Drug-resistant Triple Negative Breast Research Articles

Abstract LB030: SHR-A1921, a novel TROP-2 ADC with an optimized design and well-balanced profile between efficacy and safety

Abstract Trop-2 is a promising target for ADC therapy due to its high expression in many solid tumors. The approval of Trodelvy, a Trop-2 directed ADC, for the treatment of refractory or drug-resistant triple negative breast cancer (TNBC) demonstrated the therapeutic value of Trop-2-targeted ADC. However, a Boxed Warning for severe or life-threatening neutropenia and severe diarrhea suggests the safety of Trodelvy needs to be improved. Here, we presented a novel Trop2-directed ADC, SHR-A1921, consisting of a topoisomerase I inhibitor (Proprietary payload, SHR9265) conjugated to a proprietary IgG1 mAb via cleavable linkers. SHR-A1921 demonstrated several advantages over other Trop-2 directed ADCs in the field. SHR9265 is a novel exatecan derivative designed by Hengrui with a better liposolubility and cellular permeability. SHR-A1921 had a drug-to-antibody ratio (DAR) of 4. Compared with other Trop-2-targeted ADCs in the field, such as Trodelvy, TINA-SHR79711 (a molecule synthesized using the published structure of DS-1062), and SKB264, SHR-A1921 has considerable advantages as follows: (1) Stronger binding affinity to both human and rhesus macaque TROP-2 than TINA-SHR79711; (2) Improved plasma stability in plasma of different species presumably due to the proper steric hindrance which was purposely designed on the payload for reducing non-intended cleavage; (3) Stronger bystander cell killing effect presumably due to the increased lipophilicity of the payload vs. that of the payload in TINA-SHR79711; (4) Superior in vivo efficacy in a PSCC2 CDX Model (FaDu) with high Trop-2 expression (TGI 101% vs 53% [TINA-SHR79711] @ 1 mpk) and in an ovarian cancer CDX Model (SK-OV-3) with moderate Trop-2 expression (TGI 63% vs. 23% [TINA-SHR79711] @ 3 mpk; 87% vs. 16% [TINA-SHR79711] @ 10 mpk); (5) ≥ 2X longer half-life in patients# vs. SKB264 vs. IMMU-132, supporting more flexible dosing frequency; (6) Lower free toxin/ADC ratio# regarding PK exposure in patients compared with SKB264 (< 1% vs. 5-6%); (7) approximately linear pharmacokinetics profile in patients with T1/2 ranging from 2.5 to 4.5 days. In summary, SHR-A1921 is a novel anti-TROP2-targeted ADC with a high permeable payload and optimized DAR demonstrating great stability and high potency in both in vitro and in vivo studies. SHR-A1921 also showed compelling efficacy and good safety profile from 50+ subjects of Phase I clinical trial in China (NCT05154604). Pivotal phase III trial for NSCLC is planned in China. (Notes: 1. TINA-SHR7971 is a molecule that Hengrui synthesized using the published structure of DS-1062. 2. PSCC: pharyngeal squamous cell carcinoma. #. non-head-to-head comparison.) Citation Format: Ning He, Chunpeng Yang, Yang Yang, Zhendong Xue, Jianyan Xu, Linda Zhao, Jun Feng, Xin Ye, Zhe Zhang, Feng He. SHR-A1921, a novel TROP-2 ADC with an optimized design and well-balanced profile between efficacy and safety [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB030.

Tumor targeted combination therapeutic system for the effective treatment of drug resistant triple negative breast cancer

Breast cancer has become the malignant tumor with the largest incidence, especially the drug resistant triple negative breast cancer (TNBC). The combination therapeutic system can play a better role in resisting drug resistant TNBC. In this study, dopamine and tumor targeted folic acid modified dopamine were synthesized as carrier materials to construct melanin-like tumor targeted combination therapeutic system. The optimized nanoparticles of CPT/Fe@PDA-FA10 with efficient loading of camptothecin and iron was achieved, which showed tumor targeted delivery ability, pH sensitive controlled release, effective photothermal conversion performance and excellent anti-tumor efficacy in vitro and in vivo. CPT/Fe@PDA-FA10 plus laser could significantly kill the drug resistant tumor cells, inhibit the growth of the orthotopic drug resistant triple negative breast cancer through apoptosis/ferroptosis/photothermal treatment, and had no significant side effects on the main tissues and organs. This strategy provided a new idea for the construction and clinical application of triple-combination therapeutic system as effective treatment for drug resistant triple negative breast cancer.

