The cell surface adhesion molecule, Receptor Protein Tyrosine Phosphatase PTPµ (PTPmu/PTPRM), is proteolyzed or “cut” in human cancer. Fragments of PTPµ have been observed both outside and inside of tumor cells. These fragments have unique signaling features, and contribute to the growth and invasiveness of tumor cells. We applied over three decades of research on the Ig superfamily of cell adhesion molecules, PTPµ mediated cell adhesion in normal cells, and the study of its proteolysis in cancer cells. We designed and generated agents that bind to the PTPµ fragments but not the normal protein to specifically detect and image cancer cells. Using models of various tumor types, these agents: 1) label the main tumor mass within minutes; 2) exhibit sustained tumoral binding in comparison to conventional untargeted agents; 3) achieve specific recognition of the full extent of the tumor including invading tumor cells which are ultimately believed to lead to recurrence. By conjugating the same agents to fluorophores, metals, or radioactive isotopes, we created a platform technology that can be used to recognize cancer cells in applications that range from diagnosis to imaging to the targeted treatment of primary, invasive and metastatic tumors to “see(k) and destroy” cancer.
An integrated approach has been adopted by the World Health Organization (WHO) for diagnosing brain tumors. This approach relies on the molecular characterization of biopsied tissue in conjunction with standard histology. Diffuse gliomas (grade II to grade IV malignant brain tumors) have a wide range in overall survival. For the worst cases of glioblastoma, patients only survive for a few months while those with lower grade astrocytic and oligodendroglial tumors survive for a few years. However, a number of patients fall outside this average survival range. It is currently unknown why there are “outliers” and it is currently difficult to predict the overall survival for an individual patient.
The cell adhesion molecule PTPmu undergoes a change in multiple tumor types. We have developed a number of reagents to detect the unique PTPmu biomarker that accumulates in the tumor microenvironment. We evaluated the PTPmu biomarker in tumor samples of ~100 glioma patients. We found a correlation between high levels of the PTPmu biomarker and a doubling of overall patient survival in glioma patients (Johansen et al, 2019). Use of this novel reagent will allow differentiation of glioma patients at the time of diagnosis and will be prognostic for distinct survival outcomes. The in vitro diagnostic test works consistently and is on track to be developed as a CLIA approved laboratory test for glioma and ultimately other tumor types.
MRI is an ideal modality for high-resolution tumor imaging, and is standard of care for brain tumor diagnosis and monitoring of treatment. This is accomplished by intravenous administration of a non-specific contrast agent gadolinium (Gd) that enhances areas of large tumor masses where the blood brain barrier is disrupted. This non-specific contrast only labels the center of the primary tumor and is not capable of enhancing the full extent of the tumor including the invasive regions. By developing this agent, we created an efficient, MRI imaging agent.
When it comes to analyzing MRIs, most studies use either a change in MR signal derived from qualitative images or long acquisition times that do not allow for dynamic quantitative comparisons. We used T1 mapping in order to allow absolute T1 relaxation values to be determined. We found that the use of a molecular imaging agent with a dynamic quantitative T1 mapping MR method results in quantitative MRI results by calculating change in Gd concentration over time.
We demonstrated that the molecular MRI agent can identify a brain tumor lesion more specifically and with higher and more sustained contrast than conventional contrast agents (Johansen et al, 2017).
Radiofrequency Delivered Therapeutic
Pediatric brain tumors are the most common cause of solid cancer related deaths in children. While many pediatric brain tumors have seen clinical improvement over the past few decades, that is not the case with the most aggressive type of pediatric brain cancer, glioma. We generated drug-loaded PTPmu-targeted nanochains to specifically attack invasive brain tumor sites (Covarrubias et al, 2020). The nanochains have a triggering mechanism to induce drug release specifically at the desired location with the application of an external low-power radiofrequency field to the outside of the head.
Ultrasound Delivered Therapeutics
We evaluated how PTPmu proteolysis could be used to target gynecological tumors. Ovarian and some endometrial cancer has a high rate of proteolyzed PTPmu associated with it. We tested nanobubbles for the diagnosis and treatment for gynecological cancer with PTPmu-targeted nanobubbles that are capable of releasing drugs in response to ultrasound (Johansen et al, 2021).
The ability to image tumors and their invasive edges or boundaries in real time during surgery is of vital importance for effective surgical management of cancer. Yet tumors are difficult to image because of the invasive nature of cancer cells - they migrate away from the main tumor mass in clusters of cells that can’t be seen with either the naked eye or microscopically with white light reflectance.
Based on proteolysis, we developed a set of optical imaging agents to visualize tumors in vivo. The fluorescent agents bind to invading/dispersing cancer cells in models of glioma brain tumors. We are pioneering the use of the fluorescent imaging agent for image-guided surgical resection of brain tumors. In fact, the US FDA has approved its first fluorescent image-guided agent, 5-ALA, for use in glioblastoma (GBM) surgery. The fluorescence-guided surgical technique is currently receiving significant clinical attention given its potential for high level of effectiveness in prolonging survival outcomes for GBM patients.
In the laboratory, we have also used many innovative imaging tools, including 3-dimensional cryo-image analysis system to visualize nerves, blood vessels, and individual cancer cells in a brain tumor model. This technology was developed at CWRU. We utilize it to visualize the extent of invasion and metastasis and the labeling to tumor cells by NEO agents (Craig et al, 2016; Burden-Gulley et al, 2013; Burden-Gulley et al, 2011: Burden-Gulley et al, 2010) .
By using chelators for the gamma emitting isotope, 68Ga, we created an agent for use in PET imaging. PET has advantages over MRI in many cancer applications, and generally has better sensitivity than MRI. Furthermore, the NEO agents can be conjugated to an alpha or beta emitting isotope (225Ac or 177Lu) to deliver a lethal amount of ionizing radiation directly to cancer cells and their tumor microenvironment.