Abstract P3-12-13: Radiation enhancement with cysteine coated platinum nanoparticles

Background: Radiation is the current choice treatment for non-operable metastatic breast-brain cancer. When cancer lesions are located in sensitive areas like the brain or have excessive amounts of metastatic sites, radiation usually proves to be a more viable option than excision. Ionizing (X-ray and gamma) radiation is non-selective and affects all the tissue it penetrates. In order to concentrate the dose on tumors, high energy radiation from multiple directions is typically used, reaching the highest dose where the radiation crosses. This type of multiple angle treatment minimizes the dose to normal tissue by increasing overall normal tissue irradiation. The objective is to achieve sufficient radiation in the tumor tissue to cause the DNA strands to break and to disrupt the reproduction and maintenance of cancer cells while keeping the damage to normal tissue in a reasonable range for tissue preservation.

Metal nanoparticles have shown promising results for reinforcing the radiation dose effect. High atomic number (Z) elements absorb a greater amount of radiation because the higher density raises the probability of interaction. The metal nanoparticles interact with the energy of the ionizing radiation by either scattering or absorbing, or accumulating the energy, thus increasing the number of DNA strand breaks in the nucleus of cells.

Methods: Four breast cancer cell lines (BT-474, MDA-231, BT-549 and MCF-7) were incubated with 1-2 nm platinum nanoparticles (0-1000 μg/mL) produced with a cysteine coating. 24 hours later cells were exposed to 2 Gy radiation with a C-arm (Toshiba Infinix VF-i/SP) using 125 KVP to deliver a spectrum of KeV low energy X-rays. After 24 hours the cells were washed and analyzed using a bioluminescence assay to assess cell proliferation based on ATP production.

Results: Of the four cell lines tested the BT-474 and BT-549 demonstrated limited reduction in cell proliferation at up to the highest treatment concentration 1000 μg/mL with no radiation exposure. As a result of the limited toxicity of the platinum nanoparticles the effect from increased radiation can be more readily observe when 2 Gy radiation is added resulting a in platinum nanoparticle dose dependent decrease in proliferation in the BT-474 cell line.

Nanoparticle Toxicity Concentration of Platinum Nanoparticles (μ/mL) 02505007501000MDA-2311.000±0.0050.995±0.0120.974±0.0130.979±0.0140.777±0.014BT-5491.000±0.0131.003±0.0091.003±0.0170.969±0.0170.894±0.009MCF-71.000±0.0140.960±0.0150.927±0.0220.851±0.0220.769±0.032BT-4741.000±0.0240.961±0.0290.957±0.0330.965±0.0630.985±0.065Table 1: Indexed values for cell proliferation for the BT-474 cell

Radiation Toxicity Concentration of Platinum Nanoparticles (μ/mL) 02505007501000*0 Gy1.000±0.0240.961±0.0290.957±0.0330.965±0.0630.985±0.0652 Gy1.027±0.0380.966±0.0230.908±0.0340.870±0.0310.799±0.037Table 2: Indexed values for cell proliferation for the BT-474 cell line 0 and 2 Gy radiation doses, 6 averages. * Student T-TEST P<0.05

Conclusions: At moderate doses of low energy radiation, a reduction in cell proliferation can be detected. This data supports follow-up experiments to add a targeting protein to facilitate uptake by cancer cells based on cell receptor expression. Experiments are current being done to utilize the HER2+ cell receptor upregulation to increase internalization of the particles to achieve a greater effect.

Citation Format: Wagner S, Yue Y, Cui X, Zhang G, Bingchen H, Li D, Medina-Kauwe L. Radiation enhancement with cysteine coated platinum nanoparticles. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-12-13.

Abstract P6-17-05: A corrole nanobiologic crosses the blood-brain-barrier and recognizes triple negative breast cancer: Implications for targeting brain metastases

Patients with breast cancer metastases to the brain on average survive less than one year. These tumors tend to be resistant to current therapies, and the majority of targeted therapeutics are unable to breach the blood brain barrier (BBB) to reach these tumors, thus improved alternatives are urgently needed.

