The efficient clinical treatment of oral squamous cell carcinoma (OSCC) is still a challenge that demands the development of effective new drugs. Phenformin has been shown to produce more potent anti-tumor activities than metformin on different tumors, however, not much is known about the influence of phenformin on OSCC cells. We found that phenformin suppresses OSCC cell proliferation, and promotes OSCC cell autophagy and apoptosis to significantly inhibit OSCC cell growth both in vivo and in vitro. RNA-seq analysis revealed that autophagy pathways were the main targets of phenformin and identified two new targets DDIT4 (DNA damage inducible transcript 4) and NIBAN1 (niban apoptosis regulator 1). We found that phenformin significantly induces the expression of both DDIT4 and NIBAN1 to promote OSCC autophagy. Further, the enhanced expression of DDIT4 and NIBAN1 elicited by phenformin was not blocked by the knockdown of AMPK but was suppressed by the knockdown of transcription factor ATF4 (activation transcription factor 4), which was induced by phenformin treatment in OSCC cells. Mechanistically, these results revealed that phenformin triggers endoplasmic reticulum (ER) stress to activate PERK (protein kinase R-like ER kinase), which phosphorylates the transitional initial factor eIF2, and the increased phosphorylation of eIF2 leads to the increased translation of ATF4. In summary, we discovered that phenformin induces its new targets DDIT4 and especially NIBAN1 to promote autophagic and apoptotic cell death to suppress OSCC cell growth. Our study supports the potential clinical utility of phenformin for OSCC treatment in the future.

Altered glycolytic metabolism has been associated with chemoresistance in acute myeloid leukemia (AML). However, there are still aspects that need clarification, as well as how to explore these metabolic alterations in therapy. In the present study, we aimed to elucidate the role of glucose metabolism in the acquired resistance of AML cells to cytarabine (Ara-C) and to explore it as a therapeutic target. Resistance was induced by stepwise exposure of AML cells to increasing concentrations of Ara-C. Ara-C-resistant cells were characterized for their growth capacity, genetic alterations, metabolic profile, and sensitivity to different metabolic inhibitors. Ara-C-resistant AML cell lines, KG-1 Ara-R, and MOLM13 Ara-R presented different metabolic profiles. KG-1 Ara-R cells exhibited a more pronounced glycolytic phenotype than parental cells, with a weaker acute response to 3-bromopyruvate (3-BP) but higher sensitivity after 48 h. KG-1 Ara-R cells also display increased respiration rates and are more sensitive to phenformin than parental cells. On the other hand, MOLM13 Ara-R cells display a glucose metabolism profile similar to parental cells, as well as sensitivity to glycolytic inhibitors. These results indicate that acquired resistance to Ara-C in AML may involve metabolic adaptations, which can be explored therapeutically in the AML patient setting who developed resistance to therapy.

The effect of agonists on AMP-activated protein kinase (AMPK), mainly metformin and phenformin, has been appreciated in the treatment of multiple types of tumors. Specifically, the antitumor activity of phenformin has been demonstrated in melanomas containing the v-Raf murine sarcoma viral oncogene homolog B1 (BRAF) activating mutation. In this report, we elucidated the synergistic antitumor effects of biguanides with metabolism inhibitors on colon tumors. Phenformin with 2-deoxy-D-glucose (2DG) inhibited tumor cell growth in cancer cell lines, including HT29 cells harboring BRAF- and p53-mutations. Biochemical analyses showed that two chemotherapeutics exerted cooperative effects to reduce tumor growth through cell cycle arrest, apoptosis, and autophagy. The drugs demonstrated activity against phosphorylated ERK and the gain-of-function p53 mutant protein. To demonstrate tumor regressive effects in vivo, we established patient-derived models, including xenograft (PDX) and organoids (PDO). Co-treatment of biguanides with chemotherapeutics efficiently reduced the growth of patient-derived colon models in comparison to treatment with a single agent. These results strongly suggest that significant therapeutic advantages would be achieved by combining AMPK activators such as phenformin and cancer metabolic inhibitors such as 2DG.

