*3.4.4 Conclusions/future directions*

DeltaRex-G has displayed through numerous clinical trials its cytocidal effect on cancer cells. This effect introduces neoantigens from the tumor into the tumor microenvironment to be recognized by the immune system and targeted for destruction through T-cell mediation. Nevertheless, these cytotoxic immune responses may not be significant enough to overcome the suppressive signals from surrounding regulatory T-cells that may also be recruited to the tumor microenvironment. The addition of DeltaVax is hypothesized to heighten the development of dendritic cells and increase proliferation and activation of T-cells, thereby improving the potency of tumor-targeted DeltaRex-G. These activated T-cells can then go

on to recognize and destroy the newly introduced tumor neoantigens. This has the potential to further tumor regression and evoke long-lasting antitumor immunity.

This data therefore strongly suggests that the advancement of personalized cancer vaccination treatment has the potential to gain control of tumor growth and increase overall survival time in patients with advanced or malignant chemoresistant solid malignancies, as well as B-cell lymphomas.

### **4. Discussion/conclusion/summary**

Targeted Immunotherapy has revolutionized the way scientists and physicians conceptualize their approaches to cancer treatment and cancer checkpoint controls. Mechanistic understanding of innate and adaptive mechanisms of immunity are considered important aspects of both physiological cancer surveillance and tumor eradication, as seen in immune checkpoint control and in precision blockade of cell cycle control elements. The low immunogenicity of cancer cells, as well as the tendency of advanced cancers to create an immunosuppressive tumor microenvironment presents a technical problem of precision tumor-targeted drug delivery for both immune checkpoint antibodies and cell cycle control elements, which form a rational basis for emerging treatments. The precision of monoclonal antibodies as checkpoint inhibitors targeting cancer cells has allowed research to advance in a direction that moves away from the untoward toxicities associated with chemotherapy towards treatments that enhance the naturally powerful cytotoxic responses of the immune system. The use of checkpoint inhibitors as cancer immunotherapy has been validated in 16 indications; however, immune checkpoint inhibition is still only considered appropriate for a specific subset of patients [58], and is often confounded by serious immune-related Adverse Events (imAEs). The significance and durability of response to treatment with checkpoint inhibitor therapy is generally dependent on tumor cells having a high mutational burden or microsatellite instability that creates an increased amount of neoantigens to be recognized and eliminated by the adaptive immune system [59]. Based on the documented physiological tumor-seeking behavior and demonstrated survival value of the tumor-targeted gene therapy vectors, DeltaRex-G and DeltaVax, in treating advanced metastatic cancers, the successful adaptation of bioactive gene-targeting biotechnologies to (i) target FDA-approved off-the shelf checkpoint monoclonal antibodies to tumors, and/or (ii) recombinant "tumor-targeted" adaptor proteins have been developed, in anticipation of precisely targeting immune checkpoint inhibitors and immunostimulatory cytokines against tumors to improve clinical outcomes.

Another strategic approach is enhancing the anti-tumor properties of innate immunity. The innate immune system is also regulated by its own activating and inhibitory pathways that can be investigated as future targets for NK cell-based immunotherapy. One important characteristic to consider when making the case for focusing on boosting innate immunity is the fact that innate immune cells play a major role in immunosurveillance, acting as the first line of defense. Engaging the innate immune system is a necessary prerequisite for antigen-specific T-cells to respond, although innate immune cells such as NK cells do not require activation of T-cells to kill tumor cells [58]. NK cell activation occurs through their direct interaction with target cells, bypassing the need for antigen presentation and processing. Innate immunity is always activated prior to adaptive immunity, however, once activated, adaptive immunity has the advantage of higher specificity and lower probability of self-harm.

In recent years, the human Cyclin G1 (*CCNG1*) gene was established as a central executive element of a Commanding Cyclin G1/Cdk/Mdm2/p53 Axis: representing

**21**

interest.

