LAPC4 and LAPC9

LAPC-4, derived from a lymph node, and LAPC-9, derived from a bone metastasis, are two lines developed by the University of California, Los Angeles group under the direction of Charles Sawyers (45,47). Both xenografts produce PSA and show the desired pattern of significantly decreased PSA and tumor volume after castration, with restoration of PSA and tumor growth over time. Importantly, both of the xenografts express the wild-type androgen receptor. These characteristics make these xenografts good models to study changes associated with development of androgen-independent disease. Both of these xenografts have been used to show involvement of insulin-like growth factor (IGF) signaling in progression to androgen independence (59).

Fig. 1. LuCaP 23.1: response to castration. (A) Serum prostate-specific antigen (PSA). LuCaP 23.12 xenografts were subdivided into prolonged (<50 days; A), partial (between 20 and 50 days; ■) and minimal (<20 days; •) response to castration. (B) Tumor volume responses to castration in the same animals from (A). Animals are categorized by PSA response. (Adapted with permission from ref. 48).

Fig. 1. LuCaP 23.1: response to castration. (A) Serum prostate-specific antigen (PSA). LuCaP 23.12 xenografts were subdivided into prolonged (<50 days; A), partial (between 20 and 50 days; ■) and minimal (<20 days; •) response to castration. (B) Tumor volume responses to castration in the same animals from (A). Animals are categorized by PSA response. (Adapted with permission from ref. 48).

4.4. The LuCaP Series

Our laboratory has been deriving CaP xenografts since approx 1990. Here, we present a few examples of our studies of responses to androgen ablation and progression to androgen independence.

The first set of our xenografts for which we evaluated the response to androgen withdrawal was the LuCaP 23 series (48). Three sublines (23.1, 23.8, and 23.12) of CaP xenografts were established from different metastases of one patient. LuCaP 23.1, which originated from a lymph node metastasis, expresses wild-type androgen receptor and secretes high levels of PSA. This xenograft closely mimics the situation in patients after castration, exhibiting a high heterogeneity of response (Fig. 1). Some of the tumors regressed after androgen withdrawal, whereas the growth of other tumors was inhibited only briefly. From the recurrent LuCaP 23.1, we have established LuCaP 23.1AI, which is androgen independent and is maintained in castrated mice. Another of our xenografts that can show either an androgen-dependent or androgen-sensitive response to castration is LuCaP 35 (60). This xenograft was derived from an androgen-independent left inguinal lymph node metastasis in a patient who had undergone hormonal ablation treatments with diethylstilbestrol, orchiectomy, and flutamide. It has the wild-type androgen receptor and deletions in chromosome 8p. It is also PTEN RNA-nega-tive (61). After castration, LuCaP 35 gives the response desired for progression to androgen indepen-

0 25 50 75 100 125 150 175

Time {Days Post-Castration)

Fig. 2. LuCaP 35: response to castration. (A) LuCaP 35 was implanted subcutaneously in intact male mice, which were castrated when tumor volumes reached approx 200 mm3. The tumor volume of each individual animal is plotted. LuCaP 35 regressed to nonpalpable tumors in nearly all animals by day 30 to 50. Tumors remained dormant for a period of up to 50 days, at which point they began to regrow in the androgen-free environment. (Adapted with permission from ref. 60).

0 25 50 75 100 125 150 175

Time {Days Post-Castration)

Fig. 2. LuCaP 35: response to castration. (A) LuCaP 35 was implanted subcutaneously in intact male mice, which were castrated when tumor volumes reached approx 200 mm3. The tumor volume of each individual animal is plotted. LuCaP 35 regressed to nonpalpable tumors in nearly all animals by day 30 to 50. Tumors remained dormant for a period of up to 50 days, at which point they began to regrow in the androgen-free environment. (Adapted with permission from ref. 60).

dence. Initially, PSA serum levels fall to nearly undetectable levels. Subsequently, as illustrated in Fig. 2, tumor volume drops dramatically during a 50-day period. At approximately day 70 to 90 after castration, PSA serum levels begin to rise, followed by measurable increases in tumor volume at approx 100 days. About 70% of LuCaP 35 xenografts exhibited androgen-independent regrowth. The androgen-independent LuCaP 35 xenografts were transplanted into castrated SCID mice, and this led to establishment of the androgen-independent variant designated LuCaP 35V. LuCaP 35V is maintained in castrated SCID male mice. Interestingly, the levels of androgen receptor are increased in LuCaP 35V in comparison with androgen-sensitive LuCaP 35 (27,62).

