Targeted drug delivery strategies for precision medicines

Progress in the field of precision medicine has changed the landscape of cancer therapy. Precision medicine is propelled by technologies that enable molecular profiling, genomic analysis, and optimized drug design to tailor treatments for individual patients. Although precision medicines have resulted in some clinical successes, the use of many potential therapeutics has been hindered by pharmacological issues, including toxicities and drug resistance. Drug delivery materials and approaches have now advanced to a point where they can enable the modulation of a drug's pharmacological parameters without compromising the desired effect on molecular targets. Specifically, they can modulate a drug's pharmacokinetics, stability, absorption, and exposure to tumours and healthy tissues, and facilitate the administration of synergistic drug combinations. This Review highlights recent progress in precision therapeutics and drug delivery, and identifies opportunities for strategies to improve the therapeutic index of cancer drugs, and consequently, clinical outcomes.

Clinical Challenges in the Management of Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Metastatic Breast Cancer: A Literature Review

Endocrine therapy (ET) is integral to the treatment of hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2−) metastatic breast cancer (MBC). Aromatase inhibitors (AIs; e.g., anastrozole, letrozole, exemestane), selective estrogen receptor modulators (e.g., tamoxifen), and the selective estrogen receptor degrader, fulvestrant, inhibit tumor cell proliferation by targeting ER signaling. However, the efficacy of ET could be limited by intrinsic and acquired resistance mechanisms, which has prompted the development of targeted agents and combination strategies. In recent years, the treatment landscape for HR+, HER2− MBC has evolved rapidly. AIs, historically the first-line treatment for postmenopausal patients with HR+, HER2− MBC, have been challenged by more effective ET, such as fulvestrant alone or in combination with an AI, and the cyclin-dependent kinase (CDK)4/6 inhibitors, which have increasingly become the new standard of care. For endocrine-resistant disease (≥ second-line), clinical trials demonstrated that the mammalian target of rapamycin inhibitor, everolimus, enhanced the efficacy of exemestane or fulvestrant after progression on an AI. CDK4/6 inhibitors in combination with fulvestrant have demonstrated superior progression-free survival and overall survival versus fulvestrant alone. Recently, the combination of fulvestrant with alpelisib in phosphatidylinositol-4,5-bisphosphate 3-kinase (PIK3CA) mutated HR+, HER2− MBC following progression on or after ET was approved, based on the SOLAR-1 study. However, the optimal sequencing of treatments is unknown, especially following disease progression on a CDK4/6 inhibitor. This review aims to provide practical guidance for the management of HR+, HER2− MBC based on available data and the utility of genomic biomarkers, including germline breast cancer genes 1 and 2 (BRCA1/2) mutations, and somatic estrogen receptor alpha gene (ESR1), HER2, and PIK3CA mutations.

Neoadjuvant letrozole plus taselisib versus letrozole plus placebo in postmenopausal women with oestrogen receptor-positive, HER2-negative, early-stage breast cancer (LORELEI): a multicentre, randomised, double-blind, placebo-controlled, phase 2 trial

BACKGROUND

Endocrine therapy-based neoadjuvant treatment for luminal breast cancer allows efficient testing of new combinations before surgery. The activation of the phosphatidylinositol-3-kinase (PI3K) pathway is a known mechanism of resistance to endocrine therapy. Taselisib is an oral, selective PI3K inhibitor with enhanced activity against PIK3CA-mutant cancer cells. The LORELEI trial tested whether taselisib in combination with letrozole would result in an increased proportion of objective responses and pathological complete responses.

