Extensive Shrinkage and Long-term Stable Disease in a Teenage Female Patient With High-grade Glioma Treated With Temozolomide and Radiation in Combination With Oral Recombinant Methioninase and a Low-methionine Diet

BACKGROUND/AIM

Gliomas are the most common and recalcitrant malignant primary brain tumors. All cancer types are addicted to methionine, which is a fundamental and general hallmark of cancer known as the Hoffman effect. Particularly glioma cells exhibit methionine addiction. Because of methionine addiction, [11C]-methionine positron emission tomography (MET-PET) is widely used for glioma imaging in clinical practice, which can monitor the extent of methionine addiction. Methionine restriction including recombinant methioninase (rMETase) and a low-methionine diet, has shown high efficacy in preclinical models of gliomas, especially in combination with chemotherapy. The aim of the present study was to determine the efficacy of methionine restriction with oral rMETase (o-rMETase) and a low-methionine diet, combined with radiation and temozolomide (TMZ), on a teenage female patient with high-grade glioma.

CASE REPORT

A 16-year-old girl was diagnosed with high-grade glioma. Magnetic resonance imaging (MRI) showed a left temporal-lobe tumor with compression to the left lateral ventricle and narrowing of sulci in the left temporal lobe. After the start of methionine restriction with o-rMETase and a low-methionine diet, along with TMZ combined with radiotherapy, the tumor size shrunk at least 60%, with improvement in the left lateral ventricle and sulci. The patient's condition remains stable for 19 months without severe adverse effects.

CONCLUSION

Methionine restriction consisting of o-rMETase and a low-methionine diet, in combination with radiation and TMZ as first-line chemotherapy, were highly effective in a patient with high-grade glioma.

Targeting Methionine Addiction Combined With Low-dose Irinotecan Arrested Colon Cancer in Contrast to High-dose Irinotecan Alone, Which Was Ineffective, in a Nude-mouse Model

BACKGROUND/AIM

Colorectal cancer (CRC) is the third-leading cause of death in the world. Although the prognosis has improved due to improvement of chemotherapy, metastatic CRC is still a recalcitrant disease, with a 5-year survival of only 13%. Irinotecan (IRN) is used as first-line chemotherapy for patients with unresectable CRC. However, there are severe side effects, such as neutropenia and diarrhea, which are dose-limiting. We have previously shown that methionine restriction (MR), effected by recombinant methioninase (rMETase), lowered the effective dose of IRN of colon-cancer cells in vitro. The aim of the present study was to evaluate the efficacy of the combination of low-dose IRN and MR on colon-cancer in nude mice.

MATERIALS AND METHODS

HCT-116 colon-cancer cells were cultured and subcutaneously injected into the flank of nude mice. After the tumor size reached approximately 100 mm3, 18 mice were randomized into three groups; Group 1: untreated control on a normal diet; Group 2: high-dose IRN on a normal diet (2 mg/kg, i.p.); Group 3: low-dose IRN (1 mg/kg i.p.) on MR effected by a methionine-depleted diet.

RESULTS

There was no significant difference between the control mice and the mice treated with high-dose IRN, without MR. However, low-dose IRN combined with MR was significantly more effective than the control and arrested colon-cancer growth (p=0.03). Body weight loss was reversible in the mice treated by low-dose IRN combined with MR.

CONCLUSION

The combination of low-dose IRN and MR acted synergistically in arresting HCT-116 colon-cancer grown in nude mice. The present study indicates the MR has the potential to reduce the effective dose of IRN in the clinic.

Reduction of Tumor Biomarkers from very High to Normal and Extensive Metastatic Lesions to Undetectability in a Patient With Stage IV HER2-positive Breast Cancer Treated With Low-dose Trastuzumab Deruxtecan in Combination With Oral Recombinant Methioninase and a Low-methionine Diet

BACKGROUND/AIM

Breast cancer is the most common and the deadliest cancer among women in the world. Treatment options for HER2-positive metastatic breast cancer patients are limited. Trastuzumab deruxtecan (T-DXd), an antibody-drug conjugate (ADC), has recently been introduced as second-line chemotherapy for HER2-positive metastatic breast cancer. The aim of the present study was to evaluate the efficacy of methionine restriction with oral recombinant methioninase (o-rMETase) and a low-methionine diet combined with T-DXd, on a patient with HER2-positive recurrent stage IV breast cancer.

CASE REPORT

A 66-year-old female was diagnosed with HER2-positive metastatic breast cancer. Computed tomography (CT) indicated peritoneal dissemination, thickening of the sigmoid colon and splenic flexure and widespread bone metastases. The patient was previously treated with fulvestrant, trastuzumab, pertuzumab, paclitaxel and capecitabine which were ineffective. T-DXd was administered as a second-line chemotherapy. Since the patient experienced strong side effects, the dose of T-Dxd was decreased. The patient began methionine restriction using o-rMETase and a low-methionine diet along with T-DXd. After the start of the combined treatment, CA15-3 and CA27.29, tumor markers for breast cancer, decreased rapidly from a very high level. The levels of both tumor markers are currently normal. Additionally, peritoneal-dissemination nodules, ascites and the thickness of the sigmoid colon and splenic flexure are no longer detected on CT. The patient maintains a high performance status, without severe side effects of the combination treatment.

