I do not know about cancer cells, but for plant cell and tissue cultures there are various appropriate ROS scavengers such as ascorbic acid or its immediate precursor L-galactonic acid-g-galactone (10 microM), DPI e.g. 10 microM, catalase 10 U/ml, imidazole 10 microM. These are recommendable concentrations that were found efficient for suppressing chemical-induced cell death in plant models, but testing a wider concentration range for your cancer cells is strongly recommendable. Hope this helps. Good luck!

You can examine protein and non protein thiols

Reza's suggestion of Trolox (which is a water soluble derivative of vitamin E) is fine, though it does create an oxidized radical, so would be best combined with say ascorbate which will remove these radicals by reducing back to the active form. The link he provides is useful but rather limited, and incomplete in terms of what things do - EG ebselen also catalyses breakdown of peroxide itself.

We have used Tempol (membrane-permeable catalytic superoxide scavenger, 3 mmol/l) very successfully in intact blood vessels, cultured smooth muscle cells and other preparations - apparently no other ill effects at this concentration, and widely used. Ebselen is a potent  glutathione peroxidase mimic, which may also affect lipid peroxidation, and has been used at concentrations between 10 and 100 micromole/l. Note that these target different species - Tempol removes superoxide, ebselen peroxide. This differentiation is important, because although conventional wisdom says that superoxide is converted to peroxide rapidly by endogenous superoxide dismutase, we have found that they elicit quite different effects in smooth muscle.

We have not found acetyl-L-cysteine (NAC, 1 mM) to be very effective, possibly due to limited permeability in the cell membrane.

Regarding Elena's suggestions, I am not sure these would necessarily be OK in animal tissues. Catalase does not get into animal cells easily (it is a enzyme after all). But Do NOT use DPI !! It is not an antioxidant but a potent inhibitor of all flavoproteins (e.g. in mitochondria and NADPH  oxidase, etc), and highly non-specific at that.  

Perhaps Melatonin can be worth a try.

i have stated that have no idea about antioxidant effects in animal cell systems neither am familiar which chemicals are permeable in animal cells. It was just a suggestions based on my experience with tomato and tobacco suspension cells.

Regarding DPI - yes it is not ROS scavenger and is suggested to inhibit NADPH oxidase. We have used it in order to see if by inhibiting superoxide formation (mediated by NADPH-oxidase) the cell death response might be alleviated.  It appeared that DPI exerts different effects depending on concentration and applied cell death inducer: in camptothecin treated tomato cells DPI was effective in suppressing the cell death whereas in CdSO4-treated cells, DPI either did not have an effect or even stimulated the cell death.  If you are interested, see the attached papers. However, they might not be useful for the particular experiments with the animal cells...:)

Kind regards to all

As a major effector in ROS formation, mitochondrial dysfunction may be seen as a most relevant target in compensating a prooxidant state. Thus, the choice of "mitochondrial nutrients" (alpha-lipoic acid, ubiquinol, and acyl-carnitine), possibly in association, should be seen as a realistic tool in counteracting excess ROS formation.

NAC is not a selective antioxidant in that it cross-reacts with many different ROS,  and even metals. Attributing an observed effect to NAC could therefore be misleading. To assign if ROS have any causative roles, a first test should be identifying which of the ROS is a main species in the observation leading to the phenotype. Invariably superoxide is often the first ROS that comes out from incomplete oxygen reduction (when no strong photochemical effects are involved, which otherwise would give rise to singlet oxygen). A second question is where is that ROS source; is it enzymatic or not?

Only when you narrow down to a single ROS, can you realistically use a "more selective" scavenger to test and manipulate the outcomes. As noted by other comments above, DPI is not a good inhibitor in selectivity and does not inform much.  

For intracellular ROS: NAC, Tempol, Trolox;

but you also can check the paracrine way of h2o2 by incubating your cells with catalase in your culture medium.

GSH, Serum, NAC

https://www.researchgate.net/publication/299607409_Novel_PKC-z_to_p47phox_interaction_is_necessary_for_transformation_from_blebbishields

Article Novel PKC-? to p47phox interaction is necessary for transfor...

Perhaps one should look at the following link and get lots, if not lost :) , in the hundreds of antioxidant agents that may be closely or remotely relevant to your study

https://www.scbt.com/scbt/zh/browse/antioxidants/_/N-16fiso3

Hey Prahlad,

if you like, you can have a look at our recent review:

"Functions of ROS in macrophages and antimicrobial immunity".

In this review, we give an introduction to ROS and their sources in macrophages, summarize the versatile roles of ROS in direct and indirect antimicrobial immune defense and provide an overview of commonly used ROS probes, ROS source inhibitors and ROS scavengers (also the difference between ROS scavengers and antioxidants, which are not synonymous, is explained).

Functions of ROS in Macrophages and Antimicrobial Immunity

February 2021, Antioxidants 10(2):313

DOI: https://doi.org/10.3390/antiox10020313

All the best and stay healthy,

Marc