Breast tumors of the basal-like, hormone receptor-negative, subtype remain an unmet clinical challenge, as patients exhibit a high rate of recurrence and poor survival. Co-evolution of the malignant mammary epithelium and its underlying stroma instigates cancer-associated fibroblasts (CAFs) to endorse most, if not all, hallmarks of cancer progression. Here, we delineate a previously unappreciated role for CAFs as determinants of the molecular subtype of breast cancer. We identified a paracrine cross-talk between cancer cells expressing platelet-derived growth factor (PDGF)-CC and CAFs expressing the cognate receptors in human basal-like mammary carcinomas. Genetic or pharmacological intervention with PDGF-CC activity in mouse models of cancer resulted in conversion of basal-like breast cancers into a hormone receptor-positive state that conferred sensitivity to endocrine therapy in previously impervious tumors. We conclude that specification of the basal-like subtype of breast cancer is under microenvironmental control and therapeutically actionable in order to achieve sensitivity to endocrine therapy.

Fatty acid β-oxidation (FAO) is the main bioenergetic pathway in human prostate cancer (PCa) and a promising novel therapeutic vulnerability. Here we demonstrate therapeutic efficacy of targeting FAO in clinical prostate tumors cultured ex vivo, and identify DECR1, encoding the rate-limiting enzyme for oxidation of polyunsaturated fatty acids (PUFAs), as robustly overexpressed in PCa tissues and associated with shorter relapse-free survival. DECR1 is a negatively-regulated androgen receptor (AR) target gene and, therefore, may promote PCa cell survival and resistance to AR targeting therapeutics. DECR1 knockdown selectively inhibited β-oxidation of PUFAs, inhibited proliferation and migration of PCa cells, including treatment resistant lines, and suppressed tumor cell proliferation and metastasis in mouse xenograft models. Mechanistically, targeting of DECR1 caused cellular accumulation of PUFAs, enhanced mitochondrial oxidative stress and lipid peroxidation, and induced ferroptosis. These findings implicate PUFA oxidation via DECR1 as an unexplored facet of FAO that promotes survival of PCa cells.

The androgen receptor (AR) is the key oncogenic driver of prostate cancer and despite implementation of novel AR targeting therapies, patient outcomes for metastatic disease remain dismal. There is an urgent need to better understand androgen regulated cellular processes, in order to more effectively target the AR-dependence of prostate cancer cells through new therapeutic vulnerabilities. Transcriptomic studies have consistently identified lipid metabolism as a hallmark of enhanced AR signaling in prostate cancer, however the relationship between AR and the lipidome remain undefined. Using mass spectrometrybased lipidomics, this study revealed increased fatty acyl chain length in phospholipids from prostate cancer cells and patient-derived explants as one of the most striking androgenregulated changes to lipid metabolism. Potent and direct AR-mediated induction of ELOVL Fatty Acid Elongase 5 (ELOVL5), an enzyme that catalyzes fatty acid elongation, was demonstrated in prostate cancer cells, xenografts and clinical tumors. Assessment of mRNA and protein in large-scale datasets revealed ELOVL5 as the predominant ELOVL expressed in both primary and metastatic prostate cancer, and upregulated compared to non-malignant prostate. ELOVL5 depletion by siRNA markedly altered mitochondrial function to induce oxidative stress, resulting in significant inhibition of prostate cancer cell viability, 3D growth, and in vivo tumor growth and metastasis. Supplementation with the monounsaturated fatty acid cis-vaccenic acid, a direct product of ELOVL5 elongation, reversed the oxidative stress and associated cell viability caused by ELOVL5 knockdown. We have identified lipid elongation as a pro-survival metabolic pathway in prostate cancer that is androgenregulated, critical for metastasis and targetable via ELOVL5.