CONCLUSION

Methionine restriction consisting of o-rMETase and a low-methionine diet, in combination with T-DXd as second-line chemotherapy, was highly effective in a patient with HER2-positive stage IV breast cancer.

Extensive Synergy Between Recombinant Methioninase and Eribulin Against Fibrosarcoma Cells But Not Normal Fibroblasts

BACKGROUND/AIM

The aim of the present study was to determine the synergy of recombinant methioninase (rMETase) and the anti-tubulin agent eribulin on fibrosarcoma cells, in comparison to normal fibroblasts, in vitro.

MATERIALS AND METHODS

HT1080 human fibrosarcoma cells and HS27 human fibroblasts were used for in vitro experiments. Four groups were analyzed in vitro: No-treatment control; eribulin; rMETase; eribulin plus rMETase. Dual-color HT1080 cells which express red fluorescent protein (RFP) in the cytoplasm and green fluorescent protein (GFP) in the nuclei were used to visualize cytoplasmic and nuclear dynamics during treatment.

RESULTS

Eribulin combined with rMETase greatly decreased the viability of HT 1080 cells. In contrast, eribulin combined with rMETase did not show synergy on Hs27 normal fibroblasts. Eribulin combined with rMETase also caused more fragmentation of the nucleus than all other treatments.

CONCLUSION

The combination treatment of eribulin plus rMETase demonstrated efficacy on fibrosarcoma cells in vitro. In contrast, normal fibroblasts were resistant to this combination, indicating the potential clinical applicability of the treatment.

Selective Synergy of Rapamycin Combined With Methioninase on Cancer Cells Compared to Normal Cells

BACKGROUND/AIM

Rapamycin and recombinant methioninase (rMETase) have both shown efficacy to target cancer cells. Rapamycin prevents cancer-cell growth by inhibition of the mTOR protein kinase. rMETase, by degrading methionine, targets the methionine addiction of cancer and has been shown to improve the efficacy of chemotherapy drugs. In the present study, we aimed to determine if a synergy exists between rapamycin and rMETase when used in combination against a colorectal-carcinoma cell line, compared to normal fibroblasts, in vitro.

MATERIALS AND METHODS

The half-maximal inhibitory concentrations (IC50) of rapamycin alone and rMETase alone against the HCT-116 human colorectal-cancer cell line and Hs-27 human fibroblasts were determined using the CCK-8 Cell Viability Assay. After calculating the IC50 of each drug, we determined the efficacy of rapamycin and rMETase combined on both HCT-116 and Hs-27.

RESULTS

Hs-27 normal fibroblasts were more sensitive to rapamycin than HCT-116 colon-cancer cells (IC50=0.37 nM and IC50=1.38 nM, respectively). HCT-116 cells were more sensitive to rMETase than Hs-27 cells (IC50 0.39 U/ml and IC50 0.96 U/ml, respectively). The treatment of Hs-27 cells with the combination of rapamycin (IC50=0.37 nM) and rMETase (IC50=0.96 U/ml) showed no significant difference in their effect on Hs-27 cell viability compared to the two drugs being used separately. However, the treatment of HCT-116 cells with the combination of rapamycin (IC50=1.38 nM) and rMETase (IC50=0.39 U/ml) was able to decrease cancer-cell viability significantly more than either single-drug treatment.

CONCLUSION

Rapamycin and rMETase, when used in combination against colorectal-cancer cells, but not normal fibroblasts, in vitro, have a cancer-specific synergistic effect, suggesting that the combination of these drugs can be used as an effective, targeted cancer therapy.

[11C] Methionine-PET Imaging as a Cancer Biomarker for Methionine Addiction and Sensitivity to Methionine-restriction-based Combination Chemotherapy

BACKGROUND/AIM

Methionine addiction is a fundamental and universal hallmark of cancer, termed the Hoffman effect. Methionine addiction of cancer is greater than glucose addiction, termed the Warburg effect, as shown by the comparison of PET imaging with [11C]methionine and [18F]fluorodeoxyglucose. The aim of the present study was to determine whether [11C]methionine PET (MET-PET) images could be a biomarker of methionine addiction of cancer and potential response to methionine-restriction-based combination chemotherapy.

PATIENTS AND METHODS

In the present study a patient with invasive lobular carcinoma of the breast metastatic to axillary lymph nodes was imaged by both MET-PET and [18F]fluorodeoxyglucose PET (FDG-PET) before and after combination treatment with methionine restriction, comprising a low-methionine diet and methioninase, along with first-line chemotherapy.

RESULTS

MET-PET gave a much stronger and precise image of the patient's metastatic axillary lymph nodes than FDG-PET. The patient had a complete response to methionine restriction-based chemotherapy as shown by MET-PET.

CONCLUSION

MET-PET imaging is a biomarker of methionine-addicted cancer and potential response to methionine-restriction-based chemotherapy.

Recombinant Methioninase Decreased the Effective Dose of Irinotecan by 15-fold Against Colon Cancer Cells: A Strategy for Effective Low-toxicity Treatment of Colon Cancer

BACKGROUND/AIM

Irinotecan (IRN), a topoisomerase I inhibitor and pro-drug of SN-38, is first-line treatment of colon cancer as part of FOLFIRI and FOLFOXIRI combination chemotherapy. However, IRN causes dose-limiting adverse events such as neutropenia and diarrhea. Dose reductions are sometimes required, which reduce efficacy. Recombinant methioninase (rMETase) targets the fundamental basis of cancer, methionine addiction, known as the Hoffman effect, and enhances the efficacy of numerous chemotherapy drugs. The present study determined the efficacy of rMETase when administered in combination with IRN.

