MTHFD2 Blockade Enhances the Efficacy of β-Lapachone Chemotherapy With Ionizing Radiation in Head and Neck Squamous Cell Cancer.

Kirtikar Shukla,Allen W Tsang,David A Boothman,Cristina M Furdui,Joshua E Lewis,Naveen Singh,Melissa L Kemp

doi:10.3389/fonc.2020.536377

Abstract

Head and Neck Squamous Cell Cancer (HNSCC) presents with multiple treatment challenges limiting overall survival rates and affecting patients' quality of life. Amongst these, resistance to radiation therapy constitutes a major clinical problem in HNSCC patients compounded by origin, location, and tumor grade that limit tumor control. While cisplatin is considered the standard radiosensitizing agent for definitive or adjuvant radiotherapy, in recurrent tumors or for palliative care other chemotherapeutics such as the antifolates methotrexate or pemetrexed are also being utilized as radiosensitizers. These drugs inhibit the enzyme dihydrofolate reductase, which is essential for DNA synthesis and connects the 1-C/folate metabolism to NAD(P)H and NAD(P)+ balance in cells. In previous studies, we identified MTHFD2, a mitochondrial enzyme involved in folate metabolism, as a key contributor to NAD(P)H levels in the radiation-resistant cells and HNSCC tumors. In the study presented here, we investigated the role of MTHFD2 in the response to radiation alone and in combination with β-lapachone, a NQO1 bioactivatable drug, which generates reactive oxygen species concomitant with NAD(P)H oxidation to NAD(P)+. These studies are performed in a matched HNSCC cell model of response to radiation: the radiation resistant rSCC-61 and radiation sensitive SCC-61 cells reported earlier by our group. Radiation resistant rSCC-61 cells had increased sensitivity to β-lapachone compared to SCC-61 and knockdown of MTHFD2 in rSCC-61 cells further potentiated the cytotoxicity of β-lapachone with radiation in a dose and time-dependent manner. rSCC-61 MTHFD2 knockdown cells irradiated and treated with β-lapachone showed increased PARP1 activation, inhibition of mitochondrial respiration, decreased respiration-linked ATP production, and increased mitochondrial superoxide and protein oxidation as compared to control rSCC-61 scrambled shRNA. Thus, these studies point to MTHFD2 as a potential target for development of radiosensitizing chemotherapeutics and potentiator of β-lapachone cytotoxicity.

Highlights

Head and neck squamous cell cancer (HNSCC) is an aggressive disease with a high rate of mortality and morbidity in the United States
As radiation therapy is being used as first line treatment for Head and Neck Squamous Cell Cancer (HNSCC), and β-lap was shown previously to sensitize cells to radiation treatment [9]], we sought to quantify the impact of combined radiation and β-lap on clonogenic survival of SCC-61 and rSCC-61 cells
Federal Drug Administration approved the use of four chemotherapeutics, one targeted therapy (Cetuximab, monoclonal antibody against EGFR), and one drug combination for treatment of HNSCC

Summary

Introduction

Head and neck squamous cell cancer (HNSCC) is an aggressive disease with a high rate of mortality and morbidity in the United States. Based on the known mechanism of action, the cytotoxicity of β-lap is expected to be driven by the expression and activity of NQO1, the expression and activity of ROS-metabolizing enzymes (e.g., catalase, SOD1, etc.) [11, 14], and the availability of NAD(P)H, which is needed to support both the NQO1-catalyzed generation of ROS and the activity of key ROS-suppressing redox regulatory enzymes [e.g., thioredoxin reductase [14]]. The expression of NQO1 is regulated in cells by KEAP1/Nrf pathways, and a series of studies have established prolonged induction of NQO1 expression by ionizing radiation in lung cancer cells and in FSall mice tumors [15, 16] These findings raised the possibility of improved chemotherapeutic and radiation sensitizing activity of β-lap, which have been confirmed in numerous cancers, including HNSCC [9]

Methods

Results

Conclusion