Immune checkpoint blockades, or ICBs, have revolutionized the treatment of several advanced cancers. However, its effectiveness has plateaued due to therapeutic resistance that renders tumor-infiltrating lymphocytes, or TILs, ineffective. Therefore, finding ways to break down that resistance and rejuvenate anti-cancer TILs, so they can kill tumor cells, is an important goal for oncologists. However, any potential intervention must be performed under unusual conditions: the cancer microenvironment almost devoid of oxygen due to the rapid growth of a tumor and poor oxygen delivery by the tumor’s abnormal vasculature.
In a study published in Nature CommunicationsLewis Zhichang Shi, M.D., Ph.D., and colleagues at the University of Alabama at Birmingham show, for the first time, how HIF1α in T cells is key to the induction of interferon gamma, or IFN-γ, in that environment hypoxic. The cytokine IFN-γ is known to be essential for inducing the ability of T cells to kill tumors. Furthermore, it is known that an alternative metabolism called glycolysis, which is capable of producing energy in human cells when oxygen is not present, is similarly required for the induction of IFN-γ in T cells.
“Interestingly, under normal oxygen levels in the body, called normoxia, the induction of IFN-g and glycolysis in T cells is not mediated by HIF1α, a primary regulator of glycolysis, but by its widely considered target LDHa, such as was reported in an initial study by another group,” said Shi, a professor in the UAB Department of Radiation Oncology. “However, under hypoxic conditions it is unknown whether and how HIF1α regulates IFN-γ induction and glycolysis in T cells.”
The UAB researchers discovered that glycolysis of HIF1α is essential for the induction of IFN-γ in hypoxic T cells. HIF1α is a subunit of HIF, or hypoxia-inducible factor, that is known to play a crucial role in orchestrating cellular responses to hypoxia.
Shi and colleagues demonstrated this key role of HIF1α in hypoxia by combining genetic mouse models and metabolic flux analysis using 13C-labeled glucose tracking assays and a Seahorse analyzer, as well as pharmacological approaches.
In both human and mouse T cells that were activated under hypoxia, they found that deletion of HIF1α from T cells prevented the metabolic reprogramming switch from catabolic to anabolic metabolism, of which anaerobic glycolysis is an important component; knockdown also suppressed IFN-γ induction. Furthermore, pharmacological inhibition of T cell glycolysis under hypoxic conditions prevented the induction of IFN-γ. In contrast, stabilization of HIF1α by removing a negative regulator of HIF1α increased IFN-γ under hypoxic conditions.
In terms of cancer defense, the researchers found that hypoxic T cells that had HIF1α knocked out were less able to kill tumor cells in vitro. In vivo, tumor-bearing mice that had HIF1α deleted in T cells did not respond to ICB therapy.
The researchers then showed a way to overcome that resistance to ICB therapy. Elucidation of the mechanistic role of HIF1α deletion showed that loss of HIF1α greatly decreased glycolytic activity in hypoxic T cells, resulting in reduced intracellular acetyl-CoA and attenuated cell death induced by HIF1α. activation, or AICD. Restoration of intracellular acetyl-CoA by supplementing growth media with acetate-reactivated AICD and rescuing IFN-γ production for Hif1α-deleted hypoxic T cells.
Shi and colleagues then demonstrated, in live mice, that acetate supplementation was an effective strategy to prevent ICB resistance in mice with tumors with specific deletion of HIF1α in T cells. When mice with tumors with Hif1α deletion Given acetate supplementation followed by combination therapy with ICB, the mice had significant improvement on ICB therapy, as seen by potent suppression of tumor growth and a large reduction in tumor weight.
“TILs and tumor cells use the same metabolic pathways for their growth and function, and coexist in metabolically harsh tumor microenvironments characterized by hypoxia and poor nutrition, which places them in a fierce metabolic tug-of-war,” Shi said. “How to tilt this metabolic battle to favor TILs would be key, and we showed that acetate supplementation restored IFN-γ production in Hif1α-deleted TILs and overcame ICB resistance arising from the loss of HIF1α in the cells.” “T”.
“Our study, together with an initial report by others, convincingly shows that impaired HIF1α function in T cells is an important intrinsic mechanism of therapeutic resistance to CBIs, such as anti-CTLA-4 and anti-PD-1 /L1.” Shi said.
Co-authors with Shi on the study, “HIF1α-regulated glycolysis promotes activation-induced cell death and IFN-γ induction in hypoxic T cells,” are Hongxing Shen, Oluwagbemiga A. Ojo, Haitao Ding, Chuan Xing, Abdelrahman Yassin, Vivian Y. Shi, Zach Lewis, Ewa Podgorska and James A. Bonner, Department of Radiation Oncology, UAB; Logan J. Mullen, University of Alaska Fairbanks, Fairbanks, Alaska; M. Iqbal Hossain and Shaida A. Andrabi, UAB Department of Pharmacology and Toxicology; and Maciek R. Antoniewicz, University of Michigan, Ann Arbor, Michigan.
Support came from UAB; the UAB O’Neal Comprehensive Cancer Center; National Institutes of Health Grants CA230475-01A1, CA25972101A1, and CA279849-01A1; V Foundation Scholarship Award V2018-023; Grant ME210108 for medical research programs directed by the Department of Defense and Congress; and Cancer Research Institute CLIP grant CRI4342.
At UAB, Radiation Oncology and Pharmacology and Toxicology are departments of the Marnix E. Heersink School of Medicine. Shi is a scientist at the O’Neal Comprehensive Cancer Center and holds the ROAR Koikos-Petelos-Jones-Bragg Chair for Cancer Research.