Development of a tissue engineered human prostate tumor equivalent for use in the evaluation of cryoablative techniques

A novel in vitro model of clinical cryoablation to investigate the transition zone for focal tumor ablation

Cryoablation (CA) of solid tumors is highly effective at reducing tumor burden and eliminating small, early stage tumors. However, complete ablation is difficult to achieve and cancer recurrence is a significant barrier to treatment of larger tumors compared to resection. In this study, we explored the relationship between temperature, ice growth, and cell death using a novel in vitro model of clinical CA with the Visual-ICE (Boston Scientific) system, a clinically approved and widely utilized device. We found that increasing the duration of freezing from 1 to 2 min increased ice radius from 3.44 ± 0.13 mm to 5.29 ± 0.16 mm, and decreased the minimum temperature achieved from -22.8 ± 1.3 °C to -45.5 ± 7.9 °C. Furthermore, an additional minute of freezing increased the amount of cell death within a 5 mm radius from 42.5 ± 8.9% to 84.8 ± 1.1%. Freezing at 100% intensity leads to faster temperature drops and a higher level of cell death in the TRAMP-C2 mouse prostate cancer cell line, while lower intensities are useful for slow freezing, but result in less cell death. The width of transition zone between live and dead cells decreased by 0.4 ± 0.2 mm, increasing from one to two cycles of freeze/thaw cycles at 100% intensity. HMGB-1 levels significantly increased with 3 cycles of freeze/thaw compared to the standard 2 cycles. Overall, a longer freezing duration, higher freezing intensity, and more freeze thaw cycles led to higher levels of cancer cell death and smaller transition zones. These results have the potential to inform future preclinical research and to improve therapeutic combinations with CA.

An In Vitro Investigation into Cryoablation and Adjunctive Cryoablation/Chemotherapy Combination Therapy for the Treatment of Pancreatic Cancer Using the PANC-1 Cell Line

As the incidence of pancreatic ductal adenocarcinoma (PDAC) continues to grow, so does the need for new strategies for treatment. One such area being evaluated is cryoablation. While promising, studies remain limited and questions surrounding basic dosing (minimal lethal temperature) coupled with technological issues associated with accessing PDAC tumors and tumor proximity to vasculature and bile ducts, among others, have limited the use of cryoablation. Additionally, as chemotherapy remains the first-line of attack for PDAC, there is limited information on the impact of combining freezing with chemotherapy. As such, this study investigated the in vitro response of a PDAC cell line to freezing, chemotherapy, and the combination of chemotherapy pre-treatment and freezing. PANC-1 cells and PANC-1 tumor models were exposed to cryoablation (freezing insult) and compared to non-frozen controls. Additionally, PANC-1 cells were exposed to varying sub-clinical doses of gemcitabine or oxaliplatin alone and in combination with freezing. The results show that freezing to −10 °C did not affect viability, whereas −15 °C and −20 °C resulted in a reduction in 1 day post-freeze viability to 85% and 20%, respectively, though both recovered to controls by day 7. A complete cell loss was found following a single freeze below −25 °C. The combination of 100 nM gemcitabine (1.1 mg/m2) pre-treatment and a single freeze at −15 °C resulted in near-complete cell death (<5% survival) over the 7-day assessment interval. The combination of 8.8 µM oxaliplatin (130 mg/m2) pre-treatment and a single −15 °C freeze resulted in a similar trend of increased PANC-1 cell death. In summary, these in vitro results suggest that freezing alone to temperatures in the range of −25 °C results in a high degree of PDAC destruction. Further, the data support a potential combinatorial chemo/cryo-therapeutic strategy for the treatment of PDAC. These results suggest that a reduction in chemotherapeutic dose may be possible when offered in combination with freezing for the treatment of PDAC.

