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ABSTRACT Immune responses against oncolytic adenovirus (Ad) vectors are thought to limit vector anti-tumor efficacy. With Syrian hamsters, which are immunocompetent and whose tumors and

normal tissues are permissive for replication of Ad5-based oncolytic Ad vectors, treating with high-dose cyclophosphamide (CP) to suppress the immune system and exert chemotherapeutic

effects enhances Ad vector anti-tumor efficacy. However, long-term CP treatment and immunosuppression can lead to anemia and vector spread to normal tissues. Here, we employed three cycles

of transient high-dose CP administration plus intratumoral injection of the oncolytic Ad vector VRX-007 followed by withdrawal of CP. Each cycle lasted 4–6 weeks. This protocol allowed the

hamsters to remain healthy so the study could be continued for ∼100 days. The tumors were very well suppressed throughout the study. With immunocompetent hamsters, the vector retarded tumor

growth initially, but after 3–4 weeks the tumors resumed rapid growth and further injections of vector were ineffective. Preimmunization of the hamsters with Ad5 prevented vector spillover

from the tumor to the liver yet still allowed for effective long-term anti-tumor efficacy. Our results suggest that a clinical protocol might be developed with cycles of transient

chemotherapy plus intratumoral vector injection to achieve significant anti-tumor efficacy while minimizing the side effects of cytostatic treatment. SIMILAR CONTENT BEING VIEWED BY OTHERS

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IMMUNOCOMPETENT TRIPLE NEGATIVE MOUSE MAMMARY TUMOR MODEL Article Open access 24 January 2024 INTRODUCTION Oncolytic adenovirus (Ad) vectors are emerging as a promising form of cancer

therapy (reviewed in refs.1, 2, 3, 4, 5). To be effective, oncolytic viruses need to infect and lyse cancer cells and, in theory, spread efficiently throughout the tumor. Two major barriers

for efficient spread of the vector inside the tumor are hypothesized to include the tumor architecture (physical barrier)6, 7 and the immune system (which clears the vector from the tumor

site).8, 9 We and others have employed the Syrian hamster as a model to study the anti-tumor efficacy, biodistribution and toxicity of oncolytic Ad Serotype 5 (Ad5)-based vectors (reviewed

in refs.10, 11). The virtues of this model are that numerous Syrian hamster tumor cell lines exist that are permissive for Ad5 and that form tumors in hamsters, the tissues of the hamsters

are permissive for Ad5 replication, and the hamsters are immunocompetent. Our long-term goals are to use this model to establish general principles and to develop protocols by which

oncolytic Ad vectors can be used to treat cancer in humans. We9, 12, 13 and others8, 14, 15, 16, 17, 18 have shown that cyclophosphamide (CP) treatment of animals bearing tumors

significantly increases vector anti-tumor efficacy following intratumoral injection of the vector as compared with the untreated counterpart. We used high-dose CP in our studies; the

increased efficacy observed might be due to the immunosuppressive effect of CP that facilitates prolonged persistence and efficient spread of the vector inside the tumor.8, 9, 14 Further,

noting that CP is a chemotherapeutic alkylating agent, we have reported that high-dose CP acts additively with the Ad vector to control tumor growth.12 In our studies, long-term treatment

with CP leads to various side effects such as anemia and increased vector toxicity due to systemic vector spread and replication in normal tissues.9 To minimize the drawbacks of long-term

treatment with CP and still achieve maximum anti-tumor efficacy, in the current study we have employed repeated cycles of transient treatment with CP and vector administration. Subcutaneous

tumors were developed in Syrian hamsters using a hamster renal cancer cell line (HaK), then the hamsters were administered high-dose CP and the tumors were injected with the Ad5-based

oncolytic vector VRX-007. Red blood cell (RBC) and white blood cell (WBC) levels were monitored, and the CP treatment was discontinued temporarily until the RBC recovered. Tumor growth was

measured throughout the study. This protocol mitigated the adverse side effects of CP (for example, anemia) and allowed the study to proceed for ∼100 days. VRX-007 is being evaluated in a

phase I dose escalation clinical trial: intratumoral injection of VRX-007 into advanced solid tumors of any indication (Protocol #510-732). VRX-007 retains all Ad5 genes except those in the

