Ferroptosis in Cancer Immunotherapy—Implications for Hepatocellular Carcinoma

Round 1

Reviewer 1 Report

 

Comments/ Minor Edits:

Comments

Comment1: If possible include figures (or one combined figure) for sections 2.4 and 2.5

Comment 2: In section 2/3: Following up on Lines 321-323, it is also important to discuss about heme/heme degradation/ Heme oxygenases and the importance of heme sequestration to exert anti-tumor activities. Since heme homeostasis is also closely related to iron metabolism in cells and it is central for tumorigenesis in most forms of cancers

Comment 3: Figure 2 is “too simple”. If possible try to add more details such as molecular targets and MOA of each molecule in brief

Comment 4: More pre-clinical studies mainly to describe MOA and toxicity profiles can be discussed in some detail in the body of the review. Also, discussion on studies that combine ferroptosis with ICIs can make review more attractive

Comment 5: Importance of iron for functions of the immune system should be discussed and how induction of ferroptosis with different agents impacts functioning of immune system can be discussed in some detail

Minor Edits

1. Line 12: with “a” low survival rate
2. Line 35: rounding of the cell, and
3. Line 55: multi-kinase
4. Line 97: Lipid peroxidation and iron accumulation (in order)
5. Line 144 and 411: also
6. Line 403: Several screening studies that focus on identifying….
7. Line 532: remove colon (:) and rephrase the sentence
8. Line 557: A variety of clinical trials “are” ongoing…
9. Line 572-574: Revise sentence. Since its discovery in 2012, extensive research on ferroptosis has helped us understand iron-dependent cell death mechanisms at molecular levels..
10. Line 622: non-apoptotic
11. Line 635: We can be optimistic about the future

Author Response

• Comment1: If possible include figures (or one combined figure) for sections 2.4 and 2.5
  • We thank the reviewer for this suggestion and added a figure for sections 2.4 and 2.5 in the revised version of the manuscript (Figure 2).
• Comment 2: In section 2/3: Following up on Lines 321-323, it is also important to discuss about heme/heme degradation/ Heme oxygenases and the importance of heme sequestration to exert anti-tumor activities. Since heme homeostasis is also closely related to iron metabolism in cells and it is central for tumorigenesis in most forms of cancers.
  • We thank the reviewer for this comment and have added this important topic to the revised version of the manuscript. The role of heme in iron metabolism is discussed in section 2.2, the importance of heme sequestration in tumor therapy can be found in section 3 (introduction to ferroptosis in cancer therapy).
• Comment 3: Figure 2 is “too simple”. If possible, try to add more details such as molecular targets and MOA of each molecule in brief
  • We agree with the reviewer that Figure 2 (now Figure 3) was quite simple before and have added more details. We tried to illustrate the underlying mechanism of action for each class of molecule without “overloading” the figure as additional information can be found in Table 1.
• Comment 4: More pre-clinical studies mainly to describe MOA and toxicity profiles can be discussed in some detail in the body of the review. Also, discussion on studies that combine ferroptosis with ICIs can make review more attractive
  • We have added discussion on MOA as well as toxicity profiles in the applicable section for each molecule where information was available. Please see references [96], [97] (erastin), [52] (RSL3), [126] (SAS), [126], [127], [128] (Altretamine). Discussion on combination of ICIs with ferroptosis has been included in the new chapter 3.7 (Ferroptosis in cancer immunotherapy).
• Minor Edits

1. Line 12: with “a” low survival rate
2. Line 35: rounding of the cell, and
3. Line 55: multi-kinase
4. Line 97: Lipid peroxidation and iron accumulation (in order)
5. Line 144 and 411: also
6. Line 403: Several screening studies that focus on identifying….
7. Line 532: remove colon (:) and rephrase the sentence
8. Line 557: A variety of clinical trials “are” ongoing…
9. Line 572-574: Revise sentence. Since its discovery in 2012, extensive research on ferroptosis has helped us understand iron-dependent cell death mechanisms at molecular levels..
10. Line 622: non-apoptotic
11. Line 635: We can be optimistic about the future

We thank the reviewer for thorough reading of our manuscript, all minor edits have been incorporated into the revised version of the manuscript. 

