Multidimensional approaches in dealing with prostate cancer

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Gene 410 (2008) 1 – 8 www.elsevier.com/locate/gene

Review

Multidimensional approaches in dealing with prostate cancer Safdar Ali, Sher Ali ⁎ Molecular Genetics Laboratory, National Institute of Immunology, Aruna Asaf Ali Marg, NewDelhi-110067, India Received 19 September 2007; received in revised form 27 November 2007; accepted 29 November 2007 Available online 14 December 2007 Recieved by: A.J. van Wijnen

Abstract Prostate cancer is one of the most prevalent malignancies worldwide affecting the human male population. Different case-control, cohort or twin studies and segregation analyses point towards the presence of prostate cancer-susceptibility genes in the population. The studies have shown linkage of prostate susceptibility genes to multiple loci on chromosome 1 and single locus each on chromosomes 4, 8, 16, 17, 19, 20 and X chromosome. However, differences right from the mode of inheritance (autosomal dominant or X-linked recessive) to the target genes exist. There have been reports supporting no or weak linkage to these loci as well. Also, region (environmental factors), age and dietary habits have implications in different aspects of the disease. The important targets for treating prostate cancer are androgens and estrogen (synthesized from androgens by the action of enzyme aromatase) owing to their involvement in development and progression of prostate cancer. Further, prostate gland needs androgens (male hormones) for its normal maintenance and functioning. Besides, radiation therapy and surgical methods have also been used. The emerging areas include identifying and preparing successful vaccines from candidate peptides and gene therapy in several forms. This review deals with the paradox of linkage analyses and the various approaches in practice for treatment and management of prostate cancer. © 2007 Elsevier B.V. All rights reserved. Keywords: Linkage; Androgen; Estrogen; Radiation

1. Introduction In any given living system, cell division and cell death are well orchestrated processes to cope up with various physioloAbbreviations: AR, androgen receptor; ARE, androgen response element; CaP, carcinoma of prostate; CBP, Creb-Binding Protein; CPA, cyproterone acetate; CT, computed tomography; EDT, estrogen deprivation therapy; ER, estrogen receptor; GM-CSF, granulocyte macrophage colony-stimulating factor; HPCX, hereditary prostate cancer, X-linked; HPC, hereditary prostate cancer; IMRT, intensity-modulated radiation therapy; LOD, logarithm of the odds (to the base 10); MAB, maximal androgen blockade; MRI, magnetic resonance imaging; MRS, magnetic resonance spectroscopy; MRSI, magnetic resonance spectroscopy imaging; PAP, prostatic-acid phosphatase; PCa, prostate cancer; PCAP, predisposing for prostate cancer; PIN, prostate intraepithelial neoplasia; PSA, prostate-specific antigen; PSMA, prostate-specific membrane antigen; SRC1, steroid coactivator 1; TRAMP, transgenic adenocarcinoma of the prostate. ⁎ Corresponding author. Tel.: +91 11 2670 3753; fax: +91 11 2674 2125. E-mail addresses: [email protected], [email protected] (S. Ali). 0378-1119/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.gene.2007.11.020

gical, biochemical and environmental challenges and to maintain homeostasis. Regulation of cell cycle at the highest possible stringency level is an integral part for successful survival of any living system. Deviation in any of these mechanisms to the slightest level may result in cancer (uncontrolled cell growth) or other malignancies. There are different genetic aspects involved in different types of cancer with the underlying principle being loss of control over cell division. The prostate gland develops by the 9th week of embryonic life and is the modified wall of the proximal portion of the male urethra. Thereafter, the mesenchyme, urethra and Wolffian ducts condense to give rise to the adult prostate gland. Its main function is to store and secrete a clear, slightly alkaline fluid that constitutes up to 1/3rd volume of the seminal fluid. It also contains some smooth muscles that help expel semen during ejaculation. It needs androgens (male hormones) for its proper maintenance and function. The main male hormone,