E3 region. To investigate the role of preexisting immunity to Ad5 in vector anti-tumor efficacy and to restrict vector spillover from the tumor to normal tissues in hamsters immunosuppressed

by CP in this long-term study, we immunized the hamsters with Ad5 before CP treatment. Preexisting immunity in the hamster model resembles the situation in many cancer patients inasmuch as

most of the human population in the world has immunity to Ad5.19 We found that tumor growth was effectively suppressed in the preimmunized hamsters and that preimmunization successfully

prevented vector spillover and infection of the liver. MATERIALS AND METHODS ANIMALS Syrian (Golden) hamsters (_Mesocricetus auratus_; 4–5 weeks old) were obtained from Harlan Sprague Dawley

(Indianapolis, IN). Saint Louis University Institutional Animal Care and Use Committee approved the studies. The studies were conducted in accordance with institutional and federal

regulations. VIRUSES AND VECTORS The oncolytic Ad vector VRX-007 is based on Ad5. VRX-007 lacks most of the E3 genes and overexpresses the E3-11.6K Adenovirus Death Protein.20, 21 All other

genes in VRX-007 are intact; despite this, VRX-007 replicates with about 100-fold greater yield in human A549 human lung cancer cells than in primary bronchial epithelial cells22 and it

replicates poorly in quiescent versus proliferating primary human bronchial epithelial cells.23 Introgen Therapeutics (Houston, TX) kindly provided us with the purified stocks.13, 24 VRX-007

is named INGN 007 in some previous publications. IMMUNIZATION Single intramuscular injection of Ad5 (1 × 1010 plaque forming units (p.f.u.)) was used to generate preexisting immunity in

some groups of hamsters 15 days before injecting HaK cells to form tumors.13 ANTITUMOR THERAPY: CYCLES OF TREATMENT WITH CP, INTRATUMORAL INJECTION WITH VRX-007, AND RECOVERY FROM CP

Subcutaneous tumors were established in the hind flank of hamsters by injecting 2 × 107 hamster kidney cancer cells (HaK) in 200 μl of serum-free DMEM.13 When the mean tumor volumes reached

∼600–700 μl, the treatment procedures started. Tumors of ∼600–700 μl are considerably larger than tumors typically studied in animal models using oncolytic viral vectors. The experimental

groups are shown in Table 1. Some groups of hamsters were subjected to the cycles of CP treatment, intratumoral VRX-007 injection, then withdrawal from CP (see Figures 2 and 3). These

hamsters were treated with CP (Sigma-Aldrich, St Louis, MO), and were housed in sterile caging and fed irradiated chow and antibiotic (Baytril Bayer HealthCare (Shawnee Mission, KS)) treated

water.9, 13, 24 The initial dose of CP was 140 mg kg−1 body weight and the subsequent doses were 100 mg kg−1 twice weekly. About 1 week following the first injection of CP and coinciding

with the third CP injection, when the hamsters were severely immunosuppressed, the tumors were administered 5 daily injections of VRX-007, 1 × 1010 p.f.u. per injection. The levels of RBC

and WBC including lymphocytes were monitored by periodic analysis of complete blood counts throughout the length of the study. When the hamsters started to show signs of anemia (less than

normal RBC), the CP was withdrawn and the hamsters were allowed to recover to normal RBC levels. This withdrawal period completed the cycle. Three cycles of CP treatment–VRX-007 intratumoral

injection–withdrawal from CP were completed. The CP-VRX-007 treatment immunosuppression/chemotherapy periods were ∼18–24 days and the recovery periods were ∼14–22 days. Tumor volumes were

measured using digital calipers twice every week. HISTOPATHOLOGY The tumors from each animal were fixed in 10% neutral-buffered formalin. After fixation, the tumors were trimmed, embedded in

paraffin, sectioned (5 μm), and stained with hematoxylin-eosin. A Nikon Optiphot microscope (Nikon, Melville, NY) equipped with a Nikon DXM1200 digital camera and ACT-1 software (Nikon) was

used to capture the images. To obtain a comprehensive view of the tumor, several images were taken from one end of the tumor section to the other end traversing through the center of the

tumor. The images were then stitched together using Adobe Photoshop and Illustrator softwares. NEUTRALIZATION ASSAY Neutralization assay was performed as described previously.13, 24 The

neutralizing antibodies (NAb) titers were determined by the highest dilution of serum/tissue extract that resulted in at least 50% inhibition of cytopathic effect by 100 p.f.u. of VRX-007

assayed on A549 cells. VIRUS QUANTIFICATION IN TISSUES The whole tumor and part of the right lateral lobe of the liver were collected at the time of killing. All the tissues were frozen