PH-/Redox-Responsive Nanodroplet Combined with Ultrasound-Targeted Microbubble Destruction for the Targeted Treatment of Drug-Resistant Triple Negative Breast Cancer.

Multiple drug resistance (MDR) exists in divergent cancers including triple negative breast cancer (TNBC) and partly results in the resistance to many first-line anti-cancer agents, bringing a big challenge to TNBC management. To develop novel TNBC therapeutics, in our study, a hyaluronic acid (HA)-carboxymethyl chitosan (CMC) conjugate linked via a disulfide-bond (HA-SS-CMC, HSC) was synthesized to fabricate nanodroplets (NDs). The NDs encapsulating doxorubicin (DOX) and perfluorohexane (DOX-HSC-NDs) were prepared via a homogenization/emulsification strategy and exhibited not only high biocompatibility but also noticeable tumor cell targeting ability and dual pH/redox responsiveness. Besides, DOX-HSC-NDs can be used as a contrast-enhanced ultrasound imaging agent for specific tumor imaging. DOX-HSC-NDs in combination with ultrasound targeted microbubble destruction could improve intracellular drug aggregation and retention of MDR cells and work against multiple mechanisms of drug resistance through synergistic strategies, including up-regulating the reactive oxygen species (ROS) level, promoting apoptosis, and scavenging glutathione, while reducing the expression levels of P-glycoprotein and inhibiting the epithelial-mesenchymal transition. This combination strategy showed protective effects against TNBC in both MDA-MB-231/ADR cells and tumor-bearing mice. Our study for the first time developed and reported the ultrasound-augmented HSC-NDs as the DOX nanocarrier and provided scientific evidence to support the future application of DOX-HSC-NDs as a potential TNBC therapy.

Docosahexaenoic acid enrichment of tumor phospholipid membranes increases tumor necroptosis in mice bearing triple negative breast cancer patient-derived xenografts

Docosahexaenoic acid (DHA) reduces breast cancer tumor growth in preclinical models. To better understand how DHA amplifies the actions of docetaxel (TXT) chemotherapy, we examined the effects of two doses of dietary DHA on tumor size, membrane DHA content and necroptosis using a drug resistant triple negative breast cancer (TNBC) patient derived xenograft (PDX) model. Female NOD.Cb-PrkdcscidIl2rg mice bearing TNBC PDXs were randomized to one of three nutritionally complete diets (20% w/w fat): control (0% DHA), high DHA (3.8% HDHA), or low DHA (1.6% LDHA) with or without intraperitoneal injections of 5 mg/kg TXT, twice weekly for 6 weeks (n=8 per group). Tumors from mice fed either HDHA+TXT or LDHA+TXT were similar in size to each other, but were 36% and 32% smaller than tumors from mice fed control+TXT, respectively (P<.05). A dose effect of DHA incorporation was observed in plasma total phospholipids and in phosphatidylethanolamine and phosphatidylinositol. Both doses of DHA resulted in similarly increased necrotic tissue and decreased NFκB protein expression compared to control tumors, however only the HDHA+TXT had increased expression of necroptosis related proteins: RIPK1, RIPK3 and MLKL (P<.05). Increased MLKL was observed in the lipid raft portion of HDHA+TXT tumor extracts. This work confirms the efficacy of a combination therapy consisting of DHA supplementation and TXT chemotherapy using two doses of DHA as indicated by reduced tumor growth in a TNBC PDX model. Moreover, the results suggest that decreased growth may occur through increased DHA incorporation into tumor phospholipid membranes and necroptosis.

