Novel Agents for Metastatic Triple-Negative Breast Cancer: Finding the Positive in the Negative

Antibody-Drug Conjugates: A New Therapeutic Approach for Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive breast cancer subset associated with a worse prognosis and poor response to conventional chemotherapy. Despite recent advances in drug discovery, its management is still a challenge for clinicians, illuminating the unmet need to develop novel treatment approaches. Antibody-drug conjugates (ADC) are innovative oncology drugs that combine the specificity of monoclonal antibodies and the high efficacy of anticancer payloads, to deliver cytotoxic drugs selectively to cancer cells. Various ADCs were investigated for TNBC and have provided a promise for this aggressive women's cancer including the FDA-approved sacituzumab govitecan. In this chapter, we reviewed different ADCs studied for TNBC including their mechanisms of action, efficacy, and tolerability. Moreover, we have also discussed their therapeutic potential based on combinatorial approaches with other targeted therapies in early and metastatic TNBC.

Development and validation of nomograms for predicting survival in patients with de novo metastatic triple-negative breast cancer

Metastatic triple-negative breast cancer (mTNBC) is a heterogeneous disease with a poor prognosis. Individualized survival prediction tool is useful for this population. We constructed the predicted nomograms for breast cancer-specific survival (BCSS) and overall survival (OS) using the data identified from the Surveillance, Epidemiology, and End Results database. The Concordance index (C-index), the area under the time-dependent receiver operating characteristic curve (AUC) and the calibration curves were used for the discrimination and calibration of the nomograms in the training and validation cohorts, respectively. 1962 mTNBC patients with a median follow-up was 13 months (interquartile range, 6–22 months), 1639 (83.54%) cases died of any cause, and 1469 (74.87%) died of breast cancer. Nine and ten independent prognostic factors for BCSS and OS were identified and integrated to construct the nomograms, respectively. The C-indexes of the nomogram for BCSS and OS were 0.694 (95% CI 0.676–0.712) and 0.699 (95% CI 0.679–0.715) in the training cohort, and 0.699 (95% CI 0.686–0.712) and 0.697 (95% CI 0.679–0.715) in the validation cohort, respectively. The AUC values of the nomograms to predict 1-, 2-, and 3-year BCSS and OS indicated good specificity and sensitivity in internal and external validation. The calibration curves showed a favorable consistency between the actual and the predicted survival in the training and validation cohorts. These nomograms based on clinicopathological factors and treatment could reliably predict the survival of mTNBC patient. This may be a useful tool for individualized healthcare decision-making.

Diverse roles of tumor-stromal PDGFB-to-PDGFRβ signaling in breast cancer growth and metastasis

Over the last couple of decades, it has become increasingly apparent that the tumor microenvironment (TME) mediates every step of cancer progression and solid tumors are only able to metastasize with a permissive TME. This intricate interaction of cancer cells with their surrounding TME, or stroma, is becoming more understood with an ever greater knowledge of tumor-stromal signaling pairs such as platelet-derived growth factors (PDGF) and their cognate receptors. We and others have focused our research efforts on understanding how tumor-derived PDGFB activates platelet-derived growth factor receptor beta (PDGFRβ) signaling specifically in the breast cancer TME. In this chapter, we broadly discuss PDGF and PDGFR expression patterns and signaling in normal physiology and breast cancer. We then detail the expansive roles played by the PDGFB-to-PDGFRβ signaling pathway in modulating breast tumor growth and metastasis with a focus on specific cellular populations within the TME, which are responsive to tumor-derived PDGFB. Given the increasingly appreciated importance of PDGFB-to-PDGFRβ signaling in breast cancer progression, specifically in promoting metastasis, we end by discussing how therapeutic targeting of PDGFB-to-PDGFRβ signaling holds great promise for improving current breast cancer treatment strategies.

A Nomogram to Predict Disease-Free Survival Following Neoadjuvant Chemotherapy for Triple Negative Breast Cancer

Background

Neoadjuvant chemotherapy (NACT) is considered a standard treatment strategy for locally advanced triple negative breast cancer (TNBC). TNBC patients who achieve a pathologic complete response (pCR) are predicted to have a better prognosis while unfavorable chemo-sensitivity is still associated with a higher risk of disease relapse. The objective of this study was to construct a nomogram to predict disease-free survival (DFS) for TNBC patients following NACT.

