Incidence of mucositis in patients treated with temsirolimus-based regimens and correlation to treatment response

Mechanistic target of rapamycin inhibitors: successes and challenges as cancer therapeutics

Delineating the contributions of specific cell signalling cascades to the development and maintenance of tumours has greatly informed our understanding of tumorigenesis and has advanced the modern era of targeted cancer therapy. It has been revealed that one of the key pathways regulating cell growth, the phosphatidylinositol 3-kinase/mechanistic target of rapamycin (PI3K/mTOR) signalling axis, is commonly dysregulated in cancer. With a specific, well-tolerated inhibitor of mTOR available, the impact of inhibiting this pathway at the level of mTOR has been tested clinically. This review highlights some of the promising results seen with mTOR inhibitors in the clinic and assesses some of the challenges that remain in predicting patient outcome following mTOR-targeted therapy.

Molecular basis for class side effects associated with PI3K/AKT/mTOR pathway inhibitors

Introduction: The phosphatidylinositide 3-kinase/AKT/mammalian target of rapamycin (PI3K/AKT/mTOR) signaling pathway has emerged as an important target in cancer therapy. Numerous PI3K/AKT/mTOR pathway inhibitors are extensively studied; some are used clinically, but most of these drugs are undergoing clinical trials. Potential adverse effects, such as severe hepatotoxicity and pneumonitis, have largely restricted the application and clinical significance of these inhibitors. A summary of mechanisms underlying the adverse effects is not only significant for the development of novel PI3K/AKT/mTOR inhibitors but also beneficial for the optimal use of existing drugs. Areas covered: We report a profile of the adverse effects, which we consider the class effects of PI3K/AKT/mTOR inhibitors. This review also discusses potential molecular toxicological mechanisms of these agents, which might drive future drug discovery. Expert opinion: Severe toxicities associated with PI3K/AKT/mTOR inhibitors hinder their approval and limit long-term clinical application of these drugs. A better understanding regarding PI3K/AKT/mTOR inhibitor-induced toxicities is needed. However, the mechanisms underlying these toxicities remain unclear. Future research should focus on developing strategies to reduce toxicities of approved inhibitors as well as accelerating new drug development. This review will be useful to clinical, pharmaceutical, and toxicological researchers.

AKT and ERK dual inhibitors: The way forward?

Phosphatidylinositol 3-kinase (PI3K)/AKT pathway regulates cell growth, proliferation, survival, mobility and invasion. Mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway is also an important mitogenic signaling pathway involved in various cellular progresses. AKT, also named protein kinase B (PKB), is a primary mediator of the PI3K signaling pathway; and ERK at the end of MAPK signaling is the unique substrate and downstream effector of mitogen-activated protein/extracellular signal-regulated kinase (MEK). The AKT and ERK signaling are both aberrantly activated in a wide range of human cancers and have long been targeted for cancer therapy, but the clinical benefits of these targeted therapies have been limited due to complex cross-talk. Novel strategies, such as AKT/ERK dual inhibitors, may be needed.

Phase I study of vinblastine and temsirolimus in pediatric patients with recurrent or refractory solid tumors: Canadian Cancer Trials Group Study IND.218

Combining mammalian target of rapamycin (mTOR) inhibitors and vinca alkaloids has shown therapeutic synergy in xenograft models of pediatric cancers. This phase I study assessed safety and toxicity of temsirolimus in combination with vinblastine in children.

PROCEDURE

Patients ≥ 1 and ≤ 18 years with recurrent/refractory solid or CNS tumors were eligible. Vinblastine (4 mg/m² ) and temsirolimus (15 mg/m² ) were administered i.v. weekly, with planned dose escalation of vinblastine using a rolling six phase I design. Pharmacokinetic and pharmacodynamic data were collected.