Adipose derived mesenchymal stem cell secretome formulation as a biotherapeutic to inhibit growth of drug resistant triple negative breast cancer

In the present study, a protocol was developed for processing of human adipose derived mesenchymal stem cell secretome formulation of varying concentration. Its molecular composition was evaluated, and its effectiveness in vitro using breast cancer cell lines, and in vivo in a nude mice breast cancer model was studied to determine its role in suppressing triple negative breast cancer in a dose dependent manner. Because the secretome could have value as an add-on therapy along with a current drug, the effectiveness of the secretome both in monotherapy and in combination therapy along with paclitaxel was evaluated. The results showed significant cell kill when exposed to the secretome above 20 mg/ml at which concentration there was no toxicity to normal cells. 70 mg/ml of SF showed 90 ± 10% apoptosis and significant decrease in CD44+/CD24−, MDR1+ and PDL-1+ cancer cells. In vivo, the tumor showed no growth after daily intra tumor injections at 50 mg/ml and 100 mg/ml doses whereas substantial tumor growth occurred after saline intra tumor injection. The study concludes that SF is a potential biotherapeutic for breast cancer and could be used initially as an add-on therapy to other standard of care to provide improved efficacy without other adverse effects.

Abstract 4108: The use of conditionally reprogrammed cells for high throughput screening for novel drug combinations to treat drug resistant triple negative breast cancers

Abstract Triple negative breast cancer (TNBC) is the most aggressive form of breast cancer, with prognosis tightly dependent on its responsiveness to cytotoxic chemotherapy. Indeed, overcoming chemoresistance is a major unmet need in this disease. Patient derived xenografts (PDXs) are now widely used in research since they faithfully represent the patient's tumor. However, testing novel drug combinations is a challenge in these models since it is time consuming and quite expensive to test each novel combination. The development of conditionally reprogrammed cells (CRCs) offers the opportunity to perform high throughput screens on clinically relevant models in a more timely and less expensive manner. To this end, we developed a 7 CRCs from PDXs of drug-resistant TNBC tumors. We characterized these CRCs at the molecular level and validated drug resistance to confirm they matched treatment response in both clinical and PDX tumors from which they were derived. These CRCs underwent high-throughput screens of both compound and shRNA libraries of genes targeted by FDA-approved drugs to identify novel drug combinations as well as genetic vulnerabilities that could re-sensitize these cells to carboplatin or paclitaxel chemotherapy. We found that drugs such as mitomycin C and oxfendazole were putative chemo-sensitizers while genes such as ATR and CDK2 were identified as novel genetic vulnerabilities. Treatment of these drug-resistant cells with combinations of carboplatin with mitomycin C or with an ATR inhibitor resulted in synergistic growth inhibition in proliferation and colony formation assays. We are further validating these combinations in organoid models derived from PDXs. These results have the potential to lead to novel therapeutic strategies against chemoresistant TNBCs. Citation Format: Adriana Aguilar-Mahecha, Catherine Chabot, Nancy Santos-Martinez, Cedric Darini, Midhet Hajira, Tim Kong, Genevieve Morin, Sidong Huang, Morag Park, Mark Basik. The use of conditionally reprogrammed cells for high throughput screening for novel drug combinations to treat drug resistant triple negative breast cancers [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4108.

Kinase Chemodiversity from the Arctic: The Breitfussins.

In this work, we demonstrate that the indole-oxazole-pyrrole framework of the breitfussin family of natural products is a promising scaffold for kinase inhibition. Six new halogenated natural products, breitfussin C-H (3 - 8) were isolated and characterized from the Arctic, marine hydrozoan Thuiaria breitfussi. The structures of two of the new natural products were also confirmed by total synthesis. Two of the breitfussins (3 and 4) were found to selectively inhibit the survival of several cancer cell lines, with the lowest IC50 value of 340 nM measured against the drug-resistant triple negative breast cancer cell line MDA-MB-468, while leaving the majority of the tested cell lines not or significantly less affected. When tested against panels of protein kinases, 3 gave IC50 and Kd values as low as 200 and 390 nM against the PIM1 and DRAK1 kinases, respectively. The activity was confirmed to be mediated through ATP competitive binding in the ATP binding pocket of the kinases. Furthermore, evaluation of potential off-target and toxicological effects, as well as relevant in vitro ADME parameters for 3 revealed that the breitfussin scaffold holds promise for the development of selective kinase inhibitors.

