Phase I study of combined alpha interferon, alpha difluoromethylornithine (DFMO), and doxorubicin in advanced malignancy

Supramolecular trap for catching polyamines in cells as an anti-tumor strategy

Polyamines are essential for the growth of eukaryotic cells and can be dysregulated in tumors. Here we describe a strategy to deplete polyamines through host-guest encapsulation using a peptide-pillar[5]arene conjugate (P1P5A, P1 = RGDSK(N₃)EEEE) as a supramolecular trap. The RGD in the peptide sequence allows the molecule to bind to integrin α_vβ₃-overexpressing tumor cells. The negative charged glutamic acid residues enhance the inclusion affinities between the pillar[5]arene and cationic polyamines via electrostatic interactions and facilitate the solubility of the conjugate in aqueous media. The trap P1P5A efficiently encapsulates polyamines with association constants of 10⁵-10⁶ M^-1. We show that P1P5A has a wide spectrum of antitumor activities, and induces apoptosis via affecting the polyamine biosynthetic pathway. Experiments in vivo show that P1P5A effectively inhibits the growth of breast adenocarcinoma xenografts in female nude mice. This work reveals an approach for suppressing tumor growth by using supramolecular macrocycles to trap polyamines in tumor cells.

Herbacetin Is a Novel Allosteric Inhibitor of Ornithine Decarboxylase with Antitumor Activity

Ornithine decarboxylase (ODC) is a rate-limiting enzyme in the first step of polyamine biosynthesis that is associated with cell growth and tumor formation. Existing catalytic inhibitors of ODC have lacked efficacy in clinical testing or displayed unacceptable toxicity. In this study, we report the identification of an effective and nontoxic allosteric inhibitor of ODC. Using computer docking simulation and an in vitro ODC enzyme assay, we identified herbacetin, a natural compound found in flax and other plants, as a novel ODC inhibitor. Mechanistic investigations defined aspartate 44 in ODC as critical for binding. Herbacetin exhibited potent anticancer activity in colon cancer cell lines expressing high levels of ODC. Intraperitoneal or oral administration of herbacetin effectively suppressed HCT116 xenograft tumor growth and also reduced the number and size of polyps in a mouse model of APC-driven colon cancer (ApcMin/+). Unlike the well-established ODC inhibitor DFMO, herbacetin treatment was not associated with hearing loss. Taken together, our findings defined the natural product herbacetin as an allosteric inhibitor of ODC with chemopreventive and antitumor activity in preclinical models of colon cancer, prompting its further investigation in clinical trials.

Polyamines metabolism and breast cancer: state of the art and perspectives

Breast cancer (BC) is a common disease that generally occurs in women over the age of 50, and the risk is especially high for women over 60 years of age. One of the major BC therapeutic problems is that tumors initially responsive to chemotherapeutic approaches can progress to more aggressive forms poorly responsive to therapies. Polyamines (PAs) are small polycationic alkylamines, naturally occurring and essential for normal cell growth and development in eukaryotes. The intracellular concentration of PA is maintained within strongly controlled contents, while a dysregulation occurs in BC cells. Polyamines facilitate the interactions of transcription factors, such as estrogen receptors with their specific response element, and are involved in the proliferation of ER-negative and highly invasive BC tumor cells. Since PA metabolism has a critical role in cell death and proliferation, it represents a potential target for intervention in BC. The goal of this study was to perform a literature search reviewing the association between PA metabolism and BC, and the current evidence supporting the BC treatment targeting PA metabolism. We here describe in vitro and in vivo models, as well as the clinical trials that have been utilized to unveil the relationship between PA metabolism and BC. Polyamine pathway is still an important target for the development of BC chemotherapy via enzyme inhibitors. Furthermore, a recent promising strategy in breast anticancer therapy is to exploit the self-regulatory nature of PA metabolism using PA analogs to affect PA homeostasis. Nowadays, antineoplastic compounds targeting the PA pathway with novel mechanisms are of great interest and high social impact for BC chemotherapy.

Targeting polyamine metabolism and function in cancer and other hyperproliferative diseases

The polyamines spermidine and spermine and their diamine precursor putrescine are naturally occurring, polycationic alkylamines that are essential for eukaryotic cell growth. The requirement for and the metabolism of polyamines are frequently dysregulated in cancer and other hyperproliferative diseases, thus making polyamine function and metabolism attractive targets for therapeutic intervention. Recent advances in our understanding of polyamine function, metabolic regulation, and differences between normal cells and tumour cells with respect to polyamine biology, have reinforced the interest in this target-rich pathway for drug development.

Phase II trial of recombinant interferon-alpha-2a and eflornithine in patients with recurrent glioma

Interferons alpha and beta have been reported to cause tumor regression in a small proportion of patients with recurrent glioma. Eflornithine, an irreversible inhibitor of ornithine decarboxylase, reduces cellular polyamine levels and has also been reported to cause tumor regression in patients with recurrent anaplastic astrocytoma and glioblastoma multiforme. In vitro evidence suggests that interferon and eflornithine are synergistic. In this phase II trial, we investigated the combination of recombinant alpha interferon (36 x 10(6) units/m2 subcutaneously days 3 to 7) and eflornithine (2.25 g/m2 QID PO days 1 to 7) repeated every 28 days. All 29 patients entered in the study were evaluable for toxicity and efficacy. Toxicity consisted primarily of fever, chills, myalgia, weakness and fatigue as well as cortical dysfunction including somnolence, confusion, and exacerbation of underlying neurologic deficits. One patient died from cerebral herniation attributable to interferon. None of the patients experienced objective tumor regression. Seven patients (24%) were stable for more than six months, but the disease stability could also be explained by indolent underlying disease or inability to distinguish recurrent tumor from delayed radiation effects. Intermittent high-dose recombinant interferon alpha plus eflornithine demonstrated no definite antitumor effects in this trial.