RESULTS

Seven patients with median age 12 years (range, 8-18 years) were enrolled; all were evaluable for toxicity and six for response. At dose level 1, four of six patients developed grade 3 mucositis, of which one met duration criteria for dose-limiting toxicity (DLT). Four patients required dose omissions for grade 3 or 4 hematologic toxicity, including one prolonged neutropenia DLT. A subsequent patient was enrolled on dose level -2 (temsirolimus 10 mg/m² , vinblastine 4 mg/m² ) with no protocol-related toxicity > grade 1, except grade 2 neutropenia. Two serious adverse events (SAE) occurred-an allergic reaction to temsirolimus (grade 2) and an intracranial hemorrhage in a CNS tumor patient (grade 3)-unlikely related to study therapy. Soluble VEGFR2 was reduced at cycle 1, day 36 in keeping with inhibition of angiogenesis. Four patients achieved prolonged stable disease for a median of 5.0 months (range, 3.1-8.3 months).

CONCLUSION

The combination of weekly temsirolimus (15 mg/m² ) and vinblastine (4 mg/m² ) exceeds the maximum tolerated dose in children, with frequent oral mucositis and hematologic toxicity.

Identifying novel genes and biological processes relevant to the development of cancer therapy-induced mucositis: An informative gene network analysis

Mucositis is a complex, dose-limiting toxicity of chemotherapy or radiotherapy that leads to painful mouth ulcers, difficulty eating or swallowing, gastrointestinal distress, and reduced quality of life for patients with cancer. Mucositis is most common for those undergoing high-dose chemotherapy and hematopoietic stem cell transplantation and for those being treated for malignancies of the head and neck. Treatment and management of mucositis remain challenging. It is expected that multiple genes are involved in the formation, severity, and persistence of mucositis. We used Ingenuity Pathway Analysis (IPA), a novel network-based approach that integrates complex intracellular and intercellular interactions involved in diseases, to systematically explore the molecular complexity of mucositis. As a first step, we searched the literature to identify genes that harbor or are close to the genetic variants significantly associated with mucositis. Our literature review identified 27 candidate genes, of which ERCC1, XRCC1, and MTHFR were the most frequently studied for mucositis. On the basis of this 27-gene list, we used IPA to generate gene networks for mucositis. The most biologically significant novel molecules identified through IPA analyses included TP53, CTNNB1, MYC, RB1, P38 MAPK, and EP300. Additionally, uracil degradation II (reductive) and thymine degradation pathways (p = 1.06-08) were most significant. Finally, utilizing 66 SNPs within the 8 most connected IPA-derived candidate molecules, we conducted a genetic association study for oral mucositis in the head and neck cancer patients who were treated using chemotherapy and/or radiation therapy (186 head and neck cancer patients with oral mucositis vs. 699 head and neck cancer patients without oral mucositis). The top ranked gene identified through this association analysis was RB1 (rs2227311, p-value = 0.034, odds ratio = 0.67). In conclusion, gene network analysis identified novel molecules and biological processes, including pathways related to inflammation and oxidative stress, that are relevant to mucositis development, thus providing the basis for future studies to improve the management and treatment of mucositis in patients with cancer.

Phase I trial of MEK 1/2 inhibitor pimasertib combined with mTOR inhibitor temsirolimus in patients with advanced solid tumors

Background Dual inhibition of activated MAPK and mTOR signaling pathways may enhance the antitumor efficacy of the MEK 1/2 inhibitor pimasertib and the mTOR inhibitor temsirolimus given in combination. Methods In this phase I study, patients with refractory advanced solid tumors (NCT01378377) received once-weekly temsirolimus plus once-daily oral pimasertib in 21-day cycles in a modified 3 + 3 dose-escalation design. The maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D) of pimasertib in combination with temsirolimus, safety and pharmacokinetics (PK) were investigated. Results Of 33 patients evaluated, all experienced ≥1 treatment-emergent adverse event (TEAE) and 31 had treatment-related TEAEs, most frequently stomatitis and thrombocytopenia. TEAEs were reversible. No deaths were attributed to treatment. Nine patients had dose-limiting toxicities (stomatitis, thrombocytopenia, serum creatinine phosphokinase increase, visual impairment) and the MTD was determined as 45 mg/day pimasertib plus 25 mg/week temsirolimus. However, due to overlapping toxicities no further investigations were performed and the RP2D was not defined. PK profiles of both agents were not adversely affected. Seventeen patients (17/26 patients) had a best response of stable disease; five had stable disease lasting >12 weeks. Conclusions The RP2D was not defined and the pimasertib plus temsirolimus combination investigated did not warrant further study.