Targeting activated PI3K/mTOR signaling overcomes acquired resistance to CDK4/6-based therapies in preclinical models of hormone receptor-positive breast cancer

Background

Combined targeting of CDK4/6 and ER is now the standard of care for patients with advanced ER+/HER2− breast cancer. However, acquired resistance to these therapies frequently leads to disease progression. As such, it is critical to identify the mechanisms by which resistance to CDK4/6-based therapies is acquired and also identify therapeutic strategies to overcome resistance.

Methods

In this study, we developed and characterized multiple in vitro and in vivo models of acquired resistance to CDK4/6-based therapies. Resistant models were screened by reverse phase protein array (RPPA) for cell signaling changes that are activated in resistance.

Results

We show that either a direct loss of Rb or loss of dependence on Rb signaling confers cross-resistance to inhibitors of CDK4/6, while PI3K/mTOR signaling remains activated. Treatment with the p110α-selective PI3K inhibitor, alpelisib (BYL719), completely blocked the progression of acquired CDK4/6 inhibitor-resistant xenografts in the absence of continued CDK4/6 inhibitor treatment in models of both PIK3CA mutant and wild-type ER+/HER2− breast cancer. Triple combination therapy against PI3K:CDK4/6:ER prevented and/or delayed the onset of resistance in treatment-naive ER+/HER2− breast cancer models.

Conclusions

These data support the clinical investigation of p110α-selective inhibitors of PI3K, such as alpelisib, in patients with ER+/HER2− breast cancer who have progressed on CDK4/6:ER-based therapies. Our data also support the investigation of PI3K:CDK4/6:ER triple combination therapy to prevent the onset of resistance to the combination of endocrine therapy plus CDK4/6 inhibition.

Abstract 3825: Targeting activated PI3K/mTOR signaling overcomes resistance to CDK4/6-based therapies in preclinical ER+ breast cancer models

Addition of CDK4/6 inhibitors such as palbociclib, ribociclib or abemaciclib to endocrine-based therapies significantly improves progression-free and in some subgroups, overall survival in patients with advanced estrogen receptor-positive (ER+) breast cancer. However, acquired resistance to CDK4/6 inhibitors remains a significant unmet clinical need. It is critical to ascertain the mechanisms by which tumor cells evade CDK4/6 based therapy. In this study we screen multiple in vitro and in vivo models of acquired resistance to CDK4/6 inhibitors to identify potential resistance/escape pathways and targets for pharmaceutical intervention to overcome resistance. ER+ breast cancer cell lines of diverse molecular backgrounds were conditioned to acquire resistance to CDK4/6 inhibitors through either long-term culture in the presence of clinically relevant concentrations of inhibitors or as cell line xenografts treated through progression on a CDK4/6 inhibitor plus fulvestrant. Baseline and pharmacodynamic changes in cell signaling were measured using reverse phase protein array (RPPA) and RNAseq analysis. Acquired resistance to CDK4/6 inhibitors was associated with decreases in phosphorylated-Rb (pRb) and ER-alpha protein and increases in pAKT and pS6 relative to isogenic controls. The p110α-selective PI3K-inhibitor, alpelisib, in combination with fulvestrant or ribociclib/fulvestrant blocked pAKT signaling in xenografts progressing on palbociclib/fulvestrant and induced significant tumor regressions. Apelisib plus fulvestrant also produced robust anti-tumor responses in xenografts progressing on ribociclib/fulvestrant. Triple combination treatment with ribociclib/alpelisib/fulvestrant induced significant regressions in resistant tumors and in treatment naïve models, where complete tumor regressions occurred regardless of PIK3CA mutation status. Regressions were maintained for >9 weeks post withdrawal of treatment, indicating that therapeutic resistance may be prevented by this triple combination approach. RPPA analysis of responding tumors identified sustained inhibition of both PI3K- and CDK4/6:Rb-pathway signaling accompanied by activation of pro-apoptotic proteins. These data support clinical investigation of targeting PI3K with alpelisib in breast cancers progressing on CDK4/6 based therapies and investigation of upfront triple combination therapy prior to acquisition of resistance to CDK4/6.

Citation Format: Neil A. O'Brien, Martina SJ McDermott, Dylan F. Conklin, Alex Gaither, Tong Luo, Raul Ayala, Suruchi Salgar, Emmanuelle DiTomaso, Naveen Babbar, Faye Su, Sara A. Hurvitz, Ronald Linnartz, Kristine Rose, Samit Hirawat, Dennis J. Slamon. Targeting activated PI3K/mTOR signaling overcomes resistance to CDK4/6-based therapies in preclinical ER+ breast cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3825.

Alpelisib for PIK3CA-Mutated, Hormone Receptor-Positive Advanced Breast Cancer

BACKGROUND

PIK3CA mutations occur in approximately 40% of patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer. The PI3Kα-specific inhibitor alpelisib has shown antitumor activity in early studies.

METHODS

In a randomized, phase 3 trial, we compared alpelisib (at a dose of 300 mg per day) plus fulvestrant (at a dose of 500 mg every 28 days and once on day 15) with placebo plus fulvestrant in patients with HR-positive, HER2-negative advanced breast cancer who had received endocrine therapy previously. Patients were enrolled into two cohorts on the basis of tumor-tissue PIK3CA mutation status. The primary end point was progression-free survival, as assessed by the investigator, in the cohort with PIK3CA-mutated cancer; progression-free survival was also analyzed in the cohort without PIK3CA-mutated cancer. Secondary end points included overall response and safety.

RESULTS

A total of 572 patients underwent randomization, including 341 patients with confirmed tumor-tissue PIK3CA mutations. In the cohort of patients with PIK3CA-mutated cancer, progression-free survival at a median follow-up of 20 months was 11.0 months (95% confidence interval [CI], 7.5 to 14.5) in the alpelisib-fulvestrant group, as compared with 5.7 months (95% CI, 3.7 to 7.4) in the placebo-fulvestrant group (hazard ratio for progression or death, 0.65; 95% CI, 0.50 to 0.85; P<0.001); in the cohort without PIK3CA-mutated cancer, the hazard ratio was 0.85 (95% CI, 0.58 to 1.25; posterior probability of hazard ratio <1.00, 79.4%). Overall response among all the patients in the cohort without PIK3CA-mutated cancer was greater with alpelisib-fulvestrant than with placebo-fulvestrant (26.6% vs. 12.8%); among patients with measurable disease in this cohort, the percentages were 35.7% and 16.2%, respectively. In the overall population, the most frequent adverse events of grade 3 or 4 were hyperglycemia (36.6% in the alpelisib-fulvestrant group vs. 0.7% in the placebo-fulvestrant group) and rash (9.9% vs. 0.3%). Diarrhea of grade 3 occurred in 6.7% of patients in the alpelisib-fulvestrant group, as compared with 0.3% of those in the placebo-fulvestrant group; no diarrhea of grade 4 was reported. The percentages of patients who discontinued alpelisib and placebo owing to adverse events were 25.0% and 4.2%, respectively.

CONCLUSIONS

Treatment with alpelisib-fulvestrant prolonged progression-free survival among patients with PIK3CA-mutated, HR-positive, HER2-negative advanced breast cancer who had received endocrine therapy previously. (Funded by Novartis Pharmaceuticals; SOLAR-1 ClinicalTrials.gov number, NCT02437318.).

Abstract CT010: Efficacy results based on PIK3CA status in BELLE-3: A Phase 3 study of buparlisib (BKM120) + fulvestrant in postmenopausal women with aromatase inhibitor-treated, HR+/HER2- ABC after progression on an mTOR inhibitor

Introduction

The phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway is often activated in endocrine therapy (ET)-resistant, hormone receptor-positive (HR+) breast cancer (BC). Adding a PI3K inhibitor (PI3Ki) to ET may overcome ET or mTOR inhibitor (mTORi) resistance. In the Phase 3 BELLE-2 study, the pan-PI3Ki buparlisib (BUP) + fulvestrant (FULV) prolonged progression-free survival (PFS) in patients (pts) with HR+, human epidermal growth factor receptor 2-negative (HER2–) advanced BC (ABC), particularly in pts with PIK3CA mutations in circulating tumor DNA (ctDNA). Here, we report biomarker results from BELLE-3 (NCT01633060).

Methods

In total, 432 postmenopausal women with HR+/HER2– ABC who previously received an aromatase inhibitor and progressed on/within 30 days of ET + mTORi treatment were enrolled. Pts must not have received &gt;1 chemotherapy regimen for ABC, or any prior PI3Ki, protein kinase B (AKT) inhibitor, or FULV. Pts were randomized 2:1 to receive BUP (100 mg/day) + FULV (500 mg) or placebo (PBO) + FULV, stratified by visceral disease status. PIK3CA status was assessed by BEAMing (exons 9 and 20 only) in plasma ctDNA collected at baseline, and in archival tumor samples by polymerase chain reaction (PCR) and next-generation sequencing (NGS). The primary endpoint was locally assessed PFS (RECIST v1.1). Secondary endpoints included overall survival, overall response rate, PFS by ctDNA PIK3CA status, quality of life, and safety; with exploratory PFS analyses by PIK3CA status in tumor tissue.