Elevated cell surface levels of the human epidermal growth factor receptor subunit 3 (HER3) is associated with metastatic breast tumors, including those that spread to the brain. Elevated HER3 is also associated with resistance to a number of targeted therapies currently used in the clinic, including inhibitors of EGFR (lapatinib), HER2 (lapatinib, trastuzumab, T-DM1), HER2-3 (pertuzumab), and combination therapy.

Whereas a number of targeted therapies are currently used to combat peripheral breast tumors, the delivery of these molecules to brain metastases is limited by the blood brain barrier (BBB). This is exemplified by HER2+ breast tumors that metastasize to the brain: these tumors, while targetable outside of the central nervous system (CNS) by HER2 antibodies such as trastuzumab, are unreachable by these same antibodies because the HER2 subunit, though present on the brain endothelium, does not mediate antibody transcytosis across the blood vessel wall.

HER3, on the other hand, undergoes rapid transcytosis across the brain endothelium upon ligand binding, which normally occurs to mediate the delivery of neuregulin growth factors for neural growth and maintenance. We have developed a self-assembling nanobiological particle, HerMn, which uses HER3 as a portal for targeted entry of toxic molecules into tumor cells.

HerMn is a 10-20 nm diameter serum-stable particle comprised of a HER3-targeted cell penetration protein non-covalently assembled with a sulfonated manganese(III) corrole (S2Mn or Mn-corrole). Tumor-targeted toxicity by HerMn occurs by mitochondria membrane disruption and superoxide-mediated damage to the cytoskeleton. HerMn can also elicit tumor-selective detection by magnetic resonance imaging (MRI) due to the paramagnetic property of the corrole. HerMn distributes to the brain after systemic injection in mice, in addition to showing preferential homing and toxicity to subcutaneous tumors expressing the HER2-3 dimer. Interestingly, the Mn corrole is known to exhibit neuroprotective effects due to its antioxidant activity on normal tissue. Consistent with this, we have found that HerMn supports human cardiac cell survival ex vivo. Our studies interrogating the therapeutic potential of HerMn suggest that this nanobiologic bears the capacity for targeting toxicity to brain-metastatic breast tumors while sparing off-target tissue due to both its targeting capacity and ability to provide beneficial protective effects to normal tissue such as the brain and heart.

Citation Format: Medina-Kauwe L, Sims J, Taguiam M, Hanson C, Alonso-Valenteen F, Cui X, Wagner S, Sorasaenee K, Moats R, Marban E, Chung A, Gray H, Gross Z, Giuliano A. A corrole nanobiologic crosses the blood-brain-barrier and recognizes triple negative breast cancer: Implications for targeting brain metastases. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-17-05.

Abstract P6-13-10: Therapeutic efficacy of HER3-targeted nanobiologics on resistant tumors

Elevated cell surface levels of the human epidermal growth factor receptor subunit 3 (HER3) are associated with resistance to a number of signal-blocking breast cancer treatments, including inhibitors of EGF-R (lapatinib), HER2 (lapatinib, trastuzumab, T-DM1), HER2-3 (pertuzumab), and combination therapy. Additionally, HER3 elevation has been identified on "untarget-able" tumors such as triple-negative breast cancer (TNBC), including TNBC with acquired resistance to EGF-R inhibition. Patients with such refractory tumors currently have limited treatment options and a poor prognosis. Moreover, as up to 70% of cases resist or acquire resistance to signal-blocking therapies, an alternative approach addressing this important clinical problem has the potential for significant clinical impact.

