Abstract 6202: 6-Phosphofructo-2-kinase in regulating DNA damage and repair in EGFR-driven lung cancer

Activating mutations of epidermal growth factor receptor (mutEGFR) are established drivers of lung tumor development, aggressiveness, and resistance to targeted therapies. While targeting mutEGFR with small-molecule tyrosine kinase inhibitors (EGFR-TKIs) dramatically improved progression-free survival in patients with non-small cell lung cancers (NSCLCs), intrinsic or acquired resistance to TKI therapy limits the duration of an effective response to TKIs. Alteration in DNA damage response (DDR) plays a vital role in genomic stability and cancer progression and helps cells to escape apoptosis, limiting the efficacy of targeted therapies.

Interestingly, lung cancer cells exposed to EGFR-TKIs demonstrate attenuated glycolytic flux - one of the major providers of precursors for de novo nucleotide synthesis. A key regulator of glycolysis is the enzyme 6-phosphofructo-2-kinase (PFKFB3). PFKFB3 synthesizes fructose 2,6-bisphosphate (F2,6BP), which is a potent allosteric activator of the glycolytic rate-limiting enzyme, 6-phosphofructo-1-kinase (PFK1). Accordingly, F2,6BP controls flux throughout the entire glycolytic pathway.

In preliminary studies, we provide evidence that PFKFB3 plays multiple roles in regulating the efficacy of DDR in lung cancer cells exposed to EGFR-TKIs. We show that PFKFB3 is required for EGFR-driven glucose metabolism, which provides a list of intermediates utilized in nucleotide synthesis. PFKFB3 regulates the expression of ribonucleotide reductase small subunit M2 (RRM2) of the ribonucleotide reductase (RNR), which is important for de novo onsite synthesis of deoxynucleotide triphosphate (dNTP) during DNA replication and repair. Moreover, a PFKFB3 inhibitor, PFK-158, increases oxidative stress in mutEGFR lung cancer cell lines and, as a result, promotes DNA damage. Importantly, we found that PFKFB3 plays an important role in the chromatin binding of scaffold proteins regulating the assembly of DNA repair complex.

Our studies suggest that PFKFB3 plays an important role in DDR and provide a clear rationale to propose the use of PFKFB3 inhibitors in combination with EGFR inhibitors to increase the efficiency and/or overcome resistance to EGFR-TKIs.

Citation Format: Nadiia Lypova, Lilibeth Lanceta, Susan Dougherty, Jason Chesney, Yoannis Imbert-Fernandez. 6-Phosphofructo-2-kinase in regulating DNA damage and repair in EGFR-driven lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6202.

Abstract P1-13-18: EGFR signaling contributes to acquired resistance to CDK4/6 inhibitors in ER+ breast cancer cells in vitro and in vivo

Breast cancer driven by different hormone receptors, including estrogen receptor (ER+), is responsible for approximately 70-80% of cases among women. While endocrine therapy (ET) of ER+ primary tumors with antiestrogens or aromatase inhibitors is an effective first-line therapy, its success is limited by intrinsic and acquired resistance. Response to ET can be limited due to overexpression of cyclin D1, which promotes the activation of cyclin-dependent kinases 4 and 6 (CDK4/6). Selective inhibition of CDK4/6 and ER signaling is now standard-of-care therapy for ER+ metastatic breast cancer. CDK4/6 inhibitors (CDK4/6i), including palbociclib (PD), ribociclib, and abemaciclib, used in combination with ET, have shown improvement in progression-free survival compared to ET alone in the metastatic setting. However, the inevitable development of acquired resistance significantly limits the efficacy of this targeted therapy. Rewired signaling driven by different oncogenes, including the epidermal growth factor receptor (EGFR), overcomes the targeted inhibition of CDK4/6, which, in turn, allows cell cycle progression contributing to acquired resistance. We evaluated the expression and activity of EGFR in the panel of different matching pairs of ER- and ER+ CDK4/6i-sensitive (pS) and CDK4/6i-resistant (pR) breast cancer cell lines in vitro. Increased EGFR expression in ER+ MCF7/pR cells correlated with elevated ER phosphorylation, suggesting a direct cross-talk between EGFR and ER signaling in PD-resistant cells. Stimulation with EGF promoted ER activation, whereas estrogen stimulation promoted EGFR activation in ER+ pS and pR cell lines, indicating a direct cross-regulation between these molecular targets. Treatment of MCF7/pR cells with CDK4/6i resulted in elevated EGFR mRNA expression, confirming the dependency of resistant cells on EGFR signaling. Moreover, exposure to the EGFR inhibitors dramatically inhibited the proliferation of MCF7/pR cells compared to the parental cells, suggesting that EGFR could be an essential bypass signaling regulator contributing to resistance to CDK4/6i. We found that combined treatment with EGFRi and CDK4/6i significantly inhibited Rb phosphorylation in pR cells improving the effect of CDK4/6i on cell cycle arrest. We evaluated EGFR expression in MCF7/pS and pR mouse xenograft models in vivo. We observed a significant elevation in EGFR expression and phosphorylation in response to PD treatment, confirming the importance of EGFR signaling in maintaining the acquired resistance to CDK4/6i in ER+ breast cancer cells. Taken together, our findings suggest that EGFR signaling plays an important role in acquired resistance to CDK4/6i in ER+ breast cancer cells in vitro and in vivo and targeting EGFR with small-molecule inhibitors (like erlotinib or gefitinib) or chimeric monoclonal antibodies (i.e. cetuximab) can be a promising approach to improve CDK4/6i efficacy in breast cancer patients.