Results

BELLE-3 met its primary objective: PFS was significantly prolonged for BUP vs PBO, with hazard ratio (HR) 0.67 (95% confidence interval [CI]: 0.53–0.84; p&lt;0.001) and median PFS 3.9 vs 1.8 months. PIK3CA mutations were present in 135/348 (39%) available ctDNA samples, 109/321 (34%) tumor samples (by PCR), and 76/185 (41%) tumor samples (by NGS). PFS benefit for BUP vs PBO was higher in the PIK3CA-mutant ctDNA group (HR 0.46 [95% CI: 0.29–0.73]; median PFS 4.2 vs 1.6 months) than the PIK3CA-wild-type (WT) group (HR 0.73 [95% CI: 0.53–1.00]; median PFS 3.9 vs 2.7 months). PFS benefit was also higher in the PIK3CA-mutant tumor tissue group by PCR (HR 0.39 [95% CI: 0.23–0.65]) than the PIK3CA-WT group (HR 0.83 [95% CI: 0.60–1.14]), and in the PIK3CA-mutant tumor tissue group by NGS (HR 0.46 [95% CI: 0.26–0.82]) than the PIK3CA-WT group (HR 0.62 [95% CI: 0.40–0.97]). PIK3CA status in ctDNA and archival tissue by PCR had an overall concordance of 83%, with a sensitivity of 79% and specificity of 85%.

Conclusions

BELLE-3 met its primary endpoint in the full population. PFS benefit for BUP vs PBO was higher in pts with PIK3CA mutations detected in ctDNA or archival tissue (by PCR or NGS). Ongoing Phase 3 studies with PI3Kα-selective inhibitors will confirm the predictive value of PIK3CA mutations in ctDNA and tumor tissue on efficacy.

Citation Format: Ruth O'Regan, Carlos L. Arteaga, Thomas Bachelot, Eva Ciruelos, Per E. Lønning, Banu Sankaran, Ying A. Wang, Nicolas Scheuer, Dalila Sellami, Samit Hirawat, Angelo Di Leo. Efficacy results based on PIK3CA status in BELLE-3: A Phase 3 study of buparlisib (BKM120) + fulvestrant in postmenopausal women with aromatase inhibitor-treated, HR+/HER2- ABC after progression on an mTOR inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr CT010. doi:10.1158/1538-7445.AM2017-CT010

Updated results from MONALEESA-2, a phase 3 trial of first-line ribociclib + letrozole in hormone receptor-positive (HR+), HER2-negative (HER2–), advanced breast cancer (ABC)

1038

Background: Endocrine therapy (ET) is the basis of first-line (1L) treatment for HR+ ABC. However, ET resistance are almost universal. At the first interim analysis (IA) of MONALEESA-2 (NCT01958021), ribociclib (RIB; cyclin-dependent kinase 4/6 inhibitor) + letrozole (LET) significantly prolonged progression-free survival (PFS) vs placebo (PBO) + LET in patients (pts) with HR+, HER2– ABC.1 Here we report updated efficacy and safety data from MONALEESA-2 with a further ~11 months of follow-up. Methods: Postmenopausal women with no prior therapy for ABC were randomized 1:1 toRIB (600 mg/day, 3-weeks-on/1-week-off) + LET(2.5 mg/day, continuous) vs PBO + LET. The primary endpoint was locally assessed PFS. Secondary endpoints include overall survival (OS; key) and safety. OS significance was defined by a p-value threshold of 3.15 x 10-5. Tumor assessments were performed every 8 weeks for the first 18 months, and every 12 weeks, thereafter. Results: 668 pts were enrolled (334 in each arm). At the second IA for OS (data cut-off Jan 2, 2017), the median duration of follow-up was 26.4 months; 116 deaths and 345 PFS events had occurred. OS data remain immature, with 15.0% vs 19.8% of pt deaths in the RIB + LET vs PBO + LET arm (HR = 0.746; 95% CI: 0.517–1.078; p= 0.059). Updated PFS analyses confirmed continued treatment benefit in the RIB + LET vs PBO + LET arm. The 24-month PFS rates (RIB + LET vs PBO + LET) were 54.7% vs 35.9%. Treatment benefit was consistent across pt subgroups. The most common Grade 3/4 laboratory abnormalities (≥10% of pts; RIB + LET vs PBO + LET) were decreased neutrophils (62.6% vs 1.5%), decreased leukocytes (36.8% vs 1.5%), decreased lymphocytes (16.2% vs 3.9%), and elevated alanine aminotransferase (11.4% vs 1.2%). Conclusion: After 26+ months of follow-up, treatment benefit with 1LRIB + LET persists in postmenopausal women with HR+, HER2– ABC. The study remains immature for OS analysis. The safety profile of RIB + LET remains manageable. 1. Hortobagyi G, et al. N Engl J Med 2016;375:1738–48. Clinical trial information: NCT01958021.

Abstract P4-22-05: First-line ribociclib plus letrozole in patients with de novo HR+, HER2– advanced breast cancer (ABC): A subgroup analysis of the MONALEESA-2 trial

Background: Around 15,000 US patients per year are diagnosed with de novo ABC. Due to the absence of prior systemic treatment for breast cancer, tumors of patients with de novo ABC may exhibit a different disease biology, which could result in different tumor responses compared with patients who have relapsed breast cancer. Ribociclib is an orally bioavailable cyclin-dependent kinase (CDK) 4/6 inhibitor. Results from MONALEESA-2, a double-blind, placebo-controlled, randomized Phase 3 trial (NCT01958021), demonstrated that first-line therapy with ribociclib + letrozole significantly improved progression-free survival (PFS) vs placebo + letrozole in patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2–) ABC. Many patients with de novo ABC receive endocrine therapy in the first line and in subsequent lines; here we present results from the MONALEESA-2 study in a subpopulation of patients with de novo ABC.

Methods: Postmenopausal women (N=668) with HR+, HER2– ABC who had no prior systemic therapy for ABC were randomized 1:1 (stratified by liver and/or lung metastases) to receive ribociclib (600 mg/day; 3-weeks-on/1-week-off) + letrozole (2.5 mg/day; continuous) or placebo + letrozole. Patients with de novo ABC were eligible. Additional eligibility criteria included measurable disease or ≥1 predominantly lytic bone lesion, Eastern Cooperative Oncology Group performance status ≤1, and adequate bone marrow/organ function. Prior CDK4/6 inhibitors or systemic therapy for ABC were prohibited. Patients may have received ≤14 days of letrozole or anastrozole for ABC. The primary endpoint was locally assessed PFS; a predefined subgroup analysis evaluated PFS in patients with de novo ABC.

Results: In total, 227 patients with de novo ABC were enrolled. Patients with de novo ABC were equally distributed with 114 (34%) and 113 (34%) in the ribociclib + letrozole and placebo + letrozole arms, respectively. Median duration of exposure to study treatment in the ribociclib + letrozole vs placebo + letrozole arms was 14.1 vs 12.8 months. Treatment was discontinued in 84 (37%) patients with de novo ABC (ribociclib + letrozole vs placebo + letrozole, n [%]; 34 [30%] vs 50 [44%]). Reasons for treatment discontinuation (ribociclib + letrozole vs placebo + letrozole, n [%]) included disease progression (21 [18%] vs 41 [36%]), patient/physician decision (5 [4%] vs 6 [5%]), and adverse events (6 [5%] vs 3 [3%]). PFS was increased in patients with de novo ABC who received ribociclib + letrozole vs placebo + letrozole (hazard ratio=0.448 [95% confidence interval: 0.267–0.750]). The 12-month PFS event-free probability in patients with de novo ABC was 82% in the ribociclib + letrozole arm vs 66% in the placebo + letrozole arm.

Conclusions: The combination of ribociclib + letrozole significantly improved PFS compared with placebo + letrozole in postmenopausal women with HR+, HER2– de novo ABC at diagnosis and therefore may become an important treatment option in the de novo ABC setting.

Keywords: Advanced breast cancer; CDK4/6 inhibitor; Letrozole; Ribociclib

Citation Format: O'Shaughnessy J, Petrakova K, Sonke GS, André F, Conte P, Arteaga CL, Cameron DA, Hart LL, Villanueva C, Jakobsen EH, Lindquist D, Souami F, Li X, Germa C, Hirawat S, Hortobagyi GN. First-line ribociclib plus letrozole in patients with de novo HR+, HER2– advanced breast cancer (ABC): A subgroup analysis of the MONALEESA-2 trial [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-22-05.

Abstract P4-22-16: First-line ribociclib + letrozole in patients with HR+, HER2– advanced breast cancer (ABC) presenting with visceral metastases or bone-only disease: A subgroup analysis of the MONALEESA-2 trial

Background: Patients with ABC who present with visceral metastases have a worse outcome than patients with non-visceral disease, while patients with bone-only disease tend to have a better prognosis. Ribociclib (LEE011) is an oral, selective inhibitor of cyclin-dependent kinase (CDK) 4/6. In a Phase 3, placebo-controlled, randomized trial (MONALEESA-2; NCT01958021), first-line ribociclib (R) + letrozole (L) significantly prolonged progression-free survival (PFS) vs placebo (P) + L in patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2–) ABC, with a hazard ratio of 0.556 (95% confidence interval [CI]: 0.429–0.720; p=0.00000329) at the interim analysis cut-off date (Jan 29, 2016). Here, we present subgroup analyses in patients with visceral metastases, and those with bone-only disease.