Role of docosahexaenoic acid in enhancement of docetaxel action in patient-derived breast cancer xenografts.

The objective of this study was to investigate if DHA dietary supplementation enhances the anticancer actions of docetaxel (TXT) in two different drug resistant triple negative breast cancer (TNBC) patient-derived xenografts (PDX)s. In two experiments, female NSG mice bearing TNBC PDXs were randomized to one of two nutritionally adequate diets (20% w/w): control (0% DHA), or DHA (3.9% w/w of total fat) and injected with 0 or 5mg/kg TXT, twice weekly for 6weeks (n = 8 per group). Treatment response was determined by significant differences in tumor weight, and apoptotic, proliferation and cell cycle markers at endpoint. Mice bearing MAXF574 xenografts fed DHA diet and treated with TXT had a 57% reduction in tumor weight compared to mice fed control diet (P < 0.004), a 64% reduction compared to control + TXT (P < 0.01) and a 34% reduction compared to DHA with no TXT (P < 0.04). DHA + TXT reduced MAXF401 xenografts growth compared to control and control + TXT (by 43% and 34%, respectively, P < 0.05). In both xenografts, DHA + TXT resulted in a higher expression of proapoptotic proteins Ripk1 and Bid, lower expression of proliferation marker Ki67 and anti-apoptotic proteins Bcl-2 and Parp, and a greater increase in cell cycle arrest as measured by decreased Survivin expression when compared to control + TXT mice (P < 0.05). This work is the first to confirm that DHA supplementation during chemotherapy treatment improves TXT action in two PDX models of TNBC. The results suggest that decreases in tumor size occurred via changes in apoptosis, cell proliferation, and cell cycle pathways.

CARP-1 functional mimetics are novel inhibitors of drug-resistant triple negative breast cancers.

Doxorubicin and Cisplatin are the frontline therapeutics for treatment of the triple negative breast cancers (TNBCs). Emergence of drug-resistance often contributes to failure of drugs and poor prognosis, and thus necessitates development of new and improved modalities to treat TNBCs. We generated and characterized chemotherapy-resistant TNBC cells following their culture in chronic presence of Doxorubicin or Cisplatin, and tested whether their viabilities were inhibited by a novel class of CARP- 1 functional mimetic (CFM) compounds. Analogs of parent compound CFM-4 were obtained through structure-activity based medicinal chemistry studies. CFM-4.16, a novel analog of CFM-4, caused superior inhibition of viability of TNBC cells when used in combination with doxorubicin. Doxorubicin and cisplatin inhibited viabilities of parental cells with GI50 dose of 0.02–0.1 μM and 1.65 μM, respectively. The GI50 dose of doxorubicin for doxorubicin-resistant TNBC cells was ≥ 10.0 μM. For Cisplatin-resistant cells, the GI50 dose of Cisplatin was ≥ 6–15.0 μM for MDA-MB-468 sublines and ≥ 150.0 μM for MDA-MB-231 sublines. CFM-4.16 inhibited viability of chemotherapy-resistant TNBC cells, in part by inhibiting oncogenic cMet activation and expression, stimulating CARP-1 expression, caspase-8 cleavage and apoptosis. CFM-4.16 pretreatment enhanced anti-TNBC efficacies of inhibitors of cMET (Tevatinib) or cSrc (Dasatinib). CFM-4.16 suppressed growth of resistant TNBC cells in soft agar as well as in three-dimensional suspension cultures derived from enriched, stem-like cells. Finally, a nanolipid formulation of CFM-4.16 in combination with doxorubicin had superior efficacy in inhibiting TNBC xenograft growth. Our findings collectively demonstrate therapeutic potential of CFM-4.16 for parental and drug-resistant TNBCs.

Nanoparticle-Mediated Mitochondrial Damage Induces Apoptosis in Cancer.