immediately in liquid nitrogen and stored at −80 °C. The tissues were weighed and processed as described elsewhere.13, 25 The infectious virus titers were determined by tissue culture

infectious dose 50% (TCID50) assay on A549 cells.13, 25 STATISTICAL ANALYSIS The overall treatment effect was determined by the Kruskal–Wallis test and the Mann–Whitney _U_ test was used for

pairwise comparisons. _P_⩽0.05 was considered to be significant. RESULTS KINETICS OF RBC, WBC AND LYMPHOCYTE DECLINE AFTER TREATMENT WITH CP, THE RECOVERY KINETICS AFTER WITHDRAWAL FROM CP,

AND THE GENERATION OF NEUTRALIZING ANTIBODIES AGAINST VRX-007 Before beginning the tumor growth control study, namely cycles of CP and VRX-007 administration, we conducted an experiment to

define the kinetics of RBC, WBC and lymphocyte decline after treatment with CP, the recovery kinetics of these cells after the hamsters were taken off CP, and the generation of NAb against

VRX-007. One group of hamsters was subjected to one round of CP treatment (Figure 1a) and the second group received a second and third round of CP (Figure 1c). VRX-007 was injected

intramuscularly after the first (Figure 1a) or the second (Figure 1c) round of CP and the response of NAb at various days was determined (Figures 1b and d). The WBC (Figure 1a) and

lymphocyte (not shown) counts declined very rapidly by day 10 following the first CP treatment, and the hamsters became severely immunosuppressed. The RBC counts remained within normal range

at 10 days (Figure 1a). The hamsters from the first group were allowed to recover partially from immunosuppression, then VRX-007 was injected at day 14 (that is, 14 days after the first

injection of CP) (Figure 1a). Serum was collected at days 21, 31 and 42, and NAb titers were determined. As shown in Figure 1b, there was a moderate NAb response (∼1:400) at day 21 that

increased to 1:760 at day 42. Thus, the naïve lymphocytes that developed following withdrawal from CP were capable of mounting an NAb response against the vector after only 7 days following

withdrawal from CP. The second group of hamsters was subjected to three rounds of CP (Figure 1c). VRX-007 was injected at day 42, during the lymphocyte recovery period following the second

round of CP (Figure 1c). At 7 days following VRX-007 injection, the hamsters were treated a third time with CP, and the lymphocytes declined again. A good NAb response was observed at day 49

(∼1:1920) that probably was generated by lymphocytes between day 41 and 49 when CP was administered again. Little or no NAb was detected by day 60 (Figure 1d). Importantly, the RBC levels

for the most part recovered when the CP was withdrawn (Figures 1a and c). As such, the hamsters did not become anemic. In summary, the levels and function of RBC and lymphocytes can be

controlled by using rounds of CP treatment. Lymphocytes formed following CP withdrawal are able to generate NAb within 7 days of VRX-007 intramuscular injection. DESIGN OF THE LONG-TERM

TUMOR GROWTH CONTROL STUDY We next conducted the tumor growth control study being guided in part by the findings from Figure 1. As part of the study, we wished to evaluate the anti-tumor

efficacy of intratumoral VRX-007 in immunocompetent hamsters, the anti-tumor efficacy of cycles of treatment with CP and VRX-007, whether the cycling of CP mitigated anemia, whether cycling

controlled the levels of WBC, and the role of preexisting NAb to the vector. Six groups of hamsters bearing subcutaneous HaK tumors were established. The nature of these groups is depicted

in Table 1. These groups and the results obtained will be described in the following sections. The procedure used for the multiple cycles of transient treatment with CP followed by VRX-007

intratumoral administration is shown in Figures 2 and 3 and is described in the legend of Figure 3. The study lasted ∼100 days following the first treatment with CP. During the entire study

the RBC and WBC levels were monitored closely (Figure 2), and were used to determine the duration of CP treatment and the recovery period. The tumor growth measurements are in Figure 3. For

ease of presentation and discussion, the cumulative tumor growth is shown after the first (Figure 3a), second (Figure 3b) and third (Figure 3c) cycles of CP and vector administration. Tumors

from an arm of the experiment were harvested at days 43, 74 and 90 and the NAb titers and the amount of VRX-007 in the tumors were determined (Figure 4). Histopathology of typical

hematoxylin-eosin-stained tumors at day 46 is in Figure 5. VRX-007 IS EFFECTIVE FOR A PERIOD IN IMMUNOCOMPETENT HAMSTERS, BUT THEN TUMOR REGROWTH OCCURS AND A SECOND SERIES OF VECTOR

