Abstract B65: High levels of expression of P-glycoprotein/multidrug resistance protein result in resistance to vintafolide

Targeting surface receptors overexpressed on cancer cells is one way to specifically treat cancer versus normal cells. Vintafolide (EC145), which consists of folate linked to a cytotoxic small molecule, desacetylvinblastine hydrazide (DAVLBH), takes advantage of the overexpression of folate receptor (FR) on cancer cells. Once bound to FR, vintafolide enters the cell by endocytosis, and the reducing environment of the endosome cleaves the linker, releasing DAVLBH to destabilize microtubules. Vintafolide has shown efficacy and improved tolerability compared to DAVLBH in FR-positive preclinical models. As the first FR-targeting drug to reach the clinic, vintafolide has achieved favorable responses in Phase II clinical trials in FR-positive ovarian and lung cancer. However, some FR-positive patients in these clinical trials do not respond to vintafolide. We sought to identify potential biomarkers of resistance to aid in the future development of this and other FR-targeting drugs. Here, we confirm in both in vitro and in vivo preclinical models that high P-glycoprotein (P-gp) expression was the strongest predictor of resistance to DAVLBH in a panel of 359 cancer cell lines. Furthermore, targeted delivery of DAVLBH via the FR as in vintafolide fails to overcome P-gp mediated efflux of DAVLBH as seen in FR-expressing engineered cell lines and in vivo models. Therefore, we suggest that patients whose tumors express high levels of P-gp be excluded from future clinical trials for vintafolide as well as other FR-targeted therapeutics bearing a P-gp substrate.

Citation Format: Amy D. Guertin, Jennifer O'Neil, Alexander Stoeck, Joseph A. Reddy, Razvan Cristescu, Brian B. Haines, Marlene C. Hinton, Ryan Dorton, Alicia Bloomfield, Melissa Nelson, Marilynn Vetzel, Serguei Lejnine, Michael Nebozhyn, Theresa Zhang, Andrey Loboda, Kristen L. Picard, Emmett V. Schmidt, Isabelle Dussault, Christopher P. Leamon. High levels of expression of P-glycoprotein/multidrug resistance protein result in resistance to vintafolide. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B65.

Outcomes of a Multi-faceted Educational Intervention to Increase Student Scholarship

Objective. To increase the percentage of state, national, or international student presentations and publications. Design. A multi-faceted intervention to increase student scholarly output was developed that included: (1) a 120-minute lecture on publication of quality improvement or independent study research findings; (2) abstract workshops; (3) poster workshops; and (4) a reminder at an advanced pharmacy practice experience (APPE) meeting encouraging students to publish or present posters. The intervention effect was measured as the percent of students who presented at meetings and the number of student projects published. Assessment. A significant increase occurred in the percent of students who presented posters or published manuscripts after the intervention (64% vs 81%). Total student productivity increased from 84 to 147 posters, publications, and presentations. The number of projects presented or published increased from 50 to 77 in one year. Conclusion. This high-impact, low-cost intervention increased scholarly output and may help students stand out in a competitive job market.

Abstract 4393: Design and synthesis of novel conjugates for targeting the folate receptor: Exploiting cytotoxic GARFTase inhibitors for delivering additional chemotherapeutic payloads to cancer cells

Background:

Antifolates targeting glycinamide ribonucleotide formyltransferase (GARFTase) disrupt cell division (mitosis) by inhibiting the de novo purine biosynthesis pathway. Recently, novel GARFTase inhibitors, exhibiting high folate receptor (FR) binding affinity and low affinity for the reduced folate carrier (RFC), have been explored as chemotherapeutic agents. Theoretically, these GARFTase inhibitors could also be used as FR-targeting ligands for delivering additional payloads to tumor types over-expressing the FR. In this poster, we will present our practical approach to explore the dual role of these new GARFTase inhibitors as cytotoxic agents and as targeting ligands for delivering tubulysins. Tubulysins are natural products isolated from myxobacterial species and are highly potent mitotic poisons that inhibit tubulin polymerization.