Reviewer 2 Report

The manuscript by Kusnick et al. “Ferroptosis in cancer immunotherapy –  implications for hepatocellular carcinoma” gives an extensive overview on the role of ferroptosis in cancer immunotherapy and provides insight into therapeutic strategy. Targeting ferroptosis in cancer is an emerging topic with high potential and this manuscript covers a large body of published work including very recent studies. I only have a few minor concerns:

 

1. The most important debate is whether a strategy to induce ferroptosis can only kill cancer cells without damaging the immune cells, as immune cells are also susceptible to ferroptosis. It would be better if recent studies on this issue were discussed. (Cell Metab. 2021 May 4;33(5):1001-1012.e5. doi: 10.1016/j.cmet.2021.02.015. Cell Rep . 2021 Jun 15;35(11):109235. doi: 10.1016/j.celrep.2021.109235.

J Clin Invest . 2021 Apr 15;131(8):e139434. doi: 10.1172/JCI139434.)

2. Regarding sorafenib, although there are many reports that sorafenib induces ferroptosis, especially in HCC, the concentration used in vitro is quite high, and there is also controversy as to whether ferroptosis is really necessary for anti-tumor effect in vivo. In particular, ferroptosis is not actually considered in the clinical design of the combination of sorafenib and immunotherapy. Therefore, the description of sorafenib in clinical trials needs to be slightly toned down. However, this is my point of view, and I would like to hear the author's thoughts on it in more detail.

Author Response

• The most important debate is whether a strategy to induce ferroptosis can only kill cancer cells without damaging the immune cells, as immune cells are also susceptible to ferroptosis. It would be better if recent studies on this issue were discussed. (Cell Metab. 2021 May 4;33(5):1001-1012.e5. doi: 10.1016/j.cmet.2021.02.015. Cell Rep . 2021 Jun 15;35(11):109235. doi: 10.1016/j.celrep.2021.109235. J Clin Invest . 2021 Apr 15;131(8):e139434. doi: 10.1172/JCI139434.).
  • We thank the reviewer for this important comment and now discuss the suggested studies (see References [180], [173], [170]) as well as some additional ones on this topic (see References [79], [171]) in the respective sections of the manuscript.

 

• Regarding sorafenib, although there are many reports that sorafenib induces ferroptosis, especially in HCC, the concentration used in vitro is quite high, and there is also controversy as to whether ferroptosis is really necessary for anti-tumor effect in vivo. In particular, ferroptosis is not actually considered in the clinical design of the combination of sorafenib and immunotherapy. Therefore, the description of sorafenib in clinical trials needs to be slightly toned down. However, this is my point of view, and I would like to hear the author's thoughts on it in more detail.
  • We agree with the reviewer that the contribution of ferroptosis to the efficacy of sorafenib is not clear at the moment. However, there is evidence that sorafenib has additional functions besides it´s kinase inhibiting activity and might trigger off-target effects. We do believe that ferroptosis could very well be one of these functions as sorafenib has been shown to inhibit system x_c^-. We realize that this is controversial but think that this is due to limited data, since - as the reviewer pointed out - ferroptosis is not considered in clinical trials including sorafenib at the moment. Therefore, we rewrote the chapter on Clinical trials in HCC treatment (now chapter 3.8) trying to discuss this controversy in more detail and added some thoughts on how ferroptosis might be addressed better in clinical trials (e.g. Combinations with drugs that prevent resistance to ferroptosis).

Round 2

Reviewer 1 Report

The authors addressed most of my previous comments and added appropriate details to the manuscript in the form of text and figures. 

Comment-1

Always quote the original paper of the study: for example, for heme sequestering peptides 

Line 412-414. Please quote the original paper which discusses heme sequestering peptides and their impact on cancer progression discussed in detail  in "Elevated Heme Synthesis and Uptake Underpin Intensified Oxidative Metabolism and Tumorigenic Functions in Non–Small Cell Lung Cancer Cells" 

Thank you for the changes. The manuscript can be accepted in the journal after minor edits.

 

 

Author Response

We thank the reviewer for this important comment and now updated the reference quoting the original paper of the study (Ref 91).