INJECTION IS NOT EFFECTIVE As shown in Figure 3a, growth of tumors was rapid in preimmunized hamsters that were immunocompetent and treated with buffer alone (Imm+Buffer) or hamsters that

were immunosuppressed with CP and treated with buffer (Imm+CP+Buffer). The CP treatment retarded tumor growth slightly, but it was not statistically significant (_P_=0.347) (Figure 3a). The

buffer-injected groups were terminated at 28 days because of their large tumor burden. Injection of VRX-007 into tumors of immunocompetent hamsters (NonImm+007, Imm+007) retarded tumor

growth for 3–4 weeks compared with the buffer control (_P_=0.005) (Figure 3a). However, the vector-injected tumors then began to grow rapidly (Figure 3b). Notably, a second round of

intratumoral vector injection (5 consecutive daily injections of 1 × 1010 p.f.u. per injection, at days 29–33) did not affect the increased tumor growth rate (Figure 3b). These hamsters were

terminated at day 46. It is important to understand why VRX-007 ceased to be effective in these immunocompetent hamsters. One reason could be vector elimination by NAb. Indeed, anti-Ad5 NAb

was very high in the tumors at day 43 (∼1:40 960 in the Imm+007 group, ∼1:10 240 in the Non-Imm+007 group) (Figure 4a). Not surprisingly from these high NAb levels, vector could not be

detected in the tumors of these groups (Figure 4b). Those tumors from animals that were not treated with CP contained mostly viable cells (Figure 5, top two panels), indicating that the

tumors were growing rapidly. CP PLUS VRX-007 CAN BE ADMINISTERED IN MULTIPLE CYCLES AND ARE STRONGLY SUPPRESSIVE OF TUMOR GROWTH The following discussion pertains to the groups treated with

CP plus vector. First, considering the preimmunized group (Imm+CP+007), at 28 days, the tumors grew faster than for the NonImm+CP+007 group (_P_=0.015) (Figure 3a). This lesser vector

efficacy in the Imm+CP+007 group was likely due to the presence of NAbs inside the tumor at the time of vector administration as described in our previous studies.13 After the second cycle

of CP treatment–vector injection–recovery, tumors in both CP groups (Imm+CP+007 and Non-Imm+CP+007) were controlled much better than the tumors in the non-CP groups injected with VRX-007

(_P_=0.000) (Figure 3b). Clearly, the combination of high-dose CP treatment plus vector is much superior to either CP alone or vector alone. The question arises whether CP is enhancing

vector replication and persistence though CP’s immunosuppressive activity and/or whether CP is acting as a chemotherapeutic agent. It is noteworthy that after the second cycle of CP–vector

injection–recovery the tumors in the Imm+CP+007 group were controlled equally as well as in the NonImm+CP+007 group (_P_=0.581) (Figure 3b). As shown in Figure 4a, at day 43, NAb was found

in the tumors of the Imm+CP+007 group (∼1:320) and the NonImm+CP+007 group (∼1:40). No vector was detected in the tumors of these groups. It should be noted that the data in Figures 4a and b

are from tumors collected 14 days after the last vector injection, and also that the tumors at this point consisted mostly of necrotic areas and with limited patches of viable cells (see

Figures 5c and d). No doubt there was vector in the tumors at the time of injection; the lack of vector in the tumors at day 43 is probably due to a combination of vector neutralization by

NAb and a paucity of viable cells in the tumors from the CP-treated hamsters in which the vector can replicate. In any case, the suppression of tumor growth in the absence of vector suggests

that CP is having a chemotherapeutic effect over the period days 28–46. Starting at about day 65, tumors in both CP+vector groups started to grow again (Figure 3c). This could be because

the tumors were devoid of vector (that is, there was no vector at day 43, see Figure 4b). Also, the hamsters had been off CP for 18 days, so any chemotherapeutic effect due to CP might be

waning. A third cycle of CP treatment was administered at days 63–88, and vector was injected for a third round at days 69–73 (Figure 3c). This CP+vector treatment seemed to stop the

regrowth of tumors and cause a decrease in tumor size (Figure 3c). Measurement of tumors continued until day 90 following the first injection of vector. Remarkably, the tumors in both