METHODS

In this multicentre, randomised, double-blind, parallel-cohort, placebo-controlled phase 2, study, we enrolled postmenopausal women (aged ≥18 years) with histologically confirmed, oestrogen receptor (ER)-positive, HER2-negative, stage I-III, operable breast cancer, from 85 hospitals in 22 countries worldwide. To be eligible, patients had have an Eastern Cooperative Oncology Group (ECOG) performance status 0-1, adequate organ function, and had to have evaluable tumour tissue for PIK3CA genotyping. Patients were randomly assigned (1:1) by means of a permuted block algorithm (block size of four) via an interactive voice or web-based response system, to receive letrozole (2·5 mg/day orally, continuously) with either 4 mg of oral taselisib or placebo (on a 5 days-on, 2 days-off schedule) for 16 weeks, followed by surgery. Randomisation was stratified by tumour size and nodal status. Site staff, patients, and the sponsor were masked to treatment assignment. Coprimary endpoints were the proportion of patients who achieved an objective response by centrally assessed breast MRI and a locally assessed pathological complete response in the breast and axilla (ypT0/Tis, ypN0) at surgery in all randomly assigned patients and in patients with PIK3CA-mutant tumours. Analyses were done in the intention-to-treat population. This trial is registered with ClinicalTrials.gov, number NCT02273973, and is closed to accrual.

FINDINGS

Between Nov 12, 2014, and Aug 12, 2016, 334 participants were enrolled and randomly assigned to receive letrozole and placebo (n=168) or letrozole and taselisib (n=166). Median follow-up was 4·9 months (IQR 4·7-5·1). The study met one of its primary endpoints: the addition of taselisib to letrozole was associated with a higher proportion of patients achieving an objective response in all randomly assigned patients (66 [39%] of 168 patients in the placebo group vs 83 [50%] of 166 in the taselisib group; odds ratio [OR] 1·55, 95% CI 1·00-2·38; p=0·049) and in the PIK3CA-mutant subset (30 [38%] of 79 vs 41 [56%] of 73; OR 2·03, 95% CI 1·06-3·88; p=0·033). No significant differences were observed in pathological complete response between the two groups, either in the overall population (three [2%] of 166 in the taselisib group vs one [1%] of 168 in the placebo group; OR 3·07 [95% CI 0·32-29·85], p=0·37) or in the PIK3CA-mutant cohort (one patient [1%) vs none [0%]; OR not estimable, p=0·48). The most common grade 3-4 adverse events in the taselisib group were gastrointestinal (13 [8%] of 167 patients), infections (eight [5%]), and skin-subcutaneous tissue disorders (eight [5%]). In the placebo group, four (2%) of 167 patients had grade 3 or worse vascular disorders, two (1%) had gastrointestinal disorders, and two (1%) patients had grade 3 or worse infections and infestations. There was no grade 4 hyperglycaemia and grade 3 cases were asymptomatic. Serious adverse events were more common in the taselisib group (eight [5%] patients with infections and seven [4%] with gastrointestinal effects) than in the placebo group (one [1%] patient each with grade 3 postoperative wound and haematoma infection, grade 4 hypertensive encephalopathy, grade 3 acute cardiac failure, and grade 3 breast pain). One death occurred in the taselisib group, which was not considered to be treatment-related.

INTERPRETATION

The increase in the proportion of patients who achieved an objective response from the addition of taselisib to endocrine therapy in a neoadjuvant setting is consistent with the clinical benefit observed in hormone receptor-positive, HER2-negative, metastatic breast cancer.

FUNDING

Genentech and F Hoffmann-La Roche.

Exploring Biomarkers of Phosphoinositide 3-Kinase Pathway Activation in the Treatment of Hormone Receptor Positive, Human Epidermal Growth Receptor 2 Negative Advanced Breast Cancer