Detouring of conventional DNA damaging anticancer drugs into mitochondria to damage mitochondrial DNA is evolving as a promising strategy in chemotherapy. Inhibiting single target in mitochondria would eventually lead to the emergence of drug resistance. Moreover, targeting mitochondria selectively in cancer cells, keeping them intact in healthy cells, remains a major challenge. Herein, triphenylphosphine (TPP)-coated positively charged 131.6 nm spherical nanoparticles (NPs) comprised of α-tocopheryl succinate (TOS, inhibitor of complex II in electron transport chain) and obatoclax (Obt, inhibitor of Bcl-2) were engineered. The TOS-TPP-Obt-NPs entered into acidic lysosomes via macropinocytosis, followed by lysosomal escape and finally homed into mitochondria over a period of 24 h. Subsequently, these TOS-TPP-Obt-NPs triggered mitochondrial outer membrane permeabilization (MOMP) by inhibiting antiapoptotic Bcl-2, leading to Cytochrome C release. These TOS-TPP-Obt-NPs mediated mitochondrial damage induced cellular apoptosis through caspase-9 and caspase-3 cleavage to show improved efficacy in HeLa cells. Moreover, TOS-TPP-Obt-NPs induced MOMP in drug-resistant triple negative breast cancer cells (MDA-MB-231), leading to remarkable efficacy, compared to the combination of free drugs in higher drug concentrations. Results presented here clearly stimulate the usage of multiple drugs to perturb simultaneously diverse targets, selectively in mitochondria, as next-generation cancer therapeutics.

RIP1K and RIP3K provoked by shikonin induce cell cycle arrest in the triple negative breast cancer cell line, MDA-MB-468: necroptosis as a desperate programmed suicide pathway.

Resistance to cell death and reprogramming of metabolism are important in neoplastic cells. Increased resistance to apoptosis and recurrence of tumors are the major roadblocks to effective treatment of triple negative breast cancer. It has been thought that execution of necroptosis involves ROS generation and mitochondrial dysfunction in malignant cells. In this study, the effect of shikonin, an active substance from the dried root of Lithospermum erythrorhizon, on the induction of necroptosis or apoptosis, via RIP1K-RIP3K expressions has been examined in the triple negative breast cancer cell line. The expression levels of RIP1K and RIP3K, caspase-3 and caspase-8 activities, the levels of ROS, and mitochondrial membrane potential have been studied in the shikonin-treated MDA-MB-468 cell line. An increase in the ROS levels and a reduction in mitochondrial membrane potential have been observed in the shikonin-treated cells. Cell death has mainly occurred through necroptosis with a significant increase in the RIP1K and RIP3K expressions, and characteristic morphological changes have been observed. In the presence of Nec-1, caspase-3 mediating apoptosis has occurred in the shikonin-treated cells. The current findings have revealed that shikonin provoked mitochondrial ROS production in the triple negative breast cancer cell line, which works as a double-edged executioner's ax in the execution of necroptosis or apoptosis. The main route of cell death induced by shikonin is RIP1K-RIP3K-mediated necroptosis, but in the presence of Nec-1, apoptosis has prevailed. The present results shed a new light on the possible treatment of drug-resistant triple negative breast cancer.

Abstract B045: uPAR-targeted theranostic nanoparticles effectively decrease expression of IGF-1R and Ki67 in drug-resistant triple-negative breast cancer human xenograft