CP-treated groups were controlled very well and equally well (_P_=0.190) with a tumor volume almost equal to the starting volume. Again, the question arises, what is responsible for

retarding the tumor growth: the vector, CP or both? At day 74, 1 day after the last injection of vector in the third cycle of vector injection, high levels of vector (108 TCID50 units) were

detected in the tumors of the NonImm+CP+007 group, and much lower levels (∼103 TCID50 units) in the Imm+CP+007 group (Figure 4d). At day 90, 18 days after the last injection of vector,

vector (∼105 TCID50 units) continued to be isolated from tumors in the NonImm+CP+007 group, but not from the Imm+CP+007 group (Figure 4f). The tumors of the Imm+CP+007 group seemed to have

more NAb than the NonImm+CP+007 group at day 74 (Figure 4c) and day 90 (Figure 4e), and that could explain why the Imm+CP+007 tumors had less vector. In any case, considering that the

NonImm+CP+007 group had the most vector in the tumor yet had similar growth suppression as the Imm+CP+007 group, it seems possible that the tumor growth suppression may be due to CP

chemotherapy. However, the vector injected at days 69–73 likely contributed as well to suppression of tumor growth. Even though the tumors in the hamsters were very well controlled, some

animals died during the late phases of the study. Upon necropsy, it was found that the subcutaneous tumor had metastasized to several tissues such as lungs and kidney that might be the

reason for the deaths (Supplementary Figure 1). Therefore, we terminated the experiment at day 90 post first vector injection. Figure 5 shows the histopathology analysis of representative

tumors at day 46 of the experiment. The tumors from the non-CP-treated groups appeared to have viable cells (purple stained cells) throughout much of the tumor (Figures 5a and b), which

explains why these tumors were growing rapidly (Figure 3b). As discussed, the high NAb in these tumors likely eliminated the vector. The tumors from the CP+VRX-007 groups had very few viable

cells and large necrotic areas after the second cycle (Figures 5c and d) and also after the third cycle (data not shown). The paucity of viable cells in these latter tumors may explain why

these tumors had little vector remaining (Figure 4b) from the last injection of vector 10 days previously, and why these tumors were growing slowly, if at all. Notably, the tumor mass that

we were measuring using digital calipers (Figure 3) in the hamsters that underwent cycling comprised mainly dead tissue. SERUM NEUTRALIZING ANTIBODIES PREVENT VRX-007 SPILLOVER FROM THE

TUMOR TO THE LIVER We investigated whether serum NAb could minimize vector spillover from tumors. As shown in Figure 4g for the Imm+CP+007 group, preimmunization effectively prevented vector

spillover from the tumor to the liver at all time points (days 43, 74 and 90). The naïve hamsters (NonImm+CP+007), on the other hand, had vector in the liver: ∼106 TCID50 per gram of liver

at day 43 and ∼3 × 104 TCID50 per gram of liver at day 74 (Figure 4g). No vector was detected in the liver at day 90 (kill). DISCUSSION A notable aspect of our results is that, in

immunocompetent hamsters, VRX-007 injected intratumorally is able to retard tumor growth for 3–4 weeks, but then tumors start to grow rapidly. A second round of vector injection has no

effect on tumor growth, probably because there are high levels of NAb in the tumor. These results are important considering that clinical protocols usually recommend multiple rounds of

vector injection into patients that are for the most part immunocompetent.26, 27 Another notable aspect of our results is that the combination of intratumoral injection with VRX-007 plus

high-dose CP treatment is much more effective at suppressing tumor growth than either VRX-007 alone or CP alone. With our cycling protocol, we were able to achieve very effective long-term

control of tumor growth due to aggressive virotherapy (high dose of VRX-007) and chemotherapy (high dose of CP), while mitigating, at least to some degree, the toxic effects of high-dose CP.

