Combination of the mTOR inhibitor ridaforolimus and the anti-IGF1R monoclonal antibody dalotuzumab: preclinical characterization and phase I clinical trial

PURPOSE

Mammalian target of rapamycin (mTOR) inhibition activates compensatory insulin-like growth factor receptor (IGFR) signaling. We evaluated the ridaforolimus (mTOR inhibitor) and dalotuzumab (anti-IGF1R antibody) combination.

EXPERIMENTAL DESIGN

In vitro and in vivo models, and a phase I study in which patients with advanced cancer received ridaforolimus (10-40 mg/day every day × 5/week) and dalotuzumab (10 mg/kg/week or 7.5 mg/kg/every other week) were explored.

RESULTS

Preclinical studies demonstrated enhanced pathway inhibition with ridaforolimus and dalotuzumab. With 87 patients treated in the phase I study, main dose-limiting toxicities (DLT) of the combination were primarily mTOR-related stomatitis and asthenia at doses of ridaforolimus lower than expected, suggesting blockade of compensatory pathways in normal tissues. Six confirmed partial responses were reported (3 patients with breast cancer); 10 of 23 patients with breast cancer and 6 of 11 patients with ER(+)/high-proliferative breast cancer showed antitumor activity.

CONCLUSIONS

Our study provides proof-of-concept that inhibiting the IGF1R compensatory response to mTOR inhibition is feasible with promising clinical activity in heavily pretreated advanced cancer, particularly in ER(+)/high-proliferative breast cancer (ClinicalTrials.gov identifier: NCT00730379).

Targeting the PI3K/AKT/mTOR pathway in estrogen receptor-positive breast cancer

Approximately 70-75% of breast cancers express the estrogen receptor (ER), indicating a level of dependence on estrogen for growth. Endocrine therapy is an important class of target-directed therapy that blocks the growth-promoting effects of estrogen via ER. Although endocrine therapy continues to be the cornerstone of effective treatment of ER-positive (ER+) breast cancer, many patients with advanced ER+ breast cancer encounter de novo or acquired resistance and require more aggressive treatment such as chemotherapy. Novel approaches are needed to augment the benefit of existing endocrine therapies by prolonging time to disease progression, preventing or overcoming resistance, and delaying the use of chemotherapy. The phosphatidylinositol 3-kinase/AKT/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway is a key intracellular signaling system that drives cellular growth and survival; hyperactivation of this pathway is implicated in the tumorigenesis of ER+ breast cancer and in resistance to endocrine therapy. Moreover, preclinical and clinical evidence show that PI3K/AKT/mTOR pathway inhibition can augment the benefit of endocrine therapy in ER+ breast cancer, from the first-line setting and beyond. This article will review the fundamental role of the PI3K/AKT/mTOR pathway in driving ER+ breast tumors, and its inherent interdependence with ER signaling. In addition, ongoing strategies to combine PI3K/AKT/mTOR pathway inhibitors with endocrine therapy for improved clinical outcomes, and methods to identify patient populations that would benefit most from inhibition of the PI3K/AKT/mTOR pathway, will be evaluated.

Results of an international randomized phase III trial of the mammalian target of rapamycin inhibitor ridaforolimus versus placebo to control metastatic sarcomas in patients after benefit from prior chemotherapy

PURPOSE

Aberrant mammalian target of rapamycin (mTOR) signaling is common in sarcomas and other malignancies. Drug resistance and toxicities often limit benefits of systemic chemotherapy used to treat metastatic sarcomas. This large randomized placebo-controlled phase III trial evaluated the mTOR inhibitor ridaforolimus to assess maintenance of disease control in advanced sarcomas.

PATIENTS AND METHODS

Patients with metastatic soft tissue or bone sarcomas who achieved objective response or stable disease with prior chemotherapy were randomly assigned to receive ridaforolimus 40 mg or placebo once per day for 5 days every week. Primary end point was progression-free survival (PFS); secondary end points included overall survival (OS), best target lesion response, safety, and tolerability.