Methods: Postmenopausal women with HR+, HER2– ABC were randomized 1:1 to receive R (600 mg/day; 3-weeks-on/1-week-off) + L (2.5 mg/day; continuous) or P+L, stratified by the presence of liver and/or lung metastases. No prior CDK4/6 inhibitors or systemic therapy for ABC were allowed. Eligible patients had Eastern Cooperative Oncology Group performance status ≤1, baseline alanine/aspartate aminotransferase levels &lt;5× upper limit of normal (ULN) or &lt;2.5× ULN for patients with or without liver metastases, respectively, and ≥1 predominantly lytic bone lesion at baseline for patients with bone-only disease. Locally assessed PFS was analyzed for all patients (primary endpoint), and for predefined patient subgroups.

Results: Overall, 668 patients were randomized; 393 had visceral metastases and 147 had bone-only disease.

 Visceral metastasesBone-only disease n=393n=147 R+LP+LR+LP+L n=197n=196n=69n=78Median age, years (range)63 (23–91)63 (29–88)65 (37–85)63 (37–84)De novo metastatic disease, n (%)53 (27)55 (28)28 (41)24 (31)Non-de novo disease-free interval, n (%)≤24 months12 (6)15 (8)5 (7)6 (8)&gt;24 months132 (67)126 (64)36 (52)48 (62)Discontinued treatment, n (%)83 (42)111 (57)29 (42)40 (51)Reason for discontinuation, n (%)Disease progression56 (28)93 (47)17 (25)31 (40)Patient/physician decision10 (5)15 (8)7 (10)6 (8)Adverse events16 (8)3 (2)4 (6)2 (3)Protocol deviation001 (1)1 (1)Death1 (&lt;1)000

In patients with visceral metastases: Median PFS was not reached in the R+L arm (95% CI: 19.3–not estimable [NE]) vs 13.0 months (95% CI: 12.6 –16.5) in the P+L arm, with hazard ratio 0.535 (95% CI: 0.385–0.742). Median duration of exposure was 12.0 and 13.0 months (R and L, respectively) in the R+L arm, and 12.1 and 12.2 months (P and L, respectively) in the P+L arm.

In patients with bone-only disease: Median PFS was not reached in the R+L arm (95% CI: NE–NE) vs 15.3 months (95% CI: 13.8–NE) in the P+L arm, with hazard ratio 0.690 (95% CI: 0.381–1.249). Median duration of exposure was 12.1 and 12.6 months (R and L, respectively) in the R+L arm, and 12.7 and 12.9 months (P and L, respectively) in the P+L arm.

Conclusions: First-line R+L was well tolerated and significantly prolonged PFS vs P+L in postmenopausal women with HR+, HER2– ABC, both in patients with visceral metastases and those with bone-only disease.

Keywords: Advanced breast cancer; CDK4/6 inhibitor; Letrozole; Ribociclib

Citation Format: Burris HA, Chan A, Campone M, Blackwell KL, Winer EP, Janni W, Verma S, Burdaeva O, Alba E, Favret AM, Mondal S, Miller M, Germa C, Hirawat S, Yap YS. First-line ribociclib + letrozole in patients with HR+, HER2– advanced breast cancer (ABC) presenting with visceral metastases or bone-only disease: A subgroup analysis of the MONALEESA-2 trial [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-22-16.

Ribociclib as First-Line Therapy for HR-Positive, Advanced Breast Cancer

BACKGROUND

The inhibition of cyclin-dependent kinases 4 and 6 (CDK4/6) could potentially overcome or delay resistance to endocrine therapy in advanced breast cancer that is positive for hormone receptor (HR) and negative for human epidermal growth factor receptor 2 (HER2).

METHODS

In this randomized, placebo-controlled, phase 3 trial, we evaluated the efficacy and safety of the selective CDK4/6 inhibitor ribociclib combined with letrozole for first-line treatment in 668 postmenopausal women with HR-positive, HER2-negative recurrent or metastatic breast cancer who had not received previous systemic therapy for advanced disease. We randomly assigned the patients to receive either ribociclib (600 mg per day on a 3-weeks-on, 1-week-off schedule) plus letrozole (2.5 mg per day) or placebo plus letrozole. The primary end point was investigator-assessed progression-free survival. Secondary end points included overall survival, overall response rate, and safety. A preplanned interim analysis was performed on January 29, 2016, after 243 patients had disease progression or died. Prespecified criteria for superiority required a hazard ratio of 0.56 or less with P<1.29×10^-5.

RESULTS

The duration of progression-free survival was significantly longer in the ribociclib group than in the placebo group (hazard ratio, 0.56; 95% CI, 0.43 to 0.72; P=3.29×10^-6 for superiority). The median duration of follow-up was 15.3 months. After 18 months, the progression-free survival rate was 63.0% (95% confidence interval [CI], 54.6 to 70.3) in the ribociclib group and 42.2% (95% CI, 34.8 to 49.5) in the placebo group. In patients with measurable disease at baseline, the overall response rate was 52.7% and 37.1%, respectively (P<0.001). Common grade 3 or 4 adverse events that were reported in more than 10% of the patients in either group were neutropenia (59.3% in the ribociclib group vs. 0.9% in the placebo group) and leukopenia (21.0% vs. 0.6%); the rates of discontinuation because of adverse events were 7.5% and 2.1%, respectively.

CONCLUSIONS

Among patients receiving initial systemic treatment for HR-positive, HER2-negative advanced breast cancer, the duration of progression-free survival was significantly longer among those receiving ribociclib plus letrozole than among those receiving placebo plus letrozole, with a higher rate of myelosuppression in the ribociclib group. (Funded by Novartis Pharmaceuticals; ClinicalTrials.gov number, NCT01958021 .).

Abstract P4-14-25: Single agent and combined targeting of PI3K, mTOR, HER2 and ER signaling in a panel of HER2+/ER+ versus HER2+/ER- breast cancer cell lines

Background: Altered PI3K/mTOR signaling, through activating mutations in PIK3CA and/or PTEN loss, has been implicated in resistance to both hormonal and HER2-directed therapeutics for breast cancer. Recent data from the BOLERO-1 phase III clinical trials demonstrate an improvement in progression free survival (PFS) of 7.2 months in patients with HER2+/estrogen receptor negative (HER2+/ER-) advanced breast cancer when treated with trastuzumab and paclitaxel plus the mTORC1 inhibitor, everolimus (Afinitor ®). However, improvement in PFS was not observed in patients with HER2+/ER+ positive disease. These data suggest that hormone receptor levels may influence the response of HER2-amplifed cells to both HER2 and PI3K/mTOR directed therapies in the absence of hormonally directed therapies. In this study, we investigated the role of ER in HER2+ breast cancer by screening a large panel of HER2+/ER- and HER2+/ER+ breast cancer cell lines for responses to single agent and combined treatment with PI3K, mTOR, HER2 and ER-directed therapeutics.

Materials and Methods: The anti-proliferative activity of BKM120 (pan-PI3K inhibitor), BYL719 (p110α-specific) and everolimus were assessed as single agents or in combination with trastuzumab and/or tamoxifen in a panel of six HER2+/ER+ versus six HER2+/ER- breast cancer cell lines in two-dimensional culture. Drug response IC50s were generated from actual cell counts as measured by Z2-particle counting. Biomarker analyses were conducted using baseline mRNA microarray (Agilent) and reverse phase protein array (RPPA) profiling of each of the cell lines to determine associations with response or resistance data.

Results: RPPA analysis confirmed the presence of higher levels of ER protein in the cell lines designated as ER+ and significantly higher levels of PTEN protein were detected in those cell lines. Interestingly, each of the PI3K/mTOR pathway inhibitors tended to have increased single agent activity in the ER+ relative to the ER- lines. Combined activity with trastuzumab and either BKM120 or BYL719 was observed in 6 of the 12 cell lines tested and occurred independent of ER status. Similarly, combined activity of everolimus and trastuzumab was also observed in both HER2+/ER+ and HER2+/ER- cell lines. In 3/6 HER2+/ER+ cell lines the addition of tamoxifen provided no benefit to the combination of trastuzumab and PI3K/mTOR pathway inhibitor, whereas in two cell lines mild antagonism was observed with the triple combination. Finally, one cell line did show significant potentiation from the addition of endocrine therapy on top of HER2/PI3K/mTOR targeting.

Discussion: These data confirm levels of estrogen receptor are likely playing a role in response to single agent PI3K/mTOR pathway inhibition and highlight the potential utility of combining endocrine therapy with HER2/PI3K/mTOR-directed therapeutics in a sub-group of HER2-amplified breast cancers. Further in depth biomarker analyses may reveal additional molecular alterations responsible for this differential sensitivity to the double and triple combinations and is underway.

Citation Format: O'Brien NA, Nichols CM, Thomas J, Conklin D, Kalous O, Linnartz R, Di Tomasso E, Hurvitz SA, Hirawat S, Slamon DJ. Single agent and combined targeting of PI3K, mTOR, HER2 and ER signaling in a panel of HER2+/ER+ versus HER2+/ER- breast cancer cell lines. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-14-25.

