PMID- 30254491 OWN - NLM STAT- PubMed-not-MEDLINE LR - 20220321 IS - 1179-1322 (Print) IS - 1179-1322 (Electronic) IS - 1179-1322 (Linking) VI - 10 DP - 2018 TI - Combined use of CDK4/6 and mTOR inhibitors induce synergistic growth arrest of diffuse intrinsic pontine glioma cells via mutual downregulation of mTORC1 activity. PG - 3483-3500 LID - 10.2147/CMAR.S167095 [doi] AB - BACKGROUND: Diffuse intrinsic pontine glioma (DIPG) is a lethal type of pediatric brain tumor that is resistant to conventional chemotherapies. Palbociclib is a putative novel DIPG treatment that restricts the proliferation of rapidly dividing cancer cells via selective inhibition of cyclin-dependent kinase (CDK) 4 and CDK6. However, implementing palbociclib as a monotherapy for DIPG is unfeasible, as CDK4/6 inhibitor resistance is commonplace and palbociclib does not readily cross the blood-brain barrier (BBB) or persist in the central nervous system. To inhibit the growth of DIPG cells, we aimed to use palbociclib in combination with the rapamycin analog temsirolimus, which is known to ameliorate resistance to CDK4/6 inhibitors and inhibit BBB efflux. MATERIALS AND METHODS: We tested palbociclib and temsirolimus in three patient-derived DIPG cell lines. The expression profiles of key proteins in the CDK4/6 and mammalian target of rapamycin (mTOR) signaling pathways were assessed, respectively, to determine feasibility against DIPG. Moreover, we investigated effects on cell viability and examined in vivo drug toxicity. RESULTS: Immunoblot analyses revealed palbociclib and temsirolimus inhibited CDK4/6 and mTOR signaling through canonical perturbation of phosphorylation of the retinoblastoma (RB) and mTOR proteins, respectively; however, we observed noncanonical downregulation of mTOR by palbociclib. We demonstrated that palbociclib and temsirolimus inhibited cell proliferation in all three DIPG cell lines, acting synergistically in combination to further restrict cell growth. Flow cytometric analyses revealed both drugs caused G(1) cell cycle arrest, and clonogenic assays showed irreversible effects on cell proliferation. Palbociclib did not elicit neurotoxicity in primary cultures of normal rat hippocampi or when infused into rat brains. CONCLUSION: These data illustrate the in vitro antiproliferative effects of CDK4/6 and mTOR inhibitors in DIPG cells. Direct infusion of palbociclib into the brain, in combination with systemic delivery of temsirolimus, represents a promising new approach to developing a much-needed treatment for DIPG. FAU - Asby, Daniel J AU - Asby DJ AD - Functional Neurosurgery Research Group, Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK, steven.gill@nbt.nhs.uk. FAU - Killick-Cole, Clare L AU - Killick-Cole CL AD - Functional Neurosurgery Research Group, Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK, steven.gill@nbt.nhs.uk. FAU - Boulter, Lisa J AU - Boulter LJ AD - Functional Neurosurgery Research Group, Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK, steven.gill@nbt.nhs.uk. FAU - Singleton, William Gb AU - Singleton WG AD - Functional Neurosurgery Research Group, Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK, steven.gill@nbt.nhs.uk. AD - Department of Neurosurgery, North Bristol NHS Trust, Southmead Hospital, Bristol, UK, steven.gill@nbt.nhs.uk. FAU - Asby, Claire A AU - Asby CA AD - Department of Neurology, North Bristol NHS Trust, Southmead Hospital, Bristol, UK. FAU - Wyatt, Marcella J AU - Wyatt MJ AD - Functional Neurosurgery Research Group, Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK, steven.gill@nbt.nhs.uk. FAU - Barua, Neil U AU - Barua NU AD - Functional Neurosurgery Research Group, Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK, steven.gill@nbt.nhs.uk. AD - Department of Neurosurgery, North Bristol NHS Trust, Southmead Hospital, Bristol, UK, steven.gill@nbt.nhs.uk. FAU - Bienemann, Alison S AU - Bienemann AS AD - Functional Neurosurgery Research Group, Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK, steven.gill@nbt.nhs.uk. FAU - Gill, Steven S AU - Gill SS AD - Functional Neurosurgery Research Group, Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK, steven.gill@nbt.nhs.uk. AD - Department of Neurosurgery, North Bristol NHS Trust, Southmead Hospital, Bristol, UK, steven.gill@nbt.nhs.uk. LA - eng GR - MR/N001370/1/MRC_/Medical Research Council/United Kingdom PT - Journal Article DEP - 20180912 PL - New Zealand TA - Cancer Manag Res JT - Cancer management and research JID - 101512700 PMC - PMC6140749 OTO - NOTNLM OT - DIPG OT - brain tumor OT - cyclin-dependent kinase OT - palbociclib OT - retinoblastoma protein OT - temsirolimus COIS- Disclosure SS Gill is a consultant for Renishaw PLC. NU Barua is a consultant for Renishaw PLC. The authors report no other conflicts of interest in this work. EDAT- 2018/09/27 06:00 MHDA- 2018/09/27 06:01 PMCR- 2018/09/12 CRDT- 2018/09/27 06:00 PHST- 2018/09/27 06:00 [entrez] PHST- 2018/09/27 06:00 [pubmed] PHST- 2018/09/27 06:01 [medline] PHST- 2018/09/12 00:00 [pmc-release] AID - cmar-10-3483 [pii] AID - 10.2147/CMAR.S167095 [doi] PST - epublish SO - Cancer Manag Res. 2018 Sep 12;10:3483-3500. doi: 10.2147/CMAR.S167095. eCollection 2018.