DNA damage response and cancer immunity

The overarching goal of our laboratory is to determine how DNA damage response inhibitors (DDRi) can be used
to potentiate cancer cell killing while concurrently increasing anti-tumor immune responses after radiation therapy
(XRT). The DNA Damage Response (DDR) is a signaling system that integrates DNA repair pathways and the
cell cycle to safeguard genome stability. In addition to activating cell cycle checkpoints and DNA repair in cells
treated with XRT, the DDR limits origin firing and delays cell cycle transitions in unstressed cells. While cyclin-
dependent kinases are cell cycle accelerators, DDR kinases are cell cycle brakes and, in this analogy, DDRi
disable the brakes, causing unchecked acceleration. Here we will determine how the DDR is rewired in CD8+ T
cells to accommodate massive and concomitant DNA replication and transcription in S phase. We will also
determine the impact of DDRi in cancer and immune cells. We hypothesize that ATR kinase inhibitors induce
origin firing that causes ribonucleosides to be mis-incorporated into the genome, and that this generates chimeric
RNA-DNA fragments and type I IFN-dependent immunologic memory after XRT. To test our hypothesis in cancer
and immune cells, we have generated an innovative transplantable model of cancer. The Mcm4Chaos3/Chaos3
mouse carries a mutation in Mcm4 that destabilizes the replicative helicase. Cells derived from Mcm4Chaos3/Chaos3
mice have a 60% reduction in origin licensing. We have generated Mcm4Chaos3/Chaos3 B16 cancer cells that can
be transplanted into Mcm4wt/wt and Mcm4Chaos3/Chaos3 mice. This will allow us to separate the function of ATR that
limits origin firing from that which mediates the repair of replication forks in cancer and immune cells. In Aim 1,
we will define cell cycle kinetics and determine how ATR inhibitors induce DNA damage in immune and cancer
cells in vitro. In Aim 2, we will define cell cycle kinetics and determine whether ATR inhibitors induce DNA
damage in immune cells and type 1 interferons in vivo. In Aim 3, we will determine whether ATR inhibitors
combine with XRT to generate durable responses and immunologic memory through effects on immune and/or
cancer cells. Successful completion of this project will define how the DDR is rewired in CD8+ T cells to
accelerate cell cycle transitions and accommodate massive and concomitant DNA replication and transcription
in S phase which, accounts for ~70% of the cell cycle as G1 is abridged. These studies are highly significant as
the objective of checkpoint blockade and adoptive T cell transfer is to induce rapid division in CD8+ T cells.
Successful completion of this project will identify combinations and sequences of DDRi that potentiate cancer
cell killing while concurrently increasing anti-tumor immune responses in mouse models of cancer treated with
XRT. These studies are highly significant as we use DDRi that are currently in 115 clinical trials and XRT which
is used to treat >50% of cancer patients, >60% with curative intent.

Grant Number: 5R01CA266172-04
NIH Institute/Center: NIH
Principal Investigator: CHRISTOPHER BAKKENIST