Docetaxel and exisulind in hormone-refractory prostate cancer

Regulation of cyclic nucleotides in the urinary tract

Cyclic nucleotide levels are controlled through their synthesis from nucleotide triphosphates by cyclases and their degradation to 5'-monophosphates by phosphodiesterases (PDEs). Components controlling cyclic AMP-induced relaxation in the urinary tract include receptors, inhibitory and stimulatory G-proteins, isoforms of adenylyl cyclase and PDEs. The responsiveness of PDEs to a variety of physiological challenges is related to the presence of multiple families of isoenzymes with specific localization within tissues and within cells. At least 11 families of PDEs encode more than 50 PDE proteins produced in mammalian cells. In the urinary tract, characterization of PDE isoforms has lagged behind other systems and much of the literature was published prior to identification of PDE7, 8, 9, 10, 11. Specific PDE inhibitors regulate smooth muscle function in the bladder, urethra, prostate and ureter. The pharmacological potential of these inhibitors may include treatment of urge incontinence and the low compliance bladder, and treatment of prostate cancer. G-proteins also regulate cyclic AMP production. Changes in specific G- protein isoforms with aging, most prominently Gialpha2, cause decreased relaxation response in the aging bladder. As we have seen here with aging and certainly in other disease processes, levels of the components of adenylyl cyclase/phosphodiesterase/protein kinase can change and thus affect the relaxation response. By exploitation of differences in PDE expression in disease, such as the overexpression of PDEs in cancer, treatment options may present themselves.

Preclinical experience with docetaxel in gastrointestinal cancers

Docetaxel is a semisynthetic taxane that acts primarily by promoting microtubule assembly and preventing the depolymerization of assembled microtubules, thereby inducing mitotic block and inhibition of cell proliferation. This agent also induces apoptosis and appears to prevent angiogenesis. Although docetaxel has shown efficacy in a wide variety of tumors, it has only recently been evaluated in the treatment of gastrointestinal cancers. Data from preclinical studies have shown that docetaxel has substantial in vitro and in vivo activity against gastric, esophageal, and pancreatic tumors. The cytotoxic activity of docetaxel is generally time- and dose-dependent, and greater than that produced by other chemotherapeutic agents, including paclitaxel and anthracyclines. Studies evaluating combination regimens suggest that docetaxel has additive-to-synergistic antitumor activity against gastrointestinal cancers over that produced by the individual agents, and the increased antitumor activity appears to be schedule-dependent. These data suggest that docetaxel has promising therapeutic activity in the treatment of gastrointestinal cancers and provides a rationale for its inclusion in therapeutic protocols either as a single agent or in combination regimens. In addition to combination regimens with conventional chemotherapeutic agents, early studies with a number of novel molecularly targeted therapies in combination with docetaxel have shown encouraging results. These studies provide a basis for pursuing future clinical trials with docetaxel-based combinations of novel therapies for improving response rates in the treatment of gastrointestinal cancers.

Novel cytotoxic and biological agents for prostate cancer: Where will the money be in 2005?

In 2004, docetaxel-based chemotherapy became the first treatment capable of extending life in androgen-independent prostate cancer. The era of therapeutic nihilism in this disease has thus been put to rest and a broad range of agents is being tested with the goal of improving on the successes of 2004. Lessons learned from other tumour types will need to be applied to prostate cancer in order to harness the bounty of available ideas. Target amplification or activating mutations and not merely the presence of a target are likely to be important to the success of targeted agents. Thus, the promise of the current crop of targeted agents is most likely to be realised when pursued in the context of well-credentialed targets and tested in highly translational clinical trials that are capable not only of assessing tumour response, but also of evaluating the status of the targeted pathway. The most promising agents in clinical development are reviewed.

Update on hormone-refractory prostate cancer

PURPOSE OF REVIEW

Androgen deprivation therapy is the cornerstone treatment for men with de novo or recurrent metastatic prostate cancer. Unfortunately, androgen deprivation therapy is primarily palliative, with nearly all men progressing to an androgen-independent state. Hormone-refractory prostate cancer presents significant management challenges and is the focus of this review.

RECENT FINDINGS

Investigations into the pathophysiology of hormone-refractory prostate cancer, the exploration of chemotherapeutic combinations, novel biological targets, skeletal protectants, and radiopharmaceuticals, as well as new prognostic tools are expanding the clinician's armamentarium and improving patient outcomes.

SUMMARY

Bisphosphonates and chemotherapy are providing effective palliative approaches. Phase II trials of taxane-based regimens show higher response rates and longer survival than has typically been achieved with existing standards. Two completed randomized phase III studies to be reported in mid-2004 will more definitively answer the question of whether currently available chemotherapy can improve survival.