Methods:

We developed a general method for preparing dual drug/ligand conjugates possessing two disulfide-based self-immolative linker systems. In our synthetic protocol we relied on consecutive introduction of two heterosubstituted disulfide bonds. A GARFTase inhibitor was first connected to a hydrophilic spacer unit through the first disulfide-based linker system. The obtained conjugate contains also an S-9-fluorenylmethyl (Fm)-protected thiol in its molecular architecture. Treatment with a strong organic base resulted in spontaneous removal of the Fm moiety. The deprotected thiol reacted in situ with a propreatary thiophilic tubulysin derivative, present in the reaction mixture, and a second self-immolative disulfide-based linker system was formed.

Results:

Novel conjugates of GARFTase inhibitor with tubulysins were prepared using newly designed synthetic strategies. In a high-yielding chemoselective reaction we introduced a second disulfide bond into a molecular framework without destroying the pre-existing disulfide linker system. The versatility of this synthetic protocol was demonstrated by synthesizing several related drug conjugates.

Conclusion:

In the poster to be presented, we will disclose, for the first time, the structure and synthesis of novel conjugates of GARFTase inhibitors with tubulysins. The target compounds contain two self-immolative disulfide linker systems. The observed excellent in vivo activity in tumor xenografts demonstrates the dual role of GARFTase inhibitors as therapeutic agents and as FR-targeting ligands for simultaneously delivering two highly potent payloads.

Citation Format: Iontcho R. Vlahov, Fei You, Hanna F. Klein, Paul J. Kleindl, Melissa Nelson, Marilynn Vetzel, Joseph A. Reddy, Christopher P. Leamon, Larry H. Matherly, Aleem Gangjee. Design and synthesis of novel conjugates for targeting the folate receptor: Exploiting cytotoxic GARFTase inhibitors for delivering additional chemotherapeutic payloads to cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4393. doi:10.1158/1538-7445.AM2015-4393

The clinical application of plasma Kaposi sarcoma herpesvirus viral load as a tumour biomarker: results from 704 patients

OBJECTIVES

The aim of the study was to evaluate the role of plasma Kaposi sarcoma herpesvirus (KSHV) as a diagnostic and prognostic biomarker in people living with HIV (PLWH) and diagnosed with KSHV-associated diseases.

METHODS

Using quantitative nested polymerase chain reaction (PCR) targeting the open reading frame-26 gene of KSHV, plasma levels of KSHV were measured in consecutive PLWH with KSHV-associated diseases or as part of the investigation of lymphadenopathy.

RESULTS

Plasma KSHV assays were performed on samples from 684 PLWH and 20 HIV-seronegative people with KSHV-associated malignancies. In PLWH, plasma KSHV was detected in 39% of those with KS, 99% of those with multicentric Castleman disease (MCD), 9% of those with non-Hodgkin lymphoma (NHL), 2% of those with non-AIDS-defining malignancies and 0% of those with nonmalignant lymphadenopathy. There was no significant difference in plasma KSHV viral load among those with KS, MCD and KSHV-associated NHL. The 5-year overall survival rate from KS diagnosis of 335 PLWH was 95.2% (95% confidence interval 92.6-97.8%). Plasma KSHV viraemia did not predict overall survival in those with KS (P = 0.73), nor when those with T0 stage KS (P = 0.52) or T1 stage KS (P = 0.62) were analysed separately.

CONCLUSIONS

Measuring the plasma levels of KSHV as a biomarker in KSHV-associated disease has a very limited value in either diagnosis or prognostication. The only potential role of clinical value is the suggestion that an undetectable plasma KSHV excludes a diagnosis of MCD in PLWH.