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testosterone, is produced primarily by testicles and in small amounts by the adrenal glands. Owing to the important role of androgens in maintenance and functioning of prostate gland they are supposedly key players in PCa as well (Fig. 1). Prostate cancer (PCa) or carcinoma of prostate (CaP) is one of the most prominent cancers affecting the human male population around the world. A man has a 1/5 chance of developing PCa during his lifetime (Feuer, 1997). Notable regional differences have been observed in the populations in the prevalence of PCa with its occurring frequency highest in the African Americans and lowest in the Asian populations (Whittemore, 1994). Studies on familial clustering of PCa have shown an increased risk of an individual with several affected first-degree relatives or with an affected brother who had an early age at onset and about 9% of cases are expected to occur in families with several affected family members (Carter et al., 1992). The role of environmental factors in PCa has also been studied which highlighted the importance of immigration (Dunn, 1975), lifestyle and dietary habits (Whittemore et al., 1995). Apart from these factors, age is also a primary risk factor in PCa occurrence with incidence per 100,000 increasing from 34 to 150 to 440 in American Caucasian men of age 60, 70 and 80 years, respectively (Kosary et al., 1995). PCa is expected to be diagnosed in 15% of the men in the United States. Also, results of autopsy studies suggest that 30% of the men of age N 45 years may have prostate lesions that can be histologically identifiable as PCa (Kosary et al., 1995; Dhom, 1983). There is a good chance that these lesions remain latent for the person's lifetime but what actually triggers some of them to become biologically active metastatize and manifest as a potentially lethal disease remains a mystery till date though a genetic role is very strongly suggested. Different types of studies with variable but reasonable sample size have been done to understand the genetics of PCa. These include case-control, cohort and twin studies as well as segregation analyses. All the results point towards existence of prostate cancer-susceptibility

genes in the population but there is difference in the suggested modes of inheritance. Three independent segregation analyses support an autosomal dominant mode of inheritance. Dominant alleles with a population frequency of 0.36%–1.67% are supposed to account for ~9% of all PCa cases at age ≤85 years and ~43% cases at age ≤ 55 years (Carter et al., 1992). In contrast to this data from two studies are most consistent with an X-linked or recessive model of inheritance (Monroe et al., 1995; Narod et al., 1995). Studies have indicated linkage of prostate susceptibility genes to multiple loci on chromosome 1 and single locus each on chromosomes 4, 8, 16, 17, 19, 20 and X chromosome. 2. The loci involved 2.1. 1q24–25(HPC1) There have been number of studies indicating evidence for linkage to regions that may contain disease susceptibility loci for PCa. Smith et al. (1996) proposed the first such locus on chromosome 1q24–25 termed hereditary prostate cancer 1 (HPC1) and was supposed to account for the disease in 34% families with PCa in a data set defined by families with three or more first-degree affected relatives, PCa in three or more generations or two affected siblings diagnosed at age ≤ 60 years. Another study (Xu J and the International Consortium for Prostate Cancer Genetics, 2000) of 772 families suggests that 6% of families with hereditary prostate cancer have linkage to HPC1. The chances of having linkage to HPC1 locus is enhanced in families with an early mean age at diagnosis (b 65 years), four or more close relatives with the disease and proportionately more advanced stage disease (Grönberg et al., 1997; Grönberg et al., 1999). Apart from these, there have been several weak evidences confirming the linkage to HPC1 (Cooney et al., 1997; Hsieh et al., 1997). What's startling is the contrasting report about the same locus. McIndoe et al. (1997) studied 49 high risk prostate cancer families and found

Fig. 1. The role of androgens and estrogens in prostate cancer. Blue arrow indicates the targets for treatment of prostate cancer.

