Antitumor Activity of Rapamycin in a Phase I Trial for Patients with Recurrent PTEN-Deficient Glioblastoma

By T. Cloughesy, K. Yoshimoto, P. Nghiemphu, K. Brown, Julie Dang, Shaojun Zhu, Teli Hsueh, Yinan F. Chen, Wei Wang, D. Youngkin and 13 more. PLoS Medicine, 2008

597 citations recorded by the source corpus.

Background There is much discussion in the cancer drug development community about how to incorporate molecular tools into early-stage clinical trials to assess target modulation, measure anti-tumor activity, and enrich the clinical trial population for patients who are more likely to benefit. Small, molecularly focused clinical studies offer the promise of the early definition of optimal biologic dose and patient population. Methods and Findings Based on preclinical evidence that phosphatase and tensin homolog deleted on Chromosome 10 (PTEN) loss sensitizes tumors to the inhibition of mammalian target of rapamycin (mTOR), we conducted a proof-of-concept Phase I neoadjuvant trial of rapamycin in patients with recurrent glioblastoma, whose tumors lacked expression of the tumor suppressor PTEN. We aimed to assess the safety profile of daily rapamycin in patients with glioma, define the dose of rapamycin required for mTOR inhibition in tumor tissue, and evaluate the antiproliferative activity of rapamycin in PTEN-deficient glioblastoma. Although intratumoral rapamycin concentrations that were sufficient to inhibit mTOR in vitro were achieved in all patients, the magnitude of mTOR inhibition in tumor cells (measured by reduced ribosomal S6 protein phosphorylation) varied substantially. Tumor cell proliferation (measured by Ki-67 staining) was dramatically reduced in seven of 14 patients after 1 wk of rapamycin treatment and was associated with the magnitude of mTOR inhibition (p = 0.0047, Fisher exact test) but not the intratumoral rapamycin concentration. Tumor cells harvested from the Ki-67 nonresponders retained sensitivity to rapamycin ex vivo, indicating that clinical resistance to biochemical mTOR inhibition was not cell-intrinsic. Rapamycin treatment led to Akt activation in seven patients, presumably due to loss of negative feedback, and this activation was associated with shorter time-to-progression during post-surgical maintenance rapamycin therapy (p < 0.05, Logrank test). Conclusions Rapamycin has anticancer activity in PTEN-deficient glioblastoma and warrants further clinical study alone or in combination with PI3K pathway inhibitors. The short-term treatment endpoints used in this neoadjuvant trial design identified the importance of monitoring target inhibition and negative feedback to guide future clinical development. Trial registration: http://www.ClinicalTrials.gov (#NCT00047073).

Subfields: Genetics, Molecular Biology, Physiology

View Paper: https://www.semanticscholar.org/paper/09625cd858aeb657fe156e758f046cc21d815632

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Citations in the corpus

• The PTEN–PI3K pathway: of feedbacks and cross-talks (2008, background): “Oncogene and therefore proposed patient stratification for the utilization of mTORC1 inhibitors and dose adjustment to improve the clinical outcome (Baselga et al., 2008; Cloughesy et al., 2008).”
• The cancer biomarker problem (2008, unknown): “2 ) for 1 week before a salvage resection (which is often carried out to reduce symptoms associated with tumour recurrence after initial surgery) and then post-operatively until evidence of tumour progression was obtained by magnetic resonance imagin”
• LKB1 and AMPK control of mTOR signalling and growth (2009, background): “…analogues were shown to have palliative success in patients with PTENdeficient glioblastomas and metastatic renal cell carcinoma (Hudes et al. 2007, Cloughesy et al. 2008) Furthermore, in a pair of phase II clinical trials involving tuberous sclerosis (TSC) and lymphangioleiomyomatosis (LAM)…”
• Exciting New Advances in Neuro-Oncology (2010, background): “37 , 52 Tissue studies permit assessments of drug penetration, degree of target inhibition in vivo, and resistance mechanisms.”