Preclinical studies show that activation of AMP kinase by phenformin can augment the cytotoxic effect and RAF inhibitors in BRAF V600-mutated melanoma. We conducted a phase Ib dose-escalation trial of phenformin with standard dose dabrafenib/trametinib in patients with metastatic BRAF V600-mutated melanoma.
We used a 3+3 dose-escalation design which explored phenformin doses between 50 and 200 mg twice daily. Patients also received standard dose dabrafenib/trametinib. We measured phenformin pharmacokinetics and assessed the effect of treatment on circulating myeloid-derived suppressor cells (MDSC).
A total of 18 patients were treated at dose levels ranging from 50 to 200 mg twice daily. The planned dose-escalation phase had to be cancelled because of the COVID 19 pandemic. The most common toxicities were nausea/vomiting; there were two cases of reversible lactic acidosis. Responses were seen in 10 of 18 patients overall (56%) and in 2 of 8 patients who had received prior therapy with RAF inhibitor. Pharmacokinetic data confirmed drug bioavailability. MDSCs were measured in 7 patients treated at the highest dose levels and showed MDSC levels declined on study drug in 6 of 7 patients.
We identified the recommended phase II dose of phenformin as 50 mg twice daily when administered with dabrafenib/trametinib, although some patients will require short drug holidays. We observed a decrease in MDSCs, as predicted by preclinical studies, and may enhance immune recognition of melanoma cells.
This is the first trial using phenformin in combination with RAF/MEK inhibition in patients with BRAF V600-mutated melanoma. This is a novel strategy, based on preclinical data, to increase pAMPK while blocking the MAPK pathway in melanoma. Our data provide justification and a recommended dose for a phase II trial.

Today, many anticancer drugs are used clinically for ovarian cancer, one of the leading causes of cancer-related deaths in women. Phenformin is an antidiabetic drug of the biguanide class. It improves the antiproliferative activity in cancer cells. Hypoxia is an important component associated with ovarian cancer and its tumor microenvironment. The aim of this study was to investigate the anticancer effects of Phenformin in SKOV-3 human ovarian cancer cells under hypoxic conditions. SKOV-3 human ovarian cancer cells treated with different doses of Phenformin (0.5 mM, 1 mM, 2 mM, 5 mM) for 24 hours were subjected to WST-1 cell viability assay and Annexin V apoptosis assay. A dose-dependent decrease in cell viability with Phenformin treatment was observed. In addition, Phenformin activated percentage of apoptotic SKOV-3 cancer cells in a dose-dependent manner. In this study, Cobalt(II) chloride (CoCl2) treatment leads to increased hypoxia-inducible factor-1alpha (HIF-1α) expression and Phenformin can recover hypoxic condition. HIF-1α protein expression was significantly correlated with cell viability assay and apoptosis assay. We also found that Phenformin inhibits expression of phosphoinositide-dependent kinase 1 (PDK1) in SKOV-3 ovarian cancer cells. The ability to migrate to cancer cells was significantly reduced in a dose-dependent manner with Phenformin. This data demonstrates that Phenformin treatment can induce apoptosis and inhibit proliferation in ovarian cancer cells under hypoxic conditions. The findings reveal that HIF-1α is a new target for the treatment of ovarian cancer.

Since aerobic glycolysis was first observed in tumors almost a century ago by Otto Warburg, the field of cancer cell metabolism has sparked the interest of scientists around the world as it might offer new avenues of treatment for malignant cells. Our current study claims the discovery of gnetin H (GH) as a novel glycolysis inhibitor that can decrease metabolic activity and lactic acid synthesis and displays a strong cytostatic effect in melanoma and glioblastoma cells. Compared to most of the other glycolysis inhibitors used in combination with the complex-1 mitochondrial inhibitor phenformin (Phen), GH more potently inhibited cell growth. RNA-Seq with the T98G glioblastoma cell line treated with GH showed more than an 80-fold reduction in thioredoxin interacting protein (TXNIP) expression, indicating that GH has a direct effect on regulating a key gene involved in the homeostasis of cellular glucose. GH in combination with phenformin also substantially enhances the levels of p-AMPK, a marker of metabolic catastrophe. These findings suggest that the concurrent use of the glycolytic inhibitor GH with a complex-1 mitochondrial inhibitor could be used as a powerful tool for inducing metabolic catastrophe in cancer cells and reducing their growth.

Myeloproliferative neoplasms (MPN) are disorders characterized by an alteration at the hematopoietic stem cell (HSC) level, where the JAK2 mutation is the most common genetic alteration found in classic MPN (polycythemia vera, essential thrombocythemia, and primary myelofibrosis). We and others previously demonstrated that metformin reduced splenomegaly and platelets counts in peripheral blood in JAK2V617F pre-clinical MPN models, which highlighted the antineoplastic potential of biguanides for MPN treatment. Phenformin is a biguanide that has been used to treat diabetes, but was withdrawn due to its potential to cause lactic acidosis in patients.
We herein aimed to investigate the effects of phenformin in MPN disease burden and stem cell function in Jak2V617F-knockin MPN mice.
In vitro phenformin treatment reduced cell viability and increased apoptosis in SET2 JAK2V67F cells. Long-term treatment with 40 mg/kg phenformin in Jak2V617F knockin mice increased the frequency of LSK, myeloid progenitors (MP), and multipotent progenitors (MPP) in the bone marrow. Phenformin treatment did not affect peripheral blood counts, spleen weight, megakaryocyte count, erythroid precursors frequency, or ex vivo clonogenic capacity. Ex vivo treatment of bone marrow cells from Jak2V617F knockin mice with phenformin did not affect hematologic parameters or engraftment in recipient mice.
Phenformin increased the percentages of LSK, MP, and MPP populations, but did not reduce disease burden in Jak2V617F-knockin mice. Additional studies are necessary to further understand the effects of phenformin on early hematopoietic progenitors.

