Commentary - Journal of Cellular Immunology (2021) Volume 3, Issue 3
The Potential of Combination Therapies and Patient Stratification to Improve CCR2 Inhibition Therapeutics
Jason E. Duex1, Dan Theodorescu1,2*
1Department of Surgery (Urology), Cedars-Sinai Medical Center, Los Angeles, CA, USA
2Cedars-Sinai Samuel Oschin Comprehensive Cancer Institute, Los Angeles, CA, USA
- *Corresponding Author:
- Dan Theodorescu
Received date: April 11, 2021, Accepted date: June 14, 2021
Citation: Duex JE, Theodorescu D. The Potential of Combination Therapies and Patient Stratification to Improve CCR2 Inhibition
Therapeutics. J Cell Immunol. 2021; 3(3): 198-200.
Copyright: © 2021 Duex JE, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Bladder cancer, Tumor progression, PD-1, PD-L1, Cytokines, Checkpoint inhibitors, Immunotherapy, CCL2, CCR2
Chemokines and their receptors are the communication mechanism used by cells of the immune system, allowing them to identify and eliminate pathogens and cancerous cells. However, it is becoming clear that chemokines and their receptors are also playing a role in tumor progression and metastasis [1,2]. An example of such coopting is the CCL2-CCR2 axis. The chemokine CCL2/MCP-1 (monocyte chemoattractant protein-1) is known to bind the CCR2 receptor on monocytes  and attract them to areas of need. What is now clear is that CCR2 levels are high in tumors of a number of cancer types. For example, in bladder cancer, 12 different patient datasets  all show that CCL2 expression is higher in the more advanced, muscle invasive disease than the non-muscle invasive disease . In line with this, high CCL2 expression correlates with a worse overall survival in bladder cancer . CCL2 and CCR2 are also associated with disease progression in many other cancer types including breast, ovarian, lung and colon [6,7].
In general, the elevated levels of CCL2 and CCR2 in tumors is the result of increased recruitment of monocytes into those tumors, most often the immunosuppressive M2 class of macrophages and myeloid derived suppressor cells (MDSCs), which limit the ability of the immune system to destroy the cancer cells [7,8]. The finding that increased levels of CCL2 and CCR2 correlate with increased pathology in cancers makes the targeting of the cell surface protein CCR2 a potential therapeutic target with small molecules or therapeutic antibodies . While
clinical trials to date have observed little to no responses in patients, the drugs are well tolerated, suggesting these
drugs could be combined with those having a synergistic
mechanism of action.
A recently published study examined this concept after identifying molecular CCR2 depletion as a potential avenue for enhancing the effectiveness of immune checkpoint inhibitors (ICI) in animal models. This study employed a functional genomic screen to identify genes whose inhibition led to synthetic lethality with ICIs in several mouse tumor models . This work identified that inhibition in mouse models of two different cell surface receptors, either DDR2  or CCR2, led to enhanced tumor response when mice were also treated with the ICI anti-PD-1. The CCR2 inhibition finding is consistent with the observation that CCR2 inhibition promotes a recovery in immunity to tumors . Thus, the combination of CCR2 inhibition and ICI is an excellent combinatorial therapeutic approach to test in the clinic. In fact, a clinical trial is currently recruiting patients to investigate the combinatorial therapy of the CCR2 inhibitor BMS-813160 with Nivolumab, an ICI targeting the PD-1 molecule on immune cells. This phase II trial (NCT04123379) is focusing on patients with either non-small cell lung cancer (NSCLC) or hepatocellular carcinoma (HCC).
Another approach to improving the efficacy of CCR2 inhibition as monotherapy, or in combination with other therapeutics, would be to investigate the effect that patient stratification has on efficacy. This could be achieved by either stratification of patients by CCR2 levels in their tumors or CCL2 in their blood. To date, this stratification has not been employed. However, quantification of CCR2 protein levels in tumors has to date been approached in several ways and may be ready for clinical utility. One promising technique is tumor transcriptional profiling on formalin fixed, paraffin embedded tissue blocks. This allows for gene expression signatures to be generated for each patient and this information compared to known signatures for certain therapeutics and prognostications . For example, CCR2 gene expression levels can be
determined. Additionally, the ratio of immune cells such
as M1 macrophages (anti-tumor) to M2 macrophages
(pro-tumor), can be scored [13,14] and even estimated
computationally though various algorithms such as
CIBERSORT [5,10,16]. Using this scoring, retrospective
analysis has demonstrated that the M1-M2 scoring
ratio has a typical hazard ratio below 1 for PFS and OS
, suggesting this may be a good prognostic marker.
