Research progress of highly selective mTOR inhibitors

PI3K/AKT/mTOR is an important signaling pathway in cells, which is related to key regulators such as metabolism, cell growth, proliferation and survival in the body, and is over-activated in cancer and neurodegenerative diseases [1]. The specific process of its signaling pathway is as follows: PIP3 binds to the signaling proteins AKT and PDK1 in the cell, prompting PDK1 to phosphorylate the AKT protein to cause its activation; activated AKT phosphorylates a variety of enzymes, kinases and other downstream factors in the signaling pathway, and then participates in cell proliferation , Differentiation, apoptosis and glucose transport and other cell functions.
mTOR (mammalian target of rapamycin) is a serine/threonine protein kinase downstream of the PI3K/Akt signaling pathway. Its C-terminus is homologous to the catalytic domain of phosphatidylinositol kinase (PI3K) and belongs to an important eukaryotic Cell signals can coordinate cell growth and metabolism, affect transcription and protein synthesis, regulate cell apoptosis, autophagy, etc. It has been found that mTOR is activated in various cellular processes, such as tumor formation, angiogenesis, insulin resistance, and fat Formation and activation of lymphocytes, and expression disorders in a variety of cancers and type 2 diabetes.

The specific definition composition and structure of mTOR

mTORC1 is composed of mTOR, Raptor and mLST8, as well as non-core components PRAS40 and Deptor, where mTOR is the catalytic subunit of the complex; Raptor is a regulatory protein of mTOR, which binds to the TOR signal motif to promote the recruitment of mTORC1 substrates; mLST8 and mTORC1 catalyze The domain is related and can stabilize kinase activation. When the activity of mTORC1 decreases, PRAS40 and Deptor are recruited to further inhibit mTORC1 expression; and when mTORC1 is activated, PRAS40 and Deptor are directly phosphorylated, reducing their inhibitory effect and further activating mTORC1 signaling.

The constituent proteins of mTORC2 mainly include Rictor, mSin1, mSLT8 and Protor. Rictor, which is less conservative in eukaryotes, can interact with Protor-1; the function of mLST8 is to maintain the interaction between Rictor and mTOR, and it can also interact with Rictor. Participate in the regulation of the phosphorylation of Akt and PKCa hydrophobic groups.

mTOR effect and mechanism

mTOR participates in multiple signaling pathways in the body, including:

1. The mTOR signaling pathway can affect gene transcription and protein synthesis, and plays an important role in cell growth and proliferation.

2. The mTOR signaling pathway affects the expression of cytokines in T cells and participates in immunosuppression.

3. The mTOR signaling pathway can affect cell proliferation, making it a new target for anti-tumor therapy.

4. The mTOR signaling pathway also plays an important role in regulating exercise metabolism and other diseases.

mTOR includes two different complexes, mTORC1 and mTORC2. Both of these complexes belong to the phosphatidylinositol 3-kinase-related kinase (PIKK) protein family, but because they are located in different subcellular regions, their activation and The function is also different, which in turn can regulate different cell processes. mTORC1 mainly promotes protein synthesis, adipogenesis, energy metabolism, inhibits autophagy and lysosome formation; while mTORC2 plays an important role in actin cytoskeleton, cell survival and metabolism.

The correlation between mTOR and disease

• The mTOR inhibitor rapamycin has been proven to extend the life of mice

In some dietary regimens, limiting calories and methionine reduces mTOR activity and inhibits mitochondria, leading to longer life.

• Activating mTOR signal transduction will promote the occurrence of tumors

Disturbance of mTOR activity has been found in many cancers, including breast cancer, prostate cancer, lung cancer, melanoma, bladder cancer, brain cancer, and kidney cancer. The most common tumor suppressor gene is the mutation of PTEN gene. PTEN phosphatase negatively affects mTOR signal transduction by interfering with the action of PI3K, the upstream effector of mTOR.

• Alzheimer’s disease

In the brain of Alzheimer’s disease patients, mTOR signaling is overactive, and mTOR signaling is closely related to the presence of β-amyloid. In vitro studies have shown that β-amyloid is an activator of the PI3K/AKT pathway, which in turn can activate mTOR.

• Protein synthesis and cell growth

The activation of mTORC1 is necessary for human muscle protein synthesis and skeletal muscle hypertrophy. The continuous inactivation of mTORC1 signaling in skeletal muscle will cause the loss of muscle mass and strength during muscle atrophy in the elderly, as well as cancer and muscle atrophy due to lack of physical activity. .

• Lysosome damage inhibits mTOR and induces autophagy

The regulation of autophagy by mTOR is essentially the regulation between growth and metabolism. Autophagy is when the cell’s nutrients or energy are insufficient, in order to maintain its basic survival needs, the cell will degrade it through lysosomes. Essential proteins, as well as some relatively redundant organelles, to supply the body’s material and energy. Active mTORC1 is located on the lysosome. When the lysosomal membrane is damaged by various exogenous or endogenous agents (such as invading bacteria, membrane permeable chemicals, and producing osmotic active products), mTOR will be inhibited.