Breast Cancer Cryoablation: Assessment of the Impact of Fundamental Procedural Variables in an In Vitro Human Breast Cancer Model

INTRODUCTION

Breast cancer is the most prominent form of cancer and the second leading cause of death in women behind lung cancer. The primary modes of treatment today include surgical excision (lumpectomy, mastectomy), radiation, chemoablation, anti-HER2/neu therapy, and/or hormone therapy. The severe side effects associated with these therapies suggest a minimally invasive therapy with fewer quality of life issues would be advantageous for treatment of this pervasive disease. Cryoablation has been used in the treatment of other cancers, including prostate, skin, and cervical, for decades and has been shown to be a successful minimally invasive therapeutic option. To this end, the use of cryotherapy for the treatment of breast cancer has increased over the last several years. Although successful, one of the challenges in cryoablation is management of cancer destruction in the periphery of the ice ball as the tissue within this outer margin may not experience ablative temperatures. In breast cancer, this is of concern due to the lobular nature of the tumors. As such, in this study, we investigated the level of cell death at various temperatures associated with the margin of a cryogenic lesion as well as the impact of repetitive freezing and thawing methods on overall efficacy.

METHODS

Human breast cancer cells, MCF-7, were exposed to temperatures of -5°C, -10°C, -15°C, -20°C, or -25°C for 5-minute freeze intervals in a single or repeat freeze-thaw cycle. Samples were thawed with either passive or active warming for 5 or 10 minutes. Samples were assessed at 1, 2, and 3 days post-freeze to assess cell survival and recovery. In addition, the modes of cell death associated with freezing were assessed over the initial 24-hour post-thaw recovery period.

RESULTS

Exposure of MCF-7 cells to -5°C and -10°C resulted in minimal cell death regardless of the freeze/thaw conditions. Freezing to a temperature of -25°C resulted in complete cell death 1 day post-thaw with no cell recovery in all freeze/thaw scenarios evaluated. Exposure to a single freeze event resulted in a gradual increase in cell death at -15°C and -20°C. Application of a repeat freeze-thaw cycle (dual 5-minute freeze) resulted in an increase in cell death with complete destruction at -20°C and near complete death at -15°C (day 1 survival: single -15°C freeze/thaw = 20%; repeated -15°C freeze/thaw = 4%). Analysis of thaw interval time (5 vs 10 minute) demonstrated that the shorter 5-minute thaw interval between freezes resulted in increased cell destruction. Furthermore, investigation of thaw rate (active vs passive thawing) demonstrated that active thawing resulted in increased cell survival thereby less effective ablation compared with passive thawing (eg, -15°C 5/10/5 procedure survival, passive thaw: 4% vs active thaw: 29%).

CONCLUSIONS

In summary, these in vitro findings suggest that freezing to temperatures of 25°C results in a high degree of breast cancer cell destruction. Furthermore, the data demonstrate that the application of a repeat freeze procedure with a passive 5-minute or 10-minute thaw interval between freeze cycles increases the minimal lethal temperature to the -15°C to -20°C range. The data also demonstrate that the use of an active thawing procedure between freezes reduces ablation efficacy at temperatures associated with the iceball periphery. These findings may be important to improving future clinical applications of cryoablation for the treatment of breast cancer.

Evaluation of a Novel Cystoscopic Compatible Cryocatheter for the Treatment of Bladder Cancer

BACKGROUND: As the acceptance of cryoablative therapies for the treatment of non-metastatic cancers continues to grow, avenues for novel cryosurgical technologies and approaches have opened. Within the field of genitourinary tumors, cryosurgical treatments of bladder cancers remain largely investigational. Current modalities employ percutaneous needles or transurethral cryoballoons or sprays, and while results have been promising, each technology is limited to specific types and stages of cancers. OBJECTIVE: This study evaluated a new, self-contained transurethral cryocatheter, FrostBite-BC, for its potential to treat bladder cancer. METHODS: Thermal characteristics and ablative capacity were assessed using calorimetry, isothermal analyses, in vitro 3-dimensional tissue engineered models (TEMs), and a pilot in vivo porcine study. RESULTS: Isotherm assessment revealed surface temperatures below – 20°C within 9 sec. In vitro TEMs studies demonstrated attainment of ≤– 20°C at 6.1 mm and 8.2 mm in diameter following single and double 2 min freezes, respectively. Fluorescent imaging 24 hr post-thaw revealed uniform, ablative volumes of 326.2 mm3 and 397.9 mm3 following a single or double 2 min freeze. In vivo results demonstrated the consistent generation of ablative areas. Lesion depth was found to correlate with freeze time wherein 15 sec freezes resulted in ablation confined to the sub-mucosa and ≥30 sec full thickness ablation of the bladder wall. CONCLUSIONS: These studies demonstrate the potential of the FrostBite-BC cryocatheter as a treatment option for bladder cancer. Although preliminary, the outcomes of these studies were encouraging, and support the continued investigation into the potential of the FrostBite-BC cryocatheter as a next generation, minimally invasive cryoablative technology.

