Steroidal alkaloids are a class of secondary metabolites isolated from plants, amphibians, and marine invertebrates. Evidence accumulated in the recent two decades demonstrates that steroidal alkaloids have a wide range of bioactivities including anticancer, antimicrobial, anti-inflammatory, antinociceptive, etc., suggesting their great potential for application. It is therefore necessary to comprehensively summarize the bioactivities, especially anticancer activities and mechanisms of steroidal alkaloids. Here we systematically highlight the anticancer profiles both in vitro and in vivo of steroidal alkaloids such as dendrogenin, solanidine, solasodine, tomatidine, cyclopamine, and their derivatives. Furthermore, other bioactivities of steroidal alkaloids are also discussed. The integrated molecular mechanisms in this review can increase our understanding on the utilization of steroidal alkaloids and contribute to the development of new drug candidates. Although the therapeutic potentials of steroidal alkaloids look promising in the preclinical and clinical studies, further pharmacokinetic and clinical studies are mandated to define their efficacy and safety in cancer and other diseases.
Indole alkaloids comprise serotonin chemically know as 5-hydroxyltryptamine or 5-HT and others of their kind. These comprise the anesthetizing alkaloids of the passion flower , ophthalmic alkaloids associated with the physostigmine derived from the calabar bean as well as the uterine tonics such as ergotamine. This variety of alkaloids also comprises the Indian snakeroot or the Rauwolfia serpentaria that consist of reserpine. It may be mentioned here that reserpine contains potent hypotensive and when isolated from the entire plant possess depressive consequences. Among the numerous central nervous stimulants such as strychnine, psilocybin and johimbine, indole alkaloids comprise indole carbon-nitrogen loop. Indole carbon-nitrogen ring is also present in the fungal alkaloids ergine and psilocybin, the neurotransmitter serotonin as well as the mind jerking medication LSD. Researches have shown that these alkaloids may often impede, obstruct or even contend with the action of serotonin in the brain.
Most of the known functions of alkaloids are related to protection. For example, aporphine alkaloid liriodenine produced by the tulip tree protects it from parasitic mushrooms. In addition, the presence of alkaloids in the plant prevents insects and chordate animals from eating it. However, some animals are adapted to alkaloids and even use them in their own metabolism.  Such alkaloid-related substances as serotonin , dopamine and histamine are important neurotransmitters in animals. Alkaloids are also known to regulate plant growth.  One example of an organism that uses alkaloids for protection is the Utetheisa ornatrix , more commonly known as the ornate moth. Pyrrolizidine alkaloids render these larvae and adult moths unpalatable to many of their natural enemies like coccinelid beetles, green lacewings, insectivorous hemiptera and insectivorous bats.  Another example of alkaloids being utilized occurs in the poison hemlock moth ( Agonopterix alstroemeriana). This moth feeds on its highly toxic and alkaloid-rich host plant poison hemlock ( Conium maculatum ) during its larval stage. A. asltroemeriana may benefit twofold from the toxicity of the naturally-occurring alkaloids, both through the unpalatability of the species to predators and through the ability of A. alstroemeriana to recognize Conium maculatum as the correct location for oviposition.