Reshaping Tumor Microenvironment to Eliminate Tumor Cells by MR+KD+X

— In combination with conventional therapies for tumors such as surgery, chemoradiotherapy, and targeted therapy, exploring the feasibility and therapeutic potential of methionine restricted(MR)- ketogenic therapy(KD) based on low-methionine content yeast protein and rich in medium-chain fatty acid structured triglycerides, and combining tumor immunotherapy to reshape the tumor microenvironment(TME) into an anti-tumor immune microenvironment for the elimination of tumor cells.

Abstract  

Based on the combination of methionine restricted diet therapy to limit tumor cell growth, a nutritional ketogenic therapy rich in medium chain fatty acid structured triglycerides is constructed to inhibit tumor cell lactate synthesis, and combined with immunotherapy to reverse the tumorigenicity of the tumor microenvironment, a novel anti-tumor metabolic-immunotherapy is constructed.

Further, this anti-tumor metabolic-immunotherapy for tumors should combine the current surgery, chemoradiotherapy, and targeted therapy for the treatment of tumors. In this way, the efficacy of conventional treatment might be consolidated, the tumor microenvironment is reshaped, the immune system could be activated to fight against tumors, and reshaped tumor microenvironment could become an anti-tumor immune microenvironment to effectively inhibit and eradicate tumor cells, so as to build a new generation of tumor therapy.    

I．The importance of tumor microenvironment in tumor treatment

The latest research findings indicate that the tumor microenvironment plays a crucial role in tumor progression, including drug resistance, immune escape, and cancer metastasis. The tumor microenvironment refers to the internal environment in which tumor cells survive and metastasize. TME not only includes the tumor cells themselves, various signaling molecules, and extracellular matrix, but also includes immune cells, fibroblasts, and bone marrow-derived inflammatory cells closely related to tumor cells（Ref: The evolving tumor microenvironment: From cancer initiation to metastatic outgrowth.)。

Fig1: The Tumor Microenvironment. Quoted from: The tumor microenvironment at a glance. Journal of Cell Science. 2012.125 (23):5591-5596.

At present, research on tumor treatment in clinical practice is moving towards the direction of tumor microenvironment. It is hoped that in the future, by changing the tumor microenvironment, the growth and reproduction of tumor cells can be inhibited(Ref:Beyond genetics: driving cancer with the tumor microenvironment behind the wheel.）.

Fig2: Quoted from: Therapeutic targeting of the tumor microenvironment. Cancer Discov.  2021;11:933–59.  

II. Lactic acid production is an important characteristic of the tumor microenvironment

Metabolic reprogramming is one of the important characteristics of tumor cells, and aerobic glycolysis, also known as the "Warburg effect," is crucial for the rapid proliferation, invasion, and metastasis of tumor cells. The large amount of lactic acid produced by glycolysis in the tumor microenvironment was previously considered as a metabolic waste, but recent studies have shown that lactic acid plays a role in promoting tumor progression（Ref:The Tumor Metabolic Microenvironment: Lessons from Lactate）.

Fig3: The roles of lactate in tumor microenvironment (TME). Lactate can be strongly immunosuppressive in the tumor microenvironment (TME) or can act as a molecule that helps tumor cells to regenerate NADPH and thus maintain redox balance and support their biosynthetic demands. The low pH and low glucose concentration in the TME also support the immunosuppressive function of the TME. Lactate directly or indirectly influences every cell in the TME.

Quoted from: Lactate from the tumor microenvironment - A key obstacle in NK cell-based immunotherapies. Frontiers in Immunology. Mini Review. Oct.18. 2022.

Tumor cells export metabolic waste such as lactate into the TME to form an acidic environment. The accumulation of lactic acid in the tumor microenvironment has been shown to promote tumor progression. High concentrations of lactic acid can be transported into cells as fuel substrates for metabolism. Lactic acid can promote tumor invasion and metastasis, and is crucial for tumor angiogenesis. In addition, an increasing number of research findings indicate that lactate in the tumor microenvironment can exert immunosuppressive functions, promoting tumor development by inducing and recruiting immunosuppressive related cells and molecules (Ref: Emerging Role of Extracellular pH in Tumor Microenvironment as a Therapeutic Target for Cancer Immunotherapy).