*Immune and Cell Cycle Checkpoint Inhibitors for Cancer Immunotherapy*

a strategic locus for restoring cell cycle checkpoint control through precision gene transfer. With the development of the first tumor-targeted cancer gene therapy, DeltaRex-G [60], it became possible for patients to (i) benefit clinically, (ii) enjoy good quality of life and (iii) survive appreciably longer without experiencing the debilitating toxicities of chemotherapy. The tumor-targeted DeltaRex-G vector consists of bioactive nanoparticles displaying a high-affinity targeting motif on its surface for "pathotropic" (lesion-seeking) targeting by binding to abnormal signature (SIG) proteins found abundantly in invading tumors, and then delivering a cytocidal genetic payload, a CCNG1 cell cycle checkpoint inhibitor gene, into rapidly dividing cancer cells, tumor associated microvasculature and tumor-associated fibroblasts, without collateral damage to normal cells and non-target organs. The observed reduction in tumor matrix production and tumor destruction paved the way for enhanced innate immune cell entry into the tumor microenvironment. The enhanced immune cells consist of cytotoxic T cells, NK cells, and dendritic cells for cell recognition, destruction and autoimmunization, as well as regulatory immune cells to prevent exaggerated immune responses that cause cytokine release

Hence, DeltaRex-G eradicates cancer cells without causing immune-mediated adverse events, an unwanted complication of immune checkpoint inhibitors such as ipilimumab, nivolumab, pembrolizumab, atezolizumab, etc. Conceivably, DeltaRex-G could also be used in combination with reduced doses of immune checkpoint inhibitors to minimize off-target toxicity (imAEs) and maximize

A second tumor-targeted retrovector, DeltaVax, displaying the same high-affinity tumor-targeting motif as DeltaRex-G, but this immuno-vector—encoding both the GM-CSF gene and the pro-drug regulated HSV-tk gene, and allowing for personalized "pulsed" *in situ* vaccinations—demonstrated promising results in a small Phase I/II study conducted in Manila, Philippines with considerable clinical benefit: good quality of life and an 86% one year survival rate in patients with advanced chemotherapy-resistant Stage 4 malignancies and a uniformly poor prognosis. In the era of precision medicine, with tumor-targeted cancer gene therapy and immunotherapy coming of age, these recent advances bring great optimism to the medical and scientific communities around the world and the patients that they serve.

The authors are grateful to J Isaacs Charitable Trust (UK), Thomas Makin Family, James B. Finn Memorial, ArtistsforAveni, Capital Group, Trader Joes, Holmes Family Trust, Ronald and Linda Chelsky, Ritchie and Keri Tuazon, Lance S. Ostendorf, Norma Yaeger, Lawrence Yaeger Memorial, Martin Berwitt, Adolf Weinberger Foundation, Jun and Alice de Guzman, Dr. and Mrs. Antonio Ong for

Drs. Gordon and Hall are co-inventors of the targeted gene delivery system represented by DeltaRex-G and DeltaVax which was originally developed at the University of Southern California Keck School of Medicine, and are co-founders of Delta Next-Gene, LLC. Dr. Gordon is founder and president of the Aveni Foundation, a 501c3 public charity. NLA, TTK, DAB and SPC have no competing

*DOI: http://dx.doi.org/10.5772/intechopen.96664*

syndrome or cytokine storm.

anticancer efficacy.

**Acknowledgements**

their generous donations.

**Conflict of interest**

#### *Immune and Cell Cycle Checkpoint Inhibitors for Cancer Immunotherapy DOI: http://dx.doi.org/10.5772/intechopen.96664*

*Advances in Precision Medicine Oncology*

tant solid malignancies, as well as B-cell lymphomas.

timulatory cytokines against tumors to improve clinical outcomes.

Another strategic approach is enhancing the anti-tumor properties of innate immunity. The innate immune system is also regulated by its own activating and inhibitory pathways that can be investigated as future targets for NK cell-based immunotherapy. One important characteristic to consider when making the case for focusing on boosting innate immunity is the fact that innate immune cells play a major role in immunosurveillance, acting as the first line of defense. Engaging the innate immune system is a necessary prerequisite for antigen-specific T-cells to respond, although innate immune cells such as NK cells do not require activation of T-cells to kill tumor cells [58]. NK cell activation occurs through their direct interaction with target cells, bypassing the need for antigen presentation and processing. Innate immunity is always activated prior to adaptive immunity, however, once activated, adaptive immunity has the advantage of higher specificity and lower

In recent years, the human Cyclin G1 (*CCNG1*) gene was established as a central executive element of a Commanding Cyclin G1/Cdk/Mdm2/p53 Axis: representing