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the multiple LOD scores [logarithm of the odds (to the base 10)] for this linkage to be highly negative. A LOD score of three or more is generally taken to indicate that two gene loci are close to each other on a chromosome. It did not totally exclude the possibility of linkage of prostate susceptibility locus at HPC1 but did highlight the fact that other loci were playing a more critical role in families studied. There have been other studies with data sets comparable to the ones showing linkage to HPC1 and they show no linkage to the concerned locus (Berry et al., 2000a). 2.2. 1q42.2–43 (PCAP) A study on 47 French and German families indicated a linkage locus at chromosome 1q42.2–43 (PCAP) instead of HPC1 (Berthon et al., 1998). This was confirmed in another study of 152 families having a total of 648 affected men (Gibbs et al., 2000). The conflicting result was provided by a study on 98 unrelated families each having three or more PCa patients among first or second degree relatives showing no linkage at the concerned locus (Hsieh et al., 2001). 2.3. Xq27–28 (HPCX) A study of 360 families (North American — 262, Finnish — 57 and Swedish — 41) with 1020 affected members indicated linkage on chromosome X at Xq27–28 called as hereditary

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prostate cancer, X-linked (HPCX). The linkage was supposed to account for 16% occurrence of the disease in the cases studied (Xu et al., 1998). Other reports also supported the presence of this linkage (Hsieh et al., 2001; Bochum et al., 2002). But this locus also had its share of opposition. A study of 564 men from 254 families showed no linkage at the concerned locus (Goddard et al., 2001). Table 1 summarizes the paradoxical scenario concerning the various loci involved. The table doesn't necessarily include all the studies done in the area so far but simply highlights the unclear situation. As more studies with linkage to new and old loci come up, simultaneously, contrasting reports favoring no or weak linkage to the concerned loci also emerge. The data sets are comparable in number, though in some cases regional difference exists. The ambiguous nature of results forces us to consider the possibility where different genes might be leading to the same disease in different populations. But this needs to be substantiated unequivocally. 3. PCa and Y chromosome The analysis of the Y chromosome in patients with PCa is crucial due to its occurrence in the human males and the indispensable role of male sex hormones in the maintenance of prostate gland. Complete absence of the Y chromosome in PCa samples has been reported and was found to occur at a higher frequency than in bladder cancer. However, the cancer was not

Table 1 Linkage studies of prostate susceptibility genes in the human genome SL Locus no. 1

2

3 4

5

6 7

1p36 (CAPB)

Evidence for linkage

Evidence for no or weak linkage

a 141 families (71 high risk for prostate and 12 with both prostate and brain a 144 families with hereditary prostate cancer of cancer) (Gibbs et al., 1999). which 13 had brain cancer as well (Berthon et al., 1998). b 504 brothers with PCa from 230 multiplex sibships (Suarez et al., 2000). b 91 families (66 high risk prostate cancer families and 25 North American and Swedish families) (Smith et al., 1996). 4q24–25 a 91 families (66 high risk prostate cancer families and 25 North American a 94 hereditary prostate cancer families with 432 and Swedish families) (Smith et al., 1996). affected men (Gibbs et al., 2000). b 504 brothers with PCa from 230 multiplex sibships (Suarez et al., 2000). 8p23–22 s 254 families with a total of 564 men (Goddard et al., 2001). b 159 families with 249 affected men (Xu et al., 2001a).. 16p13 a 504 brothers with PCa from 230 multiplex sibships (Suarez et al., 2000). a 98 unrelated families each having three or more affected men in first and second degree relatives (Hsieh et al., 2001). b 94 hereditary prostate cancer families with 432 affected men b 91 families (66 high risk prostate cancer families and 25 (Gibbs et al., 2000). North American and Swedish families) (Smith et al., 1996). 17p11 a 127 pedigrees with 2402 cases (Tavtigian et al., 2001). a 159 families with 249 affected men (HPC2/ELAC2) (Xu et al., 2001b). b 98 unrelated families each having three or more affected men in first and b 504 brothers with PCa from 230 multiplex second degree relatives (Hsieh et al., 2001). sibships (Suarez et al., 2001). 19q13 a 233 families (189 with 2 affected brothers, 41 with 3 affected and I family with 2 pairs of affected brothers who were cousins) (Witte et al., 2000). 20q11–13 a 162 North American families with minimum three affected men in each a 91 families (66 high risk prostate cancer families (HPC20) family (Berry et al., 2000b). and 25 North American and Swedish families) (Smith et al., 1996). b 159 hereditary prostate cancer families (Zheng et al., 2001). b 98 unrelated families each having three or more affected men in first and second degree relatives (Hsieh et al., 2001).

