| gamma- And delta-tocotrienol display potent anticancer activity against a variety of tumors. The anticancer activity of these natural compounds is mediated by various cellular mechanisms involved in cell cycle regulation, apoptosis, autophagy and angiogenesis. Nevertheless, the usefulness of these compounds in vivo has been limited because of their low absorption, high volume of distribution, rapid metabolism and overall low bioavailability. In an effort to improve in vivo anticancer activity, tocotrienols have been subjected to electrophilic substitution reactions, such as Mannich reactions, to synthesize various oxazine derivatives. Among these oxazine derivatives of tocotrienols, compound 26, 31, 39, 40 and 44 were shown to possess enhanced anticancer activity as compared to their natural parent compounds against +SA mammary tumor cells. After confirming in vitro anticancer activity of these tocotrienol oxazine derivatives, additional in vivo follow up studies were conducted with these same oxazine derivatives formulated as novel nanoemulsions and administered by intralesional injection into +SA mammary tumors grown in syngeneic BALB/c mice. Results from these studies showed that tumor growth in tocotrienol oxazine derivative treated mice was significantly decreased as compared to tumors grown in mice treated with their respective parent tocotrienol at the end of an 11-day treatment period. Western blot analysis of tumor samples indicated that oxazine derivative treatment inhibition of tumor growth was correlated with a corresponding significant decrease in the cell cycle progression associated proteins, cyclin D1, CDK2, CDK4, CDK6 and corresponding increase in cell cycle arrest associated proteins p21 and p27. In addition, tocotrienol oxazine derivative treatment also decreased cell mitogenic and survival signaling pathways and decreased Akt and NF&kgr;13 activation. Together, these findings suggest that tocotrienol anticancer activity in vivo can be enhanced by structural modifications to produce novel oxazine derivatives, and these compounds may provide significant benefit in the treatment of breast cancer in women.;The effects of tocotrienol oxazine derivatives on +SA mammary tumor cells compensatory mechanisms to hypoxia were examined in other studies. Hypoxic conditions in +SA cells were created by treatment with CoC12, a hypoxia mimetic agent. Using nontoxic doses of CoC12 (150microM), +SA mammary tumor cells displayed a significant increase in protein expression of the hypoxia inducible factor-lalpha (HIF-lalpha). HIF-lalpha is an important protein in hypoxic tumor cells that acts to promote tumor cell survival and growth during conditions of low oxygen concentration. Treatment with 2muAM delta-tocotrienol oxazine derivative, compound 44, significantly decrease CoC1 2 induced elevations in HIF-lalpha levels. Similar treatment with 8-tocotrienol, the natural parent compound was also found to suppress hypoxia induced increases in HIP- lalpha levels, but this decrease was of lesser magnitude than that observed in +SA tumors treated with compound 44 . Treatment with compound 44 was also associated with a significant decrease in PI3K/Akt/mTOR and MAPK pathway associated protein activation. Tumor hypoxia and elevations in HIF-lalpha levels were also found to be correlated with a large increase in VEGF levels, an important angiogenesis stimulating growth factor, and treatment with compound 44 was found to decrease hypoxia induced increase in VEGF. These findings suggest that delta-tocotrienol oxazine derivative, compound 44, might be effective in treating rapidly growing breast cancers by blocking tumor cell compensatory mechanisms that are initiated in response to hypoxia. |