Phase 1 Study of Safety, Tolerability, and Pharmacokinetics of PTC299, an Inhibitor of Stress-Regulated Protein Translation

PTC299 is a novel small molecule that specifically blocks the production of protein from selected mRNAs that under certain conditions use noncanonical ribosomal translational pathways. Hypoxia, oncogenic transformation, and viral infections limit normal translation and turn on these noncanonical translation pathways that are sensitive to PTC299. Vascular endothelial cell growth factor (VEGF) is an example of a transcript that is posttranscriptionally regulated. Single doses of PTC299 (0.03 to 3 mg/kg) were administered orally to healthy volunteers in a phase 1 single ascending‐dose study. In a subsequent multiple ascending‐dose study in healthy volunteers, multiple‐dose regimens (0.3 to 1.2 mg/kg twice a day or 1.6 mg/kg 3 times a day for 7 days) were evaluated. PTC299 was well tolerated in these studies. As expected in healthy volunteers, mean plasma VEGF levels did not change. Increases in C_max and AUC of PTC299 were dose‐proportional. The target trough plasma concentration associated with preclinical efficacy was achieved within 7 days at doses of 0.6 mg/kg twice daily and above. These data demonstrate that PTC299 is orally bioavailable and well tolerated and support clinical evaluation of PTC299 in cancer, certain viral infections, or other diseases in which deregulation of translational control is a causal factor.

PI3K inhibitors as new cancer therapeutics: implications for clinical trial design

The PI3K–AKT–mTOR pathway is frequently activated in cancer. PI3K inhibitors, including the pan-PI3K inhibitor buparlisib (BKM120) and the PI3Kα-selective inhibitor alpelisib (BYL719), currently in clinical development by Novartis Oncology, may therefore be effective as anticancer agents. Early clinical studies with PI3K inhibitors have demonstrated preliminary antitumor activity and acceptable safety profiles. However, a number of unanswered questions regarding PI3K inhibition in cancer remain, including: what is the best approach for different tumor types, and which biomarkers will accurately identify the patient populations most likely to benefit from specific PI3K inhibitors? This review summarizes the strategies being employed by Novartis Oncology to help maximize the benefits of clinical studies with buparlisib and alpelisib, including stratification according to PI3K pathway activation status, selective enrollment/target enrichment (where patients with PI3K pathway-activated tumors are specifically recruited), nonselective enrollment with mandatory tissue collection, and enrollment of patients who have progressed on previous targeted agents, such as mTOR inhibitors or endocrine therapy. An overview of Novartis-sponsored and Novartis-supported trials that are utilizing these approaches in a range of cancer types, including breast cancer, head and neck squamous cell carcinoma, non-small cell lung carcinoma, lymphoma, and glioblastoma multiforme, is also described.

Abstract LB-A05: Profiling cell free DNA in breast cancer and non-small cell lung cancer using broad NGS assessment

Introduction: Cell free DNA (cfDNA) has become a promising approach for non-invasive assessment of the tumor genome. Many cfDNA assays target hotspot alterations in a focused set of genes, but do not provide a broad characterization of the cancer. We have developed and optimized a large next generation sequencing (NGS) panel covering the coding regions of over 500 genes. Using this panel, we sequenced cell free DNA from plasma and matched tumor DNA in patients with early stage breast cancer, late stage breast cancer and late stage lung cancer.

Methods: Plasma was collected from patients with cancer using a double spin protocol and, when available, matched archival tumor tissue (representing different time interval with blood collection) was obtained. Next generation sequencing libraries were generated from cell free DNA isolated from 70 plasma samples and genomic DNA from 58 matched tumor samples. The NGS libraries were enriched for the gene panel of interest and were sequenced to a targeted depth of 1,000X for plasma and 300X for matched tumors. We optimized parameters of standard bioinformatics tools to robustly call low allelic fraction events, detecting single nucleotide variants down to 1%, as well as indels and copy number alterations.

Results: We identified 8 PIK3CA hotspot alterations in plasma from late stage breast and lung cancers, in addition to many alterations across driver genes such as AKT1, EGFR, IDH2, NRAS, PTEN and TP53. In plasma samples from patients with late stage breast cancer, we found 4 ESR1 mutations exclusive to the plasma samples, of which 3 are known resistance mutations to endocrine therapy. Copy number alterations in EGFR, CCND1 and KRAS were also identified in patient plasma. When comparing the number of alterations across tumor stages, we found that late stage breast (mean = 12.5 variants) and lung cancers (mean = 12.5 variants) had a larger number of alterations present in plasma than early stage breast cancers (mean = 4.5 variants). We compared somatic mutations calls in plasma and matched tumor samples and found a concordance of 53%-67% at the variant level across patients with late stage cancers (N = 37 pairs). Higher variant level concordance was observed among plasma-tumor pairs collected less than a year apart (N = 11 pairs; 76%-84%) versus more than 5 years apart (N = 8 pairs; 41%-50%).

Conclusion: We have developed and optimized a 500+ gene panel for direct sequencing of cfDNA, and we demonstrate that this broad assessment of circulating tumor DNA can be used for non-invasive characterization of the cancer genome landscape. The number of alterations identified in patient plasma is consistent with higher levels of ctDNA being present in late stage disease than in early stage disease. The time dependent degree of concordance between plasma and tumor collection suggests that cell free DNA assays may provide a more accurate characterization of the current tumor mutational landscape than an archival tumor sample. The identification of plasma specific ESR1 alterations highlights the importance of cfDNA in the context of identifying mechanisms of resistance, particularly for metastatic disease when tumor tissue collection may not be feasible. In addition, a broad NGS panel provides the opportunity to identify lesions unevaluated by targeted assays and to discover resistance mutations.

Citation Format: Nadia Solovieff, Matt Hims, Rebecca Leary, Derek Chiang, Caroline Germa, Cristian Massacesi, Samit Hirawat, Stefan J. Scherer, Michael Morrissey, Wendy Winckler, Emmanuelle di Tomaso. Profiling cell free DNA in breast cancer and non-small cell lung cancer using broad NGS assessment. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr LB-A05.

Abstract 4698: Combination of ceritinib (LDK378) with PI3K inhibitors (buparlisib [BKM120] and alpelisib [BYL719]) demonstrates synergistic preclinical antitumor activity in ALK-rearranged non-small cell lung cancer (NSCLC)

Introduction: NSCLCs harboring rearrangements of the anaplastic lymphoma kinase (ALK) gene are highly sensitive to ALK inhibition. Ceritinib is a novel ALK inhibitor that demonstrates significant preclinical and clinical antitumor potency, including in tumors that have developed resistance to the approved ALK inhibitor crizotinib. Upregulation of the phosphatidylinositol 3-kinase (PI3K) pathway may be involved in ALK inhibitor resistance, suggesting that combining ceritinib with a PI3K inhibitor may provide synergistic antitumor activity in ALK-rearranged NSCLC. Here, we assess the synergy and antiproliferative activity of PI3K inhibitor/ceritinib combinations in crizotinib-naïve primary preclinical models of NSCLC.

Methods: In vitro experiments used the EML4−ALK-translocated lung cancer cell line H2228 to screen for synergistic combinations of ceritinib with 18 other compounds (PI3K, MEK, and CDK4/6 inhibitors, among others). In vivo experiments used a human-mouse primary xenograft lung cancer model with similar EML4−ALK translocation (LUF1656). Tumor fragments (diameter 2−3 mm) from stock mice inoculated with LUF1656 lung cancer tissue were harvested and used for inoculation into nu/nu mice for tumor development. Once mean tumor size had reached ∼150 mm3, treatment was initiated with single-agent or combination regimens of buparlisib (pan-PI3K inhibitor; 35 mg/kg QD), alpelisib (PI3Kα inhibitor; 30 mg/kg QD), or ceritinib (25 mg/kg [low dose] or 50 mg/kg [full dose] QD). All doses used were equivalent to known therapeutic doses in patients.

Results: In vitro experiments revealed the strongest antiproliferative activity when ceritinib was combined with either buparlisib or alpelisib versus the other compounds tested. In vivo, low-dose ceritinib in combination with buparlisib improved tumor growth delay over single-agent, full-dose ceritinib. Full-dose ceritinib plus alpelisib showed no significant difference in tumor growth delay versus full-dose ceritinib alone. Low-dose ceritinib plus alpelisib appeared to be better tolerated than full-dose ceritinib plus alpelisib, but with similar efficacy to low-dose ceritinib alone. A delayed tumor growth rate after treatment interruption was noted in all ceritinib combinations.

Conclusion: Synergy was observed between ceritinib and PI3K inhibitors in a crizotinib-naïve ALK-translocated lung model in vitro. In the in vivo EML4−ALK lung preclinical cancer models, low-dose ceritinib (25 mg/kg) combined with buparlisib showed improved efficacy versus full-dose ceritinib (50 mg/kg) alone. Preclinical experiments exploring combinations of PI3K- and ALK-targeted therapies in crizotinib-resistant ALK-rearranged tumors are also ongoing.