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the sole cause but was supposedly aided by chromosomal instability (Nadal et al., 2007). The human Y chromosome haplotypes around the world pose another intriguing question as to whether different haplotypes are involved in causing differential susceptibility to PCa. A study on 4 ethnic groups (930 PCa cases) showed only one lineage in the Japanese group with significant statistical predisposition to PCa and high severity disease in young individuals (Paracchini et al., 2003). Another report on Japanese population showed varying PCa susceptibility in different lineages (Ewis et al., 2006). On the contrary, in the Korean population, no association was found between Y haplogroups and PCa (Kim et al., 2007). Besides, there has been an interesting report linking PCa to the number of male offsprings. The risk of PCa in fathers decreased with increasing number of sons indicating involvement of Y chromosome in PCa in the studied population (Harlap et al., 2007). A PCa sample had 550 copies of DYZ1 as compared to 3000–4300 in normal males. Another sample depicted normally Y specific DYZ1 signal on autosome 10. This suggests involvement of DYZ1 though owing to very small sample size, no conclusion can be drawn at this stage (Pathak et al., 2006). Further genetic analyses on additional number of samples would prove the possible involvement of the Y chromosome in PCa. 4. The candidate genes The studies on prostate have given us few candidate genes to focus on but the exact role and implication of these genes with reference to PCa remains elusive. Some of the candidate genes, their chromosomal localization and role in living system have been summarized in Table 2. The list though non-exhaustive gives a fair idea of where things are headed. One of the best studied genes in this regard is that of the androgen receptor (AR). The androgens function via AR which in turn needs steroid coactivator 1 (SRC1). PCa is initially dependent on androgen but advanced stages are supposed to be androgenindependent. The role of AR in this is very important. It's interesting to note the result of reducing expression of AR using small interfering RNAs in culture of prostate cell lines. The cells showed androgen-independent growth but were dependent on AR. Reduction of SRC-1 expression significantly reduced growth and altered androgen receptor target gene regulation in both LNCaP and C4-2 cell lines (AR-positive) whereas it had no effect on the growth of the AR-negative PC-3 and DU145 prostate cancer cell lines (Agoulnik et al., 2005). The genes have been reviewed by Simard et al. (2003).

Table 2 The main candidate genes involved in prostate cancer SL Target no. gene

Localization

1

PCTA-1

Chromosome Regulation of cell 1 growth

2

PADPRP Chromosome Modulates chromatin 1 structure

3

RAB-4

Chromosome Member of Ras 1 oncogene family

4

AR

5

MSR1

X Activates expression chromosome of genes with its ligand (DHT) Chromosome Binds to poylanionic 8 ligands

6

RNASEL Chromosome Regulating gene 1 expression by modulating the translation termination process. ELAC2 Chromosome Binds to γ tubulin inducing Tavtigian et al. 17 G2 delay (2001); Korver et al. (2003)

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Role in the system

References Su et al. (1996); Gopalkrishnan et al. (2000) Lyn et al. (1993); Ueda and Hayashi (1985) Rousseau-Merck et al. (1991); DePrimo et al. (2002) Xu et al. (1998); Zhang et al. (2003) Xu et al. (2002); Platt and Gordon (2001) Carpten et al. (2002); Roy et al. (2005)

PCTA-1, prostate carcinoma tumor antigen-1; PADPRP, poly(ADP-ribose) polymerase; AR, androgen receptor; DHT, dihydroxytestosterone; MSR, macrophage scavenger receptor; RNASEL, ribonuclease L.