NF-kappaB activation in cancer: a challenge for ubiquitination- and proteasome-based therapeutic approach

Nuclear factor-kappa B (NF-kappaB) activation relies primarily on ubiquitin-mediated degradation of its inhibitor IkappaB. NF-kappaB plays an important role in many aspects of tumor development, progression, and therapy. Some types of cancer are characterized by constitutive NF-kappaB activity, whereas in others such activity is induced following chemotherapy. NF-kappaB-harboring tumors are generally resistant to chemotherapy and their eradication requires NF-kappaB inhibition. Here we describe the mechanisms of NF-kappaB activation in normal and tumor cells, review prevalent notions regarding the factor's contribution to tumorigenicity and discuss present and future options for NF-kappaB inhibition in cancer. The ubiquitination-mediated activation of NF-kappaB is intersected by another cancer-associated protein, beta-catenin. We, therefore, compare the related activation pathways and discuss the possibility of differential targeting of the involved ubiquitination machinery.

What's new in the treatment of advanced prostate cancer?

Increased insight into the biology of prostate cancer and the emergence of new therapeutic strategies and chemotherapeutic agents has changed approaches in treating patients with advanced prostate cancer. After secondary hormonal manipulations, new approaches include: second-line hormonal therapy, chemotherapy, immunotherapy with granulocyte macrophage-colony stimulating factor (GM-CSF) therapy, dendritic cell therapy, gene vaccination therapy, inhibition and/or blockade of growth factor receptors or growth factor receptor pathways, inhibition of neo-angiogenesis and inhibition of invasion and metastases.

Novel agents for the prevention of breast cancer: targeting transcription factors and signal transduction pathways

Transformation of breast cells occurs through loss or mutation of tumor suppressor genes, or activation or amplification of oncogenes, leading to deregulation of signal transduction pathways, abnormal amplification of growth signals, and aberrant expression of genes that ultimately transform the cells into invasive cancer. The goal of cancer preventive therapy, or "chemoprevention," is to eliminate premalignant cells or to block the progression of normal cells into cancer. Multiple alterations in signal pathways and transcription factors are observed in mammary gland tumorigenesis. In particular, estrogen receptor (ER) deregulation plays a critical role in breast cancer development and progress, and targeting ER with selective ER modulators (SERMs) has achieved significant reduction of breast cancer incidence in women at high risk for breast cancer. However, not all breast cancer is prevented by SERMs, because 30-40% of the tumors are ER-negative. Other receptors for retinoids, vitamin D analogs and peroxisome proliferator-activiator, along with transcription factors such as AP-1, NF-kappaB, and STATs (signal transducers and activators of transcription) affect breast tumorigenesis. This is also true for the signal transduction pathways, for example cyclooxygenase 2 (Cox-2), HER2/neu, mitogen-activated protein kinase (MAPK), and PI3K/Akt. Therefore, proteins in pathways that are altered during the process of mammary tumorigenesis may be promising targets of future chemopreventive drugs. Many newly-developed synthetic or natural compounds/agents are now under testing in preclinical studies and clinical trials. Receptor selective retinoids, receptor tyrosine kinase inhibitors (TKIs), SERMs, Cox-2 inhibitors, and others are some of the promising novel agents for the prevention of breast cancer. The chemopreventive activity of these agents and other novel signal transduction inhibitors are discussed in this chapter.

Highlights of contemporary issues in the medical management of prostate cancer

This paper highlights contemporary issues in the medical management of prostate cancer. Controversies surrounding adjuvant and neo-adjuvant hormonal therapy in localized prostate cancer are reviewed, as well as the use of chemohormonal therapy in high risk localized disease. The latent period of asymptomatic biochemical progression prior to clinical progression is an opportunity to evaluate new non-toxic therapies. In patients with advanced metastatic disease hormonal therapy and new alternatives are discussed. Chemotherapy in hormone refractory prostate cancer (HRPC) is extensively covered as well as the emerging role of molecular-targeted therapies.

Effects of docetaxel on pain due to metastatic androgen-independent prostate cancer

Bone pain commonly plagues patients with metastatic androgen-independent prostate cancer. Studies of mitoxantrone demonstrated that chemotherapy can substantially reduce this debilitating symptom. Two of the available studies examining the use of docetaxel with and without estramustine for treatment of androgen-independent prostate cancer include a detailed prospective analysis of pain and quality of life. One study required patients to have pain at entry and demonstrated significant improvement in pain. The second study enrolled patients with low prevalence and intensity of pain and did not demonstrate pain relief. The available results, although preliminary, suggest that patients with significant bone pain due to androgen-independent prostate cancer can experience substantial pain relief with docetaxel-based therapy. Larger randomized studies targeting patients with sufficient prevalence and intensity of pain are needed to refine our understanding of the contribution of docetaxel to pain control in this patient population.

Novel Clinical Trials in Androgen-Independent Prostate Cancer

Current treatments for androgen-independent prostate cancer have not shown a definitive increase in survival. Several novel drugs have made their way through preclinical testing into early clinical trials. Targets discussed in this review include apoptosis, antiangiogenesis, growth factor receptors or associated tyrosine kinases, and tumor-associated antigens targeted by vaccines. Research in this area includes testing combinations of previously studied chemotherapeutic agents as well as identifying and testing novel agents. It is these drugs, either alone or in combination, that are designed to target strategic pathways to improve survival and increase quality of life in prostate cancer patients. This review focuses on the novel agents being tested with chemotherapy in metastatic prostate cancer.