Metastatic spread of the PAIII prostatic adenocarcinoma after implantation in the tail of the rat

Hormone-Refractory Prostate Cancer in the Lobund-Wistar Rat

Research on cancer prevention and therapy must focus on the refractory disease, the fatal end-stage of cancer that develops in patients with organ-related solid tumors. Refractory cancers develop spontaneously in advanced-stage tumors or in relapsed cases after failed therapy. Because neither prevention nor therapy is currently feasible, refractory cancer is a major impediment to survival. There is a great need for an animal model of prostate cancer (PC), one that develops cancer from initial premalignant to the terminal refractory stages. We describe here a model of hormone-refractory prostate cancer (HRPC) that develops spontaneously through two stages by endogenous mechanisms in the Lobund-Wistar (LW) rat. The early premalignant, testosterone (T)-dependent stage is promoted by high levels of endogenous T, and up to age 12 months is reversible by T deprivation; without this intervention, the tumorigenic process progresses to the refractory stage, which is highly aggressive and does not respond to T deprivation or to a wide range of therapies. Initial refractory tumors are palpable at approximately 18 months of age. As they continue to grow, the tumors express characteristics seen in refractory cancers in humans (i.e., hypoxia, expression of hypoxia-inducible factors, and metastasis). Chemically induced HRPCs in LW rats manifest the same two developmental stages, but with shorter latency periods. A transplantable, metastasizing cell line (PAID) was derived from a germfree LW rat with advanced-stage cancer. Both spontaneous and chemically induced autochthonous HRPC model systems serve as outstanding models for studies on the prevention and therapy of refractory cancer.

Raloxifene (LY156758) produces antimetastatic responses and extends survival in the PAIII rat prostatic adenocarcinoma model

The benzothiophene antiestrogen, raloxifene (LY156758), has selective estrogen pharmacological antagonist activity in rats. The PAIII rat prostatic adenocarcinoma model was used to evaluate the effects of this agent on the lymphatic and pulmonary metastasis and survival in tumor-bearing male Lobund-Wistar (LW) rats. Raloxifene was inactive against colony formation of PAIII cells in vitro. Similarly, following subcutaneous (s.c.) implantation of 10(6) PAIII cells in the tail, s.c. administration of raloxifene (2.0, 10.0, or 20.0 mg/kg/day) for 30 days failed to demonstrate cytoreductive activity against primary tumor growth in the tail. However, in these same animals, raloxifene administration produced significant (P < 0.05) inhibition of PAIII metastasis from the primary tumor in the tail to the gluteal and iliac lymph nodes (maximal responses = 89% and 81% from control values, respectively). PAIII metastasis to the lungs was significantly inhibited by raloxifene treatment. Numbers of pulmonary foci in PAIII-bearing rats were significantly (P < 0.05) reduced by raloxifene administration in a dose-related manner (maximal reduction = 97% from control values). In these animals, maximal regression of 20% for ventral prostate and 21% for seminal vesicle were also seen after raloxifene administration (P < 0.05 for both). Coadministration of E2B and raloxifene had no consistent antagonistic effect upon the antitumor responses produced by raloxifene. Raloxifene (40.0 mg/kg/day for 28 days) produced marked decreases in PAIII metastasis in the lymphatic and pulmonary components. Continued administration of the compound produced significant (P < 0.05) extension of survival of PAIII-bearing rats. Further studies are needed to define the maximal antitumor efficacy and the mechanism of action of raloxifene in urogenital solid tumor animal models. These data support the contention that raloxifene represents a class of active antimetastatic agents with potential efficacy in the treatment of hormone-insensitive human prostatic cancer.

Inhibition of PAIII rat prostatic adenocarcinoma growth and metastasis by a new diarylsulfonylurea antitumor agent, LY181984

LY181984 is a compound in a series of orally active diarylsulfonylureas with broad spectrum in vivo activity against syngeneic rodent and human xenograft tumor models. The PAIII rat prostatic adenocarcinoma model was used to evaluate the effects of this antitumor agent on the lymphatic and pulmonary metastasis of the tumor in male Lobund Wistar rats. LY181984 was inactive against the proliferation of PAIII cells in vitro. Following subcutaneous implantation of 10(6) PAIII cells in the tail, oral administration of LY181984 (25.0, 50.0, or 100.0 mg./kg./day) for 30 days had no significant effects on body weight gain. LY181984 treatment produced significant (p less than 0.05) dose-dependent inhibition of primary tumor growth in the tail (max. inhibition = 46% from untreated control levels). In these same animals, LY181984 administration produced significant (p less than 0.05) dose-dependent inhibiton of PAIII metastasis from the primary tumor in the tail to the gluteal and iliac lymph nodes (maximal responses = 79% and 80% from control values, respectively). PAIII metastasis to the lungs was significantly inhibited by oral LY181984 treatment. Numbers of pulmonary foci in PAIII-bearing rats were significantly (p less than 0.05) reduced by LY181984 administration in a dose-dependent manner (maximal reduction = 78% from control values). While the non-toxic doses (less than 100.0 mg./kg./day for 28 days) of LY181984 produced marked decreases in tumor growth and metastasis, administration of the compound had no effect on the survival of PAIII-bearing rats. These data support the contention that LY181984 represents a new class of orally active antitumor and antimetastatic agents with potential efficacy in the treatment of hormone-insensitive prostatic cancer. Further studies are needed to define maximal efficacy of LY181984 and other sulfonylurea agents in urogenital solid tumor animal models.

Use of rhodamine 123 in the treatment of the Pollard III rat prostate adenocarcinoma

Significant destruction of the Pollard III rat prostate adenocarcinoma was achieved by treatment with rhodamine 123 at a dosage of 15 mg/kg every other day for 33 to 38 days. Injection of tumor remnants into untreated animals produced no tumor regrowth. Our data have demonstrated rhodamine 123 to be a significant drug for the management of the very aggressive Pollard III tumor.

Correlation of the in vivo anticoagulant, antithrombotic, and antimetastatic efficacy of warfarin in the rat

Fibrin formation has been hypothesized to be an element of the metastatic process in cancer, and pharmacological interference with such fibrin formation has been proposed as a means of antimetastatic therapy. We have tested this hypothesis through an in vivo study of warfarin in two independent rat disease models--a model of chemical-injury-induced arterial thrombosis, and a model of spontaneous metastasis. We found 0.50 mg/kg-day warfarin to be uniformly lethal after two weeks treatment. The chronic dose of 0.25 mg/kg-day was non-toxic and produced effective anticoagulation and marked antithrombotic and antimetastatic activity. The 0.125 mg/kg-day dose produced a reduction in factor IIc (50%) and factor VIIc (70%), and resulted in statistically significant antithrombotic and antimetastatic activity. The 0.0625 mg/kg-day dose failed to reduce the vitamin K-dependent clotting factors, and failed to produce any antithrombotic or antimetastatic effects. The substantial correlation (very similar dose-response effects) among the anticoagulant, antithrombotic and antimetastatic efficacies of warfarin in the rat suggests that anticoagulation provides the pharmacological mechanism underlying both the antithrombotic and the antimetastatic effects. The poor therapeutic index we observed in the rat may be the attribute which limits the efficacy of warfarin in the treatment of human cancer.