Dual targeting of HER2-positive breast cancer with trastuzumab emtansine and pertuzumab: understanding clinical trial results

Drug conjugates for the treatment of lung cancer: from drug discovery to clinical practice

A drug conjugate consists of a cytotoxic drug bound via a linker to a targeted ligand, allowing the targeted delivery of the drug to one or more tumor sites. This approach simultaneously reduces drug toxicity and increases efficacy, with a powerful combination of efficient killing and precise targeting. Antibody‒drug conjugates (ADCs) are the best-known type of drug conjugate, combining the specificity of antibodies with the cytotoxicity of chemotherapeutic drugs to reduce adverse reactions by preferentially targeting the payload to the tumor. The structure of ADCs has also provided inspiration for the development of additional drug conjugates. In recent years, drug conjugates such as ADCs, peptide‒drug conjugates (PDCs) and radionuclide drug conjugates (RDCs) have been approved by the Food and Drug Administration (FDA). The scope and application of drug conjugates have been expanding, including combination therapy and precise drug delivery, and a variety of new conjugation technology concepts have emerged. Additionally, new conjugation technology-based drugs have been developed in industry. In addition to chemotherapy, targeted therapy and immunotherapy, drug conjugate therapy has undergone continuous development and made significant progress in treating lung cancer in recent years, offering a promising strategy for the treatment of this disease. In this review, we discuss recent advances in the use of drug conjugates for lung cancer treatment, including structure-based drug design, mechanisms of action, clinical trials, and side effects. Furthermore, challenges, potential approaches and future prospects are presented.

Antibody-Drug Conjugate Targets, Drugs and Linkers

Antibody-drug conjugates offer the possibility of directing powerful cytotoxic agents to a malignant tumor while sparing normal tissue. The challenge is to select an antibody target expressed exclusively or at highly elevated levels on the surface of tumor cells and either not all or at low levels on normal cells. The current review explores 78 targets that have been explored as antibody-drug conjugate targets. Some of these targets have been abandoned, 9 or more are the targets of FDA-approved drugs, and most remain active clinical interest. Antibody-drug conjugates require potent cytotoxic drug payloads, several of these small molecules are discussed, as are the linkers between the protein component and small molecule components of the conjugates. Finally, conclusions regarding the elements for the successful antibody-drug conjugate are discussed.

Novel ADCs and Strategies to Overcome Resistance to Anti-HER2 ADCs

During recent years, a number of new compounds against HER2 have reached clinics, improving the prognosis and quality of life of HER2-positive breast cancer patients. Nonetheless, resistance to standard-of-care drugs has motivated the development of novel agents, such as new antibody-drug conjugates (ADCs). The latter are a group of drugs that benefit from the potency of cytotoxic agents whose action is specifically guided to the tumor by the target-specific antibody. Two anti-HER2 ADCs have reached the clinic: trastuzumab-emtansine and, more recently, trastuzumab-deruxtecan. In addition, several other HER2-targeted ADCs are in preclinical or clinical development, some of them with promising signs of activity. In the present review, the structure, mechanism of action, and potential resistance to all these ADCs will be described. Specific attention will be given to discussing novel strategies to circumvent resistance to ADCs.

Landmark trials in the medical oncology management of metastatic breast cancer

Significant advances in the management of metastatic breast cancer (MBC) have guided more personalized treatment according to disease biology and led to improved survival outcomes and quality of life for patients. In this review, we discuss landmark clinical trials in medical oncology that have shaped the current standard of care for MBC. Combinations of endocrine therapy with cyclin-dependent kinase 4/6 inhibitors have led to substantial improvements in overall survival, thus becoming standard first-line treatment for patients with HR-positive MBC. Inhibition of the PI3K and mTOR pathway is another promising strategy to overcome resistance to endocrine therapy. HER2-targeted therapies have also evolved with the addition of pertuzumab to trastuzumab plus a taxane demonstrating remarkable overall survival advantage in patient with HER2-positive MBC. In second or later line therapies, novel anti-HER2 antibody-drug conjugates and TKIs have durable antitumor activity, survival benefit, and encouraging efficacy in the subgroup of patients with brain metastases. Triple negative breast cancer remains the most challenging subtype due to lack of druggable targets. Immunotherapy for patients with PDL-1 expression on tumor infiltrating immune cells and poly (ADP-ribose) polymerase inhibitors for those with germline BRCA1/2 mutations are the latest approved targeted strategies in this population. Numerous obstacles still exist in treating MBC, especially for patients whose disease develops resistance to available agents. Future research is eagerly awaited to address the optimal sequence or combination of therapies and to identify better biomarkers to guide precision medicine.