Abstract Background: Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype that affects about 20% of breast cancer patients and has a high incidence in young African American women. Currently the only therapeutic options for TNBC patients is chemotherapy, however, more than 60% of TNBC patients are highly resistant to chemotherapeutic treatment. The development of novel therapeutic approaches is essential to enable treatment of patients with chemo-resistant TNBC. Our lab focuses on the development of receptor-targeted theranostic nanoparticles. We have developed a class of urokinase plasminogen activator receptor (uPAR) targeted theranostic magnetic iron oxide nanoparticles (IONPs) carrying therapeutic agents that are clinically beneficial to TNBC patients, including DNA damaging agents, such as doxorubicin (Dox) or cisplatin (Cis). We are targeting uPAR because it is highly expressed in malignant cancers including aggressive breast cancer tissues and tumor stromal cells that are enriched in TNBC tissues. Methods: Tumor fragments from TNBC patients, obtained from a Phase II clinical trial that is ongoing at the Breast Cancer Clinic in the Winship Cancer Institute, were implanted in the mammary fat pad of SCID mice. The tumor xenografts grew to about 1 cm in diameter in 12 to 15 weeks. Tumor fragments were then implanted into the mammary fat pad and passaged through nude mice for testing the therapeutic efficacy of the uPAR-targeted nanoparticle-drugs. Histological analysis of post-chemotherapy TNBC and primary tumor xenograft tissues with or without uPAR-targeted IONP-Dox was conducted using immunohistochemistry and dual immunofluorescence techniques. Results: We have previously reported that the uPAR-targeted IONP-Dox causes tumor growth inhibition following systemic delivery. Using CD44 and uPAR as biomarkers we also reported histological analysis of post-chemotherapy TNBC and primary tumor xenograft tissues showed high levels of CD44+/CD24- tumor cells and up-regulation of uPAR. Primary TNBC xenografts treated with conventional Dox had increased levels of CD44+/CD24- cells and strong uPAR expression. Conversely, the tumor tissues from the uPAR-targeted IONP-Dox treated group showed decreased levels of CD44+/CD24- and uPAR positive cells. We have further investigated the biomarkers insulin-like growth factor 1 receptor (IGF-1R) and Ki67. IGF-1R has been shown to be overexpressed in more than 50% of TNBCs and may be associated with the drug-resistant TNBC phenotype, while Ki67 is a conventional biomarker for proliferation. We observed that uPAR-targeted IONP- Dox treatment decreased IGF-1R expression compared to the control group and the group treated with conventional Dox. We also observed that Ki67 expression was decreased in the uPAR-targeted IONP- Dox treatment group compared to control group and the group treated with conventional Dox. Conclusions: Results of our study demonstrated that uPAR-targeted theranostic IONPs selectively delivers therapeutic payloads of the chemotherapeutic drug Dox to inhibit the growth of uPAR positive tumor cells. It is likely that uPAR expressing tumor cells are an aggressive and potentially drug resistant cell population that overexpress breast cancer stem-like cell biomarker (CD44+/CD24-) as well as up-regulation of a growth factor receptor, IGF-1R. These results support further investigation of theranostic nanoparticles as an approach to overcome drug resistance in TNBC. Citation Format: Jasmine M. Miller-Kleinhenz, Hongyu Zhou, Weiping Qian, Ruth O'Regan, Amelia Zelnak, Toncred Styblo, Lily Yang. uPAR-targeted theranostic nanoparticles effectively decrease expression of IGF-1R and Ki67 in drug-resistant triple-negative breast cancer human xenograft. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr B045.

29P - Genomic Analysis of Drug Resistant Triple Negative Breast Cancers: A Translational Biopsy Study

Background: Triple negative breast cancers (TNBCs) are an aggressive subtype of breast cancers, associated with a marked genomic instability, and an especially poor prognosis if they are or become resistant to chemotherapy. There is little data about the mechanisms of resistance to chemotherapy in TNBCs. Methods: The Q-CROC-3 study involves the collection of pre and post-chemotherapy biopsies from patients with TNBC in the neoadjuvant and metastatic settings. In parallel, we generated paclitaxel (PTX)-resistant TNBC cell lines. Molecular profiling including whole exome sequencing, array comparative genomic hybridization (CGH), microRNA and gene expression profiling is being performed on resistant and parental tumors and cell lines. The innovative approach in our analytic strategy is the genomic analysis of tumor subpopulations flow sorted by ploidy. This approach provides a deeper view of tumor heterogeneity and also enables the removal of contaminating stromal cells prior to genomics analysis. Results: We have developed standard operating procedures for tumor collection and processing adapted to downstream analyses. We emphasize pathological evaluation and measurement of tumor cellularity for each biopsy. Of the 41 patients recruited so far, pre-chemo and post- chemo specimens are available for 21 patients. Of these, 7 did not have enough tumor content in the biopsies collected and 9 pairs are available for analysis. Using flow-sorted array CGH, we could obtain aneuploid sub-fractions from snap frozen biopsies with as little as 17% tumor content. We observed relative increases in tumor sub-fractions after chemotherapy and identified novel copy number alterations (CNAs) in the post-chemotherapy tumors, not detectable by array CGH of the unsorted tumor sample. In parallel, we identified known molecular factors of resistance to PTX in TNBC cell lines, as well as novel mutations in DNA repair genes. Conclusion: Methods for biopsy collection and processing need to be adapted to downstream analyses. With flow sorting aCGH, it is possible to detect CNAs previously undetectable in unsorted specimens. These studies will identify molecular factors of chemotherapy resistance and novel therapeutic targets in TNBCs. Disclosure: All authors have declared no conflicts of interest.

