) cream. The therapeutic response was evaluated by modified MASI (mMASI) and melanin index (SkinColorCatch) after 2 and 4 months of treatment. Effect of treatment on the quality of life was also assessed.

RESULTS

The decrease for mMASI score was from 6.69±2.96 to 4.47±2.16 in cysteamine group and from 6.26±3.25 to 3.87±2.00 in HC group after 4 months (p values<0.001). The melanin index decreased from 37.72±10.17 to 31.47±11.90 in the cysteamine group and from 36.37±10.80 to 23.16±8.83 in HC group after 4 months (p-value=0.003 and <0.001, respectively). The difference between mMASI score at baseline and month 4 was not significant between both groups (p-value>0.05).The difference between melanin index at baseline and month 4 was significantly more pronounced in HC group (p-value=0.002). Quality of life improved in both groups (p-value<0.05), but was not significantly different between groups (p-value>0.05).

CONCLUSION

Cysteamine was confirmed to be an effective treatment for melasma, with equivalent results to HC in reducing mMASI score and improving quality of life, despite lesser melanin index reduction observed. Cysteamine and HC efficacy was confirmed in patients recalcitrant to previous treatments, by a significant reduction of mMASI and melanin index.

Potential alteration of tumor microenvironments by β-mercaptoethanol

The therapeutic effectiveness of immune checkpoint inhibitors in cancer patients is quite profound. However, it is generally accepted that further progress is curtailed by accompanying adverse events and by low cure rates linked to the tumor microenvironment. The multitudes of immune processes altered by low-molecular-weight thiols published over the past decades suggest they have potential to alter tumor microenvironment processes which could result in an increase in immune checkpoint inhibitor survival rates. Based on one of the most studied and most potent low-molecular-weight thiols, β-mercaptoethanol (BME), it is proposed that clinical assessment be undertaken to identify any BME benefits with relevance for proliferation/differentiation of immune cells, lymphocyte exhaustion, immunogenicity of tumor antigens and inactivation of suppressor cells/factors. The BME alterations projected to be most effective are: maintenance/replacement of glutathione in lymphocytes via facilitation of cysteine uptake, inhibition of suppressor cells/soluble factors and inactivation of free-radical, reactive oxygen species.

Dietary supplemented 2-mercaptoethanol prevents spontaneous and delays virally-induced murine mammary tumorigenesis

There seems to be little doubt that organosulfur compounds have enormous benefits for biological processes, especially those of diseases like cancer. The preliminary results herein define a cancer model in which benefits/mechanisms of multitudes of xenobiotic and nature's organosulfurs could easily be compared. Mice from three strains with a high incidence for naturally occurring tumors were treated daily with 2-mercaptoethanol (2-Me) starting at weaning. The 100% tumor incidence of undefined etiology in untreated BXSB-Yaa (+) males was completely prevented by 2-Me. In contrast, 2-Me treatment of female and male C3H.OL and C3H.OH congenic strains, did not change the 100% tumor incidence due to milk-borne retrovirus, MMTV(S), but did: (1) delay the appearance of tumors by 42%; (2) increase longevity 56%; and (3) increase longevity, post-tumor detection, 95%. The addition of these results to the increasingly impressive anti-cancer benefits of simple xenobiotic organosulfurs raise the question: Can they be adapted for use as a preventive modality for human cancer?

Anticancer activity and chemoprevention of xenobiotic organosulfurs in preclinical model systems

There seems to be little doubt that xenobiotic and plant derived organosulfur compounds have enormous benefits for in vitro cellular functions and for a multitude of diseases, including cancer. Since there are numerous reviews on anticancer activities of plant organosulfurs, the focus herein will be on alterations associated with xenobiotic organosulfurs. Benefits of 2-mercaptoethanol (2-Me), N-Acetyl-cysteine, cysteamine, thioproline, piroxicam, disulfiram, amifostine, sulindac, celecoxib, oltipraz and their derivates on transplanted homologous tumors and on autochthonous cancers with a viral-, radiation-, chemical carcinogen-, and undefined-etiology are assessed. Because all organosulfurs were not tested for activity in each of the etiology categories, comparative evaluations are restricted. In general, all ‘appeared’ to lower the incidence of cancer irrespective of etiology; however, since most of these values were determined at ages much younger than at a natural-end-of-life-age, differences most likely, instead, reflect a delayed initiation and/or a slowed progression of tumorigenesis. The poorest, long-term benefits of early intervention protocols occurred for viral- and chemical carcinogen-induced cancers. In addition, once tumorigenesis was beyond the initiation stage, outcomes of organosulfur therapies were extremely poor, indicating that they will not be of significant value as stand alone treatments. More importantly, except for the lifetime prevention of spontaneous and radiation-induced mammary tumors by daily dietary 2-Me, similar life long prevention of tumorigenesis was not achieved with other xenobiotics or any of nature’s plant organosulfurs. These results raise an interesting question: Is the variability in incidence found for different organosulfurs associated with (a) their structure, (b) the length of the untreated latency period, (c) treatment duration/dose, and/or (d) the etiology-inducing agent?

