Predictive and Pharmacodynamic Biomarkers of Response to the Phosphatidylinositol 3-Kinase Inhibitor Taselisib in Breast Cancer Preclinical Models

Targeting Breast Cancer: An Overlook on Current Strategies

Breast cancer (BC) is one of the most widely diagnosed cancers and a leading cause of cancer death among women worldwide. Globally, BC is the second most frequent cancer and first most frequent gynecological one, affecting women with a relatively low case-mortality rate. Surgery, radiotherapy, and chemotherapy are the main treatments for BC, even though the latter are often not aways successful because of the common side effects and the damage caused to healthy tissues and organs. Aggressive and metastatic BCs are difficult to treat, thus new studies are needed in order to find new therapies and strategies for managing these diseases. In this review, we intend to give an overview of studies in this field, presenting the data from the literature concerning the classification of BCs and the drugs used in therapy for the treatment of BCs, along with drugs in clinical studies.

Growth‐rate model predicts in vivo tumor response from in vitro data

A major challenge in oncology drug development is to elucidate why drugs that show promising results in cancer cell lines in vitro fail in mouse studies or human trials. One of the fundamental steps toward solving this problem is to better predict how in vitro potency translates into in vivo efficacy. A common approach to infer whether a model will respond in vivo is based on in vitro half‐maximal inhibitory concentration values (IC₅₀), but yields limited quantitative comparison between cell lines and drugs, potentially because cell division and death rates differ between cell lines and in vivo models. Other methods based either on mechanistic modeling or machine learning require molecular insights or extensive training data, limiting their use for early drug development. To address these challenges, we propose a mathematical model integrating in vitro growth rate inhibition values with pharmacokinetic parameters to estimate in vivo drug response. Upon calibration with a drug‐specific factor, our model yields precise estimates of tumor growth rate inhibition for in vivo studies based on in vitro data. We then demonstrate how our model can be used to study dosing schedules and perform sensitivity analyses. In addition, it provides meaningful metrics to assess association with genotypes and guide clinical trial design. By relying on commonly collected data, our approach shows great promise for optimizing drug development, better characterizing the efficacy of novel molecules targeting proliferation, and identifying more robust biomarkers of sensitivity while limiting the number of in vivo experiments.

ESR1 mutations and therapeutic resistance in metastatic breast cancer: progress and remaining challenges

Breast cancer accounts for 25% of the cancers in women worldwide. The most common subtype of breast cancer diagnosed is hormone receptor positive, which expresses the oestrogen receptor (ER). Targeting of the ER with endocrine therapy (ET) is the current standard of care for ER-positive (ER+) breast cancer, reducing the mortality by up to 40%. Resistance to ET, however, remains a major issue for ER + breast cancer, leading to recurrence and metastasis. One major driver of ET resistance is mutations in the ER gene (ESR1) leading to constitutive transcriptional activity and reduced ET sensitivity. These mutations are particularly detrimental in metastatic breast cancer (MBC) as they are present in as high as 36% of the patients. This review summarises the pre-clinical characterisation of ESR1 mutations and their association with clinical outcomes in MBC and primary disease. The clinically approved and investigational therapeutic options for ESR1 mutant breast cancer and the current clinical trials evaluating ESR1 mutations and ET resistance are also discussed. Finally, this review addresses pre-clinical models and multi-'omics' approaches for developing the next generation of therapeutics for ESR1 mutant and ET-resistant breast cancer.

Phase II Study of Taselisib in PIK3CA-Mutated Solid Tumors Other Than Breast and Squamous Lung Cancer: Results From the NCI-MATCH ECOG-ACRIN Trial (EAY131) Subprotocol I

PURPOSE

PIK3CA mutations frequently contribute to oncogenesis in solid tumors. Taselisib, a potent and selective inhibitor of phosphoinositide 3-kinase, has demonstrated clinical activity in PIK3CA-mutant breast cancer. Whether PIK3CA mutations predict sensitivity to taselisib in other cancer types is unknown. National Cancer Institute-Molecular Analysis for Therapy Choice Arm EAY131-I is a single-arm, phase II study of the safety and efficacy of taselisib in patients with advanced cancers.

METHODS

Eligible patients had tumors with an activating PIK3CA mutation. Patients with breast or squamous cell lung carcinoma, or whose cancer had KRAS or PTEN mutations, were excluded. Patients received taselisib 4 mg, orally once daily continuously, until disease progression or unacceptable toxicity. The primary end point was objective response rate. Secondary end points included progression-free survival (PFS), 6-month PFS, overall survival (OS), and identification of predictive biomarkers.

RESULTS

Seventy patients were enrolled, and 61 were eligible and initiated protocol therapy. Types of PIK3CA mutations included helical 41 of 61 (67%), kinase 11 of 61 (18%), and other 9 of 61 (15%). With a median follow-up of 35.7 months, there were no complete or partial responses. Six-month PFS was 19.9% (90% CI, 12.0 to 29.3) and median PFS was 3.1 months (90% CI, 1.8 to 3.7). Six-month OS was 60.7% (90% CI, 49.6 to 70.0) and median OS was 7.2 months (90% CI, 5.9 to 10.0). Individual comutations were too heterogeneous to correlate with clinical outcome. Fatigue, diarrhea, nausea, and hyperglycemia were the most common toxicities, and most were grade 1 and 2.

