Metastasis in the androgen-insensitive Nb rat prostatic carcinoma system

Drug Repurposing: A New Hope in Drug Discovery for Prostate Cancer

Prostate cancer (PCA), the most common cancer in men, accounted for 1.3 million new incidences in 2018. An increase in incidences is an issue of concern that should be addressed. Of all the reported prostate cancers, 85% were detected in stages III and IV, making them difficult to treat. Conventional drugs gradually lose their efficacy due to the developed resistance against them, thus requiring newer therapeutic agents to be used as monotherapy or combination. Recent research regarding treatment options has attained remarkable speed and development. Therefore, in this context, drug repurposing comes into the picture, which is defined as the "investigation of the off-patent, approved and marketed drugs for a novel therapeutic indication" which saves at least 30% of the time and cost, reducing the cost of treatment for patients, which usually runs high in cancer patients. The anticancer property of cardiac glycosides in cancers was tested in the early 1980s. The trend then shifts toward treating prostate cancer by repurposing other cardiovascular drugs. The current review mainly emphasizes the advantageous antiprostate cancer profile of conventional CVS drugs like cardiac glycosides, RAAS inhibitors, statins, heparin, and beta-blockers with underlying mechanisms.

Mechanisms of heparin induced anti-cancer activity in experimental cancer models

BACKGROUND

Retrospective analyses of clinical trials and prospective clinical studies have suggested that heparins may have an effect on cancer survival. This putative anti-cancer activity of heparins is supported by data from studies in animal tumour models.

OBJECTIVE

To clarify the various potential mechanisms of heparin anti-cancer activity we evaluated the data from pre-clinical studies in which heparins have been tested as anti-cancer therapy.

METHODS

Pre-clinical studies, published between 1960 and 2005 were assessed. Data were collected on the type and dose of heparin used, duration of exposure to heparin, interval between heparin administration and cancer cell inoculation, and the animal tumour model used. In addition, a distinction was made in the analysis between heparin effects on the primary tumour or on established metastases and effects on the metastatic potential of infused cells.

RESULTS

Heparins seemed to affect the formation of metastasis rather than the growth of primary tumours. Chemically modified heparins with no or limited anticoagulant activity also showed anti-metastatic properties. Possible mechanisms to explain the effects on the process of metastases include inhibition of blood coagulation, inhibition of cancer cell-platelet and -endothelial interactions by selectin inhibition and inhibition of cell invasion and angiogenesis.

CONCLUSION

The anti-cancer activity of heparins depends more on inhibition of metastasis formation than on the effects on primary tumour growth. These effects are probably related to both coagulation and non-coagulation dependent factors. For a definitive proof of the anti-cancer activity of heparins in the clinic, prospective randomized trials especially in patients with early metastatic disease or in the adjuvant setting are urgently needed.

Control of angiogenesis with synthetic heparin substitutes

Many diseases are dominated by persistent growth of capillary blood vessels. Tumor growth is also angiogenesis-dependent. Safe and effective angiogenesis inhibitors are needed to determine whether control of angiogenesis would be therapeutic. Heparin and certain steroids, administered together, can inhibit angiogenesis in a synergistic manner. This "pair" effect suggested that specific hydrophilic cycloamyloses may be suitable heparin substitutes. beta-Cyclodextrin tetradecasulfate administered with a steroid inhibits angiogenesis at 100 to 1000 times the effectiveness of heparin in the chick embryo bioassay. This cyclic oligosaccharide also augments the anti-angiogenic effect of angiostatic steroids against corneal neovascularization in rabbits when beta-cyclodextrin tetradecasulfate and a steroid are inserted into the cornea or applied topically as eyedrops.

The correlation of pretreatment transurethral resection of prostatic cancer with tumor dissemination and disease-free survival. A univariate and multivariate analysis

A multivariate Cox's hazard function analysis was performed on the prognostic variables selected from 240 patients with localized carcinoma of the prostate who received external beam radiotherapy to analyze the association between the method of biopsy and disease-free survival. The patients received 4500 cGy to the pelvis followed by a 2-week treatment rest and then an additional 2000 cGy to the reduced prostatic volume. Median follow-up was 4 years (range, 1-9 years). The 5-year actuarial local control rate was 91%. There was no difference in local control relative to the method of biopsy (needle biopsy or transurethral resection of the prostate [TURP]). The 5-year actuarial risks of metastases were 28% and 48% for the needle biopsy and TURP groups, respectively (P less than 0.01). The 5-year disease-free survival for the needle biopsy and TURP groups were 55% and 42%, respectively (P less than 0.05). This difference maintained statistical significance for Stage C and Grade III tumors. A multivariate analysis demonstrated that "method of biopsy" was the third most powerful variable after serum acid phosphatase level and modified Broders' grade in predicting disease-free survival. Patients who had TURP had an almost twofold higher relative risk of disease progression than those who had needle biopsy. This study established the correlation of the method of biopsy with a lower probability of disease-free survival over and above the information obtained from the clinical stage, histologic grade, presence or absence of symptoms of obstruction, acid phosphatase level, and lymph node status. The association of TURP with tumor dissemination is discussed with reference to the mechanism of metastasis formation and prevention.