Abstract 1730: A novel chimeric virus-like drug conjugate (VDC) for the potential treatment of HPV-positive tumors

Introduction: Human papillomavirus (HPV) virus-like particles (VLPs) bind to a wide variety of tumor types via modified glycosaminoglycans (GAGs) found on the tumor cell surface. This finding led to the development of the investigational virus-like drug conjugate (VDC) belzupacap sarotalocan (bel-sar, formerly AU-011), an HPV-derived VLP conjugated to a light-activated cytotoxic payload. When activated by near-infrared light, bel-sar induced rapid tumor necrosis resulting in pro-immunogenic cell death, release of tumor neoantigens and long-term anti-tumor immunity in the TC-1 tumor model. When E6 and E7 expressing TC-1 mouse tumors were treated with the VDC, E7-specific T-cells were detected in the absence of provided tumor antigens. A novel chimeric VDC (cVDC) is now in development, in which E6 and E7 are fused to the L2 capsid protein as a means to potentially further enhance the observed anti-tumor response. This cVDC could allow for the targeted cytotoxicity of HPV-positive tumors in addition to the release of supplemental tumor antigens E6 and E7 within the now pro-immunogenic tumor milieu, potentially leading to a long term anti-tumor response.

Methods: The detoxified sequences of E6 and E7 were engineered as one fusion polypeptide on the C-terminus of the L2 minor capsid protein. Both L2/E6/E7 and L2/E7/E6 protein expression vectors were generated to determine if the order of the proteins impacted L2’s ability to co-assemble with L1, the major capsid protein. The plasmids were co-expressed alongside L1 using the mammalian 293TT expression system.

Results: Both the L2/E6/E7 and L2/E7/E7 fusion proteins were expressed and co-assembled with L1 into chimeric VLPs. Fusion protein expression was validated by western blots for L2, E6 and E7, and VLPs were confirmed by electron microscopy.

Conclusions: Preliminary data indicate that chimeric VDCs containing E6 and E7 can successfully be generated using the 293TT mammalian expression system. Studies evaluating the cytotoxicity and E6 and E7 immunogenicity of the cVDC as well as the impact on tumor targeting are underway.

Citation Format: Rhonda C. Kines, Anneli Savinainen, Elisabet de los Pinos, John T. Schiller. A novel chimeric virus-like drug conjugate (VDC) for the potential treatment of HPV-positive tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1730.

Immune checkpoint inhibition combined with targeted therapy using a novel virus-like drug conjugate induces complete responses in a murine model of local and distant tumors

Metastases remain the leading cause of cancer-related death worldwide. Therefore, improving the treatment efficacy against such tumors is essential to enhance patient survival. AU-011 (belzupacap sarotalocan) is a new virus-like drug conjugate which is currently in clinical development for the treatment of small choroidal melanoma and high-risk indeterminate lesions in the eye. Upon light activation, AU-011 induces rapid necrotic cell death which is pro-inflammatory and pro-immunogenic, resulting in an anti-tumor immune response. As AU-011 is known to induce systemic anti-tumor immune responses, we investigated whether this combination therapy would also be effective against distant, untreated tumors, as a model for treating local and distant tumors by abscopal immune effects. We compared the efficacy of combining AU-011 with several different checkpoint blockade antibodies to identify optimal treatment regimens in an in vivo tumor model. We show that AU-011 induces immunogenic cell death through the release and exposure of damage-associated molecular patterns (DAMPs), resulting in the maturation of dendritic cells in vitro. Furthermore, we show that AU-011 accumulates in MC38 tumors over time and that ICI enhances the efficacy of AU-011 against established tumors in mice, resulting in complete responses for specific combinations in all treated animals bearing a single MC38 tumor. Finally, we show that AU-011 and anti-PD-L1/anti-LAG-3 antibody treatment was an optimal combination in an abscopal model, inducing complete responses in approximately 75% of animals. Our data show the feasibility of combining AU-011 with PD-L1 and LAG-3 antibodies for the treatment of primary and distant tumors.