A new strategy targeting pathways related to lactate production, transport, and lactylation will become a highly feasible approach for cancer treatment.

Fig 4 :Role of lactate in cancer. Excessive production of lactate by both, tumor and stromal cells, is associated with increased aggressiveness due to the extracellular acidification that also induces invasion and metastasis, inhibition of the antitumor immune response and resistance to therapy. Moreover, this lactate can be used as an alternative source of fuel by tumor cells.

Quoted from: Lactate in the Regulation of Tumor Microenviroment and Therapeutic Approaches. Frontiers in Oncology. Published:Nov. 01. 2019.

III. Combining MR therapy with nutritional ketogenic therapy, MR therapy directly inhibits tumor cell growth and nutritional ketogenic therapy inhibits excessive lactate synthesis in the tumor microenvironment. It should be applied in current surgical treatment, radiotherapy, chemotherapy, targeted therapy, and immunotherapy to further enhance efficacy.

Methionine addiction is a fundamental and common characteristic of tumor cell, known as the Hoffman effect. Research has found that brief deprivation of methionine in nutrient solution quickly leads to the loss of tumor forming ability of tumor stem cells, making them unable to induce tumorigenesis. At the same time, histone methylation levels significantly decrease, indicating that methionine plays an important role in the tumorigenic process of tumor stem cells.

1.In the field of tumor research and treatment using MR, the following scientific achievements(title of the Research Paper) have been made:

1: Dietary methionine influences therapy in mouse cancer models and alters human metabolism.

2: Synergy of Combining Methionine Restriction and Chemotherapy: The Disruptive Next Generation of Cancer Treatment.

3. Methionine Restriction Reduces Lung Cancer Progression and Increases Chemotherapy Response.

Fig. 5. Methionine-mediated methylation recruits UHRF1 to regulate cGAS methylation and its dissociation from chromatin and remodel the tumor immune microenvironment.

Quoted from: Methionine restriction and antitumor immunity. Trends Cancer. 2023.9(9): 705–706.

MR therapy has greater practical value in addressing the high dependence of tumor stem cells on methionine. Tumor stem cells play a crucial role in the growth, recurrence, and metastasis of cancer. They can not only replicate themselves, but also transform into various types of cancer cells, making them particularly difficult to deal with in cancer treatment. 

2. Targeting the increased lactate synthesis in the tumor microenvironment as a therapeutic target, ketogenic therapy could inhibit TME lactate synthesis. Please refer to the following research and clinical treatment results for the reference series.

Fig. 6: Proposed model of KD-induced reprogramming of an antitumor immune response: KD induces a decrease (↓) in glucose and lactate levels but an increase (↑) in ketone bodies, primarily betahydroxybutyrate (BHB). KD promotes anti-tumor immunity

Quoted from: Overcoming immunosuppression in cancer: how ketogenic diets boost immune checkpoint blockade. Cancer Immunology, Immunotherapy. Published online:Nov.13. 2024. 

a: Ketogenic diet therapy inhibits lactate production in the tumor microenvironment（Ref: Decline of Lactate in Tumor Tissue After Ketogenic Diet: In Vivo Microdialysis Study in Patients with Head and Neck Cancer.）

b: Ketogenic diet therapy enhances efficacy in cancer immunotherapy（Ref: Overcoming immunosuppression in cancer: how ketogenic diets boost immune checkpoint blockade.）.

IV. Constructing methionine restricted-nutritional ketogenic therapy for the treatment of tumors

Nutritional ketosis can be defined as intentionally restricting the intake of carbohydrates in the diet to accelerate ketone production, induce metabolic effects, stabilize blood sugar, minimize insulin release, and alleviate downstream synthetic metabolism and tumorigenic effects of long-term insulin resistance. A well formulated ketogenic diet consists of 5-10% carbohydrates.

Figure 7. Ketogenic diet mechanism of action as a cancer therapy, (→), activation; (┬), inhibition.

Quoted from: Ketogenic Diet in Cancer Prevention and Therapy: Molecular Targets and Therapeutic Opportunities. Curr. Issues Mol. Biol. 2021.43:558-589.

