Ovarian cancer is the most lethal gynecologic cancer and the fifth most common cause of cancer death among women in the United States. Although there have been incremental improvements in progression free survival over the last several decades from advances in surgical technique and combination-chemotherapy strategies, overall survival has essentially remained unchanged. Although novel therapeutics have the potential to impact overall survival and lead to more cures, drug development in this area has been limited by the availability of clinically relevant models that recapitulate the molecular and phenotypic characteristics of primary ovarian cancers.
To overcome this barrier, we have developed primary patient derived xenograft (PDX) models from every consenting patient having primary debulking surgery at Mayo Clinic since 2010 (>550 unique patients). Fresh tissues are minced and injected intraperitoneally into severe combined immunodeficient (SCID) mice without enzymatic digestion or surgical implantation. The patient-to-mouse time is typically <1.5 hours and the engraftment rate is 73%.
Ovarian PDX models have demonstrated their utility as patient surrogates. The histologic diversity is representative of the population from which they are derived with high-grade serous comprising most of the models. However, the ovarian PDX bank also includes less-common subtypes, such as clear cell, mucinous, and carcinosarcoma. Histologic and genomic fidelity is maintained within early-passage tumors. Moreover, the patient's clinical response to carboplatin and paclitaxel (a standard front-line therapy for ovarian cancer) demonstrates high correlation to the matched PDX tumor response in vivo, supporting their relevance as patient surrogates.
The models have been used for preclinical drug development and biomarker validation. One example is the correlation between PARPi response in PDXs and their homologous recombination deficiency (HRD) score. All models with a low HRD score, <42, failed to respond to PARP inhibition while models with a high HRD score showed enrichment for response to a PARPi.
Ovarian PDXs are also being used to direct patient care in a clinical trial setting at all three Mayo Clinic sites (MN, FL, and AZ). Tumors are collected at the time of debulking surgery for heterotransplantation. Subsequent xenografts are treated with standard first-line chemotherapy, similar to their matched patient in the clinic, and then PDXs are treated with standard ovarian cancer second-line therapies: liposomal doxorubicin, topotecan, gemcitabine, and paclitaxel. When patients develop platinum-resistant recurrent cancer, the chemotherapy response in the PDX is used to direct therapy in the clinic.
Many challenges continue for ovarian cancer PDX models. The use of immunocompromised mice limits the ability to study the involvement of immunity in chemotherapy responsiveness. In addition, these models are not ideal for testing novel immunotherapies, such as the immune check point inhibitors. Further work to overcome these and other limitations are needed.
Citation Format: S. John Weroha. Ovatars in preclinical drug development and clinical trial for ovarian cancer patients. [abstract]. In: Proceedings of the AACR Special Conference: Patient-Derived Cancer Models: Present and Future Applications from Basic Science to the Clinic; Feb 11-14, 2016; New Orleans, LA. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(16_Suppl):Abstract nr IA11.