MATERIALS AND METHODS

Cell viability was assessed by cultivating the HCT-116 human colorectal cancer cell line in 96-well plates at 1×103 cells per well in Dulbecco's modified Eagle's medium (DMEM). Subsequently, HCT-116 cells were treated with increasing concentrations of SN-38, the active form of IRN, ranging from 0.5 nM to 32 nM, and/or rMETase ranging from 0.125 to 8 U/ml. After treatment for 72 h, the half-maximal inhibitory concentration (IC50) of SN-38 alone and rMETase alone for HCT-116 cells were determined. Using the IC50 concentration of rMETase, we determined the IC50 of SN-38 in combination with rMETase. Cell viability was determined with the cell-counting Kit-8 with the WST-8 reagent..

RESULTS

The IC50 of rMETase alone for the HCT-116 cells was 0.55 U/ml, and the IC50 of IRN (SN-38) alone was 3.50 nM. rMETase at 0.55 U/ml lowered the IC50 of SN-38 to 0.232 nM (p<0.0001), a 15-fold reduction.

CONCLUSION

rMETase and IRN are strongly synergistic, giving rise to the possibility of lowering the effective dose of IRN for the treatment of patients with colon cancer, thereby reducing its severe toxicity. This new strategy will allow more patients with cancer to be effectively treated with IRN.

The Combination of Methioninase and Ethionine Exploits Methionine Addiction to Selectively Eradicate Osteosarcoma Cells and Not Normal Cells and Synergistically Down-regulates the Expression of C-MYC

BACKGROUND/AIM

The fundamental and general hallmark of cancer cells, methionine addiction, termed the Hoffman effect, is due to overuse of methionine for highly-increased transmethylation reactions. In the present study, we tested if the combination efficacy of recombinant methioninase (rMETase) and a methionine analogue, ethionine, could eradicate osteosarcoma cells and down-regulate the expression of c-MYC.

MATERIALS AND METHODS

143B osteosarcoma cells and Hs27 normal human fibroblasts were tested. The efficacy of rMETase alone and ethionine, alone and in their combination, on cell viability was determined with the WST-8 assay on 143B cells and Hs27 cells. c-MYC expression was examined with western immunoblotting and compared in 143B cells treated with/without rMETase, ethionine, or the combination of both rMETase and ethionine.

RESULTS

143B cells were more sensitive to both rMETase and ethionine than Hs 27 cells, with the following IC50s: rMETase (143B: 0.22 U/ml; Hs27: 0.82 U/ml); ethionine (143B: 0.24 mg/ml; Hs27: 0.42 mg/ml). The combination of rMETase and ethionine synergistically eradicated 143B cells, lowering the IC50 for ethionine 14-fold compared to ethionine alone (p<0.001). In contrast, Hs27 fibroblasts were relatively resistant to the combination. The expression of c-MYC was significantly down-regulated only by the combination of rMETase and ethionine in 143B cells (p<0.001).

CONCLUSION

In the present study, we showed, for the first time, the synergistic combination efficacy of rMETase and ethionine on osteosarcoma cells in contrast to normal fibroblasts, which were relatively resistant. The combination of rMETase and ethionine down-regulated c-MYC expression in the cancer cells. The present results indicate the combination of rMETase and ethionine may reduce the malignancy of osteosarcoma cells and can be a potential future clinical strategy.

Recombinant-methioninase-producing Escherichia coli Instilled in the Microbiome Inhibits Triple-negative Breast Cancer in an Orthotopic Cell-line Mouse Model

Background/Aim

Methionine restriction by diet and recombinant methioninase (rMETase) are effective for cancer therapy by themselves or combined with chemotherapy drugs. We previously showed that oral administration of rMETase-producing Escherichia coli JM109 (E. coli JM109-rMETase) can be installed in the mouse microbiome and inhibit colon-cancer growth in a syngeneic mouse model. In the present report, we investigated the efficacy of oral administration of E. coli JM109-rMETase in an orthotopic triple-negative breast cancer (TNBC) cell-line mouse model.

Materials and Methods

First, we established orthotopic 4T1 mouse triple-negative breast cancer on an abdominal mammary gland in female athymic nu/nu nude mice aged 4-6 weeks. After tumor growth, 15 mice were divided into three groups of 5. Group 1 was administered phosphate-buffered saline (PBS) orally by gavage twice daily as a control; Group 2 was administered non-recombinant E. coli JM109 competent cells orally by gavage twice daily as a control; Group 3 was administered E. coli JM109-rMETase cells by gavage twice daily for two weeks. Tumor size was measured with calipers twice per week. On day 15, blood methionine level was examined using an HPLC method.

Results

Oral administration of E. coli JM109-rMETase inhibited 4T1 TNBC growth significantly compared to the PBS and E. coli JM109 control groups. On day 15, the blood methionine level was significantly lower in the mice administered E. coli JM109-rMETase than in the PBS control.

Conclusion

E. coli JM109-rMETase lowered blood methionine levels and inhibited TNBC growth in an orthotopic cell-line mouse model, suggesting future clinical potential against a highly recalcitrant cancer.