Acute hepatitis C infection in HIV-negative men who have sex with men

Acute hepatitis C infection is recognized in HIV-infected men who have sex with men (MSM), but the risk in HIV-negative MSM remains unclear. We evaluated a population of MSM with acute hepatitis C. From January 2010 to May 2014, all cases of HCV antibody positive HIV-negative MSM were identified. European AIDS Network criteria were applied to determine acute infection, and 44 individuals fulfilled the criteria for acute hepatitis C. Ten were RNA negative at baseline and classed as prior spontaneous clearance. 15 (34.1%) had a previously negative HCV antibody within 1 year. 11 (25.0%) had significant elevation in ALT levels, and 18 (40.9%) were clinically diagnosed from risk exposure and history. Median age was 37 years (range 24-75). 41 (93.2%) individuals reported unprotected anal sex, 36 with (87.8%) both insertive and receptive intercourse, 4 (9.8%) with receptive intercourse, 1 (2.4%) with insertive intercourse, and no data were recorded for 3 (7.3%) patients. Individuals had an average of 7.3 reported (median 2, range 1-100) partners. 12 (27.3%) engaged in group sex, 11 (25.0%) practised fisting, 11 (25.0%) admitted using drugs during sexual activity, 16 (36.4%) reported nasal, and 9 (20.5%) reported injection drug use. 14 (31.8)% had unprotected sex whilst under the influence of recreational drugs. 29 individuals were aware of a partner's status. 2 (4.5%) individuals had sexual contact with a known HCV monoinfected partner, 13 (29.5%) with a HIV monoinfected partner and 6 (13.6%) with a HCV/HIV coinfected partner. 9 (20.5%) reported a partner/partners with no known infection. No data were available in 14 (31.8%) individuals. 13 (29.5%) individuals had a coexisting STI at the time of acute HCV diagnosis. 8 (18.2%) received HIV postexposure prophylaxis (PEP) within the 6 months prior to the HCV diagnosis (2 were participants in a HIV pre-exposure prophylaxis trial). 15 (34.1%) individuals achieved spontaneous clearance of HCV, and 11 patients received HCV treatment. Similar to the ongoing epidemic of acute HCV infection in HIV+ MSM, HIV-negative MSM remain at risk.

Efficacy of etravirine combined with darunavir or other ritonavir-boosted protease inhibitors in HIV-1-infected patients: an observational study using pooled European cohort data

OBJECTIVES

This observational study in antiretroviral treatment-experienced, HIV-1-infected adults explored the efficacy of etravirine plus darunavir/ritonavir (DRV group; n = 999) vs. etravirine plus an alternative boosted protease inhibitor (other PI group; n = 116) using pooled European cohort data.

METHODS

Two international (EuroSIDA; EUResist Network) and five national (France, Italy, Spain, Switzerland and UK) cohorts provided data (collected in 2007-2012). Stratum-adjusted (for confounding factors) Mantel-Haenszel differences in virological responses (viral load < 50 HIV-1 RNA copies/mL) and odds ratios (ORs) with 95% confidence intervals (CIs) were derived.

RESULTS

Baseline characteristics were balanced between groups except for previous use of antiretrovirals (≥ 10: 63% in the DRV group vs. 49% in the other PI group), including previous use of at least three PIs (64% vs. 53%, respectively) and mean number of PI resistance mutations (2.3 vs. 1.9, respectively). Week 24 responses were 73% vs. 75% (observed) and 49% vs. 43% (missing = failure), respectively. Week 48 responses were 75% vs. 73% and 32% vs. 30%, respectively. All 95% CIs around unadjusted and adjusted differences encompassed 0 (difference in responses) or 1 (ORs). While ORs by cohort indicated heterogeneity in response, for pooled data the difference between unadjusted and adjusted for cohort ORs was small.

CONCLUSIONS

These data do not indicate a difference in response between the DRV and other PI groups, although caution should be applied given the small size of the other PI group and the lack of randomization. This suggests that the efficacy and virology results from DUET can be extrapolated to a regimen of etravirine with a boosted PI other than darunavir/ritonavir.

Abstract 832: Pre-clinical development of EC1456: A potent Folate targeted Tubulysin SMDC