Theranostic Nanoparticles for Targeting Drug Resistant Triple Negative Breast Cancer

Triple negative breast cancer (TNBC) is the most aggressive breast cancer subtype and more than 60% of TNBCs are resistant to chemotherapy. To effectively treat chemoresistant TNBC we have developed uPAR‐targeted magnetic iron oxide nanoparticles (IONPs) carrying therapeutic agents. uPAR is highly expressed in aggressive and invasive breast cancer tissues. Our goal is to determine whether uPAR–targeted theranostic IONPs selectively deliver drugs into CD44+/CD24‐cancer stem cells (CSC) and enhance therapeutic effects in those cells. Using an orthotopic primary human TNBC xenograft model derived from surgically resected drug resistant TNBC tissues in nude mice, we have demonstrated the effect of tumor growth inhibition following systemic delivery of the targeted IONPs. Histological analysis of post‐chemotherapy TNBC and primary tumor xenograft tissues with or without uPAR‐targeted IONP‐Doxorubicin (Dox) treatment shows high expression levels of CD44 and uPAR in primary TNBC tissues and human tumor xenografts. Primary TNBC xenografts treated with conventional Dox have increased levels of CD44 and uPAR. Conversely, the tumor tissues from the uPAR‐targeted IONP‐Dox treated group show decreased levels of CD44 and uPAR expression. These results support further investigation of theranostic nanoparticles as an approach to overcome drug resistance in TNBC.Research supported by NIH grant R01 CA154129A‐01

Abstract P6-11-12: Nanoparticle-enhanced chemotherapeutics delivery in drug-resistant triple-negative breast cancer

Abstract Chemotherapeutics delivery is generally poor in tumors characterized by rapid perfusion and low blood volume fraction. Systemically administered nanoparticles can be engineered to overcome abnormal flow conditions to act as intravascular drug depots for the localized delivery of high concentrations of chemotherapeutics. The feasibility of this approach was first demonstrated using melanoma, and is now being further investigated using well-characterized human triple-negative breast cancer biopsies implanted into mice. Intravital microscopy studies of human cancer-in-mice selected for differing vascular morphologies have yielded intriguing preliminary data regarding the role of tumor vascularity in drug and particle delivery. The first-pass perfusion of a 40kDa dextran tracer revealed that BCM-2665 tumors are perfused ∼6x more rapidly than BCM-4195 tumors (11.3 ± 2.3s vs. 67.6 ± 11.0) and contain ∼30% lower volume fraction of blood (0.046 ± 0.011 vs. 0.062 ± 0.015). Interestingly, flow parameters that adversely impact drug accumulation appear to favor plateloid particle accumulation. BCM-2665 xenografts receiving an i.v. injection of 1000×400 nm particles show ∼10x more particle accumulation than BCM-4195 tumors (24.8 ± 3.2 × 103/mm3 vs. 3.5 ± 0.4 × 103/mm3). The ability of these therapeutic particles to reach tumors appears to be primarily driven by flow-related parameters, which we characterize using a combination of intravital microscopy, computed tomography, and mathematical modeling. The total number of particles accumulated within a given tumor appears to be largely driven by the number of particles entering the tumor, since ∼65–70% of entering plateloid particles are retained by the tumor vasculature. This suggests that cytotoxic intravascular drug depots may be a promising strategy for increasing the efficiency of chemotherapeutics delivery to drug-resistant tumors and is the premise of ongoing therapeutic response studies. Clearly if more drugs can be delivered to the tumors, better outcomes can be expected for the patients. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-11-12.