HER2-directed antibodies, affibodies and nanobodies as drug-delivery vehicles in breast cancer with a specific focus on radioimmunotherapy and radioimmunoimaging

PURPOSE

The aim of the present paper is to review the role of HER2 antibodies, affibodies and nanobodies as vehicles for imaging and therapy approaches in breast cancer, including a detailed look at recent clinical data from antibody drug conjugates and nanobodies as well as affibodies that are currently under development.

RESULTS

Clinical and preclinical studies have shown that the use of monoclonal antibodies in molecular imaging is impaired by slow blood clearance, associated with slow and low tumor uptake and with limited tumor penetration potential. Antibody fragments, such as nanobodies, on the other hand, can be radiolabelled with short-lived radioisotopes and provide high-contrast images within a few hours after injection, allowing early diagnosis and reduced radiation exposure of patients. Even in therapy, the small radioactively labeled nanobodies prove to be superior to radioactively labeled monoclonal antibodies due to their higher specificity and their ability to penetrate the tumor.

CONCLUSION

While monoclonal antibodies are well established drug delivery vehicles, the current literature on molecular imaging supports the notion that antibody fragments, such as affibodies or nanobodies, might be superior in this approach.

miR-126 reduces trastuzumab resistance by targeting PIK3R2 and regulating AKT/mTOR pathway in breast cancer cells

MicroRNAs (miRNAs) have been found to play a key role in drug resistance. In the current study, we aimed to explore the potential role of miR‐126 in trastuzumab resistance in breast cancer cells. We found that the trastuzumab‐resistant cell lines SKBR3/TR and BT474/TR had low expression of miR‐126 and increased ability to migrate and invade. The resistance, invasion and mobilization abilities of the cells resistant to trastuzumab were reduced by ectopic expression of miR‐126 mimics. In comparison, inhibition of miR‐126 in SKBR3 parental cells had the opposite effect of an increased resistance to trastuzumab as well as invasion and migration. It was also found that miR‐126 directly targets PIK3R2 in breast cancer cells. PIK3R2‐knockdown cells showed decreased resistance to trastuzumab, while overexpression of PIK3R2 increased trastuzumab resistance. In addition, our finding showed that overexpression of miR‐126 reduced resistance to trastuzumab in the trastuzumab‐resistant cells and that inhibition of the PIK3R2/PI3K/AKT/mTOR signalling pathway was involved in this effect. SKBR3/TR cells also showed increased sensitivity to trastuzumab mediated by miR‐126 in vivo. In conclusion, the above findings demonstrated that overexpression of miR‐126 or down‐regulation of its target gene may be a potential approach to overcome trastuzumab resistance in breast cancer cells.

HER3 targeting with an antibody-drug conjugate bypasses resistance to anti-HER2 therapies

Despite impressive clinical benefit obtained with anti‐HER2‐targeted therapies, in advances stages, especially in the metastatic setting, HER2‐positive tumors remain incurable. Therefore, it is important to develop novel strategies to fight these tumors, especially when they become resistant to available therapies. We show here that the anti‐HER3 antibody–drug conjugate EV20/MMAF exerted potent anti‐tumoral properties against several models of primary resistance and secondary resistance to common anti‐HER2 available therapies, including trastuzumab, lapatinib, neratinib, and trastuzumab‐emtansine. HER3 was expressed in these HER2⁺ breast cancer cells and knockdown experiments demonstrated that HER3 expression was required for the action of EV20/MMAF. In mice injected with trastuzumab‐resistant HER2⁺ cells, a single dose of EV20/MMAF caused complete and long‐lasting tumor regression. Mechanistically, EV20/MMAF bound to cell surface HER3 and became internalized to the lysosomes. Treatment with EV20/MMAF caused cell cycle arrest in mitosis and promoted cell death through mitotic catastrophe. These findings encourage the clinical testing of EV20/MMAF for several indications in the HER2⁺ cancer clinic, including situations in which HER2⁺ tumors become refractory to approved anti‐HER2 therapies.

Trastuzumab-Related Cardiotoxicity and Cardiac Care in Patients With HER2 Positive Metastatic Breast Cancer