Gleason scores (i.e., 2–4) indicate well differentiated tumor cells and their organization into glandular structures whereas high Gleason scores (i.e., 8–10) signify less differentiated tumor cells having a solid appearance. Poor differentiation (high Gleason score) indicates a strong prospect of the tumor penetrating the prostate capsule and invading the seminal vesicles and moving to the lymph nodes. 6. Treatment and management of PCa PCa can be regarded as one of the most potent and prevalent health challenge for the human male population. Our failure to combat PCa is supported by the steady deaths due to the disease with ~ 27,350 expected deaths due to this in US in 2006 (Jemal et al., 2006). The different approaches in treatment and management of the disease involve targeting the important hormones, radiation and gene therapy. 6.1. Androgen based therapy

5. Measure of PCa aggressiveness A pathological measure of aggressiveness assigned to a prostate tumor is the Gleason score (Gleason, 1992). It reflects the patterns of tissue architecture observed by a pathologist in two prostate biopsy or surgery samples. Each pattern is given a whole number score between 1 and 5, so the total Gleason score range is 2–10. For tissue with heterogeneous scores the maximum two scores are added to obtain the total score. Low

Growth and differentiation of the prostate gland during development is dependent on the androgens testosterone and dihydrotestosterone. However, after puberty, growth-quiescent maintenance of the organ occurs in the presence of high levels of testosterone. In cases of malignant transformation of the prostate, androgen-dependent growth resumes. The cellular effects of androgens are mediated via the AR, a ligand-activated transcription factor and member of the nuclear receptor

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superfamily. Liganded AR binds to specific sequences called androgen response elements (AREs) in the regulatory elements of target genes and promotes transcription. To facilitate this, it recruits coactivator proteins, which increase the rate of transcription by promoting histone acetylation and interacting with the basal transcriptional machinery (Bevan and Parker, 1999). The two mostly studied coactivators include SRC1 and Creb-Binding Protein (CBP). As PCa growth is initially androgen-dependent, treatment based on androgen involves removing circulating androgens and opposing their action. This can be achieved through surgical (bilateral orchiectomy) or medical castration. The latter involves the long-term use of luteinizing hormone-releasing hormone (LHRH) agonists. The two methods have shown to be equally effective in phase III trials (Denis and Murphy, 1993). An alternate approach is using estrogen or anti-androgens. Antiandrogens bind to the androgen receptor and inhibit androgendependent growth via yet to be known mechanisms (Whitaker et al., 2004). This treatment initially arrests the disease in the majority of cases. However, symptomatic relapse almost inevitably occurs 2–3 years later. The details molecular events that characterize this progression to “androgen independence” are still elusive. The term “androgen-independent” to describe advanced disease is misleading, since AR expression is almost never lost and the subsequent transcriptional events following AR stimulation still occur. It appears that in many cases the response to residual levels of androgens or other circulating hormones in the patient could be amplified due to one of the several factors including mutation of the androgen receptor and alteration in levels of cofactor proteins. The interactions between AR and its coactivator SRC1 have been characterized. There are marked differences between AR and other nuclear receptors (Bevan et al., 1999; Powell et al., 2004) which need to be further explored. Combination treatment, in the form of surgical or medical castration plus administration of an anti-androgen like flutamide, nilutamide, or cyproterone acetate (CPA) is called “maximal androgen blockade” (MAB). The use of MAB was first introduced by Labrie et al. (1982). Since then, a large number of randomized controlled trials have been conducted to evaluate the efficacy of MAB as compared with castration alone. The trials continued the trend of inconsistent results in PCa. Most failed to provide convincing evidence of improved survival with MAB but a few did show survival benefits with combined treatment (Denis et al., 1998). 6.2. Estrogen based therapy The complexity in the role of estrogen in prostate stems from the dual nature of its effects in the system. It has some useful roles as well as some harmful ones. These divergent actions are dependent on the activation of different estrogen receptor (ER) subtypes — ERα and ERβ. ERα is associated with the adverse effects i.e. abnormal cell proliferation, inflammation and development of malignancy. ERβ is involved in beneficial effects like anti-proliferation, differentiation and apoptosis. The ability of prostate gland to synthesize estrogens from a locally

