Rapalogs induce non-apoptotic, autophagy-dependent cell death in HPV-negative TP53 mutant head and neck squamous cell carcinoma
Md Maksudul Alam 1, Janmaris Marin Fermin 1, Patrick T Spiller 1, Chaning Burnett 2, Xiaohua Rong 1, Tara Moore-Medlin 1, Caden O Maxwell 1, Alok R Khandelwal 1 3, Cherie-Ann O Nathan 1 3
TP53 is easily the most frequently mutated gene in mind and neck squamous cell carcinoma (HNSCC). Patients with Warts-negative TP53 mutant HNSCC possess the worst prognosis, necessitating additional agents for treatment. Since mutant p53 causes sustained activation from the PI3K/AKT/mTOR signaling path, we investigated the result of rapalogs RAD001 and CCI-779 on Warts-negative mutTP53 HNSCC cell lines and xenografts. Rapalogs considerably reduced cell viability and colony formation. Interestingly, rapalogs-caused autophagy without any impact on apoptosis. Pretreatment with autophagy inhibitors, 3-methyladenine (3-MA) and ULK-101 saved the cell viability by inhibiting rapalog-caused autophagy, suggesting that both RAD001 and CCI-779 induce non-apoptotic autophagy-dependent cell dying (ADCD). Furthermore, rapalogs upregulated the amount of ULK1 and pULK1 S555 with concomitant downregulation from the mTORC1 path. However, pretreatment of cells with rapalogs avoided the ULK-101-mediated inhibition of ULK1 to sustained autophagy, suggesting that rapalogs induce ADCD with the activation of ULK1. To help translate our in vitro studies, we investigated the result of RAD001 in Warts-negative mutTP53 (HN31 and FaDu) tumor cell xenograft model in nude rodents. Rodents given RAD001 exhibited a substantial tumor volume reduction without induction of apoptosis, with a concomitant rise in autophagy. Further, treatment with RAD001 was connected having a considerable rise in pULK1 S555 and ULK1 levels with the inhibition of mTORC1. 3-MA reversed the result of RAD001 on FaDu tumor growth suggesting that RAD001 promotes ACDC in Warts-negative mutTP53 xenograft. This is actually the first report demonstrating that rapalogs promote non-apoptotic ADCD in Warts-negative mutTP53 HNSCC through the ULK1 path. Further research is needed to determine the promising role of rapalogs in stopping the regrowth of Warts-negative mutTP53 HNSCC.