The results presented in this paper confirm the beneficial role of an easy-to-use and low-cost thin-layer chromatography (TLC) technique for describing the retention behavior and the experimental lipophilicity parameter of two biguanide derivatives, metformin and phenformin, in both normal-phase (NP) and reversed-phase (RP) TLC systems. The retention parameters (RF, RM) obtained under different chromatographic conditions, i.e., various stationary and mobile phases in the NP-TLC and RP-TLC systems, were used to determine the lipophilicity parameter (RMW) of metformin and phenformin. This study confirms the poor lipophilicity of both metformin and phenformin. It can be stated that the optimization of chromatographic conditions, i.e., the kind of stationary phase and the composition of mobile phase, was needed to obtain the reliable value of the chromatographic lipophilicity parameter (RMW) in this study. The fewer differences in the RMW values of both biguanide derivatives were ensured by the RP-TLC system composed of RP2, RP18, and RP18W plates and the mixture composed of methanol, propan-1-ol, and acetonitrile as an organic modifier compared to the NP-TLC analysis. The new calculation procedures for logP of drugs based on topological indices 0χν, 0χ, 1χν, M, and Mν may be a certain alternative to other algorithms as well as the TLC procedure performed under optimized chromatographic conditions. The knowledge of different lipophilicity parameters of the studied biguanides can be useful in the future design of novel and more therapeutically effective metformin and phenformin formulations for antidiabetic and possible anticancer treatment. Moreover, the topological indices presented in this work may be further used in the QSAR study of the examined biguanides.

Mitochondrial electron transport chain complex I (ETCC1) is the essential core of cancer metabolism, yet potent ETCC1 inhibitors capable of safely suppressing tumor growth and metastasis in vivo are limited. From a plant extract screening, we identified petasin (PT) as a highly potent ETCC1 inhibitor with a chemical structure distinct from conventional inhibitors. PT had at least 1700 times higher activity than that of metformin or phenformin and induced cytotoxicity against a broad spectrum of tumor types. PT administration also induced prominent growth inhibition in multiple syngeneic and xenograft mouse models in vivo. Despite its higher potency, it showed no apparent toxicity toward nontumor cells and normal organs. Also, treatment with PT attenuated cellular motility and focal adhesion in vitro as well as lung metastasis in vivo. Metabolome and proteome analyses revealed that PT severely depleted the level of aspartate, disrupted tumor-associated metabolism of nucleotide synthesis and glycosylation, and downregulated major oncoproteins associated with proliferation and metastasis. These findings indicate the promising potential of PT as a potent ETCC1 inhibitor to target the metabolic vulnerability of tumor cells.

Microglial functioning depends on Ca2+ signaling. By using Ca2+ sensitive fluorescence dye, we studied how inhibition of mitochondrial respiration changed spontaneous Ca2+ signals in soma of microglial cells from 5-7-day-old rats grown under normoxic and mild-hypoxic conditions. In microglia under normoxic conditions, metformin or rotenone elevated the rate and the amplitude of Ca2+ signals 10-15 min after drug application. Addition of cyclosporin A, a blocker of mitochondrial permeability transition pore (mPTP), antioxidant trolox, or inositol 1,4,5-trisphosphate receptor (IP3R) blocker caffeine in the presence of rotenone reduced the elevated rate and the amplitude of the signals implying sensitivity to reactive oxygen species (ROS), and involvement of mitochondrial mPTP together with IP3R. Microglial cells exposed to mild hypoxic conditions for 24 h showed elevated rate and increased amplitude of Ca2+ signals. Application of metformin or rotenone but not phenformin before mild hypoxia reduced this elevated rate. Thus, metformin and rotenone had the opposing fast action in normoxia after 10-15 min and the slow action during 24 h mild-hypoxia implying activation of different signaling pathways. The slow action of metformin through inhibition of complex I could stabilize Ca2+ homeostasis after mild hypoxia and could be important for reduction of ischemia-induced microglial activation.