We have developed a protein construct, HerPBK10, which self-assembles with a variety of payloads (including nucleic acids, chemotherapy agents, and imaging agents) and uses HER3 as a portal for targeted entry into cells. In contrast to receptor-targeted antibodies and tyrosine kinase inhibitors currently used in the clinic, HerPBK10 circumvents the need to modulate signaling by inducing rapid entry of toxic molecules into tumor cells through receptor-mediated endocytosis and membrane penetration.

We have previously shown that nanobiological particles formed between HerPBK10 and therapeutic payloads can elicit targeted toxicity to HER2+ tumors due to the prevalence of HER2-3 heterodimers on the tumor cell surface, while sparing heart and liver tissue. The particles that form (20-40 nm dia.) exhibit stability in serum and no detectable immunogenicity. Here we show that such particles resolve breast tumor cells with acquired resistance to HER2 and/or EGFR inhibitors in contrast to trastuzumab, pertuzumab, and combination treatment. Additionally, therapeutic efficacy is augmented on resistant over parental tumor cells, due in part to the elevated HER3 expression associated with resistance to these inhibitors. Our studies in preclinical models show that these nanoparticles ablate the growth of tumors with both acquired and pre-existing resistance to trastuzumab. Moreover, we have found that signal-inhibitors currently used in the clinic, such as trastuzumab, effectively augment the efficacy of our nanobiologic on both naïve and inherently-resistant breast tumor cells, in part through induced elevation of HER3. Thus, current targeted molecules such as trastuzumab or lapatinib may act as adjuvants to enhance tumor cell-sensitivity to HerPBK10-particles. Such an approach may address the tumor-heterogeneity associated with resistance, and corner tumors for attack by our particles.

Citation Format: Medina-Kauwe L, Sims J, Taguiam M, Hanson C, Alonso-Valenteen F, Cui X, Chung A, Gray H, Gross Z, Giuliano A. Therapeutic efficacy of HER3-targeted nanobiologics on resistant tumors. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-13-10.

gamma-Aminobutyric acid (GABA) metabolism in mammalian neural and nonneural tissues

4-Aminobutyric acid (GABA), a major inhibitory neurotransmitter of mammalian central nervous system, is found in a wide range of organisms, from prokaryotes to vertebrates. GABA is widely distributed in nonneural tissue including peripheral nervous and endocrine systems. GABA acts on GABAA and GABAB receptors. GABAA receptors are ligand-gated chloride channels modulated by a variety of drugs. GABAB receptors are essentially presynaptic, usually coupled to potassium or calcium channels, and they function via a GTP binding protein. In neural and nonneural tissues, GABA is metabolized by three enzymes--glutamic acid decarboxylase (GAD), which produces GABA from glutamic acid, and the catabolic enzymes GABA-transaminase (GABA-T) and succinic semialdehyde dehydrogenase (SSADH). Production of succinic acid by SSADH allows entry of the GABA carbon skeleton into the tricarboxylic acid cycle. Alternate sources of GABA include putrescine, spermine, spermidine and ornithine, which produce GABA via deamination and decarboxylation reactions, while L-glutamine is an additional source of glutamic acid via deamination. GAD from mammalian brain occurs in two molecular forms, GAD65 and GAD67 (referring to subunit relative molecular weight (Mr) in kilodaltons). These different forms of GAD are the product of different genes, differing in nucleotide sequence, immunoreactivity and subcellular localization. The presence and characteristics of GAD have been investigated in a wide variety of nonneural tissues including liver, kidney, pancreas, testis, ova, oviduct, adrenal, sympathetic ganglia, gastrointestinal tract and circulating erythrocytes. In some tissues, one form (GAD65 or GAD67) predominates. GABA-T has been located in most of the same tissues, primarily through histochemical and/or immunochemical methods; GABA-T is also present in a variety of circulating cells, including platelets and lymphocytes. SSADH, the final enzyme GABA catabolism, has been detected in some of the tissues in which GAD and GABA-T have been identified, although the presence of this enzyme has not been in mammalian pancreas, ova, oviduct, testis or sympathetic ganglia.