This tumor growth suppression was achieved even though the starting tumors were large (600–700 μl) and vascularized. Another aspect of our results is that preimmunization of the hamsters

with Ad5 did not affect the long-term anti-tumor efficacy of the VRX-007+CP combination. Importantly, preimmunization was able to prevent spillover of VRX-007 from the tumors to the liver

over the course of 90 days following first intratumoral injection of vector in the hamsters that were treated with CP. CP has been employed by a number of laboratories to increase the

anti-tumor efficacy and/or to decrease the immune response to oncolytic vectors including those based on Ad,9, 12, 13, 15, 24, 28, 29 herpes simplex virus type 1,8, 16 reovirus,14 measles

virus,17, 30 vesicular stomatitis virus30 and vaccinia virus.18 A variety of CP doses and dosing regimes have been used, usually in mouse models. Peng _et al_30 concluded that 120 mg kg−1 of

CP given daily by intraperitoneal injection for 4 days was a good regime to control the humoral response to intravenously administered oncolytic measles virus or vesicular stomatitis virus,

but they did not study suppression of tumor growth. They noted that this regime was similar to CP dosing regimes used in humans for chemotherapy of cancer. With oncolytic Ads in the Syrian

hamster tumor model, low-dose CP, for example, 20 mg kg−1 intraperitoneally twice per week31 or 300 or 500 mg kg−1 given once intraperitoneally,28 has been used as a means to specifically

delete regulatory T cells. Low-dose CP, for example, metronomic dosing of 50 mg kg−1, has been used in cancer patients in combination with oncolytic Ad vectors.28, 31 Another laboratory15

working with an oncolytic Ad vector in the Syrian hamster model reported the successful use of intermediate-dose CP (37 mg kg−1, twice weekly) as well as the high-dose regime used in our

current study. As discussed above, high-dose CP administered to animal models is toxic. However, our results reported here suggest that cycles of transient chemotherapy (and

immunosuppression) using CP and vector intratumoral administration is a promising approach, one that has not been attempted previously in an immunocompetent animal model that is permissive

for replication of oncolytic Ad vectors. The procedure allowed us to control the tumor growth and to keep the hamsters healthier for a much longer time than in previous studies. We speculate

from our results that a clinical protocol might be developed with cycles of transient chemotherapy coupled with multiple rounds of intratumoral vector injection to achieve significant

antitumor efficacy while minimizing the side effects of chemotherapy and vector. Chemotherapy regimens involve repeated cycles of dosing of the chemotherapy drug followed by recovery similar

to the protocol employed by us in the current study. We used high-dose CP, but an intermediate dose such as 37 mg kg−1, twice weekly, might be sufficient.15 Also, other chemotherapeutic

agents could work as well as many of these cause transient immunosuppression. To prevent vector spread, patients could either be immunized with a replication-defective Ad before the

treatment, screened for preexisting anti-Ad NAb, or patients could be passively immunized with anti-Ad NAb.24 Chemotherapy has shown to increase the vector efficacy when used together.32

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Download references ACKNOWLEDGEMENTS We thank Jacqueline F Spencer for her help in bleeding the animals. This research was supported by grant CA118022 to WSMW from the National Institutes of

Health. AUTHOR INFORMATION Author notes * D Dhar Present address: 2Current address: Dr Dhar, Laboratory of Gene Regulation and Signal Transduction, Department of Pharmacology, University of

California, San Diego, School of Medicine, 9500 Gilman Drive, Leichtag Building, MC 0723, La Jolla, CA 92093, USA, AUTHORS AND AFFILIATIONS * Department of Molecular Microbiology and

Immunology, Saint Louis University School of Medicine, St Louis, MO, USA D Dhar, K Toth & W S M Wold Authors * D Dhar View author publications You can also search for this author

inPubMed Google Scholar * K Toth View author publications You can also search for this author inPubMed Google Scholar * W S M Wold View author publications You can also search for this

author inPubMed Google Scholar CORRESPONDING AUTHOR Correspondence to W S M Wold. ETHICS DECLARATIONS COMPETING INTERESTS The VRX-007 vector, which is owned by VirRx, is being evaluated in a

Phase I clinical trial. WSMW and KT own stock in VirRx. ADDITIONAL INFORMATION Supplementary Information accompanies the paper on Cancer Gene Therapy website SUPPLEMENTARY INFORMATION

SUPPLEMENTARY FIGURE S1 (JPG 217 KB) SUPPLEMENTARY FIGURE LEGEND (DOC 29 KB) RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Dhar, D., Toth, K. &

Wold, W. Cycles of transient high-dose cyclophosphamide administration and intratumoral oncolytic adenovirus vector injection for long-term tumor suppression in Syrian hamsters. _Cancer Gene

Ther_ 21, 171–178 (2014). https://doi.org/10.1038/cgt.2014.13 Download citation * Received: 31 October 2013 * Revised: 06 March 2014 * Accepted: 10 March 2014 * Published: 11 April 2014 *

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