Citation Format: Nadiia Lypova, Lilibeth Lanceta, Susan Daugherty, Jason Chesney, Yoannis Imbert-Fernandez. EGFR signaling contributes to acquired resistance to CDK4/6 inhibitors in ER+ breast cancer cells in vitro and in vivo. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-13-18.

Abstract 1772: EGFR signaling as a mechanism of resistance to CDK4/6 inhibitors in Palbociclib-resistant ER+ breast cancer cells

Breast cancer driven by estrogen receptor (ER) is responsible for approximately 60-70% of cases among women. Selective inhibition of cyclin-dependent kinases 4 and 6 (CDK4/6) and ER signaling is now standard-of-care therapy for ER positive (ER+) metastatic breast cancer. CDK4/6 inhibitors, including palbociclib (PD), used in combination with endocrine therapy have shown improvement in progression-free survival compared to endocrine therapy alone in the metastatic setting. However, the inevitable development of acquired resistance significantly limits the efficacy of this targeted therapy. In ER+ breast cancer resistant cells, rewired signaling driven by different oncogenes, including the epidermal growth factor receptor (EGFR), overcomes the inhibition of CDK4/6 by PD, which, in turn, allows cell cycle progression contributing to PD-resistance. We investigated the dependency of ER+ breast cancer cell lines sensitive and resistant to PD on EGFR signaling in vitro. We evaluated the expression and activity of EGFR in two different matching pairs of ER+ palbociclib-sensitive (pS) and palbociclib-resistant (pR) breast cancer cell lines (MCF7 and T47D) and observed elevated EGFR expression in MCF7/pR cells. Increased EGFR expression in MCF7/pR cells correlated with elevated ER alpha phosphorylation at S118 and S167 sites, suggesting a direct cross-talk between EGFR and ER signaling in PD-resistant cells. Serum starvation significantly decreased EGFR activity, cdk2 and cyclin D1 expression in both MCF7 and T47D PD-resistant cells compared to the parental cell lines, confirming their dependency on the presence of growth factors. Notably, stimulation with EGF promoted ER phosphorylation and expression of cell cycle related targets: cdk2, cyclin E and wee1 in both MCF7 and T47D cell lines sensitive and resistant to PD. Furthermore, stimulation with estrogen promoted EGFR activation in MCF7/pS and MCF7/pR cells, indicating a direct cross-regulation between these molecular targets. Further, exposure to the EGFR inhibitor erlotinib dramatically inhibited the proliferation of MCF7/pR cells compared to the parental cells, suggesting that EGFR could be an important bypass signaling regulator contributing to resistance to PD. We found that dual treatment with erlotinib and PD significantly inhibited Rb phosphorylation in MCF7/pR cells improving the effect of PD on cell cycle arrest. Moreover, dual treatment of MCF7/pR cells attenuated ER expression suggesting the higher dependency of ER signaling on EGFR activity in resistant cells. Taken together, our findings suggest that EGFR signaling is a mechanism of resistance in ER+ cell lines with acquired resistance to PD in vitro and that EGFR targeting can be a promising approach to improve palbociclib efficacy in breast cancer patients.

Citation Format: Nadiia Lypova, Lilibeth Lanceta, Susan M. Dougherty, Jason A. Chesney, Yoannis Imbert-Fernandez. EGFR signaling as a mechanism of resistance to CDK4/6 inhibitors in Palbociclib-resistant ER+ breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1772.

