Paradigm shifts in cancer vaccine therapy

Cancer vaccines constitute a unique therapeutic modality in that they initiate a dynamic process involving the host's immune response. Consequently, (a) repeated doses (vaccinations) over months may be required before patient clinical benefit is observed and (b) there most likely will be a "dynamic balance" between the induction and maintenance of host immune response elements to the vaccinations vs. host/tumor factors that have the potential to diminish those responses. Thus "patient response" in the form of disease stabilization and prolonged survival may be more appropriate to monitor than strictly adhering to "tumor response" in the form of Response Criteria In Solid Tumors (RECIST) criteria. This can be manifested in the form of enhanced patient benefit to subsequent therapies following vaccine therapy. This article will review these phenomena unique to cancer vaccines with emphasis on prostate cancer vaccines as a prototype for vaccine therapy. The unique features of this modality require the consideration of paradigm shifts both in the way cancer vaccine clinical trials are designed and in the way patient benefit is evaluated.

Cancer vaccines: moving beyond current paradigms

The field of cancer vaccines is currently in an active state of preclinical and clinical investigations. Although no therapeutic cancer vaccine has to date been approved by the Food and Drug Administration, several new paradigms are emerging from recent clinical findings both in the use of combination therapy approaches and, perhaps more importantly, in clinical trial design and end point analyses. This article will review recent clinical trials involving several different cancer vaccines from which data are emerging contrasting classic "tumor response" (Response Evaluation Criteria in Solid Tumors) criteria with "patient response" in the manifestation of increased patient survival post-vaccine therapy. Also described are several strategies in which cancer vaccines can be exploited in combination with other agents and therapeutic modalities that are quite unique when compared with "conventional" combination therapies. This is most likely due to the phenomena that (a) cancer vaccines initiate a dynamic immune process that can be exploited in subsequent therapies and (b) both radiation and certain chemotherapeutic agents have been shown to alter the phenotype of tumor cells as to render them more susceptible to T-cell--mediated killing. Consequently, evidence is emerging from several studies in which patient cohorts who first receive a cancer vaccine (as contrasted with control cohorts) benefit clinically from subsequent therapies.

Granulocyte macrophage colony-stimulating factor--secreting allogeneic cellular immunotherapy for hormone-refractory prostate cancer

PURPOSE

This trial evaluated the safety, clinical activity, and immunogenicity of an allogeneic cellular immunotherapy in 55 chemotherapy-naïve patients with hormone-refractory prostate cancer (HRPC). The immunotherapy, based on the GVAX platform, is a combination of two prostate carcinoma cell lines modified with the granulocyte macrophage colony-stimulating factor (GM-CSF) gene.

EXPERIMENTAL DESIGN

HRPC patients with radiologic metastases (n = 34) or rising prostate-specific antigen (PSA) only (n = 21) received a prime dose of 500 million cells and 12 boost doses of either 100 million cells (low dose) or 300 million cells (high dose) biweekly for 6 months. End points were changes in PSA, time to progression, and survival.

RESULTS

Median survival was 26.2 months (95% confidence interval, 17, 36) in the radiologic group: 34.9 months (8, 57) after treatment with the high dose (n = 10) of immunotherapy and 24.0 months (11, 35) with the low dose (n = 24). The median time to bone scan progression in the radiologic group was 5.0 months (2.6, 11.6) with the high dose and 2.8 months (2.8, 5.7) with the low dose. In the rising-PSA group (n = 21) receiving the low dose, the median time to bone scan progression was 5.9 months (5.6, not reached), and median survival was 37.5 months (29, 56). No dose-limiting or autoimmune toxicities were seen; the most common adverse events were injection site reaction and fatigue.

CONCLUSIONS

These results suggest that this GM-CSF-secreting, allogeneic cellular immunotherapy is well tolerated and may have clinical activity in patients with metastatic HRPC. Phase 3 trials to confirm these results are under way.

Management of High Risk Metastatic Prostate Cancer: The Case for Novel Therapies

PURPOSE

We reviewed the results of preliminary studies of select novel agents for metastatic prostate cancer and discuss the potential benefit of these agents for earlier stage disease, eg biochemically recurrent prostate cancer with high risk features.

