Vascular-targeted photodynamic therapy with WST11 (VTP) enables safe and efficient non-thermal ablation of solid tumors as demonstrated by recent phase II and III clinical trials with localized prostate cancer. Studies in animal models in our labs revealed that VTP of immunogenic tumors elicits innate/adaptive immune responses and over 80% cures with consequent long-lasting anti-tumor protection. Here we show that local VTP combined with immune modulation in rodents, bearing weakly immunogenic prostate and triple negative breast tumors, results in eradication of remote metastases and animal cure.
Methodology: 4T1-luc cells were subcutaneously grafted at the hind leg of Balb/C mice. Colony forming assay confirmed tumor cell spreading to the lungs already by day 7 post grafting when local VTP was delivered to the primary tumor. The study comprised: (i) animals treated by VTP alone or (ii) following 50mg/kg cyclophosphamide (CTX) on day 4 post grafting, or (iii) VTP combined with anti-CTLA4 antibodies administered on days 1, 4, 7 and 10 post VTP according to standard protocol. Appropriate control groups using immunomodulatory agents alone or untreated tumors were utilized. Cure was defined as absence of detectable primary or metastatic tumor by necropsy at 90 days. Mat-Lu-luc prostate cancer cells were grafted orthotopically in Copenhagen rats. Surgical removal of tumor bearing prostate and follow up of disease progression demonstrated that on day 10 post grafting, the day of VTP, metastatic spread has already been initiated in 57% of animals, eventually developing abdominal and visceral metastases. Treatment groups comprised (i) animals treated by VTP with or (ii) without CTX pre-treatment followed by prostate removal three days after VTP or (iii) surgery only.
Results: Treatment of primary 4T1-luc tumors with VTP resulted in a complete primary tumor ablation in 50% of treated animals. Less then 10% of animals treated with VTP alone were cured with the rest developing lung metastases, while combination with CTX resulted in 30% cures. CTX induced reduction of total cell counts in tumor draining lymph nodes (LN) and spleens on VTP day followed by cell expansion over the following four days. Significant CTX-mediated reduction of Foxp3+ cells accompanied by increase in CD8+ cells during this period could be responsible for observed anti-metastatic effect of the combined treatment. Moreover, no significant change in total CD4+ cells observed at the same time suggests expansion of T helper cell subsets with concomitant suppression of regulatory population. Anti-CTLA-4 treatment, although significantly improved primary response rates after sub-optimal VTP (56% vs 14% in combined group vs VTP), did not prevent metastases suggesting additional escape mechanisms. VTP of orthotopic prostate tumors followed by whole gland removal resulted in 45% metastatic rate vs 57% in group treated by surgery alone on the same day. Pre-treatment with 50mg/kg CTX three days prior to VTP reduced metastatic rate to 7%. These findings suggest VTP-induced immune response can be augmented by prior immune modulation.
Conclusions: Our results demonstrate that immunomodulation combined with local VTP enables systemic anti-tumor effects with impact on the development of early metastatic disease in the setting of poorly immunogenic tumors. The choice of different immune modulatory agents and timing of treatment appears to play a critical role in the treatment outcome. Further studies are in progress to evaluate combination of WST11-VTP with more than one immunomodulating agent to further characterize localized and systemic response and augment treatment success. These studies serve as pre-clinical support for clinical trials, exploiting the immunogenic effects of VTP for tumor ablation, being developed in collaboration with Memorial Sloan Kettering Cancer Center.
Note:This abstract was not presented at the conference.
Citation Format: Dina Preise, Natasha Kudinova, Uri Lindner, Keren Sasson, Ronny Uzana, Jonathan Coleman, Yoram Salomon, Avigdor Scherz. Immunomodulated VTP enables cure of metastatic prostate and breast cancers in animal models. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B012.
- ©2016 American Association for Cancer Research.