Citation Format: Emmanuelle Di Tomaso, Ronald Linnartz, Fang Li, Cristian Massacesi, Samit Hirawat. Combination of ceritinib (LDK378) with PI3K inhibitors (buparlisib [BKM120] and alpelisib [BYL719]) demonstrates synergistic preclinical antitumor activity in ALK-rearranged non-small cell lung cancer (NSCLC). [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4698. doi:10.1158/1538-7445.AM2015-4698

Abstract A26: Detecting PIK3CA mutations in circulating cell-free DNA from patients with metastatic cancer: An exploratory analysis in patients with endometrial and lung cancer

Background: Personalized therapy relies on the ability to characterize the tumor at the time of treatment. Circulating cell-free DNA (cfDNA) may offer the potential for representative mutation analysis in patients with cancer irrespective of tumor tissue availability. Recent publications have started to establish the feasibility of this approach. For example, 72.5% concordance of PIK3CA mutations was reported between temporally unmatched cfDNA and archival tumor tissue from patients with metastatic breast cancer (Higgins et al. Clin Cancer Res 2012). Here, we present a retrospective analysis evaluating the reliability of detecting PIK3CA mutations in plasma samples from patients with endometrial and lung cancer – two malignancies known to harbor alterations in the PI3K pathway.

Methods: Baseline plasma DNA samples were available from 61 patients with advanced endometrial cancer (NCT01289041) and 37 patients with advanced non-small cell lung cancer (NSCLC; NCT01297491). BEAMing technology (Richardson & Iglehart. Clin Cancer Res 2012) and Sanger analysis were used in all samples. Sanger analysis was able to detect any mutation in exons 1, 5, 7, 9, and 20, whereas only selected mutations (14 in total) known to affect PI3K function in exons 1, 4, 7, 9, and 20 could be detected in cfDNA. Plasma samples were all temporally unmatched to the archival tissue specimen. Concordance analysis was performed by comparing the mutation status of samples (i.e. the proportion of samples that were detected as either wildtype or mutant consistently) between Sanger and cfDNA sequencing.

Results: 54 of 61 patients with endometrial cancer had interpretable mutation results by both Sanger and cfDNA analysis. Concordance of PIK3CA mutation was 74% between plasma and tissue. The PIK3CA mutations detected in cfDNA were distributed over exons 1, 7, 9, and 20 (29%, 19%, 33%, and 19%, respectively). Among the 37 patients with NSCLC, overall concordance was 54%. Variant distribution of PIK3CA mutations in this small number of lung tumors appeared to differ from the usual “hotspots” as two-thirds of mutations detected by Sanger analysis were not available on the BEAMing panel.

Conclusion: Concordance for PIK3CA mutation between temporally unmatched archival specimens and blood samples in this endometrial cancer patient population was in line with the published rate for metastatic breast cancer. The different mutations identified in samples from patients with NSCLC indicate a need for better understanding of the potential role of the PI3K pathway in this tumor type.

Overall these results support the feasibility of assessing PIK3CA mutations in plasma samples. The outcomes show a similar trend to multiple recent publications, thus warranting rapid further exploration of the clinical utility of cfDNA in metastatic cancer.

Citation Format: Emmanuelle di Tomaso, Bradley Monk, Grace Dy, Douglas Robinson, Paola Aimone, Lucia Trandafir, Cristian Massacesi, Samit Hirawat. Detecting PIK3CA mutations in circulating cell-free DNA from patients with metastatic cancer: An exploratory analysis in patients with endometrial and lung cancer. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr A26.

Abstract P5-05-04: Acquired resistance to everolimus occurs independently of mTORC1 inhibition in preclinical in vivo models of ER+ breast cancer

Background: The addition of the selective mTORC1 inhibitor everolimus (RAD001/Afinitor®), to exemestane significantly prolongs progression free survival in patients with advanced hormone receptor (ER+) positive breast cancer. However, despite these improved outcomes, the majority of patients that achieve an initial clinical benefit will eventually go on to develop progressive disease. In order to prevent or delay the onset of this acquired resistance, it is essential to identify the mechanisms by which continued proliferation is being driven in these resistant tumors. In this study, we used reverse phase protein array (RPPA) technology to compare cell signaling in ER+ breast cancer cell line xenografts that were responsive to everolimus versus those that had acquired resistance to everolimus.

Materials and Methods: Xenograft models were established from three ER+ breast cancer cell lines containing different molecular alterations that confer activated PI3K/mTOR signaling; MCF7 and KPL-1 (both PIK3CA mutant) and ZR75-1 (PTEN-null). Mice were treated daily with either vehicle or 10 mg/kg everolimus until progression. Snap frozen tissue samples (n = 3) were collected from vehicle control tumors, from everolimus resistant tumors and from everolimus responsive tumors. Whole cell lysates were prepared from tumor tissues and processed for RPPA analysis. A customized panel of 27 known cancer/PI3K pathway associated signaling proteins were selected for the RPPA analysis.

Results: In the vehicle controls, significantly higher levels of pAKT, pPRAS40 and p4EBP1 were detected in the PTEN-null ZR75-1 tumors compared to the PIK3CA mutant tumors, indicating potential variations in intensity of PI3K/AKT pathway signaling depending on the initiating molecular alteration. Complete inhibition of tumor proliferation was observed in response to everolimus in all 3 xenograft models for up to 7-weeks of treatment, until tumors showed signs of progression. Significantly lower S6 phosphorylation was observed in tumors responding to everolimus, which was accompanied by feedback activation of pAKT. Significant inhibition of S6 phosphorylation was also observed in each of the ZR75-1 and MCF7 tumors that were progressing on everolimus, indicating that although the tumor cells have acquired resistance to the anti-proliferative activity of everolimus, mTORC1 signaling is still being successfully blocked. Feedback activation of pAKT was observed in the ZR75-1 resistant model, however no feedback activation of AKT occurred in the MCF7 resistant model. The KPL-1 model showed the expected loss of S6 pathway inhibition upon resistance. No significant signaling changes were observed in any of the other signaling proteins measured, including ER, HER2, EGFR, MEK and ERK. Ongoing studies to measure the mRNA expression changes in these tumors using mRNA microarrays may identify signaling pathways that are driving the proliferation of these resistant tumors.

Discussion: These preclinical data show that multiple pathways of resistance can develop in response to long-term everolimus treatment and resistance can occur despite continued inhibition of PI3K/mTOR signaling. Data from mRNA microarray experiments will be presented at the time of the meeting.

Citation Format: Neil A O'Brien, Dylan Conklin, Michaela Ching, Luo Tong, Raul Ayala, Shawnt Issakhanian, Sara A Hurvitz, Emmanuelle di Tomaso, Ronald Linnartz, Richard S Finn, Samit Hirawat, Dennis J Slamon. Acquired resistance to everolimus occurs independently of mTORC1 inhibition in preclinical in vivo models of ER+ breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-05-04.

Abstract PD1-5: Targeting PI3K overcomes in vivo resistance to everolimus in estrogen receptor (ER+) breast cancer

Background: The selective mTORC1 inhibitor everolimus (RAD001/Affinitor®) has recently been approved, in combination with exemestane, for treatment of advanced hormone receptor positive breast cancer after demonstrating significantly improved progression free survival for patients having progressed on a previous non-steroidal aromatase inhibitor. However, despite these improved outcomes many tumors go on to develop resistance to everolimus. Alterations in PI3K/AKT signaling, either through activating mutations in PIK3CA or loss of PTEN, have been shown to influence responses to everolimus treatment in vitro (Weigelt et al., 2011). In this study we used cell line xenograft models of everolimus resistance to assess the potential of a pan-PI3K inhibitor (BKM120) or a p110a-specific inhibitor (BYL719) to reverse resistance either as single agents or in combination with anti-ER therapy (Fulvestrant).

Materials and Methods: Everolimus resistant xenografts were developed from three originally everolimus sensitive ER+ cell lines carrying distinct genetic alterations that confer aberrant PI3K/AKT signaling; ZR75-1 (PTEN null), MCF7 (PIK3CA mutant) and KPL1 (wild-type). Mice were treated by daily oral everolimus (10 mg/kg) until tumors began to progress on treatment (∼ 35 days of daily treatment). Mice that developed everolimus resistant tumors were randomized into six treatment groups (n = 6) as follows: continued on everolimus (10 mg/kg), fulvestrant (5 mg/wk), BKM120 (35 mg/kg), BYL719 (50 mg/kg), fulvestrant + BKM120 or BYL719.

Results: All three cell line xenografts were initially responsive to everolimus. ZR75-1 xenografts were allowed to progress on everolimus until they reached a mean tumor volume greater than that on day zero, at which point mice were randomized into treatment groups. Tumor selected to continue on everolimus gained a mean tumor volume of 550 mm3 over the six-week duration of study, demonstrating resistance to everolimus. These tumors showed a partial response to Fulvestrant (28% TGI), BYL719 alone (40% TGI) and BYL719 combined with fulvestrant (61% TGI). In contrast, over 100% tumor growth inhibition (tumor regression) was observed with both single agent BKM120 or BKM120 plus fulvestrant. This is consistent with our in vitro findings that PTEN null tumor cells might be less sensitive to inhibition by BYL719 yet sensitive to BKM120. Data from the ongoing PIK3CA mutant and wild-type KPL1 models will inform whether these molecular subtypes of ER+ breast cancer are more sensitive to the pan-PI3K inhibitor or the p110α-specific inhibitor. Comprehensive pharmacodynamic analyses of these tumor tissues may identify the additional molecular determinants responsible for resistance to everolimus and help guide the design of future clinical studies.

