Potential new therapy of Rapalink‐1, a new generation mammalian target of rapamycin inhibitor,against sunitinib‐resistant renal cell carcinoma

Sunitinib, a multitargeted receptor tyrosine kinase inhibitor including vascular endothelial growth factor, has been widely used as a first‐line treatment against metastatic renal cell carcinoma (mRCC). However, mRCC often acquires resistance to sunitinib, rendering it difficult to treat with this agent. Recently, Rapalink‐1, a drug that links rapamycin and the mTOR kinase inhibitor MLN0128, has been developed with excellent therapeutic effects against breast cancer cells carrying mTOR resistance mutations. The aim of the present study was to evaluate the in vitro and in vivo therapeutic efficacy of Rapalink‐1 against renal cell carcinoma (RCC) compared to temsirolimus, which is commonly used as a small molecule inhibitor of mTOR and is a derivative of rapamycin. In comparison with temsirolimus, Rapalink‐1 showed significantly greater effects against proliferation, migration, invasion and cFolony formation in sunitinib‐naïve RCC cells. Inhibition was achieved through suppression of the phosphorylation of substrates in the mTOR signal pathway, such as p70S6K, eukaryotic translation initiation factor 4E‐binding protein 1 (4EBP1) and AKT. In addition, Rapalink‐1 had greater tumor suppressive effects than temsirolimus against the sunitinib‐resistant 786‐o cell line (SU‐R 786‐o), which we had previously established, as well as 3 additional SU‐R cell lines established here. RNA sequencing showed that Rapalink‐1 suppressed not only the mTOR signaling pathway but also a part of the MAPK signaling pathway, the ErbB signaling pathway and ABC transporters that were associated with resistance to several drugs. Our study suggests the possibility of a new treatment option for patients with RCC that is either sunitinib‐sensitive or sunitinib‐resistant.     

Differentiating mTOR inhibitors in renal cell carcinoma

PI3K/Akt/mTOR signalling is dysregulated in many cancers, including renal cell carcinoma (RCC), and activation of this pathway has been suggested to correlate with aggressive behavior and poor prognosis in RCC tumors. mTOR inhibition plays a principal role in the targeted treatment of many cancer types, including RCC. Although mTOR inhibitors share the same mechanism of action, differences in metabolism, formulation and dosing schedule underpin distinct PK/PD profiles such that they may be differentiated for use in a variety of treatment niches. Approved mTOR inhibitors temsirolimus and everolimus serve as important therapeutic options within the current RCC treatment paradigm, although their recommended applications differ in setting and patient population characteristics. Clinical practice guidelines recommend temsirolimus for use in treatment-naive patients with poor-prognosis metastatic RCC of any histology (predominant clear cell or non-clear cell histology). Everolimus provides a standard-of-care therapy for patients with metastatic RCC whose disease has progressed after previous vascular endothelial growth factor receptor-tyrosine kinase inhibitor therapy. As therapeutic failure impacts the vast majority of patients with RCC, sequencing strategies of available agents or simultaneous targeting of multiple members of the PI3K/Akt/mTOR pathway may provide additional clinical benefit. Various classes of agents targeting the PI3K/Akt/mTOR pathway are currently being investigated, including mTORC1/mTORC2 kinase domain inhibitors, mTOR/PI3K dual inhibitors, PI3K-selective inhibitors, and programmed cell death 6 modulators. Clinical trials of mTOR inhibitors in a variety of tumor types are ongoing, and the role of mTOR inhibitors continues to evolve across the RCC treatment landscape.     

Second-line systemic therapy for the treatment of metastatic renal cell cancer

The discovery of molecular mechanisms driving the progression of renal cell carcinoma (RCC) has led to the development of drugs that target RCC at the molecular level. Inhibition of VEGF-targeting pathways is successful as a front-line treatment in patients with metastatic RCC. In addition, bevacizumab/IFN-α, sunitinib and pazopanib are recommended for first-line use in good- or intermediate-risk patients, whereas temsirolimus is approved for poor-risk patients. Second-line options are valuable as these patients eventually progress. The present review addresses which drug is best in this second-line setting. Options for sequential therapy include tyrosine kinase inhibitor (TKI)–mTOR inhibitor or TKI–TKI sequences. We also address the question of whether sequential therapy with TKIs or the combination of VEGF followed by mTOR inhibition is the best choice for specific patients, and which sequence of TKIs is most beneficial.     