Harnessing Human Papillomavirus’ Natural Tropism to Target Tumors

Human papillomaviruses (HPV) are small non-enveloped DNA tumor viruses established as the primary etiological agent for the development of cervical cancer. Decades of research have elucidated HPV’s primary attachment factor to be heparan sulfate proteoglycans (HSPG). Importantly, wounding and exposure of the epithelial basement membrane was found to be pivotal for efficient attachment and infection of HPV in vivo. Sulfation patterns on HSPG’s become modified at the site of wounds as they serve an important role promoting tissue healing, cell proliferation and neovascularization and it is these modifications recognized by HPV. Analogous HSPG modification patterns can be found on tumor cells as they too require the aforementioned processes to grow and metastasize. Although targeting tumor associated HSPG is not a novel concept, the use of HPV to target and treat tumors has only been realized in recent years. The work herein describes how decades of basic HPV research has culminated in the rational design of an HPV-based virus-like infrared light activated dye conjugate for the treatment of choroidal melanoma.

Abstract 5331: Biological assessment of the virus-like drug conjugate AU-011 to specifically target a breadth of human cancer types

Introduction: AU-011 is a virus-like drug conjugate based on a human papillomavirus (HPV) derived virus-like particle (VLP) conjugated to a light-activated cytotoxic payload (IRDye700DX) currently in Phase II clinical trials for the treatment of primary choroidal melanoma. When activated by near-infrared light, AU-011 has a dual mechanism of action inducing rapid, tumor necrosis resulting in pro-immunogenic cell death and long-term anti-tumor immunity. HPV-derived VLPs bind a wide variety of tumor types via modified heparan sulfate proteoglycans (HSPG) found on the tumor surface. This study explores the breadth of tumor types that could benefit from a targeted treatment intervention with AU-011 and surveys genes and biological pathways that are positively and negatively associated with this targeting.

Methods: AU-011 binding, cytotoxicity and HSPG specificity was surveyed in 127 tumor cell lines representing breast, cervical, CNS (glioblastoma, astrocytoma), colon, esophageal, gastric, hematopoietic, lung, liver, melanoma (cutaneous or choroidal), oropharyngeal, ovarian, pancreas, prostate, renal, urothelial and skin cancers, and sarcomas (osteosarcomas, mesotheliomas, retinoblastomas). Publicly available gene expression data for 101 of these cell lines was cross-referenced to identify gene signatures that correlated (either positively or negatively) with AU-011 binding and cytotoxicity.

Results: AU-011 activity was observed for every tumor type examined, with some variation across several of the types. HSPG-specific binding was well-conserved across all tumor types tested except for most cells of lymphoid origin which are known to have HSPG deficiency. Collectively the tumor-derived cell lines exhibiting average binding EC50s < 100 pM were ocular cancers (choroidal melanomas and retinoblastomas) and solid tumors including urothelial, bone, breast, cervical, CNS, colon, cutaneous melanoma, esophageal, gastric, liver, lung, skin, oropharyngeal, ovarian, and renal. Urothelial, bone, breast, cervical, CNS, esophageal, gastric, liver, lung, melanoma, skin, ovarian, renal and retinoblastoma all exhibited AU-011 mediated cytotoxicity with an average potency of < 100pM. Correlative gene expression analysis demonstrated a strong association between AU-011 activity and genes involved in epithelial-to-mesenchymal transition, glycosaminoglycan biosynthesis/metabolism, and extracellular matrix interactions. Expression signatures for ribosomal activity and protein translation were negatively associated with AU-011 binding and activity.

Conclusions: Collectively these data demonstrate the wide potential applicability of AU-011 to target a number of tumor types, particularly those derived from neural or epithelial lineages. Importantly, a large portion of these tumors are accessible making their AU-011 targeting clinically translatable.

Citation Format: Rhonda C. Kines, Nathan R. Fons, Elisabet de los Pinos, John T. Schiller. Biological assessment of the virus-like drug conjugate AU-011 to specifically target a breadth of human cancer types [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5331.

