Autophagy enhancement contributes to the synergistic effect of vitamin D in temozolomide-based glioblastoma chemotherapy.
Temozolomide (TMZ), an alkylating agent, is recommended as the initial treatment for high-grade glioblastoma. TMZ is widely used, but its short half-life and the frequency of tumor resistance limit its therapeutic efficacy. In the present study, the anticancer effect of vitamin D (VD) combined with TMZ upon glioblastoma was determined, and the underlying mechanism of this effect was identified. Through cell viability, clonogenic and wound healing assays, the current study demonstrated that treatment of a C6 glioblastoma cell line with TMZ and VD resulted in significantly increasedin vitroantitumor effects compared with either VD or TMZ alone. Autophagy, hypothesized to be the dominant mechanism underlying TMZ-based tumor cell death, was maximally activated in TMZ and VD co-treated C6 cells. This was demonstrated by ultrastructural observations of autophagosomes, increased size and number of microtubule-associated protein 1 light chain 3 (LC3) puncta and increased conversion of LC3-I to LC3-II. However, the extent of apoptosis was not significantly different between cells treated with TMZ and VD and those treated with TMZ alone. Addition of the autophagy inhibitor 3-methyladenine markedly inhibited the anticancer effect of TMZ and VD treatment, indicating that the chemosensitizing effect of VD in TMZ-based glioblastoma therapy is generated through enhancement of cytotoxic autophagy. TMZ and VD co-treatment also significantly inhibited tumor progression and prolonged survival duration in rat glioblastoma orthotopic xenograft models when compared with TMZ treatment alone. Thesein vivoresults are concordant with the aforementionedin vitroresults, together revealing that the combined use of TMZ and VD exerts synergistic antitumor effects on rat models of glioblastoma and may represent an effective therapeutic strategy.
Department of Anatomy, College of Medicine, Konyang University, Daejeon 302-718, Republic of Korea.
Dong-Ho
DH
Bak
Department of Radiological Science, College of Medicine, Konyang University, Daejeon 302-718, Republic of Korea.
Seong Hee
SH
Kang
Department of Anatomy, College of Medicine, Konyang University, Daejeon 302-718, Republic of Korea.
DU Ri
DR
Choi
Department of Anatomy, College of Medicine, Konyang University, Daejeon 302-718, Republic of Korea.
Mi Na
MN
Gil
Department of Anatomy, College of Medicine, Konyang University, Daejeon 302-718, Republic of Korea.
Kwang Sik
KS
Yu
Department of Anatomy, College of Medicine, Konyang University, Daejeon 302-718, Republic of Korea.
Ji Heun
JH
Jeong
Department of Anatomy, College of Medicine, Konyang University, Daejeon 302-718, Republic of Korea.
Nam-Seob
NS
Lee
Department of Anatomy, College of Medicine, Konyang University, Daejeon 302-718, Republic of Korea.
Je-Hun
JH
Lee
Department of Anatomy, College of Medicine, Konyang University, Daejeon 302-718, Republic of Korea.
Young-Gil
YG
Jeong
Department of Physiology, College of Medicine, Konyang University, Daejeon 302-718, Republic of Korea.
Dong Kwan
DK
Kim
Industry Cooperation Foundation, Konyang University, Daejeon 302-718, Republic of Korea.
DO-Kyung
DK
Kim
Department of Anatomy, College of Medicine, Konyang University, Daejeon 302-718, Republic of Korea; Myunggok Research Institute, College of Medicine, Konyang University, Daejeon 302-718, Republic of Korea.
Jwa-Jin
JJ
Kim
Department of Anatomy, College of Medicine, Konyang University, Daejeon 302-718, Republic of Korea; Myunggok Research Institute, College of Medicine, Konyang University, Daejeon 302-718, Republic of Korea.
Seung-Yun
SY
Han
autophagy; glioblastoma; orthotopic xenograft; temozolomide; vitamin D