Preclinical trial of a new dual mTOR inhibitor,MLN0128, using renal cell carcinoma tumorgrafts

mTOR is a rational target in renal cell carcinoma (RCC) because of its role in disease progression. However, the effects of temsirolimus, the only first‐generation mTOR inhibitor approved by the FDA for first‐line treatment of metastatic RCC, on tumor reduction and progression‐free survival are minimal. Second‐generation mTOR inhibitors have not been evaluated on RCC. We compared the effects of temsirolimus and MLN0128, a potent second‐generation mTOR inhibitor, on RCC growth and metastasis using a realistic patient‐derived tissue slice graft (TSG) model. TSGs were derived from three fresh primary RCC specimens by subrenal implantation of precision‐cut tissue slices into immunodeficient mice that were randomized and treated with MLN0128, temsirolimus, or placebo. MLN0128 consistently suppressed primary RCC growth, monitored by magnetic resonance imaging (MRI), in three TSG cohorts for up to 2 months. Temsirolimus, in contrast, only transiently inhibited the growth of TSGs in one of two cohorts before resistance developed. In addition, MLN0128 reduced liver metastases, determined by human‐specific quantitative polymerase chain reaction, in two TSG cohorts, whereas temsirolimus failed to have any significant impact. Moreover, MLN0128 decreased levels of key components of the two mTOR subpathways including TORC1 targets 4EBP1, p‐S6K1, HIF1α and MTA1 and the TORC2 target c‐Myc, consistent with dual inhibition. Our results demonstrated that MLN0128 is superior to temsirolimus in inhibiting primary RCC growth as well as metastases, lending strong support for further clinical development of dual mTOR inhibitors for RCC treatment.     

Temsirolimus is highly effective as third-line treatment in chromophobe renal cell cancer

We report unexpectedly high efficacy of temsirolimus as third-line treatment in a patient with metastatic chromophobe renal cell carcinoma. After failure of two sequentially administered tyrosine kinase inhibitors, treatment with temsirolimus resulted in a prolonged partial remission of 14 months, and the response is still continuing. Up to now, no data from randomized clinical studies have been published addressing the question of efficacy of temsirolimus as third-line treatment after failure of tyrosine kinase inhibitors. The case presented here implies that temsirolimus could be a viable option for patients with metastatic chromophobe renal cell carcinoma.     

Future directions of mammalian target of rapamycin (mTOR) inhibitor therapy in renal cell carcinoma

With an explosion of available treatments for metastatic renal cell carcinoma (mRCC) in recent years, it is important to recognize that approved targeted therapies fall broadly into only two mechanistic categories. The first category, vascular endothelial growth factor (VEGF)-directed therapies, includes sunitinib, pazopanib, sorafenib and bevacizumab. The second category includes inhibitors of the mammalian target of rapamycin (mTOR), namely everolimus and temsirolimus. A pivotal trial of everolimus supports use of the agent in patients with mRCC refractory to VEGF- tyrosine kinase inhibitors (TKI) therapy, while pivotal data for temsirolimus supports use in poor-prognosis patients as first-line therapy. Multiple reviews exist to delineate the laboratory and clinical development of mTOR inhibitors. This paper will outline the future applications of these therapies. It will explore ongoing trials evaluating combinations of mTOR inhibitors with other targeted therapies, along with sequencing strategies and biomarker discovery efforts. The application of mTOR inhibitors in unique populations is also described.     