MATERIALS AND METHODS

Available data on select investigational immunotherapies as well as endothelin-A receptor antagonists and survivin inhibitors were obtained and reviewed through PubMed searches, conference proceedings and unpublished proprietary information, when available.

RESULTS

A large number of promising agents are in varying stages of development. Phase III results have been reported for the endothelin-A receptor antagonist atrasentan. Several immunotherapies are currently in phase II/III trials, namely the GM-CSF transduced tumor cell vaccine GVAX, the prostatic acid phosphatase loaded dendritic cell vaccine Provenge and the prostate specific antigen expressing poxvirus vaccine PROSTVAC-VF. Another immunotherapy, the prostate specific membrane antigen immunoconjugate MLN2704 (Millennium Pharmaceuticals, Cambridge, Massachusetts), is in phase I/II study. The first clinical inhibitors of survivin are in early phase I studies. Several of these agents, including atrasentan, have shown statistically significant but modest effects in the advanced disease setting in which they have been studied.

CONCLUSIONS

Clinical trial design with these novel therapies presents particular challenges since most of these agents may induce disease stabilization rather than disease regression. There is a risk of false-negative results and failure to recognize a potentially efficacious agent if these cytostatic agents are studied only in men with advanced, heavily pretreated disease in whom life expectancy is measured in months. We advocate the early referral and enrollment of men with high risk prostate cancer in clinical trials.

Therapeutic Vaccines for Prostate Cancer

Prostate cancer is the most common, noncutaneous cancer for men in the U.S., leading to more than 30,000 deaths a year. Vaccines for prostate cancer, which for several years have been shown to generate immunologic responses, are beginning to show significant clinical promise. At present, numerous therapeutic options are being investigated, including autologous and allogeneic whole-tumor cell vaccines, dendritic cell vaccines, and poxvirus-based vaccines. Advances in basic immunology have translated into new, more complex therapeutic strategies. The findings from current trials and the demonstrated potential to combine vaccines with conventional therapies herald a promising future for the treatment of prostate cancer. This review highlights recent advances and clinical trials in immunotherapy for prostate cancer, along with current thoughts on immunologic and clinical monitoring of these trials.

Hormone refractory prostate cancer: Management and advances

Effective therapeutic options have not existed for prostate cancer progressing after androgen deprivation therapy until very recently. Secondary hormonal manipulations offer marginal benefits. Docetaxel based chemotherapy has been demonstrated to extend survival and change the natural history of the disease in two large randomized trials. These studies have provided the impetus to combine docetaxel with novel biologic agents to further consolidate the gains in long-term outcome. With the arrival of exciting agents including vaccines, monoclonal antibodies, bone-targeted drugs, antisense oligonucleotides, anti-angiogenic drugs and small molecule receptor tyrosine kinase inhibitors, the future treatment of prostate cancer appears promising.

American Society of Clinical Oncology 41st annual meeting

For many years the annual meeting of the American Society of Clinical Oncology (ASCO) has been the premier meeting in clinical oncology, and one that is closely scrutinised by Wall Street and international investors because of the economic significance of cancer therapies to the pharmaceutical and biotechnology industries. The area of biologicals and targeted therapies exploded in the late 1990s after the blockbuster results with the monoclonal antibody rituximab in the treatment of lymphoma. Although historically a somewhat conservative organisation that is still closely tied to classical cytotoxic chemotherapy, ASCO has been able to integrate various areas of biological therapy into its scope of clinical activity. Although ASCO still has 'American' in its title, it is really the 'International' Society of Clinical Oncology, as reflected by the attendance at this year's meeting by approximately 30,000, with approximately two-thirds attending from outside the US. There were 9708 abstracts published in conjunction with the meeting, 86 of which are referenced in this review. There were 10 papers chosen for plenary presentations and many other key papers were presented at other oral abstract sessions and poster discussion session that were organised by tumour type. In addition to key papers submitted by specific tumour type, for this year's meeting there were 103 abstracts published in the session entitled 'Developmental Therapeutics: Immunotherapy', and 218 in the session entitled Developmental Therapeutics: Molecular Targets', for a total of 321 biological therapy abstracts compared with only 125 abstracts for the session entitled 'Developmental Therapeutics: Cytotoxic Therapy'. This meeting review is organised by biotherapy modality rather than tumour type.