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

To investigate the mechanism of action of the antineoplastic drug estramustine, we compared its effects on human prostate cancer cells with those of vinblastine At their respective concentrations that result in 50% inhibition of clonogenic growth, both drugs caused an accumulation of cells blocked at mitosis and similar dose- and time-dependent depolymerization of interphase microtubules Also, colcemid-resistant and colcemid-hypersensitive Chinese hamster ovary cells with tubulin mutations were collaterally cross-resistant or -sensitive to estramustine Thus, the cytotoxicity of estramustine is due to its microtubule depolymerization properties This could be caused by interaction with tubulin and/or with microtubule-associated proteins (MAPs) Previous investigations have shown that high concentrations of estramustine phosphate can inhibit microtubule polymerization in vitro by binding to MAPs However, estramustine phosphate is the clinical prodrug to estramustine, the intracellular active compound In this study, we investigated the effects of estramustine on the binding of MAPs to taxol-stabilized microtubulesin vivo In contrast to previous reports, no effect of estramustine on the binding of MAPs to microtubules was found Furthermore, we found that polymerization of purified tubulin could be inhibited by estramustine in vitro Taken together, these results demonstrate that estramustine causes depolymerization of microtubules by direct interaction with tubulin The costs of publication of this article were defrayed in part by the payment of page charges This article must therefore be hereby marked advertisement in accordance with 18 USC Section 1734 solely to indicate this fact

https://cancerres.aacrjournals.org/content/canres/53/19/4573.full.pdf

Estramustine depolymerizes microtubules by binding to tubulin

Linomide ( N -phenylmethyl-1,2-dihydro-4-hydroxyl-1-methyl-2-oxoquinoline-3-carboxamide) has a reproducible in vivo antitumor effect against a series of both androgen responsive and independent Dunning R-3327 rat prostatic cancers. This antitumor effect of linomide is host mediated. One possible mechanism involving the host is that linomide has antiangiogenic activity. An indication that linomide treatment has antiangiogenic activity is the observation that prostatic cancers from linomide treated rats have more focal necrosis than sized matched tumors from untreated rats. 

To directly test if linomide has antiangiogenic activity, a newly developed Matrigel based quantitative in vivo angiogenic assay was used. These experiments demonstrated that linomide has dose dependent, antiangiogenic activity in vivo in the rat. Additional studies demonstrated that due to its antiangiogenic activity, linomide treatment of rats bearing prostate cancers resulted in a more than 40% decrease in tumor blood flow. Blood flow to a variety of non-tumor bearing organs was not decreased suggesting that linomide selectively inhibits angiogenesis and does not induce loss of established blood vessels. Using as a model the response of human umbilical vein endothelial cells to linomide treatment in a variety of in vitro assays, linomide was demonstrated to have cytostatic but not cytotoxic effect on human umbilical vein endothelial cells at a medium concentration of ≥100 µg/ml. In addition, both endothelial cell chemotactic migration and invasion are steps in angiogenesis inhibited by linomide treatment.

https://cancerres.aacrjournals.org/content/canres/53/8/1833.full.pdf

Antiangiogenic Effects of the Quinoline-3-Carboxamide Linomide

In growth proliferation experiments on two human prostatic carcinoma cell lines, DU 145 cells were found to be more sensitive to the cytotoxic effect of estramustine and nor-nitrogen mustard than PC-3 cells. Estramustine was, however, much more cytotoxic in both cell lines than nor-nitrogen mustard.



Cytogenetic experiments revealed that estramustine produced a drastic increase of the mitotic index in both these cell lines. This increase could be accounted for by the arrest of cells in their first treatment-metaphase. The arrested metaphases exhibited all the characteristics commonly found for stathmokinetic agents such as colchicine and vinca-analogues. No mitotic arrest was found for nor-nitrogen mustard but chromosomal aberrations were found at toxic concentrations. Estradiol exhibited minimal toxicity and caused no mitotic arrest in these cell lines. The mitotic arrest induced by estramustine was found to be reversible on removal of the drug.

Estramustine-induced mitotic arrest in two human prostatic carcinoma cell lines DU 145 and PC-3.

Growth and cell survival following treatment with estramustine nor-nitrogen mustard, estradiol and testosterone of a human prostatic cancer cell line (DU 145).

Linomide ( N -phenylmethyl-1,2-dihydro-4-hydroxyl-1-methyl-2-oxoquinoline-3-carboxamide) is a quinoline 3-carboxamide which previously has been demonstrated to produce immunomodulator and antitumor effects when given in vivo . To test the possible antitumor effects of linomide against prostatic cancers, rats bearing five distinct Dunning R-3327 rat prostatic cancer sublines were treated daily with i.p. injections of linomide. These studies demonstrated that linomide has a reproducible antitumor effect against all of the prostatic cancers tested regardless of their growth rate, degree of morphologic differentiation, metastatic ability, or androgen responsiveness. This antitumor effect is observed only in vivo , not in vitro , and involves a cytotoxic response of the prostatic cancer cells. This cytotoxic response results in the retardation of the growth rate ( i.e. , increased tumor volume doubling time) of primary prostatic cancers and in metastatic lesions. Linomide's growth retardation is reversible, and thus continuous daily treatment with linomide is required for maximal antitumor response. Pretreatment of rats with linomide before tumor inoculation has no effect in addition to that produced by initiating linomide treatment at the time of tumor inoculation. No enhancement of either natural killer cell number or natural killer cell cytotoxic activity is induced by linomide treatment in the tumor-bearing rats. In addition, depletion of natural killer cell activity via injections of asialo-GMI antiserum does not prevent the antitumor effects of linomide in vivo . Likewise, the antitumor effects of linomide are also produced in prostatic cancer-bearing athymic nude rats. These results suggest that the requirement for host involvement in the antitumor effects of linomide against rat prostatic cancers may involve both immune and nonimmune host mechanism(s) ( e.g. , antiangiogenesis).

https://cancerres.aacrjournals.org/content/canres/52/11/3022.full.pdf

Beryl Hartley-Asp

Papers

Estramustine depolymerizes microtubules by binding to tubulin

Antiangiogenic Effects of the Quinoline-3-Carboxamide Linomide

Estramustine-induced mitotic arrest in two human prostatic carcinoma cell lines DU 145 and PC-3.

Growth and cell survival following treatment with estramustine nor-nitrogen mustard, estradiol and testosterone of a human prostatic cancer cell line (DU 145).

The antitumor effects of the quinoline-3-carboxamide linomide on dunning R-3327 rat prostatic cancers