Resistance to endocrine therapy (ET) is common in patients with hormone receptor positive (HR+) advanced breast cancer (ABC). Consequently, new targeted treatment options are needed in the post-ET setting, with validated biomarkers to inform treatment decisions. Hyperactivation of the phosphoinositide 3-kinase (PI3K) signaling pathway is common in ABC and is implicated in resistance to ET. The most frequent mechanism of PI3K pathway activation is activating mutations or amplification of PIK3CA, which encodes the α-isoform of the catalytic subunit of PI3K. Combining buparlisib, a pan-PI3K-targeted agent, with ET demonstrated modest clinical benefits in patients with aromatase inhibitor-resistant, HR+, human epidermal growth receptor 2 negative (HER2-) ABC in two phase III trials. Importantly, greater efficacy gains were observed in individuals with PIK3CA-mutated disease versus PIK3CA-wild-type tumors. Although the challenging safety profile did not support widespread use of this treatment combination, isoform-selective PI3K inhibitors may improve tolerability. In early clinical trials, promising disease control benefits were demonstrated with the PI3K isoform-selective inhibitors alpelisib and taselisib in patients with PIK3CA-mutated HR+, HER2- ABC. Ongoing biomarker-guided phase II/III studies may provide further opportunities to identify patients most likely to benefit from treatment with PI3K inhibitors and provide insight into optimizing the therapeutic index of PI3K inhibitors. Challenges facing the implementation of routine PIK3CA mutation testing must be addressed promptly so robust and reproducible genotyping can be obtained with liquid and tumor biopsies in a timely and cost-effective manner. IMPLICATIONS FOR PRACTICE: The development of phosphoinositide 3-kinase (PI3K) inhibitors, especially those that selectively target isoforms, may be an effective strategy for overcoming endocrine therapy resistance in hormone receptor positive, human epidermal growth receptor 2 negative advanced breast cancer. Early-phase studies have confirmed that patients with PIK3CA mutations respond best to PI3Kα-isoform inhibition. Ongoing phase III trials will provide further data regarding the efficacy and safety of PI3K inhibitors in patients with different biomarker profiles.

Impact of somatic molecular profiling on clinical trial outcomes in rare epithelial gynecologic cancer patients

OBJECTIVES

Conducting clinical trials in rare malignancies is challenging due to the limited number of patients and differences in biologic behavior. We investigated the feasibility and clinical utility of using genomic profiling for rare gynecologic malignancies.

METHODS

Rare epithelial gynecologic cancer patients were analyzed for somatic variants through an institutional molecular profiling program using the Sequenom MassArray platform or the TruSeq Amplicon Cancer Panel on the MiSeq platform. Clinical trial outcomes by RECIST 1.1, and time on treatment were evaluated.

RESULTS

From March 2012 to November 2015, 767 gynecologic patients were enrolled and 194 (27%) were classified as rare epithelial malignancies. At least one somatic mutation was identified in 72% of patients, most commonly in TP53 (39%), KRAS (28%) and PIK3CA (27%). A total of 14% of patients were treated on genotype-matched trials. There were no significant differences in overall response rate between genotype-matched versus unmatched trials, nor in median time on treatment between genotype trials and the immediate prior systemic standard treatment. Among 13 evaluable Low Grade Serous ovarian cancer patients treated on genotype-matched trials with MEK inhibitor-based targeted combinations, there were four partial responses.

CONCLUSIONS

Somatic molecular profiling is feasible and enables the identification of patients with rare gynecologic cancers who are candidates for genotype-matched clinical trials. Genotype-matched trials, predominantly MEK-based combinations in KRAS and/or NRAS mutant Low Grade Serous ovarian cancer patients, and genotype-unmatched trials, have shown potential clinical activity. Prospective trials with integrated genotyping are warranted to assess the clinical utility of next generation sequencing tests as a standard clinical application in rare malignancies.

The Role of PI3K in Met Driven Cancer: A Recap

The Receptor Tyrosine Kinase (RTK) Met, overexpressed or mutated in cancer, plays a major role in cancer progression and represents an attractive target for cancer therapy. However RTK inhibitors can lead to drug resistance, explaining the necessity to develop therapies that target downstream signaling. Phosphatidylinositide 3-kinase (PI3K) is one of the most deregulated pathways in cancer and implicated in various types of cancer. PI3K signaling is also a major signaling pathway downstream of RTK, including Met. PI3K major effectors include Akt and "mechanistic Target of Rapamycin" (mTOR), which each play key roles in numerous and various cell functions. Advancements made due to the development of molecular and pharmaceutical tools now allow us to delve into the roles of each independently. In this review, we summarize the current understanding we possess of the activation and role of PI3K/Akt/mTOR, downstream of Met, in cancer.