RESULTS

A total of 711 patients were enrolled, and 702 received blinded study drug. Ridaforolimus treatment led to a modest, although significant, improvement in PFS per independent review compared with placebo (hazard ratio [HR], 0.72; 95% CI, 0.61 to 0.85; P = .001; median PFS, 17.7 v 14.6 weeks). Ridaforolimus induced a mean 1.3% decrease in target lesion size versus a 10.3% increase with placebo (P < .001). Median OS with ridaforolimus was 90.6 weeks versus 85.3 weeks with placebo (HR, 0.93; 95% CI, 0.78 to 1.12; P = .46). Adverse events (AEs) more common with ridaforolimus included stomatitis, infections, fatigue, thrombocytopenia, noninfectious pneumonitis, hyperglycemia, and rash. Grade ≥ 3 AEs were more common with ridaforolimus than placebo (64.1% v 25.6%).

CONCLUSION

Ridaforolimus delayed tumor progression to a small statistically significant degree in patients with metastatic sarcoma who experienced benefit with prior chemotherapy. Toxicities were observed with ridaforolimus, as expected with mTOR inhibition. These data provide a foundation on which to further improve control of sarcomas.

Moving beyond response criteria: new measures of success in the treatment of sarcomas

There is an urgent need to develop new therapies for soft tissue sarcomas. Traditional cytotoxic therapies, such as doxorubicin and ifosfamide, have been the standard approach to this disease. However, newer paradigms are emerging that are less toxic while targeting dysregulated pathways, tumor hypoxia, and genetic translocations. These newer therapies require different measures of activity as standard response criteria may inaccurately measure their effectiveness. Serious consideration of select endpoints and measures of tumor response are crucial to make significant strides in the treatment of sarcomas. Current studies on soft tissue sarcomas are slowly abandoning response rates while employing progression-free survival and time to progression as improved endpoints. With time and data, our understanding of the relative activity of these agents will grow and lead to improved benefits for our patients.

Phase I/IIa trial of the mammalian target of rapamycin inhibitor ridaforolimus (AP23573; MK-8669) administered orally in patients with refractory or advanced malignancies and sarcoma

BACKGROUND

Ridaforolimus is an inhibitor of mTOR with evidence of antitumor activity in an I.V. formulation. This multicenter, open-label, 3 + 3 design nonrandomized, dose-escalation, phase I/IIa trial was conducted to determine the safety, pharmacokinetic (PK) and pharmacodynamic parameters, maximum tolerated dose, and antitumor activity of oral ridaforolimus.

PATIENTS AND METHODS

Patients with metastatic or unresectable solid tumors refractory to therapy were eligible. Seven different continuous and intermittent dosing regimens were examined.

RESULTS

One hundred and forty-seven patients were enrolled in this study among which 85 were patients with sarcoma. Stomatitis was the most common DLT observed. The dosing regimen, 40 mg QD × 5 days/week, provided the best combination of cumulative dose, dose density, and cumulative exposure, and was the recommended dosing regimen for subsequent clinical development. PK was nonlinear, with less than proportional increases in day-1 blood AUC0-∞ and Cmax, particularly with doses >40 mg. The terminal half-life estimate of ridaforolimus (QD × 5 40 mg) was 42.0 h, and the mean half-life ∼30-60 h. The clinical benefit rate, (complete response, partial response, or stable disease for ≥4 months was 24.5% for all patients and 27.1% for patients with sarcoma.

CONCLUSION

Oral ridaforolimus had an acceptable safety profile and exhibited antitumor activity in patients with sarcoma and other malignancies. ClinicalTrials.gov Identifier NCT00112372.

A single supratherapeutic dose of ridaforolimus does not prolong the QTc interval in patients with advanced cancer

Purpose

This dedicated QTc study was designed to evaluate the effect of the mammalian target of rapamycin inhibitor, ridaforolimus, on the QTc interval in patients with advanced malignancies.