Abstract 1052: 6-phosphofructo-2-kinase enhances cytotoxicity of the EGFR inhibitor erlotinib via regulation of cell cycle in non-small lung cancer cell lines

Lung tumor development and aggressiveness is largely driven by a multitude of oncogenes including the epidermal growth factor receptor (EGFR). Targeted EGFR inhibition with small-molecule tyrosine kinase inhibitors (EGFR-TKIs) such as erlotinib have initially improved progression-free survival in patients with EGFR-driven NSCLCs but failed to provide an overall survival benefit due to the development of resistance. Clinically, responses to EGFR-TKIs are evaluated by positron emission tomography using 2[18F]- fluoro-2-deoxy-glucose (18FDG-PET) as tumors consume significantly more glucose compared to adjacent normal tissue in vivo. 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFKFB3), a known driver of glycolytic flux, plays a key role in the metabolic shift that occurs during tumor progression. The product of PFKFB3, F2,6BP, regulates glucose metabolism by activating PFK1, which in turn facilitates glycolysis. Increased glycolysis fulfills the elevated tumor demands for energetic and biosynthetic precursors needed for survival and proliferation - the functions that confer resistance to targeted therapies. Here, we interrogated the hypothesis that PFKFB3 inhibition increases the efficacy of EGFR-TKIs in NSCLCs with different EGFR mutation status in vitro. We treated multiple NSCLCs models (wild type EGFR: H522, H1437; and mutated EGFR: PC9, HCC827) with erlotinib and observed a significant inhibition of cell proliferation in vitro. Erlotinib treatment resulted in G1 arrest, decreased expression and phosphorylation of cyclin dependent kinases (CDKs), Rb and accumulation of p27 in all NSCLCs. Notably, PFKFB3 silencing in TKI-treated cells dramatically decreased cell viability, indicating that PFKFB3 expression is required to maintain cell viability of G1 arrested cells. Further, co-treatment with the PFKFB3 inhibitor PFK-158 increased cell death in all NSCLCs. We found that inhibition of PFKFB3 reduced TKI-induced G1 arrest and altered cell cycle progression, switching the effect of erlotinib from cytostatic to cytotoxic. Importantly, dual treatment caused only minor changes in glycolytic flux when compared to the effects of PFK-158 or erlotinib alone suggesting that glucose metabolism did not contribute to the observed effect. Taken together, our findings suggest that a non-metabolic function of PFKFB3 limits the usefulness of EGFR-TKI in vitro and that targeting of PFKFB3 can be a promising approach to improve clinical efficacy of FDA-approved EGFR-TKIs in lung cancer patients.

Citation Format: Nadiia Lypova, Lilibeth Lanceta, Jason Chesney, Yoannis Imbert-Fernandez. 6-phosphofructo-2-kinase enhances cytotoxicity of the EGFR inhibitor erlotinib via regulation of cell cycle in non-small lung cancer cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1052.

Abstract 6001: 6-Phosphofructo-2-kinase inhibition to increase the efficacy of ER and CDK4/6 inhibitors against ER+ breast cancer

Deregulation of the estrogen receptor (ER)-cyclin D1-CDK4/6 pathway is a hallmark of ER+ breast cancer that has prompted the development of CDK4/6 inhibitors. Although administration of CDK4/6 inhibitors to patients with ER+ advanced breast cancers have resulted in an improvement in progression free survival, almost all patients invariable develop resistance and relapse over time. Activation of glucose metabolism upon CDK4/6 inhibition is becoming increasingly evident. A key stimulator of glycolysis is the PFKFB3 enzyme which synthesizes fructose 2,6-bisphosphate (F2,6BP), a potent allosteric activator of the rate-limiting 6-phosphofructo-1-kinase (PFK1). F2,6BP controls flux throughout the entire glycolytic pathway and, as a result is required for the proliferation of cancer cells. In preliminary studies, we provide evidence that PFKFB3 expression and activity is increased in response to CDK4 inhibition in ER+ breast cancer cells and that a PFKFB3 inhibitor, PFK-158, increases the anti-tumor activity of anti-CDK4 targeted therapy in vitro. Importantly, we found that ER+ cancer cells with acquired resistance to palbociclib have increased levels of PFKFB3 and are highly susceptible to the effects of PFK-158. Our studies provide a clear rationale to propose the use of PFKFB3 inhibitors in combination with CDK4/6 inhibitors as an effective strategy to increase the efficiency and/or overcome resistance to CDK4/6 inhibition.