Genomic alterations at the basis of treatment resistance in metastatic breast cancer: clinical applications

The standard of care for breast cancer has gradually evolved from empirical treatments based on clinical-pathological characteristics to the use of targeted approaches based on the molecular profile of the tumor. Consequently, an increasing number of molecularly targeted drugs have been developed. These drugs target specific alterations, called driver mutations, which confer a survival advantage to cancer cells. To date, the main challenge remains the identification of predictive biomarkers for the selection of the optimal treatment. On this basis, we evaluated a panel of 25 genes involved in the mechanisms of targeted treatment resistance, in 16 primary breast cancers and their matched recurrences, developed during treatment. Overall, we found a detection rate of mutations higher than that described in the literature. In particular, the most frequently mutated genes were ERBB2 and those involved in the PI3K/AKT/mTOR and the MAPK signaling pathways. The study revealed substantial discordances between primary tumors and metastases, stressing the need for analysis of metastatic tissues at recurrence. We observed that 85.7% of patients with an early-stage or locally advanced primary tumor showed at least one mutation in the primary tumor. This finding could explain the subsequent relapse and might therefore justify more targeted adjuvant treatments. Finally, the mutations detected in 50% of relapsed tissues could have guided subsequent treatment choices in a different way. This study demonstrates that mutation events may be present at diagnosis or arise during cancer treatment. As a result, profiling primary and metastatic tumor tissues may be a major step in defining optimal treatments.

Biological characterization of SN32976, a selective inhibitor of PI3K and mTOR with preferential activity to PI3Kα, in comparison to established pan PI3K inhibitors

Multiple therapeutic agents have been developed to target the phosphatidylinositol 3-kinase (PI3K) signaling pathway, which is frequently dysregulated in cancer promoting tumor growth and survival. These include pan PI3K inhibitors, which target class Ia PI3K isoforms and have largely shown limited single agent activity with narrow therapeutic windows in clinical trials. Here, we characterize SN32976, a novel pan PI3K inhibitor, for its biochemical potency against PI3K isoforms and mTOR, kinase selectivity, cellular activity, pharmacokinetics, pharmacodynamics and antitumor efficacy relative to five clinically-evaluated pan PI3K inhibitors: buparlisib, dactolisib, pictilisib, omipalisib and ZSTK474. SN32976 potently inhibited PI3K isoforms and mTOR, displaying preferential activity for PI3Kα and sparing of PI3Kδ relative to the other inhibitors, while showing less off-target activity than the clinical inhibitors in a panel of 442 kinases. The major metabolites of SN32976 were also potent PI3K inhibitors with similar selectivity for PI3Kα as the parent compound. SN32976 compared favorably with the clinically-evaluated PI3K inhibitors in cellular assays, inhibiting pAKT expression and cell proliferation at nM concentrations, and in animal models, inducing a greater extent and duration of pAKT inhibition in tumors than pictilisib, dactolisib and omipalisib at similarly tolerated dose levels and inhibiting tumor growth to a greater extent than dactolisib and ZSTK474 and with similar efficacy to pictilisib and omipalisib. These results suggest that SN32976 is a promising clinical candidate for cancer therapy with enhanced kinase selectivity and preferential inhibition of PI3Kα compared to first generation pan PI3K inhibitors, while retaining comparable anticancer activity.

PI3K inhibition to overcome endocrine resistance in breast cancer

INTRODUCTION

Activation of the phosphatidylinositol-3 kinase (PI3K) pathway is a critical step in oncogenesis and plays a role in the development of treatment resistance for both estrogen receptor (ER) positive and human epidermal growth factor receptor 2 (HER2) positive breast cancers. Hence, there have been efforts to therapeutically inhibit this pathway.

AREAS COVERED

Several inhibitors of PI3K are now progressing through clinical trials with varying degrees of efficacy and toxicity to date. Numerous unresolved questions remain concerning the optimal isoform selectivity of PI3K inhibitors and use of predictive biomarkers. This review examines the most important PI3K inhibitors in ER positive breast cancer to date, with a particular focus on their role in overcoming endocrine therapy resistance and the possible use of PIK3CA mutations as a predictive biomarker.

