Allyl isothiocyanate (AITC) is a phytochemical that is abundantly present in cruciferous vegetables of the Brassicaceae family, such as cabbage, broccoli, mustard, wasabi, and cauliflower. The pungent taste of these vegetables is mainly due to the content of AITC present in these vegetables. AITC is stored stably in the plant as its precursor sinigrin (a type of glucosinolate), which is physically separated from myrosin cells containing myrosinase. Upon tissue disruption, myrosinase gets released and hydrolyzes the sinigrin to produce AITC and by-products. AITC is an organosulfur compound, both an irritant and toxic, but it carries pharmacological properties, including anticancer, antibacterial, antifungal, and anti-inflammatory activities. Despite the promising anticancer effectiveness of AITC, its clinical application still possesses challenges due to several factors, i.e., low aqueous solubility, instability, and low bioavailability. In this review, the anticancer activity of AITC against several cancer models is summarized from the literature. Although the mechanism of action is still not fully understood, several pathways have been identified; these are discussed in this review. Not much attention has been given to the delivery of AITC, which hinders its clinical application. However, the few studies that have demonstrated the use of nanotechnology to facilitate the delivery of AITC are addressed.

In the area of gene-directed enzyme prodrug therapy (GDEPT), using herpes simplex virus thymidine kinase (HSV-tk) paired with prodrug ganciclovir (GCV) for cancer treatment has been extensively studied. It is a process involved with two steps whereby the gene (HSV-tk) is first delivered to malignant cells. Afterward, non-toxic GCV is administered to that site and activated to cytotoxic ganciclovir triphosphate by HSV-tk enzyme expressed exogenously. In this study, we presented a one-step approach that both gene and prodrug were delivered at the same time by incorporating them with polymeric micellar nanovectors. GCV was employed as an initiator in the ring-opening polymerization of ε-caprolactone (ε-CL) to synthesize hydrophobic GCV-poly(caprolactone) (GCV–PCL), which was furthered grafted with hydrophilic chitosan to obtain amphiphilic polymer (GCV–PCL–chitosan) for the fabrication of self-assembled micellar nanoparticles. The synthesized amphiphilic polymer was characterized using Fourier transform infrared spectroscopy and proton nuclear magnetic resonance. Micellar prodrug nanoparticles were analyzed by dynamic light scattering, zeta potential, critical micelle concentration, and transmission electron microscopy. Polymeric prodrug micelles with optimal features incorporated with HSV-tk encoding plasmids were cultivated with HT29 colorectal cancer cells and anticancer effectiveness was determined. Our results showed that prodrug GCV and HSV-tk cDNA encoded plasmid incorporated in GCV–PCL–chitosan polymeric nanocarriers could be delivered in a one-step manner to HT-29 cells and triggered high cytotoxicity.

Previous data demonstrated that the topical application of caffeine inhibited UVB-induced skin tumor formation. Studies showed that caffeine significantly diminished phospho (p)-Chk1 (Ser317) staining and increased the number of mitotic cells that expressed both cyclin B1 and caspase 3 in tumors, suggesting that caffeine induces apoptosis selectively in tumors by inhibiting the ATR/Chk1 pathway and promoting lethal mitosis. We also found that caffeine attenuated the UVB-induced decrease in mitotic cells with cyclin B1 to a greater extent in p53 knockout (KO) mice compared with p53 wild-type (WT) littermates. Therefore, we sought to investigate the mechanism by which caffeine could selectively sensitize p53-deficient cells to apoptosis following UVB exposure by inhibiting ATR/Chk1 pathway. Performing immunohistochemistry on stored tumor paraffin samples, we found an almost exclusive inverse relationship (>95%) between p53 expression and p-Chk1 (Ser317), but not p-Chk1 (Ser345), in all 42 keratoacanthomas and 11 squamous cell carcinomas examined. Tumors that expressed high levels and large areas of p53 protein had no detectable p-Chk1 (Ser317) expression, whereas tumors that expressed high levels and large areas of p-Chk1 (Ser317) protein had no detectable p53 expression. Squamous cell carcinomas that demonstrated heterogeneous p53 and p-Chk1 (Ser317) expression within the same tumor showed that the areas that expressed p53 were negative for p-Chk1 (Ser317) and the areas that expressed p-Chk1 (Ser317) were negative for p53. Similar patterns were observed for keratoacanthomas. Not only was the inverse relationship demonstrated in heterogeneous tumors that showed clusters of positive and negative cells, it was also demonstrated in heterogeneous tumors that showed mixtures of single cells either positive or negative for p53. These findings were consistent for the epidermis away from tumors that demonstrated no p-Chk1 (Ser317), but appreciable p53 protein in the basal layer. As expected, the inverse relationship could not be observed by western blotting tumors that expressed both proteins. However, tumors from p53 KO mice had elevated levels of p-Chk1 (Ser317) compared with tumors from p53 wild-type SKH-1 controls. A similar pattern was observed in normal epidermis from p53 KO mice after a single exposure to UVB, whereas p53 WT littermates induced p-Chk1 (Ser317), but to a much lesser extent. Moreover, we demonstrated that UVB-induced p-Chk1 (Ser317) was inhibited by caffeine in p53 KO epidermal cells in vitro. To our knowledge, this striking phenotypic negative association between two proteins has never been observed in skin tumors. These data illustrate the dynamic regulation of checkpoint function, suggesting that phosphorylation of Chk1 on Serine 317 is regulated by p53 status and that p53 may act as a molecular on and off switch for the phosphorylation of Chk1 on Serine 317. Citation Format: Jamie J. Bernard, You-Rong Lou, Sarah Peng, Tao Li, Paul Nghiem, Allan H. Conney, Yao-Ping Lu. Inverse relationship between p53 and phospho-Chk1 (Ser317) protein expression in UVB-induced skin tumors in SKH-1 mice. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 569. doi:10.1158/1538-7445.AM2013-569