As indicated, we have derived several xenografts that are androgen dependent or androgen sensitive (Table 1). The response of several of these xenografts to androgen ablation is shown in Fig. 3. These xenografts show a wide spectrum of responses to castration. Again, this is similar to the range of responses seen in men, where some tumors respond for only a few weeks whereas others respond for years.

Several xenografts derived by us and others from androgen-independent clinical specimens revert to an androgen-dependent/sensitive phenotype when implanted into intact mice. Similarly, LuCaP 35V, when reimplanted into intact mice, reverts to the LuCaP 35 androgen-sensitive phenotype. This implies that the androgen-dependent phenotype is the preferred growth state when androgens are present.

Although space does not permit further discussion here, important studies with CaP xenografts are underway to evaluate mechanisms of response to castration and development of androgen indepen-

Programas Intervalo Variable

Fig. 3. The response to castration (day 0) of three of our new androgen dependent/sensitive xenografts (LuCaP 69, LuCaP 73, and LuCaP 77) in comparison with LuCaP 49, which is an androgen-independent, neuroendocrine xenograft. Note the differences in tumor volume and prostate-specific antigen (PSA) serum level responses among the three responsive xenografts. LuCaP 69 is the most androgen dependent, with a dramatic drop in tumor volume and PSA serum levels for a period of at least 50 days after castration. LuCaP 73 shows a decrease in tumor growth rate but the tumor volume does not decrease, whereas PSA serum levels drop appreciably for a few weeks before rising again.

Fig. 3. The response to castration (day 0) of three of our new androgen dependent/sensitive xenografts (LuCaP 69, LuCaP 73, and LuCaP 77) in comparison with LuCaP 49, which is an androgen-independent, neuroendocrine xenograft. Note the differences in tumor volume and prostate-specific antigen (PSA) serum level responses among the three responsive xenografts. LuCaP 69 is the most androgen dependent, with a dramatic drop in tumor volume and PSA serum levels for a period of at least 50 days after castration. LuCaP 73 shows a decrease in tumor growth rate but the tumor volume does not decrease, whereas PSA serum levels drop appreciably for a few weeks before rising again.

Fig. 4. Normalized mean prostate-specific antigen (PSA) serum levels of intermittent androgen suppression (IAS) vs castrated (CAS) animals (censored data). Normalized mean PSA serum levels are expressed as a percent of serum levels at time of orchiectomy (week 0). "On" androgens signifies when animals are receiving exogenous testosterone via testosterone propionate subcutaneous pellets. (Adapted with permission from ref. 70).

Fig. 4. Normalized mean prostate-specific antigen (PSA) serum levels of intermittent androgen suppression (IAS) vs castrated (CAS) animals (censored data). Normalized mean PSA serum levels are expressed as a percent of serum levels at time of orchiectomy (week 0). "On" androgens signifies when animals are receiving exogenous testosterone via testosterone propionate subcutaneous pellets. (Adapted with permission from ref. 70).

dence. The availability of multiple models with different characteristics should enable researchers to identify key factors associated with response to castration and development of androgen independence. A number of studies have been published using gene expression array profiling before and at multiple points after castration through the timeframe leading to the androgen-independent state (63-66). Likewise, several of our xenografts are the focus of such studies (67). These studies yield many genes/factors potentially involved in this progression. Further confirmation of altered expression and subsequent experiments to validate the roles of these genes/factors in development of androgen independence are still needed.

Finally, we would like to briefly revisit a study we performed a few years ago that illustrated the concept of androgen intermittent therapy or intermittent androgen suppression (IAS). In the past, androgen ablation was an all-or-none treatment modality imposed either by surgical or by pharmaceutical castration. IAS is a modified approach, promoted initially by Akakura et al. (50), who hypothesized that keeping most of the tumor cells androgen dependent and responsive to androgen ablation would confine overall tumor growth, yield at least equivalent survival, and provide quality-of-life benefits to the patient. This is accomplished by alternating androgen-ablation treatment periods with periods of no treatment, using PSA as a valuable surrogate marker of tumor response (68,69). We modeled this process with our CaP xenograft, LuCaP 23.12 (Fig. 4). Indeed, as hypothesized, Kaplan-Meier log rank analysis of survival showed equivalent survival between IAS and standard castration-induced androgen ablation. Recently, several investigative groups have reported favorable clinical findings using the IAS approach (71-74).

Was this article helpful?

0 0

Post a comment