However, this technique does have a limitation in that an
invasive procedure is required to obtain the material prior
to any therapy that would be guided by the results. This
also means that other approaches are needed to monitor
the patient’s disease state in real-time. One non-invasive
technique that would allow for real-time monitoring is
assessing CCL2 plasma levels in patients . While the procedure involves only a simple blood draw and followon ELISA assay, further study is needed to correlate the findings with cancer progression and outcome. While the above approaches are promising, they share a limitation in that they capture data on the tumor in toto, averaging
signals from the different cell types as the tumor is
assessed as a homogeneous mixture. Alternative methods
can improve upon this aspect by assessing regions, or even
cells, individually. Immunohistochemistry (IHC) has been
used to score CCR2 levels in tissue microarrays (https://
pathology) but much of the work to date has centered
on a potential role for CCR2 in central nervous system
disorders . IHC, when fully developed for a particular
cell marker, has the benefit of providing clinicians with
geographical information within the tumor and comparing
CCR2 tumoral localization with those of other cell defining
markers, referred to as multiplex IHC [15,20]. This
additional information is particularly useful for immune
cell markers, providing both biological insights as well as
helping with prognostic and predictive determinations
for patients. Flow cytometry, or even more advanced
technologies such as imaging mass cytometry , is also
strongly suited to investigating each cell individually and
quantifying surface markers such as CCR2. Fresh tumor
samples or tumor aspirates are enzymatically treated to
yield a single cell suspension which is then probed with
several cell markers, such as CCR2. Although similar to
IHC, this technique has not been developed clinically for
CCR2 evaluation in cancer as it has been for other diseases
[21,22]. A newer technology, spurred by the advent of next
generation sequencing, is single cell sequencing (Gouin
and Theodorescu, in revision). Single cell suspensions are
prepped from fresh tumor sample or aspirates and then placed into devices which isolate cells individually. Once
isolated the nucleic acid from each cell is labeled with a
unique barcode, thereby allowing for the pooling of the
nucleic acid material for sequencing and a subsequent
ascription of the sequencing data to an individual cell
through demultiplexing. Thus, in addition to gathering
expression or mutation data from each cell, the cell type
(e.g., tumor, tumor associated fibroblast, adaptive or
innate immune cell) can be identified using well known
gene expression signatures. This allows, for example,
the determination of CCR2 levels in the tumor but also
determines which cells have the highest expression of
CCR2 . As with imaging mass cytometry, this approach
can illustrate the tumor heterogeneity (e.g., immune cell
infiltration) better than more classical techniques such
as IHC, even in multiplexed form. However, it does have
limitations in that no geography can be associated with
any of the cell info, thereby making it unclear if high
levels of CD8+ lymphocytes are within the tumor or on
the periphery. This limitation has recently been resolved
by a number of technologies that carry out numerous
spatial transcriptomics or proteomics of a tumor, allowing
visualization of gene or protein expression within the
context of tumor architecture. These vanguard technologies
are ideal for studying tumor-host interactions and also
discovering novel biomarker panels to guide monotherapy
or combinatory therapy in patients.
Therapeutic targeting of the CCR2-CCL2 axis appears to have therapeutic potential. Most notably, CCR2 inhibition exhibits substantial promise in increasing the rate of durable response in cancer patients also being treated with ICIs. Additional research is needed to identify the most accurate and practical method for determining the extent to which the CCR2-CCL2 axis is functioning for each patient and aligning that patient with the therapies that are most likely to provide them with a durable benefit.
All authors declare no competing financial interests to disclose. The manuscript has been read and approved for submission by the named authors.
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