Folate targeted small molecule drug conjugates (SMDC) have shown promising results in early stage clinical trials with Vintafolide now being evaluated in a phase 3 trial in FR-positive ovarian cancer patients. We have now developed a new group of folate conjugated Tubulysins, of which EC1456 has emerged as a lead candidate for clinical development. Treatment of nude mice bearing folate receptor (FR) positive human xenografts with EC1456 led to complete remissions (CR's) or cures in 100% of the mice at various doses and schedules. The observed activity was not accompanied by any noticeable weight loss or major organ tissue degeneration. In contrast, no significant anti-tumor activity (0 % CR's) was observed in EC1456-treated animals that were co-dosed with an excess of a benign folate ligand, thus demonstrating EC1456's target-specific activity. The enhanced therapeutic index due to folate conjugation was also evidenced by the fact that the un-targeted free drug (tubulysin B or its hydrazide form) was found to be completely inactive even when administered at highly toxic dose levels. Furthermore, when challenged with larger tumors, EC1456 again displayed remarkable anti-tumor activity with 100% cures in tumors up to 750 mm3. Complete cures were also observed in other FR positive models such as MDA-MB-231 TNBC and M109 lung tumor models. In support of our clinical strategy to treat drug resistant FR-positive cancer patients we have also shown that EC1456 was highly active against FR expressing paclitaxel and cisplatin-resistant cell lines. Taken together, these studies demonstrated that EC1456 has significant anti-tumor growth activity and tolerability, thus lending support to the ongoing Phase 1 clinical evaluation of EC1456 for advanced malignancies.

Citation Format: Joseph A. Reddy, Alicia Bloomfield, Melissa Nelson, Ryan Dorton, Marilynn Vetzel, Christopher P. Leamon. Pre-clinical development of EC1456: A potent Folate targeted Tubulysin SMDC. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 832. doi:10.1158/1538-7445.AM2014-832

Exploring the innate immunological response of an alternative nonhuman primate model of infectious disease; the common marmoset

The common marmoset (Callithrix jacchus) is increasingly being utilised as a nonhuman primate model for human disease, ranging from autoimmune to infectious disease. In order to fully exploit these models, meaningful comparison to the human host response is necessary. Commercially available reagents, primarily targeted to human cells, were utilised to assess the phenotype and activation status of key immune cell types and cytokines in naive and infected animals. Single cell suspensions of blood, spleen, and lung were examined. Generally, the phenotype of cells was comparable between humans and marmosets, with approximately 63% of all lymphocytes in the blood of marmosets being T cells, 25% B-cells, and 12% NK cells. The percentage of neutrophils in marmoset blood were more similar to human values than mouse values. Comparison of the activation status of cells following experimental systemic or inhalational infection exhibited different trends in different tissues, most obvious in cell types active in the innate immune response. This work significantly enhances the ability to understand the immune response in these animals and fortifies their use as models of infectious disease.

Folate-vinca alkaloid conjugates for cancer therapy: a structure-activity relationship

Vintafolide is a potent folate-targeted vinca alkaloid small molecule drug conjugate (SMDC) that has shown promising results in multiple clinical oncology studies. Structurally, vintafolide consists of 4 essential modules: (1) folic acid, (2) a hydrophilic peptide spacer, (3) a disulfide-containing, self-immolative linker, and (4) the cytotoxic drug, desacetylvinblastine hydrazide (DAVLBH). Here, we report a structure-activity study evaluating the biological impact of (i) substituting DAVLBH within the vintafolide molecule with other vinca alkaloid analogues such as vincristine, vindesine, vinflunine, or vinorelbine; (ii) substituting the naturally (S)-configured Asp-Arg-Asp-Asp-Cys peptide with alternative hydrophilic spacers of varied composition; and (iii) varying the composition of the linker module. A series of vinca alkaloid-containing SMDCs were synthesized and purified by HPLC and LCMS. The SMDCs were screened in vitro against folate receptor (FR)-positive cells, and anti-tumor activity was tested against well-established subcutaneous FR-positive tumor xenografts. The cytotoxic and anti-tumor activity was directly compared to that produced by vintafolide. Among all the folate vinca alkaloid SMDCs tested, DAVLBH-containing SMDCs were active, while those constructed with vincristine, vindesine, or vinorelbine analogues failed to produce meaningful biological activity. Within the DAVLBH series, having a bioreleasable, self-immolative linker system was found to be critical for activity since multiple analogues constructed with thioether-based linkers all failed to produce meaningful activity both in vitro and in vivo. Substitutions of some or all of the natural amino acids within vintafolide's hydrophilic spacer module did not significantly change the in vitro or in vivo potency of the SMDCs. Vintafolide remains one of the most potent folate-vinca alkaloid SMDCs produced to date, and continued clinical development is warranted.