Recombinant Methioninase Lowers the Effective Dose of Regorafenib Against Colon-Cancer Cells: A Strategy for Widespread Clinical Use of a Toxic Drug

Background/Aim

Regorafenib is a multi-kinase inhibitor, targeting vascular endothelial growth factor receptor 2, fibroblast growth factor receptor 1 and other oncogenic kinases. Regorafenib has efficacy in metastatic colon cancer, but has severe dose-limiting toxicities which cause patients to stop taking the drug. The aim of the present study was to determine if recombinant methioninase (rMETase) could lower the effective concentration of regorafenib in vitro against a colorectal-cancer cell line.

Materials and Methods

Firstly, we examined the half-maximal inhibitory concentration (IC50) of regorafenib alone and rMETase alone for the HCT-116 human colorectal-cancer cell line. After that, using the IC50 concentration of each drug, we investigated the efficacy of the combination of regorafenib and rMETase.

Results

While both methioninase alone (IC50=0.61 U/ml) and regorafenib alone (IC50=2.26 U/ml) inhibited the viability of HCT-116 cells, the combination of the two agents was more than twice as effective as either alone. Addition of rMETase at 0.61 U/ml lowered the IC50 of regorafenib from 2.26 μM to 1.46 μM.

Conclusion

rMETase and regorafenib are synergistic, giving rise to the possibility of lowering the effective dose of regorafenib in patients, thereby reducing its severe toxicity, allowing more cancer patients to be treated with regorafenib.

Methionine Restriction Increases Exosome Production and Secretion in Breast Cancer Cells

BACKGROUND/AIM

Methionine addiction is the elevated requirement for exogenous methionine for growth and survival of cancer cells, termed the Hoffman effect. Methionine-addicted cancer cells synthesize normal or excess amounts of methionine but still need an external source of methionine. Methionine restriction (MR) by either a methionine-free medium or in vivo by a low-methionine diet or by methioninase, selectively arrests cancer cells in the late S/G2 cell cycle phase, but not normal cells. The present study focuses on the comparison of production and secretion of exosomes by cancer cells under MR and normal conditions.

MATERIALS AND METHODS

MDA-MB-231 cells (triple-negative breast cancer), containing exosomes labeled with CD63-GFP (CD63-GFP exosomes), were visualized by fluorescence microscopy. MDA-MB-231 cells expressing exosome-specific CD63-GFP were cultured in methionine-containing (MET+) or in methionine-free (MET-) DMEM conditions. Exosomes were isolated from conditioned medium of cultured MDA-MD-231 cells by ultracentrifugation and characterized by nanoparticle tracking analysis (NTA) and Western blotting.

RESULTS

When MDA-MB-231-CD63-GFP cells were cultured under MR conditions, they arrested their growth and CD63-GFP-expressing exosomes were strongly increased in the cells. MR resulted in approximately a 2-fold increase in exosome production and secretion per cell, even though cell growth was arrested. Methionine restriction thus resulted in elevated exosome production and secretion per surviving cell.

CONCLUSION

Exosome production and secretion in the cancer cells increased under MR, suggesting a relation between MR and exosome production and secretion.

Rapid Reduction of CEA and Stable Metastasis in an NRAS-mutant Rectal-Cancer Patient Treated With FOLFIRI and Bevacizumab Combined With Oral Recombinant Methioninase and a Low-Methionine Diet Upon Metastatic Recurrence After FOLFIRI and Bevacizumab Treatment Alone

BACKGROUND/AIM

The choice of chemotherapy agents for RAS-mutant colorectal cancer is limited, and prognosis is poor compared to RAS-wild-type colorectal cancer. The purpose of the present study was to evaluate the effectiveness of methionine restriction combined with chemotherapy in a patient with NRAS-mutant rectal cancer.

PATIENTS AND METHODS

A 59-year-old female was diagnosed with lung-metastatic recurrence of NRAS-mutant rectal cancer two and a half years after resection of the primary tumor. She started chemotherapy, which consisted of fluorouracil, irinotecan (FOLFIRI), and bevacizumab, in October 2020. Eight months later, stereotactic body radiation therapy (SBRT) was performed to treat the lung metastases. She stopped chemotherapy at this point and had blood tests and computed tomography (CT) scans regularly. Her CEA level increased to 139.91 ng/ml and her lung metastasis became larger by September 2022. Therefore, she was reintroduced to FOLFIRI and bevacizumab in October 2022, and also started a low-methionine diet and oral recombinant methioninase (o-rMETase) as a supplement.

RESULTS

After starting the combination therapy with o-rMETase, a low-methionine diet, FOLFIRI, and bevacizumab, blood CEA levels very rapidly decreased and were almost within the normal limits five months later. CT findings showed the lung metastasis did not grow.

CONCLUSION

Methionine restriction comprising o-rMETase and a low-methionine diet combined with first-line chemotherapy was effective in a patient with NRAS-mutant rectal cancer in which metastasis had re-occurred after first-line chemotherapy alone.