EXPERT OPINION

We discuss some of the emerging challenges and questions encountered during the development of PI3K inhibitors from preclinical to phase III studies, including other novel biomarkers and future combinations to overcome endocrine resistance.

Impact of multi-gene mutational profiling on clinical trial outcomes in metastatic breast cancer

Purpose

Next-generation sequencing (NGS) has identified recurrent genomic alterations in metastatic breast cancer (MBC); however, the clinical utility of incorporating routine sequencing to guide treatment decisions in this setting is unclear. We examine the frequency of genomic alterations in MBC patients from academic and community hospitals and correlate with clinical outcomes.

Methods

MBC patients with good performance status were prospectively recruited at the Princess Margaret Cancer Centre (PM) in Canada. Molecular profiling on DNA extracted from FFPE archival tissues was performed on the Sequenom MassArray platform or the TruSeq Amplicon Cancer Panel (TSACP) on the MiSeq platform. Clinical trial outcomes by RECIST 1.1 and time on treatment were reviewed retrospectively.

Results

From January 2012 to November 2015, 483 MBC patients were enrolled and 440 were genotyped. At least one somatic mutation was identified in 46% of patients, most commonly in PIK3CA (28%) or TP53 (13%). Of 203 patients with ≥ 1 mutation(s), 15% were treated on genotype-matched and 9% on non-matched trials. There was no significant difference for median time on treatment for patients treated on matched vs. non-matched therapies (3.6 vs. 3.8 months; p = 0.89).

Conclusions

This study provides real-world outcomes on hotspot genotyping and small targeted panel sequencing of MBC patients from academic and community settings. Few patients were matched to clinical trials with targeted therapies. More comprehensive profiling and improved access to clinical trials may increase therapeutic options for patients with actionable mutations. Further studies are needed to evaluate if this approach leads to improved clinical outcomes.

Electronic supplementary material

The online version of this article (10.1007/s10549-017-4580-2) contains supplementary material, which is available to authorized users.

PI3K/AKT/mTOR: role in breast cancer progression, drug resistance, and treatment

Anti-cancer cancer-targeted therapies are designed to exploit a particular vulnerability in the tumor, which in most cases results from its dependence on an oncogene and/or loss of a tumor suppressor. Mutations in the phosphoinositide 3-kinase (PI3K)/AKT/mTOR pathway are freqcuently found in breast cancers and associated with cellular transformation, tumorigenesis, cancer progression, and drug resistance. Several drugs targeting PI3K/ATK/mTOR are currently in clinical trials, mainly in combination with endocrine therapy and anti-HER2 therapy. These drugs are the focus of this review.

The PI3K Pathway in Human Disease

Phosphoinositide 3-kinase (PI3K) activity is stimulated by diverse oncogenes and growth factor receptors, and elevated PI3K signaling is considered a hallmark of cancer. Many PI3K pathway-targeted therapies have been tested in oncology trials, resulting in regulatory approval of one isoform-selective inhibitor (idelalisib) for treatment of certain blood cancers and a variety of other agents at different stages of development. In parallel to PI3K research by cancer biologists, investigations in other fields have uncovered exciting and often unpredicted roles for PI3K catalytic and regulatory subunits in normal cell function and in disease. Many of these functions impinge upon oncology by influencing the efficacy and toxicity of PI3K-targeted therapies. Here we provide a perspective on the roles of class I PI3Ks in the regulation of cellular metabolism and in immune system functions, two topics closely intertwined with cancer biology. We also discuss recent progress developing PI3K-targeted therapies for treatment of cancer and other diseases.

Mechanisms of resistance to selective estrogen receptor down-regulator in metastatic breast cancer

Based on the prominent role estrogen receptor (ER) plays in breast cancer, endocrine therapy has been developed to block the ER pathway and has shown great effectiveness. Fulvestrant, the first selective ER down-regulator (SERD), was demonstrated to completely suppress ERα and notably efficient. However, resistance to fulvestrant occurs, either intrinsic or acquired during the treatment. Several potential mechanisms inducing fulvestrant resistance have been proposed, composed of activated ERα-independent compensatory growth factor signaling, stimulated downstream kinases, altered cell cycle mediators, etcetera. Experimentally, combinations of fulvestrant with targeted treatments were reported to eliminate the resistance and improve the effect of fulvestrant. Meanwhile, some clinical trials associated with the targeted combination therapies are in progress. This review focuses on the underlying mechanisms that contribute to fulvestrant resistance in ER-positive breast cancer and provides an overview of combined fulvestrant with targeted agents to shed light on optimal therapies for patients with ER-positive breast cancer.