Methods

A total of 165 TNBC patients who underwent standard NACT and surgery were retrospectively reviewed, and data on their clinicopathological factors before and after NACT were collected. Independent prognostic factors for DFS were identified by Cox regression based on lower Akaike information criteria (AIC) and Bayesian information criterion (BIC). A nomogram to predict the 2-year and 5-year DFS following NACT for TNBC was constructed based on training cohort (n = 132) and validated by a validation cohort (n = 33).

Results

Either limited or full pCR (breast-only pCR, node-only pCR, or both-pCR) indicated significantly improved DFS and overall survival (OS) (p < 0.001). Lager residual tumor size (hazard ratio [HR] 1.175, p = 0.011) and the presence of lymphatic vessel invasion (LVI) (HR 3.168, p = 0.001) were identified as independent predictors of disease relapse in the training cohort. Five variables, including age, primary tumor size, histological grade, residual tumor size, and LVI were used to establish the nomogram. The C-index of the nomogram was 0.815, and calibration curves showed an acceptable consistency between the actual and nomogram-predicted 2-year and 5-year DFS. The proposed nomogram demonstrated superior predictive performance compared with Residual Cancer Burden (RCB) classification and the 8th American Joint Committee on Cancer Post Neoadjuvant Therapy Classification (AJCC ypTNM) staging system (area under the curve [AUC] for 2-year DFS: 0.870 vs. 0.758 vs. 0.711, respectively; AUC for 5-year DFS: 0.794 vs. 0.731 vs. 0.702, respectively) in the validation cohort.

Conclusions

The nomogram proposed in our study enabled to quantify the risk of disease relapse and demonstrated superior predictive performance than a survival predict instrument. It was an easy-to-use tool for clinicians to guide individualized surveillance of TNBC patients following standard NACT.

Discovery of 8,9-seco-ent-Kaurane Diterpenoids as Potential Leads for the Treatment of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a lethal malignancy without safe and effective therapeutic drugs. In this study, the anti-TNBC bioassay-guided isolation of the medicinal plant Croton kongensis followed by the structural modification led to the construction of a small ent-kaurane diterpenoid library (1-25). With subsequent biological screening, 20 highly potent compounds (IC₅₀s < 3 μM) were identified. Among them, 8,9-seco-ent-kaurane 6 displayed comparable activity (IC₅₀s ∼ 80 nM) to doxorubicin but with better selectivity. The analysis of structure-activity relationships suggested that the cleavage of the C8-C9 bond and the presence of α,β-unsaturated ketone moiety were essential for the activity. The mechanistic study revealed that 6 induced apoptosis, autophagy, and metastasis suppression in TNBC cells via inhibition of Akt. In vivo, 6 significantly suppressed the TNBC tumor growth without causing side effects. All these results suggested that 6 may serve as a promising lead for the development of novel anti-TNBC agents in the future.

Targeting DNA Damage Response in Prostate and Breast Cancer

Steroid hormone signaling induces vast gene expression programs which necessitate the local formation of transcription factories at regulatory regions and large-scale alterations of the genome architecture to allow communication among distantly related cis-acting regions. This involves major stress at the genomic DNA level. Transcriptionally active regions are generally instable and prone to breakage due to the torsional stress and local depletion of nucleosomes that make DNA more accessible to damaging agents. A dedicated DNA damage response (DDR) is therefore essential to maintain genome integrity at these exposed regions. The DDR is a complex network involving DNA damage sensor proteins, such as the poly(ADP-ribose) polymerase 1 (PARP-1), the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), the ataxia-telangiectasia-mutated (ATM) kinase and the ATM and Rad3-related (ATR) kinase, as central regulators. The tight interplay between the DDR and steroid hormone receptors has been unraveled recently. Several DNA repair factors interact with the androgen and estrogen receptors and support their transcriptional functions. Conversely, both receptors directly control the expression of agents involved in the DDR. Impaired DDR is also exploited by tumors to acquire advantageous mutations. Cancer cells often harbor germline or somatic alterations in DDR genes, and their association with disease outcome and treatment response led to intensive efforts towards identifying selective inhibitors targeting the major players in this process. The PARP-1 inhibitors are now approved for ovarian, breast, and prostate cancer with specific genomic alterations. Additional DDR-targeting agents are being evaluated in clinical studies either as single agents or in combination with treatments eliciting DNA damage (e.g., radiation therapy, including targeted radiotherapy, and chemotherapy) or addressing targets involved in maintenance of genome integrity. Recent preclinical and clinical findings made in addressing DNA repair dysfunction in hormone-dependent and -independent prostate and breast tumors are presented. Importantly, the combination of anti-hormonal therapy with DDR inhibition or with radiation has the potential to enhance efficacy but still needs further investigation.