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expressed enzyme aromatase adds to the complexity of the situation (Ellem et al., 2004; Hiramatsu et al., 1997). Aromatase plays a very important role in development of hormone dependent or related neoplasms as breast cancer (Simpson et al., 1994). This enzyme regulates the local balance of androgens to estrogens by facilitating the conversion of testicular testosterone and androstenedione to estrogen (Fishman and Goto, 1981; Akhtar et al., 1982). Thus an aberrant increase of aromatase in the prostate would disturb the balance between androgen and estrogen leading to development of PCa. Based on its functions, estrogen deprivation therapy (EDT) was considered for treatment of PCa. The early clinical trials showed it to be promising approach in dealing with androgenindependent or advanced PCa using first and second generation aromatase inhibitors like aminogluthemide and hydrocortisone (Kruit et al., 2004). But the third generation inhibitors like anastrozole and letrozole were highly ineffective with only few patients, if any, benefiting (Smith et al., 2002; Santen et al., 2001). Thus the EDT approach which was analogous to the androgen ablation therapy (AAT) approach did not work. Though the reasons for failure remain unexplained, there is no denial of the fact that it is due to the dual effects of estrogen. Therefore, the next approach using estrogen had to be regarding the receptor subtype responsible for its adverse effects — ERα. ERα antagonist Toremifene has been used successfully in treatment of breast cancer and thus, was the foremost choice to be tried for prostate as well. When studied in transgenic adenocarcinoma of the prostate (TRAMP) mice, it decreased the incidence of prostate intraepithelial neoplasia (PIN) and PCa (Price et al., 2006). The effects on human have also been explored. In a phase IIb clinical trial of over 500 patients suffering with high grade PIN and no evidence of PCa, Toremifene decreased the emergence of PCa decreasing the incidence of progression from 48% to 29% over a period of one year (Raghow et al., 2002). This provides the evidence for estrogen playing a role in development of PCa through its receptor ERα and justifies the rationale for targeting ERα in countering PCa through estrogen. 6.3. Radiation therapy Traditional radiation therapy for PCa involved treatment of the whole gland with homogeneous high dose level but this has found to be associated with a high risk of treatment morbidity (Kuban et al., 2003). The trick lies in properly defining the target area to be treated with higher dose of radiation. Inhomogeneous gradients of dose within the gland have been administered using either prostate brachytherapy or intensitymodulated radiation therapy (IMRT). Magnetic resonance imaging (MRI) is now routinely used in addition to the conventional computed tomography (CT) to define target volume of tumor before undergoing radiation therapy. Magnetic resonance spectroscopy (MRS) and magnetic resonance spectroscopy imaging (MRSI) have already been successfully used in tumor in different body regions like neck, head and brain to measure biochemical changes within the target volume and detect biochemical markers (He et al., 2003).