Methods

We conducted a fixed-sequence, single-blind, placebo-controlled study. Patients (n = 23) received placebo on day 1 and a single 100-mg oral dose of ridaforolimus on day 2 in the fasted state. Holter electrocardiogram (ECG) monitoring was performed for 24 h after each treatment, and blood ridaforolimus concentrations were measured for 24 h after dosing. The ECGs were interpreted in a blinded fashion, and the QT interval was corrected using Fridericia’s formula (QTcF). After a washout of at least 5 days, 22 patients went on to receive a therapeutic regimen of ridaforolimus (40 mg orally once daily for 5 days per week).

Results

The upper limit of the two-sided 90 % confidence interval for the placebo-adjusted mean change from baseline in QTcF was <10 ms at each time point. No patient had a QTcF change from baseline >30 ms or QTcF interval >480 ms. Geometric mean exposure to ridaforolimus after the single 100-mg dose was comparable to previous experience with the therapeutic regimen. There appeared to be no clear relationship between individual QTcF change from baseline and ridaforolimus blood concentrations. Ridaforolimus was generally well tolerated, with adverse events consistent with prior studies.

Conclusions

Administration of the single 100-mg dose of ridaforolimus did not cause a clinically meaningful prolongation of QTcF, suggesting that patients treated with ridaforolimus have a low likelihood of delayed ventricular repolarization.

Electronic supplementary material

The online version of this article (doi:10.1007/s00280-012-1942-7) contains supplementary material, which is available to authorized users.

Multimodality therapy for metastatic sarcomas confined to the lung

Metastectomy or resection of sarcomas which have metastasized to the lung from other sites has a long and established history. At present, there are more than forty different drugs with activity in soft tissue sarcomas. A number of sarcomas demonstrate differential sensitivities to chemotherapy and targeted agents. Intimate knowledge of the biological behavior of each distinct type of sarcoma should predicate what treatment or protocol is most suitable. Certain patients might benefit from either neoadjuvant or adjuvant therapy following the resection of metastatic lesions. Much remains to be learned about the differential sensitivities of various sarcomas to different treatment regimens.

Managing stomatitis in patients treated with Mammalian target of rapamycin inhibitors

Mammalian target of rapamycin (mTOR) inhibitors are a class of targeted cancer therapeutic agents with clinical benefit for multiple tumor types. Oral ulcerations are a common side effect of mTOR inhibitors; however, the clinical findings resemble aphthous stomatitis rather than the mucositis seen with chemotherapy. Consequently, the appearance of aphthous-like oral ulcerations has been referred to as mTOR inhibitor-associated stomatitis (mIAS). The severity of mIAS can be minimized by following common preventive steps and initiating treatment at the first sign of mouth discomfort, thereby reducing the likelihood of treatment discontinuation. mIAS can be managed through prophylactic measures, such as patient education in oral hygiene and avoidance of triggers. Patients who develop mIAS may be treated topically using rinses or other local therapies, including corticosteroids. In severe cases, dose modifications may be required. Oncology nurses have an important role in the management of patients with cancer and are well positioned to offer strategies for minimizing the occurrence and impact of mIAS.

Emerging therapeutic targets for soft tissue sarcoma

Soft tissue sarcomas (STS) are malignancies of mesenchymal origin that represent approximately 1% of cancers in adults. Systematic research into the treatment of STS is challenging given its rarity and disease heterogeneity. Despite the ability to histologically subtype STS, only recently has our approach to therapy begun to differentiate along these lines. The purpose of this review is to highlight emerging therapeutic targets and therapies that hold the potential to add to the current state of systemic treatment for STS.