Prolonged trastuzumab therapy is the standard of care for women with metastatic HER2 positive (HER2+) breast cancer. There are limited data on the incidence of cardiotoxicity, its treatment implication, and cardiac care in these patients. We retrospectively identified consecutive women who received >12 months of trastuzumab treatment at Princess Margaret Cancer Centre (Toronto, ON) from 2007 to 2012 for metastatic HER2 positive breast cancer and followed them until death or August 2018. Patients were included if a pretherapy multigated acquisition scan and ≥2 subsequent follow-up scans were available. The Cardiac Review and Evaluation Committee Criteria were used to identify cardiotoxicity. Baseline characteristics and outcomes (final left ventricular ejection fraction, change in LVEF, trastuzumab interruption) were compared in patients with and without cardiotoxicity. Cardiac care and treatment received were recorded. Sixty patients (mean age 52 ± 10.4 years) were included. The median trastuzumab exposure was 37 cycles (interquartile range 23 to 56) over 28 months (interquartile range 19 to 49) and 48% received previous anthracycline therapy. The cumulative incidence of cardiotoxicity was 35% (95% CI 23 to 48) at 3 years. Patients who developed cardiotoxicity were more likely to receive third-line cancer treatments and had lower final LVEF than patients without (54.9% ± 6.3% vs 64% ± 4.9%, p <0.001). Of the 23 patients with cardiotoxicity, 10 (43%) had trastuzumab interrupted for at least 1 cycle, only 7 (30%) patients were seen by a cardiologist and 4 (17%) received cardiac medications. In conclusion, patients with metastatic breast cancer receiving prolonged trastuzumab therapy appear to have high rates of cardiotoxicity. This was associated with high rates of trastuzumab interruption, but low rates of cardiology referral and cardiac treatment, reflecting a potential cardiac care gap.

Trastuzumab Emtansine: Mechanisms of Action and Resistance, Clinical Progress, and Beyond

The approval of ado-trastuzumab emtansine (T-DM1) for clinical use represented a turning point both in HER2-positive breast cancer treatment and antibody-drug conjugate (ADC) technology. T-DM1 has proved its value and effectiveness in advanced metastatic disease as well as in the adjuvant setting. However, its therapeutic potential extends beyond the treatment of breast cancer. Around 100 clinical trials have evaluated or are studying different aspects of T-DM1, such as its role in other HER2 malignancies, rational combinations with immunotherapy, or its function in brain metastasis. Conceptually, many lessons can be learned from this ADC. Understanding its mechanisms of action and the molecular basis underlying resistance to T-DM1 may be relevant to comprehend resistances raised to other ADCs and identify pitfalls that may be overcome.

Mechanisms of resistance to trastuzumab emtansine (T-DM1) in HER2-positive breast cancer

The HER2-targeted antibody-drug conjugate trastuzumab emtansine (T-DM1) is approved for the treatment of metastatic, HER2-positive breast cancer after prior trastuzumab and taxane therapy, and has also demonstrated efficacy in the adjuvant setting in incomplete responders to neoadjuvant therapy. Despite its objective activity, intrinsic and acquired resistance to T-DM1 remains a major clinical challenge. T-DM1 mediates its activity in a number of ways, encompassing HER2 signalling blockade, Fc-mediated immune response and payload-mediated microtubule poisoning. Resistance mechanisms relating to each of these features have been demonstrated, and we outline the findings of these studies in this review. In our overview of the substantial literature on T-DM1 activity and resistance, we conclude that the T-DM1 resistance mechanisms most strongly supported by the experimental data relate to dysfunctional intracellular metabolism of the construct and subversion of DM1-mediated cell killing. Loss of dependence on signalling initiated by HER2-HER2 homodimers is not substantiated as a resistance mechanism by clinical or experimental studies, and the impact of EGFR expression and tumour immunological status requires further investigation. These findings are instructive with respect to strategies that might overcome T-DM1 resistance, including the use of second-generation anti-HER2 antibody-drug conjugates that deploy alternative linker-payload chemistries.

Metastatic behavior and overall survival according to breast cancer subtypes in stage IV inflammatory breast cancer

BACKGROUND

Distant metastatic disease is frequently observed in inflammatory breast cancer (IBC), with a poor prognosis as a consequence. The aim of this study was to analyze the association of hormone receptor (HR) and human epidermal growth factor receptor-2 (HER2) based breast cancer subtypes in stage IV inflammatory breast cancer (IBC) with preferential site of distant metastases and overall survival (OS).

METHODS

For patients with stage IV IBC, diagnosed in the Netherlands between 2005 and 2016, tumors were classified into four breast cancer subtypes: HR+/HER2-, HR+/HER2+, HR-/HER2+, and HR-/HER2-. Patient, tumor, and treatment characteristics and sites of metastases were compared. OS of the subtypes was compared using Kaplan-Meier curves and the log-rank test. Association between subtype and OS was assessed in multivariable models using logistic regression.

RESULTS

In total, 744 eligible patients were included: 340 (45.7%) tumors were HR+/HER2-, 148 (19.9%) HR-/HER2+, 131 (17.6%) HR+/HER2+, and 125 (16.8%) HR-/HER2-. Bone was the most common metastatic site in all subtypes. A significant predominance of bone metastases was found in HR+/HER2- IBC (71.5%), and liver and lung metastases in the HR-/HER2+ (41.2%) and HR-/HER2- (40.8%) subtypes, respectively. In multivariable analysis, the HR-/HER2- subtype was associated with significantly worse OS as compared to the other subtypes.