Citation Format: Lilibeth Lanceta, Nadiia Lypova, Jasson Chesney, Yoannis Imbert-Fernandez. 6-Phosphofructo-2-kinase inhibition to increase the efficacy of ER and CDK4/6 inhibitors against ER+ breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6001.

Inhibition of glucose metabolism through treatment of BRAF mutated metastatic melanoma with vemurafenib

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Background: Increased glucose metabolism is a hallmark of neoplastic cells that allows self-promotion of growth and survival. The enzyme 6-phosphofructo-2-kinase (PFKFB3) is an integral controller of glycolysis by promoting the synthesis of fructose 2,6-bisphosphonate (F2,6BP) which activates 6-phoshofructo-1-kinase (PFK-1), a rate-limiting enzyme and essential control point in the glycolytic pathway. Additionally, mitogen-activated protein kinase (MAPK) is a key signaling pathway in a number of cancers with mutations of the BRAF component, described most commonly in melanoma, resulting in constitutive activation of the MAPK pathway. We aim to demonstrate that vemurafenib, a BRAF inhibitor, has antiglycolytic activity in sensitive melanoma cell lines which may help guide development of future therapies with specific attention to PFKFB3 as a potential enzymatic target to decrease glycolytic flux thereby inhibiting tumor growth and survival. Methods: Vemurafenib sensitive and resistant variants of two separate human metastatic melanoma cell lines (451Lu and WM983) were treated with 3 mM Vemurafenib for 24 and 48 hours. Additionally, cells from aforementioned lines were probed for PFKFB3 after 24 hours of treatment with vemurafenib. Glycolysis was measured by incubating cells in complete media containing 1 mCi [5-3H]glucose for 60 minutes. [3H]H2O produced by glycolysis through enolase was measured. Results: A decrease in PFKFB3 protein expression was found in vemurafenib sensitive cells compared to controls but not in resistant cells after 24h treatment with 3 mM vemurafenib in both 451Lu and WM983 metastatic melanoma cell lines (n = 2). Treatment with vemurafenib led to decrease in glycolysis compared to untreated controls in both vemurafenib sensitive metastatic melanoma cell lines but not in resistant cell lines (n = 5). Additionally, there was a significant reduction in glycolysis in vemurafenib resistant WM983 at 48 hours compared to resistant untreated control. Conclusions: BRAF mutated metastatic melanoma cells showed decrease in PFKFB3 protein expression and decreased glycolysis after treatment with BRAF inhibitor vemurafenib. Future studies will focus on assessing metastatic melanoma cell viability and glycolytic activity after treatment with combination BRAF inhibition and PFKFB3 specific inhibition.

Abstract 2305: Targeting 6-phosphofructo-2-kinase to increase the efficacy of ER and CDK4/6 inhibitors against breast cancer

We demonstrated that estradiol stimulates the expression and activity of an enzyme, 6-phosphofructo-2-kinase (PFKFB3), that regulates glucose metabolism via allosteric stimulation of 6-phosphofructo-1-kinase. PFKFB3 expression is increased in breast cancer cells that have metastasized to lymph nodes and the combination of the anti-estrogen, fulvestrant, with a PFKFB3 inhibitor, PFK158, synergistically increases apoptosis in ER+ breast cancer cells in vitro and in vivo. Given that estradiol simultaneously increases the expression of both the regulatory subunit of CDK4/6, cyclin D1, and PFKFB3, we postulated that the combination of palbociclib with PFK158 would yield synergy against breast cancer cells. In new preliminary studies, co-treatment with palbociclib and PFK158 resulted in a marked decrease in cell proliferation in two ER+ breast cancer cell lines that was accompanied by a synergistic decrease in phospho-Retinoblastoma (Rb). Importantly, exposure of ER+ breast cancer cells to palbociclib and PFK158 causes an increase in cell cycle arrest and apoptotic cell death in vitro. Notably, this combination has no effect on cell cycle arrest or apoptosis in normal mammary cells suggesting that this therapeutic strategy may be well tolerated and selective for breast cancer.

Citation Format: Yoannis Imbert-Fernandez, Lilibeth Lanceta, Sucheta Telang, Jason Chesney. Targeting 6-phosphofructo-2-kinase to increase the efficacy of ER and CDK4/6 inhibitors against breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2305.

