Buparlisib in combination with tamoxifen in pretreated patients with hormone receptor-positive, HER2-negative advanced breast cancer molecularly stratified for PIK3CA mutations and loss of PTEN expression

Reporting on patient's body mass index (BMI) in recent clinical trials for patients with breast cancer: a systematic review

BACKGROUND

The proportion of patients with breast cancer and obesity is increasing. While the therapeutic landscape of breast cancer has been expanding, we lack knowledge about the potential differential efficacy of most drugs according to the body mass index (BMI). Here, we conducted a systematic review on recent clinical drug trials to document the dosing regimen of recent drugs, the reporting of BMI and the possible exclusion of patients according to BMI, other adiposity measurements and/or diabetes (leading comorbidity of obesity). We further explored whether treatment efficacy was evaluated according to BMI.

METHODS

A search of Pubmed and ClinicalTrials.gov was performed to identify phase I-IV trials investigating novel systemic breast cancer treatments. Dosing regimens and exclusion based on BMI, adiposity measurements or diabetes, documentation of BMI and subgroup analyses according to BMI were assessed.

RESULTS

495 trials evaluating 26 different drugs were included. Most of the drugs (21/26, 81%) were given in a fixed dose independent of patient weight. BMI was an exclusion criterion in 3 out of 495 trials. Patients with diabetes, the leading comorbidity of obesity, were excluded in 67/495 trials (13.5%). Distribution of patients according to BMI was mentioned in 8% of the manuscripts, subgroup analysis was performed in 2 trials. No other measures of adiposity/body composition were mentioned in any of the trials. Retrospective analyses on the impact of BMI were performed in 6 trials.

CONCLUSIONS

Patient adiposity is hardly considered as most novel drug treatments are given in a fixed dose. BMI is generally not reported in recent trials and few secondary analyses are performed. Given the prevalence of patients with obesity and the impact obesity can have on pharmacokinetics and cancer biology, more attention should be given by investigators and study sponsors to reporting patient's BMI and evaluating its impact on treatment efficacy and toxicity.

Molecular Targeting of the Phosphoinositide-3-Protein Kinase (PI3K) Pathway across Various Cancers

The dysregulation of the phosphatidylinositol-3-kinase (PI3K) pathway can lead to uncontrolled cellular growth and tumorigenesis. Targeting PI3K and its downstream substrates has been shown to be effective in preclinical studies and phase III trials with the approval of several PI3K pathway inhibitors by the Food and Drug Administration (FDA) over the past decade. However, the limited clinical efficacy of these inhibitors, intolerable toxicities, and acquired resistances limit the clinical application of PI3K inhibitors. This review discusses the PI3K signaling pathway, alterations in the PI3K pathway causing carcinogenesis, current and novel PI3K pathway inhibitors, adverse effects, resistance mechanisms, challenging issues, and future directions of PI3K pathway inhibitors.

Phosphoinositide 3-Kinase (PI3K) Inhibitors and Breast Cancer: An Overview of Current Achievements

The phosphatidylinositol 3-kinase (PI3K) pathway is one of the most altered pathways in human cancers, and it plays a central role in cellular growth, survival, metabolism, and cellular mobility, making it a particularly interesting therapeutic target. Recently, pan-inhibitors and then selective p110α subunit inhibitors of PI3K were developed. Breast cancer is the most frequent cancer in women and, despite therapeutic progress in recent years, advanced breast cancers remain incurable and early breast cancers are at risk of relapse. Breast cancer is divided in three molecular subtypes, each with its own molecular biology. However, PI3K mutations are found in all breast cancer subtypes in three main "hotspots". In this review, we report the results of the most recent and main ongoing studies evaluating pan-PI3K inhibitors and selective PI3K inhibitors in each breast cancer subtype. In addition, we discuss the future of their development, the various potential mechanisms of resistance to these inhibitors and the ways to circumvent them.

PI3K inhibitors in trastuzumab-resistant HER2-positive breast cancer cells with PI3K pathway alterations

The activation of the PI3K signaling pathway resulting from genetic alterations induces carcinogenesis and resistance to anticancer therapies. Breast cancer is a major malignancy that is associated with dysregulation of the PI3K signaling pathway. PIK3CA mutations and PTEN loss occur in every subtype of breast cancer. PI3K inhibitors are being evaluated in breast cancer after the success of an alpha isoform-specific PI3K inhibitor in estrogen receptor (ER)-positive/HER2-negative metastatic breast cancer. Some preclinical data indicate the potential for PI3K/mTOR targeting in combination with trastuzumab for HER2-positive breast cancer with or without expression of the estrogen receptor. However, the role of this therapy in HER2-positive breast cancer with PIK3CA mutations and/or PTEN loss remains unclear. We examined three HER2-positive, ER-negative breast cancer cell lines to determine the efficacy of a novel alpha isoform-specific PI3K inhibitor in combination with trastuzumab. The results indicated that this combination was effective in PIK3CA-mutant or PTEN-deficient breast cancer cells by inducing apoptosis and inhibiting the expression of downstream proteins. PTEN loss by siRNA modulation in parental HER2-positive cancer cells with PI3K signaling pathway alterations could not confer resistance to alpelisib or GDC-0077 plus trastuzumab. We selected the CK-MB-1 cell line without alterations in the PI3K pathway to demonstrate that PI3K inhibitors plus trastuzumab represented a biomarker-specific treatment. In vivo effects of alpelisib plus trastuzumab were tested and confirmed in a mouse model, showing the combination strategy offered the best opportunity to achieve tumor volume reduction. With known safety profiles, this cytotoxic chemotherapy-free regimen warrants further attention as a biomarker-driven strategy for treating HER2-positive breast cancer.

