Highly dynamic mitotic-spindle microtubules are among the most successful targets for anticancer therapy. Microtubule-targeted drugs, including paclitaxel and Vinca alkaloids, were previously considered to work primarily by increasing or decreasing the cellular microtubule mass. Although these effects might have a role in their chemotherapeutic actions, we now know that at lower concentrations, microtubule-targeted drugs can suppress microtubule dynamics without changing microtubule mass; this action leads to mitotic block and apoptosis. In addition to the expanding array of chemically diverse antimitotic agents, some microtubule-targeted drugs can act as vascular-targeting agents, rapidly depolymerizing microtubules of newly formed vasculature to shut down the blood supply to tumours.

Microtubules as a target for anticancer drugs.

Angiogenesis is fundamental to reproduction, development, and repair. All these processes depend on the tightly regulated growth of blood vessels that can “turn on” and “turn off” within a brief period. When blood vessels grow unabated, angiogenesis becomes pathologic and sustains the progression of many neoplastic and non-neoplastic diseases. The realization that tumor growth requires new blood vessels and the identification of chemical factors that mediate angiogenesis have broadened our understanding of pathologic processes and opened new avenues to the diagnosis and treatment of these diseases. Tumor hypervascularity was initially thought to reflect inflammatory vasodilation of preexisting host vessels, a . . .

Seminars in Medicine of the Beth Israel Hospital, Boston. Clinical applications of research on angiogenesis.

Angiogenesis is a key process in tumor growth and metastasis and is a major independent prognostic factor in breast cancer A range of cytokines stimulate the tumor neovasculature, and tumor-associated macrophages have been shown recently to produce several important angiogenic factors We have quantified macrophage infiltration using Chalkley count morphometry in a series of invasive breast carcinomas to investigate the relationship between tumor-associated macrophage infiltration and tumor angiogenesis, and prognosis There was a significant positive correlation between high vascular grade and increased macrophage index (P = 003), and a strong relationship was observed between increased macrophage counts and reduced relapse-free survival (P = 0006) and reduced overall survival (P = 0004) as an independent prognostic variable These data indicate a role for macrophages in angiogenesis and prognosis in breast cancer and that this cell type may represent an important target for immunoinhibitory therapy in breast cancer

/pdf/association-of-macrophage-infiltration-with-angiogenesis-and-4b4txqs4ov.pdf

Association of Macrophage Infiltration with Angiogenesis and Prognosis in Invasive Breast Carcinoma

A gene from human chromosome 11p112 was isolated and was shown to suppress metastasis when introduced into rat AT61 prostate cancer cells Expression of this gene, designated KAI1, was reduced in human cell lines derived from metastatic prostate tumors KAI1 specifies a protein of 267 amino acids, with four hydrophobic and presumably transmembrane domains and one large extracellular hydrophilic domain with three potential N-glycosylation sites KAI1 is evolutionarily conserved, is expressed in many human tissues, and encodes a member of a structurally distinct family of leukocyte surface glycoproteins Decreased expression of this gene may be involved in the malignant progression of prostate and other cancers

/pdf/kai1-a-metastasis-suppressor-gene-for-prostate-cancer-on-5314py54d2.pdf

KAI1, a metastasis suppressor gene for prostate cancer on human chromosome 11p11.2.

Selective induction of vascular damage within tumors represents an emerging approach to cancer treatment Histological studies have shown that several tubulin-binding agents can induce vascular damage within tumors but only at doses approximating the maximum tolerated dose, which has limited their clinical applicability In this study, we show that the combretastatin A-4 prodrug induces vascular shutdown within tumors at doses less than one-tenth of the maximum tolerated dose In vitro studies indicate that a short drug exposure results in profound long-term antiproliferative/cytotoxic effects against proliferating endothelial cells but not cells that are quiescent prior to and during drug exposure Vascular shutdown, within experimental and human breast cancer models in vivo following systemic drug administration, was demonstrated with a reduction in functional vascular volume of 93% at 6 h following drug administration and persisted over the next 12 h, with corresponding histology consistent with hemorrhagic necrosis resulting from vascular damage These actions against tumor vasculature and the broad therapeutic window demonstrate the clinical potential of these drugs and warrant further study to elucidate the mechanisms responsible for the antivascular effects of combretastatin A-4

https://cancerres.aacrjournals.org/content/canres/57/10/1829.full.pdf

Combretastatin A-4, an agent that displays potent and selective toxicity toward tumor vasculature