CONCLUSION

In this study, taselisib monotherapy had very limited activity in a heterogeneous cohort of heavily pretreated cancer patients with PIK3CA-mutated tumors; the presence of a PIK3CA mutation alone does not appear to be a sufficient predictor of taselisib activity.

PI3K inhibitors are finally coming of age

Overactive phosphoinositide 3-kinase (PI3K) in cancer and immune dysregulation has spurred extensive efforts to develop therapeutic PI3K inhibitors. Although progress has been hampered by issues such as poor drug tolerance and drug resistance, several PI3K inhibitors have now received regulatory approval - the PI3Kα isoform-selective inhibitor alpelisib for the treatment of breast cancer and inhibitors mainly aimed at the leukocyte-enriched PI3Kδ in B cell malignancies. In addition to targeting cancer cell-intrinsic PI3K activity, emerging evidence highlights the potential of PI3K inhibitors in cancer immunotherapy. This Review summarizes key discoveries that aid the clinical translation of PI3Kα and PI3Kδ inhibitors, highlighting lessons learnt and future opportunities.

ESR1 mutation as an emerging clinical biomarker in metastatic hormone receptor-positive breast cancer

In metastatic hormone receptor-positive breast cancer, ESR1 mutations are a common cause of acquired resistance to the backbone of therapy, estrogen deprivation by aromatase inhibition. How these mutations affect tumor sensitivity to established and novel therapies are active areas of research. These therapies include estrogen receptor-targeting agents, such as selective estrogen receptor modulators, covalent antagonists, and degraders (including tamoxifen, fulvestrant, and novel agents), and combination therapies, such as endocrine therapy plus CDK4/6, PI3K, or mTORC1 inhibition. In this review, we summarize existing knowledge surrounding the mechanisms of action of ESR1 mutations and roles in resistance to aromatase inhibition. We then analyze the recent literature on how ESR1 mutations affect outcomes in estrogen receptor-targeting and combination therapies. For estrogen receptor-targeting therapies such as tamoxifen and fulvestrant, ESR1 mutations cause relative resistance in vitro but do not clearly lead to resistance in patients, making novel agents in this category promising. Regarding combination therapies, ESR1 mutations nullify any aromatase inhibitor component of the combination. Thus, combinations using endocrine alternatives to aromatase inhibition, or combinations where the non-endocrine component is efficacious as monotherapy, are still effective against ESR1 mutations. These results emphasize the importance of investigating combinatorial resistance, challenging as these efforts are. We also discuss future directions and open questions, such as studying the differences among distinct ESR1 mutations, asking how to adjust clinical decisions based on molecular surveillance testing, and developing novel therapies that are effective against ESR1 mutations.

Correlative studies investigating effects of PI3K inhibition on peripheral leukocytes in metastatic breast cancer: potential implications for immunotherapy

PURPOSE

Patients with localized breast cancer have a 5-year survival rate > 99% compared to patients with metastatic breast cancer (MBC) that have a 5-year survival rate of ~ 27%. Unregulated PI3K/AKT signaling is a common characteristic of MBC, making it a desirable therapeutic target for tumors with activating mutations in this pathway. Interestingly, inhibition of the PI3K/AKT pathway can affect signaling in immune cells, which could potentially alter the immune phenotype of patients undergoing therapy with these drugs. The purpose of this study is to evaluate how PI3K inhibition affects the immune cells of MBC patients during treatment.

METHODS

We investigated the effects of PI3K inhibition on the immune cell populations in peripheral blood of MBC patients enrolled in 4 different clinical trials utilizing PI3K inhibitors. Peripheral blood was drawn at different points in patient treatment cycles to record immune cell fluctuations in response to therapy.

RESULTS

MBC patients who responded to treatment with a positive fold-change in cytotoxic T cell population, had an average duration of treatment response of 31.4 months. In contrast, MBC patients who responded to treatment with a negative fold-change in cytotoxic T-cell population, had an average duration of therapeutic response of 5 months. These data suggest that patients with a more robust, initial anti-tumor T cell response may have a longer therapeutic response compared to patients who do not have a robust, initial anti-tumor T cell response.

CONCLUSIONS

These results highlight the potential for PI3K inhibition to sensitize tumors to immune checkpoint inhibitors, thus providing additional therapeutic options for patients with MBC.

Breast Cancer: A Molecularly Heterogenous Disease Needing Subtype-Specific Treatments

Breast cancer is the most commonly occurring cancer in women. There were over two-million new cases in world in 2018. It is the second leading cause of death from cancer in western countries. At the molecular level, breast cancer is a heterogeneous disease, which is characterized by high genomic instability evidenced by somatic gene mutations, copy number alterations, and chromosome structural rearrangements. The genomic instability is caused by defects in DNA damage repair, transcription, DNA replication, telomere maintenance and mitotic chromosome segregation. According to molecular features, breast cancers are subdivided in subtypes, according to activation of hormone receptors (estrogen receptor and progesterone receptor), of human epidermal growth factors receptor 2 (HER2), and or BRCA mutations. In-depth analyses of the molecular features of primary and metastatic breast cancer have shown the great heterogeneity of genetic alterations and their clonal evolution during disease development. These studies have contributed to identify a repertoire of numerous disease-causing genes that are altered through different mutational processes. While early-stage breast cancer is a curable disease in about 70% of patients, advanced breast cancer is largely incurable. However, molecular studies have contributed to develop new therapeutic approaches targeting HER2, CDK4/6, PI3K, or involving poly(ADP-ribose) polymerase inhibitors for BRCA mutation carriers and immunotherapy.