Reactive species (RS) are implicated in various drug-based therapies for cancer and are crucial regulators of cellular rhythms. Yet the effects of anticancer drugs on the temporal variations of individual RS have not yet been reported. It so happens that the impact of temporal changes of RS on cells has not been reported in any system except in microalgae through earlier work in our lab. Analyses of the basal and altered rhythms of RS in cancer and normal cells are expected to facilitate an understanding of stress response and RS homeostasis in cancer treatment. Thus far, the intracellular antioxidant levels have been used in the study of rhythms associated with RS homeostasis. The present study highlights the limitations of the antioxidant approach.
Here, we have shown that RS, such as superoxide and hydroxyl, have an endogenous rhythm in cancer cells. These rhythms can be reset by RS generating chemicals, including anticancer drugs, as well as by high concentrations of solvents. We also show that the HCT116 colon cancer cells exhibit an inherent rhythm of pseudo-steady-state (PSS) levels of intracellular superoxide (SOX), an important ROS, which is reset by the SOX inducer, menadione (MD). This reset was dependent on the p53 status of the cells, and it increased the sensitivity of the cells to MD by 2-fold. The period of oscillation showed a linear correlation with MD concentration, given by T, in h = 23.52 1.05 [MD concentration in µM].
Further, a mathematical model for understanding better the molecular mechanisms involved in rhythm reset was developed. Biologically meaningful parameters were obtained through parameter estimation techniques; the model can predict experimental profiles of SOX, establish qualitative relations between interacting species in the system, and serves as an important tool to understand the profiles of various species. The model was also able to successfully predict the rhythm reset in MD treated hepatoma cell line, HepG2.

We also report for the first time, the existence of endogenous rhythms in the PSS levels of RS, particularly superoxide and hydroxyl radicals, in the cervical cancer cell line, SiHa. Also, we show that the RS rhythm characteristics, particularly frequency and amplitude, are entrained (reset) by the anticancer drugs, menadione, and curcumin. Curcumin, the more effective of the two drugs (IC50 =15 µM) induced reset of superoxide and hydroxyl rhythms from 15.4 to 9 h, and 25 to 11 h, respectively, as well as caused up-regulation of these radical levels by about 3-fold. However, menadione (IC50 = 20 µM) affected only the superoxide levels (3 fold increase) and rhythm (period = 11 h). Drug treatment at time points correlating to different endogenous RS levels also shows up to a 20 % increase in cytotoxicity. Further, we show a lack of correlation between the intracellular RS and antioxidant levels; thus, the traditional practice of using antioxidant enzyme levels as surrogate markers of intracellular oxidative stress extent is invalid. Therefore, we propose RS rhythm as a generic target to manipulate for improved cancer therapy.

Publications:

Kizhuveetil, U., Palukuri, M.V., Sharma, P. et al. Entrainment of superoxide rhythm by menadione in HCT116 colon cancer cells. Sci Rep 9, 3347 (2019) https://urlprotection-tko.global.sonicwall.com/click?PV=1&MSGID=202007040818390120641&URLID=3&ESV=10.0.6.3447&IV=4C9B2135390A30888044F5C0ECD80AEE&TT=1593850725736&ESN=CXQOHEPGXzUN6uJ3kfn7hPysMmp%2FbsoiIbUP1fEpum8%3D&KV=1536961729279&ENCODED_URL=https%3A%2F%2Fdoi.org&HK=386B976A0381D3CC337EACA6DADA14EF1689D0C85A0DC2998EB0EBCF3EABA85F/ 10.1038/s41598-019-40017-7

Kizhuveetil, U., Omer, S., Karunagaran, D. et al. Improved redox anti-cancer treatment efficacy through reactive species rhythm manipulation. Sci Rep 10, 1588 (2020). https://urlprotection-tko.global.sonicwall.com/click?PV=1&MSGID=202007040818390120641&URLID=1&ESV=10.0.6.3447&IV=E04CA835561416DA4FFFE5D3E2BEB34C&TT=1593850725736&ESN=CnO6xp%2BQ%2BmYjLdInIEs47bWv%2FqIeOGQdXeLsYZOyTP8%3D&KV=1536961729279&ENCODED_URL=https%3A%2F%2Fdoi.org%2F10.1038%2Fs41598-020-58579-2&HK=960AA407AA515B634760D580840230BAFD9FD6DD9DA36961DF948304793A0B6B