Hello Jiaming Guo

The sensitivity of cells to radiation is proportional to the degree of proliferative activity and inversely proportional to the degree of differentiation. In other words, undifferentiated cells with high mitotic capability are more radiosensitive. So, tissues rich in actively dividing cells generally show high sensitivity to radiation, whereas those with few such cells have low radio sensitivity.

For instance, epithelial tumors, are considered to have moderate radio sensitivity. Among these tumors, undifferentiated carcinoma and small cell carcinoma have relatively high radio sensitivity, followed by squamous cell carcinoma.

Also, you need to note that radio sensitivity depends not only on the histologic type of the tumor but also on other factors like oxygen concentration in the tumor and the mitotic cycle of tumor cells.

Please refer to the article given below for more information.

https://www.med.or.jp/english/pdf/2004_02/079_083.pdf

You would need to consider other factors as well that affect radio sensitivity.

Best.

What Malcom refers to is the "Law of Bergonie & Tribondeau". This is misunderstood in the Anglophone literature, due to a mistranslation (from their French) of their reported observations. A more correct translation of their reported "appear to be more radiosensitive" is not the "are more radiosensitive" as translated in Radiation Research. What best explains the B&T observations is that a cell that has been sterilized (lost it's reproductive integrity or clonogenicity) will not be seen to be sterilized until it attempts to divide (mitosis) and fails (most apoptosis in solid tissues occurs after a failed mitosis). This is best exemplified in lethally irradiated hibernating squirrels, which are very radioresistant compared to active squirrels, but once brought out of hibernation, die with the same time course post-hibernation as that observed for normally active squirrels post-irradiation (see CS Lange, DPhil thesis, Oxford University, Fac Med, Bodleian Library, 1968). Hence, radiosensitivity should be measured in terms of loss of reproductive integrity (ability to proliferate ad infinitum, or clonogenicity, where a sufficiently large number of divisions (at least 10) are taken as the endpoint).

Re.: Jiaming Guo's question, Cancer cure depends on the elimination or sterilization (loss of reproductive integrity) of the tumor cells (or more particularly, the Cancer Stem Cells), the proliferation of which lead to patient morbidity and mortality. Hence, any gene necessary for maintenance of reproductive integrity (like those involved in DNA Double-strand Break repair) will be essential for cell survival of reproductive integrity if no other DSB repair pathway remains available.

Probably you need to provide more data to obtain a proper answer. For instance, how do you measure radiosensitivity? If it's just with a viability assay, it's not uncommon to see a lower decrease of viability in your model, as hyperproliferation can compensate for the potential excess of cell death. If you analyze apoptosis and see a lower level of apoptotic cells, not look unlogical if your tumor suppressor is involved in apoptosis regulation. What kind of IR you use, gamma or UV, because the pathways involved could vary.

In fact, you already know you are working with a tumor suppressor? that means, you Kd/KO the gene in an in vivo model and see an increase of tumor prone? Or you just speculate behaves as tumor suppresor?. Do you know in which specific pathways your gene is involved? It is possible for different molecules to see the results you described if are involved in cell cycle, apòptosis/senescence shift, metabolism, etc. Or if are complex molecules with multi-tasks (e.g. RNA binding proteins, epigenetic regulators, chromatin modifiers).

To sum up, your results are plausible but further information is needed to give an explanation.

we can assess the radiosensitivity by detect the proliferation of those cell that treated with gradient dose of radiation . you can set a negative control of 0 dose , then you can find whether there are some differences.

Hello Malcolm,

Thanks for your nice answer!

I think what you mentioned above can be mainly summarized as the "Law of Bergonie & Tribondeau". As you told me, proliferation is just one of most important factors that affect cell radiosensitivity so maybe I should take other relevant factors into consideration.

Thanks again for your inspiration!

Best.

Jiaming

Malcolm Nobre

Hi Professor Lange,

Thanks for your wonderful explanation!

As you mentioned "This is misunderstood in the Anglophone literature, due to a mistranslation (from their French) of their reported observations", if it is ture, we ufortunately have been misunderstanding this "law" for years! Even when I discuss with our students. Do you mean what the "B & T" law just told us that Hemotopoietic system seems to be more sensitive to radiation just because we can observe the loss of reproductive integrity earlier (as the cell divide faster and achieve the endpoint sooner)? This is very important for our interpreting the relevant issues.

I appreciate your nice reply!

Jiaming

Christopher Lange

Hi Miguel,

Thanks for your professional analysis!

We used gamma radiation to treat lung cancer cells. Actually the tumor bearing nude mice data showed that konceing out this gene promoted tumor proliferation. But the viability assay data by CCK8 was not stable, seeming to cause radiosensitization after knocking out it. Unfortunately, apoptosis assay data were not quite stable as well! That is why I am so confused.

Thanks for your nice consideration !

Jiaming

Miguel Gallardo

Thank you @Jiaming Guo. Further to your point, tumors with faster proliferation (turnover) shrink more rapidly after therapy (radiation or chemo), but also repopulate (recur) faster. Hence it is the level of depopulation (loss of reproductive integrity) that matters (of the CSCs) that matters for cure. By the way, the B&T studies were with ram testicles.

Great！@Professor Lange. So how do usually test the "reproductive integrity" of each cell line? We tyied many batches clonogenic assay and the data were not consistent yet. I am really interested in how people test the radiosensitivity for convenievce and for good quality besides clonogeic, MTT and apoptosis.

Many Thanks!

Reproductive integrity has usually been measured using the colony-forming assay, either in monolayer single cell plating experiments or in 3D (for suspension or adherent cells cultured in double layer agar culture, or in vivo as in spleen-colony (nodule) assay in mice (NSG). For tumors, the CSC survival measurement for control vs treated cells in freshly formed Spheroids (Hybrid Spheroid Assay) in 96-well ultra low attachment treated round bottomed plates, where up to 15 division by an initial CSC can be measured, is the most useful measurement.

The problem with MTT assay is that it measures proliferation of a population of cells, not the performance of individual cells. Hence, a small fast growing subpopulation dominates the result. The clonogenic assay does not have this problem. Apoptosis is seen in a subset of reproductively dead cells for most non hematological cells. If looking for apoptosis, the Annexin V + PI - cells is the best assay because it detects cells at the earliest stages of apoptosis.

Thanks professor Lange!

Your answers provided lots of knowledge of great value! Though I have been done these experiments for years, the depth of understanding into them should be strenthened still. I appreciate it very much!

Christopher Lange

In my opinion, despite different radiosensitivities, the dose response relationship for proliferation in most cells can be J-shaped (low doses may stimulate proliferation, regardless of radiosensitivity). However, the max dose that leads to a higher proliferation may be very low in some cells. Rajan and Pandey have recently shown that in contrast to the tumoricidal effects seen at high doses, human lung adenocarcinoma (A549) cells (known to show low dose hyper-radiosensitivity (HRS)) irradiated with low doses of alpha radiation were more proliferative and tumor volume increased both in vitro and in vivo.

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Thanks very much!

@SMJ Mortazavi