Background The combination of everolimus and the imidazoquinoline derivative, BEZ235 (dactolisib), a dual PI3K/mTOR inhibitor, demonstrated synergy in a preclinical model. Objective To establish clinical feasibility, a phase Ib dose-escalation trial investigating safety and pharmacokinetics of this combination in patients with advanced tumors was performed. Patients and Methods BEZ235 was orally administered daily in escalating doses of 200, 400, and 800 mg along with everolimus at 2.5 mg daily in 28-day cycles. Nineteen patients were enrolled. Adverse events and tumor responses were evaluated using CTCAE v4.0 and RECIST 1.1, respectively. Pharmacokinetic analyses were performed. Results Common toxicities observed included fatigue, diarrhea, nausea, mucositis, and elevated liver enzymes. No confirmed responses were observed. BEZ235 pharmacokinetics exhibited dose-proportional increases in C_max and AUC_0-24 over the three doses, with high inter-individual variability. Non-compartmental and population pharmacokinetic-based simulations indicated significant increases in everolimus C_max and AUC_0-24 on day 28 and decreased clearance to 13.41 L/hr. Conclusions The combination of BEZ235 and everolimus demonstrated limited efficacy and tolerance. BEZ235 systemic exposure increased in a dose-proportional manner while oral bioavailability was quite low, which may be related to gastrointestinal-specific toxicity. The changes in steady-state pharmacokinetics of everolimus with BEZ235 highlight potential drug–drug interactions when these two drugs are administered together. Clinicaltrials.gov: NCT01508104

Tamoxifen is a widely utilized antiestrogen in the treatment and chemoprevention of breast cancer. Clinical studies document that tamoxifen administration markedly enhances the systemic elimination of other drugs. Additionally, tamoxifen enhances its own clearance following repeated dosing. The mechanisms that underlie these clinically important events remain unresolved. Here, we report that tamoxifen and its metabolite 4-hydroxytamoxifen markedly induce cytochrome P450 3A4, a drug-metabolizing enzyme of central importance, in primary cultures of human hepatocytes. Tamoxifen and 4-hydroxytamoxifen (1–10 μM) significantly increased the CYP3A4 expression and activity (measured as the rate of testosterone 6β-hydroxylation). Maximal induction was achieved at the 5 μM level. At this level, tamoxifen and 4-hydroxytamoxifen caused a 1.5- to 3.3-fold (mean, 2.1-fold) and 3.4- to 17-fold (mean, 7.5-fold) increase in the CYP3A4 activity, respectively. In comparison, rifampicin treatment resulted in a 6- to 16-fold (mean, 10.5-fold) increase. We also observed corresponding increase in the CYP3A4 immunoreactive protein and mRNA levels. Furthermore, tamoxifen and 4-hydroxytamoxifen efficaciously activated the human pregnane X receptor (hPXR; also known as the steroid xenobiotic receptor), a key regulator ofCYP3A4 expression. The efficacy of tamoxifen and 4-hydroxytamoxifen relative to rifampicin for hPXR activation was ∼30 and 60%, respectively. Our results indicate that the mechanism of tamoxifen-mediated alteration in drug clearance pathways in humans may involve CYP3A4 induction by the parent drug and/or its metabolite. Furthermore, the CYP3A4 induction may be a result of hPXR activation. These findings have important implications for optimizing the use of tamoxifen and in the development of newer antiestrogens.

Genetic and epigenetic mechanisms determine SCD inhibitor sensitivity and acquired resistance through FOSB in cancer.

Summary:  Purpose: In clinical studies, topiramate (TPM) was shown to cause a dose‐dependent increase in the clearance of ethinyl estradiol. We hypothesized that this interaction results from induction of hepatic cytochrome P450 (CYP) 3A4 by TPM. Accordingly, we investigated whether TPM induces CYP3A4 in primary human hepatocytes and activates the human pregnane X receptor (hPXR), a nuclear receptor that serves as a regulator of CYP3A4 transcription. Methods: Human hepatocytes were treated for 72 h with TPM (10, 25, 50, 100, 250, and 500 μM) and known inducers, phenobarbital (PB; 2 mM), and rifampicin (10 μM). The rate of testosterone 6β‐hydroxylation by hepatocytes served as a marker for CYP3A4 activity. The CYP3A4‐specific protein and mRNA levels were determined by using Western and Northern blot analyses, respectively. The hPXR activation was assessed with cell‐based reporter gene assay. Results: Compared with controls, TPM (50–500 μM)–treated hepatocytes exhibited a considerable increase in the CYP3A4 activity (1. 6‐ to 8.2‐fold), protein levels (4.6‐ to 17.3‐fold), and mRNA levels (1.9‐ to 13.3‐fold). Comparatively, rifampicin (10 μM) effected 14.5‐, 25.3‐, and a 20.3‐fold increase in CYP3A4 activity, immunoreactive protein levels, and mRNA levels, respectively. TPM (50–500 μM) caused 1.3‐ to 3‐fold activation of the hPXR, whereas rifampicin (10 μM) caused a 6‐fold activation. Conclusions: The observed induction of CYP3A4 by TPM, especially at the higher concentrations, provides a potential mechanistic explanation of the reported increase in the ethinyl estradiol clearance by TPM. It also is suggestive of other potential interactions when high‐dose TPM therapy is used.

A glioblastoma (GBM) is one of the most aggressive, infiltrative, and treatment-resistant malignancies of the central nervous system (CNS). The current standard of care for GBMs include maximally safe tumor resection, followed by concurrent adjuvant radiation treatment and chemotherapy with the DNA alkylating agent temozolomide (TMZ), which was approved by the FDA in 2005 based on a marginal increase (~2 months) in overall survival (OS) levels. This treatment approach, while initially successful in containing and treating GBM, almost invariably fails to prevent tumor recurrence. In addition to the limited therapeutic benefit, TMZ also causes debilitating adverse events (AEs) that significantly impact the quality of life of GBM patients. Some of the most common AEs include hematologic (e.g., thrombocytopenia, neutropenia, anemia) and non-hematologic (e.g., nausea, vomiting, constipation, dizziness) toxicities. Recurrent GBMs are often resistant to TMZ and other DNA-damaging agents. Thus, there is an urgent need to devise strategies to potentiate TMZ activity, to overcome drug resistance, and to reduce dose-dependent AEs. Here, we analyze major mechanisms of the TMZ resistance-mediated intracellular signaling activation of DNA repair pathways and the overexpression of drug transporters. We review some of the approaches investigated to counteract these mechanisms of resistance to TMZ, including the use of chemosensitizers and drug delivery strategies to enhance tumoral drug exposure.