Discussion: These pre-clinical data indicate that targeting PI3K either alone or in combination with fulvestrant overcomes resistance to everolimus in ER+ breast cancer.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr PD1-5.

Challenges in the clinical development of PI3K inhibitors

The PI3K/Akt/mTOR pathway is one of the most frequently dysregulated signaling pathways in cancer and an important target for drug development. PI3K signaling plays a fundamental role in tumorigenesis, governing cell proliferation, survival, motility, and angiogenesis. Activation of the pathway is frequently observed in a variety of tumor types and can occur through several mechanisms. These mechanisms include (but are not limited to) upregulated signaling via the aberrant activation of receptors upstream of PI3K, amplification or gain-of-function mutations in the PIK3CA gene encoding the p110α catalytic subunit of PI3K, and inactivation of PTEN through mutation, deletion, or epigenetic silencing. PI3K pathway activation may occur as part of primary tumorigenesis, or as an adaptive response (via molecular alterations or increased phosphorylation of pathway components) that may lead to resistance to anticancer therapies. A range of PI3K inhibitors are being investigated for the treatment of different types of cancer; broad clinical development plans require a flexible yet well-structured approach to clinical trial design.

Abstract P4-08-01: PI3K/mTOR inhibition overcomes in vitro and in vivo trastuzumab resistance independent of feedback activation of pAKT

Background: Aberrant activity of the PI3K/mTOR pathway has been implicated in resistance to trastuzumab and anti-hormonal therapy for HER2-amplified and ER-positive breast cancer, respectively. Previous studies in our laboratory and others have shown that increased PI3K/mTOR signaling, either through PTEN loss or activating PIK3CA mutations, can confer resistance to trastuzumab therapy. In this study, we assessed the potential of targeting the PI3K/mTOR pathway in overcoming both de novo and acquired trastuzumab resistance.

Materials and Methods: The in vitro activity of the pan-PI3K inhibitor BKM120, the mTORC1 inhibitor RAD001 and the dual PI3K/mTORC1/2 inhibitor BEZ235 were evaluated in a panel of 49 human breast cancer and immortalized cell lines. The in vivo activity of these molecules was assessed in six cell line xenografts models representing, ER+/HER2− (KPL-1, ZR75-1), ER+/HER2+ (UACC812, MDA361), ER−/HER2+ (SUM190), PIK3CA mutant (SUM190, MDA361), PTEN-null (ZR75-1) and trastuzumab resistant (BT-TR) breast cancer. Finally, the effect of PI3K/mTOR inhibition on feedback activation of PI3K signaling and compensatory pathways was measured by Western blot, immunohistochemistry (IHC) and reverse phase protein analysis (RPPA) of control and treated cell lysates/tumors.

Results: Using a sensitivity cut-off of an IC50 of &lt; 1 µmol/L, 16 of the 18 HER2-amplified breast cancer cell lines and 8 of 10 cell lines with activating mutations in PIK3CA were sensitive to the pan-PI3K inhibitor BKM120. BEZ235 showed the most potent efficacy across the panel with IC50s &lt; 100 nmol/L for each of the 49 cell lines tested. The HER2-amplified/PIK3CA mutant cell lines were also unexpectedly sensitive to the mTORC1 inhibitor RAD001, this was despite the silencing of mTORC1 signaling being followed by a feedback increase in phospho-AKT signaling. Furthermore, each of these molecules showed remarkable in vivo activity across the panel of xenografts models. BKM120, RAD001 and BEZ235 induced both tumor stabilization and regression independent of PTEN, PI3K, ER and HER2 status. Pharmacodynamic analysis of tumor tissue revealed that BEZ235 and RAD001 both inhibited mTORC1 signaling as indicated by a reduction in the levels of phosphorylated ribosomal protein S6 (pS6). However, in contrast to BKM120 and BEZ235, RAD001 did not induce a reduction in the levels of pAKT (S473 or TH308) yet showed comparable in vivo efficacy to each of these molecules. Finally, combined targeting of HER2 and PI3K/mTOR in vitro increased the anti-proliferative activity of the molecules and led to an increased induction of apoptosis. The efficacy of these molecules (alone or in combination with trastuzumab) was assessed in a model of in vivo trastuzumab resistance generated through long-term treatment of the trastuzumab sensitive BT474 cells (BT-TR). All PI3Ki induced complete inhibition of tumor proliferation in monotherapy, while the combination of trastuzumab and each of these molecules induced tumor regression in the trastuzumab resistant tumors.

Discussion: These pre-clinical data indicate that targeting the PI3K/mTOR pathway either alone or in combination with trastuzumab is effective strategy for overcoming trastuzumab resistance.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-08-01.

P3-16-01: Safety Profile and Clinical Activity of Single-Agent BKM120, a Pan-Class I PI3K Inhibitor, for the Treatment of Patients with Metastatic Breast Carcinoma

Background

Phosphatidylinositol 3-kinase (PI3K) is critical to cancer cell growth, survival, and metabolism. BKM120 is an oral pan-class I (α, β, γ, δ) PI3K inhibitor that has demonstrated in vitro and in vivo tumor cell growth inhibition in a range of cancer types including breast cancer.

Materials and methods: The Phase I study CBKM120X2101 investigating single-agent daily BKM120 in patients (pts) with advanced solid tumors has been recently completed with the maximum tolerated dose established at 100 mg/day. Here, we report the analysis of metastatic breast carcinoma (MBC) pts enrolled in this study.

Results: Overall, 83 pts have enrolled, 21 of whom have MBC. At the cut-off date of 25th February 2011, 20 MBC pts were evaluable: 1 pt at 80 mg, 1 pt at 150 mg and 18 pts at 100 mg. Patient characteristics were as follows: median age 55 years (range 37–71); performance status ECOG 0/1/2 for 7/12/1 pts, respectively; visceral disease was reported in 16 pts, including liver, 10 pts (50%); lung, 9 pts (45%); and pleura, 5 pts (25%); all pts had &gt;3 lines of systemic therapy (3-12). The median time from last treatment and study entry was 46 days (29-235). The median duration of BKM120 treatment administered was 7.5 weeks (1.0−96.4). The most frequent grade 3 drug-related adverse events (AEs) were: transaminases increase, 4 pts; psychiatric disorders, 3 pts, consisting of anxiety, affective disorder, and mood alteration (1 pt each); diarrhea, 2 pts; fatigue, 2 pts; and hyperglycemia, 1 pt. The only grade 4 drug-related AE was hyperglycemia, reported in 1 pt at 150 mg. Most AEs were manageable with treatment interruption and dose reductions. Eighteen pts were evaluable for objective tumor response by RECIST. Two pts (11%) exhibited partial responses, which were confirmed in a triple-negative MBC pt, and unconfirmed in an ER+ HER2− MBC pt. For these 2 pts, the treatment duration was 29+ (ongoing) and 6 months, respectively. An additional 9 pts (50%) had stable disease, lasting &gt;4 months in 7 pts (35%).

Conclusions: This preliminary analysis showed that BKM120 has single-agent activity in heavily pretreated pts with MBC, and an acceptable safety profile. Molecular profiling and updated pharmacokinetic results will be presented at the meeting.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-16-01.

Chronic ataluren (PTC124) treatment of nonsense mutation cystic fibrosis

In a subset of patients with cystic fibrosis (CF), nonsense mutations (premature stop codons) disrupt production of full-length, functional CF transmembrane conductance regulator (CFTR). Ataluren (PTC124) allows ribosomal readthrough of premature stop codons in mRNA. We evaluated drug activity and safety in patients with nonsense mutation CF who took ataluren three times daily (morning, midday and evening) for 12 weeks at either a lower dose (4, 4 and 8 mg·kg(-1)) or higher dose (10, 10 and 20 mg·kg(-1)). The study enrolled 19 patients (10 males and nine females aged 19-57 yrs; dose: lower 12, higher seven) with a classic CF phenotype, at least one CFTR nonsense mutation allele, and an abnormal nasal total chloride transport. Both ataluren doses were similarly active, improving total chloride transport with a combined mean change of -5.4 mV (p<0.001), and on-treatment responses (at least -5 mV improvement) and hyperpolarisations (values more electrically negative than -5 mV) in 61% (p<0.001) and 56% (p = 0.002) of patients. CFTR function was greater with time and was accompanied by trends toward improvements in pulmonary function and CF-related coughing. Adverse clinical and laboratory findings were uncommon and usually mild. Chronic ataluren administration produced time-dependent improvements in CFTR activity and clinical parameters with generally good tolerability.

Ataluren (PTC124) induces cystic fibrosis transmembrane conductance regulator protein expression and activity in children with nonsense mutation cystic fibrosis

RATIONALE

Nonsense (premature stop codon) mutations in mRNA for the cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis (CF) in approximately 10% of patients. Ataluren (PTC124) is an oral drug that permits ribosomes to readthrough premature stop codons in mRNA to produce functional protein.