Phase II study of the mammalian target of rapamycin inhibitor ridaforolimus in patients with advanced bone and soft tissue sarcomas

PURPOSE

Ridaforolimus is an inhibitor of mammalian target of rapamycin, an integral component of the phosphatidyl 3-kinase/AKT signaling pathway, with early evidence of activity in sarcomas. This multicenter, open-label, single-arm, phase II trial was conducted to assess the antitumor activity of ridaforolimus in patients with distinct subtypes of advanced sarcomas.

PATIENTS AND METHODS

Patients with metastatic or unresectable soft tissue or bone sarcomas received ridaforolimus 12.5 mg administered as a 30-minute intravenous infusion once daily for 5 days every 2 weeks. The primary end point was clinical benefit response (CBR) rate (complete response or partial response [PR] or stable disease ≥ 16 weeks). Safety, progression-free survival (PFS), overall survival (OS), time to progression, and duration of response were also evaluated.

RESULTS

A total of 212 patients were treated in four separate histologic cohorts. In this heavily pretreated population, 61 patients (28.8%) achieved CBR. Median PFS was 15.3 weeks; median OS was 40 weeks. Response Evaluation Criteria in Solid Tumors (RECIST) confirmed response rate was 1.9%, with four patients achieving confirmed PR (two with osteosarcoma, one with spindle cell sarcoma, and one with malignant fibrous histiocytoma). Archival tumor protein markers analyzed were not correlated with CBR. Related adverse events were generally mild or moderate and consisted primarily of stomatitis, mucosal inflammation, mouth ulceration, rash, and fatigue.

CONCLUSION

Single-agent ridaforolimus in patients with advanced and pretreated sarcomas led to PFS results that compare favorably with historical metrics. A phase III trial based on these data will further define ridaforolimus activity in sarcomas.

Ridaforolimus: a promising drug in the treatment of soft-tissue sarcoma and other malignancies

Ridaforolimus (deforolimus; AP23573; MK-8669) is a novel sirolimus derivative manufactured by ARIAD Pharmaceuticals and acquired by Merck. It is a small-molecule kinase inhibitor of the mTOR in clinical development for the treatment of cancer. Both intravenous and oral formulations of the agent are being tested in cancer clinical trials. In preclinical and clinical studies, ridaforolimus exhibited significant antitumor activity with acceptable safety and tolerability. With single-agent ridaforolimus, mucositis and myelosuppression were dose-limiting toxicities. In advanced soft-tissue sarcoma, single-agent ridaforolimus was associated with a 29% clinical benefit rate and 2% partial response rate. A Phase III trial has recently been reported to have met its primary end point.

A role for maintenance therapy in managing sarcoma

Despite the use of recommended chemotherapy regimens, patients with metastatic sarcomas have a poor prognosis. To date, the median overall survival for metastatic disease remains less than 18 months. First-line treatment of most metastatic sarcomas consists of chemotherapy with or without surgical excision of residual disease, followed by "watchful waiting" until disease progression or recurrence. According to the current treatment paradigm, recommended by United States and European clinical guidelines, chemotherapy is administered for a fixed number of cycles, and then a watchful waiting approach is taken once a best response is achieved. Single-agent doxorubicin remains the standard for treatment of most soft-tissue sarcomas (STS), as combination and dose-intense regimens have largely failed to improve survival. Combination chemotherapy is the standard treatment approach for osteosarcoma and Ewing's sarcoma, but outcomes are poor for patients with recurrent disease. In order to improve outcomes (in particular, progression-free survival [PFS] and overall survival [OS]), strategies shown to be effective in other solid malignancies, such as maintenance therapy and long-term treatment with targeted therapy, are being investigated in patients with advanced sarcomas. One potential promising approach is the use of mammalian target of rapamycin (mTOR) inhibitors for maintenance therapy. One such mTOR inhibitor, ridaforolimus (AP23573, MK-8669), is currently being evaluated in patients with advanced bone and STS in the ongoing Sarcoma mUlti-Center Clinical Evaluation of the Efficacy of riDaforolimus (SUCCEED) trial.