Targeting Methionine Addiction of Cancer Cells with Methioninase

All types of cancer cells are addicted to methionine, which is known as the Hoffman effect. Restricting methionine inhibits the growth and proliferation of all tested types of cancer cells, leaving normal cells unaffected. Targeting methionine addiction with methioninase (METase), either alone or in combination with common cancer chemotherapy drugs, has been shown as an effective and safe therapy in various types of cancer cells and animal cancer models. About six years ago, recombinant METase (rMETase) was found to be able to be taken orally as a supplement, resulting in anecdotal positive results in patients with advanced cancer. Currently, there are 8 published clinical studies on METase, including two from the 1990s and six more recent ones. This review focuses on the results of clinical studies on METase-mediated methionine restriction, in particular, on the dosage of oral rMETase taken alone as a supplement or in combination with common chemotherapeutic agents in patients with advanced cancer.

Colon-cancer liver metastasis is effectively targeted by recombinant methioninase (rMETase) in an orthotopic mouse model

BACKGROUND

Colorectal cancer liver metastasis (CCLM) is the most frequent cause of death of colorectal cancer. Development of novel new effective therapy is needed for CCLM patients to improve outcome. The aim of the present study was to investigate the efficacy of recombinant methioninase (rMETase) on a CCLM orthotopic mouse model of liver metastasis established using the human colon cancer cell line HT29 expressing red fluorescent protein (RFP).

MATERIALS AND METHODS

Orthotopic CCLM nude mouse models were randomized into two groups: control group (n = 6, PBS 200 µl, i.p., daily); rMETase group (n = 6, 100 units/200 µl, i.p., daily). Tumor volume was measured on day 0 and day 15. Body weight was measured twice a week. All mice were sacrificed on day 15.

RESULTS

rMETase significantly inhibited the increase of the liver metastasis as determined by RFP fluorescence area and intensity (p = 0.016 and 0.015, respectively). There was no significant difference of body weight between either group on any day.

CONCLUSIONS

The present study suggests that rMETase has future potential therapy for CCLM in the clinic.

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

All cancer cell types are methionine-addicted, which is termed the Hoffman effect. Cancer cells, unlike normal cells, cannot survive without large amount of methionine. In general, when methionine is depleted, both normal cells and cancer cells synthesize methionine from homocysteine, but cancer cells consume large amounts of methionine and they cannot survive without exogenous methionine. For this reason, methionine restriction has been shown to be effective against many cancers in vitro and in vivo. Methionine restriction arrests cancer cells in the S/G₂-phase of the cell cycle. Cytotoxic agents that act in the S/G₂-phase are highly effective when used in combination with methionine restriction due to the cancer cells being trapped in S/G₂-phase, unlike normal cells which arrest in G₁/G₀-phase. Combining methionine restriction and chemotherapeutic drugs for cancer treatment is termed the Hoffman protocol. The efficacy of many cytotoxic agents and molecular-targeted drugs in combination with methionine restriction has been demonstrated. The most effective method of methionine restriction is the administration of recombinant methioninase (rMETase), which degrades methionine. The efficacy of rMETase has been reported in mice and human patients by oral administration. The present review describes studies on anticancer drugs that showed synergistic efficacy in combination with methionine restriction, including rMETase administration. It is proposed that the next disruptive generation of cancer chemotherapy should employ current therapy in combination with methionine restriction for all cancer types.

Oncogenes and Methionine Addiction of Cancer: Role of c-MYC

BACKGROUND/AIM

Methionine addiction is a general and fundamental hallmark of cancer cells, termed the Hoffman effect. Previously Vanhamme and Szpirer showed that methionine addiction could be induced by transfection of the activated HRAS1 gene to a normal cell line. In the present study, we investigated the role of the c-MYC oncogene in methionine addiction of cancer, by comparison of c-Myc expression and malignancy of methionine-addicted osteosarcoma cells and rare methionine-independent revertants, derived from the methionine-addicted cells.

MATERIALS AND METHODS

Methionine-independent revertant 143B osteosarcoma cells (143B-R) were derived from methionine-addicted parental 143B osteosarcoma cells (143B-P), by continuous culture in medium depleted of methionine by recombinant methioninase. To compare in vitro malignancy of methionine-addicted parental cells and methionine-independent revertant cells, the following experiments were performed: for 143B-P and 143B-R cells, cell proliferation capacity was measured with a cell-counting assay, and colony-formation capacity was determined on plastic and in soft agar, all in methionine-containing Dulbecco's Modified Eagle's Medium (DMEM). Tumor growth was measured in orthotopic xenograft nude-mouse models, to compare in vivo malignancy of 143B-P and 143B-R cells. c-MYC expression was examined with western immunoblotting and compared in 143B-P and 143B-R cells.

RESULTS

143B-R cells had reduced cell proliferation capacity, compared to 143B-P cells, in methionine-containing medium (p=0.003). 143B-R cells had reduced colony formation capacity on plastic (p=0.003) and in soft agar, compared to 143B-P cells in methionine-containing medium. 143B-R cells had reduced tumor growth in orthotopic xenograft nude-mouse models, compared to 143B-P cells, (p=0.002). These results demonstrate that 143B-R methionine-independent revertant cells lost malignancy. Expression of c-MYC was reduced in 143B-R methionine-independent revertant osteosarcoma cells, compared to 143B-P cells, (p=0.0007).

CONCLUSION

The present study demonstrated that c-MYC expression is linked to malignancy and methionine addiction of cancer cells. The present study on c-MYC, and the previous study on HRAS1, suggest that oncogenes may play a role in methionine addiction, which is a hallmark of all cancers, as well as in malignancy.