Assessment of Cryosurgical Device Performance Using a 3D Tissue-Engineered Cancer Model

As the clinical use of cryoablation for the treatment of cancer has increased, so too has the need for knowledge on the dynamic environment within the frozen mass created by a cryoprobe. While a number of factors exist, an understanding of the iceball size, critical isotherm distribution/penetration, and the resultant lethal zone created by a cryoprobe are critical for clinical application. To this end, cryoprobe performance is typically characterized based on the iceball size and temperature penetration in phantom gel models. Although informative, these models do not provide information as to the impact of heat input from surrounding tissue nor give any information on the ablative zone created. As such, we evaluated the use of a tissue-engineered tumor model (TEM) to assess cryoprobe performance including iceball size, real-time thermal profile distribution, and resultant ablative zone. Studies were conducted using an Endocare V-probe cryoprobe, with a 10/5/10 double freeze–thaw protocol using prostate and renal cancer TEMs. The data demonstrate the generation of a 33- to 38-cm3 frozen mass with the V-Probe cryoprobe following the double freeze of which ∼12.7 and 6.5 cm3 was at or below −20°C and −40°C, respectively. Analysis of ablation zone using fluorescence microscopy 24 hours postthaw demonstrated that the internal ∼40% of the frozen mass was completely ablated, whereas in the periphery of the iceball (outer 1 cm region), a gradient of partial to minimal destruction was observed. These findings correlated well with clinical reports on renal and prostate cancer cryoablation. Overall, this study demonstrates that TEMs provide an effective model for a more complete characterization of cryoablation device performance. The data demonstrate that while the overall iceball size generated in the TEM was consistent with published reports from phantom models, the integration of an external heat load, circulation, and cellular components more closely reflect an in vivo setting and the impact of penetration of the critical (−20°C and −40°C) isotherms into the tissue. This is important as it is well appreciated in clinical practice that the heat load of a tissue, cryoprobe proximity to vasculature, and so on, can impact outcome. The TEM model provides a means of characterizing the impact on ablative dose delivery allowing for a better understanding of probe performance and potential impact on ablative outcome.

Re-purposing cryoablation: a combinatorial 'therapy' for the destruction of tissue

It is now recognized that the tumor microenvironment creates a protective neo-tissue that isolates the tumor from the various defense strategies of the body. Evidence demonstrates that, with successive therapeutic attempts, cancer cells acquire resistance to individual treatment modalities. For example, exposure to cytotoxic drugs results in the survival of approximately 20-30% of the cancer cells as only dividing cells succumb to each toxic exposure. With follow-up treatments, each additional dose results in tumor-associated fibroblasts secreting surface-protective proteins, which enhance cancer cell resistance. Similar outcomes are reported following radiotherapy. These defensive strategies are indicative of evolved capabilities of cancer to assure successful tumor growth through well-established anti-tumor-protective adaptations. As such, successful cancer management requires the activation of multiple cellular 'kill switches' to prevent initiation of diverse protective adaptations. Thermal therapies are unique treatment modalities typically applied as monotherapies (without repetition) thereby denying cancer cells the opportunity to express defensive mutations. Further, the destructive mechanisms of action involved with cryoablation (CA) include both physical and molecular insults resulting in the disruption of multiple defensive strategies that are not cell cycle dependent and adds a damaging structural (physical) element. This review discusses the application and clinical outcomes of CA with an emphasis on the mechanisms of cell death induced by structural, metabolic, vascular and immune processes. The induction of diverse cell death cascades, resulting in the activation of apoptosis and necrosis, allows CA to be characterized as a combinatorial treatment modality. Our understanding of these mechanisms now supports adjunctive therapies that can augment cell death pathways.