Targeting the sugar metabolism of tumors with a first-in-class 6-phosphofructo-2-kinase (PFKFB4) inhibitor

Human tumors exhibit increased glucose uptake and metabolism as a result of high demand for ATP and anabolic substrates and this metabolotype is a negative prognostic indicator for survival. Recent studies have demonstrated that cancer cells from several tissue origins and genetic backgrounds require the expression of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 4 (PFKFB4), a regulatory enzyme that synthesizes an allosteric activator of glycolysis, fructose-2,6-bisphosphate. We report the discovery of a first-in-class PFKFB4 inhibitor, 5-(n-(8-methoxy-4-quinolyl)amino)pentyl nitrate (5MPN), using structure-based virtual computational screening. We find that 5MPN is a selective inhibitor of PFKFB4 that suppresses the glycolysis and proliferation of multiple human cancer cell lines but not non-transformed epithelial cells in vitro. Importantly, 5MPN has high oral bioavailability and per os administration of a non-toxic dose of 5MPN suppresses the glucose metabolism and growth of tumors in mice.

How Heme Oxygenase-1 Prevents Heme-Induced Cell Death

Earlier observations indicate that free heme is selectively toxic to cells lacking heme oxygenase-1 (HO-1) but how this enzyme prevents heme toxicity remains unexplained. Here, using A549 (human lung cancer) and immortalized human bronchial epithelial cells incubated with exogenous heme, we find knock-down of HO-1 using siRNA does promote the accumulation of cell-associated heme and heme-induced cell death. However, it appears that the toxic effects of heme are exerted by “loose” (probably intralysosomal) iron because cytotoxic effects of heme are lessened by pre-incubation of HO-1 deficient cells with desferrioxamine (which localizes preferentially in the lysosomal compartment). Desferrioxamine also decreases lysosomal rupture promoted by intracellularly generated hydrogen peroxide. Supporting the importance of endogenous oxidant production, both chemical and siRNA inhibition of catalase activity predisposes HO-1 deficient cells to heme-mediated killing. Importantly, it appears that HO-1 deficiency somehow blocks the induction of ferritin; control cells exposed to heme show ~10-fold increases in ferritin heavy chain expression whereas in heme-exposed HO-1 deficient cells ferritin expression is unchanged. Finally, overexpression of ferritin H chain in HO-1 deficient cells completely prevents heme-induced cytotoxicity. Although two other products of HO-1 activity–CO and bilirubin–have been invoked to explain HO-1-mediated cytoprotection, we conclude that, at least in this experimental system, HO-1 activity triggers the induction of ferritin and the latter is actually responsible for the cytoprotective effects of HO-1 activity.

Estradiol stimulates glucose metabolism via 6-phosphofructo-2-kinase (PFKFB3)

Estradiol (E2) administered to estrogen receptor-positive (ER(+)) breast cancer patients stimulates glucose uptake by tumors. Importantly, this E2-induced metabolic flare is predictive of the clinical effectiveness of anti-estrogens and, as a result, downstream metabolic regulators of E2 are expected to have utility as targets for the development of anti-breast cancer agents. The family of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases (PFKFB1-4) control glycolytic flux via their product, fructose-2,6-bisphosphate (F26BP), which activates 6-phosphofructo-1-kinase (PFK-1). We postulated that E2 might promote PFKFB3 expression, resulting in increased F26BP and glucose uptake. We demonstrate that PFKFB3 expression is highest in stage III lymph node metastases relative to normal breast tissues and that exposure of human MCF-7 breast cancer cells to E2 causes a rapid increase in [(14)C]glucose uptake and glycolysis that is coincident with an induction of PFKFB3 mRNA (via ER binding to its promoter), protein expression and the intracellular concentration of its product, F26BP. Importantly, selective inhibition of PFKFB3 expression and activity using siRNA or a PFKFB3 inhibitor markedly reduces the E2-mediated increase in F26BP, [(14)C]glucose uptake, and glycolysis. Furthermore, co-treatment of MCF-7 cells with the PFKFB3 inhibitor and the anti-estrogen ICI 182,780 synergistically induces apoptotic cell death. These findings demonstrate for the first time that the estrogen receptor directly promotes PFKFB3 mRNA transcription which, in turn, is required for the glucose metabolism and survival of breast cancer cells. Importantly, these results provide essential preclinical information that may allow for the ultimate design of combinatorial trials of PFKFB3 antagonists with anti-estrogen therapies in ER(+) stage IV breast cancer patients.