MICA: Monocyte and macrophage manipulation for the control of chemotherapy-induced pain

Chronic neuropathic pain develops following damage or disease of the nervous system caused by injury, diabetes, or cancer treatment with chemotherapy drugs. Neuropathic pain is difficult to treat, with current drugs being relatively ineffective and often having significant side effects. Effective control of neuropathic pain may dramatically improve the quality of life of many patients. In particular, chemotherapy drug treatment for cancer often results in pain in the hands and feet experienced by 30-40% of patients. This undesired side effect limits the dose of cancer drug that patients can be given and is the main reason for stopping treatment.
Therefore, a better understanding of the mechanisms by which chemotherapy treatment causes painful side effects can bring new ideas on how to prevent and/or attenuate this type of pain and facilitate the development of new medicines. We use mice in our studies as they also demonstrate pain-related behaviour in their hind paws when given chemotherapy drugs.
In a recent study that paved the way to this research project, we asked how Vincristine causes pain. Vincristine is commonly used for leukemias and results in complaints of pain that can occur as early as the first treatment and may last indefinitely. Similarly, mice display pain-like behavior within the first day of vincristine injection and during a subsequent two week-treatment. As pain killers could be given to patients with the chemotherapy drug to prevent the development of pain, we focused on the mechanisms responsible for the very initial pain. We found that vincristine causes damage to blood vessels around the nerves. When this happens, specialised blood cells leave the blood flow and enter the nerve where they activate pain nerves which convey signals to the spinal cord on their way to the brain where pain is perceived. We showed that by stopping these cells leaving the blood flow, vincristine-induced pain can indeed be prevented.
In this research project we will use another chemotherapy drug, paclitaxel that is also used for leukemias and shares pain as an undesirable side effect. We will inject vincristine or paclitaxel in mice in order to mirror chemotherapy treatments in patients. In these models, we will look for what causes pain to start but also to remain for very long time. In these mice models, we plan to identify molecules inside and on the outside of the blood cells that can be targeted with novel compounds to stop their exit from blood, constituting new types of pain treatment.
We have a good idea of where to start and plan to test the pain-relieving effect of drug-like compounds which will stop blood cells leaving the blood flow. In order to do this, we will join forces with the pharmaceutical company Medivir which will design and provide such compounds. In addition we will examine the potential pain-relieving effect of compounds which are commercially available and will stop cells entering the nerve by a different mechanism.
The ultimate aim of our research is to provide new information that will help in the design of new pain relieving medicines, thus allowing chemotherapy treatments to be used more effectively, without painful side effects, thus improving the quality of life of the patient.

Painful peripheral neuropathy constitutes a major dose limiting side effect of chemotherapeutics that remains poorly controlled by available analgesics. Elucidation of mechanisms underlying chemotherapy-induced pain will identify targets for prophylactic and therapeutic analgesia.
We recently showed that monocyte/macrophage infiltration in sciatic nerve orchestrates the development of vincristine (VCR)-induced allodynia in mice. Specifically, VCR administration induced expression of endothelial adhesion molecules and CX3CR1+ monocyte infiltration into the sciatic nerve. CX3CR1 receptor activation with endothelial fractalkine (FKN) induced formation of reactive oxygen species (ROS) by macrophages. ROS activated TRPA1 channels on sensory axons which evoked a pain response. VCR-allodynia was prevented by blocking monocyte trafficking into the sciatic nerve. However, mouse (and human) monocytes include a heterogeneous population of cells. Here we plan to identify the specific monocyte subsets that mediate initiation and maintenance of VCR- and paclitaxel-induced allodynia. Our hypothesis is that chemotherapeutic administration results in alteration of sciatic nerve microvasculature so that patrolling monocytes (CX3CR1+CCR2-) are retained by the endothelium as an early response. They trigger the generation of a local inflammatory environment and promote inflammatory monocyte (CX3CR1+CCR2+) to infiltrate the nerve. By combining behavior and immunohistochemistry with intravital microscopy in transgenic mice (KCL), we will define location and function of monocyte subsets in the sciatic nerve during chemotherapy-allodynia. Furthermore, we will establish whether manipulation of monocyte trafficking in the sciatic nerve provides prophylactic and therapeutic analgesia by testing CCR2 receptor antagonists and peripherally restricted Medivir cathepsin S inhibitors (by inhibiting enzymatic release of endothelial FKN, CX3CR1-monocyte activation is blocked).

Neuropathy constitutes the major dose-limiting side-effect of chemotherapy. The key symptom of this condition reported by patients is pain which is poorly controlled by available analgesics. Thus there is an unmet clinical need for the development of new strategies that ideally prevent the onset and establishment of chemotherapy-induced pain by interfering with the mechanism by which the pain occurs, without reducing the cancer fighting abilities of anti-neoplastic agents.
This proposal aims to advance our understanding of the role of inflammatory cells in the pathology of chemotherapy-induced pain in order to provide new targets and treatments for prophylactic and therapeutic analgesia.

Besides scientists investigating neuroinflammation mechanisms underlying chronic pain with the aim of identifying new therapeutic targets, a wider group of beneficiaries will use the outputs of the proposed research.

Patients undergoing chemotherapy treatment. The findings of this pre-clinical research will have direct relevance to the clinical problem and will provide important evidence for the therapeutic potential of new targets for the treatment of chemotherapy-induced pain. Medivir has a long standing interest in the development of cathepsin S inhibitors for the treatment of chronic pain. In the short-term our research could lead to a clinical trial on the analgesic effect of CatS inhibitors in patients undergoing chemotherapy treatment for cancer.
In the longer-term development of a new treatment strategy to prevent or reduce the pain associated with chemotherapy treatment, thus improving patient's quality of life and allowing chemotherapeutic agent to be maintained at most effective dose, thus increasing chance of effective treatment.

Commercial private sector: The mechanistic insights from this research will provide confidence and real time guidance to the industrial partner in its on-going development of proprietary CatS inhibitors. In the short term, the pharmaceutical industry will benefit from our approach. By examining the analgesic efficacy of CatS inhibitors, we will guide drug discovery teams in this area. There is a substantial effort in both small and big industries at developing CatS inhibitors for autoimmune diseases as well as neuropathic pain. Thus, companies developing CatS inhibitors will find a rationale for exploring compound analgesic efficacy with an impact on pain associated with chemotherapy treatment. Similarly, companies exploring therapeutic avenues for chemokine receptor antagonists will be provided with a rationale and preclinical evidence for considering CCR2 receptor antagonists for chemotherapy-induced pain. In the longer term, our research could lead to a clinical trial of CatS inhibitors and CCR2 receptor antagonists in chemotherapy-pain sufferers.

The research staff and KCL students working on this project will interact with scientists bringing various skills and expertise by including inflammation, neuroscience and drug discovery teams. The interdisciplinary nature of the research project will encourage staff to use their ingenuity and think outside the box thereby improving their professional skills. The collaboration with our partners at Medivir will increase the staff's employability by forging the right mindset towards drug discovery research. The collaboration will also provide an insight into drug development and key in vitro pharmacology, drug metabolism and pharmacokinetic parameters used in preclinical drug development. Such skills will be valuable for continuing a career in academia as well as industry by performing basic science with translational impact. Finally, the collaboration and exchange of knowledge with industry will expose staff to issues such as intellectual property, public health and ethical concerns.