Antitumor activity of ridaforolimus and potential cell-cycle determinants of sensitivity in sarcoma and endometrial cancer models

Ridaforolimus is a nonprodrug rapamycin analogue that potently inhibits mTOR and has shown significant activity in patients with metastatic sarcoma and endometrial cancer, two diseases where high unmet need remains. Here, we evaluated the activity of ridaforolimus in preclinical models of these tumor types and used these models to explore molecular correlates of sensitivity. The in vitro sensitivity of a panel of sarcoma and endometrial cancer cell lines was established by measuring the effect of ridaforolimus on cell proliferation rate, revealing broad inhibition at low nanomolar concentrations. Additional benefit was found when ridaforolimus was combined with agents used to treat sarcoma and endometrial cancer patients. In vivo, potent antitumor activity of ridaforolimus associated with inhibition of mTOR signaling was observed in sarcoma and endometrial xenograft models. Immunoblot analysis was conducted to assess the expression and activation state of multiple signaling proteins in the phosphoinositide-3-kinase/AKT/mTOR and cell-cycle pathways. In endometrial but not sarcoma cell lines, the absence of PTEN or elevated levels of phosphorylated or total AKT was associated with greater sensitivity. However, in both tumor types, the proportion of cells in the G(0)-G(1) phase before treatment correlated significantly with ridaforolimus sensitivity. Consistent with this, expression of several G(1) phase cell-cycle proteins, notably p21 and p27, was higher in more sensitive lines. These results underscore the promise of ridaforolimus as a single agent or combination treatment of these tumor types and suggest novel potential predictive biomarkers of sensitivity to an mTOR inhibitor based on cell-cycle status.

Clinical activity of mammalian target of rapamycin inhibitors in solid tumors

The phosphatidylinositol 3-kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) pathway is vital for cell metabolism, growth, and proliferation. mTOR is frequently upregulated in many tumor types and hence has become an important target in cancer treatment. Sirolimus and its derivatives (rapalogs) interact with the intracellular receptor FK506 binding protein 12 (FKBP12), forming a complex with high affinity for mTOR and thus disrupting its activity. Rapalogs are being evaluated extensively in cancer patients with different formulations and schedules. Significant clinical activity has led to their approval for the treatment of kidney cancer, mantle cell lymphoma, and subependymal giant cell astrocytoma; however, despite increasing knowledge about cancer cell biology, their activity in other malignancies is unclear. Further research is needed to identify optimal dosage, administration and targeted combination as well as the subset of patients likely to respond to mTOR/PI3K inhibition. This review focuses on a discussion of the pathway, its implications in cancer biology and results of clinical trials of rapalogs alone or in combination, organizing them by common malignancy type.

New drugs for aggressive B-cell and T-cell lymphomas

Over the past decade an unprecedented number of new drugs for lymphomas have been developed. Most of these new drugs target molecules or pathways that are important for the growth and proliferation of lymphomas. The introduction of the B-lymphoma specific monoclonal anti-CD20 antibody, rituximab, has improved the prognosis of patients with B-cell lymphomas more than any other drug in the past 50 years; today less than half of the patients with aggressive B-cell lymphomas die of their disease than in the pre-rituximab era. Many new drugs are now available for clinical testing in addition to new CD20 antibodies and antibodies directed against other surface molecules specifically or preferentially expressed on the lymphoma-cell surface. A prerequisite for the development of these drugs was the recognition of aberrant cell-signal transduction involved in lymphoma pathogenesis and progression. New therapeutic targets include receptor tyrosine and cyclin-dependent kinases, histone deacetylases, and molecules involved in the regulation of apoptosis. The definition of the role of these new drugs alone or in combination with established chemotherapy regimens in adequately designed prospective trials represents one of the major challenges in clinical lymphoma research.