RAD-001: future directions

The clinical activity of inhibitors of the mammalian target of rapamycin (mTOR) has clearly been demonstrated in patients with renal cell carcinoma. mTOR and its kinase activity is regulated by a series of upstream and downstream elements that include phosphoinositide 3-kinase (PI3K), Akt, and the tumor suppressor phosphatase and tensin homolog (PTEN). A series of preclinical and clinical findings have provided proof of principle demonstrating the relevance of this pathway in renal cell carcinoma (RCC) pathogenesis and progression. The activity of the mTOR inhibitors temsirolimus and everolimus in advanced RCC is reviewed briefly, and the future directions with this class of agents in the therapy of advanced renal cell carcinoma discussed.     

The clinical potential of temsirolimus in second or later lines of treatment for metastatic renal cell carcinoma

An impressive variety of targeted therapies has been approved for the treatment of metastatic renal cell carcinoma (mRCC). Despite promising progress, there are still unmet clinical needs. The optimal sequence of these agents in the therapeutic setting has not yet been determined. Most available data address first- and second-line therapy of clear cell RCC. The mTOR inhibitor temsirolimus has been approved for first-line treatment of mRCC, and there are new data addressing the use of temsirolimus in later therapeutic lines. Temsirolimus has discerning features compared with other currently registered drugs, such as its intravenous administration route–providing predictable bioavailability and adherence to treatment–and potential benefit in nonclear cell histologies. Here, we review the available literature on temsirolimus, with reference to data also available for everolimus, to determine its clinical potential in mRCC.     

Second-line systemic therapy for the treatment of metastatic renal cell cancer

The discovery of molecular mechanisms driving the progression of renal cell carcinoma (RCC) has led to the development of drugs that target RCC at the molecular level. Inhibition of VEGF-targeting pathways is successful as a front-line treatment in patients with metastatic RCC. In addition, bevacizumab/IFN-α, sunitinib and pazopanib are recommended for first-line use in good- or intermediate-risk patients, whereas temsirolimus is approved for poor-risk patients. Second-line options are valuable as these patients eventually progress. The present review addresses which drug is best in this second-line setting. Options for sequential therapy include tyrosine kinase inhibitor (TKI)-mTOR inhibitor or TKI-TKI sequences. We also address the question of whether sequential therapy with TKIs or the combination of VEGF followed by mTOR inhibition is the best choice for specific patients, and which sequence of TKIs is most beneficial.     

RAD-001: future directions

The clinical activity of inhibitors of the mammalian target of rapamycin (mTOR) has clearly been demonstrated in patients with renal cell carcinoma. mTOR and its kinase activity is regulated by a series of upstream and downstream elements that include phosphoinositide 3-kinase (PI3K), Akt, and the tumor suppressor phosphatase and tensin homolog (PTEN). A series of preclinical and clinical findings have provided proof of principle demonstrating the relevance of this pathway in renal cell carcinoma (RCC) pathogenesis and progression. The activity of the mTOR inhibitors temsirolimus and everolimus in advanced RCC is reviewed briefly, and the future directions with this class of agents in the therapy of advanced renal cell carcinoma discussed.     

Comparative efficacy of vascular endothelial growth factor (VEGF) tyrosine kinase inhibitor (TKI) and mammalian target of rapamycin (mTOR) inhibitor as second-line therapy in patients with metastatic renal cell carcinoma after the failure of first-line VEGF TKI

Sequential therapy is a standard strategy used to overcome the limitations of targeted agents in metastatic renal cell carcinoma. It remains unclear whether a mammalian target of rapamycin (mTOR) inhibitor is a more effective second-line therapy after first-line vascular endothelial growth factor tyrosine kinase inhibitor (VEGF TKI) has failed than the alternative, VEGF TKI. A clinical database was used to identify all patients with renal cell carcinoma who failed at first-line VEGF TKI and then treated with second-line VEGF TKI or mTOR inhibitors in the Asan Medical Center. Patient medical characteristics, radiological response and survival status were assessed. Of the 83 patients who met the inclusion criteria, 41 received second-line VEGF TKI [sunitinib (n?=?16) and sorafenib (n?=?25)] and 42 were treated with mTOR inhibitors [temsirolimus (n?=?11) and everolimus (n?=?31)]. After a median follow-up duration of 23.9?months (95?% CI, 17.8?C30.0), progression-free survival was 3.0?months for both groups [hazard ratio (HR, VEGF TKI vs. mTOR inhibitor)?=?0.97, 95?% CI 0.59?C1.62, P?=?0.92]. Overall survival was 10.6?months for the VEGF TKI group and 8.2?months for the mTOR inhibitor group (HR?=?0.98, 95?% CI 0.57?C1.68, P?=?0.94). The two groups did not differ significantly in terms of disease control rate (51?% for VEGF TKI and 59?% for mTOR inhibitor, P?=?0.75). Second-line VEGF TKI seems to be as effective as mTOR inhibitors and may be a viable option as a second-line agent after first-line anti-VEGF agents have failed.     