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The prognosis for breast cancer patients diagnosed with brain metastases is poor, with survival time measured merely in months. This can largely be attributed to the limited treatment options capable of reaching the tumor as a result of the highly restrictive blood-brain barrier (BBB). While methods of overcoming this barrier have been developed and employed with current treatment options, the majority are highly invasive and nonspecific, leading to severe neurotoxic side effects. A novel approach to address these issues is the development of therapeutics targeting receptor-mediated transport mechanisms on the BBB endothelial cell membranes. Using this approach, we intercalated doxorubicin (DOX) into a bifunctional aptamer targeting the transferrin receptor on the BBB and epithelial cell adhesion molecule (EpCAM) on metastatic cancer cells. The ability of the DOXloaded aptamer to transcytose the BBB and selectively deliver the payload to EpCAM-positive tumors was evaluated in an in vitro model and confirmed for the first time in vivo using the MDA-MB-231 breast cancer metastasis model (MDA-MB-231Br). We show that colocalized aptamer and DOX are clearly detectable within the brain lesions 75 min postadministration. Collectively, results from this study demonstrate that through intercalation of a cytotoxic drug into the bifunctional aptamer, a therapeutic delivery vehicle can be developed for specific targeting of EpCAM-positive brain metastases.

Purpose: CS-1008 (tigatuzumab; phase I/II), an antihuman death receptor 5 (DR5) agonist, induces apoptosis and has cytotoxic activity against human cancer cell lines. This study reports on the preclinical validation of 111In-labeled anti-DR5 humanized antibody CS-1008 as a diagnostic tool to study the DR5 occupancy in patients with cancer and establish dose ranges for receptor saturation kinetics in vivo.Experimental Design: CS-1008 was radiolabeled and characterized for DR5 binding and labeling efficiency on TRAIL-sensitive DR5-positive colorectal cancer cells (COLO 205 and WiDr). Pharmacokinetic and biodistribution studies were conducted in BALB/c nu/nu mice bearing COLO 205, WiDr, or DR5-negative CT26 colon tumors. Planar gamma camera imaging and computerized tomography (CT) images were obtained to study receptor occupancy in vivo.Results: Scatchard analysis showed high and specific binding affinity ( In-labeled CS-1008. Saturation of DR5 corresponded to maximal in vivo antitumor efficacy. Conclusions: Imaging of DR5 receptor occupancy in vivo correlates with tumor concentration and in vivo efficacy, and is a novel molecular imaging technique that can be used to determine receptor occupancy and effective dose levels of DR5 agonist antibodies in the clinic.

Subtype A2 of the erythropoietin-producing hepatocellular tyrosine kinase (EphA2) cell surface receptor is expressed in a range of epithelial cancers. This study evaluated the molecular imaging of EphA2 expression in vivo in mouse tumor models using SPECT/MR and PET/MR and a humanized anti-EphA2 antibody, DS-8895a. Methods: DS-8895a was labeled with 111 In, 125 I, and 89 Zr and assessed for radiochemical purity, immunoreactivity (Lindmo analysis), antigen-binding affinity (Scatchard analysis), and serum stability in vitro. In vivo biodistribution, imaging, and pharmacokinetic studies were performed with SPECT/MR and PET/MR. A dose-escalation study was also performed to determine EphA2 receptor saturability through tissue and imaging quantitative analysis. Results: All conjugates demonstrated good serum stability and specific binding to EphA2-expressing cells in vitro. In vivo biodistribution studies showed high uptake of 111 In-CHX-A″-DTPA-DS8895a and 89 Zr-Df-Bz-NCS-DS-8895a in EphA2-expressing xenograft models, with no specific uptake in normal tissues. In comparison, retention of 125 I-DS-8895a in tumors was lower because of internalization of the radioconjugate and dehalogenation. These results were confirmed by SPECT/MR and PET/MR. EphA2 receptor saturation was observed at the 30 mg/kg dose. Conclusion: Molecular imaging of tumor uptake of DS-8895a allows noninvasive measurement of EphA2 expression in tumors in vivo and determination of receptor saturation. 89 Zr-Df-Bz-NCS-DS-8895a is suited for human bioimaging trials on the basis of superior imaging characteristics and will inform DS-8895a dose assessment and patient response evaluation in clinical trials.

Purpose:The monoclonal antibody (mAb) 14C5 is a murine IgG1directed against a yet undefined molecule involved in cell substrate adhesion found on the surface of malignant breast cancer tissue. mAb 14C5 is able to inhibit cell substrate adhesion and invasion of breast cancer cells in vitro. In normal tissues as well as in the stroma surrounding in situ carcinomas of the breast, no expression of the antigen 14C5 occurs. The aim of this study was to investigate the in vitro and in vivo targeting properties of