2022 Joint Usage and Research Report
Title of Research Project

Targeting PARP7-AHR axis to Improve Cancer
Immunotherapy

InstitutionApplicant

Job title

University of Oslo

Under40

Under35

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Professor Jason Matthews

and Name
Institution
Research

Job titlecollaborators

and Name(Please add lines as

Institutionappropriate)

Job title
and Name

Host researcher at IGM

Professor Akinori Takaoka

Purpose of the Research Project

Poly-ADP-ribose polymerase 7 (PARP7) is upregulated in(approx. 250 words)

response to cellular stress, such as genomic instability, and thearylhydrocarbon

receptor(AHR),aligand

activatedtranscription factor. Using a variety of in vitro models andwhole-body and tissue specific Parp7-/- mice, we reported that
Parp7-/- are have enhanced AHR and IFN responses. PARP7
negatively regulates IFN signaling, which in the context ofcancer allows tumor cells to “hide” from immunosurveillance.
Since these actions of PARP7 depend on its catalytic activity,
PARP7 loss or its inhibition in tumor cells should release the“brake” that cancer cells use to evade the immune system.
Recently, small molecule inhibition of PARP7 was shown torestore IFN signaling and in essence release the brake thatcancer cells use to evade the immune system. However, PARP7
also negatively regulates AHR, and its loss increases AHRsignaling. Although AHR is best known for mediating dioxin
toxicity, AHR drives pro-survival processes via kynureninedependent mechanisms to increase tumor growth and promote
an immunosuppressive tumor microenvironment. When coexpressed with PARP7, AHR activation would be expected tocounteract the anti-tumor effects of PARP7 inhibition. Thissuggests that inhibiting both PARP7 and AHR may offer
therapeutic benefit for patients with tumors that express bothproteins.
We hypothesize that loss or inhibition of PARP7 will reducetumor growth by increasing anti-tumor immune responses;
however, for tumors that express AHR, PARP7 inhibition will
increase tumor growth. Therefore, AHR inhibition will improve
the therapeutic benefit of PARP7 inhibition.
Development of the ResearchOver the course of the past year, we have exchanged emails andProject and Results

ideas related to the research supported by the Joint Research(approx.. 850 words)

Program. A formal web-based meeting was not organized but*Enter the number of web

will be done in the future until other alternatives are possible.

meetings.

Due to uncertainty of travel restrictions, a physical visit did notoccur. A physical visit to the host lab is planned for 2024.
Results:
WP1: Determine the effect of inhibition/loss of PARP7 on tumor
cell growth. Here we proposed to test the intrinsic role of PARP7
in human and murine tumor cells. We will use the following
human cell lines, MDA-MB-231 and MDA-MB-468 cells, andmurine cell lines, EO771, and PyMT cells that were derived
from murine mammary tumors.

Task 1.1. Generation of PARP7 knockout cancer cell lines.
CRISPR/Cas9 targeted gene editing will be used to generate PARP7
knock-out (PARP7ko) and AHRko human breast cancer cell lines,
MCF7, MDAMB231, MDAMB468) and mouse breast cancer celllines: EO771, PyMT). Not EO771 cells, were found to be AHR
negative, so generating AHRKO cells was not necessary. As
expected, PARP7ko increased type I IFN and AHR signaling. AHRko
differentially affected type I IFN, which varied among cell lines. NoAHR signaling was observed in AHRko cells.

Task 1.2. Investigate and biochemical characterize novel PARP7inhibitors. We tested 3 different PARP7 inhibitors all of which
resulted in increased type I IFN and AHR signaling.
WP 2: Determine the effects of PARP7 immune cell-dependent
tumour cell killing. This WP included 2 task: Task 2.1. Coculture studies with human cans and cytotoxic T lymphocytes;
Task 2.2. Co-culture of cancer cells with CD8+ T lymphocytes ofmacrophages from PARP7+/+ or PARP7-/- mice. We made little
progress on these tasks during the past year.

WP3. Determine the impact of inhibition/loss of PARP7 onmammary tumor growth in vivo. In this WP, we used Parp7H532A
mice in which a single point mutation was introduced into thePARP7 catalytic domain, resulting in a PARP7 protein devoid ofcatalytic activity. We injected Parp7WT and Parp7ko EO771 cells
in syngeneic tumor models using our Parp7+/+ or Parp7H532A
mice as hosts. These studies will determine differences between
loss of PARP7 activity in tumor cells but not the host, versus
loss of PARP7 activity in the host but not in tumor cells on solidtumor growth. In xenograft studies, PARP7 loss had no effect ontumor growth. In contrast, we observed that injection of
wildtype cells into catalytically-dead Parp7H532A mice resulted
in smaller tumors compared with cells injected into Parp7+/+mice. Parp7H532A mice injected with Parp7KO cells failed todevelop tumors after 30 days and those that developed
regressed. Similar studies are planned for PyMT PARP7ko cells
that express AHR to test the impact of PARP7 loss on tumor
growth in cancer cells that express AHR. These studies areongoing.
In task 3.2, we will determine the effect of loss of PARP7
catalytic on spontaneous mammary tumor growth by using themammary specific polyomavirus middle T antigen (MMTVPyMT) to generate a MMTVPyMT; Parp7H532A line. TheMMTVPyMT mice have been purchased on the experiments
should be completed by in early 2024.
Overall, progress has been good on the project, except for WP2,
and we look forward to a continued strong researchcollaboration in the upcoming years.
【Conference, symposium, workshop etc.】

Publication*EntertheinformationofPARP7 2022, Cold Spring Harbor March 2022.

conference or journal (vol. page.
Year.) where the above work
was presented.
【Journals】
Some of this work will be submitted to for publication in the latespring of 2023.