Virus-Like Particle-Drug Conjugates Induce Protective, Long-lasting Adaptive Antitumor Immunity in the Absence of Specifically Targeted Tumor Antigens

This study examined the ability of a papillomavirus-like particle drug conjugate, belzupacap sarotalocan (AU-011), to eradicate subcutaneous tumors after intravenous injection and to subsequently elicit long-term antitumor immunity in the TC-1 syngeneic murine tumor model. Upon in vitro activation with near-infrared light (NIR), AU-011-mediated cell killing was proimmunogenic in nature, resulting in the release of damage-associated molecular patterns such as DNA, ATP, and HMGB-1, activation of caspase-1, and surface relocalization of calreticulin and HSP70 on killed tumor cells. A single in vivo administration of AU-011 followed by NIR caused rapid cell death, leading to long-term tumor regression in ∼50% of all animals. Within hours of treatment, calreticulin surface expression, caspase-1 activation, and depletion of immunosuppressive leukocytes were observed in tumors. Combination of AU-011 with immune-checkpoint inhibitor antibodies, anti-CTLA-4 or anti-PD-1, improved therapeutic efficacy, resulting in 70% to 100% complete response rate that was durable 100 days after treatment, with 50% to 80% of those animals displaying protection from secondary tumor rechallenge. Depletion of CD4⁺ or CD8⁺ T cells, either at the time of AU-011 treatment or secondary tumor rechallenge of tumor-free mice, indicated that both cell populations are vital to AU-011's ability to eradicate primary tumors and induce long-lasting antitumor protection. Tumor-specific CD8⁺ T-cell responses could be observed in circulating peripheral blood mononuclear cells within 3 weeks of AU-011 treatment. These data, taken together, support the conclusion that AU-011 has a direct cytotoxic effect on tumor cells and induces long-term antitumor immunity, and this activity is enhanced when combined with checkpoint inhibitor antibodies.

An Infrared Dye-Conjugated Virus-like Particle for the Treatment of Primary Uveal Melanoma

The work outlined herein describes AU-011, a novel recombinant papillomavirus-like particle (VLP) drug conjugate and its initial evaluation as a potential treatment for primary uveal melanoma. The VLP is conjugated with a phthalocyanine photosensitizer, IRDye 700DX, that exerts its cytotoxic effect through photoactivation with a near-infrared laser. We assessed the anticancer properties of AU-011 in vitro utilizing a panel of human cancer cell lines and in vivo using murine subcutaneous and rabbit orthotopic xenograft models of uveal melanoma. The specificity of VLP binding (tumor targeting), mediated through cell surface heparan sulfate proteoglycans (HSPG), was assessed using HSPG-deficient cells and by inclusion of heparin in in vitro studies. Our results provide evidence of potent and selective anticancer activity, both in vitro and in vivo AU-011 activity was blocked by inhibiting its association with HSPG using heparin and using cells lacking surface HSPG, indicating that the tumor tropism of the VLP was not affected by dye conjugation and cell association is critical for AU-011-mediated cytotoxicity. Using the uveal melanoma xenograft models, we observed tumor uptake following intravenous (murine) and intravitreal (rabbit) administration and, after photoactivation, potent dose-dependent tumor responses. Furthermore, in the rabbit orthotopic model, which closely models uveal melanoma as it presents in the clinic, tumor treatment spared the retina and adjacent ocular structures. Our results support further clinical development of this novel therapeutic modality that might transform visual outcomes and provide a targeted therapy for the early-stage treatment of patients with this rare and life-threatening disease. Mol Cancer Ther; 17(2); 565-74. ©2017 AACR.