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MRS works on the principle of nuclear magnetic resonance to identify the chemical form of element present. A number of metabolites present in prostate have 1H. This makes it possible to use 1H MRS for investigating PCa. Some of the molecules that can be targeted with 1H MRS are choline, creatine, citrate and lactate. The requirement of choline for cellular membrane and repair makes higher choline level an indicator for active tumor. Areas having infiltration by prostate adenocarcinoma have a comparatively high choline/citrate ratio with reference to normal prostatic tissues. This can thus be used for defining and targeting areas affected by PCa (Kaji et al., 1998). The sensitivity of MRS in studying PCa varies from 38.5% to 77% specificity from 38.5% to 78% and when combined with MRI it has a sensitivity of 100% (Kurhanewicz et al., 2000; Pucar et al., 2005; Scheidler et al., 1999; Yuen et al., 2004). Also, MRS has the potential to detect recurrence of disease after treatment. The most common parameter for checking the success of treatment is serum prostate-specific antigen (PSA). This is however not a good choice as its level gets affected in patients undergoing androgen depriving therapy. Also, the levels are abnormal after external radiation therapy and may take up to 4 years to reach a stable level (Takamiya et al., 2003). MRS can act as an early indicator of treatments success by detecting metabolic atrophy as both normal as well as abnormal cells cannot grow without metabolism. If used together with PSA and biopsy the monitoring would be most reliable (Pickett et al., 2004). 6.4. Gene therapy The beginning of combating PCa with gene therapy started with the effort to create a patient specific vaccine by growing tumor cells from patients and then infecting the cells with granulocyte macrophage colony-stimulating factor (GM-CSF), a cytokine that enhances antigen presentation, expressing retrovirus. Then, the cells expressing GM-CSF are lethally irradiated before injecting under the skin. In a phase I human gene therapy trial, 8 immunocompetent patients were injected with cells expressing GM-CSF. Side effects were pruritis, erythema, and swelling at vaccination sites. T-cell responses were evident in 2/8 patients before vaccination and in 7/8 patients after treatment. B-cell responses were also induced. Sera from 3/8 vaccinated men contained new antibodies recognizing polypeptides of 26, 31, and 150 kDa in protein extracts from prostate cells. The 150-kDa polypeptide was expressed by LNCaP and PC-3 PCa cells, as well as by normal prostate epithelial cells, but not by prostate stromal cells. No antibodies against PSA were detected (Raghow et al., 2002). This has been followed by the development of GVAX® which is a GM-CSF secreting vaccine. It has been tried in N 200 patients in different phase I/II trials. The reports suggest that vaccination is safe and immune tolerance can be broken against PCa (Simons and Sacks, 2006a). A non-patient-specific phase I/II trial PCa immunotherapy has been done in hormone therapy-naïve patients with PSA relapse following radical prostatectomy and absence of radiologic metastases. The patients show a favorable safety profile

and are immunologically active (Simons et al., 2006b). These promising results have pushed the approach to be tested in phase III trials. Another approach in this field is based on suicide gene therapy. It uses the expression of a prodrug activation enzyme which itself is non-toxic just like the prodrug. The enzyme converts the prodrug to a toxic drug which kills the cell. The enzyme which has been used for clinical trials is the thymidine kinase gene from the Herpesvirus (HSV-tk) which converts anti-herpetic agents (Ganciclovir or valacyclovir) to cytotoxic agents. This also leads to killing the surrounding cells of the cells expressing the enzyme (bystander effect). A number of phase I/II trials have been conducted. The results, though ambiguous, advocate the usage of this approach not individually but together with radiation therapy because ganciclovir can act as a radiation sensitizer as well (Hassan et al., 2000; van der Linden et al., 2005). 7. Conclusions Our efforts in dealing with one of the greatest challenges of the human male population, PCa, have had limited success till date. The existing gaps in the understanding of PCa need to be filled up for more effective diagnostics and treatment. This would involve having a complete knowledge of AR dysfunctions, its network in PCa and specific actions of estrogen through its varying receptors, among others. There have been promising results with different approaches but none of them comes near to handling of the disease worldwide in a satisfactory manner. The removal of androgens results in immediate improvement of patients condition in most cases but it simultaneously enhances the development of hormone independent PCa. The initial results on combination of gene and radiation therapy are really encouraging and need further impetus. But not all the effective treatment procedures can be used in combination with each other. As for instance, hormone therapy affects the prostate metabolism and so MRS results thereafter won't depict a true picture of the situation. Alternately, search for vaccines is also going on. The various vaccine candidates identified from PSA, prostate-specific membrane antigen (PSMA) and prostatic-acid phosphatase (PAP) need to be explored further with vigor. Though, ethnicity seems to be playing a role in deciding on candidate peptides for vaccines, it is still a promising approach (Matsueda et al., 2005). Also, the effectiveness of minimally invasive surgical therapy in management of benign prostatic hyperplasia and leptin based treatment in cases of obesity associated PCa exhibit a great potential of these approaches in combating the disease. Apart from these approaches, diagnostics for early detection of PCa need to be developed. This can be based on age specific expression profile of different candidate genes in prostate. Also, considering the ambiguity in genetic results worldwide so far the option of having separate diagnostics for populations may be explored. Acknowledgments This work was supported by a DBT grant no. BT/PR2752/ AAQ/01/113/2001 and DST grant no. SP/SO/DO3/99 to SA and a core grant from the Department of Biotechnology,

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