Mechanisms of Disease: survival benefit of temsirolimus validates a role for mTOR in the management of advanced RCC

Temsirolimus is a specific inhibitor of mammalian target of rapamycin (mTOR) that is approved for the treatment of advanced renal cell carcinoma. mTOR is unique among antitumor drug targets because it is a convergence point for many signaling pathways. Activation of mTOR by various growth signals increases the synthesis of proteins needed for cell-cycle progression and tumor growth. Temsirolimus demonstrates a significant improvement in overall survival in patients with advanced renal cell carcinoma and poor-prognostic features, thereby validating the importance of mTOR in the natural history of this disease. mTOR might also be an important target in other tumor types, and more than 100 ongoing clinical trials are designed to identify additional malignancies that respond to temsirolimus and other mTOR inhibitors, either alone or in combination with other targeted agents or chemotherapy.     

Optimal treatment of poor-risk renal cell carcinoma patients with mTOR inhibitors and anti-VEGFR agents

Poor-risk metastatic renal cell carcinoma (RCC) includes a subgroup of patients with unfavorable prognosis, according to both the Motzer and Heng criteria. Overall, owing to the poor prognosis of these patients, the approach is still a challenge for the first and subsequent lines of treatment, particularly for rare histologies other than clear cell renal cell carcinoma. In this review, we investigated the present treatment option of poor-risk metastatic RCC. Areas covered are data with first and further line of therapy with mTOR inhibitors and other agents but without cytoreductive nephrectomy or rare histologies. The current data on systemic therapy in poor-risk metastatic RCC maintain temsirolimus as the preferred first-line therapy. New agents targeting immune checkpoints are being developed in clinical trials.     

Acquired resistance to temsirolimus in human renal cell carcinoma cells is mediated by the constitutive activation of signal transduction pathways through mTORC2

Background:

The objective of this study was to characterise the mechanism underlying acquired resistance to temsirolimus, an inhibitor of mammalian target of rapamycin (mTOR), in renal cell carcinoma (RCC).

Methods:

A parental human RCC cell line, ACHN (ACHN/P), was continuously exposed to increasing doses of up to 20 μM of temsirolimus, and a cell line resistant to temsirolimus (ACHN/R), showing a sixfold higher IC₅₀ than that of ACHN/P, was developed.

Results:

Following treatment with temsirolimus, phosphorylation of S6 kinase in ACHN/P was markedly inhibited, whereas there was no detectable expression of phosphorylated S6 in ACHN/R before and after temsirolimus treatment. However, AKT and p44/42 mitogen-activated protein kinase (MAPK) were constitutively phosphorylated even after temsirolimus treatment in ACHN/R, but not in ACHN/P. There was no significant difference between the sensitivities of ACHN/P and ACHN/R to KU0063794, a dual inhibitor of mTOR complex 1 (mTORC1) and mTORC2. Similar sensitivities to temsirolimus in ACHN/P and ACHN/R could be achieved by additional treatment with specific inhibitors of AKT- and MAPK-signaling pathways.

Conclusion:

The activation of signal transduction pathways via mTORC2, but not via mTORC1, may have an important role in the acquisition of a resistant phenotype to temsirolimus in RCC.     

