Human Prostatic Cancer Cells Are Sensitive to Programmed (Apoptotic) Death Induced by the Antiangiogenic Agent Linomide

Human prostatic cancer cells have a remarkably low rate of proliferation even when they have metastasized to the bone and have become androgen independent (Berges et al., Clin. Cancer Res., 1: 473-480, 1995). Due to this low proliferation, patients with such androgen-independent metastatic prostatic cancer cells are rarely treated successfully with the presently available chemotherapeutic agents. Therefore, new approaches are urgently needed which are not dependent on the rate of cancer cell proliferation for their effectiveness. One such approach is to inhibit the angiogenic response within localized and metastatic cancer deposits, since the resultant hypoxia-induced tumor cell death does not require cell proliferation. We have previously demonstrated that the quinoline-3-carboxamide, linomide, is an p.o. active agent which inhibits tumor angiogenesis and thus blood flow in a variety of rat prostatic cancers independent of their growth rate, androgen sensitivity, or metastatic ability. Because of its antiangiogenic effects, linomide treatment induces the hypoxic death of rat prostatic cancer cells, thus inhibiting their net growth and metastases. To determine whether human prostatic cancer cells are similarly sensitive to hypoxia-induced death caused by linomide inhibition of tumor angiogenesis, androgen-independent TSU and PC-3 human prostatic cancer cells were xenotransplanted into SCID mice that were either untreated or treated p.o. with linomide. These studies demonstrated that linomide treatment decreases microvessel density in both androgen-independent human prostatic cancers. Microvessel density was decreased from 1.8 ± 0.4% of the total area in control tumors to 1.0 ± 0.2% in linomide-treated TSU tumors [i.e., a 44% decrease in microvessel density (P < 0.05)]. Similarly, a 56% decrease (P < 0.05) was observed in the microvessel density of PC-3 tumors (i.e., 2.7 ± 0.8% of the area in control tumor versus 1.2 ±0.2% in the linomide-treated tumors). This inhibition of angiogenesis increased cell death in both TSU and PC-3 cancer cells. This is reflected in both an increase in the area of necrosis and an increase in the apoptotic index in non-necrotic areas. In untreated TSU tumors, 40 ± 2% of tumor volume was necrotic Linomide treatment increased this necrotic percentage to 59 ± 2% [i.e., 48% increase (P < 0.05)]. Linomide therapy also increased apoptotic cell death in non-necrotic tumor areas. In the untreated TSU tumors, 2.9 ± 0.6% of tumor cells were apoptotic in the non-necrotic areas, and in the linomide-treated TSU tumors this percentage increased to 3.6 ± 0.4% [i.e., 24% increase (P < 0.05)]. The percentage of necrosis in control PC-3 tumors was 5 ± 4%, and in linomide-treated PC-3 tumors it was 16 ± 4% [i.e., 220% increase in necrosis (P < 0.05)]. The percentage of apoptotic cells was 1.6 ± 0.1% in the non-necrotic areas in untreated PC-3 tumors versus 4.2 ± 0.7% in linomide-treated tumors (i.e., 163% increase (P < 0.05)]. These results demonstrate that androgen-independent human prostate cancer cells are sensitive to hypoxia-induced death brought about by the antiangiogenic effects of p.o. linomide treatment.