• Scleroderma

Scleroderma, also called systemic sclerosis, is a chronic systemic autoimmune disease characterized by hardening of the skin, which can severely affect internal organs. mTOR plays a role in fibrotic diseases and autoimmunity, and is currently being studied as a treatment for scleroderma by blocking the mTORC signal transduction pathway.

The direction of mTOR treatment

• Prevent transplant rejection

mTOR inhibitors, such as rapamycin, have been used to prevent transplant rejection.

• Glycogen Storage Disease

Rapamycin can inhibit mTORC1, thereby increasing the phosphorylation of GS (glycogen synthase) in skeletal muscle. This is a potential new treatment for glycogen storage diseases, involving the accumulation of glycogen in muscles.

• Anti-cancer

mTOR inhibitors have been used to treat a variety of malignant tumors, including renal cell carcinoma, pancreatic cancer, and breast cancer. However, the specific mechanism of action of these drugs is not very clear. Research predicts that it will affect tumor angiogenesis and G1/S conversion Come to work.

• Anti-aging

mTOR inhibitors can be used to treat and prevent age-related diseases such as neurodegenerative diseases. After short-term treatment with mTOR inhibitors, among the elderly (65 years and older), the number of infections in the treated subjects within one year cut back.

The history of mTOR inhibitors

mTOR belongs to the PI3K-related kinase family. It is involved in mediating growth, nutrition, energy acquisition, etc. to regulate cell proliferation, apoptosis, etc., and mTOR is a key position in tumor signaling pathways, so mTOR inhibitors are widely used as tumor targets To treatment.

Sirolimus (rapamycin), everolimus, temsirolimus, and Ridaforolimus are the first-generation inhibitors of mTOR, and they are collectively called rapamycin and its derivatives. The first generation of mTOR inhibitors mainly inhibit the complex mTORC1, which may cause negative feedback on the PI3K signaling pathway to be affected, thereby enhancing the phosphorylation activity of AKT, making patients with drugs prone to drug resistance.

The second-generation mTOR inhibitor can simultaneously inhibit the complexes mTORC1 and mTORC2, and theoretically can reduce the phosphorylation of AKT by blocking mTORC2. The second-generation mTOR inhibitors are now in clinical trials, including OSI027s, INK128, AZD8055, AZD2014, etc.

Rapalink, the third-generation mTOR inhibitor, is a more powerful drug by linking two drugs, rapamycin and MLN0128, in molecular structure. Rapalink can enter cancer cells and turn off the mTOR signal. The ability of Rapalink to inhibit tumor growth was tested in animal experiments and found that it can reduce the size of tumors that are resistant to first or second generation mTOR inhibitors.

The latest research progress of mTOR inhibitors

The recently reported PQR309(1)[2], a PI3K/mTOR inhibitor with brain permeability and oral biological activity, is currently in phase II clinical trials for the treatment of lymphoma and solid tumors. By introducing substituents with specific spatial requirements and certain electronic properties, a highly selective and efficient mTOR inhibitor PQR620 has been developed (3) [3]. The main idea is to increase the binding affinity to mTOR kinase by replacing the trifluoromethyl group in PQR309(1) with a difluoromethyl group, and then use the introduction of a morpholine group to reduce PI3K binding.

mTOR can promote cell proliferation, growth and survival, and is over-activated in many tumors and central nervous system diseases. PQR620(3) showed the selectivity of mTOR over PI3K and protein kinase, and effectively prevented the growth of cancer cells in 66 cancer cell line groups. In C57BL/6J mice and Sprague Dawley, the maximum concentration in plasma and brain (Cmax) is reached after 30 minutes, and the half-life (t1/2) is> 5 hours; in ovarian cancer mouse xenograft model (OVCAR-3) , PQR620(3) can obviously inhibit tumor growth after daily administration, and it has good tolerance in rats and mice. In short, pre-clinical data shows that PQR620(3) can effectively and selectively inhibit mTOR kinase, and has anti-tumor effects in vitro and in vivo, indicating that the compound is worthy of further research and testing.

References:

1, Saxton, R. A; Sabatini, D. M. mTOR signaling ingrowth, metabolism, and disease. Cell 2017, 168, 960– 976.

2, Beaufils, F;Cmiljanovic, N; et al. 5-(4, 6-dimorpholino-1, 3, 5-triazin-2-yl)-4-(trifluoromethyl)pyridin-2-amine (PQR309), a potent, brain-penetrant, orally bioavailable,pan-class I PI3K/mTOR inhibitor as clinical candidate in oncology. J. Med.Chem. 2017, 60, 7524-7538.

3, Denise Rageot, Thomas Bohnacker, et al. Discoveryand Preclinical Characterization of 5-[4,6-Bis({3-oxa-8-azabicyclo[3.2.1]octan-8-yl})-1,3,5 -triazin-2-yl]-4-(difluoromethyl)pyridin-2-amine(PQR620), a Highly Potent and Selective mTORC1/2 Inhibitor for Cancer and Neurological Disorders. J. Med. Chem. 2018, 61, 22, 10084- 10105.