4th International Symposium on Leukemia and Lymphoma – Molecular Pharmacology and New Treatment Modalitie

Renal cell carcinomas (RCCs) represent one of the ten leading cancer entities with an increasing incidence especially in the western world. Unfortunately, about 25% of the patients develop metastatic RCC (mRCC) associated with a most unfavorable prognosis. In the recent years, various new agents targeting VEGF or VEGF receptor (VEGFR) or the mTOR pathway have been approved for the treatment of mRCC with significant prolongation of progression-free survival and, in part, of overall survival (OS). Targeting the mTOR kinase is an interesting option for mRCC. Temsirolimus, one of the available mTOR inhibitors, has been approved as a single agent in poor-risk mRCC patients based on the pivotal Phase III trial showing a significant superiority in OS versus IFN-α or temsirolimus + IFN-α, which has been verified by a pivotal Phase III trial. The benefit has been shown for clear cell carcinoma and papillary RCC as well. For poor prognosis patients, temsirolimus improves median survival by 3.6 months. In second-line treatment compared with sorafenib following first-line treatment with sunitinib temsirolimus showed a relative progression-free survival benefit for patients with nonclear cell RCC with temsirolimus. The median OS for the temsirolimus group was 12.27 and 16.64 months for the sorafenib group. In 2007, the US FDA granted approval for temsirolimus for the treatment of advanced RCC.     

A Phase I Study of Temsirolimus and Bryostatin‐1 in Patients With Metastatic Renal Cell Carcinoma and Soft Tissue Sarcoma

Background.

Temsirolimus, an inhibitor of mammalian target of rapamycin (mTOR) complex 1, is approved for the treatment of metastatic renal cell carcinoma (RCC). Bryostatin-1 inhibits protein kinase C, a downstream effector of mTOR complex 2. We observed antitumor effects with the combination of temsirolimus and bryostatin-1 in RCC cell lines.

Methods.

Four cohorts of patients received weekly bryostatin-1 (20 μg/m²) with temsirolimus (10, 15, 25, or 37.5 mg) in 28-day cycles.

Results.

Thirty patients received a total of 138 cycles across four dose levels. Twenty-five patients had RCC (17 clear cell, 7 papillary, and 1 unclassified). Two sarcoma patients with prior cytotoxic therapy experienced dose-limiting toxicity at 15 mg of temsirolimus (grade 3 neutropenia and grade 3 hypophosphatemia). Subsequently, patients with prior cytotoxic therapy were excluded. Two additional dose-limiting toxicities were noted with 37.5 mg of temsirolimus (grade 3 neutropenia and grade 3 creatinine elevation). Consequently, the maximum tolerated dose was defined as temsirolimus at 25 mg and bryostatin-1 at 20 μg/m² every 28 days. Of the 25 RCC patients, 3 patients had partial responses that lasted for 14 months, 28 months, and ≥80 months, respectively. Partial responses were seen in both clear cell and papillary histology.

Conclusion.

This combination of 37.5 mg of temsirolimus with 20 μg/m² of bryostatin-1 was reasonably safe and well tolerated. Durable responses were observed in 3 of 25 patients with RCC.     

Targeted inhibition of mammalian target of rapamycin for the treatment of advanced renal cell carcinoma

Clinical trials have validated the importance of mammalian target of rapamycin (mTOR) as a targeted mechanism in the treatment of renal cell carcinoma (RCC). Temsirolimus, an mTOR inhibitor that is approved for treatment of advanced RCC, has demonstrated both overall survival benefits and progression‐free survival benefits versus interferon?α as first‐line treatment for patients with poor prognostic features. Exploratory subset analyses indicated that temsirolimus benefits patients with RCC regardless of tumor histology or nephrectomy status. Everolimus, the second mTOR inhibitor to demonstrate activity in RCC, improved progression‐free survival versus placebo in patients whose disease progressed after treatment with vascular endothelial growth factor receptor tyrosine kinase inhibitors (sunitinib, sorafenib, or both); benefit was observed for all risk groups. Deforolimus also exhibited antitumor activity against RCC in early clinical studies. There is now compelling clinical evidence for the effectiveness of targeting mTOR in the treatment of RCC. Cancer 2009. © 2009 American Cancer Society.     