There are also a few research reports that ketone bodies are not conducive to effective treatment of tumors (Ref: An unexpected role for the ketogenic diet in triggering tumor metastasis by modulating BACH1- mediated transcription.).

The main component currently used in low-carbon ketogenic therapy is triglycerides containing medium chain fatty acids. This type of oil includes coconut oil, palm kernel oil, natural medium chain fatty acid glycerides, and artificially synthesized structural lipids - medium long chain fatty acid triglycerides. Due to the fact that coconut oil and palm kernel oil have a saturated fatty acid content of 90% (while lard has a saturated fatty acid content of only 40%), they are widely used in the human body. In addition, these patients often have cardiovascular diseases, which may lead to serious cardiovascular side effects. The American Heart Association strongly opposes their use. Pure medium chain fatty acid glycerides (caprylic acid glycerides) are highly irritating to the gastrointestinal and biliary tracts of the human body, causing symptoms such as abdominal pain, nausea, and vomiting, which prevent patients from using them for extended periods of time as required by the treatment course.

Based on human safety, clinical efficacy, human tolerance, and patient convenience, rich in medium chain fatty acid structured triglycerides might become the most superior product for low-carbon ketogenic therapy. A novel nutritional ketogenic therapy is constructed based on the use of medium-long chain fatty structured triglycerides and high content resistant starch as components.

Based on low content methionine yeast protein (yeast protein has better nutritional value than the other two low methionine soybean concentration proteins and collagen) and rich in medium chain fatty acid structured triglycerides, combined with yeast extract (depurine) rich in B vitamins and  multiple coenzyme components and high content resistant starch, a new nutritional methionine restricted -ketogenic therapy is constructed (MR inhibits tumor cell growth, ketone body energy supply inhibits lactate synthesis in the anti-tumor immune microenvironment), which rapidly generates ketones to replace glucose energy supply, overcomes the main side effect of ketogenic therapy - keto flu , and increases the adhesion of this therapy. MR combined with ketogenic diet therapy makes it easier to quantify and control the daily intake of Methionine. This achieves the goal of truly applying it to clinical treatment.  So that it could be truly applied to clinical treatment.

At the same time, the application of high content resistant starch in nutritional ketogenic diet therapy can increase the adhesion of this therapy without changing dietary habits.

This new anti-tumor metabolite immunotherapy would be applied in current cancer surgery, radiotherapy, chemotherapy, targeted therapy, and immunotherapy to further enhance efficacy and bring new hope to anti-tumor treatment.

V. The Extended application fields of methionine restricted- nutritional ketogenic therapy in the future.

According to the principle, this new therapy can be further applied in the following medical fields:

1.    May Enable PI3K inhibitor drugs to exert the expected high anti-tumor efficacy(Ref: Oncogenic PI3K Promotes Methionine Dependency in Breast Cancer Cells Through the Cystine-Glutamate Antiporter xCT）.  

2.The enhanced CAR-T cell therapy can achieved better therapeutic effects （Ref:1、Effects of methionine deficiency on B7H3-DAP12-CAR-T cells in the treatment of lung squamous cell carcinoma。2. Very-low-carbohydrate diet enhances human T-cell immunity through immunometabolic reprogramming.）.

3.Stem cell therapy has a promoting effect(Ref:1.Dietary interventions as regulators of stem cell behavior in homeostasis and disease。2.Ketone Body Signaling Mediates Intestinal Stem Cell Homeostasis and Adaptation to Diet. 3. CRISPR–Cas9 screens reveal regulators of ageing in neural stem cells.).

4.Tumor stem cells receive more effective treatment（Ref:1.Methionine Restriction Reduces Lung Cancer Progression and Increases Chemotherapy Response. 2. Synergy of Combining Methionine Restriction and Chemotherapy: The Disruptive Next Generation of Cancer Treatment.）.

Note: This article is my understanding and supposition of tumor occurrence, progression, and treatment. The occurrence, progression, and treatment of tumors have always been the very difficult problems to overcome, so there certainly are shortcomings and inaccuracies in this article.

Thank you for your reading.