Saswat: Your molecule shows antiproliferative effect; it arrests G1 phase. Are the concentrations at which you notice anticancer effect and free radical generation the same? Natural products with anti-inflammatory activity and even certain antioxidants upregulate ROS and cause transient cell cycle arrest. Your biologically active compound may be generating ROS generation and causing mitochondrial dysfunction, which triggers apoptosis. Induction of apoptosis in cancer cells appears to be a major focus of compounds exhibiting anti-cancer action.

It is known that many anti-cancer drugs, such as anthracyclines (doxorubicin, etc.) that are in clinical use, increase ROS generation and therefore it somehow contributes to their cytotoxicity.

They can also suppress apoptosis in some cases.

In general ROS are capable of killing cancer cells. Best example of this kind is PDT.  

Does anyone know if ROS may trigger pro-survival (or anti-apoptotic) signals in cancer cells? If so, please share any references.

Georgi Yordanov: Yes, autophagy is a pro-survival mechanism that prevents apoptosis and is induced by ROS. The central players are PARP1 and the DNA damage caused by ROS. Biochemical Pharmacology 83 (2012) 747–757. Clearly to much ROS will not only activate autophagy, but also parthanatos (a form of necrosis).

georgi, it seems to that the normal aging process (accelerates the accumulation of free radicals which cause havoc in the nuclear DNA creating altered cell types*+ plus these same free radicals also alter the bodies ability recognize & eradicate this "new" cell-line). Hence, Ca is born!  The solution would then be to reduce the ROS to that of a 20 *yr//old as rapidly as possible not only would this stop the production of these rouge cells (Ca) but clear the :"eyes" of the bodies own immune system to recognize & eradicate them. Has science progressed to the state that we can halt the aging process?  The answer is yes!, not chronologically , of course, but biochemically! The Elliott Cresson Award,* was given to Dr, Joe  McCord for the discovery of Superoxide Dismutase (SOD) the chief intracellular antioxidant enzyme.that starts decreasing at  age 20 & continues to do so until death occurs by slowly oxidizing (rusting) from from the inside out! Either by accelerating any of the 250+ diseases aggravated if not caused by ROS (oxidative stress) or "nalural" causes..

The solution then would be to stop the decline in the McCord units of SOD intracellularly & be able to maintain them at the level of a 20 yr/o ,indefinitely!  This also has been accomplished !  There is no way one could ingest enough direct antioxidants (which only work on a 1:1 ratio ie, 1 molecule Vit. C to 1 molecule free radical & its done) to make a dent in the trillions of free radicals that bombard our systems daily ;we need to "activate" our own intracellular enzymes with a 1:1,000,000/sec and that's every sec. Now, how could this be possible & why haven't I heard about this before? This same Dr.who was smart enough to discover the problem was also inspired to produce the solution. He went to the age diffing substances of India, china & Japan. By using his discovery of SOD & his ability to measure it intracellularly he began testing to see what effect these herbs had on the levels of SOD produced; what part of the plant was the most effective (root, stem, leaf, flower, or seed) then reduced the concentration to just enough to produce the level of a 20 *yr/o (to reduce side effects) trial & error-ed the ratios of each of 5 herbs* , & got perfect synergy. This Natural product was so unique that 6 US patents were given as well as 1 in China & 1 in Australia. LifeVantage has been giving out their patented product all over the world to various institutions to carry on these breakthrough studies. See pubmed.com /oxidative stress/protandim for 16 completed of the 30+ still in progress. & the studies below:

These peer reviewed studies go on to show that these ancient products activate the cells by way of a Nerf2 pathway ,to not only increase the units of SOD but also catalase ,& glutathione (which is increased 300%). it also affect some 3000 genes some increasing their effect & others toning them down.*

*www.liveit.com

*https://mail.google.com/mail/ca/u/0/#sent/14732fa1ab4c2158?projector=1

*https://www.youtube.com/watch?v=vR-k3ucVj2o

*https://www.youtube.com/watch?v=Us2VU-POhII

*https://mail.google.com/mail/ca/u/0/?shva=1#sent/1476b8da95870edb?projector=1

Not necessarily ROS leads to cell death always. Sometimes it's even increase in cell proliferation, but yes in general it leads to cell death.

ROS can have a number of effects.   Prolfierative/anti proliferative.  Pro apoptotic etc.  ROS can also be produced by many different sources including mitochondria and enzymes such as NOX.  I think you need to carefully consider the context in which your cells exist (the abnormalities the tumour carry, the extracellular environment , the environment of the cell organelles), the production / source of ROS and the antioxidant environment and stress signalling pathways the cells activate.  So in short, I think pro and antioxidant strategies may be equally viable therapeutic strategies 

Yes, increase in ROS or decrease in ROS neutralizing ability can lead to cell death specialy in cancer cells which are already coping with increased stress. 

If your drug is partially affecting microtubules then it may lead to aneuploidy/chromosomal instability which can result in oxidative stress.

Or massive effect on microtubules lead to apoptosis and the observed ROS may be the aftereffect of apoptosis.

In my opinion go through this paper entitled "Targeting cancer cells by ROS-mediated mechanisms: a radical therapeutic approach?".This will help to sort out your query!!

you may also follow "Cancer cell killing via ROS: To increase or decrease,

that is the question "

http://www.nature.com/nrd/journal/v8/n7/full/nrd2803.html