Current Data with Mammalian Target of Rapamycin Inhibitors in Advanced Renal Cell Carcinoma

Mammalian target of rapamycin (mTOR) is the key regulator of cell growth and proliferation. Alterations in the mTOR signaling pathway can lead to neoplastic transformation and progression. The inhibition of mTOR blocks the progression of the cell cycle from G1 to S phase, leading to cell growth arrest and apoptosis. Thus, mTOR is a promising target for the treatment of human malignancies. Rapamycin and its analogues, including temsirolimus, everolimus, and AP23573, block the mTOR signaling pathway and induce a cellular state akin to starvation, with significant antitumor activity in a variety of malignancies, including renal cell carcinoma (RCC). Current data from ongoing clinical trials suggest that mTOR-targeted therapy with rapamycin derivatives is well tolerated with significant clinical activity in patients with advanced-stage RCC. Specifically, temsirolimus as monotherapy has demdemonstrated improved progression-free and overall survival in patients with poor-risk advanced-stage RCC. Everolimus has also demonstrated promising antitumor activity in patients with metastatic RCC. However, optimal dose, treatment schedule, selection of patients, and appropriate combination strategies with other novel agents need to be defined for mTORtargeted therapies in the treatment of advanced-stage RCC.     

What Role Do Combinations of Interferon and Targeted Agents Play in the First-Line Therapy of Metastatic Renal Cell Carcinoma?

Interferons (IFNs) are a class of cytokines with pleotropic actions that regulate a variety of cellular activities. Clinical trials with recombinant IFNs (IFN-α2a and IFN-α2b) have demonstrated clinical activity in patients with advanced renal cell carcinoma (RCC). Their efficacy is characterized by a low overall tumor regression rate of < 15%, progression-free survival of 4-5 months, and overall median survival of 10-18 months. This cytokine became the standard of care for patients with metastatic RCC and was then used as the comparator arm in a series of phase II and III clinical trials that have defined a new treatment paradigm for patients with advanced RCC. This paradigm uses the tyrosine kinase inhibitors (TKIs) sorafenib and sunitinib, the mammalian target of rapamycin (mTOR) inhibitor temsirolimus, and the vascular endothelial growth factor monoclonal antibody bevacizumab. These 3 categories of agents were then investigated in combination with IFN-α in a series of preclinical and clinical studies. The collective data from these reports suggest the combination of IFN-α and bevacizumab is active and has a role in RCC therapy, whereas combinations with the TKIs or mTOR inhibitors have limited efficacy and/or excessive toxicity. The clinical and preclinical studies leading to these conclusions are reviewed herein.     

Current data with mammalian target of rapamycin inhibitors in advanced-stage renal cell carcinoma

Mammalian target of rapamycin (mTOR) is the key regulator of cell growth and proliferation. Alterations in the mTOR signaling pathway can lead to neoplastic transformation and progression. The inhibition of mTOR blocks the progression of the cell cycle from G1 to S phase, leading to cell growth arrest and apoptosis. Thus, mTOR is a promising target for the treatment of human malignancies. Rapamycin and its analogues, including temsirolimus, everolimus, and AP23573, block the mTOR signaling pathway and induce a cellular state akin to starvation, with significant antitumor activity in a variety of malignancies, including renal cell carcinoma (RCC). Current data from ongoing clinical trials suggest that mTOR-targeted therapy with rapamycin derivatives is well tolerated with significant clinical activity in patients with advanced-stage RCC. Specifically, temsirolimus as monotherapy has demdemonstrated improved progression-free and overall survival in patients with poor-risk advanced-stage RCC. Everolimus has also demonstrated promising antitumor activity in patients with metastatic RCC. However, optimal dose, treatment schedule, selection of patients, and appropriate combination strategies with other novel agents need to be defined for mTORtargeted therapies in the treatment of advanced-stage RCC.