Phase I Dose-Escalation Study of Taselisib, an Oral PI3K Inhibitor, in Patients with Advanced Solid Tumors

Taselisib is a potent and selective tumor growth inhibitor through PI3K pathway suppression. Thirty-four patients with locally advanced or metastatic solid tumors were treated (phase I study, modified 3+3 dose escalation; 5 cohorts; 3-16 mg taselisib once-daily capsule). Taselisib pharmacokinetics were dose-proportional; mean half-life was 40 hours. Frequent dose-dependent, treatment-related adverse events included diarrhea, hyperglycemia, decreased appetite, nausea, rash, stomatitis, and vomiting. At 12 and 16 mg dose levels, dose-limiting toxicities (DLT) were observed, with an accumulation of higher-grade adverse events after the cycle 1 DLT assessment window. Pharmacodynamic findings showed pathway inhibition at ≥3 mg in patient tumor samples, consistent with preclinical PIK3CA-mutant tumor xenograft models. Confirmed response rate was 36% for PIK3CA-mutant tumor patients with measurable disease [5/14: 4 breast cancer (3 patients at 12 mg); 1 non-small cell lung cancer], where responses started at 3 mg, and 0% in patients with tumors without known PIK3CA hotspot mutations (0/15).Significance: Preliminary data consistent with preclinical data indicate increased antitumor activity of taselisib in patients with PIK3CA-mutant tumors (in comparison with patients with tumors without known activating PIK3CA hotspot mutations) starting at the lowest dose tested of 3 mg, thereby supporting higher potency for taselisib against PIK3CA-mutant tumors. Cancer Discov; 7(7); 704-15. ©2017 AACR.See related commentary by Rodon and Tabernero, p. 666This article is highlighted in the In This Issue feature, p. 653.

CDK4/6 Inhibition in Breast Cancer: Mechanisms of Response and Treatment Failure

PURPOSE OF REVIEW

To describe the role of D-type cyclins and CDKs 4 and 6 in breast cancer, and to discuss potential biomarkers for sensitivity or resistance to CDK4/6 inhibitors.

RECENT FINDINGS

A small number of preclinical and clinical studies have explored potential mechanisms of CDK4/6 inhibitor response and resistance in breast cancer. Putative markers of response include ER-positivity, luminal patterns of gene expression, high cyclin D1 levels, and low p16 levels. Possible resistance mechanisms include loss of Rb function, overexpression/amplification of cyclin E, and CDK6 amplification. Most these remain speculative and have not been validated in clinical specimens.

SUMMARY

If early successes with CDK4/6 inhibitors are to be capitalized upon, it is critical that our understanding of CDK4/6 biology in breast cancer extends beyond its current rudimentary state. Only then we will be able to develop rational therapeutic combinations that further enhance the efficacy of these agents.

Endocrine resistance in hormone-responsive breast cancer: mechanisms and therapeutic strategies

The majority of breast cancers may be considered hormone responsive due to expression of hormone receptors (HR+). Although endocrine therapy is always considered for advanced HR+ breast cancer, the emergence of resistance is inevitable over time and is present from the start in a proportion of patients. In this review, we explore the mechanisms underlying de novo and acquired resistance to endocrine therapy. We comprehensively review newly approved and emerging therapies that have been developed to counteract specific mechanisms of resistance. We discuss the challenges pertinent to this therapeutic arena including the potential relief of negative regulatory feedback inhibition with compensatory pathway activation and the evolution of molecular changes in HR+ breast cancers during treatment. We discuss strategies to address these challenges in order to develop rational therapy approaches for patients with advanced HR+ breast cancer.