Temperature-dependent activation of differential apoptotic pathways during cryoablation in a human prostate cancer model

BACKGROUND

Critical to the continual improvement of cryoablation efficacy is deciphering the biochemical responses of cells to low-temperature exposure. The identification of delayed-onset cell death has allowed for the manipulation of cellular responses through the regulation of apoptosis. We hypothesized that in addition to delayed apoptotic events associated with mild subfreezing temperatures (10 to -25 °C), cells exposed to ultra-low temperatures (<-30 °C) may undergo rapid, early-onset apoptosis.

METHODS

Human prostate cancer model and cells (PC-3) were exposed to temperatures of -60, -30 and -15 °C to simulate a cryoablative procedure. Using a combination of flow-cytometry, fluorescent microscopy and western blot analyses, samples were assessed at various times post thaw to identify the presence, levels and the pathways involved in cell death.

RESULTS

Exposure to temperatures <-30 °C yielded a significant apoptotic population within 30 min of thawing, peaking at 90 min (~40%), and by 6 h, only necrosis was observed. In samples only reaching temperatures >-30 °C, apoptosis was not noted until 6-24 h post thaw, with the levels of apoptosis reaching ~10% (-15 °C) and ~25% (-30 °C) at 6 h post thaw. Further, it was found that early-onset apoptosis progressed through a membrane-mediated mechanism, whereas delayed apoptosis progressed through a mitochondrial path.

CONCLUSIONS

These data demonstrate the impact of apoptotic continuum, whereby the more severe cryogenic stress activated the extrinsic, membrane-regulated pathway, whereas less severe freezing activated the intrinsic, mitochondrial-mediated path. The rapid induction and progression of apoptosis at ultra-low temperatures provides an explanation as to why such results have not previously been identified following freezing. Ultimately, an understanding of the events and signaling pathways involved in triggering apoptosis following freezing may provide a path for selective induction of the rapid-onset and delayed programmed cell death pathways in an effort to improve the overall cryoablation efficacy.

Vitamin D(3) cryosensitization increases prostate cancer susceptibility to cryoablation via mitochondrial-mediated apoptosis and necrosis

OBJECTIVES

To investigate the effect and molecular mechanisms of action of Vitamin D(3) (VD(3) ) as a neo-adjunctive agent before cryosurgery in an effort to increase treatment efficacy for prostate cancer (CaP). To eliminate the potential for disease recurrence that exists at the periphery of the freeze lesion, where temperatures may be insufficient to destroy both androgen-sensitive (AS) and androgen-insensitive (AI) CaP.

METHODS

Human CaP cells, LNCaP, were each genetically altered to express the AS and AI phenotypes and subjected to VD(3) treatment and freezing in an in vitro and tissue-engineered model. Cell viability, caspase inhibitor and western blot studies were used to determine the basis of the different responses of AI and AS cells to VD(3) cryosensitization.

RESULTS

VD(3) was found to be a highly effective cryosensitizer, resulting in a >50% overall increase in cell death after -15 °C freezing. Fluorescence microscopy, western blot analysis and caspase protease assays confirmed that the increased activation of apoptosis was modulated through a mitochondrial-mediated pathway. Caspase inhibition studies showed that apoptosis played an integral role in cell death, with VD(3) cryosensitivation-induced apoptotic events responsible for >30% of the overall cell death after -15 °C freezing.