Human papillomavirus capsids preferentially bind and infect tumor cells

We previously determined that human papillomavirus (HPV) virus-like particles (VLPs) and pseudovirions (PsV) did not, respectively, bind to or infect intact epithelium of the cervicovaginal tract. However, they strongly bound heparan sulfate proteoglycans (HSPG) on the basement membrane of disrupted epithelium and infected the keratinocytes that subsequently entered the disrupted site. We here report that HPV capsids (VLP and PsV) have the same restricted tropism for a wide variety of disrupted epithelial and mesothelial tissues, whereas intact tissues remain resistant to binding. However, the HPV capsids directly bind and infect most tumor-derived cell lines in vitro and have analogous tumor-specific properties in vivo, after local or intravenous injection, using orthotopic models for human ovarian and lung cancer, respectively. The pseudovirions also specifically infected implanted primary human ovarian tumors. Heparin and ι-carrageenan blocked binding and infection of all tumor lines tested, implying that tumor cell binding is HSPG-dependent. A survey using a panel of modified heparins indicates that N-sulfation and, to a lesser degree, O-6 sulfation of the surface HSPG on the tumors are important for HPV binding. Therefore, it appears that tumor cells consistently evolve HSPG modification patterns that mimic the pattern normally found on the basement membrane but not on the apical surfaces of normal epithelial or mesothelial cells. Consequently, appropriately modified HPV VLPs and/or PsV could be useful reagents to detect and potentially treat a remarkably broad spectrum of cancers.

Vaccination with human papillomavirus pseudovirus-encapsidated plasmids targeted to skin using microneedles

Human papilloma virus-like particles (HPV VLP) serve as the basis of the current licensed vaccines for HPV. We have previously shown that encapsidation of DNA expressing the model antigen M/M2 from respiratory syncytial virus (RSV) in HPV pseudovirions (PsV) is immunogenic when delivered intravaginally. Because the HPV capsids confer tropism for basal epithelium, they represent attractive carriers for vaccination targeted to the skin using microneedles. In this study we asked: 1) whether HPV16 VLP administered by microneedles could induce protective immune responses to HPV16 and 2) whether HPV16 PsV-encapsidated plasmids delivered by microneedles could elicit immune responses to both HPV and the antigen delivered by the transgene. Mice immunized with HPV16 VLP coated microneedles generated robust neutralizing antibody responses and were protected from HPV16 challenge. Microneedle arrays coated with HPV16-M/M2 or HPV16-F protein (genes of RSV) were then tested and dose-dependent HPV and F-specific antibody responses were detected post-immunization, and M/M2-specific T-cell responses were detected post RSV challenge, respectively. HPV16 PsV-F immunized mice were fully protected from challenge with HPV16 PsV and had reduced RSV viral load in lung and nose upon intranasal RSV challenge. In summary, HPV16 PsV-encapsidated DNA delivered by microneedles induced neutralizing antibody responses against HPV and primed for antibody and T-cell responses to RSV antigens encoded by the encapsidated plasmids. Although the immunogenicity of the DNA component was just above the dose response threshold, the HPV-specific immunity was robust. Taken together, these data suggest microneedle delivery of lyophilized HPV PsV could provide a practical, thermostable combined vaccine approach that could be developed for clinical evaluation.

Antibody to the gp120 V1/V2 loops and CD4+ and CD8+ T cell responses in protection from SIVmac251 vaginal acquisition and persistent viremia

The human papillomavirus pseudovirions (HPV-PsVs) approach is an effective gene-delivery system that can prime or boost an immune response in the vaginal tract of nonhuman primates and mice. Intravaginal vaccination with HPV-PsVs expressing SIV genes, combined with an i.m. gp120 protein injection, induced humoral and cellular SIV-specific responses in macaques. Priming systemic immune responses with i.m. immunization with ALVAC-SIV vaccines, followed by intravaginal HPV-PsV-SIV/gp120 boosting, expanded and/or recruited T cells in the female genital tract. Using a stringent repeated low-dose intravaginal challenge with the highly pathogenic SIVmac251, we show that although these regimens did not demonstrate significant protection from virus acquisition, they provided control of viremia in a number of animals. High-avidity Ab responses to the envelope gp120 V1/V2 region correlated with delayed SIVmac251 acquisition, whereas virus levels in mucosal tissues were inversely correlated with antienvelope CD4(+) T cell responses. CD8(+) T cell depletion in animals with controlled viremia caused an increase in tissue virus load in some animals, suggesting a role for CD8(+) T cells in virus control. This study highlights the importance of CD8(+) cells and antienvelope CD4(+) T cells in curtailing virus replication and antienvelope V1/V2 Abs in preventing SIVmac251 acquisition.