**4. Discussion/conclusion/summary**

on to recognize and destroy the newly introduced tumor neoantigens. This has the potential to further tumor regression and evoke long-lasting antitumor immunity. This data therefore strongly suggests that the advancement of personalized cancer vaccination treatment has the potential to gain control of tumor growth and increase overall survival time in patients with advanced or malignant chemoresis-

Targeted Immunotherapy has revolutionized the way scientists and physicians conceptualize their approaches to cancer treatment and cancer checkpoint controls. Mechanistic understanding of innate and adaptive mechanisms of immunity are considered important aspects of both physiological cancer surveillance and tumor eradication, as seen in immune checkpoint control and in precision blockade of cell cycle control elements. The low immunogenicity of cancer cells, as well as the tendency of advanced cancers to create an immunosuppressive tumor microenvironment presents a technical problem of precision tumor-targeted drug delivery for both immune checkpoint antibodies and cell cycle control elements, which form a rational basis for emerging treatments. The precision of monoclonal antibodies as checkpoint inhibitors targeting cancer cells has allowed research to advance in a direction that moves away from the untoward toxicities associated with chemotherapy towards treatments that enhance the naturally powerful cytotoxic responses of the immune system. The use of checkpoint inhibitors as cancer immunotherapy has been validated in 16 indications; however, immune checkpoint inhibition is still only considered appropriate for a specific subset of patients [58], and is often confounded by serious immune-related Adverse Events (imAEs). The significance and durability of response to treatment with checkpoint inhibitor therapy is generally dependent on tumor cells having a high mutational burden or microsatellite instability that creates an increased amount of neoantigens to be recognized and eliminated by the adaptive immune system [59]. Based on the documented physiological tumor-seeking behavior and demonstrated survival value of the tumor-targeted gene therapy vectors, DeltaRex-G and DeltaVax, in treating advanced metastatic cancers, the successful adaptation of bioactive gene-targeting biotechnologies to (i) target FDA-approved off-the shelf checkpoint monoclonal antibodies to tumors, and/or (ii) recombinant "tumor-targeted" adaptor proteins have been developed, in anticipation of precisely targeting immune checkpoint inhibitors and immunos-

**20**

probability of self-harm.

a strategic locus for restoring cell cycle checkpoint control through precision gene transfer. With the development of the first tumor-targeted cancer gene therapy, DeltaRex-G [60], it became possible for patients to (i) benefit clinically, (ii) enjoy good quality of life and (iii) survive appreciably longer without experiencing the debilitating toxicities of chemotherapy. The tumor-targeted DeltaRex-G vector consists of bioactive nanoparticles displaying a high-affinity targeting motif on its surface for "pathotropic" (lesion-seeking) targeting by binding to abnormal signature (SIG) proteins found abundantly in invading tumors, and then delivering a cytocidal genetic payload, a CCNG1 cell cycle checkpoint inhibitor gene, into rapidly dividing cancer cells, tumor associated microvasculature and tumor-associated fibroblasts, without collateral damage to normal cells and non-target organs. The observed reduction in tumor matrix production and tumor destruction paved the way for enhanced innate immune cell entry into the tumor microenvironment. The enhanced immune cells consist of cytotoxic T cells, NK cells, and dendritic cells for cell recognition, destruction and autoimmunization, as well as regulatory immune cells to prevent exaggerated immune responses that cause cytokine release syndrome or cytokine storm.

Hence, DeltaRex-G eradicates cancer cells without causing immune-mediated adverse events, an unwanted complication of immune checkpoint inhibitors such as ipilimumab, nivolumab, pembrolizumab, atezolizumab, etc. Conceivably, DeltaRex-G could also be used in combination with reduced doses of immune checkpoint inhibitors to minimize off-target toxicity (imAEs) and maximize anticancer efficacy.

A second tumor-targeted retrovector, DeltaVax, displaying the same high-affinity tumor-targeting motif as DeltaRex-G, but this immuno-vector—encoding both the GM-CSF gene and the pro-drug regulated HSV-tk gene, and allowing for personalized "pulsed" *in situ* vaccinations—demonstrated promising results in a small Phase I/II study conducted in Manila, Philippines with considerable clinical benefit: good quality of life and an 86% one year survival rate in patients with advanced chemotherapy-resistant Stage 4 malignancies and a uniformly poor prognosis.

In the era of precision medicine, with tumor-targeted cancer gene therapy and immunotherapy coming of age, these recent advances bring great optimism to the medical and scientific communities around the world and the patients that they serve.