Synergy of oral recombinant methioninase (rMETase) and 5-fluorouracil on poorly differentiated gastric cancer

Gastric cancer is highly malignant and recalcitrant to first line chemotherapies that include 5-fluorouracil (5-FU). Cancer cells are addicted to methionine for their proliferation and survival. Methionine addiction of cancer is known as the Hoffman effect. Methionine restriction with recombinant methioninase (rMETase) has been shown to selectively starve cancer cells and has shown synergy with cytotoxic chemotherapy including 5-FU. The present study aimed to investigate the efficacy of rMETase alone and the combination with 5-FU on poorly differentiated human gastric cancer cell lines (MKN45, NUGC3, and NUGC4) in vitro and vivo. rMETase suppressed the tumor growth of 3 kinds of poorly differentiated gastric cancer cells in vitro. The fluorescence ubiquitination-based cell cycle indicator (FUCCI) demonstrated cancer cells treated with rMETase were selectively trapped in the S/G₂ phase of the cell cycle. In the present study, subcutaneous MKN45 gastric cancer models were randomized into four groups when the tumor volume reached 100 mm³: G1: untreated control; G2: 5-FU (i.p., 50 mg/kg, weekly, three weeks); G3: oral-rMETase (o-rMETase) (p.o., 100 units/body, daily, three weeks); G4: 5-FU with o-rMETase (5-FU; i.p., 50 mg/kg, weekly, three weeks o-rMETase; p.o., 100 units/body, daily, three weeks). All mice were sacrificed on day 22. Body weight and estimated tumor volume were measured twice a week. 5-FU and o-rMETase suppressed tumor growth as monotherapies on day 18 (p = 0.044 and p = 0.044). However, 5-FU combined with o-rMETase was significantly superior to each monotherapy (p < 0.001 and p < 0.001, respectively) and induced extensive necrosis compared to other groups. The combination of 5-FU and o-rMETase shows promise for transformative therapy for poorly differentiated gastric cancer in the clinic.

Superiority of [(11)C]methionine over [(18)F]deoxyglucose for PET Imaging of Multiple Cancer Types Due to the Methionine Addiction of Cancer

Positron emission tomography (PET) is widely used to detect cancers. The usual isotope for PET imaging of cancer is [¹⁸F]deoxyglucose. The premise of using [¹⁸F]deoxyglucose is that cancers are addicted to glucose (The Warburg effect). However, cancers are more severely addicted to methionine (The Hoffman effect). [¹¹C]methionine PET (MET-PET) has been effectively used for the detection of glioblastoma and other cancers in the brain, and in comparison, MET-PET has been shown to be more sensitive and accurate than [¹⁸F]deoxyglucose PET (FDG-PET). However, MET-PET has been limited to cancers in the brain. The present report describes the first applications of MET-PET to cancers of multiple organs, including rectal, bladder, lung, and kidney. The results in each case show that MET-PET is superior to FDG-PET due to the methionine addiction of cancer and suggest that the broad application of MET-PET should be undertaken for cancer detection.

Recombinant Oral Methioninase (o-rMETase) Combined With Oxaliplatinum Plus 5-Fluorouracil Improves Survival of Mice With Massive Colon-Cancer Peritoneal Carcinomatosis

BACKGROUND/AIM

The present study aimed to determine if oral methioninase (o-rMETase) combined with oxaliplatinum (OXA) plus 5-fluorouracil (5-FU) increases survival of mice with peritoneal-carcinomatosis formed from HCT-116 green fluorescent protein (GFP)-expressing colon-cancer cells implanted intra-peritoneally in nude mice.

MATERIALS AND METHODS

HCT-116-GFP human colon-cancer cells (2×10⁶) were injected intraperitoneally in athymic nude mice. Forty-five HCT-116-GFP colon-cancer peritoneal-carcinomatosis nude-mouse models were divided into the following groups: untreated control; combination of 5-FU (50 mg/kg, once a week), plus OXA (6 mg/kg, once a week); combination of 5-FU + OXA + o-rMETase (100 unit/day). Tumor growth was followed weekly using non-invasive GFP imaging for 3 weeks. At necropsy, tumor tissue was obtained. Frozen sections were made for fluorescence imaging. Tumor tissues were also stained with hematoxylin and eosin. The date of death of all mice was recorded.

RESULTS

o-rMETase combined with 5-FU + OXA significantly reduced peritoneal growth of the HCT-116 tumor compared to the untreated control or the combination 5-FU and OXA group. Histological analysis revealed extensive necrosis induced by the o-rMETase + 5-FU + OXA combination. The combination of 5-FU plus OXA and o-rMETase achieved significantly longer survival of the mice with peritoneal carcinomatosis compared to the control or combination of 5-FU plus OXA treatments.

CONCLUSION

o-rMETase shows future clinical promise for increasing the survival of patients with peritoneal metastasis of colon cancer when combined with first-line treatment of this recalcitrant disease.

Oral Installation of Recombinant Methioninase-producing Escherichia coli into the Microbiome Inhibits Colon-cancer Growth in a Syngeneic Mouse Model

BACKGROUND/AIM

All cancer types so far tested are methionine-addicted. Targeting the methionine addiction of cancer with recombinant methioninase (rMETase) has shown great progress in vitro, in mouse models, and in the clinic. However, administration of rMETase requires multiple doses per day. In the present study, we determined if rMETase-producing Escherichia coli JM109 (E. coli JM109-rMETase) might be an effective anticancer agent when installed into the microbiome.