CONCLUSION

Breast cancer subtypes in stage IV IBC are associated with distinct patterns of metastatic spread and display notable differences in OS. The use of breast cancer subtypes can guide a more patient-tailored staging directed to metastatic site and extend of disease.

Immunotherapy in breast cancer: Current status and future directions

Breast cancer, one of the leading causes of death in women in the United States, challenges therapeutic success in patients due to tumor heterogeneity, treatment resistance, metastasis and disease recurrence. Knowledge of immune system involvement in normal breast development and breast cancer has led to extensive research into the immune landscape of breast cancer and multiple immunotherapy clinical trials in breast cancer patients. However, poor immunogenicity and T-cell infiltration along with heightened immunosuppression in the tumor microenvironment have been identified as potential challenges to the success of immunotherapy in breast cancer. Oncodrivers, owing to their enhanced expression and stimulation of tumor cell proliferation and survival, present an excellent choice for targeted immunotherapy development in breast cancer. Loss of anti-tumor immune response specific to oncodrivers has been reported in breast cancer patients as well. Dendritic cell vaccines have been tested for their efficacy in generating anti-tumor T-cell response against specific tumor-associated antigens and oncodrivers and have shown improved survival outcome in patients. Here, we review the current status of immunotherapy in breast cancer, focusing on dendritic cell vaccines and their therapeutic application in breast cancer. We further discuss future directions of breast cancer immunotherapy and potential combination strategies involving dendritic cell vaccines and existing chemotherapeutics for improved efficacy and better survival outcome in breast cancer.

Acquired Resistance to Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) combine the tumor selectivity of antibodies with the potency of cytotoxic small molecules thereby constituting antibody-mediated chemotherapy. As this inherently limits the adverse effects of the chemotherapeutic, such approaches are heavily pursued by pharma and biotech companies and have resulted in four FDA (Food and Drug Administration)-approved ADCs. However, as with other cancer therapies, durable responses are limited by the fact that under cell stress exerted by these drugs, tumors can acquire mechanisms of escape. Resistance can develop against the antibody component of ADCs by down-regulation/mutation of the targeted cell surface antigen or against payload toxicity by up-regulation of drug efflux transporters. Unique resistance mechanisms specific for the mode of action of ADCs have also emerged, like altered internalization or cell surface recycling of the targeted tumor antigen, changes in the intracellular routing or processing of ADCs, and impaired release of the toxic payload into the cytosol. These evasive changes are tailored to the specific nature and interplay of the three ADC constituents: the antibody, the linker, and the payload. Hence, they do not necessarily endow broad resistance to ADC therapy. This review summarizes preclinical and clinical findings that shed light on the mechanisms of acquired resistance to ADC therapies.

Targeted neoadjuvant therapy in the HER-2-positive breast cancer patients: a systematic review and meta-analysis

Aim

To evaluate efficacy and safety of lapatinib or trastuzumab alone or both plus chemotherapy for the treatment of breast cancer patients with positive HER-2 expression.

Methods

Cochrane Central Register of Controlled Trials, PubMed, MEDLINE, OVID, Embase, Chinese Biomedical Literature Database, and China Academic Journals Database were searched from 1994 through December 2017 using the keywords "breast cancer", "preoperative", "neo-adjuvant", "lapatinib", "pertuzumab", "Herceptin", and "trastuzumab".

Results

Meta-analysis found that pathological complete response (PCR; risk ratio [RR]=0.82, 95% CI: 0.72-0.93) and tall PCR (tPCR; RR=0.77, 95% CI: 0.67-0.88) of chemotherapy plus lapatinib were significantly less effective or safe compared to that of chemotherapy plus trastuzumab (P<0.05). PCR (RR=1.30, 95% CI: 1.15-1.47) and tPCR (RR=1.32, 95% CI: 1.16-1.50) of chemotherapy plus both lapatinib and trastuzumab were significantly superior to that of chemotherapy plus trastuzumab alone (P<0.05). However, there was no significant difference in breast reservation rate between chemotherapy plus lapatinib vs chemotherapy plus trastuzumab (RR=0.91, 95% CI: 0.72-1.16) or chemotherapy plus both lapatinib and trastuzumab (RR=1.11, 95% CI: 0.73-1.68, P>0.05). Incidence of diarrhea, hepatic toxicity, and skin rash in the groups of chemotherapy plus lapatinib or chemotherapy plus both lapatinib and trastuzumab was significantly higher than that in chemotherapy plus trastuzumab (P<0.05).

Conclusion

Efficacy of lapatinib was less than that of trastuzumab, but incidence of adverse effect of lapatinib was higher than that of trastuzumab. Combination of chemotherapy plus both lapatinib and trastuzumab could significantly increase PCR and tPCR in breast cancer patients, but rate of breast conservation, event-free survival, and overall survival was not significantly improved. Incidence of diarrhea, hepatic toxicity, and skin rash was significantly increased in the groups using lapatinib.