Optical imaging of HPV infection in a murine model

The development of animal models of HPV infection has given investigators a new set of tools to expand basic knowledge of the early events of infection in vivo. The use of HPV pseudovirions, in which the viral genome has been replaced with a reporter pseudogenome, in combination with advanced imaging techniques has facilitated and simplified studies using these models. Herein we provide details for a murine model of cervicovaginal HPV infection in conjunction with several methods for imaging and quantitating the transduced genes, both ex vivo and in vivo.

Intravaginal immunization with HPV vectors induces tissue-resident CD8+ T cell responses

The induction of persistent intraepithelial CD8+ T cell responses may be key to the development of vaccines against mucosally transmitted pathogens, particularly for sexually transmitted diseases. Here we investigated CD8+ T cell responses in the female mouse cervicovaginal mucosa after intravaginal immunization with human papillomavirus vectors (HPV pseudoviruses) that transiently expressed a model antigen, respiratory syncytial virus (RSV) M/M2, in cervicovaginal keratinocytes. An HPV intravaginal prime/boost with different HPV serotypes induced 10-fold more cervicovaginal antigen-specific CD8+ T cells than priming alone. Antigen-specific T cell numbers decreased only 2-fold after 6 months. Most genital antigen-specific CD8+ T cells were intra- or subepithelial, expressed αE-integrin CD103, produced IFN-γ and TNF-α, and displayed in vivo cytotoxicity. Using a sphingosine-1-phosphate analog (FTY720), we found that the primed CD8+ T cells proliferated in the cervicovaginal mucosa upon HPV intravaginal boost. Intravaginal HPV prime/boost reduced cervicovaginal viral titers 1,000-fold after intravaginal challenge with vaccinia virus expressing the CD8 epitope M2. In contrast, intramuscular prime/boost with an adenovirus type 5 vector induced a higher level of systemic CD8+ T cells but failed to induce intraepithelial CD103+CD8+ T cells or protect against recombinant vaccinia vaginal challenge. Thus, HPV vectors are attractive gene-delivery platforms for inducing durable intraepithelial cervicovaginal CD8+ T cell responses by promoting local proliferation and retention of primed antigen-specific CD8+ T cells.

Targeting the vaginal mucosa with human papillomavirus pseudovirion vaccines delivering simian immunodeficiency virus DNA

The majority of HIV infections occur via mucosal transmission. Vaccines that induce memory T and B cells in the female genital tract may prevent the establishment and systemic dissemination of HIV. We tested the immunogenicity of a vaccine that uses human papillomavirus (HPV)-based gene transfer vectors, also called pseudovirions (PsVs), to deliver SIV genes to the vaginal epithelium. Our findings demonstrate that this vaccine platform induces gene expression in the genital tract in both cynomolgus and rhesus macaques. Intravaginal vaccination with HPV16, HPV45, and HPV58 PsVs delivering SIV Gag DNA induced Gag-specific Abs in serum and the vaginal tract, and T cell responses in blood, vaginal mucosa, and draining lymph nodes that rapidly expanded following intravaginal exposure to SIV(mac251.) HPV PsV-based vehicles are immunogenic, which warrant further testing as vaccine candidates for HIV and may provide a useful model to evaluate the benefits and risks of inducing high levels of SIV-specific immune responses at mucosal sites prior to SIV infection.

Effect of Pap smear collection and carrageenan on cervicovaginal human papillomavirus-16 infection in a rhesus macaque model

BACKGROUND

Human papillomavirus (HPV) infection of the genital mucosa is thought to require trauma to the cervicovaginal epithelium. Therefore, we determined whether a cytology specimen collection procedure (Pap smear), which disrupts the epithelium by design, renders the cervix more susceptible to HPV infection in a primate model.