CONCLUSIONS

The present study suggests that the use of VD(3) as a cryosensitizer increases cryoablation efficacy through the increased activity of apoptosis as well as through necrosis. The data show that through VD(3) treatment the overall level of AI CaP cell tolerance to freezing is reduced to a level similar to that of AS CaP. VD(3) pre-treatment in conjunction with cryoablation may increase treatment efficacy and reduce disease recurrence for CaP patients.

Experimental cryosurgery investigations in vivo

Cryosurgery is the use of freezing temperatures to elicit an ablative response in a targeted tissue. This review provides a global overview of experimentation in vivo which has been the basis of advancement of this widely applied therapeutic option. The cellular and tissue-related events that underlie the mechanisms of destruction, including direct cell injury (cryolysis), vascular stasis, apoptosis and necrosis, are described and are related to the optimal methods of technique of freezing to achieve efficacious therapy. In vivo experiments with major organs, including wound healing, the putative immunological response following thawing, and the use of cryoadjunctive strategies to enhance cancer cell sensitivity to freezing, are described.

Inhibition of the aquaporin 3 water channel increases the sensitivity of prostate cancer cells to cryotherapy

Aquaporins (AQPs) are intrinsic membrane proteins that facilitate selective water and small solute movement across the plasma membrane. In this study, we investigate the role of inhibiting AQPs in sensitising prostate cancer cells to cryotherapy. PC-3 and DU145 prostate cancer cells were cooled to 0, −5 and −10°C. The expression of AQP3 in response to freezing was determined using real-time quantitative polymerase chain reaction (RT–qPCR) and western blot analysis. Aquaporins were inhibited using mercuric chloride (HgCl₂) and small interfering RNA (siRNA) duplex, and cell survival was assessed using a colorimetric assay. There was a significant increase in AQP3 expression in response to freezing. Cells treated with AQP3 siRNA were more sensitive to cryoinjury compared with control cells (P<0.001). Inhibition of the AQPs by HgCl₂ also increased the sensitivity of both cell lines to cryoinjury and there was a complete loss of cell viability at −10°C (P<0.01). In conclusion, we have shown that AQP3 is involved directly in cryoinjury. Inhibition of AQP3 increases the sensitivity of prostate cancer cells to freezing. This strategy may be exploited in the clinic to improve the efficacy of prostate cryotherapy.

Cryosurgical technique: assessment of the fundamental variables using human prostate cancer model systems

Cryosurgery offers a promising therapeutic alternative for the treatment of prostate cancer. While often successful, complete cryoablation of cancerous tissues sometimes fails due to technical challenges. Factors such as the end temperature, cooling rate, duration of the freezing episode, and repetition of the freezing cycle have been reported to influence cryosurgical outcome. Accordingly, we investigated the effects of these variables in an in vitro prostate cancer model. Human prostate cancer PC-3 and LNCaP cultures were exposed to a range of sub-zero temperatures (-5 to -40 degrees C), and cells were thawed followed by return to 37 degrees C. Post-thaw viability was assessed using a variety of fluorescent probes including alamarBlue (metabolic activity), calceinAM (membrane integrity), and propidium iodide (necrosis). Freeze duration following ice nucleation was investigated using single and double freezing cycles (5, 10, and 20 min). The results demonstrated that lower freezing temperatures yielded greater cell death, and that LNCaP cells were more susceptible to freezing than PC-3 cells. At -15 degrees C, PC-3 yielded approximately 55% viability versus approximately 20% viability for LNCaP. Double freezing cycles were found to be more than twice as destructive versus a single freeze-thaw cycle. Both cell types experienced increased cell death when exposed to freezing temperatures for longer durations. When thawing rates were considered, passive (slower) thawing following freezing yielded greater cell death than active (faster) thawing. A 20% difference in viability between passive and active thawing was observed for PC-3 for a 10 min freeze. Finally, the results demonstrate that just reaching -40 degrees C in vitro may not be sufficient to obtain complete cell death. The data support the use of extended freeze times, multiple freeze-thaw cycles, and passive thawing to provide maximum cell destruction.