Role of PI3K Isoforms in Osteosarcoma and Angiosarcoma/Hemangiosarcoma
The PI3K/AKT-mTOR pathway has been shown to be dysregulated in many different types of cancers. These alterations include the mutation of the PIK3CA gene and the deletion of the negative regulator of the pathway, PTEN. Despite evidence that PI3K plays a role in many cancers, specific contributions of the four individual PI3K isoforms, α, β, δ, and γ, have not been established. We are investigating the role of these isoforms in human and canine osteosarcoma (OS) and angiosarcoma/hemangiosarcoma (AS/HSA), two sarcomas which are very common in canine patients are relatively rare in humans. We have analyzed the PI3K isoform expression in a panel of human and canine sarcoma cell lines, and have found that the α, β, and δ isoforms are expressed in all lines studied thus far, while the γ isoform is not. Expression of PI3K-δ is a surprising finding as the δ and γ isoforms are typically expressed exclusively in leukocytes, while the α and β isoforms are ubiquitously expressed. Our ongoing studies employ a combination of CRISPR/Cas9 and lentiviral shRNA approaches to further interrogate the contribution of specific PI3K isoforms to sarcoma biology, particularly with respect to metastasis and resistance to immune checkpoint blockade
Monocarboxylate Transporter Function in Sarcomas
A unique feature of cancer cells is their ability to undergo aerobic glycolysis (known as the Warburg effect), allowing them to thrive in a variety of environmental conditions. Monocarboxylate transporters (MCTs) are key facilitators of aerobic glycolysis, moving lactic acid across the plasma membrane, and are critical for growth and metastasis of glycolytic tumors. We are interrogating the role of MCTs in canine and human osteosarcoma (OS) to better understand the biology driving metabolic dysregulation in OS and its contribution to the development of metastatic disease. As both canine and human OS patients typically succumb to drug-resistant metastatic disease, defining mechanisms driving metabolic regulation in the context of the tumor microenvironment and how this can be exploited for synthetic lethality will contribute to the development of more effective therapeutics for OS in both people and dogs. Our data demonstrate that MCT expression is not consistent between primary and metastatic OS tumors, suggesting that tumor cells may easily adapt to changing microenvironment stressors. Furthermore, loss of MCT expression appears to modulate tumor cell invasion, while not impacting proliferation or survival. We are currently exploring the connection between STAT3, (a transcription factor typically constitutively active in OS), FOXM1, another transcription factor important in tumor cell biology) and regulation of MCT expression and function in OS.
Comparative Genomics
Spontaneous canine cancers recapitulate the human condition with respect to clinical progression, response to therapy, as well as histologic and molecular profiles. The breeding of dogs for specific phenotypic traits resulted in numerous dog breeds, with increased risk for certain diseases. We have a longstanding history of utilizing spontaneous cancers in dogs to study complex interactions in cancer, with the ultimate goal of informing future human studies and helping improve therapeutic outcomes in both canine and human cancer. We are currently working with the Dana Farber Cancer Institute and Translational Genomics Research Institute to define the genomic landscape of canine OS to define shared aberrations that can be targeted to improve immunotherapeutic outcomes. We also have an ongoing collaboration with the Broad Institute to characterize the genomic landscape of human and canine AS/HSA to identify common targets for therapeutic intervention that can be validated in the canine disease prior to initiation of human clinical trials.
Role of STAT3 and gp130 in Osteosarcoma
Osteosarcoma (OS) is a primary bone malignancy with a high tendency to metastasize. It is generally classified as a rare cancer with 800-1000 new cases per year, primarily occurring within adolescents and children. While overall 60-70% of affected patients are effectively cured of disease, OS exhibits a poor prognosis with a low survival rate in patients with metastatic disease due to inherent chemoresistance and poor response to immunotherapeutics. We have been evaluating the contribution of STAT3, a transcription factor that regulates proliferation, survival, metastasis and chemotherapy resistance, in OS and have found constitutive activation in most OS cell lines and primary tumor samples. While our data indicate that STAT3 does not directly regulate cell proliferation and survival, recent work from our laboratory and that of our collaborators at Nationwide Children’s Hospital suggests that STAT3 plays a pivotal role in driving key microenvironment interactions that support metastatic seeding and immune escape. Furthermore, IL-6 family members (including oncostatin M and IL-11, among others) appear to drive STAT3 phosphorylation in OS tumor cells through gp130 signaling, supporting growth and survival in the lung microenvironment. To better define these interactions, we are using a combination of CRISPR/Cas9 and lentiviral shRNA approaches to alter expression of STAT3, as well as gp130, in OS cell lines to assess their impact on tumor cell growth, survival and metastatic seeding in vivo using both xenogeneic and syngeneic mouse models.