Phosphatase and Tensin Homolog Deleted on Chromosome Ten (PTEN) Derived from Bone Marrow Stromal Cells Promotes the Development of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) remains a threat to women’s life with a lack of targeted therapy. This study aimed to explore the role of PTEN derived from BMSCs in TNBC. We carried out a retrospective analysis of 65 TNBC patients and 30 healthy subjects from October 2016 to January 2021 with a 10-year follow up. PTEN expression in TNBC tissues and cells was determined by RTqPCR. Functional experiments were conducted to evaluate PTEN’s effect on TNBC cell biological behaviors using MTT assay and Transwell assay, as well as on PI3K-Akt-HIF-1α-VEGF signaling transduction. PTEN was up-regulated in TNBC tissues relative to healthy controls and it was negatively associated with the survival rate. In in vitro experiments, PTEN overexpression increased cell viability and invasion and knocking down of PTEN exerted opposite effect. The expression of PI3K was directly regulated by PTEN. Up-regulation of PTEN resulted in a decline in HIF-1α, Akt and VEGF expressions, which were elevated after knocking down of PTEN. In conclusion, PTEN derived from BMSCs promotes TNBC cell development through blocking PI3K-Akt-HIF-1α-VEGF signaling pathway, providing a new theoretical basis for targeted therapy of TNBC.

Which Is the Most Appropriate PI3K Inhibitor for Breast Cancer Patients with or without PIK3CA Status Mutant? A Systematic Review and Network Meta-Analysis

Objective

The phosphatidylinositol 3-kinase (PI3K) signaling pathway is a promising treatment target for patients with breast cancer (BC). Our study aimed to evaluate the most effective and safe PI3K inhibitor for patients with BC, especially in PIK3CA mutation.

Methods

Electronics databases were systematically searched from their inception to June 2020 for published randomized controlled trials (RCTs) comparing PI3K inhibitor therapy versus non-PI3K inhibitor therapy in patients with BC that mentioned or reported data of PIK3CA-mutated patient subgroups. Eligible RCTs had to report at least one of the following clinical outcomes: objective response rate (ORR), progression-free survival (PFS), or adverse events (AE).

Results

Nine eligible RCTs involving 3872 BC patients and four PI3K inhibitor therapy arms (i.e., alpelisib, buparlisib, pictilisib, and taselisib) were included. In evaluating ORR, beneficial significant results of PI3K inhibitors could be found in the PIK3CA mutated group (1.952, 1.012 to 3.766); analogous results could also be found in 6m-PFS (1.519, 1.144 to 2.018) and PFS from HR data (-0.346, -0.525 to -0.168). From pairwise and network meta-analyses, buparlisib showed the most favorable ORR, as it was significantly different from fulvestrant in the PIK3CA-mutated patient group (2.80, 1.56 to 5.03). Alpelisib ranked first in the assessment of 6m-PFS and was significantly different from fulvestrant in the PIK3CA-mutated group (2.33, 1.45 to 3.44). The above PI3K inhibitors had good safety with few serious AEs. PROSPERO registration CRD42020193932.

Conclusion

The PI3K inhibitors alpelisib and buparlisib appear to have superior efficacy and safety therapeutic choices for patients with BC, especially in PIK3CA-mutated patients.

Buparlisib in combination with tamoxifen in pretreated patients with hormone receptor-positive, HER2-negative advanced breast cancer molecularly stratified for PIK3CA mutations and loss of PTEN expression

The PIKTAM study evaluated the efficacy and safety of the PI3K inhibitor buparlisib in combination with tamoxifen in hormone receptor-positive (HR⁺ ), HER2-negative advanced breast cancer patients after failure of prior endocrine therapy. In this open-label, single-arm phase II trial, 25 patients were enrolled in 11 sites in Germany. Patients were stratified according to PIK3CA mutation status (tissue and cfDNA from serum samples) and/or loss of PTEN expression. Patients received buparlisib (100 mg) and tamoxifen (20 mg) once daily on a continuous schedule (28-day cycle) until progression or unacceptable toxicity. Primary endpoint was overall 6-month progression-free survival (PFS) rate. Key secondary endpoints included the 6-month PFS rate in subpopulations, PFS, overall survival, overall response rate (ORR), disease control rate (DCR), and safety. Overall, the 6-month PFS rate was 33.3% (n/N = 7/21, one-sided 95% CI 16.8-100) and median PFS was 6.1 (CI 2.6-10.6) months. The ORR and DCR were 12.5% and 44%. The PIK3CA-mutated subgroup consistently showed the highest 6-month PFS rate (62.5%, n/N = 5/8), median PFS (8.7 months), ORR (40%), and DCR (80%). No new safety signals emerged. Most common adverse events were gastrointestinal disorders (56%), psychiatric/mood disorders (48%), skin rash/hypersensitivity (44%), cardiovascular (40%), and hepatic (32%) events. The trial was prematurely terminated due to the substantially altered risk-benefit profile of buparlisib. Nevertheless, PIK3CA mutations emerged as a clinically feasible and useful biomarker for combined PI3K inhibition and endocrine therapy in patients with HR⁺ breast cancer. Further biomarker-stratified studies with isoform-specific PI3K inhibitors are warranted. EudraCT No: 2014-000599-24.