OBJECTIVES

To evaluate ataluren activity, safety, and pharmacokinetics in children with nonsense mutation CF.

METHODS

Patients were assessed in two 28-day cycles, comprising 14 days on and 14 days off ataluren. Patients took ataluren three times per day (morning, midday, and evening) with randomization to the order of receiving a lower dose (4, 4, and 8 mg/kg) and a higher dose (10, 10, and 20 mg/kg) in the two cycles.

MEASUREMENTS AND MAIN RESULTS

The study enrolled 30 patients (16 male and 14 female, ages 6 through 18 yr) with a nonsense mutation in at least one allele of the CFTR gene, a classical CF phenotype, and abnormal baseline nasal epithelial chloride transport. Ataluren induced a nasal chloride transport response (at least a -5-mV improvement) or hyperpolarization (value more electrically negative than -5 mV) in 50% and 47% of patients, respectively, with more hyperpolarizations at the higher dose. Improvements were seen in seven of nine nonsense mutation genotypes represented. Ataluren significantly increased the proportion of nasal epithelial cells expressing apical full-length CFTR protein. Adverse events and laboratory abnormalities were infrequent and usually mild. Ataluren pharmacokinetics were similar to those in adults.

CONCLUSIONS

In children with nonsense mutation CF, ataluren can induce functional CFTR production and is well tolerated.

Influence of food on the pharmacokinetics (PK) of panobinostat (LBH589), an orally active histone deacetylase inhibitor, in patients with advanced cancer

2550

Background: The effect of food on the bioavailability and PK of panobinostat (PAN) are of considerable importance in allowing appropriate dosing of chronic oral cancer therapy. Methods: Patients (pts) with advanced cancer received 20 mg PAN twice a week of a 21-day cycle and were randomized to receive 1 of 6 treatment sequences where PAN PK was evaluated weekly under fasting, high fat and normal breakfast. Serial blood samples were collected for PAN PK evaluations on Days 1, 8, and 15. Plasma PAN concentrations were measured by LC-MS-MS. PK parameters were estimated by using non-compartmental analysis. Results: A total of 34 patients were evaluated. PAN was generally well tolerated with no significant lab, ECG, or other safety concerns. No residual PAN concentrations were detected in pre-dose samples on Days 8 and 15. Meal conditions and PAN PK parameters expressed as either mean (CV%) or median [range] or ratio are described in the Table . The overall exposure and inter-patient variability (CV 59%) remained unchanged with or without food, whereas Cmax was transiently reduced (<45%) by food. Although tumor response was not the main objective, a pt with recurrent RCC, following sunitinib and sorafenib treatment, has achieved a PR after ∼6 cycles of PAN and is continued on study. Conclusions: Since the overall extent of absorption and variability was not changed due to food, PAN administration with or without food is unlikely to significantly impact systemic PAN exposure in cancer patients. PAN can be administered without regards to food in future studies.

[Table: see text]

[Table: see text]

A drug interaction study between ketoconazole and panobinostat (LBH589), an orally active histone deacetylase inhibitor, in patients with advanced cancer

2501

Background: The effects of ketoconazole (keto), a potent CYP3A inhibitor, on the pharmacokinetics (PK) of panobinostat (PAN) were investigated in an open-label, multicenter, cross-over, single sequence study. Methods: Patients (pts) with advanced solid tumors or NHL received single-agent PAN at 20 mg on Day 1 and single-agent keto at 400 mg daily on Days 5–9. On Day 8, PAN 20 mg was administered 1 hour after keto. All pts had adequate organ function and ECOG performance status <2. Serial plasma samples were collected for PAN PK evaluations on Days 1 and 8 and pre- and post-dose keto samples on Days 5, 8, and 9. Plasma PAN and keto concentrations were measured by LC-MS-MS. PK parameters were estimated by using non-compartmental analysis. Genotyping analysis of CYP3A4*1B, CYP3A5*2, *3, *6 and *7 were performed by using AmpliChip CYP450. Results: Fourteen Caucasian patients (9M, 5F) were enrolled with a median age of 59. Fourteen pts had homozygous wide-type CYP3A4*1A genotype, 11 pts had homozygous CYP3A5*3, and three pts had heterozygous CYP3A5*1/*3 genotype. No residual PAN concentrations were detected in pre-dose samples on Day 8. PAN PK parameters were calculated as either mean (CV%), median [range] or ratio (see Table). Single-dose PAN did not affect keto concentrations. Co-administration of keto and PAN increased PAN Cmax and AUC by 1.6- and 1.7-fold, respectively, but with no change in Tmax. There was no apparent difference in PAN PK between pts who carried CYP3A5*1 allele and homozygous CYP3A5*3 carriers. Conclusions: The less than 2-fold increase in PAN AUC upon co-administration suggests that CYP3A contribution to the total clearance of PAN is low. The observed interaction is not considered clinically relevant, as PAN doses are at least 2-fold greater than 20 mg (40 and 60 mg) have been safely administered in pts. CYP3A4 inhibitors should have no major impact on the exposure of PAN and may be co-administered when medically necessary.

[Table: see text]

[Table: see text]

Elucidation of the metabolic and elimination pathways of panobinostat (LBH589) using [14C]-panobinostat

2549

Background: Panobinostat (PAN), a hydroxamic acid derivative, is a potent pan-deacetylase inhibitor, demonstrating anti-tumor activities in a wide variety of preclinical models and showing promising clinical activity. This study elucidates the metabolic and elimination pathways of PAN using [14C]-PAN. Methods: Four patients with advanced cancer received a single oral 20 mg dose of [14C]-PAN (50 μCi). Whole blood, plasma, urine, and feces were collected over 7 days. Total radioactivity was measured in blood, plasma, and excreta by liquid scintillation counting. PAN and its metabolite concentrations in plasma and excreta were measured by LC-MS/MS and HPLC with radiometric detection. Patients were monitored for safety. Results: The single PAN dose was well tolerated with no clinically significant laboratory or ECG abnormalities observed. PAN had a rapid oral absorption [median Tmax 0.8 h (range, 0.5–1 h)] and moderate elimination (median t1/2 31 h). The median t1/2 for blood and plasma radioactivity was 54 and 75 hours, respectively. Mass balance was achieved with ≥87% of the administered radioactivity being recovered in the excreta of all patients after 7 days. 44–77% and 29–51% of the dose was recovered in the feces and urine, respectively. Unchanged PAN accounted for ≤3% of the administered dose in the feces, suggesting good oral absorption. The most prominent metabolic pathways involved modifications of the hydroxamic acid (HA) side chain, to form an amide via reduction, carboxylic acid via either hydrolysis or one- and two-carbon (M1) shortening of the HA side chain. Oxygenation and glucuronidation were also observed. PAN accounted for ≤9% of the total radioactivity AUC. The most abundant circulating metabolites in plasma were the glucuronide of M1 (19%) and carbamoyl glucuronide of PAN (13%). At least 40 metabolites, many at trace levels, were observed circulating in plasma. Conclusions: PAN and its metabolites are equally excreted in the urine and feces. Elimination of PAN is primarily by metabolism via reduction, hydrolysis, oxidation and glucuronidation. The balanced elimination and absence of a single major route of PAN metabolism suggest that clinical drug-drug interactions are unlikely with PAN.

[Table: see text]

Effectiveness of PTC124 treatment of cystic fibrosis caused by nonsense mutations: a prospective phase II trial

BACKGROUND

In about 10% of patients worldwide and more than 50% of patients in Israel, cystic fibrosis results from nonsense mutations (premature stop codons) in the messenger RNA (mRNA) for the cystic fibrosis transmembrane conductance regulator (CFTR). PTC124 is an orally bioavailable small molecule that is designed to induce ribosomes to selectively read through premature stop codons during mRNA translation, to produce functional CFTR.

METHODS

This phase II prospective trial recruited adults with cystic fibrosis who had at least one nonsense mutation in the CFTR gene. Patients were assessed in two 28-day cycles. During the first cycle, patients received PTC124 at 16 mg/kg per day in three doses every day for 14 days, followed by 14 days without treatment; in the second cycle, patients received 40 mg/kg of PTC124 in three doses every day for 14 days, followed by 14 days without treatment. The primary outcome had three components: change in CFTR-mediated total chloride transport; proportion of patients who responded to treatment; and normalisation of chloride transport, as assessed by transepithelial nasal potential difference (PD) at baseline, at the end of each 14-day treatment course, and after 14 days without treatment. The trial was registered with who.int/ictrp, and with clinicaltrials.gov, number NCT00237380.

FINDINGS

Transepithelial nasal PD was evaluated in 23 patients in the first cycle and in 21 patients in the second cycle. Mean total chloride transport increased in the first treatment phase, with a change of -7.1 (SD 7.0) mV (p<0.0001), and in the second, with a change of -3.7 (SD 7.3) mV (p=0.032). We recorded a response in total chloride transport (defined as a change in nasal PD of -5 mV or more) in 16 of the 23 patients in the first cycle's treatment phase (p<0.0001) and in eight of the 21 patients in the second cycle (p<0.0001). Total chloride transport entered the normal range for 13 of 23 patients in the first cycle's treatment phase (p=0.0003) and for nine of 21 in the second cycle (p=0.02). Two patients given PTC124 had constipation without intestinal obstruction, and four had mild dysuria. No drug-related serious adverse events were recorded.

