Preclinical Model Systems to Study GBM and AML
In vitro cellular models
One of the biggest challenges associated with GBM is the recurrence of the tumor which becomes refractory to the multimodal treatment of radio-chemotherapy. Once tumor is resected and radiation is given, patients do not come for multiple biopsies but only when there is a relapse. Therefore, molecular steps that lead to the relapse cannot be studied from biopsy samples. For this reason, we recapitulated the clinical scenario of resistance in Glioblastoma in our laboratory in an in vitro cellular model generated from primary cultures of fresh Primary Grade IV GBM patient tumors and GBM cell lines. This model system enable us to capture therapy 'Escapers/Residual/Persister' cells, that are otherwise inaccessible. We have shown that the residual cells are responsible for relapse in GBM. Using these models we are now trying to understand the molecular events that provide residual and recurrent cells survival advantage. Furthermore, in collaboration with Dr. Abhijit Majumder at IIT, Bombay, who has developed a polyacrylamide hydrogels system with matrices of different stiffness, we could recapitulate the brain-like microenvironment in terms of mechanosensing properties for studying the cell-ECM interactions in vitro.
We have also developed an evolutionary cellular model of chemotherapy resistance in Acute myeloid leukemia (AML). This model captures the persisters or residual cells, equivalent to the minimal residual disease observed in the patients. These cells eventually evolve to acquire high resistance to the chemotherapy and become refractory to the drugs as seen in the patients, thus recapitulating clinical settings. Using this model we have identified molecules that mark the onset of acquired resistance. We are using this model to delineate novel molecular pathways responsible for acquired AML resistance.
In vivo orthotopic pre-clinical mouse models
In order to decode the underlying molecular mechanisms responsible for GBM therapy resistance and recurrence in vivo, we have established orthotopic mouse models by intracranial injections of GBM cell lines and patient samples (patient-derived orthotopic xenografts PDOX). The superiority of orthotopic models lies in their higher ability to recapitulate the original tumor. A detailed understanding of these resistance mechanisms can help to develop novel therapeutic regimes, which can potentially prevent or delay tumor recurrence and significantly improve patient survival. Similarly, in the case of Acute Myeloid Leukemia (AML), despite the achievement of complete morphological remission in 60-70% of cases, most of them relapse. The presence of less than 5% of bone marrow blasts serve as a post-therapy prognosticator and is termed as the minimal residual disease (MRD) state, presence of residual cells has been reported to be correlated with poor therapy response and survival, thereby suggesting a vital role of these residual cells in resistance and relapse. However, a complete understanding of the active resistance mechanisms in these residual AML cells formed in vivo is lacking. Thus, we are developing a preclinical mouse model to recapitulate the clinical scenario of MRD state in order to examine the molecular mechanisms of resistance in these MRD cells.