Establishment and characterization of a clinically relevant in vitro chemo- radioresistant cervical cancer model to understand the mechanistics of therapy resistance

In locally advanced cervical cancer (LACC) patients, concurrent chemo-radiotherapy (CCRT) is the mainstay of treatment wherein 30 - 40% patients exhibit relapse within first 2-3 years of treatment, indicating acquirement of resistance to combination (chemo and radio) therapy. However, there is a lack of robust model system to comprehend the molecular events arising post combination therapy contributing to chemo-radioresistance. Further, about 99.7% cervical lesions show presence of human papilloma virus (HPV) and persistent infection with "high-risk" subtypes like 16, 18, 31, 33 and 45 has been demonstrated in promotion of both pre-invasive and invasive cervical cancers. Previous studies from our lab have demonstrated that significantly high persistent HPV 16/18 DNA viral load in immediate post treatment period in LACC treated with CCRT correlated with high loco-regional and overall relapses, indicating a possible association of high persistent HPV 16/18 DNA viral load with chemo-radioresistance. Thus, it is important to understand the association of HPV infection with chemo-radioresistance. With regard to this, in the present study we attempt to establish an in vitro chemo-radioresistant cervical cancer model simulating the clinical treatment regimen. Briefly, HPV 16 positive SiHa cells were treated with fractionated radiotherapy concurrently with cisplatin. Following generation of the resistant line, its cellular, molecular, phenotypic and transcriptomic characterization was performed at early, mid and late interval resistant cells Delayed doubling time, increased colony formation post cisplatin and radiation exposure, increased migration, elevated expression of anti-apoptotic, drug influx/efflux markers and HPV onco-proteins were observed in the resistant cells compared to parent. Ultrastructural alterations like enlarged cell and nucleus, spherical mitochondria, and enlarged golgi stacks were observed in resistant cells. To conclude, the study will provide an in-depth understanding of sequential molecular events occurring during the acquirement of chemo-radioresistance and can be utilized for development of new therapeutic strategies that may have translational value. (author)