INTERPRETATION

In patients with cystic fibrosis who have a premature stop codon in the CFTR gene, oral administration of PTC124 to suppress nonsense mutations reduces the epithelial electrophysiological abnormalities caused by CFTR dysfunction.

Phase 1 studies assessing the safety, PK, and VEGF-modulating effects of PTC299, a novel VEGF expression inhibitor

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Background: VEGF expression is regulated posttranscriptionally through the 5’- and 3’- untranslated regions (UTRs) of its mRNA. PTC299 is a novel, orally bioavailable, small molecule that acts via the VEGF 5’-UTR to selectively inhibit tumor VEGF production. In multiple preclinical human tumor xenograft models, PTC299 reduces elevated human VEGF levels in tumor and in circulation, decreases tumor microvessel density, and substantially slows tumor growth. With cytotoxic agents or with other antiangiogenics, PTC299 enhances tumor growth delay. Methods: PTC299 safety in animal toxicology studies supported Phase 1 studies in healthy volunteers. The first study was a Phase 1 single-dose (SD) trial. The second study was a Phase 1, multiple-dose (MD) study assessing BID or TID dosing for 7 days. During dose escalations, 8 subjects (4 males, 4 females; 6 PTC299, 2 placebo) per cohort were randomized in a double-blind manner. A fed-fasting crossover was performed in 12 subjects (6 males, 6 females) in the SD study. Subjects underwent clinical observations, laboratory testing, and blood sampling for PK and circulating VEGF. Results: In the SD study, 52 subjects (age range 18–55 years) were enrolled (40 at 5 dose levels and 12 to assess food effects. In the MD study, 32 subjects (age range 31–78 years) were enrolled (24 to BID dosing and 8 to TID dosing). AEs included: headache, dizziness nausea, vomiting, and stomach discomfort (all Grade 1); and diarrhea (Grade 2). No bleeding, clotting, hypertension, or proteinuria occurred. Cmax and AUC increased proportional to dose. There was a ∼40% increase in the Cmax with food, but no change in AUC. Mean PTC299 Cmax and AUC increased by ∼2-fold over 7 days, exceeding target trough plasma concentrations active in xenograft models. A 2-compartment model describes the PK data. Circulating VEGF levels are being assayed. Conclusions: PTC299 is the first drug designed to modulate post-transcriptional control mechanisms to treat human disease. In these initial studies, PTC299 shows safety at plasma exposures associated with preclinical activity and can be taken without regard to food. Final clinical data on dose ranging, safety, PK, and circulating VEGF levels will be presented. Studies of PTC299 in patients with cancer are being initiated.

No significant financial relationships to disclose.

Safety, tolerability, and pharmacokinetics of PTC124, a nonaminoglycoside nonsense mutation suppressor, following single- and multiple-dose administration to healthy male and female adult volunteers

Nonsense (premature stop codon) mutations are causative in 5% to 15% of patients with monogenetic inherited disorders. PTC124, a 284-Dalton 1,2,4-oxadiazole, promotes ribosomal readthrough of premature stop codons in mRNA and offers therapeutic potential for multiple genetic diseases. The authors conducted 2 phase I studies of PTC124 in 62 healthy adult volunteers. The initial, single-dose study evaluated doses of 3 to 200 mg/kg and assessed fed-fasting status on pharmacokinetics following a dose of 50 mg/kg. The subsequent multiple-dose study evaluated doses from 10 to 50 mg/kg/dose twice per day (bid) for up to 14 days. PTC124 administered orally as a liquid suspension was palatable and well tolerated through single doses of 100 mg/kg. At 150 and 200 mg/kg, PTC124 induced mild headache, dizziness, and gastrointestinal events. With repeated doses through 50 mg/kg/dose bid, reversible transaminase elevations <2 times the upper limit of normal were sometimes observed. Immunoblot analyses of peripheral blood mononuclear cell extracts revealed no protein elongation due to nonspecific ribosomal readthrough of normal stop codons. PTC124 plasma concentrations exceeding the 2- to 10-microg/mL values associated with activity in preclinical genetic disease models were safely achieved. No sex-related differences in pharmacokinetics were seen. No drug accumulation with repeated dosing was apparent. Diurnal variation was observed, with greater PTC124 exposures after evening doses. PTC124 excretion in the urine was <2%. PTC124 pharmacokinetics were described by a 1-compartment model. Collectively, the data support initiation of phase II studies of PTC124 in patients with nonsense mutation-mediated cystic fibrosis and Duchenne muscular dystrophy.

A Phase I dose-finding study using an innovative sequential biweekly schedule of irinotecan followed 24 hours later by capecitabine

BACKGROUND

Irinotecan and capecitabine have a broad spectrum of activity in human malignancy and are synergistic in an animal model when irinotecan precedes capecitabine.

PATIENTS AND METHODS

A Phase I design of the combination of irinotecan IV Day 1 with capecitabine on Days 2-8 every 2 weeks was evaluated in 27 adult patients with solid tumors. Two sequential schema were used: Arm A fixed the dose of irinotecan at 100 mg/m(2) and escalated capecitabine in cohorts, and arm B fixed the dose of capecitabine at 750 mg/m(2) PO BID and escalated the dosage of irinotecan.

RESULTS

Neutropenia was dose limiting with nausea and diarrhea as the most common nonhematological toxicities. Significant interpatient variation in toxicity occurred despite uniform dosing. No Grade IV toxicities were encountered. Grade III toxicity occurred in first cycle in 15 percent (3/20) patients in arm A and 29 percent (2/7) of patients in arm B. All toxicities were reversible. Repetitive dosing was feasible with prolonged disease stabilization in 8 patients.

CONCLUSIONS

The suggested Phase II dose of this combination and schedule is irinotecan 100 mg/m(2) and capecitabine 1000 mg/m(2) BID. Some patients tolerated a capecitabine dose as high as 1250 mg/m(2) BID.

PTC124 targets genetic disorders caused by nonsense mutations

Nonsense mutations promote premature translational termination and cause anywhere from 5-70% of the individual cases of most inherited diseases. Studies on nonsense-mediated cystic fibrosis have indicated that boosting specific protein synthesis from <1% to as little as 5% of normal levels may greatly reduce the severity or eliminate the principal manifestations of disease. To address the need for a drug capable of suppressing premature termination, we identified PTC124-a new chemical entity that selectively induces ribosomal readthrough of premature but not normal termination codons. PTC124 activity, optimized using nonsense-containing reporters, promoted dystrophin production in primary muscle cells from humans and mdx mice expressing dystrophin nonsense alleles, and rescued striated muscle function in mdx mice within 2-8 weeks of drug exposure. PTC124 was well tolerated in animals at plasma exposures substantially in excess of those required for nonsense suppression. The selectivity of PTC124 for premature termination codons, its well characterized activity profile, oral bioavailability and pharmacological properties indicate that this drug may have broad clinical potential for the treatment of a large group of genetic disorders with limited or no therapeutic options.

A phase I study of the safety and pharmacokinetics of edotecarin (J-107088), a novel topoisomerase I inhibitor, in patients with advanced solid tumors

PURPOSE

To assess the maximum tolerated dose, safety, and pharmacokinetic (PK) profile of escalating doses of the novel topoisomerase I (topo I) inhibitor edotecarin (J-107088) given as a 2-h intravenous (IV) infusion once every 21 days in patients with advanced solid tumors who had not responded to standard therapy.

PATIENTS AND METHODS

Twenty-nine patients (18M:11F) received a 2-h IV infusion of edotecarin in doses of 6, 8, 11, 13, or 15 mg/m(2) every 21 days (with an additional 1-2 weeks permitted for recovery) and were evaluated for safety, PK, and tumor response.

RESULTS

The most common non-hematologic toxicities were grade 1-2 nausea, fatigue, anorexia, vomiting, and fever. The most common hematologic toxicities were grade 1-2 thrombocytopenia and grade 3-4 neutropenia, leukopenia, and anemia. No grade 3-4 diarrhea was reported. Dose-limiting toxicities were observed in four patients at the 15 mg/m(2) dose and one patient at the 13 mg/m(2) dose. These toxicities included grade 3 nausea, vomiting, headache, and fatigue, as well as grade 4 neutropenia and febrile neutropenia. The maximum tolerated dose was declared at 15 mg/m(2). One patient with bladder cancer had a confirmed partial response at a dose of 13 mg/m(2). There was a trend to dose-proportional increases in edotecarin peak plasma concentrations and area under the curve values. Renal excretion of edotecarin was minimal (3-8% of the dose).

CONCLUSION

The recommended Phase II dose of edotecarin is 13 mg/m(2) once every 21 days. The toxicities in this study were those typical of cytotoxic chemotherapy and less severe than those associated with other topo I inhibitors. The observed safety profile and preliminary evidence of clinical benefit warrant further investigation of this drug as monotherapy or part of combination therapy in patients with solid tumors.