[35S]cysteamine: facile synthesis, in vivo biokinetics, and subcellular distribution

Whereas chemical radioprotection against external beams of ionizing radiation is well studied in radiobiology, the aspects relating to tissue incorporated radionuclides have received little attention. The increased use of radionuclides in diagnostic and therapeutic nuclear medicine, as well as the presence of both manmade and natural radioactivity in the environment, indeed call for such investigations. Our ongoing work on a variety of radioprotectors has revealed that cysteamine (MEA), S-2-aminoethylisothio uroniumbromide hydrobromide (AET), and others (e.g. ascorbic acid), protect spermatogonial cells in mouse testis from the effects of chronic irradiation with intratesticularly localized radionuclides. In these experiments, dose modification factors ranging from 2 to 4 and 10 to 14 were obtained using spermhead survival and induction of spermhead abnormalities, respectively, as the biological end points. Similar experiments were carried out by changing the mode of administration of cysteamine to oral intubation. In these studies a dose modification factor of approximately 3 was observed in the spermhead survival assay. In an effort to understand the protection offered by MEA, the present work describes a one-pot synthesis of high specific activity [35S]cysteamine from elemental [35S]sulphur and its use in determining the biokinetics and biodistribution of MEA following intratesticular (i.t.) or oral administration in mice.

Enhancement by sulpiride of the inhibitory effects of cysteamine on gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats

The effects of sulpiride on cysteamine inhibition of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and on the BUdR labelling index of gastric mucosa were investigated in inbred Wistar rats. After 25 weeks of oral treatment with MNNG, rats received one of the following alternate-day injections: cysteamine (2 doses), cysteamine (2 doses) plus sulpiride or sulpiride. At week 52, prolonged administration of cysteamine significantly reduced the incidence of adenocarcinomas of the glandular stomach. Cysteamine at low dose had no effect on the incidence of gastric cancers, but a combination of low-dose cysteamine and sulpiride caused a significantly greater reduction in the incidence of gastric cancers. Administration of sulpiride alone had no influence on gastric carcinogenesis. The labelling index of the antral mucosa was significantly lower in rats treated with high but not low doses of cysteamine. However, a combination of low-dose cysteamine and sulpiride significantly decreased the labelling index of the antral mucosa. Our findings indicate that cysteamine suppressed gastric carcinogenesis and that sulpiride enhanced this inhibition. Because sulpiride is a dopamine antagonist, these findings also indicate that dopamine may play an important role in cysteamine inhibition of gastric carcinogenesis.

Tissue norepinephrine depletion as a mechanism for cysteamine inhibition of colon carcinogenesis induced by azoxymethane in Wistar rats

The effects of cysteamine (2-aminoethanethiol hydrochloride) on the incidence, number and histology of colon tumors induced by azoxymethane (AOM), and on the norepinephrine concentration in the colon wall tissue and the labelling indices of colon mucosa and colon cancers were investigated in Wistar rats. Rats received 10 weekly injections of 7.4 mg/kg body weight of AOM and alternate-day subcutaneous injections of 25 mg/kg of cysteamine in 0.9% NaCl solution until the end of the experiment. At week 40, prolonged administration of cysteamine significantly reduced the incidence and number of colon tumors. Histologically, the adenocarcinomas that did develop in rats treated with cysteamine exhibited high mucin-producing activity. Administration of cysteamine caused significant decreases in the norepinephrine concentration in colon tissue and in the labelling indices of colon mucosa and cancers. Our findings indicate that cysteamine inhibits the development of colon tumors. This action may be related to its effect in decreasing norepinephrine concentration in the colon wall tissues and subsequently in decreasing proliferation of colon cancer cells.