MATERIALS AND METHODS

E. coli JM109-rMETase was administered to a syngeneic model of MC38 colon cancer growing subcutaneously in C57BL/6 mice. JM109-rMETase was administered orally by gavage to the mice twice per day. Tumor size was measured with calipers.

RESULTS

The administration of E. coli JM109-rMETase twice a day significantly inhibited MC38 colon-cancer growth. E. coli JM109-rMETase was found in the stool of treated mice, indicating it had entered the microbiome.

CONCLUSION

The present study indicates the potential of microbiome-based treatment of cancer targeting methionine addiction.

Reversion of methionine addiction of osteosarcoma cells to methionine independence results in loss of malignancy, modulation of the epithelial-mesenchymal phenotype and alteration of histone-H3 lysine-methylation

Methionine addiction, a fundamental and general hallmark of cancer, known as the Hoffman Effect, is due to altered use of methionine for increased and aberrant transmethylation reactions. However, the linkage of methionine addiction and malignancy of cancer cells is incompletely understood. An isogenic pair of methionine-addicted parental osteosarcoma cells and their rare methionine-independent revertant cells enabled us to compare them for malignancy, their epithelial-mesenchymal phenotype, and pattern of histone-H3 lysine-methylation. Methionine-independent revertant 143B osteosarcoma cells (143B-R) were selected from methionine-addicted parental cells (143B-P) by their chronic growth in low-methionine culture medium for 4 passages, which was depleted of methionine by recombinant methioninase (rMETase). Cell-migration capacity was compared with a wound-healing assay and invasion capability was compared with a transwell assay in 143B-P and 143B-R cells in vitro. Tumor growth and metastatic potential were compared after orthotopic cell-injection into the tibia bone of nude mice in vivo. Epithelial-mesenchymal phenotypic expression and the status of H3 lysine-methylation were determined with western immunoblotting. 143B-P cells had an IC50 of 0.20 U/ml and 143B-R cells had an IC50 of 0.68 U/ml for treatment with rMETase, demonstrating that 143B-R cells had regained the ability to grow in low methionine conditions. 143B-R cells had reduced cell migration and invasion capability in vitro, formed much smaller tumors than 143B-P cells and lost metastatic potential in vivo, indicating loss of malignancy in 143B-R cells. 143B-R cells showed gain of the epithelial marker, ZO-1 and loss of mesenchymal markers, vimentin, Snail, and Slug and, an increase of histone H3K9me3 and H3K27me3 methylation and a decrease of H3K4me3, H3K36me3, and H3K79me3 methylation, along with their loss of malignancy. These results suggest that shifting the balance in histone methylases might be a way to decrease the malignant potential of cells. The present results demonstrate the rationale to target methionine addiction for improved sarcoma therapy.

Long-term Stable Disease in a Rectal-cancer Patient Treated by Methionine Restriction With Oral Recombinant Methioninase and a Low-methionine Diet

BACKGROUND/AIM

Rectal cancer is a recalcitrant disease with limited treatment options. Pre-clinical studies have shown the efficacy of methionine restriction with a low-methionine diet and oral recombinant methioninase (o-rMETase) for colorectal cancer. There are also clinical studies on methionine restriction with o-rMETase for other recalcitrant cancer types. The goal of the present study was to determine the efficacy of a low-methionine diet and o-rMETase on a rectal cancer patient.

PATIENT AND METHODS

A 55-year-old man diagnosed with recurrent locally-advanced rectal-cancer was treated with o-rMETase and a low-methionine diet, during which time, he did not receive standard chemotherapy. Disease stability was monitored by carcinoembryonic antigen (CEA) levels, sigmoidoscopy, and computed tomography (CT).

RESULTS

The patient was diagnosed with stage II rectal cancer (adenocarcinoma) in 2018. After neoadjuvant chemoradiotherapy, the patient received total mesorectal excision (TME) in 2018. Local recurrence was found by sigmoidoscopy one year later. The patient was given chemotherapy, the recurrent lesion shrunk, and was then removed endoscopically in December 2019, with positive margins. The tumor did not become apparent for about a year after that. An endoscopic examination performed in December 2020, revealed a local recurrence. Since that time, the patient had an elevated CEA. The patient went on o-rMETase and a low-methionine diet from January 2021. Since then, the patient's CEA level has remained stable for the next year and a half. He received sigmoidoscopy and CT regularly, and the tumor size has not changed.

CONCLUSION

This patient's clinical course indicates that o-rMETase and a low-methionine diet may be effective for rectal cancer, for long-term disease stabilization. Further case studies and clinical trials are needed to determine the generality of the present result.

Stage IV Pancreatic Cancer Patient Treated With FOLFIRINOX Combined With Oral Methioninase: A Highly-Rare Case With Long-term Stable Disease

BACKGROUND

Pancreatic cancer is one of the most recalcitrant cancers, and more effective therapy is needed. Pre-clinical studies have shown that patient-derived orthotopic xenograft (PDOX) mouse models of pancreatic cancer are effectively treated with oral recombinant methioninase (o-rMETase).