METHODS

In a series of female rhesus macaques, a speculum examination was performed with (n = 8) or without (n = 4) a cytology specimen collection procedure as it is commonly practiced in a gynecology clinic. An internal digital examination was performed after specimen collection using Surgilube (n = 4) or 1% iota-carrageenan, a previously indentified HPV inhibitor (n = 4) as the lubricant. The cervix was then inoculated with HPV16 pseudovirions expressing red fluorescent protein. After 3 days, the reproductive tracts were excised and the cervix was cryosectioned. Sections were analyzed by fluorescent confocal microscopy for the number of red fluorescent protein-positive keratinocytes.

RESULTS

Substantial infection of the ectocervix, the transformation zone, and the endocervix was detected, but only in conjunction with the cytology specimen collection procedure (cytology using Surgilube vs without cytology using Surgilube, mean = 84 infectious events per section vs mean = 0.05 infectious events per section, difference = 84 infectious events per section, 95% confidence interval = 19 to 384 infectious events per section). When the carrageenan gel was substituted for Surgilube for an internal digital examination, the mean number of infectious events decreased (carrageenan gel vs Surgilube, mean = 3.5 events per section vs mean = 84 infectious events per section difference = 81 events per section, 95% confidence interval = 33 to 213 events per section).

CONCLUSIONS

These findings indicate that cytology screening in women might lead to a transient enhancement of susceptibility to HPV infection and that use of a carrageenan-based gel during the examination might mitigate this enhancement.

In vivo longitudinal imaging of experimental human papillomavirus infection in mice with a multicolor fluorescence mini-endoscopy system

Human papillomavirus (HPV) infection is the most common sexually transmitted infection. Vaccines for HPV infection can reduce the risk of developing cervical cancer. To further improve such vaccines and to explore other methods of preventing or treating viral infection, longitudinal studies in experimental animals are desirable. Here, we describe a newly developed multicolor endoscopic fluorescence imaging system to visualize early HPV infection with fluorescent protein-encoded pseudoviruses (PsV) in the female genital tract of living mice. With this imaging method, the course of HPV PsV infection and the effects of intervention to prevent infection can be monitored in a single mouse over time. Female immunocompetent or athymic mice were pretreated with a vaginal spermicide and then HPV PsV composed of an authentic viral capsid and encapsidating green or red fluorescent protein (GFP or RFP) reporter gene was intravaginally instilled. Expression of GFP or RFP was detected 1 day after PsV challenge, which peaked after 2 or 3 days and decreasing thereafter. No fluorescence was detected in vaccine-treated immunocompetent mice. By using serial infection of the same PsV type (HPV16) encoding either GFP or RFP, different infection patterns of repeated exposure can be monitored. This method offers the ability to monitor experimental virus infections before and after intervention, thereby accelerating the development of appropriate prevention and therapy.

Immunogenic display of diverse peptides, including a broadly cross-type neutralizing human papillomavirus L2 epitope, on virus-like particles of the RNA bacteriophage PP7

The immunogenicity of an antigen can be dramatically increased by displaying it in a dense, multivalent context, such as on the surface of a virus or virus-like particle (VLP). Here we describe a highly versatile VLP platform for peptide display based on VLPs of the RNA bacteriophage PP7. We show that this platform can be used for the engineered display of specific peptide sequences as well as for the construction of random peptide libraries. Peptides representing the FLAG epitope, the V3 loop of HIV gp120, and a broadly cross-type neutralizing epitope from L2, the minor capsid protein of Human Papillomavirus type 16 (HPV16), were inserted into an exposed surface loop of a form of PP7 coat protein in which the two identical polypeptides of coat were fused together to form a single-chain dimer. The recombinant proteins assembled into VLPs, displayed these peptides on their surfaces, and induced high-titer antibody responses. The single-chain dimer was also highly tolerant of random 6-, 8-, and 10-amino acid insertions. PP7 VLPs displaying the HPV16 L2 epitope generated robust anti-HPV16 L2 serum antibodies after intramuscular injection that protected mice from genital infection with HPV16 pseudovirus as well as a heterologous HPV pseudovirus type, HPV45. Thus, PP7 VLPs are well-suited for the display of a wide diversity of peptides in a highly immunogenic format.