Systemic therapy of non-resectable metastatic melanoma

In advanced metastatic melanoma (non-resectable stage III/IV), the prognosis still remains poor, with median survival times between six and twelve months. Systemic therapeutic approaches for metastatic melanoma include chemotherapy, immunotherapy, immunochemotherapy, small molecules and targeted therapy. In this review, we will focus on the various treatment modalities as well as new agents used for targeted therapy.

Phase Ib study of weekly mammalian target of rapamycin inhibitor ridaforolimus (AP23573; MK-8669) with weekly paclitaxel

BACKGROUND

The additive cytotoxicity in vitro prompted a clinical study evaluating the non-prodrug rapamycin analogue ridaforolimus (AP23573; MK-8669; formerly deforolimus) administered i.v. combined with paclitaxel (PTX; Taxol).

MATERIALS AND METHODS

Patients with taxane-sensitive solid tumors were eligible. The main dose escalation foresaw 50% ridaforolimus increments from 25 mg with a fixed PTX dose of 80 mg/m(2), both given weekly 3 weeks in a 4-week cycle. Collateral levels with a lower dose of either drug were planned upon achievement of the maximum tolerated dose in the main escalation. Pharmacodynamic studies in plasma, peripheral blood mononuclear cells (PBMCs) and skin biopsies and pharmacokinetic (PK) interaction studies at cycles 1 and 2 were carried out.

RESULTS

Two recommended doses were determined: 37.5 mg ridaforolimus/60 mg/m(2) PTX and 12.5 mg/80 mg/m(2). Most frequent toxic effects were mouth sores (79%), anemia (79%), fatigue (59%), neutropenia (55%) and dermatitis (48%). Two partial responses were observed in pharyngeal squamous cell and pancreatic carcinoma. Eight patients achieved stable disease > or =4 months. No drug interaction emerged from PK studies. Decrease of eukaryotic initiation factor 4E-binding protein1 (4E-BP1) phosphorylation was shown in PBMCs. Similar inhibition of phosphorylation of 4E-BP1 and mitogen-activated protein kinase was present in reparative epidermis and vascular tissues, respectively.

CONCLUSION

Potential antiangiogenic effects and encouraging antitumor activity justify further development of the combination.

Targeting the mTOR pathway using deforolimus in cancer therapy

The mammalian target of rapamycin (mTOR) is an intracellular protein with a key role in cellular protein synthesis and energy balance that influences many aspects of cell growth and proliferation, including differentiation, cell-cycle progression, angiogenesis, protein degradation and apoptosis. mTOR can be activated by numerous oncogenic signals, such as growth factor activation through the EGF, IGF and VEGF receptors, mutation and silencing of the PTEN tumor suppressor gene, activating mutations in the PI3K catalytic subunit, Akt amplification and the Ras-Raf-MEK pathway. Once activated, the cellular functions of mTOR are achieved through its downstream targets, 4E-BP1 and p70S6K1. The mTOR pathway can be further regulated through a negative feedback loop, which may lead to resistance to specific inhibitors of mTOR. This review will outline the mTOR signaling pathway, which is often activated in cancers and account for tumor proliferation and growth, highlight the rationale in targeting mTOR with a focus on the preclinical and clinical development of one of these inhibitors, deforolimus (AP23573, MK-8669), and discuss potential benefit and barriers to these agents being introduced in the clinic.

The emerging safety profile of mTOR inhibitors, a novel class of anticancer agents

Mammalian target of rapamycin (mTOR) has emerged as an important target for cancer therapy. Rapamycin has a distinct, well-documented toxicity profile and most of the toxicity data has been reported in patients with organ transplantation. Newer mTOR inhibitors have slightly different pharmacokinetic properties, yet they present toxicity profiles similar to rapamycin. Most of these toxicities are mild to moderate in severity and can be managed clinically by dose modification and supportive measures. Mucositis and pneumonitis are the most commonly reported toxicities, but they rarely lead to treatment discontinuation. Pathogenesis of pneumonitis is uncertain, but various hypotheses have been suggested, including cell-mediated immune response to the drug.