CASE REPORT

A 62-year-old woman diagnosed with stage IV pancreatic cancer was treated with the combination of 5-fluorouracil/leucovorin, irinotecan, and oxaliplatinum (FOLFIRINOX) every two weeks and o-rMETase twice a day as a supplement. The patient was also on a low-methionine diet. Disease progression was monitored by CA19-9 and computed tomography. The patient initially responded to FOLFIRINOX, shown by a great reduction in CA19-9 levels, with tumor shrinkage shown by computed tomography. The patient began taking o-rMETase and went on a low-methionine diet one year after diagnosis which she has maintained without side effects for 7 months. The patient's CA19-9 level and tumor size remain stable 19 months after diagnosis. The patient is alive and has maintained a high performance status. Historical data show that less than 5% of stage IV pancreatic-cancer patients on FOLFIRINOX have stable disease 1.5 years after diagnosis.

CONCLUSION

The combination of o-rMETase and FOLFIRINOX may be synergistic in stage IV pancreatic cancer.

Methionine Restriction: Ready for Prime Time in the Cancer Clinic?

Attempts to selectively starve cancers in the clinic have been made at least since the time of Warburg beginning 100 years ago. Calorie-restriction or low-carbohydrate diets have had limited success with cancer patients. Methionine restriction is another strategy to selectively starve cancer cells, since cancers are addicted to methionine, unlike normal cells. Methionine addiction of cancer is termed the Hoffman effect. Numerous preclinical studies over the past half century have shown methionine restriction to be highly effective against all major cancer types and synergistic with chemotherapy. Low-methionine medical diets can be effective in lowering methionine and have shown some clinical promise, but they are not palatable and thereby not sustainable. However, selectively choosing among plant-based foods allows a variety of low-methionine diets that are sustainable. Our laboratory has developed a methioninase that can be administered orally as a supplement and has resulted in anecdotal positive results in patients with advanced cancer, including hormone-independent prostate cancer, and other recalcitrant cancers. The question is whether methionine restriction through a low-methionine diet, or even greater methionine restriction with methioninase in combination with a low-methionine diet, is ready for prime time in the clinic, especially in combination with other synergistic therapy. The question will hopefully be answered in the near future, especially for advanced cancer patients who have failed all standard therapy.

Oral-recombinant Methioninase Converts an Osteosarcoma from Methotrexate-resistant to -sensitive in a Patient-derived Orthotopic-xenograft (PDOX) Mouse Model

BACKGROUND/AIM

Osteosarcoma is the most common bone sarcoma. Although surgery and chemotherapy are initially effective, the 5-year survival is approximately 60% to 80%, and has not improved over three decades. We have previously shown that methionine restriction (MR) induced by oral recombinant methioninase (o-rMETase), is effective against osteosarcoma in patient-derived orthotopic xenograft (PDOX) nude-mouse models. In the present report, the efficacy of the combination of oral o-rMETase and methotrexate (MTX) was examined in an osteosarcoma PDOX mouse model.

MATERIALS AND METHODS

An osteosarcoma-PDOX model was previously established by implanting tumor fragments into the proximal tibia of nude mice. The osteosarcoma PDOX models were randomized into four groups: control; o-rMETase alone; MTX alone; combination of o-rMETase and MTX. The mice were sacrificed after 4 weeks of treatment.

RESULTS

The combination of o-rMETase and MTX showed significantly higher efficacy compared to the control group (p=0.04). The combination also showed significantly higher efficacy compared to MTX alone (p=0.04). No significant efficacy of o-rMETase alone or MTX alone compared to control was shown (p=0.21, 1.00, respectively). Only the combination of o-rMETase and MTX reduced the cancer-cell density in the osteosarcoma tumor.

CONCLUSION

rMETase converted an osteosarcoma PDOX from MTX-resistant to MTX-sensitive and thereby shows future clinical potential.

Is the Hoffman Effect for Methionine Overuse Analogous to the Warburg Effect for Glucose Overuse in Cancer?

The general cancer-specific metabolic defect of methionine (MET) dependence is due to MET overuse for aberrant transmethylation reactions. The excess use of MET for aberrant transmethylation reactions apparently diverts methyl groups from DNA. The resulting global DNA hypomethylation is also a general phenomenon in cancer and leads to unstable genomes and aneuploid karyotypes. The excessive and aberrant use of MET in cancer is readily observed in [¹¹C]-MET-PET imaging, where high uptake of [¹¹C]-MET results in a very strong and selective tumor signal compared to normal tissue background for brain cancer and possibly other cancers. [¹¹C]-MET is superior to [¹⁸C]-fluorodeoxyglucose (FDG) for PET imaging, suggesting that MET overuse in cancer ("Hoffman effect") is greater than glucose overuse in cancer ("Warburg effect").

L-[Methyl-11C] Methionine-Positron-Emission Tomography (MET-PET)

Methionine (MET) dependence is a cancer-specific metabolic abnormality that is due to MET overuse for aberrant transmethylation reactions. [¹¹C]-MET is very useful for positron-emission tomography (PET) due to MET overuse in malignant tumors. Many benefits of MET-PET have been demonstrated. MET-PET can differentiate recurrent glioma and necrosis. [¹¹C]-MET-PET can also predict prognosis in gliomas better than [¹⁸F]-FDG PET. [¹¹C]-MET-PET is better than MRI for predicting survival in low-grade glioma (LGG). MET-PET has greater specificity for detecting residual tumor after surgery than MRI.