The effect of estramustine [estradiol 3-N-bis(2-chloroethyl)carbamate] on the human prostatic tumor cell line 1013L was investigated. Cell proliferation experiments revealed that estramustine cytotoxicity varied during the different phases of cell growth. Maximum cell killing was found in early log phase, but cell death also occurred in the stationary phase. Mitotic arrest was found at cytotoxic concentrations throughout the log phase. Subcellular distribution studies showed that the cellular uptake of estramustine increased throughout the log phase and remained steady during the stationary phase. Nuclear uptake in contrast was similar in all phases, whereas a preferential binding to the nuclear protein matrix was found to increase throughout the log phase and even during the stationary phase of growth. This implicates the nuclear protein matrix as a target for estramustine cytotoxicity.

Nuclear protein matrix as a target for estramustine‐induced cell death

The present study was carried out with the 10 known or suspected spindle poisons of the Commission of the European Communities program to study aneuploidy induction. We have investigated these substance of the assembly of isolated bovine microtubules at 10, 100 and 1000 μM and studied morphology by electron microscopy. The substances could be grouped into two categories, strong and weak inhibitors. Colchicine, vinblastine and thiomerosal were strong inhibitors; cadmium chloride, thiabendazole, chloral hydrate, hydroquinone, diazepam and econazole were weak inhibitors, The latter three causing aberrant forms visible on electron microscopy. Pyrimethamine did not inhibit the assembly of microtubules, but produced aberrant forms.

Effects of potential aneuploidy inducing agents on microtubule assembly in vitro

: Caffeine, caffeine derivatives and chromosomal aberrations IV. Synergism between Mitomycin Cand caffeine in Chinese hamster cells

Malignant cells possess a high degree of proteolytic activity in which the plasminogen activator system plays an important role. An increased expression of urokinase type plasminogen activator (uPA) is of significance for degradation of the extracellular tumor matrix, facilitating invasiveness and growth. Inhibition of the active site of uPA makes it possible to evaluate the significance of uPA in tumor growth. We report here experiments on a uPA-producing human prostate xenograft (DU 145) using a competitive inhibitor of uPA, p-aminobenzamidine. In vitro experiments with DU 145 cells showed that p-aminobenzamidine caused a dose-dependent inhibition of uPA activity. DU 145 cells were inoculated s.c. in SCID mice and, once tumors were established, treatment with p-aminobenzamidine added to drinking water was started and lasted for 23 days. Mice receiving 250 mg/kg/day of p-aminobenzamidine showed a clear decrease in tumor-growth rate compared to the non-treated mice, resulting in 64% lower final tumor weight. In addition, uPA-antigen levels in the membrane fractions of DU 145 tumors from p-aminobenzamidine-treated mice were found to be decreased by 59%. We also show that p-aminobenzamidine has an anti-proliferative effect in cell culture at low cell number, correlating with a dose-dependent decrease in uPA production. In conclusion, we show that a low-molecular-weight uPA-inhibitor, p-aminobenzamidine, has a growth-inhibitory effect on a solid uPA-producing tumor.

Beryl Hartley-Asp

Papers

Nuclear protein matrix as a target for estramustine‐induced cell death

Effects of potential aneuploidy inducing agents on microtubule assembly in vitro

: Caffeine, caffeine derivatives and chromosomal aberrations IV. Synergism between Mitomycin Cand caffeine in Chinese hamster cells

The urokinase inhibitor p-aminobenzamidine inhibits growth of a human prostate tumor in SCID mice.

Estramustine-Induced Mitotic Arrest in Two Human Prostatic Carcinoma Cell Lines DU 145 and PC-3